WO2024105514A1 - Secondary battery - Google Patents

Secondary battery Download PDF

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Publication number
WO2024105514A1
WO2024105514A1 PCT/IB2023/061347 IB2023061347W WO2024105514A1 WO 2024105514 A1 WO2024105514 A1 WO 2024105514A1 IB 2023061347 W IB2023061347 W IB 2023061347W WO 2024105514 A1 WO2024105514 A1 WO 2024105514A1
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Prior art keywords
positive electrode
active material
electrode active
lithium
crystal structure
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PCT/IB2023/061347
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French (fr)
Japanese (ja)
Inventor
高橋辰義
三上真弓
吉谷友輔
平原誉士
山崎舜平
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株式会社半導体エネルギー研究所
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Publication of WO2024105514A1 publication Critical patent/WO2024105514A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0561—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of inorganic materials only
    • H01M10/0562—Solid materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0568—Liquid materials characterised by the solutes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals

Definitions

  • One embodiment of the present invention relates to a secondary battery.
  • the present invention is not limited to the above fields, and relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, or an electronic device, or a manufacturing method thereof.
  • a positive electrode active material with a layered rock-salt crystal structure is expected to achieve high capacity because the diffusion paths of lithium ions exist two-dimensionally within the crystal structure.
  • a positive electrode active material with a layered rock-salt crystal structure is said to be prone to thermal runaway if too many lithium ions are released during charging because the crystal structure is destroyed, posing a safety issue.
  • Lithium cobalt oxide (LiCoO 2 ) and the like are known as positive electrode active materials with a layered rock salt crystal structure.
  • Lithium cobalt oxide has a layered rock salt crystal structure, and lithium ions can move two-dimensionally between layers consisting of CoO 6 octahedra, so the cycle characteristics are also good.
  • lithium cobalt oxide has a problem of phase change accompanying charge and discharge. For example, when lithium ions are desorbed to a certain extent during charging, lithium cobalt oxide undergoes a phase change from hexagonal to monoclinic. Therefore, in order to use it with good cycle characteristics, the amount of lithium ions desorbed is limited.
  • Patent Document 1 proposes a configuration in which an additive element is added to lithium cobalt oxide.
  • research on the crystal structure of positive electrode active materials is also being conducted, as in Non-Patent Documents 1 to 4.
  • XRD X-ray diffraction
  • fluorides such as fluorite (calcium fluoride) have long been used as fluxes in steelmaking and other processes.
  • Patent Document 1 It is possible to obtain a positive electrode active material according to Patent Document 1 and the like, but there is still room for improvement in various aspects, such as high voltage characteristics, for example, discharge capacity at high voltage, or cycle characteristics at high voltage. Furthermore, there is still room for improvement in the high voltage characteristics with respect to the electrolyte.
  • one aspect of the present invention aims to provide a positive electrode active material that is stable even at high voltages.
  • Another aspect of the present invention aims to provide a secondary battery that includes the positive electrode active material and an electrolyte that is stable even at high voltages.
  • the lithium salt is preferably one or more selected from LiPF6 , LiClO4, LiAsF6 , LiBF4 , LiAlCl4 , LiSCN , LiBr, LiI , Li2SO4 , Li2B10Cl10 , Li2B12Cl12, LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3 , LiC ( C2F5SO2 ) 3 , LiN ( CF3SO2 ) 2 , LiN ( C4F9SO2 )( CF3SO2 ), and LiN( C2F5SO2 ) 2 .
  • the organic solvent is preferably one or more selected from ethylene carbonate, propylene carbonate, butylene carbonate, chloroethylene carbonate, vinylene carbonate, ⁇ -butyrolactone, ⁇ -valerolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane, dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, and sultone.
  • the dinitrile compound preferably has succinonitrile, adiponitrile, or ethylene glycol bis(propionitrile) ether.
  • the dinitrile compound preferably contains two or more selected from succinonitrile, adiponitrile, and ethylene glycol bis(propionitrile) ether.
  • the halide solid electrolyte is preferably a fluoride solid electrolyte.
  • the fluoride solid electrolyte preferably comprises LiF , LiYF4 , Li3AlF6 , or Li2ZrF6 .
  • the inside of the particles of the positive electrode active material contains magnesium.
  • One aspect of the present invention can provide a positive electrode active material that is stable even at high voltages.
  • Another aspect of the present invention can provide a secondary battery that includes the positive electrode active material and an electrolyte that is stable even at high voltages.
  • FIG. 1A1 and 1A2 are cross-sectional views of a positive electrode active material
  • FIGS. 1B1 and 1B2 are partial cross-sectional views of the positive electrode active material.
  • FIG. 2 is an example of a TEM image in which the crystal orientations are roughly consistent.
  • Fig. 3A is an example of an STEM image in which the crystal orientations are roughly consistent
  • Fig. 3B is an FFT pattern of a region of the rock-salt crystal RS
  • Fig. 3C is an FFT pattern of a region of the layered rock-salt crystal LRS.
  • FIG. 4 is a diagram illustrating a crystal structure of a positive electrode active material according to one embodiment of the present invention.
  • FIG. 5 is a diagram illustrating the crystal structure of the positive electrode active material.
  • FIG. 6A1 and 6A2 are partial cross-sectional views of the positive electrode active material
  • Fig. 6B1 to Fig. 6C are calculation results of the crystal plane and magnesium distribution of lithium cobalt oxide.
  • 7A and 7B are cross-sectional views of the positive electrode active material
  • FIGS. 7C1 and 7C2 are partial cross-sectional views of the positive electrode active material.
  • FIG. 8 shows an XRD pattern calculated from the crystal structure.
  • FIG. 9 shows an XRD pattern calculated from the crystal structure.
  • 10A and 10B are diagrams showing XRD patterns calculated from the crystal structure.
  • 11A to 11C show the lattice constants calculated from XRD.
  • 12A to 12C show the lattice constants calculated from XRD.
  • FIG. 13A and 13B are cross-sectional views of the positive electrode active material.
  • FIG. 14 is a cross-sectional view of the positive electrode active material.
  • FIG. 15 is a phase diagram showing the relationship between the composition of lithium fluoride and magnesium fluoride and the temperature.
  • FIG. 16 is a diagram illustrating the charge depth and lattice constant of the positive electrode active material.
  • 17A to 17C are explanatory diagrams relating to powder resistivity measurement.
  • 18A to 18C are diagrams illustrating a method for manufacturing a positive electrode active material.
  • FIG. 19 is a diagram illustrating a method for producing a positive electrode active material.
  • 20A to 20C are diagrams illustrating a method for manufacturing a positive electrode active material.
  • FIG. 21 is a diagram illustrating a method for manufacturing a positive electrode active material.
  • FIG. 22 is a diagram illustrating a method for manufacturing a positive electrode active material.
  • FIG. 23 is a diagram illustrating a method for manufacturing a positive electrode active material.
  • 24A and 24B are cross-sectional views of the positive electrode.
  • 25A and 25B are diagrams illustrating a solid electrolyte secondary battery.
  • 26A is an exploded perspective view of a coin-type secondary battery
  • FIG. 26B is a perspective view of the coin-type secondary battery
  • FIG. 26C is a cross-sectional perspective view thereof.
  • Fig. 27A is a diagram showing an example of a cylindrical secondary battery.
  • Fig. 27B is a diagram showing an example of a cylindrical secondary battery.
  • Fig. 27A is a diagram showing an example of a cylindrical secondary battery.
  • FIG. 27C is a diagram showing an example of a plurality of cylindrical secondary batteries.
  • Fig. 27D is a diagram showing an example of a power storage system having a plurality of cylindrical secondary batteries.
  • 28A and 28B are diagrams for explaining an example of a secondary battery, and
  • FIG. 28C is a diagram showing the inside of the secondary battery.
  • 29A to 29C are diagrams illustrating an example of a secondary battery.
  • 30A and 30B are diagrams showing the external appearance of a secondary battery.
  • 31A to 31C are diagrams illustrating a method for manufacturing a secondary battery.
  • 32A to 32D are diagrams illustrating an example of a transportation vehicle, and
  • Fig. 32E is a diagram illustrating an example of an artificial satellite.
  • FIG. 33A is a diagram showing an electric bicycle, FIG.
  • FIG. 33B is a diagram showing a secondary battery of the electric bicycle
  • FIG. 33C is a diagram showing a scooter.
  • 34A to 34E are diagrams illustrating an example of an electronic device.
  • FIG. 35 is a graph showing the results of powder resistivity measurements.
  • 36A and 36B are graphs showing the cycle test results.
  • FIG. 37 is a graph showing the results of powder resistivity measurements.
  • the space group is expressed using short notation of the international notation (or Hermann-Mauguin notation).
  • the crystal plane and crystal direction are expressed using Miller indices.
  • the notation of the space group, crystal plane, and crystal direction is expressed by adding a superscript bar to the number, but in this specification, due to format restrictions, instead of adding a bar above the number, a - (minus sign) may be added before the number.
  • individual directions indicating directions within a crystal are expressed with [ ]
  • collective directions indicating all equivalent directions are expressed with ⁇ >
  • individual faces indicating crystal faces are expressed with ( )
  • collective faces with equivalent symmetry are expressed with ⁇ ⁇ .
  • trigonal crystals represented by the space group R-3m are generally expressed as a composite hexagonal lattice of hexagonal crystals for ease of understanding of the structure, and in this specification, unless otherwise specified, the space group R-3m will be expressed as a composite hexagonal lattice.
  • the space group R-3m will be expressed as a composite hexagonal lattice.
  • not only (hkl) but also (hkil) may be used as Miller indices.
  • i is -(h+k).
  • the space group is identified by XRD, electron diffraction, neutron diffraction, etc. Therefore, belonging to a certain space group, belonging to a certain space group, or being a certain space group can be rephrased as being identified with a certain space group.
  • the arrangement of anions in cubic close-packed refers to a state in which the second layer of anions is arranged above the gaps of the anions packed in the first layer, and the third layer of anions is arranged directly above the gaps of the anions in the second layer, but not directly above the anions in the first layer. Therefore, the anions do not have to be strictly cubic lattices.
  • the analysis results do not necessarily have to be theoretical. For example, in an FFT (fast Fourier transform) pattern such as an electron beam diffraction pattern or a TEM image, a spot may appear at a position slightly different from the theoretical position. For example, if the deviation in orientation from the theoretical position is 5 degrees or less, or 2.5 degrees or less, it can be said to have a cubic close-packed structure.
  • FFT fast Fourier transform
  • the layered rock-salt crystal structure refers to a crystal structure that has a rock-salt type ion arrangement in which cations and anions are arranged alternately, and in which the transition metal M and lithium are regularly arranged to form a two-dimensional plane, allowing two-dimensional diffusion of lithium ions. Defects such as missing cations or anions may also be present. Strictly speaking, the layered rock-salt crystal structure may have a structure in which the lattice of the rock-salt crystal is distorted.
  • a rock salt type crystal structure refers to a structure having a cubic crystal structure such as the space group Fm-3m, in which cations and anions are arranged alternately. Note that there may be a deficiency of cations or anions.
  • particles are not limited to those having a spherical shape (a circular cross-sectional shape), but the cross-sectional shape of each particle may be an ellipse, a rectangle, a trapezoid, a cone, a square with rounded corners, an asymmetric shape, etc., and each particle may also be irregular in shape.
  • the smooth surface of an active material means that the surface roughness of a cross section of the active material is at least 10 nm or less when the surface unevenness information is quantified from measurement data.
  • a cross section is, for example, a cross section obtained when observing with a STEM (Scanning Transmission Electron Microscope) image.
  • the positive electrode active material refers to a compound having a transition metal and oxygen that is capable of inserting and removing lithium ions. Carbonates, hydroxyl groups, and the like that are adsorbed after the preparation of the positive electrode active material are not included in the positive electrode active material. Lithium salts, organic solvents, binders, conductive materials, or compounds derived from these that are attached after the preparation of the positive electrode active material are also not included in the positive electrode active material.
  • the theoretical capacity of a positive electrode active material refers to the amount of electricity when all of the lithium that can be inserted and removed from the positive electrode active material is removed.
  • the theoretical capacity of LiCoO2 is 274 mAh/g
  • the theoretical capacity of LiNiO2 is 275 mAh/g
  • the theoretical capacity of LiMn2O4 is 148 mAh/g.
  • the amount of lithium remaining in the positive electrode active material compared to the theoretical capacity may be indicated by x in the composition formula, for example, x in Li x CoO 2 , or x in Li x MO 2.
  • M means a transition metal that is oxidized and reduced with the insertion and desorption of lithium.
  • Li x CoO 2 can be appropriately read as Li x MO 2.
  • x in Li x CoO 2 is small means 0.1 ⁇ x ⁇ 0.24.
  • the charge capacity and discharge capacity used to calculate x in Li x CoO 2 are preferably measured under conditions where there is no short circuit and where there is no or little effect of decomposition of the lithium salt. For example, data on a secondary battery that has experienced a sudden change in capacity that is considered to be due to a short circuit should not be used to calculate x.
  • homogeneity refers to the phenomenon in which, in a solid consisting of multiple elements (e.g., A, B, C), a certain element (e.g., A) is distributed with similar characteristics in a specific region. Note that it is sufficient that the concentration of the element in the specific regions is substantially the same. For example, it is sufficient that the difference in element concentration between the specific regions is within 10%. Examples of specific regions include the surface layer, the surface, the convex portion, the concave portion, the bulk, etc.
  • uneven distribution means that the concentration of an element in one area is different from that in other areas. It is synonymous with segregation, precipitation, non-uniformity, bias, or the presence of a mixture of areas of high concentration and areas of low concentration.
  • the characteristics of a positive electrode active material in this specification it is not necessary that all of the positive electrode active materials in the secondary battery have that characteristic.
  • the characteristics of the coating can be confirmed in 50% or more, preferably 70% or more, and more preferably 90% or more of the total number of randomly selected three or more positive electrode active material particles, it can be said that there is an effect of sufficiently improving the characteristics of the positive electrode active material and the secondary battery having it.
  • the coating surface is 50% or more, preferably 70% or more, and more preferably 90% or more of the positive electrode active material particle, so that the effect of the coating can be fully exerted.
  • the materials (positive electrode active material, negative electrode active material, lithium salt, etc.) of a secondary battery are described in a state before degradation.
  • a secondary battery having a discharge capacity of 97% or more of its rated capacity can be said to be in a state before degradation.
  • the rated capacity conforms to JIS C8711:2019.
  • the state of the materials of a secondary battery before degradation is referred to as an initial product or initial state
  • the state after degradation (a state in which the secondary battery has a discharge capacity of less than 97% of its rated capacity) may be referred to as a product in use or in use state, or a used product or used state.
  • a lithium ion secondary battery refers to a battery that uses lithium ions as carrier ions, but the carrier ions of the present invention are not limited to lithium ions.
  • an alkali metal ion or an alkaline earth metal ion can be used as the carrier ion of the present invention, and specifically, sodium ions can be applied.
  • the present invention can be understood by reading lithium ions as sodium ions.
  • the carrier ion it may be referred to as a secondary battery.
  • a full cell refers to a battery cell assembled with different electrodes on both sides, such as a positive/negative unit cell.
  • a half cell refers to a battery cell assembled with lithium metal as the counter electrode.
  • the (001) plane and the (003) plane may be collectively referred to as the (00l) plane.
  • the (00l) plane may be referred to as the C plane, the basal plane, or the like.
  • lithium ions have a two-dimensional diffusion path. In other words, it can be said that the diffusion path of lithium ions exists along the surface.
  • a surface on which the diffusion path of lithium ions is exposed that is, a surface other than the surface on which lithium ions are inserted and removed (specifically the (001) plane), may be referred to as an edge surface.
  • secondary particles refer to particles formed by agglomeration of primary particles.
  • primary particles are sometimes called single particles.
  • single crystals refer to crystals in a state where there are no grain boundaries inside the particle, and are sometimes called particles having a single crystal (called single crystal grains).
  • Polycrystals refer to crystals in a state where there are grain boundaries inside the particle, and are also called polycrystalline particles. Polycrystalline particles may be said to be an aggregate of multiple crystallites, and grain boundaries may be said to be the interfaces that exist between two or more crystallites.
  • a and/or B may be used, but this is an example of a description that includes only A, only B, and both A and B.
  • FIG. 1A1 and FIG. 1A2 each show a cross-sectional view of a positive electrode active material 100 according to one embodiment of the present invention.
  • the cross-sectional shape of the positive electrode active material 100 may be particulate.
  • the positive electrode active material 100 in FIG. 1A1 has a surface layer 100a and an interior 100b. In the figure, the boundary between the surface layer 100a and the interior 100b is shown by a dashed line. This boundary is an example.
  • the positive electrode active material 100 in FIG. 1A2 has a surface layer 100a and an interior 100b, and further has a defect portion 100c such as a crack and a grain boundary 101, which will be described later. In the figure, the grain boundary 101 is shown by a dashed line. This dashed line is an example. Enlarged views of the vicinity of A-B in FIG. 1A1 are shown in FIG. 1B1 and FIG. 1B2.
  • the grain boundary 101 refers to, for example, a portion where particles of the positive electrode active material 100 are stuck together, a portion where the crystal orientation of the positive electrode active material 100 changes, i.e., a portion where the repetition of bright and dark lines in an STEM image or the like becomes discontinuous, a portion containing many crystal defects, a portion where the crystal structure is disordered, etc.
  • the crystal defect refers to a defect that can be observed in a cross-sectional TEM (transmission electron microscope) or cross-sectional STEM image, etc., that is, a structure in which other atoms have entered between the lattices, a cavity, etc.
  • the grain boundary 101 can be said to be one type of planar defect.
  • the vicinity of the grain boundary 101 refers to a region within 10 nm of the grain boundary 101.
  • the surface layer 100a of the positive electrode active material 100 refers to, for example, a region within 50 nm from the particle surface toward the inside, more preferably within 35 nm from the particle surface toward the inside, even more preferably within 20 nm from the particle surface toward the inside, and most preferably within 10 nm from the particle surface toward the inside.
  • Toward the inside means a direction perpendicular or approximately perpendicular to the particle surface, and perpendicular or approximately perpendicular means 80° to 100° with respect to the tangent of the particle surface. Surfaces caused by slips, cracks, and/or cracks may also be referred to as the particle surface.
  • the surface layer 100a is synonymous with the surface vicinity, surface vicinity region, or shell.
  • the region deeper than the surface layer 100a of the positive electrode active material is called the interior 100b.
  • the interior 100b is synonymous with the interior region or core.
  • the particle surface of the positive electrode active material 100 refers to the surface of the composite oxide including the surface layer 100a and the interior 100b. Therefore, the positive electrode active material 100 does not include metal oxides that do not have lithium sites that can contribute to charging and discharging, such as aluminum oxide (Al 2 O 3 ), carbonates that are chemically adsorbed after the preparation of the positive electrode active material, and hydroxyl groups. Note that metal oxides that do not have lithium sites may be attached to the positive electrode active material 100. The attached metal oxides have a crystal structure that does not match that of the interior 100b, for example.
  • the positive electrode active material 100 does not include lithium salts, organic solvents, binders, conductive materials, or compounds derived from these that are attached to the positive electrode active material 100.
  • the positive electrode active material 100 is a compound containing oxygen and a transition metal capable of inserting and removing lithium ions
  • the interface between the region where the transition metal M (e.g., Co, Ni, Mn, Fe, etc.) that is oxidized and reduced with the insertion and removal of lithium ions and oxygen is present and the region where it is not present is the particle surface of the positive electrode active material.
  • Surfaces created by slips, cracks, and/or cracks can also be said to be the surface of the positive electrode active material because the transition metal M and oxygen are present.
  • a protective film may be attached to the surface, but the protective film is not included in the positive electrode active material.
  • a single layer film or a multilayer film selected from carbon, metal, oxide, resin, etc. may be used.
  • the detection amount of the characteristic X-ray of the transition metal M is 50% of the sum of the average value M AVE of the detection amount of the characteristic X-ray of the transition metal M in the interior and the average value M BG of the detection amount of the characteristic X-ray of the transition metal M in the background, or a point where the detection amount of the characteristic X-ray of oxygen is 50% of the sum of the average value O AVE of the detection amount of the characteristic X-ray of the oxygen in the interior and the average value O BG of the detection amount of the characteristic X-ray of the oxygen in the background.
  • the point where the detection amount of the characteristic X-ray of the transition metal M is 50% of the sum of the average detection amount of the characteristic X-ray of the transition metal M in the interior and the average detection amount of the characteristic X-ray of the transition metal M in the background is different from the point where the detection amount of the characteristic X-ray of oxygen is 50% of the sum of the average detection amount of the characteristic X-ray of oxygen in the interior and the average detection amount of the characteristic X-ray of oxygen in the background, it is considered that it is due to the influence of metal oxides, carbonates, etc.
  • the point where the detection amount of the characteristic X-ray of the transition metal M is 50% of the sum of the average detection amount M AVE of the characteristic X-ray of the transition metal M in the interior and the average detection amount M BG of the characteristic X-ray of the transition metal M in the background can be adopted as the surface position of the positive electrode active material in STEM-EDX-ray analysis.
  • the surface position of the positive electrode active material in STEM-EDX-ray analysis can be determined using the M AVE and M BG of the element with the largest amount of detection of characteristic X-rays in the interior.
  • the average value M BG of the background detection amount of the characteristic X-rays of the transition metal M can be obtained, for example, by averaging an outer range of 2 nm or more, preferably 3 nm or more, avoiding the vicinity where the detection amount of the characteristic X-rays of the transition metal M begins to increase.
  • the average value M AVE of the detection amount of the characteristic X-rays of the internal transition metal M can be obtained, for example, by averaging an outer range of 2 nm or more, preferably 3 nm or more, in a region where the detection amounts of the characteristic X-rays of the transition metal M and oxygen become saturated and stable, for example, a region that is 30 nm or more, preferably 50 nm deep from the region where the detection amount of the characteristic X-rays of the transition metal M begins to increase.
  • the average value O BG of the background detection amount of the characteristic X-rays of oxygen and the average value O AVE of the detection amount of the characteristic X-rays of the internal oxygen can also be obtained in a similar manner.
  • the surface of the positive electrode active material 100 in a cross-sectional STEM image or the like is the boundary between an area where an image derived from the crystal structure of the positive electrode active material is observed and an area where it is not observed, and is the outermost area where atomic columns derived from the atomic nuclei of metal elements having a larger atomic number than lithium among the metal elements constituting the positive electrode active material are confirmed. Alternatively, it is the intersection point of a tangent drawn to the brightness profile from the surface to the inside of the cross-sectional STEM image and the axis in the depth direction.
  • the surface in a cross-sectional STEM image or the like may be determined in conjunction with an analysis with higher spatial resolution.
  • the spatial resolution of STEM-EDX is at least about 1 nm. Therefore, the maximum value of the additive element profile can deviate by about 1 nm. For example, even if the maximum value of the additive element profile of magnesium or the like is outside the surface determined above, it can be considered an error if the difference between the maximum value and the surface is less than 1 nm.
  • a peak in STEM-ED X-ray analysis refers to the detection intensity in each element profile, or the maximum amount of characteristic X-rays detected for each element.
  • noise in STEM-ED X-ray analysis can be a measurement value with a half-width less than the spatial resolution (R), for example, less than R/2.
  • the effects of noise can be reduced by scanning the same location multiple times under the same conditions.
  • the integrated values measured over six scans can be used as the profile for each element.
  • the number of scans is not limited to six, and more scans can be performed and the average can be used as the profile for each element.
  • STEM-EDX analysis can be performed, for example, as follows.
  • a protective film is deposited on the surface of the positive electrode active material.
  • carbon can be deposited as a protective film using a carbon coating unit of an ion sputtering device (Hitachi High-Tech MC1000).
  • the positive electrode active material is then sliced to prepare a STEM cross-sectional sample.
  • a FIB-SEM device Hitachi High-Tech XVision 200TBS
  • the finishing conditions for the slice processing can be, for example, an acceleration voltage of 10 kV.
  • the sliced sample can be picked up by an MPS (micro-probing system).
  • STEM-EDX-ray analysis for example, a STEM device (Hitachi High-Tech HD-2700) can be used, and the EDX detector can be EDAX's Octane T Ultra W (Dual EDS).
  • the acceleration voltage of the STEM device is set to 200 kV, and the emission current is set to 6 ⁇ A to 10 ⁇ A, and a portion of the sliced sample with minimal depth and unevenness is measured.
  • the magnification is, for example, about 150,000 times.
  • the conditions for EDX-ray analysis can be drift correction, line width 42 nm, pitch 0.2 nm, and frame number 6 or more.
  • the positive electrode active material 100 needs to have a transition metal capable of oxidation and reduction in order to maintain charge neutrality even when lithium ions are inserted and removed.
  • the positive electrode active material 100 preferably mainly uses cobalt as a transition metal responsible for the oxidation and reduction reaction. In addition to cobalt, at least one or two selected from nickel and manganese may be used. If the transition metals contained in the positive electrode active material 100 are 75 atomic % or more, preferably 90 atomic % or more, and more preferably 95 atomic % or more of cobalt, there are many advantages such as relatively easy synthesis, easy handling, and excellent cycle characteristics.
  • the positive electrode active material 100 can be made of lithium cobalt oxide (LiCoO 2 ) to which an additive element is added.
  • the stability when x in Li x CoO 2 is small is better than that of a composite oxide in which nickel such as lithium nickel oxide (LiNiO 2 ) accounts for the majority of the transition metal. This is thought to be because cobalt is less affected by distortion due to the Jahn-Teller effect than nickel.
  • the strength of the Jahn-Teller effect in a composite oxide having a transition metal varies depending on the number of electrons in the d orbital of the transition metal.
  • the additive elements contained in the positive electrode active material 100 are preferably one or more selected from magnesium, fluorine, nickel, aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, bromine, and beryllium.
  • the sum of the transition metals among the additive elements is preferably less than 25 atomic %, more preferably less than 10 atomic %, and even more preferably less than 5 atomic %.
  • the positive electrode active material 100 can include lithium cobalt oxide with added magnesium, lithium cobalt oxide with added fluorine, lithium cobalt oxide with added magnesium and fluorine, lithium cobalt oxide with added magnesium, fluorine and titanium, lithium cobalt oxide with added magnesium, fluorine and aluminum, lithium cobalt oxide with added magnesium, fluorine and nickel, lithium cobalt oxide with added magnesium, fluorine, nickel and aluminum, etc.
  • the additive element is preferably dissolved in the positive electrode active material 100. Therefore, for example, when performing a line analysis using STEM-EDX, the depth at which the amount of detection of the characteristic X-rays of the additive element increases is preferably located deeper than the depth at which the amount of detection of the characteristic X-rays of the transition metal M, which is the main component of the positive electrode active material, increases, i.e., inside the positive electrode active material 100.
  • the depth at which the amount of detection of characteristic X-rays of a certain element increases in STEM-EDX line analysis refers to the depth at which measurement values that can be determined to be not noise in terms of intensity, spatial resolution, etc. are continuously obtained.
  • added elements further stabilize the crystal structure of the positive electrode active material 100, as described below.
  • the presence of the added elements in the surface layer 100a and/or the interior 100b can stabilize the crystal structure.
  • the added elements are synonymous with a mixture or a part of the raw material.
  • the positive electrode active material 100 is substantially free of manganese, the above-mentioned advantages of being relatively easy to synthesize and handle, and having excellent cycle characteristics, are even greater.
  • the concentration of manganese contained in the positive electrode active material 100 is preferably, for example, 600 ppm wt or less, more preferably 100 ppm wt or less.
  • the layered rock salt type composite oxide has a high discharge capacity, has a two-dimensional lithium ion diffusion path, is suitable for lithium ion insertion/extraction reaction, and is excellent as a positive electrode active material for a secondary battery. Therefore, it is preferable that the inner part 100b, which occupies most of the volume of the positive electrode active material 100, has a layered rock salt type crystal structure. In FIG.
  • the surface layer 100a of the positive electrode active material 100 has a function of reinforcing the layered structure of the octahedrons of cobalt and oxygen in the interior 100b so that it is not destroyed even if lithium is removed from the positive electrode active material 100 by charging.
  • the surface layer 100a functions as a barrier film for the positive electrode active material 100.
  • the surface layer 100a which is the outer periphery of the positive electrode active material 100, reinforces the positive electrode active material 100.
  • the reinforcement here means suppressing structural changes in the surface layer 100a and interior 100b of the positive electrode active material 100, including oxygen desorption, and/or suppressing oxidative decomposition of the organic solvent on the surface of the positive electrode active material 100.
  • the surface layer 100a has a different crystal structure from the inner portion 100b. It is also preferable that the surface layer 100a has a composition and crystal structure that are more stable at room temperature (25°C) than the inner portion 100b. For example, it is preferable that at least a part of the surface layer 100a of the positive electrode active material 100 has a rock salt type crystal structure. Alternatively, it is preferable that the surface layer 100a has both a layered rock salt type and a rock salt type crystal structure. Alternatively, it is preferable that the surface layer 100a has the characteristics of both a layered rock salt type and a rock salt type crystal structure.
  • Another additive element such as aluminum or manganese, preferably has a concentration gradient and a concentration peak in a deeper region than additive element A, as shown by the shade of the hatch in FIG. 1B2.
  • the concentration peak may be present in the surface layer 100a, or may be deeper than the surface layer 100a.
  • An additive element having such a concentration gradient will be referred to as additive element B.
  • additive element A and additive element B can be distinguished by the concentration gradient of the additive element, that is, the concentration distribution.
  • magnesium which is one of the additive elements A, tends to become a divalent cation, and since magnesium ions are more stable at the lithium site than at the cobalt site in the layered rock salt crystal structure, they tend to enter the lithium site.
  • magnesium is present at an appropriate concentration at the lithium site of the surface layer 100a, it is easy to maintain the layered rock salt crystal structure. This is presumed to be because the magnesium ions present at the lithium site function as pillars supporting the CoO 2 layers.
  • the surface layer 100a may have a rock salt crystal structure.
  • magnesium may be present at an appropriate concentration at the lithium site of the interior 100b, and even when magnesium is present at an appropriate concentration at the lithium site of the interior 100b, it can function as a pillar supporting the CoO 2 layers, and the layered rock salt crystal structure can be maintained. Furthermore, the presence of magnesium can suppress the detachment of oxygen around magnesium when x in Li x CoO 2 is, for example, 0.24 or less. Furthermore, the presence of magnesium can be expected to increase the density of the positive electrode active material 100. Furthermore, if the magnesium concentration in the surface layer 100a is high, it is expected that the corrosion resistance against the hydrofluoric acid produced by decomposition of the electrolyte will be improved.
  • magnesium does not adversely affect the insertion and removal of lithium ions during charging and discharging, and can provide the above benefits to the positive electrode active material.
  • it may have a negative effect on the insertion and removal of lithium ions.
  • the effect of stabilizing the crystal structure may be reduced. This is thought to be because magnesium ions enter the cobalt site in addition to the lithium site.
  • unnecessary magnesium compounds oxides, fluorides, etc.
  • the discharge capacity of the positive electrode active material may decrease. This is thought to be because too many magnesium ions enter the lithium site, reducing the amount of lithium that contributes to charging and discharging.
  • the amount of magnesium contained in the entire positive electrode active material 100 is appropriate.
  • the number of magnesium atoms is preferably 0.002 to 0.06 times the number of cobalt atoms, more preferably 0.005 to 0.03 times, and even more preferably about 0.01 times.
  • the amount of magnesium contained in the entire positive electrode active material 100 here may be a value obtained by performing an elemental analysis of the entire positive electrode active material 100 using, for example, GD-MS (glow discharge mass spectrometry) or ICP-MS (inductively coupled plasma mass spectrometry), or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material 100.
  • Nickel which is one of the additive elements A, can exist on either the cobalt site or the lithium site.
  • nickel ions are located on the cobalt site, the oxidation-reduction potential is lower than that of cobalt, which is preferable since it leads to an increase in discharge capacity.
  • the shift of the layered structure consisting of octahedra of cobalt and oxygen can be suppressed.
  • the change in volume accompanying charging and discharging is suppressed.
  • the elastic modulus increases, that is, the material becomes hard. This is presumably because nickel present at the lithium site also functions as a pillar supporting the CoO 2 layers. Therefore, it is expected that the crystal structure will be more stable, particularly in a charged state at high temperatures, for example, 45°C or higher, which is preferable.
  • NiO nickel oxide
  • nickel is considered to be less likely to dissolve into the electrolyte during charging than the other elements listed above. Therefore, it is considered to be highly effective in stabilizing the crystal structure of the surface layer in the charged state.
  • the presence of nickel in the interior 100b also has the effect of stabilizing the internal crystal structure.
  • Ni2 + is the most stable, and nickel has a higher trivalent ionization energy than cobalt. Therefore, it is known that nickel and oxygen alone do not form a spinel crystal structure. Therefore, nickel is thought to have the effect of suppressing the phase change from the layered rock salt type to the spinel type crystal structure.
  • an excess of nickel is undesirable because it increases the influence of distortion due to the Jahn-Teller effect. Also, an excess of nickel may adversely affect the insertion and extraction of lithium.
  • the amount of nickel contained in the entire positive electrode active material 100 is appropriate.
  • the number of nickel atoms contained in the positive electrode active material 100 is preferably more than 0% and not more than 7.5% of the number of cobalt atoms, preferably 0.05% to 4%, preferably 0.1% to 2%, and more preferably 0.2% to 1%.
  • the number of nickel atoms contained in the positive electrode active material 100 is preferably more than 0% and not more than 7.5% of the number of cobalt atoms, preferably 0.05% to 4%, preferably 0.1% to 2%, and more preferably 0.2% to 1%.
  • Or more than 0% and not more than 4% is preferable.
  • Or more than 0% and not more than 2% is preferable.
  • Or more than 0.05% to 7.5% is preferable.
  • Or more than 0.05% to 2% is preferable.
  • Or more than 0.1% to 7.5% is preferable.
  • Or more than 0.1% to 4% is preferable.
  • the amount of nickel shown here may be, for example, a value obtained by performing elemental analysis of the entire positive electrode active material using GD-MS, ICP-MS, etc., or may be based on the value of the raw material composition in the process of producing the positive electrode active material.
  • Aluminum which is one of the additive elements B, can be present at the cobalt site in the layered rock salt crystal structure.
  • Aluminum which is a typical element, becomes a trivalent cation and does not change its valence, so lithium around the aluminum is less likely to move during charging and discharging. Therefore, aluminum and the lithium around it function as columns and can suppress changes in the crystal structure.
  • Aluminum also has the effect of suppressing the elution of surrounding cobalt and improving continuous charging resistance.
  • the Al-O bond is stronger than the Co-O bond, it can suppress the detachment of oxygen around the aluminum.
  • the amount of aluminum contained in the entire positive electrode active material 100 is appropriate.
  • the number of aluminum atoms contained in the entire positive electrode active material 100 is preferably 0.05% to 4% of the number of cobalt atoms, preferably 0.1% to 2% and more preferably 0.3% to 1.5%.
  • 0.05% to 2% is preferable.
  • 0.1% to 4% is preferable.
  • the amount contained in the entire positive electrode active material 100 here may be, for example, a value obtained by performing elemental analysis of the entire positive electrode active material 100 using GD-MS, ICP-MS, or the like, or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material 100.
  • fluorine which is one of the additive elements A
  • fluorine is a monovalent anion
  • fluorine in the surface layer portion 100a when part of the oxygen is replaced by fluorine in the surface layer portion 100a, the lithium ion desorption energy is reduced.
  • the redox potential of the cobalt ion accompanying the desorption of lithium ions differs depending on the presence or absence of fluorine.
  • the cobalt ion when there is no fluorine, the cobalt ion changes from trivalent to tetravalent with the desorption of lithium ions.
  • fluorine when there is fluorine, the cobalt ion changes from divalent to trivalent with the desorption of lithium ions.
  • the redox potential of the cobalt ion is different between the two.
  • the positive electrode active material 100 when part of the oxygen is replaced by fluorine in the surface layer portion 100a of the positive electrode active material 100, it can be said that the desorption and insertion of lithium ions near the fluorine is likely to occur smoothly. Therefore, when the positive electrode active material 100 is used in a secondary battery, the charge/discharge characteristics, large current characteristics, etc. can be improved. In addition, the presence of fluorine in the surface layer portion 100a having the surface that is in contact with the electrolyte can effectively improve the corrosion resistance against hydrofluoric acid. As described in the following embodiment, when the melting point of fluorides such as lithium fluoride is lower than that of other additive element sources, it can function as a flux (also called a fluxing agent) that lowers the melting point of the other additive element sources.
  • a flux also called a fluxing agent
  • the fluorine compound has LiF and MgF2 , as shown in Figure 15 (quoted and added from Non-Patent Document 10, Figure 5), the eutectic point P of LiF and MgF2 is around 742°C (T1), so in the heating step after mixing the additive element containing fluorine, it is preferable to set the heating temperature to 742°C or higher.
  • titanium oxide which is one of the additive elements A, is known to have superhydrophilicity. Therefore, by making the cathode active material 100 have titanium oxide in the surface layer portion 100a, it is possible that the wettability with a highly polar solvent will be improved. When used as a secondary battery, the interface between the cathode active material 100 and the highly polar electrolyte will have good contact, which may suppress an increase in internal resistance.
  • phosphorus which is one of the additive elements A
  • phosphorus it is preferable for phosphorus to be present in the surface layer 100a as a compound containing phosphorus and oxygen.
  • the positive electrode active material 100 contains phosphorus
  • the phosphorus reacts with the hydrofluoric acid generated by the decomposition of the organic solvent or the lithium salt, which may reduce the concentration of hydrofluoric acid in the organic solvent, which is preferable.
  • hydrofluoric acid may be generated by hydrolysis.
  • hydrofluoric acid may be generated by a reaction between polyvinylidene fluoride (PVDF) used as a binder and an alkaline component.
  • PVDF polyvinylidene fluoride
  • the low concentration of hydrofluoric acid in the organic solvent may suppress corrosion of the current collector and/or peeling of the coating 104.
  • the low concentration of hydrofluoric acid in the organic solvent may suppress a decrease in adhesion due to gelation and/or insolubilization of PVDF.
  • the stability in the state where x in Li x CoO 2 is smaller than 1 is extremely high, which is preferable.
  • the number of phosphorus atoms is preferably 1% or more and 20% or less of the number of cobalt atoms, more preferably 2% or more and 10% or less, and even more preferably 3% or more and 8% or less. Or 1% or more and 10% or less is preferable. Or 2% or more and 20% or less is preferable. Or 2% or more and 8% or less is preferable. Or 3% or more and 20% or less is preferable. Or 3% or more and 10% or less is preferable.
  • the number of magnesium atoms is preferably 0.1% or more and 10% or less of the number of cobalt atoms, more preferably 0.5% or more and 5% or less, and more preferably 0.7% or more and 4% or less. Or 0.1% or more and 5% or less is preferable. Or 0.1% or more and 4% or less is preferable. Or 0.5% or more and 10% or less is preferable. Or 0.5% or more and 4% or less is preferable.
  • the concentration of cobalt, phosphorus, and magnesium shown here may be values obtained by performing elemental analysis of the entire positive electrode active material 100 using, for example, GD-MS, ICP-MS, or the like, or may be based on values of the composition of raw materials in the process of producing the positive electrode active material 100.
  • the positive electrode active material 100 has a crack
  • a recess corresponding to the defect portion 100c is formed, but the recess contains phosphorus, more specifically, a compound containing phosphorus and oxygen, and the compound fills the recess, thereby preventing the crack from progressing.
  • magnesium is added in a step before nickel.
  • magnesium and nickel are added in the same step.
  • Magnesium has a large ionic radius and tends to remain in the surface layer of lithium cobalt oxide regardless of the step in which it is added, whereas nickel can diffuse widely inside the lithium cobalt oxide if magnesium is not present. Therefore, if nickel is added before magnesium, there is a concern that nickel will diffuse into the lithium cobalt oxide and not remain in the desired amount in the surface layer.
  • additive elements with different distributions such as additive element A and additive element B, in combination, because it is possible to stabilize the crystal structure in a wider region.
  • additive element B such as aluminum
  • additive element B is not essential for the surface, since the surface can be sufficiently stabilized by additive element A, such as magnesium or nickel. Rather, it is preferable for aluminum to be distributed widely in a deeper region.
  • aluminum is continuously detected in a region from 1 nm to 25 nm in the depth direction from the surface. It is preferable that aluminum is distributed widely in a region from 0 nm to 100 nm from the surface, preferably from 0.5 nm to 50 nm from the surface, because it is possible to stabilize the crystal structure in a wider region.
  • each additive element When multiple additive elements are included as described above, the effects of each additive element are synergistic and can contribute to further stabilization of the surface layer 100a.
  • the inclusion of magnesium, nickel, and aluminum is highly effective in providing a stable composition and crystal structure, and is therefore preferable.
  • the surface layer 100a has a higher concentration of cobalt than magnesium.
  • Mg the number of magnesium atoms
  • Co the number of cobalt atoms
  • the surface layer 100a has a higher concentration of cobalt than nickel.
  • the surface layer 100a has a higher concentration of cobalt than aluminum.
  • the surface layer 100a has a higher concentration of cobalt than fluorine.
  • the surface layer 100a has a higher concentration of magnesium than nickel.
  • the number of nickel atoms is 1/6 or less of the number of magnesium atoms.
  • magnesium, nickel, and aluminum have a higher concentration in the surface layer 100a than in the interior 100b
  • magnesium, nickel, and aluminum are present randomly and in a sparse manner in the interior 100b.
  • magnesium and aluminum are present at appropriate concentrations in the lithium sites in the interior 100b, it has the effect of making it easier to maintain the layered rock-salt crystal structure, as described above.
  • nickel is present at an appropriate concentration in the interior 100b, it is possible to suppress the shifting of the layered structure consisting of octahedra of cobalt and oxygen, as described above.
  • magnesium and nickel are present together, a synergistic effect of suppressing the elution of magnesium can be expected, as described above.
  • the crystal structure changes continuously from the interior 100b toward the surface.
  • the crystal orientation of the surface layer 100a and the interior 100b are consistent or approximately consistent.
  • rock salt type and rock salt type crystal structure characteristics can be determined by electron diffraction, TEM images, cross-sectional STEM images, etc.
  • the rock salt type has no distinction between the cation sites, but the layered rock salt type has two types of cation sites in the crystal structure, one of which is mostly occupied by lithium and the other by a transition metal.
  • the layered structure in which two-dimensional planes of cations and two-dimensional planes of anions are alternately arranged is the same for both the rock salt type and the layered rock salt type.
  • the central spot (transmitted spot) of the bright spots of the electron diffraction pattern corresponding to the crystal planes forming this two-dimensional plane is set as the origin 000
  • the bright spot closest to the central spot is, for example, the (111) plane in the rock salt type in an ideal state, and, for example, the (003) plane in the layered rock salt type.
  • the distance between the bright spots on the (003) plane of LiCoO 2 is observed to be about half the distance between the bright spots on the (111) plane of MgO. Therefore, when the analysis area has two phases, for example, MgO with a rock-salt crystal structure and LiCoO2 with a layered rock-salt crystal structure, the electron beam diffraction pattern has a plane orientation in which bright spots with strong brightness and bright spots with weak brightness are arranged alternately. Bright spots common to the rock-salt type and layered rock-salt type have strong brightness, while bright spots occurring only in the layered rock-salt type have weak brightness.
  • Layered rock salt crystals and the anions in rock salt crystals have a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that the anions in the O3' type and monoclinic O1(15) crystals described below also have a cubic close-packed structure. Therefore, when a layered rock salt crystal and a rock salt crystal come into contact, there are crystal faces where the cubic close-packed structure formed by the anions is oriented in the same direction.
  • the anions on the ⁇ 111 ⁇ plane of the cubic crystal structure have a triangular lattice.
  • the layered rock-salt crystal structure is in space group R-3m and is a rhombohedral structure, but is generally represented as a composite hexagonal lattice to make the structure easier to understand, and the (0001) plane of the layered rock-salt crystal structure has a hexagonal lattice.
  • the triangular lattice on the cubic ⁇ 111 ⁇ plane has the same atomic arrangement as the hexagonal lattice on the (0001) plane of the layered rock-salt crystal structure.
  • the compatibility of the two lattices can be said to be the alignment of the cubic close-packed structures.
  • the space group of the layered rock salt crystal and O3' type crystal is R-3m, which is different from the space group Fm-3m (the space group of general rock salt crystals) of the rock salt crystal, so the Miller indices of the crystal planes that satisfy the above conditions are different between the layered rock salt crystal structure and O3' type crystal structure and the rock salt crystal structure.
  • the crystal orientation is roughly the same.
  • the three-dimensional structural similarity in which the crystal orientation is roughly the same, or the same crystallographic orientation is called topotaxis.
  • Crystal orientations in the two regions roughly coincide can be determined from TEM (Transmission Electron Microscope) images, STEM (Scanning Transmission Electron Microscope) images, HAADF-STEM (High-angle Annular Dark Field Scanning TEM) images, ABF-STEM (Annular Bright-Field Scanning Transmission Electron Microscope) images, electron beam diffraction patterns, and FFT patterns of TEM and STEM images.
  • TEM Transmission Electron Microscope
  • STEM Sccanning Transmission Electron Microscope
  • HAADF-STEM High-angle Annular Dark Field Scanning TEM
  • ABF-STEM Annular Bright-Field Scanning Transmission Electron Microscope
  • Figure 2 shows an example of a TEM image in which the orientation of the layered rock salt crystal LRS and the rock salt crystal RS roughly coincides. Images reflecting the crystal structure are obtained in TEM images, STEM images, HAADF-STEM images, ABF-STEM images, etc.
  • a contrast originating from a crystal plane is obtained.
  • the contrast originating from the (0003) plane is obtained as a repetition of bright bands (bright strips) and dark bands (dark strips). Therefore, when a repetition of bright lines and dark lines is observed in a TEM image and the angle between the bright lines (for example, L RS and L LRS shown in FIG.
  • lithium cobalt oxide having a layered rock-salt crystal structure is observed perpendicular to the c-axis
  • the arrangement of the cobalt atoms is observed perpendicular to the c-axis as a bright line or an arrangement of highly bright dots
  • the arrangement of the lithium atoms and oxygen atoms is observed as a dark line or a region of low brightness.
  • fluorine (atomic number 9) and magnesium (atomic number 12) are added to the lithium cobalt oxide.
  • Figure 3A shows an example of an STEM image in which the orientations of the layered rock-salt crystal LRS and the rock-salt crystal RS are roughly the same.
  • Figure 3B shows the FFT pattern of the region of the rock-salt crystal RS
  • Figure 3C shows the FFT pattern of the region of the layered rock-salt crystal LRS.
  • the composition, JCPDS card number, and d-values and angles calculated from the data on the JCPDS card are shown on the left of Figures 3B and 3C.
  • the measured values are shown on the right.
  • the spot marked with an O is the zeroth order diffraction.
  • the spot marked A in Figure 3B is due to the 11-1 reflection of the cubic crystal.
  • the spot marked A in Figure 3C is due to the 0003 reflection of the layered rock salt type. From Figures 3B and 3C, it can be seen that the orientation of the 11-1 reflection of the cubic crystal and the orientation of the 0003 reflection of the layered rock salt type roughly coincide. In other words, it can be seen that the line passing through AO in Figure 3B is roughly parallel to the line passing through AO in Figure 3C. Here, roughly coincident and roughly parallel mean that the angle is 5 degrees or less, or 2.5 degrees or less.
  • the ⁇ 0003> orientation of the layered rock salt type may roughly match the ⁇ 11-1> orientation of the rock salt type.
  • these reciprocal lattice points are spot-like, that is, not continuous with other reciprocal lattice points. The fact that the reciprocal lattice points are spot-like and not continuous with other reciprocal lattice points indicates high crystallinity.
  • a spot not originating from the 0003 reflection of the layered rock salt type may be observed in a reciprocal lattice space different from the orientation of the 0003 reflection of the layered rock salt type.
  • the spot marked B in FIG. 3C is originating from the 1014 reflection of the layered rock salt type. This may be observed at an angle of 52° to 56° (i.e., ⁇ AOB is 52° to 56°) from the orientation of the reciprocal lattice point (A in FIG.
  • spots not originating from the 11-1 reflection of a cubic crystal may be observed in a reciprocal lattice space other than the orientation where the 11-1 reflection of a cubic crystal is observed.
  • the spot marked B in FIG. 3B originates from the 200 reflection of a cubic crystal. This is because a diffraction spot may be observed at an angle of 54° to 56° (i.e., ⁇ AOB is 54° to 56°) from the orientation of the reflection (A in FIG. 3B) originating from the 11-1 of a cubic crystal.
  • ⁇ AOB is 54° to 56°
  • this index is only an example, and does not necessarily have to match this.
  • a reciprocal lattice point equivalent to 11-1 and 200 may be used.
  • positive electrode active materials with a layered rock salt crystal structure tend to have the (0003) plane and its equivalent planes, as well as the (10-14) plane and its equivalent planes, as crystal planes.
  • the positive electrode active material particles can be processed into thin slices with a FIB (Focused Ion Beam) or the like so that the (0003) plane can be observed with an electron beam incident at [12-10] in the TEM or the like.
  • FIB Flucused Ion Beam
  • the interior 100b of the positive electrode active material 100 preferably has a low density of defects. Defects include line defects, planar defects, and point defects. Some line defects are sometimes called dislocations. Furthermore, the positive electrode active material 100 preferably has a large crystallite size measured by XRD. In other words, the interior 100b preferably has high crystallinity. Furthermore, the surface of the positive electrode active material 100 preferably is smooth. These characteristics are important factors that support the reliability of the positive electrode active material 100 when used in a secondary battery. If the reliability of the positive electrode active material is high, the upper limit of the charging voltage of the secondary battery can be increased, resulting in a secondary battery with a high charge/discharge capacity.
  • Dislocations in the interior 100b can be observed, for example, by TEM. If the density of defects is sufficiently low, dislocations may not be observed in a specific 1 ⁇ m square of the observed sample.
  • the crystallite size is larger, as described below, when x in Li x CoO 2 is smaller than 1, the O3′ type crystal structure is more easily maintained, and shortening of the c-axis length is more easily suppressed.
  • the XRD diffraction pattern for calculating the crystallite size is preferably obtained from only the positive electrode active material, but may also be obtained from the positive electrode containing the positive electrode active material, current collector, binder, conductive material, etc.
  • the particles of the positive electrode active material may be oriented so that the crystal planes of the particles of the positive electrode active material are aligned in one direction due to the influence of pressure during the manufacturing process. If the orientation is too strong, the crystallite size may not be calculated accurately, so it is more preferable to obtain the XRD diffraction pattern by removing the positive electrode active material layer from the positive electrode, removing the binder, etc.
  • Another method is to apply grease to a silicon non-reflective plate and attach a powder sample of the positive electrode active material, etc. to the silicon non-reflective plate.
  • the crystallite size can be calculated using, for example, Bruker D8 ADVANCE, CuK ⁇ radiation as the X-ray source, 2 ⁇ between 15° and 90°, increment 0.005, LYNXEYE XE-T as the detector, and the diffraction pattern obtained using ICSD coll. code. 172909 as the literature value of lithium cobalt oxide. Analysis can be performed using DIFFRAC. TOPAS ver. 6 as the crystal structure analysis software, and can be set, for example, as follows. Emission Profile: CuKa5.
  • LVol-IB which is the crystallite size calculated by the above method, as the crystallite size. Note that if the calculated Preferred Orientation is less than 0.8, the orientation of the sample may be too strong and the sample may not be suitable for determining the crystallite size.
  • the positive electrode active material 100 has the above-mentioned distribution of the additive elements and/or the crystal structure in the discharged state, and therefore the crystal structure when x in Li x CoO 2 is small is different from that of conventional positive electrode active materials.
  • small x means 0.1 ⁇ x ⁇ 0.24.
  • the change in the crystal structure of a conventional positive electrode active material is shown in Fig. 5.
  • the conventional positive electrode active material shown in Fig. 5 is lithium cobalt oxide ( LiCoO2 ) that does not have any added elements.
  • the change in the crystal structure of lithium cobalt oxide that does not have any added elements is described in Non-Patent Documents 1 to 3, etc.
  • lithium occupies an octahedral site, and there are three CoO 2 layers in the unit cell. Therefore, this crystal structure is sometimes called an O3 type crystal structure.
  • the CoO 2 layer refers to a structure in which an octahedral structure in which oxygen is six-coordinated to cobalt is continuous on a plane in an edge-sharing state. This is sometimes called a layer consisting of an octahedron of cobalt and oxygen.
  • conventional lithium cobalt oxide has a crystal structure that is highly symmetrical with lithium when x is about 0.5, and belongs to the monoclinic space group P2/m.
  • This structure has one CoO2 layer in the unit cell. Therefore, it is sometimes called O1 type or monoclinic (denoted as monoclinic in the figure) O1 type.
  • the positive electrode active material has a crystal structure of the trigonal space group P-3m1, and one CoO2 layer is present in the unit cell. Therefore, this crystal structure may be called O1 type or trigonal (denoted as trigonal in the figure) O1 type.
  • the trigonal crystal may be converted to a composite hexagonal lattice and called a hexagonal O1 type.
  • This structure can be said to be a structure in which a CoO 2 structure such as trigonal O1 type and a LiCoO 2 structure such as R-3m O3 are alternately stacked. Therefore, this crystal structure may be called an H1-3 type crystal structure (H1-3 in the figure).
  • H1-3 H1-3 in the figure.
  • the number of cobalt atoms per unit cell in the H1-3 type crystal structure is twice that of other structures.
  • the c-axis of the H1-3 type crystal structure is shown in a figure in which the c-axis is 1/2 of the unit cell.
  • the coordinates of cobalt and oxygen in the unit cell can be expressed as Co (0,0,0.42150 ⁇ 0.00016), O1 (0,0,0.27671 ⁇ 0.00045), and O2 (0,0,0.11535 ⁇ 0.00045).
  • O1 and O2 are oxygen atoms.
  • Which unit cell should be used to express the crystal structure of the positive electrode active material can be determined, for example, by Rietveld analysis of the XRD pattern. In this case, it is sufficient to adopt the unit cell that results in the smallest GOF (goodness of fit) value.
  • conventional lithium cobalt oxide repeatedly changes its crystal structure (i.e., undergoes a non-equilibrium phase change) between the H1-3 type crystal structure and the R-3m O 3 structure in the discharged state.
  • the H1-3 type crystal structure has a structure in which two CoO layers are continuous, such as the trigonal O1 type, and is therefore likely to be unstable.
  • the crystal structure of conventional lithium cobalt oxide breaks down when it is repeatedly charged and discharged so that x is 0.24 or less.
  • the breakdown of the crystal structure leads to a deterioration in cycle characteristics. This is because the breakdown of the crystal structure reduces the number of sites where lithium can exist stably and makes it difficult to insert and remove lithium ions.
  • the change in the crystal structure in the discharge state where x in Li x CoO 2 is 1 and the state where x is 0.24 or less is smaller than that of the conventional positive electrode active material. More specifically, the deviation of the CoO 2 layer in the state where x is 1 and the state where x is 0.24 or less can be reduced.
  • the volume change of the positive electrode active material 100 is smaller than the volume change of the conventional positive electrode active material. Therefore, the positive electrode active material 100 is less likely to collapse in crystal structure even when charging and discharging such that x is 0.24 or less are repeated, and excellent cycle characteristics can be realized.
  • the positive electrode active material 100 can have a more stable crystal structure than the conventional positive electrode active material in the state where x in Li x CoO 2 is 0.24 or less. Therefore, the positive electrode active material 100 is less likely to cause a short circuit when the state where x in Li x CoO 2 is 0.24 or less is maintained. In such a case, the safety of the secondary battery is further improved, which is preferable.
  • the interior 100b of the positive electrode active material 100 when x in Li x CoO 2 is 1, approximately 0.2, and approximately 0.15.
  • the interior 100b occupies most of the volume of the positive electrode active material 100 and is the part that contributes greatly to charge and discharge, so it can be said that the displacement of the CoO 2 layer and the change in volume are the most problematic parts.
  • the positive electrode active material 100 has the same crystal structure as conventional lithium cobalt oxide, R-3m O3.
  • the positive electrode active material 100 has a different crystal structure from that of conventional lithium cobalt oxide when x is 0.24 or less, for example, about 0.2 and about 0.15, in which case the lithium cobalt oxide has an H1-3 type crystal structure.
  • the symmetry of the CoO2 layer is the same as that of O3. Therefore, this crystal structure is called an O3' type crystal structure.
  • This crystal structure is shown in FIG. 4 with R-3m O3'.
  • the O3' type crystal structure can show the coordinates of cobalt and oxygen in the unit cell within the range of Co(0,0,0.5), O(0,0,x), 0.20 ⁇ x ⁇ 0.25.
  • the coordinates, a-axis and c-axis values can be calculated by estimating the crystal structure from the XRD pattern and using TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker).
  • the positive electrode active material 100 has a crystal structure belonging to the monoclinic space group P2/m. In this case, one CoO2 layer exists in the unit cell. In addition, the amount of lithium present in the positive electrode active material 100 at this time is about 15 atomic % in the discharged state. Therefore, this crystal structure is called a monoclinic O1(15) type crystal structure. This crystal structure is shown in FIG. 4 with P2/m monoclinic O1(15).
  • the monoclinic O1(15) crystal structure has the coordinates of cobalt and oxygen in the unit cell as follows: Co1(0.5,0,0.5), Co2(0,0.5,0.5), O1(X O1 , 0, Z O1 ), 0.23 ⁇ XO1 ⁇ 0.24, 0.61 ⁇ ZO1 ⁇ 0.65, O2(X O2 , 0.5, Z O2 ),
  • the lattice constant of the unit cell can be expressed as follows: 0.75 ⁇ X O2 ⁇ 0.78, 0.68 ⁇ Z O2 ⁇ 0.71.
  • a 4.880 ⁇ 0.05 ⁇
  • b 2.817 ⁇ 0.05 ⁇
  • this crystal structure can show the lattice constant even in the space group R-3m if a certain degree of error is allowed.
  • the coordinates of cobalt and oxygen in the unit cell are as follows: Co(0,0,0.5), O(0,0,Z O ), The range of Z O can be expressed as 0.21 ⁇ Z O ⁇ 0.23.
  • the difference in volume per the same number of cobalt atoms between R-3m O3 in a discharged state and the O3' type crystal structure is 2.5% or less, more specifically 2.2% or less, typically 1.8%.
  • the difference in volume per the same number of cobalt atoms between R-3m O3 in a discharged state and the monoclinic O1(15) crystal structure is 3.3% or less, more specifically 3.0% or less, typically 2.5%.
  • Table 1 shows the difference in volume per cobalt atom between R-3m O3 in a discharged state, O3', monoclinic O1(15), H1-3 type, and trigonal O1.
  • ICSD coll. code. 172909 and 88721 can be referred to.
  • H1-3 Non-Patent Document 3 can be referred to.
  • O3' and monoclinic O1(15) the lattice constants can be calculated from the respective XRD patterns.
  • the difference in volume between the H1-3 crystal structure and the R-3m O3 crystal structure in a discharged state can be calculated when comparing per the same number of cobalt atoms.
  • the volume change rate (%) in the table above when the denominator is the R-3m O3 crystal structure in a discharged state, the difference in volume is 3.9%. In other words, the difference in volume exceeds 3.5%, and is extremely large.
  • the difference in volume between R-3m O3 in a discharged state and the O3' type crystal structure can be calculated when comparing per the same number of cobalt atoms.
  • the volume change rate (%) in the above table when the denominator is the R-3m O3 type crystal structure in a discharged state, the difference in volume is 1.8%. In other words, the difference in volume is less than 2.5%, more specifically less than 2.2%, which is very small.
  • the difference in volume between R-3m O3 in a discharged state and the monoclinic O1(15) type crystal structure can be calculated when comparing per the same number of cobalt atoms.
  • the volume change rate (%) in the table above when the denominator is the R-3m O3 type crystal structure in a discharged state, the difference in volume is 2.5%. In other words, the difference in volume is less than 3.3%, more specifically less than 3.0%, which is very small.
  • the positive electrode active material 100 when x in Li x CoO 2 is small, that is, when a large amount of lithium is released, the change in the crystal structure is suppressed more than in the conventional positive electrode active material.
  • the volume change of the positive electrode active material 100 is smaller than that of the conventional positive electrode active material. Therefore, the crystal structure of the positive electrode active material 100 is not easily broken even when charging and discharging are repeated such that x is 0.24 or less. Therefore, the positive electrode active material 100 suppresses the decrease in the charge and discharge capacity in the charge and discharge cycle.
  • the positive electrode active material 100 since more lithium can be stably used than in the conventional positive electrode active material, the positive electrode active material 100 has a large discharge capacity per weight and per volume. Therefore, by using the positive electrode active material 100, a secondary battery with a high discharge capacity per weight and per volume can be manufactured.
  • the positive electrode active material 100 may have an O3' type crystal structure when x in Li x CoO 2 is 0.15 or more and 0.24 or less, and it is estimated that the positive electrode active material 100 may have an O3' type crystal structure even when x is more than 0.24 and 0.27 or less. It has also been confirmed that the positive electrode active material 100 may have a monoclinic O1 (15) type crystal structure when x in Li x CoO 2 is more than 0.1 and 0.2 or less, typically when x is 0.15 or more and 0.17 or less.
  • the crystal structure is not necessarily limited to the above range of x because it is affected by not only x in Li x CoO 2 but also the number of charge and discharge cycles, charge and discharge current, temperature, etc.
  • the positive electrode active material 100 may have only O3' type, may have only monoclinic O1 (15) type, or may have both crystal structures. Also, all of the particles in the inside 100b of the positive electrode active material 100 do not have to have O3' type and/or monoclinic O1 (15) type crystal structures. They may contain other crystal structures, or may be partially amorphous.
  • the state in which x in Li x CoO 2 is small can be said to be a state in which it is charged at a high charging voltage.
  • a charging voltage of 4.6 V or more based on the potential of lithium metal can be said to be a high charging voltage.
  • the charging voltage is expressed based on the potential of lithium metal.
  • the positive electrode active material 100 is preferable because it can maintain a crystal structure with the symmetry of R-3m O3 even when charged at a high charging voltage, for example, a voltage of 4.6 V or more at 25°C. It can also be said that it is preferable because it can adopt an O3' type crystal structure when charged at a higher charging voltage, for example, a voltage of 4.65 V or more and 4.7 V or less at 25°C. It can also be said that it is preferable because it can adopt a monoclinic O1(15) type crystal structure when charged at an even higher charging voltage, for example, a voltage of more than 4.7 V and 4.8 V or less at 25°C.
  • the positive electrode active material 100 Even with the positive electrode active material 100, if the charging voltage is further increased, the H1-3 type crystal structure may finally be observed. As described above, the crystal structure is affected by the number of charge/discharge cycles, the charge/discharge current, temperature, etc., so when the charging voltage is lower, for example, even if the charging voltage is 4.5 V or more and less than 4.6 V at 25°C, the positive electrode active material 100 may be able to have an O3' type crystal structure. Similarly, when the counter electrode is lithium metal, at 25°C, charging at a voltage of 4.65 V or more and 4.7 V or less may result in a monoclinic O1(15) type crystal structure. The voltage reached during charging is called the upper limit voltage.
  • the voltage of the secondary battery drops by the amount of the graphite potential compared to the above.
  • the potential of graphite is about 0.05 V to 0.2 V based on the potential of lithium metal. Therefore, in the case of a secondary battery using graphite as the negative electrode active material, the battery has the same crystal structure as above when the voltage is the voltage above minus the graphite potential.
  • lithium is shown to exist at all lithium sites with equal probability, but this is not limited to the above.
  • Lithium may be present biasedly at some lithium sites, or may have symmetry, for example, as in monoclinic O1( Li0.5CoO2 ) shown in Fig. 5.
  • the distribution of lithium can be analyzed, for example, by neutron diffraction .
  • the O3' and monoclinic O1(15) type crystal structures have random lithium between the layers, but are similar to the CdCl2 type crystal structure.
  • This CdCl2 type-like crystal structure is close to the crystal structure of lithium nickel oxide when it is charged to Li0.06NiO2 , but it is known that pure lithium cobalt oxide or layered rock salt type positive electrode active materials containing a large amount of cobalt do not usually have the CdCl2 type crystal structure.
  • FIG. 16 shows the change in the c-axis length of the conventional lithium cobalt oxide described in Non-Patent Document 4.
  • the horizontal axis of FIG. 16 is the value of x in Li x CoO 2
  • the vertical axis is the c-axis length.
  • the round markers are hexagonal phases
  • the diamond markers are monoclinic phases.
  • the c-axis length shortens according to the change in x in Li x CoO 2.
  • phase transition from the monoclinic O3 to the H1-3 phase is a phase transition associated with the desorption of lithium ions, it is thought that the phase transition occurs from the surface of the positive electrode active material, which is the region where lithium ions are first removed, but it may eventually extend to the entire positive electrode active material.
  • the phase transition to spinel is a phase transition accompanied by the desorption of oxygen, so it is considered to occur from the surface from which oxygen is easily desorbed.
  • Lithium cobalt oxide that becomes H1-3 when x in Li x CoO 2 is about 0.2 does not have an additive element in the surface layer part, or the distribution of the additive element in the surface layer part is insufficient, so oxygen is easily desorbed from the surface and it may be easily phase-changed to a spinel type crystal structure.
  • the spinel type crystal structure may be more likely to phase-change to a rock salt type crystal structure. These phase changes may be particularly likely to propagate in the direction perpendicular to the c-axis. When the region of the spinel type crystal structure and the rock salt type crystal structure increases, the charge/discharge capacity of the positive electrode active material decreases.
  • the added elements present in the surface layer are expected to suppress the phase change to spinel.
  • the concentration gradient of the added element is the same in multiple locations on the surface layer 100a of the positive electrode active material 100.
  • the reinforcement resulting from the added element is present homogeneously in the surface layer 100a. Even if a portion of the surface layer 100a is reinforced, if there is a portion without reinforcement, there is a risk that stress will concentrate in the portion without reinforcement. If stress concentrates in a portion of the positive electrode active material 100, defects such as cracks may occur there, which may lead to cracking of the positive electrode active material and a decrease in discharge capacity.
  • the additive element does not necessarily have to have the same concentration gradient in the entire surface layer 100a of the positive electrode active material 100.
  • Enlarged views of the vicinity of C-D in FIG. 1A1 are shown in FIG. 6A1 and FIG. 6A2.
  • An example of the distribution of additive element A in the vicinity of C-D in FIG. 1A1 is shown in FIG. 6A1
  • an example of the distribution of additive element B in the vicinity of C-D is shown in FIG. 6A2.
  • the vicinity of C-D has a layered rock salt type crystal structure of R-3m, and the surface is (001) oriented.
  • the (001) oriented surface may have a different distribution of added elements from other surfaces.
  • the (001) oriented surface and its surface layer 100a may have a distribution of one or more concentration peaks selected from added element A and added element B limited to a shallower portion from the surface compared to surfaces other than the (001) orientation.
  • the (001) oriented surface and its surface layer 100a may have a lower concentration of one or more selected from added element A and added element B compared to surfaces other than the (001) orientation.
  • the (001) oriented surface and its surface layer 100a may not have a detectable concentration of one or more selected from added element A and added element B.
  • the CoO 2 layer is relatively stable, it is more stable for the surface of the positive electrode active material 100 to have a (001) orientation. The main diffusion path of lithium ions during charge and discharge is not exposed on the (001) plane.
  • the diffusion paths of lithium ions are exposed on surfaces other than those with the (001) orientation. Therefore, the surfaces and surface layer 100a other than those with the (001) orientation are important regions for maintaining the diffusion paths of lithium ions, and at the same time, they are prone to becoming unstable because they are the regions from which lithium ions are first desorbed. Therefore, reinforcing the surfaces and surface layer 100a other than those with the (001) orientation is extremely important for maintaining the crystal structure of the entire positive electrode active material 100.
  • the positive electrode active material 100 it is important that the distribution of the added elements in the surface other than the (001) orientation and in the surface layer 100a thereof is as shown in FIG. 1B1 or FIG. 1B2.
  • nickel is particularly preferable to be detected in the surface other than the (001) orientation and in the surface layer 100a thereof.
  • the concentration of the added elements may be low or absent as described above.
  • the magnesium distribution in the (001) oriented surface and its surface layer 100a preferably has a half-width of 10 nm to 200 nm, more preferably 50 nm to 150 nm, and even more preferably 80 nm to 120 nm.
  • the magnesium distribution in the non-(001) oriented surface and its surface layer 100a preferably has a half-width of more than 200 nm to 500 nm, more preferably more than 200 nm to 300 nm, and even more preferably 230 nm to 270 nm.
  • the distribution of nickel in the surface that is not (001) oriented and in the surface layer 100a thereof preferably has a half-width of 30 nm or more and 150 nm or less, more preferably 50 nm or more and 130 nm or less, and even more preferably 70 nm or more and 110 nm or less.
  • the additive elements spread mainly through the diffusion path of lithium ions. Therefore, it is easy to make the distribution of the additive elements in the surface other than the (001) orientation and the surface layer 100a thereof into a preferred range.
  • FIG. 6B1 shows the results of calculations on a (104) oriented surface and its surface layer 100a. Calculations were performed using classical molecular dynamics. LiCoO 2 (LCO) was placed at the bottom of the system, and LiF and MgF 2 were placed at the top of the system as magnesium, lithium and fluorine sources. The ensemble was NVT, the density of the initial structure was 1.8 g/cm 3 , the temperature of the system was 2000 K, the elapsed time was 100 psec, the potential was optimized with the LCO crystal structure, the other atoms were mixed with UFF, the number of atoms in the system was about 10,000, and the charge of the system was neutral. To simplify the figure, Co atoms and Mg atoms are excerpted and shown.
  • Figure 6B2 shows the results of a similar calculation up to 200 psec
  • Figure 6B3 shows the results up to 1200 psec.
  • magnesium diffuses through the following process: (1) Lithium is desorbed from LCO due to heat. (2) Magnesium enters the lithium layer of LCO and diffuses inward. (3) Lithium from LiF enters the lithium layer of LCO, replacing the lithium that was desorbed in (1).
  • Figure 6C shows the results of calculations similar to those of Figure 6B1, except that the orientation is (001).
  • Figure 6C shows that the magnesium atoms remain on the surface of the LCO.
  • Figure 6C shows the results of calculations after 100 psec has elapsed.
  • the material is prepared by heating for, for example, 2 hours or more, so it is believed that the magnesium atoms diffuse slowly into the interior of the LCO.
  • the additive elements are mixed and heated, and the additive elements can be distributed more favorably on the surface other than the (001) orientation and on the surface layer 100a thereof than on the (001) plane by the production method.
  • lithium in the surface layer portion 100a will be desorbed from LiCoO2 by the initial heating, which will make it easier to distribute added elements such as magnesium in high concentrations in the surface layer portion.
  • the surface of the positive electrode active material 100 is smooth and has few irregularities, but this is not necessarily the case for the entire surface of the positive electrode active material 100.
  • a composite oxide having a layered rock salt type crystal structure of R-3m is prone to slippage on a surface parallel to the (001) surface, for example, on a surface where lithium is arranged.
  • slippage may occur parallel to the (001) surface, as shown by the arrow in FIG. 7B, by going through a process such as pressing, resulting in deformation.
  • the additional element may not be present on the new surface and its surface layer 100a that are generated as a result of the slip.
  • E-F in FIG. 7B is an example of the new surface and its surface layer 100a that are generated as a result of the slip. Enlarged views of the area around E-F are shown in FIG. 7C1 and FIG. 7C2. Unlike FIG. 1B1 to FIG. 1B2, additional element A and additional element B are not distributed in FIG. 7C1 and FIG. 7C2.
  • the additive element contained in the positive electrode active material 100 is at least partially distributed unevenly in the crystal grain boundaries 101 and their vicinity, in addition to the distribution as described above.
  • the magnesium concentration at and near the grain boundaries 101 of the positive electrode active material 100 is higher than that in other regions of the interior 100b. It is also preferable that the fluorine concentration at and near the grain boundaries 101 is higher than that in other regions of the interior 100b. It is also preferable that the nickel concentration at and near the grain boundaries 101 is higher than that in other regions of the interior 100b. It is also preferable that the aluminum concentration at and near the grain boundaries 101 is higher than that in other regions of the interior 100b.
  • the grain boundary 101 is a type of planar defect. Therefore, like the particle surface, it is prone to become unstable and changes in the crystal structure are likely to begin. Therefore, if the concentration of the added element at and near the grain boundary 101 is high, changes in the crystal structure can be more effectively suppressed.
  • the magnesium concentration and fluorine concentration are high at and near the grain boundaries 101, even if cracks occur along the grain boundaries 101 of the positive electrode active material 100, the magnesium concentration and fluorine concentration will be high near the surface created by the cracks. Therefore, the corrosion resistance to hydrofluoric acid can be improved even in the positive electrode active material after cracks have occurred.
  • the median diameter (D50) is preferably 1 ⁇ m or more and 100 ⁇ m or less, more preferably 2 ⁇ m or more and 40 ⁇ m or less, and even more preferably 5 ⁇ m or more and 30 ⁇ m or less. Or 1 ⁇ m or more and 40 ⁇ m or less is preferable.
  • Or 1 ⁇ m or more and 30 ⁇ m or less is preferable. Or 2 ⁇ m or more and 100 ⁇ m or less is preferable. Or 2 ⁇ m or more and 30 ⁇ m or less is preferable. Or 5 ⁇ m or more and 100 ⁇ m or less is preferable. Or 5 ⁇ m or more and 40 ⁇ m or less is preferable.
  • the volume resistivity of the powder of the positive electrode active material 100 at a pressure of 64 MPa is preferably 1.0 ⁇ 10 4 ⁇ cm or more, more preferably 1.0 ⁇ 10 5 ⁇ cm or more, and even more preferably 1.0 ⁇ 10 6 ⁇ cm or more. Also, at a pressure of 64 MPa, the volume resistivity is preferably 1.0 ⁇ 10 9 ⁇ cm or less, more preferably 1.0 ⁇ 10 8 ⁇ cm or less, and even more preferably 1.0 ⁇ 10 7 ⁇ cm or less.
  • the powder resistivity becomes high. Therefore, the above volume resistivity can be used as an indicator that the surface layer portion 100a has been well formed. Specifically, the presence of the surface layer portion 100a can be determined by the volume resistivity being higher than that of a positive electrode active material that does not have the added element.
  • the powder volume resistivity measuring device preferably has a first mechanism 10 having a terminal for resistance measurement and a second mechanism 11 for applying pressure to the powder sample (sample) to be measured.
  • the second mechanism 11 has a cylinder for introducing the powder sample and may have a piston that can move up and down inside the cylinder. A spring or the like is connected to the piston, and pressure can be applied to the sample in the cylinder.
  • the first mechanism 10 may have a measurement electrode that contacts the bottom surface of the cylinder.
  • MCP-PD51 manufactured by Mitsubishi Chemical Analytech Co., Ltd.
  • Loresta GP can be used as a resistance meter.
  • Loresta GP can be used to measure low resistance samples by the four-probe method as shown in FIG. 17B
  • Hiresta UP can be used to measure high resistance samples by the two-terminal method as shown in FIG. 17C.
  • the measurement environment is preferably a stable environment such as a dry room, but may be a general laboratory environment.
  • the dry room environment is preferably, for example, a temperature environment of 20°C to 25°C and a dew point environment of -40°C or less.
  • a typical laboratory environment may be a temperature environment of 15°C to 30°C and a humidity environment of 30% to 70%.
  • the second mechanism 11 has a measuring section, in which the sample is placed in a cylinder and the bottom surface of the cylinder is in contact with a measuring electrode, and the measuring section has a structure including a piston or the like capable of applying pressure to the sample.
  • the measuring section also has a structure for measuring the thickness of the sample.
  • the electrical resistance of the powder and the thickness of the powder are measured while pressure is applied to the powder.
  • the pressure applied to the powder can be measured under a number of conditions.
  • the electrical resistance and thickness of the powder can be measured under pressure conditions of 13 MPa, 25 MPa, 38 MPa, 51 MPa, and 64 MPa.
  • the volume resistivity of the powder can be calculated from the measured electrical resistance and thickness of the powder.
  • volume resistivity is found by multiplying the electrical resistance of the powder by the area of the measurement electrode in contact with the powder and dividing by the thickness of the powder.
  • volume resistivity is found by multiplying the electrical resistance of the powder by a correction coefficient and then multiplying it by the thickness of the powder.
  • the correction coefficient is a value that changes depending on the sample shape, dimensions, and measurement position, and can be calculated using the calculation software built into the Loresta GP.
  • the volume resistivity of the powder of the positive electrode active material 100 is preferably 1.0 ⁇ 10 4 ⁇ cm or more at a pressure of 64 MPa, more preferably 1.0 ⁇ 10 5 ⁇ cm or more, and more preferably 1.0 ⁇ 10 6 ⁇ cm or more. Also, at a pressure of 64 MPa, it is preferably 1.0 ⁇ 10 9 ⁇ cm or less, more preferably 1.0 ⁇ 10 8 ⁇ cm or less, and more preferably 1.0 ⁇ 10 7 ⁇ cm or less.
  • a battery having the positive electrode active material 100 exhibiting such a volume resistivity exhibits favorable cycle characteristics in a charge-discharge cycle test under high voltage conditions.
  • a certain positive electrode active material is a positive electrode active material 100 having an O3′ type and/or monoclinic O1(15) type crystal structure when x in Li x CoO 2 is small can be determined by analyzing a positive electrode having a positive electrode active material with a small x in Li x CoO 2 using XRD, electron beam diffraction, neutron beam diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), or the like.
  • XRD is particularly preferred because it can analyze the symmetry of transition metals such as cobalt contained in the positive electrode active material with high resolution, it can compare the degree of crystallinity and the orientation of the crystals, it can analyze the periodic distortion of the lattice and the crystallite size, and it can obtain sufficient accuracy even when the positive electrode obtained by disassembling the secondary battery is measured as it is.
  • powder XRD can obtain diffraction peaks that reflect the crystal structure of the interior 100b of the positive electrode active material 100, which occupies most of the volume of the positive electrode active material 100.
  • the positive electrode active material When analyzing crystallite size by powder XRD, it is preferable to perform the measurement while excluding the influence of the orientation of the positive electrode active material particles due to pressure, etc. For example, it is preferable to take the positive electrode active material from the positive electrode obtained by disassembling a secondary battery, prepare a powder sample, and then perform the measurement.
  • the positive electrode active material 100 is characterized in that there is little change in the crystal structure when x in Li x CoO 2 is 1 and when it is 0.24 or less. Materials that have a crystal structure that changes significantly when charged at a high voltage and that accounts for 50 wt % or more of the crystal structure are not preferred because they cannot withstand repeated high-voltage charging and discharging.
  • the O3' or monoclinic O1(15) crystal structure is not obtained by simply adding an additive element.
  • lithium cobalt oxide having magnesium and fluorine, or lithium cobalt oxide having magnesium and aluminum is common, depending on the concentration and distribution of the additive element, there are cases where x in Li x CoO 2 is 0.24 or less and the O3' and/or monoclinic O1(15) crystal structure is 60 wt% or more, and cases where the H1-3 crystal structure is 50 wt% or more.
  • the positive electrode active material 100 even in the case of the positive electrode active material 100, if x is too small, such as 0.1 or less, or under conditions where the charging voltage exceeds 4.9 V, an H1-3 type or trigonal O1 type crystal structure may be produced. Therefore, to determine whether or not it is a positive electrode active material 100, analysis of the crystal structure, such as XRD, and information such as the charging capacity or charging voltage are required.
  • the positive electrode active material has a small x value
  • its crystal structure may change when exposed to air.
  • the crystal structure may change from O3' type or monoclinic O1(15) type to H1-3 type. Therefore, it is preferable to handle all samples used for crystal structure analysis in an inert atmosphere such as an argon atmosphere.
  • Whether the distribution of added elements in a certain positive electrode active material is as described above can be determined by analyzing it using, for example, XPS, energy dispersive X-ray spectroscopy (EDX), electron probe microanalysis (EPMA), etc.
  • EDX energy dispersive X-ray spectroscopy
  • EPMA electron probe microanalysis
  • the crystal structure of the surface layer 100a, the grain boundaries 101, etc. can be analyzed by electron beam diffraction of a cross section of the positive electrode active material 100.
  • Charging for determining whether a certain composite oxide is the positive electrode active material 100 can be performed by preparing, for example, a coin-type secondary battery (CR2032 type, diameter 20 mm, height 3.2 mm) as a half cell with a counter electrode of lithium metal.
  • the coin-type secondary battery has a positive electrode having the positive electrode active material 100, lithium metal, an electrolyte, a separator, a positive electrode can, and a negative electrode can.
  • the positive electrode can be prepared by coating a positive electrode current collector made of aluminum foil with a slurry of a mixture of a positive electrode active material, a conductive material, and a binder.
  • Lithium metal can be used for the counter electrode.
  • the potential of the secondary battery and the potential of the positive electrode are different. Unless otherwise specified, the voltage and potential in this specification are the potential of the positive electrode.
  • the electrolyte contains a lithium salt, a solvent, and an additive.
  • the lithium salt is 1 mol/L lithium hexafluorophosphate (LiPF 6 ).
  • vinylene carbonate (VC) is used as an additive, and the electrolyte is made by mixing VC at 2 wt % with the mixed solvent in which the lithium salt is dissolved.
  • a 25 ⁇ m thick polypropylene porous film can be used as the separator.
  • the positive and negative electrode cans can be made of stainless steel (SUS).
  • the coin-type secondary battery prepared under the above conditions is charged to an arbitrary voltage (for example, 4.5V, 4.55V, 4.6V, 4.65V, 4.7V, 4.75V or 4.8V).
  • the voltage reached during charging is called the upper limit voltage.
  • the charging method is not particularly limited as long as it is possible to charge to an arbitrary voltage over a sufficient period of time.
  • the current in CC charging can be 20mA/g or more and 100mA/g or less.
  • CV charging can be terminated at 2mA/g or more and 10mA/g or less. In order to observe the phase change of the positive electrode active material, it is desirable to charge at such a small current value.
  • the temperature is 25°C or 45°C.
  • the coin-type secondary battery is disassembled in a glove box in an argon atmosphere and the positive electrode is taken out, and a positive electrode active material with an arbitrary charging capacity can be obtained.
  • XRD can be performed by sealing the battery in a sealed container in an argon atmosphere.
  • the conditions for the multiple charge/discharge cycles may be different from the above-mentioned charging conditions.
  • charging can be performed by constant current charging at a current value of 20 mA/g to 100 mA/g up to an arbitrary voltage (e.g., 4.6 V, 4.65 V, 4.7 V, 4.75 V, or 4.8 V), followed by constant voltage charging until the current value becomes 2 mA/g to 10 mA/g, and discharging at a constant current of 20 mA/g to 100 mA/g up to 2.5 V (called CC discharge).
  • CC discharge a constant current of 20 mA/g to 100 mA/g up to 2.5 V
  • the battery when analyzing the crystal structure in the discharged state after multiple charge/discharge cycles, the battery can be discharged at a constant current of 20 mA/g or more and 100 mA/g or less until the voltage reaches 2.5 V, for example.
  • the XRD measurement apparatus and conditions are not particularly limited.
  • the measurement can be performed using the following apparatus and conditions.
  • XRD device Bruker AXS, D8 ADVANCE
  • X-ray source CuK ⁇ ray output: 40 kV, 40 mA
  • Divergence angle Div. Slit, 0.5° Detector: LynxEye Scan method: 2 ⁇ / ⁇ continuous scan Measurement range (2 ⁇ ): 15° to 90° Step width (2 ⁇ ): 0.01°
  • Setting count time 1 second/step Sample stage rotation: 15 rpm
  • the obtained diffraction pattern can be analyzed by using the analysis software DIFFRAC.EVA to remove the peak of CuK ⁇ 2 ray, and a diffraction pattern by CuK ⁇ 1 ray can be obtained.
  • the analysis software can also be used to correct the background.
  • the measurement sample is a powder, it is sometimes called powder X-ray diffraction, and the sample can be set by placing it in a glass sample holder, or sprinkling the sample on a greased silicon non-reflective plate, or by other methods.
  • the measurement sample is a positive electrode
  • the positive electrode can be attached to a substrate with double-sided tape, and the positive electrode active material layer can be set according to the measurement surface required by the device. Even when the measurement sample is a positive electrode, the binder and conductive material of the positive electrode active material layer are amorphous, and a diffraction pattern corresponding to the powder X-ray diffraction of the positive electrode active material can be obtained.
  • Figures 10A and 10B show the diffraction patterns of the O3' type crystal structure, the monoclinic O1(15) type crystal structure, and the H1-3 type crystal structure, with Figure 10A showing an enlarged view of the region in which the 2 ⁇ range is 18° to 21°, and Figure 10B showing an enlarged view of the region in which the 2 ⁇ range is 42° to 46°.
  • the patterns of LiCoO 2 (O3) and CoO 2 (O1) were created using Reflex Powder Diffraction, one of the modules of Materials Studio (BIOVIA), from crystal structure information obtained from ICSD (Inorganic Crystal Structure Database) (see Non-Patent Document 5).
  • the diffraction pattern of the H1-3 type crystal structure was similarly created from the crystal structure information described in Non-Patent Document 3.
  • the diffraction patterns of the O3′ type and monoclinic O1(15) type crystal structures were estimated from the diffraction pattern of the positive electrode active material 100, and fitting was performed using TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker Corporation), and diffraction patterns were created in the same manner as for the others.
  • the positive electrode active material 100 has an O3'-type and/or monoclinic O1 (15)-type crystal structure when x in Li x CoO 2 is small, but not all positive electrode active material particles may have an O3'-type and/or monoclinic O1 (15)-type crystal structure. In other words, some positive electrode active material particles may have other crystal structures or may be amorphous.
  • the O3'-type and/or monoclinic O1 (15)-type crystal structure is preferably 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more.
  • the O3'-type and/or monoclinic O1 (15)-type crystal structure is 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more, it can be a positive electrode active material with sufficiently excellent cycle characteristics.
  • the O3' type and/or monoclinic O1(15) type crystal structure is 35 wt% or more, more preferably 40 wt% or more, and even more preferably 43 wt% or more.
  • the H1-3 type and O1 type crystal structures are 50 wt % or less.
  • each peak after charging is sharp, i.e., the half-width, for example, the full width at half maximum, is narrow.
  • the half-width varies depending on the XRD measurement conditions and the value of 2 ⁇ , even for peaks arising from the same crystal phase.
  • the full width at half maximum is preferably, for example, 0.2° or less, more preferably 0.15° or less, and even more preferably 0.12° or less. Note that not all peaks necessarily meet this requirement. If some peaks meet this requirement, it can be said that the crystallinity of the crystal phase is high. Such high crystallinity contributes sufficiently to stabilizing the crystal structure after charging.
  • the crystallite size of the O3' type and monoclinic O1 (15) crystal structures of the positive electrode active material 100 is only reduced to about 1/20 of LiCoO 2 (O3) in the discharged state. Therefore, even under the same XRD measurement conditions as the positive electrode before charging and discharging, when x in Li x CoO 2 is smaller than 1, a clear peak of the O3' type and/or monoclinic O1 (15) crystal structure can be confirmed.
  • the crystallite size becomes small and the peak becomes broad and small. The crystallite size can be determined from the half-width of the XRD peak.
  • the positive electrode active material 100 has a small influence of the Jahn-Teller effect.
  • the positive electrode active material 100 may contain transition metals such as nickel and manganese as additive elements in addition to cobalt.
  • Figure 11 shows the results of calculating the lattice constants of the a-axis and c-axis using XRD when the positive electrode active material 100 has a layered rock salt type crystal structure and contains cobalt and nickel.
  • Figure 11A shows the result for the a-axis
  • Figure 11B shows the result for the c-axis. Note that the XRD patterns used for these calculations are for the powder after the synthesis of the positive electrode active material, and before it is incorporated into the positive electrode.
  • the nickel concentration on the horizontal axis indicates the nickel concentration when the sum of the number of cobalt and nickel atoms is taken as 100%.
  • the positive electrode active material was produced according to the production method shown in Figure 18 described later, except that no aluminum source was used.
  • Figure 12 shows the results of estimating the a-axis and c-axis lattice constants using XRD when the positive electrode active material 100 has a layered rock salt type crystal structure and contains cobalt and manganese.
  • Figure 12A shows the a-axis result
  • Figure 12B shows the c-axis result.
  • the lattice constants shown in Figure 12 are based on XRD measurements of the powder after synthesis of the positive electrode active material and before incorporation into the positive electrode.
  • the manganese concentration on the horizontal axis indicates the concentration of manganese when the sum of the number of cobalt and manganese atoms is taken as 100%.
  • the positive electrode active material was produced according to the production method shown in Figure 18 described later, except that a manganese source was used instead of a nickel source, and no aluminum source was used.
  • Figure 11C shows the value obtained by dividing the a-axis lattice constant by the c-axis lattice constant (a-axis/c-axis) for the positive electrode active material whose lattice constant results are shown in Figures 11A and 11B.
  • Figure 12C shows the value obtained by dividing the a-axis lattice constant by the c-axis lattice constant (a-axis/c-axis) for the positive electrode active material whose lattice constant results are shown in Figures 12A and 12B.
  • Figure 11C shows that the a-axis/c-axis tend to change significantly when the nickel concentration is 5% and 7.5%, and the distortion of the a-axis is large when the nickel concentration is 7.5%. This distortion may be due to the Jahn-Teller distortion of trivalent nickel. It is suggested that an excellent positive electrode active material with small Jahn-Teller distortion can be obtained when the nickel concentration is less than 7.5%.
  • FIG. 12A suggests that when the manganese concentration is 5% or more, the behavior of the change in lattice constant is different and does not follow Vegard's law. This suggests that when the manganese concentration is 5% or more, the crystal structure is different. Therefore, it is preferable that the manganese concentration is, for example, 4% or less.
  • nickel concentration and manganese concentration ranges do not necessarily apply to the surface layer 100a.
  • concentrations in the surface layer 100a may be higher than those described above.
  • the preferable range of the lattice constant was considered, and it was found that, in the positive electrode active material of one embodiment of the present invention, in the layered rock salt crystal structure of the positive electrode active material 100 in a state where no charging or discharging is performed or in a discharged state, which can be estimated from the XRD pattern, the a-axis lattice constant is preferably greater than 2.814 ⁇ 10 ⁇ 10 m and smaller than 2.817 ⁇ 10 ⁇ 10 m, and the c-axis lattice constant is preferably greater than 14.05 ⁇ 10 ⁇ 10 m and smaller than 14.07 ⁇ 10 ⁇ 10 m.
  • the state where no charging or discharging is performed may be, for example, a powder state before the positive electrode of a secondary battery is prepared.
  • the value obtained by dividing the lattice constant of the a-axis by the lattice constant of the c-axis is greater than 0.20000 and less than 0.20049.
  • a first peak may be observed at 2 ⁇ of 18.50° or more and 19.30° or less, and a second peak may be observed at 2 ⁇ of 38.00° or more and 38.80° or less.
  • XPS> In X-ray photoelectron spectroscopy (XPS), in the case of inorganic oxides, when monochromatic aluminum K ⁇ rays are used as the X-ray source, it is possible to analyze a region from the surface to a depth of about 2 to 8 nm (usually 5 nm or less), so that the concentration of each element can be quantitatively analyzed in a region about half the depth of the surface layer 100a. In addition, narrow scan analysis can be used to analyze the bonding state of the elements.
  • XPS X-ray photoelectron spectroscopy
  • the positive electrode active material 100 preferably has a higher concentration of one or more selected from the additive elements in the surface layer 100a than in the interior 100b. This is synonymous with the fact that the concentration of one or more selected from the additive elements in the surface layer 100a is preferably higher than the average concentration of the entire positive electrode active material 100. Therefore, for example, it can be said that the concentration of one or more additive elements selected from the surface layer 100a measured by XPS or the like is preferably higher than the average concentration of the additive elements in the entire positive electrode active material 100 measured by ICP-MS or GD-MS or the like. For example, it is preferable that the magnesium concentration of at least a part of the surface layer 100a measured by XPS or the like is higher than the average magnesium concentration of the entire positive electrode active material 100.
  • the nickel concentration of at least a part of the surface layer 100a is higher than the average nickel concentration of the entire positive electrode active material 100. It is also preferable that the aluminum concentration of at least a part of the surface layer 100a is higher than the average aluminum concentration of the entire positive electrode active material 100. It is also preferable that the fluorine concentration in at least a portion of the surface layer 100a is higher than the average fluorine concentration in the entire positive electrode active material 100.
  • the surface and surface layer 100a of the positive electrode active material 100 do not contain carbonates, hydroxyl groups, etc. that are chemically adsorbed after the preparation of the positive electrode active material 100. Also, they do not contain electrolyte, binder, conductive material, or compounds derived from these that are attached to the surface of the positive electrode active material 100. Therefore, when quantifying the elements contained in the positive electrode active material, corrections may be made to exclude carbon, hydrogen, excess oxygen, excess fluorine, etc. that can be detected by surface analysis such as XPS. For example, XPS makes it possible to separate the types of bonds by analysis, and corrections may be made to exclude C-F bonds derived from the binder.
  • the samples such as the positive electrode active material and the positive electrode active material layer may be washed to remove the electrolyte, binder, conductive material, or compounds derived from these that are attached to the surface of the positive electrode active material.
  • lithium may dissolve into the solvent used for washing, but even in this case, the added element is unlikely to dissolve, so the atomic ratio of the added element is not affected.
  • the concentration of the added element may also be expressed using the ratio to cobalt (called the cobalt ratio).
  • the cobalt ratio is preferable because it allows comparisons to be made while reducing the influence of carbonates and the like that are chemically adsorbed after the positive electrode active material is produced.
  • the ratio Mg/Co of the number of magnesium and cobalt atoms as determined by XPS analysis is preferably 0.4 or more and 1.5 or less.
  • the ratio Mg/Co as determined by ICP-MS analysis is preferably 0.001 or more and 0.06 or less.
  • the concentrations of lithium and cobalt in the surface layer portion 100a are higher than the concentrations of one or more additive elements selected from the additive elements contained in the surface layer portion 100a measured by XPS or the like.
  • the concentration of at least a part of the cobalt in the surface layer portion 100a measured by XPS or the like is higher than the concentration of at least a part of the magnesium in the surface layer portion 100a measured by XPS or the like.
  • the concentration of lithium is higher than the concentration of magnesium.
  • the concentration of cobalt is higher than the concentration of nickel.
  • the concentration of lithium is higher than the concentration of nickel. It is also preferable that the concentration of cobalt is higher than the concentration of aluminum. It is also preferable that the concentration of lithium is higher than the concentration of aluminum. It is also preferable that the concentration of cobalt is higher than the concentration of fluorine. It is also preferable that the concentration of lithium is higher than the concentration of fluorine.
  • the additive element B such as aluminum
  • the additive element B is widely distributed in a deep region, for example, a region having a depth from the surface of 5 nm to 50 nm. Therefore, it is more preferable that the additive element B, such as aluminum, is detected in an analysis of the entire positive electrode active material 100 using ICP-MS, GD-MS, etc., but its concentration is not detected by XPS, etc.
  • the number of magnesium atoms was preferably 0.4 to 1.2 times, more preferably 0.65 to 1.0 times, relative to the number of cobalt atoms.
  • the number of nickel atoms was preferably 0.15 times or less, more preferably 0.03 to 0.13 times, relative to the number of cobalt atoms.
  • the number of aluminum atoms was preferably 0.12 times or less, more preferably 0.09 times or less, relative to the number of cobalt atoms.
  • the number of fluorine atoms was preferably 0.3 to 0.9 times, more preferably 0.1 to 1.1 times, relative to the number of cobalt atoms.
  • the above ranges indicate that these additive elements are not attached to a narrow area on the surface of the positive electrode active material 100, but are widely distributed in the surface layer 100a of the positive electrode active material 100 at a preferred concentration.
  • monochromated aluminum K ⁇ rays can be used as the X-ray source.
  • the take-off angle can be set to, for example, 45°.
  • the measurement can be performed using the following apparatus and conditions.
  • the peak showing the bond energy between fluorine and other elements is preferably 682 eV or more and less than 685 eV, and more preferably about 684.3 eV. This is a different value from both the bond energy of lithium fluoride, 685 eV, and the bond energy of magnesium fluoride, 686 eV.
  • the peak showing the bond energy between magnesium and other elements is preferably equal to or greater than 1302 eV and less than 1304 eV, and more preferably about 1303 eV. This is a different value from the bond energy of magnesium fluoride, which is 1305 eV, and is close to the bond energy of magnesium oxide.
  • ⁇ EDX> It is preferable that one or more selected from the additive elements contained in the positive electrode active material 100 have a concentration gradient. It is more preferable that the depth from the surface of the concentration peak differs depending on the additive element in the positive electrode active material 100.
  • the concentration gradient of the additive element can be evaluated, for example, by exposing a cross section of the positive electrode active material 100 by FIB or the like and analyzing the cross section by EDX, EPMA, or the like.
  • EDX area analysis In EDX measurements, performing measurements while scanning an area and evaluating the area in two dimensions is called EDX area analysis. Performing measurements while scanning linearly and evaluating the distribution of atomic concentrations within the positive electrode active material is called line analysis. Furthermore, data extracted from a linear area from EDX area analysis is sometimes called line analysis. Measuring an area without scanning is called point analysis.
  • EDX surface analysis can quantitatively analyze the concentration of the added element in the surface layer 100a, the interior 100b, and near the grain boundary 101 of the positive electrode active material 100.
  • EDX ray analysis can analyze the concentration distribution and maximum value of the added element.
  • analysis using a thinned sample such as STEM-EDX is more suitable because it can analyze the concentration distribution in the depth direction from the surface to the center of the positive electrode active material in a specific region without being affected by the distribution in the depth direction.
  • the concentration of each added element, particularly added element A, in the surface layer portion 100a is higher than the concentration of each added element, particularly added element A, in the interior portion 100b.
  • the magnesium concentration in the surface layer 100a is higher than the magnesium concentration in the interior 100b.
  • the peak of the magnesium concentration in the surface layer 100a is preferably present at a depth of 3 nm from the surface of the positive electrode active material 100 toward the center, more preferably at a depth of 1 nm, and even more preferably at a depth of 0.5 nm. It is preferable that the magnesium distribution decays to 60% or less of the peak at a point 1 nm deep from the peak top. It is also preferable that the magnesium distribution decays to 30% or less of the peak at a point 2 nm deep from the peak top. Note that the concentration peak here refers to the maximum value of the concentration.
  • the distribution of fluorine overlaps with the distribution of magnesium.
  • the difference in the depth direction between the peak of the fluorine concentration and the peak of the magnesium concentration is preferably within 10 nm, more preferably within 3 nm, and even more preferably within 1 nm.
  • the fluorine concentration peak of the surface layer 100a is preferably present at a depth of 3 nm from the surface toward the center of the positive electrode active material 100, more preferably at a depth of 1 nm, and even more preferably at a depth of 0.5 nm. Furthermore, it is more preferable for the fluorine concentration peak to be slightly closer to the surface than the magnesium concentration peak, as this increases resistance to hydrofluoric acid. For example, it is more preferable for the fluorine concentration peak to be 0.5 nm or more closer to the surface than the magnesium concentration peak, and even more preferable for it to be 1.5 nm or more closer to the surface.
  • the nickel concentration peak in the surface layer 100a is preferably present at a depth of up to 3 nm from the surface toward the center of the positive electrode active material 100, more preferably at a depth of up to 1 nm, and even more preferably at a depth of up to 0.5 nm.
  • the nickel distribution preferably overlaps with the magnesium distribution.
  • the difference in depth between the nickel concentration peak and the magnesium concentration peak is preferably within 10 nm, more preferably within 3 nm, and even more preferably within 1 nm.
  • the magnesium, nickel, or fluorine concentration peak is closer to the surface than the aluminum concentration peak of the surface layer 100a when EDX-ray analysis is performed.
  • the aluminum concentration peak is preferably present at a depth of 0.5 nm to 50 nm from the surface toward the center of the positive electrode active material 100, and more preferably at a depth of 5 nm to 50 nm.
  • the ratio of the number of atoms of magnesium Mg and cobalt Co (Mg/Co) at the peak of the magnesium concentration is preferably 0.05 to 0.6, more preferably 0.1 to 0.4.
  • the ratio of the number of atoms of aluminum Al and cobalt Co (Al/Co) at the peak of the aluminum concentration is preferably 0.05 to 0.6, more preferably 0.1 to 0.45.
  • the ratio of the number of atoms of nickel Ni and cobalt Co (Ni/Co) at the peak of the nickel concentration is preferably 0 to 0.2, more preferably 0.01 to 0.1.
  • the ratio of the number of atoms of fluorine F and cobalt Co (F/Co) at the peak of the fluorine concentration is preferably 0 to 1.6, more preferably 0.1 to 1.4.
  • the surface of the positive electrode active material 100 in the EDX analysis results can be estimated, for example, as follows: For an element that is uniformly present in the interior 100b of the positive electrode active material 100, such as oxygen or cobalt, the surface is determined as the point where the amount detected in the interior 100b is half that of the element.
  • the surface can be estimated using the amount of detected oxygen. Specifically, first, the average oxygen concentration O ave is obtained from the region in the interior 100b where the amount of detected oxygen is stable. At this time, if oxygen O bg that is thought to be due to chemical adsorption or background is detected in a region that can be clearly determined to be outside the surface, the average oxygen concentration O ave can be obtained by subtracting O bg from the measured value. The measurement point that shows a value that is 1/2 of this average value O ave , that is, a measurement value closest to 1/2O ave , can be estimated to be the surface of the positive electrode active material.
  • the surface can also be estimated in the same manner as above using the amount of cobalt detected.
  • the sum of the amounts of multiple transition metals detected can be used to make a similar estimation.
  • the amount of transition metals detected, including cobalt, is less susceptible to the effects of chemical adsorption, making it suitable for estimating the surface.
  • the ratio (A/Co) of the number of atoms of the added element A to the cobalt Co in the vicinity of the crystal grain boundary 101 is preferably 0.020 or more and 0.50 or less. More preferably, it is 0.025 or more and 0.30 or less. Still more preferably, it is 0.030 or more and 0.20 or less. Or it is preferably 0.020 or more and 0.30 or less. Or it is preferably 0.020 or more and 0.20 or less. Or it is preferably 0.025 or more and 0.50 or less. Or it is preferably 0.025 or more and 0.20 or less. Or it is preferably 0.030 or more and 0.50 or less. Or it is preferably 0.030 or more and 0.30 or less.
  • the ratio of the number of magnesium atoms to the number of cobalt atoms (Mg/Co) in the vicinity of the grain boundary 101 is preferably 0.020 or more and 0.50 or less. Further, it is preferably 0.025 or more and 0.30 or less. Further, it is preferably 0.030 or more and 0.20 or less. Or it is preferably 0.020 or more and 0.30 or less. Or it is preferably 0.020 or more and 0.20 or less. Or it is preferably 0.025 or more and 0.50 or less. Or it is preferably 0.025 or more and 0.20 or less. Or it is preferably 0.030 or more and 0.50 or less.
  • the additive element is not attached to a narrow area on the surface of the positive electrode active material 100, but is widely distributed at a preferred concentration in the surface layer 100a of the positive electrode active material 100.
  • EPMA Electro Probe Microanalysis
  • Area analysis can analyze the distribution of each element.
  • EPMA surface analysis is performed on the cross section of the positive electrode active material 100, it is preferable that one or more selected from the added elements have a concentration gradient, similar to the EDX analysis results. It is also more preferable that the depth from the surface of the concentration peak differs depending on the added element. The preferred range of the concentration peak of each added element is also the same as in the case of EDX.
  • EPMA analyzes a region from the surface to a depth of about 1 ⁇ m. Therefore, the quantitative values of each element may differ from the measurement results obtained using other analytical methods. For example, when the surface analysis of the positive electrode active material 100 is performed using EPMA, the concentration of each added element present in the surface layer 100a may be lower than the results of XPS.
  • the positive electrode active material 100 may exhibit a characteristic voltage change during charging.
  • the voltage change can be read from a dQ/dV vs V curve obtained by differentiating (dQ/dV) the capacity (Q) of the charging curve with respect to the voltage (V).
  • dQ/dV the capacity of the charging curve with respect to the voltage (V).
  • a non-equilibrium phase change occurs around the peak in the dQ/dV vs V curve, and the crystal structure changes significantly.
  • a non-equilibrium phase change refers to a phenomenon that causes a non-linear change in a physical quantity.
  • the positive electrode active material 100 may have a broad peak near 4.55V in the dQ/dV vs. V curve.
  • the peak near 4.55V reflects the change in voltage when the phase changes from the O3 type crystal structure to the O3' type crystal structure. Therefore, the broadness of this peak means that the change in energy required for lithium extraction is smaller than when the peak is sharp, that is, the change in the crystal structure is smaller. The smaller these changes are, the less the influence of the shift of the CoO2 layer and the change in volume is, and therefore, preferable.
  • the first peak when the maximum value appearing in the dQ/dV vs. V curve of the charging curve between 4.5 V and 4.6 V is defined as the first peak, it can be said that the first peak is sufficiently broad and is preferable if the full width at half maximum of the first peak is 0.10 V or more.
  • the full width at half maximum of the first peak is defined as the difference between the average value HWHM 1 of the first peak and the first minimum value when the minimum value of the dQ/dV value appearing in the range between 4.3 V and 4.5 V is defined as the first minimum value, and the average value HWHM 2 of the first peak and the second minimum value when the minimum value of the dQ/dV value appearing in the range between 4.6 V and 4.8 V is defined as the second minimum value.
  • charging can be performed at a constant current of 10 mA/g up to 4.9 V.
  • the data capture interval during charging can be set to capture the voltage and current at 1 second intervals or when there is a 1 mV voltage fluctuation.
  • the charge capacity is calculated by integrating the current value and time.
  • the difference between the nth and n+1th data of the above charging capacity data is defined as the nth value of the capacity change dQ.
  • the difference between the nth and n+1th data of the above voltage data is defined as the nth value of the voltage change dV.
  • the dQ/dV value may be calculated from the moving average of a certain number of intervals for the difference in voltage and charge capacity.
  • the number of intervals may be set to, for example, 500.
  • the average value of dQ from the nth to the n+500th is calculated, and similarly the average value of dV from the nth to the n+500th is calculated.
  • the dQ/dV value can be dQ (average of 500 pieces)/dV (average of 500 pieces).
  • the moving average value of 500 sections can be used for the voltage on the horizontal axis in the dQ/dV vs V graph. Note that when using a moving average of 500 sections as described above, it is preferable not to use the data from the 501st data from the end to the last data in the dQ/dV vs V graph, as the data is more susceptible to noise.
  • the multiple charge/discharge conditions may be different from the above-mentioned charging conditions.
  • charging may be performed at a constant current of 20 mA/g to 100 mA/g at any voltage (e.g., 4.6 V, 4.65 V, 4.7 V, 4.75 V, or 4.8 V), followed by constant voltage charging until the current value is 2 mA/g to 10 mA/g, and discharging at a constant current of 20 mA/g to 100 mA/g until the voltage reaches 2.5 V.
  • the phase changes from the O3 type crystal structure to the O3' type crystal structure at around 4.55V, and the O3 type crystal structure at this time has x in Li x CoO 2 of about 0.3.
  • ⁇ Discharge curve and dQ/dV vs V curve> Furthermore, when the positive electrode active material 100 is charged at a high voltage and then discharged at a low current of, for example, 40 mA/g or less, a characteristic voltage change may appear near the end of discharge. This change can be clearly confirmed by the presence of at least one peak in the range of voltages up to 3.5 V, lower than the peak that appears around 3.9 V, in the dQ/dV vs. V curve obtained from the discharge curve.
  • the positive electrode active material 100 preferably has cobalt and nickel and magnesium as additive elements.
  • a part of Co 3+ is replaced by Ni 3+
  • a part of Li + is replaced by Mg 2+ .
  • the Ni 3+ may be reduced to Ni 2+ .
  • a part of Li + may be replaced by Mg 2+ , and accordingly, Co 3+ in the vicinity of Mg 2+ may be reduced to Co 2+ .
  • a part of Co 3+ may be replaced by Mg 2+ , and accordingly, Co 3+ in the vicinity of Mg 2+ may be oxidized to Co 4+ .
  • the positive electrode active material 100 preferably has one or more of Ni 2+ , Ni 3+ , Co 2+ and Co 4+ .
  • the spin density caused by one or more of Ni 2+ , Ni 3+ , Co 2+ and Co 4+ per weight of the positive electrode active material 100 is preferably 2.0 ⁇ 10 17 spins/g or more and 1.0 ⁇ 10 21 spins/g or less.
  • the spin density in the positive electrode active material can be analyzed, for example, using electron spin resonance (ESR).
  • ESR electron spin resonance
  • the positive electrode active material 100 preferably has a smooth surface with few irregularities.
  • a smooth surface with few irregularities indicates that the effect of the flux described below is fully exerted and the surfaces of the additive element source and lithium cobalt oxide are melted. Therefore, this is one factor indicating that the distribution of the additive element in the surface layer portion 100a is good.
  • That the surface is smooth and has few irregularities can be determined, for example, from a cross-sectional SEM image or cross-sectional TEM image of the positive electrode active material 100, the specific surface area of the positive electrode active material 100, etc.
  • the surface smoothness can be quantified from a cross-sectional SEM image of the positive electrode active material 100 as follows:
  • the cathode active material 100 is processed by FIB or the like to expose the cross section. At this time, it is preferable to cover the cathode active material 100 with a protective film, a protective agent, or the like.
  • an SEM image of the interface between the protective film or the like and the cathode active material 100 is taken.
  • interface extraction is performed using image processing software.
  • the interface line between the protective film or the like and the cathode active material 100 is selected using an automatic selection tool or the like, and data is extracted to a spreadsheet software or the like.
  • this surface roughness is the surface roughness at least at 400 nm from the outer periphery of the particle of the cathode active material.
  • the particle surface of the positive electrode active material 100 of this embodiment preferably has a root mean square (RMS) surface roughness, which is an index of roughness, of less than 3 nm, preferably less than 1 nm, and more preferably less than 0.5 nm.
  • RMS root mean square
  • the image processing software used for noise processing, interface extraction, etc. is not particularly limited, but for example, "ImageJ" described in Non-Patent Documents 7 to 9 can be used.
  • Spreadsheet software, etc. is also not particularly limited, but for example, Microsoft Office Excel can be used.
  • the surface smoothness of the positive electrode active material 100 can also be quantified from the ratio of the actual specific surface area S R measured by a constant volume gas adsorption method to the ideal specific surface area S i .
  • the ideal specific surface area S i is calculated assuming that all particles have the same diameter D50, the same weight, and an ideal spherical shape.
  • the median diameter (D50) can be measured using a particle size distribution analyzer that uses a laser diffraction/scattering method.
  • the specific surface area can be measured using a specific surface area measuring device that uses, for example, a constant volume gas adsorption method.
  • the positive electrode active material 100 preferably has a ratio S R /S i of the ideal specific surface area S i determined from the median diameter (D50) to the actual specific surface area S R of 2.1 or less.
  • the surface smoothness can be quantified from a cross-sectional SEM image of the positive electrode active material 100 by the following method.
  • a surface SEM image of the positive electrode active material 100 is obtained.
  • a conductive coating may be applied as a pretreatment before observation.
  • the observation surface is preferably perpendicular to the electron beam.
  • a grayscale image contains luminance (brightness information).
  • the change in luminance can be quantified in relation to the number of gradations. This numerical value is called the grayscale value.
  • a histogram is a three-dimensional representation of the gradation distribution in the target area, and is also called a luminance histogram. Obtaining a luminance histogram makes it possible to visually evaluate the unevenness of the positive electrode active material in an easily understandable manner.
  • the difference between the maximum and minimum values of the above grayscale value of the positive electrode active material 100 is preferably 120 or less, more preferably 115 or less, and even more preferably 70 or more and 115 or less.
  • the standard deviation of the grayscale value is preferably 11 or less, more preferably 8 or less, and even more preferably 4 or more and 8 or less.
  • the distribution of the additive elements, including magnesium, contained in the surface layer of the positive electrode active material 100 may change slightly during repeated charging and discharging. For example, the distribution of the additive elements may become better, and the electronic conduction resistance may decrease. As a result, the electrical resistance at the beginning of the charge and discharge cycle, that is, the resistance component R (0.1s) with a fast response measured by the current rest method, may decrease.
  • the resistance component R (0.1s) with a fast response measured by the current rest method may be lower in the n+1th charge than in the nth charge.
  • the n+1th discharge capacity may be higher than the nth discharge capacity.
  • n 1, that is, when comparing the first charge with the second charge
  • the second charge capacity may be larger, especially in a positive electrode active material that does not contain an additive element, so it is preferable that n is, for example, 2 or more and 10 or less.
  • the charge/discharge capacity is about the same as the rated capacity, for example, 97% or more of the rated capacity, it can be said to be in the early stage of the charge/discharge cycle.
  • ⁇ Raman spectroscopy> As described above, it is preferable that at least a part of the surface layer 100a of the positive electrode active material 100 has a rock salt type crystal structure. Therefore, when the positive electrode active material 100 and a positive electrode having the same are analyzed by Raman spectroscopy, it is preferable that a cubic crystal structure such as a rock salt type is also observed along with the layered rock salt crystal structure.
  • peaks are observed at 470 cm -1 to 490 cm -1 and 580 cm -1 to 600 cm - 1 in layered rock salt LiCoO2
  • a peak is observed at 665 cm -1 to 685 cm -1 in cubic CoOx (0 ⁇ x ⁇ 1) (rock salt Co1 - yO (0 ⁇ y ⁇ 1) or spinel Co3O4 ).
  • the integrated intensity of each peak is defined as I1 from 470 cm -1 to 490 cm -1 , I2 from 580 cm -1 to 600 cm - 1, and I3 from 665 cm -1 to 685 cm -1 , it is preferable that the value of I3/I2 is 1% or more and 10% or less, and more preferably 3% or more and 9% or less.
  • the surface layer 100a of the positive electrode active material 100 has a rock salt type crystal structure within a preferred range.
  • the characteristics of the rock salt type crystal structure are observed in the electron microbeam diffraction pattern as well as the layered rock salt crystal structure.
  • the characteristics of the rock salt type crystal structure are not too strong in the surface layer 100a, especially in the outermost surface (for example, 1 nm deep from the surface), taking into account the above-mentioned difference in sensitivity. This is because the presence of an additive element such as magnesium in the lithium layer while maintaining the layered rock salt type crystal structure can ensure a diffusion path for lithium and has a stronger function of stabilizing the crystal structure than when the outermost surface is covered with a rock salt type crystal structure.
  • a micro-electron beam diffraction pattern is obtained from a region having a depth of 1 nm or less from the surface, and a micro-electron beam diffraction pattern is obtained from a region having a depth of 3 nm to 10 nm, it is preferable that the difference in the lattice constant calculated from these patterns is small.
  • the difference in lattice constant calculated from a measurement point at a depth of 1 nm or less from the surface and a measurement point at a depth of 3 nm to 10 nm is preferably 0.1 ⁇ or less for the a-axis, and 1.0 ⁇ or less for the c-axis. It is more preferable that the difference is 0.05 ⁇ or less for the a-axis, and more preferably 0.6 ⁇ or less for the c-axis. It is even more preferable that the difference is 0.04 ⁇ or less for the a-axis, and even more preferably 0.3 ⁇ or less for the c-axis.
  • the positive electrode active material 100 may have recesses, cracks, depressions, V-shaped cross sections, etc. These are defects, and repeated charging and discharging may cause elution of cobalt, collapse of the crystal structure, cracking of the positive electrode active material 100, desorption of oxygen, etc. However, if an additive element is present so as to fill the defect portion 100c as shown in FIG. 1B, elution of cobalt, etc. can be suppressed. Therefore, the reliability and cycle characteristics of a secondary battery using the positive electrode active material 100 can be improved.
  • the additive element contained in the positive electrode active material 100 may adversely affect the insertion and desorption of lithium.
  • the positive electrode active material 100 when used in a secondary battery, it may cause an increase in internal resistance and a decrease in discharge capacity.
  • the additive element may not be distributed throughout the entire surface layer 100a, and the effect of suppressing deterioration of the crystal structure may be insufficient.
  • the additive element needs to be in an appropriate concentration in the positive electrode active material 100, but adjusting this concentration is not easy.
  • the positive electrode active material 100 has a region where the additive element is unevenly distributed, some of the excess atoms of the additive element are removed from the interior 100b of the positive electrode active material 100, and an appropriate additive element concentration can be achieved in the interior 100b.
  • This makes it possible to suppress an increase in internal resistance and a decrease in discharge capacity when the battery is made into a secondary battery.
  • Being able to suppress an increase in the internal resistance of a secondary battery is an extremely desirable characteristic, particularly when charging and discharging at a large current, for example, at 400 mA/g or more.
  • the positive electrode active material 100 having an area where the additive element is unevenly distributed it is permissible to mix the additive element in excess to some extent during the manufacturing process. This allows for a wider margin in production, which is preferable.
  • Figures 13A and 13B show an example of a positive electrode active material 100 having a coating portion 104 attached thereto.
  • Figure 13A shows a positive electrode active material 100 having a surface portion 100a and an interior portion 100b as well as a coating portion 104.
  • Figure 13B shows a positive electrode active material 100 having a protruding portion 103 in addition to the surface portion 100a and an interior portion 100b, and further having a coating portion 104.
  • the coating portion 104 is preferably formed by, for example, deposition of decomposition products of lithium salt and organic solvent accompanying charge and discharge.
  • x in Li x CoO 2 is 0.24 or less
  • the charge and discharge cycle characteristics will be improved by having a coating portion derived from lithium salt, organic solvent, or additive on the surface of the positive electrode active material 100. This is due to reasons such as suppressing an increase in impedance on the surface of the positive electrode active material or suppressing the elution of cobalt.
  • the coating portion 104 preferably has, for example, carbon, oxygen, and fluorine.
  • the coating portion 104 having one or more selected from boron, nitrogen, sulfur, and fluorine may be a good quality coating portion and is preferable.
  • the coating portion 104 does not have to cover the entire positive electrode active material 100. For example, it is sufficient to cover 50% or more of the surface of the positive electrode active material 100, more preferably 70% or more, and even more preferably 90% or more.
  • the positive electrode active material when the positive electrode active material is charged at 4.5 V or higher, or when it is charged and discharged in a high temperature environment, such as 45°C or higher, progressive defects may develop that progress from the surface deep into the material.
  • the phenomenon in which defects progress to form holes in the positive electrode active material can be called pitting corrosion, and the holes that develop as a result of this phenomenon are also called pits in this specification.
  • Figure 14 shows a schematic cross-sectional view of a positive electrode active material 51 having pits. Also shown is a crystal plane 55 parallel to the arrangement of cations. Since Figure 14 is a cross-sectional view, pits 54 and pits 58 are shown as holes, but the shape of these openings is not circular but has depth and is groove-like. Also, as shown by pits 54 and pits 58, unlike recesses 52, they tend to form parallel to the arrangement of lithium ions.
  • Positive electrode active material 51 also has surface layer 53 and surface layer 56 where the added element is present.
  • the added element is reduced from surface layer 53 and/or surface layer 56, and it is expected that the function of the barrier film is reduced.
  • the crystal structure of lithium cobalt oxide breaks down in the vicinity of where the pits form, resulting in a crystal structure different from that of the layered rock salt type. When the crystal structure breaks down, it inhibits the diffusion and release of lithium ions, which are carrier ions, and therefore the pits are thought to be a factor in the deterioration of cycle characteristics.
  • the source of the pits may be point defects. It is thought that point defects in the positive electrode active material change with repeated charging and discharging, and are either chemically or electrochemically eroded by the surrounding lithium salts and organic solvents, or the material deteriorates, causing the pits. This deterioration does not occur uniformly on the surface of the positive electrode active material, but rather occurs in localized areas.
  • the positive electrode active material 51 in FIG. 14 has cracks 57.
  • the cracks 57 are also called fissures, and may occur due to the expansion and contraction of the positive electrode active material caused by charging and discharging.
  • cracks and pits are different. This is because cracks may exist but pits do not exist immediately after the preparation of the positive electrode active material.
  • the pits can be said to be holes formed by several layers of cobalt and oxygen being removed by charging and discharging under high voltage conditions of, for example, 4.5 V or more or at high temperatures (45° C. or more), and can also be said to be places where cobalt has dissolved.
  • the cracks refer to, for example, new surfaces formed by the application of physical pressure, or cracks caused by the grain boundaries 101.
  • the cracks may occur due to the expansion and contraction of the positive electrode active material caused by charging and discharging.
  • the pits may also occur from the cracks and/or cavities inside the positive electrode active material.
  • This embodiment can be used in combination with other embodiments.
  • the method of adding the added elements is important. At the same time, it is also important that the crystallinity of the interior 100b is good.
  • the process of producing the positive electrode active material 100 it is preferable to first synthesize lithium cobalt oxide, and then mix in the additive element source and perform a heat treatment.
  • the annealing temperature is too high, cation mixing occurs, increasing the possibility that an added element, such as magnesium, will enter the cobalt site.
  • Magnesium present at the cobalt site has no effect of maintaining the layered rock salt type crystal structure of R-3m when x in Li x CoO 2 is small.
  • the heat treatment temperature is too high, there are concerns about adverse effects such as cobalt being reduced to divalent and lithium being evaporated.
  • a material that functions as a flux with the additive element source.
  • Any material that has a lower melting point than lithium cobalt oxide can function as a flux.
  • fluorine compounds such as lithium fluoride are suitable. Adding a flux lowers the melting point of the additive element source and lithium cobalt oxide. Lowering the melting point makes it easier to distribute the additive element well at a temperature where cation mixing is unlikely to occur.
  • the initial heating causes lithium to be removed from part of the surface layer 100a of the lithium cobalt oxide, resulting in a better distribution of the added elements. It is believed that the initial heating reduces the density of defects, including the dislocations described above.
  • the distribution of the additive elements can be easily differentiated by initial heating through the following mechanism.
  • lithium is released from a part of the surface layer 100a by initial heating.
  • the lithium cobalt oxide having the lithium-deficient surface layer 100a is mixed with an additive element source, such as a nickel source, an aluminum source, or a magnesium source, and heated.
  • an additive element source such as a nickel source, an aluminum source, or a magnesium source
  • magnesium is a typical divalent element
  • nickel is a transition metal but is prone to becoming a divalent ion. Therefore, a rock salt phase containing Mg 2+ and Ni 2+ , and Co 2+ reduced by the deficiency of lithium is formed in a part of the surface layer 100a.
  • this phase is formed in a part of the surface layer 100a, it may not be clearly confirmed in an electron microscope image such as STEM and an electron beam diffraction pattern.
  • nickel is likely to dissolve and diffuse to the interior 100b when the surface layer 100a is a layered rock-salt type lithium cobalt oxide, but is likely to remain in the surface layer 100a when part of the surface layer 100a is rock-salt type. Therefore, by performing initial heating, it is possible to make it easier for divalent additive elements such as nickel to remain in the surface layer 100a.
  • the effect of this initial heating is particularly large on the surface other than the (001) orientation of the positive electrode active material 100 and on its surface layer 100a.
  • the Me-O distance in rock salt Ni0.5Mg0.5O is 2.09 ⁇
  • the Me-O distance in rock salt MgO is 2.11 ⁇ .
  • the Me-O distance in spinel NiAl2O4 is 2.0125 ⁇
  • the bond distance between metals other than lithium and oxygen is shorter than the above.
  • the Al-O distance in layered rock salt type LiAlO2 is 1.905 ⁇ (Li-O distance is 2.11 ⁇ ).
  • the Co-O distance in layered rock salt type LiCoO2 is 1.9224 ⁇ (Li-O distance is 2.0916 ⁇ ).
  • the ionic radius of 6-coordinate aluminum is 0.535 ⁇
  • the ionic radius of 6-coordinate oxygen is 1.4 ⁇
  • the sum of these is 1.935 ⁇ .
  • Initial heating is also expected to have the effect of increasing the crystallinity of the layered rock-salt crystal structure in the interior 100b.
  • initial heating is not necessarily required.
  • other heating steps such as annealing, by controlling the atmosphere, temperature, time, etc., it may be possible to produce a positive electrode active material 100 having O3′ type and/or monoclinic O1(15) type when x in Li x CoO 2 is small.
  • Step S11 In step S11 shown in FIG. 18A, a lithium source (Li source) and a cobalt source (Co source) are prepared as starting materials, that is, lithium and transition metal materials, respectively.
  • Li source Li source
  • Co source cobalt source
  • the lithium source it is preferable to use a compound containing lithium, such as lithium carbonate, lithium hydroxide, lithium nitrate, or lithium fluoride. It is preferable that the lithium source has high purity, for example, a material with a purity of 99.99% or more.
  • cobalt source it is preferable to use a compound containing cobalt, such as cobalt oxide or cobalt hydroxide.
  • the cobalt source is preferably of high purity, for example, a material with a purity of 3N (99.9%) or more, preferably 4N (99.99%) or more, more preferably 4N5 (99.995%) or more, and even more preferably 5N (99.999%) or more may be used.
  • a high purity material impurities in the positive electrode active material can be controlled. As a result, the capacity of the secondary battery is increased and/or the reliability of the secondary battery is improved.
  • the cobalt source has high crystallinity, for example, single crystal grains.
  • the crystallinity of the cobalt source can be evaluated using TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope) images, ABF-STEM (annular bright-field scanning transmission electron microscope) images, etc., or evaluation using X-ray diffraction (XRD), electron beam diffraction, neutron beam diffraction, etc.
  • XRD X-ray diffraction
  • step S12 the lithium source and the cobalt source are pulverized and mixed to prepare a mixed material.
  • the pulverization and mixing can be performed in a dry or wet manner.
  • the wet method is preferable because it can be crushed into smaller pieces.
  • a solvent is prepared.
  • ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. can be used. It is more preferable to use an aprotic solvent that is less likely to react with lithium.
  • dehydrated acetone with a purity of 99.5% or more is used. It is preferable to mix the lithium source and the cobalt source with dehydrated acetone with a purity of 99.5% or more, in which the moisture content is suppressed to 10 ppm or less, and then pulverize and mix them.
  • dehydrated acetone with the above-mentioned purity it is possible to reduce impurities that may be mixed in.
  • a ball mill, a bead mill, or the like can be used as a means for grinding and mixing.
  • a ball mill it is preferable to use aluminum oxide balls or zirconium oxide balls as the media. Zirconium oxide balls are preferable because they emit less impurities.
  • the peripheral speed it is preferable to set the peripheral speed to 100 mm/s or more and 2000 mm/s or less in order to suppress contamination from the media. In this embodiment, the peripheral speed is set to 838 mm/s (rotation speed 400 rpm, ball mill diameter 40 mm).
  • step S13 shown in FIG. 18A the mixed material is heated.
  • the heating is preferably performed at 800° C. or more and 1100° C. or less, more preferably at 900° C. or more and 1000° C. or less, and even more preferably at about 950° C. If the temperature is too low, the decomposition and melting of the lithium source and the cobalt source may be insufficient. On the other hand, if the temperature is too high, defects may occur due to lithium transpiration from the lithium source and/or cobalt being excessively reduced. For example, cobalt may change from trivalent to divalent, inducing oxygen defects, etc.
  • the heating time should be between 1 hour and 100 hours, and more preferably between 2 hours and 20 hours.
  • the rate of temperature rise depends on the heating temperature reached, but should be between 80°C/h and 250°C/h. For example, if heating at 1000°C for 10 hours, the rate of temperature rise should be 200°C/h.
  • the heating is preferably performed in an atmosphere with little water, such as dry air, for example, an atmosphere with a dew point of ⁇ 50° C. or less, more preferably an atmosphere with a dew point of ⁇ 80° C. or less.
  • the heating is performed in an atmosphere with a dew point of ⁇ 93° C.
  • the impurity concentrations of CH 4 , CO, CO 2 , H 2 , and the like in the heating atmosphere should each be 5 ppb (parts per billion) or less.
  • the heating atmosphere is preferably an atmosphere containing oxygen.
  • the heating atmosphere is preferably an atmosphere containing oxygen.
  • the flow rate of the dry air is preferably 10 L/min.
  • the method of continuously introducing oxygen into the reaction chamber and having oxygen flow through the reaction chamber is called flow.
  • the heating atmosphere is an atmosphere containing oxygen
  • a method that does not allow flow may be used.
  • the reaction chamber may be depressurized and then filled with oxygen (or purged) to prevent the oxygen from entering or leaving the reaction chamber.
  • the pressure in the reaction chamber may be depressurized until the differential pressure gauge indicates -970 hPa, and then oxygen may be filled to 50 hPa.
  • the material After heating, the material can be allowed to cool naturally, but it is preferable that the time it takes to cool from the specified temperature to room temperature is within a range of 10 to 50 hours. However, cooling to room temperature is not always necessary, as long as the material is cooled to a temperature acceptable for the next step.
  • the heating in this process may be performed using a rotary kiln or a roller hearth kiln. Heating using a rotary kiln can be performed while stirring, whether it is a continuous or batch type.
  • the crucible used for heating is preferably made of aluminum oxide.
  • Aluminum oxide crucibles are made of a material that does not easily release impurities. In this embodiment, an aluminum oxide crucible with a purity of 99.9% is used. It is preferable to place a lid on the crucible when heating. This prevents the material from volatilizing.
  • a used crucible refers to one that has undergone the process of putting in and heating materials containing lithium, transition metal M, and/or additive elements two or less times.
  • a used crucible refers to one that has undergone the process of putting in and heating materials containing lithium, transition metal M, and/or additive elements three or more times. This is because when a new crucible is used, there is a risk that some of the materials, including lithium fluoride, may be absorbed, diffused, moved, and/or attached to the sheath during heating.
  • the material After heating, the material may be crushed and sieved as necessary. When recovering the heated material, it may be transferred from the crucible to a mortar and then recovered.
  • the mortar is preferably made of aluminum oxide or zirconium oxide.
  • Aluminum oxide mortars are made of a material that does not easily release impurities. Specifically, an aluminum oxide mortar with a purity of 90% or more, preferably 99% or more, is used. Note that the same heating conditions as those in step S13 can be applied to the heating steps described below other than step S13.
  • lithium cobalt oxide (LiCoO 2 ) can be synthesized as shown in step S14 in FIG. 18A.
  • the composite oxide is produced by a solid phase method, but the composite oxide may also be produced by a coprecipitation method.
  • the composite oxide may also be produced by a hydrothermal method.
  • step S14 pre-synthesized lithium cobalt oxide may be used.
  • steps S11 to S13 may be omitted.
  • the concentration of each element in lithium cobalt oxide that can be used in step S14 will be described.
  • the concentration of each element can be obtained.
  • Tables 2 to 4 show the concentration of each element for four types of lithium cobalt oxide (material Sm-1, material Sm-2, material Sm-3, and material Sm-4). For ease of viewing, the tables are divided into three tables, Tables 2 to 4.
  • Matrix means the main component
  • Binder means the auxiliary electrode
  • Source means that there is an influence from the components of the measuring device
  • ⁇ means that it was below the detection limit
  • ⁇ means that the interfering elements overlap but are below the numerical value
  • ⁇ means that there is variation or that the interfering elements overlap partially but are semi-quantitative values.
  • the measured value of each element in ppm weight (written as ppm wt) can be multiplied by the atomic weight of each element and converted into a percentage to give an atomic %.
  • Tables 2 to 4 show the element concentrations of lithium cobalt oxide that can be used in step S14.
  • Step S15 the lithium cobalt oxide is heated in step S15 shown in Fig. 18A. Since this is the first heating of the lithium cobalt oxide, the heating in step S15 may be called initial heating. Alternatively, since this heating is performed before step S20 described below, it may be called preheating or pretreatment.
  • initial heating causes lithium to be released from part of the surface layer 100a of the lithium cobalt oxide. It is also expected to have the effect of increasing the crystallinity of the interior 100b. Impurities may be mixed into the lithium source and/or cobalt source prepared in step S11, etc. Initial heating can reduce the amount of impurities in the lithium cobalt oxide completed in step S14.
  • the initial heating has the effect of smoothing the surface of the lithium cobalt oxide.
  • a smooth surface means that there are few irregularities, the composite oxide is generally rounded, and the corners are also rounded. Furthermore, a surface is called smooth when there is little foreign matter adhering to it. Foreign matter is thought to be a cause of unevenness, so it is preferable that it does not adhere to the surface.
  • the heating conditions can be selected from those described in step S13.
  • the heating temperature of this step should be lower than the temperature of step S13 in order to maintain the crystal structure of the complex oxide.
  • the heating time of this step should be shorter than the time of step S13 in order to maintain the crystal structure of the complex oxide. For example, heating should be performed at a temperature of 700°C to 1000°C for 2 hours to 20 hours.
  • the effect of increasing the crystallinity of the inner portion 100b is, for example, the effect of mitigating distortion, misalignment, etc. resulting from differences in shrinkage of the lithium cobalt oxide produced in step S13.
  • the heating in step S13 may cause a temperature difference between the surface and the inside of the lithium cobalt oxide.
  • the temperature difference may induce a shrinkage difference. It is also believed that the temperature difference causes the shrinkage difference because the fluidity of the surface and the inside is different.
  • the energy related to the shrinkage difference causes an internal stress difference in the lithium cobalt oxide.
  • the internal stress difference is also called strain, and this energy is sometimes called strain energy.
  • the internal stress is removed by the initial heating in step S15, or in other words, the strain energy is thought to be homogenized by the initial heating in step S15.
  • the strain energy is homogenized, the strain of the lithium cobalt oxide is relaxed. As a result, the surface of the lithium cobalt oxide may become smooth. This is also called the surface being improved. In other words, it is thought that the shrinkage difference caused in the lithium cobalt oxide is relaxed after step S15, and the surface of the composite oxide becomes smooth.
  • the shrinkage difference may cause microscopic misalignment, such as crystal misalignment, in the lithium cobalt oxide.
  • microscopic misalignment such as crystal misalignment
  • the misalignment it is possible to equalize the misalignment in the composite oxide.
  • the surface of the composite oxide may become smooth. This is also referred to as the alignment of crystal grains.
  • step S15 it is believed that through step S15, the misalignment of crystals and the like that has occurred in the composite oxide is alleviated, and the surface of the composite oxide becomes smooth.
  • lithium cobalt oxide which has a smooth surface, it reduces deterioration during charging and discharging as a secondary battery and prevents cracking of the positive electrode active material.
  • lithium cobalt oxide that has been synthesized in advance may be used in step S14.
  • steps S11 to S13 can be omitted.
  • step S15 By carrying out step S15 on lithium cobalt oxide that has been synthesized in advance, lithium cobalt oxide with a smooth surface can be obtained.
  • step S20 an additive element A source (A source) to be added to the lithium cobalt oxide that has been initially heated is prepared.
  • a source an additive element A source to be added to the lithium cobalt oxide that has been initially heated.
  • the additive element A can be added evenly. Therefore, it is preferable to add the additive element A after the initial heating.
  • the step of preparing the additive element A source will be described with reference to FIG. 18B and FIG. 18C.
  • a starting material for a source of an additive element A (A source) to be added to lithium cobalt oxide is prepared.
  • a lithium source may be prepared together with the starting material.
  • additive element A As the starting material for the source of additive element A, a compound having the additive elements described in the previous embodiment, for example additive element A and additive element B, can be used. Specifically, one or more compounds selected from magnesium, fluorine, nickel, aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, and boron can be used. Also, one or two elements selected from bromine and beryllium can be used.
  • the starting material can be called a magnesium source (Mg source) as in step S21.
  • the magnesium source can be magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, or the like.
  • multiple magnesium sources described above may be used.
  • the starting material can be called a fluorine source (F source) as in step S21.
  • the fluorine source that can be used include lithium fluoride (LiF), magnesium fluoride ( MgF2 ), aluminum fluoride ( AlF3 ), titanium fluoride ( TiF4 ), cobalt fluoride ( CoF2 , CoF3 ), nickel fluoride ( NiF2 ), zirconium fluoride ( ZrF4 ), vanadium fluoride ( VF5 ), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride ( ZnF2 ), calcium fluoride ( CaF2 ), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride ( BaF2 ), cerium fluoride ( CeF3 , CeF4 ), lanthanum fluoride ( LaF3 ), and sodium
  • Magnesium fluoride can be used as both a fluorine source and a magnesium source. Lithium fluoride can also be used as a lithium source. Other lithium sources that can be used in step S21 include lithium carbonate.
  • the fluorine source may be a gas, such as fluorine ( F2 ), carbon fluoride, sulfur fluoride, or oxygen fluoride ( OF2 , O2F2 , O3F2 , O4F2 , O5F2 , O6F2 , O2F ) , which may be mixed into the atmosphere in the heating step described below.
  • F2 fluorine
  • OF2 , O2F2 , O3F2 , O4F2 , O5F2 , O6F2 , O2F oxygen fluoride
  • lithium fluoride (LiF) is prepared as the fluorine source
  • magnesium fluoride (MgF 2 ) is prepared as the fluorine source and magnesium source.
  • the amount of lithium fluoride increases, there is a concern that the lithium becomes excessive and the cycle characteristics deteriorate.
  • “near” refers to a value that is greater than 0.9 times and less than 1.1 times the value.
  • Step S22> 18B the magnesium source and the fluorine source are pulverized and mixed. This step can be performed under the pulverization and mixing conditions selected from those described in step S12.
  • Step S23> 18B the material crushed and mixed as described above is collected to obtain a source of additive element A (source A).
  • source A a source of additive element A
  • the source of additive element A shown in step S23 has a plurality of starting materials and can be called a mixture.
  • the particle size of the mixture is preferably a median diameter (D50) of 600 nm or more and 10 ⁇ m or less, more preferably 1 ⁇ m or more and 5 ⁇ m or less. Even when a single material is used as the source of the additive element, the median diameter (D50) is preferably 600 nm or more and 10 ⁇ m or less, more preferably 1 ⁇ m or more and 5 ⁇ m or less.
  • Such a finely powdered mixture makes it easier to uniformly attach the mixture to the surface of the lithium cobalt oxide particles when mixed with the lithium cobalt oxide in a later process. If the mixture is uniformly attached to the surface of the lithium cobalt oxide particles, it is preferable because it makes it easier to uniformly distribute or diffuse the additive element in the surface layer portion 100a of the composite oxide after heating.
  • Step S21 A process different from that shown in FIG. 18B will be described with reference to FIG. 18C.
  • step S21 shown in FIG. 18C four types of compounds are prepared as starting materials for the source of the additive element A to be added to lithium cobalt oxide. That is, the types of starting materials in FIG. 18C are different from those in FIG. 18B.
  • a lithium source may be prepared together with the starting materials.
  • a magnesium source Mg source
  • a fluorine source F source
  • a nickel source Ni source
  • an aluminum source Al source
  • the magnesium source and the fluorine source can be selected from the compounds described in FIG. 18B.
  • Nickel oxide, nickel hydroxide, etc. can be used as the nickel source.
  • Aluminum oxide, aluminum hydroxide, etc. can be used as the aluminum source.
  • Steps S22 and S23 shown in FIG. 18C are similar to the steps described in FIG. 18B.
  • lithium cobalt oxide is mixed with a source of additive element A.
  • the mixing conditions in step S31 are preferably milder than those in step S12 in order not to destroy the shape of the lithium cobalt oxide particles.
  • dry mixing is a milder condition than wet mixing.
  • a ball mill, a bead mill, etc. can be used for mixing.
  • zirconium oxide balls it is preferable to use zirconium oxide balls as the media.
  • the mixture is mixed dry in a ball mill using zirconium oxide balls with a diameter of 1 mm at 150 rpm for 1 hour.
  • the mixture is also performed in a dry room with a dew point of -100°C or higher and -10°C or lower.
  • Step S32> 18A the mixed material is collected to obtain a mixture 903.
  • the material may be crushed and then sieved, if necessary.
  • Figures 18A to 18C illustrate a manufacturing method in which the additive element is added only after initial heating
  • the present invention is not limited to the above method.
  • the additive element may be added at another timing, or may be added multiple times. The timing may be changed depending on the element.
  • an additive element may be added to the lithium source and the cobalt source in step S11, that is, in the stage of the starting material for the composite oxide. Then, in step S13, lithium cobalt oxide having the additive element can be obtained. In this case, there is no need to separate the steps S11 to S14 from the steps S21 to S23. This is a simple and highly productive method.
  • lithium cobalt oxide that already contains some of the added elements may be used.
  • steps S11 to S14 and some of the steps in step S20 can be omitted. This is a simple and highly productive method.
  • a magnesium source and a fluorine source or a magnesium source, a fluorine source, a nickel source, and an aluminum source may be added as in step S20.
  • Step S33> 18A the mixture 903 is heated.
  • the heating conditions can be selected from those described in step S13.
  • the heating time is preferably 2 hours or more.
  • the lower limit of the heating temperature in step S33 must be equal to or higher than the temperature at which the reaction between the lithium cobalt oxide and the additive element source proceeds.
  • the temperature at which the reaction proceeds may be any temperature at which mutual diffusion of elements contained in the lithium cobalt oxide and the additive element source occurs, and may be lower than the melting temperature of these materials.
  • An oxide is used as an example for explanation, and it is known that solid-phase diffusion occurs at a temperature 0.757 times the melting temperature Tm (Tammann temperature Td ). Therefore, the heating temperature in step S33 may be 650°C or higher.
  • the reaction proceeds more easily if the temperature is equal to or higher than the melting temperature of one or more of the materials contained in the mixture 903.
  • the eutectic point of LiF and MgF2 is around 742°C, so that the lower limit of the heating temperature in step S33 is preferably set to 742°C or higher.
  • the lower limit of the heating temperature is more preferably 830° C. or higher.
  • the upper limit of the heating temperature is below the melting point of lithium cobalt oxide (1130°C). At temperatures close to the melting point, there is a concern that lithium cobalt oxide may decompose, albeit only slightly. Therefore, it is more preferable for the temperature to be 1000°C or lower, even more preferable for the temperature to be 950°C or lower, and even more preferable for the temperature to be 900°C or lower.
  • the heating temperature in step S33 is preferably 650°C to 1130°C, more preferably 650°C to 1000°C, even more preferably 650°C to 950°C, and even more preferably 650°C to 900°C.
  • 742°C to 1130°C is preferred, more preferably 742°C to 1000°C, even more preferably 742°C to 950°C, and even more preferably 742°C to 900°C.
  • 800°C to 1100°C, 830°C to 1130°C is preferred, more preferably 830°C to 1000°C, even more preferably 830°C to 950°C, and even more preferably 830°C to 900°C.
  • the heating temperature in step S33 is preferably lower than that in step S13.
  • some materials for example LiF, which is a fluorine source, may function as a flux.
  • This function allows the heating temperature to be lowered below the melting point of lithium cobalt oxide, for example to between 742°C and 950°C, and additive elements such as magnesium can be distributed in the surface layer to produce a positive electrode active material with good characteristics.
  • LiF has a lower specific gravity in a gaseous state than oxygen
  • LiF may volatilize when heated, and the amount of LiF in the mixture 903 will decrease if LiF volatilizes. This weakens the function as a flux. Therefore, it is necessary to heat while suppressing the volatilization of LiF.
  • LiF is not used as the fluorine source, etc.
  • Li on the LiCoO2 surface may react with F of the fluorine source to generate LiF, which may volatilize. Therefore, even if a fluoride with a melting point higher than LiF is used, it is necessary to suppress the volatilization in the same way.
  • the heating in this process is preferably performed so that the particles of mixture 903 do not stick to each other. If the particles of mixture 903 stick to each other during heating, the contact area with oxygen in the atmosphere decreases, and the route along which the added elements (e.g., fluorine) diffuse is blocked, which may result in poor distribution of the added elements (e.g., magnesium and fluorine) in the surface layer.
  • the added elements e.g., fluorine
  • the additive element e.g., fluorine
  • a smooth positive electrode active material with few irregularities can be obtained. Therefore, in order to maintain the smooth state of the surface after the heating in step S15 in this process or to make it even smoother, it is better for the particles of mixture 903 not to stick together.
  • the flow rate of the oxygen-containing atmosphere in the kiln When heating in a rotary kiln, it is preferable to control the flow rate of the oxygen-containing atmosphere in the kiln. For example, it is preferable to reduce the flow rate of the oxygen-containing atmosphere, or to first purge the atmosphere and not flow the atmosphere after introducing the oxygen atmosphere into the kiln. Flowing oxygen can cause the fluorine source to evaporate, which is not preferable in terms of maintaining the smoothness of the surface.
  • the mixture 903 can be heated in an atmosphere containing LiF, for example, by placing a lid on the container containing the mixture 903.
  • the heating time varies depending on conditions such as the heating temperature, the size of the lithium cobalt oxide in step S14, and the composition.
  • the heating temperature a lower temperature or a shorter time may be more preferable than when the lithium cobalt oxide is large.
  • the heating temperature is preferably, for example, 650° C. or more and 950° C. or less.
  • the heating time is preferably, for example, 3 hours or more and 60 hours or less, more preferably 10 hours or more and 30 hours or less, and even more preferably about 20 hours.
  • the cooling time after heating is preferably, for example, 10 hours or more and 50 hours or less.
  • the heating temperature is preferably, for example, 650° C. or more and 950° C. or less.
  • the heating time is preferably, for example, 1 hour or more and 10 hours or less, and more preferably about 5 hours.
  • the cooling time after heating is preferably, for example, 10 hours or more and 50 hours or less.
  • step S34 shown in Fig. 18A the heated material is collected and crushed as necessary to obtain the positive electrode active material 100. At this time, it is preferable to further sieve the collected particles.
  • the positive electrode active material 100 of one embodiment of the present invention can be produced.
  • the positive electrode active material of one embodiment of the present invention has a smooth surface.
  • Method for producing a positive electrode active material 2 which is one embodiment of the present invention and is different from method for producing a positive electrode active material 1, will be described with reference to Figs. 19 to 20C.
  • Method for producing a positive electrode active material 2 differs from method for producing 1 mainly in the number of times additive elements are added and the mixing method. For other descriptions, the description of method for producing 1 can be referred to.
  • steps S11 to S15 are performed in the same manner as in FIG. 17A to prepare lithium cobalt oxide that has undergone initial heating.
  • Step S20a Next, as shown in step S20a, it is preferable to add an additive element A1 to the lithium cobalt oxide that has been subjected to the initial heating.
  • step S21 shown in Fig. 20A starting materials for obtaining a first additive element source (A1 source) are prepared.
  • A1 source a first additive element source
  • a magnesium source and a fluorine source are prepared.
  • the starting materials for obtaining the first additive element A1 source can be selected from the starting materials for obtaining the additive element A source described in step S21 shown in Fig. 17B.
  • one or more selected from magnesium, fluorine, and calcium can be suitably used as the first additive element A1
  • a compound having one selected from magnesium, fluorine, and calcium can be used as the starting material for obtaining it.
  • Steps S21 to S23 shown in FIG. 20A can be performed under the same conditions as steps S21 to S23 shown in FIG. 17B.
  • the first additive element source (A1 source) can be obtained in step S23.
  • steps S31 to S33 shown in FIG. 19 can be performed in the same manner as steps S31 to S33 shown in FIG. 17A.
  • step S33 the heated material is collected to produce lithium cobalt oxide containing the additive element A1. This is also called a second composite oxide to distinguish it from the composite oxide in step S14.
  • Step S40> In step S40 shown in Fig. 19, a second additional element A2 is added.
  • the second additional element A2 will be described with reference to Figs. 20B and 20C.
  • step S41 shown in FIG. 20B starting materials for obtaining the second additive element source (A2 source) are prepared.
  • a nickel source (Ni source) and an aluminum source (Al source) are prepared.
  • the aluminum source (Al source) may be omitted.
  • the starting materials for obtaining the second additive element (A2) source can be selected from the starting materials for the additive element A source described in step S21 shown in FIG. 17B.
  • the second additive element A2 any one or more selected from nickel, titanium, boron, zirconium, and aluminum can be suitably used, and the starting material for obtaining this may be a compound having any one selected from nickel, titanium, boron, zirconium, and aluminum.
  • Steps S41 to S43 shown in FIG. 20B can be performed under the same conditions as steps S21 to S23 shown in FIG. 17B.
  • the second additive element source (A2 source) can be obtained in step S43.
  • FIG. 20C shows a modified example of the steps described with reference to FIG. 20B.
  • step S41 shown in FIG. 20C a nickel source (Ni source) and an aluminum source (Al source) are prepared, and in step S42a, they are each crushed independently.
  • step S43 multiple second additive element sources (A2 sources) are prepared.
  • the steps in FIG. 20C differ from FIG. 20B in that the additive elements are crushed independently in step S42a.
  • steps S51 to S53 shown in Fig. 19 can be performed under the same conditions as steps S31 to S34 shown in Fig. 17A.
  • the conditions for step S53 relating to the heating step may be a lower temperature and a shorter time than those for step S33.
  • step S54 the positive electrode active material 100 according to one embodiment of the present invention can be produced.
  • the positive electrode active material according to one embodiment of the present invention has a smooth surface.
  • the additive element is introduced into lithium cobalt oxide separately as additive element A1 and additive element A2.
  • additive element A1 and additive element A2 By introducing them separately, the distribution of each additive element in the depth direction can be changed. For example, it is possible to profile additive element A1 so that it has a higher concentration in the surface layer than in the interior, and to profile additive element A2 so that it has a higher concentration in the interior than in the surface layer.
  • the initial heating shown in this embodiment is performed on lithium cobalt oxide. Therefore, the initial heating is preferably performed under conditions that are lower than the heating temperature for obtaining lithium cobalt oxide and shorter than the heating time for obtaining lithium cobalt oxide.
  • the step of adding an additive element to lithium cobalt oxide is preferably performed after the initial heating. This addition step can be divided into two or more steps. Following this order of steps is preferable because the smoothness of the surface obtained by the initial heating is maintained.
  • the coprecipitation method is a method in which poorly soluble salts are precipitated and precipitated when the ion concentration becomes supersaturated from an aqueous solution containing two or more metal ions.
  • the coprecipitation method is a method in which the mixing of metal salts in the precipitate is more uniform than when the solid phase method of the second embodiment is used, and it is easy to position magnesium in the interior 100b.
  • Fig. 22 is a flow diagram in which some steps of Fig. 21 are omitted, so the common parts will be described together.
  • Fig. 22 is an example of a process in which some steps can be omitted and productivity is high.
  • a cobalt source 81 (referred to as Co source in the drawings) is prepared.
  • the cobalt source 81 is one of the starting materials for the positive electrode active material.
  • the cobalt source 81 uses a compound containing cobalt (referred to as cobalt compound).
  • the cobalt compound may be, for example, cobalt sulfate, cobalt chloride, or cobalt nitrate, or a hydrate thereof.
  • Cobalt alkoxide or an organic cobalt complex may also be used as the cobalt compound.
  • organic acids of cobalt such as cobalt acetate or a hydrate thereof may also be used as the cobalt compound.
  • the organic acid includes citric acid, oxalic acid, formic acid, butyric acid, etc. in addition to acetic acid.
  • an aqueous cobalt solution When using a solution as the cobalt source 81, prepare an aqueous solution containing the above-mentioned cobalt compound (referred to as an aqueous cobalt solution).
  • a magnesium source 82 (referred to as Mg source in the drawings) is prepared.
  • the magnesium source 82 is one of the starting materials for the positive electrode active material.
  • a compound containing magnesium (referred to as magnesium compound) is used as the magnesium source 82.
  • the magnesium compound may be, for example, magnesium sulfate, magnesium chloride, magnesium nitrate, or a hydrate thereof.
  • magnesium aqueous solution an aqueous solution containing the above magnesium compound (hereinafter referred to as magnesium aqueous solution).
  • a nickel source may be used instead of the magnesium source 82 shown in Figures 21 and 22, or in addition to the magnesium source 82.
  • a nickel source specifically, an aqueous nickel solution is prepared.
  • a chelating agent 83 is prepared as shown in Fig. 21.
  • the chelating agent 83 may be omitted, and for example, Fig. 22 shows a flow diagram in which the chelating agent 83 is not prepared.
  • the chelating agent 83 is an aqueous solution in which glycine, oxine, 1-nitroso-2-naphthol, 2-mercaptobenzothiazole or EDTA (ethylenediaminetetraacetic acid) is dissolved, and this will be referred to as an aqueous chelating solution.
  • glycine, oxine, 1-nitroso-2-naphthol or 2-mercaptobenzothiazole may be used.
  • Water preferably pure water, is used as the above solvent.
  • the above-mentioned chelating agent is preferable to general complexing agents in that it is a complexing agent that forms a chelate compound.
  • a general complexing agent such as ammonia water may be used instead of the chelating agent.
  • a chelating agent is preferable because it can suppress the generation of unnecessary crystal nuclei and promote crystal growth. When the generation of unnecessary nuclei is suppressed, the generation of fine particles is also suppressed, so hydroxides (sometimes called precursors) with good particle size distribution can be obtained. In addition, the use of a chelating agent can slow down the acid-base reaction, and the gradual progress of the reaction can result in hydroxides that are close to spherical.
  • an aqueous glycine solution is preferable because it makes it easier to control the pH of the solution in the reaction vessel during the coprecipitation reaction in step S131 of FIG. 21 and FIG. 22.
  • the glycine concentration of the aqueous glycine solution is preferably 0.05 mol/L or more and 0.5 mol/L or less, and more preferably 0.1 mol/L or more and 0.2 mol/L or less.
  • the pure water used in the above chelate aqueous solution is water having a resistivity of 1 M ⁇ cm or more, more preferably 10 M ⁇ cm or more, and even more preferably 15 M ⁇ cm or more. Water that satisfies the above resistivity range has high purity and contains very few impurities, and is therefore preferable for use in acid-base reactions.
  • step S114 shown in Figures 21 and 22 will be described.
  • a cobalt source 81 and a magnesium source 82 are mixed.
  • a mixed solution 91 of a cobalt compound and a magnesium compound is obtained by the mixing in this step.
  • the cobalt compound and the magnesium compound are dissolved in the mixed solution.
  • the water used in this step may be the above-mentioned pure water.
  • the mixed solution 91 is an acidic solution and may be called an acid solution.
  • the alkaline aqueous solution 84 may be, for example, an aqueous solution containing sodium hydroxide, potassium hydroxide, lithium hydroxide, or ammonia, and is not limited to these aqueous solutions as long as it functions as a pH adjuster.
  • it may be an aqueous solution in which multiple types selected from sodium hydroxide, potassium hydroxide, and lithium hydroxide are dissolved in water.
  • the water used may be the above-mentioned pure water.
  • a chelating agent 85 is prepared.
  • the chelating agent 85 may be made of the same material as the chelating agent 83 described above.
  • the chelating agent 85 may be omitted, and Fig. 22 shows a flow diagram in which the chelating agent 85 is not prepared. In the case of Fig. 22, however, it is preferable to put water 86, preferably pure water, in the reaction vessel as the filling liquid.
  • the chelating agent 85 may be placed in a reaction vessel used in step S131 described below, and may be referred to as a charging liquid or an adjustment liquid.
  • the chelating agent 85 refers to an aqueous solution in the initial reaction state.
  • the chelating agent 85 it is possible to suppress the generation of unnecessary crystal nuclei and promote their growth, and by suppressing the generation of unnecessary nuclei, the generation of fine particles is suppressed, so that a hydroxide with a good particle size distribution can be obtained, or the acid-base reaction can be delayed, and the reaction can proceed gradually to obtain a hydroxide that is close to spherical.
  • Step S131 the mixed solution 91 and the alkaline aqueous solution 84 are mixed in a reaction vessel.
  • the mixed solution 91 and the alkaline aqueous solution 84 react with each other to produce a hydroxide 95 as a precursor.
  • the chemical reaction in step S131 can be described as a neutralization reaction, an acid-base reaction, or a coprecipitation reaction.
  • a composite hydroxide 95 (simply referred to as hydroxide 95) having cobalt and magnesium as the transition metal M is precipitated.
  • the hydroxide 95 can be called a precursor of the positive electrode active material 100.
  • the hydroxide 95 can also be called a compound of cobalt and magnesium, and therefore may be referred to as a cobalt magnesium compound.
  • the solution in the reaction vessel may be stirred using a stirring means.
  • the stirring means may have a stirrer or stirring blades.
  • the stirring may be performed at a rotation speed of 500 rpm to 1500 rpm, preferably 800 rpm to 1200 rpm.
  • Two to six stirring blades may be provided. For example, when using four stirring blades, they may be arranged in a cross shape when viewed from above.
  • magnesium and cobalt can be mixed uniformly. That is, a hydroxide 95 in which magnesium exists in the interior 100b can be obtained.
  • the positive electrode active material 100 formed through such hydroxide 95 can enjoy the effects of magnesium.
  • magnesium may be unevenly distributed in the surface layer 100a rather than in the interior 100b of the positive electrode active material 100. Even if magnesium is present in the surface layer 100a, the positive electrode active material 100 can still enjoy the effects of magnesium. For example, magnesium can suppress defects in the positive electrode active material.
  • reaction conditions When reacting the mixed solution 91 with the alkaline aqueous solution 84 according to the coprecipitation reaction, the pH of the solution in the reaction vessel is adjusted to 9 or more and 13 or less, preferably 9.8 or more and 12.5 or less. This range is preferable because it allows the particle size of the hydroxide 95 to be large. Outside this range, the productivity may be reduced, and the obtained hydroxide 95 may be more likely to contain impurities.
  • the mixed liquid 91 When the mixed liquid 91 is placed in a reaction vessel and the alkaline aqueous solution 84 is dropped into the reaction vessel, it is advisable to maintain the pH of the solution in the reaction vessel within the range of the above conditions. Also, when the alkaline aqueous solution 84 is placed in a reaction vessel and the mixed liquid 91 is dropped into the reaction vessel, it is advisable to maintain the pH of the solution in the reaction vessel within the range of the above conditions.
  • the liquid delivery speed (also called the dripping speed) of the mixed liquid 91 or the alkaline aqueous solution 84 may be set to 0.01 mL/min to 1 mL/min, preferably 0.05 mL/min to 0.5 mL/min, when the solution in the reaction vessel is 200 mL to 350 mL.
  • the alkaline aqueous solution 84 may be dripped so that the pH of the solution in the reaction vessel is constant.
  • a pump is provided in the tank that stores the mixed liquid 91 or the alkaline aqueous solution 84, etc., and the dripping speed can be controlled by the pump. The pump can also control the amount of dripping.
  • the dripping speed may be changed in multiple stages, for example, the dripping speed may be gradually increased.
  • Adjust the temperature of the solution in the reaction vessel to be between 50°C and 90°C. After checking the temperature of the solution, it is recommended to start dropping.
  • the above range is preferable because it allows the particle size of the resulting hydroxide 95 to be large.
  • the inside of the reaction vessel should preferably be an inert atmosphere.
  • nitrogen gas should be introduced at a flow rate of 0.5 L/min to 1.2 L/min.
  • nitrogen gas may be introduced by bubbling into the liquid in the reaction vessel.
  • the precipitate 92 contains cobalt magnesium hydroxide.
  • Step S132 and S133 The filtration in step S132 and the drying process in step S133 shown in FIG. 21 will be described.
  • the precipitate 92 contains impurities other than the hydroxide 95. Therefore, in order to recover the hydroxide 95, the filtration in step S132 is preferably performed.
  • the filtration can be performed by suction filtration or reduced pressure filtration. Centrifugation may be used instead of filtration.
  • suction filtration it is preferable to wash the reaction product precipitated in the reaction vessel with water (e.g., pure water, etc.) and then with an organic solvent with a low boiling point (e.g., acetone, etc.). It is also preferable to perform suction filtration multiple times. Note that step S132 does not have to be performed as shown in FIG. 22.
  • the product after filtration may be further dried in step S133.
  • the product may be dried at 60°C or higher and 90°C or lower for 0.5 hours to 20 hours, preferably 12 hours to 20 hours.
  • the drying is preferably performed in an atmosphere with little oxygen.
  • a bell jar type vacuum device having a container (referred to as a bell jar) whose inside can be evacuated to a vacuum and a vacuum pump connected to the bell jar can be used.
  • a vacuum drying furnace may be used, and the vacuum drying furnace has a vacuum pump connected to the drying furnace.
  • the vacuum pump of the bell jar type vacuum device and the vacuum drying furnace may be a dry pump, a turbo molecular pump, an oil rotary pump, a cryopump, or a mechanical booster pump.
  • the vacuum atmosphere in the bell jar type vacuum device and the vacuum drying furnace includes an atmosphere reduced in pressure so that the differential pressure gauge of each device is -0.1 MPa or higher but less than -0.08 MPa.
  • a gas containing nitrogen may be flowed into the container of the bell jar type vacuum device and the vacuum drying furnace. In this manner, hydroxide 95 can be obtained. Thorough drying is preferable because it reduces impurities, such as moisture or hydroxyl groups, from the obtained hydroxide 95. Note that step S133 does not have to be performed, as shown in FIG. 21.
  • Heating may be performed instead of or in addition to the drying in step S133.
  • the heating temperature is preferably 700°C or more and less than 1200°C, more preferably 800°C or more and less than 1100°C, and even more preferably 900°C or more and less than 1000°C.
  • the heating time can be, for example, 1 hour or more and 100 hours or less, and preferably 2 hours or more and 20 hours or less.
  • the oxide is formed instead of the hydroxide.
  • the hydroxide 95 obtained through such a process may be either single particles or secondary particles, but it is preferable for the crystallites to be large.
  • Li source 88 A lithium compound is prepared as the lithium source 88 (referred to as Li source in the drawings) shown in FIGS.
  • lithium hydroxide, lithium carbonate, lithium oxide or lithium nitrate is prepared.
  • the atomic ratio of lithium to the sum of the atomic ratios of cobalt, magnesium, etc. (referred to as Li/(Co+Mg)) is 0.9 to 1.2, preferably 1.0 to 1.09.
  • the lithium compound is weighed so as to satisfy the above range.
  • hydroxide 95 with reduced moisture or hydroxyl groups is used, Li/(Co+Mg) becomes an appropriate value, which is preferable.
  • the lithium compound may be crushed in advance.
  • the lithium compound may be crushed in a mortar for 5 to 15 minutes.
  • the mortar is preferably made of a material that does not easily release impurities, and specifically, an alumina mortar with a purity of 90% or more, preferably 99% or more, may be used.
  • a wet crushing method using a ball mill or the like may also be used. In the wet crushing method, acetone or dehydrated acetone may be used as the solvent, and the rotation speed may be set to 200 to 400 rpm, and crushing may be performed for 10 to 15 hours.
  • the lithium compound after crushing may also be sieved.
  • the lithium compound may also be crushed using a crushing and classifying device.
  • step S151 will be described.
  • the hydroxide 95 and the lithium source 88 are mixed.
  • a mixed mixture 96 is obtained.
  • a mortar, a rotation/revolution stirrer, or the like may be used as a means for mixing the hydroxide 95 and the lithium source 88.
  • a ball mill or a bead mill may be used as the media.
  • Alumina balls or zirconia balls may be used for the ball mill or bead mill.
  • centrifugal force is applied to the media, making it possible to micronize the particles.
  • Dry grinding involves grinding in an inert gas or air, and can grind materials to a particle size of 3.5 ⁇ m or less, preferably 3 ⁇ m or less.
  • Wet grinding involves grinding in a liquid, and can grind materials to a particle size of 1 ⁇ m or less. In other words, if you want to reduce the particle size, you should use the wet grinding method.
  • Step S154 the mixture 96 is heated.
  • Step S154 may be referred to as main baking.
  • the heating step may be performed multiple times, or preliminary baking at a lower temperature may be performed before the main baking.
  • the heating temperature is preferably 700°C or more and less than 1200°C, more preferably 800°C or more and less than 1100°C, and even more preferably 900°C or more and 1000°C or less.
  • heating is performed at a temperature at which at least the hydroxide 95 and the lithium source 88 diffuse into each other.
  • the heating time in step S154 can be, for example, from 1 hour to 100 hours, and preferably from 2 hours to 20 hours.
  • the atmosphere in the processing chamber in step S154 preferably contains oxygen.
  • atmospheres containing oxygen include an oxygen atmosphere, a dry air atmosphere, an air atmosphere, and an atmosphere in which oxygen is mixed with other gases (e.g., one or more gases selected from nitrogen and noble gases).
  • gases e.g., one or more gases selected from nitrogen and noble gases.
  • An example of a noble gas is argon.
  • the atmosphere may be a mixture of two or more gases selected from nitrogen and noble gases.
  • the atmosphere in the process chamber in step S154 preferably has a low moisture content.
  • the dew point of the atmosphere is preferably, for example, -50°C or less, and more preferably -80°C or less. Dry air can be suitably used in the temperature increase step and the temperature holding step.
  • impurities that may be mixed into the material may be suppressed by setting the impurity concentrations of CH4 , CO, CO2 , and H2 in the atmosphere to 5 ppb (parts per billion) or less.
  • the gas flow rate may be, for example, 0.1 L/min or more and 0.7 L/min or less per 1 L of processing chamber volume.
  • the volume of the processing chamber is 40 L, it is preferable to set the flow rate at or near 10 L/min.
  • the gas in question may be, for example, oxygen gas, dry air, nitrogen gas, noble gas, or a mixture of two or more selected from these gases.
  • a method may be used to prevent the gas from entering or leaving the processing chamber.
  • the atmosphere in the processing chamber may be replaced with a gas containing oxygen to prevent the gas from entering or leaving the processing chamber.
  • the processing chamber may also be depressurized before introducing the gas. Specifically, for example, the processing chamber may be depressurized until the differential pressure gauge indicates -970 hPa, and then gas may be introduced until the pressure reaches 50 hPa.
  • the crucible, scabbard, setter, or container used during heating should preferably be made of a material that does not easily release impurities.
  • a crucible made of alumina with a purity of 99.9% should be used.
  • a scabbard made of mullite-cordierite (Al 2 O 3 , SiO 2 , MgO) should be used.
  • the mortar when recovering the material after heating, it is preferable to move it from the crucible to a mortar and then recover it, as this prevents impurities from being mixed into the material.
  • the mortar it is preferable for the mortar to be made of a material that does not easily release impurities, and specifically, it is recommended to use a mortar made of alumina or zirconia with a purity of 90% or more, preferably 99% or more.
  • Step S155 a crushing step is carried out.
  • a sieve with a mesh size of 40 ⁇ m to 60 ⁇ m may be used to classify the particles.
  • oxide 98 can be obtained without carrying out the crushing step in step S155.
  • the oxide 98 shown in Fig. 21 and Fig. 22 will be described.
  • the oxide 98 is formed at least through the heating in step S154, and may be called a composite oxide.
  • the oxide 98 may also be used as the positive electrode active material 100.
  • Step S156 shown in FIG. 21 will be described. It is more preferable to perform heating in order to obtain oxide 98 without defects. This heating may be called initial heating to distinguish it from other heating treatments.
  • the heating treatment in step S156 is expected to have the effect of reducing defects, the effect of increasing the crystallinity of the internal layered rock salt type crystal structure, or the effect of smoothing the surface. Although all of these can be said to be effects on oxide 98, since the positive electrode active material 100 may reflect the shape of oxide 98, the positive electrode active material 100 can also be expected to have the effect of reducing defects, the effect of increasing the crystallinity of the internal layered rock salt type crystal structure, or the effect of smoothing the surface.
  • the heating conditions in step S156 can be selected from the heating conditions described in step S154. In addition, it is preferable that the heating temperature in step S156 is lower than the heating temperature in step S154.
  • the atmosphere in the processing chamber in step S156 can be selected from the atmospheres described in step S154. It is also preferable that the atmosphere in the processing chamber in step S156 contains oxygen.
  • the heat treatment in step S156 causes lithium to be released from a portion of the surface layer of the oxide 98, which further improves the distribution of the additive elements described below. More specifically, it is believed that the heat treatment makes it easier to make the distribution different depending on the additive element, due to the following mechanism.
  • lithium is released from a portion of the surface layer of the oxide 98 by the heat treatment in step S156.
  • the oxide 98 lacking lithium in the surface layer is mixed with an additive element source, such as a nickel source, an aluminum source, or a magnesium source, as described below, and heated.
  • an additive element source such as a nickel source, an aluminum source, or a magnesium source, as described below.
  • magnesium is a typical divalent element
  • nickel is a transition metal but is prone to becoming a divalent ion.
  • a rock salt phase containing Mg 2+ , Ni 2+ , and Co 2+ reduced due to the lack of lithium is formed in a portion of the surface layer of the oxide 98.
  • this phase since this phase is formed in a portion of the surface layer of the oxide 98, it may not be clearly confirmed in an electron microscope image such as STEM or an electron beam diffraction pattern.
  • a lithium source may be added to the oxide 98 before step S156.
  • step S156 does not necessarily have to be performed.
  • the additive element source 89 shown in Figures 21 and 22 will be described.
  • the additive element source 89 can use the additive elements described in the above manufacturing methods 1 and 2.
  • the mixing conditions in step S171 can be selected from the mixing conditions in step S151.
  • the mixing conditions in step S171 should be set to a rotation speed of 100 rpm or more and 200 rpm or less so that the oxide 98 does not disintegrate.
  • the magnesium source may be omitted as the additive element source 89.
  • the aluminum source may be omitted as the additive element source 89.
  • step S172 the mixture 99 is heated.
  • the heating in step S172 must be at a temperature at which the reaction between the oxide 98 and the additive element source 89 proceeds or higher.
  • the temperature at which the reaction proceeds may be any temperature at which interdiffusion between the oxide 98 and the additive element source 89 occurs, and may be lower than the melting temperature of these materials.
  • An oxide will be used as an example, and it is known that interdiffusion occurs at a temperature 0.757 times the melting temperature Tm (Tammann temperature Td ). Therefore, the heating temperature in step S172 may be 500°C or higher.
  • the reaction is likely to proceed more easily if the temperature is equal to or higher than the temperature at which the oxide 98 and the additive element source 89 are partially melted.
  • the heating in step S172 should be set to 700°C or higher.
  • the heating in step S172 should be set to 742°C or higher.
  • the heating temperature must be below the melting point of oxide 98.
  • the heating temperature in step S172 should be lower than that in step S152.
  • the heating temperature in step S172 should also be lower than that in step S154.
  • oxide 98 may decompose, albeit only slightly.
  • the melting point of lithium cobalt oxide is 1130°C, and from temperatures just before that, around 1000°C, lithium evaporation or cation mixing of lithium and cobalt becomes more likely to occur, so the heating temperature is preferably 1000°C or lower, more preferably 950°C or lower, and even more preferably 900°C or lower.
  • the heating temperature in step S172 is preferably 500°C or higher and lower than 1130°C, more preferably 700°C or higher and 1000°C or lower, even more preferably 700°C or higher and 950°C or lower, and even more preferably 700°C or higher and 900°C or lower.
  • 742°C or higher and 1130°C or lower is preferable, more preferably 742°C or higher and 1000°C or lower, even more preferably 742°C or higher and 950°C or lower, and even more preferably 742°C or higher and 900°C or lower.
  • 800°C or higher and 1130°C or lower, 830°C or higher and 1130°C or lower is preferable, 830°C or higher and 1000°C or lower is more preferable, 830°C or higher and 950°C or lower is even more preferable, and 830°C or higher and 900°C or lower is even more preferable.
  • LiF which is a fluorine source
  • This function allows the heating temperature in step S172 to be lowered to below the melting point of the oxide 98, for example, to 742°C or higher and 950°C or lower, and also allows the additive element source to spread uniformly in the surface layer. As a result, a positive electrode active material 100 having an additive element in the surface layer can be manufactured.
  • LiF has a lower specific gravity in a gaseous state than oxygen
  • LiF is not used as the fluorine source, etc.
  • Li on the surface of oxide 98 may react with F in a fluorine source other than LiF, resulting in the production of LiF, which may then sublime. Therefore, even if a fluoride with a higher melting point than LiF is used as a fluorine source other than LiF, it is still necessary to suppress sublimation in the same way.
  • the heating in step S172 can be performed using a roller hearth kiln.
  • the roller hearth kiln can heat the reaction vessel containing the mixture 99 while moving it around the kiln with a lid placed on it. By placing the lid, the mixture 99 can be heated in an atmosphere containing LiF, and the sublimation, i.e., reduction, of the LiF in the mixture 99 can be suppressed.
  • step S172 It is also possible to carry out the heating in step S172 using a rotary kiln. It is preferable that the atmosphere inside the rotary kiln contains oxygen, and that heating is carried out while controlling the flow rate of oxygen. In order to suppress the sublimation, i.e., reduction, of LiF in mixture 99, it is preferable to reduce the flow rate of oxygen.
  • One method of reducing the flow rate of oxygen is to first introduce oxygen into the kiln and hold it there for a certain period of time, and then not introduce oxygen thereafter.
  • Step S173 a crushing step is performed.
  • a sieve with a mesh size of 40 ⁇ m or more and 60 ⁇ m or less may be used to perform classification. By performing this operation, adhesion between particles can be suppressed.
  • the positive electrode active material 100 can be obtained without performing the crushing step of step S173.
  • the positive electrode active material 100 can be manufactured in the manner described above.
  • the positive electrode active material 100 can reflect the shape of the precursor hydroxide 95.
  • lithium cobalt oxide can be obtained that also contains magnesium inside. Magnesium that is not dissolved may diffuse to the surface layer of the lithium cobalt oxide.
  • lithium cobalt oxide can be obtained in which the added element remains in the surface layer. It is preferable that the added element is dissolved in the lithium cobalt oxide in the surface layer.
  • the lithium cobalt oxide is preferable because it has few impurities.
  • sulfur may be detected in the lithium cobalt oxide.
  • the sulfur concentration can be measured by performing elemental analysis of the entire particle of the positive electrode active material using GD-MS, ICP-MS, etc.
  • the method of introducing the additive element source 89 into the oxide 98 in one go has been exemplified, but it may be introduced into the oxide 98 in two or more separate steps. Therefore, in manufacturing method 4, a method of preparing a first additive element A1 source 89a and a second additive element A2 source 89b and dividing the introduction into two steps will be described with reference to Fig. 23. Note that the steps up to step S155 in Fig. 23 are the same as step S155 described in manufacturing method 3, and in manufacturing method 2, oxide 98a can be obtained through step S155.
  • a first additive element A1 source 89a is prepared. It is preferable to use a compound having an additive element selected from the additive element sources described above, and for example, magnesium and/or fluorine can be used as the additive element. Specifically, it is preferable to prepare a first additive element A1 source 89a containing a Mg source and a F source. The Mg source may be omitted.
  • Steps S171a to S173a> 23 steps S171a to S173a are carried out. Note that steps S171a to S173a will not be described because they are similar to steps S171 to S173 described in the manufacturing method 1. In the manufacturing method 2, an oxide 98b can be obtained through step S173a.
  • a second additive element A2 source 89b is prepared. It is preferable to use a compound having an additive element selected from the additive element sources described above, and it is further preferable to use an additive element different from the first additive element A1 source 89a for the second additive element A2 source 89b. Aluminum and/or nickel can be used as such an additive element. Specifically, it is preferable to prepare an Al source and a Ni source as shown in FIG. 20B or FIG. 20C as the second additive element A2 source 89b. The Al source may be omitted. In this manner, the second additive element A2 source 89b can be obtained.
  • steps S171b to S173b are carried out. Note that steps S171b to S173b are similar to steps S171a to S173b described above, and therefore will not be described.
  • positive electrode active material 100 can be obtained through step S173b.
  • This embodiment can be used in combination with other embodiments.
  • [Positive electrode] 24A shows an example of a cross-sectional view of a positive electrode 503 used in a secondary battery.
  • the positive electrode 503 has a positive electrode active material layer 502 on a positive electrode current collector 501.
  • the positive electrode active material layer 502 contains a positive electrode active material 100, a positive electrode active material 562, a conductive material 553, a conductive material 554, and an electrolyte solution 530.
  • the positive electrode active material layer 502 also has a binder (not shown).
  • the secondary battery may have a structure including either the conductive material 553 or the conductive material 554.
  • the D50 of the positive electrode active material 100 is 1 ⁇ m or more and 50 ⁇ m or less, preferably 5 ⁇ m or more and 30 ⁇ m or less. In order to increase the packing density, it is advisable to add a positive electrode active material 562 having a different D50.
  • the D50 of the positive electrode active material 562 is preferably 1/10 to 1/6 of the D50 of the positive electrode active material 100.
  • the positive electrode active material 100 may have the same composition as the positive electrode active material 562, or may have a different composition.
  • the same composition includes positive electrode active materials having the same main composition, with the difference being the presence or absence of added elements, etc.
  • the different composition includes positive electrode active materials having different main compositions.
  • the positive electrode active material 100 and the positive electrode active material 562 may contain an additive element.
  • the additive element may be unevenly distributed or may be thinly distributed inside.
  • the surface layer may contain the additive element.
  • the concentration of the additive element in the surface layer may differ from the concentration of the additive element in the interior, and it is preferable that the concentration of the additive element in the surface layer is higher than the concentration in the interior. This is sometimes called the additive element being unevenly distributed in the surface layer.
  • the positive electrode active material 100 and the positive electrode active material 562 are sometimes called positive electrode active material particles, but the shape of the positive electrode active material can be a variety of shapes other than particulate.
  • FIG. 24B shows a positive electrode 503 having a positive electrode active material in a shape other than particulate.
  • the description is omitted because it is the same as FIG. 24A.
  • the positive electrode active material 100 and the positive electrode active material 562 shown in Figures 24A and 24B are shown as primary particles, but they may be secondary particles. Also, the positive electrode active material 100 and the positive electrode active material 562 are preferably single particles.
  • the positive electrode has a positive electrode active material layer and a positive electrode current collector.
  • the positive electrode active material layer has a positive electrode active material, and may have a conductive material and a binder.
  • a positive electrode active material produced using the manufacturing method described in the previous embodiment may be used.
  • a positive electrode active material with a relatively small D50 and a positive electrode active material with a relatively large D50 may be mixed and used.
  • the positive electrode active material according to one embodiment of the present invention may also be mixed with other positive electrode active materials.
  • positive electrode active material examples include composite oxides having an olivine type crystal structure, a layered rock salt type crystal structure, or a spinel type crystal structure, such as LiFePO4 , LiFeO2 , LiNiO2 , LiMn2O4 , V2O5 , Cr2O5 , and MnO2 .
  • LiMn2O4 lithium nickel oxide
  • a lithium manganese composite oxide that can be expressed by the composition formula Li a Mn b M c O d can be used.
  • the element M is preferably a metal element selected from lithium and manganese, or silicon or phosphorus, and more preferably nickel.
  • the composition of metal, silicon, phosphorus, etc. of the entire particle of the lithium manganese composite oxide can be measured, for example, using ICP-MS.
  • the composition of oxygen of the entire particle of the lithium manganese composite oxide can be measured, for example, using EDX. In addition, it can be obtained by using valence evaluation of melt gas analysis and XAFS (X-ray absorption fine structure) analysis in combination with ICP-MS analysis.
  • the lithium manganese composite oxide refers to an oxide containing at least lithium and manganese, and may contain one or more elements selected from the group consisting of chromium, cobalt, aluminum, nickel, iron, magnesium, molybdenum, zinc, indium, gallium, copper, titanium, niobium, silicon, phosphorus, and the like.
  • the conductive material serves to assist the current path between the active material and the current collector, or the current path between a plurality of active materials.
  • the conductive material may have a material with a lower resistance than the active material. Due to its role, the conductive material is also called a conductive assistant or a conductive agent.
  • the conductive material is typically a carbon material or a metal material.
  • the conductive material is particulate, and examples of particulate conductive materials include carbon black (furnace black, acetylene black, graphite, etc.). Most carbon blacks have a smaller particle size than the positive electrode active material.
  • the conductive material is fibrous, and examples of such fibrous conductive materials include carbon nanotubes (CNT) and VGCF (registered trademark).
  • the conductive material can be in sheet form, and an example of a sheet-shaped conductive material is multilayer graphene. Sheet-shaped conductive materials can appear thread-like in the cross section of the positive electrode.
  • Particulate conductive materials can penetrate into gaps in the positive electrode active material and are also prone to agglomeration. Therefore, particulate conductive materials can assist the conductive paths between nearby positive electrode active materials. Fibrous conductive materials also have bent regions, but are larger than the positive electrode active materials. Therefore, fibrous conductive materials can assist the conductive paths between distant positive electrode active materials in addition to adjacent positive electrode active materials. In this way, it is a good idea to mix conductive materials of two or more shapes.
  • the weight of the carbon black in the mixed slurry state should be 1.5 to 20 times, preferably 2 to 9.5 times, that of the multi-layer graphene.
  • the carbon black does not aggregate and is easily dispersed. Furthermore, when the mixing ratio of multi-layer graphene and carbon black is within the above range, the electrode density can be made higher than when only carbon black is used as the conductive material. By increasing the electrode density, the capacity per unit weight can be increased.
  • graphene includes multi-layer graphene and multi-graphene.
  • graphene refers to a material that has carbon, has a shape such as a plate or sheet, and has a two-dimensional structure formed of six-membered carbon rings. The two-dimensional structure formed of six-membered carbon rings may be called a carbon sheet.
  • Graphene compounds include graphene oxide, multi-layer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multi-layer graphene oxide, reduced multi-graphene oxide, graphene quantum dots, and the like. In other words, graphene compounds may have functional groups.
  • Graphene or graphene compounds preferably have a curved shape. Graphene or graphene compounds may be rolled up, and rolled up graphene may be called carbon nanofibers.
  • graphene oxide refers to a material that contains carbon and oxygen, has a sheet-like shape, and has functional groups, particularly epoxy groups, carboxy groups, or hydroxy groups.
  • reduced graphene oxide refers to a material that has carbon and oxygen, has a sheet-like shape, and has a two-dimensional structure formed of six-membered carbon rings. Although reduced graphene oxide can function as a single sheet, multiple sheets may be stacked. Reduced graphene oxide preferably has a portion where the carbon concentration is greater than 80 atomic% and the oxygen concentration is 2 atomic% or more and 15 atomic% or less. By setting such carbon and oxygen concentrations, it can function as a highly conductive conductive material even in small amounts. In addition, reduced graphene oxide preferably has an intensity ratio G/D of the G band to the D band in the Raman spectrum of 1 or more. Reduced graphene oxide with such an intensity ratio can function as a highly conductive conductive material even in small amounts.
  • Fluorine-containing graphene may be used as the graphene compound.
  • the fluorine in the graphene compound may be adsorbed on the surface.
  • the fluorine-containing graphene may be produced by contacting graphene with a fluorine compound (called fluorination treatment). Fluorine (F 2 ) or a fluorine compound may be used for the fluorination treatment.
  • fluorine compound hydrofluoric acid, halogen fluoride (ClF 3 , IF 5 , etc.), gaseous fluoride (BF 3 , NF 3 , PF 5 , SiF 4 , SF 6 , etc.), metal fluoride (LiF, NiF 2 , AlF 3 , MgF 2 , etc.), etc. are preferable.
  • gaseous fluoride is preferably used, and the gaseous fluoride may be diluted with an inert gas.
  • the temperature of the fluorination treatment is preferably room temperature, but is preferably 0° C. or more and 250° C. or less, which includes the room temperature. When the fluorination treatment is performed at 0° C. or more, fluorine can be adsorbed on the surface of the graphene.
  • the graphene compound may have excellent electrical properties such as high electrical conductivity, and excellent physical properties such as high flexibility and high mechanical strength.
  • the graphene compound may have a sheet-like shape.
  • the graphene compound may have a curved surface, which allows for surface contact with low contact resistance.
  • even if the graphene compound is thin it may have very high electrical conductivity, and a conductive path can be efficiently formed in the active material layer with a small amount. Therefore, by using the graphene compound as a conductive material, the contact area between the active material and the conductive material can be increased.
  • the graphene compound may cover 80% or more of the area of the active material. It is preferable that the graphene compound is wrapped around at least a part of the active material particles.
  • the graphene compound is overlapped on at least a part of the active material particles. It is also preferable that the shape of the graphene compound matches at least a part of the shape of the active material particles.
  • the shape of the active material particles refers to, for example, the unevenness of a single active material particle or the unevenness formed by multiple active material particles. It is also preferable that the graphene compound surrounds at least a part of the active material particles.
  • the graphene compound may have holes.
  • active material particles with a small particle size for example, active material particles of 1 ⁇ m or less
  • the specific surface area of the active material particles is large, and more conductive paths connecting the active material particles are required.
  • Rapid charging and discharging refers to charging and discharging at, for example, 200 mA/g, 400 mA/g, or 1000 mA/g or more.
  • the sheet-like graphene or graphene compound may be uniformly dispersed.
  • the multiple graphene or graphene compounds are formed so as to partially cover the multiple active materials or to be attached to the surfaces of the multiple granular active materials, and are in surface contact with each other.
  • a mesh-like graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net) can be formed by bonding multiple graphenes or graphene compounds together.
  • the graphene net covers the active material, the graphene net can also function as a binder that bonds the active materials together. Therefore, the amount of binder can be reduced or no binder can be used, and the ratio of active material to the electrode volume and electrode weight can be improved. In other words, the discharge capacity of the secondary battery can be increased.
  • graphene oxide As the graphene or graphene compound, mix it with the active material to form an active material layer, and then reduce it. In other words, it is preferable that the completed active material layer has reduced graphene oxide.
  • graphene oxide which has extremely high dispersibility in a polar solvent, to form the graphene or graphene compound, the graphene or graphene compound can be dispersed approximately uniformly inside the active material layer.
  • the graphene or graphene compound remaining in the active material layer partially overlaps and is dispersed to such an extent that they are in surface contact with each other, thereby forming a three-dimensional conductive path.
  • the reduction of the graphene oxide may be performed, for example, by heat treatment or by using a reducing agent.
  • graphene or graphene compounds enable surface contact with low contact resistance, and therefore can improve the electrical conductivity between a smaller amount of active material and graphene or graphene compounds than with ordinary conductive materials.
  • the entire surface of the active material can be covered with a conductive graphene compound as a coating, and further a conductive path can be formed between the active material particles with the graphene compound.
  • a material used in forming the graphene compound may be mixed into the active material layer together with the graphene compound.
  • particles used as a catalyst in forming the graphene compound may be mixed with the graphene compound.
  • catalysts in forming the graphene compound include particles having silicon oxide (SiO 2 , SiO x (x ⁇ 2)), aluminum oxide, iron, nickel, ruthenium, iridium, platinum, copper, germanium, etc.
  • the particle size D50 is preferably 1 ⁇ m or less, more preferably 100 nm or less.
  • acetylene black (abbreviated as AB) can be used as a conductive material. Fluorine-containing acetylene black may also be used. The fluorine in the fluorine-containing acetylene black is preferably adsorbed on the surface. Fluorine-containing acetylene black can be produced by contacting acetylene black with a fluorine compound (called fluorination treatment). The fluorination treatment described for graphene can be applied to acetylene black.
  • carbon fiber materials also referred to as carbon nanotubes, or CNTs
  • CNTs carbon nanotubes
  • Fluorine-containing carbon nanotubes may also be used.
  • the fluorine in the fluorine-containing carbon nanotubes is preferably adsorbed on the surface.
  • Fluorine-containing carbon nanotubes can also be produced by contacting carbon nanotubes with a fluorine compound (called a fluorination treatment).
  • the fluorination treatment described for graphene can also be applied to carbon nanotubes.
  • the binder is necessary to firmly bond the powdered active material without covering the surface of the active material. Furthermore, the binder must be adhesive to the current collector. In other words, it is recommended that the binder be made of a material that has an adhesive component. Furthermore, in consideration of the expansion of the active material, the binder should be sufficiently flexible and should be able to respond to changes in the state of the active material. The binder must also be compatible with the electrolyte. Furthermore, since extremely strong oxidation and reduction reactions occur in secondary batteries, a binder that does not deteriorate or has low reactivity to these reactions is desired.
  • the binder it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, or ethylene-propylene-diene copolymer.
  • SBR styrene-butadiene rubber
  • fluororubber can be used as the binder.
  • a water-soluble polymer as the binder.
  • polysaccharides can be used as the water-soluble polymer.
  • the polysaccharide one or more of cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, regenerated cellulose, and starch can be used.
  • CMC carboxymethyl cellulose
  • methyl cellulose methyl cellulose
  • ethyl cellulose methyl cellulose
  • hydroxypropyl cellulose diacetyl cellulose
  • regenerated cellulose regenerated cellulose
  • polystyrene polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose as the binder.
  • PVDF polyvinylidene fluoride
  • PAN polyacrylonitrile
  • a material with particularly excellent viscosity adjustment effect may be used in combination with other materials.
  • rubber materials have excellent adhesive strength and/or elasticity, it may be difficult to adjust the viscosity when mixed with a solvent. In such cases, it is preferable to mix with a material with particularly excellent viscosity adjustment effect.
  • a water-soluble polymer may be used as a material with particularly excellent viscosity adjustment effect.
  • the above-mentioned polysaccharides for example, carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, and diacetylcellulose, cellulose derivatives such as regenerated cellulose, starch, etc. may be used.
  • CMC carboxymethylcellulose
  • methylcellulose methylcellulose
  • ethylcellulose methylcellulose
  • hydroxypropylcellulose hydroxypropylcellulose
  • diacetylcellulose cellulose derivatives such as regenerated cellulose, starch, etc.
  • the solubility of cellulose derivatives such as carboxymethylcellulose can be increased by converting them into salts, such as sodium salt and ammonium salt of carboxymethylcellulose, making them more effective as viscosity adjusters. Increasing the solubility can also increase the dispersibility of the active material and other components when preparing the electrode slurry.
  • the cellulose and cellulose derivatives used as electrode binders include their salts.
  • Water-soluble polymers stabilize the viscosity by dissolving in water, and can stably disperse active materials and other materials combined as binders, such as styrene-butadiene rubber, in an aqueous solution.
  • binders such as styrene-butadiene rubber
  • binders such as styrene-butadiene rubber
  • cellulose derivatives such as carboxymethyl cellulose
  • functional groups such as hydroxyl groups and carboxyl groups, and because they have functional groups, the polymers are expected to interact with each other and widely cover the surface of the active material.
  • a passive film is a film with no electrical conductivity or a film with extremely low electrical conductivity.
  • a passive film when a passive film is formed on the surface of the active material, it can suppress decomposition of the electrolyte at the battery reaction potential. Furthermore, it is even more desirable for the passive film to suppress electrical conductivity while still being able to conduct lithium ions.
  • the positive electrode current collector As the positive electrode current collector, a material having high conductivity, such as metals such as stainless steel, gold, platinum, aluminum, and titanium, and alloys thereof, can be used. In addition, it is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. In addition, an aluminum alloy to which an element that improves heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, is added can be used. In addition, it may be formed of a metal element that reacts with silicon to form a silicide.
  • Examples of metal elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel.
  • the current collector can be appropriately used in a shape such as a foil, plate, sheet, mesh, punched metal, or expanded metal. It is preferable to use a current collector having a thickness of 5 ⁇ m or more and 30 ⁇ m or less.
  • the negative electrode includes a negative electrode active material layer and a negative electrode current collector.
  • the negative electrode active material layer may include a conductive material and a binder.
  • Negative electrode active material for example, an alloy material and/or a carbon material can be used.
  • an element capable of carrying out a charge/discharge reaction by alloying/dealloying reaction with lithium can be used.
  • a material containing one or more elements selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used.
  • Such elements have a larger charge/discharge capacity than carbon, and silicon in particular has a high theoretical capacity of 4200 mAh/g. For this reason, it is preferable to use silicon as the negative electrode active material. Compounds containing these elements may also be used.
  • Examples include SiO, Mg2Si , Mg2Ge , SnO, SnO2 , Mg2Sn , SnS2 , V2Sn3 , FeSn2 , CoSn2 , Ni3Sn2 , Cu6Sn5 , Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7 , CoSb3 , InSb , SbSn , etc.
  • elements capable of carrying out charge/discharge reactions by alloying/dealloying reactions with lithium, and compounds containing such elements may be referred to as alloying materials.
  • SiO refers to, for example, silicon monoxide.
  • SiO can be expressed as SiO x .
  • x preferably has a value of 1 or close to 1.
  • x is preferably 0.2 or more and 1.5 or less, more preferably 0.3 or more and 1.2 or less.
  • x is preferably 0.2 or more and 1.2 or less.
  • x is preferably 0.3 or more and 1.5 or less.
  • the carbon material may be graphite, easily graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, carbon black, etc.
  • Examples of graphite include artificial graphite and natural graphite.
  • Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite.
  • MCMB mesocarbon microbeads
  • spherical graphite having a spherical shape can be used as the artificial graphite.
  • MCMB may have a spherical shape, which is preferable.
  • it is relatively easy to reduce the surface area of MCMB which may be preferable.
  • Examples of natural graphite include flake graphite and spheroidized natural graphite.
  • graphite When lithium ions are inserted into graphite (when a lithium-graphite intercalation compound is formed), graphite exhibits a low potential (0.05 V to 0.3 V vs. Li/Li + ) similar to that of lithium metal. This allows lithium ion secondary batteries to exhibit a high operating voltage. Furthermore, graphite is preferable because it has the advantages of a relatively high discharge capacity per unit volume, a relatively small volume expansion, low cost, and higher safety than lithium metal.
  • oxides such as titanium dioxide ( TiO2 ) , lithium titanium oxide ( Li4Ti5O12 ), lithium graphite intercalation compound ( LixC6 ), niobium pentoxide ( Nb2O5 ), tungsten dioxide ( WO2 ), and molybdenum dioxide ( MoO2 ) can be used as the negative electrode active material.
  • TiO2 titanium dioxide
  • Li4Ti5O12 lithium titanium oxide
  • LixC6 lithium graphite intercalation compound
  • Nb2O5 niobium pentoxide
  • WO2 tungsten dioxide
  • MoO2 molybdenum dioxide
  • Li2.6Co0.4N is preferable because it shows a large discharge capacity (900mAh/g, 1890mAh/ cm3 ).
  • the nitride of lithium and a transition metal When a nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, and therefore it is preferable that the nitride of lithium and a transition metal is combined with a material that does not contain lithium ions as a positive electrode active material, such as V 2 O 5 or Cr 3 O 8. Even when a material that contains lithium ions is used as the positive electrode active material, the nitride of lithium and a transition metal can be used as the negative electrode active material by desorbing the lithium ions contained in the positive electrode active material in advance.
  • a material that undergoes a conversion reaction can be used as the negative electrode active material.
  • a transition metal oxide that does not form an alloy with lithium such as cobalt oxide (CoO), nickel oxide (NiO), or iron oxide (FeO) may be used as the negative electrode active material.
  • materials that undergo a conversion reaction include oxides such as Fe2O3 , CuO, Cu2O , RuO2 , and Cr2O3 , sulfides such as CoS0.89 , NiS , and CuS, nitrides such as Zn3N2 , Cu3N , and Ge3N4 , phosphides such as NiP2 , FeP2 , and CoP3 , and fluorine compounds such as FeF3 and BiF3 .
  • oxides such as Fe2O3 , CuO, Cu2O , RuO2 , and Cr2O3
  • sulfides such as CoS0.89 , NiS , and CuS
  • nitrides such as Zn3N2 , Cu3N , and Ge3N4
  • phosphides such as NiP2 , FeP2 , and CoP3
  • fluorine compounds such as FeF3 and BiF3 .
  • the conductive material and binder that can be used in the negative electrode active material layer can be the same materials as the conductive material and binder that can be used in the positive electrode active material layer.
  • the negative electrode current collector may be made of the same material as the positive electrode current collector, but it is preferable that the negative electrode current collector is made of a material that does not form an alloy with carrier ions such as lithium.
  • the secondary battery has an electrolyte containing carrier ions.
  • the electrolyte is not limited to an electrolyte containing an organic solvent that is liquid at room temperature, but includes a solid electrolyte, and also includes an electrolyte (semi-solid electrolyte) that contains both an organic solvent that is liquid at room temperature and a solid electrolyte that is solid at room temperature.
  • an electrolyte in which a lithium salt is dissolved in an organic solvent that is liquid at room temperature is sometimes called an electrolyte solution.
  • Organic solvents that are liquid at room temperature An example of an organic solvent that is liquid at room temperature is described below.
  • the organic solvent that is liquid at room temperature is preferably an aprotic organic solvent, and for example, one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, ⁇ -butyrolactone, ⁇ -valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate (EP), propyl propionate (PP), methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc. can be used.
  • the ionic liquid is composed of a cation and an anion, and includes an organic cation and an anion.
  • Examples of the organic cation used in the organic solvent include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations.
  • Examples of the anion used in the organic solvent include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.
  • the lithium salt to be dissolved in the organic solvent may be, for example , one or more selected from LiPF6 , LiClO4 , LiAsF6 , LiBF4 , LiAlCl4 , LiSCN, LiBr , LiI, Li2SO4, Li2B10Cl10, Li2B12Cl12, LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3 , LiC ( C2F5SO2 ) 3 , LiN ( CF3SO2 ) 2 , LiN ( C4F9SO2 ) ( CF3SO2 ) , and LiN( C2F5SO2 ) 2 .
  • the organic solvent may have an additive.
  • the additive can suppress the reactive decomposition of the electrolyte that may occur on the positive electrode surface or the negative electrode surface when the secondary battery is operated at high voltage and/or high temperature.
  • vinylene carbonate (VC), propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), and lithium bis(oxalate)borate (LiBOB) can be used as the additive.
  • LiBOB is particularly preferred because it is easy to form a good coating.
  • VC or FEC is preferred because it can form a good coating on the negative electrode during charging and discharging to improve cycle characteristics.
  • the additive may contain a compound represented by the following general formula (G1).
  • the following general formula (G1) is a compound having two cyano groups, and can be called a dinitrile compound.
  • R represents a hydrocarbon having 1 to 5 carbon atoms.
  • R represents a hydrocarbon having 2 to 4 carbon atoms.
  • G1 Specific examples of the above general formula (G1) include succinonitrile, glutaronitrile, adiponitrile (ADN), and ethylene glycol bis(propionitrile) ether (EGBE).
  • one or more dinitrile compounds can be used as an additive.
  • fluorobenzene may be added to the organic solvent.
  • concentration of the additive may be, for example, 0.1 wt% or more and 5 wt% or less with respect to the entire electrolyte.
  • PS or EGBE are preferable because they form a good coating on the positive electrode during charging and discharging, thereby improving cycle characteristics.
  • FB is preferable because it improves the wettability of the organic solvent to the positive electrode and the negative electrode.
  • Dinitrile compounds are preferable because the nitrile groups are oriented to the positive electrode and the negative electrode, inhibiting the oxidative decomposition of the organic solvent, thereby improving the voltage resistance.
  • dinitrile compounds are preferable because they can prevent the dissolution of copper during overdischarge when a current collector having copper is used for the negative electrode. Considering the use of secondary batteries at high voltages, it is preferable to add a nitrile compound.
  • a semi-solid material called a polymer gel electrolyte can be used as the organic solvent.
  • a polymer gel electrolyte increases safety against leakage, etc. Also, it is possible to make the battery cell thinner and lighter.
  • Polymers that can be gelled include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, fluorine-based polymer gel, etc.
  • polymer for example, a polymer having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, etc., and copolymers containing these can be used.
  • PEO polyethylene oxide
  • PVDF-HFP which is a copolymer of PVDF and hexafluoropropylene (HFP)
  • the polymer formed may have a porous shape.
  • the above volume ratio may be the volume ratio before mixing with the electrolyte, and the outside air when mixing the electrolyte may be room temperature (typically 25° C.).
  • EC is a cyclic carbonate and has a high relative dielectric constant, and therefore has the effect of promoting the dissociation of lithium salts.
  • EC has a high viscosity and a high freezing point (melting point) of 38°C, so when EC alone is used as an organic solvent, it is difficult to use it in a low-temperature environment. Therefore, the organic solvent specifically described as one aspect of the present invention is not EC alone, but further contains EMC and DMC.
  • EMC is a chain carbonate, has the effect of reducing the viscosity of the electrolyte, and has a freezing point of -54°C.
  • DMC is also a chain carbonate, has the effect of reducing the viscosity of the electrolyte, and has a freezing point of -43°C.
  • the lithium salt to be dissolved in an organic solvent suitable for low temperatures can be selected from the lithium salts described above.
  • Additives contained in organic solvents suitable for low temperatures can be selected from the additives mentioned above.
  • the secondary battery preferably has a separator.
  • the separator may be made of, for example, paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyolefin, or polyurethane.
  • the separator is preferably processed into an envelope shape and disposed so as to encase either the positive electrode or the negative electrode.
  • the separator may have a multi-layer structure.
  • an organic material film such as polypropylene or polyethylene may be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture of these.
  • the ceramic material for example, aluminum oxide particles or silicon oxide particles may be used.
  • the fluorine material for example, PVDF or polytetrafluoroethylene may be used.
  • the polyamide material for example, nylon or aramid (meta-aramid or para-aramid) may be used.
  • Coating with ceramic-based materials improves oxidation resistance, suppressing the deterioration of the separator during high-voltage charging and discharging, and improving the reliability of the secondary battery.
  • Coating with fluorine-based materials also makes it easier for the separator and electrodes to adhere to each other, improving output characteristics.
  • Coating with polyamide-based materials, especially aramid improves heat resistance, improving the safety of the secondary battery.
  • both sides of a polypropylene film may be coated with a mixture of aluminum oxide and aramid.
  • the surface of the polypropylene film that comes into contact with the positive electrode may be coated with a mixture of aluminum oxide and aramid, and the surface that comes into contact with the negative electrode may be coated with a fluorine-based material.
  • the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, so the discharge capacity per volume of the secondary battery can be increased.
  • the exterior body of the secondary battery can be made of, for example, a metal material such as aluminum and/or a resin material.
  • a film-shaped exterior body can also be used.
  • a three-layer structure film can be used in which a thin metal film having excellent flexibility such as aluminum, stainless steel, copper, nickel, etc. is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc., and an insulating synthetic resin film such as a polyamide-based resin or polyester-based resin is further provided on the thin metal film as the outer surface of the exterior body.
  • a multilayer structure film such as a three-layer structure that has aluminum is sometimes referred to as an aluminum laminate film.
  • Solid electrolyte instead of the electrolyte, a solid electrolyte having an inorganic material such as a sulfide or oxide, or a solid electrolyte having a polymer material such as a PEO (polyethylene oxide) can be used.
  • a solid electrolyte When a solid electrolyte is used, the installation of a separator and/or a spacer becomes unnecessary.
  • the entire battery can be solidified, there is no risk of leakage, and safety is dramatically improved.
  • Secondary batteries using solid electrolytes are expected to be chemically stable even at high potentials compared to secondary batteries with liquid electrolytes. Therefore, an all-solid-state secondary battery using the positive electrode active material obtained in the above embodiment is expected to have good charge/discharge characteristics even when the charging voltage is 4.8 V or more, for example 5.0 V.
  • a secondary battery 400 As shown in FIG. 25A, a secondary battery 400 according to one embodiment of the present invention has a positive electrode 410, a solid electrolyte layer 420, and a negative electrode 430.
  • the positive electrode 410 has a positive electrode current collector 413 and a positive electrode active material layer 414.
  • the positive electrode active material layer 414 has a positive electrode active material 411 and a solid electrolyte 421.
  • the positive electrode active material 411 is made of a positive electrode active material produced by the manufacturing method described in the previous embodiment.
  • the positive electrode active material layer 414 may also contain a conductive agent and a binder.
  • the solid electrolyte layer 420 has a solid electrolyte 421.
  • the solid electrolyte layer 420 is located between the positive electrode 410 and the negative electrode 430, and is a region that has neither the positive electrode active material 411 nor the negative electrode active material 431.
  • the negative electrode 430 has a negative electrode current collector 433 and a negative electrode active material layer 434.
  • the negative electrode active material layer 434 has a negative electrode active material 431 and a solid electrolyte 421.
  • the negative electrode active material layer 434 may also have a conductive agent and a binder.
  • the negative electrode 430 may not have a solid electrolyte 421, as shown in FIG. 25B. Using metallic lithium for the negative electrode 430 is preferable because it can improve the energy density of the secondary battery 400.
  • the solid electrolyte 421 in the solid electrolyte layer 420 may be, for example, a sulfide solid electrolyte, an oxide solid electrolyte, a halide solid electrolyte, or the like.
  • Sulfide solid electrolytes include thiolithicons ( Li10GeP2S12 , Li3.25Ge0.25P0.75S4 , etc. ), sulfide glasses ( 70Li2S.30P2S5 , 30Li2S.26B2S3.44LiI , 63Li2S.36SiS2.1Li3PO4 , 57Li2S.38SiS2.5Li4SiO4 , 50Li2S.50GeS2 , etc. ) , and sulfide crystallized glasses ( Li7P3S11 , Li3.25P0.95S4 , etc. ) . Sulfide solid electrolytes have the advantages of being highly conductive, being able to be synthesized at low temperatures, and being relatively soft, which makes it easier to maintain conductive paths even after charging and discharging.
  • oxide solid electrolytes examples include materials having a perovskite crystal structure (La2 /3- xLi3xTiO3 , etc. ), materials having a NASICON crystal structure (Li1 + xAlxTi2 -x ( PO4 ) 3 , etc.), materials having a garnet crystal structure ( Li7La3Zr2O12 , etc. ), materials having a LISICON crystal structure ( Li14ZnGe4O16 , etc. ), LLZO (Li7La3Zr2O12) , oxide glass ( Li3PO4 -Li4SiO4 , 50Li4SiO4.50Li3BO3 , etc.
  • oxide solid electrolyte has an advantage that it is stable in the air.
  • Halide solid electrolytes include LiAlCl4 , Li3InBr6 , LiF, LiYF4 , Li3AlF6 , Li2ZrF6 , LiCl, LiBr , LiI , etc. Of these , LiF, LiYF4 , Li3AlF6 , and Li2ZrF6 are called fluoride solid electrolytes, and are suitable for use in secondary batteries at high voltages due to their wide potential window (V vs. Li metal).
  • composite materials in which these halide solid electrolytes are filled into the pores of porous aluminum oxide and/or porous silica can also be used as solid electrolytes.
  • the solid electrolyte on the positive electrode side may be different from the solid electrolyte on the negative electrode side.
  • a solid electrolyte with high oxidation resistance may be used on the positive electrode side
  • a solid electrolyte with high reduction resistance may be used on the negative electrode side.
  • the positive electrode active material 100 having an O3' type crystal structure has a high oxidation potential, so it is particularly desirable to use a solid electrolyte with high oxidation resistance.
  • Li1 + xAlxTi2 -x ( PO4 ) 3 (0 ⁇ x ⁇ 1) (hereinafter, LATP) having a NASICON crystal structure is preferable because it contains aluminum and titanium, which are elements that may be contained in the positive electrode active material used in the secondary battery 400 of one embodiment of the present invention, and therefore a synergistic effect can be expected in improving cycle characteristics. In addition, it is expected to improve productivity by reducing the number of steps.
  • the NASICON crystal structure refers to a compound represented by M2 ( XO4 ) 3 (M: transition metal, X: S, P, As, Mo, W, etc.), which has a structure in which MO6 octahedrons and XO4 tetrahedrons are arranged three-dimensionally with vertices shared.
  • Fig. 26A is an exploded perspective view of a coin-type (single-layer flat) secondary battery
  • Fig. 26B is an external view
  • Fig. 26C is a cross-sectional view thereof.
  • Coin-type secondary batteries are mainly used in small electronic devices.
  • Figure 26A is a schematic diagram that shows the overlapping of components (vertical relationship and positional relationship). Therefore, Figure 26A and Figure 26B are not completely corresponding views.
  • a positive electrode 304, a separator 310, a negative electrode 307, a spacer 322, and a washer 312 are stacked. These are sealed with a negative electrode can 302, a positive electrode can 301, and a gasket. Note that the gasket for sealing is not shown in Fig. 26A.
  • the spacer 322 and the washer 312 are used to protect the inside or to fix the position inside the can when the positive electrode can 301 and the negative electrode can 302 are crimped together.
  • the spacer 322 and the washer 312 are made of stainless steel or an insulating material.
  • the positive electrode 304 is a laminated structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305.
  • Figure 26B is an oblique view of the completed coin-type secondary battery.
  • the coin-type secondary battery 300 has a positive electrode can 301, which also serves as a positive electrode terminal, and a negative electrode can 302, which also serves as a negative electrode terminal, which are insulated and sealed with a gasket 303 made of polypropylene or the like.
  • the positive electrode 304 is formed of a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with the positive electrode current collector.
  • the negative electrode 307 is formed of a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with the negative electrode current collector.
  • the negative electrode 307 is not limited to a laminated structure, and may be a lithium metal foil or a lithium-aluminum alloy foil.
  • the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 each need only have an active material layer formed on one side.
  • the positive electrode can 301 and the negative electrode can 302 can be made of metals such as nickel, aluminum, titanium, etc., which are corrosion-resistant to the electrolyte, or alloys of these metals or alloys of these metals with other metals (e.g., stainless steel, etc.). In order to prevent corrosion by the electrolyte, etc., it is preferable to coat them with nickel or aluminum.
  • the positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307.
  • the negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte, and as shown in FIG. 26C, the positive electrode can 301 is placed at the bottom, and the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are stacked in this order, and the positive electrode can 301 and the negative electrode can 302 are crimped together via a gasket 303 to produce a coin-shaped secondary battery 300.
  • a cylindrical secondary battery 616 has a positive electrode cap (battery lid) 601 on the top surface, and a battery can (external can) 602 on the side and bottom surfaces.
  • the positive electrode cap 601 and the battery can (external can) 602 are insulated by a gasket (insulating packing) 610.
  • Figure 27B is a schematic diagram showing a cross section of a cylindrical secondary battery.
  • the cylindrical secondary battery shown in Figure 27B has a positive electrode cap (battery lid) 601 on the top surface, and a battery can (external can) 602 on the side and bottom surfaces.
  • the positive electrode cap and battery can (external can) 602 are insulated by a gasket (insulating packing) 610.
  • a battery element Inside the hollow cylindrical battery can 602, a battery element is provided in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 sandwiched between them. Although not shown, the battery element is wound around a central axis. One end of the battery can 602 is closed and the other end is open.
  • metals such as nickel, aluminum, and titanium that are resistant to corrosion by the electrolyte, or alloys of these metals and other metals (e.g., stainless steel, etc.) can be used.
  • the battery element in which the positive electrode, negative electrode, and separator are wound is sandwiched between a pair of opposing insulating plates 608 and 609.
  • a nonaqueous electrolyte (not shown) is injected inside the battery can 602 in which the battery element is provided.
  • the nonaqueous electrolyte can be the same as that of a coin-type secondary battery.
  • a cylindrical secondary battery 616 can be obtained that has a high capacity, a high discharge capacity, and excellent cycle characteristics.
  • a positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606.
  • the positive electrode terminal 603 can be made of a metal material such as aluminum.
  • the negative electrode terminal 607 can be made of a metal material such as copper.
  • the positive electrode terminal 603 is resistance-welded to a safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602.
  • the safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611.
  • the safety valve mechanism 613 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the increase in the internal pressure of the battery exceeds a predetermined threshold value.
  • the PTC element 611 is a thermosensitive resistor whose resistance increases when the temperature increases, and limits the amount of current due to the increase in resistance to prevent abnormal heat generation.
  • the PTC element 611 may be made of a barium titanate (BaTiO 3 ) based semiconductor ceramic or the like.
  • FIG. 27C shows an example of a power storage system 615.
  • the power storage system 615 has multiple secondary batteries 616.
  • the positive electrode of each secondary battery is in contact with and electrically connected to a conductor 624 separated by an insulator 625.
  • the conductor 624 is electrically connected to a control circuit 620 via wiring 623.
  • the negative electrode of each secondary battery is electrically connected to the control circuit 620 via wiring 626.
  • As the control circuit 620 a charge/discharge control circuit that performs charging and discharging, or a protection circuit that prevents overcharging and/or overdischarging can be applied.
  • Figure 27D shows an example of a power storage system 615.
  • the power storage system 615 has multiple secondary batteries 616, which are sandwiched between a conductive plate 628 and a conductive plate 614.
  • the multiple secondary batteries 616 are electrically connected to the conductive plate 628 and the conductive plate 614 by wiring 627.
  • the multiple secondary batteries 616 may be connected in parallel, in series, or in parallel and then further connected in series.
  • Multiple secondary batteries 616 may be connected in parallel and then further connected in series.
  • a temperature control device may be provided between the multiple secondary batteries 616.
  • the secondary batteries 616 When the secondary batteries 616 are overheated, they can be cooled by the temperature control device, and when the secondary batteries 616 are too cold, they can be heated by the temperature control device. This makes the performance of the power storage system 615 less susceptible to the effects of the outside air temperature.
  • the power storage system 615 is electrically connected to the control circuit 620 via wiring 621 and wiring 622.
  • Wiring 621 is electrically connected to the positive electrodes of the multiple secondary batteries 616 via conductive plate 628
  • wiring 622 is electrically connected to the negative electrodes of the multiple secondary batteries 616 via conductive plate 614.
  • the secondary battery 913 shown in FIG. 28A has a wound body 950 with terminals 951 and 952 provided inside the housing 930.
  • the wound body 950 is immersed in an electrolyte inside the housing 930.
  • the terminal 952 contacts the housing 930, and the terminal 951 does not contact the housing 930 by using an insulating material or the like.
  • the housing 930 is shown separated for convenience, but in reality, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930.
  • the housing 930 can be made of a metal material (such as aluminum) or a laminate of a metal material and a resin material.
  • the housing 930 shown in FIG. 28A may be formed from a plurality of materials.
  • the secondary battery 913 shown in FIG. 28B has housings 930a and 930b bonded together, and a wound body 950 is provided in the area surrounded by the housings 930a and 930b.
  • the housing 930a can be made of a metal material or a laminate of a metal material and an organic resin.
  • an insulating material such as an organic resin on the surface on which the antenna is formed, it is possible to suppress shielding of the electric field by the secondary battery 913. Note that if the shielding of the electric field by the housing 930a is small, the antenna may be provided inside the housing 930a.
  • the housing 930b can be made of, for example, a metal material or a laminate of a metal material and an organic resin.
  • the wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933.
  • the wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the separator 933 in between, and the laminated sheet is wound. Note that the stack of the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked multiple times.
  • a secondary battery 913 having a wound body 950a as shown in FIG. 29 may be used.
  • the wound body 950a shown in FIG. 29A has a negative electrode 931, a positive electrode 932, and a separator 933.
  • the negative electrode 931 has a negative electrode active material layer 931a.
  • the positive electrode 932 has a positive electrode active material layer 932a.
  • a secondary battery 913 with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.
  • the separator 933 has a width wider than the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap the negative electrode active material layer 931a and the positive electrode active material layer 932a. From the viewpoint of safety, it is preferable that the width of the negative electrode active material layer 931a is wider than that of the positive electrode active material layer 932a. Furthermore, a wound body 950a having such a shape is preferable because of its good safety and productivity.
  • the negative electrode 931 is electrically connected to a terminal 951 by ultrasonic bonding, welding, or crimping.
  • the terminal 951 is electrically connected to a terminal 911a.
  • the positive electrode 932 is electrically connected to a terminal 952 by ultrasonic bonding, welding, or crimping.
  • the terminal 952 is electrically connected to a terminal 911b.
  • the wound body 950a and the electrolyte are covered by the housing 930 to form the secondary battery 913. It is preferable to provide the housing 930 with a safety valve, an overcurrent protection element, and the like.
  • the safety valve is a valve that opens when the inside of the housing 930 reaches a certain internal pressure to prevent the battery from exploding.
  • the secondary battery 913 may have multiple wound bodies 950a. By using multiple wound bodies 950a, the secondary battery 913 can have a larger discharge capacity.
  • the secondary battery 913 shown in FIGS. 29B and 29C refer to the description of the secondary battery 913 shown in FIGS. 28A and 28B.
  • a laminated secondary battery 500 has a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.
  • FIG. 30A shows the external view of the positive electrode 503 and the negative electrode 506.
  • the positive electrode 503 has a positive electrode collector 501, and the positive electrode active material layer 502 is formed on the surface of the positive electrode collector 501.
  • the positive electrode 503 also has a region where the positive electrode collector 501 is partially exposed (hereinafter referred to as a tab region).
  • the negative electrode 506 has a negative electrode collector 504, and the negative electrode active material layer 505 is formed on the surface of the negative electrode collector 504.
  • the negative electrode 506 also has a region where the negative electrode collector 504 is partially exposed, that is, a tab region. Note that the area or shape of the tab region of the positive electrode 503 and the negative electrode 506 is not limited to the example shown in FIG. 30A.
  • a positive electrode 503 and a negative electrode 506 as shown in FIG. 31A.
  • an example is shown in which five sets of negative electrodes 506 and four sets of positive electrodes 503 are used. This can also be called a stack consisting of the negative electrode 506, the separator 507, and the positive electrode 503.
  • the tab regions of the positive electrodes 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode 503.
  • ultrasonic welding or the like may be used for the joining.
  • the tab regions of the negative electrodes 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode 506.
  • the exterior body 509 is folded at the portion indicated by the dashed line. After that, the outer periphery of the exterior body 509 is joined.
  • the joining for example, thermocompression bonding or the like may be used.
  • an area (hereinafter referred to as an inlet) that is not joined is provided on a part (or one side) of the exterior body 509 so that the electrolyte can be introduced later.
  • the electrolyte is introduced into the inside of the exterior body 509 through an inlet provided in the exterior body 509.
  • the electrolyte is preferably introduced under a reduced pressure atmosphere or an inert atmosphere.
  • the inlet is joined. In this manner, the laminated secondary battery 500 can be produced.
  • a secondary battery 500 By using the positive electrode active material 100 of one embodiment of the present invention for the positive electrode 503, a secondary battery 500 can be obtained that has a high capacity, a high discharge capacity, and excellent cycle characteristics.
  • a secondary battery according to one embodiment of the present invention When a secondary battery according to one embodiment of the present invention is installed in a vehicle, it is possible to realize a next-generation clean energy vehicle such as a hybrid vehicle (HV), an electric vehicle (EV), or a plug-in hybrid vehicle (PHV).
  • the secondary battery can also be installed in agricultural machinery, mopeds including electrically assisted bicycles, motorcycles, electric wheelchairs, electric carts, ships, submarines, aircraft, rockets, artificial satellites, space probes, planetary probes, or spacecraft.
  • the secondary battery according to one embodiment of the present invention can be a high-capacity secondary battery. Therefore, the secondary battery according to one embodiment of the present invention is suitable for miniaturization and weight reduction, and can be suitably used in transportation vehicles.
  • Figures 32A to 32D show an example of a transportation vehicle using one embodiment of the present invention.
  • the automobile 2001 shown in Figure 32A is an electric automobile that uses an electric motor as a power source for running. Or, it is a hybrid automobile that can appropriately select and use an electric motor and an engine as a power source for running.
  • a secondary battery is mounted on the vehicle, an example of the secondary battery shown in embodiment 4 is installed in one or more locations.
  • the automobile 2001 shown in Figure 32A has a battery pack 2200, and the battery pack 2200 has a secondary battery module to which multiple secondary batteries are connected. It is further preferable that the automobile has a charging control device that is electrically connected to the secondary battery module.
  • automobile 2001 can charge the secondary battery of automobile 2001 by receiving power supply from an external charging facility using a plug-in method or a contactless power supply method.
  • the charging method or connector standard may be a predetermined method such as CHAdeMO (registered trademark) or Combo.
  • the charging facility may be a charging station provided in a commercial facility, or may be a home power source.
  • a power storage device mounted on automobile 2001 can be charged by an external power supply using plug-in technology. Charging can be performed by converting AC power to DC power via a conversion device such as an AC-DC converter.
  • a power receiving device can be mounted on the vehicle and charging can be performed by supplying power contactlessly from a ground power transmitting device.
  • charging can be performed not only while the vehicle is stopped but also while it is moving.
  • This contactless power supply method can also be used to transmit and receive power between two vehicles.
  • solar cells can be provided on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped or moving. An electromagnetic induction method or a magnetic field resonance method can be used for such contactless power supply.
  • Figure 32B shows a large transport vehicle 2002 with an electrically controlled motor as an example of a transport vehicle.
  • the transport vehicle 2002 has a battery pack 2201, which has a secondary battery module with multiple secondary batteries connected together.
  • the secondary battery module of the transport vehicle 2002 is, for example, a four-cell unit of secondary batteries with a nominal voltage of 3.0V to 5.0V, with 48 cells connected in series for a maximum voltage of 170V.
  • the number of secondary batteries that make up the secondary battery module of the battery pack 2201 it has the same functions as Figure 32A, so a description will be omitted.
  • Figure 32C shows, as an example, a large transport vehicle 2003 having an electrically controlled motor.
  • the transport vehicle 2003 has a battery pack 2202, which has a secondary battery module in which multiple secondary batteries are connected.
  • the secondary battery module of the transport vehicle 2003 has a maximum voltage of 600V, for example, with more than 100 secondary batteries with a nominal voltage of 3.0V to 5.0V connected in series. Therefore, a secondary battery with small characteristic variations is required.
  • a secondary battery with stable battery characteristics can be manufactured, and mass production at low cost from the viewpoint of yield is possible.
  • FIG. 32D shows an aircraft 2004 having an engine that burns fuel.
  • the aircraft 2004 shown in FIG. 32D has wheels for takeoff and landing, and can therefore be considered part of a transportation vehicle. It has a battery pack 2203 that includes a secondary battery module formed by connecting multiple secondary batteries and a charging control device.
  • the secondary battery module of the aircraft 2004 has a maximum voltage of 32 V, for example, with eight 4 V secondary batteries connected in series. Other than the number of secondary batteries constituting the secondary battery module of the battery pack 2203, it has the same functions as those in FIG. 32A, so a description thereof will be omitted.
  • Figure 32E shows an example of an artificial satellite 2005 equipped with a secondary battery 2204. Since the artificial satellite 2005 is used in the extremely low temperature of outer space, it is preferable that the artificial satellite 2005 is equipped with a secondary battery 2204, which is an embodiment of the present invention and has excellent low temperature resistance. It is further preferable that the secondary battery 2204 is mounted inside the artificial satellite 2005 while being covered with a heat-retaining material.
  • FIG. 33A is an example of an electric bicycle using a secondary battery of one embodiment of the present invention.
  • a secondary battery 8701 of one embodiment of the present invention can be applied to a power storage device 8702, and power from the secondary battery is supplied to a motor that assists a rider.
  • the power storage device 8702 is preferably portable, and FIG. 33B shows the power storage device 8702 removed from the bicycle.
  • the power storage device 8702 may have a display unit 8703 that can display the remaining battery level, etc.
  • the power storage device 8702 may also have a control circuit 8704 that can control charging of the secondary battery or detect an abnormality.
  • the control circuit 8704 is electrically connected to the positive and negative electrodes of the secondary battery 8701.
  • An electric bicycle equipped with a secondary battery of one embodiment of the present invention is safe even when operated at a high voltage.
  • FIG. 33C is an example of a two-wheeled vehicle using the secondary battery of one embodiment of the present invention.
  • a scooter 8600 shown in FIG. 33C includes a power storage device 8602, a side mirror 8601, and a turn signal light 8603.
  • the secondary battery 8701 of one embodiment of the present invention can be applied to the power storage device 8702, and power from the secondary battery is supplied to the turn signal light 8603.
  • a two-wheeled vehicle equipped with the secondary battery of one embodiment of the present invention is safe even when operated at high voltage.
  • the scooter 8600 shown in FIG. 33C can store the power storage device 8602 in the under-seat storage 8604.
  • the power storage device 8602 can be stored in the under-seat storage 8604 even if the under-seat storage 8604 is small.
  • a secondary battery according to one embodiment of the present invention in an electronic device will be described.
  • the secondary battery according to one embodiment of the present invention is preferable because it is unlikely to ignite.
  • Examples of electronic devices in which a secondary battery is mounted include television devices (also called televisions or television receivers), monitors for computers, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game machines, portable information terminals, audio playback devices, and large game machines such as pachinko machines.
  • portable information terminals include notebook personal computers, tablet terminals, e-book terminals, and mobile phones.
  • FIG 34A shows an example of a mobile phone.
  • the mobile phone 2100 includes a display portion 2102 built into a housing 2101, operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. Note that the mobile phone 2100 includes a secondary battery 2107.
  • a mobile phone equipped with the secondary battery 2107 of one embodiment of the present invention is safe even when operated at high voltage.
  • the mobile phone 2100 can execute various applications such as mobile phone calls, e-mail, text browsing and creation, music playback, Internet communication, and computer games.
  • the operation button 2103 can have various functions, such as time setting, power on/off operation, wireless communication on/off operation, silent mode and power saving mode.
  • the functions of the operation button 2103 can be freely set by an operating system built into the mobile phone 2100.
  • the mobile phone 2100 is also capable of performing standardized short-range wireless communication. For example, it can communicate with a wireless headset to enable hands-free calling.
  • the mobile phone 2100 also includes an external connection port 2104, and can directly exchange data with other information terminals via a connector. Charging can also be performed via the external connection port 2104. Note that charging may also be performed by wireless power supply without using the external connection port 2104.
  • the mobile phone 2100 has a sensor.
  • a sensor it is preferable that a fingerprint sensor, a pulse sensor, a body temperature sensor or other human body sensor, a touch sensor, a pressure sensor, an acceleration sensor, or the like is installed.
  • Figure 34B shows an unmanned aerial vehicle 2300 having multiple rotors 2302.
  • the unmanned aerial vehicle 2300 is sometimes called a drone.
  • the unmanned aerial vehicle 2300 has a secondary battery 2301 according to one embodiment of the present invention, a camera 2303, and an antenna (not shown).
  • the unmanned aerial vehicle 2300 can be remotely controlled via the antenna.
  • the unmanned aerial vehicle 2300 equipped with the secondary battery 2301 according to one embodiment of the present invention is safe even when operated at high voltage. Furthermore, it can be used safely for a long period of time.
  • Figure 34C shows an example of a robot.
  • the robot 6400 shown in Figure 34C includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a movement mechanism 6408, a computing device, etc.
  • the microphone 6402 has a function of detecting the user's voice and environmental sounds.
  • the speaker 6404 has a function of emitting sound.
  • the robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.
  • the display unit 6405 has a function of displaying various information.
  • the robot 6400 can display information desired by the user on the display unit 6405.
  • the display unit 6405 may be equipped with a touch panel.
  • the display unit 6405 may also be a removable information terminal, and by installing it in a fixed position on the robot 6400, charging and data transfer are possible.
  • the upper camera 6403 and the lower camera 6406 have the function of capturing images of the surroundings of the robot 6400.
  • the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the moving mechanism 6408.
  • the robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.
  • the robot 6400 includes a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or electronic component in its internal area. Furthermore, a robot equipped with the secondary battery 6409 according to one embodiment of the present invention is safe even when operated at high voltage. Furthermore, it can be used safely for a long period of time.
  • FIG. 34D illustrates an example of a portable electric fan.
  • the portable electric fan 6200 illustrated in FIG. 34D includes a secondary battery 6209 according to one embodiment of the present invention, an operation button 6205, a fan 6202, an external connection port 6204, and the like, and the secondary battery 6209 is housed in a housing 6201.
  • the portable electric fan 6200 can rotate the fan 6202 by operating a motor using power supplied from the secondary battery 6209, and the secondary battery 6209 can be charged via the external connection port 6204.
  • the secondary battery 6209 is an example of a cylindrical secondary battery, but the shape is not particularly limited.
  • the portable electric fan 6200 equipped with the secondary battery 6209 according to one embodiment of the present invention is safe even when operated at a high voltage. Furthermore, it can be used safely for a long period of time.
  • Figure 34E shows an example of a cleaning robot.
  • the cleaning robot 6300 has a display unit 6302 arranged on the top surface of the housing 6301, multiple cameras 6303 arranged on the side, a brush 6304, an operation button 6305, a secondary battery 6306, various sensors, and the like.
  • the cleaning robot 6300 is equipped with tires, a suction port, and the like.
  • the cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust 6310 from a suction port provided on the bottom surface of the housing 6301.
  • the cleaning robot 6300 can analyze the image captured by the camera 6303 and determine whether or not there is an obstacle such as a wall, furniture, or a step. Furthermore, if an object that may become entangled in the brush 6304, such as a wire, is detected by image analysis, the rotation of the brush 6304 can be stopped.
  • the cleaning robot 6300 includes a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or electronic component in its internal area. Furthermore, the cleaning robot 6300 equipped with the secondary battery 6209 according to one embodiment of the present invention is safe even when operated at a high voltage. Furthermore, it can be used safely for a long period of time.
  • step S14 in Fig. 18A a commercially available lithium cobalt oxide (CellSeed C-10N, manufactured by Nippon Chemical Industry Co., Ltd.) having cobalt as the transition metal M and no particular additive element was prepared.
  • the GD-MS measurement result of CellSeed C-10N satisfied the range of material Sm-3 in the above-mentioned embodiment 1.
  • the initial heating in step S15 was not performed.
  • LiF was prepared as an F source
  • MgF2 was prepared as an Mg source.
  • LiF and MgF2 were weighed out so that the molar ratio of LiF: MgF2 was 1:3, and dehydrated acetone was added as a solvent to wet mix and pulverize to obtain the A1 source.
  • step S31 the A1 source was weighed out so that the number of magnesium atoms contained in the A1 source was 0.1% of the number of cobalt atoms contained in the lithium cobalt oxide, and was dry-mixed with the lithium cobalt oxide.
  • step S33 of FIG. 18A the mixture 903 was heated.
  • the heating conditions were 850° C. and 60 hours.
  • a lid was placed on the crucible containing the mixture 903.
  • the crucible and lid were made of alumina.
  • oxygen was supplied at a flow rate of 10 L/min so that the inside of the crucible was an oxygen-containing atmosphere (flow).
  • sample 1-1 was obtained as lithium cobalt oxide containing magnesium and fluorine (corresponding to the positive electrode active material 100 in step S34).
  • the focus was on magnesium, which is an additive element, so no A2 source was added.
  • samples 1-2, 1-3, 1-4, 1-5, and 1-6 were also prepared. Samples 1-2, 1-3, 1-4, 1-5, and 1-6 differ from sample 1-1 in the magnesium ratio of the A1 source in step S21 shown in FIG. 18B.
  • Sample 1-2 was prepared under the same conditions as sample 1-1, except that the number of magnesium atoms in the A1 source was weighed out to be 0.5% of the number of cobalt atoms in the lithium cobalt oxide, and then dry-mixed with the lithium cobalt oxide.
  • Sample 1-3 was prepared under the same conditions as sample 1-1, except that the number of magnesium atoms in the A1 source was weighed out to be 1.0% of the number of cobalt atoms in the lithium cobalt oxide, and then dry-mixed with the lithium cobalt oxide.
  • Sample 1-4 was prepared under the same conditions as sample 1-1, except that the number of magnesium atoms in the A1 source was weighed out to be 2.0% of the number of cobalt atoms in the lithium cobalt oxide, and then dry-mixed with the lithium cobalt oxide.
  • Sample 1-5 was prepared under the same conditions as sample 1-1, except that the number of magnesium atoms in the A1 source was weighed out to be 3.0% of the number of cobalt atoms in the lithium cobalt oxide, and then dry-mixed with the lithium cobalt oxide.
  • Sample 1-6 was prepared under the same conditions as sample 1-1, except that the number of magnesium atoms in the A1 source was weighed out to be 6.0% of the number of cobalt atoms in the lithium cobalt oxide, and then dry-mixed with the lithium cobalt oxide.
  • the method for measuring the volume resistivity of the powder was the method described in ⁇ Powder Resistance Measurement> in embodiment 1.
  • the measurement device used was an MCP-PD51 manufactured by Mitsubishi Chemical Analytech Co., Ltd. As each resistance meter has a different range in which it can measure with high accuracy, the most suitable resistance meter was selected according to the resistivity of the sample.
  • the measurements were also performed in a typical laboratory environment (i.e., a temperature environment of 15°C to 30°C).
  • the powder was set in the measurement section, and the electrical resistance and volume of the powder were measured under pressure conditions of 13 MPa, 25 MPa, 38 MPa, 51 MPa, and 64 MPa, to obtain the volume resistivity of the powder of each sample. The results are shown in Figure 35.
  • the powder resistance of lithium cobalt oxide containing magnesium increases with the amount of A1 source mixed. It is believed that magnesium and the like are located in the surface layer, which increases the powder resistance of the positive electrode active material. Specifically, it was found that the volume resistivity of the powder of sample 1-2 was 1.0 ⁇ 10 4 ⁇ cm or more at a pressure of 64 MPa. It was also found that the volume resistivity of the powder of sample 1-3 was 1.0 ⁇ 10 6 ⁇ cm or more at a pressure of 64 MPa. It was also found that the volume resistivity of the powder of sample 1-6 was 1.0 ⁇ 10 7 ⁇ cm or more at a pressure of 64 MPa.
  • the volume resistivity at a pressure of 64 MPa is preferably 5.0 ⁇ 10 3 ⁇ cm or more, more preferably 1.0 ⁇ 10 4 ⁇ cm or more, more preferably 1.0 ⁇ 10 5 ⁇ cm or more, more preferably 5.0 ⁇ 10 5 ⁇ cm or more, and more preferably 1.0 ⁇ 10 6 ⁇ cm or more.
  • the volume resistivity at a pressure of 13 MPa is preferably 2.0 ⁇ 10 4 ⁇ cm or more, more preferably 2.0 ⁇ 10 5 ⁇ cm or more, more preferably 5.0 ⁇ 10 5 ⁇ cm or more, more preferably 1.0 ⁇ 10 6 ⁇ cm or more, and more preferably 2.0 ⁇ 10 6 ⁇ cm or more.
  • the volume resistivity is preferably 1.0 ⁇ 10 4 ⁇ cm or more when the pressure is 64 MPa, and 2.0 ⁇ 10 4 ⁇ cm or more when the pressure is 13 MPa. Also, it is preferably 1.0 ⁇ 10 5 ⁇ cm or more when the pressure is 64 MPa, and 2.0 ⁇ 10 5 ⁇ cm or more when the pressure is 13 MPa. Furthermore, it is preferably 5.0 ⁇ 10 5 ⁇ cm or more when the pressure is 64 MPa, and 1.0 ⁇ 10 6 ⁇ cm or more when the pressure is 13 MPa.
  • Samples 1-2, 1-3, and 1-6 have higher insulating properties than Sample 2 by one to five orders of magnitude, preferably two to three orders of magnitude.
  • the powder volume resistivity was measured at room temperature (25°C), but it is considered that Samples 1-2, 1-3, and 1-6 have higher insulating properties than Sample 2 even at temperatures higher than room temperature. Therefore, when Samples 1-2, 1-3, and 1-6 are applied to a secondary battery, a highly safe secondary battery can be provided. Furthermore, it is preferable to apply Samples 1-2, 1-3, and 1-6 to a secondary battery using a solid electrolyte.
  • half cells coin-type secondary batteries (called half cells) were fabricated using Sample 1-1, Sample 1-2, Sample 1-3, Sample 1-4, Sample 1-5, and Sample 1-6 as the positive electrode active material.
  • the positive electrode active material was prepared, acetylene black (AB) was prepared as a conductive material, and polyvinylidene fluoride (PVDF) was prepared as a binder.
  • the PVDF was prepared by dissolving it in N-methyl-2-pyrrolidone (NMP) at a weight ratio of 5%.
  • NMP N-methyl-2-pyrrolidone
  • the positive electrode active material, AB, and PVDF were mixed in a ratio of 95:3:2 (weight ratio) to prepare a slurry, which was then applied to an aluminum positive electrode current collector.
  • NMP was used as the solvent for the slurry.
  • the slurry was applied to the positive electrode current collector, and the solvent was evaporated to form a positive electrode active material layer on the positive electrode current collector.
  • a pressing process was performed using a roll press machine.
  • the pressing process was performed under conditions of a linear pressure of 210 kN/m.
  • the upper and lower rolls of the roll press machine were both set at 120°C.
  • the above steps resulted in the production of positive electrodes having each sample.
  • the amount of active material carried by the positive electrode was approximately 7 mg/ cm2 .
  • the half cell using sample 1-1 as the positive electrode active material was called cell 1-1
  • the half cell using sample 1-2 as the positive electrode active material was called cell 1-2
  • the half cell using sample 1-3 as the positive electrode active material was called cell 1-3
  • the half cell using sample 1-4 as the positive electrode active material was called cell 1-4
  • the half cell using sample 1-5 as the positive electrode active material was called cell 1-5
  • the half cell using sample 1-6 as the positive electrode active material was called cell 1-6.
  • a porous polypropylene film was used as the separator for the half-cell.
  • Lithium metal was used as the negative electrode (counter electrode) of the half cell.
  • the cells 1-1 to 1-6 were placed in a thermostatic chamber maintained at 25° C., and a cycle of the following charge and discharge conditions was repeated 50 times.
  • Charge conditions CCCV charge, 0.5C rate, 4.6V, 0.05C cutoff Discharge conditions: CC discharge, 0.5C rate, 2.5V
  • the current value corresponding to 1C was set to 200 mA/g per weight of the positive electrode active material.
  • the charge condition of 4.6 V is called the upper limit voltage, and the upper limit voltage is maintained during the CV charge period.
  • the discharge condition of 2.5 V is called the lower limit voltage.
  • the results of the charge-discharge cycle test are shown in Figures 36A and 36B.
  • the vertical axis shows the discharge capacity (mAh/g) and the horizontal axis shows the number of cycles in the charge-discharge cycle test
  • the vertical axis shows the discharge capacity retention rate (%) and the horizontal axis shows the number of cycles in the charge-discharge cycle test.
  • the discharge capacity in the cycle that showed the maximum discharge capacity for each cell in the charge-discharge cycle test was set to 100%.
  • the discharge capacity at one cycle was 221.3 mAh/g for cell 1-2, 212.4 mAh/g for cell 1-3, 208.5 mAh/g for cell 1-4, and 208.5 mAh/g for cell 1-5. It was found that cell 1-2, cell 1-3, cell 1-4, and cell 1-5 had an initial discharge capacity of 200 mAh/g or more, preferably 210 mAh/g or more, and thus exhibited excellent initial discharge capacity.
  • the discharge capacity at 50 cycles was 215.2 mAh/g for cell 1-2, 210.7 mAh/g for cell 1-3, 199.9 mAh/g for cell 1-4, and 192.5 mAh/g for cell 1-5. It was found that cell 1-2, cell 1-3, cell 1-4, and cell 1-5 had a discharge capacity at 50 cycles of 190 mAh/g or more, preferably 200 mAh/g or more, and thus exhibited excellent discharge capacity.
  • lithium ions can be inserted and removed even in a positive electrode active material in which an additive element such as magnesium is located in the surface layer 100a.
  • the discharge capacity retention rate at 50 cycles was 96.1% for cell 1-2, 96.2% for cell 1-3, 93.3% for cell 1-4, and 91.8% for cell 1-5.
  • Cell 1-2, cell 1-3, cell 1-4, and cell 1-5 showed excellent discharge capacity retention rates, and it was found that the discharge capacity retention rate at 50 cycles was 90% or more, preferably 95% or more.
  • Cell 1-6 had a superior discharge capacity retention rate compared to cell 1-1, but a lower value compared to cells 1-2 to 1-5.
  • Sample 1-6 used as the positive electrode active material of cell 1-6 had a volume resistivity of 3.3 ⁇ 10 7 ⁇ cm at 64 MPa, as shown in Figure 35. In order to obtain a secondary battery with a higher discharge capacity than these, it is considered desirable to make the volume resistivity of the positive electrode active material lower than 3.3 ⁇ 10 7 ⁇ cm at 64 MPa.
  • LiCoO2 was prepared in the same manner as in Sample 2 of Example 1 in step S14 of Fig. 19. The sample was renamed to Sample 2-1.
  • step S14 The LiCoO 2 of step S14 was subjected to the initial heating of step S15 of Fig. 19. This was designated as sample 2-2.
  • step S15 a composite oxide was produced in step S34a of FIG. 19 in the same manner as in Example 1.
  • the number of magnesium atoms in the A1 source was set to 1.0% of the number of cobalt atoms in the lithium cobalt oxide. This was designated sample 2-3.
  • Nickel and aluminum were added as the A2 source to the composite oxide of step S34a according to step S40 to produce the positive electrode active material 100 of step S54 in FIG. 19.
  • the number of nickel atoms in the A2 source was set to 0.5% of the number of cobalt atoms in the lithium cobalt oxide.
  • the number of aluminum atoms in the A2 source was set to 0.5% of the number of cobalt atoms in the lithium cobalt oxide. This was designated sample 2-4.
  • the powder volume resistivity was measured in the same manner as in Example 1. To measure the volume resistivity of the powder of each sample, the powder was set in a measuring section with a radius of 1 cm, and the electrical resistance and volume of the powder were measured under pressure conditions of 13 MPa, 25 MPa, 38 MPa, 51 MPa, and 64 MPa, to obtain the volume resistivity of the powder of each sample. The results are shown in Figure 37.
  • the volume resistivity of sample 2-2 was higher than that of sample 2-1.
  • the volume resistivity of sample 2-3 was also higher than that of sample 2-2.
  • the volume resistivity of sample 2-4 was also higher than that of sample 2-2, but lower than that of sample 2-3. In other words, the volume resistivity values were highest in the order of sample 2-1, sample 2-2, sample 2-4, and sample 2-3.
  • the volume resistivity is preferably 5.0 ⁇ 10 3 ⁇ cm or more, more preferably 1.0 ⁇ 10 4 ⁇ cm or more, more preferably 1.0 ⁇ 10 5 ⁇ cm or more, more preferably 5.0 ⁇ 10 5 ⁇ cm or more, and more preferably 1.0 ⁇ 10 6 ⁇ cm or more.
  • the volume resistivity at a pressure of 13 MPa is preferably 2.0 ⁇ 10 4 ⁇ cm or more, more preferably 2.0 ⁇ 10 5 ⁇ cm or more, more preferably 5.0 ⁇ 10 5 ⁇ cm or more, more preferably 1.0 ⁇ 10 6 ⁇ cm or more, and more preferably 2.0 ⁇ 10 6 ⁇ cm or more.
  • the volume resistivity is preferably 1.0 ⁇ 10 4 ⁇ cm or more when the pressure is 64 MPa, and 2.0 ⁇ 10 4 ⁇ cm or more when the pressure is 13 MPa. Also, it is preferably 1.0 ⁇ 10 5 ⁇ cm or more when the pressure is 64 MPa, and 2.0 ⁇ 10 5 ⁇ cm or more when the pressure is 13 MPa. Furthermore, it is preferably 5.0 ⁇ 10 5 ⁇ cm or more when the pressure is 64 MPa, and 1.0 ⁇ 10 6 ⁇ cm or more when the pressure is 13 MPa.
  • sample 2-4 and sample 2-3 are preferably applied to secondary batteries using solid electrolytes.
  • GD-MS was measured for Sample 2-1, Sample 2-2, Sample 2-3, and Sample 2-4.
  • the element concentration (ppm wt) is shown in the table below. Note that the element concentrations other than those shown in the table below are omitted.
  • sample 2-1 corresponds to material Sm-3 shown in the above embodiment. Furthermore, when sample 2-1 and sample 2-2 are compared, it is suggested that the concentration of magnesium, aluminum, titanium and nickel does not change when the initial heating of step S15 is performed alone, and the concentration of fluorine tends to increase. Furthermore, it was found that the concentration of magnesium detected by GD-MS becomes 100 ppm wt or more and 3000 ppm wt or less when the process of adding a compound having magnesium as the additive element A1 is performed as in sample 2-3 and sample 2-4. Since the compound having magnesium used as the additive element A1 contains fluorine, the concentration of fluorine increased in sample 2-3.
  • the concentration of fluorine in sample 2-4 increased more than in samples 2-1 and 2-2, but decreased more than in sample 2-3. This suggests the possibility that fluorine may have sublimated due to the firing after the addition of the additive element A2. Furthermore, there was no change in the titanium concentration in any of the samples. It was found that by adding a compound containing nickel as the additive element A2, as in sample 2-4, the nickel concentration detected by GD-MS was 200 ppm wt or more and 3000 ppm wt or less.
  • magnesium, aluminum, and nickel were not detected by XPS in sample 2-2, but were detected by XPS in sample 2-4. This suggests that magnesium, aluminum, and nickel do not segregate in the surface layer by the initial heating in step S15 alone. It was found that magnesium, aluminum, and nickel can be detected by XPS by adding additive element A1 and additive element A2 to lithium cobalt oxide (C-10N).
  • 100 Positive electrode active material
  • 100a Surface layer
  • 100b Interior
  • 100c Defect
  • 101 Grain boundary
  • 103 Convex
  • 104 Coating

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Abstract

Provided is a secondary battery that is safe when used at high voltages. Specifically provided is a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein: the positive electrode has a positive electrode active material; the positive electrode active material contains lithium cobalt oxide and magnesium; the electrolyte contains a lithium salt, an organic solvent and an additive; the additive contains a dinitrile compound; the negative electrode contains a carbon material; and when a battery assembled using the positive electrode and lithium metal as a counter electrode and the positive electrode charged to a voltage of 4.7 V is subjected to a powder X-ray diffraction analysis using a CuKα1 beam, there is a diffraction peak at at least 2θ=19.25±0.12 degrees and 2θ=45.47±0.10 degrees.

Description

二次電池Secondary battery
本発明の一形態は、二次電池に関する。なお本発明の一態様は上記分野に限定されず、半導体装置、表示装置、発光装置、蓄電装置、照明装置または電子機器、またはそれらの製造方法に関する。 One embodiment of the present invention relates to a secondary battery. Note that the present invention is not limited to the above fields, and relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, or an electronic device, or a manufacturing method thereof.
近年、高出力、高容量であるリチウムイオン二次電池（二次電池とも記す）は需要が急速拡大し、繰り返し利用可能なエネルギー源として現代社会に不可欠なものとなっている。 In recent years, the demand for high-output, high-capacity lithium-ion secondary batteries (also referred to as secondary batteries) has expanded rapidly, and they have become indispensable in modern society as a reusable energy source.
リチウムイオン二次電池は、高容量であることと、安全性を両立させることは難しいと言われている。たとえば層状岩塩型結晶構造を有する正極活物質は、その結晶構造内でリチウムイオンの拡散経路が二次元的に存在するため、高容量化が期待されている。しかしながら層状岩塩型結晶構造を有する正極活物質は、充電時にリチウムイオンが脱離しすぎると、結晶構造が壊れるため熱暴走に至りやすいとされており、安全性の観点で課題を抱えていた。 It is said that it is difficult for lithium-ion secondary batteries to achieve both high capacity and safety. For example, a positive electrode active material with a layered rock-salt crystal structure is expected to achieve high capacity because the diffusion paths of lithium ions exist two-dimensionally within the crystal structure. However, a positive electrode active material with a layered rock-salt crystal structure is said to be prone to thermal runaway if too many lithium ions are released during charging because the crystal structure is destroyed, posing a safety issue.
層状岩塩型結晶構造の正極活物質として、コバルト酸リチウム（ＬｉＣｏＯ２）等が知られている。コバルト酸リチウムは層状岩塩型結晶構造を有し、ＣｏＯ６八面体からなる層間をリチウムイオンが二次元的に移動することができるため、サイクル特性も良好である。しかしコバルト酸リチウムは、充放電に伴う相変化という課題があった。たとえば充電時、リチウムイオンがある程度脱離してしまうと、コバルト酸リチウムは六方晶から単斜晶への相変化が生じる。そのため、良好なサイクル特性で利用するには、リチウムイオンの脱離量を制限させていた。これらを解決するために、特許文献１ではコバルト酸リチウムに添加元素を加えた構成を提案している。また非特許文献１乃至非特許文献４のように、正極活物質の結晶構造に関する研究も行われている。 Lithium cobalt oxide (LiCoO 2 ) and the like are known as positive electrode active materials with a layered rock salt crystal structure. Lithium cobalt oxide has a layered rock salt crystal structure, and lithium ions can move two-dimensionally between layers consisting of CoO 6 octahedra, so the cycle characteristics are also good. However, lithium cobalt oxide has a problem of phase change accompanying charge and discharge. For example, when lithium ions are desorbed to a certain extent during charging, lithium cobalt oxide undergoes a phase change from hexagonal to monoclinic. Therefore, in order to use it with good cycle characteristics, the amount of lithium ions desorbed is limited. In order to solve these problems, Patent Document 1 proposes a configuration in which an additive element is added to lithium cobalt oxide. In addition, research on the crystal structure of positive electrode active materials is also being conducted, as in Non-Patent Documents 1 to 4.
またＸＲＤ（Ｘ−ｒａｙ　Ｄｉｆｆｒａｃｔｉｏｎ、Ｘ線回折）は、正極活物質の結晶構造の解析に用いられる手法の一つである。非特許文献５に記載されたＩＣＳＤ（Ｉｎｏｒｇａｎｉｃ　Ｃｒｙｓｔａｌ　Ｓｔｒｕｃｔｕｒｅ　Ｄａｔａｂａｓｅ）を用いることにより、ＸＲＤデータの解析を行うことができると知られている。またリートベルト法解析には、たとえば非特許文献６に記載された解析プログラムＲＩＥＴＡＮ−ＦＰを用いることが知られている。また画像処理ソフトには、非特許文献７乃至非特許文献９に記載されたＩｍａｇｅＪを用いることが知られている。 XRD (X-ray diffraction) is one of the methods used to analyze the crystal structure of positive electrode active materials. It is known that XRD data can be analyzed by using the Inorganic Crystal Structure Database (ICSD) described in Non-Patent Document 5. It is also known that the analysis program RIETAN-FP described in Non-Patent Document 6 is used for Rietveld method analysis. It is also known that ImageJ described in Non-Patent Documents 7 to 9 is used as image processing software.
また、非特許文献１０のように蛍石（フッ化カルシウム）等のフッ化物は古くから製鉄などにおいて融剤として用いられている。 Furthermore, as shown in Non-Patent Document 10, fluorides such as fluorite (calcium fluoride) have long been used as fluxes in steelmaking and other processes.
また、非特許文献１１のようにシャノンのイオン半径が知られている。 In addition, Shannon's ionic radius is known, as shown in Non-Patent Document 11.
特開２０１８−１９５５８１号公報JP 2018-195581 A
上記特許文献１等に従って正極活物質を得ることが可能であるが、高電圧特性、例えば高電圧での放電容量、又は高電圧でのサイクル特性といった様々な面で改善の余地が残されている。さらに、電解質に対する高電圧特性を改善する余地が残されている。 It is possible to obtain a positive electrode active material according to Patent Document 1 and the like, but there is still room for improvement in various aspects, such as high voltage characteristics, for example, discharge capacity at high voltage, or cycle characteristics at high voltage. Furthermore, there is still room for improvement in the high voltage characteristics with respect to the electrolyte.
上記記載を鑑み、本発明の一態様は、高電圧でも安定な正極活物質を提供することを課題とする。また本発明の一態様は、上記正極活物質と共に、高電圧でも安定な電解質を備えた二次電池を提供することを課題の一とする。 In view of the above, one aspect of the present invention aims to provide a positive electrode active material that is stable even at high voltages. Another aspect of the present invention aims to provide a secondary battery that includes the positive electrode active material and an electrolyte that is stable even at high voltages.
なお、上記課題の記載は、他の課題の存在を妨げるものではない。さらに明細書、図面、請求項の記載から、上記課題以外の課題を抽出することが可能である。そして本発明の一態様は、上記課題の全てを解決する必要はなく、少なくともいずれか一の課題を解決するものである。 Note that the description of the above problems does not preclude the existence of other problems. Furthermore, it is possible to extract problems other than the above problems from the description of the specification, drawings, and claims. One aspect of the present invention does not need to solve all of the above problems, but rather solves at least one of the problems.
本発明の一態様は、正極と、負極と、電解質と、を有する二次電池であって、正極は、正極活物質を有し、正極活物質は、コバルト酸リチウムとマグネシウムとを有し、電解質は、リチウム塩、有機溶媒及び添加剤を有し、添加剤は、ジニトリル化合物を有し、負極は、炭素材料を有し、正極と、対極にリチウム金属を用いて組み立てた電池に対して、４．７Ｖの電圧まで充電した正極をＣｕＫα１線による粉末Ｘ線回折で分析したとき、少なくとも２θ＝１９．２５±０．１２°、および２θ＝４５．４７±０．１０°に回折ピークを有する、二次電池である。 One aspect of the present invention is a secondary battery having a positive electrode, a negative electrode, and an electrolyte, the positive electrode having a positive electrode active material, the positive electrode active material having lithium cobalt oxide and magnesium, the electrolyte having a lithium salt, an organic solvent, and an additive, the additive having a dinitrile compound, the negative electrode having a carbon material, and a battery assembled using a positive electrode and a lithium metal counter electrode, the positive electrode charged to a voltage of 4.7 V is analyzed by powder X-ray diffraction using CuKα1 radiation, and the secondary battery has diffraction peaks at least at 2θ=19.25±0.12° and 2θ=45.47±0.10°.
本発明の別の一態様は、正極と、負極と、電解質と、を有する二次電池であって、正極は、正極活物質を有し、正極活物質は、コバルト酸リチウムとマグネシウムとを有し、電解質は、リチウム塩、有機溶媒及び添加剤を有し、添加剤は、ジニトリル化合物を有し、負極は、炭素材料を有し、正極と、対極にリチウム金属を用いて組み立てた電池に対して、４．７５Ｖの電圧まで充電した正極をＣｕＫα１線による粉末Ｘ線回折で分析したとき、少なくとも２θ＝１９．４７±０．１０°、および２θ＝４５．６２±０．０５°に回折ピークを有する、二次電池である。 Another aspect of the present invention is a secondary battery having a positive electrode, a negative electrode, and an electrolyte, the positive electrode having a positive electrode active material, the positive electrode active material having lithium cobalt oxide and magnesium, the electrolyte having a lithium salt, an organic solvent, and an additive, the additive having a dinitrile compound, the negative electrode having a carbon material, and a battery assembled using a positive electrode and a lithium metal counter electrode, the positive electrode being charged to a voltage of 4.75 V, when analyzed by powder X-ray diffraction using CuKα1 radiation, the secondary battery has diffraction peaks at least at 2θ=19.47±0.10° and 2θ=45.62±0.05°.
本発明の別の一態様は、正極と、負極と、電解質と、を有する二次電池であって、正極は、正極活物質を有し、正極活物質は、コバルト酸リチウムとマグネシウムとを有し、電解質は、リチウム塩、有機溶媒及び添加剤を有し、添加剤は、ジニトリル化合物を有し、負極は、炭素材料を有し、正極と、対極にリチウム金属を用いて組み立てた電池に対して、４．８Ｖの電圧まで充電した正極をＣｕＫα１線による粉末Ｘ線回折で分析したとき、少なくとも２θ＝１９．４７±０．１０°、および２θ＝４５．６２±０．０５°に回折ピークを有する、二次電池である。 Another aspect of the present invention is a secondary battery having a positive electrode, a negative electrode, and an electrolyte, the positive electrode having a positive electrode active material, the positive electrode active material having lithium cobalt oxide and magnesium, the electrolyte having a lithium salt, an organic solvent, and an additive, the additive having a dinitrile compound, the negative electrode having a carbon material, and a battery assembled using a positive electrode and a lithium metal counter electrode, the positive electrode being charged to a voltage of 4.8 V, when analyzed by powder X-ray diffraction using CuKα1 radiation, the secondary battery has diffraction peaks at least at 2θ=19.47±0.10° and 2θ=45.62±0.05°.
本発明において、リチウム塩は、ＬｉＰＦ６、ＬｉＣｌＯ４、ＬｉＡｓＦ６、ＬｉＢＦ４、ＬｉＡｌＣｌ４、ＬｉＳＣＮ、ＬｉＢｒ、ＬｉＩ、Ｌｉ２ＳＯ４、Ｌｉ２Ｂ１０Ｃｌ１０、Ｌｉ２Ｂ１２Ｃｌ１２、ＬｉＣＦ３ＳＯ３、ＬｉＣ４Ｆ９ＳＯ３、ＬｉＣ（ＣＦ３ＳＯ２）３、ＬｉＣ（Ｃ２Ｆ５ＳＯ２）３、ＬｉＮ（ＣＦ３ＳＯ２）２、ＬｉＮ（Ｃ４Ｆ９ＳＯ２）（ＣＦ３ＳＯ２）、及びＬｉＮ（Ｃ２Ｆ５ＳＯ２）２等から選ばれた一又は二以上を用いると好ましい。 In the present invention, the lithium salt is preferably one or more selected from LiPF6 , LiClO4, LiAsF6 , LiBF4 , LiAlCl4 , LiSCN , LiBr, LiI , Li2SO4 , Li2B10Cl10 , Li2B12Cl12, LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3 , LiC ( C2F5SO2 ) 3 , LiN ( CF3SO2 ) 2 , LiN ( C4F9SO2 )( CF3SO2 ), and LiN( C2F5SO2 ) 2 .
本発明において、有機溶媒は、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、クロロエチレンカーボネート、ビニレンカーボネート、γ−ブチロラクトン、γ−バレロラクトン、ジメチルカーボネート、ジエチルカーボネート、エチルメチルカーボネート、ギ酸メチル、酢酸メチル、酢酸エチル、プロピオン酸メチル、プロピオン酸エチル、プロピオン酸プロピル、酪酸メチル、１，３−ジオキサン、１，４−ジオキサン、ジメトキシエタン、ジメチルスルホキシド、ジエチルエーテル、メチルジグライム、アセトニトリル、ベンゾニトリル、テトラヒドロフラン、スルホラン、及びスルトンから選ばれた一又は二以上を用いると好ましい。 In the present invention, the organic solvent is preferably one or more selected from ethylene carbonate, propylene carbonate, butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane, dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, and sultone.
本発明において、ジニトリル化合物はスクシノニトリル、アジポニトリル、又はエチレングリコールビス（プロピオニトリル）エーテルを有すると好ましい。 In the present invention, the dinitrile compound preferably has succinonitrile, adiponitrile, or ethylene glycol bis(propionitrile) ether.
本発明において、ジニトリル化合物はスクシノニトリル、アジポニトリル、及びエチレングリコールビス（プロピオニトリル）エーテルから選ばれた二以上を有すると好ましい。 In the present invention, the dinitrile compound preferably contains two or more selected from succinonitrile, adiponitrile, and ethylene glycol bis(propionitrile) ether.
本発明の別の一態様は、正極と、負極と、固体電解質と、を有する二次電池であって、正極は、正極活物質を有し、正極活物質は、コバルト酸リチウムとマグネシウムとを有し、固体電解質は、ハロゲン化物固体電解質を有し、負極は、炭素材料を有し、正極と、対極にリチウム金属を用いて組み立てた電池に対して、４．７Ｖの電圧まで充電した正極をＣｕＫα１線による粉末Ｘ線回折で分析したとき、少なくとも２θ＝１９．２５±０．１２°、および２θ＝４５．４７±０．１０°に回折ピークを有する、二次電池である。 Another aspect of the present invention is a secondary battery having a positive electrode, a negative electrode, and a solid electrolyte, the positive electrode having a positive electrode active material, the positive electrode active material having lithium cobalt oxide and magnesium, the solid electrolyte having a halide solid electrolyte, and the negative electrode having a carbon material, and a battery assembled using a positive electrode and a lithium metal counter electrode, the positive electrode charged to a voltage of 4.7 V is analyzed by powder X-ray diffraction using CuKα1 radiation, and the secondary battery has diffraction peaks at least at 2θ=19.25±0.12° and 2θ=45.47±0.10°.
本発明の別の一態様は、正極と、負極と、固体電解質と、を有する二次電池であって、正極は、正極活物質を有し、正極活物質は、コバルト酸リチウムとマグネシウムとを有し、固体電解質は、ハロゲン化物固体電解質を有し、負極は、炭素材料を有し、正極と、対極にリチウム金属を用いて組み立てた電池に対して、４．７５Ｖの電圧まで充電した正極をＣｕＫα１線による粉末Ｘ線回折で分析したとき、少なくとも２θ＝１９．４７±０．１０°、および２θ＝４５．６２±０．０５°に回折ピークを有する、二次電池である。 Another aspect of the present invention is a secondary battery having a positive electrode, a negative electrode, and a solid electrolyte, the positive electrode having a positive electrode active material, the positive electrode active material having lithium cobalt oxide and magnesium, the solid electrolyte having a halide solid electrolyte, and the negative electrode having a carbon material, and a battery assembled using a positive electrode and lithium metal as a counter electrode, the positive electrode charged to a voltage of 4.75 V is analyzed by powder X-ray diffraction using CuKα1 radiation, and the secondary battery has diffraction peaks at least at 2θ=19.47±0.10° and 2θ=45.62±0.05°.
本発明の別の一態様は、正極と、負極と、固体電解質と、を有する二次電池であって、正極は、正極活物質を有し、正極活物質は、コバルト酸リチウムとマグネシウムとを有し、固体電解質は、ハロゲン化物固体電解質を有し、負極は、炭素材料を有し、正極と、対極にリチウム金属を用いて組み立てた電池に対して、４．８Ｖの電圧まで充電した正極をＣｕＫα１線による粉末Ｘ線回折で分析したとき、少なくとも２θ＝１９．４７±０．１０°、および２θ＝４５．６２±０．０５°に回折ピークを有する、二次電池である。 Another aspect of the present invention is a secondary battery having a positive electrode, a negative electrode, and a solid electrolyte, the positive electrode having a positive electrode active material, the positive electrode active material having lithium cobalt oxide and magnesium, the solid electrolyte having a halide solid electrolyte, and the negative electrode having a carbon material, and when the positive electrode is charged to a voltage of 4.8 V and analyzed by powder X-ray diffraction using CuKα1 radiation, the secondary battery has diffraction peaks at least at 2θ=19.47±0.10° and 2θ=45.62±0.05° for a battery assembled using a positive electrode and lithium metal as a counter electrode.
本発明において、ハロゲン化物固体電解質はフッ化物固体電解質であると好ましい。 In the present invention, the halide solid electrolyte is preferably a fluoride solid electrolyte.
本発明において、フッ化物固体電解質は、ＬｉＦ、ＬｉＹＦ４、Ｌｉ３ＡｌＦ６、又はＬｉ２ＺｒＦ６を有すると好ましい。 In the present invention, the fluoride solid electrolyte preferably comprises LiF , LiYF4 , Li3AlF6 , or Li2ZrF6 .
本発明において、正極活物質の粒子内部がマグネシウムを有すると好ましい。 In the present invention, it is preferable that the inside of the particles of the positive electrode active material contains magnesium.
本発明の一態様により、高電圧でも安定な正極活物質を提供することができる。また本発明の一態様により、上記正極活物質と共に、高電圧でも安定な電解質を備えた二次電池を提供することができる。 One aspect of the present invention can provide a positive electrode active material that is stable even at high voltages. Another aspect of the present invention can provide a secondary battery that includes the positive electrode active material and an electrolyte that is stable even at high voltages.
なお、これらの効果の記載は、他の効果の存在を妨げるものではない。なお、本発明の一態様は、必ずしも、これらの効果の全てを有する必要はない。なお、これら以外の効果は、明細書、図面、請求項などの記載から、自ずと明らかとなるものであり、明細書、図面、請求項などの記載から、これら以外の効果を抽出することが可能である。 Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not necessarily have to have all of these effects. Note that effects other than these will become apparent from the description in the specification, drawings, claims, etc., and it is possible to extract effects other than these from the description in the specification, drawings, claims, etc.
図１Ａ１及び図１Ａ２は正極活物質の断面図、図１Ｂ１および図１Ｂ２は正極活物質の断面図の一部である。
図２は結晶の配向が概略一致しているＴＥＭ像の例である。
図３Ａは結晶の配向が概略一致しているＳＴＥＭ像の例である。図３Ｂは岩塩型結晶ＲＳの領域のＦＦＴパターン、図３Ｃは層状岩塩型結晶ＬＲＳの領域のＦＦＴパターンである。
図４は本発明の一態様である正極活物質の結晶構造を説明する図である。
図５は正極活物質の結晶構造を説明する図である。
図６Ａ１および図６Ａ２は正極活物質の断面図の一部である。図６Ｂ１乃至図６Ｃは、コバルト酸リチウムの結晶面とマグネシウムの分布について計算した結果である。
図７Ａおよび図７Ｂは正極活物質の断面図、図７Ｃ１および図７Ｃ２は正極活物質の断面図の一部である。
図８は結晶構造から計算されるＸＲＤパターンを示す図である。
図９は結晶構造から計算されるＸＲＤパターンを示す図である。
図１０Ａおよび図１０Ｂは結晶構造から計算されるＸＲＤパターンを示す図である。
図１１Ａ乃至図１１ＣはＸＲＤから算出される格子定数である。
図１２Ａ乃至図１２ＣはＸＲＤから算出される格子定数である。
図１３Ａおよび図１３Ｂは正極活物質の断面図である。
図１４は正極活物質の断面図である。
図１５はフッ化リチウムとフッ化マグネシウムの組成及び温度の関係を示す相図である。
図１６は、正極活物質の充電深度と格子定数を説明する図である。
図１７Ａ乃至図１７Ｃは、粉体抵抗測定に関する説明図である。
図１８Ａ乃至図１８Ｃは正極活物質の作製方法を説明する図である。
図１９は正極活物質の作製方法を説明する図である。
図２０Ａ乃至図２０Ｃは正極活物質の作製方法を説明する図である。
図２１は正極活物質の作製方法を説明する図である。
図２２は正極活物質の作製方法を説明する図である。
図２３は正極活物質の作製方法を説明する図である。
図２４Ａ及び図２４Ｂは正極の断面図である。
図２５Ａ及び図２５Ｂは、固体電解質二次電池を説明する図である。
図２６Ａはコイン型二次電池の分解斜視図であり、図２６Ｂはコイン型二次電池の斜視図であり、図２６Ｃはその断面斜視図である。
図２７Ａは、円筒型の二次電池の例を示す図である。図２７Ｂは、円筒型の二次電池の例を示す図である。図２７Ｃは、複数の円筒型の二次電池の例を示す図である。図２７Ｄは、複数の円筒型の二次電池を有する蓄電システムの例を示す図である。
図２８Ａ及び図２８Ｂは、二次電池の例を説明する図であり、図２８Ｃは、二次電池の内部の様子を示す図である。
図２９Ａ乃至図２９Ｃは、二次電池の例を説明する図である。
図３０Ａ及び図３０Ｂは、二次電池の外観を示す図である。
図３１Ａ乃至図３１Ｃは、二次電池の作製方法を説明する図である。
図３２Ａ乃至図３２Ｄは、輸送用車両の一例を説明する図である。図３２Ｅは、人工衛星の一例を説明する図である。
図３３Ａは、電動自転車を示す図であり、図３３Ｂは、電動自転車の二次電池を示す図であり、図３３Ｃは、スクータを示す図である。
図３４Ａ乃至図３４Ｅは、電子機器の一例を説明する図である。
図３５は、粉体抵抗測定の結果を示すグラフである。
図３６Ａ及び図３６Ｂは、サイクル試験結果を示すグラフである。
図３７は、粉体抵抗測定の結果を示すグラフである。 1A1 and 1A2 are cross-sectional views of a positive electrode active material, and FIGS. 1B1 and 1B2 are partial cross-sectional views of the positive electrode active material.
FIG. 2 is an example of a TEM image in which the crystal orientations are roughly consistent.
Fig. 3A is an example of an STEM image in which the crystal orientations are roughly consistent, Fig. 3B is an FFT pattern of a region of the rock-salt crystal RS, and Fig. 3C is an FFT pattern of a region of the layered rock-salt crystal LRS.
FIG. 4 is a diagram illustrating a crystal structure of a positive electrode active material according to one embodiment of the present invention.
FIG. 5 is a diagram illustrating the crystal structure of the positive electrode active material.
6A1 and 6A2 are partial cross-sectional views of the positive electrode active material, and Fig. 6B1 to Fig. 6C are calculation results of the crystal plane and magnesium distribution of lithium cobalt oxide.
7A and 7B are cross-sectional views of the positive electrode active material, and FIGS. 7C1 and 7C2 are partial cross-sectional views of the positive electrode active material.
FIG. 8 shows an XRD pattern calculated from the crystal structure.
FIG. 9 shows an XRD pattern calculated from the crystal structure.
10A and 10B are diagrams showing XRD patterns calculated from the crystal structure.
11A to 11C show the lattice constants calculated from XRD.
12A to 12C show the lattice constants calculated from XRD.
13A and 13B are cross-sectional views of the positive electrode active material.
FIG. 14 is a cross-sectional view of the positive electrode active material.
FIG. 15 is a phase diagram showing the relationship between the composition of lithium fluoride and magnesium fluoride and the temperature.
FIG. 16 is a diagram illustrating the charge depth and lattice constant of the positive electrode active material.
17A to 17C are explanatory diagrams relating to powder resistivity measurement.
18A to 18C are diagrams illustrating a method for manufacturing a positive electrode active material.
FIG. 19 is a diagram illustrating a method for producing a positive electrode active material.
20A to 20C are diagrams illustrating a method for manufacturing a positive electrode active material.
FIG. 21 is a diagram illustrating a method for manufacturing a positive electrode active material.
FIG. 22 is a diagram illustrating a method for manufacturing a positive electrode active material.
FIG. 23 is a diagram illustrating a method for manufacturing a positive electrode active material.
24A and 24B are cross-sectional views of the positive electrode.
25A and 25B are diagrams illustrating a solid electrolyte secondary battery.
26A is an exploded perspective view of a coin-type secondary battery, FIG. 26B is a perspective view of the coin-type secondary battery, and FIG. 26C is a cross-sectional perspective view thereof.
Fig. 27A is a diagram showing an example of a cylindrical secondary battery. Fig. 27B is a diagram showing an example of a cylindrical secondary battery. Fig. 27C is a diagram showing an example of a plurality of cylindrical secondary batteries. Fig. 27D is a diagram showing an example of a power storage system having a plurality of cylindrical secondary batteries.
28A and 28B are diagrams for explaining an example of a secondary battery, and FIG. 28C is a diagram showing the inside of the secondary battery.
29A to 29C are diagrams illustrating an example of a secondary battery.
30A and 30B are diagrams showing the external appearance of a secondary battery.
31A to 31C are diagrams illustrating a method for manufacturing a secondary battery.
32A to 32D are diagrams illustrating an example of a transportation vehicle, and Fig. 32E is a diagram illustrating an example of an artificial satellite.
FIG. 33A is a diagram showing an electric bicycle, FIG. 33B is a diagram showing a secondary battery of the electric bicycle, and FIG. 33C is a diagram showing a scooter.
34A to 34E are diagrams illustrating an example of an electronic device.
FIG. 35 is a graph showing the results of powder resistivity measurements.
36A and 36B are graphs showing the cycle test results.
FIG. 37 is a graph showing the results of powder resistivity measurements.
以下では、本発明の実施の形態について図面を用いて詳細に説明する。ただし、本発明は以下の説明に限定されず、その形態及び詳細を様々に変更し得ることは、当業者であれば容易に理解される。また、本発明は以下に示す実施の形態の記載内容に限定して解釈されるものではない。 Below, the embodiment of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and those skilled in the art will easily understand that the form and details can be modified in various ways. Furthermore, the present invention should not be interpreted as being limited to the description of the embodiment shown below.
本明細書等において、空間群は国際表記（またはＨｅｒｍａｎｎ−Ｍａｕｇｕｉｎ記号）のＳｈｏｒｔ　ｎｏｔａｔｉｏｎを用いて表記する。またミラー指数を用いて結晶面及び結晶方向を表記する。空間群、結晶面、および結晶方向の表記は、結晶学上、数字に上付きのバーを付して表現するが、本明細書等では書式の制約上、数字の上にバーを付す代わりに、数字の前に−（マイナス符号）を付して表現する場合がある。また、結晶内の方向を示す個別方位は［　］で、等価な方向すべてを示す集合方位は＜　＞で、結晶面を示す個別面は（　）で、等価な対称性を有する集合面は｛　｝でそれぞれ表現する。また空間群Ｒ−３ｍで表される三方晶は、構造の理解のしやすさのため、一般に六方晶の複合六方格子で表され、本明細書等も特に言及しない限り空間群Ｒ−３ｍは複合六方格子で表すこととする。またミラー指数として（ｈｋｌ）だけでなく（ｈｋｉｌ）を用いることがある。ここでｉは−（ｈ＋ｋ）である。 In this specification, the space group is expressed using short notation of the international notation (or Hermann-Mauguin notation). The crystal plane and crystal direction are expressed using Miller indices. In crystallography, the notation of the space group, crystal plane, and crystal direction is expressed by adding a superscript bar to the number, but in this specification, due to format restrictions, instead of adding a bar above the number, a - (minus sign) may be added before the number. In addition, individual directions indicating directions within a crystal are expressed with [ ], collective directions indicating all equivalent directions are expressed with < >, individual faces indicating crystal faces are expressed with ( ), and collective faces with equivalent symmetry are expressed with { }. In addition, trigonal crystals represented by the space group R-3m are generally expressed as a composite hexagonal lattice of hexagonal crystals for ease of understanding of the structure, and in this specification, unless otherwise specified, the space group R-3m will be expressed as a composite hexagonal lattice. In addition, not only (hkl) but also (hkil) may be used as Miller indices. Here i is -(h+k).
本明細書等において、空間群はＸＲＤ、電子線回折、中性子線回折等によって同定されるものである。そのため、ある空間群に帰属する、ある空間群に属する、またはある空間群であるとは、ある空間群に同定されると言い換えることができる。 In this specification, the space group is identified by XRD, electron diffraction, neutron diffraction, etc. Therefore, belonging to a certain space group, belonging to a certain space group, or being a certain space group can be rephrased as being identified with a certain space group.
本明細書等において、陰イオンの配置がおおむね立方最密充填に近ければ、立方最密充填とみなすことができる。立方最密充填の陰イオンの配置とは、一層目に充填された陰イオンの空隙の上に二層目の陰イオンが配置され、三層目の陰イオンが、二層目の陰イオンの空隙の直上であって、一層目の陰イオンの直上でない位置に配置された状態を指す。そのため陰イオンは厳密に立方格子でなくてもよい。また、現実の結晶は必ず欠陥を有するため、分析結果が必ずしも理論通りでなくてもよい。たとえば電子線回折パターンまたはＴＥＭ像等のＦＦＴ（高速フーリエ変換）パターンにおいて、理論上の位置と若干異なる位置にスポットが現れてもよい。たとえば理論上の位置との方位のずれが５度以下、または２．５度以下であれば立方最密充填構造をとるといってよい。 In this specification, if the arrangement of anions is roughly close to cubic close-packed, it can be considered as cubic close-packed. The arrangement of anions in cubic close-packed refers to a state in which the second layer of anions is arranged above the gaps of the anions packed in the first layer, and the third layer of anions is arranged directly above the gaps of the anions in the second layer, but not directly above the anions in the first layer. Therefore, the anions do not have to be strictly cubic lattices. In addition, since real crystals always have defects, the analysis results do not necessarily have to be theoretical. For example, in an FFT (fast Fourier transform) pattern such as an electron beam diffraction pattern or a TEM image, a spot may appear at a position slightly different from the theoretical position. For example, if the deviation in orientation from the theoretical position is 5 degrees or less, or 2.5 degrees or less, it can be said to have a cubic close-packed structure.
本明細書等において、層状岩塩型結晶構造とは、陽イオンと陰イオンが交互に配列する岩塩型のイオン配列を有し、遷移金属Ｍとリチウムが規則配列して二次元平面を形成するため、リチウムイオンの二次元的拡散が可能である結晶構造をいう。なお陽イオンまたは陰イオンの欠損等の欠陥があってもよい。また、層状岩塩型結晶構造は、厳密に言えば、岩塩型結晶の格子が歪んだ構造となっている場合がある。 In this specification, the layered rock-salt crystal structure refers to a crystal structure that has a rock-salt type ion arrangement in which cations and anions are arranged alternately, and in which the transition metal M and lithium are regularly arranged to form a two-dimensional plane, allowing two-dimensional diffusion of lithium ions. Defects such as missing cations or anions may also be present. Strictly speaking, the layered rock-salt crystal structure may have a structure in which the lattice of the rock-salt crystal is distorted.
本明細書等において、岩塩型の結晶構造とは、空間群Ｆｍ−３ｍをはじめとする立方晶系の結晶構造を有し、陽イオンと陰イオンが交互に配列している構造をいう。なお陽イオンまたは陰イオンの欠損があってもよい。 In this specification, a rock salt type crystal structure refers to a structure having a cubic crystal structure such as the space group Fm-3m, in which cations and anions are arranged alternately. Note that there may be a deficiency of cations or anions.
本明細書等において、粒子とは球形（断面形状が円）のみを指すことに限定されず、個々の粒子の断面形状が楕円形、長方形、台形、錐形、角が丸まった四角形、非対称の形状などであってもよく、さらに個々の粒子は不定形であってもよい。 In this specification, particles are not limited to those having a spherical shape (a circular cross-sectional shape), but the cross-sectional shape of each particle may be an ellipse, a rectangle, a trapezoid, a cone, a square with rounded corners, an asymmetric shape, etc., and each particle may also be irregular in shape.
本明細書等において、活物質の表面がなめらかな状態は、活物質の一断面において、表面の凹凸情報を測定データより数値化したとき、少なくとも１０ｎｍ以下の表面粗さを有するということができる。本明細書等において、一断面は、たとえばＳＴＥＭ（Ｓｃａｎｎｉｎｇ　Ｔｒａｎｓｍｉｓｓｉｏｎ　Ｅｌｅｃｔｒｏｎ　Ｍｉｃｒｏｓｃｏｐｅ、走査透過型電子顕微鏡）像で観察する際に取得する断面である。 In this specification, the smooth surface of an active material means that the surface roughness of a cross section of the active material is at least 10 nm or less when the surface unevenness information is quantified from measurement data. In this specification, a cross section is, for example, a cross section obtained when observing with a STEM (Scanning Transmission Electron Microscope) image.
本明細書等において、正極活物質とは、リチウムイオンの挿入脱離が可能な、遷移金属と酸素を有する化合物をいう。正極活物質の作製後に吸着した炭酸塩、ヒドロキシ基等は正極活物質に含まないとする。また正極活物質の作製後に付着したリチウム塩、有機溶媒、バインダ、導電材、またはこれら由来の化合物も正極活物質に含まないとする。 In this specification, the positive electrode active material refers to a compound having a transition metal and oxygen that is capable of inserting and removing lithium ions. Carbonates, hydroxyl groups, and the like that are adsorbed after the preparation of the positive electrode active material are not included in the positive electrode active material. Lithium salts, organic solvents, binders, conductive materials, or compounds derived from these that are attached after the preparation of the positive electrode active material are also not included in the positive electrode active material.
本明細書等において、正極活物質の理論容量とは、正極活物質が有する挿入および脱離が可能なリチウムが全て脱離した場合の電気量をいう。例えば、ＬｉＣｏＯ２の理論容量は２７４ｍＡｈ／ｇ、ＬｉＮｉＯ２の理論容量は２７５ｍＡｈ／ｇ、ＬｉＭｎ２Ｏ４の理論容量は１４８ｍＡｈ／ｇである。 In this specification, the theoretical capacity of a positive electrode active material refers to the amount of electricity when all of the lithium that can be inserted and removed from the positive electrode active material is removed. For example, the theoretical capacity of LiCoO2 is 274 mAh/g, the theoretical capacity of LiNiO2 is 275 mAh/g, and the theoretical capacity of LiMn2O4 is 148 mAh/g.
本明細書等において、正極活物質中に理論容量に比してリチウムがどの程度残っているかを、組成式中のｘ、たとえばＬｉｘＣｏＯ２中のｘ、またはＬｉｘＭＯ２中のｘで示すことがある。ここでＭはリチウムの挿入および脱離に伴い酸化還元する遷移金属を意味する。本明細書等では、ＬｉｘＣｏＯ２は適宜ＬｉｘＭＯ２に読み替えることができる。二次電池中の正極活物質の場合、ｘ＝（理論容量−充電容量）／理論容量とすることができる。たとえばＬｉＣｏＯ２を正極活物質に用いた二次電池を充電して２１９．２ｍＡｈ／ｇとした場合、Ｌｉ０．２ＣｏＯ２またはｘ＝０．２ということができる。ＬｉｘＣｏＯ２中のｘが小さいとは、たとえば０．１＜ｘ≦０．２４をいう。また正極活物質から脱離したリチウムが、理論容量に対してどの程度であるかを充電深度という場合がある。本明細書等において、充電深度＝１−ｘに相当する。 In the present specification, the amount of lithium remaining in the positive electrode active material compared to the theoretical capacity may be indicated by x in the composition formula, for example, x in Li x CoO 2 , or x in Li x MO 2. Here, M means a transition metal that is oxidized and reduced with the insertion and desorption of lithium. In the present specification, Li x CoO 2 can be appropriately read as Li x MO 2. In the case of a positive electrode active material in a secondary battery, x = (theoretical capacity - charging capacity) / theoretical capacity can be used. For example, when a secondary battery using LiCoO 2 as a positive electrode active material is charged to 219.2 mAh / g, it can be said that Li 0.2 CoO 2 or x = 0.2. For example, x in Li x CoO 2 is small means 0.1 < x ≦ 0.24. In addition, the extent to which lithium is desorbed from the positive electrode active material compared to the theoretical capacity may be called the charge depth. In this specification and the like, this corresponds to charge depth=1−x.
ＬｉｘＣｏＯ２中のｘの算出に用いる充電容量および放電容量は、ショートしていない、かつ、リチウム塩の分解の影響がないまたは少ない条件で計測することが好ましい。たとえばショートとみられる急激な容量の変化が生じた二次電池のデータはｘの算出に使用してはならない。 The charge capacity and discharge capacity used to calculate x in Li x CoO 2 are preferably measured under conditions where there is no short circuit and where there is no or little effect of decomposition of the lithium salt. For example, data on a secondary battery that has experienced a sudden change in capacity that is considered to be due to a short circuit should not be used to calculate x.
コバルト酸リチウムが化学量論比をおよそ満たす場合、ＬｉＣｏＯ２でありｘ＝１である。このときリチウムサイトのリチウムイオンの占有率は１００％といえる。また放電が終了した二次電池に含まれるコバルト酸リチウムも、ＬｉＣｏＯ２であり、ｘ＝１といってよい。ここでいう放電が終了したとは、たとえば正極活物質重量当たり１００ｍＡ／ｇの電流で、電圧が２．５Ｖ（対極リチウム）以下となった状態をいう。リチウムイオン二次電池では、リチウムサイトのリチウムの占有率がｘ＝１となり、それ以上リチウムが入らなくなると、電圧が急激に低下する。このとき、放電が終了したといえる。一般的にＬｉＣｏＯ２を用いたリチウムイオン二次電池では、放電電圧が２．５Ｖになるまでに放電電圧が急激に降下するため、上記の条件で放電が終了したとする。また放電が終了した正極は、ＸＲＤパターン等で分析すると一般的なＬｉＣｏＯ２の結晶構造を有することが確認できる。 When the lithium cobalt oxide approximately satisfies the stoichiometric ratio, it is LiCoO 2 and x=1. At this time, the occupancy rate of the lithium ions on the lithium site can be said to be 100%. The lithium cobalt oxide contained in the secondary battery after discharge is also LiCoO 2 and x=1. The discharge is completed here when, for example, the voltage is 2.5V (counter electrode lithium) or less at a current of 100mA/g per weight of the positive electrode active material. In a lithium ion secondary battery, when the occupancy rate of lithium on the lithium site becomes x=1 and no more lithium is added, the voltage drops sharply. At this time, it can be said that the discharge is completed. In general, in a lithium ion secondary battery using LiCoO 2 , the discharge voltage drops sharply until the discharge voltage reaches 2.5V, so the discharge is completed under the above conditions. In addition, when the positive electrode after discharge is analyzed by XRD pattern or the like, it can be confirmed that it has a general LiCoO 2 crystal structure.
本明細書等において、均質とは、複数の元素（例えばＡ、Ｂ、Ｃ）からなる固体において、ある元素（例えばＡ）が特定の領域に同様の特徴を有して分布する現象をいう。なお特定の領域同士の元素の濃度が実質的に同一であればよい。たとえば特定領域同士の元素濃度の差が１０％以内であればよい。特定の領域としてはたとえば表層部、表面、凸部、凹部、バルクなどが挙げられる。 In this specification, homogeneity refers to the phenomenon in which, in a solid consisting of multiple elements (e.g., A, B, C), a certain element (e.g., A) is distributed with similar characteristics in a specific region. Note that it is sufficient that the concentration of the element in the specific regions is substantially the same. For example, it is sufficient that the difference in element concentration between the specific regions is within 10%. Examples of specific regions include the surface layer, the surface, the convex portion, the concave portion, the bulk, etc.
本明細書等において、偏在とはある領域における元素の濃度が他の領域と異なることをいう。偏析、析出、不均一、偏り、または濃度が高い箇所と濃度が低い箇所が混在する、と同義である。 In this specification, uneven distribution means that the concentration of an element in one area is different from that in other areas. It is synonymous with segregation, precipitation, non-uniformity, bias, or the presence of a mixture of areas of high concentration and areas of low concentration.
本明細書等において、正極活物質の特徴について述べる場合、二次電池が有する正極活物質の全てがその特徴を有していなくてもよい。たとえば正極活物質粒子の特徴を述べる場合、たとえばランダムに３個以上選択した正極活物質粒子の全個数うち５０％以上の個数、好ましくは７０％以上の個数、より好ましくは９０％以上の個数で、被膜の特徴が確認できれば、十分に正極活物質及びそれを有する二次電池の特性を向上させる効果があるということができる。また一個の正極活物質粒子において、被膜の形成面は正極活物質粒子の５０％以上、好ましくは７０％以上、より好ましくは９０％以上あることで、被膜の効果を十分に発揮できる。 When describing the characteristics of a positive electrode active material in this specification, it is not necessary that all of the positive electrode active materials in the secondary battery have that characteristic. For example, when describing the characteristics of positive electrode active material particles, if the characteristics of the coating can be confirmed in 50% or more, preferably 70% or more, and more preferably 90% or more of the total number of randomly selected three or more positive electrode active material particles, it can be said that there is an effect of sufficiently improving the characteristics of the positive electrode active material and the secondary battery having it. Furthermore, in one positive electrode active material particle, the coating surface is 50% or more, preferably 70% or more, and more preferably 90% or more of the positive electrode active material particle, so that the effect of the coating can be fully exerted.
本明細書等において、特に言及しない限り、二次電池が有する材料（正極活物質、負極活物質、リチウム塩等）は、劣化前の状態について説明するものとする。たとえば、二次電池の定格容量の９７％以上の放電容量を有する場合は、劣化前の状態と言うことができる。定格容量は、ＪＩＳ　Ｃ８７１１：２０１９に準拠する。なお、本明細書等において、二次電池が有する材料の劣化前の状態を、初期品、または初期状態と呼称し、劣化後の状態（二次電池の定格容量の９７％未満の放電容量を有する場合の状態）を、使用中品または使用中の状態、あるいは使用済み品または使用済み状態と呼称する場合がある。 In this specification, unless otherwise specified, the materials (positive electrode active material, negative electrode active material, lithium salt, etc.) of a secondary battery are described in a state before degradation. For example, a secondary battery having a discharge capacity of 97% or more of its rated capacity can be said to be in a state before degradation. The rated capacity conforms to JIS C8711:2019. In this specification, the state of the materials of a secondary battery before degradation is referred to as an initial product or initial state, and the state after degradation (a state in which the secondary battery has a discharge capacity of less than 97% of its rated capacity) may be referred to as a product in use or in use state, or a used product or used state.
本明細書等においてリチウムイオン二次電池は、キャリアイオンにリチウムイオンを用いた電池を指すが、本発明のキャリアイオンはリチウムイオンに限定されない。例えば本発明のキャリアイオンとしてアルカリ金属イオン、又はアルカリ土類金属イオンを用いることができ、具体的にはナトリウムイオン等を適用することができる。この場合、リチウムイオンをナトリウムイオン等と読み替え、本発明を理解することができる。またキャリアイオンに何ら限定がない場合、二次電池と記すことがある。 In this specification, a lithium ion secondary battery refers to a battery that uses lithium ions as carrier ions, but the carrier ions of the present invention are not limited to lithium ions. For example, an alkali metal ion or an alkaline earth metal ion can be used as the carrier ion of the present invention, and specifically, sodium ions can be applied. In this case, the present invention can be understood by reading lithium ions as sodium ions. In addition, when there is no limitation on the carrier ion, it may be referred to as a secondary battery.
本明細書等において、フルセルとは、正極／負極の単位セルのように、両側に異なる電極が位置するように組み立てた電池セルを意味する。本明細書等において、ハーフセルとは、リチウム金属を対極にして組み立てた電池セルを意味する。 In this specification, a full cell refers to a battery cell assembled with different electrodes on both sides, such as a positive/negative unit cell. In this specification, a half cell refers to a battery cell assembled with lithium metal as the counter electrode.
本明細書等において、（００１）面、及び（００３）面などを、まとめて（００ｌ）面として呼ぶ場合がある。なお本明細書等において、（００ｌ）面は、Ｃ面、ベーサル面などと呼ぶ場合がある。また、コバルト酸リチウムにおいてリチウムイオンは、二次元の拡散経路を有する。すなわちリチウムイオンの拡散経路は面に沿って存在しているといえる。本明細書等において、リチウムイオンの拡散経路が露出した面、つまりリチウムイオンが挿入脱離する面（具体的には（００１）面）以外の面を、エッジ面と呼ぶことがある。 In this specification, the (001) plane and the (003) plane may be collectively referred to as the (00l) plane. In this specification, the (00l) plane may be referred to as the C plane, the basal plane, or the like. In addition, in lithium cobalt oxide, lithium ions have a two-dimensional diffusion path. In other words, it can be said that the diffusion path of lithium ions exists along the surface. In this specification, a surface on which the diffusion path of lithium ions is exposed, that is, a surface other than the surface on which lithium ions are inserted and removed (specifically the (001) plane), may be referred to as an edge surface.
本明細書等において、二次粒子とは一次粒子が凝集することにより形成された粒子を指す。また本明細書等において、一次粒子を単粒子と呼ぶことがある。また本明細書等において単結晶は、粒子の内部に粒界が存在しない状態の結晶を指し、単結晶を有する粒子（単結晶粒と呼ぶ）と呼ぶことがある。多結晶は粒子の内部に粒界が存在した状態の結晶を指し、多結晶粒子とも呼ぶ。多結晶粒子は複数の結晶子の集合体と言ってもよく、粒界は２つ以上の結晶子の間に存在する界面といってもよい。 In this specification, secondary particles refer to particles formed by agglomeration of primary particles. In this specification, primary particles are sometimes called single particles. In this specification, single crystals refer to crystals in a state where there are no grain boundaries inside the particle, and are sometimes called particles having a single crystal (called single crystal grains). Polycrystals refer to crystals in a state where there are grain boundaries inside the particle, and are also called polycrystalline particles. Polycrystalline particles may be said to be an aggregate of multiple crystallites, and grain boundaries may be said to be the interfaces that exist between two or more crystallites.
本明細書等において、「Ａ及び／又はＢ」と記載することがあるが、これはＡのみ、Ｂのみ、及びＡ及びＢを包含するときの一記載例である。 In this specification, the term "A and/or B" may be used, but this is an example of a description that includes only A, only B, and both A and B.
（実施の形態１）
本実施の形態では、図１乃至図１７を用いて、本発明の一態様である正極活物質１００について説明する。 (Embodiment 1)
In this embodiment, a positive electrode active material 100 which is one embodiment of the present invention will be described with reference to FIGS.
図１Ａ１及び図１Ａ２はそれぞれ、本発明の一態様である正極活物質１００の断面図を示す。正極活物質１００の断面形状は粒子状を有するとよい。図１Ａ１の正極活物質１００は表層部１００ａ及び内部１００ｂを有する。図中、破線で表層部１００ａと内部１００ｂの境界を示す。当該境界は一例である。図１Ａ２の正極活物質１００は表層部１００ａ及び内部１００ｂを有し、さらに後述するクラック等の欠陥部１００ｃ、結晶粒界１０１を有する。図中、一点破線で結晶粒界１０１を示す。当該一点破線は一例である。図１Ａ１中のＡ−Ｂ付近を拡大した図を図１Ｂ１および図１Ｂ２に示す。 FIG. 1A1 and FIG. 1A2 each show a cross-sectional view of a positive electrode active material 100 according to one embodiment of the present invention. The cross-sectional shape of the positive electrode active material 100 may be particulate. The positive electrode active material 100 in FIG. 1A1 has a surface layer 100a and an interior 100b. In the figure, the boundary between the surface layer 100a and the interior 100b is shown by a dashed line. This boundary is an example. The positive electrode active material 100 in FIG. 1A2 has a surface layer 100a and an interior 100b, and further has a defect portion 100c such as a crack and a grain boundary 101, which will be described later. In the figure, the grain boundary 101 is shown by a dashed line. This dashed line is an example. Enlarged views of the vicinity of A-B in FIG. 1A1 are shown in FIG. 1B1 and FIG. 1B2.
本明細書等において、結晶粒界１０１とは、たとえば正極活物質１００の粒子同士が固着している部分、正極活物質１００で結晶方位が変わる部分、つまりＳＴＥＭ像等における明線と暗線の繰り返しが不連続になった部分、結晶欠陥を多く含む部分、結晶構造が乱れている部分等をいう。また結晶欠陥とは断面ＴＥＭ（透過型電子顕微鏡）、断面ＳＴＥＭ像等で観察可能な欠陥、つまり格子間に他の原子が入り込んだ構造、空洞等をいうこととする。結晶粒界１０１は、面欠陥の一つといえる。また結晶粒界１０１の近傍とは、結晶粒界１０１から１０ｎｍ以内の領域をいうこととする。 In this specification, the grain boundary 101 refers to, for example, a portion where particles of the positive electrode active material 100 are stuck together, a portion where the crystal orientation of the positive electrode active material 100 changes, i.e., a portion where the repetition of bright and dark lines in an STEM image or the like becomes discontinuous, a portion containing many crystal defects, a portion where the crystal structure is disordered, etc. Furthermore, the crystal defect refers to a defect that can be observed in a cross-sectional TEM (transmission electron microscope) or cross-sectional STEM image, etc., that is, a structure in which other atoms have entered between the lattices, a cavity, etc. The grain boundary 101 can be said to be one type of planar defect. Furthermore, the vicinity of the grain boundary 101 refers to a region within 10 nm of the grain boundary 101.
本明細書等において、正極活物質１００の表層部１００ａとは、例えば、粒子表面から内部に向かって５０ｎｍ以内、より好ましくは粒子表面から内部に向かって３５ｎｍ以内、さらに好ましくは粒子表面から内部に向かって２０ｎｍ以内、最も好ましくは粒子表面から内部に向かって１０ｎｍ以内の領域をいう。内部に向かうとは、粒子表面から垂直または略垂直な方向を意味し、垂直または略垂直とは、粒子表面の接線に対して８０°以上１００°以下とする。スリップ、ひび及び／又はクラックにより生じた面も粒子表面といってよい。表層部１００ａは、表面近傍、表面近傍領域またはシェルと同義である。 In this specification, the surface layer 100a of the positive electrode active material 100 refers to, for example, a region within 50 nm from the particle surface toward the inside, more preferably within 35 nm from the particle surface toward the inside, even more preferably within 20 nm from the particle surface toward the inside, and most preferably within 10 nm from the particle surface toward the inside. Toward the inside means a direction perpendicular or approximately perpendicular to the particle surface, and perpendicular or approximately perpendicular means 80° to 100° with respect to the tangent of the particle surface. Surfaces caused by slips, cracks, and/or cracks may also be referred to as the particle surface. The surface layer 100a is synonymous with the surface vicinity, surface vicinity region, or shell.
また正極活物質の表層部１００ａより深い領域を、内部１００ｂと呼ぶ。内部１００ｂは、内部領域またはコアと同義である。 The region deeper than the surface layer 100a of the positive electrode active material is called the interior 100b. The interior 100b is synonymous with the interior region or core.
正極活物質１００の粒子表面とは、表層部１００ａおよび内部１００ｂを含む複合酸化物の表面をいうこととする。そのため正極活物質１００は、酸化アルミニウム（Ａｌ２Ｏ３）をはじめとする充放電に寄与しうるリチウムサイトを有さない金属酸化物、正極活物質の作製後に化学吸着した炭酸塩、ヒドロキシ基等は含まないとする。なおリチウムサイトを有さない金属酸化物は正極活物質１００に付着していることがある。付着した金属酸化物は、たとえば内部１００ｂと結晶構造が一致しない。 The particle surface of the positive electrode active material 100 refers to the surface of the composite oxide including the surface layer 100a and the interior 100b. Therefore, the positive electrode active material 100 does not include metal oxides that do not have lithium sites that can contribute to charging and discharging, such as aluminum oxide (Al 2 O 3 ), carbonates that are chemically adsorbed after the preparation of the positive electrode active material, and hydroxyl groups. Note that metal oxides that do not have lithium sites may be attached to the positive electrode active material 100. The attached metal oxides have a crystal structure that does not match that of the interior 100b, for example.
また正極活物質１００に付着したリチウム塩、有機溶媒、バインダ、導電材、またはこれら由来の化合物も正極活物質１００には含まない。 Also, the positive electrode active material 100 does not include lithium salts, organic solvents, binders, conductive materials, or compounds derived from these that are attached to the positive electrode active material 100.
正極活物質１００はリチウムイオンの挿入脱離が可能な遷移金属と酸素を有する化合物であるため、リチウムイオンの挿入脱離に伴い酸化還元する遷移金属Ｍ（たとえばＣｏ、Ｎｉ、Ｍｎ、Ｆｅ等）および酸素が存在する領域と、存在しない領域の界面を、正極活物質の粒子表面とする。スリップ、ひび及び／又はクラックにより生じた面も遷移金属Ｍ及び酸素が存在するため正極活物質の表面といってよい。 Since the positive electrode active material 100 is a compound containing oxygen and a transition metal capable of inserting and removing lithium ions, the interface between the region where the transition metal M (e.g., Co, Ni, Mn, Fe, etc.) that is oxidized and reduced with the insertion and removal of lithium ions and oxygen is present and the region where it is not present is the particle surface of the positive electrode active material. Surfaces created by slips, cracks, and/or cracks can also be said to be the surface of the positive electrode active material because the transition metal M and oxygen are present.
正極活物質を分析に供する際、表面に保護膜を付ける場合があるが、保護膜は正極活物質には含まれない。保護膜としては、炭素、金属、酸化物、樹脂等から選ばれた単層膜または多層膜が用いられる場合がある。断面ＳＴＥＭ−ＥＤＸ線分析の際、保護膜を付ける場合があるが、当該線分析等における正極活物質の表面の位置とは、上記遷移金属Ｍの特性Ｘ線の検出量が、内部の上記遷移金属Ｍの特性Ｘ線の検出量の平均値ＭＡＶＥと、バックグラウンドの上記遷移金属Ｍの特性Ｘ線の検出量の平均値ＭＢＧとの和の５０％になる点、または酸素の特性Ｘ線の検出量が、内部の酸素の特性Ｘ線の検出量の平均値ＯＡＶＥと、バックグラウンドの酸素の特性Ｘ線の検出量の平均値ＯＢＧとの和の５０％になる点とする。なお、上記遷移金属Ｍの特性Ｘ線の検出量が内部の上記遷移金属Ｍの特性Ｘ線の検出量の平均値とバックグラウンドの上記遷移金属Ｍの特性Ｘ線の検出量の平均値の和の５０％になる点と、酸素の特性Ｘ線の検出量が内部の酸素の特性Ｘ線の検出量の平均値とバックグラウンドの酸素の特性Ｘ線の検出量の平均値の和の５０％になる点とが、異なる場合は、表面に付着する酸素を含む金属酸化物、炭酸塩等の影響と考えられるため、上記遷移金属Ｍの特性Ｘ線の検出量が内部の上記遷移金属Ｍの特性Ｘ線の検出量の平均値ＭＡＶＥと、バックグラウンドの上記遷移金属Ｍの特性Ｘ線の検出量の平均値ＭＢＧとの和の５０％になる点をＳＴＥＭ−ＥＤＸ線分析の際の正極活物質の表面の位置として採用することができる。また遷移金属Ｍを複数有する正極活物質の場合、内部における特性Ｘ線の検出量が最も多い元素のＭＡＶＥおよびＭＢＧを用いてＳＴＥＭ−ＥＤＸ線分析の際の正極活物質の表面の位置を定めることができる。 When the positive electrode active material is subjected to analysis, a protective film may be attached to the surface, but the protective film is not included in the positive electrode active material. As the protective film, a single layer film or a multilayer film selected from carbon, metal, oxide, resin, etc. may be used. When a protective film is attached during cross-sectional STEM-EDX-ray analysis, the position of the surface of the positive electrode active material in the line analysis, etc. is a point where the detection amount of the characteristic X-ray of the transition metal M is 50% of the sum of the average value M AVE of the detection amount of the characteristic X-ray of the transition metal M in the interior and the average value M BG of the detection amount of the characteristic X-ray of the transition metal M in the background, or a point where the detection amount of the characteristic X-ray of oxygen is 50% of the sum of the average value O AVE of the detection amount of the characteristic X-ray of the oxygen in the interior and the average value O BG of the detection amount of the characteristic X-ray of the oxygen in the background. In addition, when the point where the detection amount of the characteristic X-ray of the transition metal M is 50% of the sum of the average detection amount of the characteristic X-ray of the transition metal M in the interior and the average detection amount of the characteristic X-ray of the transition metal M in the background is different from the point where the detection amount of the characteristic X-ray of oxygen is 50% of the sum of the average detection amount of the characteristic X-ray of oxygen in the interior and the average detection amount of the characteristic X-ray of oxygen in the background, it is considered that it is due to the influence of metal oxides, carbonates, etc. containing oxygen attached to the surface, so that the point where the detection amount of the characteristic X-ray of the transition metal M is 50% of the sum of the average detection amount M AVE of the characteristic X-ray of the transition metal M in the interior and the average detection amount M BG of the characteristic X-ray of the transition metal M in the background can be adopted as the surface position of the positive electrode active material in STEM-EDX-ray analysis. In addition, in the case of a positive electrode active material having a plurality of transition metals M, the surface position of the positive electrode active material in STEM-EDX-ray analysis can be determined using the M AVE and M BG of the element with the largest amount of detection of characteristic X-rays in the interior.
バックグラウンドの上記遷移金属Ｍの特性Ｘ線の検出量の平均値ＭＢＧは、たとえば遷移金属Ｍの特性Ｘ線の検出量が増加を始める近辺を避けて外側の２ｎｍ以上、好ましくは３ｎｍ以上の範囲を平均して求めることができる。また内部の遷移金属Ｍの特性Ｘ線の検出量の平均値ＭＡＶＥは、遷移金属Ｍおよび酸素の特性Ｘ線の検出量が飽和し安定した領域、たとえば遷移金属Ｍの特性Ｘ線の検出量が増加を始める領域から深さ３０ｎｍ以上、好ましくは５０ｎｍを超える部分で、２ｎｍ以上、好ましくは３ｎｍ以上の範囲を平均して求めることができる。バックグラウンドの酸素の特性Ｘ線の検出量の平均値ＯＢＧおよび内部の酸素の特性Ｘ線の検出量の平均値ＯＡＶＥも同様に求めることができる。 The average value M BG of the background detection amount of the characteristic X-rays of the transition metal M can be obtained, for example, by averaging an outer range of 2 nm or more, preferably 3 nm or more, avoiding the vicinity where the detection amount of the characteristic X-rays of the transition metal M begins to increase. The average value M AVE of the detection amount of the characteristic X-rays of the internal transition metal M can be obtained, for example, by averaging an outer range of 2 nm or more, preferably 3 nm or more, in a region where the detection amounts of the characteristic X-rays of the transition metal M and oxygen become saturated and stable, for example, a region that is 30 nm or more, preferably 50 nm deep from the region where the detection amount of the characteristic X-rays of the transition metal M begins to increase. The average value O BG of the background detection amount of the characteristic X-rays of oxygen and the average value O AVE of the detection amount of the characteristic X-rays of the internal oxygen can also be obtained in a similar manner.
また断面ＳＴＥＭ像等における正極活物質１００の表面とは、正極活物質の結晶構造に由来する像が観察される領域と、観察されない領域の境界であって、正極活物質を構成する金属元素の中でリチウムより原子番号の大きな金属元素の原子核に由来する原子カラムが確認される領域の最も外側とする。または断面ＳＴＥＭ像の、表面から内部に向かった輝度のプロファイルに引いた接線と、深さ方向の軸の交点とする。断面ＳＴＥＭ像等における表面は、より空間分解能の高い分析と併せて判断してもよい。 The surface of the positive electrode active material 100 in a cross-sectional STEM image or the like is the boundary between an area where an image derived from the crystal structure of the positive electrode active material is observed and an area where it is not observed, and is the outermost area where atomic columns derived from the atomic nuclei of metal elements having a larger atomic number than lithium among the metal elements constituting the positive electrode active material are confirmed. Alternatively, it is the intersection point of a tangent drawn to the brightness profile from the surface to the inside of the cross-sectional STEM image and the axis in the depth direction. The surface in a cross-sectional STEM image or the like may be determined in conjunction with an analysis with higher spatial resolution.
また、ＳＴＥＭ−ＥＤＸの空間分解能は最小でも１ｎｍ程度である。そのため添加元素プロファイルの最大値は１ｎｍ程度ずれることがあり得る。たとえば上記で求めた表面より外側にマグネシウム等の添加元素プロファイルの最大値があっても、最大値と表面の差が１ｎｍ未満であれば、誤差とみなすことができる。 In addition, the spatial resolution of STEM-EDX is at least about 1 nm. Therefore, the maximum value of the additive element profile can deviate by about 1 nm. For example, even if the maximum value of the additive element profile of magnesium or the like is outside the surface determined above, it can be considered an error if the difference between the maximum value and the surface is less than 1 nm.
またＳＴＥＭ−ＥＤＸ線分析におけるピークとは、各元素プロファイルにおける検出強度、または元素毎の特性Ｘ線の検出量の最大値をいうこととする。なおＳＴＥＭ−ＥＤＸ線分析におけるノイズとしては、空間分解能（Ｒ）以下、たとえばＲ／２以下の半値幅の測定値などが考えられる。 In addition, a peak in STEM-ED X-ray analysis refers to the detection intensity in each element profile, or the maximum amount of characteristic X-rays detected for each element. Note that noise in STEM-ED X-ray analysis can be a measurement value with a half-width less than the spatial resolution (R), for example, less than R/2.
同一箇所を同一条件で複数回スキャンすることでノイズの影響を軽減できる。たとえば６スキャン測定した積算値を各元素のプロファイルとすることができる。スキャン回数は６に限られず、それ以上行って、その平均を各元素のプロファイルとすることもできる。 The effects of noise can be reduced by scanning the same location multiple times under the same conditions. For example, the integrated values measured over six scans can be used as the profile for each element. The number of scans is not limited to six, and more scans can be performed and the average can be used as the profile for each element.
ＳＴＥＭ−ＥＤＸ線分析は、たとえば以下のように行うことができる。まず正極活物質の表面に保護膜を蒸着する。たとえばイオンスパッタ装置（日立ハイテク製ＭＣ１０００）のカーボンコーティングユニットにて、保護膜として炭素を蒸着することができる。 STEM-EDX analysis can be performed, for example, as follows. First, a protective film is deposited on the surface of the positive electrode active material. For example, carbon can be deposited as a protective film using a carbon coating unit of an ion sputtering device (Hitachi High-Tech MC1000).
次に正極活物質を薄片化しＳＴＥＭ断面試料を作製する。たとえばＦＩＢ−ＳＥＭ装置（日立ハイテク製ＸＶｉｓｉｏｎ２００ＴＢＳ）を用いて試料の厚さを５０ｎｍ以上８０ｎｍ以下とすることができる。薄片化加工における仕上げ条件は、たとえば加速電圧１０ｋＶとすることができる。薄片化した試料のピックアップはＭＰＳ（マイクロプロービングシステム）で行うことができる。 The positive electrode active material is then sliced to prepare a STEM cross-sectional sample. For example, a FIB-SEM device (Hitachi High-Tech XVision 200TBS) can be used to make the sample 50 nm to 80 nm thick. The finishing conditions for the slice processing can be, for example, an acceleration voltage of 10 kV. The sliced sample can be picked up by an MPS (micro-probing system).
ＳＴＥＭ−ＥＤＸ線分析は、たとえばＳＴＥＭ装置（日立ハイテク製ＨＤ−２７００）を用いて、ＥＤＸ検出器は、ＥＤＡＸのＯｃｔａｎｅ　Ｔ　Ｕｌｔｒａ　Ｗ（Ｄｕａｌ　ＥＤＳ）を使用することができる。ＥＤＸ線分析時は、ＳＴＥＭ装置の加速電圧を２００ｋＶ、エミッション電流が６μＡ以上１０μＡ以下になるよう設定し、薄片化した試料のうち奥行きおよび凹凸の少ない箇所を測定する。倍率はたとえば１５万倍程度とする。ＥＤＸ線分析の条件は、ドリフト補正有り、線幅４２ｎｍ、ピッチ０．２ｎｍ、フレーム数６回以上とすることができる。 For STEM-EDX-ray analysis, for example, a STEM device (Hitachi High-Tech HD-2700) can be used, and the EDX detector can be EDAX's Octane T Ultra W (Dual EDS). During EDX-ray analysis, the acceleration voltage of the STEM device is set to 200 kV, and the emission current is set to 6 μA to 10 μA, and a portion of the sliced sample with minimal depth and unevenness is measured. The magnification is, for example, about 150,000 times. The conditions for EDX-ray analysis can be drift correction, line width 42 nm, pitch 0.2 nm, and frame number 6 or more.
＜含有元素＞
正極活物質１００は、リチウムイオンが挿入脱離しても電荷中性を保つために、酸化還元が可能な遷移金属を有する必要がある。正極活物質１００は酸化還元反応を担う遷移金属として主にコバルトを用いることが好ましい。コバルトに加えて、ニッケルおよびマンガンから選ばれる少なくとも一または二を用いてもよい。正極活物質１００が有する遷移金属のうち、コバルトが７５原子％以上、好ましくは９０原子％以上、さらに好ましくは９５原子％以上であると、合成が比較的容易で取り扱いやすく優れたサイクル特性を有するなど利点が多く好ましい。例えば正極活物質１００はコバルト酸リチウム（ＬｉＣｏＯ２）に添加元素が加えられたものを用いることができる。コバルト酸リチウムの組成は厳密にＬｉ：Ｃｏ：Ｏ＝１：１：２に限定されるものではなく、正極活物質１００は、リチウムと、コバルトと、酸素と、添加元素と、を有すればよい。 <Elements>
The positive electrode active material 100 needs to have a transition metal capable of oxidation and reduction in order to maintain charge neutrality even when lithium ions are inserted and removed. The positive electrode active material 100 preferably mainly uses cobalt as a transition metal responsible for the oxidation and reduction reaction. In addition to cobalt, at least one or two selected from nickel and manganese may be used. If the transition metals contained in the positive electrode active material 100 are 75 atomic % or more, preferably 90 atomic % or more, and more preferably 95 atomic % or more of cobalt, there are many advantages such as relatively easy synthesis, easy handling, and excellent cycle characteristics. For example, the positive electrode active material 100 can be made of lithium cobalt oxide (LiCoO 2 ) to which an additive element is added. The composition of lithium cobalt oxide is not strictly limited to Li:Co:O=1:1:2, and the positive electrode active material 100 may have lithium, cobalt, oxygen, and an additive element.
また正極活物質１００の遷移金属のうちコバルトが７５原子％以上、好ましくは９０原子％以上、さらに好ましくは９５原子％以上であると、ニッケル酸リチウム（ＬｉＮｉＯ２）等のニッケルが遷移金属の過半を占めるような複合酸化物と比較して、ＬｉｘＣｏＯ２中のｘが小さいときの安定性がより優れる。これはニッケルよりもコバルトの方が、ヤーン・テラー効果による歪みの影響が小さいためと考えられる。遷移金属を有する複合酸化物におけるヤーン・テラー効果は、遷移金属のｄ軌道の電子の数により、その効果の強さが異なる。ニッケル酸リチウム等の８面体配位の低スピンニッケル（ＩＩＩ）が遷移金属の過半を占めるような層状岩塩型の複合酸化物は、ヤーン・テラー効果の影響が大きく、ニッケルと酸素の８面体からなる層に歪みが生じやすい。そのため充放電サイクルにおいて結晶構造の崩れが生じる懸念が高まる。またニッケルイオンはコバルトイオンと比較して大きく、リチウムイオンの大きさに近い。そのためニッケル酸リチウムのようにニッケルが遷移金属の過半を占めるような層状岩塩型の複合酸化物ではニッケルとリチウムのカチオンミキシングが生じやすいという課題がある。 Furthermore, when the transition metal of the positive electrode active material 100 is 75 atomic % or more, preferably 90 atomic % or more, and more preferably 95 atomic % or more, the stability when x in Li x CoO 2 is small is better than that of a composite oxide in which nickel such as lithium nickel oxide (LiNiO 2 ) accounts for the majority of the transition metal. This is thought to be because cobalt is less affected by distortion due to the Jahn-Teller effect than nickel. The strength of the Jahn-Teller effect in a composite oxide having a transition metal varies depending on the number of electrons in the d orbital of the transition metal. A layered rock salt type composite oxide in which low-spin nickel (III) in octahedral coordination such as lithium nickel oxide accounts for the majority of the transition metal is greatly affected by the Jahn-Teller effect, and distortion is likely to occur in the layer consisting of octahedrons of nickel and oxygen. Therefore, there is an increased concern that the crystal structure will collapse during the charge and discharge cycle. In addition, nickel ions are larger than cobalt ions and are close to the size of lithium ions. Therefore, in layered rock-salt complex oxides in which nickel accounts for the majority of the transition metal, such as lithium nickel oxide, there is a problem in that cation mixing of nickel and lithium is likely to occur.
正極活物質１００が有する添加元素としては、マグネシウム、フッ素、ニッケル、アルミニウム、チタン、ジルコニウム、バナジウム、鉄、マンガン、クロム、ニオブ、ヒ素、亜鉛、ケイ素、硫黄、リン、ホウ素、臭素、及びベリリウムから選ばれた一または二以上を用いることが好ましい。また添加元素のうち遷移金属の和は、２５原子％未満が好ましく、１０原子％未満がより好ましく、５原子％未満がさらに好ましい。 The additive elements contained in the positive electrode active material 100 are preferably one or more selected from magnesium, fluorine, nickel, aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, bromine, and beryllium. The sum of the transition metals among the additive elements is preferably less than 25 atomic %, more preferably less than 10 atomic %, and even more preferably less than 5 atomic %.
つまり正極活物質１００は、マグネシウムが添加されたコバルト酸リチウム、フッ素が添加されたコバルト酸リチウム、マグネシウムおよびフッ素が添加されたコバルト酸リチウム、マグネシウム、フッ素およびチタンが添加されたコバルト酸リチウム、マグネシウム、フッ素およびアルミニウムが添加されたコバルト酸リチウム、マグネシウム、フッ素およびニッケルが添加されたコバルト酸リチウム、マグネシウム、フッ素、ニッケルおよびアルミニウムが添加されたコバルト酸リチウム、等を有することができる。 That is, the positive electrode active material 100 can include lithium cobalt oxide with added magnesium, lithium cobalt oxide with added fluorine, lithium cobalt oxide with added magnesium and fluorine, lithium cobalt oxide with added magnesium, fluorine and titanium, lithium cobalt oxide with added magnesium, fluorine and aluminum, lithium cobalt oxide with added magnesium, fluorine and nickel, lithium cobalt oxide with added magnesium, fluorine, nickel and aluminum, etc.
添加元素は、正極活物質１００に固溶していることが好ましい。そのため例えば、ＳＴＥＭ−ＥＤＸの線分析を行った際に、添加元素の特性Ｘ線の検出量が増加する深さは、正極活物質の主成分である遷移金属Ｍの特性Ｘ線の検出量が増加する深さよりも、深い位置、すなわち正極活物質１００の内部に位置していることが好ましい。 The additive element is preferably dissolved in the positive electrode active material 100. Therefore, for example, when performing a line analysis using STEM-EDX, the depth at which the amount of detection of the characteristic X-rays of the additive element increases is preferably located deeper than the depth at which the amount of detection of the characteristic X-rays of the transition metal M, which is the main component of the positive electrode active material, increases, i.e., inside the positive electrode active material 100.
なお本明細書等において、ＳＴＥＭ−ＥＤＸの線分析においてある元素の特性Ｘ線の検出量が増加する深さとは、強度および空間分解能等の観点でノイズでないと判断できる測定値が、連続して得られるようになる深さ、をいうこととする。 In this specification, the depth at which the amount of detection of characteristic X-rays of a certain element increases in STEM-EDX line analysis refers to the depth at which measurement values that can be determined to be not noise in terms of intensity, spatial resolution, etc. are continuously obtained.
これらの添加元素が、後述するように正極活物質１００が有する結晶構造をより安定化させる。別言すると、添加元素が表層部１００ａ及び／又は内部１００ｂに存在していることで結晶構造を安定化させることができる。なお本明細書等において添加元素は混合物、原料の一部と同義である。 These added elements further stabilize the crystal structure of the positive electrode active material 100, as described below. In other words, the presence of the added elements in the surface layer 100a and/or the interior 100b can stabilize the crystal structure. In this specification, the added elements are synonymous with a mixture or a part of the raw material.
なお添加元素として、必ずしもマグネシウム、フッ素、ニッケル、アルミニウム、チタン、ジルコニウム、バナジウム、鉄、マンガン、クロム、ニオブ、ヒ素、亜鉛、ケイ素、硫黄、リン、ホウ素、臭素、またはベリリウムを含まなくてもよい。 Additive elements do not necessarily have to include magnesium, fluorine, nickel, aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, bromine, or beryllium.
たとえばマンガンを実質的に含まない正極活物質１００とすると、合成が比較的容易で取り扱いやすく、優れたサイクル特性を有するといった上記の利点がより大きくなる。正極活物質１００に含まれるマンガンの濃度はたとえば６００ｐｐｍ　ｗｔ以下、より好ましくは１００ｐｐｍ　ｗｔ以下であることが好ましい。 For example, if the positive electrode active material 100 is substantially free of manganese, the above-mentioned advantages of being relatively easy to synthesize and handle, and having excellent cycle characteristics, are even greater. The concentration of manganese contained in the positive electrode active material 100 is preferably, for example, 600 ppm wt or less, more preferably 100 ppm wt or less.
＜結晶構造＞
本発明の一態様である正極活物質１００の結晶構造について説明する。 <Crystal structure>
The crystal structure of the positive electrode active material 100 according to one embodiment of the present invention will be described.
≪ＬｉｘＣｏＯ２中のｘが１のとき≫
正極活物質１００は放電状態、つまりＬｉｘＣｏＯ２中のｘ＝１の場合に、空間群Ｒ−３ｍに帰属する層状岩塩型の結晶構造を有することが好ましい。層状岩塩型の複合酸化物は、放電容量が高く、二次元的なリチウムイオンの拡散経路を有しリチウムイオンの挿入／脱離反応に適しており、二次電池の正極活物質として優れる。そのため特に、正極活物質１００の体積の大半を占める内部１００ｂが層状岩塩型の結晶構造を有することが好ましい。図４ではＬｉｘＣｏＯ２のｘの値を横軸に示し、ｘの値に応じた結晶構造を示す。図４の凡例に示すが、ｘの値に応じてリチウムの占有率を１、０．２、０．１５とする。例えば図４において、ｘ＝１のときの結晶構造は、層状岩塩型の結晶構造を示し、図中Ｒ−３ｍ　Ｏ３を付す。 <When x in Li x CoO 2 is 1>
The positive electrode active material 100 preferably has a layered rock salt type crystal structure belonging to the space group R-3m in a discharged state, that is, when x=1 in Li x CoO 2. The layered rock salt type composite oxide has a high discharge capacity, has a two-dimensional lithium ion diffusion path, is suitable for lithium ion insertion/extraction reaction, and is excellent as a positive electrode active material for a secondary battery. Therefore, it is preferable that the inner part 100b, which occupies most of the volume of the positive electrode active material 100, has a layered rock salt type crystal structure. In FIG. 4, the value of x in Li x CoO 2 is shown on the horizontal axis, and the crystal structure according to the value of x is shown. As shown in the legend of FIG. 4, the occupancy rate of lithium is set to 1, 0.2, or 0.15 according to the value of x. For example, in FIG. 4, the crystal structure when x=1 shows a layered rock salt type crystal structure, and is marked with R-3m O3 in the figure.
一方、正極活物質１００の表層部１００ａは、充電により正極活物質１００からリチウムが抜けても、内部１００ｂのコバルトと酸素の８面体からなる層状構造が壊れないよう補強する機能を有することが好ましい。または表層部１００ａが正極活物質１００のバリア膜として機能することが好ましい。または正極活物質１００の外周部である表層部１００ａが正極活物質１００を補強することが好ましい。ここでいう補強とは、酸素の脱離をはじめとする正極活物質１００の表層部１００ａおよび内部１００ｂの構造変化を抑制すること、及び／又は有機溶媒が正極活物質１００の表面で酸化分解されることを抑制することをいう。 On the other hand, it is preferable that the surface layer 100a of the positive electrode active material 100 has a function of reinforcing the layered structure of the octahedrons of cobalt and oxygen in the interior 100b so that it is not destroyed even if lithium is removed from the positive electrode active material 100 by charging. Alternatively, it is preferable that the surface layer 100a functions as a barrier film for the positive electrode active material 100. Alternatively, it is preferable that the surface layer 100a, which is the outer periphery of the positive electrode active material 100, reinforces the positive electrode active material 100. The reinforcement here means suppressing structural changes in the surface layer 100a and interior 100b of the positive electrode active material 100, including oxygen desorption, and/or suppressing oxidative decomposition of the organic solvent on the surface of the positive electrode active material 100.
そのため表層部１００ａは、内部１００ｂと異なる結晶構造を有していることが好ましい。また表層部１００ａは、内部１００ｂよりも室温（２５℃）で安定な組成および結晶構造であることが好ましい。例えば、正極活物質１００の表層部１００ａの少なくとも一部が、岩塩型の結晶構造を有することが好ましい。または表層部１００ａは、層状岩塩型と岩塩型の結晶構造の両方の結晶構造を有していることが好ましい。または表層部１００ａは、層状岩塩型と岩塩型の結晶構造の両方の特徴を有することが好ましい。 Therefore, it is preferable that the surface layer 100a has a different crystal structure from the inner portion 100b. It is also preferable that the surface layer 100a has a composition and crystal structure that are more stable at room temperature (25°C) than the inner portion 100b. For example, it is preferable that at least a part of the surface layer 100a of the positive electrode active material 100 has a rock salt type crystal structure. Alternatively, it is preferable that the surface layer 100a has both a layered rock salt type and a rock salt type crystal structure. Alternatively, it is preferable that the surface layer 100a has the characteristics of both a layered rock salt type and a rock salt type crystal structure.
表層部１００ａは充電時にリチウムイオンが最初に脱離する領域であり、内部１００ｂよりもリチウム濃度が低くなりやすい領域である。また表層部１００ａが有する正極活物質１００の粒子表面の原子は、一部の結合が切断された状態ともいえる。そのため表層部１００ａは不安定になりやすく、結晶構造の劣化が始まりやすい領域といえる。一方で表層部１００ａを十分に安定にできれば、ＬｉｘＣｏＯ２中のｘが１より小さいときでも、たとえばｘが０．２４以下でも内部１００ｂのコバルトと酸素の８面体からなる層状構造を壊れにくくすることができる。さらには、内部１００ｂのコバルトと酸素の８面体からなる層のずれを抑制することができる。 The surface layer 100a is the region where lithium ions are first desorbed during charging, and is the region where the lithium concentration is likely to be lower than that of the inside 100b. In addition, the atoms on the particle surface of the positive electrode active material 100 in the surface layer 100a can be said to be in a state where some bonds are broken. Therefore, the surface layer 100a is likely to become unstable, and can be said to be a region where deterioration of the crystal structure is likely to begin. On the other hand, if the surface layer 100a can be sufficiently stabilized, even when x in Li x CoO 2 is smaller than 1, for example, even when x is 0.24 or less, the layered structure consisting of cobalt and oxygen octahedrons in the inside 100b can be made less likely to be broken. Furthermore, the shift of the layer consisting of cobalt and oxygen octahedrons in the inside 100b can be suppressed.
表層部１００ａを安定な組成および結晶構造とするために、表層部１００ａは添加元素を有することが好ましく、添加元素を複数有することがより好ましい。また表層部１００ａは内部１００ｂよりも添加元素から選ばれた一または二以上の濃度が高いことが好ましい。また正極活物質１００が有する添加元素から選ばれた一または二以上は濃度勾配を有していることが好ましい。また添加元素によって正極活物質１００での濃度分布が異なっていることがより好ましい。たとえば添加元素によって濃度ピークの表面からの深さが異なっていることがより好ましい。ここでいう濃度ピークとは濃度の極大値をいうこととし、添加元素によって表層部１００ａまたは粒子表面から５０ｎｍ以下に濃度ピークが位置することが好ましい。 In order to give the surface layer 100a a stable composition and crystal structure, it is preferable that the surface layer 100a has an additive element, and more preferably has multiple additive elements. It is also preferable that the surface layer 100a has a higher concentration of one or more selected from the additive elements than the interior 100b. It is also preferable that the one or more selected from the additive elements contained in the positive electrode active material 100 have a concentration gradient. It is also more preferable that the concentration distribution in the positive electrode active material 100 differs depending on the additive element. For example, it is more preferable that the depth from the surface of the concentration peak differs depending on the additive element. The concentration peak here refers to the maximum value of the concentration, and it is preferable that the concentration peak is located 50 nm or less from the surface layer 100a or the particle surface depending on the additive element.
たとえば添加元素の一部、マグネシウム、フッ素、ニッケル、チタン、ケイ素、リン、ホウ素、カルシウム等は図１Ｂ１にグラデーションで示すように、内部１００ｂから表面に向かって高くなる濃度勾配を有することが好ましい。このような濃度勾配を有する添加元素を添加元素Ａと呼ぶこととする。添加元素Ａは濃度ピークが表層部１００ａに存在するとよい。 For example, some of the additive elements, such as magnesium, fluorine, nickel, titanium, silicon, phosphorus, boron, and calcium, preferably have a concentration gradient that increases from the interior 100b toward the surface, as shown by the gradation in FIG. 1B1. An additive element that has such a concentration gradient will be referred to as additive element A. It is preferable that the concentration peak of additive element A exists in the surface layer portion 100a.
別の添加元素、たとえばアルミニウム、マンガン等は図１Ｂ２にハッチの濃さで示すように、濃度勾配を有しかつ添加元素Ａよりも深い領域に濃度ピークを有することが好ましい。濃度ピークは表層部１００ａに存在してもよいし、表層部１００ａより深くてもよい。たとえば表面から内部に向かって５ｎｍ以上３０ｎｍ以下の領域にピークを有することが好ましい。このような濃度勾配を有する添加元素を添加元素Ｂと呼ぶこととする。すなわち添加元素の濃度勾配の仕方、つまり濃度分布の仕方で、添加元素Ａ及び添加元素Ｂを区別することができる。 Another additive element, such as aluminum or manganese, preferably has a concentration gradient and a concentration peak in a deeper region than additive element A, as shown by the shade of the hatch in FIG. 1B2. The concentration peak may be present in the surface layer 100a, or may be deeper than the surface layer 100a. For example, it is preferable for the peak to be in a region of 5 nm to 30 nm from the surface toward the inside. An additive element having such a concentration gradient will be referred to as additive element B. In other words, additive element A and additive element B can be distinguished by the concentration gradient of the additive element, that is, the concentration distribution.
〔マグネシウム〕
たとえば添加元素Ａの一つであるマグネシウムは２価の陽イオンになりやすく、マグネシウムイオンは層状岩塩型の結晶構造におけるコバルトサイトよりもリチウムサイトに存在する方が安定であるため、リチウムサイトに入りやすい。マグネシウムが表層部１００ａのリチウムサイトに適切な濃度で存在することで、層状岩塩型の結晶構造を保持しやすい。これはリチウムサイトに存在するマグネシウムイオンが、ＣｏＯ２層同士を支える柱として機能するためと推測される。また酸化マグネシウムは岩塩型の結晶構造を有するため、表層部１００ａが岩塩型の結晶構造を有することがある。なおマグネシウムは内部１００ｂのリチウムサイトに適切な濃度で存在していてもよく、マグネシウムが、内部１００ｂのリチウムサイトに適切な濃度で存在することによっても、ＣｏＯ２層同士を支える柱として機能することができ、層状岩塩型の結晶構造を保持することができる。またマグネシウムが存在することで、ＬｉｘＣｏＯ２中のｘがたとえば０．２４以下の状態においてマグネシウムの周囲の酸素の脱離を抑制することができる。またマグネシウムが存在することで正極活物質１００の密度が高くなることが期待できる。また表層部１００ａのマグネシウム濃度が高いと、電解液が分解して生じたフッ酸に対する耐食性が向上することも期待できる。 〔magnesium〕
For example, magnesium, which is one of the additive elements A, tends to become a divalent cation, and since magnesium ions are more stable at the lithium site than at the cobalt site in the layered rock salt crystal structure, they tend to enter the lithium site. When magnesium is present at an appropriate concentration at the lithium site of the surface layer 100a, it is easy to maintain the layered rock salt crystal structure. This is presumed to be because the magnesium ions present at the lithium site function as pillars supporting the CoO 2 layers. Furthermore, since magnesium oxide has a rock salt crystal structure, the surface layer 100a may have a rock salt crystal structure. Note that magnesium may be present at an appropriate concentration at the lithium site of the interior 100b, and even when magnesium is present at an appropriate concentration at the lithium site of the interior 100b, it can function as a pillar supporting the CoO 2 layers, and the layered rock salt crystal structure can be maintained. Furthermore, the presence of magnesium can suppress the detachment of oxygen around magnesium when x in Li x CoO 2 is, for example, 0.24 or less. Furthermore, the presence of magnesium can be expected to increase the density of the positive electrode active material 100. Furthermore, if the magnesium concentration in the surface layer 100a is high, it is expected that the corrosion resistance against the hydrofluoric acid produced by decomposition of the electrolyte will be improved.
マグネシウムは、適切な濃度であれば充放電に伴うリチウムイオンの挿入および脱離に悪影響を及ぼさず上記のメリットを正極活物質へ与えることができる。しかしマグネシウムが過剰であるとリチウムイオンの挿入および脱離に悪影響が出る恐れがある。さらに結晶構造の安定化への効果が小さくなってしまう場合がある。これはマグネシウムイオンが、リチウムサイトに加えてコバルトサイトにも入るようになるためと考えられる。加えて、リチウムサイトにもコバルトサイトにも置換しない、不要なマグネシウム化合物（酸化物およびフッ化物等）が正極活物質の表面等に偏析し、二次電池の抵抗成分となる恐れがある。また正極活物質のマグネシウム濃度が高くなるのに伴って正極活物質の放電容量が減少することがある。これはリチウムサイトにマグネシウムイオンが入りすぎ、充放電に寄与するリチウム量が減少するためと考えられる。 At an appropriate concentration, magnesium does not adversely affect the insertion and removal of lithium ions during charging and discharging, and can provide the above benefits to the positive electrode active material. However, if there is an excess of magnesium, it may have a negative effect on the insertion and removal of lithium ions. Furthermore, the effect of stabilizing the crystal structure may be reduced. This is thought to be because magnesium ions enter the cobalt site in addition to the lithium site. In addition, unnecessary magnesium compounds (oxides, fluorides, etc.) that do not substitute for either the lithium site or the cobalt site may segregate on the surface of the positive electrode active material, and may become resistance components of the secondary battery. In addition, as the magnesium concentration of the positive electrode active material increases, the discharge capacity of the positive electrode active material may decrease. This is thought to be because too many magnesium ions enter the lithium site, reducing the amount of lithium that contributes to charging and discharging.
そのため、正極活物質１００全体が有するマグネシウムが適切な量であることが好ましい。たとえばマグネシウムの原子数はコバルトの原子数の０．００２倍以上０．０６倍以下が好ましく、０．００５倍以上０．０３倍以下がより好ましく、０．０１倍程度がさらに好ましい。ここでいう正極活物質１００全体が有するマグネシウムの量とは、例えばＧＤ−ＭＳ（グロー放電質量分析法）、ＩＣＰ−ＭＳ（誘導結合プラズマ質量分析）等を用いて正極活物質１００の全体の元素分析を行った値であってもよいし、正極活物質１００の作製の過程における原料の配合の値に基づいたものであってもよい。 Therefore, it is preferable that the amount of magnesium contained in the entire positive electrode active material 100 is appropriate. For example, the number of magnesium atoms is preferably 0.002 to 0.06 times the number of cobalt atoms, more preferably 0.005 to 0.03 times, and even more preferably about 0.01 times. The amount of magnesium contained in the entire positive electrode active material 100 here may be a value obtained by performing an elemental analysis of the entire positive electrode active material 100 using, for example, GD-MS (glow discharge mass spectrometry) or ICP-MS (inductively coupled plasma mass spectrometry), or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material 100.
〔ニッケル〕
また添加元素Ａの一つであるニッケルは、コバルトサイトとリチウムサイトのどちらにも存在しうる。コバルトサイトにニッケルイオンが位置すると、コバルトと比較して酸化還元電位が低くなるため放電容量増加につながり好ましい。 〔nickel〕
Nickel, which is one of the additive elements A, can exist on either the cobalt site or the lithium site. When nickel ions are located on the cobalt site, the oxidation-reduction potential is lower than that of cobalt, which is preferable since it leads to an increase in discharge capacity.
またニッケルイオンがリチウムサイトに存在する場合、コバルトと酸素の８面体からなる層状構造のずれが抑制されうる。また充放電に伴う体積の変化が抑制される。また弾性係数が大きくなる、つまり硬くなる。これはリチウムサイトに存在するニッケルも、ＣｏＯ２層同士を支える柱として機能するためと推測される。そのため特に高温、たとえば４５℃以上での充電状態において結晶構造がより安定になることが期待でき好ましい。 In addition, when nickel ions are present at the lithium site, the shift of the layered structure consisting of octahedra of cobalt and oxygen can be suppressed. Also, the change in volume accompanying charging and discharging is suppressed. Also, the elastic modulus increases, that is, the material becomes hard. This is presumably because nickel present at the lithium site also functions as a pillar supporting the CoO 2 layers. Therefore, it is expected that the crystal structure will be more stable, particularly in a charged state at high temperatures, for example, 45°C or higher, which is preferable.
また酸化ニッケル（ＮｉＯ）の陽イオンと陰イオン間の距離は、ＭｇＯおよびＣｏＯよりも、ＬｉＣｏＯ２の陽イオンと陰イオン間の距離の平均に近く、ＬｉＣｏＯ２と配向が一致しやすい。 In addition, the distance between the cations and anions of nickel oxide (NiO) is closer to the average distance between the cations and anions of LiCoO2 than those of MgO and CoO, and the orientation of NiO is more likely to match that of LiCoO2.
またマグネシウム、アルミニウム、コバルト、ニッケルの順にイオン化傾向が小さくなる（Ｍｇ＞Ａｌ＞Ｃｏ＞Ｎｉ）。そのため充電時にニッケルは上記の他の元素より電解液に溶出しにくいと考えられる。そのため充電状態において表層部の結晶構造を安定化させる効果が高いと考えられる。ニッケルが内部１００ｂに存在することで、内部の結晶構造を安定化させる効果も奏する。 In addition, the order of ionization tendency is lowest for magnesium, aluminum, cobalt, and nickel (Mg>Al>Co>Ni). Therefore, nickel is considered to be less likely to dissolve into the electrolyte during charging than the other elements listed above. Therefore, it is considered to be highly effective in stabilizing the crystal structure of the surface layer in the charged state. The presence of nickel in the interior 100b also has the effect of stabilizing the internal crystal structure.
さらにニッケルはＮｉ２＋、Ｎｉ３＋、Ｎｉ４＋のうちＮｉ２＋が最も安定であり、ニッケルはコバルトと比較して３価のイオン化エネルギーが大きい。そのためニッケルと酸素のみではスピネル型の結晶構造を取らないことが知られている。そのためニッケルは、層状岩塩型からスピネル型の結晶構造への相変化を抑制する効果があると考えられる。 Furthermore, of the three nickel states Ni2 + , Ni3 + , and Ni4 + , Ni2 + is the most stable, and nickel has a higher trivalent ionization energy than cobalt. Therefore, it is known that nickel and oxygen alone do not form a spinel crystal structure. Therefore, nickel is thought to have the effect of suppressing the phase change from the layered rock salt type to the spinel type crystal structure.
一方でニッケルが過剰であるとヤーン・テラー効果による歪みの影響が強まり好ましくない。またニッケルが過剰であるとリチウムの挿入および脱離に悪影響が出る恐れがある。 On the other hand, an excess of nickel is undesirable because it increases the influence of distortion due to the Jahn-Teller effect. Also, an excess of nickel may adversely affect the insertion and extraction of lithium.
そのため正極活物質１００全体が有するニッケルが適切な量であることが好ましい。たとえば正極活物質１００が有するニッケルの原子数は、コバルトの原子数の０％を超えて７．５％以下が好ましく、０．０５％以上４％以下が好ましく、０．１％以上２％以下が好ましく、０．２％以上１％以下がより好ましい。または０％を超えて４％以下が好ましい。または０％を超えて２％以下が好ましい。または０．０５％以上７．５％以下が好ましい。または０．０５％以上２％以下が好ましい。または０．１％以上７．５％以下が好ましい。または０．１％以上４％以下が好ましい。ここで示すニッケルの量は例えば、ＧＤ−ＭＳ、ＩＣＰ−ＭＳ等を用いて正極活物質の全体の元素分析を行った値であってもよいし、正極活物質の作製の過程における原料の配合の値に基づいてもよい。 Therefore, it is preferable that the amount of nickel contained in the entire positive electrode active material 100 is appropriate. For example, the number of nickel atoms contained in the positive electrode active material 100 is preferably more than 0% and not more than 7.5% of the number of cobalt atoms, preferably 0.05% to 4%, preferably 0.1% to 2%, and more preferably 0.2% to 1%. Or more than 0% and not more than 4% is preferable. Or more than 0% and not more than 2% is preferable. Or more than 0.05% to 7.5% is preferable. Or more than 0.05% to 2% is preferable. Or more than 0.1% to 7.5% is preferable. Or more than 0.1% to 4% is preferable. The amount of nickel shown here may be, for example, a value obtained by performing elemental analysis of the entire positive electrode active material using GD-MS, ICP-MS, etc., or may be based on the value of the raw material composition in the process of producing the positive electrode active material.
〔アルミニウム〕
また添加元素Ｂの一つであるアルミニウムは層状岩塩型の結晶構造におけるコバルトサイトに存在しうる。典型元素であるアルミニウムは３価の陽イオンとなり、価数が変化しないため、充放電の際もアルミニウム周辺のリチウムは移動しにくい。そのためアルミニウムとその周辺のリチウムが柱として機能し、結晶構造の変化を抑制しうる。またアルミニウムは周囲のコバルトの溶出を抑制し、連続充電耐性を向上する効果がある。またＡｌ−Ｏの結合はＣｏ−Ｏ結合よりも強いため、アルミニウムの周囲の酸素の脱離を抑制することができる。これらの効果により、熱安定性が向上する。そのため添加元素としてアルミニウムを有すると、二次電池に正極活物質１００を用いたときの安全性を向上できる。また充放電を繰り返しても結晶構造が崩れにくい正極活物質１００とすることができる。 〔aluminum〕
Aluminum, which is one of the additive elements B, can be present at the cobalt site in the layered rock salt crystal structure. Aluminum, which is a typical element, becomes a trivalent cation and does not change its valence, so lithium around the aluminum is less likely to move during charging and discharging. Therefore, aluminum and the lithium around it function as columns and can suppress changes in the crystal structure. Aluminum also has the effect of suppressing the elution of surrounding cobalt and improving continuous charging resistance. In addition, since the Al-O bond is stronger than the Co-O bond, it can suppress the detachment of oxygen around the aluminum. These effects improve thermal stability. Therefore, if aluminum is included as an additive element, it is possible to improve safety when the positive electrode active material 100 is used in a secondary battery. In addition, it is possible to obtain a positive electrode active material 100 whose crystal structure is less likely to collapse even when repeatedly charged and discharged.
一方でアルミニウムが過剰であるとリチウムイオンの挿入および脱離に悪影響が出る恐れがある。 On the other hand, excess aluminum may adversely affect the insertion and removal of lithium ions.
そのため正極活物質１００全体が有するアルミニウムが適切な量であることが好ましい。たとえば正極活物質１００の全体が有するアルミニウムの原子数は、コバルトの原子数の０．０５％以上４％以下が好ましく、０．１％以上２％以下が好ましく、０．３％以上１．５％以下がより好ましい。または０．０５％以上２％以下が好ましい。または０．１％以上４％以下が好ましい。ここでいう正極活物質１００全体が有する量とはたとえば、ＧＤ−ＭＳ、ＩＣＰ−ＭＳ等を用いて正極活物質１００の全体の元素分析を行った値であってもよいし、正極活物質１００の作製の過程における原料の配合の値に基づいてもよい。 Therefore, it is preferable that the amount of aluminum contained in the entire positive electrode active material 100 is appropriate. For example, the number of aluminum atoms contained in the entire positive electrode active material 100 is preferably 0.05% to 4% of the number of cobalt atoms, preferably 0.1% to 2% and more preferably 0.3% to 1.5%. Alternatively, 0.05% to 2% is preferable. Alternatively, 0.1% to 4% is preferable. The amount contained in the entire positive electrode active material 100 here may be, for example, a value obtained by performing elemental analysis of the entire positive electrode active material 100 using GD-MS, ICP-MS, or the like, or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material 100.
〔フッ素〕
また添加元素Ａの一つであるフッ素は１価の陰イオンであり、表層部１００ａにおいて酸素の一部がフッ素に置換されていると、リチウムイオン脱離エネルギーが小さくなる。これは、リチウムイオン脱離に伴うコバルトイオンの酸化還元電位が、フッ素の有無によって異なることによる。つまりフッ素を有さない場合は、リチウムイオン脱離に伴いコバルトイオンは３価から４価に変化する。一方フッ素を有する場合は、リチウムイオン脱離に伴いコバルトイオンは２価から３価に変化する。両者で、コバルトイオンの酸化還元電位が異なる。そのため正極活物質１００の表層部１００ａにおいて酸素の一部がフッ素に置換されていると、フッ素近傍のリチウムイオンの脱離および挿入がスムースに起きやすいと言える。そのため正極活物質１００を二次電池に用いたときに充放電特性、大電流特性等を向上させることができる。また電解液に接する部分である表面を有する表層部１００ａにフッ素が存在することで、フッ酸に対する耐食性を効果的に向上させることができる。また後の実施の形態で述べるが、フッ化リチウムをはじめとするフッ化物の融点が、他の添加元素源の融点より低い場合、当該他の添加元素源の融点を下げる融剤（フラックス剤ともいう）として機能しうる。フッ素化合物がＬｉＦ及びＭｇＦ２を有する場合、図１５（非特許文献１０、図５より引用し加筆）に示すようにＬｉＦとＭｇＦ２の共融点Ｐは７４２℃付近（Ｔ１）であるため、フッ素を含む添加元素を混合した後の加熱工程において、加熱温度を７４２℃以上とすると好ましい。 [Fluorine]
In addition, fluorine, which is one of the additive elements A, is a monovalent anion, and when part of the oxygen is replaced by fluorine in the surface layer portion 100a, the lithium ion desorption energy is reduced. This is because the redox potential of the cobalt ion accompanying the desorption of lithium ions differs depending on the presence or absence of fluorine. In other words, when there is no fluorine, the cobalt ion changes from trivalent to tetravalent with the desorption of lithium ions. On the other hand, when there is fluorine, the cobalt ion changes from divalent to trivalent with the desorption of lithium ions. The redox potential of the cobalt ion is different between the two. Therefore, when part of the oxygen is replaced by fluorine in the surface layer portion 100a of the positive electrode active material 100, it can be said that the desorption and insertion of lithium ions near the fluorine is likely to occur smoothly. Therefore, when the positive electrode active material 100 is used in a secondary battery, the charge/discharge characteristics, large current characteristics, etc. can be improved. In addition, the presence of fluorine in the surface layer portion 100a having the surface that is in contact with the electrolyte can effectively improve the corrosion resistance against hydrofluoric acid. As described in the following embodiment, when the melting point of fluorides such as lithium fluoride is lower than that of other additive element sources, it can function as a flux (also called a fluxing agent) that lowers the melting point of the other additive element sources. When the fluorine compound has LiF and MgF2 , as shown in Figure 15 (quoted and added from Non-Patent Document 10, Figure 5), the eutectic point P of LiF and MgF2 is around 742°C (T1), so in the heating step after mixing the additive element containing fluorine, it is preferable to set the heating temperature to 742°C or higher.
また添加元素Ａの一つであるチタンの酸化物は超親水性を有することが知られている。そのため、表層部１００ａにチタン酸化物を有する正極活物質１００とすることで、極性の高い溶媒に対して濡れ性がよくなる可能性がある。二次電池としたときに正極活物質１００と、極性の高い電解液との界面の接触が良好となり、内部抵抗の上昇を抑制できる可能性がある。 In addition, titanium oxide, which is one of the additive elements A, is known to have superhydrophilicity. Therefore, by making the cathode active material 100 have titanium oxide in the surface layer portion 100a, it is possible that the wettability with a highly polar solvent will be improved. When used as a secondary battery, the interface between the cathode active material 100 and the highly polar electrolyte will have good contact, which may suppress an increase in internal resistance.
また添加元素Ａの一つであるリンを表層部１００ａに有すると、ＬｉｘＣｏＯ２中のｘが小さい状態を保持した場合において、ショートを抑制できる場合があり好ましい。たとえばリンと酸素を含む化合物として表層部１００ａに存在することが好ましい。 In addition, when phosphorus, which is one of the additive elements A, is present in the surface layer 100a, it is preferable because it may be possible to suppress short circuits when x in Li x CoO 2 is kept small. For example, it is preferable for phosphorus to be present in the surface layer 100a as a compound containing phosphorus and oxygen.
正極活物質１００がリンを有する場合には、有機溶媒またはリチウム塩の分解により発生したフッ酸とリンが反応し、有機溶媒中のフッ酸濃度を低下できる可能性があり好ましい。 When the positive electrode active material 100 contains phosphorus, the phosphorus reacts with the hydrofluoric acid generated by the decomposition of the organic solvent or the lithium salt, which may reduce the concentration of hydrofluoric acid in the organic solvent, which is preferable.
リチウム塩がＬｉＰＦ６を有する場合、加水分解により、フッ酸が発生する恐れがある。また、バインダとして用いられるポリフッ化ビニリデン（ＰＶＤＦ）とアルカリ成分との反応によりフッ酸が発生する恐れもある。有機溶媒中のフッ酸濃度が低いことにより、集電体の腐食及び／又は被覆部１０４のはがれを抑制できる場合がある。また有機溶媒中のフッ酸濃度が低いことにより、ＰＶＤＦのゲル化及び／又は不溶化による接着性の低下を抑制できる場合がある。 When the lithium salt contains LiPF6 , hydrofluoric acid may be generated by hydrolysis. In addition, hydrofluoric acid may be generated by a reaction between polyvinylidene fluoride (PVDF) used as a binder and an alkaline component. The low concentration of hydrofluoric acid in the organic solvent may suppress corrosion of the current collector and/or peeling of the coating 104. The low concentration of hydrofluoric acid in the organic solvent may suppress a decrease in adhesion due to gelation and/or insolubilization of PVDF.
正極活物質１００がマグネシウムと共にリンを有すると、ＬｉｘＣｏＯ２中のｘが１より小さい状態における安定性が極めて高くなり好ましい。正極活物質１００がリンを有する場合、リンの原子数は、コバルトの原子数の１％以上２０％以下が好ましく、２％以上１０％以下がより好ましく、３％以上８％以下がさらに好ましい。または１％以上１０％以下が好ましい。または１％以上８％以下が好ましい。または２％以上２０％以下が好ましい。または２％以上８％以下が好ましい。または３％以上２０％以下が好ましい。または３％以上１０％以下が好ましい。加えてマグネシウムの原子数は、コバルトの原子数の０．１％以上１０％以下が好ましく、０．５％以上５％以下がより好ましく、０．７％以上４％以下がより好ましい。または０．１％以上５％以下が好ましい。または０．１％以上４％以下が好ましい。または０．５％以上１０％以下が好ましい。または０．５％以上４％以下が好ましい。または０．７％以上１０％以下が好ましい。または０．７％以上５％以下が好ましい。ここで示すコバルト、リンおよびマグネシウムの濃度は例えば、ＧＤ−ＭＳ、ＩＣＰ−ＭＳ等を用いて正極活物質１００の全体の元素分析を行った値であってもよいし、正極活物質１００の作製の過程における原料の配合の値に基づいてもよい。 When the positive electrode active material 100 has phosphorus together with magnesium, the stability in the state where x in Li x CoO 2 is smaller than 1 is extremely high, which is preferable. When the positive electrode active material 100 has phosphorus, the number of phosphorus atoms is preferably 1% or more and 20% or less of the number of cobalt atoms, more preferably 2% or more and 10% or less, and even more preferably 3% or more and 8% or less. Or 1% or more and 10% or less is preferable. Or 2% or more and 20% or less is preferable. Or 2% or more and 8% or less is preferable. Or 3% or more and 20% or less is preferable. Or 3% or more and 10% or less is preferable. In addition, the number of magnesium atoms is preferably 0.1% or more and 10% or less of the number of cobalt atoms, more preferably 0.5% or more and 5% or less, and more preferably 0.7% or more and 4% or less. Or 0.1% or more and 5% or less is preferable. Or 0.1% or more and 4% or less is preferable. Or 0.5% or more and 10% or less is preferable. Or 0.5% or more and 4% or less is preferable. Alternatively, the concentration of cobalt, phosphorus, and magnesium shown here may be values obtained by performing elemental analysis of the entire positive electrode active material 100 using, for example, GD-MS, ICP-MS, or the like, or may be based on values of the composition of raw materials in the process of producing the positive electrode active material 100.
また正極活物質１００がクラックを有する場合、たとえば欠陥部１００ｃに相当する凹部が形成されるが、凹部にリン、より具体的には例えばリンと酸素を含む化合物が存在し、当該化合物が凹部を埋め込んでいることにより、クラックの進行が抑制されうる。 In addition, when the positive electrode active material 100 has a crack, a recess corresponding to the defect portion 100c is formed, but the recess contains phosphorus, more specifically, a compound containing phosphorus and oxygen, and the compound fills the recess, thereby preventing the crack from progressing.
〔複数の元素の相乗効果〕
さらに表層部１００ａにマグネシウムとニッケルを併せて有する場合、２価のマグネシウムイオンの近くでは２価のニッケルイオンがより安定に存在できる可能性がある。そのためＬｉｘＣｏＯ２中のｘが１より小さい状態でもマグネシウムの溶出が抑制されうる。そのため表層部１００ａの安定化に寄与しうる。内部１００ｂにマグネシウムとニッケルを併せて有する場合も２価のマグネシウムイオンの近くでは２価のニッケルイオンがより安定に存在できる可能性がある。 [Synergistic effect of multiple elements]
Furthermore, when magnesium and nickel are present together in the surface layer 100a, divalent nickel ions may be able to exist more stably near the divalent magnesium ions. Therefore, even when x in Li x CoO 2 is smaller than 1, the elution of magnesium may be suppressed. This may contribute to the stabilization of the surface layer 100a. When magnesium and nickel are present together in the interior 100b, divalent nickel ions may be able to exist more stably near the divalent magnesium ions.
同様の理由で、作製工程においては、コバルト酸リチウムに添加元素を加える際、マグネシウムはニッケルよりも前の工程で添加されることが好ましい。またはマグネシウムとニッケルは同じ工程で添加されることが好ましい。マグネシウムはイオン半径が大きく、どの工程で添加してもコバルト酸リチウムの表層部に留まりやすいのに対して、ニッケルはマグネシウムが存在しない場合、コバルト酸リチウムの内部に広く拡散しうる。そのためマグネシウムの前にニッケルが添加されると、ニッケルがコバルト酸リチウムの内部に拡散してしまい、表層部に好ましい量で残らない懸念がある。 For the same reason, in the manufacturing process, when adding an additive element to lithium cobalt oxide, it is preferable that magnesium is added in a step before nickel. Alternatively, it is preferable that magnesium and nickel are added in the same step. Magnesium has a large ionic radius and tends to remain in the surface layer of lithium cobalt oxide regardless of the step in which it is added, whereas nickel can diffuse widely inside the lithium cobalt oxide if magnesium is not present. Therefore, if nickel is added before magnesium, there is a concern that nickel will diffuse into the lithium cobalt oxide and not remain in the desired amount in the surface layer.
また添加元素Ａと添加元素Ｂのように分布が異なる添加元素を併せて有すると、より広い領域の結晶構造を安定化でき好ましい。たとえば正極活物質１００は添加元素Ａの一であるマグネシウムおよびニッケルと、添加元素Ｂの一であるアルミニウムと、を共に有すると、添加元素Ａと添加元素Ｂの一方しか有さない場合よりも広い領域の結晶構造を安定化できる。このように正極活物質１００が添加元素Ａと添加元素Ｂを併せて有する場合は、表面の安定化はマグネシウム、ニッケル等の添加元素Ａによって十分に果たせるため、アルミニウムなどの添加元素Ｂは表面に必須ではない。むしろアルミニウムはより深い領域に広く分布することが好ましい。たとえば表面から深さ方向１ｎｍ以上２５ｎｍ以下の領域では連続的にアルミニウムが検出されることが好ましい。アルミニウムは表面から０ｎｍ以上１００ｎｍ以下の領域、好ましくは表面から０．５ｎｍ以上５０ｎｍ以内の領域に広く分布する方が、より広い領域の結晶構造を安定化でき好ましい。 Also, it is preferable to have additive elements with different distributions, such as additive element A and additive element B, in combination, because it is possible to stabilize the crystal structure in a wider region. For example, when the positive electrode active material 100 has both magnesium and nickel, which are additive elements A, and aluminum, which is one of additive elements B, it is possible to stabilize the crystal structure in a wider region than when it has only one of additive elements A and additive element B. In this way, when the positive electrode active material 100 has both additive elements A and additive element B, additive element B, such as aluminum, is not essential for the surface, since the surface can be sufficiently stabilized by additive element A, such as magnesium or nickel. Rather, it is preferable for aluminum to be distributed widely in a deeper region. For example, it is preferable that aluminum is continuously detected in a region from 1 nm to 25 nm in the depth direction from the surface. It is preferable that aluminum is distributed widely in a region from 0 nm to 100 nm from the surface, preferably from 0.5 nm to 50 nm from the surface, because it is possible to stabilize the crystal structure in a wider region.
上記のように複数の添加元素を有すると、それぞれの添加元素の効果が相乗し表層部１００ａのさらなる安定化に寄与しうる。特にマグネシウム、ニッケルおよびアルミニウムを有すると安定な組成および結晶構造とする効果が高く好ましい。 When multiple additive elements are included as described above, the effects of each additive element are synergistic and can contribute to further stabilization of the surface layer 100a. In particular, the inclusion of magnesium, nickel, and aluminum is highly effective in providing a stable composition and crystal structure, and is therefore preferable.
ただし表層部１００ａが添加元素と酸素の化合物のみで占められると、リチウムイオンの挿入脱離が難しくなってしまうため好ましくない。たとえば表層部１００ａが、ＭｇＯ、ＭｇＯとＮｉＯ（ＩＩ）が固溶した構造、及び／又はＭｇＯとＣｏＯ（ＩＩ）が固溶した構造のみで占められるのは好ましくない。そのため表層部１００ａは少なくともコバルトを有し、放電状態においてはリチウムも有し、リチウムイオンの挿入脱離の経路を有している必要がある。 However, if the surface layer 100a is occupied only by a compound of the added element and oxygen, it is not preferable because it makes it difficult to insert and remove lithium ions. For example, it is not preferable for the surface layer 100a to be occupied only by MgO, a structure in which MgO and NiO(II) are solid-solved, and/or a structure in which MgO and CoO(II) are solid-solved. Therefore, the surface layer 100a must contain at least cobalt, and in the discharged state, it must also contain lithium, and must have a path for the insertion and removal of lithium ions.
十分にリチウムイオンの挿入脱離の経路を確保するために、表層部１００ａはマグネシウムよりもコバルトの濃度が高いことが好ましい。たとえばマグネシウムの原子数（Ｍｇと記す）とコバルトの原子数（Ｃｏと記す）の比Ｍｇ／Ｃｏは０．６２以下であることが好ましい。また表層部１００ａはニッケルよりもコバルトの濃度が高いことが好ましい。また表層部１００ａはアルミニウムよりもコバルトの濃度が高いことが好ましい。また表層部１００ａはフッ素よりもコバルトの濃度が高いことが好ましい。 In order to ensure sufficient paths for the insertion and removal of lithium ions, it is preferable that the surface layer 100a has a higher concentration of cobalt than magnesium. For example, it is preferable that the ratio Mg/Co of the number of magnesium atoms (referred to as Mg) to the number of cobalt atoms (referred to as Co) is 0.62 or less. It is also preferable that the surface layer 100a has a higher concentration of cobalt than nickel. It is also preferable that the surface layer 100a has a higher concentration of cobalt than aluminum. It is also preferable that the surface layer 100a has a higher concentration of cobalt than fluorine.
さらにニッケルが多すぎるとリチウムイオンの拡散を阻害する恐れがあるため、表層部１００ａはニッケルよりもマグネシウムの濃度が高いことが好ましい。たとえばニッケルの原子数はマグネシウムの原子数の１／６以下であることが好ましい。 Furthermore, since too much nickel may hinder the diffusion of lithium ions, it is preferable that the surface layer 100a has a higher concentration of magnesium than nickel. For example, it is preferable that the number of nickel atoms is 1/6 or less of the number of magnesium atoms.
また添加元素の一部、特にマグネシウム、ニッケルおよびアルミニウムは、内部１００ｂよりも表層部１００ａの濃度が高いことが好ましいものの、マグネシウム、ニッケルおよびアルミニウムは内部１００ｂにもランダムかつ希薄に存在することが好ましい。マグネシウムおよびアルミニウムが内部１００ｂのリチウムサイトに適切な濃度で存在すると、上記と同様に層状岩塩型の結晶構造を保持しやすくできるといった効果がある。またニッケルが内部１００ｂに適切な濃度で存在すると、上記と同様にコバルトと酸素の８面体からなる層状構造のずれが抑制されうる。またマグネシウムとニッケルを併せて有する場合も上記と同様にマグネシウムの溶出を抑制する相乗効果が期待できる。 In addition, although it is preferable that some of the added elements, particularly magnesium, nickel, and aluminum, have a higher concentration in the surface layer 100a than in the interior 100b, it is also preferable that magnesium, nickel, and aluminum are present randomly and in a sparse manner in the interior 100b. When magnesium and aluminum are present at appropriate concentrations in the lithium sites in the interior 100b, it has the effect of making it easier to maintain the layered rock-salt crystal structure, as described above. When nickel is present at an appropriate concentration in the interior 100b, it is possible to suppress the shifting of the layered structure consisting of octahedra of cobalt and oxygen, as described above. When magnesium and nickel are present together, a synergistic effect of suppressing the elution of magnesium can be expected, as described above.
また上述のような添加元素の濃度勾配に起因して、内部１００ｂから、表面に向かって結晶構造が連続的に変化することが好ましい。または表層部１００ａと内部１００ｂの結晶の配向が一致または概略一致していることが好ましい。 Furthermore, due to the concentration gradient of the added element as described above, it is preferable that the crystal structure changes continuously from the interior 100b toward the surface. Alternatively, it is preferable that the crystal orientation of the surface layer 100a and the interior 100b are consistent or approximately consistent.
たとえば層状岩塩型の内部１００ｂから、岩塩型、または岩塩型と層状岩塩型の両方の特徴を有する表面および表層部１００ａに向かって結晶構造が連続的に変化することが好ましい。または岩塩型、または岩塩型と層状岩塩型の両方の特徴を有する表層部１００ａと、層状岩塩型の内部１００ｂの配向が一致または概略一致していることが好ましい。 For example, it is preferable that the crystal structure changes continuously from the interior 100b of the layered rock salt type toward the surface and surface layer 100a, which has characteristics of the rock salt type or both the rock salt type and the layered rock salt type. It is also preferable that the orientation of the surface layer 100a, which has characteristics of the rock salt type or both the rock salt type and the layered rock salt type, and the interior 100b of the layered rock salt type are consistent or approximately consistent.
なお本明細書等において、リチウムとコバルトをはじめとする遷移金属を含む複合酸化物が有する、空間群Ｒ−３ｍに帰属する層状岩塩型の結晶構造とは、陽イオンと陰イオンが交互に配列する岩塩型のイオン配列を有し、遷移金属とリチウムが規則配列して二次元平面を形成するため、リチウムの二次元的拡散が可能である結晶構造をいう。なお陽イオンまたは陰イオンの欠損等の欠陥があってもよい。また、層状岩塩型結晶構造は、厳密に言えば、岩塩型結晶の格子が歪んだ構造となっている場合がある。 In this specification, the layered rock-salt type crystal structure belonging to the space group R-3m, which is possessed by a composite oxide containing lithium and a transition metal such as cobalt, refers to a crystal structure having a rock-salt type ion arrangement in which cations and anions are arranged alternately, and in which the transition metal and lithium are regularly arranged to form a two-dimensional plane, allowing two-dimensional diffusion of lithium. Defects such as missing cations or anions may be present. Strictly speaking, the layered rock-salt type crystal structure may have a structure in which the lattice of the rock-salt type crystal is distorted.
また岩塩型の結晶構造とは、空間群Ｆｍ−３ｍをはじめとする立方晶系の結晶構造を有し、陽イオンと陰イオンが交互に配列している構造をいう。なお陽イオンまたは陰イオンの欠損があってもよい。 A rock-salt crystal structure is a structure that has a cubic crystal structure, such as the space group Fm-3m, in which cations and anions are arranged alternately. Note that there may be a deficiency of cations or anions.
また層状岩塩型と岩塩型の結晶構造の特徴の両方を有することは、電子線回折、ＴＥＭ像、断面ＳＴＥＭ像等によって判断することができる。 In addition, the fact that it has both layered rock salt type and rock salt type crystal structure characteristics can be determined by electron diffraction, TEM images, cross-sectional STEM images, etc.
岩塩型は陽イオンのサイトに区別がないが、層状岩塩型は結晶構造の陽イオンのサイトが２種あり、１つはリチウムが大半を占有し、もう１つは遷移金属が占有する。陽イオンの二次元平面と陰イオンの二次元平面とが交互に配列する積層構造は、岩塩型も層状岩塩型も同じである。この二次元平面を形成する結晶面に対応する電子線回折パターンの輝点の中で、中心のスポット（透過斑点）を原点０００とした際、中心のスポットに最も近い輝点は、理想的な状態の岩塩型ではたとえば（１１１）面、層状岩塩型ではたとえば（００３）面になる。たとえば岩塩型結晶構造のＭｇＯと層状岩塩型結晶構造のＬｉＣｏＯ２の電子線回折パターンを比較する場合、ＬｉＣｏＯ２の（００３）面の輝点間の距離は、ＭｇＯの（１１１）面の輝点間の距離のおよそ半分程度の距離に観察される。そのため分析領域に、たとえば岩塩型結晶構造のＭｇＯと層状岩塩型結晶構造のＬｉＣｏＯ２の２相を有する場合、電子線回折パターンでは、強い輝度の輝点と、弱い輝度の輝点とが交互に配列する面方位が存在する。岩塩型と層状岩塩型で共通する輝点は強い輝度となり、層状岩塩型のみで生じる輝点は弱い輝度となる。 The rock salt type has no distinction between the cation sites, but the layered rock salt type has two types of cation sites in the crystal structure, one of which is mostly occupied by lithium and the other by a transition metal. The layered structure in which two-dimensional planes of cations and two-dimensional planes of anions are alternately arranged is the same for both the rock salt type and the layered rock salt type. When the central spot (transmitted spot) of the bright spots of the electron diffraction pattern corresponding to the crystal planes forming this two-dimensional plane is set as the origin 000, the bright spot closest to the central spot is, for example, the (111) plane in the rock salt type in an ideal state, and, for example, the (003) plane in the layered rock salt type. For example, when comparing the electron diffraction patterns of MgO with a rock salt type crystal structure and LiCoO 2 with a layered rock salt type crystal structure, the distance between the bright spots on the (003) plane of LiCoO 2 is observed to be about half the distance between the bright spots on the (111) plane of MgO. Therefore, when the analysis area has two phases, for example, MgO with a rock-salt crystal structure and LiCoO2 with a layered rock-salt crystal structure, the electron beam diffraction pattern has a plane orientation in which bright spots with strong brightness and bright spots with weak brightness are arranged alternately. Bright spots common to the rock-salt type and layered rock-salt type have strong brightness, while bright spots occurring only in the layered rock-salt type have weak brightness.
また断面ＳＴＥＭ像等では、層状岩塩型の結晶構造をｃ軸に垂直な方向から観察したとき、強い輝度で観察される層と、弱い輝度で観察される層が交互に観察される。岩塩型の結晶構造は陽イオンのサイトに区別がないためこのような特徴はみられない。岩塩型の結晶構造と層状岩塩型の結晶構造の両方の特徴を有する結晶構造の場合、特定の結晶方位から観察すると、断面ＳＴＥＭ像等では強い輝度で観察される層と、弱い輝度で観察される層が交互に観察され、さらに弱い輝度の層、すなわちリチウム層の一部にリチウムより原子番号の大きい金属が存在する。 In addition, when a layered rock-salt crystal structure is observed from a direction perpendicular to the c-axis in cross-sectional STEM images, layers observed with strong brightness and layers observed with weak brightness are observed alternating. This characteristic is not seen in rock-salt crystal structures because there is no distinction in the cation sites. In the case of a crystal structure that has the characteristics of both rock-salt crystal structures and layered rock-salt crystal structures, when observed from a specific crystal orientation, layers observed with strong brightness and layers observed with weak brightness are observed alternating in cross-sectional STEM images, and furthermore, a metal with an atomic number higher than lithium is present in part of the weak brightness layer, i.e. the lithium layer.
層状岩塩型結晶、および岩塩型結晶の陰イオンは立方最密充填構造（面心立方格子構造）をとる。後述するＯ３’型および単斜晶Ｏ１（１５）結晶も、陰イオンは立方最密充填構造をとると推定される。そのため層状岩塩型結晶と岩塩型結晶が接するとき、陰イオンにより構成される立方最密充填構造の向きが揃う結晶面が存在する。 Layered rock salt crystals and the anions in rock salt crystals have a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that the anions in the O3' type and monoclinic O1(15) crystals described below also have a cubic close-packed structure. Therefore, when a layered rock salt crystal and a rock salt crystal come into contact, there are crystal faces where the cubic close-packed structure formed by the anions is oriented in the same direction.
または、以下のように説明することもできる。立方晶の結晶構造の｛１１１｝面における陰イオンは三角格子を有する。層状岩塩型結晶構造は空間群Ｒ−３ｍであって、菱面体構造であるが、構造の理解を容易にするため一般に複合六方格子で表現され、層状岩塩型結晶構造の（０００１）面は六角格子を有する。立方晶｛１１１｝面の三角格子は、層状岩塩型結晶構造の（０００１）面の六角格子と同様の原子配列を有する。両者の格子が整合性を持つことを、立方最密充填構造の向きが揃うということができる。 Alternatively, it can be explained as follows. The anions on the {111} plane of the cubic crystal structure have a triangular lattice. The layered rock-salt crystal structure is in space group R-3m and is a rhombohedral structure, but is generally represented as a composite hexagonal lattice to make the structure easier to understand, and the (0001) plane of the layered rock-salt crystal structure has a hexagonal lattice. The triangular lattice on the cubic {111} plane has the same atomic arrangement as the hexagonal lattice on the (0001) plane of the layered rock-salt crystal structure. The compatibility of the two lattices can be said to be the alignment of the cubic close-packed structures.
ただし、層状岩塩型結晶およびＯ３’型結晶の空間群はＲ−３ｍであり、岩塩型結晶の空間群Ｆｍ−３ｍ（一般的な岩塩型結晶の空間群）とは異なるため、上記の条件を満たす結晶面のミラー指数は層状岩塩型結晶構造およびＯ３’型結晶構造と、岩塩型結晶構造とでは異なる。本明細書では、層状岩塩型結晶構造、Ｏ３’型結晶構造および岩塩型結晶構造において、陰イオンにより構成される立方最密充填構造の向きが揃うとき、結晶の配向が概略一致する、と言う場合がある。また、結晶の配向が概略一致するような三次元的な構造上の類似性を有すること、または結晶学的に同じ配向であることをトポタキシ（ｔｏｐｏｔａｘｙ）という。 However, the space group of the layered rock salt crystal and O3' type crystal is R-3m, which is different from the space group Fm-3m (the space group of general rock salt crystals) of the rock salt crystal, so the Miller indices of the crystal planes that satisfy the above conditions are different between the layered rock salt crystal structure and O3' type crystal structure and the rock salt crystal structure. In this specification, when the orientation of the cubic close-packed structure formed by anions is aligned in the layered rock salt crystal structure, O3' type crystal structure, and rock salt crystal structure, it may be said that the crystal orientation is roughly the same. In addition, the three-dimensional structural similarity in which the crystal orientation is roughly the same, or the same crystallographic orientation, is called topotaxis.
二つの領域の結晶の配向が概略一致することは、ＴＥＭ（Ｔｒａｎｓｍｉｓｓｉｏｎ　Ｅｌｅｃｔｒｏｎ　Ｍｉｃｒｏｓｃｏｐｅ、透過型電子顕微鏡）像、ＳＴＥＭ（Ｓｃａｎｎｉｎｇ　Ｔｒａｎｓｍｉｓｓｉｏｎ　Ｅｌｅｃｔｒｏｎ　Ｍｉｃｒｏｓｃｏｐｅ、走査型透過電子顕微鏡）像、ＨＡＡＤＦ−ＳＴＥＭ（Ｈｉｇｈ−ａｎｇｌｅ　Ａｎｎｕｌａｒ　Ｄａｒｋ　Ｆｉｅｌｄ　Ｓｃａｎｎｉｎｇ　ＴＥＭ、高角散乱環状暗視野走査透過電子顕微鏡）像、ＡＢＦ−ＳＴＥＭ（Ａｎｎｕｌａｒ　Ｂｒｉｇｈｔ−Ｆｉｅｌｄ　Ｓｃａｎｎｉｎｇ　Ｔｒａｎｓｍｉｓｓｉｏｎ　Ｅｌｅｃｔｒｏｎ　Ｍｉｃｒｏｓｃｏｐｅ、環状明視野走査透過電子顕微鏡）像、電子線回折パターン、ＴＥＭ像およびＳＴＥＭ像等のＦＦＴパターン等から判断することができる。ＸＲＤ（Ｘ−ｒａｙ　Ｄｉｆｆｒａｃｔｉｏｎ、Ｘ線回折）、電子線回折、中性子線回折等も判断の材料にすることができる。 That the crystal orientations in the two regions roughly coincide can be determined from TEM (Transmission Electron Microscope) images, STEM (Scanning Transmission Electron Microscope) images, HAADF-STEM (High-angle Annular Dark Field Scanning TEM) images, ABF-STEM (Annular Bright-Field Scanning Transmission Electron Microscope) images, electron beam diffraction patterns, and FFT patterns of TEM and STEM images. XRD (X-ray diffraction), electron diffraction, neutron diffraction, etc. can also be used as a basis for judgment.
図２に、層状岩塩型結晶ＬＲＳと岩塩型結晶ＲＳの配向が概略一致しているＴＥＭ像の例を示す。ＴＥＭ像、ＳＴＥＭ像、ＨＡＡＤＦ−ＳＴＥＭ像、ＡＢＦ−ＳＴＥＭ像等では、結晶構造を反映した像が得られる。 Figure 2 shows an example of a TEM image in which the orientation of the layered rock salt crystal LRS and the rock salt crystal RS roughly coincides. Images reflecting the crystal structure are obtained in TEM images, STEM images, HAADF-STEM images, ABF-STEM images, etc.
たとえばＴＥＭの高分解能像等では、結晶面に由来するコントラストが得られる。電子線の回折および干渉によって、たとえば層状岩塩型の複合六方格子のｃ軸と垂直に電子線が入射した場合、（０００３）面に由来するコントラストが明るい帯（明るいストリップ）と暗い帯（暗いストリップ）の繰り返しとして得られる。そのためＴＥＭ像において明線と暗線の繰り返しが観察され、明線同士（たとえば図２に示すＬＲＳとＬＬＲＳ）の角度が５度以下、または２．５度以下である場合、結晶面が概略一致している、すなわち結晶の配向が概略一致していると判断することができる。同様に、暗線同士の角度が５度以下、または２．５度以下である場合も、結晶の配向が概略一致していると判断することができる。 For example, in a high-resolution TEM image, a contrast originating from a crystal plane is obtained. When an electron beam is incident perpendicularly to the c-axis of a layered rock-salt composite hexagonal lattice, for example, due to the diffraction and interference of the electron beam, the contrast originating from the (0003) plane is obtained as a repetition of bright bands (bright strips) and dark bands (dark strips). Therefore, when a repetition of bright lines and dark lines is observed in a TEM image and the angle between the bright lines (for example, L RS and L LRS shown in FIG. 2) is 5 degrees or less or 2.5 degrees or less, it can be determined that the crystal planes are roughly aligned, that is, the crystal orientations are roughly aligned. Similarly, when the angle between the dark lines is 5 degrees or less or 2.5 degrees or less, it can also be determined that the crystal orientations are roughly aligned.
またＨＡＡＤＦ−ＳＴＥＭ像では、原子番号に比例したコントラストが得られ、原子番号が大きい元素ほど明るく観察される。たとえば空間群Ｒ−３ｍに属する層状岩塩型のコバルト酸リチウムの場合、コバルト（原子番号２７）が最も原子番号が大きいため、コバルト原子の位置で電子線が強く散乱され、コバルト原子の配列が明線もしくは強い輝度の点の配列として観察される。そのため層状岩塩型の結晶構造を有するコバルト酸リチウムをｃ軸と垂直に観察した場合、ｃ軸と垂直にコバルト原子の配列が明線もしくは強い輝度の点の配列として観察され、リチウム原子、酸素原子の配列は暗線もしくは輝度の低い領域として観察される。コバルト酸リチウムの添加元素としてフッ素（原子番号９）およびマグネシウム（原子番号１２）を有する場合も同様である。 In addition, in HAADF-STEM images, contrast proportional to the atomic number is obtained, and elements with higher atomic numbers are observed brighter. For example, in the case of layered rock-salt lithium cobalt oxide belonging to the space group R-3m, cobalt (atomic number 27) has the highest atomic number, so the electron beam is strongly scattered at the position of the cobalt atom, and the arrangement of the cobalt atoms is observed as a bright line or an arrangement of highly bright dots. Therefore, when lithium cobalt oxide having a layered rock-salt crystal structure is observed perpendicular to the c-axis, the arrangement of the cobalt atoms is observed perpendicular to the c-axis as a bright line or an arrangement of highly bright dots, and the arrangement of the lithium atoms and oxygen atoms is observed as a dark line or a region of low brightness. The same is true when fluorine (atomic number 9) and magnesium (atomic number 12) are added to the lithium cobalt oxide.
そのためＨＡＡＤＦ−ＳＴＥＭ像において、結晶構造の異なる二つの領域で明線と暗線の繰り返しが観察され、明線同士の角度が５度以下、または２．５度以下である場合、原子の配列が概略一致している、すなわち結晶の配向が概略一致していると判断することができる。同様に、暗線同士の角度が５度以下、または２．５度以下である場合も、結晶の配向が概略一致していると判断することができる。 Therefore, in a HAADF-STEM image, when repeated bright and dark lines are observed in two regions with different crystal structures and the angle between the bright lines is 5 degrees or less or 2.5 degrees or less, it can be determined that the atomic arrangements are roughly consistent, i.e., the crystal orientations are roughly consistent. Similarly, when the angle between the dark lines is 5 degrees or less or 2.5 degrees or less, it can be determined that the crystal orientations are roughly consistent.
なおＡＢＦ−ＳＴＥＭでは原子番号が小さい元素ほど明るく観察されるが、原子番号に応じたコントラストが得られる点ではＨＡＡＤＦ−ＳＴＥＭと同様であるため、ＨＡＡＤＦ−ＳＴＥＭ像と同様に結晶の配向を判断することができる。 In ABF-STEM, elements with smaller atomic numbers are observed brighter, but like HAADF-STEM, it is possible to obtain contrast according to the atomic number, so the crystal orientation can be determined in the same way as with HAADF-STEM images.
図３Ａに層状岩塩型結晶ＬＲＳと岩塩型結晶ＲＳの配向が概略一致しているＳＴＥＭ像の例を示す。岩塩型結晶ＲＳの領域のＦＦＴパターンを図３Ｂに、層状岩塩型結晶ＬＲＳの領域のＦＦＴパターンを図３Ｃに示す。図３Ｂおよび図３Ｃの左に組成、ＪＣＰＤＳのカードナンバー、およびＪＣＰＤＳカードのデータから計算されるｄ値および角度を示す。右に実測値を示す。Ｏを付したスポットは０次回折である。 Figure 3A shows an example of an STEM image in which the orientations of the layered rock-salt crystal LRS and the rock-salt crystal RS are roughly the same. Figure 3B shows the FFT pattern of the region of the rock-salt crystal RS, and Figure 3C shows the FFT pattern of the region of the layered rock-salt crystal LRS. The composition, JCPDS card number, and d-values and angles calculated from the data on the JCPDS card are shown on the left of Figures 3B and 3C. The measured values are shown on the right. The spot marked with an O is the zeroth order diffraction.
図３ＢでＡを付したスポットは立方晶の１１−１反射に由来するものである。図３ＣでＡを付したスポットは層状岩塩型の０００３反射に由来するものである。図３Ｂおよび図３Ｃから、立方晶の１１−１反射の方位と、層状岩塩型の０００３反射の方位と、が概略一致していることがわかる。すなわち図３ＢのＡＯを通る直線と、図３ＣのＡＯを通る直線と、が概略平行であることがわかる。ここでいう概略一致および概略平行とは、角度が５度以下、または２．５度以下であることをいう。 The spot marked A in Figure 3B is due to the 11-1 reflection of the cubic crystal. The spot marked A in Figure 3C is due to the 0003 reflection of the layered rock salt type. From Figures 3B and 3C, it can be seen that the orientation of the 11-1 reflection of the cubic crystal and the orientation of the 0003 reflection of the layered rock salt type roughly coincide. In other words, it can be seen that the line passing through AO in Figure 3B is roughly parallel to the line passing through AO in Figure 3C. Here, roughly coincident and roughly parallel mean that the angle is 5 degrees or less, or 2.5 degrees or less.
このようにＦＦＴパターンおよび電子線回折パターンでは、層状岩塩型結晶と岩塩型結晶の配向が概略一致していると、層状岩塩型の〈０００３〉方位と、岩塩型の〈１１−１〉方位と、が概略一致する場合がある。このとき、これらの逆格子点はスポット状であること、つまり他の逆格子点と連続していないことが好ましい。逆格子点がスポット状で、他の逆格子点と連続していないことは、結晶性が高いことを意味する。 In this way, in the FFT pattern and the electron diffraction pattern, if the orientations of the layered rock salt crystal and the rock salt crystal roughly match, the <0003> orientation of the layered rock salt type may roughly match the <11-1> orientation of the rock salt type. In this case, it is preferable that these reciprocal lattice points are spot-like, that is, not continuous with other reciprocal lattice points. The fact that the reciprocal lattice points are spot-like and not continuous with other reciprocal lattice points indicates high crystallinity.
また、上述のように立方晶の１１−１反射の方位と、層状岩塩型の０００３反射の方位と、が概略一致している場合、電子線の入射方位によっては、層状岩塩型の０００３反射の方位とは異なる逆格子空間上に、層状岩塩型の０００３反射由来ではないスポットが観測されることがある。例えば図３ＣでＢを付したスポットは、層状岩塩型の１０１４反射に由来するものである。これは、層状岩塩型の０００３反射由来の逆格子点（図３ＣのＡ）の方位から、５２°以上５６°以下の角度であり（すなわち∠ＡＯＢが５２°以上５６°以下であり）、ｄが０．１９ｎｍ以上０．２１ｎｍ以下の箇所に観測されることがある。なおこの指数は一例であり、必ずしもこれに一致している必要は無い。例えば、０００３と１０１４と等価な逆格子点でも良い。 Also, as described above, when the orientation of the 11-1 reflection of the cubic crystal and the orientation of the 0003 reflection of the layered rock salt type are roughly the same, depending on the incidence orientation of the electron beam, a spot not originating from the 0003 reflection of the layered rock salt type may be observed in a reciprocal lattice space different from the orientation of the 0003 reflection of the layered rock salt type. For example, the spot marked B in FIG. 3C is originating from the 1014 reflection of the layered rock salt type. This may be observed at an angle of 52° to 56° (i.e., ∠AOB is 52° to 56°) from the orientation of the reciprocal lattice point (A in FIG. 3C) originating from the 0003 reflection of the layered rock salt type, and at a location where d is 0.19 nm to 0.21 nm. Note that this index is just an example, and does not necessarily have to be the same. For example, a reciprocal lattice point equivalent to 0003 and 1014 may be used.
同様に立方晶の１１−１反射が観測された方位とは別の逆格子空間上に、立方晶の１１−１反射由来ではないスポットが観測されることがある。例えば、図３ＢでＢを付したスポットは、立方晶の２００反射に由来するものである。これは、立方晶の１１−１由来の反射（図３ＢのＡ）の方位から、５４°以上５６°以下の角度である（すなわち∠ＡＯＢが５４°以上５６°以下である）箇所に回折スポットが観測されることがある。なおこの指数は一例であり、必ずしもこれに一致している必要は無い。例えば、１１−１と２００と等価な逆格子点でも良い。 Similarly, spots not originating from the 11-1 reflection of a cubic crystal may be observed in a reciprocal lattice space other than the orientation where the 11-1 reflection of a cubic crystal is observed. For example, the spot marked B in FIG. 3B originates from the 200 reflection of a cubic crystal. This is because a diffraction spot may be observed at an angle of 54° to 56° (i.e., ∠AOB is 54° to 56°) from the orientation of the reflection (A in FIG. 3B) originating from the 11-1 of a cubic crystal. Note that this index is only an example, and does not necessarily have to match this. For example, a reciprocal lattice point equivalent to 11-1 and 200 may be used.
なお、コバルト酸リチウムをはじめとする層状岩塩型結晶構造の正極活物質は、（０００３）面およびこれと等価な面、並びに（１０−１４）面およびこれと等価な面が結晶面として現れやすいことが知られている。そのため例えば（０００３）面をＴＥＭ等で観察する場合は、まずＳＥＭ等で（０００３）面と予想される結晶面が観察される正極活物質粒子を選び、たとえばＴＥＭ等において電子線が［１２−１０］入射として（０００３）面を観察できるように当該正極活物質粒子をＦＩＢ（Ｆｏｃｕｓｅｄ　Ｉｏｎ　Ｂｅａｍ）等で薄片加工することが可能である。結晶の配向の一致について判断したいときは、層状岩塩型の（０００３）面が観察しやすいよう薄片化することが好ましい。 It is known that positive electrode active materials with a layered rock salt crystal structure, such as lithium cobalt oxide, tend to have the (0003) plane and its equivalent planes, as well as the (10-14) plane and its equivalent planes, as crystal planes. For example, when observing the (0003) plane with a TEM or the like, first select positive electrode active material particles in which a crystal plane expected to be the (0003) plane is observed with a SEM or the like, and then the positive electrode active material particles can be processed into thin slices with a FIB (Focused Ion Beam) or the like so that the (0003) plane can be observed with an electron beam incident at [12-10] in the TEM or the like. When it is desired to determine the coincidence of the crystal orientations, it is preferable to slice the layered rock salt type (0003) plane so that it is easy to observe.
また正極活物質１００の内部１００ｂは、欠陥の密度が少ないことが好ましい。欠陥には線欠陥、面欠陥、及び点欠陥が含まれる。線欠陥の一部を転位と呼ぶことがある。また正極活物質１００は、ＸＲＤにより測定される結晶子サイズが大きいことが好ましい。換言すれば内部１００ｂは結晶性が高いことが好ましい。また正極活物質１００の表面はなめらかであることが好ましい。これらの特徴は、二次電池に用いた際の正極活物質１００の信頼性を支える重要な要素である。正極活物質の信頼性が高ければ二次電池の充電電圧の上限を高くすることができ、充放電容量の高い二次電池とすることができる。 Furthermore, the interior 100b of the positive electrode active material 100 preferably has a low density of defects. Defects include line defects, planar defects, and point defects. Some line defects are sometimes called dislocations. Furthermore, the positive electrode active material 100 preferably has a large crystallite size measured by XRD. In other words, the interior 100b preferably has high crystallinity. Furthermore, the surface of the positive electrode active material 100 preferably is smooth. These characteristics are important factors that support the reliability of the positive electrode active material 100 when used in a secondary battery. If the reliability of the positive electrode active material is high, the upper limit of the charging voltage of the secondary battery can be increased, resulting in a secondary battery with a high charge/discharge capacity.
内部１００ｂの転位はたとえばＴＥＭで観察することができる。欠陥の密度が十分に少ない場合、観察試料の特定の１μｍ四方に転位が観察されない場合がある。 Dislocations in the interior 100b can be observed, for example, by TEM. If the density of defects is sufficiently low, dislocations may not be observed in a specific 1 μm square of the observed sample.
結晶子サイズが大きいほど、後述するようにＬｉｘＣｏＯ２中のｘが１より小さい状態においてＯ３’型の結晶構造等が保たれやすく、ｃ軸長の短縮が抑制されやすい。 As the crystallite size is larger, as described below, when x in Li x CoO 2 is smaller than 1, the O3′ type crystal structure is more easily maintained, and shortening of the c-axis length is more easily suppressed.
ＴＥＭにより観察される欠陥、代表的には線欠陥が少ないほど、ＸＲＤにより測定される結晶子サイズは大きくなると考えられる。 The fewer defects, typically line defects, observed by TEM, the larger the crystallite size measured by XRD is believed to be.
結晶子サイズを算出する際のＸＲＤの回折パターンは、正極活物質のみの状態で取得することが好ましいが、正極活物質に加えて集電体、バインダ及び導電材等を含む正極の状態で取得してもよい。ただし正極の状態では、作製工程における加圧等の影響で、正極活物質の粒子が、当該正極活物質の粒子の結晶面が一方向に揃うように配向している可能性がある。配向が強いと結晶子サイズが正確に算出できない恐れがあるため、正極から正極活物質層を取出し、溶媒等を用いて正極活物質層中のバインダ等をある程度取り除いてから試料ホルダに充填する等の方法でＸＲＤの回折パターンを取得することがより好ましい。またシリコン無反射板上にグリースを塗布し、正極活物質等の粉体サンプルを当該シリコン無反射板に付着させるといった方法もある。 The XRD diffraction pattern for calculating the crystallite size is preferably obtained from only the positive electrode active material, but may also be obtained from the positive electrode containing the positive electrode active material, current collector, binder, conductive material, etc. However, in the positive electrode state, the particles of the positive electrode active material may be oriented so that the crystal planes of the particles of the positive electrode active material are aligned in one direction due to the influence of pressure during the manufacturing process. If the orientation is too strong, the crystallite size may not be calculated accurately, so it is more preferable to obtain the XRD diffraction pattern by removing the positive electrode active material layer from the positive electrode, removing the binder, etc. in the positive electrode active material layer to a certain extent using a solvent, etc., and then filling the sample holder. Another method is to apply grease to a silicon non-reflective plate and attach a powder sample of the positive electrode active material, etc. to the silicon non-reflective plate.
結晶子サイズの算出には、たとえばＢｒｕｋｅｒ　Ｄ８　ＡＤＶＡＮＣＥを用い、Ｘ線源としてＣｕＫα線、２θは１５°以上９０°以下、ｉｎｃｒｅｍｅｎｔ　０．００５、検出器をＬＹＮＸＥＹＥ　ＸＥ−Ｔとして取得した回折パターンと、コバルト酸リチウムの文献値としてＩＣＳＤ　ｃｏｌｌ．ｃｏｄｅ．１７２９０９を用いることができる。結晶構造解析ソフトウェアとしてＤＩＦＦＲＡＣ．ＴＯＰＡＳ　ｖｅｒ．６を用いて解析を行うことができ、たとえば以下のように設定することができる。
Ｅｍｉｓｓｉｏｎ　Ｐｒｏｆｉｌｅ：ＣｕＫａ５．ｌａｍ
Ｂａｃｋｇｒｏｕｎｄ：Ｃｈｅｂｙｃｈｅｖ　ｐｏｌｙｎｏｍｉａｌ、５次
Ｉｎｓｔｒｕｍｅｎｔ
　Ｐｒｉｍａｒｙ　ｒａｄｉｕｓ：２８０ｍｍ
　Ｓｅｃｏｎｄａｒｙ　ｒａｄｉｕｓ：２８０ｍｍ
　Ｌｉｎｅａｒ　ＰＳＤ　２Ｔｈ　ａｎｇｕｌａｒ　ｒａｎｇｅ：２．９
　ＦＤＳ　ａｎｇｌｅ：０．３
Ｆｕｌｌ　Ａｘｉａｌ　Ｃｏｎｖｏｌｕｔｉｏｎ
　Ｆｉｌａｍｅｎｔ　ｌｅｎｇｔｈ：１２ｍｍ
　Ｓａｍｐｌｅ　ｌｅｎｇｔｈ：１５ｍｍ
　Ｒｅｃｅｉｖｉｎｇ　Ｓｌｉｔ　ｌｅｎｇｔｈ：１２ｍｍ
　Ｐｒｉｍａｒｙ　Ｓｏｌｌｅｒｓ：２．５
　Ｓｅｃｏｎｄａｒｙ　Ｓｏｌｌｅｒｓ：２．５
Ｃｏｒｒｅｃｔｉｏｎｓ
　Ｓｐｅｃｉｍｅｎ　ｄｉｓｐｌａｃｅｍｅｎｔ：Ｒｅｆｉｎｅ
　ＬＰ　Ｆａｃｔｏｒ：０ The crystallite size can be calculated using, for example, Bruker D8 ADVANCE, CuKα radiation as the X-ray source, 2θ between 15° and 90°, increment 0.005, LYNXEYE XE-T as the detector, and the diffraction pattern obtained using ICSD coll. code. 172909 as the literature value of lithium cobalt oxide. Analysis can be performed using DIFFRAC. TOPAS ver. 6 as the crystal structure analysis software, and can be set, for example, as follows.
Emission Profile: CuKa5. lam
Background: Chebychev polynomial, 5th Instrument
Primary radius: 280 mm
Secondary radius: 280 mm
Linear PSD 2Th angular range: 2.9
FDS angle: 0.3
Full Axial Convolution
Filament length: 12mm
Sample length: 15 mm
Receiving Slit Length: 12mm
Primary Sollers: 2.5
Secondary Sollers: 2.5
Corrections
Special displacement: Refine
LP Factor: 0
上記の手法で算出された結晶子サイズであるＬＶｏｌ−ＩＢの値を結晶子サイズとして採用することが好ましい。なお算出されたＰｒｅｆｅｒｒｅｄ　Ｏｒｉｅｎｔａｔｉｏｎが０．８未満の場合、サンプルの配向が強すぎるため当該サンプルは結晶子サイズを求めるには適さない場合がある。 It is preferable to use the value of LVol-IB, which is the crystallite size calculated by the above method, as the crystallite size. Note that if the calculated Preferred Orientation is less than 0.8, the orientation of the sample may be too strong and the sample may not be suitable for determining the crystallite size.
≪ＬｉｘＣｏＯ２中のｘが小さい状態≫
正極活物質１００は、放電状態において上述のような添加元素の分布及び／又は結晶構造を有することに起因して、ＬｉｘＣｏＯ２中のｘが小さい状態での結晶構造が、従来の正極活物質と異なる。なおここでｘが小さいとは、０．１＜ｘ≦０．２４をいうこととする。 <<When x in Li x CoO 2 is small>>
The positive electrode active material 100 has the above-mentioned distribution of the additive elements and/or the crystal structure in the discharged state, and therefore the crystal structure when x in Li x CoO 2 is small is different from that of conventional positive electrode active materials. Here, small x means 0.1<x≦0.24.
図４乃至図１０を用いて、ＬｉｘＣｏＯ２中のｘ（ｘ　ｉｎ　ＬｉｘＣｏＯ２）の変化に伴う結晶構造の変化について、従来の正極活物質と正極活物質１００を比較しながら説明する。 4 to 10, the change in crystal structure accompanying the change in x in Li x CoO 2 (x in Li x CoO 2 ) will be described while comparing a conventional positive electrode active material with the positive electrode active material 100. FIG.
従来の正極活物質の結晶構造の変化を図５に示す。図５に示す従来の正極活物質は、特に添加元素を有さないコバルト酸リチウム（ＬｉＣｏＯ２）である。特に添加元素を有さないコバルト酸リチウムの結晶構造の変化は非特許文献１乃至非特許文献３等に述べられている。 The change in the crystal structure of a conventional positive electrode active material is shown in Fig. 5. The conventional positive electrode active material shown in Fig. 5 is lithium cobalt oxide ( LiCoO2 ) that does not have any added elements. The change in the crystal structure of lithium cobalt oxide that does not have any added elements is described in Non-Patent Documents 1 to 3, etc.
図５にＲ−３ｍ　Ｏ３を付してＬｉｘＣｏＯ２中のｘ＝１のコバルト酸リチウムが有する結晶構造を示す。この結晶構造はリチウムが８面体（Ｏｃｔａｈｅｄｒａｌ）サイトを占有し、ユニットセル中にＣｏＯ２層が３層存在する。そのためこの結晶構造をＯ３型結晶構造と呼ぶ場合がある。なお、ＣｏＯ２層とはコバルトに酸素が６配位した８面体構造が、稜共有の状態で平面に連続した構造をいうこととする。これをコバルトと酸素の８面体からなる層、という場合もある。 FIG. 5 shows the crystal structure of lithium cobalt oxide with x=1 in Li x CoO 2 , with R-3m O3. In this crystal structure, lithium occupies an octahedral site, and there are three CoO 2 layers in the unit cell. Therefore, this crystal structure is sometimes called an O3 type crystal structure. Note that the CoO 2 layer refers to a structure in which an octahedral structure in which oxygen is six-coordinated to cobalt is continuous on a plane in an edge-sharing state. This is sometimes called a layer consisting of an octahedron of cobalt and oxygen.
また従来のコバルト酸リチウムは、ｘ＝０．５程度のときリチウムの対称性が高まり、単斜晶系の空間群Ｐ２／ｍに帰属する結晶構造を有することが知られている。この構造はユニットセル中にＣｏＯ２層が１層存在する。そのためＯ１型、または単斜晶（図中ｍｏｎｏｃｌｉｎｉｃと記す）Ｏ１型と呼ぶ場合がある。 It is also known that conventional lithium cobalt oxide has a crystal structure that is highly symmetrical with lithium when x is about 0.5, and belongs to the monoclinic space group P2/m. This structure has one CoO2 layer in the unit cell. Therefore, it is sometimes called O1 type or monoclinic (denoted as monoclinic in the figure) O1 type.
またｘ＝０のときの正極活物質は、三方晶系の空間群Ｐ−３ｍ１の結晶構造を有し、やはりユニットセル中にＣｏＯ２層が１層存在する。そのためこの結晶構造を、Ｏ１型、または三方晶（図中ｔｒｉｇｏｎａｌと記す）Ｏ１型と呼ぶ場合がある。また三方晶を複合六方格子に変換し、六方晶Ｏ１型と呼ぶ場合もある。 In addition, when x = 0, the positive electrode active material has a crystal structure of the trigonal space group P-3m1, and one CoO2 layer is present in the unit cell. Therefore, this crystal structure may be called O1 type or trigonal (denoted as trigonal in the figure) O1 type. In addition, the trigonal crystal may be converted to a composite hexagonal lattice and called a hexagonal O1 type.
またｘ＝０．１２程度のときの従来のコバルト酸リチウムは、空間群Ｒ−３ｍの結晶構造を有する。この構造は、三方晶Ｏ１型のようなＣｏＯ２の構造と、Ｒ−３ｍ　Ｏ３のようなＬｉＣｏＯ２の構造と、が交互に積層された構造ともいえる。そのためこの結晶構造を、Ｈ１−３型結晶構造（図中Ｈ１−３と記す）と呼ぶ場合がある。なお、実際のリチウムイオンの挿入脱離が正極活物質内で均一に生じるとは限らず、リチウムの濃度がまだらになりうるため、実験的にはｘ＝０．２５程度からＨ１−３型結晶構造が観測される。また実際にはＨ１−３型結晶構造は、ユニットセルあたりのコバルト原子の数が他の構造の２倍となっている。しかし図５をはじめ本明細書では、他の結晶構造と比較しやすくするためＨ１−３型結晶構造のｃ軸をユニットセルの１／２にした図で示すこととする。 Furthermore, conventional lithium cobalt oxide when x=0.12 has a crystal structure of space group R-3m. This structure can be said to be a structure in which a CoO 2 structure such as trigonal O1 type and a LiCoO 2 structure such as R-3m O3 are alternately stacked. Therefore, this crystal structure may be called an H1-3 type crystal structure (H1-3 in the figure). Note that the actual insertion and desorption of lithium ions does not necessarily occur uniformly in the positive electrode active material, and the concentration of lithium may become uneven, so experimentally, an H1-3 type crystal structure is observed from about x=0.25. In addition, in reality, the number of cobalt atoms per unit cell in the H1-3 type crystal structure is twice that of other structures. However, in FIG. 5 and other documents, in order to make it easier to compare with other crystal structures, the c-axis of the H1-3 type crystal structure is shown in a figure in which the c-axis is 1/2 of the unit cell.
Ｈ１−３型結晶構造は一例として、非特許文献３に記載があるように、ユニットセルにおけるコバルトと酸素の座標を、Ｃｏ（０，０，０．４２１５０±０．０００１６）、Ｏ１（０，０，０．２７６７１±０．０００４５）、Ｏ２（０，０，０．１１５３５±０．０００４５）と表すことができる。Ｏ１およびＯ２はそれぞれ酸素原子である。正極活物質が有する結晶構造をいずれのユニットセルを用いて表すべきかは、例えばＸＲＤパターンのリートベルト解析により判断することができる。この場合はＧＯＦ（ｇｏｏｄｎｅｓｓ　ｏｆ　ｆｉｔ）の値が小さくなるユニットセルを採用すればよい。 As an example of the H1-3 type crystal structure, as described in Non-Patent Document 3, the coordinates of cobalt and oxygen in the unit cell can be expressed as Co (0,0,0.42150±0.00016), O1 (0,0,0.27671±0.00045), and O2 (0,0,0.11535±0.00045). O1 and O2 are oxygen atoms. Which unit cell should be used to express the crystal structure of the positive electrode active material can be determined, for example, by Rietveld analysis of the XRD pattern. In this case, it is sufficient to adopt the unit cell that results in the smallest GOF (goodness of fit) value.
ＬｉｘＣｏＯ２中のｘが０．２４以下になるような充電と、放電とを繰り返すと、従来のコバルト酸リチウムはＨ１−３型結晶構造と、放電状態のＲ−３ｍ　Ｏ３の構造と、の間で結晶構造の変化（つまり非平衡な相変化）を繰り返すことになる。 When charging and discharging are repeated such that x in Li x CoO 2 becomes 0.24 or less, conventional lithium cobalt oxide repeatedly changes its crystal structure (i.e., undergoes a non-equilibrium phase change) between the H1-3 type crystal structure and the R-3m O 3 structure in the discharged state.
しかしながら、これらの２つの結晶構造は、ＣｏＯ２層のずれが大きい。図５に点線および矢印で示すように、Ｈ１−３型結晶構造では、ＣｏＯ２層が放電状態のＲ−３ｍ　Ｏ３から大きくずれている。このようなダイナミックな構造変化は、結晶構造の安定性に悪影響を与えうる。 However, these two crystal structures have a large deviation in the CoO2 layer. As shown by the dotted line and arrow in Fig. 5, in the H1-3 type crystal structure, the CoO2 layer is significantly deviated from that of R-3mO3 in the discharged state. Such a dynamic structural change can adversely affect the stability of the crystal structure.
さらにこれらの２つの結晶構造は体積の差も大きい。同数のコバルト原子あたりで比較した場合、Ｈ１−３型結晶構造と放電状態のＲ−３ｍ　Ｏ３型結晶構造の体積の差は３．５％を超え、代表的には３．９％以上である。 Furthermore, there is a large difference in volume between these two crystal structures. When compared per the same number of cobalt atoms, the difference in volume between the H1-3 crystal structure and the R-3m O3 crystal structure in a discharged state exceeds 3.5%, typically 3.9% or more.
加えて、Ｈ１−３型結晶構造が有する、三方晶Ｏ１型のようにＣｏＯ２層が連続した構造は不安定である可能性が高い。 In addition, the H1-3 type crystal structure has a structure in which two CoO layers are continuous, such as the trigonal O1 type, and is therefore likely to be unstable.
そのため、ｘが０．２４以下になるような充電と、放電を繰り返すと従来のコバルト酸リチウムの結晶構造は崩れていく。結晶構造の崩れが、サイクル特性の悪化を引き起こす。これは、結晶構造が崩れることで、リチウムが安定して存在できるサイトが減少し、またリチウムイオンの挿入脱離が難しくなるためである。 As a result, the crystal structure of conventional lithium cobalt oxide breaks down when it is repeatedly charged and discharged so that x is 0.24 or less. The breakdown of the crystal structure leads to a deterioration in cycle characteristics. This is because the breakdown of the crystal structure reduces the number of sites where lithium can exist stably and makes it difficult to insert and remove lithium ions.
一方、図４に示す正極活物質１００では、ＬｉｘＣｏＯ２中のｘが１の放電状態と、ｘが０．２４以下の状態における結晶構造の変化が従来の正極活物質よりも少ない。より具体的には、ｘが１の状態と、ｘが０．２４以下の状態におけるＣｏＯ２層のずれを小さくすることができる。同じ数のコバルト原子を有する正極活物質１００と従来の正極活物質を比較すると、正極活物質１００の体積変化は従来の正極活物質の体積変化より小さい。よって、正極活物質１００は、ｘが０．２４以下になるような充電と放電とを繰り返しても結晶構造が崩れにくく、優れたサイクル特性を実現することができる。また、正極活物質１００は、ＬｉｘＣｏＯ２中のｘが０．２４以下の状態において従来の正極活物質よりも安定な結晶構造を取り得る。よって、正極活物質１００は、ＬｉｘＣｏＯ２中のｘが０．２４以下の状態を保持した場合において、ショートが生じづらい。そのような場合には二次電池の安全性がより向上し好ましい。 On the other hand, in the positive electrode active material 100 shown in FIG. 4, the change in the crystal structure in the discharge state where x in Li x CoO 2 is 1 and the state where x is 0.24 or less is smaller than that of the conventional positive electrode active material. More specifically, the deviation of the CoO 2 layer in the state where x is 1 and the state where x is 0.24 or less can be reduced. When comparing the positive electrode active material 100 having the same number of cobalt atoms with the conventional positive electrode active material, the volume change of the positive electrode active material 100 is smaller than the volume change of the conventional positive electrode active material. Therefore, the positive electrode active material 100 is less likely to collapse in crystal structure even when charging and discharging such that x is 0.24 or less are repeated, and excellent cycle characteristics can be realized. In addition, the positive electrode active material 100 can have a more stable crystal structure than the conventional positive electrode active material in the state where x in Li x CoO 2 is 0.24 or less. Therefore, the positive electrode active material 100 is less likely to cause a short circuit when the state where x in Li x CoO 2 is 0.24 or less is maintained. In such a case, the safety of the secondary battery is further improved, which is preferable.
ＬｉｘＣｏＯ２中のｘが１、０．２程度および０．１５程度のときに正極活物質１００の内部１００ｂが有する結晶構造を図４に示す。内部１００ｂは正極活物質１００の体積の大半を占め、充放電に大きく寄与する部分であるため、ＣｏＯ２層のずれおよび体積の変化が最も問題となる部分といえる。 4 shows the crystal structure of the interior 100b of the positive electrode active material 100 when x in Li x CoO 2 is 1, approximately 0.2, and approximately 0.15. The interior 100b occupies most of the volume of the positive electrode active material 100 and is the part that contributes greatly to charge and discharge, so it can be said that the displacement of the CoO 2 layer and the change in volume are the most problematic parts.
正極活物質１００はｘ＝１のとき、従来のコバルト酸リチウムと同じＲ−３ｍ　Ｏ３の結晶構造を有する。 When x = 1, the positive electrode active material 100 has the same crystal structure as conventional lithium cobalt oxide, R-3m O3.
しかし正極活物質１００は、従来のコバルト酸リチウムがＨ１−３型結晶構造となるようなｘが０．２４以下、たとえば０．２程度および０．１５程度のとき、これと異なる構造の結晶を有する。 However, the positive electrode active material 100 has a different crystal structure from that of conventional lithium cobalt oxide when x is 0.24 or less, for example, about 0.2 and about 0.15, in which case the lithium cobalt oxide has an H1-3 type crystal structure.
ｘ＝０．２程度のときの正極活物質１００は、三方晶系の空間群Ｒ−３ｍに帰属される結晶構造を有する。これはＣｏＯ２層の対称性がＯ３と同じである。よって、この結晶構造をＯ３’型結晶構造と呼ぶこととする。図４にＲ−３ｍ　Ｏ３’を付してこの結晶構造を示す。 The positive electrode active material 100 when x=0.2 has a crystal structure belonging to the trigonal space group R-3m. The symmetry of the CoO2 layer is the same as that of O3. Therefore, this crystal structure is called an O3' type crystal structure. This crystal structure is shown in FIG. 4 with R-3m O3'.
Ｏ３’型の結晶構造は、ユニットセルにおけるコバルトと酸素の座標を、Ｃｏ（０，０，０．５）、Ｏ（０，０，ｘ）、０．２０≦ｘ≦０．２５の範囲内で示すことができる。またユニットセルの格子定数は、ａ軸は２．７９７≦ａ≦２．８３７（Å）が好ましく、２．８０７≦ａ≦２．８２７（Å）がより好ましく、代表的にはａ＝２．８１７（Å）である。ｃ軸は１３．６８１≦ｃ≦１３．８８１（Å）が好ましく、１３．７５１≦ｃ≦１３．８１１（Å）がより好ましく、代表的にはｃ＝１３．７８１（Å）である。座標、ａ軸及びｃ軸の値は、ＸＲＤパターンから結晶構造を推定し、ＴＯＰＡＳ　ｖｅｒ．３（Ｂｒｕｋｅｒ社製結晶構造解析ソフトウェア）を用いて算出することができる。 The O3' type crystal structure can show the coordinates of cobalt and oxygen in the unit cell within the range of Co(0,0,0.5), O(0,0,x), 0.20≦x≦0.25. The lattice constant of the unit cell is preferably 2.797≦a≦2.837 (Å), more preferably 2.807≦a≦2.827 (Å), typically a=2.817 (Å). The c-axis is preferably 13.681≦c≦13.881 (Å), more preferably 13.751≦c≦13.811 (Å), typically c=13.781 (Å). The coordinates, a-axis and c-axis values can be calculated by estimating the crystal structure from the XRD pattern and using TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker).
またｘ＝０．１５程度のときの正極活物質１００は、単斜晶系の空間群Ｐ２／ｍに帰属される結晶構造を有する。これはユニットセル中にＣｏＯ２層が１層存在する。またこのとき正極活物質１００中に存在するリチウムは放電状態の１５原子％程度である。よってこの結晶構造を単斜晶Ｏ１（１５）型結晶構造と呼ぶこととする。図４にＰ２／ｍ　単斜晶Ｏ１（１５）を付してこの結晶構造を示す。 When x=0.15, the positive electrode active material 100 has a crystal structure belonging to the monoclinic space group P2/m. In this case, one CoO2 layer exists in the unit cell. In addition, the amount of lithium present in the positive electrode active material 100 at this time is about 15 atomic % in the discharged state. Therefore, this crystal structure is called a monoclinic O1(15) type crystal structure. This crystal structure is shown in FIG. 4 with P2/m monoclinic O1(15).
単斜晶Ｏ１（１５）型の結晶構造は、ユニットセルにおけるコバルトと酸素の座標を、
Ｃｏ１（０．５，０，０．５）、
Ｃｏ２（０，０．５，０．５）、
Ｏ１（ＸＯ１，０，ＺＯ１）、
０．２３≦ＸＯ１≦０．２４、０．６１≦ＺＯ１≦０．６５、
Ｏ２（ＸＯ２，０．５，ＺＯ２）、
０．７５≦ＸＯ２≦０．７８、０．６８≦ＺＯ２≦０．７１、の範囲内で示すことができる。またユニットセルの格子定数は、
ａ＝４．８８０±０．０５Å、
ｂ＝２．８１７±０．０５Å、
ｃ＝４．８３９±０．０５Å、
α＝９０°、
β＝１０９．６±０．１°、
γ＝９０°である。 The monoclinic O1(15) crystal structure has the coordinates of cobalt and oxygen in the unit cell as follows:
Co1(0.5,0,0.5),
Co2(0,0.5,0.5),
O1(X O1 , 0, Z O1 ),
0.23≦ XO1 ≦0.24, 0.61≦ ZO1 ≦0.65,
O2(X O2 , 0.5, Z O2 ),
The lattice constant of the unit cell can be expressed as follows: 0.75≦X O2 ≦0.78, 0.68≦Z O2 ≦0.71.
a = 4.880 ± 0.05 Å,
b = 2.817 ± 0.05 Å,
c = 4.839 ± 0.05 Å,
α=90°,
β=109.6±0.1°,
γ=90°.
なおこの結晶構造は、ある程度の誤差を許容すれば空間群Ｒ−３ｍでも格子定数を示すことが可能である。この場合のユニットセルにおけるコバルトと酸素の座標は、
Ｃｏ（０，０，０．５）、
Ｏ（０，０，ＺＯ）、
０．２１≦ＺＯ≦０．２３、の範囲内で示すことができる。
またユニットセルの格子定数は、
ａ＝２．８１７±０．０２Å、
ｃ＝１３．６８±０．１Åである。 In addition, this crystal structure can show the lattice constant even in the space group R-3m if a certain degree of error is allowed. In this case, the coordinates of cobalt and oxygen in the unit cell are as follows:
Co(0,0,0.5),
O(0,0,Z O ),
The range of Z O can be expressed as 0.21≦Z O ≦0.23.
The lattice constant of the unit cell is
a = 2.817 ± 0.02 Å,
c=13.68±0.1 Å.
Ｏ３’型および単斜晶Ｏ１（１５）型結晶構造のいずれも、コバルト、ニッケル、マグネシウム等のイオンが酸素６配位位置を占める。なおリチウムおよびマグネシウムなどの軽元素は酸素４配位位置を占める場合がありうる。 In both the O3' and monoclinic O1(15) crystal structures, ions of cobalt, nickel, magnesium, etc. occupy 6-coordinate oxygen positions. Light elements such as lithium and magnesium may occupy 4-coordinate oxygen positions.
図４中に点線で示すように、放電状態のＲ−３ｍ　Ｏ３と、Ｏ３’および単斜晶Ｏ１（１５）型結晶構造とではＣｏＯ２層のずれがほとんどない。 As shown by the dotted line in FIG. 4, there is almost no deviation of the CoO 2 layer between R-3m O3 in the discharged state and O3' and the monoclinic O1(15) type crystal structure.
また放電状態のＲ−３ｍ　Ｏ３と、Ｏ３’型結晶構造の同数のコバルト原子あたりの体積の差は２．５％以下、より詳細には２．２％以下、代表的には１．８％である。 Furthermore, the difference in volume per the same number of cobalt atoms between R-3m O3 in a discharged state and the O3' type crystal structure is 2.5% or less, more specifically 2.2% or less, typically 1.8%.
また放電状態のＲ−３ｍ　Ｏ３と、単斜晶Ｏ１（１５）型結晶構造の同数のコバルト原子あたりの体積の差は３．３％以下、より詳細には３．０％以下、代表的には２．５％である。 The difference in volume per the same number of cobalt atoms between R-3m O3 in a discharged state and the monoclinic O1(15) crystal structure is 3.3% or less, more specifically 3.0% or less, typically 2.5%.
表１に、放電状態のＲ−３ｍ　Ｏ３と、Ｏ３’、単斜晶Ｏ１（１５）、Ｈ１−３型および三方晶Ｏ１のコバルト原子１つあたりの体積の差を示す。表１の算出に用いた放電状態のＲ−３ｍ　Ｏ３及び三方晶Ｏ１の各結晶構造の格子定数は、ＩＣＳＤ　ｃｏｌｌ．ｃｏｄｅ．１７２９０９および８８７２１を参照することができる。Ｈ１−３については非特許文献３を参照することができる。Ｏ３’、単斜晶Ｏ１（１５）についてはそれぞれのＸＲＤパターンから算出することができる。 Table 1 shows the difference in volume per cobalt atom between R-3m O3 in a discharged state, O3', monoclinic O1(15), H1-3 type, and trigonal O1. For the lattice constants of the crystal structures of R-3m O3 in a discharged state and trigonal O1 used in the calculation of Table 1, ICSD coll. code. 172909 and 88721 can be referred to. For H1-3, Non-Patent Document 3 can be referred to. For O3' and monoclinic O1(15), the lattice constants can be calculated from the respective XRD patterns.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
上表のコバルト１個当たりの体積を用いて、同数のコバルト原子あたりで比較した場合、Ｈ１−３型結晶構造と放電状態のＲ−３ｍ　Ｏ３型結晶構造の体積の差を求めることができる。上表の体積変化率（％）に示すが、分母を放電状態のＲ−３ｍ　Ｏ３型結晶構造としたとき、体積の差は３．９％となった。つまり当該体積の差は３．５％を超え、非常に大きいことがわかる。 Using the volume per cobalt in the table above, the difference in volume between the H1-3 crystal structure and the R-3m O3 crystal structure in a discharged state can be calculated when comparing per the same number of cobalt atoms. As shown in the volume change rate (%) in the table above, when the denominator is the R-3m O3 crystal structure in a discharged state, the difference in volume is 3.9%. In other words, the difference in volume exceeds 3.5%, and is extremely large.
上表のコバルト１個当たりの体積を用いて、同数のコバルト原子あたりで比較した場合、放電状態のＲ−３ｍ　Ｏ３と、Ｏ３’型結晶構造の体積の差を求めることができる。上表の体積変化率（％）に示すが、分母を放電状態のＲ−３ｍ　Ｏ３型結晶構造としたとき、体積の差は１．８％となった。つまり当該体積の差は、２．５％以下、より詳細には２．２％以下であり、非常に小さいことがわかる。 Using the volume per cobalt in the above table, the difference in volume between R-3m O3 in a discharged state and the O3' type crystal structure can be calculated when comparing per the same number of cobalt atoms. As shown in the volume change rate (%) in the above table, when the denominator is the R-3m O3 type crystal structure in a discharged state, the difference in volume is 1.8%. In other words, the difference in volume is less than 2.5%, more specifically less than 2.2%, which is very small.
上表のコバルト１個当たりの体積を用いて、同数のコバルト原子あたりで比較した場合、放電状態のＲ−３ｍ　Ｏ３と、単斜晶Ｏ１（１５）型結晶構造の体積の差を求めることができる。上表の体積変化率（％）に示すが、分母を放電状態のＲ−３ｍ　Ｏ３型結晶構造としたとき、体積の差は２．５％となった。つまり当該体積の差は、３．３％以下、より詳細には３．０％以下であり、非常に小さいことがわかる。 Using the volume per cobalt in the table above, the difference in volume between R-3m O3 in a discharged state and the monoclinic O1(15) type crystal structure can be calculated when comparing per the same number of cobalt atoms. As shown in the volume change rate (%) in the table above, when the denominator is the R-3m O3 type crystal structure in a discharged state, the difference in volume is 2.5%. In other words, the difference in volume is less than 3.3%, more specifically less than 3.0%, which is very small.
このように正極活物質１００では、ＬｉｘＣｏＯ２中のｘが小さいとき、つまり多くのリチウムが脱離したときの結晶構造の変化が、従来の正極活物質よりも抑制されている。同じ数のコバルト原子を有する正極活物質１００と従来の正極活物質を比較すると、正極活物質１００の体積変化は従来の正極活物質の体積変化より小さい。そのため正極活物質１００は、ｘが０．２４以下になるような充電と放電とを繰り返しても結晶構造が崩れにくい。そのため、正極活物質１００は充放電サイクルにおける充放電容量の低下が抑制される。また従来の正極活物質よりも多くのリチウムを安定して利用できるため、正極活物質１００は重量あたりおよび体積あたりの放電容量が大きい。そのため正極活物質１００を用いることで、重量あたりおよび体積あたりの放電容量の高い二次電池を作製できる。 In this way, in the positive electrode active material 100, when x in Li x CoO 2 is small, that is, when a large amount of lithium is released, the change in the crystal structure is suppressed more than in the conventional positive electrode active material. When comparing the positive electrode active material 100 having the same number of cobalt atoms with the conventional positive electrode active material, the volume change of the positive electrode active material 100 is smaller than that of the conventional positive electrode active material. Therefore, the crystal structure of the positive electrode active material 100 is not easily broken even when charging and discharging are repeated such that x is 0.24 or less. Therefore, the positive electrode active material 100 suppresses the decrease in the charge and discharge capacity in the charge and discharge cycle. In addition, since more lithium can be stably used than in the conventional positive electrode active material, the positive electrode active material 100 has a large discharge capacity per weight and per volume. Therefore, by using the positive electrode active material 100, a secondary battery with a high discharge capacity per weight and per volume can be manufactured.
なお正極活物質１００は、ＬｉｘＣｏＯ２中のｘが０．１５以上０．２４以下のときＯ３’型の結晶構造を有する場合があることが確認され、ｘが０．２４を超えて０．２７以下でもＯ３’型の結晶構造を有すると推定されている。またＬｉｘＣｏＯ２中のｘが０．１を超えて０．２以下、代表的にはｘが０．１５以上０．１７以下のとき単斜晶Ｏ１（１５）型の結晶構造を有する場合があることが確認されている。しかし結晶構造はＬｉｘＣｏＯ２中のｘだけでなく充放電サイクル数、充放電電流、温度等の影響を受けるため、必ずしも上記のｘの範囲に限定されない。 It has been confirmed that the positive electrode active material 100 may have an O3' type crystal structure when x in Li x CoO 2 is 0.15 or more and 0.24 or less, and it is estimated that the positive electrode active material 100 may have an O3' type crystal structure even when x is more than 0.24 and 0.27 or less. It has also been confirmed that the positive electrode active material 100 may have a monoclinic O1 (15) type crystal structure when x in Li x CoO 2 is more than 0.1 and 0.2 or less, typically when x is 0.15 or more and 0.17 or less. However, the crystal structure is not necessarily limited to the above range of x because it is affected by not only x in Li x CoO 2 but also the number of charge and discharge cycles, charge and discharge current, temperature, etc.
そのため正極活物質１００はＬｉｘＣｏＯ２中のｘが０．１を超えて０．２４以下のとき、Ｏ３’型のみを有してもよいし、単斜晶Ｏ１（１５）型のみを有してもよいし、両方の結晶構造を有してもよい。また正極活物質１００の内部１００ｂの粒子のすべてがＯ３’型及び／又は単斜晶Ｏ１（１５）型の結晶構造でなくてもよい。他の結晶構造を含んでいてもよいし、一部が非晶質であってもよい。 Therefore, when x in Li x CoO 2 is more than 0.1 and is 0.24 or less, the positive electrode active material 100 may have only O3' type, may have only monoclinic O1 (15) type, or may have both crystal structures. Also, all of the particles in the inside 100b of the positive electrode active material 100 do not have to have O3' type and/or monoclinic O1 (15) type crystal structures. They may contain other crystal structures, or may be partially amorphous.
またＬｉｘＣｏＯ２中のｘが小さい状態にするには、一般的には高い充電電圧で充電する必要がある。そのためＬｉｘＣｏＯ２中のｘが小さい状態を、高い充電電圧で充電した状態と言い換えることができる。たとえばリチウム金属の電位を基準として４．６Ｖ以上の電圧で、２５℃の環境でＣＣ／ＣＶ充電すると、従来の正極活物質ではＨ１−３型結晶構造が現れる。そのためリチウム金属の電位を基準として４．６Ｖ以上の充電電圧は高い充電電圧ということができる。また本明細書等において、特に言及しない場合、充電電圧はリチウム金属の電位を基準として表すとする。 In addition, in order to make the x in Li x CoO 2 small, it is generally necessary to charge at a high charging voltage. Therefore, the state in which x in Li x CoO 2 is small can be said to be a state in which it is charged at a high charging voltage. For example, when CC/CV charging is performed at a voltage of 4.6 V or more based on the potential of lithium metal in an environment of 25° C., the H1-3 type crystal structure appears in the conventional positive electrode active material. Therefore, a charging voltage of 4.6 V or more based on the potential of lithium metal can be said to be a high charging voltage. In addition, in this specification, unless otherwise specified, the charging voltage is expressed based on the potential of lithium metal.
そのため正極活物質１００は、高い充電電圧、たとえば２５℃において４．６Ｖ以上の電圧で充電しても、Ｒ−３ｍ　Ｏ３の対称性を有する結晶構造を保持できるため好ましい、と言い換えることができる。またより高い充電電圧、例えば２５℃において４．６５Ｖ以上４．７Ｖ以下の電圧で充電したときＯ３’型の結晶構造を取り得るため好ましい、と言い換えることができる。さらに高い充電電圧、例えば２５℃において４．７Ｖを超えて４．８Ｖ以下の電圧で充電したとき単斜晶Ｏ１（１５）型の結晶構造を取り得るため好ましい、と言い換えることができる。 Therefore, the positive electrode active material 100 is preferable because it can maintain a crystal structure with the symmetry of R-3m O3 even when charged at a high charging voltage, for example, a voltage of 4.6 V or more at 25°C. It can also be said that it is preferable because it can adopt an O3' type crystal structure when charged at a higher charging voltage, for example, a voltage of 4.65 V or more and 4.7 V or less at 25°C. It can also be said that it is preferable because it can adopt a monoclinic O1(15) type crystal structure when charged at an even higher charging voltage, for example, a voltage of more than 4.7 V and 4.8 V or less at 25°C.
正極活物質１００でもさらに充電電圧を高めるとようやく、Ｈ１−３型結晶構造が観測される場合がある。また上述したように結晶構造は充放電サイクル数、充放電電流、温度等の影響を受けるため、充電電圧がより低い場合、たとえば充電電圧が２５℃において４．５Ｖ以上４．６Ｖ未満でも、正極活物質１００はＯ３’型結晶構造を取り得る場合が有る。同様に２５℃において、対極リチウム金属のとき４．６５Ｖ以上４．７Ｖ以下の電圧で充電したときに単斜晶Ｏ１（１５）型の結晶構造を取り得る場合がある。充電時の到達電圧を上限電圧と呼ぶ。 Even with the positive electrode active material 100, if the charging voltage is further increased, the H1-3 type crystal structure may finally be observed. As described above, the crystal structure is affected by the number of charge/discharge cycles, the charge/discharge current, temperature, etc., so when the charging voltage is lower, for example, even if the charging voltage is 4.5 V or more and less than 4.6 V at 25°C, the positive electrode active material 100 may be able to have an O3' type crystal structure. Similarly, when the counter electrode is lithium metal, at 25°C, charging at a voltage of 4.65 V or more and 4.7 V or less may result in a monoclinic O1(15) type crystal structure. The voltage reached during charging is called the upper limit voltage.
なお、二次電池において例えば負極活物質として黒鉛を用いる場合、上記よりも黒鉛の電位の分だけ二次電池の電圧が低下する。黒鉛の電位はリチウム金属の電位を基準として０．０５Ｖ乃至０．２Ｖ程度である。そのため負極活物質として黒鉛を用いた二次電池の場合は、上記の電圧から黒鉛の電位を差し引いた電圧のとき上記と同様の結晶構造を有する。 Note that, for example, when graphite is used as the negative electrode active material in a secondary battery, the voltage of the secondary battery drops by the amount of the graphite potential compared to the above. The potential of graphite is about 0.05 V to 0.2 V based on the potential of lithium metal. Therefore, in the case of a secondary battery using graphite as the negative electrode active material, the battery has the same crystal structure as above when the voltage is the voltage above minus the graphite potential.
また図４のＯ３’および単斜晶Ｏ１（１５）ではリチウムが全てのリチウムサイトに等しい確率で存在するように示したが、これに限らない。一部のリチウムサイトに偏って存在していてもよいし、たとえば図５に示す単斜晶Ｏ１（Ｌｉ０．５ＣｏＯ２）のような対称性を有していてもよい。リチウムの分布は、たとえば中性子線回折により分析することができる。 In addition, in O3' and monoclinic O1(15) in Fig. 4, lithium is shown to exist at all lithium sites with equal probability, but this is not limited to the above. Lithium may be present biasedly at some lithium sites, or may have symmetry, for example, as in monoclinic O1( Li0.5CoO2 ) shown in Fig. 5. The distribution of lithium can be analyzed, for example, by neutron diffraction .
またＯ３’および単斜晶Ｏ１（１５）型の結晶構造は、層間にランダムにリチウムを有するもののＣｄＣｌ２型の結晶構造に類似する結晶構造であるということもできる。このＣｄＣｌ２型に類似した結晶構造は、ニッケル酸リチウムをＬｉ０．０６ＮｉＯ２まで充電したときの結晶構造と近いが、純粋なコバルト酸リチウム、またはコバルトを多く含む層状岩塩型の正極活物質では通常ＣｄＣｌ２型の結晶構造を取らないことが知られている。 It can also be said that the O3' and monoclinic O1(15) type crystal structures have random lithium between the layers, but are similar to the CdCl2 type crystal structure. This CdCl2 type-like crystal structure is close to the crystal structure of lithium nickel oxide when it is charged to Li0.06NiO2 , but it is known that pure lithium cobalt oxide or layered rock salt type positive electrode active materials containing a large amount of cobalt do not usually have the CdCl2 type crystal structure.
上述したように、従来のコバルト酸リチウムと正極活物質１００は、充電深度の変化、すなわちＬｉｘＣｏＯ２中のｘの変化に応じて、結晶構造が変化する。非特許文献４に記載されている従来のコバルト酸リチウムのｃ軸長の変化を図１６に示す。図１６の横軸はＬｉＸＣｏＯ２におけるｘの値であり、縦軸はｃ軸長である。図１６において丸いマーカーは六方晶系、ひし形のマーカーは単斜晶系の相である。図１６の丸いマーカーで示すように、六方晶のＨ１−３相ではＬｉｘＣｏＯ２中のｘの変化に応じて、ｃ軸長が短縮する。単斜晶のＯ３からＨ１−３相への相転移はリチウムイオンの脱離に伴う相転移であるため、リチウムイオンが最初に抜ける領域である正極活物質の表面から相転移が生じると考えられるが、やがて正極活物質全体に及びうる。 As described above, the conventional lithium cobalt oxide and the positive electrode active material 100 change in crystal structure according to the change in the charge depth, that is, the change in x in Li x CoO 2. FIG. 16 shows the change in the c-axis length of the conventional lithium cobalt oxide described in Non-Patent Document 4. The horizontal axis of FIG. 16 is the value of x in Li x CoO 2 , and the vertical axis is the c-axis length. In FIG. 16, the round markers are hexagonal phases, and the diamond markers are monoclinic phases. As shown by the round markers in FIG. 16, in the hexagonal H1-3 phase, the c-axis length shortens according to the change in x in Li x CoO 2. Since the phase transition from the monoclinic O3 to the H1-3 phase is a phase transition associated with the desorption of lithium ions, it is thought that the phase transition occurs from the surface of the positive electrode active material, which is the region where lithium ions are first removed, but it may eventually extend to the entire positive electrode active material.
また添加元素を有していてもその分布が不十分な場合は、ＬｉｘＣｏＯ２中のｘが０．２程度のときＨ１−３となる。たとえば表層部のマグネシウム濃度の最大値が１原子％未満では、ｃ軸長の短縮が生じるためＯ３’型の結晶構造とならないと考えられる。 Furthermore, even if an additive element is present, if its distribution is insufficient, it will become H1-3 when x in Li x CoO 2 is about 0.2. For example, if the maximum value of the magnesium concentration in the surface layer is less than 1 atomic %, it is considered that the c-axis length is shortened and the O3' type crystal structure is not obtained.
また図示しないがスピネルへの相転移は、酸素の脱離に伴う相転移であるため、酸素が脱離しやすい表面から起こると考えられる。ＬｉｘＣｏＯ２中のｘが０．２程度のときＨ１−３になるコバルト酸リチウムは、表層部に添加元素を有さない、または表層部の添加元素の分布が不十分であるため、表面から酸素が脱離しやすく、スピネル型結晶構造に相変化しやすい可能性がある。スピネル型結晶構造はさらに岩塩型結晶構造に相変化しやすい可能性がある。これらの相変化は、特にｃ軸に垂直な方向に伝播しやすい可能性がある。スピネル型結晶構造および岩塩型結晶構造の領域が増加すると、正極活物質の充放電容量は低下する。 Although not shown, the phase transition to spinel is a phase transition accompanied by the desorption of oxygen, so it is considered to occur from the surface from which oxygen is easily desorbed. Lithium cobalt oxide that becomes H1-3 when x in Li x CoO 2 is about 0.2 does not have an additive element in the surface layer part, or the distribution of the additive element in the surface layer part is insufficient, so oxygen is easily desorbed from the surface and it may be easily phase-changed to a spinel type crystal structure. The spinel type crystal structure may be more likely to phase-change to a rock salt type crystal structure. These phase changes may be particularly likely to propagate in the direction perpendicular to the c-axis. When the region of the spinel type crystal structure and the rock salt type crystal structure increases, the charge/discharge capacity of the positive electrode active material decreases.
つまり表層部に存在する添加元素は、スピネルへの相変化を抑制する機能があると期待される。 In other words, the added elements present in the surface layer are expected to suppress the phase change to spinel.
また添加元素の濃度勾配は、正極活物質１００の表層部１００ａの複数個所において同じような勾配であることが好ましい。つまり添加元素に由来する補強が表層部１００ａに均質に存在することが好ましい。表層部１００ａの一部に補強があっても、補強のない部分が存在すれば、ない部分に応力が集中する恐れがある。正極活物質１００の一部に応力が集中すると、そこからクラック等の欠陥が生じ、正極活物質の割れおよび放電容量の低下につながる恐れがある。 Furthermore, it is preferable that the concentration gradient of the added element is the same in multiple locations on the surface layer 100a of the positive electrode active material 100. In other words, it is preferable that the reinforcement resulting from the added element is present homogeneously in the surface layer 100a. Even if a portion of the surface layer 100a is reinforced, if there is a portion without reinforcement, there is a risk that stress will concentrate in the portion without reinforcement. If stress concentrates in a portion of the positive electrode active material 100, defects such as cracks may occur there, which may lead to cracking of the positive electrode active material and a decrease in discharge capacity.
ただし必ずしも、正極活物質１００の表層部１００ａ全てにおいて添加元素が同じような濃度勾配を有していなくてもよい。図１Ａ１中のＣ−Ｄ付近を拡大した図を図６Ａ１および図６Ａ２に示す。図１Ａ１のＣ−Ｄ付近の添加元素Ａの分布の例を図６Ａ１に、Ｃ−Ｄ付近の添加元素Ｂの分布の例を図６Ａ２に示す。 However, the additive element does not necessarily have to have the same concentration gradient in the entire surface layer 100a of the positive electrode active material 100. Enlarged views of the vicinity of C-D in FIG. 1A1 are shown in FIG. 6A1 and FIG. 6A2. An example of the distribution of additive element A in the vicinity of C-D in FIG. 1A1 is shown in FIG. 6A1, and an example of the distribution of additive element B in the vicinity of C-D is shown in FIG. 6A2.
ここで、Ｃ−Ｄ付近はＲ−３ｍの層状岩塩型の結晶構造を有し、表面は（００１）配向であるとする。（００１）配向した表面は、その他の表面と添加元素の分布が異なっていてもよい。たとえば、（００１）配向した表面とその表層部１００ａは、添加元素Ａおよび添加元素Ｂから選ばれた一または二以上の濃度ピークの分布が、（００１）配向以外の表面と比較して表面から浅い部分に限定されていてもよい。または、（００１）配向した表面とその表層部１００ａは、（００１）配向以外の表面と比較して添加元素Ａおよび添加元素Ｂから選ばれた一または二以上の濃度が低くてもよい。または、（００１）配向した表面とその表層部１００ａは、添加元素Ａおよび添加元素Ｂから選ばれた一または二以上の濃度が検出されなくてもよい。 Here, the vicinity of C-D has a layered rock salt type crystal structure of R-3m, and the surface is (001) oriented. The (001) oriented surface may have a different distribution of added elements from other surfaces. For example, the (001) oriented surface and its surface layer 100a may have a distribution of one or more concentration peaks selected from added element A and added element B limited to a shallower portion from the surface compared to surfaces other than the (001) orientation. Alternatively, the (001) oriented surface and its surface layer 100a may have a lower concentration of one or more selected from added element A and added element B compared to surfaces other than the (001) orientation. Alternatively, the (001) oriented surface and its surface layer 100a may not have a detectable concentration of one or more selected from added element A and added element B.
Ｒ−３ｍの層状岩塩型の結晶構造では、（００１）面に平行に陽イオンが配列している。これはＣｏＯ２層と、リチウム層と、が（００１）面と平行に交互に積層した構造であるということができる。そのためリチウムイオンの拡散経路も（００１）面に平行に存在する。 In the layered rock salt crystal structure of R-3m, cations are arranged parallel to the (001) plane. This can be said to be a structure in which CoO2 layers and lithium layers are alternately stacked parallel to the (001) plane. Therefore, the diffusion path of lithium ions also exists parallel to the (001) plane.
ＣｏＯ２層は比較的安定であるため、正極活物質１００の表面は（００１）配向である方が安定である。（００１）面には充放電におけるリチウムイオンの主な拡散経路は露出していない。 Since the CoO 2 layer is relatively stable, it is more stable for the surface of the positive electrode active material 100 to have a (001) orientation. The main diffusion path of lithium ions during charge and discharge is not exposed on the (001) plane.
一方、（００１）配向以外の表面ではリチウムイオンの拡散経路が露出している。そのため（００１）配向以外の表面および表層部１００ａは、リチウムイオンの拡散経路を保つために重要な領域であると同時に、リチウムイオンが最初に脱離する領域であるため不安定になりやすい。そのため（００１）配向以外の表面および表層部１００ａを補強することが、正極活物質１００全体の結晶構造を保つために極めて重要である。 On the other hand, the diffusion paths of lithium ions are exposed on surfaces other than those with the (001) orientation. Therefore, the surfaces and surface layer 100a other than those with the (001) orientation are important regions for maintaining the diffusion paths of lithium ions, and at the same time, they are prone to becoming unstable because they are the regions from which lithium ions are first desorbed. Therefore, reinforcing the surfaces and surface layer 100a other than those with the (001) orientation is extremely important for maintaining the crystal structure of the entire positive electrode active material 100.
そのため本発明の別の一態様の正極活物質１００では、（００１）配向以外の表面およびその表層部１００ａの添加元素の分布が図１Ｂ１または図１Ｂ２に示すような分布となっていることが重要である。添加元素の中でも特にニッケルが（００１）配向以外の表面およびその表層部１００ａに検出されることが好ましい。一方、（００１）配向した表面およびその表層部１００ａでは上述のように添加元素の濃度は低くてもよいし、またはなくてもよい。 Therefore, in the positive electrode active material 100 according to another embodiment of the present invention, it is important that the distribution of the added elements in the surface other than the (001) orientation and in the surface layer 100a thereof is as shown in FIG. 1B1 or FIG. 1B2. Of the added elements, nickel is particularly preferable to be detected in the surface other than the (001) orientation and in the surface layer 100a thereof. On the other hand, in the (001) oriented surface and in the surface layer 100a thereof, the concentration of the added elements may be low or absent as described above.
たとえば、（００１）配向した表面とその表層部１００ａにおけるマグネシウムの分布は、その半値幅が１０ｎｍ以上２００ｎｍ以下であることが好ましく、５０ｎｍ以上１５０ｎｍ以下であることがより好ましく、８０ｎｍ以上１２０ｎｍ以下であるとさらに好ましい。また（００１）配向でない表面とその表層部１００ａにおけるマグネシウムの分布は、その半値幅が２００ｎｍを超えて５００ｎｍ以下であることが好ましく、２００ｎｍを超えて３００ｎｍ以下であることがより好ましく、２３０ｎｍ以上２７０ｎｍ以下であることがさらに好ましい。 For example, the magnesium distribution in the (001) oriented surface and its surface layer 100a preferably has a half-width of 10 nm to 200 nm, more preferably 50 nm to 150 nm, and even more preferably 80 nm to 120 nm. The magnesium distribution in the non-(001) oriented surface and its surface layer 100a preferably has a half-width of more than 200 nm to 500 nm, more preferably more than 200 nm to 300 nm, and even more preferably 230 nm to 270 nm.
また（００１）配向でない表面とその表層部１００ａにおけるニッケルの分布は、その半値幅が３０ｎｍ以上１５０ｎｍ以下であることが好ましく、５０ｎｍ以上１３０ｎｍ以下であることがより好ましく、７０ｎｍ以上１１０ｎｍ以下であることがさらに好ましい。 Furthermore, the distribution of nickel in the surface that is not (001) oriented and in the surface layer 100a thereof preferably has a half-width of 30 nm or more and 150 nm or less, more preferably 50 nm or more and 130 nm or less, and even more preferably 70 nm or more and 110 nm or less.
後の実施の形態で説明する、純度の高いＬｉＣｏＯ２を作製した後に、添加元素を後から混合して加熱する作製方法は、主にリチウムイオンの拡散経路を介して添加元素が広がる。そのため（００１）配向以外の表面およびその表層部１００ａの添加元素の分布を好ましい範囲にしやすい。 In the manufacturing method described in the following embodiment, in which high-purity LiCoO2 is manufactured, and then additive elements are mixed and heated, the additive elements spread mainly through the diffusion path of lithium ions. Therefore, it is easy to make the distribution of the additive elements in the surface other than the (001) orientation and the surface layer 100a thereof into a preferred range.
図６Ｂ１乃至図６Ｃを用いて、純度の高いＬｉＣｏＯ２を作製した後に、添加元素を混合して加熱した場合の添加元素の分布ついて計算した結果について説明する。 6B1 to 6C, the results of calculations of the distribution of additive elements when high purity LiCoO 2 is produced, and then additive elements are mixed and heated will be described.
図６Ｂ１は、（１０４）配向している表面およびその表層部１００ａについて計算した結果である。古典的分子動力学法で計算した。系の下部にＬｉＣｏＯ２（ＬＣＯ）を、系の上部にマグネシウム源、リチウム源およびフッ素源としてＬｉＦとＭｇＦ２を配した。アンサンブルはＮＶＴ、初期構造の密度は１．８ｇ／ｃｍ３、系の温度は２０００Ｋ、経過時間は１００ｐｓｅｃ、ポテンシャルはＬＣＯ結晶構造にて最適化しその他の原子はＵＦＦとの混合、系の原子数は約１万個、系の電荷は中性とした。図を簡潔にするため、Ｃｏ原子とＭｇ原子を抜粋して示す。 FIG. 6B1 shows the results of calculations on a (104) oriented surface and its surface layer 100a. Calculations were performed using classical molecular dynamics. LiCoO 2 (LCO) was placed at the bottom of the system, and LiF and MgF 2 were placed at the top of the system as magnesium, lithium and fluorine sources. The ensemble was NVT, the density of the initial structure was 1.8 g/cm 3 , the temperature of the system was 2000 K, the elapsed time was 100 psec, the potential was optimized with the LCO crystal structure, the other atoms were mixed with UFF, the number of atoms in the system was about 10,000, and the charge of the system was neutral. To simplify the figure, Co atoms and Mg atoms are excerpted and shown.
図６Ｂ２は同様に２００ｐｓｅｃ、図６Ｂ３は１２００ｐｓｅｃまで計算した結果である。 Figure 6B2 shows the results of a similar calculation up to 200 psec, and Figure 6B3 shows the results up to 1200 psec.
以上の計算から、下記のような過程でマグネシウムが拡散している様子が推察される。（１）熱でリチウムがＬＣＯから脱離する。（２）マグネシウムがＬＣＯのリチウム層に入り、内部へ拡散する。（３）ＬｉＦ由来のリチウムがＬＣＯのリチウム層に入り、（１）で脱離したリチウムが補完される。 From the above calculations, it is inferred that magnesium diffuses through the following process: (1) Lithium is desorbed from LCO due to heat. (2) Magnesium enters the lithium layer of LCO and diffuses inward. (3) Lithium from LiF enters the lithium layer of LCO, replacing the lithium that was desorbed in (1).
１００ｐｓｅｃ経過した図６Ｂ１からマグネシウム原子がＬＣＯ内に拡散している様子が明らかである。コバルト原子の配列に沿ってマグネシウム原子が拡散していき、１２００ｐｓｅｃ経過した図６Ｂ３では、系の上部に用意したマグネシウム原子がほぼ全てＬＣＯに取り込まれる。 From Figure 6B1, which shows 100 psec, it is clear that magnesium atoms are diffusing into the LCO. The magnesium atoms diffuse along the arrangement of cobalt atoms, and in Figure 6B3, which shows 1200 psec, almost all of the magnesium atoms prepared at the top of the system are incorporated into the LCO.
図６Ｃは、（００１）配向とした他は図６Ｂ１と同様に計算した結果である。図６Ｃでは、マグネシウム原子はＬＣＯの表面にとどまっている様子がわかる。ただし図６Ｃは１００ｐｓｅｃ経過した場合の計算結果である。実際の正極活物質１００ではたとえば２時間以上の加熱を行い作製するため、マグネシウム原子はＬＣＯの内部にゆっくりと拡散すると考えられる。 Figure 6C shows the results of calculations similar to those of Figure 6B1, except that the orientation is (001). Figure 6C shows that the magnesium atoms remain on the surface of the LCO. However, Figure 6C shows the results of calculations after 100 psec has elapsed. In actual positive electrode active material 100, the material is prepared by heating for, for example, 2 hours or more, so it is believed that the magnesium atoms diffuse slowly into the interior of the LCO.
このように純度の高いＬｉＣｏＯ２を作製した後に、添加元素を混合して加熱する作製方法により、（００１）面よりも、（００１）配向以外の表面およびその表層部１００ａの添加元素を好ましい分布にすることができる。 In this way, after producing high-purity LiCoO 2 , the additive elements are mixed and heated, and the additive elements can be distributed more favorably on the surface other than the (001) orientation and on the surface layer 100a thereof than on the (001) plane by the production method.
また後述する初期加熱を経る作製方法では、初期加熱により表層部１００ａのリチウムがＬｉＣｏＯ２から脱離することが期待できるため、さらにマグネシウムをはじめとする添加元素を高濃度に表層部に分布させやすくなる。 In addition, in the manufacturing method that involves initial heating, which will be described later, it is expected that lithium in the surface layer portion 100a will be desorbed from LiCoO2 by the initial heating, which will make it easier to distribute added elements such as magnesium in high concentrations in the surface layer portion.
また、正極活物質１００の表面はなめらかで凹凸が少ないことが好ましいが、必ずしも、正極活物質１００が有する表面の全てがそうでなくてもよい。Ｒ−３ｍの層状岩塩型の結晶構造を有する複合酸化物は、（００１）面に平行な面、たとえばリチウムが配列した面においてスリップが生じやすい。たとえば図７Ａのように、（００１）面が存在する場合は、プレス等の工程を経ることで図７Ｂ中に矢印で示したように（００１）面と平行にスリップが起こり、変形する場合がある。 In addition, it is preferable that the surface of the positive electrode active material 100 is smooth and has few irregularities, but this is not necessarily the case for the entire surface of the positive electrode active material 100. A composite oxide having a layered rock salt type crystal structure of R-3m is prone to slippage on a surface parallel to the (001) surface, for example, on a surface where lithium is arranged. For example, as shown in FIG. 7A, when a (001) surface is present, slippage may occur parallel to the (001) surface, as shown by the arrow in FIG. 7B, by going through a process such as pressing, resulting in deformation.
この場合、スリップした結果新たに生じた表面およびその表層部１００ａには、添加元素が存在しない場合がある。図７Ｂ中のＥ−Ｆはスリップした結果新たに生じた表面およびその表層部１００ａの例である。Ｅ−Ｆ付近を拡大した図を図７Ｃ１および図７Ｃ２に示す。図７Ｃ１および図７Ｃ２では、図１Ｂ１乃至図１Ｂ２と異なり添加元素Ａおよび添加元素Ｂが分布しない。 In this case, the additional element may not be present on the new surface and its surface layer 100a that are generated as a result of the slip. E-F in FIG. 7B is an example of the new surface and its surface layer 100a that are generated as a result of the slip. Enlarged views of the area around E-F are shown in FIG. 7C1 and FIG. 7C2. Unlike FIG. 1B1 to FIG. 1B2, additional element A and additional element B are not distributed in FIG. 7C1 and FIG. 7C2.
しかしスリップは（００１）面に平行に生じやすいため、新たに生じた表面およびその表層部１００ａは（００１）配向となりやすい。この場合リチウムイオンの拡散経路が露出せず、比較的安定であるため、添加元素が存在しなくても問題がほとんどない。 However, because slippage tends to occur parallel to the (001) plane, the newly formed surface and its surface layer 100a tend to have a (001) orientation. In this case, the diffusion path of lithium ions is not exposed, and it is relatively stable, so there are almost no problems even if no additive elements are present.
なお上述のように、組成がＬｉＣｏＯ２、結晶構造がＲ−３ｍの層状岩塩型を有する複合酸化物では、（００１）面と平行にコバルト原子が配列する。またＨＡＡＤＦ−ＳＴＥＭ像では、ＬｉＣｏＯ２のうち原子番号の最も大きいコバルトの輝度が最も高くなる。そのためＨＡＡＤＦ−ＳＴＥＭ像において、輝度の高い原子の配列はコバルト原子の配列と考えてよい。この輝度の高い配列の繰り返しは、結晶縞または格子縞と同義である。 As described above, in a composite oxide having a layered rock salt type with a composition of LiCoO2 and a crystal structure of R-3m, cobalt atoms are arranged parallel to the (001) plane. In addition, in the HAADF-STEM image, the brightness of cobalt, which has the largest atomic number in LiCoO2 , is the highest. Therefore, in the HAADF-STEM image, the arrangement of atoms with high brightness can be considered to be the arrangement of cobalt atoms. The repetition of this arrangement with high brightness is synonymous with crystal fringes or lattice fringes.
≪結晶粒界≫
正極活物質１００が有する添加元素は、上記のような分布に加え、少なくとも一部は結晶粒界１０１およびその近傍に偏在していることがより好ましい。 <Grain Boundaries>
It is more preferable that the additive element contained in the positive electrode active material 100 is at least partially distributed unevenly in the crystal grain boundaries 101 and their vicinity, in addition to the distribution as described above.
たとえば正極活物質１００の結晶粒界１０１およびその近傍のマグネシウム濃度が、内部１００ｂの他の領域よりも高いことが好ましい。また結晶粒界１０１およびその近傍のフッ素濃度も内部１００ｂの他の領域より高いことが好ましい。また結晶粒界１０１およびその近傍のニッケル濃度も内部１００ｂの他の領域より高いことが好ましい。また結晶粒界１０１およびその近傍のアルミニウム濃度も内部１００ｂの他の領域より高いことが好ましい。 For example, it is preferable that the magnesium concentration at and near the grain boundaries 101 of the positive electrode active material 100 is higher than that in other regions of the interior 100b. It is also preferable that the fluorine concentration at and near the grain boundaries 101 is higher than that in other regions of the interior 100b. It is also preferable that the nickel concentration at and near the grain boundaries 101 is higher than that in other regions of the interior 100b. It is also preferable that the aluminum concentration at and near the grain boundaries 101 is higher than that in other regions of the interior 100b.
結晶粒界１０１は面欠陥の一つである。そのため粒子表面と同様不安定になりやすく結晶構造の変化が始まりやすい。そのため、結晶粒界１０１およびその近傍の添加元素濃度が高ければ、結晶構造の変化をより効果的に抑制することができる。 The grain boundary 101 is a type of planar defect. Therefore, like the particle surface, it is prone to become unstable and changes in the crystal structure are likely to begin. Therefore, if the concentration of the added element at and near the grain boundary 101 is high, changes in the crystal structure can be more effectively suppressed.
また、結晶粒界１０１およびその近傍のマグネシウム濃度およびフッ素濃度が高い場合、正極活物質１００の結晶粒界１０１に沿ってクラックが生じた場合でも、クラックにより生じた表面の近傍でマグネシウム濃度およびフッ素濃度が高くなる。そのためクラックが生じた後の正極活物質においてもフッ酸に対する耐食性を高めることができる。 In addition, when the magnesium concentration and fluorine concentration are high at and near the grain boundaries 101, even if cracks occur along the grain boundaries 101 of the positive electrode active material 100, the magnesium concentration and fluorine concentration will be high near the surface created by the cracks. Therefore, the corrosion resistance to hydrofluoric acid can be improved even in the positive electrode active material after cracks have occurred.
＜粒径＞
正極活物質１００の粒径は、大きすぎるとリチウムの拡散が難しくなる、集電体に塗工したときに活物質層の表面が粗くなりすぎる、等の問題がある。一方、小さすぎると、集電体への塗工時に活物質層を担持しにくくなる、電解液との反応が過剰に進む等の問題点も生じる。そのため、メディアン径（Ｄ５０）が、１μｍ以上１００μｍ以下が好ましく、２μｍ以上４０μｍ以下であることがより好ましく、５μｍ以上３０μｍ以下がさらに好ましい。または１μｍ以上４０μｍ以下が好ましい。または１μｍ以上３０μｍ以下が好ましい。または２μｍ以上１００μｍ以下が好ましい。または２μｍ以上３０μｍ以下が好ましい。または５μｍ以上１００μｍ以下が好ましい。または５μｍ以上４０μｍ以下が好ましい。 <Particle size>
If the particle size of the positive electrode active material 100 is too large, there are problems such as the diffusion of lithium being difficult, and the surface of the active material layer being too rough when applied to the current collector. On the other hand, if the particle size is too small, there are problems such as the active material layer being difficult to support when applied to the current collector, and the reaction with the electrolyte proceeding excessively. Therefore, the median diameter (D50) is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less. Or 1 μm or more and 40 μm or less is preferable. Or 1 μm or more and 30 μm or less is preferable. Or 2 μm or more and 100 μm or less is preferable. Or 2 μm or more and 30 μm or less is preferable. Or 5 μm or more and 100 μm or less is preferable. Or 5 μm or more and 40 μm or less is preferable.
＜粉体抵抗測定＞
正極活物質１００の粉体の体積抵抗率について説明する。 <Powder Resistance Measurement>
The volume resistivity of the powder of the positive electrode active material 100 will be described.
正極活物質１００の粉体における体積抵抗率は、６４ＭＰａの圧力において１．０×１０４Ω・ｃｍ以上であることが好ましく、１．０×１０５Ω・ｃｍ以上であることがより好ましく、１．０×１０６Ω・ｃｍ以上であることがより好ましい。また、６４ＭＰａの圧力において１．０×１０９Ω・ｃｍ以下であることが好ましく、１．０×１０８Ω・ｃｍ以下であることがより好ましく、１．０×１０７Ω・ｃｍ以下であることがより好ましい。 The volume resistivity of the powder of the positive electrode active material 100 at a pressure of 64 MPa is preferably 1.0×10 4 Ω·cm or more, more preferably 1.0×10 5 Ω·cm or more, and even more preferably 1.0×10 6 Ω·cm or more. Also, at a pressure of 64 MPa, the volume resistivity is preferably 1.0×10 9 Ω·cm or less, more preferably 1.0×10 8 Ω·cm or less, and even more preferably 1.0×10 7 Ω·cm or less.
表層部１００ａにおいてマグネシウムが適切な濃度で存在し、例えば表層部１００ａのマグネシウム濃度が内部１００ｂのマグネシウム濃度より高いと粉体抵抗率が高くなる。そのため上記の体積抵抗率は、表層部１００ａが良好に形成されたことを示す指標とすることができる。具体的には添加元素を有さない正極活物質の体積抵抗率と比べて高い値を示すことで、表層部１００ａが存在するということができる。 When magnesium is present at an appropriate concentration in the surface layer portion 100a, for example when the magnesium concentration in the surface layer portion 100a is higher than the magnesium concentration in the interior portion 100b, the powder resistivity becomes high. Therefore, the above volume resistivity can be used as an indicator that the surface layer portion 100a has been well formed. Specifically, the presence of the surface layer portion 100a can be determined by the volume resistivity being higher than that of a positive electrode active material that does not have the added element.
次に、正極活物質１００の粉体における体積抵抗率の測定方法について説明する。 Next, we will explain how to measure the volume resistivity of the powder of the positive electrode active material 100.
図１７Ａに示すように、粉体の体積抵抗率の測定装置は、抵抗測定用の端子を有する第１の機構１０と、測定対象である粉体試料（サンプル）に圧力を加える第２の機構１１と、を有することが好ましい。第２の機構１１は、粉体試料を投入するシリンダーを有し、シリンダー内を上下することのできるピストンを有するとよい。ピストンにはばね等が連結され、シリンダー内のサンプルに圧力を加えることができる。第１の機構１０はシリンダーの底面に接する、測定用電極を有するとよい。このような測定用電極と、測定対象である粉体に圧力を加える機構と、を有する測定装置として例えば、三菱化学アナリテック社製のＭＣＰ−ＰＤ５１を用いることができる。抵抗計としては、ロレスタ−ＧＰ又はハイレスタ−ＵＰを用いることができる。ロレスタ−ＧＰは図１７Ｂに示すような四探針法により低抵抗サンプルの測定に用いることができ、ハイレスタ−ＵＰは図１７Ｃに示すような二端子法により高抵抗サンプルの測定に用いることができる。なお、測定環境として、ドライルームなどの安定した環境であることが好ましいが、一般的な実験室の環境であってもよい。ドライルームの環境として、例えば２０℃以上２５℃以下の温度環境、かつマイナス４０℃以下の露点環境であることが好ましい。一般的な実験室の環境として、１５℃以上３０℃以下の温度環境、３０％以上７０％以下の湿度環境であってもよい。 As shown in FIG. 17A, the powder volume resistivity measuring device preferably has a first mechanism 10 having a terminal for resistance measurement and a second mechanism 11 for applying pressure to the powder sample (sample) to be measured. The second mechanism 11 has a cylinder for introducing the powder sample and may have a piston that can move up and down inside the cylinder. A spring or the like is connected to the piston, and pressure can be applied to the sample in the cylinder. The first mechanism 10 may have a measurement electrode that contacts the bottom surface of the cylinder. As a measuring device having such a measurement electrode and a mechanism for applying pressure to the powder to be measured, for example, MCP-PD51 manufactured by Mitsubishi Chemical Analytech Co., Ltd. can be used. As a resistance meter, Loresta GP or Hiresta UP can be used. Loresta GP can be used to measure low resistance samples by the four-probe method as shown in FIG. 17B, and Hiresta UP can be used to measure high resistance samples by the two-terminal method as shown in FIG. 17C. Note that the measurement environment is preferably a stable environment such as a dry room, but may be a general laboratory environment. The dry room environment is preferably, for example, a temperature environment of 20°C to 25°C and a dew point environment of -40°C or less. A typical laboratory environment may be a temperature environment of 15°C to 30°C and a humidity environment of 30% to 70%.
上記に示す測定装置を用いる粉体の体積抵抗率の測定について説明する。まず、粉体サンプルを第２の機構１１にセットする。第２の機構１１は測定部を有し、測定部において、サンプルはシリンダーに投入され、シリンダーの底面と、測定用電極と、が接する構造となっており、かつサンプルに圧力を加えることが可能なピストン等を有する構造となっている。また、測定部はサンプルの厚さを測定するための構造も有している。 The measurement of the volume resistivity of powder using the measuring device shown above will now be described. First, a powder sample is set in the second mechanism 11. The second mechanism 11 has a measuring section, in which the sample is placed in a cylinder and the bottom surface of the cylinder is in contact with a measuring electrode, and the measuring section has a structure including a piston or the like capable of applying pressure to the sample. The measuring section also has a structure for measuring the thickness of the sample.
粉体の体積抵抗率の測定において、粉体に圧力を加えた状態で、粉体の電気抵抗測定と、粉体の厚さ計測を実施する。粉体に加える圧力は、複数条件で実施することができる。例えば、１３ＭＰａ、２５ＭＰａ、３８ＭＰａ、５１ＭＰａ、及び６４ＭＰａのそれぞれの圧力条件において、粉体の電気抵抗と、粉体の厚さと、を計測することができる。計測した粉体の電気抵抗と粉体の厚さの値から、粉体の体積抵抗率を算出することができる。 When measuring the volume resistivity of a powder, the electrical resistance of the powder and the thickness of the powder are measured while pressure is applied to the powder. The pressure applied to the powder can be measured under a number of conditions. For example, the electrical resistance and thickness of the powder can be measured under pressure conditions of 13 MPa, 25 MPa, 38 MPa, 51 MPa, and 64 MPa. The volume resistivity of the powder can be calculated from the measured electrical resistance and thickness of the powder.
体積抵抗率の計算方法について説明する。ハイレスタ−ＵＰを用いて二端子法で測定する場合は、粉体の電気抵抗に、粉体と接する測定用電極の面積をかけ、粉体の厚さで割れば、体積抵抗率が求まる。また、ロレスタ−ＧＰを用いて四探針法で測定する場合は、粉体の電気抵抗に、補正係数をかけ、粉体の厚さをかければ、体積抵抗率が求まる。補正係数は、試料形状、寸法、及び測定位置により変化する値であり、ロレスタ−ＧＰに内蔵されている演算ソフトによって求めることが可能である。 We will explain how to calculate volume resistivity. When measuring with the two-terminal method using the Hiresta UP, the volume resistivity is found by multiplying the electrical resistance of the powder by the area of the measurement electrode in contact with the powder and dividing by the thickness of the powder. When measuring with the four-probe method using the Loresta GP, the volume resistivity is found by multiplying the electrical resistance of the powder by a correction coefficient and then multiplying it by the thickness of the powder. The correction coefficient is a value that changes depending on the sample shape, dimensions, and measurement position, and can be calculated using the calculation software built into the Loresta GP.
上記に示すような測定を行う場合、正極活物質１００の粉体における体積抵抗率は、６４ＭＰａの圧力において１．０×１０４Ω・ｃｍ以上であることが好ましく、１．０×１０５Ω・ｃｍ以上であることがより好ましく、１．０×１０６Ω・ｃｍ以上であることがより好ましい。また、６４ＭＰａの圧力において１．０×１０９Ω・ｃｍ以下であることが好ましく、１．０×１０８Ω・ｃｍ以下であることがより好ましく、１．０×１０７Ω・ｃｍ以下であることがより好ましい。このような体積抵抗率を示す正極活物質１００を有する電池は、高電圧条件での充放電サイクル試験において好ましいサイクル特性を示す。 When the above-mentioned measurements are performed, the volume resistivity of the powder of the positive electrode active material 100 is preferably 1.0×10 4 Ω·cm or more at a pressure of 64 MPa, more preferably 1.0×10 5 Ω·cm or more, and more preferably 1.0×10 6 Ω·cm or more. Also, at a pressure of 64 MPa, it is preferably 1.0×10 9 Ω·cm or less, more preferably 1.0×10 8 Ω·cm or less, and more preferably 1.0×10 7 Ω·cm or less. A battery having the positive electrode active material 100 exhibiting such a volume resistivity exhibits favorable cycle characteristics in a charge-discharge cycle test under high voltage conditions.
＜分析方法＞
ある正極活物質が、ＬｉｘＣｏＯ２中のｘが小さいときＯ３’型及び／又は単斜晶Ｏ１（１５）型の結晶構造を有する正極活物質１００であるか否かは、ＬｉｘＣｏＯ２中のｘが小さい正極活物質を有する正極を、ＸＲＤ、電子線回折、中性子線回折、電子スピン共鳴（ＥＳＲ）、核磁気共鳴（ＮＭＲ）等を用いて解析することで判断できる。 <Analysis method>
Whether or not a certain positive electrode active material is a positive electrode active material 100 having an O3′ type and/or monoclinic O1(15) type crystal structure when x in Li x CoO 2 is small can be determined by analyzing a positive electrode having a positive electrode active material with a small x in Li x CoO 2 using XRD, electron beam diffraction, neutron beam diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), or the like.
特にＸＲＤは、正極活物質が有するコバルト等の遷移金属の対称性を高分解能で解析できる、結晶性の高さおよび結晶の配向性を比較できる、格子の周期性歪みおよび結晶子サイズの解析ができる、二次電池を解体して得た正極をそのまま測定しても十分な精度を得られる、等の点で好ましい。ＸＲＤのなかでも粉末ＸＲＤでは、正極活物質１００の体積の大半を占める正極活物質１００の内部１００ｂの結晶構造を反映した回折ピークが得られる。 XRD is particularly preferred because it can analyze the symmetry of transition metals such as cobalt contained in the positive electrode active material with high resolution, it can compare the degree of crystallinity and the orientation of the crystals, it can analyze the periodic distortion of the lattice and the crystallite size, and it can obtain sufficient accuracy even when the positive electrode obtained by disassembling the secondary battery is measured as it is. Among the XRD methods, powder XRD can obtain diffraction peaks that reflect the crystal structure of the interior 100b of the positive electrode active material 100, which occupies most of the volume of the positive electrode active material 100.
なお粉末ＸＲＤで結晶子サイズを解析する場合、加圧等による正極活物質粒子の配向の影響を除いて測定することが好ましい。たとえば二次電池を解体して得た正極から正極活物質を取り出し、粉末サンプルとしてから測定することが好ましい。 When analyzing crystallite size by powder XRD, it is preferable to perform the measurement while excluding the influence of the orientation of the positive electrode active material particles due to pressure, etc. For example, it is preferable to take the positive electrode active material from the positive electrode obtained by disassembling a secondary battery, prepare a powder sample, and then perform the measurement.
正極活物質１００は、これまで述べたようにＬｉｘＣｏＯ２中のｘが１のときと、０．２４以下のときで結晶構造の変化が少ないことが特徴である。高電圧で充電したとき、結晶構造の変化が大きな結晶構造が５０ｗｔ％以上を占める材料は、高電圧の充電と放電との繰り返しに耐えられないため好ましくない。 As described above, the positive electrode active material 100 is characterized in that there is little change in the crystal structure when x in Li x CoO 2 is 1 and when it is 0.24 or less. Materials that have a crystal structure that changes significantly when charged at a high voltage and that accounts for 50 wt % or more of the crystal structure are not preferred because they cannot withstand repeated high-voltage charging and discharging.
また添加元素を添加するだけではＯ３’型または単斜晶Ｏ１（１５）型の結晶構造をとらない場合があることに注意が必要である。例えばマグネシウムおよびフッ素を有するコバルト酸リチウム、またはマグネシウムおよびアルミニウムを有するコバルト酸リチウム、という点で共通していても、添加元素の濃度および分布次第で、ＬｉｘＣｏＯ２中のｘが０．２４以下でＯ３’型及び／又は単斜晶Ｏ１（１５）型の結晶構造が６０ｗｔ％以上になる場合と、Ｈ１−３型結晶構造が５０ｗｔ％以上を占める場合と、がある。 It is also important to note that there are cases where the O3' or monoclinic O1(15) crystal structure is not obtained by simply adding an additive element. For example, even if lithium cobalt oxide having magnesium and fluorine, or lithium cobalt oxide having magnesium and aluminum, is common, depending on the concentration and distribution of the additive element, there are cases where x in Li x CoO 2 is 0.24 or less and the O3' and/or monoclinic O1(15) crystal structure is 60 wt% or more, and cases where the H1-3 crystal structure is 50 wt% or more.
また正極活物質１００でも、ｘが０．１以下など小さすぎる場合、または充電電圧が４．９Ｖを超えるような条件ではＨ１−３型または三方晶Ｏ１型の結晶構造が生じる場合もある。そのため、正極活物質１００であるか否かを判断するには、ＸＲＤをはじめとする結晶構造についての解析と、充電容量または充電電圧等の情報が必要である。 In addition, even in the case of the positive electrode active material 100, if x is too small, such as 0.1 or less, or under conditions where the charging voltage exceeds 4.9 V, an H1-3 type or trigonal O1 type crystal structure may be produced. Therefore, to determine whether or not it is a positive electrode active material 100, analysis of the crystal structure, such as XRD, and information such as the charging capacity or charging voltage are required.
ただし、ｘが小さい状態の正極活物質は、大気に触れると結晶構造の変化を起こす場合がある。例えばＯ３’型および単斜晶Ｏ１（１５）型の結晶構造からＨ１−３型結晶構造に変化する場合がある。そのため、結晶構造の分析に供するサンプルはすべてアルゴン雰囲気等の不活性雰囲気でハンドリングすることが好ましい。 However, when the positive electrode active material has a small x value, its crystal structure may change when exposed to air. For example, the crystal structure may change from O3' type or monoclinic O1(15) type to H1-3 type. Therefore, it is preferable to handle all samples used for crystal structure analysis in an inert atmosphere such as an argon atmosphere.
またある正極活物質が有する添加元素の分布が、上記で説明したような状態であるか否かは、たとえばＸＰＳ、エネルギー分散型Ｘ線分光法（ＥＤＸ：Ｅｎｅｒｇｙ　Ｄｉｓｐｅｒｓｉｖｅ　Ｘ−ｒａｙ　Ｓｐｅｃｔｒｏｓｃｏｐｙ）、ＥＰＭＡ（電子プローブ微小分析）等を用いて解析することで判断できる。 Whether the distribution of added elements in a certain positive electrode active material is as described above can be determined by analyzing it using, for example, XPS, energy dispersive X-ray spectroscopy (EDX), electron probe microanalysis (EPMA), etc.
また表層部１００ａ、結晶粒界１０１等の結晶構造は、正極活物質１００の断面の電子線回折等で分析することができる。 The crystal structure of the surface layer 100a, the grain boundaries 101, etc. can be analyzed by electron beam diffraction of a cross section of the positive electrode active material 100.
≪充電方法≫
ある複合酸化物が、正極活物質１００であるか否かを判断するための充電は、例えば対極リチウム金属となるハーフセルとしてコイン型の二次電池（ＣＲ２０３２タイプ、直径２０ｍｍ高さ３．２ｍｍ）を作製して行うことができる。コイン型の二次電池は、正極活物質１００を有する正極、リチウム金属、電解液、セパレータ、正極缶、および負極缶を有する。 ≪How to charge≫
Charging for determining whether a certain composite oxide is the positive electrode active material 100 can be performed by preparing, for example, a coin-type secondary battery (CR2032 type, diameter 20 mm, height 3.2 mm) as a half cell with a counter electrode of lithium metal. The coin-type secondary battery has a positive electrode having the positive electrode active material 100, lithium metal, an electrolyte, a separator, a positive electrode can, and a negative electrode can.
より具体的には、正極には、正極活物質、導電材およびバインダを混合したスラリーを、アルミニウム箔の正極集電体に塗工したものを用いることができる。 More specifically, the positive electrode can be prepared by coating a positive electrode current collector made of aluminum foil with a slurry of a mixture of a positive electrode active material, a conductive material, and a binder.
対極にはリチウム金属を用いることができる。なお対極にリチウム金属以外の材料を用いたときは、二次電池の電位と正極の電位が異なる。本明細書等における電圧および電位は、特に言及しない場合、正極の電位である。 Lithium metal can be used for the counter electrode. When a material other than lithium metal is used for the counter electrode, the potential of the secondary battery and the potential of the positive electrode are different. Unless otherwise specified, the voltage and potential in this specification are the potential of the positive electrode.
電解液はリチウム塩と、溶媒と、添加剤とを有する。リチウム塩には、１ｍｏｌ／Ｌの六フッ化リン酸リチウム（ＬｉＰＦ６）を用いる。溶媒には、エチレンカーボネート（ＥＣ）とジエチルカーボネート（ＤＥＣ）がＥＣ：ＤＥＣ＝３：７（体積比）を有する混合溶媒を用いた。さらに、添加剤としてビニレンカーボネート（ＶＣ）を用い、リチウム塩が溶解した混合溶媒に対して、ＶＣが２ｗｔ％で混合されたものを電解液に用いる。 The electrolyte contains a lithium salt, a solvent, and an additive. The lithium salt is 1 mol/L lithium hexafluorophosphate (LiPF 6 ). The solvent is a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of EC:DEC=3:7. Furthermore, vinylene carbonate (VC) is used as an additive, and the electrolyte is made by mixing VC at 2 wt % with the mixed solvent in which the lithium salt is dissolved.
セパレータには厚さ２５μｍのポリプロピレン多孔質フィルムを用いることができる。 A 25 μm thick polypropylene porous film can be used as the separator.
正極缶及び負極缶には、ステンレス（ＳＵＳ）で形成されているものを用いることができる。 The positive and negative electrode cans can be made of stainless steel (SUS).
上記条件で作製したコイン型の二次電池を、任意の電圧（たとえば４．５Ｖ、４．５５Ｖ、４．６Ｖ、４．６５Ｖ、４．７Ｖ、４．７５Ｖまたは４．８Ｖ）まで充電する。充電時の到達電圧を上限電圧と呼ぶ。任意の電圧まで十分に時間をかけて充電できれば充電方法は特に限定されない。たとえば定電圧充電及び定電流充電（ＣＣＣＶ充電と呼ぶ）を用いる場合、ＣＣ充電における電流は、２０ｍＡ／ｇ以上１００ｍＡ／ｇ以下で行うことができる。ＣＶ充電は２ｍＡ／ｇ以上１０ｍＡ／ｇ以下で終了することができる。正極活物質の相変化を観測するためには、このような小さい電流値で充電を行うことが望ましい。温度は２５℃または４５℃とする。このようにして充電した後に、コイン型の二次電池をアルゴン雰囲気のグローブボックス中で解体して正極を取り出せば、任意の充電容量の正極活物質を得られる。この後に各種分析を行う際、外界成分との反応を抑制するため、アルゴン雰囲気で密封することが好ましい。例えばＸＲＤは、アルゴン雰囲気の密閉容器内に封入して行うことができる。また充電完了後、速やかに正極を取り出し分析に供することが好ましい。具体的には充電完了後１時間以内が好ましく、３０分以内がより好ましい。 The coin-type secondary battery prepared under the above conditions is charged to an arbitrary voltage (for example, 4.5V, 4.55V, 4.6V, 4.65V, 4.7V, 4.75V or 4.8V). The voltage reached during charging is called the upper limit voltage. The charging method is not particularly limited as long as it is possible to charge to an arbitrary voltage over a sufficient period of time. For example, when constant voltage charging and constant current charging (called CCCV charging) are used, the current in CC charging can be 20mA/g or more and 100mA/g or less. CV charging can be terminated at 2mA/g or more and 10mA/g or less. In order to observe the phase change of the positive electrode active material, it is desirable to charge at such a small current value. The temperature is 25°C or 45°C. After charging in this manner, the coin-type secondary battery is disassembled in a glove box in an argon atmosphere and the positive electrode is taken out, and a positive electrode active material with an arbitrary charging capacity can be obtained. When various analyses are performed after this, it is preferable to seal in an argon atmosphere in order to suppress reactions with external components. For example, XRD can be performed by sealing the battery in a sealed container in an argon atmosphere. After charging is completed, it is preferable to quickly remove the positive electrode and subject it to analysis. Specifically, it is preferable to do so within one hour after charging is completed, and more preferably within 30 minutes.
また複数回充放電した後の充電状態の結晶構造を分析する場合、該複数回の充放電条件は上記の充電条件と異なっていてもよい。たとえば充電は任意の電圧（たとえば４．６Ｖ、４．６５Ｖ、４．７Ｖ、４．７５Ｖまたは４．８Ｖ）まで、電流値２０ｍＡ／ｇ以上１００ｍＡ／ｇ以下で定電流充電し、その後電流値が２ｍＡ／ｇ以上１０ｍＡ／ｇ以下となるまで定電圧充電し、放電は２．５Ｖになるまで、２０ｍＡ／ｇ以上１００ｍＡ／ｇ以下で定電流放電（ＣＣ放電と呼ぶ）とすることができる。 When analyzing the crystal structure in the charged state after multiple charge/discharge cycles, the conditions for the multiple charge/discharge cycles may be different from the above-mentioned charging conditions. For example, charging can be performed by constant current charging at a current value of 20 mA/g to 100 mA/g up to an arbitrary voltage (e.g., 4.6 V, 4.65 V, 4.7 V, 4.75 V, or 4.8 V), followed by constant voltage charging until the current value becomes 2 mA/g to 10 mA/g, and discharging at a constant current of 20 mA/g to 100 mA/g up to 2.5 V (called CC discharge).
さらに複数回充放電した後の放電状態の結晶構造を分析する場合も、たとえば２．５Ｖになるまで、電流値２０ｍＡ／ｇ以上１００ｍＡ／ｇ以下で定電流放電とすることができる。 Furthermore, when analyzing the crystal structure in the discharged state after multiple charge/discharge cycles, the battery can be discharged at a constant current of 20 mA/g or more and 100 mA/g or less until the voltage reaches 2.5 V, for example.
≪ＸＲＤ≫
ＸＲＤ測定の装置および条件は特に限定されない。たとえば下記のような装置および条件で測定することができる。
ＸＲＤ装置　：Ｂｒｕｋｅｒ　ＡＸＳ社製、Ｄ８　ＡＤＶＡＮＣＥ
Ｘ線源　：ＣｕＫα線
出力　：４０ｋＶ、４０ｍＡ
発散角　：Ｄｉｖ．Ｓｌｉｔ、０．５°
検出器：ＬｙｎｘＥｙｅ
スキャン方式　：２θ／θ連続スキャン
測定範囲（２θ）　：１５°以上９０°以下
ステップ幅（２θ）　：０．０１°設定
計数時間　：１秒間／ステップ
試料台回転　：１５ｒｐｍ <XRD>
The XRD measurement apparatus and conditions are not particularly limited. For example, the measurement can be performed using the following apparatus and conditions.
XRD device: Bruker AXS, D8 ADVANCE
X-ray source: CuKα ray output: 40 kV, 40 mA
Divergence angle: Div. Slit, 0.5°
Detector: LynxEye
Scan method: 2θ/θ continuous scan Measurement range (2θ): 15° to 90° Step width (2θ): 0.01° Setting count time: 1 second/step Sample stage rotation: 15 rpm
得られた回折パターンについて、解析ソフトウェアＤＩＦＦＲＡＣ．ＥＶＡを用いてＣｕＫα２線のピークを除去することができ、ＣｕＫα１線による回折パターンを得ることができる。また解析ソフトウェアを用いてバックグラウンドの補正も行うことができる。測定サンプルが粉末の場合を粉末Ｘ線回折と呼ぶことがあり、ガラスのサンプルホルダーに入れる、またはグリースを塗ったシリコン無反射板にサンプルを振りかける、等の手法でセッティングすることができる。測定サンプルが正極の場合は、正極を基板に両面テープで貼り付け、正極活物質層を装置の要求する測定面に合わせてセッティングすることができる。測定サンプルを正極とした場合も、正極活物質層が有するバインダ及び導電材等は非晶質であり、正極活物質の粉末Ｘ線回折に対応した回折パターンを得ることができる。 The obtained diffraction pattern can be analyzed by using the analysis software DIFFRAC.EVA to remove the peak of CuKα 2 ray, and a diffraction pattern by CuKα 1 ray can be obtained. The analysis software can also be used to correct the background. When the measurement sample is a powder, it is sometimes called powder X-ray diffraction, and the sample can be set by placing it in a glass sample holder, or sprinkling the sample on a greased silicon non-reflective plate, or by other methods. When the measurement sample is a positive electrode, the positive electrode can be attached to a substrate with double-sided tape, and the positive electrode active material layer can be set according to the measurement surface required by the device. Even when the measurement sample is a positive electrode, the binder and conductive material of the positive electrode active material layer are amorphous, and a diffraction pattern corresponding to the powder X-ray diffraction of the positive electrode active material can be obtained.
Ｏ３’型の結晶構造と、単斜晶Ｏ１（１５）型の結晶構造と、Ｈ１−３型結晶構造のモデルから計算される、ＣｕＫα１線による理想的な回折パターンを図８、図９、図１０Ａおよび図１０Ｂに示す。各図において横軸は２θ（°）を示す。また比較のためＬｉｘＣｏＯ２中のｘ＝１のＬｉＣｏＯ２　Ｏ３と、ｘ＝０の三方晶Ｏ１の結晶構造から計算される理想的な回折パターンも示す。図１０Ａおよび図１０Ｂは、Ｏ３’型結晶構造、単斜晶Ｏ１（１５）型結晶構造とＨ１−３型結晶構造の回折パターンを併記したものであり、図１０Ａは２θの範囲が１８°以上２１°以下の領域、図１０Ｂは２θの範囲が４２°以上４６°以下の領域について拡大したものである。なお、ＬｉＣｏＯ２（Ｏ３）およびＣｏＯ２（Ｏ１）のパターンはＩＣＳＤ（Ｉｎｏｒｇａｎｉｃ　Ｃｒｙｓｔａｌ　Ｓｔｒｕｃｔｕｒｅ　Ｄａｔａｂａｓｅ）（非特許文献５参照）より入手した結晶構造情報からＭａｔｅｒｉａｌｓ　Ｓｔｕｄｉｏ（ＢＩＯＶＩＡ）のモジュールの一つである、Ｒｅｆｌｅｘ　Ｐｏｗｄｅｒ　Ｄｉｆｆｒａｃｔｉｏｎを用いて作成した。２θの範囲は１５°から７５°とし、Ｓｔｅｐ　ｓｉｚｅ＝０．０１、波長λ１＝１．５４０５６２×１０−１０ｍ、λ２は設定なし、Ｍｏｎｏｃｈｒｏｍａｔｏｒはｓｉｎｇｌｅとした。Ｈ１−３型結晶構造の回折パターンは非特許文献３に記載の結晶構造情報から同様に作成した。Ｏ３’型および単斜晶Ｏ１（１５）型の結晶構造の回折パターンは正極活物質１００の回折パターンから結晶構造を推定し、ＴＯＰＡＳ　ｖｅｒ．３（Ｂｒｕｋｅｒ社製結晶構造解析ソフトウェア）を用いてフィッティングし、他と同様に回折パターンを作成した。 The ideal diffraction patterns calculated from the models of the O3' type crystal structure, the monoclinic O1(15) type crystal structure, and the H1-3 type crystal structure by CuKα 1 radiation are shown in Figures 8, 9, 10A, and 10B. In each figure, the horizontal axis indicates 2θ (°). For comparison, the ideal diffraction patterns calculated from LiCoO 2 O3 with x = 1 in Li x CoO 2 and the trigonal O1 crystal structure with x = 0 are also shown. Figures 10A and 10B show the diffraction patterns of the O3' type crystal structure, the monoclinic O1(15) type crystal structure, and the H1-3 type crystal structure, with Figure 10A showing an enlarged view of the region in which the 2θ range is 18° to 21°, and Figure 10B showing an enlarged view of the region in which the 2θ range is 42° to 46°. The patterns of LiCoO 2 (O3) and CoO 2 (O1) were created using Reflex Powder Diffraction, one of the modules of Materials Studio (BIOVIA), from crystal structure information obtained from ICSD (Inorganic Crystal Structure Database) (see Non-Patent Document 5). The range of 2θ was 15° to 75°, Step size = 0.01, wavelength λ1 = 1.540562 × 10 -10 m, λ2 was not set, and the monochromator was single. The diffraction pattern of the H1-3 type crystal structure was similarly created from the crystal structure information described in Non-Patent Document 3. The diffraction patterns of the O3′ type and monoclinic O1(15) type crystal structures were estimated from the diffraction pattern of the positive electrode active material 100, and fitting was performed using TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker Corporation), and diffraction patterns were created in the same manner as for the others.
図８、図１０Ａおよび図１０Ｂに示すように、Ｏ３’型の結晶構造では、２θ＝１９．２５±０．１２°（１９．１３°以上１９．３７°未満）、および２θ＝４５．４７±０．１０°（４５．３７°以上４５．５７°未満）にピークが出現する。 As shown in Figures 8, 10A, and 10B, in the O3' type crystal structure, peaks appear at 2θ = 19.25 ± 0.12° (19.13° or more and less than 19.37°) and 2θ = 45.47 ± 0.10° (45.37° or more and less than 45.57°).
また単斜晶Ｏ１（１５）型の結晶構造では、２θ＝１９．４７±０．１０°（１９．３７°以上１９．５７°以下）、および２θ＝４５．６２±０．０５°（４５．５７°以上４５．６７°以下）にピークが出現する。 In addition, in the monoclinic O1(15) type crystal structure, peaks appear at 2θ = 19.47 ± 0.10° (19.37° to 19.57°) and 2θ = 45.62 ± 0.05° (45.57° to 45.67°).
しかし図９、図１０Ａおよび図１０Ｂに示すように、Ｈ１−３型結晶構造および三方晶Ｏ１ではこれらの位置にピークは出現しない。そのため、ＬｉｘＣｏＯ２中の１よりｘが小さい状態で１９．１３°以上１９．３７°未満及び／又は１９．３７°以上１９．５７°以下、並びに４５．３７°以上４５．５７°未満及び／又は４５．５７°以上４５．６７°以下にピークが出現することは、正極活物質１００の特徴であるといえる。 However, as shown in Figures 9, 10A and 10B, no peaks appear at these positions in the H1-3 type crystal structure and trigonal O1. Therefore, it can be said that it is a characteristic of the positive electrode active material 100 that peaks appear at 19.13° or more and less than 19.37° and/or 19.37° or more and less than 19.57° and/or 45.37° or more and less than 45.57° and/or 45.57° or more and less than 45.67° when x is smaller than 1 in Li x CoO 2.
これは、ｘ＝１と、ｘ≦０．２４の結晶構造で、ＸＲＤのピーク位置が近いということもできる。より具体的には、ｘ＝１と、ｘ≦０．２４の結晶構造の主なピークのうち２θが４２°以上４６°以下に出現するピークについて、２θの差が、０．７°以下、より好ましくは０．５°以下であるということができる。 This means that the XRD peak positions are close between the crystal structures with x=1 and x≦0.24. More specifically, for the main peaks in the crystal structures with x=1 and x≦0.24 that appear at 2θ between 42° and 46°, the difference in 2θ is 0.7° or less, more preferably 0.5° or less.
なお、正極活物質１００はＬｉｘＣｏＯ２中のｘが小さいときＯ３’型及び／又は単斜晶Ｏ１（１５）型の結晶構造を有するが、すべての正極活物質粒子がＯ３’型及び／又は単斜晶Ｏ１（１５）型の結晶構造でなくてもよい。つまりいくつかの正極活物質粒子は他の結晶構造であってもよいし、非晶質であってもよい。ただし、回折パターンについてリートベルト解析を行ったとき、Ｏ３’型及び／又は単斜晶Ｏ１（１５）型の結晶構造が５０ｗｔ％以上であることが好ましく、６０ｗｔ％以上であることがより好ましく、６６ｗｔ％以上であることがさらに好ましい。Ｏ３’型及び／又は単斜晶Ｏ１（１５）型の結晶構造が５０ｗｔ％以上、より好ましくは６０ｗｔ％以上、さらに好ましくは６６ｗｔ％以上あれば、十分にサイクル特性に優れた正極活物質とすることができる。 In addition, the positive electrode active material 100 has an O3'-type and/or monoclinic O1 (15)-type crystal structure when x in Li x CoO 2 is small, but not all positive electrode active material particles may have an O3'-type and/or monoclinic O1 (15)-type crystal structure. In other words, some positive electrode active material particles may have other crystal structures or may be amorphous. However, when a Rietveld analysis is performed on the diffraction pattern, the O3'-type and/or monoclinic O1 (15)-type crystal structure is preferably 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more. If the O3'-type and/or monoclinic O1 (15)-type crystal structure is 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more, it can be a positive electrode active material with sufficiently excellent cycle characteristics.
また、測定開始から１００サイクル以上の充放電を経ても、リートベルト解析を行ったときＯ３’型及び／又は単斜晶Ｏ１（１５）型の結晶構造が３５ｗｔ％以上であることが好ましく、４０ｗｔ％以上であることがより好ましく、４３ｗｔ％以上であることがさらに好ましい。 Furthermore, even after 100 or more charge/discharge cycles from the start of measurement, when Rietveld analysis is performed, it is preferable that the O3' type and/or monoclinic O1(15) type crystal structure is 35 wt% or more, more preferably 40 wt% or more, and even more preferably 43 wt% or more.
また、同様にリートベルト解析を行ったとき、Ｈ１−３型およびＯ１型結晶構造が５０ｗｔ％以下であることが好ましい。 Furthermore, when a Rietveld analysis is performed similarly, it is preferable that the H1-3 type and O1 type crystal structures are 50 wt % or less.
また回折パターンにおけるピークの鋭さ、つまり半値幅は結晶性の高さを示す。そのため、充電後の各ピークは鋭い、すなわち半値幅、たとえば半値全幅が狭い方が好ましい。半値幅は、同じ結晶相から生じたピークでも、ＸＲＤの測定条件および２θの値によっても異なる。上述した測定条件の場合は、２θ＝４３°以上４６°以下に観測されるピークにおいて、半値全幅は例えば０．２°以下が好ましく、０．１５°以下がより好ましく、０．１２°以下がさらに好ましい。なお必ずしも全てのピークがこの要件を満たしていなくてもよい。一部のピークがこの要件を満たせば、その結晶相の結晶性が高いことがいえる。このような高い結晶性は、十分に充電後の結晶構造の安定化に寄与する。 The sharpness of the peaks in the diffraction pattern, i.e., the half-width, indicates the degree of crystallinity. Therefore, it is preferable that each peak after charging is sharp, i.e., the half-width, for example, the full width at half maximum, is narrow. The half-width varies depending on the XRD measurement conditions and the value of 2θ, even for peaks arising from the same crystal phase. In the case of the measurement conditions described above, for peaks observed at 2θ = 43° to 46°, the full width at half maximum is preferably, for example, 0.2° or less, more preferably 0.15° or less, and even more preferably 0.12° or less. Note that not all peaks necessarily meet this requirement. If some peaks meet this requirement, it can be said that the crystallinity of the crystal phase is high. Such high crystallinity contributes sufficiently to stabilizing the crystal structure after charging.
また、正極活物質１００が有するＯ３’型および単斜晶Ｏ１（１５）の結晶構造の結晶子サイズは、放電状態のＬｉＣｏＯ２（Ｏ３）の１／２０程度までしか低下しない。そのため、充放電前の正極と同じＸＲＤの測定条件であっても、ＬｉｘＣｏＯ２中のｘが１より小さいとき明瞭なＯ３’型及び／又は単斜晶Ｏ１（１５）の結晶構造のピークが確認できる。一方従来のＬｉＣｏＯ２では、一部がＯ３’型及び／又は単斜晶Ｏ１（１５）の結晶構造に似た構造を取りえたとしても、結晶子サイズが小さくなり、ピークはブロードで小さくなる。結晶子サイズは、ＸＲＤピークの半値幅から求めることができる。 In addition, the crystallite size of the O3' type and monoclinic O1 (15) crystal structures of the positive electrode active material 100 is only reduced to about 1/20 of LiCoO 2 (O3) in the discharged state. Therefore, even under the same XRD measurement conditions as the positive electrode before charging and discharging, when x in Li x CoO 2 is smaller than 1, a clear peak of the O3' type and/or monoclinic O1 (15) crystal structure can be confirmed. On the other hand, in conventional LiCoO 2 , even if a part of the structure is similar to the O3' type and/or monoclinic O1 (15) crystal structure, the crystallite size becomes small and the peak becomes broad and small. The crystallite size can be determined from the half-width of the XRD peak.
正極活物質１００においては、前述の通りヤーン・テラー効果の影響が小さいことが好ましい。ヤーン・テラー効果の影響が小さい範囲であれば、コバルトの他に添加元素としてニッケル、マンガン等の遷移金属を有してもよい。 As described above, it is preferable that the positive electrode active material 100 has a small influence of the Jahn-Teller effect. As long as the influence of the Jahn-Teller effect is small, the positive electrode active material 100 may contain transition metals such as nickel and manganese as additive elements in addition to cobalt.
正極活物質において、ＸＲＤ分析を用いて、ヤーン・テラー効果の影響が小さいと推測されるニッケルおよびマンガンの割合および格子定数の範囲について考察する。 In positive electrode active materials, we use XRD analysis to consider the proportions of nickel and manganese and the range of lattice constants in which the influence of the Jahn-Teller effect is assumed to be small.
図１１は、正極活物質１００が層状岩塩型の結晶構造を有し、コバルトとニッケルを有する場合において、ＸＲＤを用いてａ軸およびｃ軸の格子定数を算出した結果を示す。図１１Ａがａ軸、図１１Ｂがｃ軸の結果である。なお、これらの算出に用いたＸＲＤパターンは、正極活物質の合成を行った後の粉体であり、正極に組み込む前のものである。横軸のニッケル濃度は、コバルトとニッケルの原子数の和を１００％とした場合のニッケルの濃度を示す。正極活物質は、アルミニウム源を用いない他は後述する図１８の作製方法に準じて作製した。 Figure 11 shows the results of calculating the lattice constants of the a-axis and c-axis using XRD when the positive electrode active material 100 has a layered rock salt type crystal structure and contains cobalt and nickel. Figure 11A shows the result for the a-axis, and Figure 11B shows the result for the c-axis. Note that the XRD patterns used for these calculations are for the powder after the synthesis of the positive electrode active material, and before it is incorporated into the positive electrode. The nickel concentration on the horizontal axis indicates the nickel concentration when the sum of the number of cobalt and nickel atoms is taken as 100%. The positive electrode active material was produced according to the production method shown in Figure 18 described later, except that no aluminum source was used.
図１２には、正極活物質１００が層状岩塩型の結晶構造を有し、コバルトとマンガンを有する場合において、ＸＲＤを用いてａ軸およびｃ軸の格子定数を見積もった結果を示す。図１２Ａがａ軸、図１２Ｂがｃ軸の結果である。なお、図１２に示す格子定数は、正極活物質の合成を行った後の粉体であり、正極に組み込む前に測定したＸＲＤによるものである。横軸のマンガン濃度は、コバルトとマンガンの原子数の和を１００％とした場合のマンガンの濃度を示す。正極活物質は、ニッケル源に代えてマンガン源を用い、さらにアルミニウム源を用いない他は後述する図１８の作製方法に準じて作製した。 Figure 12 shows the results of estimating the a-axis and c-axis lattice constants using XRD when the positive electrode active material 100 has a layered rock salt type crystal structure and contains cobalt and manganese. Figure 12A shows the a-axis result, and Figure 12B shows the c-axis result. Note that the lattice constants shown in Figure 12 are based on XRD measurements of the powder after synthesis of the positive electrode active material and before incorporation into the positive electrode. The manganese concentration on the horizontal axis indicates the concentration of manganese when the sum of the number of cobalt and manganese atoms is taken as 100%. The positive electrode active material was produced according to the production method shown in Figure 18 described later, except that a manganese source was used instead of a nickel source, and no aluminum source was used.
図１１Ｃには、図１１Ａおよび図１１Ｂに格子定数の結果を示した正極活物質について、ａ軸の格子定数をｃ軸の格子定数で割った値（ａ軸／ｃ軸）を示す。図１２Ｃには、図１２Ａおよび図１２Ｂに格子定数の結果を示した正極活物質について、ａ軸の格子定数をｃ軸の格子定数で割った値（ａ軸／ｃ軸）を示す。 Figure 11C shows the value obtained by dividing the a-axis lattice constant by the c-axis lattice constant (a-axis/c-axis) for the positive electrode active material whose lattice constant results are shown in Figures 11A and 11B. Figure 12C shows the value obtained by dividing the a-axis lattice constant by the c-axis lattice constant (a-axis/c-axis) for the positive electrode active material whose lattice constant results are shown in Figures 12A and 12B.
図１１Ｃより、ニッケル濃度が５％と７．５％ではａ軸／ｃ軸が顕著に変化する傾向がみられ、ニッケル濃度７．５％ではａ軸の歪みが大きくなっている。この歪みは三価のニッケルのヤーン・テラー歪みに起因する可能性がある。ニッケル濃度が７．５％未満において、ヤーン・テラー歪みの小さい、優れた正極活物質が得られることが示唆される。 Figure 11C shows that the a-axis/c-axis tend to change significantly when the nickel concentration is 5% and 7.5%, and the distortion of the a-axis is large when the nickel concentration is 7.5%. This distortion may be due to the Jahn-Teller distortion of trivalent nickel. It is suggested that an excellent positive electrode active material with small Jahn-Teller distortion can be obtained when the nickel concentration is less than 7.5%.
次に、図１２Ａより、マンガン濃度が５％以上においては、格子定数の変化の挙動が異なり、ベガード則に従わないことが示唆される。よって、マンガン濃度が５％以上では結晶構造が異なることが示唆される。よって、マンガンの濃度は例えば、４％以下が好ましい。 Next, FIG. 12A suggests that when the manganese concentration is 5% or more, the behavior of the change in lattice constant is different and does not follow Vegard's law. This suggests that when the manganese concentration is 5% or more, the crystal structure is different. Therefore, it is preferable that the manganese concentration is, for example, 4% or less.
なお、上記のニッケル濃度およびマンガン濃度の範囲は、表層部１００ａにおいては必ずしもあてはまらない。すなわち、表層部１００ａにおいては、上記の濃度より高くてもよい。 Note that the above nickel concentration and manganese concentration ranges do not necessarily apply to the surface layer 100a. In other words, the concentrations in the surface layer 100a may be higher than those described above.
以上より、格子定数の好ましい範囲について考察を行ったところ、本発明の一態様の正極活物質において、ＸＲＤパターンから推定できる、充放電を行わない状態、あるいは放電状態の正極活物質１００が有する層状岩塩型の結晶構造において、ａ軸の格子定数が２．８１４×１０−１０ｍより大きく２．８１７×１０−１０ｍより小さく、かつｃ軸の格子定数が１４．０５×１０−１０ｍより大きく１４．０７×１０−１０ｍより小さいことが好ましいことがわかった。充放電を行わない状態とは例えば、二次電池の正極を作製する前の粉体の状態であってもよい。 From the above, the preferable range of the lattice constant was considered, and it was found that, in the positive electrode active material of one embodiment of the present invention, in the layered rock salt crystal structure of the positive electrode active material 100 in a state where no charging or discharging is performed or in a discharged state, which can be estimated from the XRD pattern, the a-axis lattice constant is preferably greater than 2.814×10 −10 m and smaller than 2.817×10 −10 m, and the c-axis lattice constant is preferably greater than 14.05×10 −10 m and smaller than 14.07×10 −10 m. The state where no charging or discharging is performed may be, for example, a powder state before the positive electrode of a secondary battery is prepared.
あるいは、充放電を行わない状態、あるいは放電状態の正極活物質１００が有する層状岩塩型の結晶構造において、ａ軸の格子定数をｃ軸の格子定数で割った値（ａ軸／ｃ軸）が０．２００００より大きく０．２００４９より小さいことが好ましい。 Alternatively, in the layered rock-salt crystal structure of the positive electrode active material 100 in a state where no charge or discharge is performed or in a discharged state, it is preferable that the value obtained by dividing the lattice constant of the a-axis by the lattice constant of the c-axis (a-axis/c-axis) is greater than 0.20000 and less than 0.20049.
あるいは、充放電を行わない状態、あるいは放電状態の正極活物質１００が有する層状岩塩型の結晶構造において、ＸＲＤ分析をしたとき、２θが１８．５０°以上１９．３０°以下に第１のピークが観測され、かつ２θが３８．００°以上３８．８０°以下に第２のピークが観測される場合がある。 Alternatively, when XRD analysis is performed on the layered rock salt type crystal structure of the positive electrode active material 100 in a state where no charge or discharge is performed or in a discharged state, a first peak may be observed at 2θ of 18.50° or more and 19.30° or less, and a second peak may be observed at 2θ of 38.00° or more and 38.80° or less.
≪ＸＰＳ≫
Ｘ線光電子分光（ＸＰＳ）では、無機酸化物の場合で、Ｘ線源として単色アルミニウムのＫα線を用いると、表面から２ｎｍ乃至８ｎｍ程度（通常５ｎｍ以下）の深さまでの領域の分析が可能であるため、表層部１００ａの深さに対して約半分の領域について、各元素の濃度を定量的に分析することができる。また、ナロースキャン分析をすれば元素の結合状態を分析することができる。 <XPS>
In X-ray photoelectron spectroscopy (XPS), in the case of inorganic oxides, when monochromatic aluminum Kα rays are used as the X-ray source, it is possible to analyze a region from the surface to a depth of about 2 to 8 nm (usually 5 nm or less), so that the concentration of each element can be quantitatively analyzed in a region about half the depth of the surface layer 100a. In addition, narrow scan analysis can be used to analyze the bonding state of the elements.
正極活物質１００は、添加元素から選ばれた一または二以上の濃度が内部１００ｂよりも表層部１００ａにおいて高いことが好ましい。これは表層部１００ａにおける添加元素から選ばれた一または二以上の濃度が、正極活物質１００全体の平均よりも高いことが好ましい、と同義である。そのためたとえば、ＸＰＳ等で測定される表層部１００ａから選ばれた一または二以上の添加元素の濃度が、ＩＣＰ−ＭＳ、あるいはＧＤ−ＭＳ等で測定される正極活物質１００全体の平均の添加元素の濃度よりも高いことが好ましい、ということができる。たとえばＸＰＳ等で測定される表層部１００ａの少なくとも一部のマグネシウムの濃度が、正極活物質１００全体のマグネシウム濃度の平均よりも高いことが好ましい。また表層部１００ａの少なくとも一部のニッケルの濃度が、正極活物質１００全体のニッケル濃度の平均よりも高いことが好ましい。また表層部１００ａの少なくとも一部のアルミニウムの濃度が、正極活物質１００全体のアルミニウム濃度の平均よりも高いことが好ましい。また表層部１００ａの少なくとも一部のフッ素の濃度が、正極活物質１００全体のフッ素濃度の平均よりも高いことが好ましい。 The positive electrode active material 100 preferably has a higher concentration of one or more selected from the additive elements in the surface layer 100a than in the interior 100b. This is synonymous with the fact that the concentration of one or more selected from the additive elements in the surface layer 100a is preferably higher than the average concentration of the entire positive electrode active material 100. Therefore, for example, it can be said that the concentration of one or more additive elements selected from the surface layer 100a measured by XPS or the like is preferably higher than the average concentration of the additive elements in the entire positive electrode active material 100 measured by ICP-MS or GD-MS or the like. For example, it is preferable that the magnesium concentration of at least a part of the surface layer 100a measured by XPS or the like is higher than the average magnesium concentration of the entire positive electrode active material 100. It is also preferable that the nickel concentration of at least a part of the surface layer 100a is higher than the average nickel concentration of the entire positive electrode active material 100. It is also preferable that the aluminum concentration of at least a part of the surface layer 100a is higher than the average aluminum concentration of the entire positive electrode active material 100. It is also preferable that the fluorine concentration in at least a portion of the surface layer 100a is higher than the average fluorine concentration in the entire positive electrode active material 100.
なお正極活物質１００の表面および表層部１００ａには、正極活物質１００作製後に化学吸着した炭酸塩、ヒドロキシ基等は含まないとする。また正極活物質１００の表面に付着した電解液、バインダ、導電材、またはこれら由来の化合物も含まないとする。そのため正極活物質が有する元素を定量するときは、ＸＰＳをはじめとする表面分析で検出されうる炭素、水素、過剰な酸素、過剰なフッ素等を除外する補正をしてもよい。例えば、ＸＰＳでは結合の種類を解析で分離することが可能であり、バインダ由来のＣ−Ｆ結合を除外する補正をおこなってもよい。 The surface and surface layer 100a of the positive electrode active material 100 do not contain carbonates, hydroxyl groups, etc. that are chemically adsorbed after the preparation of the positive electrode active material 100. Also, they do not contain electrolyte, binder, conductive material, or compounds derived from these that are attached to the surface of the positive electrode active material 100. Therefore, when quantifying the elements contained in the positive electrode active material, corrections may be made to exclude carbon, hydrogen, excess oxygen, excess fluorine, etc. that can be detected by surface analysis such as XPS. For example, XPS makes it possible to separate the types of bonds by analysis, and corrections may be made to exclude C-F bonds derived from the binder.
さらに各種分析に供する前に、正極活物質の表面に付着した電解液、バインダ、導電材、またはこれら由来の化合物を除くために、正極活物質および正極活物質層等の試料に対して洗浄等を行ってもよい。このとき洗浄に用いる溶媒等にリチウムが溶け出す場合があるが、たとえその場合であっても、添加元素は溶け出しにくいため、添加元素の原子数比に影響があるものではない。 Furthermore, before being subjected to various analyses, the samples such as the positive electrode active material and the positive electrode active material layer may be washed to remove the electrolyte, binder, conductive material, or compounds derived from these that are attached to the surface of the positive electrode active material. At this time, lithium may dissolve into the solvent used for washing, but even in this case, the added element is unlikely to dissolve, so the atomic ratio of the added element is not affected.
また添加元素の濃度は、コバルトとの比（コバルト比と呼ぶ）を用いて示してもよい。コバルト比を用いることにより、正極活物質を作製後に化学吸着した炭酸塩等の影響を減じて比較することができ好ましい。たとえばＸＰＳの分析によるマグネシウムとコバルトの原子数の比Ｍｇ／Ｃｏは、０．４以上１．５以下であることが好ましい。一方ＩＣＰ−ＭＳの分析によるＭｇ／Ｃｏは０．００１以上０．０６以下であることが好ましい。 The concentration of the added element may also be expressed using the ratio to cobalt (called the cobalt ratio). Using the cobalt ratio is preferable because it allows comparisons to be made while reducing the influence of carbonates and the like that are chemically adsorbed after the positive electrode active material is produced. For example, the ratio Mg/Co of the number of magnesium and cobalt atoms as determined by XPS analysis is preferably 0.4 or more and 1.5 or less. On the other hand, the ratio Mg/Co as determined by ICP-MS analysis is preferably 0.001 or more and 0.06 or less.
同様に正極活物質１００は、十分にリチウムイオンの挿入脱離の経路を確保するために、表層部１００ａにおいて各添加元素よりもリチウムおよびコバルトの濃度が高いことが好ましい。これはＸＰＳ等で測定される表層部１００ａが有する添加元素から選ばれた一または二以上の各添加元素の濃度よりも、表層部１００ａのリチウムおよびコバルトの濃度が高いことが好ましい、ということができる。たとえばＸＰＳ等で測定される表層部１００ａの少なくとも一部のマグネシウムの濃度よりも、ＸＰＳ等で測定される表層部１００ａの少なくとも一部のコバルトの濃度が高いことが好ましい。同様にマグネシウムの濃度よりも、リチウムの濃度が高いことが好ましい。またニッケルの濃度よりも、コバルトの濃度が高いことが好ましい。同様にニッケルの濃度よりも、リチウムの濃度が高いことが好ましい。またアルミニウムの濃度よりもコバルトの濃度が高いことが好ましい。同様にアルミニウムの濃度よりも、リチウムの濃度が高いことが好ましい。またフッ素の濃度よりもコバルトの濃度が高いことが好ましい。同様にフッ素の濃度よりもリチウムの濃度が高いことが好ましい。 Similarly, in the positive electrode active material 100, in order to secure a sufficient path for the insertion and desorption of lithium ions, it is preferable that the concentrations of lithium and cobalt in the surface layer portion 100a are higher than the concentrations of one or more additive elements selected from the additive elements contained in the surface layer portion 100a measured by XPS or the like. For example, it is preferable that the concentration of at least a part of the cobalt in the surface layer portion 100a measured by XPS or the like is higher than the concentration of at least a part of the magnesium in the surface layer portion 100a measured by XPS or the like. Similarly, it is preferable that the concentration of lithium is higher than the concentration of magnesium. It is also preferable that the concentration of cobalt is higher than the concentration of nickel. It is also preferable that the concentration of lithium is higher than the concentration of nickel. It is also preferable that the concentration of cobalt is higher than the concentration of aluminum. It is also preferable that the concentration of lithium is higher than the concentration of aluminum. It is also preferable that the concentration of cobalt is higher than the concentration of fluorine. It is also preferable that the concentration of lithium is higher than the concentration of fluorine.
さらにアルミニウムをはじめとする添加元素Ｂは深い領域、たとえば表面からの深さが５ｎｍ以上５０ｎｍ以内の領域に広く分布する方がより好ましい。そのため、ＩＣＰ−ＭＳ、ＧＤ−ＭＳ等を用いた正極活物質１００全体の分析ではアルミニウムをはじめとする添加元素Ｂが検出されるものの、ＸＰＳ等ではこれの濃度が検出されないと、より好ましい。 Furthermore, it is more preferable that the additive element B, such as aluminum, is widely distributed in a deep region, for example, a region having a depth from the surface of 5 nm to 50 nm. Therefore, it is more preferable that the additive element B, such as aluminum, is detected in an analysis of the entire positive electrode active material 100 using ICP-MS, GD-MS, etc., but its concentration is not detected by XPS, etc.
さらに正極活物質１００についてＸＰＳ分析をしたとき、コバルトの原子数に対して、マグネシウムの原子数は０．４倍以上１．２倍以下が好ましく、０．６５倍以上１．０倍以下がより好ましい。またコバルトの原子数に対して、ニッケルの原子数は０．１５倍以下が好ましく、０．０３倍以上０．１３倍以下がより好ましい。またコバルトの原子数に対して、アルミニウムの原子数は０．１２倍以下が好ましく、０．０９倍以下がより好ましい。またコバルトの原子数に対して、フッ素の原子数は０．３倍以上０．９倍以下が好ましく、０．１倍以上１．１倍以下がより好ましい。上記のような範囲であることは、これらの添加元素が正極活物質１００の表面の狭い範囲に付着するのではなく、正極活物質１００の表層部１００ａに好ましい濃度で広く分布していることを示すといえる。 Furthermore, when the positive electrode active material 100 was subjected to XPS analysis, the number of magnesium atoms was preferably 0.4 to 1.2 times, more preferably 0.65 to 1.0 times, relative to the number of cobalt atoms. The number of nickel atoms was preferably 0.15 times or less, more preferably 0.03 to 0.13 times, relative to the number of cobalt atoms. The number of aluminum atoms was preferably 0.12 times or less, more preferably 0.09 times or less, relative to the number of cobalt atoms. The number of fluorine atoms was preferably 0.3 to 0.9 times, more preferably 0.1 to 1.1 times, relative to the number of cobalt atoms. The above ranges indicate that these additive elements are not attached to a narrow area on the surface of the positive electrode active material 100, but are widely distributed in the surface layer 100a of the positive electrode active material 100 at a preferred concentration.
ＸＰＳ分析を行う場合には例えば、Ｘ線源として単色化アルミニウムＫα線を用いることができる。また、取出角は例えば４５°とすればよい。たとえば下記の装置および条件で測定することができる。
測定装置　：ＰＨＩ社製、ＱｕａｎｔｅｒａＩＩ
Ｘ線源　：単色化Ａｌ　Ｋα（１４８６．６ｅＶ）
検出領域　：１００μｍφ
検出深さ　：約４~５ｎｍ（取出角４５°）
測定スペクトル　：ワイドスキャン、各検出元素のナロースキャン When performing XPS analysis, for example, monochromated aluminum Kα rays can be used as the X-ray source. The take-off angle can be set to, for example, 45°. For example, the measurement can be performed using the following apparatus and conditions.
Measuring device: Quantera II, manufactured by PHI
X-ray source: Monochromated Al Kα (1486.6 eV)
Detection area: 100 μm φ
Detection depth: Approximately 4 to 5 nm (take-off angle 45°)
Measurement spectrum: Wide scan, narrow scan of each detected element
また正極活物質１００についてＸＰＳ分析したとき、フッ素と他の元素の結合エネルギーを示すピークは６８２ｅＶ以上６８５ｅＶ未満であることが好ましく、６８４．３ｅＶ程度であることがさらに好ましい。これは、フッ化リチウムの結合エネルギーである６８５ｅＶ、およびフッ化マグネシウムの結合エネルギーである６８６ｅＶのいずれとも異なる値である。 Furthermore, when the positive electrode active material 100 is subjected to XPS analysis, the peak showing the bond energy between fluorine and other elements is preferably 682 eV or more and less than 685 eV, and more preferably about 684.3 eV. This is a different value from both the bond energy of lithium fluoride, 685 eV, and the bond energy of magnesium fluoride, 686 eV.
さらに、正極活物質１００についてＸＰＳ分析したとき、マグネシウムと他の元素の結合エネルギーを示すピークは、１３０２ｅＶ以上１３０４ｅＶ未満であることが好ましく、１３０３ｅＶ程度であることがさらに好ましい。これは、フッ化マグネシウムの結合エネルギーである１３０５ｅＶと異なる値であり、酸化マグネシウムの結合エネルギーに近い値である。 Furthermore, when the positive electrode active material 100 is subjected to XPS analysis, the peak showing the bond energy between magnesium and other elements is preferably equal to or greater than 1302 eV and less than 1304 eV, and more preferably about 1303 eV. This is a different value from the bond energy of magnesium fluoride, which is 1305 eV, and is close to the bond energy of magnesium oxide.
≪ＥＤＸ≫
正極活物質１００が有する添加元素から選ばれた一または二以上は濃度勾配を有していることが好ましい。また正極活物質１００は添加元素によって、濃度ピークの表面からの深さが異なっていることがより好ましい。添加元素の濃度勾配はたとえば、ＦＩＢ等により正極活物質１００の断面を露出させ、その断面をＥＤＸ、ＥＰＭＡ等を用いて分析することで評価できる。 <EDX>
It is preferable that one or more selected from the additive elements contained in the positive electrode active material 100 have a concentration gradient. It is more preferable that the depth from the surface of the concentration peak differs depending on the additive element in the positive electrode active material 100. The concentration gradient of the additive element can be evaluated, for example, by exposing a cross section of the positive electrode active material 100 by FIB or the like and analyzing the cross section by EDX, EPMA, or the like.
ＥＤＸ測定のうち、領域内を走査しながら測定し、領域内を２次元に評価することをＥＤＸ面分析と呼ぶ。また線状に走査しながら測定し、原子濃度について正極活物質内の分布を評価することを線分析と呼ぶ。さらにＥＤＸの面分析から、線状の領域のデータを抽出したものを線分析と呼ぶ場合もある。またある領域について走査せずに測定することを点分析と呼ぶ。 In EDX measurements, performing measurements while scanning an area and evaluating the area in two dimensions is called EDX area analysis. Performing measurements while scanning linearly and evaluating the distribution of atomic concentrations within the positive electrode active material is called line analysis. Furthermore, data extracted from a linear area from EDX area analysis is sometimes called line analysis. Measuring an area without scanning is called point analysis.
ＥＤＸ面分析（例えば元素マッピング）により、正極活物質１００の表層部１００ａ、内部１００ｂおよび結晶粒界１０１近傍等における、添加元素の濃度を定量的に分析することができる。また、ＥＤＸ線分析により、添加元素の濃度分布および最大値を分析することができる。またＳＴＥＭ−ＥＤＸのように薄片化したサンプルを用いる分析は、奥行き方向の分布の影響を受けずに、特定の領域における正極活物質の表面から中心に向かった深さ方向の濃度分布を分析でき、より好適である。 EDX surface analysis (e.g., element mapping) can quantitatively analyze the concentration of the added element in the surface layer 100a, the interior 100b, and near the grain boundary 101 of the positive electrode active material 100. In addition, EDX ray analysis can analyze the concentration distribution and maximum value of the added element. In addition, analysis using a thinned sample such as STEM-EDX is more suitable because it can analyze the concentration distribution in the depth direction from the surface to the center of the positive electrode active material in a specific region without being affected by the distribution in the depth direction.
そのため正極活物質１００についてＥＤＸ面分析またはＥＤＸ点分析したとき、表層部１００ａの各添加元素、特に添加元素Ａの濃度が、内部１００ｂの各添加元素、特に添加元素Ａの濃度よりも高いことが好ましい。 Therefore, when EDX surface analysis or EDX point analysis is performed on the positive electrode active material 100, it is preferable that the concentration of each added element, particularly added element A, in the surface layer portion 100a is higher than the concentration of each added element, particularly added element A, in the interior portion 100b.
たとえば添加元素としてマグネシウムを有する正極活物質１００についてＥＤＸ面分析またはＥＤＸ点分析したとき、表層部１００ａのマグネシウム濃度が、内部１００ｂのマグネシウム濃度よりも高いことが好ましい。またＥＤＸ線分析をしたとき、表層部１００ａのマグネシウム濃度のピークは、正極活物質１００の表面から中心に向かった深さ３ｎｍまでに存在することが好ましく、深さ１ｎｍまでに存在することがより好ましく、深さ０．５ｎｍまでに存在することがさらに好ましい。またマグネシウムの分布はピークトップから深さ１ｎｍの点でピークの６０％以下に減衰することが好ましい。またピークトップから深さ２ｎｍの点でピークの３０％以下に減衰することが好ましい。なおここでいう濃度のピークとは、濃度の極大値をいうこととする。 For example, when EDX surface analysis or EDX point analysis is performed on a positive electrode active material 100 having magnesium as an added element, it is preferable that the magnesium concentration in the surface layer 100a is higher than the magnesium concentration in the interior 100b. When EDX ray analysis is performed, the peak of the magnesium concentration in the surface layer 100a is preferably present at a depth of 3 nm from the surface of the positive electrode active material 100 toward the center, more preferably at a depth of 1 nm, and even more preferably at a depth of 0.5 nm. It is preferable that the magnesium distribution decays to 60% or less of the peak at a point 1 nm deep from the peak top. It is also preferable that the magnesium distribution decays to 30% or less of the peak at a point 2 nm deep from the peak top. Note that the concentration peak here refers to the maximum value of the concentration.
また添加元素としてマグネシウムおよびフッ素を有する正極活物質１００では、フッ素の分布は、マグネシウムの分布と重畳することが好ましい。たとえばフッ素濃度のピークと、マグネシウム濃度のピークの深さ方向の差が１０ｎｍ以内であると好ましく、３ｎｍ以内であるとより好ましく、１ｎｍ以内であるとさらに好ましい。 Furthermore, in the positive electrode active material 100 having magnesium and fluorine as added elements, it is preferable that the distribution of fluorine overlaps with the distribution of magnesium. For example, the difference in the depth direction between the peak of the fluorine concentration and the peak of the magnesium concentration is preferably within 10 nm, more preferably within 3 nm, and even more preferably within 1 nm.
またＥＤＸ線分析をしたとき、表層部１００ａのフッ素濃度のピークは、正極活物質１００の表面から中心に向かった深さ３ｎｍまでに存在することが好ましく、深さ１ｎｍまでに存在することがより好ましく、深さ０．５ｎｍまでに存在することがさらに好ましい。またフッ素濃度のピークはマグネシウムの濃度のピークよりもわずかに表面側に存在すると、フッ酸への耐性が増してより好ましい。たとえばフッ素濃度のピークはマグネシウムの濃度のピークよりも０．５ｎｍ以上表面側であるとより好ましく、１．５ｎｍ以上表面側であるとさらに好ましい。 In addition, when EDX-ray analysis is performed, the fluorine concentration peak of the surface layer 100a is preferably present at a depth of 3 nm from the surface toward the center of the positive electrode active material 100, more preferably at a depth of 1 nm, and even more preferably at a depth of 0.5 nm. Furthermore, it is more preferable for the fluorine concentration peak to be slightly closer to the surface than the magnesium concentration peak, as this increases resistance to hydrofluoric acid. For example, it is more preferable for the fluorine concentration peak to be 0.5 nm or more closer to the surface than the magnesium concentration peak, and even more preferable for it to be 1.5 nm or more closer to the surface.
また添加元素としてニッケルを有する正極活物質１００では、表層部１００ａのニッケル濃度のピークは、正極活物質１００の表面から中心に向かった深さ３ｎｍまでに存在することが好ましく、深さ１ｎｍまでに存在することがより好ましく、深さ０．５ｎｍまでに存在することがさらに好ましい。またマグネシウムおよびニッケルを有する正極活物質１００では、ニッケルの分布は、マグネシウムの分布と重畳することが好ましい。たとえばニッケル濃度のピークと、マグネシウム濃度のピークの深さ方向の差が１０ｎｍ以内であると好ましく、３ｎｍ以内であるとより好ましく、１ｎｍ以内であるとさらに好ましい。 Furthermore, in the positive electrode active material 100 having nickel as an added element, the nickel concentration peak in the surface layer 100a is preferably present at a depth of up to 3 nm from the surface toward the center of the positive electrode active material 100, more preferably at a depth of up to 1 nm, and even more preferably at a depth of up to 0.5 nm. Furthermore, in the positive electrode active material 100 having magnesium and nickel, the nickel distribution preferably overlaps with the magnesium distribution. For example, the difference in depth between the nickel concentration peak and the magnesium concentration peak is preferably within 10 nm, more preferably within 3 nm, and even more preferably within 1 nm.
また正極活物質１００が添加元素としてアルミニウムを有する場合は、ＥＤＸ線分析をしたとき、表層部１００ａのアルミニウム濃度のピークよりも、マグネシウム、ニッケルまたはフッ素の濃度のピークが表面に近いことが好ましい。例えばアルミニウム濃度のピークは正極活物質１００の表面から中心に向かった深さ０．５ｎｍ以上５０ｎｍ以下に存在することが好ましく、深さ５ｎｍ以上５０ｎｍ以下に存在することがより好ましい。 In addition, when the positive electrode active material 100 contains aluminum as an added element, it is preferable that the magnesium, nickel, or fluorine concentration peak is closer to the surface than the aluminum concentration peak of the surface layer 100a when EDX-ray analysis is performed. For example, the aluminum concentration peak is preferably present at a depth of 0.5 nm to 50 nm from the surface toward the center of the positive electrode active material 100, and more preferably at a depth of 5 nm to 50 nm.
また正極活物質１００についてＥＤＸ線分析、面分析または点分析をしたとき、マグネシウム濃度のピークにおけるマグネシウムＭｇとコバルトＣｏの原子数の比（Ｍｇ／Ｃｏ）は０．０５以上０．６以下が好ましく、０．１以上０．４以下がより好ましい。アルミニウム濃度のピークにおけるアルミニウムＡｌとコバルトＣｏの原子数の比（Ａｌ／Ｃｏ）は０．０５以上０．６以下が好ましく、０．１以上０．４５以下がより好ましい。ニッケル濃度のピークにおけるニッケルＮｉとコバルトＣｏの原子数の比（Ｎｉ／Ｃｏ）は０以上０．２以下が好ましく、０．０１以上０．１以下がより好ましい。フッ素濃度のピークにおけるフッ素ＦとコバルトＣｏの原子数の比（Ｆ／Ｃｏ）は０以上１．６以下が好ましく、０．１以上１．４以下がより好ましい。 In addition, when EDX-ray analysis, surface analysis, or point analysis is performed on the positive electrode active material 100, the ratio of the number of atoms of magnesium Mg and cobalt Co (Mg/Co) at the peak of the magnesium concentration is preferably 0.05 to 0.6, more preferably 0.1 to 0.4. The ratio of the number of atoms of aluminum Al and cobalt Co (Al/Co) at the peak of the aluminum concentration is preferably 0.05 to 0.6, more preferably 0.1 to 0.45. The ratio of the number of atoms of nickel Ni and cobalt Co (Ni/Co) at the peak of the nickel concentration is preferably 0 to 0.2, more preferably 0.01 to 0.1. The ratio of the number of atoms of fluorine F and cobalt Co (F/Co) at the peak of the fluorine concentration is preferably 0 to 1.6, more preferably 0.1 to 1.4.
なおＥＤＸ線分析結果における正極活物質１００の表面は、たとえば以下のように推定することができる。正極活物質１００の内部１００ｂにおいて均一に存在する元素、たとえば酸素またはコバルトについて、内部１００ｂの検出量の１／２となった点を表面とする。 The surface of the positive electrode active material 100 in the EDX analysis results can be estimated, for example, as follows: For an element that is uniformly present in the interior 100b of the positive electrode active material 100, such as oxygen or cobalt, the surface is determined as the point where the amount detected in the interior 100b is half that of the element.
正極活物質１００は複合酸化物であるため、酸素の検出量を用いて表面を推定することができる。具体的には、まず内部１００ｂの酸素の検出量が安定している領域から酸素濃度の平均値Ｏａｖｅを求める。このとき明らかに表面より外と判断できる領域に化学吸着またはバックグラウンドによると考えられる酸素Ｏｂｇが検出される場合は、測定値からＯｂｇを減じて酸素濃度の平均値Ｏａｖｅとすることができる。この平均値Ｏａｖｅの１／２の値、つまり１／２Ｏａｖｅに最も近い測定値を示した測定点を、正極活物質の表面であると推定することができる。 Since the positive electrode active material 100 is a composite oxide, the surface can be estimated using the amount of detected oxygen. Specifically, first, the average oxygen concentration O ave is obtained from the region in the interior 100b where the amount of detected oxygen is stable. At this time, if oxygen O bg that is thought to be due to chemical adsorption or background is detected in a region that can be clearly determined to be outside the surface, the average oxygen concentration O ave can be obtained by subtracting O bg from the measured value. The measurement point that shows a value that is 1/2 of this average value O ave , that is, a measurement value closest to 1/2O ave , can be estimated to be the surface of the positive electrode active material.
またコバルトの検出量を用いても上記と同様に表面を推定することができる。または複数の遷移金属の検出量の和を用いて同様に推定することもできる。コバルトをはじめとする遷移金属の検出量は化学吸着の影響を受けにくい点で、表面の推定に好適である。 The surface can also be estimated in the same manner as above using the amount of cobalt detected. Alternatively, the sum of the amounts of multiple transition metals detected can be used to make a similar estimation. The amount of transition metals detected, including cobalt, is less susceptible to the effects of chemical adsorption, making it suitable for estimating the surface.
また正極活物質１００について線分析または面分析をしたとき、結晶粒界１０１近傍における添加元素ＡとコバルトＣｏの原子数の比（Ａ／Ｃｏ）は０．０２０以上０．５０以下が好ましい。さらには０．０２５以上０．３０以下が好ましい。さらには０．０３０以上０．２０以下が好ましい。または０．０２０以上０．３０以下が好ましい。または０．０２０以上０．２０以下が好ましい。または０．０２５以上０．５０以下が好ましい。または０．０２５以上０．２０以下が好ましい。または０．０３０以上０．５０以下が好ましい。または０．０３０以上０．３０以下が好ましい。 Furthermore, when the positive electrode active material 100 is subjected to a line analysis or an area analysis, the ratio (A/Co) of the number of atoms of the added element A to the cobalt Co in the vicinity of the crystal grain boundary 101 is preferably 0.020 or more and 0.50 or less. More preferably, it is 0.025 or more and 0.30 or less. Still more preferably, it is 0.030 or more and 0.20 or less. Or it is preferably 0.020 or more and 0.30 or less. Or it is preferably 0.020 or more and 0.20 or less. Or it is preferably 0.025 or more and 0.50 or less. Or it is preferably 0.025 or more and 0.20 or less. Or it is preferably 0.030 or more and 0.50 or less. Or it is preferably 0.030 or more and 0.30 or less.
たとえば添加元素がマグネシウムのとき、正極活物質１００について線分析または面分析をしたとき、結晶粒界１０１近傍におけるマグネシウムとコバルトの原子数の比（Ｍｇ／Ｃｏ）は、０．０２０以上０．５０以下が好ましい。さらには０．０２５以上０．３０以下が好ましい。さらには０．０３０以上０．２０以下が好ましい。または０．０２０以上０．３０以下が好ましい。または０．０２０以上０．２０以下が好ましい。または０．０２５以上０．５０以下が好ましい。または０．０２５以上０．２０以下が好ましい。または０．０３０以上０．５０以下が好ましい。または０．０３０以上０．３０以下が好ましい。また正極活物質１００の複数個所、たとえば３箇所以上において上記の範囲であると、添加元素が正極活物質１００の表面の狭い範囲に付着するのではなく、正極活物質１００の表層部１００ａに好ましい濃度で広く分布していることを示しているといえる。 For example, when the added element is magnesium, when a line analysis or area analysis is performed on the positive electrode active material 100, the ratio of the number of magnesium atoms to the number of cobalt atoms (Mg/Co) in the vicinity of the grain boundary 101 is preferably 0.020 or more and 0.50 or less. Further, it is preferably 0.025 or more and 0.30 or less. Further, it is preferably 0.030 or more and 0.20 or less. Or it is preferably 0.020 or more and 0.30 or less. Or it is preferably 0.020 or more and 0.20 or less. Or it is preferably 0.025 or more and 0.50 or less. Or it is preferably 0.025 or more and 0.20 or less. Or it is preferably 0.030 or more and 0.50 or less. Or it is preferably 0.030 or more and 0.30 or less. Furthermore, if the above range is present at multiple locations, for example, three or more locations, of the positive electrode active material 100, it can be said that this indicates that the additive element is not attached to a narrow area on the surface of the positive electrode active material 100, but is widely distributed at a preferred concentration in the surface layer 100a of the positive electrode active material 100.
≪ＥＰＭＡ≫
ＥＰＭＡ（電子プローブ微小分析）も元素の定量が可能である。面分析ならば各元素の分布を分析することができる。 <EPMA>
EPMA (Electron Probe Microanalysis) can also quantify elements. Area analysis can analyze the distribution of each element.
正極活物質１００の断面についてＥＰＭＡ面分析をしたとき、ＥＤＸの分析結果と同様に、添加元素から選ばれた一または二以上は濃度勾配を有していることが好ましい。また添加元素によって、濃度ピークの表面からの深さが異なっていることがより好ましい。各添加元素の濃度ピークの好ましい範囲も、ＥＤＸの場合と同様である。 When EPMA surface analysis is performed on the cross section of the positive electrode active material 100, it is preferable that one or more selected from the added elements have a concentration gradient, similar to the EDX analysis results. It is also more preferable that the depth from the surface of the concentration peak differs depending on the added element. The preferred range of the concentration peak of each added element is also the same as in the case of EDX.
ただしＥＰＭＡでは表面から１μｍ程度の深さまでの領域を分析する。そのため、各元素の定量値が他の分析法を用いた測定結果と異なる場合がある。たとえば正極活物質１００の表面分析をＥＰＭＡで行ったとき、表層部１００ａに存在する各添加元素の濃度が、ＸＰＳの結果より低くなる場合がある。 However, EPMA analyzes a region from the surface to a depth of about 1 μm. Therefore, the quantitative values of each element may differ from the measurement results obtained using other analytical methods. For example, when the surface analysis of the positive electrode active material 100 is performed using EPMA, the concentration of each added element present in the surface layer 100a may be lower than the results of XPS.
≪充電曲線とｄＱ／ｄＶｖｓＶ曲線≫
正極活物質１００は、充電していくとき特徴的な電圧の変化が表れることがある。電圧の変化は、充電曲線の容量（Ｑ）を電圧（Ｖ）で微分（ｄＱ／ｄＶ）することで得られるｄＱ／ｄＶｖｓＶ曲線から読み取ることができる。たとえばｄＱ／ｄＶｖｓＶ曲線におけるピークの前後では、非平衡な相変化が起き、結晶構造が大きく変わっていると考えられる。なお本明細書等において、非平衡な相変化とは、物理量の非線形変化を起こす現象をいうこととする。 <Charging curve and dQ/dV vs V curve>
The positive electrode active material 100 may exhibit a characteristic voltage change during charging. The voltage change can be read from a dQ/dV vs V curve obtained by differentiating (dQ/dV) the capacity (Q) of the charging curve with respect to the voltage (V). For example, it is considered that a non-equilibrium phase change occurs around the peak in the dQ/dV vs V curve, and the crystal structure changes significantly. In this specification, a non-equilibrium phase change refers to a phenomenon that causes a non-linear change in a physical quantity.
正極活物質１００は、ｄＱ／ｄＶｖｓＶ曲線において、４．５５Ｖ付近にブロードなピークを有する場合がある。４．５５Ｖ付近のピークは、Ｏ３型結晶構造からＯ３’型結晶構造へと相変化する際の電圧の変化を反映している。そのためこのピークがブロードであることは、ピークが鋭い場合よりもリチウムが引き抜かれるために必要なエネルギーの変化が少ない、すなわち結晶構造の変化が少ないことを意味する。これらの変化は少ない方が、ＣｏＯ２層のずれおよび体積の変化の影響が少なく、好ましい。 The positive electrode active material 100 may have a broad peak near 4.55V in the dQ/dV vs. V curve. The peak near 4.55V reflects the change in voltage when the phase changes from the O3 type crystal structure to the O3' type crystal structure. Therefore, the broadness of this peak means that the change in energy required for lithium extraction is smaller than when the peak is sharp, that is, the change in the crystal structure is smaller. The smaller these changes are, the less the influence of the shift of the CoO2 layer and the change in volume is, and therefore, preferable.
より具体的には、充電曲線のｄＱ／ｄＶｖｓＶ曲線において、４．５Ｖ以上４．６Ｖ以下に現れる最大値を第１のピークとしたとき、第１のピークの半値全幅が０．１０Ｖ以上であると十分にブロードであるといえ、好ましい。本明細書等において第１のピークの半値全幅は、４．３Ｖ以上４．５Ｖ以下に現れるｄＱ／ｄＶ値の最小値を第１の最小値としたときの、第１のピークと第１の最小値との平均値ＨＷＨＭ１と、４．６Ｖ以上４．８Ｖ以下に現れるｄＱ／ｄＶ値の最小値を第２の最小値としたときの第１のピークと第２の最小値との平均値ＨＷＨＭ２と、の差とする。 More specifically, when the maximum value appearing in the dQ/dV vs. V curve of the charging curve between 4.5 V and 4.6 V is defined as the first peak, it can be said that the first peak is sufficiently broad and is preferable if the full width at half maximum of the first peak is 0.10 V or more. In this specification and the like, the full width at half maximum of the first peak is defined as the difference between the average value HWHM 1 of the first peak and the first minimum value when the minimum value of the dQ/dV value appearing in the range between 4.3 V and 4.5 V is defined as the first minimum value, and the average value HWHM 2 of the first peak and the second minimum value when the minimum value of the dQ/dV value appearing in the range between 4.6 V and 4.8 V is defined as the second minimum value.
ｄＱ／ｄＶｖｓＶ曲線を取得する際の充電は、たとえば４．９Ｖまで１０ｍＡ／ｇで定電流充電とすることができる。また初回充電のｄＱ／ｄＶを取得するときは、測定前に２０ｍＡ／ｇ以上１００ｍＡ／ｇ以下で２．５Ｖまで放電したのちに上記充電を開始することが好ましい。 When obtaining the dQ/dV vs. V curve, charging can be performed at a constant current of 10 mA/g up to 4.9 V. When obtaining the dQ/dV of the initial charge, it is preferable to start the above charging after discharging to 2.5 V at 20 mA/g or more and 100 mA/g or less before measurement.
充電時のデータ取り込み間隔の設定は、たとえば１秒間隔または１ｍＶの電圧変動があったときの電圧および電流を取り込む設定とすることができる。電流値と時間を積算した値を充電容量とする。 The data capture interval during charging can be set to capture the voltage and current at 1 second intervals or when there is a 1 mV voltage fluctuation. The charge capacity is calculated by integrating the current value and time.
上記充電容量のデータの、ｎ番目とｎ＋１番目データの差分を、容量の変化ｄＱのｎ番目の値とする。同様に上記電圧データの、ｎ番目とｎ＋１番目データの差分を、電圧の変化ｄＶのｎ番目の値とする。 The difference between the nth and n+1th data of the above charging capacity data is defined as the nth value of the capacity change dQ. Similarly, the difference between the nth and n+1th data of the above voltage data is defined as the nth value of the voltage change dV.
ただし上記のデータを用いると微細なノイズの影響が大きいため、電圧および充電容量の差分について、ある区間数の移動平均からｄＱ／ｄＶ値を求めてもよい。区間数はたとえば５００とすることができる。 However, since the use of the above data is subject to the large influence of minute noise, the dQ/dV value may be calculated from the moving average of a certain number of intervals for the difference in voltage and charge capacity. The number of intervals may be set to, for example, 500.
具体的には、ｄＱのｎ番目からｎ＋５００番目までの平均値を算出し、同様にｄＶのｎ番目からｎ＋５００番目までの平均値を算出する。ｄＱ（５００個平均）／ｄＶ（５００個平均）を、ｄＱ／ｄＶ値とすることができる。ｄＱ／ｄＶｖｓＶグラフにおける横軸の電圧も、同じように区間数５００の移動平均の値を用いることができる。なお上記のような区間数５００の移動平均を用いる場合は、最後から５０１番目のデータから最後のデータはノイズの影響が大きくなるため、ｄＱ／ｄＶｖｓＶグラフには用いないことが好ましい。 Specifically, the average value of dQ from the nth to the n+500th is calculated, and similarly the average value of dV from the nth to the n+500th is calculated. The dQ/dV value can be dQ (average of 500 pieces)/dV (average of 500 pieces). Similarly, the moving average value of 500 sections can be used for the voltage on the horizontal axis in the dQ/dV vs V graph. Note that when using a moving average of 500 sections as described above, it is preferable not to use the data from the 501st data from the end to the last data in the dQ/dV vs V graph, as the data is more susceptible to noise.
また複数回充放電した後のｄＱ／ｄＶｖｓＶ曲線を分析する場合、該複数回の充放電条件は上記の充電条件と異なっていてもよい。たとえば充電は任意の電圧（たとえば４．６Ｖ、４．６５Ｖ、４．７Ｖ、４．７５Ｖまたは４．８Ｖ）、２０ｍＡ／ｇ以上１００ｍＡ／ｇ以下で定電流充電し、その後電流値が２ｍＡ／ｇ以上１０ｍＡ／ｇ以下となるまで定電圧充電し、放電は２．５Ｖになるまで、２０ｍＡ／ｇ以上１００ｍＡ／ｇ以下で定電流放電とすることができる。 When analyzing the dQ/dV vs. V curve after multiple charge/discharge cycles, the multiple charge/discharge conditions may be different from the above-mentioned charging conditions. For example, charging may be performed at a constant current of 20 mA/g to 100 mA/g at any voltage (e.g., 4.6 V, 4.65 V, 4.7 V, 4.75 V, or 4.8 V), followed by constant voltage charging until the current value is 2 mA/g to 10 mA/g, and discharging at a constant current of 20 mA/g to 100 mA/g until the voltage reaches 2.5 V.
なお、４．５５Ｖ付近においてＯ３型結晶構造からＯ３’型結晶構造へと相変化するが、このときのＯ３型結晶構造はＬｉｘＣｏＯ２中のｘが０．３程度である。これは図５で説明したｘ＝１のＯ３型結晶構造と同じ対称性を有するが、ＣｏＯ２層間の距離は若干異なる。本明細書等において、ｘの大きさの異なるＯ３型結晶構造を区別する場合、ｘ＝１のＯ３型結晶構造をＯ３（２θ＝１８．８５）、ｘ＝０．３程度のＯ３型結晶構造をＯ３（２θ＝１８．５７）ということとする。これは、ＸＲＤ測定において２θが１９°付近に現れるピークの位置が、ＣｏＯ２層間距離と対応するためである。 In addition, the phase changes from the O3 type crystal structure to the O3' type crystal structure at around 4.55V, and the O3 type crystal structure at this time has x in Li x CoO 2 of about 0.3. This has the same symmetry as the O3 type crystal structure with x = 1 described in Figure 5, but the distance between the CoO 2 layers is slightly different. In this specification, when distinguishing between O3 type crystal structures with different x values, the O3 type crystal structure with x = 1 is called O3 (2θ = 18.85), and the O3 type crystal structure with x = 0.3 is called O3 (2θ = 18.57). This is because the position of the peak that appears around 2θ 19° in the XRD measurement corresponds to the CoO 2 layer distance.
≪放電曲線とｄＱ／ｄＶｖｓＶ曲線≫
また、正極活物質１００は、高電圧で充電した後、たとえば４０ｍＡ／ｇ以下の低い電流で放電すると、放電終了間近に特徴的な電圧の変化が表れることがある。この変化は、放電曲線から求めたｄＱ／ｄＶｖｓＶ曲線において、３．９Ｖ前後に出現するピークよりも低電圧で、３．５Ｖまでの範囲に、少なくとも１つのピークが存在することで明瞭に確かめることができる。 <Discharge curve and dQ/dV vs V curve>
Furthermore, when the positive electrode active material 100 is charged at a high voltage and then discharged at a low current of, for example, 40 mA/g or less, a characteristic voltage change may appear near the end of discharge. This change can be clearly confirmed by the presence of at least one peak in the range of voltages up to 3.5 V, lower than the peak that appears around 3.9 V, in the dQ/dV vs. V curve obtained from the discharge curve.
≪ＥＳＲ≫
正極活物質１００はコバルトを有し、添加元素としてニッケルおよびマグネシウムを有することが好ましい。その結果一部のＣｏ３＋がＮｉ３＋に置換され、また一部のＬｉ＋がＭｇ２＋に置換されることが好ましい。Ｌｉ＋がＭｇ２＋に置換されることに伴い、当該Ｎｉ３＋は還元されて、Ｎｉ２＋になることがある。また、一部のＬｉ＋がＭｇ２＋に置換され、それに伴いＭｇ２＋近傍のＣｏ３＋が還元されてＣｏ２＋になる場合がある。また、一部のＣｏ３＋がＭｇ２＋に置換され、それに伴いＭｇ２＋近傍のＣｏ３＋が酸化されてＣｏ４＋になる場合がある。 <<ESR>>
The positive electrode active material 100 preferably has cobalt and nickel and magnesium as additive elements. As a result, it is preferable that a part of Co 3+ is replaced by Ni 3+ , and a part of Li + is replaced by Mg 2+ . As Li + is replaced by Mg 2+ , the Ni 3+ may be reduced to Ni 2+ . In addition, a part of Li + may be replaced by Mg 2+ , and accordingly, Co 3+ in the vicinity of Mg 2+ may be reduced to Co 2+ . In addition, a part of Co 3+ may be replaced by Mg 2+ , and accordingly, Co 3+ in the vicinity of Mg 2+ may be oxidized to Co 4+ .
したがって正極活物質１００は、Ｎｉ２＋、Ｎｉ３＋、Ｃｏ２＋及びＣｏ４＋のいずれか一以上を有することが好ましい。また、正極活物質１００の重量当たりのＮｉ２＋、Ｎｉ３＋、Ｃｏ２＋及びＣｏ４＋のいずれか一以上に起因するスピン密度が、２．０×１０１７ｓｐｉｎｓ／ｇ以上１．０×１０２１ｓｐｉｎｓ／ｇ以下であることが好ましい。前述のスピン密度を有する正極活物質１００とすることで、特に充電状態での結晶構造が安定となり好ましい。なお、マグネシウム濃度が高すぎると、Ｎｉ２＋、Ｎｉ３＋、Ｃｏ２＋及びＣｏ４＋のいずれか一以上に起因するスピン密度が低くなる場合がある。 Therefore, the positive electrode active material 100 preferably has one or more of Ni 2+ , Ni 3+ , Co 2+ and Co 4+ . In addition, the spin density caused by one or more of Ni 2+ , Ni 3+ , Co 2+ and Co 4+ per weight of the positive electrode active material 100 is preferably 2.0×10 17 spins/g or more and 1.0×10 21 spins/g or less. By making the positive electrode active material 100 have the above-mentioned spin density, the crystal structure is stable, especially in the charged state, which is preferable. Note that if the magnesium concentration is too high, the spin density caused by one or more of Ni 2+ , Ni 3+ , Co 2+ and Co 4+ may be low.
正極活物質中のスピン密度は、例えば、電子スピン共鳴法（ＥＳＲ：Ｅｌｅｃｔｒｏｎ　Ｓｐｉｎ　Ｒｅｓｏｎａｎｃｅ）などを用いて分析することができる。 The spin density in the positive electrode active material can be analyzed, for example, using electron spin resonance (ESR).
≪表面粗さと比表面積≫
正極活物質１００は、表面がなめらかで凹凸が少ないことが好ましい。表面がなめらかで凹凸が少ないことは、後述する融剤の効果が十分に発揮されて、添加元素源とコバルト酸リチウムの表面が溶融したことを示す。そのため表層部１００ａにおける添加元素の分布が良好であることを示す一つの要素である。 <Surface roughness and specific surface area>
The positive electrode active material 100 preferably has a smooth surface with few irregularities. A smooth surface with few irregularities indicates that the effect of the flux described below is fully exerted and the surfaces of the additive element source and lithium cobalt oxide are melted. Therefore, this is one factor indicating that the distribution of the additive element in the surface layer portion 100a is good.
表面がなめらかで凹凸が少ないことは、たとえば正極活物質１００の断面ＳＥＭ像または断面ＴＥＭ像、正極活物質１００の比表面積等から判断することができる。 That the surface is smooth and has few irregularities can be determined, for example, from a cross-sectional SEM image or cross-sectional TEM image of the positive electrode active material 100, the specific surface area of the positive electrode active material 100, etc.
たとえば以下のように、正極活物質１００の断面ＳＥＭ像から表面のなめらかさを数値化することができる。 For example, the surface smoothness can be quantified from a cross-sectional SEM image of the positive electrode active material 100 as follows:
まず正極活物質１００をＦＩＢ等により加工して断面を露出させる。このとき保護膜、保護剤等で正極活物質１００を覆うことが好ましい。次に保護膜等と正極活物質１００との界面のＳＥＭ像を撮影する。該ＳＥＭ像に画像処理ソフトでノイズ処理を行う。たとえばガウスぼかし（σ＝２）を行った後、二値化を行う。さらに画像処理ソフトで界面抽出を行う。さらに自動選択ツール等で保護膜等と正極活物質１００との界面ラインを選択し、データを表計算ソフト等に抽出する。表計算ソフト等の機能を用いて、回帰曲線（二次回帰）から補正を行い、傾き補正後データからラフネス算出用パラメータを求め、標準偏差を算出した二乗平均平方根表面粗さ（ＲＭＳ）を求める。また、この表面粗さは、正極活物質は少なくとも粒子外周の４００ｎｍにおける表面粗さである。 First, the cathode active material 100 is processed by FIB or the like to expose the cross section. At this time, it is preferable to cover the cathode active material 100 with a protective film, a protective agent, or the like. Next, an SEM image of the interface between the protective film or the like and the cathode active material 100 is taken. The SEM image is subjected to noise processing using image processing software. For example, Gaussian blurring (σ=2) is performed, and then binarization is performed. Furthermore, interface extraction is performed using image processing software. Furthermore, the interface line between the protective film or the like and the cathode active material 100 is selected using an automatic selection tool or the like, and data is extracted to a spreadsheet software or the like. Using the functions of the spreadsheet software or the like, correction is performed from the regression curve (quadratic regression), and parameters for calculating roughness are obtained from the data after the slope correction, and the root mean square surface roughness (RMS) is calculated by calculating the standard deviation. In addition, this surface roughness is the surface roughness at least at 400 nm from the outer periphery of the particle of the cathode active material.
本実施の形態の正極活物質１００の粒子表面においては、ラフネスの指標である二乗平均平方根（ＲＭＳ）表面粗さは３ｎｍ未満、好ましくは１ｎｍ未満、さらに好ましくは０．５ｎｍ未満の二乗平均平方根表面粗さ（ＲＭＳ）であることが好ましい。 The particle surface of the positive electrode active material 100 of this embodiment preferably has a root mean square (RMS) surface roughness, which is an index of roughness, of less than 3 nm, preferably less than 1 nm, and more preferably less than 0.5 nm.
なおノイズ処理、界面抽出等を行う画像処理ソフトについては特に限定されないが、たとえば非特許文献７乃至非特許文献９に記載の「ＩｍａｇｅＪ」を用いることができる。また表計算ソフト等についても特に限定されないが、たとえばＭｉｃｒｏｓｏｆｔ　Ｏｆｆｉｃｅ　Ｅｘｃｅｌを用いることができる。 The image processing software used for noise processing, interface extraction, etc. is not particularly limited, but for example, "ImageJ" described in Non-Patent Documents 7 to 9 can be used. Spreadsheet software, etc. is also not particularly limited, but for example, Microsoft Office Excel can be used.
またたとえば、定容法によるガス吸着法にて測定した実際の比表面積ＳＲと、理想的な比表面積Ｓｉとの比からも、正極活物質１００の表面のなめらかさを数値化することができる。 In addition, the surface smoothness of the positive electrode active material 100 can also be quantified from the ratio of the actual specific surface area S R measured by a constant volume gas adsorption method to the ideal specific surface area S i .
理想的な比表面積Ｓｉは、すべての粒子の直径がＤ５０と同じであり、重量が同じであり、形状は理想的な球であるとして計算して求める。 The ideal specific surface area S i is calculated assuming that all particles have the same diameter D50, the same weight, and an ideal spherical shape.
メディアン径（Ｄ５０）は、レーザ回折・散乱法を用いた粒度分布計等によって測定することができる。比表面積は、たとえば定容法によるガス吸着法を用いた比表面積測定装置等によって測定することができる。 The median diameter (D50) can be measured using a particle size distribution analyzer that uses a laser diffraction/scattering method. The specific surface area can be measured using a specific surface area measuring device that uses, for example, a constant volume gas adsorption method.
正極活物質１００は、メディアン径（Ｄ５０）から求めた理想的な比表面積Ｓｉと、実際の比表面積ＳＲの比ＳＲ／Ｓｉが２．１以下であることが好ましい。 The positive electrode active material 100 preferably has a ratio S R /S i of the ideal specific surface area S i determined from the median diameter (D50) to the actual specific surface area S R of 2.1 or less.
または、下記のような方法によっても正極活物質１００の断面ＳＥＭ像から表面のなめらかさを数値化することができる。 Alternatively, the surface smoothness can be quantified from a cross-sectional SEM image of the positive electrode active material 100 by the following method.
まず正極活物質１００の表面ＳＥＭ像を取得する。このとき観察前処理として導電性コーティングを施してもよい。観察面は電子線と垂直であることが好ましい。複数のサンプルを比較する場合は測定条件および観察面積を同じとする。 First, obtain a surface SEM image of the positive electrode active material 100. At this time, a conductive coating may be applied as a pretreatment before observation. The observation surface is preferably perpendicular to the electron beam. When comparing multiple samples, the measurement conditions and observation area are the same.
次に画像処理ソフト（たとえば「ＩｍａｇｅＪ」）を用いて上記のＳＥＭ像をたとえば８ビットに変換した画像（これをグレースケール画像と呼ぶ）を取得する。グレースケール画像は輝度（明るさ情報）を含んでいる。たとえば８ビットのグレースケール画像では、輝度を２の８乗＝２５６階調で表すことができる。暗い部分は階調数が低くなり、明るい部分は階調数が高くなる。階調数と関連付けて輝度変化を数値化することができる。当該数値をグレースケール値と呼ぶ。グレースケール値を取得することで正極活物質の凹凸を数値として評価することが可能となる。 Next, image processing software (for example, "ImageJ") is used to convert the SEM image to, for example, 8-bit, to obtain an image (called a grayscale image). A grayscale image contains luminance (brightness information). For example, in an 8-bit grayscale image, luminance can be expressed as 2 to the power of 8 = 256 gradations. Dark areas have lower gradations, and bright areas have higher gradations. The change in luminance can be quantified in relation to the number of gradations. This numerical value is called the grayscale value. By obtaining the grayscale value, it is possible to numerically evaluate the unevenness of the positive electrode active material.
さらに対象領域の輝度変化をヒストグラムで表すことも可能となる。ヒストグラムとは対象領域における階調分布を立体的に示したものであり、輝度ヒストグラムとも呼ぶ。輝度ヒストグラムを取得することで正極活物質の凹凸を視覚的にわかりやすく、評価することが可能となる。 It is also possible to display the luminance change in the target area using a histogram. A histogram is a three-dimensional representation of the gradation distribution in the target area, and is also called a luminance histogram. Obtaining a luminance histogram makes it possible to visually evaluate the unevenness of the positive electrode active material in an easily understandable manner.
正極活物質１００は、上記グレースケール値の最大値と最小値との差が１２０以下であることが好ましく、１１５以下であることがより好ましく、７０以上１１５以下であることがさらに好ましい。またグレースケール値の標準偏差は、１１以下となることが好ましく、８以下であることがより好ましく、４以上８以下であることがさらに好ましい。 The difference between the maximum and minimum values of the above grayscale value of the positive electrode active material 100 is preferably 120 or less, more preferably 115 or less, and even more preferably 70 or more and 115 or less. The standard deviation of the grayscale value is preferably 11 or less, more preferably 8 or less, and even more preferably 4 or more and 8 or less.
≪電流休止法≫
正極活物質１００が表層部に有するマグネシウムをはじめとする添加元素は、充放電を繰り返す過程で分布が若干変化する場合がある。たとえば添加元素の分布がより良好になり、電子伝導抵抗が低下する場合がある。そのため充放電サイクルの初期において電気的な抵抗、すなわち電流休止法により測定される応答が速い抵抗成分Ｒ（０．１ｓ）が下がる場合がある。 <Current rest method>
The distribution of the additive elements, including magnesium, contained in the surface layer of the positive electrode active material 100 may change slightly during repeated charging and discharging. For example, the distribution of the additive elements may become better, and the electronic conduction resistance may decrease. As a result, the electrical resistance at the beginning of the charge and discharge cycle, that is, the resistance component R (0.1s) with a fast response measured by the current rest method, may decrease.
たとえばｎ（ｎは１より大きい整数）回目の充電と、ｎ＋１回目の充電を比較したとき、電流休止法により測定される応答が速い抵抗成分Ｒ（０．１ｓ）がｎ回目よりもｎ＋１回目で低くなる場合がある。これに伴い、ｎ回目の放電容量よりも、ｎ＋１回目の放電容量が高い場合がある。ｎが１の場合、つまり初回充電と２回目の充電を比較したとき、２回目の充電容量が大きくなることは、特に添加元素を含まない正極活物質でもありうるため、ｎはたとえば二以上１０以下であることが好ましい。ただし充放電サイクルの初期であればこれに限らない。定格容量と同程度、たとえば定格容量の９７％以上の充放電容量を有する場合は充放電サイクルの初期ということができる。 For example, when comparing the nth (n is an integer greater than 1) charge with the n+1th charge, the resistance component R (0.1s) with a fast response measured by the current rest method may be lower in the n+1th charge than in the nth charge. As a result, the n+1th discharge capacity may be higher than the nth discharge capacity. When n is 1, that is, when comparing the first charge with the second charge, the second charge capacity may be larger, especially in a positive electrode active material that does not contain an additive element, so it is preferable that n is, for example, 2 or more and 10 or less. However, this is not limited to the case as long as it is in the early stage of the charge/discharge cycle. When the charge/discharge capacity is about the same as the rated capacity, for example, 97% or more of the rated capacity, it can be said to be in the early stage of the charge/discharge cycle.
≪ラマン分光法≫
正極活物質１００は、上述したように、表層部１００ａの少なくとも一部が、岩塩型の結晶構造を有することが好ましい。そのため、正極活物質１００およびこれを有する正極をラマン分光法で分析したとき、層状岩塩の結晶構造と共に、岩塩型をはじめとする立方晶系の結晶構造も観測されることが好ましい。後述するＨＡＡＤＦ−ＳＴＥＭ像および極微電子線回折パターンでは、観察時の奥行き方向にある程度の頻度でリチウム位置に置換したコバルト、および酸素４配位位置に存在するコバルト等が無いと、ＨＡＡＤＦ−ＳＴＥＭ像および極微電子線回折パターンの輝点として検出することができない。一方で、ラマン分光法はＣｏ−Ｏなどの結合の振動モードをとらえる分析であるため、該当するＣｏ−Ｏ結合の存在量が少なくても、対応する振動モードの波数のピークが観測できる場合がある。さらに、ラマン分光法は、表層部の面積数μｍ２、深さ１μｍくらいの範囲を測定できるため、粒子表面にのみ存在する状態を感度よく捉えることができる。 <Raman spectroscopy>
As described above, it is preferable that at least a part of the surface layer 100a of the positive electrode active material 100 has a rock salt type crystal structure. Therefore, when the positive electrode active material 100 and a positive electrode having the same are analyzed by Raman spectroscopy, it is preferable that a cubic crystal structure such as a rock salt type is also observed along with the layered rock salt crystal structure. In the HAADF-STEM image and the ultrafine electron beam diffraction pattern described later, if there is no cobalt substituted at the lithium position with a certain frequency in the depth direction during observation, and no cobalt present at the oxygen 4 coordination position, it cannot be detected as a bright spot in the HAADF-STEM image and the ultrafine electron beam diffraction pattern. On the other hand, since Raman spectroscopy is an analysis that captures the vibration mode of bonds such as Co-O, even if the amount of the corresponding Co-O bond is small, the wave number peak of the corresponding vibration mode may be observed. Furthermore, since Raman spectroscopy can measure the surface layer area of several μm 2 and the depth of about 1 μm, it is possible to capture the state that exists only on the particle surface with good sensitivity.
たとえばレーザ波長５３２ｎｍのとき、層状岩塩型のＬｉＣｏＯ２では、４７０ｃｍ−１乃至４９０ｃｍ−１、５８０ｃｍ−１乃至６００ｃｍ−１にピーク（振動モード：Ｅｇ、Ａ１ｇ）が観測される。一方、立方晶系ＣｏＯｘ（０＜ｘ＜１）（岩塩型Ｃｏ１−ｙＯ（０＜ｙ＜１）またはスピネル型Ｃｏ３Ｏ４）では、６６５ｃｍ−１乃至６８５ｃｍ−１にピーク（振動モード：Ａ１ｇ）が観測される。 For example, at a laser wavelength of 532 nm, peaks (vibration modes: Eg , A1g ) are observed at 470 cm -1 to 490 cm -1 and 580 cm -1 to 600 cm - 1 in layered rock salt LiCoO2 , while a peak (vibration mode: A1g ) is observed at 665 cm -1 to 685 cm -1 in cubic CoOx (0<x<1) (rock salt Co1 - yO (0<y<1) or spinel Co3O4 ).
そのため、各ピークの積分強度のうち、４７０ｃｍ−１乃至４９０ｃｍ−１をＩ１、５８０ｃｍ−１乃至６００ｃｍ−１をＩ２、６６５ｃｍ−１乃至６８５ｃｍ−１をＩ３としたとき、Ｉ３／Ｉ２の値が１％以上１０％以下であることが好ましく、３％以上９％以下であることがより好ましい。 Therefore, when the integrated intensity of each peak is defined as I1 from 470 cm -1 to 490 cm -1 , I2 from 580 cm -1 to 600 cm - 1, and I3 from 665 cm -1 to 685 cm -1 , it is preferable that the value of I3/I2 is 1% or more and 10% or less, and more preferably 3% or more and 9% or less.
上記のような範囲で岩塩型をはじめとする立方晶系の結晶構造が観測されれば、正極活物質１００の表層部１００ａが好ましい範囲で岩塩型の結晶構造を有しているといえる。 If a cubic crystal structure, including a rock salt type, is observed within the above range, it can be said that the surface layer 100a of the positive electrode active material 100 has a rock salt type crystal structure within a preferred range.
≪極微電子線回折パターン≫
ラマン分光法と同様に極微電子線回折パターンでも、層状岩塩の結晶構造と共に、岩塩型の結晶構造の特徴も観察されることが好ましい。ただしＳＴＥＭ像および極微電子線回折パターンにおいては、上述の感度の違いも踏まえ、表層部１００ａ、なかでも最表面（たとえば表面から深さ１ｎｍ）において岩塩型の結晶構造の特徴が強くなりすぎないことが好ましい。最表面が岩塩型の結晶構造で覆われるよりも、層状岩塩型の結晶構造を有したままリチウム層にマグネシウム等の添加元素が存在する方が、リチウムの拡散経路を確保でき、かつ結晶構造を安定化させる機能がより強くなるためである。 <Microelectron diffraction pattern>
As in the Raman spectroscopy, it is preferable that the characteristics of the rock salt type crystal structure are observed in the electron microbeam diffraction pattern as well as the layered rock salt crystal structure. However, in the STEM image and the electron microbeam diffraction pattern, it is preferable that the characteristics of the rock salt type crystal structure are not too strong in the surface layer 100a, especially in the outermost surface (for example, 1 nm deep from the surface), taking into account the above-mentioned difference in sensitivity. This is because the presence of an additive element such as magnesium in the lithium layer while maintaining the layered rock salt type crystal structure can ensure a diffusion path for lithium and has a stronger function of stabilizing the crystal structure than when the outermost surface is covered with a rock salt type crystal structure.
そのためたとえば表面から深さ１ｎｍ以下の領域の極微電子線回折パターンと、深さ３ｎｍ以上１０ｎｍ以下までの領域の極微電子線回折パターンとを取得したとき、これらから算出される格子定数の差が小さい方が好ましい。 For example, when a micro-electron beam diffraction pattern is obtained from a region having a depth of 1 nm or less from the surface, and a micro-electron beam diffraction pattern is obtained from a region having a depth of 3 nm to 10 nm, it is preferable that the difference in the lattice constant calculated from these patterns is small.
たとえば表面から深さ１ｎｍ以下の測定箇所と、深さ３ｎｍ以上１０ｎｍ以下までの測定箇所から算出される格子定数の差は、ａ軸について０．１Å以下であると好ましく、ｃ軸について１．０Å以下であると好ましい。またａ軸について０．０５Å以下であるとより好ましく、ｃ軸について０．６Å以下であるとより好ましい。またａ軸について０．０４Å以下であるとさらに好ましく、ｃ軸について０．３Å以下であるとさらに好ましい。 For example, the difference in lattice constant calculated from a measurement point at a depth of 1 nm or less from the surface and a measurement point at a depth of 3 nm to 10 nm is preferably 0.1 Å or less for the a-axis, and 1.0 Å or less for the c-axis. It is more preferable that the difference is 0.05 Å or less for the a-axis, and more preferably 0.6 Å or less for the c-axis. It is even more preferable that the difference is 0.04 Å or less for the a-axis, and even more preferably 0.3 Å or less for the c-axis.
＜追加の特徴＞
正極活物質１００は凹部、クラック、窪み、断面Ｖ字形などを有する場合がある。これらは欠陥の一つであり、充放電を繰り返すとこれらからコバルトの溶出、結晶構造の崩れ、正極活物質１００の割れ、酸素の脱離などが生じる恐れがある。しかし、図１Ｂに示すような欠陥部１００ｃを埋め込むように添加元素が存在すると、コバルトの溶出などを抑制することができる。そのため、正極活物質１００を用いた二次電池の信頼性およびサイクル特性を向上することができる。 Additional Features
The positive electrode active material 100 may have recesses, cracks, depressions, V-shaped cross sections, etc. These are defects, and repeated charging and discharging may cause elution of cobalt, collapse of the crystal structure, cracking of the positive electrode active material 100, desorption of oxygen, etc. However, if an additive element is present so as to fill the defect portion 100c as shown in FIG. 1B, elution of cobalt, etc. can be suppressed. Therefore, the reliability and cycle characteristics of a secondary battery using the positive electrode active material 100 can be improved.
上述したように正極活物質１００が有する添加元素は、過剰であるとリチウムの挿入および脱離に悪影響が出る恐れがある。また正極活物質１００を二次電池に用いたときに内部抵抗の上昇、放電容量の低下等を招く恐れもある。一方、不足であると表層部１００ａ全体に分布せず、結晶構造の劣化を抑制する効果が不十分になる恐れがある。このように添加元素は正極活物質１００において適切な濃度である必要があるが、その調整は容易ではない。 As described above, if the additive element contained in the positive electrode active material 100 is in excess, it may adversely affect the insertion and desorption of lithium. In addition, when the positive electrode active material 100 is used in a secondary battery, it may cause an increase in internal resistance and a decrease in discharge capacity. On the other hand, if there is an insufficient amount, the additive element may not be distributed throughout the entire surface layer 100a, and the effect of suppressing deterioration of the crystal structure may be insufficient. Thus, the additive element needs to be in an appropriate concentration in the positive electrode active material 100, but adjusting this concentration is not easy.
そのため正極活物質１００が、添加元素が偏在する領域を有していると、過剰な添加元素の原子の一部が正極活物質１００の内部１００ｂから除かれ、内部１００ｂにおいて適切な添加元素濃度とすることができる。これにより二次電池としたときの内部抵抗の上昇、放電容量の低下等を抑制することができる。二次電池の内部抵抗の上昇を抑制できることは、特に大電流での充放電、たとえば４００ｍＡ／ｇ以上での充放電において極めて好ましい特性である。 Therefore, if the positive electrode active material 100 has a region where the additive element is unevenly distributed, some of the excess atoms of the additive element are removed from the interior 100b of the positive electrode active material 100, and an appropriate additive element concentration can be achieved in the interior 100b. This makes it possible to suppress an increase in internal resistance and a decrease in discharge capacity when the battery is made into a secondary battery. Being able to suppress an increase in the internal resistance of a secondary battery is an extremely desirable characteristic, particularly when charging and discharging at a large current, for example, at 400 mA/g or more.
また添加元素が偏在している領域を有する正極活物質１００では、作製工程においてある程度過剰に添加元素を混合することが許容される。そのため生産におけるマージンが広くなり好ましい。 In addition, in the positive electrode active material 100 having an area where the additive element is unevenly distributed, it is permissible to mix the additive element in excess to some extent during the manufacturing process. This allows for a wider margin in production, which is preferable.
また図１３Ａ及び図１３Ｂに被覆部１０４が付着した正極活物質１００の例を示す。図１３Ａは表層部１００ａ及び内部１００ｂに加えて被覆部１０４を有する正極活物質１００を示す。図１３Ｂは表層部１００ａ及び内部１００ｂに加えて凸部１０３を有し、さらに被覆部１０４を有する正極活物質１００を示す。 Figures 13A and 13B show an example of a positive electrode active material 100 having a coating portion 104 attached thereto. Figure 13A shows a positive electrode active material 100 having a surface portion 100a and an interior portion 100b as well as a coating portion 104. Figure 13B shows a positive electrode active material 100 having a protruding portion 103 in addition to the surface portion 100a and an interior portion 100b, and further having a coating portion 104.
被覆部１０４はたとえば充放電に伴いリチウム塩および有機溶媒の分解物が堆積して形成されたものであることが好ましい。特にＬｉｘＣｏＯ２中のｘが０．２４以下となるような充電を繰り返す場合、正極活物質１００の表面にリチウム塩、有機溶媒、又は添加剤由来の被覆部を有することで、充放電サイクル特性が向上することが期待される。これは正極活物質表面のインピーダンスの上昇を抑制する、またはコバルトの溶出を抑制する、等の理由による。被覆部１０４はたとえば炭素、酸素およびフッ素を有することが好ましい。さらに電解液にＬｉＢＯＢ、及び／又はＳＵＮ（スベロニトリル）といった添加剤を加えた場合などは良質な被覆部を得られやすい。そのため、ホウ素、窒素、硫黄およびフッ素から選ばれた一または二以上を有する被覆部１０４は良質な被覆部である場合があり好ましい。また被覆部１０４は正極活物質１００の全てを覆っていなくてもよい。たとえば、正極活物質１００の表面の５０％以上を覆っていればよく、７０％以上であればより好ましく、９０％以上であればさらに好ましい。 The coating portion 104 is preferably formed by, for example, deposition of decomposition products of lithium salt and organic solvent accompanying charge and discharge. In particular, when charging is repeated such that x in Li x CoO 2 is 0.24 or less, it is expected that the charge and discharge cycle characteristics will be improved by having a coating portion derived from lithium salt, organic solvent, or additive on the surface of the positive electrode active material 100. This is due to reasons such as suppressing an increase in impedance on the surface of the positive electrode active material or suppressing the elution of cobalt. The coating portion 104 preferably has, for example, carbon, oxygen, and fluorine. Furthermore, when additives such as LiBOB and/or SUN (suberonitrile) are added to the electrolyte, a good quality coating portion is easily obtained. Therefore, the coating portion 104 having one or more selected from boron, nitrogen, sulfur, and fluorine may be a good quality coating portion and is preferable. In addition, the coating portion 104 does not have to cover the entire positive electrode active material 100. For example, it is sufficient to cover 50% or more of the surface of the positive electrode active material 100, more preferably 70% or more, and even more preferably 90% or more.
また正極活物質は、４．５Ｖ以上で充電するような条件、または高温、たとえば４５℃以上の環境で充放電することにより、表面から内部に向かって深くまで進む進行性の欠陥が生じる場合がある。正極活物質において欠陥が進行して穴を形成する現象を孔食（Ｐｉｔｔｉｎｇ　Ｃｏｒｒｏｓｉｏｎ）とも呼ぶことができ、この現象で発生した穴を本明細書ではピットとも呼ぶ。 In addition, when the positive electrode active material is charged at 4.5 V or higher, or when it is charged and discharged in a high temperature environment, such as 45°C or higher, progressive defects may develop that progress from the surface deep into the material. The phenomenon in which defects progress to form holes in the positive electrode active material can be called pitting corrosion, and the holes that develop as a result of this phenomenon are also called pits in this specification.
図１４にピットを有する正極活物質５１の断面模式図を示す。陽イオンの配列と平行な結晶面５５を併せて示した。図１４は断面図であるためピット５４およびピット５８を穴として示しているが、これらの開口形状は円ではなく奥行きがあり溝のような形状を有する。またピット５４およびピット５８に示すように、凹部５２と異なりリチウムイオンの配列と平行に生じやすい。 Figure 14 shows a schematic cross-sectional view of a positive electrode active material 51 having pits. Also shown is a crystal plane 55 parallel to the arrangement of cations. Since Figure 14 is a cross-sectional view, pits 54 and pits 58 are shown as holes, but the shape of these openings is not circular but has depth and is groove-like. Also, as shown by pits 54 and pits 58, unlike recesses 52, they tend to form parallel to the arrangement of lithium ions.
また正極活物質５１は、添加元素の存在する表層部５３および表層部５６を有する。ピットが生じると表層部５３及び／又は表層部５６から添加元素が減少し、バリア膜の機能が減じていると予想される。またピットができる近傍ではコバルト酸リチウムの結晶構造が崩れ、層状岩塩型とは異なった結晶構造になると考えられる。結晶構造が崩れるとキャリアイオンであるリチウムイオンの拡散及び放出を阻害するため、ピットはサイクル特性劣化の要因と考えられる。 Positive electrode active material 51 also has surface layer 53 and surface layer 56 where the added element is present. When pits occur, the added element is reduced from surface layer 53 and/or surface layer 56, and it is expected that the function of the barrier film is reduced. It is also thought that the crystal structure of lithium cobalt oxide breaks down in the vicinity of where the pits form, resulting in a crystal structure different from that of the layered rock salt type. When the crystal structure breaks down, it inhibits the diffusion and release of lithium ions, which are carrier ions, and therefore the pits are thought to be a factor in the deterioration of cycle characteristics.
ピットの発生源は点欠陥の可能性がある。正極活物質が有する点欠陥が充放電を繰り返すことで変化し、周囲のリチウム塩および有機溶媒等によって化学的または電気化学的に侵食されるか、若しくは材質が劣化してピットが生じると考えられる。この劣化は、正極活物質の表面で均一に発生するのではなく、局部的に集中して生じる。 The source of the pits may be point defects. It is thought that point defects in the positive electrode active material change with repeated charging and discharging, and are either chemically or electrochemically eroded by the surrounding lithium salts and organic solvents, or the material deteriorates, causing the pits. This deterioration does not occur uniformly on the surface of the positive electrode active material, but rather occurs in localized areas.
また、図１４の正極活物質５１はクラック５７を有する。クラック５７は割れ目とも呼ばれ、充放電による正極活物質の膨張および収縮により発生する場合がある。本明細書において、クラックとピットは異なるものとする。これは正極活物質の作製直後にクラックは存在してもピットは存在しないためである。ピットは、たとえば４．５Ｖ以上の高電圧条件または高温（４５℃以上）下で充放電することにより、コバルトおよび酸素が何層分か抜けた穴とも言え、コバルトが溶出した箇所ともいえる。クラックはたとえば物理的な圧力が加えられることで生じる新たな面、或いは結晶粒界１０１が起因となって生じた割れ目を指す。充放電による正極活物質の膨張および収縮によりクラックが発生する場合もある。また、クラック及び／又は正極活物質内部の空洞からピットが発生する場合もある。 Also, the positive electrode active material 51 in FIG. 14 has cracks 57. The cracks 57 are also called fissures, and may occur due to the expansion and contraction of the positive electrode active material caused by charging and discharging. In this specification, cracks and pits are different. This is because cracks may exist but pits do not exist immediately after the preparation of the positive electrode active material. The pits can be said to be holes formed by several layers of cobalt and oxygen being removed by charging and discharging under high voltage conditions of, for example, 4.5 V or more or at high temperatures (45° C. or more), and can also be said to be places where cobalt has dissolved. The cracks refer to, for example, new surfaces formed by the application of physical pressure, or cracks caused by the grain boundaries 101. The cracks may occur due to the expansion and contraction of the positive electrode active material caused by charging and discharging. The pits may also occur from the cracks and/or cavities inside the positive electrode active material.
本実施の形態は、他の実施の形態と組み合わせ用いることができる。 This embodiment can be used in combination with other embodiments.
（実施の形態２）
本実施の形態では、本発明を実施する一形態である正極活物質１００の作製方法の例について説明する。 (Embodiment 2)
In this embodiment, an example of a method for producing a positive electrode active material 100 which is one embodiment of the present invention will be described.
先の実施の形態で説明したような添加元素の分布、組成、及び／又は結晶構造を有する正極活物質１００を作製するためには、添加元素の加え方が重要である。同時に内部１００ｂの結晶性が良好であることも重要である。 In order to produce a positive electrode active material 100 having the distribution, composition, and/or crystal structure of the added elements as described in the previous embodiment, the method of adding the added elements is important. At the same time, it is also important that the crystallinity of the interior 100b is good.
そのため正極活物質１００の作製工程において、まずコバルト酸リチウムを合成し、その後添加元素源を混合して加熱処理を行うことが好ましい。 Therefore, in the process of producing the positive electrode active material 100, it is preferable to first synthesize lithium cobalt oxide, and then mix in the additive element source and perform a heat treatment.
コバルト源と、リチウム源と同じステップで添加元素源を混合して、添加元素を有するコバルト酸リチウムを合成する方法では、表層部１００ａの添加元素濃度を高めることが難しい。またコバルト酸リチウムを合成した後、添加元素源を混合するのみで加熱を行わなければ、添加元素はコバルト酸リチウムに固溶することなく付着するのみである。十分な加熱を経なければ、やはり添加元素を良好に分布させることが難しい。そのためコバルト酸リチウムを合成してから添加元素源を混合し、加熱処理を行うことが好ましい。この添加元素源を混合した後の加熱処理をアニールという場合がある。 In the method of synthesizing lithium cobalt oxide containing additive elements by mixing a cobalt source and an additive element source in the same step as the lithium source, it is difficult to increase the additive element concentration in the surface layer 100a. Furthermore, if the additive element source is only mixed after the lithium cobalt oxide is synthesized without heating, the additive element will only adhere to the lithium cobalt oxide without dissolving in the lithium cobalt oxide. Without sufficient heating, it is still difficult to distribute the additive element well. For this reason, it is preferable to synthesize lithium cobalt oxide, mix the additive element source, and then perform a heat treatment. This heat treatment after mixing the additive element source is sometimes called annealing.
しかしながらアニールの温度が高すぎると、カチオンミキシングが生じて添加元素、たとえばマグネシウムがコバルトサイトに入る可能性が高まる。コバルトサイトに存在するマグネシウムは、ＬｉｘＣｏＯ２中のｘが小さいときＲ−３ｍの層状岩塩型の結晶構造を保つ効果がない。さらに、加熱処理の温度が高すぎると、コバルトが還元されて２価になってしまう、リチウムが蒸散するなどの悪影響も懸念される。 However, if the annealing temperature is too high, cation mixing occurs, increasing the possibility that an added element, such as magnesium, will enter the cobalt site. Magnesium present at the cobalt site has no effect of maintaining the layered rock salt type crystal structure of R-3m when x in Li x CoO 2 is small. Furthermore, if the heat treatment temperature is too high, there are concerns about adverse effects such as cobalt being reduced to divalent and lithium being evaporated.
そこで添加元素源と共に、融剤として機能する材料を混合することが好ましい。コバルト酸リチウムより融点が低ければ、融剤として機能する材料といえる。たとえばフッ化リチウムをはじめとするフッ素化合物が好適である。融剤を加えることで、添加元素源と、コバルト酸リチウムの融点降下が起こる。融点降下させることでカチオンミキシングが生じにくい温度で、添加元素を良好に分布させることが容易となる。 Therefore, it is preferable to mix a material that functions as a flux with the additive element source. Any material that has a lower melting point than lithium cobalt oxide can function as a flux. For example, fluorine compounds such as lithium fluoride are suitable. Adding a flux lowers the melting point of the additive element source and lithium cobalt oxide. Lowering the melting point makes it easier to distribute the additive element well at a temperature where cation mixing is unlikely to occur.
〔初期加熱〕
さらにコバルト酸リチウムを合成した後、添加元素を混合する前にも加熱を行うとより好ましい。この加熱を初期加熱という場合がある。 [Initial heating]
It is more preferable to heat the lithium cobalt oxide after synthesis and before mixing with the additive element. This heating is sometimes called initial heating.
初期加熱により、コバルト酸リチウムの表層部１００ａの一部からリチウムが脱離する影響で、添加元素の分布がさらに良好になる。初期加熱により上述した転位を含む欠陥の密度が少なくなると考えられる。 The initial heating causes lithium to be removed from part of the surface layer 100a of the lithium cobalt oxide, resulting in a better distribution of the added elements. It is believed that the initial heating reduces the density of defects, including the dislocations described above.
より詳細には以下のような機序で、初期加熱により添加元素によって分布を異ならせやすくなると考えられる。まず初期加熱により表層部１００ａの一部からリチウムが脱離する。次にこのリチウムが欠乏した表層部１００ａを有するコバルト酸リチウムと、ニッケル源、アルミニウム源、マグネシウム源をはじめとする添加元素源を混合し加熱する。添加元素のうちマグネシウムは２価の典型元素であり、ニッケルは遷移金属であるが２価のイオンになりやすい。そのため表層部１００ａの一部に、Ｍｇ２＋およびＮｉ２＋と、リチウムの欠乏により還元されたＣｏ２＋と、を有する岩塩型の相が形成される。ただし、この相が形成されるのは表層部１００ａの一部であるため、ＳＴＥＭなどの電子顕微鏡像および電子線回折パターンにおいて明瞭に確認できない場合もある。 More specifically, it is believed that the distribution of the additive elements can be easily differentiated by initial heating through the following mechanism. First, lithium is released from a part of the surface layer 100a by initial heating. Next, the lithium cobalt oxide having the lithium-deficient surface layer 100a is mixed with an additive element source, such as a nickel source, an aluminum source, or a magnesium source, and heated. Among the additive elements, magnesium is a typical divalent element, and nickel is a transition metal but is prone to becoming a divalent ion. Therefore, a rock salt phase containing Mg 2+ and Ni 2+ , and Co 2+ reduced by the deficiency of lithium is formed in a part of the surface layer 100a. However, since this phase is formed in a part of the surface layer 100a, it may not be clearly confirmed in an electron microscope image such as STEM and an electron beam diffraction pattern.
添加元素のうちニッケルは、表層部１００ａが層状岩塩型のコバルト酸リチウムの場合は固溶しやすく内部１００ｂまで拡散するが、表層部１００ａの一部が岩塩型の場合は表層部１００ａにとどまりやすい。そのため、初期加熱を行うことでニッケルをはじめとする２価の添加元素を表層部１００ａに留まりやすくすることができる。この初期加熱の効果は特に正極活物質１００の（００１）配向以外の表面およびその表層部１００ａにおいて大きい。 Of the additive elements, nickel is likely to dissolve and diffuse to the interior 100b when the surface layer 100a is a layered rock-salt type lithium cobalt oxide, but is likely to remain in the surface layer 100a when part of the surface layer 100a is rock-salt type. Therefore, by performing initial heating, it is possible to make it easier for divalent additive elements such as nickel to remain in the surface layer 100a. The effect of this initial heating is particularly large on the surface other than the (001) orientation of the positive electrode active material 100 and on its surface layer 100a.
またこれらの岩塩型では、金属Ｍｅと酸素の結合距離（Ｍｅ−Ｏ距離）が層状岩塩型よりも長くなる傾向にある。 In addition, in these rock salt types, the bond distance between the metal Me and oxygen (Me-O distance) tends to be longer than in the layered rock salt type.
たとえば岩塩型Ｎｉ０．５Ｍｇ０．５ＯにおけるＭｅ−Ｏ距離は２．０９Å、岩塩型ＭｇＯにおけるＭｅ−Ｏ距離は２．１１Åである。また仮に表層部１００ａの一部にスピネル型の相が形成されたとしても、スピネル型ＮｉＡｌ２Ｏ４のＭｅ−Ｏ距離は２．０１２５Å、スピネル型ＭｇＡｌ２Ｏ４のＭｅ−Ｏ距離は２．０２Åである。いずれもＭｅ−Ｏ距離は２Åを超える。なお１Å＝１０−１０ｍである。 For example, the Me-O distance in rock salt Ni0.5Mg0.5O is 2.09 Å , and the Me-O distance in rock salt MgO is 2.11 Å. Even if a spinel phase is formed in a part of the surface layer 100a, the Me-O distance in spinel NiAl2O4 is 2.0125 Å, and the Me-O distance in spinel MgAl2O4 is 2.02 Å. In both cases, the Me-O distance exceeds 2 Å. Note that 1 Å= 10-10 m.
一方、層状岩塩型では、リチウム以外の金属と酸素の結合距離は上記より短い。たとえば層状岩塩型ＬｉＡｌＯ２におけるＡｌ−Ｏ距離は１．９０５Å（Ｌｉ−Ｏ距離は２．１１Å）である。また層状岩塩型ＬｉＣｏＯ２におけるＣｏ−Ｏ距離は１．９２２４Å（Ｌｉ−Ｏ距離は２．０９１６Å）である。 On the other hand, in the layered rock salt type, the bond distance between metals other than lithium and oxygen is shorter than the above. For example, the Al-O distance in layered rock salt type LiAlO2 is 1.905 Å (Li-O distance is 2.11 Å). Also, the Co-O distance in layered rock salt type LiCoO2 is 1.9224 Å (Li-O distance is 2.0916 Å).
なお非特許文献１１のシャノンのイオン半径によれば、６配位のアルミニウムのイオン半径は０．５３５Å、６配位の酸素のイオン半径は１．４Åであり、これらの和は１．９３５Åである。 According to the Shannon ionic radius in Non-Patent Document 11, the ionic radius of 6-coordinate aluminum is 0.535 Å, the ionic radius of 6-coordinate oxygen is 1.4 Å, and the sum of these is 1.935 Å.
以上から、アルミニウムは、岩塩型よりも層状岩塩型のリチウム以外のサイトでより安定に存在すると考えられる。そのため、アルミニウムは表層部１００ａの中でも岩塩型の相を有する表面に近い領域よりも、層状岩塩型を有するより深い領域、及び／又は内部１００ｂに分布しやすい。 From the above, it is believed that aluminum is more stable in non-lithium sites in the layered rock-salt type than in the rock-salt type. Therefore, aluminum is more likely to be distributed in the deeper regions having the layered rock-salt type and/or in the interior 100b than in the regions close to the surface having the rock-salt type phase in the surface layer portion 100a.
また初期加熱により、内部１００ｂの層状岩塩型の結晶構造の結晶性を高める効果も期待できる。 Initial heating is also expected to have the effect of increasing the crystallinity of the layered rock-salt crystal structure in the interior 100b.
そのため、特にＬｉｘＣｏＯ２中のｘがたとえば０．１５以上０．１７以下のときに単斜晶Ｏ１（１５）型結晶構造を有する正極活物質１００を作製するには、この初期加熱を行うことが好ましい。 Therefore, it is preferable to perform this initial heating in order to produce a cathode active material 100 having a monoclinic O1(15) type crystal structure, particularly when x in Li x CoO 2 is, for example, 0.15 or more and 0.17 or less.
しかし、必ずしも初期加熱は行わなくてもよい。他の加熱工程、たとえばアニールにおいて、雰囲気、温度、時間等を制御することで、ＬｉｘＣｏＯ２中のｘが小さいときにＯ３’型及び／又は単斜晶Ｏ１（１５）型を有する正極活物質１００を作製できる場合がある。 However, initial heating is not necessarily required. In other heating steps, such as annealing, by controlling the atmosphere, temperature, time, etc., it may be possible to produce a positive electrode active material 100 having O3′ type and/or monoclinic O1(15) type when x in Li x CoO 2 is small.
《正極活物質の製造方法１》
アニールおよび初期加熱を経る正極活物質１００の製造方法１について、図１８Ａ乃至図１８Ｃを用いて説明する。 <<Production method 1 of positive electrode active material>>
Method 1 for producing positive electrode active material 100, which undergoes annealing and initial heating, will be described with reference to FIGS. 18A to 18C.
＜ステップＳ１１＞
図１８Ａに示すステップＳ１１では、出発材料であるリチウム及び遷移金属の材料として、それぞれリチウム源（Ｌｉ源）及びコバルト源（Ｃｏ源）を準備する。 <Step S11>
In step S11 shown in FIG. 18A, a lithium source (Li source) and a cobalt source (Co source) are prepared as starting materials, that is, lithium and transition metal materials, respectively.
リチウム源としては、リチウムを有する化合物を用いると好ましく、例えば炭酸リチウム、水酸化リチウム、硝酸リチウム、又はフッ化リチウム等を用いることができる。リチウム源は純度が高いと好ましく、例えば純度が９９．９９％以上の材料を用いるとよい。 As the lithium source, it is preferable to use a compound containing lithium, such as lithium carbonate, lithium hydroxide, lithium nitrate, or lithium fluoride. It is preferable that the lithium source has high purity, for example, a material with a purity of 99.99% or more.
コバルト源としては、コバルトを有する化合物を用いると好ましく、例えば酸化コバルト、水酸化コバルト等を用いることができる。 As the cobalt source, it is preferable to use a compound containing cobalt, such as cobalt oxide or cobalt hydroxide.
コバルト源は純度が高いと好ましく、例えば純度が３Ｎ（９９．９％）以上、好ましくは４Ｎ（９９．９９％）以上、より好ましくは４Ｎ５（９９．９９５％）以上、さらに好ましくは５Ｎ（９９．９９９％）以上の材料を用いるとよい。高純度の材料を用いることで、正極活物質の不純物を制御することができる。その結果、二次電池の容量が高まり、及び／又は二次電池の信頼性が向上する。 The cobalt source is preferably of high purity, for example, a material with a purity of 3N (99.9%) or more, preferably 4N (99.99%) or more, more preferably 4N5 (99.995%) or more, and even more preferably 5N (99.999%) or more may be used. By using a high purity material, impurities in the positive electrode active material can be controlled. As a result, the capacity of the secondary battery is increased and/or the reliability of the secondary battery is improved.
加えて、コバルト源の結晶性が高いと好ましく、例えば単結晶粒を有するとよい。コバルト源の結晶性の評価としては、ＴＥＭ（透過型電子顕微鏡）像、ＳＴＥＭ（走査透過型電子顕微鏡）像、ＨＡＡＤＦ−ＳＴＥＭ（高角散乱環状暗視野走査透過電子顕微鏡）像、ＡＢＦ−ＳＴＥＭ（環状明視野走査透過電子顕微鏡）像等による評価、またはＸ線回折（ＸＲＤ）、電子線回折、中性子線回折等の評価がある。なお、上記の結晶性の評価に関する手法は、コバルト源だけではなく、その他の結晶性の評価にも適用することができる。 In addition, it is preferable that the cobalt source has high crystallinity, for example, single crystal grains. The crystallinity of the cobalt source can be evaluated using TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope) images, ABF-STEM (annular bright-field scanning transmission electron microscope) images, etc., or evaluation using X-ray diffraction (XRD), electron beam diffraction, neutron beam diffraction, etc. Note that the above-mentioned methods for evaluating crystallinity can be applied not only to cobalt sources but also to evaluation of other crystallinity.
＜ステップＳ１２＞
次に、図１８Ａに示すステップＳ１２として、リチウム源及びコバルト源を粉砕及び混合して、混合材料を作製する。粉砕及び混合は、乾式または湿式で行うことができる。湿式はより小さく解砕することができるため好ましい。湿式で行う場合は、溶媒を準備する。溶媒としてはアセトン等のケトン、エタノール及びイソプロパノール等のアルコール、エーテル、ジオキサン、アセトニトリル、Ｎ−メチル−２−ピロリドン（ＮＭＰ）等を用いることができる。リチウムと反応が起こりにくい、非プロトン性溶媒を用いることがより好ましい。本実施の形態では、純度が９９．５％以上の脱水アセトンを用いることとする。水分含有量を１０ｐｐｍ以下まで抑えた、純度が９９．５％以上の脱水アセトンにリチウム源及びコバルト源を混合して、粉砕及び混合を行うと好適である。上記のような純度の脱水アセトンを用いることで、混入しうる不純物を低減することができる。 <Step S12>
Next, in step S12 shown in FIG. 18A, the lithium source and the cobalt source are pulverized and mixed to prepare a mixed material. The pulverization and mixing can be performed in a dry or wet manner. The wet method is preferable because it can be crushed into smaller pieces. When performing the wet method, a solvent is prepared. As the solvent, ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. can be used. It is more preferable to use an aprotic solvent that is less likely to react with lithium. In this embodiment, dehydrated acetone with a purity of 99.5% or more is used. It is preferable to mix the lithium source and the cobalt source with dehydrated acetone with a purity of 99.5% or more, in which the moisture content is suppressed to 10 ppm or less, and then pulverize and mix them. By using dehydrated acetone with the above-mentioned purity, it is possible to reduce impurities that may be mixed in.
粉砕及び混合の手段にはボールミル、またはビーズミル等を用いることができる。ボールミルを用いる場合は、メディアとして酸化アルミニウムボール又は酸化ジルコニウムボールを用いるとよい。酸化ジルコニウムボールは不純物の排出が少なく好ましい。また、ボールミル、またはビーズミル等を用いる場合、メディアからのコンタミネーションを抑制するために、周速を、１００ｍｍ／ｓ以上２０００ｍｍ／ｓ以下とするとよい。本実施の形態では、周速８３８ｍｍ／ｓ（回転数４００ｒｐｍ、ボールミルの直径４０ｍｍ）として実施する。 A ball mill, a bead mill, or the like can be used as a means for grinding and mixing. When using a ball mill, it is preferable to use aluminum oxide balls or zirconium oxide balls as the media. Zirconium oxide balls are preferable because they emit less impurities. Furthermore, when using a ball mill, a bead mill, or the like, it is preferable to set the peripheral speed to 100 mm/s or more and 2000 mm/s or less in order to suppress contamination from the media. In this embodiment, the peripheral speed is set to 838 mm/s (rotation speed 400 rpm, ball mill diameter 40 mm).
＜ステップＳ１３＞
次に、図１８Ａに示すステップＳ１３として、上記混合材料を加熱する。加熱は、８００℃以上１１００℃以下で行うことが好ましく、９００℃以上１０００℃以下で行うことがより好ましく、９５０℃程度がさらに好ましい。温度が低すぎると、リチウム源及びコバルト源の分解及び溶融が不十分となるおそれがある。一方温度が高すぎると、リチウム源からリチウムが蒸散する、及び／又はコバルトが過剰に還元される、などが原因となり欠陥が生じるおそれがある。例えばコバルトが３価から２価へ変化し、酸素欠陥などが誘発されることがある。 <Step S13>
Next, in step S13 shown in FIG. 18A, the mixed material is heated. The heating is preferably performed at 800° C. or more and 1100° C. or less, more preferably at 900° C. or more and 1000° C. or less, and even more preferably at about 950° C. If the temperature is too low, the decomposition and melting of the lithium source and the cobalt source may be insufficient. On the other hand, if the temperature is too high, defects may occur due to lithium transpiration from the lithium source and/or cobalt being excessively reduced. For example, cobalt may change from trivalent to divalent, inducing oxygen defects, etc.
加熱時間は短すぎるとコバルト酸リチウムが合成されないが、長すぎると生産性が低下する。たとえば加熱時間は１時間以上１００時間以下とするとよく、２時間以上２０時間以下とすることがさらに好ましい。 If the heating time is too short, lithium cobalt oxide will not be synthesized, but if it is too long, productivity will decrease. For example, the heating time should be between 1 hour and 100 hours, and more preferably between 2 hours and 20 hours.
昇温レートは、加熱温度の到達温度によるが、８０℃／ｈ以上２５０℃／ｈ以下がよい。たとえば１０００℃で１０時間加熱する場合、昇温レートは２００℃／ｈとするとよい。 The rate of temperature rise depends on the heating temperature reached, but should be between 80°C/h and 250°C/h. For example, if heating at 1000°C for 10 hours, the rate of temperature rise should be 200°C/h.
加熱は、乾燥空気等の水が少ない雰囲気で行うことが好ましく、例えば露点が−５０℃以下、より好ましくは露点が−８０℃以下の雰囲気がよい。本実施の形態においては、露点−９３℃の雰囲気にて、加熱を行うこととする。また材料中に混入しうる不純物を抑制するためには、加熱雰囲気におけるＣＨ４、ＣＯ、ＣＯ２、及びＨ２等の不純物濃度が、それぞれ５ｐｐｂ（ｐａｒｔｓ　ｐｅｒ　ｂｉｌｌｉｏｎ）以下にするとよい。 The heating is preferably performed in an atmosphere with little water, such as dry air, for example, an atmosphere with a dew point of −50° C. or less, more preferably an atmosphere with a dew point of −80° C. or less. In this embodiment, the heating is performed in an atmosphere with a dew point of −93° C. In order to suppress impurities that may be mixed into the material, the impurity concentrations of CH 4 , CO, CO 2 , H 2 , and the like in the heating atmosphere should each be 5 ppb (parts per billion) or less.
加熱雰囲気として酸素を有する雰囲気が好ましい。例えば反応室に乾燥空気を導入し続ける方法がある。この場合、乾燥空気の流量は１０Ｌ／ｍｉｎとすることが好ましい。酸素を反応室へ導入し続け、酸素が反応室内を流れている方法をフローと呼ぶ。 The heating atmosphere is preferably an atmosphere containing oxygen. For example, there is a method of continuously introducing dry air into the reaction chamber. In this case, the flow rate of the dry air is preferably 10 L/min. The method of continuously introducing oxygen into the reaction chamber and having oxygen flow through the reaction chamber is called flow.
加熱雰囲気を、酸素を有する雰囲気とする場合、フローさせないやり方でもよい。例えば反応室を減圧してから酸素を充填し（パージし、といってもよい）、当該酸素が反応室から出入りしないようにする方法でもよい。たとえば反応室の差圧計が−９７０ｈＰａとなるまで減圧してから、５０ｈＰａまで酸素を充填すればよい。 When the heating atmosphere is an atmosphere containing oxygen, a method that does not allow flow may be used. For example, the reaction chamber may be depressurized and then filled with oxygen (or purged) to prevent the oxygen from entering or leaving the reaction chamber. For example, the pressure in the reaction chamber may be depressurized until the differential pressure gauge indicates -970 hPa, and then oxygen may be filled to 50 hPa.
加熱後の冷却は自然放冷でよいが、規定温度から室温までの降温時間が１０時間以上５０時間以下に収まると好ましい。ただし、必ずしも室温までの冷却は要せず、次のステップが許容する温度まで冷却されればよい。 After heating, the material can be allowed to cool naturally, but it is preferable that the time it takes to cool from the specified temperature to room temperature is within a range of 10 to 50 hours. However, cooling to room temperature is not always necessary, as long as the material is cooled to a temperature acceptable for the next step.
本工程の加熱は、ロータリーキルン又はローラーハースキルンによる加熱を行ってもよい。ロータリーキルンによる加熱は、連続式、バッチ式いずれの場合でも攪拌しながら加熱することができる。 The heating in this process may be performed using a rotary kiln or a roller hearth kiln. Heating using a rotary kiln can be performed while stirring, whether it is a continuous or batch type.
加熱の際に用いる、るつぼは酸化アルミニウムのるつぼが好ましい。酸化アルミニウムのるつぼは不純物を放出しにくい材質である。本実施の形態においては、純度が９９．９％の酸化アルミニウムのるつぼを用いる。るつぼには蓋を配して加熱すると好ましい。材料の揮発を防ぐことができる。 The crucible used for heating is preferably made of aluminum oxide. Aluminum oxide crucibles are made of a material that does not easily release impurities. In this embodiment, an aluminum oxide crucible with a purity of 99.9% is used. It is preferable to place a lid on the crucible when heating. This prevents the material from volatilizing.
またるつぼは新品のものよりも、中古のものを用いることが好ましい。本明細書等において新品のるつぼとは、リチウム、遷移金属Ｍ、及び／又は添加元素を含む材料を入れて加熱する工程が２回以下のものをいうこととする。また中古のるつぼとは、リチウム、遷移金属Ｍ及び／又は添加元素を含む材料を入れて加熱する工程を３回以上経たものということとする。これは新品のるつぼを用いると、加熱の際にフッ化リチウムをはじめとする材料の一部がさやに吸収、拡散、移動及び／又は付着する恐れがあるためである。これらにより材料の一部が失われると、特に正極活物質の表層部の元素の分布が好ましい範囲にならない懸念が高まる。一方で中古のるつぼではこの恐れが少ない。 In addition, it is preferable to use a used crucible rather than a new one. In this specification, a new crucible refers to one that has undergone the process of putting in and heating materials containing lithium, transition metal M, and/or additive elements two or less times. A used crucible refers to one that has undergone the process of putting in and heating materials containing lithium, transition metal M, and/or additive elements three or more times. This is because when a new crucible is used, there is a risk that some of the materials, including lithium fluoride, may be absorbed, diffused, moved, and/or attached to the sheath during heating. If some of the materials are lost as a result of this, there is an increased concern that the distribution of elements, particularly in the surface layer of the positive electrode active material, may not be within a preferred range. On the other hand, this risk is less likely with a used crucible.
加熱が終わったあと、必要に応じて粉砕し、さらにふるいを実施してもよい。加熱後の材料を回収する際に、るつぼから乳鉢へ移動させたのち回収してもよい。また、当該乳鉢は酸化アルミニウムの乳鉢又は酸化ジルコニウムの乳鉢を用いると好適である。酸化アルミニウムの乳鉢は不純物を放出しにくい材質である。具体的には、純度が９０％以上、好ましくは純度が９９％以上の酸化アルミニウムの乳鉢を用いる。なお、ステップＳ１３以外の後述の加熱の工程においても、ステップＳ１３と同等の加熱条件を適用できる。 After heating, the material may be crushed and sieved as necessary. When recovering the heated material, it may be transferred from the crucible to a mortar and then recovered. The mortar is preferably made of aluminum oxide or zirconium oxide. Aluminum oxide mortars are made of a material that does not easily release impurities. Specifically, an aluminum oxide mortar with a purity of 90% or more, preferably 99% or more, is used. Note that the same heating conditions as those in step S13 can be applied to the heating steps described below other than step S13.
＜ステップＳ１４＞
以上の工程により、図１８Ａに示すステップＳ１４で示すコバルト酸リチウム（ＬｉＣｏＯ２）を合成することができる。 <Step S14>
Through the above steps, lithium cobalt oxide (LiCoO 2 ) can be synthesized as shown in step S14 in FIG. 18A.
ステップＳ１１乃至ステップＳ１４のように固相法で複合酸化物を作製する例を示したが、共沈法で複合酸化物を作製してもよい。また水熱法で複合酸化物を作製してもよい。 In the example shown in steps S11 to S14, the composite oxide is produced by a solid phase method, but the composite oxide may also be produced by a coprecipitation method. The composite oxide may also be produced by a hydrothermal method.
さらにステップＳ１４としてあらかじめ合成されたコバルト酸リチウムを用いてもよい。この場合、ステップＳ１１乃至ステップＳ１３を省略することができる。 Furthermore, in step S14, pre-synthesized lithium cobalt oxide may be used. In this case, steps S11 to S13 may be omitted.
ここで、ステップＳ１４に用いることができるコバルト酸リチウムの各元素濃度について説明する。コバルト酸リチウムをグロー放電質量分析法（ＧＤ−ＭＳ：Ｇｌｏｗ　Ｄｉｓｃｈａｒｇｅ　Ｍａｓｓ　Ｓｐｅｃｔｒｏｍｅｔｒｙ）を用いて分析すると、各元素の濃度を得ることができる。表２乃至表４には４種のコバルト酸リチウム（材料Ｓｍ−１、材料Ｓｍ−２、材料Ｓｍ−３、材料Ｓｍ−４）ごとの各元素濃度を示す。なお、見やすくするため、表を表２乃至表４の３つに分けて記載している。また表においてＭａｔｒｉｘとあるのは主成分であることを意味し、Ｂｉｎｄｅｒは補助電極を意味し、Ｓｏｕｒｃｅは測定装置の部材由来の影響があることを意味し、「＜」は検出下限未満であったことを意味し、「≦」は妨害元素が重なっているが、数値以下であることを意味し、「~」はばらつきがみられた、又は妨害元素が一部重なっているが、半定量値であることを意味する。またｐｐｍ　ｗｅｉｇｈｔ（ｐｐｍ　ｗｔと記す）で得られた各元素の測定値に、それぞれ各元素の原子量を乗算し、結果を百分率するとａｔｏｍｉｃ％に換算できる。 Here, the concentration of each element in lithium cobalt oxide that can be used in step S14 will be described. When lithium cobalt oxide is analyzed using glow discharge mass spectrometry (GD-MS), the concentration of each element can be obtained. Tables 2 to 4 show the concentration of each element for four types of lithium cobalt oxide (material Sm-1, material Sm-2, material Sm-3, and material Sm-4). For ease of viewing, the tables are divided into three tables, Tables 2 to 4. In the tables, Matrix means the main component, Binder means the auxiliary electrode, Source means that there is an influence from the components of the measuring device, "<" means that it was below the detection limit, "≦" means that the interfering elements overlap but are below the numerical value, and "~" means that there is variation or that the interfering elements overlap partially but are semi-quantitative values. Additionally, the measured value of each element in ppm weight (written as ppm wt) can be multiplied by the atomic weight of each element and converted into a percentage to give an atomic %.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
表２乃至表４よりステップＳ１４に用いることができるコバルト酸リチウムの各元素濃度を読み取ることができる。 Tables 2 to 4 show the element concentrations of lithium cobalt oxide that can be used in step S14.
＜ステップＳ１５＞
次に、図１８Ａに示すステップＳ１５としてコバルト酸リチウムを加熱する。コバルト酸リチウムに対する最初の加熱のため、ステップＳ１５の加熱を初期加熱と呼ぶことがある。または以下に示すステップＳ２０の前に加熱するものであるため、予備加熱又は前処理と呼ぶことがある。 <Step S15>
Next, the lithium cobalt oxide is heated in step S15 shown in Fig. 18A. Since this is the first heating of the lithium cobalt oxide, the heating in step S15 may be called initial heating. Alternatively, since this heating is performed before step S20 described below, it may be called preheating or pretreatment.
初期加熱により、上述したようにコバルト酸リチウムの表層部１００ａの一部からリチウムが脱離する。また内部１００ｂの結晶性を高める効果が期待できる。またステップＳ１１等で準備したリチウム源及び／又はコバルト源には、不純物が混入していることがある。ステップＳ１４で完成したコバルト酸リチウムから不純物を低減させることが、初期加熱によって可能である。 As described above, initial heating causes lithium to be released from part of the surface layer 100a of the lithium cobalt oxide. It is also expected to have the effect of increasing the crystallinity of the interior 100b. Impurities may be mixed into the lithium source and/or cobalt source prepared in step S11, etc. Initial heating can reduce the amount of impurities in the lithium cobalt oxide completed in step S14.
さらに初期加熱を経ることで、コバルト酸リチウムの表面がなめらかになる効果がある。表面がなめらかとは、凹凸が少なく、複合酸化物が全体的に丸みを帯び、さらに角部が丸みを帯びる様子をいう。さらに、表面へ付着した異物が少ない状態をなめらかと呼ぶ。異物は凹凸の要因となると考えられ、表面へ付着しない方が好ましい。 Furthermore, the initial heating has the effect of smoothing the surface of the lithium cobalt oxide. A smooth surface means that there are few irregularities, the composite oxide is generally rounded, and the corners are also rounded. Furthermore, a surface is called smooth when there is little foreign matter adhering to it. Foreign matter is thought to be a cause of unevenness, so it is preferable that it does not adhere to the surface.
この初期加熱には、リチウム源を用意しなくてよい。または、添加元素源を用意しなくてよい。または、融剤として機能する材料を用意しなくてよい。 For this initial heating, it is not necessary to provide a lithium source. Or, it is not necessary to provide a source of an additive element. Or, it is not necessary to provide a material that functions as a flux.
本工程の加熱時間は短すぎると十分な効果が得られないが、長すぎると生産性が低下する。たとえばステップＳ１３で説明した加熱条件から選択して実施することができる。当該加熱条件に補足すると、本工程の加熱温度は、複合酸化物の結晶構造を維持するため、ステップＳ１３の温度より低くするとよい。また本工程の加熱時間は、複合酸化物の結晶構造を維持するため、ステップＳ１３の時間より短くするとよい。例えば７００℃以上１０００℃以下の温度で、２時間以上２０時間以下の加熱を行うとよい。 If the heating time of this step is too short, sufficient effect will not be obtained, but if it is too long, productivity will decrease. For example, the heating conditions can be selected from those described in step S13. In addition to the heating conditions, the heating temperature of this step should be lower than the temperature of step S13 in order to maintain the crystal structure of the complex oxide. Furthermore, the heating time of this step should be shorter than the time of step S13 in order to maintain the crystal structure of the complex oxide. For example, heating should be performed at a temperature of 700°C to 1000°C for 2 hours to 20 hours.
また内部１００ｂの結晶性を高める効果とは、たとえばステップＳ１３で作製したコバルト酸リチウムが有する収縮差等に由来する歪み、ずれ等を緩和する効果である。 The effect of increasing the crystallinity of the inner portion 100b is, for example, the effect of mitigating distortion, misalignment, etc. resulting from differences in shrinkage of the lithium cobalt oxide produced in step S13.
コバルト酸リチウムは、ステップＳ１３の加熱によって、コバルト酸リチウムの表面と内部に温度差が生じることがある。温度差が生じると収縮差が誘発されることがある。温度差により、表面と内部の流動性が異なるため収縮差が生じるとも考えられる。収縮差に関連するエネルギーは、コバルト酸リチウムに内部応力の差を与えてしまう。内部応力の差は歪みとも称され、当該エネルギーを歪みエネルギーと呼ぶことがある。内部応力はステップＳ１５の初期加熱により除去され、別言すると歪みエネルギーはステップＳ１５の初期加熱により均質化されると考えられる。歪みエネルギーが均質化されるとコバルト酸リチウムの歪みが緩和される。これに伴いコバルト酸リチウムの表面がなめらかになる可能性がある。表面が改善されたとも称する。別言すると、ステップＳ１５を経るとコバルト酸リチウムに生じた収縮差が緩和され、複合酸化物の表面がなめらかになると考えられる。 The heating in step S13 may cause a temperature difference between the surface and the inside of the lithium cobalt oxide. The temperature difference may induce a shrinkage difference. It is also believed that the temperature difference causes the shrinkage difference because the fluidity of the surface and the inside is different. The energy related to the shrinkage difference causes an internal stress difference in the lithium cobalt oxide. The internal stress difference is also called strain, and this energy is sometimes called strain energy. The internal stress is removed by the initial heating in step S15, or in other words, the strain energy is thought to be homogenized by the initial heating in step S15. When the strain energy is homogenized, the strain of the lithium cobalt oxide is relaxed. As a result, the surface of the lithium cobalt oxide may become smooth. This is also called the surface being improved. In other words, it is thought that the shrinkage difference caused in the lithium cobalt oxide is relaxed after step S15, and the surface of the composite oxide becomes smooth.
また収縮差は上記コバルト酸リチウムにミクロなずれ、例えば結晶のずれを生じさせることがある。当該ずれを低減するためにも、本工程を実施するとよい。本工程を経ると、上記複合酸化物のずれを均一化させることが可能である。ずれが均一化されると、複合酸化物の表面がなめらかになる可能性がある。結晶粒の整列が行われたとも称する。別言すると、ステップＳ１５を経ると複合酸化物に生じた結晶等のずれが緩和され、複合酸化物の表面がなめらかになると考えられる。 Furthermore, the shrinkage difference may cause microscopic misalignment, such as crystal misalignment, in the lithium cobalt oxide. In order to reduce such misalignment, it is advisable to carry out this process. Through this process, it is possible to equalize the misalignment in the composite oxide. When the misalignment is equalized, the surface of the composite oxide may become smooth. This is also referred to as the alignment of crystal grains. In other words, it is believed that through step S15, the misalignment of crystals and the like that has occurred in the composite oxide is alleviated, and the surface of the composite oxide becomes smooth.
表面がなめらかなコバルト酸リチウムを正極活物質として用いると、二次電池として充放電した際の劣化が少なくなり、正極活物質の割れを防ぐことができる。 When lithium cobalt oxide, which has a smooth surface, is used as the positive electrode active material, it reduces deterioration during charging and discharging as a secondary battery and prevents cracking of the positive electrode active material.
再掲するが、ステップＳ１４としてあらかじめ合成されたコバルト酸リチウムを用いてもよい。この場合、ステップＳ１１乃至ステップＳ１３を省略することができる。あらかじめ合成されたコバルト酸リチウムに対してステップＳ１５を実施することで、表面がなめらかなコバルト酸リチウムを得ることができる。 As mentioned above, lithium cobalt oxide that has been synthesized in advance may be used in step S14. In this case, steps S11 to S13 can be omitted. By carrying out step S15 on lithium cobalt oxide that has been synthesized in advance, lithium cobalt oxide with a smooth surface can be obtained.
＜ステップＳ２０＞
次にステップＳ２０に示すように、初期加熱を経たコバルト酸リチウムに加える添加元素Ａ源（Ａ源）を用意する。初期加熱を経たコバルト酸リチウムに添加元素Ａを加えると、添加元素Ａをムラなく添加することができる。よって、初期加熱後に添加元素Ａを添加する順が好ましい。添加元素Ａ源を用意するステップについて、図１８Ｂ、及び図１８Ｃを用いて説明する。 <Step S20>
Next, as shown in step S20, an additive element A source (A source) to be added to the lithium cobalt oxide that has been initially heated is prepared. When the additive element A is added to the lithium cobalt oxide that has been initially heated, the additive element A can be added evenly. Therefore, it is preferable to add the additive element A after the initial heating. The step of preparing the additive element A source will be described with reference to FIG. 18B and FIG. 18C.
＜ステップＳ２１＞
図１８Ｂに示すステップＳ２１では、コバルト酸リチウムに添加する添加元素Ａ源（Ａ源）の出発材料を用意する。当該出発材料と合わせて、リチウム源を準備してもよい。 <Step S21>
18B, a starting material for a source of an additive element A (A source) to be added to lithium cobalt oxide is prepared. A lithium source may be prepared together with the starting material.
添加元素Ａ源の出発材料としては、先の実施の形態で説明した添加元素、たとえば添加元素Ａおよび添加元素Ｂを有する化合物を用いることができる。具体的にはマグネシウム、フッ素、ニッケル、アルミニウム、チタン、ジルコニウム、バナジウム、鉄、マンガン、クロム、ニオブ、ヒ素、亜鉛、ケイ素、硫黄、リンおよびホウ素から選ばれた化合物の一または二以上を用いることができる。また臭素、及びベリリウムから選ばれた一または二を用いることもできる。 As the starting material for the source of additive element A, a compound having the additive elements described in the previous embodiment, for example additive element A and additive element B, can be used. Specifically, one or more compounds selected from magnesium, fluorine, nickel, aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, and boron can be used. Also, one or two elements selected from bromine and beryllium can be used.
添加元素Ａ源にマグネシウムを有する化合物を選んだとき、出発材料はステップＳ２１のようにマグネシウム源（Ｍｇ源）と呼ぶことができる。当該マグネシウム源としては、フッ化マグネシウム、酸化マグネシウム、水酸化マグネシウム、又は炭酸マグネシウム等を用いることができる。また上述したマグネシウム源を複数用いてもよい。 When a compound containing magnesium is selected as the source of the additive element A, the starting material can be called a magnesium source (Mg source) as in step S21. The magnesium source can be magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, or the like. In addition, multiple magnesium sources described above may be used.
添加元素Ａ源にフッ素を有する化合物選んだとき、出発材料はステップＳ２１のようにフッ素源（Ｆ源）と呼ぶことができる。当該フッ素源としては、例えばフッ化リチウム（ＬｉＦ）、フッ化マグネシウム（ＭｇＦ２）、フッ化アルミニウム（ＡｌＦ３）、フッ化チタン（ＴｉＦ４）、フッ化コバルト（ＣｏＦ２、ＣｏＦ３）、フッ化ニッケル（ＮｉＦ２）、フッ化ジルコニウム（ＺｒＦ４）、フッ化バナジウム（ＶＦ５）、フッ化マンガン、フッ化鉄、フッ化クロム、フッ化ニオブ、フッ化亜鉛（ＺｎＦ２）、フッ化カルシウム（ＣａＦ２）、フッ化ナトリウム（ＮａＦ）、フッ化カリウム（ＫＦ）、フッ化バリウム（ＢａＦ２）、フッ化セリウム（ＣｅＦ３、ＣｅＦ４）、フッ化ランタン（ＬａＦ３）、又は六フッ化アルミニウムナトリウム（Ｎａ３ＡｌＦ６）等を用いることができる。なかでも、フッ化リチウムは融点が８４８℃と比較的低く、後述する加熱工程で溶融しやすいため好ましい。 When a compound having fluorine is selected as the source of the additive element A, the starting material can be called a fluorine source (F source) as in step S21. Examples of the fluorine source that can be used include lithium fluoride (LiF), magnesium fluoride ( MgF2 ), aluminum fluoride ( AlF3 ), titanium fluoride ( TiF4 ), cobalt fluoride ( CoF2 , CoF3 ), nickel fluoride ( NiF2 ), zirconium fluoride ( ZrF4 ), vanadium fluoride ( VF5 ), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride ( ZnF2 ), calcium fluoride ( CaF2 ), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride ( BaF2 ), cerium fluoride ( CeF3 , CeF4 ), lanthanum fluoride ( LaF3 ), and sodium aluminum hexafluoride ( Na3AlF6 ). Among these, lithium fluoride is preferred because it has a relatively low melting point of 848° C. and is easily melted in the heating step described below.
フッ化マグネシウムはフッ素源としてもマグネシウム源としても用いることができる。またフッ化リチウムはリチウム源としても用いることができる。ステップＳ２１に用いられるその他のリチウム源は炭酸リチウムがある。 Magnesium fluoride can be used as both a fluorine source and a magnesium source. Lithium fluoride can also be used as a lithium source. Other lithium sources that can be used in step S21 include lithium carbonate.
またフッ素源は気体でもよく、フッ素（Ｆ２）、フッ化炭素、フッ化硫黄、又はフッ化酸素（ＯＦ２、Ｏ２Ｆ２、Ｏ３Ｆ２、Ｏ４Ｆ２、Ｏ５Ｆ２、Ｏ６Ｆ２、Ｏ２Ｆ）等を用い、後述する加熱工程において雰囲気中に混合させてもよい。また上述したフッ素源を複数用いてもよい。 The fluorine source may be a gas, such as fluorine ( F2 ), carbon fluoride, sulfur fluoride, or oxygen fluoride ( OF2 , O2F2 , O3F2 , O4F2 , O5F2 , O6F2 , O2F ) , which may be mixed into the atmosphere in the heating step described below. A plurality of the above-mentioned fluorine sources may be used.
本実施の形態では、フッ素源としてフッ化リチウム（ＬｉＦ）を準備し、フッ素源及びマグネシウム源としてフッ化マグネシウム（ＭｇＦ２）を準備する。フッ化リチウムとフッ化マグネシウムは、ＬｉＦ：ＭｇＦ２＝６５：３５（モル比）程度で混合すると融点を下げる効果が最も高くなる。一方、フッ化リチウムが多くなると、リチウムが過剰になりすぎサイクル特性が悪化する懸念がある。そのため、フッ化リチウムとフッ化マグネシウムのモル比は、ＬｉＦ：ＭｇＦ２＝ｘ：１（０≦ｘ≦１．９）であることが好ましく、ＬｉＦ：ＭｇＦ２＝ｘ：１（０．１≦ｘ≦０．５）がより好ましく、ＬｉＦ：ＭｇＦ２＝ｘ：１（ｘ＝０．３３近傍）がさらに好ましい。なお本明細書等において近傍とは、その値の０．９倍より大きく１．１倍より小さい値とする。 In this embodiment, lithium fluoride (LiF) is prepared as the fluorine source, and magnesium fluoride (MgF 2 ) is prepared as the fluorine source and magnesium source. When lithium fluoride and magnesium fluoride are mixed at about LiF:MgF 2 = 65:35 (molar ratio), the effect of lowering the melting point is maximized. On the other hand, if the amount of lithium fluoride increases, there is a concern that the lithium becomes excessive and the cycle characteristics deteriorate. Therefore, the molar ratio of lithium fluoride and magnesium fluoride is preferably LiF:MgF 2 = x:1 (0≦x≦1.9), more preferably LiF:MgF 2 = x:1 (0.1≦x≦0.5), and even more preferably LiF:MgF 2 = x:1 (near x = 0.33). In this specification, etc., "near" refers to a value that is greater than 0.9 times and less than 1.1 times the value.
＜ステップＳ２２＞
次に、図１８Ｂに示すステップＳ２２では、マグネシウム源及びフッ素源を粉砕及び混合する。本工程は、ステップＳ１２で説明した粉砕及び混合の条件から選択して実施することができる。 <Step S22>
18B, the magnesium source and the fluorine source are pulverized and mixed. This step can be performed under the pulverization and mixing conditions selected from those described in step S12.
＜ステップＳ２３＞
次に、図１８Ｂに示すステップＳ２３では、上記で粉砕、混合した材料を回収して、添加元素Ａ源（Ａ源）を得ることができる。なお、ステップＳ２３に示す添加元素Ａ源は、複数の出発材料を有するものであり、混合物と呼ぶことができる。 <Step S23>
18B, the material crushed and mixed as described above is collected to obtain a source of additive element A (source A). Note that the source of additive element A shown in step S23 has a plurality of starting materials and can be called a mixture.
上記混合物の粒径は、メディアン径（Ｄ５０）が６００ｎｍ以上１０μｍ以下であることが好ましく、１μｍ以上５μｍ以下であることがより好ましい。添加元素源として、一種の材料を用いた場合においても、メディアン径（Ｄ５０）が６００ｎｍ以上１０μｍ以下であることが好ましく、１μｍ以上５μｍ以下であることがより好ましい。 The particle size of the mixture is preferably a median diameter (D50) of 600 nm or more and 10 μm or less, more preferably 1 μm or more and 5 μm or less. Even when a single material is used as the source of the additive element, the median diameter (D50) is preferably 600 nm or more and 10 μm or less, more preferably 1 μm or more and 5 μm or less.
このような微粉化された混合物（添加元素が１種の場合も含む）であると、後の工程でコバルト酸リチウムと混合したときに、コバルト酸リチウムの粒子の表面に混合物を均一に付着させやすい。コバルト酸リチウムの粒子の表面に混合物が均一に付着していると、加熱後に複合酸化物の表層部１００ａに均一に添加元素を分布又は拡散させやすいため好ましい。 Such a finely powdered mixture (including the case where only one type of additive element is included) makes it easier to uniformly attach the mixture to the surface of the lithium cobalt oxide particles when mixed with the lithium cobalt oxide in a later process. If the mixture is uniformly attached to the surface of the lithium cobalt oxide particles, it is preferable because it makes it easier to uniformly distribute or diffuse the additive element in the surface layer portion 100a of the composite oxide after heating.
＜ステップＳ２１＞
図１８Ｂとは異なる工程について図１８Ｃを用いて説明する。図１８Ｃに示すステップＳ２１では、コバルト酸リチウムに添加する添加元素Ａ源の出発材料として４種の化合物を用意する。すなわち図１８Ｃは図１８Ｂとは出発材料の種類が異なる。図１８Ｃにおいても、出発材料と合わせて、リチウム源を準備してもよい。 <Step S21>
A process different from that shown in FIG. 18B will be described with reference to FIG. 18C. In step S21 shown in FIG. 18C, four types of compounds are prepared as starting materials for the source of the additive element A to be added to lithium cobalt oxide. That is, the types of starting materials in FIG. 18C are different from those in FIG. 18B. In FIG. 18C, a lithium source may be prepared together with the starting materials.
４種の出発材料を用意する例として、図１８ＣのステップＳ２１のように、マグネシウム源（Ｍｇ源）、フッ素源（Ｆ源）、ニッケル源（Ｎｉ源）、及びアルミニウム源（Ａｌ源）を準備する。なお、マグネシウム源及びフッ素源は図１８Ｂで説明した化合物等から選択することができる。ニッケル源としては、酸化ニッケル、水酸化ニッケル等を用いることができる。アルミニウム源としては、酸化アルミニウム、水酸化アルミニウム、等を用いることができる。 As an example of preparing four types of starting materials, a magnesium source (Mg source), a fluorine source (F source), a nickel source (Ni source), and an aluminum source (Al source) are prepared as shown in step S21 of FIG. 18C. The magnesium source and the fluorine source can be selected from the compounds described in FIG. 18B. Nickel oxide, nickel hydroxide, etc. can be used as the nickel source. Aluminum oxide, aluminum hydroxide, etc. can be used as the aluminum source.
＜ステップＳ２２及びステップＳ２３＞
図１８Ｃに示すステップＳ２２及びステップＳ２３は、図１８Ｂで説明したステップと同様である。 <Steps S22 and S23>
Steps S22 and S23 shown in FIG. 18C are similar to the steps described in FIG. 18B.
＜ステップＳ３１＞
次に、図１８Ａに示すステップＳ３１では、コバルト酸リチウムと、添加元素Ａ源（Ａ源）とを混合する。コバルト酸リチウム中のコバルトの原子数（Ｃｏと記す）と、添加元素Ａ源が有するマグネシウムの原子数（Ｍｇと記す）との比は、Ｃｏ：Ｍｇ＝１００：ｙ（０．１≦ｙ≦６）であることが好ましく、Ｍ：Ｍｇ＝１００：ｙ（０．３≦ｙ≦３）であることがより好ましい。 <Step S31>
18A, lithium cobalt oxide is mixed with a source of additive element A. The ratio of the number of cobalt atoms (referred to as Co) in the lithium cobalt oxide to the number of magnesium atoms (referred to as Mg) in the source of additive element A is preferably Co:Mg=100:y (0.1≦y≦6), and more preferably M:Mg=100:y (0.3≦y≦3).
ステップＳ３１の混合は、コバルト酸リチウムの粒子の形状を破壊させないためにステップＳ１２の混合よりも穏やかな条件とすることが好ましい。例えば、ステップＳ１２の混合よりも回転数が少ない、または時間が短い条件とすることが好ましい。また湿式よりも乾式のほうが穏やかな条件であると言える。混合には例えばボールミル、ビーズミル等を用いることができる。ボールミルを用いる場合は、例えばメディアとして酸化ジルコニウムボールを用いることが好ましい。 The mixing conditions in step S31 are preferably milder than those in step S12 in order not to destroy the shape of the lithium cobalt oxide particles. For example, it is preferable to use conditions with a lower rotation speed or shorter mixing time than in step S12. It can also be said that dry mixing is a milder condition than wet mixing. For example, a ball mill, a bead mill, etc. can be used for mixing. When using a ball mill, it is preferable to use zirconium oxide balls as the media.
本実施の形態では、直径１ｍｍの酸化ジルコニウムボールを用いたボールミルで、１５０ｒｐｍ、１時間、乾式で混合することとする。また該混合は、露点が−１００℃以上−１０℃以下のドライルームで行うこととする。 In this embodiment, the mixture is mixed dry in a ball mill using zirconium oxide balls with a diameter of 1 mm at 150 rpm for 1 hour. The mixture is also performed in a dry room with a dew point of -100°C or higher and -10°C or lower.
＜ステップＳ３２＞
次に、図１８ＡのステップＳ３２において、上記で混合した材料を回収し、混合物９０３を得る。回収の際、必要に応じて解砕した後にふるいを実施してもよい。 <Step S32>
18A, the mixed material is collected to obtain a mixture 903. When collecting the material, it may be crushed and then sieved, if necessary.
なお図１８Ａ乃至図１８Ｃでは、初期加熱を経た後にのみ添加元素を加える製造方法について説明しているが、本発明は上記方法に限定されない。添加元素は他のタイミングで加えてもよいし、複数回にわたって加えてもよい。元素によってタイミングを変えてもよい。 Note that although Figures 18A to 18C illustrate a manufacturing method in which the additive element is added only after initial heating, the present invention is not limited to the above method. The additive element may be added at another timing, or may be added multiple times. The timing may be changed depending on the element.
たとえばステップＳ１１の段階、つまり複合酸化物の出発材料の段階で添加元素をリチウム源及びコバルト源へ添加してもよい。その後ステップＳ１３で添加元素を有するコバルト酸リチウムを得ることができる。この場合は、ステップＳ１１乃至ステップＳ１４の工程と、ステップＳ２１乃至ステップＳ２３の工程を分ける必要がない。簡便で生産性が高い方法であるといえる。 For example, an additive element may be added to the lithium source and the cobalt source in step S11, that is, in the stage of the starting material for the composite oxide. Then, in step S13, lithium cobalt oxide having the additive element can be obtained. In this case, there is no need to separate the steps S11 to S14 from the steps S21 to S23. This is a simple and highly productive method.
また、あらかじめ添加元素の一部を有するコバルト酸リチウムを用いてもよい。たとえばマグネシウム及びフッ素が添加されたコバルト酸リチウムを用いれば、ステップＳ１１乃至ステップＳ１４、およびステップＳ２０の一部の工程を省略することができる。簡便で生産性が高い方法であるといえる。 Alternatively, lithium cobalt oxide that already contains some of the added elements may be used. For example, if lithium cobalt oxide to which magnesium and fluorine have been added is used, steps S11 to S14 and some of the steps in step S20 can be omitted. This is a simple and highly productive method.
また、あらかじめマグネシウム及びフッ素が添加されたコバルト酸リチウムに対して、ステップＳ１５の加熱を行った後、ステップＳ２０のようにマグネシウム源及びフッ素源、又はマグネシウム源、フッ素源、ニッケル源、及びアルミニウム源を添加してもよい。 Also, after heating in step S15 to lithium cobalt oxide to which magnesium and fluorine have been added in advance, a magnesium source and a fluorine source, or a magnesium source, a fluorine source, a nickel source, and an aluminum source may be added as in step S20.
＜ステップＳ３３＞
次に、図１８Ａに示すステップＳ３３では、混合物９０３を加熱する。ステップＳ１３で説明した加熱条件から選択して実施することができる。加熱時間は２時間以上が好ましい。 <Step S33>
18A, the mixture 903 is heated. The heating conditions can be selected from those described in step S13. The heating time is preferably 2 hours or more.
ここで加熱温度について補足する。ステップＳ３３の加熱温度の下限は、コバルト酸リチウムと添加元素源との反応が進む温度以上である必要がある。反応が進む温度とは、コバルト酸リチウムと添加元素源との有する元素の相互拡散が起きる温度であればよく、これらの材料の溶融温度よりも低くてもよい。酸化物を例にして説明するが、溶融温度Ｔｍの０．７５７倍（タンマン温度Ｔｄ）から固相拡散が起こることがわかっている。そのため、ステップＳ３３における加熱温度としては、６５０℃以上であればよい。 Here, a supplementary note on the heating temperature is provided. The lower limit of the heating temperature in step S33 must be equal to or higher than the temperature at which the reaction between the lithium cobalt oxide and the additive element source proceeds. The temperature at which the reaction proceeds may be any temperature at which mutual diffusion of elements contained in the lithium cobalt oxide and the additive element source occurs, and may be lower than the melting temperature of these materials. An oxide is used as an example for explanation, and it is known that solid-phase diffusion occurs at a temperature 0.757 times the melting temperature Tm (Tammann temperature Td ). Therefore, the heating temperature in step S33 may be 650°C or higher.
勿論、混合物９０３が有する材料から選ばれた一または二以上が溶融する温度以上であると、より反応が進みやすい。例えば、添加元素源として、ＬｉＦ及びＭｇＦ２を有する場合、ＬｉＦとＭｇＦ２の共融点は７４２℃付近であるため、ステップＳ３３の加熱温度の下限は７４２℃以上とすると好ましい。 Of course, the reaction proceeds more easily if the temperature is equal to or higher than the melting temperature of one or more of the materials contained in the mixture 903. For example, when LiF and MgF2 are contained as the additive element source, the eutectic point of LiF and MgF2 is around 742°C, so that the lower limit of the heating temperature in step S33 is preferably set to 742°C or higher.
また、ＬｉＣｏＯ２：ＬｉＦ：ＭｇＦ２＝１００：０．３３：１（モル比）となるように混合して得られた混合物９０３は、示差走査熱量測定（ＤＳＣ測定）において８３０℃付近に吸熱ピークが観測される。よって、加熱温度の下限は８３０℃以上がより好ましい。 Furthermore, in the mixture 903 obtained by mixing so that LiCoO 2 :LiF:MgF 2 = 100:0.33:1 (molar ratio), an endothermic peak is observed near 830° C. in differential scanning calorimetry (DSC measurement). Therefore, the lower limit of the heating temperature is more preferably 830° C. or higher.
加熱温度は高い方が反応が進みやすく、加熱時間が短く済み、生産性が高く好ましい。 The higher the heating temperature, the easier the reaction will proceed, the shorter the heating time will be, and the higher the productivity will be, which is preferable.
加熱温度の上限はコバルト酸リチウムの融点（１１３０℃）未満とする。融点の近傍の温度では、微量ではあるがコバルト酸リチウムの分解が懸念される。そのため、１０００℃以下であるとより好ましく、９５０℃以下であるとさらに好ましく、９００℃以下であるとさらに好ましい。 The upper limit of the heating temperature is below the melting point of lithium cobalt oxide (1130°C). At temperatures close to the melting point, there is a concern that lithium cobalt oxide may decompose, albeit only slightly. Therefore, it is more preferable for the temperature to be 1000°C or lower, even more preferable for the temperature to be 950°C or lower, and even more preferable for the temperature to be 900°C or lower.
これらを踏まえると、ステップＳ３３における加熱温度としては、６５０℃以上１１３０℃以下が好ましく、６５０℃以上１０００℃以下がより好ましく、６５０℃以上９５０℃以下がさらに好ましく、６５０℃以上９００℃以下がさらに好ましい。また、７４２℃以上１１３０℃以下が好ましく、７４２℃以上１０００℃以下がより好ましく、７４２℃以上９５０℃以下がさらに好ましく、７４２℃以上９００℃以下がさらに好ましい。また、８００℃以上１１００℃以下、８３０℃以上１１３０℃以下が好ましく、８３０℃以上１０００℃以下がより好ましく、８３０℃以上９５０℃以下がさらに好ましく、８３０℃以上９００℃以下がさらに好ましい。なおステップＳ３３における加熱温度は、ステップＳ１３よりも低いとよい。 In light of these, the heating temperature in step S33 is preferably 650°C to 1130°C, more preferably 650°C to 1000°C, even more preferably 650°C to 950°C, and even more preferably 650°C to 900°C. Also, 742°C to 1130°C is preferred, more preferably 742°C to 1000°C, even more preferably 742°C to 950°C, and even more preferably 742°C to 900°C. Also, 800°C to 1100°C, 830°C to 1130°C is preferred, more preferably 830°C to 1000°C, even more preferably 830°C to 950°C, and even more preferably 830°C to 900°C. The heating temperature in step S33 is preferably lower than that in step S13.
さらに混合物９０３を加熱する際、フッ素源等に起因するフッ素またはフッ化物の分圧を適切な範囲に制御することが好ましい。 Furthermore, when heating the mixture 903, it is preferable to control the partial pressure of fluorine or fluoride resulting from the fluorine source, etc., within an appropriate range.
本実施の形態で説明する製造方法では、一部の材料、例えばフッ素源であるＬｉＦが融剤として機能する場合がある。この機能により加熱温度をコバルト酸リチウムの融点未満、例えば７４２℃以上９５０℃以下にまで低温化でき、表層部にマグネシウムをはじめとする添加元素を分布させ、良好な特性の正極活物質を作製できる。 In the manufacturing method described in this embodiment, some materials, for example LiF, which is a fluorine source, may function as a flux. This function allows the heating temperature to be lowered below the melting point of lithium cobalt oxide, for example to between 742°C and 950°C, and additive elements such as magnesium can be distributed in the surface layer to produce a positive electrode active material with good characteristics.
しかし、ＬｉＦは酸素よりも気体状態での比重が軽いため、加熱によりＬｉＦが揮発する可能性があり、揮発すると混合物９０３中のＬｉＦが減少してしまう。すると融剤としての機能が弱くなってしまう。よって、ＬｉＦの揮発を抑制しつつ、加熱する必要がある。なお、フッ素源等としてＬｉＦを用いなかったとしても、ＬｉＣｏＯ２表面のＬｉとフッ素源のＦが反応して、ＬｉＦが生じ、揮発する可能性もある。そのため、ＬｉＦより融点が高いフッ化物を用いたとしても、同じように揮発の抑制が必要である。 However, since LiF has a lower specific gravity in a gaseous state than oxygen, LiF may volatilize when heated, and the amount of LiF in the mixture 903 will decrease if LiF volatilizes. This weakens the function as a flux. Therefore, it is necessary to heat while suppressing the volatilization of LiF. Even if LiF is not used as the fluorine source, etc., Li on the LiCoO2 surface may react with F of the fluorine source to generate LiF, which may volatilize. Therefore, even if a fluoride with a melting point higher than LiF is used, it is necessary to suppress the volatilization in the same way.
そこで、ＬｉＦを含む雰囲気で混合物９０３を加熱すること、すなわち、加熱炉内のＬｉＦの分圧が高い状態で混合物９０３を加熱することが好ましい。このような加熱により混合物９０３中のＬｉＦの揮発を抑制することができる。 Therefore, it is preferable to heat the mixture 903 in an atmosphere containing LiF, that is, to heat the mixture 903 in a state where the partial pressure of LiF in the heating furnace is high. By heating in this manner, it is possible to suppress the volatilization of the LiF in the mixture 903.
本工程の加熱は、混合物９０３の粒子同士が固着しないように加熱すると好ましい。加熱中に混合物９０３粒子同士が固着すると、雰囲気中の酸素との接触面積が減る、及び添加元素（例えばフッ素）が拡散する経路を阻害することにより、表層部への添加元素（例えばマグネシウム及びフッ素）の分布が悪化する可能性がある。 The heating in this process is preferably performed so that the particles of mixture 903 do not stick to each other. If the particles of mixture 903 stick to each other during heating, the contact area with oxygen in the atmosphere decreases, and the route along which the added elements (e.g., fluorine) diffuse is blocked, which may result in poor distribution of the added elements (e.g., magnesium and fluorine) in the surface layer.
また、添加元素（例えばフッ素）が表層部に均一に分布するとなめらかで凹凸が少ない正極活物質を得られると考えられている。そのため本工程でステップＳ１５の加熱を経た、表面がなめらかな状態を維持する又はより一層なめらかになるためには、混合物９０３の粒子同士が固着しない方がよい。 It is also believed that if the additive element (e.g., fluorine) is uniformly distributed in the surface layer, a smooth positive electrode active material with few irregularities can be obtained. Therefore, in order to maintain the smooth state of the surface after the heating in step S15 in this process or to make it even smoother, it is better for the particles of mixture 903 not to stick together.
また、ロータリーキルンによって加熱する場合は、キルン内の酸素を含む雰囲気の流量を制御して加熱することが好ましい。例えば酸素を含む雰囲気の流量を少なくする、最初に雰囲気をパージしキルン内に酸素雰囲気を導入した後は雰囲気のフローはしない、等が好ましい。酸素をフローするとフッ素源が蒸散する可能性があり、表面のなめらかさを維持するためには好ましくない。 When heating in a rotary kiln, it is preferable to control the flow rate of the oxygen-containing atmosphere in the kiln. For example, it is preferable to reduce the flow rate of the oxygen-containing atmosphere, or to first purge the atmosphere and not flow the atmosphere after introducing the oxygen atmosphere into the kiln. Flowing oxygen can cause the fluorine source to evaporate, which is not preferable in terms of maintaining the smoothness of the surface.
ローラーハースキルンによって加熱する場合は、例えば混合物９０３の入った容器に蓋を配することでＬｉＦを含む雰囲気で混合物９０３を加熱することができる。 When heating using a roller hearth kiln, the mixture 903 can be heated in an atmosphere containing LiF, for example, by placing a lid on the container containing the mixture 903.
加熱時間について補足する。加熱時間は、加熱温度、ステップＳ１４のコバルト酸リチウムの大きさ、及び組成等の条件により変化する。コバルト酸リチウムが小さい場合は、大きい場合よりも低い温度または短い時間がより好ましい場合がある。 A note on the heating time: The heating time varies depending on conditions such as the heating temperature, the size of the lithium cobalt oxide in step S14, and the composition. When the lithium cobalt oxide is small, a lower temperature or a shorter time may be more preferable than when the lithium cobalt oxide is large.
図１８ＡのステップＳ１４のコバルト酸リチウムのメディアン径（Ｄ５０）が１２μｍ程度の場合、加熱温度は、例えば６５０℃以上９５０℃以下が好ましい。加熱時間は例えば３時間以上６０時間以下が好ましく、１０時間以上３０時間以下がより好ましく、２０時間程度がさらに好ましい。なお、加熱後の降温時間は、例えば１０時間以上５０時間以下とすることが好ましい。 When the median diameter (D50) of the lithium cobalt oxide in step S14 of FIG. 18A is about 12 μm, the heating temperature is preferably, for example, 650° C. or more and 950° C. or less. The heating time is preferably, for example, 3 hours or more and 60 hours or less, more preferably 10 hours or more and 30 hours or less, and even more preferably about 20 hours. The cooling time after heating is preferably, for example, 10 hours or more and 50 hours or less.
一方、ステップＳ１４のコバルト酸リチウムのメディアン径（Ｄ５０）が５μｍ程度の場合、加熱温度は例えば６５０℃以上９５０℃以下が好ましい。加熱時間は例えば１時間以上１０時間以下が好ましく、５時間程度がより好ましい。なお、加熱後の降温時間は、例えば１０時間以上５０時間以下とすることが好ましい。 On the other hand, when the median diameter (D50) of the lithium cobalt oxide in step S14 is about 5 μm, the heating temperature is preferably, for example, 650° C. or more and 950° C. or less. The heating time is preferably, for example, 1 hour or more and 10 hours or less, and more preferably about 5 hours. The cooling time after heating is preferably, for example, 10 hours or more and 50 hours or less.
＜ステップＳ３４＞
次に、図１８Ａに示すステップＳ３４では、加熱した材料を回収し、必要に応じて解砕して、正極活物質１００を得る。このとき、回収された粒子をさらに、ふるいにかけると好ましい。以上の工程により、本発明の一形態の正極活物質１００を作製することができる。本発明の一形態の正極活物質は表面がなめらかである。 <Step S34>
Next, in step S34 shown in Fig. 18A, the heated material is collected and crushed as necessary to obtain the positive electrode active material 100. At this time, it is preferable to further sieve the collected particles. By the above steps, the positive electrode active material 100 of one embodiment of the present invention can be produced. The positive electrode active material of one embodiment of the present invention has a smooth surface.
《正極活物質の製造方法２》
次に、本発明を実施する一形態であって、正極活物質の製造方法１とは異なる正極活物質の製造方法２について、図１９乃至図２０Ｃを用いて説明する。正極活物質の製造方法２は主に添加元素を加える回数および混合方法が製造方法１とは異なる。その他の記載は製造方法１の記載を参照することができる。 <<Production method 2 of positive electrode active material>>
Next, a method for producing a positive electrode active material 2, which is one embodiment of the present invention and is different from method for producing a positive electrode active material 1, will be described with reference to Figs. 19 to 20C. Method for producing a positive electrode active material 2 differs from method for producing 1 mainly in the number of times additive elements are added and the mixing method. For other descriptions, the description of method for producing 1 can be referred to.
図１９において、図１７Ａと同様にステップＳ１１乃至Ｓ１５までを行い、初期加熱を経たコバルト酸リチウムを準備する。 In FIG. 19, steps S11 to S15 are performed in the same manner as in FIG. 17A to prepare lithium cobalt oxide that has undergone initial heating.
＜ステップＳ２０ａ＞
次にステップＳ２０ａに示すように、初期加熱を経たコバルト酸リチウムに添加元素Ａ１を加えることが好ましい。 <Step S20a>
Next, as shown in step S20a, it is preferable to add an additive element A1 to the lithium cobalt oxide that has been subjected to the initial heating.
＜ステップＳ２１＞
図２０Ａに示すステップＳ２１では、第１の添加元素源（Ａ１源）を得るための出発材料を準備する。図２０Ａではたとえばマグネシウム源、及びフッ素源を準備する。なお第１の添加元素Ａ１源を得るための出発材料としては、図１７Ｂに示すステップＳ２１で説明した添加元素Ａ源を得るための出発材料の中から選択して用いることができる。例えば、第１の添加元素Ａ１としてマグネシウム、フッ素、及びカルシウムの中から選ばれるいずれか一または複数を好適に用いることができ、これを得るための出発材料としてはマグネシウム、フッ素、及びカルシウムの中から選ばれるいずれか一を有する化合物を用いるとよい。 <Step S21>
In step S21 shown in Fig. 20A, starting materials for obtaining a first additive element source (A1 source) are prepared. In Fig. 20A, for example, a magnesium source and a fluorine source are prepared. The starting materials for obtaining the first additive element A1 source can be selected from the starting materials for obtaining the additive element A source described in step S21 shown in Fig. 17B. For example, one or more selected from magnesium, fluorine, and calcium can be suitably used as the first additive element A1, and a compound having one selected from magnesium, fluorine, and calcium can be used as the starting material for obtaining it.
図２０Ａに示すステップＳ２１乃至ステップＳ２３については、図１７Ｂに示すステップＳ２１乃至ステップＳ２３と同様の条件で行うことができる。その結果、ステップＳ２３で第１の添加元素源（Ａ１源）を得ることができる。 Steps S21 to S23 shown in FIG. 20A can be performed under the same conditions as steps S21 to S23 shown in FIG. 17B. As a result, the first additive element source (A1 source) can be obtained in step S23.
また、図１９に示すステップＳ３１乃至Ｓ３３については、図１７Ａに示すステップＳ３１乃至Ｓ３３と同様の工程にて行うことができる。 Furthermore, steps S31 to S33 shown in FIG. 19 can be performed in the same manner as steps S31 to S33 shown in FIG. 17A.
＜ステップＳ３４ａ＞
次に、ステップＳ３３で加熱した材料を回収し、添加元素Ａ１を有するコバルト酸リチウムを作製する。ステップＳ１４の複合酸化物と区別するため第２の複合酸化物とも呼ぶ。 <Step S34a>
Next, in step S33, the heated material is collected to produce lithium cobalt oxide containing the additive element A1. This is also called a second composite oxide to distinguish it from the composite oxide in step S14.
＜ステップＳ４０＞
図１９に示すステップＳ４０では、第２の添加元素Ａ２を添加する。第２の添加元素Ａ２について、図２０Ｂ及び図２０Ｃも参照しながら説明する。 <Step S40>
In step S40 shown in Fig. 19, a second additional element A2 is added. The second additional element A2 will be described with reference to Figs. 20B and 20C.
＜ステップＳ４１＞
図２０Ｂに示すステップＳ４１では、第２の添加元素源（Ａ２源）を得るための出発材料を準備する。図２０Ｂではたとえば、ニッケル源（Ｎｉ源）、及びアルミニウム源（Ａｌ源）を準備する。アルミニウム源（Ａｌ源）は省略してもよい。なお第２の添加元素（Ａ２）源を得るための出発材料としては、図１７Ｂに示すステップＳ２１で説明した添加元素Ａ源の出発材料の中から選択して用いることができる。例えば、第２の添加元素Ａ２として、ニッケル、チタン、ホウ素、ジルコニウム、及びアルミニウムの中から選ばれるいずれか一または複数を好適に用いることができ、これを得るための出発材料はニッケル、チタン、ホウ素、ジルコニウム、及びアルミニウムの中から選ばれるいずれか一を有する化合物を用いるとよい。 <Step S41>
In step S41 shown in FIG. 20B, starting materials for obtaining the second additive element source (A2 source) are prepared. In FIG. 20B, for example, a nickel source (Ni source) and an aluminum source (Al source) are prepared. The aluminum source (Al source) may be omitted. The starting materials for obtaining the second additive element (A2) source can be selected from the starting materials for the additive element A source described in step S21 shown in FIG. 17B. For example, as the second additive element A2, any one or more selected from nickel, titanium, boron, zirconium, and aluminum can be suitably used, and the starting material for obtaining this may be a compound having any one selected from nickel, titanium, boron, zirconium, and aluminum.
図２０Ｂに示すステップＳ４１乃至ステップＳ４３については、図１７Ｂに示すステップＳ２１乃至ステップＳ２３と同様の条件で行うことができる。その結果、ステップＳ４３で第２の添加元素源（Ａ２源）を得ることができる。 Steps S41 to S43 shown in FIG. 20B can be performed under the same conditions as steps S21 to S23 shown in FIG. 17B. As a result, the second additive element source (A2 source) can be obtained in step S43.
また、図２０Ｃには、図２０Ｂを用いて説明したステップの変形例を示す。図２０Ｃに示すステップＳ４１ではニッケル源（Ｎｉ源）、及びアルミニウム源（Ａｌ源）を準備し、ステップＳ４２ａではそれぞれ独立に粉砕する。その結果、ステップＳ４３では、複数の第２の添加元素源（Ａ２源）を準備することとなる。図２０Ｃのステップは、ステップＳ４２ａにて添加元素を独立に粉砕していることが図２０Ｂと異なる。 Furthermore, FIG. 20C shows a modified example of the steps described with reference to FIG. 20B. In step S41 shown in FIG. 20C, a nickel source (Ni source) and an aluminum source (Al source) are prepared, and in step S42a, they are each crushed independently. As a result, in step S43, multiple second additive element sources (A2 sources) are prepared. The steps in FIG. 20C differ from FIG. 20B in that the additive elements are crushed independently in step S42a.
＜ステップＳ５１乃至ステップＳ５３＞
次に、図１９に示すステップＳ５１乃至ステップＳ５３は、図１７Ａに示すステップＳ３１乃至ステップＳ３４と同様の条件にて行うことができる。加熱工程に関するステップＳ５３の条件はステップＳ３３より低い温度且つ短い時間でよい。以上の工程により、ステップＳ５４では、本発明の一形態の正極活物質１００を作製することができる。本発明の一形態の正極活物質は表面がなめらかである。 <Steps S51 to S53>
Next, steps S51 to S53 shown in Fig. 19 can be performed under the same conditions as steps S31 to S34 shown in Fig. 17A. The conditions for step S53 relating to the heating step may be a lower temperature and a shorter time than those for step S33. Through the above steps, in step S54, the positive electrode active material 100 according to one embodiment of the present invention can be produced. The positive electrode active material according to one embodiment of the present invention has a smooth surface.
図１９及び図２０に示すように、製造方法２では、コバルト酸リチウムへの添加元素を添加元素Ａ１と、添加元素Ａ２とに分けて導入する。分けて導入することにより、各添加元素の深さ方向の分布を変えることができる。例えば、添加元素Ａ１を内部に比べて表層部で高い濃度となるようにプロファイルし、添加元素Ａ２を表層部に比べて内部で高い濃度となるようにプロファイルすることも可能である。 As shown in Figures 19 and 20, in manufacturing method 2, the additive element is introduced into lithium cobalt oxide separately as additive element A1 and additive element A2. By introducing them separately, the distribution of each additive element in the depth direction can be changed. For example, it is possible to profile additive element A1 so that it has a higher concentration in the surface layer than in the interior, and to profile additive element A2 so that it has a higher concentration in the interior than in the surface layer.
本実施の形態で示した初期加熱を経ると表面がなめらかな正極活物質を得ることができる。 After the initial heating process described in this embodiment, a positive electrode active material with a smooth surface can be obtained.
本実施の形態で示した初期加熱は、コバルト酸リチウムに対して実施する。よって初期加熱は、コバルト酸リチウムを得るための加熱温度よりも低く、かつコバルト酸リチウムを得るための加熱時間よりも短い条件が好ましい。コバルト酸リチウムに添加元素を添加する工程は、初期加熱後が好ましい。当該添加工程は２回以上に分けることが可能である。このような工程順に従うと、初期加熱で得られた表面のなめらかさは維持されるため好ましい。 The initial heating shown in this embodiment is performed on lithium cobalt oxide. Therefore, the initial heating is preferably performed under conditions that are lower than the heating temperature for obtaining lithium cobalt oxide and shorter than the heating time for obtaining lithium cobalt oxide. The step of adding an additive element to lithium cobalt oxide is preferably performed after the initial heating. This addition step can be divided into two or more steps. Following this order of steps is preferable because the smoothness of the surface obtained by the initial heating is maintained.
《正極活物質の製造方法３》
上記製造方法１及び２では、固相法を用いたフローを説明したが、製造方法３では共沈法を有するフローを図２１及び図２２を用いて説明する。なお共沈法とは、二以上の金属イオンを含む水溶液から、イオン濃度が過飽和の状態となった際に、難溶性塩が析出して沈殿する方法である。共沈法は、実施の形態２等の固相法を用いた場合と比べて、沈殿物における金属塩の混合の均一性が高く、マグネシウムを内部１００ｂに位置させやすい方法といえる。なお図２２は図２１の一部の手順を省略したフロー図であるため共通部分はまとめて説明する。図２２は一部の手順を省略することができ、生産性が高い工程の一例である。 <<Production method 3 of positive electrode active material>>
In the above manufacturing methods 1 and 2, the flow using the solid phase method has been described, but in the manufacturing method 3, a flow including the coprecipitation method will be described with reference to Figs. 21 and 22. The coprecipitation method is a method in which poorly soluble salts are precipitated and precipitated when the ion concentration becomes supersaturated from an aqueous solution containing two or more metal ions. The coprecipitation method is a method in which the mixing of metal salts in the precipitate is more uniform than when the solid phase method of the second embodiment is used, and it is easy to position magnesium in the interior 100b. Note that Fig. 22 is a flow diagram in which some steps of Fig. 21 are omitted, so the common parts will be described together. Fig. 22 is an example of a process in which some steps can be omitted and productivity is high.
＜コバルト源＞
図２１及び図２２に示すようにコバルト源８１（図面ではＣｏ源と記す）を用意する。コバルト源８１は、正極活物質の出発材料の一つである。またコバルト源８１は、コバルトを有する化合物（コバルト化合物と記す）を用いる。コバルト化合物は、たとえば硫酸コバルト、塩化コバルト、若しくは硝酸コバルト、またはこれらの水和物を用いることができる。またコバルト化合物として、コバルトアルコキシド、または有機コバルト錯体を用いてもよい。またさらにコバルト化合物として、酢酸コバルトをはじめとするコバルトの有機酸、またはこれらの水和物を用いてもよい。なお本明細書等において、有機酸とは、酢酸以外に、クエン酸、シュウ酸、ギ酸、または酪酸等を含む。 <Cobalt source>
As shown in FIG. 21 and FIG. 22, a cobalt source 81 (referred to as Co source in the drawings) is prepared. The cobalt source 81 is one of the starting materials for the positive electrode active material. The cobalt source 81 uses a compound containing cobalt (referred to as cobalt compound). The cobalt compound may be, for example, cobalt sulfate, cobalt chloride, or cobalt nitrate, or a hydrate thereof. Cobalt alkoxide or an organic cobalt complex may also be used as the cobalt compound. Furthermore, organic acids of cobalt such as cobalt acetate or a hydrate thereof may also be used as the cobalt compound. In this specification and the like, the organic acid includes citric acid, oxalic acid, formic acid, butyric acid, etc. in addition to acetic acid.
コバルト源８１として溶液を用いる場合、上記コバルト化合物を有する水溶液（コバルト水溶液と記す）を用意する。 When using a solution as the cobalt source 81, prepare an aqueous solution containing the above-mentioned cobalt compound (referred to as an aqueous cobalt solution).
＜マグネシウム源＞
図２１及び図２２に示すようにマグネシウム源８２（図面ではＭｇ源と記す）を用意する。マグネシウム源８２は、正極活物質の出発材料の一つである。またマグネシウム源８２は、マグネシウムを有する化合物（マグネシウム化合物と記す）を用いる。マグネシウム化合物は、たとえば硫酸マグネシウム、塩化マグネシウム、若しくは硝酸マグネシウム、またはこれらの水和物を用いることができる。 <Magnesium source>
As shown in Figures 21 and 22, a magnesium source 82 (referred to as Mg source in the drawings) is prepared. The magnesium source 82 is one of the starting materials for the positive electrode active material. In addition, a compound containing magnesium (referred to as magnesium compound) is used as the magnesium source 82. The magnesium compound may be, for example, magnesium sulfate, magnesium chloride, magnesium nitrate, or a hydrate thereof.
マグネシウム源８２として溶液を用いる場合、上記マグネシウム化合物を有する水溶液（マグネシウム水溶液と記す）を用意する。 When using a solution as the magnesium source 82, prepare an aqueous solution containing the above magnesium compound (hereinafter referred to as magnesium aqueous solution).
＜マグネシウム源以外＞
図２１及び図２２に示したマグネシウム源８２に代えて、又はマグネシウム源８２に加えてニッケル源を用いてもよい。ニッケル源を用いる場合、具体的にはニッケル水溶液を用意する。 <Other than magnesium sources>
A nickel source may be used instead of the magnesium source 82 shown in Figures 21 and 22, or in addition to the magnesium source 82. When a nickel source is used, specifically, an aqueous nickel solution is prepared.
＜キレート剤＞
図２１に示すようにキレート剤８３を用意する。またキレート剤８３は省略することができ、たとえば図２２にはキレート剤８３を用意しないフロー図を示す。 <Chelating Agent>
A chelating agent 83 is prepared as shown in Fig. 21. The chelating agent 83 may be omitted, and for example, Fig. 22 shows a flow diagram in which the chelating agent 83 is not prepared.
キレート剤８３は、グリシン、オキシン、１−ニトロソ−２−ナフトール、２−メルカプトベンゾチアゾールまたはＥＤＴＡ（エチレンジアミン四酢酸）が溶解した水溶液であり、これをキレート水溶液と記す。なお、グリシン、オキシン、１−ニトロソ−２−ナフトールまたは２−メルカプトベンゾチアゾールから選ばれた複数種を用いてもよい。上記溶媒として、水、好ましくは純水を用いる。 The chelating agent 83 is an aqueous solution in which glycine, oxine, 1-nitroso-2-naphthol, 2-mercaptobenzothiazole or EDTA (ethylenediaminetetraacetic acid) is dissolved, and this will be referred to as an aqueous chelating solution. Note that multiple types selected from glycine, oxine, 1-nitroso-2-naphthol or 2-mercaptobenzothiazole may be used. Water, preferably pure water, is used as the above solvent.
上述したキレート剤は、キレート化合物を作る錯化剤である点で、一般的な錯化剤より好ましい。勿論一般的な錯化剤であるアンモニア水等をキレート剤に代えて用いてもよい。 The above-mentioned chelating agent is preferable to general complexing agents in that it is a complexing agent that forms a chelate compound. Of course, a general complexing agent such as ammonia water may be used instead of the chelating agent.
キレート剤を用いることで、結晶の核の不要な発生を抑え、結晶の成長を促すことができ好ましい。不要な核の発生が抑制されると微粒子の生成が抑制されるため、粒度分布が良好な水酸化物（これを前駆体と呼ぶことがある）を得ることができる。またキレート剤を用いることで、酸塩基反応を遅らせることができ、徐々に反応が進むことで球状に近い水酸化物を得ることができる。 The use of a chelating agent is preferable because it can suppress the generation of unnecessary crystal nuclei and promote crystal growth. When the generation of unnecessary nuclei is suppressed, the generation of fine particles is also suppressed, so hydroxides (sometimes called precursors) with good particle size distribution can be obtained. In addition, the use of a chelating agent can slow down the acid-base reaction, and the gradual progress of the reaction can result in hydroxides that are close to spherical.
グリシン水溶液を用いることは、図２１及び図２２のステップＳ１３１の共沈反応時における反応容器の溶液のｐＨを制御しやすくなり好ましい。さらにグリシン水溶液のグリシン濃度は、０．０５ｍｏｌ／Ｌ以上０．５ｍｏｌ／Ｌ以下、好ましくは０．１ｍｏｌ／Ｌ以上０．２ｍｏｌ／Ｌ以下とするとよい。 The use of an aqueous glycine solution is preferable because it makes it easier to control the pH of the solution in the reaction vessel during the coprecipitation reaction in step S131 of FIG. 21 and FIG. 22. Furthermore, the glycine concentration of the aqueous glycine solution is preferably 0.05 mol/L or more and 0.5 mol/L or less, and more preferably 0.1 mol/L or more and 0.2 mol/L or less.
＜純水＞
上記キレート水溶液に用いられる純水とは、比抵抗が１ＭΩ・ｃｍ以上の水、より好ましくは比抵抗が１０ＭΩ・ｃｍ以上の水、さらに好ましくは比抵抗が１５ＭΩ・ｃｍ以上の水である。上記比抵抗の範囲を満たす水は純度が高く、含有される不純物が非常に少ないため、酸塩基反応に用いると好ましい。 <Pure water>
The pure water used in the above chelate aqueous solution is water having a resistivity of 1 MΩ cm or more, more preferably 10 MΩ cm or more, and even more preferably 15 MΩ cm or more. Water that satisfies the above resistivity range has high purity and contains very few impurities, and is therefore preferable for use in acid-base reactions.
＜ステップＳ１１４＞
次に図２１及び図２２に示すステップＳ１１４について説明する。ステップＳ１１４では、コバルト源８１とマグネシウム源８２とを混合する。本ステップの混合によりコバルト化合物と、マグネシウム化合物との混合液９１を得る。混合液中ではコバルト化合物及びマグネシウム化合物は溶解している。本ステップにおける水は上述の純水を用いるとよい。混合液９１は酸性を示す溶液であり、酸溶液と呼ぶことができる。 <Step S114>
Next, step S114 shown in Figures 21 and 22 will be described. In step S114, a cobalt source 81 and a magnesium source 82 are mixed. A mixed solution 91 of a cobalt compound and a magnesium compound is obtained by the mixing in this step. The cobalt compound and the magnesium compound are dissolved in the mixed solution. The water used in this step may be the above-mentioned pure water. The mixed solution 91 is an acidic solution and may be called an acid solution.
＜アルカリ性水溶液＞
次に図２１及び図２２に示すアルカリ性水溶液８４について説明する。 <Alkaline aqueous solution>
Next, the alkaline aqueous solution 84 shown in FIGS. 21 and 22 will be described.
アルカリ性水溶液８４は、たとえば水酸化ナトリウム、水酸化カリウム、水酸化リチウムまたはアンモニアを有する水溶液を用いればよく、ｐＨ調整剤として機能すればこれら水溶液に限定されない。たとえば水酸化ナトリウム、水酸化カリウム、または水酸化リチウムから選ばれた複数種を水に溶解させた水溶液でもよい。水は上記純水を用いるとよい。 The alkaline aqueous solution 84 may be, for example, an aqueous solution containing sodium hydroxide, potassium hydroxide, lithium hydroxide, or ammonia, and is not limited to these aqueous solutions as long as it functions as a pH adjuster. For example, it may be an aqueous solution in which multiple types selected from sodium hydroxide, potassium hydroxide, and lithium hydroxide are dissolved in water. The water used may be the above-mentioned pure water.
＜キレート剤（張込液）＞
図２１に示すようにキレート剤８５を用意する。キレート剤８５は上述のキレート剤８３と同様の材料を用いればよい。またキレート剤８５は省略することができ、たとえば図２２にはキレート剤８５を用意しなかったフロー図を示す。ただし図２２の場合は、張込液として反応容器には水８６、好ましくは純水を入れておくとよい。 <Chelating agent (filling solution)>
As shown in Fig. 21, a chelating agent 85 is prepared. The chelating agent 85 may be made of the same material as the chelating agent 83 described above. The chelating agent 85 may be omitted, and Fig. 22 shows a flow diagram in which the chelating agent 85 is not prepared. In the case of Fig. 22, however, it is preferable to put water 86, preferably pure water, in the reaction vessel as the filling liquid.
図２１に示すキレート剤８５について補足する。キレート剤８５は後述のステップＳ１３１に用いる反応容器に入れておくとよく、張込液または調整液と記す場合がある。別言するとキレート剤８５は反応初期状態の水溶液を指す。ここでもキレート剤８５を用いることで、上述したように結晶の核の不要な発生を抑え、成長を促すことができ、不要な核の発生が抑制されると微粒子の生成が抑制されるため、粒度分布が良好な水酸化物を得ることができる、または酸塩基反応を遅らせることができ、徐々に反応が進むことで球状に近い水酸化物を得ることができる、といった効果を奏することができる。 Additional information regarding the chelating agent 85 shown in FIG. 21. The chelating agent 85 may be placed in a reaction vessel used in step S131 described below, and may be referred to as a charging liquid or an adjustment liquid. In other words, the chelating agent 85 refers to an aqueous solution in the initial reaction state. Here again, by using the chelating agent 85, as described above, it is possible to suppress the generation of unnecessary crystal nuclei and promote their growth, and by suppressing the generation of unnecessary nuclei, the generation of fine particles is suppressed, so that a hydroxide with a good particle size distribution can be obtained, or the acid-base reaction can be delayed, and the reaction can proceed gradually to obtain a hydroxide that is close to spherical.
＜ステップＳ１３１＞
図２１及び図２２に示すステップＳ１３１について説明する。ステップＳ１３１では、混合液９１と、アルカリ性水溶液８４とを反応容器で混合する。ステップＳ１３１の混合により、混合液９１と、アルカリ性水溶液８４とが反応して、前駆体として水酸化物９５が製造される。ステップＳ１３１における化学反応は、中和反応、酸塩基反応、または共沈反応と記すことができる。上記の共沈反応により、遷移金属Ｍとしてコバルト及びマグネシウムを有する複合水酸化物９５（単に水酸化物９５と記す）が沈殿する。水酸化物９５は正極活物質１００の前駆体と呼べる。また水酸化物９５はコバルト及びマグネシウムの化合物とも呼べるためコバルトマグネシウム化合物と記すことがある。 <Step S131>
Step S131 shown in FIG. 21 and FIG. 22 will be described. In step S131, the mixed solution 91 and the alkaline aqueous solution 84 are mixed in a reaction vessel. By the mixing in step S131, the mixed solution 91 and the alkaline aqueous solution 84 react with each other to produce a hydroxide 95 as a precursor. The chemical reaction in step S131 can be described as a neutralization reaction, an acid-base reaction, or a coprecipitation reaction. By the above coprecipitation reaction, a composite hydroxide 95 (simply referred to as hydroxide 95) having cobalt and magnesium as the transition metal M is precipitated. The hydroxide 95 can be called a precursor of the positive electrode active material 100. The hydroxide 95 can also be called a compound of cobalt and magnesium, and therefore may be referred to as a cobalt magnesium compound.
ステップＳ１３１において、反応容器では攪拌手段を用いて溶液を攪拌しておくとよい。攪拌手段はスターラーまたは攪拌翼等を有する。溶液を攪拌する際、５００ｒｐｍ以上１５００ｒｐｍ以下、好ましくは８００ｒｐｍ以上１２００ｒｐｍ以下の回転速度で攪拌するとよい。また攪拌翼は２枚以上６枚以下設けることができ、たとえば４枚の攪拌翼とする場合、上方からみて十字状に配置するとよい。 In step S131, the solution in the reaction vessel may be stirred using a stirring means. The stirring means may have a stirrer or stirring blades. When stirring the solution, the stirring may be performed at a rotation speed of 500 rpm to 1500 rpm, preferably 800 rpm to 1200 rpm. Two to six stirring blades may be provided. For example, when using four stirring blades, they may be arranged in a cross shape when viewed from above.
ステップＳ１３１のような共沈反応により、マグネシウムとコバルトとは均一に混合することが可能である。すなわち、マグネシウムが内部１００ｂに存在した水酸化物９５を得ることができる。このような水酸化物９５を経て形成された正極活物質１００はマグネシウムの効果を享受できる。 By the coprecipitation reaction in step S131, magnesium and cobalt can be mixed uniformly. That is, a hydroxide 95 in which magnesium exists in the interior 100b can be obtained. The positive electrode active material 100 formed through such hydroxide 95 can enjoy the effects of magnesium.
ただしマグネシウムがコバルトに固溶しづらい場合、または後述の加熱処理などを経た場合、正極活物質１００において、マグネシウムは内部１００ｂよりも表層部１００ａへ偏在することもある。表層部１００ａにマグネシウムが存在する場合においても、正極活物質１００はマグネシウムの効果を享受することができる。例えばマグネシウムにより正極活物質の欠陥を抑制することができる。 However, if magnesium is difficult to dissolve in cobalt, or if the material undergoes a heat treatment, as described below, magnesium may be unevenly distributed in the surface layer 100a rather than in the interior 100b of the positive electrode active material 100. Even if magnesium is present in the surface layer 100a, the positive electrode active material 100 can still enjoy the effects of magnesium. For example, magnesium can suppress defects in the positive electrode active material.
＜反応条件＞
共沈反応に従って混合液９１と、アルカリ性水溶液８４とを反応させる場合、反応容器の溶液のｐＨは９以上１３以下、好ましくはｐＨを９．８以上１２．５以下となるようにする。上記範囲は、水酸化物９５の粒子径を大きくでき好ましい。上記範囲外では、生産性が低くなり、また得られる水酸化物９５が不純物を含有しやすくなってしまうことがある。 <Reaction conditions>
When reacting the mixed solution 91 with the alkaline aqueous solution 84 according to the coprecipitation reaction, the pH of the solution in the reaction vessel is adjusted to 9 or more and 13 or less, preferably 9.8 or more and 12.5 or less. This range is preferable because it allows the particle size of the hydroxide 95 to be large. Outside this range, the productivity may be reduced, and the obtained hydroxide 95 may be more likely to contain impurities.
混合液９１を反応容器に入れ、アルカリ性水溶液８４を反応容器へ滴下する場合、反応容器の溶液のｐＨを上記条件の範囲に維持するとよい。またアルカリ性水溶液８４を反応容器に入れ、混合液９１を滴下する場合も、反応容器の溶液のｐＨを上記条件の範囲に維持するとよい。 When the mixed liquid 91 is placed in a reaction vessel and the alkaline aqueous solution 84 is dropped into the reaction vessel, it is advisable to maintain the pH of the solution in the reaction vessel within the range of the above conditions. Also, when the alkaline aqueous solution 84 is placed in a reaction vessel and the mixed liquid 91 is dropped into the reaction vessel, it is advisable to maintain the pH of the solution in the reaction vessel within the range of the above conditions.
混合液９１またはアルカリ性水溶液８４の送液速度（滴下速度とも呼ぶ）は、反応容器の溶液が２００ｍＬ以上３５０ｍＬ以下の場合、０．０１ｍＬ／分以上１ｍＬ／分以下、好ましくは０．０５ｍＬ／分以上０．５ｍＬ／分以下とするとよい。アルカリ性水溶液８４は反応容器の溶液のｐＨが一定になるように滴下すればよい。混合液９１又はアルカリ性水溶液８４等を貯留するタンクにはポンプが設けられ、当該ポンプにより滴下速度を制御することができる。ポンプは滴下量を制御することもできる。滴下速度は多段階に変化させてもよく、たとえば滴下速度を徐々に速くしてもよい。 The liquid delivery speed (also called the dripping speed) of the mixed liquid 91 or the alkaline aqueous solution 84 may be set to 0.01 mL/min to 1 mL/min, preferably 0.05 mL/min to 0.5 mL/min, when the solution in the reaction vessel is 200 mL to 350 mL. The alkaline aqueous solution 84 may be dripped so that the pH of the solution in the reaction vessel is constant. A pump is provided in the tank that stores the mixed liquid 91 or the alkaline aqueous solution 84, etc., and the dripping speed can be controlled by the pump. The pump can also control the amount of dripping. The dripping speed may be changed in multiple stages, for example, the dripping speed may be gradually increased.
反応容器の溶液の温度は５０℃以上９０℃以下となるように調整する。溶液の温度を確認した後、滴下を開始するとよい。上記範囲は、得られる水酸化物９５の粒子径を大きくすることができ好ましい。 Adjust the temperature of the solution in the reaction vessel to be between 50°C and 90°C. After checking the temperature of the solution, it is recommended to start dropping. The above range is preferable because it allows the particle size of the resulting hydroxide 95 to be large.
また反応容器内は不活性雰囲気とするとよい。たとえば窒素雰囲気とする場合、窒素ガスを０．５Ｌ／分以上１．２Ｌ／分以下の流量で導入するとよい。さらに反応容器の液体に対して窒素ガスをバブリング導入してもよい。 The inside of the reaction vessel should preferably be an inert atmosphere. For example, when creating a nitrogen atmosphere, nitrogen gas should be introduced at a flow rate of 0.5 L/min to 1.2 L/min. Furthermore, nitrogen gas may be introduced by bubbling into the liquid in the reaction vessel.
また反応容器には還流冷却器を配置するとよい。還流冷却器により、窒素ガスを反応容器から放出させることができ、水は反応容器に戻すことができる。 It is also a good idea to place a reflux condenser in the reaction vessel, which allows the nitrogen gas to be released from the reaction vessel and the water to be returned to the reaction vessel.
上記反応を経ると反応容器に反応生成物として沈殿物９２が得られる。沈殿物９２にはコバルトマグネシウム水酸化物が含まれる。 After the above reaction, a precipitate 92 is obtained as a reaction product in the reaction vessel. The precipitate 92 contains cobalt magnesium hydroxide.
＜ステップＳ１３２、ステップＳ１３３＞
図２１に示すステップＳ１３２のろ過、及びステップＳ１３３の乾燥工程について説明する。沈殿物９２は水酸化物９５以外にも不純物を有する。そこで水酸化物９５を回収するために、好ましくはステップＳ１３２のろ過を行う。ろ過は吸引ろ過、または減圧ろ過を適用できる。ろ過以外には遠心分離を適用してもよい。吸引ろ過を用いる場合、反応容器に沈殿した反応生成物を水（たとえば純水等）で洗浄し、その後、沸点の低い有機溶剤（たとえばアセトン等）で洗浄すると好ましい。また吸引濾過は複数回実施するとよい。なお図２２に示すようにステップＳ１３２は実施しなくともよい。 <Steps S132 and S133>
The filtration in step S132 and the drying process in step S133 shown in FIG. 21 will be described. The precipitate 92 contains impurities other than the hydroxide 95. Therefore, in order to recover the hydroxide 95, the filtration in step S132 is preferably performed. The filtration can be performed by suction filtration or reduced pressure filtration. Centrifugation may be used instead of filtration. When using suction filtration, it is preferable to wash the reaction product precipitated in the reaction vessel with water (e.g., pure water, etc.) and then with an organic solvent with a low boiling point (e.g., acetone, etc.). It is also preferable to perform suction filtration multiple times. Note that step S132 does not have to be performed as shown in FIG. 22.
ろ過後の生成物にはさらにステップＳ１３３の乾燥を行うとよい。たとえば６０℃以上９０℃以下において、０．５時間以上２０時間以下、好ましくは１２時間以上２０時間以下で乾燥させる。乾燥は酸素が少ない雰囲気で行うと好ましい。たとえば真空下で乾燥を行う場合、内部を真空に排気できる容器（ベルジャーと記す）と、ベルジャーに接続された真空ポンプとを有するベルジャー型真空装置を用いることができる。また真空雰囲気で乾燥を行う場合、真空乾燥炉を用いてもよく、真空乾燥炉は乾燥炉に接続された真空ポンプを有する。ベルジャー型真空装置及び真空乾燥炉が有する真空ポンプには、ドライポンプ、ターボ分子ポンプ、油回転ポンプ、クライオポンプ又はメカニカルブースタ−ポンプを用いることができる。ベルジャー型真空装置及び真空乾燥炉における真空雰囲気は、各装置が有する差圧計が、−０．１ＭＰａ以上−０．０８ＭＰａ未満となるように減圧した雰囲気が含まれる。窒素雰囲気で加熱を行う場合、ベルジャー型真空装置及び真空乾燥炉が有する容器内に窒素を含むガスを流せばよい。このようにして水酸化物９５を得ることができる。十分乾燥させることにより、得られた水酸化物９５から不純物、例えば水分又はヒドロキシ基が低減されるため好ましい。なお図２１に示すようにステップＳ１３３は実施しなくともよい。 The product after filtration may be further dried in step S133. For example, the product may be dried at 60°C or higher and 90°C or lower for 0.5 hours to 20 hours, preferably 12 hours to 20 hours. The drying is preferably performed in an atmosphere with little oxygen. For example, when drying is performed under vacuum, a bell jar type vacuum device having a container (referred to as a bell jar) whose inside can be evacuated to a vacuum and a vacuum pump connected to the bell jar can be used. When drying is performed in a vacuum atmosphere, a vacuum drying furnace may be used, and the vacuum drying furnace has a vacuum pump connected to the drying furnace. The vacuum pump of the bell jar type vacuum device and the vacuum drying furnace may be a dry pump, a turbo molecular pump, an oil rotary pump, a cryopump, or a mechanical booster pump. The vacuum atmosphere in the bell jar type vacuum device and the vacuum drying furnace includes an atmosphere reduced in pressure so that the differential pressure gauge of each device is -0.1 MPa or higher but less than -0.08 MPa. When heating is performed in a nitrogen atmosphere, a gas containing nitrogen may be flowed into the container of the bell jar type vacuum device and the vacuum drying furnace. In this manner, hydroxide 95 can be obtained. Thorough drying is preferable because it reduces impurities, such as moisture or hydroxyl groups, from the obtained hydroxide 95. Note that step S133 does not have to be performed, as shown in FIG. 21.
なお、ステップＳ１３３の乾燥に代えて又は加えて加熱を実施してもよい。加熱温度は７００℃以上１２００℃未満とすることが好ましく、８００℃以上１１００℃未満とすることがより好ましく、９００℃以上１０００℃未満がさらに好ましい。加熱時間はたとえば１時間以上１００時間以下とすることができ、２時間以上２０時間以下とすることが好ましい。加熱後は水酸化物ではなく酸化物となる。 Heating may be performed instead of or in addition to the drying in step S133. The heating temperature is preferably 700°C or more and less than 1200°C, more preferably 800°C or more and less than 1100°C, and even more preferably 900°C or more and less than 1000°C. The heating time can be, for example, 1 hour or more and 100 hours or less, and preferably 2 hours or more and 20 hours or less. After heating, the oxide is formed instead of the hydroxide.
このような工程を経て得られた水酸化物９５は、単粒子でも二次粒子でもよいが、結晶子が大きいと好ましい。 The hydroxide 95 obtained through such a process may be either single particles or secondary particles, but it is preferable for the crystallites to be large.
＜リチウム源＞
図２１及び図２２に示すリチウム源８８（図面ではＬｉ源と記す）としてリチウム化合物を用意する。 <Lithium source>
A lithium compound is prepared as the lithium source 88 (referred to as Li source in the drawings) shown in FIGS.
リチウム化合物として、水酸化リチウム、炭酸リチウム、酸化リチウムまたは硝酸リチウムを用意する。コバルト、及びマグネシウム等の原子数比の和に対するリチウムの原子数比（これをＬｉ／（Ｃｏ＋Ｍｇ）と記す）は、０．９以上１．２以下、好ましくは１．０以上１．０９以下がよい。上記範囲を満たすようにリチウム化合物を秤量する。水分又はヒドロキシ基が低減された水酸化物９５を用いると、Ｌｉ／（Ｃｏ＋Ｍｇ）が適切な値となり好ましい。 As the lithium compound, lithium hydroxide, lithium carbonate, lithium oxide or lithium nitrate is prepared. The atomic ratio of lithium to the sum of the atomic ratios of cobalt, magnesium, etc. (referred to as Li/(Co+Mg)) is 0.9 to 1.2, preferably 1.0 to 1.09. The lithium compound is weighed so as to satisfy the above range. When hydroxide 95 with reduced moisture or hydroxyl groups is used, Li/(Co+Mg) becomes an appropriate value, which is preferable.
リチウム化合物は粉砕しておくとよい。たとえば乳鉢を用いて５分間以上１５分間以下の時間で粉砕する。当該乳鉢は不純物を放出しにくい材質が好ましく、具体的には、純度が９０％以上、好ましくは純度が９９％以上のアルミナの乳鉢を用いるとよい。またボールミル等を用いた湿式粉砕法を用いてもよい。湿式粉砕法では、溶媒にアセトン又は脱水アセトンを用いることができ、回転数２００ｒｐｍ以上４００ｒｐｍ以下とし、１０時間以上１５時間以下で粉砕するとよい。また粉砕後のリチウム化合物はふるいでふるっておいてもよい。さらに粉砕分級装置を用いてリチウム化合物を粉砕してもよい。 The lithium compound may be crushed in advance. For example, the lithium compound may be crushed in a mortar for 5 to 15 minutes. The mortar is preferably made of a material that does not easily release impurities, and specifically, an alumina mortar with a purity of 90% or more, preferably 99% or more, may be used. A wet crushing method using a ball mill or the like may also be used. In the wet crushing method, acetone or dehydrated acetone may be used as the solvent, and the rotation speed may be set to 200 to 400 rpm, and crushing may be performed for 10 to 15 hours. The lithium compound after crushing may also be sieved. The lithium compound may also be crushed using a crushing and classifying device.
＜ステップＳ１５１＞
図２１及び図２２に示すステップＳ１５１について説明する。ステップＳ１５１では、水酸化物９５とリチウム源８８とを混合する。その後、混合された混合物９６を得る。水酸化物９５とリチウム源８８とを混合する手段に乳鉢、又は自転公転攪拌装置等を用いるとよい。 <Step S151>
21 and 22, step S151 will be described. In step S151, the hydroxide 95 and the lithium source 88 are mixed. Then, a mixed mixture 96 is obtained. A mortar, a rotation/revolution stirrer, or the like may be used as a means for mixing the hydroxide 95 and the lithium source 88.
水酸化物９５とリチウム源８８との混合と同じステップで粉砕を行う場合、メディアとしてボールミルまたはビーズミルを用いるとよい。ボールミルまたはビーズミルにはアルミナボールまたはジルコニアボールを用いることができる。ボールミルまたはビーズミルでは、メディアに遠心力が付加されるため、微粒子化が可能となる。ただしメディア等からのコンタミネーションが懸念される場合は、上記ジルコニアボールを用いつつ、周速を１００ｍｍ／秒以上２０００ｍｍ／秒以下とすることが好ましい。 When grinding is performed in the same step as mixing the hydroxide 95 and the lithium source 88, a ball mill or a bead mill may be used as the media. Alumina balls or zirconia balls may be used for the ball mill or bead mill. In a ball mill or bead mill, centrifugal force is applied to the media, making it possible to micronize the particles. However, if there is a concern about contamination from the media, it is preferable to use the above-mentioned zirconia balls and set the peripheral speed to 100 mm/sec or more and 2000 mm/sec or less.
混合と粉砕とを同じステップで行う場合に用いることができる粉砕法としては、乾式粉砕法と湿式粉砕法とがある。乾式粉砕法は、不活性ガスまたは空気中で粉砕するものであり、粒子径が３．５μｍ以下、好ましくは３μｍ以下まで粉砕することができる。湿式粉砕法は液体中で粉砕するものであり、粒子径が１μｍ以下まで粉砕することができる。すなわち粒子径を小さくしたい場合は湿式粉砕法を用いるとよい。 When mixing and grinding are performed in the same step, there are two grinding methods that can be used: dry grinding and wet grinding. Dry grinding involves grinding in an inert gas or air, and can grind materials to a particle size of 3.5 μm or less, preferably 3 μm or less. Wet grinding involves grinding in a liquid, and can grind materials to a particle size of 1 μm or less. In other words, if you want to reduce the particle size, you should use the wet grinding method.
このようにして混合物９６を得る。 In this way, mixture 96 is obtained.
＜ステップＳ１５４＞
次に図２１及び図２２に示すステップＳ１５４について説明する。ステップＳ１５４では、混合物９６を加熱する。ステップＳ１５４は本焼成と記すことがある。加熱に関するステップは、複数回実施してもよく、本焼成の前に温度を下げた仮焼成を実施してもよい。 <Step S154>
Next, step S154 shown in Fig. 21 and Fig. 22 will be described. In step S154, the mixture 96 is heated. Step S154 may be referred to as main baking. The heating step may be performed multiple times, or preliminary baking at a lower temperature may be performed before the main baking.
ステップＳ１５４として、加熱温度は７００℃以上１２００℃未満とすることが好ましく、８００℃以上１１００℃未満とすることがより好ましく、９００℃以上１０００℃以下とすることがさらに好ましい。本加熱処理を経て酸化物９８を製造する際、少なくとも水酸化物９５とリチウム源８８とが相互に拡散する温度で加熱する。 In step S154, the heating temperature is preferably 700°C or more and less than 1200°C, more preferably 800°C or more and less than 1100°C, and even more preferably 900°C or more and 1000°C or less. When producing the oxide 98 through this heating process, heating is performed at a temperature at which at least the hydroxide 95 and the lithium source 88 diffuse into each other.
ステップＳ１５４の加熱時間はたとえば１時間以上１００時間以下とすることができ、２時間以上２０時間以下とすることが好ましい。 The heating time in step S154 can be, for example, from 1 hour to 100 hours, and preferably from 2 hours to 20 hours.
ステップＳ１５４の処理室の雰囲気は、酸素を含むことが好ましい。酸素を含む雰囲気として、例えば、酸素雰囲気、乾燥空気雰囲気、大気雰囲気、酸素と他のガス（例えば、窒素及び貴ガスから選ばれる一以上）とを混合した雰囲気が挙げられる。貴ガスとして、例えば、アルゴンが挙げられる。また、雰囲気として、窒素及び貴ガスから選ばれる二以上を混合して用いてもよい。 The atmosphere in the processing chamber in step S154 preferably contains oxygen. Examples of atmospheres containing oxygen include an oxygen atmosphere, a dry air atmosphere, an air atmosphere, and an atmosphere in which oxygen is mixed with other gases (e.g., one or more gases selected from nitrogen and noble gases). An example of a noble gas is argon. In addition, the atmosphere may be a mixture of two or more gases selected from nitrogen and noble gases.
ステップＳ１５４の処理室の雰囲気は、水分が少ないことが好ましい。雰囲気の露点は、例えば、−５０℃以下が好ましく、さらには−８０℃以下が好ましい。昇温工程及び温度保持工程は、乾燥空気を好適に用いることができる。また、雰囲気におけるＣＨ４、ＣＯ、ＣＯ２、及びＨ２等の不純物濃度をそれぞれ５ｐｐｂ（ｐａｒｔｓ　ｐｅｒ　ｂｉｌｌｉｏｎ）以下にすることにより、材料に混入しうる不純物を抑制できる場合がある。 The atmosphere in the process chamber in step S154 preferably has a low moisture content. The dew point of the atmosphere is preferably, for example, -50°C or less, and more preferably -80°C or less. Dry air can be suitably used in the temperature increase step and the temperature holding step. In addition, impurities that may be mixed into the material may be suppressed by setting the impurity concentrations of CH4 , CO, CO2 , and H2 in the atmosphere to 5 ppb (parts per billion) or less.
ステップＳ１５４の処理室にガスを導入し続ける方法がある。この方法は、処理室内にガスが流れているともいえる。この場合、ガスの流量は例えば、処理室の体積１Ｌあたり、０．１Ｌ／ｍｉｎ以上０．７Ｌ／ｍｉｎ以下とすればよい。処理室の容積が４０Ｌである場合には、１０Ｌ／ｍｉｎまたはその近傍とすることが好ましい。なお、当該ガスとして、例えば、酸素ガス、乾燥空気、窒素ガス、貴ガス、及びこれらのガスから選ばれる二以上を混合したガスを用いることができる。 There is a method of continuously introducing gas into the processing chamber in step S154. This method can also be said to be flowing gas into the processing chamber. In this case, the gas flow rate may be, for example, 0.1 L/min or more and 0.7 L/min or less per 1 L of processing chamber volume. When the volume of the processing chamber is 40 L, it is preferable to set the flow rate at or near 10 L/min. Note that the gas in question may be, for example, oxygen gas, dry air, nitrogen gas, noble gas, or a mixture of two or more selected from these gases.
ステップＳ１５４の処理室の雰囲気を所望のガスで置換した後、当該ガスが処理室から出入りしないようにする方法を用いてもよい。例えば、処理室内の雰囲気を、酸素を含むガスで置換し、当該ガスが処理室から出入りしないようにすることができる。また、処理室を減圧してから、ガスを導入してもよい。具体的には、例えば、処理室を、差圧計が−９７０ｈＰａを示すまで減圧してから、５０ｈＰａの圧力となるまでガスを導入すればよい。 After replacing the atmosphere in the processing chamber in step S154 with the desired gas, a method may be used to prevent the gas from entering or leaving the processing chamber. For example, the atmosphere in the processing chamber may be replaced with a gas containing oxygen to prevent the gas from entering or leaving the processing chamber. The processing chamber may also be depressurized before introducing the gas. Specifically, for example, the processing chamber may be depressurized until the differential pressure gauge indicates -970 hPa, and then gas may be introduced until the pressure reaches 50 hPa.
加熱の際に用いる、るつぼ、サヤ、セッター、または容器は不純物を放出しにくい材質であると好ましい。たとえば純度が９９．９％のアルミナのるつぼを用いるとよい。量産する場合にはムライト・コーディライト（Ａｌ２Ｏ３、ＳｉＯ２、ＭｇＯ）のサヤを用いるとよい。 The crucible, scabbard, setter, or container used during heating should preferably be made of a material that does not easily release impurities. For example, a crucible made of alumina with a purity of 99.9% should be used. For mass production, a scabbard made of mullite-cordierite (Al 2 O 3 , SiO 2 , MgO) should be used.
また加熱が終わった材料を回収する際に、るつぼから乳鉢へ移動させたのち、回収すると材料に不純物が混入しないため好ましい。また、当該乳鉢についても、不純物を放出しにくい材質が好ましく、具体的には、純度が９０％以上、好ましくは純度が９９％以上のアルミナ又はジルコニアの乳鉢を用いるとよい。 In addition, when recovering the material after heating, it is preferable to move it from the crucible to a mortar and then recover it, as this prevents impurities from being mixed into the material. In addition, it is preferable for the mortar to be made of a material that does not easily release impurities, and specifically, it is recommended to use a mortar made of alumina or zirconia with a purity of 90% or more, preferably 99% or more.
＜ステップＳ１５５＞
図２１に示したステップＳ１５５について説明する。ステップＳ１５５では解砕工程を実施する。たとえば目開きの径が４０μｍ以上６０μｍ以下のふるいを用いて分級する作業を行うとよい。しかしながら図２２のようにステップＳ１５５の解砕工程を実施しなくとも酸化物９８を得ることができる。 <Step S155>
Step S155 shown in Fig. 21 will now be described. In step S155, a crushing step is carried out. For example, a sieve with a mesh size of 40 µm to 60 µm may be used to classify the particles. However, as shown in Fig. 22, oxide 98 can be obtained without carrying out the crushing step in step S155.
＜複合酸化物＞
図２１及び図２２に示した酸化物９８について説明する。酸化物９８は少なくともステップＳ１５４の加熱を経て形成されたものであり、複合酸化物と呼ぶことがある。また酸化物９８は正極活物質１００として用いることもできる。 <Complex oxide>
The oxide 98 shown in Fig. 21 and Fig. 22 will be described. The oxide 98 is formed at least through the heating in step S154, and may be called a composite oxide. The oxide 98 may also be used as the positive electrode active material 100.
＜ステップＳ１５６＞
図２１に示したステップＳ１５６について説明する。欠陥のない酸化物９８を得るために、加熱を行うとより好ましい。この加熱を他の加熱処理と区別するために初期加熱と呼んでもよい。ステップＳ１５６の加熱処理により、欠陥を減らす効果、内部の層状岩塩型の結晶構造の結晶性を高める効果、又は表面を滑らかにする効果が期待できる。いずれも酸化物９８に対する効果と言えるが、正極活物質１００は酸化物９８の形状等を反映することがあるため、正極活物質１００においても、欠陥を減らす効果、内部の層状岩塩型の結晶構造の結晶性を高める効果、又は表面を滑らかにする効果が期待できる。 <Step S156>
Step S156 shown in FIG. 21 will be described. It is more preferable to perform heating in order to obtain oxide 98 without defects. This heating may be called initial heating to distinguish it from other heating treatments. The heating treatment in step S156 is expected to have the effect of reducing defects, the effect of increasing the crystallinity of the internal layered rock salt type crystal structure, or the effect of smoothing the surface. Although all of these can be said to be effects on oxide 98, since the positive electrode active material 100 may reflect the shape of oxide 98, the positive electrode active material 100 can also be expected to have the effect of reducing defects, the effect of increasing the crystallinity of the internal layered rock salt type crystal structure, or the effect of smoothing the surface.
ステップＳ１５６の加熱条件は、ステップＳ１５４で述べた加熱条件から選ぶことができる。また、ステップＳ１５６の加熱温度は、ステップＳ１５４の加熱温度よりも低いと好ましい。 The heating conditions in step S156 can be selected from the heating conditions described in step S154. In addition, it is preferable that the heating temperature in step S156 is lower than the heating temperature in step S154.
ステップＳ１５６の処理室の雰囲気は、ステップＳ１５４で述べた雰囲気から選ぶことができる。またステップＳ１５６の処理室の雰囲気は酸素を含むことが好ましい。 The atmosphere in the processing chamber in step S156 can be selected from the atmospheres described in step S154. It is also preferable that the atmosphere in the processing chamber in step S156 contains oxygen.
ステップＳ１５６の加熱処理により、酸化物９８の表層部の一部からリチウムが脱離する影響で、後述する添加元素の分布がさらに良好になる。より詳細には以下のような機序で、当該加熱処理により添加元素によって分布を異ならせやすくなると考えられる。まずステップＳ１５６の加熱処理により、酸化物９８の表層部の一部からリチウムが脱離する。次に、表層部のリチウムが欠乏した酸化物９８と、後述するようにニッケル源、アルミニウム源、マグネシウム源をはじめとする添加元素源を混合し加熱する。添加元素のうちマグネシウムは２価の典型元素であり、ニッケルは遷移金属であるが２価のイオンになりやすい。そのため酸化物９８の表層部の一部に、Ｍｇ２＋及びＮｉ２＋と、リチウムの欠乏により還元されたＣｏ２＋と、を有する岩塩型の相が形成される。ただし、この相が形成されるのは酸化物９８の表層部の一部であるため、ＳＴＥＭなどの電子顕微鏡像及び電子線回折パターンにおいて明瞭に確認できない場合もある。 The heat treatment in step S156 causes lithium to be released from a portion of the surface layer of the oxide 98, which further improves the distribution of the additive elements described below. More specifically, it is believed that the heat treatment makes it easier to make the distribution different depending on the additive element, due to the following mechanism. First, lithium is released from a portion of the surface layer of the oxide 98 by the heat treatment in step S156. Next, the oxide 98 lacking lithium in the surface layer is mixed with an additive element source, such as a nickel source, an aluminum source, or a magnesium source, as described below, and heated. Among the additive elements, magnesium is a typical divalent element, and nickel is a transition metal but is prone to becoming a divalent ion. Therefore, a rock salt phase containing Mg 2+ , Ni 2+ , and Co 2+ reduced due to the lack of lithium is formed in a portion of the surface layer of the oxide 98. However, since this phase is formed in a portion of the surface layer of the oxide 98, it may not be clearly confirmed in an electron microscope image such as STEM or an electron beam diffraction pattern.
ステップＳ１５６の加熱処理により、酸化物９８の表層部の一部からリチウムが脱離する場合、ステップＳ１５６の前に、酸化物９８にリチウム源を添加してもよい。 If lithium is released from a portion of the surface layer of the oxide 98 by the heat treatment in step S156, a lithium source may be added to the oxide 98 before step S156.
しかし、必ずしもステップＳ１５６の加熱処理は行わなくてもよい。 However, the heating process of step S156 does not necessarily have to be performed.
＜添加元素源＞
図２１及び図２２に示した添加元素源８９について説明する。添加元素源８９は、上記製造方法１及び２で説明した添加元素を用いることができる。添加元素源８９を用意する際、図２０Ｂ及び図２０Ｃに示すように２種以上の添加元素を用いることも可能である。 <Source of added elements>
The additive element source 89 shown in Figures 21 and 22 will be described. The additive element source 89 can use the additive elements described in the above manufacturing methods 1 and 2. When preparing the additive element source 89, it is also possible to use two or more kinds of additive elements as shown in Figures 20B and 20C.
＜ステップＳ１７１＞
図２１及び図２２に示すステップＳ１７１では添加元素源８９と、酸化物９８とを混合する。その後、混合物９９を形成する。ステップＳ１７１の混合は、ステップＳ１５１の混合条件から選ぶことができる。ステップＳ１７１の混合は、酸化物９８が崩壊しないように回転数を１００ｒｐｍ以上２００ｒｐｍ以下とするとよい。添加元素源８９としてマグネシウム源は省略してもよい。また添加元素源８９としてアルミニウム源は省略してもよい。 <Step S171>
21 and 22, an additive element source 89 and an oxide 98 are mixed. Then, a mixture 99 is formed. The mixing conditions in step S171 can be selected from the mixing conditions in step S151. The mixing conditions in step S171 should be set to a rotation speed of 100 rpm or more and 200 rpm or less so that the oxide 98 does not disintegrate. The magnesium source may be omitted as the additive element source 89. The aluminum source may be omitted as the additive element source 89.
＜ステップＳ１７２＞
図２１及び図２２に示すステップＳ１７２について説明する。ステップＳ１７２では混合物９９に対して加熱を行う。 <Step S172>
21 and 22, step S172 will be described. In step S172, the mixture 99 is heated.
ここで加熱温度について補足する。ステップＳ１７２の加熱は、酸化物９８と添加元素源８９との反応が進む温度以上である必要がある。反応が進む温度とは、酸化物９８と添加元素源８９との相互拡散が起きる温度であればよく、これらの材料の溶融温度よりも低くてもよい。酸化物を例にして説明するが、溶融温度Ｔｍの０．７５７倍（タンマン温度Ｔｄ）から相互拡散が起こることがわかっている。そのため、ステップＳ１７２の加熱温度としては、５００℃以上であればよい。 Here, a supplementary note on the heating temperature will be provided. The heating in step S172 must be at a temperature at which the reaction between the oxide 98 and the additive element source 89 proceeds or higher. The temperature at which the reaction proceeds may be any temperature at which interdiffusion between the oxide 98 and the additive element source 89 occurs, and may be lower than the melting temperature of these materials. An oxide will be used as an example, and it is known that interdiffusion occurs at a temperature 0.757 times the melting temperature Tm (Tammann temperature Td ). Therefore, the heating temperature in step S172 may be 500°C or higher.
勿論、酸化物９８と添加元素源８９との一部が溶融する温度以上であると、反応が進みやすく好ましい。たとえば、添加元素源８９として、ＬｉＦ及びＭｇＦ２を有する場合、ステップＳ１７２の加熱は７００℃以上にするとよい。特に、ＬｉＦとＭｇＦ２の共融点は７４２℃付近であるため、ステップＳ１７２の加熱は７４２℃以上とすることが好ましい。 Of course, the reaction is likely to proceed more easily if the temperature is equal to or higher than the temperature at which the oxide 98 and the additive element source 89 are partially melted. For example, when the additive element source 89 contains LiF and MgF2 , the heating in step S172 should be set to 700°C or higher. In particular, since the eutectic point of LiF and MgF2 is around 742°C, the heating in step S172 should be set to 742°C or higher.
加熱温度が高いと反応が進みやすく、加熱時間が短く済み、生産性が高く好ましい。 Higher heating temperatures are preferable because they facilitate the reaction, shorten the heating time, and increase productivity.
ただし加熱温度は酸化物９８の融点未満とする。すなわちステップＳ１７２の加熱は、ステップＳ１５２の加熱より温度が低いとよい。またステップＳ１７２の加熱は、ステップＳ１５４の加熱より温度が低いとよい。融点の近傍の温度では、微量ではあるが酸化物９８の分解が懸念される。コバルト酸リチウムの融点は１１３０℃であり、その手前の１０００℃程度からリチウムの蒸散、又はリチウムとコバルトのカチオンミキシング等が生じやすくなり、加熱温度は１０００℃以下であるとより好ましく、９５０℃以下であるとさらに好ましく、９００℃以下であるとさらに好ましい。 However, the heating temperature must be below the melting point of oxide 98. In other words, the heating temperature in step S172 should be lower than that in step S152. The heating temperature in step S172 should also be lower than that in step S154. At temperatures close to the melting point, there is a concern that oxide 98 may decompose, albeit only slightly. The melting point of lithium cobalt oxide is 1130°C, and from temperatures just before that, around 1000°C, lithium evaporation or cation mixing of lithium and cobalt becomes more likely to occur, so the heating temperature is preferably 1000°C or lower, more preferably 950°C or lower, and even more preferably 900°C or lower.
これらを踏まえると、ステップＳ１７２の加熱の加熱温度としては、５００℃以上１１３０℃未満が好ましく、７００℃以上１０００℃以下がより好ましく、７００℃以上９５０℃以下がさらに好ましく、７００℃以上９００℃以下がさらに好ましい。また、７４２℃以上１１３０℃以下が好ましく、７４２℃以上１０００℃以下がより好ましく、７４２℃以上９５０℃以下がさらに好ましく、７４２℃以上９００℃以下がさらに好ましい。また、８００℃以上１１３０℃以下、８３０℃以上１１３０℃以下が好ましく、８３０℃以上１０００℃以下がより好ましく、８３０℃以上９５０℃以下がさらに好ましく、８３０℃以上９００℃以下がさらに好ましい。 In light of these, the heating temperature in step S172 is preferably 500°C or higher and lower than 1130°C, more preferably 700°C or higher and 1000°C or lower, even more preferably 700°C or higher and 950°C or lower, and even more preferably 700°C or higher and 900°C or lower. Also, 742°C or higher and 1130°C or lower is preferable, more preferably 742°C or higher and 1000°C or lower, even more preferably 742°C or higher and 950°C or lower, and even more preferably 742°C or higher and 900°C or lower. Also, 800°C or higher and 1130°C or lower, 830°C or higher and 1130°C or lower is preferable, 830°C or higher and 1000°C or lower is more preferable, 830°C or higher and 950°C or lower is even more preferable, and 830°C or higher and 900°C or lower is even more preferable.
さらに混合物９９を加熱する際、加熱環境におけるフッ素源等に起因するフッ素またはフッ化物の分圧を適切な範囲に制御することが好ましい。 Furthermore, when heating the mixture 99, it is preferable to control the partial pressure of fluorine or fluoride resulting from the fluorine source, etc. in the heating environment within an appropriate range.
本製造方法では、フッ素源であるＬｉＦが融剤として機能する場合がある。この機能によりステップＳ１７２の加熱の温度を酸化物９８の融点未満、たとえば７４２℃以上９５０℃以下にまで低温化でき、添加元素源が表層部にて均一に広がることもできる。その結果、表層部に添加元素を有せしめた正極活物質１００を製造できる。 In this manufacturing method, LiF, which is a fluorine source, may function as a flux. This function allows the heating temperature in step S172 to be lowered to below the melting point of the oxide 98, for example, to 742°C or higher and 950°C or lower, and also allows the additive element source to spread uniformly in the surface layer. As a result, a positive electrode active material 100 having an additive element in the surface layer can be manufactured.
しかし、ＬｉＦは酸素よりも気体状態での比重が軽いため、加熱によりＬｉＦが昇華する可能性があり、昇華すると混合物９９中のＬｉＦが減少してしまう。すると融剤としての機能が弱くなってしまう。よって、ＬｉＦの昇華を抑制しつつ、加熱する必要がある。なお、フッ素源等としてＬｉＦを用いなかったとしても、酸化物９８の表面のＬｉとＬｉＦ以外のフッ素源のＦが反応して、ＬｉＦが生じ、昇華する可能性もある。そのため、ＬｉＦ以外のフッ素源として、ＬｉＦより融点が高いフッ化物を用いたとしても、同じように昇華の抑制が必要である。 However, since LiF has a lower specific gravity in a gaseous state than oxygen, there is a possibility that LiF may sublime when heated, and if it sublimes, the amount of LiF in mixture 99 will decrease. This will weaken its function as a flux. Therefore, it is necessary to heat while suppressing the sublimation of LiF. Even if LiF is not used as the fluorine source, etc., Li on the surface of oxide 98 may react with F in a fluorine source other than LiF, resulting in the production of LiF, which may then sublime. Therefore, even if a fluoride with a higher melting point than LiF is used as a fluorine source other than LiF, it is still necessary to suppress sublimation in the same way.
昇華を抑制するには、Ｆを含む雰囲気で混合物９９を加熱する方法がある。混合物９９を加熱する加熱炉内の雰囲気をＬｉＦの分圧が高い状態とする方法である。別の方法として、混合物９９を入れる反応容器に蓋を配する方法がある。このような方法等により混合物９９中のＬｉＦの昇華、すなわちＬｉＦの減少を抑制することができる。 To suppress sublimation, there is a method of heating mixture 99 in an atmosphere containing F. This method involves making the atmosphere in the heating furnace in which mixture 99 is heated a state in which the partial pressure of LiF is high. Another method is to place a lid on the reaction vessel in which mixture 99 is placed. By using methods such as these, it is possible to suppress the sublimation of LiF in mixture 99, i.e., the reduction in LiF.
ローラーハースキルンによってステップＳ１７２の加熱を行うことが可能である。ローラーハースキルンは混合物９９の入った反応容器に蓋を配した状態で窯内を移動しながら加熱することが可能である。蓋を配することで、ＬｉＦを含む雰囲気で混合物９９を加熱することができ、混合物９９中のＬｉＦの昇華、すなわち減少を抑制することができる。 The heating in step S172 can be performed using a roller hearth kiln. The roller hearth kiln can heat the reaction vessel containing the mixture 99 while moving it around the kiln with a lid placed on it. By placing the lid, the mixture 99 can be heated in an atmosphere containing LiF, and the sublimation, i.e., reduction, of the LiF in the mixture 99 can be suppressed.
また、ロータリーキルンによってステップＳ１７２の加熱を行うことも可能である。ロータリーキルンは、窯内の雰囲気は酸素を含むものとし、酸素の流量を制御しながら加熱すると好ましい。混合物９９中のＬｉＦの昇華、すなわち減少を抑制するためには、酸素の流量を少なくする方が好ましい。酸素の流量を少なくするには、最初に窯に酸素を導入して一定期間保持しておき、その後は酸素を導入しない等の方法がある。 It is also possible to carry out the heating in step S172 using a rotary kiln. It is preferable that the atmosphere inside the rotary kiln contains oxygen, and that heating is carried out while controlling the flow rate of oxygen. In order to suppress the sublimation, i.e., reduction, of LiF in mixture 99, it is preferable to reduce the flow rate of oxygen. One method of reducing the flow rate of oxygen is to first introduce oxygen into the kiln and hold it there for a certain period of time, and then not introduce oxygen thereafter.
このような工程により、表面がなめらかで凹凸が少ない正極活物質１００を得られると考えられている。 It is believed that this process produces a positive electrode active material 100 with a smooth surface and minimal irregularities.
＜ステップＳ１７３＞
図２１に示したステップＳ１７３について説明する。ステップＳ１７３では解砕工程を実施する。たとえば目開きの径が４０μｍ以上６０μｍ以下のふるいを用いて分級する作業を行うとよい。当該作業を行うことにより、粒子同士の固着を抑制できる。しかしながら図２２のようにステップＳ１７３の解砕工程を実施しなくとも正極活物質１００を得ることができる。 <Step S173>
Step S173 shown in FIG. 21 will be described. In step S173, a crushing step is performed. For example, a sieve with a mesh size of 40 μm or more and 60 μm or less may be used to perform classification. By performing this operation, adhesion between particles can be suppressed. However, as shown in FIG. 22, the positive electrode active material 100 can be obtained without performing the crushing step of step S173.
上記に従い、正極活物質１００を製造することができる。正極活物質１００は前駆体である水酸化物９５の形状を反映することができる。また上述した製造方法に従うと、マグネシウムが内部にもあるコバルト酸リチウムを得ることができる。固溶できなかったマグネシウムはコバルト酸リチウムの表層部に拡散する場合がある。さらに添加元素が表層部に留まったコバルト酸リチウムを得ることができる。添加元素は表層部にて、コバルト酸リチウムに固溶しているとよい。 The positive electrode active material 100 can be manufactured in the manner described above. The positive electrode active material 100 can reflect the shape of the precursor hydroxide 95. Furthermore, by following the manufacturing method described above, lithium cobalt oxide can be obtained that also contains magnesium inside. Magnesium that is not dissolved may diffuse to the surface layer of the lithium cobalt oxide. Furthermore, lithium cobalt oxide can be obtained in which the added element remains in the surface layer. It is preferable that the added element is dissolved in the lithium cobalt oxide in the surface layer.
さらに当該コバルト酸リチウムは不純物が少ないため好ましい。ただし出発材料に硫化物を使用する場合は当該コバルト酸リチウムから硫黄が検出されることがある。ＧＤ−ＭＳ、ＩＣＰ−ＭＳ等を用いて正極活物質の粒子全体の元素分析を行い、硫黄の濃度を測定することができる。 Furthermore, the lithium cobalt oxide is preferable because it has few impurities. However, if a sulfide is used as the starting material, sulfur may be detected in the lithium cobalt oxide. The sulfur concentration can be measured by performing elemental analysis of the entire particle of the positive electrode active material using GD-MS, ICP-MS, etc.
《正極活物質の製造方法４》
上記製造方法３では添加元素源８９を１回で酸化物９８へ導入する方法を例示したが、２回以上に分けて酸化物９８へ導入してもよい。そこで製造方法４では、図２３を用いて、第１の添加元素Ａ１源８９ａ、第２の添加元素Ａ２源８９ｂを用意して、２回に分ける方法を説明する。なお図２３のステップＳ１５５までは製造方法３で述べたステップＳ１５５と同様であり、製造方法２ではステップＳ１５５を経て酸化物９８ａを得ることができる。 <<Production method 4 of positive electrode active material>>
In the above-mentioned manufacturing method 3, the method of introducing the additive element source 89 into the oxide 98 in one go has been exemplified, but it may be introduced into the oxide 98 in two or more separate steps. Therefore, in manufacturing method 4, a method of preparing a first additive element A1 source 89a and a second additive element A2 source 89b and dividing the introduction into two steps will be described with reference to Fig. 23. Note that the steps up to step S155 in Fig. 23 are the same as step S155 described in manufacturing method 3, and in manufacturing method 2, oxide 98a can be obtained through step S155.
＜第１の添加元素Ａ１源＞
図２３に示すように第１の添加元素Ａ１源８９ａを用意する。上述した添加元素源から選ばれた添加元素を有する化合物を用いると好ましく、例えば添加元素としてマグネシウム及び／又はフッ素を用いることができる。具体的には第１の添加元素Ａ１源８９ａとして、Ｍｇ源とＦ源とを含むものを用意するとよい。なおＭｇ源は省略してもよい。 <Source of First Additive Element A1>
As shown in Fig. 23, a first additive element A1 source 89a is prepared. It is preferable to use a compound having an additive element selected from the additive element sources described above, and for example, magnesium and/or fluorine can be used as the additive element. Specifically, it is preferable to prepare a first additive element A1 source 89a containing a Mg source and a F source. The Mg source may be omitted.
＜ステップＳ１７１ａ乃至ステップＳ１７３ａ＞
次いで図２３に示すようにステップＳ１７１ａ乃至ステップＳ１７３ａを実施する。なお、ステップＳ１７１ａ乃至ステップＳ１７３ａは、製造方法１で述べたステップＳ１７１乃至ステップＳ１７３と同様であるため説明を省略する。製造方法２ではステップＳ１７３ａを経て酸化物９８ｂを得ることができる。 <Steps S171a to S173a>
23, steps S171a to S173a are carried out. Note that steps S171a to S173a will not be described because they are similar to steps S171 to S173 described in the manufacturing method 1. In the manufacturing method 2, an oxide 98b can be obtained through step S173a.
＜第２の添加元素Ａ２源＞
次いで図２３に示すように第２の添加元素Ａ２源８９ｂを用意する。上述した添加元素源から選ばれた添加元素を有する化合物を用いると好ましく、さらに第２の添加元素Ａ２源８９ｂは、第１の添加元素Ａ１源８９ａと異なる添加元素を用いると好ましい。このような添加元素として、アルミニウム及び／又はニッケルを用いることができる。具体的には第２の添加元素Ａ２源８９ｂとして、図２０Ｂ又は図２０Ｃに示したようなＡｌ源とＮｉ源とを用意するとよい。なおＡｌ源は省略してもよい。このようにして第２の添加元素Ａ２源８９ｂを得ることができる。 <Source of second additive element A2>
Next, as shown in FIG. 23, a second additive element A2 source 89b is prepared. It is preferable to use a compound having an additive element selected from the additive element sources described above, and it is further preferable to use an additive element different from the first additive element A1 source 89a for the second additive element A2 source 89b. Aluminum and/or nickel can be used as such an additive element. Specifically, it is preferable to prepare an Al source and a Ni source as shown in FIG. 20B or FIG. 20C as the second additive element A2 source 89b. The Al source may be omitted. In this manner, the second additive element A2 source 89b can be obtained.
＜ステップＳ１７１ｂ乃至ステップＳ１７３ｂ＞
次いで図２１に示すようにステップＳ１７１ｂ乃至ステップＳ１７３ｂを実施する。なおステップＳ１７１ｂ乃至ステップＳ１７３ｂは、上述したステップＳ１７１ａ乃至ステップＳ１７３ｂ等と同様であるため説明を省略する。製造方法２ではステップＳ１７３ｂを経て正極活物質１００を得ることができる。 <Steps S171b to S173b>
21, steps S171b to S173b are carried out. Note that steps S171b to S173b are similar to steps S171a to S173b described above, and therefore will not be described. In manufacturing method 2, positive electrode active material 100 can be obtained through step S173b.
本実施の形態は、他の実施の形態と組み合わせて用いることができる。 This embodiment can be used in combination with other embodiments.
（実施の形態３）
本実施の形態では、図２４を用いて本発明の一態様の二次電池の例について説明する。 (Embodiment 3)
In this embodiment, an example of a secondary battery of one embodiment of the present invention will be described with reference to FIGS.
＜二次電池の構成例１＞
以下に、正極、負極及び電解液が、外装体に収容された二次電池を例にとって説明する。 <Configuration Example 1 of Secondary Battery>
The following description will be given taking as an example a secondary battery in which a positive electrode, a negative electrode and an electrolyte are housed in an exterior body.
［正極］
図２４Ａに、二次電池に用いられる正極５０３の断面図の一例を示す。正極５０３は、正極集電体５０１上に正極活物質層５０２を有する。正極活物質層５０２は正極活物質１００、正極活物質５６２、導電材５５３、導電材５５４、及び電解液５３０を含む。正極活物質層５０２はバインダ（図示しない）も有する。二次電池は、導電材５５３及び導電材５５４のいずれか一方を有する構成でもよい。 [Positive electrode]
24A shows an example of a cross-sectional view of a positive electrode 503 used in a secondary battery. The positive electrode 503 has a positive electrode active material layer 502 on a positive electrode current collector 501. The positive electrode active material layer 502 contains a positive electrode active material 100, a positive electrode active material 562, a conductive material 553, a conductive material 554, and an electrolyte solution 530. The positive electrode active material layer 502 also has a binder (not shown). The secondary battery may have a structure including either the conductive material 553 or the conductive material 554.
正極活物質１００のＤ５０は１μｍ以上５０μｍ以下、好ましくは５μｍ以上３０μｍ以下である。充填密度を高めるため、Ｄ５０の異なる正極活物質５６２を加えるとよい。正極活物質５６２のＤ５０は、正極活物質１００のＤ５０の１／１０以上１／６以下となると好ましい。正極活物質１００と正極活物質５６２とが混在した活物質に対して粒度分布測定を行うと、極大値が異なる２つのピークが確認される。勿論、二以上のピークが確認されてもよい。なお、正極活物質５６２を有さなくとも充填密度を高めることが可能である。 The D50 of the positive electrode active material 100 is 1 μm or more and 50 μm or less, preferably 5 μm or more and 30 μm or less. In order to increase the packing density, it is advisable to add a positive electrode active material 562 having a different D50. The D50 of the positive electrode active material 562 is preferably 1/10 to 1/6 of the D50 of the positive electrode active material 100. When particle size distribution measurement is performed on an active material in which the positive electrode active material 100 and the positive electrode active material 562 are mixed, two peaks with different maximum values are confirmed. Of course, two or more peaks may be confirmed. It is possible to increase the packing density even without the positive electrode active material 562.
図２４Ａでは表層部と内部の境界に点線を付すが、境界は図２４Ａのように明確なものとは限らない。 In Figure 24A, the boundary between the surface and the interior is indicated by a dotted line, but the boundary is not necessarily as clear as in Figure 24A.
正極活物質１００は、正極活物質５６２と同一の組成でもよいし、異なる組成でもよい。同一の組成である場合としては、正極活物質の主要な組成が同じで、添加元素等の有無の違いがあるものを含む。異なる組成である場合としては、正極活物質の主要な組成が異なるものが含まれる。 The positive electrode active material 100 may have the same composition as the positive electrode active material 562, or may have a different composition. The same composition includes positive electrode active materials having the same main composition, with the difference being the presence or absence of added elements, etc. The different composition includes positive electrode active materials having different main compositions.
再掲するが、正極活物質１００及び正極活物質５６２は添加元素を有するとよい。添加元素は、偏在していてもよいし、内部に薄く分布していてもよい。 As stated above, the positive electrode active material 100 and the positive electrode active material 562 may contain an additive element. The additive element may be unevenly distributed or may be thinly distributed inside.
添加元素は、表層部が有してもよい。表層部にある添加元素の濃度は、内部にある添加元素の濃度と濃度差があるとよく、添加元素は、内部の濃度より表層部の濃度の方が高いと好ましい。これを添加元素が表層部に偏在していると呼ぶことがある。 The surface layer may contain the additive element. The concentration of the additive element in the surface layer may differ from the concentration of the additive element in the interior, and it is preferable that the concentration of the additive element in the surface layer is higher than the concentration in the interior. This is sometimes called the additive element being unevenly distributed in the surface layer.
正極活物質１００及び正極活物質５６２は正極活物質粒子と呼ばれることがあるが、正極活物質の形状は粒子状以外の多様な形状をとる。図２４Ｂでは図２４Ａと異なり粒子状以外の形状の正極活物質を有する正極５０３を示す。図２４Ｂにおいて、正極活物質の形状以外は、図２４Ａと同様のため説明を省略する。 The positive electrode active material 100 and the positive electrode active material 562 are sometimes called positive electrode active material particles, but the shape of the positive electrode active material can be a variety of shapes other than particulate. Unlike FIG. 24A, FIG. 24B shows a positive electrode 503 having a positive electrode active material in a shape other than particulate. In FIG. 24B, other than the shape of the positive electrode active material, the description is omitted because it is the same as FIG. 24A.
図２４Ａ及び図２４Ｂに示した正極活物質１００及び正極活物質５６２は、一次粒子のように示すが、これらは二次粒子であってもよい。また正極活物質１００及び正極活物質５６２は、単粒子が好ましい。 The positive electrode active material 100 and the positive electrode active material 562 shown in Figures 24A and 24B are shown as primary particles, but they may be secondary particles. Also, the positive electrode active material 100 and the positive electrode active material 562 are preferably single particles.
正極は、正極活物質層及び正極集電体を有する。正極活物質層は正極活物質を有し、導電材及びバインダを有していてもよい。正極活物質には、先の実施の形態で説明した製造方法を用いて作製した正極活物質を用いることができ、たとえば相対的にＤ５０の小さい正極活物質と、相対的にＤ５０の大きい正極活物質とを混合して用いてもよい。 The positive electrode has a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer has a positive electrode active material, and may have a conductive material and a binder. For the positive electrode active material, a positive electrode active material produced using the manufacturing method described in the previous embodiment may be used. For example, a positive electrode active material with a relatively small D50 and a positive electrode active material with a relatively large D50 may be mixed and used.
また本発明の一態様である正極活物質と、他の正極活物質を混合して用いてもよい。 The positive electrode active material according to one embodiment of the present invention may also be mixed with other positive electrode active materials.
他の正極活物質としてはたとえばオリビン型の結晶構造、層状岩塩型の結晶構造、またはスピネル型の結晶構造を有する複合酸化物等がある。例えば、ＬｉＦｅＰＯ４、ＬｉＦｅＯ２、ＬｉＮｉＯ２、ＬｉＭｎ２Ｏ４、Ｖ２Ｏ５、Ｃｒ２Ｏ５、ＭｎＯ２等の化合物が挙げられる。 Other examples of the positive electrode active material include composite oxides having an olivine type crystal structure, a layered rock salt type crystal structure, or a spinel type crystal structure, such as LiFePO4 , LiFeO2 , LiNiO2 , LiMn2O4 , V2O5 , Cr2O5 , and MnO2 .
また、他の正極活物質としてＬｉＭｎ２Ｏ４等のマンガンを含むスピネル型の結晶構造を有するリチウム含有材料と、ニッケル酸リチウム（ＬｉＮｉＯ２またはＬｉＮｉ１−ｘＭｘＯ２（０＜ｘ＜１）（Ｍ＝Ｃｏ、Ａｌ等））を混合したものを用いると好ましい。該構成とすることによって、二次電池の特性を向上させることができる。 In addition, it is preferable to use a mixture of a lithium-containing material having a spinel -type crystal structure containing manganese, such as LiMn2O4 , and lithium nickel oxide (LiNiO2 or LiNi1-xMxO2 ( 0 < x<1) (M=Co, Al, etc.)) as another positive electrode active material. By using this composition, the characteristics of the secondary battery can be improved.
また、他の正極活物質として、組成式ＬｉａＭｎｂＭｃＯｄで表すことができるリチウムマンガン複合酸化物を用いることができる。ここで、元素Ｍは、リチウム、マンガン以外から選ばれた金属元素、またはシリコン、リンを用いることが好ましく、ニッケルであることがさらに好ましい。また、リチウムマンガン複合酸化物の粒子全体を測定する場合、放電時に０＜ａ／（ｂ＋ｃ）＜２、かつｃ＞０、かつ０．２６≦（ｂ＋ｃ）／ｄ＜０．５（ただしａ、ｂ、ｃ、ｄは０を除く）を満たすことが好ましい。なお、リチウムマンガン複合酸化物の粒子全体の金属、シリコン、リン等の組成は、例えばＩＣＰ−ＭＳを用いて測定することができる。またリチウムマンガン複合酸化物の粒子全体の酸素の組成は、例えばＥＤＸを用いて測定することが可能である。また、ＩＣＰ−ＭＳ分析と併用して、融解ガス分析、ＸＡＦＳ（Ｘ線吸収微細構造）分析の価数評価を用いることで求めることができる。なお、リチウムマンガン複合酸化物とは、少なくともリチウムとマンガンとを含む酸化物をいい、クロム、コバルト、アルミニウム、ニッケル、鉄、マグネシウム、モリブデン、亜鉛、インジウム、ガリウム、銅、チタン、ニオブ、シリコン、及びリンなどからなる群から選ばれた一または二以上の元素を含んでいてもよい。 In addition, as another positive electrode active material, a lithium manganese composite oxide that can be expressed by the composition formula Li a Mn b M c O d can be used. Here, the element M is preferably a metal element selected from lithium and manganese, or silicon or phosphorus, and more preferably nickel. In addition, when measuring the entire particle of the lithium manganese composite oxide, it is preferable to satisfy 0<a/(b+c)<2, c>0, and 0.26≦(b+c)/d<0.5 (wherein a, b, c, and d are excluding 0) during discharge. The composition of metal, silicon, phosphorus, etc. of the entire particle of the lithium manganese composite oxide can be measured, for example, using ICP-MS. The composition of oxygen of the entire particle of the lithium manganese composite oxide can be measured, for example, using EDX. In addition, it can be obtained by using valence evaluation of melt gas analysis and XAFS (X-ray absorption fine structure) analysis in combination with ICP-MS analysis. The lithium manganese composite oxide refers to an oxide containing at least lithium and manganese, and may contain one or more elements selected from the group consisting of chromium, cobalt, aluminum, nickel, iron, magnesium, molybdenum, zinc, indium, gallium, copper, titanium, niobium, silicon, phosphorus, and the like.
［導電材］
導電材は活物質と集電体との間の電流パス、又は複数の活物質間の電流パス等を補助する機能を果たす。このような機能を果たすために導電材は活物質より抵抗の低い材料を有するとよい。導電材は、その役割から導電助剤又は導電付与剤とも呼ばれる。 [Conductive material]
The conductive material serves to assist the current path between the active material and the current collector, or the current path between a plurality of active materials. In order to fulfill such a function, the conductive material may have a material with a lower resistance than the active material. Due to its role, the conductive material is also called a conductive assistant or a conductive agent.
導電材は、代表的には炭素材料又は金属材料が用いられる。導電材は粒子状をなし、当該粒子状の導電材としてカーボンブラック（ファーネスブラック、アセチレンブラック、黒鉛など）がある。カーボンブラックは正極活物質より小さな粒径を有するものが多い。導電材は繊維状をなし、当該繊維状の導電材としてカーボンナノチューブ（ＣＮＴ）、ＶＧＣＦ（登録商標）がある。導電材はシート状のものがあり、例えばシート状の導電材として多層グラフェンがある。シート状の導電材は正極の断面において、糸状に見えることがある。 The conductive material is typically a carbon material or a metal material. The conductive material is particulate, and examples of particulate conductive materials include carbon black (furnace black, acetylene black, graphite, etc.). Most carbon blacks have a smaller particle size than the positive electrode active material. The conductive material is fibrous, and examples of such fibrous conductive materials include carbon nanotubes (CNT) and VGCF (registered trademark). The conductive material can be in sheet form, and an example of a sheet-shaped conductive material is multilayer graphene. Sheet-shaped conductive materials can appear thread-like in the cross section of the positive electrode.
粒子状の導電材は正極活物質等の隙間に入り込むことが可能であり、また凝集しやすい。そのため粒子状の導電材は近くに配置された正極活物質間の導電パスを補助することができる。繊維状の導電材は、折れ曲がった領域も有するが、正極活物質より大きなものとなる。そのため繊維状の導電材は、隣接した正極活物質間に加えて、離れた正極活物質間の導電パスを補助することもできる。このように導電材は二以上の形状のものを混合するとよい。 Particulate conductive materials can penetrate into gaps in the positive electrode active material and are also prone to agglomeration. Therefore, particulate conductive materials can assist the conductive paths between nearby positive electrode active materials. Fibrous conductive materials also have bent regions, but are larger than the positive electrode active materials. Therefore, fibrous conductive materials can assist the conductive paths between distant positive electrode active materials in addition to adjacent positive electrode active materials. In this way, it is a good idea to mix conductive materials of two or more shapes.
シート状の導電材として多層グラフェンを用い、粒子状の導電材としてカーボンブラックを用いた場合、これらが混合されたスラリーの状態で、カーボンブラックの重量が多層グラフェンの１．５倍以上２０倍以下、好ましくは２倍以上９．５倍以下の重量となるとよい。 When multi-layer graphene is used as the sheet-like conductive material and carbon black is used as the particulate conductive material, the weight of the carbon black in the mixed slurry state should be 1.5 to 20 times, preferably 2 to 9.5 times, that of the multi-layer graphene.
多層グラフェンとカーボンブラックの混合割合を上記範囲とすると、カーボンブラックが凝集せずに、分散しやすい。また、多層グラフェンとカーボンブラックの混合割合を上記範囲とすると、カーボンブラックのみを導電材に用いた場合よりも電極密度を高くすることができる。電極密度を高くすることで、単位重量当たりの容量を大きくすることができる。 When the mixing ratio of multi-layer graphene and carbon black is within the above range, the carbon black does not aggregate and is easily dispersed. Furthermore, when the mixing ratio of multi-layer graphene and carbon black is within the above range, the electrode density can be made higher than when only carbon black is used as the conductive material. By increasing the electrode density, the capacity per unit weight can be increased.
さらに多層グラフェンとカーボンブラックの混合割合を上記範囲とすることで、急速充電に対応することができる。 Furthermore, by keeping the mixing ratio of multi-layer graphene and carbon black within the above range, it is possible to support rapid charging.
本明細書等においてグラフェンは多層グラフェン、マルチグラフェンを含む。別言すると、グラフェンとは、炭素を有し、平板状、シート状等の形状を有し、炭素６員環で形成された二次元的構造を有するものをいう。該炭素６員環で形成された二次元的構造は炭素シートと呼ぶ場合がある。またグラフェン化合物とは、酸化グラフェン、多層酸化グラフェン、マルチ酸化グラフェン、還元された酸化グラフェン、還元された多層酸化グラフェン、還元されたマルチ酸化グラフェン、グラフェン量子ドット等を含む。別言すると、グラフェン化合物は官能基を有してもよい。またグラフェン又はグラフェン化合物は屈曲した形状を有することが好ましい。またグラフェン又はグラフェン化合物は丸まっていてもよく、丸まったグラフェンをカーボンナノファイバーと呼ぶことがある。 In this specification, graphene includes multi-layer graphene and multi-graphene. In other words, graphene refers to a material that has carbon, has a shape such as a plate or sheet, and has a two-dimensional structure formed of six-membered carbon rings. The two-dimensional structure formed of six-membered carbon rings may be called a carbon sheet. Graphene compounds include graphene oxide, multi-layer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multi-layer graphene oxide, reduced multi-graphene oxide, graphene quantum dots, and the like. In other words, graphene compounds may have functional groups. Graphene or graphene compounds preferably have a curved shape. Graphene or graphene compounds may be rolled up, and rolled up graphene may be called carbon nanofibers.
本明細書等において酸化グラフェンとは、炭素と、酸素を有し、シート状の形状を有し、官能基、特にエポキシ基、カルボキシ基またはヒドロキシ基を有するものをいう。 In this specification, graphene oxide refers to a material that contains carbon and oxygen, has a sheet-like shape, and has functional groups, particularly epoxy groups, carboxy groups, or hydroxy groups.
本明細書等において還元された酸化グラフェンとは、炭素と、酸素を有し、シート状の形状を有し、炭素６員環で形成された二次元的構造を有するものをいう。還元された酸化グラフェンは１枚でも機能するが、複数枚が積層されていてもよい。還元された酸化グラフェンは、炭素の濃度が８０ａｔｏｍｉｃ％より大きく、酸素の濃度が２ａｔｏｍｉｃ％以上１５ａｔｏｍｉｃ％以下である部分を有することが好ましい。このような炭素濃度及び酸素濃度とすることで、少量でも導電性の高い導電材として機能することができる。また還元された酸化グラフェンは、ラマンスペクトルにおけるＧバンドとＤバンドの強度比Ｇ／Ｄが１以上であることが好ましい。このような強度比である還元された酸化グラフェンは、少量でも導電性の高い導電材として機能することができる。 In this specification, reduced graphene oxide refers to a material that has carbon and oxygen, has a sheet-like shape, and has a two-dimensional structure formed of six-membered carbon rings. Although reduced graphene oxide can function as a single sheet, multiple sheets may be stacked. Reduced graphene oxide preferably has a portion where the carbon concentration is greater than 80 atomic% and the oxygen concentration is 2 atomic% or more and 15 atomic% or less. By setting such carbon and oxygen concentrations, it can function as a highly conductive conductive material even in small amounts. In addition, reduced graphene oxide preferably has an intensity ratio G/D of the G band to the D band in the Raman spectrum of 1 or more. Reduced graphene oxide with such an intensity ratio can function as a highly conductive conductive material even in small amounts.
グラフェン化合物として、フッ素含有グラフェンを用いてもよい。グラフェン化合物中にあるフッ素は、表面に吸着しているとよい。またフッ素含有グラフェンは、グラフェンとフッ素化合物が接触すること（フッ化処理と呼ぶ）により作製することができる。フッ化処理にはフッ素（Ｆ２）又はフッ素化合物を用いるとよい。フッ素化合物として、フッ酸、フッ化ハロゲン（ＣｌＦ３、ＩＦ５等）、ガス状フッ化物（ＢＦ３、ＮＦ３、ＰＦ５、ＳｉＦ４、ＳＦ６等）、金属フッ化物（ＬｉＦ、ＮｉＦ２、ＡｌＦ３、ＭｇＦ２等）等が好ましい。フッ化処理には、ガス状フッ化物を用いると好ましく、ガス状フッ化物を不活性ガスで希釈してもよい。フッ化処理の温度は室温がよいが、当該室温が含まれる０℃以上２５０℃以下がよい。０℃以上でフッ化処理を行うと、グラフェンの表面にフッ素を吸着させることができる。 Fluorine-containing graphene may be used as the graphene compound. The fluorine in the graphene compound may be adsorbed on the surface. The fluorine-containing graphene may be produced by contacting graphene with a fluorine compound (called fluorination treatment). Fluorine (F 2 ) or a fluorine compound may be used for the fluorination treatment. As the fluorine compound, hydrofluoric acid, halogen fluoride (ClF 3 , IF 5 , etc.), gaseous fluoride (BF 3 , NF 3 , PF 5 , SiF 4 , SF 6 , etc.), metal fluoride (LiF, NiF 2 , AlF 3 , MgF 2 , etc.), etc. are preferable. For the fluorination treatment, gaseous fluoride is preferably used, and the gaseous fluoride may be diluted with an inert gas. The temperature of the fluorination treatment is preferably room temperature, but is preferably 0° C. or more and 250° C. or less, which includes the room temperature. When the fluorination treatment is performed at 0° C. or more, fluorine can be adsorbed on the surface of the graphene.
グラフェン化合物は、高い導電性を有するという優れた電気特性と、高い柔軟性及び高い機械的強度を有するという優れた物理特性と、を有する場合がある。また、グラフェン化合物はシート状の形状を有する。グラフェン化合物は、湾曲面を有する場合があり、接触抵抗の低い面接触を可能とする。また、薄くても導電性が非常に高い場合があり、少ない量で効率よく活物質層内で導電パスを形成することができる。そのため、グラフェン化合物を導電材として用いることにより、活物質と導電材との接触面積を増大させることができる。グラフェン化合物は活物質の８０％以上の面積を覆っているとよい。なお、グラフェン化合物が活物質粒子の少なくとも一部にまとわりついていると好ましい。また、グラフェン化合物が活物質粒子の少なくとも一部の上に重なっていると好ましい。また、グラフェン化合物の形状が活物質粒子の形状の少なくとも一部に一致していると好ましい。該活物質粒子の形状とは、たとえば、単一の活物質粒子が有する凹凸、または複数の活物質粒子によって形成される凹凸をいう。また、グラフェン化合物が活物質粒子の少なくとも一部を囲んでいることが好ましい。また、グラフェン化合物は穴が空いていてもよい。 The graphene compound may have excellent electrical properties such as high electrical conductivity, and excellent physical properties such as high flexibility and high mechanical strength. The graphene compound may have a sheet-like shape. The graphene compound may have a curved surface, which allows for surface contact with low contact resistance. In addition, even if the graphene compound is thin, it may have very high electrical conductivity, and a conductive path can be efficiently formed in the active material layer with a small amount. Therefore, by using the graphene compound as a conductive material, the contact area between the active material and the conductive material can be increased. The graphene compound may cover 80% or more of the area of the active material. It is preferable that the graphene compound is wrapped around at least a part of the active material particles. It is also preferable that the graphene compound is overlapped on at least a part of the active material particles. It is also preferable that the shape of the graphene compound matches at least a part of the shape of the active material particles. The shape of the active material particles refers to, for example, the unevenness of a single active material particle or the unevenness formed by multiple active material particles. It is also preferable that the graphene compound surrounds at least a part of the active material particles. The graphene compound may have holes.
粒子径の小さい活物質粒子、例えば１μｍ以下の活物質粒子を用いる場合には、活物質粒子の比表面積が大きく、活物質粒子同士を繋ぐ導電パスがより多く必要となる。このような場合には、少ない量でも効率よく導電パスを形成することができるグラフェン化合物を用いると好ましい。 When using active material particles with a small particle size, for example, active material particles of 1 μm or less, the specific surface area of the active material particles is large, and more conductive paths connecting the active material particles are required. In such cases, it is preferable to use a graphene compound, which can efficiently form conductive paths even in small amounts.
上述のような性質を有するため、急速充電及び急速放電が要求される二次電池には、グラフェン化合物を導電材として用いることが特に有効である。例えば２輪または４輪の車両用二次電池、ドローン用二次電池などは急速充電及び急速放電が要求される場合がある。またモバイル電子機器などでは急速充電特性が要求される場合がある。急速充放電とは、たとえば２００ｍＡ／ｇ、４００ｍＡ／ｇ、または１０００ｍＡ／ｇ以上の充電及び放電をいうこととする。 Because of the above-mentioned properties, it is particularly effective to use graphene compounds as conductive materials for secondary batteries that require rapid charging and rapid discharging. For example, secondary batteries for two-wheeled or four-wheeled vehicles and secondary batteries for drones may require rapid charging and rapid discharging. Rapid charging characteristics may also be required for mobile electronic devices. Rapid charging and discharging refers to charging and discharging at, for example, 200 mA/g, 400 mA/g, or 1000 mA/g or more.
活物質層において、シート状のグラフェンまたはグラフェン化合物は均一に分散するとよい。複数のグラフェンまたはグラフェン化合物は、複数の活物質を一部覆うように、あるいは複数の粒状の活物質の表面上に張り付くように形成されているため、互いに面接触している。 In the active material layer, the sheet-like graphene or graphene compound may be uniformly dispersed. The multiple graphene or graphene compounds are formed so as to partially cover the multiple active materials or to be attached to the surfaces of the multiple granular active materials, and are in surface contact with each other.
ここで、複数のグラフェンまたはグラフェン化合物同士が結合することにより、網目状のグラフェン化合物シート（以下グラフェン化合物ネットまたはグラフェンネットと呼ぶ）を形成することができる。活物質をグラフェンネットが被覆する場合に、グラフェンネットは活物質同士を結合するバインダとしても機能することができる。よって、バインダの量を少なくすることができる、又はバインダを使用しないことができるため、電極体積及び電極重量に占める活物質の比率を向上させることができる。すなわち、二次電池の放電容量を増加させることができる。 Here, a mesh-like graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net) can be formed by bonding multiple graphenes or graphene compounds together. When the graphene net covers the active material, the graphene net can also function as a binder that bonds the active materials together. Therefore, the amount of binder can be reduced or no binder can be used, and the ratio of active material to the electrode volume and electrode weight can be improved. In other words, the discharge capacity of the secondary battery can be increased.
ここで、グラフェンまたはグラフェン化合物として酸化グラフェンを用い、活物質と混合して活物質層を形成後、還元することが好ましい。つまり完成後の活物質層は還元された酸化グラフェンを有することが好ましい。グラフェンまたはグラフェン化合物の形成に、極性溶媒中での分散性が極めて高い酸化グラフェンを用いることにより、グラフェンまたはグラフェン化合物を活物質層の内部において概略均一に分散させることができる。均一に分散した酸化グラフェンを含有する分散媒から溶媒を揮発除去し、酸化グラフェンを還元するため、活物質層に残留するグラフェンまたはグラフェン化合物は部分的に重なり合い、互いに面接触する程度に分散していることで三次元的な導電パスを形成することができる。なお、酸化グラフェンの還元は、例えば熱処理により行ってもよいし、還元剤を用いて行ってもよい。 Here, it is preferable to use graphene oxide as the graphene or graphene compound, mix it with the active material to form an active material layer, and then reduce it. In other words, it is preferable that the completed active material layer has reduced graphene oxide. By using graphene oxide, which has extremely high dispersibility in a polar solvent, to form the graphene or graphene compound, the graphene or graphene compound can be dispersed approximately uniformly inside the active material layer. Since the solvent is volatilized and removed from the dispersion medium containing the uniformly dispersed graphene oxide and the graphene oxide is reduced, the graphene or graphene compound remaining in the active material layer partially overlaps and is dispersed to such an extent that they are in surface contact with each other, thereby forming a three-dimensional conductive path. The reduction of the graphene oxide may be performed, for example, by heat treatment or by using a reducing agent.
従って、活物質と点接触するアセチレンブラック等の粒状の導電材と異なり、グラフェンまたはグラフェン化合物は接触抵抗の低い面接触を可能とするものであるから、通常の導電材よりも少量の活物質とグラフェンまたはグラフェン化合物との電気伝導性を向上させることができる。 Therefore, unlike granular conductive materials such as acetylene black, which make point contact with the active material, graphene or graphene compounds enable surface contact with low contact resistance, and therefore can improve the electrical conductivity between a smaller amount of active material and graphene or graphene compounds than with ordinary conductive materials.
また、予め、スプレードライ装置を用いることで、活物質の表面全体を覆って導電材であるグラフェン化合物を被覆部として形成し、さらに活物質同士間にグラフェン化合物で導電パスを形成することもできる。 In addition, by using a spray dryer in advance, the entire surface of the active material can be covered with a conductive graphene compound as a coating, and further a conductive path can be formed between the active material particles with the graphene compound.
またグラフェン化合物と共に、グラフェン化合物を形成する際に用いる材料を活物質層に混合してもよい。たとえばグラフェン化合物を形成する際の触媒として用いる粒子を、グラフェン化合物と共に混合してもよい。グラフェン化合物を形成する際の触媒としてはたとえば、酸化ケイ素（ＳｉＯ２、ＳｉＯｘ（ｘ＜２））、酸化アルミニウム、鉄、ニッケル、ルテニウム、イリジウム、プラチナ、銅、ゲルマニウム等を有する粒子が挙げられる。該粒子径はＤ５０が１μｍ以下であると好ましく、１００ｎｍ以下であることがより好ましい。 In addition, a material used in forming the graphene compound may be mixed into the active material layer together with the graphene compound. For example, particles used as a catalyst in forming the graphene compound may be mixed with the graphene compound. Examples of catalysts in forming the graphene compound include particles having silicon oxide (SiO 2 , SiO x (x<2)), aluminum oxide, iron, nickel, ruthenium, iridium, platinum, copper, germanium, etc. The particle size D50 is preferably 1 μm or less, more preferably 100 nm or less.
導電材としてグラフェン以外にアセチレンブラック（ＡＢと記す）を適用できる。さらにフッ素含有アセチレンブラックを用いてもよい。フッ素含有アセチレンブラック中にあるフッ素は、表面に吸着しているとよい。またフッ素含有アセチレンブラックは、アセチレンブラックとフッ素化合物が接触すること（フッ化処理と呼ぶ）により作製することができる。フッ化処理についてはグラフェンで説明した内容を、アセチレンブラックに適用できる。 In addition to graphene, acetylene black (abbreviated as AB) can be used as a conductive material. Fluorine-containing acetylene black may also be used. The fluorine in the fluorine-containing acetylene black is preferably adsorbed on the surface. Fluorine-containing acetylene black can be produced by contacting acetylene black with a fluorine compound (called fluorination treatment). The fluorination treatment described for graphene can be applied to acetylene black.
導電材としてグラフェン及びアセチレンブラック以外に炭素繊維材料（カーボンナノチューブ、又はＣＮＴと記す）を適用できる。さらにフッ素含有カーボンナノチューブを用いてもよい。フッ素含有カーボンナノチューブ中にあるフッ素は、表面に吸着しているとよい。またフッ素含有カーボンナノチューブは、カーボンナノチューブとフッ素化合物が接触すること（フッ化処理と呼ぶ）により作製することができる。フッ化処理についてはグラフェンで説明した内容を、カーボンナノチューブに適用できる。 In addition to graphene and acetylene black, carbon fiber materials (also referred to as carbon nanotubes, or CNTs) can be used as conductive materials. Fluorine-containing carbon nanotubes may also be used. The fluorine in the fluorine-containing carbon nanotubes is preferably adsorbed on the surface. Fluorine-containing carbon nanotubes can also be produced by contacting carbon nanotubes with a fluorine compound (called a fluorination treatment). The fluorination treatment described for graphene can also be applied to carbon nanotubes.
［バインダ］
バインダは活物質表面を覆い隠すことなく、粉末状態の活物質の接着を強固にするために必要である。さらにバインダは集電体に対して接着性を示す必要がある。すなわちバインダは接着成分を有する材料を用いるとよい。さらに活物質の膨張を踏まえるとバインダは、十分な可撓性を示すとよく、活物質の状態変化に対応できるとよい。またバインダは電解液との相溶性を示す必要もある。さらに二次電池ではきわめて強力な酸化反応及び還元反応が生じるため、当該反応に対して劣化しない、又は反応性の低いバインダが望まれる。 [Binder]
The binder is necessary to firmly bond the powdered active material without covering the surface of the active material. Furthermore, the binder must be adhesive to the current collector. In other words, it is recommended that the binder be made of a material that has an adhesive component. Furthermore, in consideration of the expansion of the active material, the binder should be sufficiently flexible and should be able to respond to changes in the state of the active material. The binder must also be compatible with the electrolyte. Furthermore, since extremely strong oxidation and reduction reactions occur in secondary batteries, a binder that does not deteriorate or has low reactivity to these reactions is desired.
バインダとしては、例えば、スチレン−ブタジエンゴム（ＳＢＲ）、スチレン−イソプレン−スチレンゴム、アクリロニトリル−ブタジエンゴム、ブタジエンゴム、エチレン−プロピレン−ジエン共重合体などのゴム材料を用いることが好ましい。またバインダとして、フッ素ゴムを用いることができる。 As the binder, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, or ethylene-propylene-diene copolymer. Furthermore, fluororubber can be used as the binder.
また、バインダとしては、例えば水溶性の高分子を用いることが好ましい。水溶性の高分子としては、例えば多糖類などを用いることができる。多糖類としては、カルボキシメチルセルロース（ＣＭＣ）、メチルセルロース、エチルセルロース、ヒドロキシプロピルセルロース、ジアセチルセルロース、再生セルロースなどのセルロース誘導体、澱粉などのうち一以上を用いることができる。また、これらの水溶性の高分子を、前述のゴム材料と併用して用いると、さらに好ましい。 Furthermore, it is preferable to use, for example, a water-soluble polymer as the binder. For example, polysaccharides can be used as the water-soluble polymer. As the polysaccharide, one or more of cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, regenerated cellulose, and starch can be used. Furthermore, it is even more preferable to use these water-soluble polymers in combination with the above-mentioned rubber material.
または、バインダとしては、ポリスチレン、ポリアクリル酸メチル、ポリメタクリル酸メチル（ポリメチルメタクリレート、ＰＭＭＡ）、ポリアクリル酸ナトリウム、ポリビニルアルコール（ＰＶＡ）、ポリエチレンオキシド（ＰＥＯ）、ポリプロピレンオキシド、ポリイミド、ポリ塩化ビニル、ポリテトラフルオロエチレン、ポリエチレン、ポリプロピレン、ポリイソブチレン、ポリエチレンテレフタレート、ナイロン、ポリフッ化ビニリデン（ＰＶＤＦ）、ポリアクリロニトリル（ＰＡＮ）、エチレンプロピレンジエンポリマー、ポリ酢酸ビニル、ニトロセルロース等の材料を用いることが好ましい。 Alternatively, it is preferable to use materials such as polystyrene, polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose as the binder.
バインダは上記のうち複数を組み合わせて使用してもよい。 You may use a combination of multiple binders from the above.
例えば粘度調整効果の特に優れた材料と、他の材料とを組み合わせて使用してもよい。例えばゴム材料等は接着力及び／又は弾性力に優れる反面、溶媒に混合した場合に粘度調整が難しい場合がある。このような場合には例えば、粘度調整効果の特に優れた材料と混合することが好ましい。粘度調整効果の特に優れた材料としては、例えば水溶性高分子を用いるとよい。また、粘度調整効果に特に優れた水溶性高分子としては、前述の多糖類、例えばカルボキシメチルセルロース（ＣＭＣ）、メチルセルロース、エチルセルロース、ヒドロキシプロピルセルロース及びジアセチルセルロース、再生セルロースなどのセルロース誘導体、澱粉などを用いることができる。 For example, a material with particularly excellent viscosity adjustment effect may be used in combination with other materials. For example, while rubber materials have excellent adhesive strength and/or elasticity, it may be difficult to adjust the viscosity when mixed with a solvent. In such cases, it is preferable to mix with a material with particularly excellent viscosity adjustment effect. For example, a water-soluble polymer may be used as a material with particularly excellent viscosity adjustment effect. In addition, as water-soluble polymers with particularly excellent viscosity adjustment effect, the above-mentioned polysaccharides, for example, carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, and diacetylcellulose, cellulose derivatives such as regenerated cellulose, starch, etc. may be used.
なお、カルボキシメチルセルロースなどのセルロース誘導体は、例えばカルボキシメチルセルロースのナトリウム塩及びアンモニウム塩などの塩とすることにより溶解度が上がり、粘度調整剤としての効果を発揮しやすくなる。溶解度が高くなることにより電極のスラリーを作製する際に活物質及び他の構成要素の分散性を高めることもできる。本明細書においては、電極のバインダとして使用するセルロース及びセルロース誘導体としては、それらの塩も含むものとする。 The solubility of cellulose derivatives such as carboxymethylcellulose can be increased by converting them into salts, such as sodium salt and ammonium salt of carboxymethylcellulose, making them more effective as viscosity adjusters. Increasing the solubility can also increase the dispersibility of the active material and other components when preparing the electrode slurry. In this specification, the cellulose and cellulose derivatives used as electrode binders include their salts.
水溶性高分子は水に溶解することにより粘度を安定化させ、また活物質及びバインダとして組み合わせる他の材料、例えばスチレンブタジエンゴムなどを、水溶液中に安定して分散させることができる。また、官能基を有するために活物質表面に安定に吸着しやすいことが期待される。また、例えばカルボキシメチルセルロースなどのセルロース誘導体は、例えば水酸基及びカルボキシル基などの官能基を有する材料が多く、官能基を有するために高分子同士が相互作用し、活物質表面を広く覆って存在することが期待される。 Water-soluble polymers stabilize the viscosity by dissolving in water, and can stably disperse active materials and other materials combined as binders, such as styrene-butadiene rubber, in an aqueous solution. In addition, because they have functional groups, they are expected to be easily and stably adsorbed onto the surface of active materials. Furthermore, many cellulose derivatives, such as carboxymethyl cellulose, have functional groups, such as hydroxyl groups and carboxyl groups, and because they have functional groups, the polymers are expected to interact with each other and widely cover the surface of the active material.
活物質表面を覆う、または表面に接するバインダが膜を形成する場合には、不動態膜としての役割を果たして電解液の分解を抑える効果も期待される。ここで、不動態膜とは、電気の伝導性のない膜、または電気伝導性の極めて低い膜であり、例えば活物質の表面に不動態膜が形成された場合には、電池反応電位において、電解液の分解を抑制することができる。また、不動態膜は、電気の伝導性を抑えるとともに、リチウムイオンは伝導できるとさらに望ましい。 When the binder covers the surface of the active material or contacts the surface and forms a film, it is expected to act as a passive film and have the effect of suppressing decomposition of the electrolyte. Here, a passive film is a film with no electrical conductivity or a film with extremely low electrical conductivity. For example, when a passive film is formed on the surface of the active material, it can suppress decomposition of the electrolyte at the battery reaction potential. Furthermore, it is even more desirable for the passive film to suppress electrical conductivity while still being able to conduct lithium ions.
［正極集電体］
正極集電体としては、ステンレス、金、白金、アルミニウム、チタン等の金属、及びこれらの合金など、導電性が高い材料を用いることができる。また正極集電体に用いる材料は、正極の電位で溶出しないことが好ましい。また、シリコン、チタン、ネオジム、スカンジウム、モリブデンなどの耐熱性を向上させる元素が添加されたアルミニウム合金を用いることができる。また、シリコンと反応してシリサイドを形成する金属元素で形成してもよい。シリコンと反応してシリサイドを形成する金属元素としては、ジルコニウム、チタン、ハフニウム、バナジウム、ニオブ、タンタル、クロム、モリブデン、タングステン、コバルト、ニッケル等がある。集電体は、箔状、板状、シート状、網状、パンチングメタル状、エキスパンドメタル状等の形状を適宜用いることができる。集電体は、厚みが５μｍ以上３０μｍ以下のものを用いるとよい。 [Positive electrode current collector]
As the positive electrode current collector, a material having high conductivity, such as metals such as stainless steel, gold, platinum, aluminum, and titanium, and alloys thereof, can be used. In addition, it is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. In addition, an aluminum alloy to which an element that improves heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, is added can be used. In addition, it may be formed of a metal element that reacts with silicon to form a silicide. Examples of metal elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collector can be appropriately used in a shape such as a foil, plate, sheet, mesh, punched metal, or expanded metal. It is preferable to use a current collector having a thickness of 5 μm or more and 30 μm or less.
〔負極〕
負極は、負極活物質層及び負極集電体を有する。また、負極活物質層は、導電材及びバインダを有していてもよい。 [Negative Electrode]
The negative electrode includes a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer may include a conductive material and a binder.
［負極活物質］
負極活物質としては、例えば合金材料及び／又は炭素材料等を用いることができる。 [Negative electrode active material]
As the negative electrode active material, for example, an alloy material and/or a carbon material can be used.
負極活物質として、リチウムとの合金化・脱合金化反応により充放電反応を行うことが可能な元素を用いることができる。例えば、シリコン、スズ、ガリウム、アルミニウム、ゲルマニウム、鉛、アンチモン、ビスマス、銀、亜鉛、カドミウム、インジウム等から選ばれた一または二以上を含む材料を用いることができる。このような元素は炭素と比べて充放電容量が大きく、特にシリコンは理論容量が４２００ｍＡｈ／ｇと高い。このため、負極活物質にシリコンを用いることが好ましい。また、これらの元素を有する化合物を用いてもよい。例えば、ＳｉＯ、Ｍｇ２Ｓｉ、Ｍｇ２Ｇｅ、ＳｎＯ、ＳｎＯ２、Ｍｇ２Ｓｎ、ＳｎＳ２、Ｖ２Ｓｎ３、ＦｅＳｎ２、ＣｏＳｎ２、Ｎｉ３Ｓｎ２、Ｃｕ６Ｓｎ５、Ａｇ３Ｓｎ、Ａｇ３Ｓｂ、Ｎｉ２ＭｎＳｂ、ＣｅＳｂ３、ＬａＳｎ３、Ｌａ３Ｃｏ２Ｓｎ７、ＣｏＳｂ３、ＩｎＳｂ、ＳｂＳｎ等がある。ここで、リチウムとの合金化・脱合金化反応により充放電反応を行うことが可能な元素、及び該元素を有する化合物等を合金材料と呼ぶ場合がある。 As the negative electrode active material, an element capable of carrying out a charge/discharge reaction by alloying/dealloying reaction with lithium can be used. For example, a material containing one or more elements selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used. Such elements have a larger charge/discharge capacity than carbon, and silicon in particular has a high theoretical capacity of 4200 mAh/g. For this reason, it is preferable to use silicon as the negative electrode active material. Compounds containing these elements may also be used. Examples include SiO, Mg2Si , Mg2Ge , SnO, SnO2 , Mg2Sn , SnS2 , V2Sn3 , FeSn2 , CoSn2 , Ni3Sn2 , Cu6Sn5 , Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7 , CoSb3 , InSb , SbSn , etc. Here, elements capable of carrying out charge/discharge reactions by alloying/dealloying reactions with lithium, and compounds containing such elements, may be referred to as alloying materials.
本明細書等において、ＳｉＯは例えば一酸化シリコンを指す。あるいはＳｉＯは、ＳｉＯｘと表すこともできる。ここでｘは１又はその近傍の値を有することが好ましい。例えばｘは、０．２以上１．５以下が好ましく、０．３以上１．２以下がより好ましい。または０．２以上１．２以下が好ましい。または０．３以上１．５以下が好ましい。 In this specification and the like, SiO refers to, for example, silicon monoxide. Alternatively, SiO can be expressed as SiO x . Here, x preferably has a value of 1 or close to 1. For example, x is preferably 0.2 or more and 1.5 or less, more preferably 0.3 or more and 1.2 or less. Alternatively, x is preferably 0.2 or more and 1.2 or less. Alternatively, x is preferably 0.3 or more and 1.5 or less.
炭素材料としては、黒鉛、易黒鉛化性炭素（ソフトカーボン）、難黒鉛化性炭素（ハードカーボン）、カーボンナノチューブ、グラフェン、カーボンブラック等を用いればよい。 The carbon material may be graphite, easily graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, carbon black, etc.
黒鉛としては、人造黒鉛、天然黒鉛等が挙げられる。人造黒鉛としては例えば、メソカーボンマイクロビーズ（ＭＣＭＢ）、コークス系人造黒鉛、ピッチ系人造黒鉛等が挙げられる。ここで人造黒鉛として、球状の形状を有する球状黒鉛を用いることができる。例えば、ＭＣＭＢは球状の形状を有する場合があり、好ましい。また、ＭＣＭＢはその表面積を小さくすることが比較的容易であり、好ましい場合がある。天然黒鉛としては例えば、鱗片状黒鉛、球状化天然黒鉛等が挙げられる。 Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape, which is preferable. In addition, it is relatively easy to reduce the surface area of MCMB, which may be preferable. Examples of natural graphite include flake graphite and spheroidized natural graphite.
黒鉛は、リチウムイオンが黒鉛に挿入されたとき（リチウム黒鉛層間化合物の生成時）にリチウム金属と同程度に低い電位を示す（０．０５Ｖ以上０．３Ｖ以下　ｖｓ．Ｌｉ／Ｌｉ＋）。これにより、リチウムイオン二次電池は高い作動電圧を示すことができる。さらに、黒鉛は、単位体積当たりの放電容量が比較的高い、体積膨張が比較的小さい、安価である、リチウム金属に比べて安全性が高い等の利点を有するため、好ましい。 When lithium ions are inserted into graphite (when a lithium-graphite intercalation compound is formed), graphite exhibits a low potential (0.05 V to 0.3 V vs. Li/Li + ) similar to that of lithium metal. This allows lithium ion secondary batteries to exhibit a high operating voltage. Furthermore, graphite is preferable because it has the advantages of a relatively high discharge capacity per unit volume, a relatively small volume expansion, low cost, and higher safety than lithium metal.
また、負極活物質として、二酸化チタン（ＴｉＯ２）、リチウムチタン酸化物（Ｌｉ４Ｔｉ５Ｏ１２）、リチウム黒鉛層間化合物（ＬｉｘＣ６）、五酸化ニオブ（Ｎｂ２Ｏ５）、二酸化タングステン（ＷＯ２）、二酸化モリブデン（ＭｏＯ２）等の酸化物を用いることができる。 In addition, oxides such as titanium dioxide ( TiO2 ) , lithium titanium oxide ( Li4Ti5O12 ), lithium graphite intercalation compound ( LixC6 ), niobium pentoxide ( Nb2O5 ), tungsten dioxide ( WO2 ), and molybdenum dioxide ( MoO2 ) can be used as the negative electrode active material.
また、負極活物質として、リチウムと遷移金属の窒化物である、Ｌｉ３Ｎ型構造をもつＬｉ３−ｘＭｘＮ（Ｍ＝Ｃｏ、Ｎｉ、Ｃｕ）を用いることができる。例えば、Ｌｉ２．６Ｃｏ０．４Ｎは大きな放電容量（９００ｍＡｈ／ｇ、１８９０ｍＡｈ／ｃｍ３）を示し好ましい。 As the negative electrode active material, Li3 - xMxN (M = Co, Ni, Cu) having a Li3N type structure, which is a nitride of lithium and a transition metal , can be used. For example, Li2.6Co0.4N is preferable because it shows a large discharge capacity (900mAh/g, 1890mAh/ cm3 ).
リチウムと遷移金属の窒化物を用いると、負極活物質中にリチウムイオンを含むため、正極活物質としてリチウムイオンを含まないＶ２Ｏ５、Ｃｒ３Ｏ８等の材料と組み合わせることができ好ましい。なお、正極活物質にリチウムイオンを含む材料を用いる場合でも、あらかじめ正極活物質に含まれるリチウムイオンを脱離させることで、負極活物質としてリチウムと遷移金属の窒化物を用いることができる。 When a nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, and therefore it is preferable that the nitride of lithium and a transition metal is combined with a material that does not contain lithium ions as a positive electrode active material, such as V 2 O 5 or Cr 3 O 8. Even when a material that contains lithium ions is used as the positive electrode active material, the nitride of lithium and a transition metal can be used as the negative electrode active material by desorbing the lithium ions contained in the positive electrode active material in advance.
また、コンバージョン反応が生じる材料を負極活物質として用いることもできる。例えば、酸化コバルト（ＣｏＯ）、酸化ニッケル（ＮｉＯ）、酸化鉄（ＦｅＯ）等の、リチウムとの合金を作らない遷移金属酸化物を負極活物質に用いてもよい。コンバージョン反応が生じる材料としては、さらに、Ｆｅ２Ｏ３、ＣｕＯ、Ｃｕ２Ｏ、ＲｕＯ２、Ｃｒ２Ｏ３等の酸化物、ＣｏＳ０．８９、ＮｉＳ、ＣｕＳ等の硫化物、Ｚｎ３Ｎ２、Ｃｕ３Ｎ、Ｇｅ３Ｎ４等の窒化物、ＮｉＰ２、ＦｅＰ２、ＣｏＰ３等のリン化物、ＦｅＦ３、ＢｉＦ３等のフッ素化合物などが挙げられる。 Also, a material that undergoes a conversion reaction can be used as the negative electrode active material. For example, a transition metal oxide that does not form an alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), or iron oxide (FeO), may be used as the negative electrode active material. Further examples of materials that undergo a conversion reaction include oxides such as Fe2O3 , CuO, Cu2O , RuO2 , and Cr2O3 , sulfides such as CoS0.89 , NiS , and CuS, nitrides such as Zn3N2 , Cu3N , and Ge3N4 , phosphides such as NiP2 , FeP2 , and CoP3 , and fluorine compounds such as FeF3 and BiF3 .
負極活物質層が有することのできる導電材及びバインダとしては、正極活物質層が有することのできる導電材及びバインダと同様の材料を用いることができる。 The conductive material and binder that can be used in the negative electrode active material layer can be the same materials as the conductive material and binder that can be used in the positive electrode active material layer.
［負極集電体］
負極集電体には、正極集電体と同様の材料を用いることができる。なお負極集電体は、リチウム等のキャリアイオンと合金化しない材料を用いることが好ましい。 [Negative electrode current collector]
The negative electrode current collector may be made of the same material as the positive electrode current collector, but it is preferable that the negative electrode current collector is made of a material that does not form an alloy with carrier ions such as lithium.
［電解質］
二次電池はキャリアイオンが含まれる電解質を有する。本明細書等において、電解質には、常温で液体である有機溶媒が含まれるものに限定されず、固体電解質が含まれ、常温で液体である有機溶媒と、常温で固体である固体電解質の双方を含む電解質（半固体の電解質）も含まれる。なお、常温で液体である有機溶媒にリチウム塩が溶解されたものを電解液と呼ぶことがある。 [Electrolytes]
The secondary battery has an electrolyte containing carrier ions. In this specification and the like, the electrolyte is not limited to an electrolyte containing an organic solvent that is liquid at room temperature, but includes a solid electrolyte, and also includes an electrolyte (semi-solid electrolyte) that contains both an organic solvent that is liquid at room temperature and a solid electrolyte that is solid at room temperature. Note that an electrolyte in which a lithium salt is dissolved in an organic solvent that is liquid at room temperature is sometimes called an electrolyte solution.
＜常温で液体である有機溶媒＞
常温で液体である有機溶媒の一例について、以下に説明する。 <Organic solvents that are liquid at room temperature>
An example of an organic solvent that is liquid at room temperature is described below.
常温で液体である有機溶媒は、非プロトン性有機溶媒が好ましく、例えば、エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、ブチレンカーボネート、クロロエチレンカーボネート、ビニレンカーボネート、γ−ブチロラクトン、γ−バレロラクトン、ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、エチルメチルカーボネート（ＥＭＣ）、ギ酸メチル、酢酸メチル、酢酸エチル、プロピオン酸メチル、プロピオン酸エチル（ＥＰ）、プロピオン酸プロピル（ＰＰ）、酪酸メチル、１，３−ジオキサン、１，４−ジオキサン、ジメトキシエタン（ＤＭＥ）、ジメチルスルホキシド、ジエチルエーテル、メチルジグライム、アセトニトリル、ベンゾニトリル、テトラヒドロフラン、スルホラン、スルトン等の一又は二以上を用いることができる。 The organic solvent that is liquid at room temperature is preferably an aprotic organic solvent, and for example, one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate (EP), propyl propionate (PP), methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc. can be used.
常温で液体である有機溶媒として、難燃性及び難揮発性であるイオン液体（常温溶融塩）を一つ又は複数用いることで、電池セルの内部短絡又は過充電等によって内部温度が上昇しても、電池セルの破裂及び発火などを防ぐことができる。イオン液体は、カチオンとアニオンからなり、有機カチオンとアニオンとを含む。有機溶媒に用いる有機カチオンとして、四級アンモニウムカチオン、三級スルホニウムカチオン、及び四級ホスホニウムカチオン等の脂肪族オニウムカチオン、又はイミダゾリウムカチオン及びピリジニウムカチオン等の芳香族カチオンが挙げられる。また、有機溶媒に用いるアニオンとして、１価のアミド系アニオン、１価のメチド系アニオン、フルオロスルホン酸アニオン、パーフルオロアルキルスルホン酸アニオン、テトラフルオロボレートアニオン、パーフルオロアルキルボレートアニオン、ヘキサフルオロホスフェートアニオン、又はパーフルオロアルキルホスフェートアニオン等が挙げられる。 By using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as an organic solvent that is liquid at room temperature, it is possible to prevent the battery cell from bursting or catching fire, even if the internal temperature of the battery cell rises due to an internal short circuit or overcharging. The ionic liquid is composed of a cation and an anion, and includes an organic cation and an anion. Examples of the organic cation used in the organic solvent include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of the anion used in the organic solvent include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.
また、上記有機溶媒に溶解させるリチウム塩としては、例えばＬｉＰＦ６、ＬｉＣｌＯ４、ＬｉＡｓＦ６、ＬｉＢＦ４、ＬｉＡｌＣｌ４、ＬｉＳＣＮ、ＬｉＢｒ、ＬｉＩ、Ｌｉ２ＳＯ４、Ｌｉ２Ｂ１０Ｃｌ１０、Ｌｉ２Ｂ１２Ｃｌ１２、ＬｉＣＦ３ＳＯ３、ＬｉＣ４Ｆ９ＳＯ３、ＬｉＣ（ＣＦ３ＳＯ２）３、ＬｉＣ（Ｃ２Ｆ５ＳＯ２）３、ＬｉＮ（ＣＦ３ＳＯ２）２、ＬｉＮ（Ｃ４Ｆ９ＳＯ２）（ＣＦ３ＳＯ２）、及びＬｉＮ（Ｃ２Ｆ５ＳＯ２）２等から選ばれた一又は二以上を用いることができる。 The lithium salt to be dissolved in the organic solvent may be, for example , one or more selected from LiPF6 , LiClO4 , LiAsF6 , LiBF4 , LiAlCl4 , LiSCN, LiBr , LiI, Li2SO4, Li2B10Cl10, Li2B12Cl12, LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3 , LiC ( C2F5SO2 ) 3 , LiN ( CF3SO2 ) 2 , LiN ( C4F9SO2 ) ( CF3SO2 ) , and LiN( C2F5SO2 ) 2 .
＜添加剤＞
上記有機溶媒は添加剤を有してもよい。添加剤により、高電圧及び／又は高温で二次電池を動作させるときに、正極表面又は負極表面で生じうる電解質の反応分解を抑制することができる。添加剤として例えばビニレンカーボネート（ＶＣ）、プロパンスルトン（ＰＳ）、ｔｅｒｔ−ブチルベンゼン（ＴＢＢ）、フルオロエチレンカーボネート（ＦＥＣ）、リチウムビス（オキサレート）ボレート（ＬｉＢＯＢ）を用いるとよい。ＬｉＢＯＢは良好な被膜を形成しやすく、特に好ましい。ＶＣ又はＦＥＣは充放電時に負極に良好な被膜を形成しサイクル特性を向上させることができ好ましい。 <Additives>
The organic solvent may have an additive. The additive can suppress the reactive decomposition of the electrolyte that may occur on the positive electrode surface or the negative electrode surface when the secondary battery is operated at high voltage and/or high temperature. For example, vinylene carbonate (VC), propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), and lithium bis(oxalate)borate (LiBOB) can be used as the additive. LiBOB is particularly preferred because it is easy to form a good coating. VC or FEC is preferred because it can form a good coating on the negative electrode during charging and discharging to improve cycle characteristics.
添加剤として、下記一般式（Ｇ１）に示す化合物を有してもよい。下記一般式（Ｇ１）はシアノ基を２つ有する化合物であり、ジニトリル化合物と呼ぶことができる。 The additive may contain a compound represented by the following general formula (G1). The following general formula (G1) is a compound having two cyano groups, and can be called a dinitrile compound.
Figure JPOXMLDOC01-appb-C000005
Figure JPOXMLDOC01-appb-C000005
上記一般式（Ｇ１）において、Ｒは炭素数が１以上５以下の炭化水素を表す。好ましくは、上記一般式（Ｇ１）において、Ｒは炭素数が２以上４以下の炭化水素を表す。 In the above general formula (G1), R represents a hydrocarbon having 1 to 5 carbon atoms. Preferably, in the above general formula (G1), R represents a hydrocarbon having 2 to 4 carbon atoms.
上記一般式（Ｇ１）の具体例として、たとえばスクシノニトリル、グルタロニトリル、アジポニトリル（ＡＤＮ）、又はエチレングリコールビス（プロピオニトリル）エーテル（ＥＧＢＥ）が挙げられる。 Specific examples of the above general formula (G1) include succinonitrile, glutaronitrile, adiponitrile (ADN), and ethylene glycol bis(propionitrile) ether (EGBE).
下記にスクシノニトリルの構造式（Ｈ１）を示す。 The structural formula of succinonitrile (H1) is shown below.
Figure JPOXMLDOC01-appb-C000006
Figure JPOXMLDOC01-appb-C000006
下記にグルタロニトリルの構造式（Ｈ２）を示す。 The structural formula of glutaronitrile (H2) is shown below.
Figure JPOXMLDOC01-appb-C000007
Figure JPOXMLDOC01-appb-C000007
下記にアジポニトリルの構造式（Ｈ３）を示す。 The structural formula of adiponitrile (H3) is shown below.
Figure JPOXMLDOC01-appb-C000008
Figure JPOXMLDOC01-appb-C000008
下記にエチレングリコールビス（プロピオニトリル）エーテルの構造式（Ｈ４）を示す。 The structural formula (H4) of ethylene glycol bis(propionitrile) ether is shown below.
Figure JPOXMLDOC01-appb-C000009
Figure JPOXMLDOC01-appb-C000009
添加剤として、ジニトリル化合物のいずれか一種または二種以上を用いることができる。 As an additive, one or more dinitrile compounds can be used.
さらにフルオロベンゼンを上記有機溶媒に添加してもよい。添加剤の濃度は、例えば電解液全体に対して０．１ｗｔ％以上５ｗｔ％以下とすればよい。ＰＳ又はＥＧＢＥは充放電時に正極に良好な被膜を形成しサイクル特性を向上させることができ好ましい。ＦＢは正極及び負極への有機溶媒のぬれ性が向上するため好ましい。ジニトリル化合物は、ニトリル基が正極及び負極に配向して、有機溶媒の酸化分解を阻害するため耐電圧性を向上させることができ好ましい。さらにジニトリル化合物は、負極に銅を有する集電体を用いた場合、過放電の際に銅の溶解を防ぐことができ好ましい。高電圧での二次電池の使用を踏まえると、ニトリル化合物を添加することが好ましい。 Furthermore, fluorobenzene may be added to the organic solvent. The concentration of the additive may be, for example, 0.1 wt% or more and 5 wt% or less with respect to the entire electrolyte. PS or EGBE are preferable because they form a good coating on the positive electrode during charging and discharging, thereby improving cycle characteristics. FB is preferable because it improves the wettability of the organic solvent to the positive electrode and the negative electrode. Dinitrile compounds are preferable because the nitrile groups are oriented to the positive electrode and the negative electrode, inhibiting the oxidative decomposition of the organic solvent, thereby improving the voltage resistance. Furthermore, dinitrile compounds are preferable because they can prevent the dissolution of copper during overdischarge when a current collector having copper is used for the negative electrode. Considering the use of secondary batteries at high voltages, it is preferable to add a nitrile compound.
常温で液体である必要はなく、有機溶媒としてポリマーゲル電解質と呼ばれる半固体材料を用いてもよい。ポリマーゲル電解質を用いることで、漏液性等に対する安全性が高まる。また、電池セルの薄型化及び軽量化が可能である。 It does not have to be liquid at room temperature, and a semi-solid material called a polymer gel electrolyte can be used as the organic solvent. Using a polymer gel electrolyte increases safety against leakage, etc. Also, it is possible to make the battery cell thinner and lighter.
ゲル化されるポリマーとして、シリコーンゲル、アクリルゲル、アクリロニトリルゲル、ポリエチレンオキサイド系ゲル、ポリプロピレンオキサイド系ゲル、フッ素系ポリマーのゲル等を用いることができる。 Polymers that can be gelled include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, fluorine-based polymer gel, etc.
ポリマーとしては、例えばポリエチレンオキシド（ＰＥＯ）などのポリアルキレンオキシド構造を有するポリマー、ＰＶＤＦ、及びポリアクリロニトリル等、及びそれらを含む共重合体等を用いることができる。例えばＰＶＤＦとヘキサフルオロプロピレン（ＨＦＰ）の共重合体であるＰＶＤＦ−ＨＦＰを用いることができる。また、形成されるポリマーは、多孔質形状を有してもよい。 As the polymer, for example, a polymer having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, etc., and copolymers containing these can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. In addition, the polymer formed may have a porous shape.
＜低温用に好ましい有機溶媒の例＞
低温用に好ましい有機溶媒の一例について、以下に説明する。 <Examples of organic solvents preferred for low temperature use>
An example of an organic solvent suitable for low temperature use is described below.
低温用に好ましい有機溶媒は、エチレンカーボネート（ＥＣ）と、エチルメチルカーボネート（ＥＭＣ）と、ジメチルカーボネート（ＤＭＣ）と、を含み、前記エチレンカーボネート、前記エチルメチルカーボネート、及び前記ジメチルカーボネートの全含有量を１００ｖｏｌ％としたとき、前記エチレンカーボネート、前記エチルメチルカーボネート、及び前記ジメチルカーボネートの体積比が、ｘ：ｙ：１００−ｘ−ｙ（ただし、５≦ｘ≦３５であり、０＜ｙ＜６５である。）であるものを用いることができる。より具体的には、ＥＣと、ＥＭＣと、ＤＭＣと、を、ＥＣ：ＥＭＣ：ＤＭＣ＝３０：３５：３５（体積比）で含んだ有機溶媒を用いることができる。なお、上記の体積比は、電解液の混合前における体積比であってもよく、電解液を混合する際の外気は室温（代表的には、２５℃）であってもよい。 The organic solvent preferred for low temperatures includes ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), and when the total content of the ethylene carbonate, the ethyl methyl carbonate, and the dimethyl carbonate is 100 vol%, the volume ratio of the ethylene carbonate, the ethyl methyl carbonate, and the dimethyl carbonate is x:y:100-x-y (where 5≦x≦35 and 0<y<65). More specifically, an organic solvent containing EC, EMC, and DMC in a ratio of EC:EMC:DMC=30:35:35 (volume ratio) can be used. The above volume ratio may be the volume ratio before mixing with the electrolyte, and the outside air when mixing the electrolyte may be room temperature (typically 25° C.).
ＥＣは、環状カーボネートであり、高い比誘電率を有するため、リチウム塩の解離を促進させる効果を有する。一方で、ＥＣは、粘度が高く、凝固点（融点）が３８℃と高いため、有機溶媒としてＥＣ単体を用いた場合、低温環境下での使用が難しい。そこで、本発明の一態様として具体的に説明する有機溶媒は、ＥＣ単体ではなく、ＥＭＣとＤＭＣを更に含む。ＥＭＣは、鎖状カーボネートであり、電解液の粘度を下げる効果を有する上に、凝固点が−５４℃である。また、ＤＭＣも、鎖状カーボネートであり、電解液の粘度を下げる効果を有する上に、凝固点が−４３℃である。このような物性を有するＥＣ、ＥＭＣ、及びＤＭＣを、これら３つの有機溶媒の全含有量を１００ｖｏｌ％として、２５℃での体積比が、ｘ：ｙ：１００−ｘ−ｙ（ただし、５≦ｘ≦３５であり、０＜ｙ＜６５である。）となるように混合した有機溶媒を用いて作製された電解質は、凝固点が−４０℃以下という特徴を有する。 EC is a cyclic carbonate and has a high relative dielectric constant, and therefore has the effect of promoting the dissociation of lithium salts. On the other hand, EC has a high viscosity and a high freezing point (melting point) of 38°C, so when EC alone is used as an organic solvent, it is difficult to use it in a low-temperature environment. Therefore, the organic solvent specifically described as one aspect of the present invention is not EC alone, but further contains EMC and DMC. EMC is a chain carbonate, has the effect of reducing the viscosity of the electrolyte, and has a freezing point of -54°C. DMC is also a chain carbonate, has the effect of reducing the viscosity of the electrolyte, and has a freezing point of -43°C. An electrolyte prepared using an organic solvent in which EC, EMC, and DMC having such physical properties are mixed so that the volume ratio at 25°C is x:y:100-x-y (where 5≦x≦35 and 0<y<65) when the total content of these three organic solvents is 100 vol%, has the characteristic of having a freezing point of -40°C or less.
電池セルに用いられている一般的な電解質は、−２０℃程度で凝固してしまうため、−４０℃で充放電できる電池を作製することは困難である。低温用電解質の有機溶媒として説明した上記電解質は、凝固点が−４０℃以下であるため、−４０℃という極低温環境下においても充放電可能な電池セルを実現できる。 General electrolytes used in battery cells freeze at around -20°C, making it difficult to create batteries that can be charged and discharged at -40°C. The electrolyte described above as an organic solvent for low-temperature electrolytes has a freezing point of -40°C or lower, making it possible to create battery cells that can be charged and discharged even in extremely low-temperature environments such as -40°C.
また、低温用に好ましい有機溶媒に溶解させるリチウム塩は、上述のリチウム塩から選択できる。 The lithium salt to be dissolved in an organic solvent suitable for low temperatures can be selected from the lithium salts described above.
また低温用に好ましい有機溶媒が有する添加剤は、上述の添加剤から選択できる。 Additives contained in organic solvents suitable for low temperatures can be selected from the additives mentioned above.
〔セパレータ〕
二次電池は、セパレータを有することが好ましい。セパレータとしては、例えば、紙、不織布、ガラス繊維、セラミックス、或いはナイロン（ポリアミド）、ビニロン（ポリビニルアルコール系繊維）、ポリエステル、アクリル、ポリオレフィン、ポリウレタンを用いた合成繊維等で形成されたものを用いることができる。セパレータはエンベロープ状に加工し、正極または負極のいずれか一方を包むように配置することが好ましい。 [Separator]
The secondary battery preferably has a separator. The separator may be made of, for example, paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyolefin, or polyurethane. The separator is preferably processed into an envelope shape and disposed so as to encase either the positive electrode or the negative electrode.
セパレータは多層構造であってもよい。例えばポリプロピレン、ポリエチレン等の有機材料フィルムに、セラミックス系材料、フッ素系材料、ポリアミド系材料、またはこれらを混合したもの等をコートすることができる。セラミックス系材料としては、例えば酸化アルミニウム粒子、酸化シリコン粒子等を用いることができる。フッ素系材料としては、例えばＰＶＤＦ、ポリテトラフルオロエチレン等を用いることができる。ポリアミド系材料としては、例えばナイロン、アラミド（メタ系アラミド、パラ系アラミド）等を用いることができる。 The separator may have a multi-layer structure. For example, an organic material film such as polypropylene or polyethylene may be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture of these. As the ceramic material, for example, aluminum oxide particles or silicon oxide particles may be used. As the fluorine material, for example, PVDF or polytetrafluoroethylene may be used. As the polyamide material, for example, nylon or aramid (meta-aramid or para-aramid) may be used.
セラミックス系材料をコートすると耐酸化性が向上するため、高電圧充放電の際のセパレータの劣化を抑制し、二次電池の信頼性を向上させることができる。またフッ素系材料をコートするとセパレータと電極が密着しやすくなり、出力特性を向上させることができる。ポリアミド系材料、特にアラミドをコートすると、耐熱性が向上するため、二次電池の安全性を向上させることができる。 Coating with ceramic-based materials improves oxidation resistance, suppressing the deterioration of the separator during high-voltage charging and discharging, and improving the reliability of the secondary battery. Coating with fluorine-based materials also makes it easier for the separator and electrodes to adhere to each other, improving output characteristics. Coating with polyamide-based materials, especially aramid, improves heat resistance, improving the safety of the secondary battery.
例えばポリプロピレンのフィルムの両面に酸化アルミニウムとアラミドの混合材料をコートしてもよい。また、ポリプロピレンのフィルムの、正極と接する面に酸化アルミニウムとアラミドの混合材料をコートし、負極と接する面にフッ素系材料をコートしてもよい。 For example, both sides of a polypropylene film may be coated with a mixture of aluminum oxide and aramid. Alternatively, the surface of the polypropylene film that comes into contact with the positive electrode may be coated with a mixture of aluminum oxide and aramid, and the surface that comes into contact with the negative electrode may be coated with a fluorine-based material.
多層構造のセパレータを用いると、セパレータ全体の厚さが薄くても二次電池の安全性を保つことができるため、二次電池の体積あたりの放電容量を大きくすることができる。 By using a multi-layer separator, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, so the discharge capacity per volume of the secondary battery can be increased.
〔外装体〕
二次電池が有する外装体としては、例えばアルミニウムなどの金属材料及び／又は樹脂材料を用いることができる。また、フィルム状の外装体を用いることもできる。フィルムとしては、例えばポリエチレン、ポリプロピレン、ポリカーボネート、アイオノマー、ポリアミド等の材料からなる膜上に、アルミニウム、ステンレス、銅、ニッケル等の可撓性に優れた金属薄膜を設け、さらに該金属薄膜上に外装体の外面としてポリアミド系樹脂、ポリエステル系樹脂等の絶縁性合成樹脂膜を設けた三層構造のフィルムを用いることができる。三層構造のような多層構造のフィルムであって、アルミニウムを有するものをアルミラミネートフィルムと記すことがある。 [Exterior body]
The exterior body of the secondary battery can be made of, for example, a metal material such as aluminum and/or a resin material. A film-shaped exterior body can also be used. As the film, for example, a three-layer structure film can be used in which a thin metal film having excellent flexibility such as aluminum, stainless steel, copper, nickel, etc. is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc., and an insulating synthetic resin film such as a polyamide-based resin or polyester-based resin is further provided on the thin metal film as the outer surface of the exterior body. A multilayer structure film such as a three-layer structure that has aluminum is sometimes referred to as an aluminum laminate film.
＜二次電池の構成例２＞
［固体電解質］
電解液の代わりに、硫化物系または酸化物系等の無機物材料を有する固体電解質、ＰＥＯ（ポリエチレンオキシド）系等の高分子材料を有する固体電解質等を用いることができる。固体電解質を用いる場合には、セパレータ及び／又はスペーサの設置が不要となる。また、電池全体を固体化できるため、漏液のおそれがなくなり安全性が飛躍的に向上する。 <Configuration Example 2 of Secondary Battery>
[Solid electrolyte]
Instead of the electrolyte, a solid electrolyte having an inorganic material such as a sulfide or oxide, or a solid electrolyte having a polymer material such as a PEO (polyethylene oxide) can be used. When a solid electrolyte is used, the installation of a separator and/or a spacer becomes unnecessary. In addition, since the entire battery can be solidified, there is no risk of leakage, and safety is dramatically improved.
固体電解質を用いた二次電池（固体二次電池とも呼ぶ）は、液体の電解液を有する二次電池と比較して高い電位でも化学的に安定であることが期待できる。そのため、先の実施の形態で得られる正極活物質を用いた全固体二次電池は、充電電圧を４．８Ｖ以上、たとえば５．０Ｖとしても良好な充放電特性を得られることが期待できる。 Secondary batteries using solid electrolytes (also called solid-state secondary batteries) are expected to be chemically stable even at high potentials compared to secondary batteries with liquid electrolytes. Therefore, an all-solid-state secondary battery using the positive electrode active material obtained in the above embodiment is expected to have good charge/discharge characteristics even when the charging voltage is 4.8 V or more, for example 5.0 V.
以下に、二次電池の構成の一例として、固体二次電池の構成について説明する。 Below, we will explain the configuration of a solid-state secondary battery as an example of the configuration of a secondary battery.
図２５Ａに示すように、本発明の一態様の二次電池４００は、正極４１０、固体電解質層４２０および負極４３０を有する。 As shown in FIG. 25A, a secondary battery 400 according to one embodiment of the present invention has a positive electrode 410, a solid electrolyte layer 420, and a negative electrode 430.
正極４１０は正極集電体４１３および正極活物質層４１４を有する。正極活物質層４１４は正極活物質４１１および固体電解質４２１を有する。正極活物質４１１には、先の実施の形態で説明した製造方法を用いて作製した正極活物質を用いる。また正極活物質層４１４は、導電剤およびバインダを有していてもよい。 The positive electrode 410 has a positive electrode current collector 413 and a positive electrode active material layer 414. The positive electrode active material layer 414 has a positive electrode active material 411 and a solid electrolyte 421. The positive electrode active material 411 is made of a positive electrode active material produced by the manufacturing method described in the previous embodiment. The positive electrode active material layer 414 may also contain a conductive agent and a binder.
固体電解質層４２０は固体電解質４２１を有する。固体電解質層４２０は、正極４１０と負極４３０の間に位置し、正極活物質４１１および負極活物質４３１のいずれも有さない領域である。 The solid electrolyte layer 420 has a solid electrolyte 421. The solid electrolyte layer 420 is located between the positive electrode 410 and the negative electrode 430, and is a region that has neither the positive electrode active material 411 nor the negative electrode active material 431.
負極４３０は負極集電体４３３および負極活物質層４３４を有する。負極活物質層４３４は負極活物質４３１および固体電解質４２１を有する。また負極活物質層４３４は、導電剤およびバインダを有していてもよい。なお、負極４３０に金属リチウムを用いる場合は、図２５Ｂのように、固体電解質４２１を有さない負極４３０とすることができる。負極４３０に金属リチウムを用いると、二次電池４００のエネルギー密度を向上させることができ好ましい。 The negative electrode 430 has a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 has a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also have a conductive agent and a binder. When metallic lithium is used for the negative electrode 430, the negative electrode 430 may not have a solid electrolyte 421, as shown in FIG. 25B. Using metallic lithium for the negative electrode 430 is preferable because it can improve the energy density of the secondary battery 400.
固体電解質層４２０が有する固体電解質４２１としては、たとえば硫化物固体電解質、酸化物固体電解質、ハロゲン化物固体電解質等を用いることができる。 The solid electrolyte 421 in the solid electrolyte layer 420 may be, for example, a sulfide solid electrolyte, an oxide solid electrolyte, a halide solid electrolyte, or the like.
硫化物固体電解質には、チオリシコン（Ｌｉ１０ＧｅＰ２Ｓ１２、Ｌｉ３．２５Ｇｅ０．２５Ｐ０．７５Ｓ４等）、硫化物ガラス（７０Ｌｉ２Ｓ・３０Ｐ２Ｓ５、３０Ｌｉ２Ｓ・２６Ｂ２Ｓ３・４４ＬｉＩ、６３Ｌｉ２Ｓ・３６ＳｉＳ２・１Ｌｉ３ＰＯ４、５７Ｌｉ２Ｓ・３８ＳｉＳ２・５Ｌｉ４ＳｉＯ４、５０Ｌｉ２Ｓ・５０ＧｅＳ２等）、硫化物結晶化ガラス（Ｌｉ７Ｐ３Ｓ１１、Ｌｉ３．２５Ｐ０．９５Ｓ４等）が含まれる。硫化物固体電解質は、高い伝導度を有する材料がある、低い温度で合成可能、また比較的やわらかいため充放電を経ても導電経路が保たれやすい等の利点がある。 Sulfide solid electrolytes include thiolithicons ( Li10GeP2S12 , Li3.25Ge0.25P0.75S4 , etc. ), sulfide glasses ( 70Li2S.30P2S5 , 30Li2S.26B2S3.44LiI , 63Li2S.36SiS2.1Li3PO4 , 57Li2S.38SiS2.5Li4SiO4 , 50Li2S.50GeS2 , etc. ) , and sulfide crystallized glasses ( Li7P3S11 , Li3.25P0.95S4 , etc. ) . Sulfide solid electrolytes have the advantages of being highly conductive, being able to be synthesized at low temperatures, and being relatively soft, which makes it easier to maintain conductive paths even after charging and discharging.
酸化物固体電解質には、ペロブスカイト型結晶構造を有する材料（Ｌａ２／３−ｘＬｉ３ｘＴｉＯ３等）、ＮＡＳＩＣＯＮ型結晶構造を有する材料（Ｌｉ１＋ＸＡｌＸＴｉ２−Ｘ（ＰＯ４）３等）、ガーネット型結晶構造を有する材料（Ｌｉ７Ｌａ３Ｚｒ２Ｏ１２等）、ＬＩＳＩＣＯＮ型結晶構造を有する材料（Ｌｉ１４ＺｎＧｅ４Ｏ１６等）、ＬＬＺＯ（Ｌｉ７Ｌａ３Ｚｒ２Ｏ１２）、酸化物ガラス（Ｌｉ３ＰＯ４−Ｌｉ４ＳｉＯ４、５０Ｌｉ４ＳｉＯ４・５０Ｌｉ３ＢＯ３等）、酸化物結晶化ガラス（Ｌｉ１．０７Ａｌ０．６９Ｔｉ１．４６（ＰＯ４）３、Ｌｉ１．５Ａｌ０．５Ｇｅ１．５（ＰＯ４）３等）が含まれる。酸化物固体電解質は、大気中で安定であるといった利点がある。 Examples of oxide solid electrolytes include materials having a perovskite crystal structure (La2 /3- xLi3xTiO3 , etc. ), materials having a NASICON crystal structure (Li1 + xAlxTi2 -x ( PO4 ) 3 , etc.), materials having a garnet crystal structure ( Li7La3Zr2O12 , etc. ), materials having a LISICON crystal structure ( Li14ZnGe4O16 , etc. ), LLZO (Li7La3Zr2O12) , oxide glass ( Li3PO4 -Li4SiO4 , 50Li4SiO4.50Li3BO3 , etc. ) , oxide crystallized glass ( Li1.07Al0.69Ti1.46 ( PO4 ) 3 , etc. ), and oxide glass- ceramics ( Li1.07Al0.69Ti1.46 ( PO4 ) 3 ). , Li1.5Al0.5Ge1.5 ( PO4 ) 3 , etc. The oxide solid electrolyte has an advantage that it is stable in the air.
ハロゲン化物固体電解質には、ＬｉＡｌＣｌ４、Ｌｉ３ＩｎＢｒ６、ＬｉＦ、ＬｉＹＦ４、Ｌｉ３ＡｌＦ６、Ｌｉ２ＺｒＦ６、ＬｉＣｌ、ＬｉＢｒ、ＬｉＩ等が含まれる。これらのうちＬｉＦ、ＬｉＹＦ４、Ｌｉ３ＡｌＦ６、Ｌｉ２ＺｒＦ６をフッ化物固体電解質と呼び、電位窓（Ｖ　ｖｓ．Ｌｉ金属）が高いため、高電圧で二次電池を使用する際に好適である。 Halide solid electrolytes include LiAlCl4 , Li3InBr6 , LiF, LiYF4 , Li3AlF6 , Li2ZrF6 , LiCl, LiBr , LiI , etc. Of these , LiF, LiYF4 , Li3AlF6 , and Li2ZrF6 are called fluoride solid electrolytes, and are suitable for use in secondary batteries at high voltages due to their wide potential window (V vs. Li metal).
また、これらハロゲン化物固体電解質を、ポーラス酸化アルミニウムおよび／またはポーラスシリカの細孔に充填したコンポジット材料も固体電解質として用いることができる。 In addition, composite materials in which these halide solid electrolytes are filled into the pores of porous aluminum oxide and/or porous silica can also be used as solid electrolytes.
また、異なる固体電解質を混合して用いてもよい。さらに正極側の固体電解質と負極側の固体電解質とを異ならせてもよい。例えば正極側には酸化耐性の高い固体電解質を用い、負極側には還元耐性の高い固体電解質を用いるとよい。Ｏ３’型の結晶構造を有する正極活物質１００は酸化電位が高くなるため、酸化耐性の高い固体電解質を用いることが特に望ましい。 Different solid electrolytes may also be mixed and used. Furthermore, the solid electrolyte on the positive electrode side may be different from the solid electrolyte on the negative electrode side. For example, a solid electrolyte with high oxidation resistance may be used on the positive electrode side, and a solid electrolyte with high reduction resistance may be used on the negative electrode side. The positive electrode active material 100 having an O3' type crystal structure has a high oxidation potential, so it is particularly desirable to use a solid electrolyte with high oxidation resistance.
中でも、ＮＡＳＩＣＯＮ型結晶構造を有するＬｉ１＋ｘＡｌｘＴｉ２−ｘ（ＰＯ４）３（０＜ｘ＜１）（以下、ＬＡＴＰ）は、アルミニウムとチタンという、本発明の一態様の二次電池４００に用いる正極活物質が有してもよい元素を含むため、サイクル特性の向上について相乗効果が期待でき好ましい。また、工程の削減による生産性の向上も期待できる。なお本明細書等において、ＮＡＳＩＣＯＮ型結晶構造とは、Ｍ２（ＸＯ４）３（Ｍ：遷移金属、Ｘ：Ｓ、Ｐ、Ａｓ、Ｍｏ、Ｗ等）で表される化合物であり、ＭＯ６八面体とＸＯ４四面体が頂点を共有して３次元的に配列した構造を有するものをいう。 Among them, Li1 + xAlxTi2 -x ( PO4 ) 3 (0<x<1) (hereinafter, LATP) having a NASICON crystal structure is preferable because it contains aluminum and titanium, which are elements that may be contained in the positive electrode active material used in the secondary battery 400 of one embodiment of the present invention, and therefore a synergistic effect can be expected in improving cycle characteristics. In addition, it is expected to improve productivity by reducing the number of steps. Note that in this specification and the like, the NASICON crystal structure refers to a compound represented by M2 ( XO4 ) 3 (M: transition metal, X: S, P, As, Mo, W, etc.), which has a structure in which MO6 octahedrons and XO4 tetrahedrons are arranged three-dimensionally with vertices shared.
本実施の形態は、他の実施の形態又は実施例と適宜組み合わせて用いることができる。 This embodiment can be used in appropriate combination with other embodiments or examples.
（実施の形態４）
本実施の形態では、先の実施の形態で説明した製造方法によって作製された正極を有する二次電池の例を説明する。 (Embodiment 4)
In this embodiment mode, an example of a secondary battery having a positive electrode manufactured by the manufacturing method described in the previous embodiment mode will be described.
［コイン型二次電池］
コイン型の二次電池の一例について説明する。図２６Ａはコイン型（単層偏平型）の二次電池の分解斜視図であり、図２６Ｂは、外観図であり、図２６Ｃは、その断面図である。コイン型の二次電池は主に小型の電子機器に用いられる。 [Coin-type secondary battery]
An example of a coin-type secondary battery will be described. Fig. 26A is an exploded perspective view of a coin-type (single-layer flat) secondary battery, Fig. 26B is an external view, and Fig. 26C is a cross-sectional view thereof. Coin-type secondary batteries are mainly used in small electronic devices.
なお、図２６Ａでは、わかりやすくするために部材の重なり（上下関係、及び位置関係）がわかるように模式図としている。従って図２６Ａと図２６Ｂは完全に一致する対応図とはしていない。 Note that in order to make it easier to understand, Figure 26A is a schematic diagram that shows the overlapping of components (vertical relationship and positional relationship). Therefore, Figure 26A and Figure 26B are not completely corresponding views.
図２６Ａでは、正極３０４、セパレータ３１０、負極３０７、スペーサ３２２、ワッシャー３１２を重ねている。これらを負極缶３０２と正極缶３０１とガスケットで封止している。なお、図２６Ａにおいて、封止のためのガスケットは図示していない。スペーサ３２２、ワッシャー３１２は、正極缶３０１と負極缶３０２を圧着する際に、内部を保護または缶内の位置を固定するために用いられている。スペーサ３２２、ワッシャー３１２はステンレスまたは絶縁材料を用いる。 In Fig. 26A, a positive electrode 304, a separator 310, a negative electrode 307, a spacer 322, and a washer 312 are stacked. These are sealed with a negative electrode can 302, a positive electrode can 301, and a gasket. Note that the gasket for sealing is not shown in Fig. 26A. The spacer 322 and the washer 312 are used to protect the inside or to fix the position inside the can when the positive electrode can 301 and the negative electrode can 302 are crimped together. The spacer 322 and the washer 312 are made of stainless steel or an insulating material.
正極集電体３０５上に正極活物質層３０６が形成された積層構造を正極３０４としている。 The positive electrode 304 is a laminated structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305.
図２６Ｂは、完成したコイン型の二次電池の斜視図である。 Figure 26B is an oblique view of the completed coin-type secondary battery.
コイン型の二次電池３００は、正極端子を兼ねた正極缶３０１と負極端子を兼ねた負極缶３０２とが、ポリプロピレン等で形成されたガスケット３０３で絶縁シールされている。正極３０４は、正極集電体３０５と、これと接するように設けられた正極活物質層３０６により形成される。また、負極３０７は、負極集電体３０８と、これに接するように設けられた負極活物質層３０９により形成される。また、負極３０７は、積層構造に限定されず、リチウム金属箔またはリチウムとアルミニウムの合金箔を用いてもよい。 The coin-type secondary battery 300 has a positive electrode can 301, which also serves as a positive electrode terminal, and a negative electrode can 302, which also serves as a negative electrode terminal, which are insulated and sealed with a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed of a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with the positive electrode current collector. The negative electrode 307 is formed of a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with the negative electrode current collector. The negative electrode 307 is not limited to a laminated structure, and may be a lithium metal foil or a lithium-aluminum alloy foil.
なお、コイン型の二次電池３００に用いる正極３０４及び負極３０７は、それぞれ活物質層は片面のみに形成すればよい。 Note that the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 each need only have an active material layer formed on one side.
正極缶３０１、負極缶３０２には、電解液に対して耐食性のあるニッケル、アルミニウム、チタン等の金属、若しくはこれらの合金又はこれらと他の金属との合金（例えばステンレス鋼等）を用いることができる。また、電解液などによる腐食を防ぐため、ニッケルまたはアルミニウム等を被覆することが好ましい。正極缶３０１は正極３０４と、負極缶３０２は負極３０７とそれぞれ電気的に接続する。 The positive electrode can 301 and the negative electrode can 302 can be made of metals such as nickel, aluminum, titanium, etc., which are corrosion-resistant to the electrolyte, or alloys of these metals or alloys of these metals with other metals (e.g., stainless steel, etc.). In order to prevent corrosion by the electrolyte, etc., it is preferable to coat them with nickel or aluminum. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307.
これら負極３０７、正極３０４及びセパレータ３１０を電解液に浸し、図２６Ｃに示すように、正極缶３０１を下にして正極３０４、セパレータ３１０、負極３０７、負極缶３０２をこの順で積層し、正極缶３０１と負極缶３０２とをガスケット３０３を介して圧着してコイン形の二次電池３００を製造する。 The negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte, and as shown in FIG. 26C, the positive electrode can 301 is placed at the bottom, and the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are stacked in this order, and the positive electrode can 301 and the negative electrode can 302 are crimped together via a gasket 303 to produce a coin-shaped secondary battery 300.
上記の構成を有することで、且つ、放電容量が高く、且つ、サイクル特性に優れたコイン型の二次電池３００とすることができる。 By having the above configuration, it is possible to obtain a coin-type secondary battery 300 with high discharge capacity and excellent cycle characteristics.
［円筒型二次電池］
円筒型の二次電池の例について図２７Ａを参照して説明する。円筒型の二次電池６１６は、図２７Ａに示すように、上面に正極キャップ（電池蓋）６０１を有し、側面及び底面に電池缶（外装缶）６０２を有している。これら正極キャップ６０１と電池缶（外装缶）６０２とは、ガスケット（絶縁パッキン）６１０によって絶縁されている。 [Cylindrical secondary battery]
An example of a cylindrical secondary battery will be described with reference to Fig. 27A. As shown in Fig. 27A, a cylindrical secondary battery 616 has a positive electrode cap (battery lid) 601 on the top surface, and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap 601 and the battery can (external can) 602 are insulated by a gasket (insulating packing) 610.
図２７Ｂは、円筒型の二次電池の断面を模式的に示した図である。図２７Ｂに示す円筒型の二次電池は、上面に正極キャップ（電池蓋）６０１を有し、側面及び底面に電池缶（外装缶）６０２を有している。これら正極キャップと電池缶（外装缶）６０２とは、ガスケット（絶縁パッキン）６１０によって絶縁されている。 Figure 27B is a schematic diagram showing a cross section of a cylindrical secondary battery. The cylindrical secondary battery shown in Figure 27B has a positive electrode cap (battery lid) 601 on the top surface, and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap and battery can (external can) 602 are insulated by a gasket (insulating packing) 610.
中空円柱状の電池缶６０２の内側には、帯状の正極６０４と負極６０６とがセパレータ６０５を間に挟んで捲回された電池素子が設けられている。図示しないが、電池素子は中心軸を中心に捲回されている。電池缶６０２は、一端が閉じられ、他端が開いている。電池缶６０２には、電解液に対して耐腐食性のあるニッケル、アルミニウム、チタン等の金属、又はこれらの合金、これらと他の金属との合金（例えば、ステンレス鋼等）を用いることができる。また、電解液による腐食を防ぐため、ニッケル及びアルミニウム等を電池缶６０２に被覆することが好ましい。電池缶６０２の内側において、正極、負極及びセパレータが捲回された電池素子は、対向する一対の絶縁板６０８、絶縁板６０９により挟まれている。また、電池素子が設けられた電池缶６０２の内部には、非水電解液（図示せず）が注入されている。非水電解液は、コイン型の二次電池と同様のものを用いることができる。 Inside the hollow cylindrical battery can 602, a battery element is provided in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 sandwiched between them. Although not shown, the battery element is wound around a central axis. One end of the battery can 602 is closed and the other end is open. For the battery can 602, metals such as nickel, aluminum, and titanium that are resistant to corrosion by the electrolyte, or alloys of these metals and other metals (e.g., stainless steel, etc.) can be used. In addition, in order to prevent corrosion by the electrolyte, it is preferable to coat the battery can 602 with nickel, aluminum, etc. Inside the battery can 602, the battery element in which the positive electrode, negative electrode, and separator are wound is sandwiched between a pair of opposing insulating plates 608 and 609. In addition, a nonaqueous electrolyte (not shown) is injected inside the battery can 602 in which the battery element is provided. The nonaqueous electrolyte can be the same as that of a coin-type secondary battery.
円筒型の蓄電池に用いる正極及び負極は捲回するため、集電体の両面に活物質を形成することが好ましい。 Since the positive and negative electrodes used in cylindrical storage batteries are wound, it is preferable to form active material on both sides of the current collector.
本発明の一態様である正極活物質１００を正極６０４に用いることで、高容量、且つ、放電容量が高く、且つ、サイクル特性に優れた円筒型の二次電池６１６とすることができる。 By using the positive electrode active material 100 of one embodiment of the present invention for the positive electrode 604, a cylindrical secondary battery 616 can be obtained that has a high capacity, a high discharge capacity, and excellent cycle characteristics.
正極６０４には正極端子（正極集電リード）６０３が接続され、負極６０６には負極端子（負極集電リード）６０７が接続される。正極端子６０３は、アルミニウムなどの金属材料を用いることができる。負極端子６０７は、銅などの金属材料を用いることができる。正極端子６０３は安全弁機構６１３に、負極端子６０７は電池缶６０２の底にそれぞれ抵抗溶接される。安全弁機構６１３は、ＰＴＣ（Ｐｏｓｉｔｉｖｅ　Ｔｅｍｐｅｒａｔｕｒｅ　Ｃｏｅｆｆｉｃｉｅｎｔ）素子６１１を介して正極キャップ６０１と電気的に接続されている。安全弁機構６１３は電池の内圧の上昇が所定の閾値を超えた場合に、正極キャップ６０１と正極６０４との電気的な接続を切断するものである。また、ＰＴＣ素子６１１は温度が上昇した場合に抵抗が増大する熱感抵抗素子であり、抵抗の増大により電流量を制限して異常発熱を防止するものである。ＰＴＣ素子６１１には、チタン酸バリウム（ＢａＴｉＯ３）系半導体セラミックス等を用いることができる。 A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. The positive electrode terminal 603 can be made of a metal material such as aluminum. The negative electrode terminal 607 can be made of a metal material such as copper. The positive electrode terminal 603 is resistance-welded to a safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 613 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the increase in the internal pressure of the battery exceeds a predetermined threshold value. The PTC element 611 is a thermosensitive resistor whose resistance increases when the temperature increases, and limits the amount of current due to the increase in resistance to prevent abnormal heat generation. The PTC element 611 may be made of a barium titanate (BaTiO 3 ) based semiconductor ceramic or the like.
図２７Ｃに、蓄電システム６１５の一例を示す。蓄電システム６１５は複数の二次電池６１６を有する。それぞれの二次電池の正極は、絶縁体６２５で分離された導電体６２４に接触し、電気的に接続されている。導電体６２４は配線６２３を介して、制御回路６２０に電気的に接続されている。また、それぞれの二次電池の負極は、配線６２６を介して制御回路６２０に電気的に接続されている。制御回路６２０として、充放電などを行う充放電制御回路、または過充電もしくは／及び過放電を防止する保護回路を適用することができる。 Figure 27C shows an example of a power storage system 615. The power storage system 615 has multiple secondary batteries 616. The positive electrode of each secondary battery is in contact with and electrically connected to a conductor 624 separated by an insulator 625. The conductor 624 is electrically connected to a control circuit 620 via wiring 623. The negative electrode of each secondary battery is electrically connected to the control circuit 620 via wiring 626. As the control circuit 620, a charge/discharge control circuit that performs charging and discharging, or a protection circuit that prevents overcharging and/or overdischarging can be applied.
図２７Ｄに、蓄電システム６１５の一例を示す。蓄電システム６１５は複数の二次電池６１６を有し、複数の二次電池６１６は、導電板６２８及び導電板６１４の間に挟まれている。複数の二次電池６１６は、配線６２７により導電板６２８及び導電板６１４と電気的に接続される。複数の二次電池６１６は、並列接続されていてもよいし、直列接続されていてもよいし、並列に接続された後さらに直列に接続されていてもよい。複数の二次電池６１６を有する蓄電システム６１５を構成することで、大きな電力を取り出すことができる。 Figure 27D shows an example of a power storage system 615. The power storage system 615 has multiple secondary batteries 616, which are sandwiched between a conductive plate 628 and a conductive plate 614. The multiple secondary batteries 616 are electrically connected to the conductive plate 628 and the conductive plate 614 by wiring 627. The multiple secondary batteries 616 may be connected in parallel, in series, or in parallel and then further connected in series. By configuring the power storage system 615 to have multiple secondary batteries 616, it is possible to extract a large amount of power.
複数の二次電池６１６が、並列に接続された後、さらに直列に接続されてもよい。 Multiple secondary batteries 616 may be connected in parallel and then further connected in series.
また、複数の二次電池６１６の間に温度制御装置を有していてもよい。二次電池６１６が過熱されたときは、温度制御装置により冷却し、二次電池６１６が冷えすぎているときは温度制御装置により加熱することができる。そのため蓄電システム６１５の性能が外気温に影響されにくくなる。 Furthermore, a temperature control device may be provided between the multiple secondary batteries 616. When the secondary batteries 616 are overheated, they can be cooled by the temperature control device, and when the secondary batteries 616 are too cold, they can be heated by the temperature control device. This makes the performance of the power storage system 615 less susceptible to the effects of the outside air temperature.
また、図２７Ｄにおいて、蓄電システム６１５は制御回路６２０に配線６２１及び配線６２２を介して電気的に接続されている。配線６２１は導電板６２８を介して複数の二次電池６１６の正極に、配線６２２は導電板６１４を介して複数の二次電池６１６の負極に、それぞれ電気的に接続される。 In addition, in FIG. 27D, the power storage system 615 is electrically connected to the control circuit 620 via wiring 621 and wiring 622. Wiring 621 is electrically connected to the positive electrodes of the multiple secondary batteries 616 via conductive plate 628, and wiring 622 is electrically connected to the negative electrodes of the multiple secondary batteries 616 via conductive plate 614.
［二次電池の他の構造例］
二次電池の他の構造例について図２８及び図２９を用いて説明する。 [Other structural examples of secondary batteries]
Another structural example of the secondary battery will be described with reference to FIGS.
図２８Ａに示す二次電池９１３は、筐体９３０の内部に端子９５１と端子９５２が設けられた捲回体９５０を有する。捲回体９５０は、筐体９３０の内部で電解液中に浸される。端子９５２は、筐体９３０に接し、端子９５１は、絶縁材などを用いることにより筐体９３０に接していない。なお、図２８Ａでは、便宜のため、筐体９３０を分離して図示しているが、実際は、捲回体９５０が筐体９３０に覆われ、端子９５１及び端子９５２が筐体９３０の外に延在している。筐体９３０としては、金属材料（例えばアルミニウムなど）又は金属材料と樹脂材料との積層体を用いることができる。 The secondary battery 913 shown in FIG. 28A has a wound body 950 with terminals 951 and 952 provided inside the housing 930. The wound body 950 is immersed in an electrolyte inside the housing 930. The terminal 952 contacts the housing 930, and the terminal 951 does not contact the housing 930 by using an insulating material or the like. Note that in FIG. 28A, the housing 930 is shown separated for convenience, but in reality, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (such as aluminum) or a laminate of a metal material and a resin material.
なお、図２８Ｂに示すように、図２８Ａに示す筐体９３０を複数の材料によって形成してもよい。例えば、図２８Ｂに示す二次電池９１３は、筐体９３０ａと筐体９３０ｂが貼り合わされており、筐体９３０ａ及び筐体９３０ｂで囲まれた領域に捲回体９５０が設けられている。 As shown in FIG. 28B, the housing 930 shown in FIG. 28A may be formed from a plurality of materials. For example, the secondary battery 913 shown in FIG. 28B has housings 930a and 930b bonded together, and a wound body 950 is provided in the area surrounded by the housings 930a and 930b.
筐体９３０ａとしては、金属材料または金属材料と有機樹脂との積層体を用いることができる。特に、アンテナが形成される面に有機樹脂などの絶縁材料を用いることにより、二次電池９１３による電界の遮蔽を抑制できる。なお、筐体９３０ａによる電界の遮蔽が小さければ、筐体９３０ａの内部にアンテナを設けてもよい。筐体９３０ｂとしては、例えば金属材料金属材料または金属材料と有機樹脂との積層体を用いることができる。 The housing 930a can be made of a metal material or a laminate of a metal material and an organic resin. In particular, by using an insulating material such as an organic resin on the surface on which the antenna is formed, it is possible to suppress shielding of the electric field by the secondary battery 913. Note that if the shielding of the electric field by the housing 930a is small, the antenna may be provided inside the housing 930a. The housing 930b can be made of, for example, a metal material or a laminate of a metal material and an organic resin.
さらに、捲回体９５０の構造について図２８Ｃに示す。捲回体９５０は、負極９３１と、正極９３２と、セパレータ９３３と、を有する。捲回体９５０は、セパレータ９３３を挟んで負極９３１と、正極９３２が重なり合って積層され、該積層シートを捲回させた捲回体である。なお、負極９３１と、正極９３２と、セパレータ９３３と、の積層を、さらに複数重ねてもよい。 Furthermore, the structure of the wound body 950 is shown in FIG. 28C. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the separator 933 in between, and the laminated sheet is wound. Note that the stack of the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked multiple times.
また、図２９に示すような捲回体９５０ａを有する二次電池９１３としてもよい。図２９Ａに示す捲回体９５０ａは、負極９３１と、正極９３２と、セパレータ９３３と、を有する。負極９３１は負極活物質層９３１ａを有する。正極９３２は正極活物質層９３２ａを有する。 Also, a secondary battery 913 having a wound body 950a as shown in FIG. 29 may be used. The wound body 950a shown in FIG. 29A has a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 has a negative electrode active material layer 931a. The positive electrode 932 has a positive electrode active material layer 932a.
本発明の一態様である正極活物質１００を正極９３２に用いることで、高容量、且つ、放電容量が高く、且つ、サイクル特性に優れた二次電池９１３とすることができる。 By using the positive electrode active material 100 of one embodiment of the present invention for the positive electrode 932, a secondary battery 913 with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.
セパレータ９３３は、負極活物質層９３１ａ及び正極活物質層９３２ａよりも広い幅を有し、負極活物質層９３１ａ及び正極活物質層９３２ａと重畳するように捲回されている。また正極活物質層９３２ａよりも負極活物質層９３１ａの幅が広いことが安全性の点で好ましい。またこのような形状の捲回体９５０ａは安全性及び生産性がよく好ましい。 The separator 933 has a width wider than the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap the negative electrode active material layer 931a and the positive electrode active material layer 932a. From the viewpoint of safety, it is preferable that the width of the negative electrode active material layer 931a is wider than that of the positive electrode active material layer 932a. Furthermore, a wound body 950a having such a shape is preferable because of its good safety and productivity.
図２９Ｂに示すように、負極９３１は、超音波接合、溶接、または圧着により端子９５１と電気的に接続される。端子９５１は端子９１１ａと電気的に接続される。また正極９３２は、超音波接合、溶接、または圧着により端子９５２と電気的に接続される。端子９５２は端子９１１ｂと電気的に接続される。 As shown in FIG. 29B, the negative electrode 931 is electrically connected to a terminal 951 by ultrasonic bonding, welding, or crimping. The terminal 951 is electrically connected to a terminal 911a. The positive electrode 932 is electrically connected to a terminal 952 by ultrasonic bonding, welding, or crimping. The terminal 952 is electrically connected to a terminal 911b.
図２９Ｃに示すように、筐体９３０により捲回体９５０ａ及び電解液が覆われ、二次電池９１３となる。筐体９３０には安全弁、過電流保護素子等を設けることが好ましい。安全弁は、電池破裂を防止するため、筐体９３０の内部が所定の内圧になると開放する弁である。 As shown in FIG. 29C, the wound body 950a and the electrolyte are covered by the housing 930 to form the secondary battery 913. It is preferable to provide the housing 930 with a safety valve, an overcurrent protection element, and the like. The safety valve is a valve that opens when the inside of the housing 930 reaches a certain internal pressure to prevent the battery from exploding.
図２９Ｂに示すように二次電池９１３は複数の捲回体９５０ａを有していてもよい。複数の捲回体９５０ａを用いることで、より放電容量の大きい二次電池９１３とすることができる。図２９Ｂ及び図２９Ｃに示す二次電池９１３の他の要素は、図２８Ａ及び図２８Ｂに示す二次電池９１３の記載を参照することができる。 As shown in FIG. 29B, the secondary battery 913 may have multiple wound bodies 950a. By using multiple wound bodies 950a, the secondary battery 913 can have a larger discharge capacity. For other elements of the secondary battery 913 shown in FIGS. 29B and 29C, refer to the description of the secondary battery 913 shown in FIGS. 28A and 28B.
＜ラミネート型二次電池＞
次に、ラミネート型の二次電池の例について、外観図の一例を図３０Ａ及び図３０Ｂに示す。図３０Ａ及び図３０Ｂに示すように、ラミネート型の二次電池５００は、正極５０３、負極５０６、セパレータ５０７、外装体５０９、正極リード電極５１０、及び負極リード電極５１１を有する。 <Laminated secondary battery>
Next, an example of an external view of a laminated secondary battery is shown in Figures 30A and 30B. As shown in Figures 30A and 30B, a laminated secondary battery 500 has a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.
図３０Ａには、正極５０３及び負極５０６の外観図を示す。正極５０３は正極集電体５０１を有し、正極活物質層５０２は正極集電体５０１の表面に形成されている。また、正極５０３は正極集電体５０１が一部露出する領域（以下、タブ領域という）を有する。負極５０６は負極集電体５０４を有し、負極活物質層５０５は負極集電体５０４の表面に形成されている。また、負極５０６は負極集電体５０４が一部露出する領域、すなわちタブ領域を有する。なお、正極５０３及び負極５０６が有するタブ領域の面積または形状は、図３０Ａに示す例に限られない。 FIG. 30A shows the external view of the positive electrode 503 and the negative electrode 506. The positive electrode 503 has a positive electrode collector 501, and the positive electrode active material layer 502 is formed on the surface of the positive electrode collector 501. The positive electrode 503 also has a region where the positive electrode collector 501 is partially exposed (hereinafter referred to as a tab region). The negative electrode 506 has a negative electrode collector 504, and the negative electrode active material layer 505 is formed on the surface of the negative electrode collector 504. The negative electrode 506 also has a region where the negative electrode collector 504 is partially exposed, that is, a tab region. Note that the area or shape of the tab region of the positive electrode 503 and the negative electrode 506 is not limited to the example shown in FIG. 30A.
＜ラミネート型二次電池の作製方法＞
図３０Ａに外観図を示すラミネート型の二次電池５００の作製方法の一例について、図３１Ａ乃至図３１Ｃを用いて説明する。 <Method of manufacturing laminated secondary battery>
An example of a method for manufacturing the laminated secondary battery 500 whose external view is shown in FIG. 30A will be described with reference to FIGS. 31A to 31C.
まず、図３１Ａに示すように正極５０３、及び負極５０６を用意する。次いで図３１Ｂのように、負極５０６、セパレータ５０７及び正極５０３を積層する。ここでは負極５０６を５組、正極５０３を４組使用する例を示す。これは、負極５０６と、セパレータ５０７と、正極５０３と、からなる積層体とも呼べる。次に、正極５０３のタブ領域同士の接合と、最表面の正極５０３のタブ領域への正極リード電極５１０の接合を行う。接合には、例えば超音波溶接等を用いればよい。同様に、負極５０６のタブ領域同士の接合と、最表面の負極５０６のタブ領域への負極リード電極５１１の接合を行う。 First, prepare a positive electrode 503 and a negative electrode 506 as shown in FIG. 31A. Next, stack the negative electrode 506, the separator 507, and the positive electrode 503 as shown in FIG. 31B. Here, an example is shown in which five sets of negative electrodes 506 and four sets of positive electrodes 503 are used. This can also be called a stack consisting of the negative electrode 506, the separator 507, and the positive electrode 503. Next, the tab regions of the positive electrodes 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode 503. For example, ultrasonic welding or the like may be used for the joining. Similarly, the tab regions of the negative electrodes 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode 506.
次に、図３１Ｃに示すように、外装体５０９上に、上記の積層体を配置する。 Next, as shown in Figure 31C, the above laminate is placed on the exterior body 509.
次に、図３１Ｃに示すように、外装体５０９を破線で示した部分で折り曲げる。その後、外装体５０９の外周部を接合する。接合には例えば熱圧着等を用いればよい。この時、後に電解液を入れることができるように、外装体５０９の一部（または一辺）に接合されない領域（以下、導入口という）を設ける。 Next, as shown in FIG. 31C, the exterior body 509 is folded at the portion indicated by the dashed line. After that, the outer periphery of the exterior body 509 is joined. For the joining, for example, thermocompression bonding or the like may be used. At this time, an area (hereinafter referred to as an inlet) that is not joined is provided on a part (or one side) of the exterior body 509 so that the electrolyte can be introduced later.
次に、外装体５０９に設けられた導入口から、電解液を外装体５０９の内側へ導入する。電解液の導入は、減圧雰囲気下、或いは不活性雰囲気下で行うことが好ましい。そして最後に、導入口を接合する。このようにして、ラミネート型の二次電池５００を作製することができる。 Next, the electrolyte is introduced into the inside of the exterior body 509 through an inlet provided in the exterior body 509. The electrolyte is preferably introduced under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is joined. In this manner, the laminated secondary battery 500 can be produced.
本発明の一態様である正極活物質１００を正極５０３に用いることで、高容量、且つ、放電容量が高く、且つ、サイクル特性に優れた二次電池５００とすることができる。 By using the positive electrode active material 100 of one embodiment of the present invention for the positive electrode 503, a secondary battery 500 can be obtained that has a high capacity, a high discharge capacity, and excellent cycle characteristics.
本実施の形態は、他の実施の形態又は実施例と適宜組み合わせて用いることができる。 This embodiment can be used in appropriate combination with other embodiments or examples.
（実施の形態５）
本実施の形態では、本発明の一態様の二次電池を有する車両の例を示す。本発明の一態様である二次電池は発火しづらく好ましい。 (Embodiment 5)
In this embodiment, an example of a vehicle including a secondary battery according to one embodiment of the present invention will be described. The secondary battery according to one embodiment of the present invention is preferable because it is unlikely to catch fire.
本発明の一態様である二次電池を車両に搭載すると、ハイブリッド車（ＨＶ）、電気自動車（ＥＶ）、又はプラグインハイブリッド車（ＰＨＶ）等の次世代クリーンエネルギー自動車を実現できる。また、農業機械、電動アシスト自転車を含む原動機付自転車、自動二輪車、電動車椅子、電動カート、船舶、潜水艦、航空機、ロケット、人工衛星、宇宙探査機、惑星探査機、または宇宙船に二次電池を搭載することもできる。本発明の一態様の二次電池は高容量の二次電池とすることができる。そのため本発明の一態様の二次電池は、小型化、軽量化に適しており、輸送用車両に好適に用いることができる。 When a secondary battery according to one embodiment of the present invention is installed in a vehicle, it is possible to realize a next-generation clean energy vehicle such as a hybrid vehicle (HV), an electric vehicle (EV), or a plug-in hybrid vehicle (PHV). The secondary battery can also be installed in agricultural machinery, mopeds including electrically assisted bicycles, motorcycles, electric wheelchairs, electric carts, ships, submarines, aircraft, rockets, artificial satellites, space probes, planetary probes, or spacecraft. The secondary battery according to one embodiment of the present invention can be a high-capacity secondary battery. Therefore, the secondary battery according to one embodiment of the present invention is suitable for miniaturization and weight reduction, and can be suitably used in transportation vehicles.
図３２Ａ乃至図３２Ｄにおいて、本発明の一態様を用いた輸送用車両を例示する。図３２Ａに示す自動車２００１は、走行のための動力源として電気モータを用いる電気自動車である。または、走行のための動力源として電気モータとエンジンを適宜選択して用いることが可能なハイブリッド自動車である。二次電池を車両に搭載する場合、実施の形態４で示した二次電池の一例を一箇所または複数個所に設置する。図３２Ａに示す自動車２００１は、電池パック２２００を有し、電池パック２２００は、複数の二次電池を接続させた二次電池モジュールを有する。さらに二次電池モジュールに電気的に接続する充電制御装置を有すると好ましい。 Figures 32A to 32D show an example of a transportation vehicle using one embodiment of the present invention. The automobile 2001 shown in Figure 32A is an electric automobile that uses an electric motor as a power source for running. Or, it is a hybrid automobile that can appropriately select and use an electric motor and an engine as a power source for running. When a secondary battery is mounted on the vehicle, an example of the secondary battery shown in embodiment 4 is installed in one or more locations. The automobile 2001 shown in Figure 32A has a battery pack 2200, and the battery pack 2200 has a secondary battery module to which multiple secondary batteries are connected. It is further preferable that the automobile has a charging control device that is electrically connected to the secondary battery module.
また、自動車２００１は、自動車２００１が有する二次電池にプラグイン方式または非接触給電方式等により外部の充電設備から電力供給を受けて、充電することができる。充電に際しては、充電方法またはコネクタの規格等はＣＨＡｄｅＭＯ（登録商標）またはコンボ等の所定の方式で適宜行えばよい。充電設備は、商用施設に設けられた充電ステーションでもよく、また家庭の電源であってもよい。例えば、プラグイン技術によって、外部からの電力供給により自動車２００１に搭載された蓄電装置を充電することができる。充電は、ＡＣＤＣコンバータ等の変換装置を介して、交流電力を直流電力に変換して行うことができる。 In addition, automobile 2001 can charge the secondary battery of automobile 2001 by receiving power supply from an external charging facility using a plug-in method or a contactless power supply method. When charging, the charging method or connector standard may be a predetermined method such as CHAdeMO (registered trademark) or Combo. The charging facility may be a charging station provided in a commercial facility, or may be a home power source. For example, a power storage device mounted on automobile 2001 can be charged by an external power supply using plug-in technology. Charging can be performed by converting AC power to DC power via a conversion device such as an AC-DC converter.
また、図示しないが、受電装置を車両に搭載し、地上の送電装置から電力を非接触で供給して充電することもできる。この非接触給電方式の場合には、道路または外壁に送電装置を組み込むことで、停車中に限らず走行中に充電を行うこともできる。また、この非接触給電の方式を利用して、２台の車両同士で電力の送受電を行ってもよい。さらに、車両の外装部に太陽電池を設け、停車時または走行時に二次電池の充電を行ってもよい。このような非接触での電力の供給には、電磁誘導方式または磁界共鳴方式を用いることができる。 Although not shown, a power receiving device can be mounted on the vehicle and charging can be performed by supplying power contactlessly from a ground power transmitting device. In the case of this contactless power supply method, by incorporating a power transmitting device into the road or an exterior wall, charging can be performed not only while the vehicle is stopped but also while it is moving. This contactless power supply method can also be used to transmit and receive power between two vehicles. Furthermore, solar cells can be provided on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped or moving. An electromagnetic induction method or a magnetic field resonance method can be used for such contactless power supply.
図３２Ｂは、輸送用車両の一例として電気により制御するモータを有した大型の輸送車２００２を示している。輸送車２００２は、電池パック２２０１を有し、電池パック２２０１は、複数の二次電池を接続させた二次電池モジュールを有する。輸送車２００２の二次電池モジュールは、例えば公称電圧３．０Ｖ以上５．０Ｖ以下の二次電池を４個セルユニットとし、４８セルを直列に接続した１７０Ｖを最大電圧とする。電池パック２２０１の二次電池モジュールを構成する二次電池の数などが違う以外は、図３２Ａと同様な機能を備えているので説明は省略する。 Figure 32B shows a large transport vehicle 2002 with an electrically controlled motor as an example of a transport vehicle. The transport vehicle 2002 has a battery pack 2201, which has a secondary battery module with multiple secondary batteries connected together. The secondary battery module of the transport vehicle 2002 is, for example, a four-cell unit of secondary batteries with a nominal voltage of 3.0V to 5.0V, with 48 cells connected in series for a maximum voltage of 170V. Other than the number of secondary batteries that make up the secondary battery module of the battery pack 2201, it has the same functions as Figure 32A, so a description will be omitted.
図３２Ｃは、一例として電気により制御するモータを有した大型の輸送車両２００３を示している。輸送車両２００３は、電池パック２２０２を有し、電池パック２２０２は、複数の二次電池を接続させた二次電池モジュールを有する。輸送車両２００３の二次電池モジュールは、例えば公称電圧３．０Ｖ以上５．０Ｖ以下の二次電池を百個以上直列に接続した６００Ｖを最大電圧とする。従って、特性バラツキの小さい二次電池が求められる。実施の形態１、２等で説明した正極活物質１００を正極に用いた二次電池を用いることで、安定した電池特性を有する二次電池を製造することができ、歩留まりの観点から低コストで大量生産が可能である。 Figure 32C shows, as an example, a large transport vehicle 2003 having an electrically controlled motor. The transport vehicle 2003 has a battery pack 2202, which has a secondary battery module in which multiple secondary batteries are connected. The secondary battery module of the transport vehicle 2003 has a maximum voltage of 600V, for example, with more than 100 secondary batteries with a nominal voltage of 3.0V to 5.0V connected in series. Therefore, a secondary battery with small characteristic variations is required. By using a secondary battery using the positive electrode active material 100 described in embodiments 1 and 2 as the positive electrode, a secondary battery with stable battery characteristics can be manufactured, and mass production at low cost from the viewpoint of yield is possible.
図３２Ｄは、一例として燃料を燃焼するエンジンを有した航空機２００４を示している。図３２Ｄに示す航空機２００４は、離着陸用の車輪を有しているため、輸送車両の一部とも言え、複数の二次電池を接続させて二次電池モジュールを構成し、二次電池モジュールと充電制御装置とを含む電池パック２２０３を有している。 As an example, FIG. 32D shows an aircraft 2004 having an engine that burns fuel. The aircraft 2004 shown in FIG. 32D has wheels for takeoff and landing, and can therefore be considered part of a transportation vehicle. It has a battery pack 2203 that includes a secondary battery module formed by connecting multiple secondary batteries and a charging control device.
航空機２００４の二次電池モジュールは、例えば４Ｖの二次電池を８個直列に接続した３２Ｖを最大電圧とする。電池パック２２０３の二次電池モジュールを構成する二次電池の数などが異なる以外は、図３２Ａと同様な機能を備えているので説明は省略する。 The secondary battery module of the aircraft 2004 has a maximum voltage of 32 V, for example, with eight 4 V secondary batteries connected in series. Other than the number of secondary batteries constituting the secondary battery module of the battery pack 2203, it has the same functions as those in FIG. 32A, so a description thereof will be omitted.
図３２Ｅは、一例として二次電池２２０４を備えた人工衛星２００５を示している。人工衛星２００５は極低温の宇宙空間で使用されるため、低温耐性に優れた本発明の一態様である二次電池２２０４を備えることが好ましい。また、人工衛星２００５の内部において、保温部材に覆われた状態で二次電池２２０４が搭載されることがさらに好ましい。 Figure 32E shows an example of an artificial satellite 2005 equipped with a secondary battery 2204. Since the artificial satellite 2005 is used in the extremely low temperature of outer space, it is preferable that the artificial satellite 2005 is equipped with a secondary battery 2204, which is an embodiment of the present invention and has excellent low temperature resistance. It is further preferable that the secondary battery 2204 is mounted inside the artificial satellite 2005 while being covered with a heat-retaining material.
本実施の形態は、他の実施の形態又は実施例と適宜組み合わせて用いることができる。 This embodiment can be used in appropriate combination with other embodiments or examples.
（実施の形態６）
本実施の形態では、二次電池を車両に搭載する一例として、二輪車、自転車に本発明の一態様であるリチウムイオン電池を搭載する例を示す。 (Embodiment 6)
In this embodiment, as an example of mounting a secondary battery on a vehicle, an example in which a lithium ion battery according to one embodiment of the present invention is mounted on a two-wheeled vehicle or a bicycle will be described.
図３３Ａは、本発明の一態様の二次電池を用いた電動自転車の一例である。電動自転車８７００は、蓄電装置８７０２に本発明の一態様の二次電池８７０１を適用することができ、二次電池からの電力は運転者をアシストするモータへ供給される。蓄電装置８７０２は、持ち運びができるとよく、図３３Ｂに自転車から取り外した状態を示している。また、蓄電装置８７０２は、バッテリ残量などを表示できる表示部８７０３を有するとよい。また蓄電装置８７０２は、二次電池の充電制御または異常検知が可能な制御回路８７０４を有するとよい。制御回路８７０４は、二次電池８７０１の正極及び負極と電気的に接続されている。また、本発明の一態様の二次電池を搭載した電動自転車は高電圧で動作しても安全である。 FIG. 33A is an example of an electric bicycle using a secondary battery of one embodiment of the present invention. In an electric bicycle 8700, a secondary battery 8701 of one embodiment of the present invention can be applied to a power storage device 8702, and power from the secondary battery is supplied to a motor that assists a rider. The power storage device 8702 is preferably portable, and FIG. 33B shows the power storage device 8702 removed from the bicycle. The power storage device 8702 may have a display unit 8703 that can display the remaining battery level, etc. The power storage device 8702 may also have a control circuit 8704 that can control charging of the secondary battery or detect an abnormality. The control circuit 8704 is electrically connected to the positive and negative electrodes of the secondary battery 8701. An electric bicycle equipped with a secondary battery of one embodiment of the present invention is safe even when operated at a high voltage.
図３３Ｃは、本発明の一態様の二次電池を用いた二輪車の一例である。図３３Ｃに示すスクータ８６００は、蓄電装置８６０２、サイドミラー８６０１、方向指示灯８６０３を備える。蓄電装置８７０２に本発明の一態様の二次電池８７０１を適用することができ、二次電池からの電力は、方向指示灯８６０３へ供給される。また、本発明の一態様の二次電池を搭載した二輪車は高電圧で動作しても安全である。 FIG. 33C is an example of a two-wheeled vehicle using the secondary battery of one embodiment of the present invention. A scooter 8600 shown in FIG. 33C includes a power storage device 8602, a side mirror 8601, and a turn signal light 8603. The secondary battery 8701 of one embodiment of the present invention can be applied to the power storage device 8702, and power from the secondary battery is supplied to the turn signal light 8603. In addition, a two-wheeled vehicle equipped with the secondary battery of one embodiment of the present invention is safe even when operated at high voltage.
また、図３３Ｃに示すスクータ８６００は、座席下収納８６０４に、蓄電装置８６０２を収納することができる。蓄電装置８６０２は、座席下収納８６０４が小型であっても、座席下収納８６０４に収納することができる。 Furthermore, the scooter 8600 shown in FIG. 33C can store the power storage device 8602 in the under-seat storage 8604. The power storage device 8602 can be stored in the under-seat storage 8604 even if the under-seat storage 8604 is small.
本実施の形態は、他の実施の形態又は実施例と適宜組み合わせて用いることができる。 This embodiment can be used in appropriate combination with other embodiments or examples.
（実施の形態７）
本実施の形態では、本発明の一態様である二次電池を電子機器に実装する例について説明する。本発明の一態様である二次電池は発火しづらく好ましい。二次電池を実装する電子機器として、例えば、テレビジョン装置（テレビ、又はテレビジョン受信機ともいう）、コンピュータ用などのモニタ、デジタルカメラ、デジタルビデオカメラ、デジタルフォトフレーム、携帯電話機（携帯電話、携帯電話装置ともいう）、携帯型ゲーム機、携帯情報端末、音響再生装置、パチンコ機などの大型ゲーム機などが挙げられる。携帯情報端末としてはノート型パーソナルコンピュータ、タブレット型端末、電子書籍端末、携帯電話機などがある。 (Seventh embodiment)
In this embodiment, an example of mounting a secondary battery according to one embodiment of the present invention in an electronic device will be described. The secondary battery according to one embodiment of the present invention is preferable because it is unlikely to ignite. Examples of electronic devices in which a secondary battery is mounted include television devices (also called televisions or television receivers), monitors for computers, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game machines, portable information terminals, audio playback devices, and large game machines such as pachinko machines. Examples of portable information terminals include notebook personal computers, tablet terminals, e-book terminals, and mobile phones.
図３４Ａは、携帯電話機の一例を示している。携帯電話機２１００は、筐体２１０１に組み込まれた表示部２１０２の他、操作ボタン２１０３、外部接続ポート２１０４、スピーカ２１０５、マイク２１０６などを備えている。なお、携帯電話機２１００は、二次電池２１０７を有している。また、本発明の一態様の二次電池２１０７を搭載した携帯電話機は高電圧で動作しても安全である。 Figure 34A shows an example of a mobile phone. The mobile phone 2100 includes a display portion 2102 built into a housing 2101, operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. Note that the mobile phone 2100 includes a secondary battery 2107. A mobile phone equipped with the secondary battery 2107 of one embodiment of the present invention is safe even when operated at high voltage.
携帯電話機２１００は、移動電話、電子メール、文章閲覧及び作成、音楽再生、インターネット通信、コンピュータゲームなどの種々のアプリケーションを実行することができる。 The mobile phone 2100 can execute various applications such as mobile phone calls, e-mail, text browsing and creation, music playback, Internet communication, and computer games.
操作ボタン２１０３は、時刻設定のほか、電源のオン、オフ動作、無線通信のオン、オフ動作、マナーモードの実行及び解除、省電力モードの実行及び解除など、様々な機能を持たせることができる。例えば、携帯電話機２１００に組み込まれたオペレーティングシステムにより、操作ボタン２１０３の機能を自由に設定することもできる。 The operation button 2103 can have various functions, such as time setting, power on/off operation, wireless communication on/off operation, silent mode and power saving mode. For example, the functions of the operation button 2103 can be freely set by an operating system built into the mobile phone 2100.
また、携帯電話機２１００は、通信規格化された近距離無線通信を実行することが可能である。例えば無線通信可能なヘッドセットと相互通信することによって、ハンズフリーで通話することもできる。 The mobile phone 2100 is also capable of performing standardized short-range wireless communication. For example, it can communicate with a wireless headset to enable hands-free calling.
また、携帯電話機２１００は、外部接続ポート２１０４を備え、他の情報端末とコネクタを介して直接データのやりとりを行うことができる。また外部接続ポート２１０４を介して充電を行うこともできる。なお、充電動作は外部接続ポート２１０４を介さずに無線給電により行ってもよい。 The mobile phone 2100 also includes an external connection port 2104, and can directly exchange data with other information terminals via a connector. Charging can also be performed via the external connection port 2104. Note that charging may also be performed by wireless power supply without using the external connection port 2104.
また、携帯電話機２１００は、センサを有することが好ましい。センサとしては、例えば、指紋センサ、脈拍センサ、体温センサ等の人体センサ、タッチセンサ、加圧センサ、または加速度センサ等が搭載されることが好ましい。 Furthermore, it is preferable that the mobile phone 2100 has a sensor. As the sensor, it is preferable that a fingerprint sensor, a pulse sensor, a body temperature sensor or other human body sensor, a touch sensor, a pressure sensor, an acceleration sensor, or the like is installed.
図３４Ｂは、複数のローター２３０２を有する無人航空機２３００である。無人航空機２３００はドローンと呼ばれることもある。無人航空機２３００は、本発明の一態様である二次電池２３０１と、カメラ２３０３と、アンテナ（図示しない）を有する。無人航空機２３００はアンテナを介して遠隔操作することができる。また、本発明の一態様の二次電池２３０１を搭載した無人航空機２３００は高電圧で動作しても安全である。さらに、長期間に渡って長時間の安全な使用ができる。 Figure 34B shows an unmanned aerial vehicle 2300 having multiple rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 has a secondary battery 2301 according to one embodiment of the present invention, a camera 2303, and an antenna (not shown). The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. Furthermore, the unmanned aerial vehicle 2300 equipped with the secondary battery 2301 according to one embodiment of the present invention is safe even when operated at high voltage. Furthermore, it can be used safely for a long period of time.
図３４Ｃは、ロボットの一例を示している。図３４Ｃに示すロボット６４００は、二次電池６４０９、照度センサ６４０１、マイクロフォン６４０２、上部カメラ６４０３、スピーカ６４０４、表示部６４０５、下部カメラ６４０６及び障害物センサ６４０７、移動機構６４０８、演算装置等を備える。 Figure 34C shows an example of a robot. The robot 6400 shown in Figure 34C includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a movement mechanism 6408, a computing device, etc.
マイクロフォン６４０２は、使用者の話し声及び環境音等を検知する機能を有する。また、スピーカ６４０４は、音声を発する機能を有する。ロボット６４００は、マイクロフォン６４０２及びスピーカ６４０４を用いて、使用者とコミュニケーションをとることが可能である。 The microphone 6402 has a function of detecting the user's voice and environmental sounds. The speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.
表示部６４０５は、種々の情報の表示を行う機能を有する。ロボット６４００は、使用者の望みの情報を表示部６４０５に表示することが可能である。表示部６４０５は、タッチパネルを搭載していてもよい。また、表示部６４０５は取り外しのできる情報端末であっても良く、ロボット６４００の定位置に設置することで、充電及びデータの受け渡しを可能とする。 The display unit 6405 has a function of displaying various information. The robot 6400 can display information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a removable information terminal, and by installing it in a fixed position on the robot 6400, charging and data transfer are possible.
上部カメラ６４０３及び下部カメラ６４０６は、ロボット６４００の周囲を撮像する機能を有する。また、障害物センサ６４０７は、移動機構６４０８を用いてロボット６４００が前進する際の進行方向における障害物の有無を察知することができる。ロボット６４００は、上部カメラ６４０３、下部カメラ６４０６及び障害物センサ６４０７を用いて、周囲の環境を認識し、安全に移動することが可能である。 The upper camera 6403 and the lower camera 6406 have the function of capturing images of the surroundings of the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the moving mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.
ロボット６４００は、その内部領域に本発明の一態様に係る二次電池６４０９と、半導体装置または電子部品を備える。また、本発明の一態様の二次電池６４０９を搭載したロボットは高電圧で動作しても安全である。さらに、長期間に渡って長時間の安全な使用ができる。 The robot 6400 includes a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or electronic component in its internal area. Furthermore, a robot equipped with the secondary battery 6409 according to one embodiment of the present invention is safe even when operated at high voltage. Furthermore, it can be used safely for a long period of time.
図３４Ｄは、携帯用扇風機の一例を示している。図３４Ｄに示す携帯用扇風機６２００は、本発明の一態様である二次電池６２０９、操作ボタン６２０５、ファン６２０２、外部接続ポート６２０４などを有し、二次電池６２０９は筐体６２０１に収容されている。携帯用扇風機６２００は、二次電池６２０９から供給された電力によりモータを動作させてファン６２０２を回転させていることができ、当該二次電池６２０９は外部接続ポート６２０４を介して充電を行うことができる。二次電池６２０９は、円筒型の二次電池の例を示しているが特に形状は限定されない。また、本発明の一態様の二次電池６２０９を搭載した携帯用扇風機６２００は高電圧で動作しても安全である。さらに、長期間に渡って長時間の安全な使用ができる。 FIG. 34D illustrates an example of a portable electric fan. The portable electric fan 6200 illustrated in FIG. 34D includes a secondary battery 6209 according to one embodiment of the present invention, an operation button 6205, a fan 6202, an external connection port 6204, and the like, and the secondary battery 6209 is housed in a housing 6201. The portable electric fan 6200 can rotate the fan 6202 by operating a motor using power supplied from the secondary battery 6209, and the secondary battery 6209 can be charged via the external connection port 6204. The secondary battery 6209 is an example of a cylindrical secondary battery, but the shape is not particularly limited. Furthermore, the portable electric fan 6200 equipped with the secondary battery 6209 according to one embodiment of the present invention is safe even when operated at a high voltage. Furthermore, it can be used safely for a long period of time.
図３４Ｅは、掃除ロボットの一例を示している。掃除ロボット６３００は、筐体６３０１上面に配置された表示部６３０２、側面に配置された複数のカメラ６３０３、ブラシ６３０４、操作ボタン６３０５、二次電池６３０６、各種センサなどを有する。図示されていないが、掃除ロボット６３００には、タイヤ、吸い込み口等が備えられている。掃除ロボット６３００は自走し、ゴミ６３１０を検知し、筐体６３０１下面に設けられた吸い込み口からゴミ６３１０を吸引することができる。 Figure 34E shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 arranged on the top surface of the housing 6301, multiple cameras 6303 arranged on the side, a brush 6304, an operation button 6305, a secondary battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is equipped with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust 6310 from a suction port provided on the bottom surface of the housing 6301.
掃除ロボット６３００は、カメラ６３０３が撮影した画像を解析し、壁、家具または段差などの障害物の有無を判断することができる。また、画像解析により、配線などブラシ６３０４に絡まりそうな物体を検知した場合は、ブラシ６３０４の回転を止めることができる。掃除ロボット６３００は、その内部領域に本発明の一態様に係る二次電池６３０６と、半導体装置または電子部品を備える。また、本発明の一態様の二次電池６２０９を搭載した掃除ロボット６３００は高電圧で動作しても安全である。さらに、長期間に渡って長時間の安全な使用ができる。 The cleaning robot 6300 can analyze the image captured by the camera 6303 and determine whether or not there is an obstacle such as a wall, furniture, or a step. Furthermore, if an object that may become entangled in the brush 6304, such as a wire, is detected by image analysis, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 includes a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or electronic component in its internal area. Furthermore, the cleaning robot 6300 equipped with the secondary battery 6209 according to one embodiment of the present invention is safe even when operated at a high voltage. Furthermore, it can be used safely for a long period of time.
本実施の形態は、他の実施の形態又は実施例と適宜組み合わせて用いることができる。 This embodiment can be used in appropriate combination with other embodiments or examples.
＜正極活物質の製造＞
図１８に示す作製方法を参照しながら本実施例で作製した正極活物質について説明する。 <Production of Positive Electrode Active Material>
The positive electrode active material produced in this example will be described with reference to the production method shown in FIG.
図１８ＡのステップＳ１４のＬｉＣｏＯ２として、遷移金属Ｍとしてコバルトを有し、添加元素を特に有さない市販のコバルト酸リチウム（日本化学工業株式会社製、セルシードＣ−１０Ｎ）を用意した。セルシードＣ−１０ＮのＧＤ−ＭＳ測定結果は、上記実施の形態１の材料Ｓｍ−３の範囲を満たした。本実施例では、添加元素であるマグネシウムに着目したため、ステップＳ１５の初期加熱を行なわなかった。 As LiCoO2 in step S14 in Fig. 18A, a commercially available lithium cobalt oxide (CellSeed C-10N, manufactured by Nippon Chemical Industry Co., Ltd.) having cobalt as the transition metal M and no particular additive element was prepared. The GD-MS measurement result of CellSeed C-10N satisfied the range of material Sm-3 in the above-mentioned embodiment 1. In this example, since attention was paid to magnesium, which is an additive element, the initial heating in step S15 was not performed.
図１８Ｂで示したステップＳ２１に従って、Ｆ源としてＬｉＦを用意し、Ｍｇ源としてＭｇＦ２を用意した。ＬｉＦとＭｇＦ２のｍｏｌ比が、ＬｉＦ：ＭｇＦ２＝１：３となるよう秤量し、溶媒として脱水アセトンを加えて湿式で混合及び粉砕してＡ１源とした。 18B, LiF was prepared as an F source, and MgF2 was prepared as an Mg source. LiF and MgF2 were weighed out so that the molar ratio of LiF: MgF2 was 1:3, and dehydrated acetone was added as a solvent to wet mix and pulverize to obtain the A1 source.
次に図１８ＡのステップＳ３１及びステップＳ３２に従って、Ａ１源を添加して混合物９０３を得た。ステップＳ３１として、Ａ１源が有するマグネシウムの原子数が、コバルト酸リチウムが有するコバルトの原子数に対して０．１％となるように秤量して、コバルト酸リチウムと乾式で混合した。 Next, according to steps S31 and S32 of FIG. 18A, the A1 source was added to obtain a mixture 903. In step S31, the A1 source was weighed out so that the number of magnesium atoms contained in the A1 source was 0.1% of the number of cobalt atoms contained in the lithium cobalt oxide, and was dry-mixed with the lithium cobalt oxide.
次に図１８ＡのステップＳ３３として、混合物９０３を加熱した。加熱条件は、８５０℃及び６０時間とした。加熱の際、混合物９０３をいれたるつぼに蓋を配置した。るつぼ及び蓋はアルミナ製のものを用いた。るつぼ内が酸素を有する雰囲気となるように、加熱に用いた炉において、酸素を１０Ｌ／ｍｉｎの流量で供給した（フロー）。加熱により、マグネシウム及びフッ素を有するコバルト酸リチウムとして、サンプル１−１を得た（ステップＳ３４の正極活物質１００に相当）。本実施例では添加元素であるマグネシウムに着目したため、Ａ２源は添加しなかった。 Next, in step S33 of FIG. 18A, the mixture 903 was heated. The heating conditions were 850° C. and 60 hours. During heating, a lid was placed on the crucible containing the mixture 903. The crucible and lid were made of alumina. In the furnace used for heating, oxygen was supplied at a flow rate of 10 L/min so that the inside of the crucible was an oxygen-containing atmosphere (flow). By heating, sample 1-1 was obtained as lithium cobalt oxide containing magnesium and fluorine (corresponding to the positive electrode active material 100 in step S34). In this example, the focus was on magnesium, which is an additive element, so no A2 source was added.
サンプル１−１の他に、サンプル１−２、サンプル１−３、サンプル１−４、サンプル１−５、及びサンプル１−６を作製した。サンプル１−２、サンプル１−３、サンプル１−４、サンプル１−５、及びサンプル１−６は、図１８Ｂで示したステップＳ２１におけるＡ１源のマグネシウム割合が、サンプル１−１と異なっている。 In addition to sample 1-1, samples 1-2, 1-3, 1-4, 1-5, and 1-6 were also prepared. Samples 1-2, 1-3, 1-4, 1-5, and 1-6 differ from sample 1-1 in the magnesium ratio of the A1 source in step S21 shown in FIG. 18B.
サンプル１−２は、Ａ１源が有するマグネシウムの原子数が、コバルト酸リチウムが有するコバルトの原子数に対して０．５％となるように秤量して、コバルト酸リチウムと乾式で混合したこと以外は、サンプル１−１と同じ条件で作製した。 Sample 1-2 was prepared under the same conditions as sample 1-1, except that the number of magnesium atoms in the A1 source was weighed out to be 0.5% of the number of cobalt atoms in the lithium cobalt oxide, and then dry-mixed with the lithium cobalt oxide.
サンプル１−３は、Ａ１源が有するマグネシウムの原子数が、コバルト酸リチウムが有するコバルトの原子数に対して１．０％となるように秤量して、コバルト酸リチウムと乾式で混合したこと以外は、サンプル１−１と同じ条件で作製した。 Sample 1-3 was prepared under the same conditions as sample 1-1, except that the number of magnesium atoms in the A1 source was weighed out to be 1.0% of the number of cobalt atoms in the lithium cobalt oxide, and then dry-mixed with the lithium cobalt oxide.
サンプル１−４は、Ａ１源が有するマグネシウムの原子数が、コバルト酸リチウムが有するコバルトの原子数に対して２．０％となるように秤量して、コバルト酸リチウムと乾式で混合したこと以外は、サンプル１−１と同じ条件で作製した。 Sample 1-4 was prepared under the same conditions as sample 1-1, except that the number of magnesium atoms in the A1 source was weighed out to be 2.0% of the number of cobalt atoms in the lithium cobalt oxide, and then dry-mixed with the lithium cobalt oxide.
サンプル１−５は、Ａ１源が有するマグネシウムの原子数が、コバルト酸リチウムが有するコバルトの原子数に対して３．０％となるように秤量して、コバルト酸リチウムと乾式で混合したこと以外は、サンプル１−１と同じ条件で作製した。 Sample 1-5 was prepared under the same conditions as sample 1-1, except that the number of magnesium atoms in the A1 source was weighed out to be 3.0% of the number of cobalt atoms in the lithium cobalt oxide, and then dry-mixed with the lithium cobalt oxide.
サンプル１−６は、Ａ１源が有するマグネシウムの原子数が、コバルト酸リチウムが有するコバルトの原子数に対して６．０％となるように秤量して、コバルト酸リチウムと乾式で混合したこと以外は、サンプル１−１と同じ条件で作製した。 Sample 1-6 was prepared under the same conditions as sample 1-1, except that the number of magnesium atoms in the A1 source was weighed out to be 6.0% of the number of cobalt atoms in the lithium cobalt oxide, and then dry-mixed with the lithium cobalt oxide.
＜比較正極活物質の作製＞
本実施例の比較例には、特に処理を行わないコバルト酸リチウム（日本化学工業株式会社製、セルシードＣ−１０Ｎ）を用意した。これをサンプル２とした。 <Preparation of Comparative Positive Electrode Active Material>
As a comparative example for this embodiment, lithium cobalt oxide (Cellseed C-10N, manufactured by Nippon Chemical Industry Co., Ltd.) that was not subjected to any particular treatment was prepared. This was designated as Sample 2.
下表にはサンプル１−１乃至サンプル１−６及びサンプル２の条件をまとめて示す。 The table below summarizes the conditions for Samples 1-1 to 1-6 and Sample 2.
Figure JPOXMLDOC01-appb-T000010
Figure JPOXMLDOC01-appb-T000010
＜粉体抵抗測定＞
サンプル１−２、サンプル１−３、サンプル１−６及びサンプル２について、粉体の体積抵抗率を測定した。 <Powder Resistance Measurement>
For Samples 1-2, 1-3, 1-6 and 2, the volume resistivity of the powder was measured.
粉体の体積抵抗率の測定方法として、実施の形態１の＜粉体抵抗測定＞において説明した方法を用いた。測定装置として、三菱化学アナリテック社製のＭＣＰ−ＰＤ５１を用いた。抵抗計は、それぞれ精度よく測定可能なレンジが異なるため、サンプルの抵抗率に応じて最適な抵抗計を選択した。また測定は、一般的な実験室環境（すなわち、１５℃以上３０℃以下の温度環境）で行った。 The method for measuring the volume resistivity of the powder was the method described in <Powder Resistance Measurement> in embodiment 1. The measurement device used was an MCP-PD51 manufactured by Mitsubishi Chemical Analytech Co., Ltd. As each resistance meter has a different range in which it can measure with high accuracy, the most suitable resistance meter was selected according to the resistivity of the sample. The measurements were also performed in a typical laboratory environment (i.e., a temperature environment of 15°C to 30°C).
各サンプルの粉体の体積抵抗率の測定として、粉体を測定部にセットし、１３ＭＰａ、２５ＭＰａ、３８ＭＰａ、５１ＭＰａ、及び６４ＭＰａのそれぞれの圧力条件において、粉体の電気抵抗と、粉体の体積と、を計測し、各サンプルの粉体の体積抵抗率を得た。結果を、図３５に示す。 To measure the volume resistivity of the powder of each sample, the powder was set in the measurement section, and the electrical resistance and volume of the powder were measured under pressure conditions of 13 MPa, 25 MPa, 38 MPa, 51 MPa, and 64 MPa, to obtain the volume resistivity of the powder of each sample. The results are shown in Figure 35.
図３５に示すように、マグネシウムを有するコバルト酸リチウムは、Ａ１源の混合量が多いほど、粉体抵抗が大きくなることが分かった。マグネシウムなどが表層部に位置し、正極活物質の粉体抵抗を高くしたと考えられる。具体的には、サンプル１−２の粉体における体積抵抗率は、６４ＭＰａの圧力において１．０×１０４Ω・ｃｍ以上であることがわかった。またサンプル１−３の粉体における体積抵抗率は、６４ＭＰａの圧力において１．０×１０６Ω・ｃｍ以上であることがわかった。またサンプル１−６の粉体における体積抵抗率は、６４ＭＰａの圧力において１．０×１０７Ω・ｃｍ以上であることがわかった。 As shown in FIG. 35, it was found that the powder resistance of lithium cobalt oxide containing magnesium increases with the amount of A1 source mixed. It is believed that magnesium and the like are located in the surface layer, which increases the powder resistance of the positive electrode active material. Specifically, it was found that the volume resistivity of the powder of sample 1-2 was 1.0×10 4 Ω·cm or more at a pressure of 64 MPa. It was also found that the volume resistivity of the powder of sample 1-3 was 1.0×10 6 Ω·cm or more at a pressure of 64 MPa. It was also found that the volume resistivity of the powder of sample 1-6 was 1.0×10 7 Ω·cm or more at a pressure of 64 MPa.
図３５より、圧力が６４ＭＰａのときの体積抵抗率は５．０×１０３Ω・ｃｍ以上であることが好ましく、１．０×１０４Ω・ｃｍ以上であることがより好ましく、１．０×１０５Ω・ｃｍ以上であることがより好ましく、５．０×１０５Ω・ｃｍ以上であることがより好ましく、１．０×１０６Ω・ｃｍ以上であることがより好ましい。 From FIG. 35, it can be seen that the volume resistivity at a pressure of 64 MPa is preferably 5.0×10 3 Ω·cm or more, more preferably 1.0×10 4 Ω·cm or more, more preferably 1.0×10 5 Ω·cm or more, more preferably 5.0×10 5 Ω·cm or more, and more preferably 1.0×10 6 Ω·cm or more.
また、図３５より、圧力が１３ＭＰａのときの体積抵抗率は２．０×１０４Ω・ｃｍ以上であることが好ましく、２．０×１０５Ω・ｃｍ以上であることがより好ましく、５．０×１０５Ω・ｃｍ以上であることがより好ましく、１．０×１０６Ω・ｃｍ以上であることがより好ましく、２．０×１０６Ω・ｃｍ以上であることがより好ましい。 Furthermore, from FIG. 35 , the volume resistivity at a pressure of 13 MPa is preferably 2.0×10 4 Ω·cm or more, more preferably 2.0×10 5 Ω·cm or more, more preferably 5.0×10 5 Ω·cm or more, more preferably 1.0×10 6 Ω·cm or more, and more preferably 2.0×10 6 Ω·cm or more.
圧力が低い条件では、圧力が高い条件と比較して体積抵抗率は高くなる傾向がある。そのため、体積抵抗率は、圧力が６４ＭＰａのときに１．０×１０４Ω・ｃｍ以上であり、且つ圧力が１３ＭＰａのときに２．０×１０４Ω・ｃｍ以上であることが好ましい。また、圧力が６４ＭＰａのときに１．０×１０５Ω・ｃｍ以上であり、且つ圧力が１３ＭＰａのときに２．０×１０５Ω・ｃｍ以上であることが好ましい。さらには、圧力が６４ＭＰａのときに５．０×１０５Ω・ｃｍ以上であり、且つ圧力が１３ＭＰａのときに１．０×１０６Ω・ｃｍ以上であることが好ましいといえる。 Under low pressure conditions, the volume resistivity tends to be higher than under high pressure conditions. Therefore, the volume resistivity is preferably 1.0×10 4 Ω·cm or more when the pressure is 64 MPa, and 2.0×10 4 Ω·cm or more when the pressure is 13 MPa. Also, it is preferably 1.0×10 5 Ω·cm or more when the pressure is 64 MPa, and 2.0×10 5 Ω·cm or more when the pressure is 13 MPa. Furthermore, it is preferably 5.0×10 5 Ω·cm or more when the pressure is 64 MPa, and 1.0×10 6 Ω·cm or more when the pressure is 13 MPa.
またサンプル１−２、サンプル１−３、及びサンプル１−６は、サンプル２より１桁以上５桁以下、好ましくは２桁以上３桁以下の範囲で絶縁性が高いといえる。本実施例では室温（２５℃）で粉体体積抵抗率を測定したが、室温より高い温度においても同様にサンプル１−２、サンプル１−３、及びサンプル１−６は、サンプル２より絶縁性が高いと考えられる。よって、サンプル１−２、サンプル１−３、及びサンプル１−６を二次電池に適用すると、安全性の高い二次電池を提供できる。さらにサンプル１−２、サンプル１−３、及びサンプル１−６は、固体電解質を用いた二次電池に適用すると好ましい。 Furthermore, it can be said that Samples 1-2, 1-3, and 1-6 have higher insulating properties than Sample 2 by one to five orders of magnitude, preferably two to three orders of magnitude. In this example, the powder volume resistivity was measured at room temperature (25°C), but it is considered that Samples 1-2, 1-3, and 1-6 have higher insulating properties than Sample 2 even at temperatures higher than room temperature. Therefore, when Samples 1-2, 1-3, and 1-6 are applied to a secondary battery, a highly safe secondary battery can be provided. Furthermore, it is preferable to apply Samples 1-2, 1-3, and 1-6 to a secondary battery using a solid electrolyte.
＜ハーフセルの作製＞
次に、サンプル１−１、サンプル１−２、サンプル１−３、サンプル１−４、サンプル１−５、及びサンプル１−６を正極活物質として用いたコイン型の二次電池（ハーフセルと呼ぶ）を作製した。 <Preparation of half-cell>
Next, coin-type secondary batteries (called half cells) were fabricated using Sample 1-1, Sample 1-2, Sample 1-3, Sample 1-4, Sample 1-5, and Sample 1-6 as the positive electrode active material.
まず、正極活物質を用意し、導電材としてアセチレンブラック（ＡＢ）を用意し、結着剤としてポリフッ化ビニリデン（ＰＶＤＦ）を用意した。ＰＶＤＦはあらかじめＮ−メチル−２−ピロリドン（ＮＭＰ）に対して重量比で５％の割合で溶解したものを用意した。次に、正極活物質：ＡＢ：ＰＶＤＦ＝９５：３：２（重量比）で混合してスラリーを作製し、当該スラリーをアルミニウムの正極集電体に塗工した。スラリーの溶媒として、ＮＭＰを用いた。 First, the positive electrode active material was prepared, acetylene black (AB) was prepared as a conductive material, and polyvinylidene fluoride (PVDF) was prepared as a binder. The PVDF was prepared by dissolving it in N-methyl-2-pyrrolidone (NMP) at a weight ratio of 5%. Next, the positive electrode active material, AB, and PVDF were mixed in a ratio of 95:3:2 (weight ratio) to prepare a slurry, which was then applied to an aluminum positive electrode current collector. NMP was used as the solvent for the slurry.
次に、正極集電体にスラリーを塗工した後、溶媒を揮発させ、正極集電体上に正極活物質層を形成した。 Then, the slurry was applied to the positive electrode current collector, and the solvent was evaporated to form a positive electrode active material layer on the positive electrode current collector.
その後、上記の正極集電体上の正極活物質層の密度を高めるため、ロールプレス機によってプレス処理を行った。プレス処理の条件は、線圧２１０ｋＮ／ｍとした。なお、ロールプレス機の上部ロール及び下部ロールは、いずれも１２０℃とした。 Then, in order to increase the density of the positive electrode active material layer on the positive electrode current collector, a pressing process was performed using a roll press machine. The pressing process was performed under conditions of a linear pressure of 210 kN/m. The upper and lower rolls of the roll press machine were both set at 120°C.
以上の工程により、各サンプルを有する正極を得た。正極の活物質担持量はおよそ７ｍｇ／ｃｍ２とした。正極活物質としてサンプル１−１を用いたハーフセルをセル１−１と呼び、正極活物質としてサンプル１−２を用いたハーフセルをセル１−２と呼び、正極活物質としてサンプル１−３を用いたハーフセルをセル１−３と呼び、正極活物質としてサンプル１−４を用いたハーフセルをセル１−４と呼び、正極活物質としてサンプル１−５を用いたハーフセルをセル１−５と呼び、正極活物質としてサンプル１−６を用いたハーフセルをセル１−６と呼ぶ。 The above steps resulted in the production of positive electrodes having each sample. The amount of active material carried by the positive electrode was approximately 7 mg/ cm2 . The half cell using sample 1-1 as the positive electrode active material was called cell 1-1, the half cell using sample 1-2 as the positive electrode active material was called cell 1-2, the half cell using sample 1-3 as the positive electrode active material was called cell 1-3, the half cell using sample 1-4 as the positive electrode active material was called cell 1-4, the half cell using sample 1-5 as the positive electrode active material was called cell 1-5, and the half cell using sample 1-6 as the positive electrode active material was called cell 1-6.
ハーフセルの電解液として、キシダ化学社製、ＬＢＧ−００９２８、１ｍｏｌ／Ｌ　ＬｉＰＦ６　ＥＣ：ＤＥＣ（３：７ｖ／ｖ％）＋ＶＣ２ｗｔ％を用意した。これはエチレンカーボネート（ＥＣ）とジエチルカーボネート（ＤＥＣ）をＥＣ：ＤＥＣ＝３：７（体積比）で混合した混合溶媒に、リチウム塩として１ｍｏｌ／Ｌの六フッ化リン酸リチウム（ＬｉＰＦ６）を加え、さらに添加剤としてビニレンカーボネート（ＶＣ）を用意し、リチウム塩が溶解した混合溶媒に対して２ｗｔ％加えたものである。ハーフセルのセパレータにはポリプロピレンの多孔質フィルムを用いた。 The electrolyte for the half-cell was prepared as follows: LBG-00928, 1 mol/L LiPF6 EC:DEC (3:7 v/v%) + 2 wt% VC, manufactured by Kishida Chemical Co., Ltd. This was prepared by adding 1 mol/L lithium hexafluorophosphate ( LiPF6 ) as a lithium salt to a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a ratio of EC:DEC = 3:7 (volume ratio), and further adding 2 wt% vinylene carbonate (VC) as an additive to the mixed solvent in which the lithium salt was dissolved. A porous polypropylene film was used as the separator for the half-cell.
ハーフセルの負極（対極）はリチウム金属を用いた。 Lithium metal was used as the negative electrode (counter electrode) of the half cell.
＜充放電サイクル試験＞
上記のセル１−１乃至セル１−６を用いて、充放電サイクル試験を行った。 <Charge/discharge cycle test>
A charge-discharge cycle test was carried out using the above-mentioned cells 1-1 to 1-6.
試験条件として、セル１−１乃至セル１−６を２５℃に保持された恒温槽に配置して、以下の充放電条件のサイクルを５０回繰り返した。
充電条件：ＣＣＣＶ充電、０．５Ｃレート、４．６Ｖ、０．０５Ｃカットオフ
放電条件：ＣＣ放電、０．５Ｃレート、２．５Ｖ
本充放電サイクル試験において、１Ｃに相当する電流値は正極活物質重量当たり２００ｍＡ／ｇとした。充電条件の４．６Ｖは上限電圧とよび、ＣＶ充電の期間は上限電圧に保持される。放電条件の２．５Ｖは下限電圧と呼ばれる。充放電サイクル試験の結果を、図３６Ａ及び図３６Ｂに示す。 As test conditions, the cells 1-1 to 1-6 were placed in a thermostatic chamber maintained at 25° C., and a cycle of the following charge and discharge conditions was repeated 50 times.
Charge conditions: CCCV charge, 0.5C rate, 4.6V, 0.05C cutoff Discharge conditions: CC discharge, 0.5C rate, 2.5V
In this charge-discharge cycle test, the current value corresponding to 1C was set to 200 mA/g per weight of the positive electrode active material. The charge condition of 4.6 V is called the upper limit voltage, and the upper limit voltage is maintained during the CV charge period. The discharge condition of 2.5 V is called the lower limit voltage. The results of the charge-discharge cycle test are shown in Figures 36A and 36B.
図３６Ａは、縦軸を放電容量（ｍＡｈ／ｇ）、横軸を充放電サイクル試験のサイクル数とし、図３６Ｂは、縦軸を放電容量の維持率（％）、横軸を充放電サイクル試験のサイクル数として示している。なお、図３６Ｂにおいて、充放電サイクル試験において、各セルでの最大の放電容量を示したサイクルにおける放電容量を、それぞれ１００％とした。 In Figure 36A, the vertical axis shows the discharge capacity (mAh/g) and the horizontal axis shows the number of cycles in the charge-discharge cycle test, while in Figure 36B, the vertical axis shows the discharge capacity retention rate (%) and the horizontal axis shows the number of cycles in the charge-discharge cycle test. In Figure 36B, the discharge capacity in the cycle that showed the maximum discharge capacity for each cell in the charge-discharge cycle test was set to 100%.
充放電サイクル試験において１サイクル時の放電容量（初回放電容量と呼ぶ）は、セル１−２で２２１．３ｍＡｈ／ｇであり、セル１−３で２１２．４ｍＡｈ／ｇであり、セル１−４で２０８．５ｍＡｈ／ｇであり、セル１−５で２０８．５ｍＡｈ／ｇであった。セル１−２、セル１−３、セル１−４、及びセル１−５は初回放電容量が２００ｍＡｈ／ｇ以上、好ましくは２１０ｍＡｈ／ｇ以上であり、優れた初回放電容量を示すことがわかった。 In the charge-discharge cycle test, the discharge capacity at one cycle (referred to as the initial discharge capacity) was 221.3 mAh/g for cell 1-2, 212.4 mAh/g for cell 1-3, 208.5 mAh/g for cell 1-4, and 208.5 mAh/g for cell 1-5. It was found that cell 1-2, cell 1-3, cell 1-4, and cell 1-5 had an initial discharge capacity of 200 mAh/g or more, preferably 210 mAh/g or more, and thus exhibited excellent initial discharge capacity.
充放電サイクル試験において５０サイクル時の放電容量は、セル１−２で２１５．２ｍＡｈ／ｇであり、セル１−３で２１０．７ｍＡｈ／ｇであり、セル１−４で１９９．９ｍＡｈ／ｇであり、セル１−５で１９２．５ｍＡｈ／ｇであった。セル１−２、セル１−３、セル１−４、及びセル１−５は５０サイクル時の放電容量が１９０ｍＡｈ／ｇ以上、好ましくは２００ｍＡｈ／ｇ以上であり、優れた放電容量を示すことがわかった。 In the charge-discharge cycle test, the discharge capacity at 50 cycles was 215.2 mAh/g for cell 1-2, 210.7 mAh/g for cell 1-3, 199.9 mAh/g for cell 1-4, and 192.5 mAh/g for cell 1-5. It was found that cell 1-2, cell 1-3, cell 1-4, and cell 1-5 had a discharge capacity at 50 cycles of 190 mAh/g or more, preferably 200 mAh/g or more, and thus exhibited excellent discharge capacity.
表層部１００ａにマグネシウムなどの添加元素が位置した正極活物質であっても、リチウムイオンの挿入脱離が可能であるとわかった。 It was found that lithium ions can be inserted and removed even in a positive electrode active material in which an additive element such as magnesium is located in the surface layer 100a.
充放電サイクル試験において５０サイクル時の放電容量維持率は、セル１−２で９６．１％であり、セル１−３で９６．２％であり、セル１−４で９３．３％であり、セル１−５で９１．８％であった。セル１−２、セル１−３、セル１−４、及びセル１−５は優れた放電容量維持率を示し、５０サイクル時の放電容量維持率が９０％以上、好ましくは９５％以上であるとわかった。 In the charge-discharge cycle test, the discharge capacity retention rate at 50 cycles was 96.1% for cell 1-2, 96.2% for cell 1-3, 93.3% for cell 1-4, and 91.8% for cell 1-5. Cell 1-2, cell 1-3, cell 1-4, and cell 1-5 showed excellent discharge capacity retention rates, and it was found that the discharge capacity retention rate at 50 cycles was 90% or more, preferably 95% or more.
セル１−６は、セル１−１と比較すると放電容量の維持率が優れた結果であったが、セル１−２乃至セル１−５に比べて低い値となった。また、セル１−６の正極活物質として用いたサンプル１−６は、図３５より６４ＭＰａのとき体積抵抗率が３．３×１０７Ω・ｃｍであった。これらより放電容量の高い二次電池を得るには正極活物質の体積抵抗率を、６４ＭＰａのとき３．３×１０７Ω・ｃｍより低くするとよいと考えられる。 Cell 1-6 had a superior discharge capacity retention rate compared to cell 1-1, but a lower value compared to cells 1-2 to 1-5. Sample 1-6 used as the positive electrode active material of cell 1-6 had a volume resistivity of 3.3×10 7 Ω·cm at 64 MPa, as shown in Figure 35. In order to obtain a secondary battery with a higher discharge capacity than these, it is considered desirable to make the volume resistivity of the positive electrode active material lower than 3.3×10 7 Ω·cm at 64 MPa.
本実施例では、正極活物質１００の作製工程における、粉体抵抗の変化を分析した。粉体抵抗測定のサンプルとして、サンプル２−１、サンプル２−２、サンプル２−３、及びサンプル２−４を準備した。 In this example, the change in powder resistance during the manufacturing process of the positive electrode active material 100 was analyzed. Samples 2-1, 2-2, 2-3, and 2-4 were prepared as samples for powder resistance measurement.
＜粉体抵抗測定サンプルの作製＞
図１９に示す作製方法を参照しながら、粉体抵抗測定のサンプルとして、サンプル２−１、サンプル２−２、サンプル２−３、及びサンプル２−４について説明する。なお、作製方法の詳細は、実施例１と同じ条件とした。 <Preparation of Powder Resistivity Measurement Sample>
Samples 2-1, 2-2, 2-3, and 2-4 for powder resistance measurement will be described with reference to the preparation method shown in Fig. 19. The details of the preparation method were the same as those in Example 1.
実施例１のサンプル２と同様に、図１９のステップＳ１４のＬｉＣｏＯ２を準備した。サンプル名を改めて、これをサンプル２−１とした。 LiCoO2 was prepared in the same manner as in Sample 2 of Example 1 in step S14 of Fig. 19. The sample was renamed to Sample 2-1.
ステップＳ１４のＬｉＣｏＯ２に図１９のステップＳ１５の初期加熱を実施した。これをサンプル２−２とした。 The LiCoO 2 of step S14 was subjected to the initial heating of step S15 of Fig. 19. This was designated as sample 2-2.
ステップＳ１５を経て実施例１と同様に、図１９のステップＳ３４ａの複合酸化物を作製した。Ａ１源が有するマグネシウムの原子数が、コバルト酸リチウムが有するコバルトの原子数に対して１．０％となるようにした。これをサンプル２−３とした。 After step S15, a composite oxide was produced in step S34a of FIG. 19 in the same manner as in Example 1. The number of magnesium atoms in the A1 source was set to 1.0% of the number of cobalt atoms in the lithium cobalt oxide. This was designated sample 2-3.
ステップＳ３４ａの複合酸化物にステップＳ４０に従ってＡ２源としてニッケル及びアルミニウムを添加して、図１９のステップＳ５４の正極活物質１００を作製した。Ａ２源が有するニッケルの原子数が、コバルト酸リチウムが有するコバルトの原子数に対して０．５％となるようにした。さらにＡ２源が有するアルミニウムの原子数が、コバルト酸リチウムが有するコバルトの原子数に対して０．５％となるようにした。これをサンプル２−４とした。 Nickel and aluminum were added as the A2 source to the composite oxide of step S34a according to step S40 to produce the positive electrode active material 100 of step S54 in FIG. 19. The number of nickel atoms in the A2 source was set to 0.5% of the number of cobalt atoms in the lithium cobalt oxide. Furthermore, the number of aluminum atoms in the A2 source was set to 0.5% of the number of cobalt atoms in the lithium cobalt oxide. This was designated sample 2-4.
下表にはサンプル２−１乃至サンプル２−４の条件をまとめて示す。 The table below summarizes the conditions for samples 2-1 to 2-4.
Figure JPOXMLDOC01-appb-T000011
Figure JPOXMLDOC01-appb-T000011
＜粉体抵抗測定＞
サンプル２−１、サンプル２−２、サンプル２−３、及びサンプル２−４について、粉体の体積抵抗率を測定した。 <Powder Resistance Measurement>
The volume resistivity of the powder was measured for Samples 2-1, 2-2, 2-3, and 2-4.
粉体の体積抵抗率の測定方法は、実施例１と同様にした。各サンプルの粉体の体積抵抗率の測定として、粉体を半径１ｃｍの測定部にセットし、１３ＭＰａ、２５ＭＰａ、３８ＭＰａ、５１ＭＰａ、及び６４ＭＰａのそれぞれの圧力条件において、粉体の電気抵抗と、粉体の体積と、を計測し、各サンプルの粉体の体積抵抗率を得た。結果を、図３７に示す。 The powder volume resistivity was measured in the same manner as in Example 1. To measure the volume resistivity of the powder of each sample, the powder was set in a measuring section with a radius of 1 cm, and the electrical resistance and volume of the powder were measured under pressure conditions of 13 MPa, 25 MPa, 38 MPa, 51 MPa, and 64 MPa, to obtain the volume resistivity of the powder of each sample. The results are shown in Figure 37.
粉体の体積抵抗率の測定の結果、図３７に示すように、サンプル２−２の体積抵抗率は、サンプル２−１の体積抵抗率よりも高かった。また、サンプル２−３の体積抵抗率は、サンプル２−２の体積抵抗率よりも高かった。また、サンプル２−４の体積抵抗率は、サンプル２−２の体積抵抗率よりも高く、サンプル２−３の体積抵抗率よりも低かった。つまり、体積抵抗率の値は、サンプル２−１、サンプル２−２、サンプル２−４、及びサンプル２−３の順に高い結果であった。 As a result of measuring the volume resistivity of the powder, as shown in FIG. 37, the volume resistivity of sample 2-2 was higher than that of sample 2-1. The volume resistivity of sample 2-3 was also higher than that of sample 2-2. The volume resistivity of sample 2-4 was also higher than that of sample 2-2, but lower than that of sample 2-3. In other words, the volume resistivity values were highest in the order of sample 2-1, sample 2-2, sample 2-4, and sample 2-3.
図３７より、圧力が６４ＭＰａのときの体積抵抗率は５．０×１０３Ω・ｃｍ以上であることが好ましく、１．０×１０４Ω・ｃｍ以上であることがより好ましく、１．０×１０５Ω・ｃｍ以上であることがより好ましく、５．０×１０５Ω・ｃｍ以上であることがより好ましく、１．０×１０６Ω・ｃｍ以上であることがより好ましい。 From FIG. 37, when the pressure is 64 MPa, the volume resistivity is preferably 5.0×10 3 Ω·cm or more, more preferably 1.0×10 4 Ω·cm or more, more preferably 1.0×10 5 Ω·cm or more, more preferably 5.0×10 5 Ω·cm or more, and more preferably 1.0×10 6 Ω·cm or more.
また、図３７より、圧力が１３ＭＰａのときの体積抵抗率は２．０×１０４Ω・ｃｍ以上であることが好ましく、２．０×１０５Ω・ｃｍ以上であることがより好ましく、５．０×１０５Ω・ｃｍ以上であることがより好ましく、１．０×１０６Ω・ｃｍ以上であることがより好ましく、２．０×１０６Ω・ｃｍ以上であることがより好ましい。 Furthermore, from FIG. 37, the volume resistivity at a pressure of 13 MPa is preferably 2.0×10 4 Ω·cm or more, more preferably 2.0×10 5 Ω·cm or more, more preferably 5.0×10 5 Ω·cm or more, more preferably 1.0×10 6 Ω·cm or more, and more preferably 2.0×10 6 Ω·cm or more.
圧力が低い条件では、圧力が高い条件と比較して体積抵抗率は高くなる傾向がある。そのため、体積抵抗率は、圧力が６４ＭＰａのときに１．０×１０４Ω・ｃｍ以上であり、且つ圧力が１３ＭＰａのときに２．０×１０４Ω・ｃｍ以上であることが好ましい。また、圧力が６４ＭＰａのときに１．０×１０５Ω・ｃｍ以上であり、且つ圧力が１３ＭＰａのときに２．０×１０５Ω・ｃｍ以上であることが好ましい。さらには、圧力が６４ＭＰａのときに５．０×１０５Ω・ｃｍ以上であり、且つ圧力が１３ＭＰａのときに１．０×１０６Ω・ｃｍ以上であることが好ましいといえる。 Under low pressure conditions, the volume resistivity tends to be higher than under high pressure conditions. Therefore, the volume resistivity is preferably 1.0×10 4 Ω·cm or more when the pressure is 64 MPa, and 2.0×10 4 Ω·cm or more when the pressure is 13 MPa. Also, it is preferably 1.0×10 5 Ω·cm or more when the pressure is 64 MPa, and 2.0×10 5 Ω·cm or more when the pressure is 13 MPa. Furthermore, it is preferably 5.0×10 5 Ω·cm or more when the pressure is 64 MPa, and 1.0×10 6 Ω·cm or more when the pressure is 13 MPa.
本実施例では室温（２５℃）で粉体体積抵抗率を測定したが、室温より高い温度においても同様に、粉体体積抵抗率はサンプル２−１、サンプル２−２、サンプル２−４、及びサンプル２−３の順に高くなると考えられる。そのため、安全性の高い二次電池を得るには、サンプル２−４、及びサンプル２−３を用いるとよい。さらにサンプル２−４、及びサンプル２−３は、固体電解質を用いた二次電池に適用すると好ましい。 In this example, the powder volume resistivity was measured at room temperature (25°C), but it is believed that even at temperatures higher than room temperature, the powder volume resistivity increases in the order of sample 2-1, sample 2-2, sample 2-4, and sample 2-3. Therefore, to obtain a secondary battery with high safety, it is recommended to use sample 2-4 and sample 2-3. Furthermore, sample 2-4 and sample 2-3 are preferably applied to secondary batteries using solid electrolytes.
＜ＧＤ−ＭＳ測定＞
サンプル２−１、サンプル２−２、サンプル２−３、及びサンプル２−４について、ＧＤ−ＭＳを測定した。下表に各元素濃度（ｐｐｍ　ｗｔ）を示す。なお、下表で示した元素以外の元素濃度は省略した。 <GD-MS Measurement>
GD-MS was measured for Sample 2-1, Sample 2-2, Sample 2-3, and Sample 2-4. The element concentration (ppm wt) is shown in the table below. Note that the element concentrations other than those shown in the table below are omitted.
Figure JPOXMLDOC01-appb-T000012
Figure JPOXMLDOC01-appb-T000012
表７よりサンプル２−１は上記実施の形態で示した材料Ｓｍ−３に対応するものと考えられた。またサンプル２−１とサンプル２−２とを比較すると、ステップＳ１５の初期加熱を実施したのみではマグネシウム、アルミニウム、チタン及びニッケルの濃度に変化がなく、フッ素の濃度は増加する傾向が示唆された。またサンプル２−３及びサンプル２−４のように添加元素Ａ１としてマグネシウムを有する化合物を添加する工程を経ると、ＧＤ−ＭＳによって検出されるマグネシウムの濃度は１００ｐｐｍ　ｗｔ以上３０００ｐｐｍ　ｗｔ以下となることがわかった。なお添加元素Ａ１に用いたマグネシウムを有する化合物にはフッ素が含まれることから、サンプル２−３ではフッ素の濃度が増加した。一方でサンプル２−４ではサンプル２−１及びサンプル２−２よりフッ素の濃度が増加したが、サンプル２−３よりはフッ素の濃度が減少した。このことから、添加元素Ａ２を添加した後の焼成によりフッ素が昇華した可能性が示唆された。なおいずれのサンプルにおいてもチタン濃度に変化はなかった。ニッケルはサンプル２−４のように添加元素Ａ２としてニッケルを有する化合物を添加することで、ＧＤ−ＭＳによって検出されるニッケルの濃度が２００ｐｐｍ　ｗｔ以上３０００ｐｐｍ　ｗｔ以下となることがわかった。 From Table 7, it was considered that sample 2-1 corresponds to material Sm-3 shown in the above embodiment. Furthermore, when sample 2-1 and sample 2-2 are compared, it is suggested that the concentration of magnesium, aluminum, titanium and nickel does not change when the initial heating of step S15 is performed alone, and the concentration of fluorine tends to increase. Furthermore, it was found that the concentration of magnesium detected by GD-MS becomes 100 ppm wt or more and 3000 ppm wt or less when the process of adding a compound having magnesium as the additive element A1 is performed as in sample 2-3 and sample 2-4. Since the compound having magnesium used as the additive element A1 contains fluorine, the concentration of fluorine increased in sample 2-3. On the other hand, the concentration of fluorine in sample 2-4 increased more than in samples 2-1 and 2-2, but decreased more than in sample 2-3. This suggests the possibility that fluorine may have sublimated due to the firing after the addition of the additive element A2. Furthermore, there was no change in the titanium concentration in any of the samples. It was found that by adding a compound containing nickel as the additive element A2, as in sample 2-4, the nickel concentration detected by GD-MS was 200 ppm wt or more and 3000 ppm wt or less.
＜ＸＰＳ測定＞
サンプル２−２及びサンプル２−４について、ＸＰＳ測定を実施した。下表には各元素の定量値（ａｔｏｍｉｃ％）を示す。 <XPS Measurement>
XPS measurements were carried out on Sample 2-2 and Sample 2-4. The quantitative values (atomic %) of each element are shown in the table below.
Figure JPOXMLDOC01-appb-T000013
Figure JPOXMLDOC01-appb-T000013
下表には表８から求めた存在比を示す。 The table below shows the abundance ratios obtained from Table 8.
Figure JPOXMLDOC01-appb-T000014
Figure JPOXMLDOC01-appb-T000014
表８よりサンプル２−２ではマグネシウム、アルミニウム及びニッケルはＸＰＳでは検出されず、サンプル２−４ではマグネシウム、アルミニウム及びニッケルがＸＰＳで検出された。ステップＳ１５の初期加熱だけではマグネシウム、アルミニウム及びニッケルが表層部に偏析しないことが示唆された。添加元素Ａ１及び添加元素Ａ２をコバルト酸リチウム（Ｃ−１０Ｎ）へ添加することで、マグネシウム、アルミニウム及びニッケルがＸＰＳで検出されることがわかった。 From Table 8, magnesium, aluminum, and nickel were not detected by XPS in sample 2-2, but were detected by XPS in sample 2-4. This suggests that magnesium, aluminum, and nickel do not segregate in the surface layer by the initial heating in step S15 alone. It was found that magnesium, aluminum, and nickel can be detected by XPS by adding additive element A1 and additive element A2 to lithium cobalt oxide (C-10N).
１００：正極活物質、１００ａ：表層部、１００ｂ：内部、１００ｃ：欠陥部、１０１：結晶粒界、１０３：凸部、１０４：被覆部 100: Positive electrode active material, 100a: Surface layer, 100b: Interior, 100c: Defect, 101: Grain boundary, 103: Convex, 104: Coating

Claims (11)

  1. 　正極と、負極と、電解質と、を有する二次電池であって、
    　前記正極は、正極活物質を有し、
    　前記正極活物質は、コバルト酸リチウムとマグネシウムとを有し、
    　前記電解質は、リチウム塩、有機溶媒及び添加剤を有し、
    　前記添加剤は、ジニトリル化合物を有し、
    　前記負極は、炭素材料を有し、
    　前記正極と、対極にリチウム金属を用いて組み立てた電池に対して上限電圧４．７５Ｖの電圧まで充電した前記正極をＣｕＫα１線によるＸ線回折で分析したとき、前記正極活物質は少なくとも２θ＝１９．４７±０．１０°、および２θ＝４５．６２±０．０５°に回折ピークを有する、
    　二次電池。     A secondary battery having a positive electrode, a negative electrode, and an electrolyte,
    The positive electrode has a positive electrode active material,
    The positive electrode active material includes lithium cobalt oxide and magnesium,
    The electrolyte comprises a lithium salt, an organic solvent, and an additive;
    The additive comprises a dinitrile compound,
    The negative electrode comprises a carbon material,
    When a battery is assembled using the positive electrode and a lithium metal counter electrode, and the positive electrode is charged to a voltage of 4.75 V, the positive electrode active material has diffraction peaks at least at 2θ=19.47±0.10° and 2θ=45.62±0.05° when analyzed by X-ray diffraction using CuKα 1 ray.
    Secondary battery.
  2. 　正極と、負極と、電解質と、を有する二次電池であって、
    　前記正極は、正極活物質を有し、
    　前記正極活物質は、コバルト酸リチウムとマグネシウムとを有し、
    　前記電解質は、リチウム塩、有機溶媒及び添加剤を有し、
    　前記添加剤は、ジニトリル化合物を有し、
    　前記負極は、炭素材料を有し、
    　前記正極と、対極にリチウム金属を用いて組み立てた電池に対して上限電圧４．８Ｖの電圧まで充電した前記正極をＣｕＫα１線によるＸ線回折で分析したとき、前記正極活物質は少なくとも２θ＝１９．４７±０．１０°、および２θ＝４５．６２±０．０５°に回折ピークを有する、
    　二次電池。     A secondary battery having a positive electrode, a negative electrode, and an electrolyte,
    The positive electrode has a positive electrode active material,
    The positive electrode active material includes lithium cobalt oxide and magnesium,
    The electrolyte comprises a lithium salt, an organic solvent, and an additive;
    The additive comprises a dinitrile compound,
    The negative electrode comprises a carbon material,
    When a battery is assembled using the positive electrode and a lithium metal counter electrode, and the positive electrode is charged to a voltage of 4.8 V, the positive electrode active material has diffraction peaks at least at 2θ=19.47±0.10° and 2θ=45.62±0.05° when analyzed by X-ray diffraction using CuKα 1 ray.
    Secondary battery.
  3. 　請求項１又は２において、
    　前記リチウム塩は、ＬｉＰＦ６、ＬｉＣｌＯ４、ＬｉＡｓＦ６、ＬｉＢＦ４、ＬｉＡｌＣｌ４、ＬｉＳＣＮ、ＬｉＢｒ、ＬｉＩ、Ｌｉ２ＳＯ４、Ｌｉ２Ｂ１０Ｃｌ１０、Ｌｉ２Ｂ１２Ｃｌ１２、ＬｉＣＦ３ＳＯ３、ＬｉＣ４Ｆ９ＳＯ３、ＬｉＣ（ＣＦ３ＳＯ２）３、ＬｉＣ（Ｃ２Ｆ５ＳＯ２）３、ＬｉＮ（ＣＦ３ＳＯ２）２、ＬｉＮ（Ｃ４Ｆ９ＳＯ２）（ＣＦ３ＳＯ２）、及びＬｉＮ（Ｃ２Ｆ５ＳＯ２）２等から選ばれた一又は二以上を用いる、
    　二次電池。     In claim 1 or 2,
    The lithium salt is one or more selected from LiPF6 , LiClO4 , LiAsF6 , LiBF4 , LiAlCl4 , LiSCN , LiBr, LiI , Li2SO4, Li2B10Cl10 , Li2B12Cl12 , LiCF3SO3 , LiC4F9SO3 , LiC (CF3SO2) 3 , LiC ( C2F5SO2 ) 3 , LiN ( CF3SO2 ) 2 , LiN ( C4F9SO2 ) ( CF3SO2 ), and LiN( C2F5SO2 ) 2 , etc.
    Secondary battery.
  4. 　請求項１又は２において、
    　前記有機溶媒は、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、クロロエチレンカーボネート、ビニレンカーボネート、γ−ブチロラクトン、γ−バレロラクトン、ジメチルカーボネート、ジエチルカーボネート、エチルメチルカーボネート、ギ酸メチル、酢酸メチル、酢酸エチル、プロピオン酸メチル、プロピオン酸エチル、プロピオン酸プロピル、酪酸メチル、１，３−ジオキサン、１，４−ジオキサン、ジメトキシエタン、ジメチルスルホキシド、ジエチルエーテル、メチルジグライム、アセトニトリル、ベンゾニトリル、テトラヒドロフラン、スルホラン、及びスルトンから選ばれた一又は二以上を用いる、
    　二次電池。     In claim 1 or 2,
    The organic solvent is one or more selected from ethylene carbonate, propylene carbonate, butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane, dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, and sultone.
    Secondary battery.
  5. 　請求項１又は２において、
    　前記ジニトリル化合物はスクシノニトリル、アジポニトリル、及びエチレングリコールビス（プロピオニトリル）エーテルから選ばれた一以上を有する、
    　二次電池。     In claim 1 or 2,
    The dinitrile compound is at least one selected from succinonitrile, adiponitrile, and ethylene glycol bis(propionitrile) ether;
    Secondary battery.
  6. 　正極と、負極と、固体電解質と、を有する二次電池であって、
    　前記正極は、正極活物質を有し、
    　前記正極活物質は、コバルト酸リチウムとマグネシウムとを有し、
    　前記固体電解質は、ハロゲン化物固体電解質を有し、
    　前記負極は、炭素材料を有し、
    　前記正極と、対極にリチウム金属を用いて組み立てた電池に対して、上限電圧４．７Ｖの電圧まで充電した前記正極をＣｕＫα１線によるＸ線回折で分析したとき、前記正極活物質は少なくとも２θ＝１９．２５±０．１２°、および２θ＝４５．４７±０．１０°に回折ピークを有する、
    　二次電池。     A secondary battery having a positive electrode, a negative electrode, and a solid electrolyte,
    The positive electrode has a positive electrode active material,
    The positive electrode active material includes lithium cobalt oxide and magnesium,
    the solid electrolyte comprises a halide solid electrolyte,
    The negative electrode comprises a carbon material,
    When a battery is assembled using the positive electrode and lithium metal as a counter electrode, and the positive electrode is charged to a voltage of an upper limit voltage of 4.7 V, the positive electrode active material has diffraction peaks at least at 2θ=19.25±0.12° and 2θ=45.47±0.10° when analyzed by X-ray diffraction using CuKα 1 ray.
    Secondary battery.
  7. 　正極と、負極と、固体電解質と、を有する二次電池であって、
    　前記正極は、正極活物質を有し、
    　前記正極活物質は、コバルト酸リチウムとマグネシウムとを有し、
    　前記固体電解質は、ハロゲン化物固体電解質を有し、
    　前記負極は、炭素材料を有し、
    　前記正極と、対極にリチウム金属を用いて組み立てた電池に対して、上限電圧４．７５Ｖの電圧まで充電した前記正極をＣｕＫα１線によるＸ線回折で分析したとき、前記正極活物質は少なくとも２θ＝１９．４７±０．１０°、および２θ＝４５．６２±０．０５°に回折ピークを有する、
    　二次電池。     A secondary battery having a positive electrode, a negative electrode, and a solid electrolyte,
    The positive electrode has a positive electrode active material,
    The positive electrode active material includes lithium cobalt oxide and magnesium,
    the solid electrolyte comprises a halide solid electrolyte,
    The negative electrode comprises a carbon material,
    When a battery is assembled using the positive electrode and lithium metal as a counter electrode, and the positive electrode is charged to a voltage of an upper limit voltage of 4.75 V, the positive electrode active material has diffraction peaks at least at 2θ=19.47±0.10° and 2θ=45.62±0.05° when analyzed by X-ray diffraction using CuKα 1 ray.
    Secondary battery.
  8. 　正極と、負極と、固体電解質と、を有する二次電池であって、
    　前記正極は、正極活物質を有し、
    　前記正極活物質は、コバルト酸リチウムとマグネシウムとを有し、
    　前記固体電解質は、ハロゲン化物固体電解質を有し、
    　前記負極は、炭素材料を有し、
    　前記正極と、対極にリチウム金属を用いて組み立てた電池に対して、上限電圧４．８Ｖの電圧まで充電した前記正極をＣｕＫα１線によるＸ線回折で分析したとき、前記正極活物質は少なくとも２θ＝１９．４７±０．１０°、および２θ＝４５．６２±０．０５°に回折ピークを有する、
    　二次電池。     A secondary battery having a positive electrode, a negative electrode, and a solid electrolyte,
    The positive electrode has a positive electrode active material,
    The positive electrode active material includes lithium cobalt oxide and magnesium,
    the solid electrolyte comprises a halide solid electrolyte,
    The negative electrode comprises a carbon material,
    When a battery is assembled using the positive electrode and lithium metal as a counter electrode, and the positive electrode is charged to a voltage of an upper limit voltage of 4.8 V, the positive electrode active material has diffraction peaks at least at 2θ=19.47±0.10° and 2θ=45.62±0.05° when analyzed by X-ray diffraction using CuKα 1 ray.
    Secondary battery.
  9. 　請求項６乃至請求項８のいずれか一において、
    　前記ハロゲン化物固体電解質はフッ化物固体電解質である、
    　二次電池。     In any one of claims 6 to 8,
    The halide solid electrolyte is a fluoride solid electrolyte.
    Secondary battery.
  10. 　請求項９において、
    　前記フッ化物固体電解質は、ＬｉＦ、ＬｉＹＦ４、Ｌｉ３ＡｌＦ６、又はＬｉ２ＺｒＦ６を有する、
    　二次電池。     In claim 9,
    The fluoride solid electrolyte comprises LiF , LiYF4 , Li3AlF6 , or Li2ZrF6 ;
    Secondary battery.
  11. 　請求項１乃至請求項３、及び請求項６乃至請求項８のいずれか一において、
    　前記正極活物質は、粒子の内部にマグネシウムを有する、
    　二次電池。     In any one of claims 1 to 3 and claims 6 to 8,
    The positive electrode active material has magnesium inside the particles.
    Secondary battery.
PCT/IB2023/061347 2022-11-17 2023-11-10 Secondary battery WO2024105514A1 (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2010282948A (en) * 2009-05-01 2010-12-16 Toyota Motor Corp Solid electrolyte material
JP2016536776A (en) * 2014-09-29 2016-11-24 シェンヂェン キヤプケム テクノロジー 力ンパニー リミテッドＳｈｅｎｚｈｅｎ Ｃａｐｃｈｅｍ Ｔｅｃｈｎｏｌｏｇｙ Ｃｏ．，Ｌｔｄ． High voltage lithium ion battery electrolyte and high voltage lithium ion battery
WO2021252963A1 (en) * 2020-06-11 2021-12-16 Natron Energy, Inc. Electrolyte additives for an electrochemical cell
JP2022070247A (en) * 2020-10-26 2022-05-12 株式会社半導体エネルギー研究所 Secondary battery and electronic apparatus
JP2022165490A (en) * 2021-04-20 2022-11-01 トヨタ自動車株式会社 battery

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2010282948A (en) * 2009-05-01 2010-12-16 Toyota Motor Corp Solid electrolyte material
JP2016536776A (en) * 2014-09-29 2016-11-24 シェンヂェン キヤプケム テクノロジー 力ンパニー リミテッドＳｈｅｎｚｈｅｎ Ｃａｐｃｈｅｍ Ｔｅｃｈｎｏｌｏｇｙ Ｃｏ．，Ｌｔｄ． High voltage lithium ion battery electrolyte and high voltage lithium ion battery
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