WO2024157131A1 - リチウムイオン二次電池 - Google Patents

リチウムイオン二次電池 Download PDF

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Publication number
WO2024157131A1
WO2024157131A1 PCT/IB2024/050504 IB2024050504W WO2024157131A1 WO 2024157131 A1 WO2024157131 A1 WO 2024157131A1 IB 2024050504 W IB2024050504 W IB 2024050504W WO 2024157131 A1 WO2024157131 A1 WO 2024157131A1
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Prior art keywords
positive electrode
active material
electrode active
lithium
crystal structure
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English (en)
French (fr)
Japanese (ja)
Inventor
山崎舜平
門馬洋平
黒澤奈緒
川月惇史
高橋辰義
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Semiconductor Energy Laboratory Co Ltd
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Semiconductor Energy Laboratory Co Ltd
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Priority to JP2024572521A priority Critical patent/JPWO2024157131A1/ja
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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
    • H01M10/058—Construction or manufacture
    • 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
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • 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
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • 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
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers

Definitions

  • One aspect of the present invention relates to an object, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, a manufacture, or a composition of matter.
  • One aspect of the present invention relates to a power storage device including a secondary battery, a semiconductor device, a display device, a light-emitting device, a lighting device, an electronic device, or a manufacturing method thereof.
  • electronic devices refer to devices that have a power storage device in general, and electro-optical devices that have a power storage device, information terminal devices that have a power storage device, etc. are all electronic devices.
  • lithium-ion secondary batteries lithium-ion capacitors
  • air batteries air batteries
  • all-solid-state batteries all-solid-state batteries.
  • demand for high-output, high-capacity lithium-ion secondary batteries in particular has expanded rapidly in line with the development of the semiconductor industry, and they have become indispensable in today's information society as a rechargeable energy source.
  • Patent Documents 1 to 3 there has been active work on improving the positive electrode active material in the positive electrode of secondary batteries (e.g., Patent Documents 1 to 3). Research is also being conducted on the crystal structure of positive electrode active materials (e.g., Non-Patent Documents 1 to 5). Studies are also being conducted on controlling the crystal orientation of positive electrode active materials (e.g., Patent Documents 4 and 5).
  • X-ray diffraction is one of the techniques used to analyze the crystal structure of positive electrode active materials.
  • XRD data can be analyzed by using the Inorganic Crystal Structure Database (ICSD) introduced in Non-Patent Document 6.
  • ICSD Inorganic Crystal Structure Database
  • the lattice constant of lithium cobalt oxide described in Non-Patent Document 7 can be referenced from ICSD.
  • the analysis program RIETAN-FP Non-Patent Document 8
  • VESTA Non-Patent Document 9 can be used as software for drawing crystal structures.
  • ImageJ (Non-Patent Documents 10 to 12) is known as an example of image processing software.
  • this software for example, the shape of the positive electrode active material can be analyzed.
  • Microelectron diffraction is also effective in identifying the crystal structure of the positive electrode active material, particularly the crystal structure of the surface layer.
  • the analysis program ReciPro can be used to analyze the electron diffraction pattern.
  • fluorides such as fluorite (calcium fluoride) have long been used as fluxes in ironmaking and other processes, and their physical properties have been studied (Non-Patent Documents 14 and 15).
  • Lithium-ion secondary batteries have room for improvement in many areas, including discharge capacity, cycle characteristics, reliability, safety, and cost.
  • Another object of one embodiment of the present invention is to provide a positive electrode active material, a composite oxide, a power storage device, or a manufacturing method thereof.
  • One aspect of the present invention is a lithium ion secondary battery having a positive electrode and a negative electrode, the positive electrode having a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, the negative electrode having a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, the positive electrode active material layer has a positive electrode active material in a region where the positive electrode current collector and the negative electrode current collector face each other, the positive electrode active material has a layered rock salt type crystal structure belonging to the space group R-3m, and in the positive electrode active material layer, 50% or more of the particles of the positive electrode active material have an angle between the c-axis of the crystal structure and the normal to the negative electrode current collector of 60 degrees or more and 120 degrees or less.
  • the positive electrode active material layer has graphene, and the positive electrode active material has a region in contact with the graphene on a surface having a normal in a direction intersecting the c-axis of the crystal structure, which is a lithium ion secondary battery.
  • the positive electrode active material is a lithium composite oxide containing cobalt.
  • the positive electrode active material is a lithium composite oxide containing nickel, cobalt, and manganese.
  • one aspect of the present invention is a lithium ion secondary battery having a positive electrode and a negative electrode, the positive electrode having a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, the negative electrode having a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, the positive electrode active material layer has a positive electrode active material in a region where the positive electrode current collector and the negative electrode current collector face each other, the positive electrode active material has an olivine-type crystal structure belonging to the space group pnma, and in the positive electrode active material layer, 50% or more of the particles of the positive electrode active material have an angle between the [010] direction of the crystal structure and the normal to the negative electrode current collector of 0 degrees or more and 30 degrees or less.
  • the positive electrode active material is a lithium ion secondary battery having lithium iron phosphate.
  • One aspect of the present invention can provide a positive electrode active material or composite oxide that can be used in a lithium ion secondary battery and that suppresses a decrease in discharge capacity during charge/discharge cycles.
  • a positive electrode active material or composite oxide that does not easily lose its crystal structure even after repeated charge/discharge can be provided.
  • a positive electrode active material or composite oxide that has a large discharge capacity can be provided.
  • a secondary battery that is safe or highly reliable can be provided.
  • one embodiment of the present invention can provide a positive electrode active material, a composite oxide, a power storage device, or a manufacturing method thereof.
  • FIG. 1A is a cross-sectional view illustrating the internal structure of a secondary battery
  • FIG. 1B is a cross-sectional view illustrating a positive electrode and an electrolyte of the secondary battery.
  • FIG. 2 is a perspective view illustrating a crystal plane in a layered rock-salt crystal structure represented by a space group of R-3m.
  • FIG. 3 is a diagram illustrating the direction in which lithium ions tend to move in the positive electrode active material and the positional relationship between the positive electrode current collector and the negative electrode current collector.
  • 4A and 4B are cross-sectional views illustrating the direction of the c-axis of a positive electrode active material 100A in the positive electrode.
  • 5A and 5B are cross-sectional views illustrating the [010] direction of a positive electrode active material 100B in the positive electrode.
  • 6A and 6B are cross-sectional views of the positive electrode active material.
  • 7A to 7D are diagrams illustrating the phase change of the positive electrode active material.
  • FIG. 8 is a diagram illustrating the charge depth and lattice constant of the positive electrode active material.
  • 9A is a diagram illustrating an example of a method for manufacturing a positive electrode active material
  • FIGS. 9B and 9C are diagrams illustrating an example of a heating method in the manufacturing method.
  • 10A and 10B are diagrams illustrating an example of a method for manufacturing a positive electrode active material.
  • FIG. 11A and 11B are diagrams illustrating an example of a method for manufacturing a positive electrode active material.
  • FIG. 12 is a diagram illustrating an example of a method for producing a positive electrode active material.
  • FIG. 13 is a diagram illustrating an example of a method for producing a positive electrode active material.
  • FIG. 14 is a diagram illustrating an example of a method for producing a positive electrode active material.
  • 15A and 15B are diagrams illustrating an example of a manufacturing apparatus, and Fig. 15C is a diagram illustrating a cross section of the manufacturing apparatus.
  • 16A and 16B are cross-sectional schematic diagrams of a batch-type rotary kiln, and
  • FIG. 16C is a diagram showing an example of a time chart during heat treatment.
  • FIG. 17 is a phase diagram showing the relationship between the composition of lithium fluoride and magnesium fluoride and the temperature.
  • FIG. 18 is a phase diagram showing the relationship between the composition of lithium fluoride and aluminum fluoride and the temperature.
  • FIG. 19 is an example of a TEM image in which the crystal orientations are roughly consistent.
  • Fig. 20A is an example of an STEM image in which the crystal orientations are roughly consistent
  • Fig. 20B is an FFT pattern of a region of the rock-salt crystal RS
  • Fig. 20C is an FFT pattern of a region of the layered rock-salt crystal LRS.
  • FIG. 21 is a diagram illustrating the crystal structure of the positive electrode active material.
  • FIG. 22 is a diagram illustrating the crystal structure of a conventional positive electrode active material.
  • FIG. 21 is a diagram illustrating the crystal structure of the positive electrode active material.
  • FIG. 23 is a diagram showing an XRD pattern calculated from the crystal structure.
  • FIG. 24 shows an XRD pattern calculated from the crystal structure.
  • 25A and 25B are diagrams showing XRD patterns calculated from the crystal structure.
  • FIG. 26 is a diagram illustrating the crystal structure of the positive electrode active material.
  • 27A and 27B illustrate a positive electrode active material according to one embodiment of the present invention.
  • FIG. 28 illustrates a method for manufacturing a positive electrode active material according to one embodiment of the present invention.
  • FIG. 29 illustrates a method for manufacturing a positive electrode active material according to one embodiment of the present invention.
  • FIG. 30 is a diagram showing the external appearance of a secondary battery.
  • 31A to 31C are diagrams illustrating a method for manufacturing a secondary battery.
  • 32A to 32H are diagrams illustrating an example of an electronic device.
  • 33A to 33D are diagrams illustrating an example of an electronic device.
  • 34A to 34C are diagrams illustrating an example of an electronic device.
  • 35A to 35C are diagrams illustrating an example of a vehicle.
  • 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 space group, crystal plane, and crystal direction are expressed by adding a superscript bar to the numbers, but in this specification, due to format restrictions, instead of adding a bar above the numbers, a - (minus sign) may be added before the numbers.
  • Individual directions that indicate directions within a crystal are expressed with [ ]
  • collective directions that indicate all equivalent directions are expressed with ⁇ >
  • individual faces that indicate crystal faces are expressed with ( )
  • collective faces with equivalent symmetry are expressed with ⁇ ⁇ .
  • trigonal crystals expressed as space group R-3m are generally sometimes expressed as a composite hexagonal lattice of hexagonal crystals for ease of understanding the structure.
  • hkl not only (hkl) but also (hkil) may be used as Miller indices.
  • i is -(h+k).
  • crystal planes and the like are represented as a compound hexagonal lattice unless otherwise specified.
  • particles does not necessarily refer to spherical shapes (cross-sectional shape being circular), but may refer to shapes such as ellipses, rectangles, trapezoids, triangles, squares with rounded corners, asymmetric shapes, and the like in cross-sectional shape of individual particles, and furthermore, individual particles may be irregular in shape.
  • 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 274 mAh/g
  • the theoretical capacity of LiMn2O4 is 148 mAh/g.
  • the amount of lithium that can be inserted and removed from the positive electrode active material is indicated by x in the composition formula, for example, x in Li x CoO 2.
  • x (theoretical capacity - charging capacity) / theoretical capacity.
  • Li 0.2 CoO 2 or x 0.2.
  • x in Li x CoO 2 is small means 0.1 ⁇ x ⁇ 0.24.
  • the completion of discharge here refers to a state in which the voltage is 3.0 V or 2.5 V or less at a current of 100 mA/g or less.
  • the charge capacity and/or discharge capacity used to calculate x in Li x CoO 2 is measured under conditions that are free of or have little influence from short circuit and/or decomposition of the electrolyte, etc. For example, data from 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.
  • the space group of a crystal structure is identified by XRD, electron diffraction, neutron diffraction, etc. Therefore, in this specification and the like, the terms “belonging to a certain space group,” “belonging to a certain space group,” or “being a certain space group” can be rephrased as "identified with a certain space group.”
  • Cubic close packing of anions 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 second layer of anions, but not directly above the anions in the first layer. Therefore, the anions do not have to be strictly cubic lattices. Also, since real crystals always have defects, the analysis results do not necessarily have to be theoretical. For example, in the electron diffraction pattern or FFT (fast Fourier transform) pattern of a TEM image, etc., spots may appear in a position slightly different from the theoretical position. For example, if the orientation with respect to the theoretical position is 5 degrees or less, or 2.5 degrees or less, it can be said to have a cubic close packing structure.
  • FFT fast Fourier transform
  • the distribution of a certain element refers to the region in which the element is continuously detected in a certain continuous analytical method without being a noise region.
  • a region in which the element is continuously detected in a non-noise region can also be defined as a region in which the element is always detected when the analysis is performed multiple times.
  • positive electrode active materials to which additive elements have been added may be referred to as composite oxides, positive electrode materials, positive electrode materials, positive electrode materials for secondary batteries, etc.
  • secondary particles refer to particles formed by agglomeration of primary particles.
  • agglomeration includes a state of gathering, and does not matter what kind of binding force acts between multiple primary particles. In other words, it may be any of covalent bonds, ionic bonds, hydrophobic interactions, van der Waals forces, and other intermolecular interactions, and multiple binding forces may be acting.
  • primary particles refer to particles with no visible grain boundaries on the outside.
  • single particles refer to particles with no visible grain boundaries on the outside. Single particles are sometimes called primary particles because they are particles with no visible grain boundaries on the outside.
  • single crystals refer to crystals with no visible grain boundaries inside the particles
  • polycrystals refer to crystals with grain boundaries inside the particles.
  • Polycrystals may be said to be an aggregate of multiple crystallites, and grain boundaries may be said to be the interfaces existing between two or more crystallites. In polycrystals, it is preferable that the crystallites are aligned in the same direction.
  • the positive electrode active material of one embodiment of the present invention has a stable crystal structure even at high voltages. Because the crystal structure of the positive electrode active material is stable in the charged state, it is possible to suppress the decrease in charge/discharge capacity that accompanies repeated charging and discharging.
  • a short circuit in a secondary battery not only causes problems in the charging and/or discharging operations of the secondary battery, but may also lead to heat generation and fire.
  • it is preferable that short circuits are suppressed even at high charging voltages.
  • the positive electrode active material of one embodiment of the present invention suppresses short circuits even at high charging voltages. Therefore, a secondary battery that achieves both high discharge capacity and safety can be obtained.
  • ignition in a nail penetration test means that a flame is observed outside the exterior body within one minute after the nail is inserted. Or, it means that thermal runaway has occurred in the secondary battery. For example, if the temperature rise of the secondary battery exceeds 130°C, it can be said that thermal runaway has occurred. The temperature at this time can be measured by a temperature sensor attached to the exterior body of the secondary battery. It can also be said that ignition has occurred if, after the completion of the nail penetration test, solid thermal decomposition products derived from the positive electrode and/or negative electrode are observed at a location 2 cm or more away from the point of insertion.
  • lithium-ion secondary cells and lithium-ion secondary assembled batteries (hereinafter referred to as lithium-ion secondary batteries) can be said to be in a pre-degradation state when they have a discharge capacity of 97% or more of their rated capacity.
  • the rated capacity complies with JIS C 8711:2019.
  • they are not limited to the above JIS standards, but also comply with various JIS and IEC standards for electric vehicle propulsion, industrial use, etc.
  • the state of the materials in a secondary battery before degradation is referred to as an initial product or initial state
  • the state after degradation (the state when the secondary battery has a discharge capacity of less than 97% of the rated capacity) may be referred to as a product in use or in use state, or a used product or used state.
  • the battery according to one embodiment of the present invention includes a positive electrode, a negative electrode, and an electrolyte.
  • the electrolyte includes an electrolytic solution
  • the battery includes a separator between the positive electrode and the negative electrode.
  • the battery may further include an exterior body that covers at least a part of the periphery of the positive electrode, the negative electrode, and the electrolyte.
  • the positive electrode and positive electrode active material of the battery according to one embodiment of the present invention will be mainly described.
  • the positive electrode active material of the battery will be described in embodiments 2 and 3, and the remaining configuration of the lithium ion battery according to one embodiment of the present invention will be described in detail in embodiment 4.
  • FIG. 1A is a schematic cross-sectional view illustrating the internal structure of a battery 10.
  • the battery 10 has a positive electrode 11, a negative electrode 12, and a separator 13.
  • the positive electrode 11 has a positive electrode collector 21 and a positive electrode active material layer 22 on the positive electrode collector 21, and the negative electrode 12 has a negative electrode collector 31 and a negative electrode active material layer 32.
  • the positive electrode active material layer 22 and the negative electrode active material layer 32 face each other with the separator 13 in between.
  • the positive electrode collector 21 and the negative electrode collector 31 face each other with the separator 13 in between.
  • an electrolyte 51 is present in the voids in the positive electrode active material layer 22, the voids in the separator 13, and the voids in the negative electrode active material layer 32.
  • FIG. 1A illustrates one positive electrode 11, one negative electrode 12, and one separator 13, the lithium ion battery of one embodiment of the present invention is not limited to this structure. It may have a structure having two positive electrodes 11, two negative electrodes 12, and two separators 13, or may have more than this number stacked. Also, instead of the stacked structure shown in FIG. 1A, it may have a wound structure.
  • FIG. 1B is an enlarged view of part A enclosed by a dashed line in FIG. 1A.
  • the positive electrode 11 has a positive electrode current collector 21 and a positive electrode active material layer 22.
  • the positive electrode active material layer 22 has a positive electrode active material 100 and a conductive material 41.
  • the positive electrode active material layer 22 may have a binder in addition to the positive electrode active material 100 and the conductive material 41.
  • the voids in the positive electrode active material layer 22 are preferably filled with electrolyte 51 as shown in the figure.
  • the voids in the positive electrode active material layer 22 refer to areas in the positive electrode active material layer 22 other than the solid components (positive electrode active material, conductive material, etc.).
  • the conductive material is also called a conductive agent or conductive assistant, and is made of a carbon material.
  • attaching does not only refer to the physical adhesion between the active material and the conductive material, but also includes cases where a covalent bond is formed, where the conductive material is bonded by van der Waals forces, where a part of the surface of the active material is covered by the conductive material, where the conductive material is embedded in the surface irregularities of the active material, and where the two materials are electrically connected even if they are not in contact with each other.
  • the conductive material 41 may be a particulate conductive material, a fibrous conductive material, or a sheet-like conductive material, and may be used alone or in combination.
  • FIG. 1B shows an example in which a sheet-like conductive material is used as the conductive material 41, but a fibrous conductive material and a particulate conductive material may be used here, or a fibrous conductive material and a sheet-like conductive material may be further used, or a particulate conductive material and a sheet-like conductive material may be used.
  • particulate conductive materials for example, one or more of the following can be used: carbon black such as acetylene black and furnace black; artificial graphite; and graphite such as natural graphite.
  • carbon fibers such as mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers can be used.
  • carbon fibers carbon nanofibers or carbon nanotubes can be used.
  • Carbon nanotubes can be produced, for example, by vapor phase growth methods.
  • graphene compounds include graphene, multi-layer graphene, multi-graphene, graphene oxide, multi-layer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multi-layer graphene oxide, reduced multi-graphene oxide, and the like.
  • Graphene compounds refer to compounds that have carbon, have a shape such as a plate or sheet, and have 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.
  • the graphene compound may have a functional group.
  • the content of the conductive material 41 relative to the total amount of the positive electrode active material layer 22 is preferably 0.1 wt% or more and 10 wt% or less, and more preferably 0.5 wt% or more and 5 wt% or less.
  • graphene compounds Unlike particulate conductive materials such as carbon black, which make point contact with the positive electrode active material, graphene compounds enable surface contact with low contact resistance, so a smaller amount than normal conductive materials can improve the electrical conductivity between the particulate positive electrode active material and the graphene compound. This makes it possible to increase the ratio of active material in the active material layer, thereby increasing the discharge capacity of the battery.
  • positive electrode active material 100 a composite oxide having a layered rock salt type crystal structure of space group R-3m can be used (positive electrode active material 100A).
  • positive electrode active material 100A which is a composite oxide having a layered rock salt type crystal structure of space group R-3m
  • the particle surface exposed in a direction intersecting the (00l) plane can also be referred to as a particle surface having a normal in a direction intersecting the c-axis.
  • the positive electrode active material 100 it is preferable for the positive electrode active material 100 to have a region in contact with the conductive material 41 on a particle surface having a normal in a direction intersecting the c-axis.
  • any one or more of lithium cobalt oxide, lithium nickel-cobalt-manganese oxide, lithium nickel-cobalt-aluminate, and lithium nickel-manganese-aluminate can be used.
  • 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, etc.
  • composite oxides such as lithium cobalt oxide and lithium nickel-cobalt-manganese oxide
  • lithium has a two-dimensional diffusion path. In other words, it can be said that the lithium diffusion path exists along the surface.
  • a surface on which the lithium diffusion path is exposed that is, a surface other than the surface where lithium is inserted and removed (specifically the (00l) surface), may be referred to as an edge surface.
  • the two-dimensional diffusion path along the (00l) plane has higher electronic conductivity than the direction perpendicular to the (001) plane.
  • the diffusion path of electrons exists along the plane in composite oxides such as lithium cobalt oxide and lithium nickel-cobalt-manganese oxide.
  • the electronic conductivity of the positive electrode active material 100 and the conductive material 41 can be increased by contacting the conductive material on the particle surface exposed in the direction intersecting the (00l) plane of the composite oxide rather than contacting the conductive material on the particle surface parallel to the (00l) plane.
  • the electronic conductivity in the positive electrode active material layer 22 can be increased by the positive electrode active material 100 having a region in contact with the conductive material 41 on the particle surface having a normal in a direction intersecting the c-axis.
  • Figure 2 is a perspective view explaining typical crystal planes in a complex oxide having a layered rock salt type crystal structure of space group R-3m, such as lithium cobalt oxide and lithium nickel-cobalt-manganese oxide.
  • Figure 2 shows a schematic diagram of various crystal planes appearing on the particle surface of the complex oxide. Examples of particle surfaces having a normal in a direction intersecting with the c-axis in Figure 2 include the (104) plane, (012) plane, (1-12) plane, and (110) plane, as well as planes equivalent to these. However, since facet planes such as those in Figure 2 may not appear on the particle surface of an actual complex oxide, the particle surface having a normal in a direction intersecting with the c-axis does not refer to a specific crystal plane.
  • composite oxides such as lithium cobalt oxide and lithium nickel-cobalt-manganese oxide have a diffusion path for lithium ions on the (00l) plane.
  • composite oxides such as lithium cobalt oxide and lithium nickel-cobalt-manganese oxide have high electronic conductivity on the (00l) plane. That is, in composite oxides having a layered rock salt type crystal structure of space group R-3m, lithium ions and electrons tend to move in a direction parallel to the (00l) plane.
  • the movement of lithium ions during charging of a lithium ion secondary battery is such that lithium ions are released from the particle surface of the positive electrode active material into the electrolyte, and lithium ions are inserted from the electrolyte into the negative electrode active material.
  • the movement of electrons during charging of a lithium ion secondary battery is such that, at the positive electrode, when lithium ions are released from the positive electrode active material, electrons flow through the positive electrode current collector to the external circuit, and at the negative electrode, electrons flow from the external circuit through the negative electrode current collector to the negative electrode active material.
  • the movement of lithium ions and electrons during charging of a lithium ion secondary battery is in the opposite direction to the above-mentioned flows.
  • the movement of lithium ions and the movement of electrons can be explained as follows.
  • the direction in which the lithium ions move during charging is the normal direction of the positive electrode collector 21
  • the direction in which the lithium ions move during discharging is the normal direction of the negative electrode collector 31.
  • FIGS. 4A and 4B are cross-sectional views showing modified examples of the structure of the positive electrode 11 shown in FIG. 1B.
  • the arrow in the circle shown inside the positive electrode active material 100A indicates the direction of the c-axis of the complex oxide having a layered rock-salt type crystal structure of space group R-3m.
  • the solid arrow on the right side of the figure indicates the direction Dn of the normal to the negative electrode current collector 31.
  • the shape of the positive electrode active material 100A shown in Figure 4 etc. may be simplified or exaggerated for ease of viewing, and the shape of the positive electrode active material 100A of one embodiment of the present invention is not limited to the shape shown in Figure 4 etc.
  • the charging and discharging of the battery 10 becomes smooth and the output characteristics can be improved.
  • the angle between the normal to the negative electrode collector 31 and the c-axis of the crystal structure is 50 degrees or more and 130 degrees or less, preferably 60 degrees or more and 120 degrees or less, it can be said that the normal direction is aligned with the (00l) plane.
  • the number of particles whose c-axes are aligned with the normal to the negative electrode collector 31 is preferably 50% or more, more preferably 60% or more, of the total number of particles of the positive electrode active material 100 in the positive electrode active material layer 22.
  • This state can be called a state in which the positive electrode active material 100 is oriented.
  • the volume of the positive electrode active material 100 in which the normal to the negative electrode collector 31 and the c-axis are aligned is preferably 50% or more, more preferably 60% or more, relative to the total volume of the positive electrode active material 100 in the positive electrode active material layer 22. Such a state can be called a state in which the positive electrode active material 100 is oriented.
  • the area of the cross section of the positive electrode active material 100 in which the normal to the negative electrode collector 31 and the c-axis are aligned is preferably 50% or more, more preferably 60% or more, relative to the total area of the cross section of the positive electrode active material 100.
  • Such a state can be called a state in which the positive electrode active material 100 is oriented.
  • XRD analysis, TEM analysis, EBSD (electron backscatter diffraction pattern), etc. can be used as a method for analyzing the above orientation.
  • the positive electrode active material layer 22 in which the positive electrode active material 100A is oriented can be produced by applying a magnetic field during the production of the positive electrode active material layer 22.
  • the strength of the magnetic field can be, for example, 1 T or more, 2 T or more, 3 T or more, 4 T or more, 5 T or more, 6 T or more, 7 T or more, 8 T or more, 9 T or more, 10 T or more, or 15 T or more.
  • An electromagnet can be used as a method for applying the magnetic field.
  • FIG. 4A also shows a schematic diagram of the shape of the positive electrode active material 100A in which the length of a particular side is not extremely long, that is, the shape is close to a cube, close to a sphere, close to a regular octahedron, close to a regular dodecahedron, or a shape with rounded corners of any of these shapes.
  • the positive electrode active material 100A has such a shape, it is easy to orient the positive electrode active material 100A in a particular direction by applying a magnetic field when the positive electrode active material layer 22 is produced.
  • the shape of the positive electrode active material 100A is not limited to the above shapes.
  • the positive electrode active material layer 22 can be fabricated in such a way that the positive electrode active material 100A is oriented as shown in FIG. 4B, even if a magnetic field is not applied during fabrication of the positive electrode active material layer 22.
  • the complex oxide that can be used for the positive electrode active material 100 is not limited to this, and particles of a complex oxide having an olivine type crystal structure of space group pnma, such as lithium iron phosphate (LiFePO 4 ), can be used as the positive electrode active material 100 (positive electrode active material 100B).
  • the diffusion direction of lithium ions is the [010] direction.
  • the [010] direction of the composite oxide having an olivine-type crystal structure of the space group pnma is aligned with the normal direction of the negative electrode current collector 31 means that the angle between the [010] direction and the normal is 0 degrees or more and 40 degrees or less, and preferably 0 degrees or more and 30 degrees or less.
  • the positive electrode active material 100B when particles of a complex oxide having an olivine-type crystal structure of space group pnma are used as the positive electrode active material 100B, the number of particles in which the normal to the negative electrode current collector 31 and the [010] direction of the positive electrode active material 100 are aligned with respect to the total number of particles is preferably 50% or more, and more preferably 60% or more. This state can be called a state in which the positive electrode active material 100B is oriented.
  • FIGS. 5A and 5B show an example of an oriented state of the positive electrode active material 100B, which is a composite oxide having an olivine-type crystal structure of space group pnma.
  • FIG. 5A shows a schematic example of a shape of the positive electrode active material 100B in which the length of a particular side is not extremely long, that is, a shape close to a cube, a shape close to a sphere, a shape close to a regular octahedron, a shape close to a regular dodecahedron, or a shape with rounded corners of any of these shapes.
  • the positive electrode active material 100B has such a shape, it is easy to orient the positive electrode active material 100B in a particular direction by applying a magnetic field when the positive electrode active material layer 22 is produced.
  • the shape of the positive electrode active material 100B is not limited to the above shapes.
  • LiM1PO 4 As a composite oxide having an olivine type crystal structure of the space group pnma, for example, LiM1PO 4 (M1 is one or more selected from Fe, Ni, Co, and Mn) can be used.
  • LiM1PO 4 include LiFePO 4 , LiNiPO 4 , LiCoPO 4 , LiMnPO 4 , LiFe a Ni b PO 4 , LiFe a Co b PO 4 , LiFe a Mn b PO 4 , LiNi a Co b PO 4 , LiNi a Mn b PO 4 (a+b is less than or equal to 1, 0 ⁇ a ⁇ 1, 0 ⁇ b ⁇ 1), LiFe c Ni d CoePO 4 , LiFe c Ni d Mn e PO 4 , LiNi c Co d Mne PO 4 (c+d+e is 1 or less, 0 ⁇ c ⁇ 1, 0 ⁇ d ⁇ 1, 0 ⁇ e
  • the positive electrode active material layer 22 in which the positive electrode active material 100B is oriented can be produced by applying a magnetic field during the production of the positive electrode active material layer 22.
  • the strength of the magnetic field may be, for example, 1 T or more, 2 T or more, 3 T or more, 4 T or more, 5 T or more, 6 T or more, 7 T or more, 8 T or more, 9 T or more, 10 T or more, or 15 T or more.
  • An electromagnet can be used as a method for applying the magnetic field.
  • FIG. 5A also shows a schematic diagram of the shape of the positive electrode active material 100B in which the length of a particular side is not extremely long, that is, the shape is close to a cube, close to a sphere, close to a regular octahedron, close to a regular dodecahedron, or a shape with rounded corners of any of these shapes.
  • the positive electrode active material 100B has such a shape, it is easy to orient the positive electrode active material 100B in a particular direction by applying a magnetic field when the positive electrode active material layer 22 is produced.
  • the shape of the positive electrode active material 100B is not limited to the above shapes.
  • the positive electrode active material 100B when the positive electrode active material 100B is formed into a shape in which a particular side is extremely long, such as a plate, flake, wire, column, or other shape, and the short side direction is in the [010] direction of the crystal, even if a magnetic field is not applied during the preparation of the positive electrode active material layer 22, the positive electrode active material 100B can be oriented as shown in FIG. 5B.
  • a positive electrode active material 100A which is lithium cobalt oxide (also referred to as a lithium composite oxide containing cobalt) as an example of the positive electrode active material 100 in Embodiment 1 and a manufacturing method thereof will be described with reference to FIGS.
  • FIG. 6A and 6B are cross-sectional views of a positive electrode active material 100A1 according to one embodiment of the present invention.
  • the positive electrode active material 100A1 has a surface layer 100a and an inner portion 100b.
  • the boundary between the surface layer 100a and the inner portion 100b is indicated by a dashed line.
  • (001) in the figure indicates the (001) plane of lithium cobalt oxide (LiCoO 2 ).
  • LiCoO 2 belongs to the space group R-3m.
  • the positive electrode active material 100A1 has lithium, cobalt, oxygen, and an additive element.
  • the positive electrode active material 100A1 has lithium cobalt oxide to which an additive element has been added.
  • the additive elements contained in the positive electrode active material 100A1 are preferably one or more selected from magnesium, nickel, aluminum, fluorine, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, bromine, and beryllium.
  • the maximum concentration of magnesium in the surface layer 100a observed in EDX-ray analysis is preferably 1 atomic % or more, more preferably 10 atomic % or more.
  • the concentration of magnesium in the surface layer 100a is preferably 3 atomic % or more and 60 atomic % or less, more preferably 3 atomic % or more and 20 atomic % or less.
  • the concentration of magnesium in the surface layer 100a may be about 50 atomic %, for example, 45 atomic % or more and 55 atomic % or less.
  • Magnesium is preferably dissolved in the surface layer of the positive electrode active material, and is particularly preferably present at the lithium site.
  • the volume of the surface layer 100a is small compared to the overall volume of the positive electrode active material 100A1, it can be considered that the charge/discharge capacity of the positive electrode active material 100A1 remains almost unchanged even if the concentration of the added element in the surface layer 100a is high as described above.
  • nickel is also preferably present in the surface layer 100a.
  • Ni(II) is present at the lithium site in the surface layer 100a and is expected to suppress the external release of magnesium. This makes it possible to further increase the magnesium concentration in the surface layer 100a.
  • the external release here refers to, for example, elution from the positive electrode active material that accompanies charging when used in a secondary battery, and/or magnesium not being able to completely dissolve when heated in the positive electrode active material production process, segregating to a part of the surface, etc., to form a compound different from the positive electrode active material.
  • a representative example of the compound different from the positive electrode active material here is magnesium oxide.
  • titanium is also preferably present in the surface layer 100a.
  • the presence of titanium in the surface layer 100a is expected to promote the diffusion of lithium ions during charging and discharging. This may improve the charge and discharge rate.
  • the charge of Ti(IV) may have the effect of reducing the oxidation number of cobalt in lithium cobalt oxide and stabilizing the crystal structure.
  • fluorine is also present in the surface layer 100a. Like nickel, fluorine is expected to function to stabilize magnesium in the surface layer 100a.
  • the concentration (atomic %) of an element in the surface layer 100a refers to the concentration (atomic %) obtained from EDX ray analysis including the surface layer 100a, unless otherwise specified. Since lithium is not detected by EDX, it is not used to calculate the concentration. Unless otherwise specified, the concentration (atomic %) of each element observed by EDX ray analysis is the concentration (atomic %) when the sum of carbon, oxygen, fluorine, magnesium, aluminum, silicon, phosphorus, sulfur, calcium, titanium, manganese, iron, cobalt, nickel, and gallium is taken as 100 atomic %. Details of EDX analysis will be described later.
  • additive elements that are preferably present in the surface layer 100a include, in addition to the above-mentioned "magnesium and fluorine,” for example, “magnesium and aluminum,” “magnesium and nickel,” “magnesium and titanium,” “magnesium, nickel and aluminum,” “magnesium, titanium and aluminum,” “magnesium, fluorine and aluminum,” “magnesium, fluorine and nickel,” “magnesium, fluorine and titanium,” “magnesium, nickel, fluorine and aluminum,” and “magnesium, titanium, fluorine and aluminum.”
  • the average concentration of magnesium in the interior 100b is 0.03 atomic % or more and 1 atomic % or less.
  • the average concentration of nickel in the interior 100b is 100 ppm wt or more and 300 ppm wt or less, i.e., 0.0042 atomic % or more and 0.0126 atomic % or less.
  • the positive electrode active material 100A1 has an additive element in the surface layer 100a and the interior 100b as described above, which results in a more stable composition and crystal structure during charging. This allows the positive electrode active material 100A1 to have an O3' type crystal structure during charging.
  • the positive electrode active material 100A1 having an O3' type crystal structure during charging has extremely good charge and discharge cycle characteristics when used in a secondary battery. It is also expected to be highly safe.
  • FIG. 7A to 7D are schematic diagrams showing phase changes in the crystal structure of the positive electrode active material accompanying the desorption of lithium.
  • O3 in Fig. 7A is a schematic diagram of the crystal structure of the interior 100b of the positive electrode active material 100A1 according to one embodiment of the present invention in a discharged state, that is, when x in Li x CoO 2 is 1. It is believed that magnesium and nickel are present in some of the lithium sites of the interior 100b, and aluminum and nickel are present in some of the cobalt sites.
  • O3' shown in FIG. 7B is a schematic diagram of the crystal structure of the inside 100b of the positive electrode active material 100A1 of one embodiment of the present invention in a high voltage charging state, for example, when x in Li x CoO 2 is about 0.2.
  • the details of the O3' type crystal structure will be described later.
  • aluminum present in the cobalt site suppresses the desorption of lithium nearby.
  • magnesium and nickel are present in some of the lithium sites as in the discharge state. Therefore, it is believed that lithium present in the inside 100b exists randomly in the lithium site and does not form clusters. It is also believed that even if clusters are formed, the clusters can be made sufficiently small.
  • the effect of the added element that suppresses the formation of clusters of lithium ions in this way is called the pinning effect. It is believed that the effect is dominated by the average interatomic distance between magnesium and oxygen. This effect suppresses the contraction of the c-axis length of the positive electrode active material 100A1. In addition, since the concentration of magnesium is high in the surface layer portion 100a, the effect of suppressing the contraction of the c-axis length is further enhanced, and this effect can be transmitted to the inside 100b. It is believed that by suppressing the contraction of the c-axis length, O3' appears in the interior 100b and immediately below the surface layer 100a when x in Li x CoO 2 is about 0.2.
  • the H1-3 phase shown in FIG. 7C is a schematic diagram of a crystal structure when x in Li x CoO 2 is about 0.2 in the case where no additional element is particularly included.
  • the lithium cobalt oxide lithium moves as shown by the arrow in the figure to form clusters, and the lithium-containing layer and the lithium-free layer alternately appear, resulting in the H1-3 phase (Non-Patent Document 5).
  • the c-axis length of lithium cobalt oxide changes with the phase change (Non-Patent Document 4).
  • the change in the c-axis length of the conventional lithium cobalt oxide described in Non-Patent Document 4 is shown in FIG. 8.
  • the dashed arrow in the figure indicates the direction when charging from a discharged state to a charged state.
  • the round markers are hexagonal phases, and the diamond-shaped markers are monoclinic phases.
  • the c-axis length shrinks, as shown by the diamond-shaped marker in FIG. 8.
  • the phase transition from the O3 phase to the H1-3 phase is accompanied by the desorption of lithium ions, and is therefore thought to occur from the surface of the positive electrode active material, which is the region from which lithium ions are first desorbed, but may eventually spread to the entire positive electrode active material.
  • the H1-3 phase will be formed when x in Li x CoO 2 is about 0.2.
  • the maximum magnesium concentration in the surface layer is less than 1 atomic %, it is considered that the c-axis length will shrink and the O3' phase will not be formed.
  • 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 the H1-3 phase 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 the phase may be easily changed to a spinel type crystal structure.
  • the spinel type crystal structure may be more likely to change into 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 and discharge capacity of the positive electrode active material decreases.
  • the cation of the rock salt oxide in the surface layer 100a is Mg(II) or Co(II).
  • the cobalt in the spinel crystal structure Co3O4 or LiCo2O4 is Co(II), Co(III) or Co(IV).
  • the cobalt in the discharged LiCoO2 is Co(III), and the cobalt in the charged LixCoO2 (0 ⁇ x ⁇ 1) is Co(III) or Co(IV). Therefore, the region between the Co(IV) in the interior 100b in the discharged LixCoO2 (0 ⁇ x ⁇ 1) and the Co(II) or Mg(II) in the surface layer 100a may tend to change phase to a spinel having Co(III) as a buffer.
  • Method 1 for producing positive electrode active material 100A1 In order to form the surface layer 100a and the inner portion 100b having the additive elements as described above and to obtain the positive electrode active material 100A1 in which O3′ is expressed when x in Li x CoO 2 is about 0.2, not only the additive elements and their amounts but also the heating conditions in the preparation process are important.
  • the positive electrode active material 100A1 can be produced, for example, by the flow shown in Figure 9A.
  • Step S11 First, in step S11 shown in FIG. 9A, 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, for example, cobalt oxide such as tricobalt tetroxide, cobalt hydroxide, etc.
  • cobalt oxide such as tricobalt tetroxide, cobalt hydroxide, etc.
  • 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 lattice images obtained using a TEM (transmission electron microscope) device, and images obtained using a STEM (scanning transmission electron microscope) device, such as HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope) images and ABF-STEM (annular bright-field scanning transmission electron microscope) images, or evaluation using X-ray diffraction (XRD), electron beam diffraction, neutron beam diffraction, etc.
  • XRD X-ray diffraction
  • the above methods for evaluating crystallinity can be applied not only to cobalt sources, but also to evaluating the crystallinity of other sources.
  • 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 particles.
  • 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 recommended to use aluminum oxide balls or zirconium oxide balls as the grinding media. Zirconium oxide balls are preferable because they emit fewer impurities.
  • the peripheral speed is set 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. 9A the mixed material is heated.
  • the heating is preferably performed while changing the temperature in multiple stages.
  • the first heating step is expected to reduce crystal defects in the positive electrode active material.
  • the second heating step is expected to diffuse the added element into the surface layer of the positive electrode active material.
  • an additive element source (A source) during either or both of the period time 1 during which the first heating temperature is maintained and the period time 2 during which the second heating temperature is maintained.
  • a source additive element source
  • the additive element sources are mixed at both time 1 and time 2, it is preferable to mix the magnesium source and the nickel source at different times. If they are mixed at the same time, the nickel may inhibit the magnesium from dissolving in the positive electrode active material. For example, it is preferable to mix the nickel source and the aluminum source during the period time 1 during which the first heating temperature is maintained, and mix the aluminum source and the fluorine source during the period time 2 during which the second heating temperature is maintained. It is expected that such a mixing order will make it easier to distribute the nickel and aluminum in the interior 100b of the positive electrode active material 100A1.
  • heating may be performed at a second heating temperature (Temp. 2) higher than the first heating temperature, and then heating may be performed at a third heating temperature (Temp. 3) higher than the second heating temperature.
  • a second heating temperature Temporative temperature
  • a third heating temperature Temporative 3) higher than the second heating temperature.
  • the method of producing the positive electrode active material 100A1 of one embodiment of the present invention by a single heat treatment as shown in Figures 9A to 9C is highly productive and is preferable.
  • the container (which may be called a sheath, pot, or crucible) used in the heating process including step S13 is preferably made of aluminum oxide.
  • An aluminum oxide sheath is a material that does not easily release impurities. In this embodiment, an aluminum oxide sheath with a purity of 99.9% is used. It is preferable to place a lid on the sheath when heating, as this can prevent the material from volatilizing. It is preferable to attach additive elements such as magnesium and fluorine to the container in advance.
  • an additive element source such as a magnesium source or a fluorine source and/or a lithium source and being heated in the heating process. By using such a container, it is possible to further increase the magnesium concentration in the surface layer portion 100a.
  • Step S34 Through the above steps, the positive electrode active material 100A1 can be produced (step S34).
  • an additive element source may be mixed at the same time as the lithium source and the cobalt source in step S11.
  • magnesium and/or nickel may be mixed as the A1 source in step S11.
  • magnesium and/or nickel may be mixed again as the A2 source in step S13, or other additive elements may be mixed as the A2 source.
  • Method 1 for preparing positive electrode active material please refer to Method 1 for preparing positive electrode active material.
  • an additive element may be mixed with lithium cobalt oxide that has been synthesized in advance, and then the mixture may be heated.
  • step S14 lithium cobalt oxide synthesized in advance is prepared. In this case, steps S11 to S13 can be omitted.
  • LiCoO 2 in step S14 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 additional element is prepared.
  • step S21 lithium fluoride is prepared as a fluorine source, magnesium fluoride is prepared as a magnesium source, and LiF: MgF2 is weighed out to be 1:3 (molar ratio).
  • Step S22> LiF and MgF2 are mixed in dehydrated acetone and stirred at a rotation speed of 400 rpm for 12 hours to prepare an additive element source (Mg & F source).
  • a ball mill can be used for mixing, and zirconium oxide balls can be used as the grinding media.
  • 20 mL of dehydrated acetone, 22 g of zirconium oxide balls (1 mm ⁇ ), and a total of about 9 g of F source and Mg source are mixed in a 45 mL capacity container of a mixing ball mill. Then, the mixture is sieved with a sieve having 300 ⁇ m holes to obtain the Mg & F source (step S23).
  • step S31 lithium cobalt oxide and the Mg&F source are mixed.
  • the mixture can be stirred for one hour at a rotation speed of 150 rpm. This is a gentler stirring condition than that for obtaining the Mg&F source.
  • the mixture is sieved with a sieve having 300 ⁇ m openings to obtain a mixture 903 with a uniform particle size (step S32).
  • step S33 the mixture 903 is heated to obtain a positive electrode active material.
  • step S13 in the method 1 for producing a positive electrode active material can be referred to.
  • a magnesium source, a fluorine source, and a nickel source may be mixed with lithium cobalt oxide that has been synthesized in advance, and the mixture may be heated.
  • step S22b nickel hydroxide that has been subjected to a pulverization process is prepared as a nickel source, and the nickel hydroxide is weighed out so that it is 0.5 mol % of the lithium cobalt oxide.
  • a magnesium source, a fluorine source, a nickel source, and an aluminum source may be mixed with lithium cobalt oxide that has been synthesized in advance, and the mixture may be heated.
  • step S22c aluminum hydroxide that has been subjected to a pulverization process is prepared as an aluminum source, and the aluminum hydroxide is weighed out so that the content is 0.5 mol % of the lithium cobalt oxide.
  • lithium cobalt oxide synthesized in advance may be mixed with an aluminum source in addition to a magnesium source, a fluorine source, and a nickel source, and then heated. Also, mixing and heating of the magnesium source and the fluorine source may be performed separately from mixing and heating of the nickel source and the aluminum source. It is also more preferable to perform heating after synthesizing lithium cobalt oxide and before mixing with the additive element. This heating is sometimes called initial heating.
  • Step S15> 12 the lithium cobalt oxide synthesized in advance is heated.
  • the heating causes lithium to be desorbed from a part of the surface layer 100a of the lithium cobalt oxide, which leads to a more improved distribution of the additive elements.
  • 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 of the 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 100A1 and on its surface layer 100a.
  • the Me-O distance in rock salt Ni0.5Mg0.5O is 2.09x10-1 nm
  • the Me-O distance in rock salt MgO is 2.11x10-1 nm.
  • the Me-O distance in spinel NiAl2O4 is 2.0125x10-1 nm
  • the Me-O distance in spinel MgAl2O4 is 2.02x10-1 nm. In both cases , the Me-O distance exceeds 2x10-1 nm.
  • 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 ⁇ 10-1 nm (Li-O distance is 2.11 ⁇ 10-1 nm).
  • the Co-O distance in layered rock salt type LiCoO2 is 1.9224 ⁇ 10-1 nm (Li-O distance is 2.0916 ⁇ 10-1 nm).
  • the ionic radius of hexacoordinated aluminum is 0.535 ⁇ 10 ⁇ 1 nm
  • the ionic radius of hexacoordinated oxygen is 1.4 ⁇ 10 ⁇ 1 nm
  • the sum of these is 1.935 ⁇ 10 ⁇ 1 nm.
  • Initial heating is also expected to have the effect of increasing the crystallinity of the layered rock salt type crystal structure in the interior 100b.
  • a positive electrode active material 100A1 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.
  • 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 100A1 having an O3′ type and/or a monoclinic O1(15) type when x in Li x CoO 2 is small.
  • step S41 nickel hydroxide that has been subjected to a pulverization process is prepared as the nickel source, and aluminum hydroxide that has been subjected to a pulverization process is prepared as the aluminum source.
  • the nickel hydroxide and aluminum hydroxide are weighed out so that they are 0.5 mol % of the lithium cobalt oxide, and 0.5 mol % of the lithium cobalt oxide.
  • step S51 a nickel source, an aluminum source, and a composite oxide prepared in the same manner as in the method 3 for preparing a positive electrode active material are mixed together.
  • lithium cobalt oxide synthesized in advance may be mixed with at least one of a nickel source and an aluminum source, heated, and then mixed with a magnesium source and a fluorine source and heated again.
  • step S31 nickel hydroxide that has been subjected to a pulverization process is prepared as the nickel source, and aluminum hydroxide that has been subjected to a pulverization process is prepared as the aluminum source.
  • the nickel hydroxide is weighed out so as to be 0.5 mol% of the lithium cobalt oxide.
  • an aluminum source may also be prepared in step S31.
  • aluminum hydroxide that has been subjected to a pulverization process is prepared, and is weighed out so as to be 0.5 mol% of the lithium cobalt oxide.
  • lithium cobalt oxide synthesized in advance may be mixed with at least one of a nickel source and an aluminum source and heated, then a magnesium source and a fluorine source may be mixed and heated, and at least one of a nickel source and an aluminum source may be further mixed and heated.
  • a magnesium source and a fluorine source may be mixed and heated
  • at least one of a nickel source and an aluminum source may be further mixed and heated.
  • Heating in the positive electrode active material preparation method 1 to the positive electrode active material preparation method 8 may be performed using a rotary kiln or a roller hearth kiln. Heating in a rotary kiln can be performed while stirring in either a continuous or batch type. As an example of an apparatus that can be used for heating, a batch type rotary kiln will be described below.
  • ⁇ Batch type rotary kiln> 15A shows a schematic cross-sectional view of a batch-type rotary kiln 110.
  • the rotary kiln 110 has a kiln body 111, a heating means 112, a raw material supplying means 113, and an atmosphere control means 116.
  • the rotary kiln 110 also preferably has a control panel 115 and a measuring device 120.
  • the kiln body 111 is fixed to a plate 118.
  • the kiln body 111 is roughly cylindrical, with a raw material supply means 113 connected to one end and a material recovery means 114 at the other end.
  • the kiln body rotates to agitate the material to be treated that has been placed inside the kiln.
  • the heating means 112 has the function of heating the kiln body 111 to 700°C or higher and 1200°C or lower.
  • the heating means for example, a silicon carbide heater, a carbon heater, a metal heater, or a molybdenum disilicide heater can be used.
  • the raw material supply means 113 has the function of feeding the material to be treated into the kiln body 111.
  • the atmosphere control means 116 has the function of controlling the atmosphere inside the kiln body 111.
  • An example of the atmosphere control means 116 is a gas introduction line. It is preferable that the gas introduced contains oxygen.
  • the measuring device 120 can measure, for example, the atmosphere inside the kiln body 111.
  • gas chromatography (GC), mass spectrometer (MS), GC-MS, infrared spectroscopy (IR), or Fourier transform infrared spectroscopy (FT-IR) can be applied.
  • GC gas chromatography
  • MS mass spectrometer
  • IR infrared spectroscopy
  • FT-IR Fourier transform infrared spectroscopy
  • the measuring device 120 may be a measuring device other than the atmosphere, as long as it can confirm that the heating conditions are favorable.
  • a quartz crystal vibration film thickness meter or the like may be provided at or around the exhaust port as the measuring device 120.
  • the lithium fluoride can also be quantitatively measured by measuring the film thickness of the discharged lithium fluoride as it cools and accumulates using a quartz crystal vibration film thickness meter.
  • multiple measuring devices 120 may be provided, and multiple types of measuring devices may be provided.
  • the control panel 115 can control the heating temperature, atmosphere, etc. of the kiln body 111.
  • the control panel 115 preferably has a function of sending signals to the heating means 112 and the atmosphere control means 116.
  • the heating means 112 preferably has a function of performing heating based on a signal sent from the control panel 115.
  • the atmosphere control means 116 preferably has a function of introducing gas, etc. based on a signal sent from the control panel 115.
  • control panel 115 is provided with information on the data measured by the measuring device 120.
  • the control panel 115 has a function of, for example, analyzing the information on the data measured by the measuring device 120 and controlling the heating means 112, atmosphere control means 116, etc. based on the results of the analysis.
  • the heating means 112 can determine the heater output, etc., according to the information of the data measured by the measuring device 120. Also, the atmosphere control means 116 can determine the gas flow rate, or whether or not to supply gas, etc., according to the information of the data measured by the measuring device 120.
  • the rotary kiln 110 can agitate the material to be treated by rotating the kiln body 111 during heating, so the particles of the material to be treated are less likely to stick together.
  • the process of rotating the kiln body 111 is the sticking prevention process.
  • the batch method shown in Figure 15A is preferable because it allows for easy atmosphere control.
  • a rotary kiln 110a may be used that has a kiln body 111a with an internal blade 117 for stirring.
  • Figure 15B is a schematic cross-sectional view of a batch-type rotary kiln 110a
  • Figure 15C is a cross-sectional view of the kiln body 111a taken along the line A-A' in Figure 15B.
  • FIGS. 15B and 15C show an example of a kiln body 111a having one straight blade 117, but this is not a limitation of one aspect of the present invention. Multiple blades 117 may be provided. The blade 117 may also have another shape, such as a spiral shape.
  • FIG. 16A shows another example of a cross-sectional schematic diagram of a batch-type rotary kiln 110.
  • the rotary kiln 110 has a kiln body 111, which is a rotating drum, a heating means 112, a vibration means 119, a raw material supplying means 113, and a material recovery means 114.
  • the rotary kiln 110 also has a control panel 115, a gas supplying means 121, and a gas exhausting means 122.
  • the gas exhausting means 122 may be provided with a pump for exhausting gas inside the kiln body 111, a valve for preventing backflow, a detoxifying device (combustion detoxifying device or plasma detoxifying device) for detoxifying gas before being released into the outside air, and the like.
  • a detoxifying device combustion detoxifying device or plasma detoxifying device
  • fluorinated gas is used as the piping for supplying gas, it is preferable to use piping having an inner wall made of a material that is difficult to react with fluorinated gas, and multiple valves may be provided for each piping to prevent gas leakage.
  • materials that do not easily react with fluoride gas are used not only for the piping but also for the connecting parts, for example, the connecting part between the piping and the furnace, the connecting part between the piping and the gas supply means 121, and the connecting part between the piping and the gas exhaust means 122.
  • FIG. 16B shows a schematic cross-sectional view of the batch-type rotary kiln 110 taken along the dashed line ab in FIG. 16A.
  • the kiln body 111 is cylindrical, and an outer cylinder portion, i.e., heating means 112, is provided to surround the inner cylinder portion, i.e., the kiln body 111.
  • the kiln body 111 is fixed to a plate 118.
  • a part of the heating means 112 has an opening, and a vibration means 119 is provided so as to contact the inner cylinder portion.
  • the vibration means 119 is moved to apply an impact or vibration only to the kiln body 111, which serves as a process to suppress adhesion of powder to the inner wall of the furnace tube.
  • a container filled with powder and covered with a lid can be placed inside the core tube of the kiln body 111 and heated while rotating.
  • a container filled with powder and covered with a lid
  • an aluminum oxide container can be used as the container.
  • Figure 16C shows an example of a time chart for the heat treatment.
  • the temperature is raised to 900°C at a rate of 200°C per hour, and then maintained at 900°C for two hours, after which it is allowed to cool naturally.
  • Figure 16C also shows an example in which the furnace tube is vibrated for 6.5 hours from the start of heating, and the vibration is stopped when the material is allowed to cool naturally.
  • the surface layer 100a of the positive electrode active material 100A1 refers to, for example, a region within 50 nm from the surface toward the inside, more preferably within 35 nm from the surface toward the inside, even more preferably within 20 nm from the surface toward the inside, and most preferably within 10 nm from the surface toward the inside, perpendicular or approximately perpendicular from the surface. Note that approximately perpendicular is 80° or more and 100° or less. Surfaces caused by cracks and/or cracks may also be called surfaces.
  • the surface layer 100a is synonymous with the surface vicinity, the surface vicinity region, or the shell.
  • the surface layer 100a has an edge region 100a1 and a basal region 100a2.
  • the straight line marked (00l) represents the (00l) plane.
  • the edge region 100a1 has a surface exposed in a direction intersecting with the (00l) plane, and the region within 50 nm from the surface toward the inside, more preferably within 35 nm from the surface toward the inside, even more preferably within 20 nm from the surface toward the inside, and most preferably within 10 nm perpendicular or approximately perpendicular from the surface toward the inside is called the edge region 100a1.
  • intersecting means that the angle between the perpendicular line of the first surface (the (00l) plane) and the normal line of the second surface (the surface of the positive electrode active material 100A1) is 10 degrees or more and 90 degrees or less, more preferably 30 degrees or more and 90 degrees or less.
  • the basal region 100a2 has a surface parallel to the (00l) plane, and the region within 50 nm from the surface toward the inside, more preferably within 35 nm from the surface toward the inside, even more preferably within 20 nm from the surface toward the inside, and most preferably within 10 nm perpendicular or nearly perpendicular from the surface toward the inside is called the basal region 100a2.
  • "parallel” here means that the angle between the perpendicular to the first surface (the (00l) plane) and the normal to the second surface (the surface of the positive electrode active material 100A1) is 0 degrees or more and 5 degrees or less, more preferably 0 degrees or more and 2.5 degrees or less.
  • the area 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 surface of the positive electrode active material 100A1 refers to the surface of the composite oxide including the surface layer 100a and the interior 100b. Therefore, the positive electrode active material 100A1 does not include metal oxides such as aluminum oxide (Al 2 O 3 ) that do not have lithium sites that can contribute to charging and discharging, carbonates that are chemically adsorbed after the preparation of the positive electrode active material, hydroxyl groups, etc.
  • the attached metal oxide refers to a metal oxide whose crystal structure does not match that of the interior 100b, for example.
  • magnesium and nickel have a detection amount peak on the surface or within 3 nm from the reference point. It is also preferable that the distributions of magnesium and nickel overlap.
  • the detection amount peaks of magnesium and nickel may be at the same depth, or the magnesium peak may be closer to the surface, or the nickel peak may be closer to the surface.
  • the difference in depth between the detection amount peak of nickel and the detection amount peak of magnesium is preferably within 3 nm, and more preferably within 1 nm.
  • the detectable amount of fluorine in the surface layer 100a is greater than the detectable amount inside. It is also preferable that the detectable amount peak is located closer to the surface of the surface layer 100a. For example, it is preferable that the detectable amount peak is located on the surface or within 3 nm from the reference point. Similarly, it is preferable that the detectable amount of titanium, silicon, phosphorus, boron and/or calcium is greater than the detectable amount inside the surface layer 100a. It is also preferable that the detectable amount peak is located closer to the surface of the surface layer 100a. For example, it is preferable that the detectable amount peak is located on the surface or within 3 nm from the reference point.
  • aluminum has a different distribution from the above-mentioned magnesium and nickel.
  • the depth of the peak of the detection amount in the surface layer 100a from the surface or from a reference point in EDX-ray analysis described later is different for magnesium and nickel from that of aluminum.
  • the peak of the detection amount here refers to the maximum value of the detection amount in the surface layer 100a or within 50 nm from the surface.
  • the detection amount refers to, for example, the count in EDX-ray analysis.
  • the distributions of magnesium and aluminum may overlap, or there may be little overlap between the distributions of magnesium and aluminum.
  • the peak of the detection amount of aluminum may be present in the surface layer 100a or may be deeper than the surface layer 100a. For example, it is preferable that the peak is present on the surface or in a region of 5 nm to 30 nm from the reference point toward the inside.
  • manganese it is preferable for manganese to have a detection peak inside magnesium.
  • the added element does not necessarily have to have the same concentration gradient or distribution throughout the entire surface layer 100a of the positive electrode active material 100A1.
  • An example of the depth direction of the (001) surface of lithium cobalt oxide in the positive electrode active material 100A1 is shown by arrows Y1-Y2 in FIG. 6.
  • the (001) oriented surface crossed by the arrows Y1-Y2 may have a different distribution of additive elements from other surfaces.
  • the (001) oriented surface and its surface layer 100a may have a lower detection amount of one or more selected from additive elements compared to surfaces other than the (001) oriented surface. Specifically, the detection amount of magnesium and/or nickel may be low.
  • the (001) oriented surface and its surface layer 100a may have one or more selected from additive elements that are not detected or that are detected at 1 atomic % or less. Specifically, nickel may not be detected or that are detected at 1 atomic % or less.
  • the (001) oriented surface and its surface layer 100a may have a peak of detection amount of one or more selected from additive elements that is shallower from the surface compared to surfaces other than the (001) oriented surface. Specifically, the peaks in the detected amounts of magnesium and aluminum may be shallower than those in other surfaces.
  • the CoO 2 layer is relatively stable, it is more stable for the surface of the positive electrode active material 100A1 to have a (001) orientation. The main diffusion path of lithium ions during charging and discharging 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 become 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 100A1.
  • the additive elements in the surface other than the (001) oriented surface and in the surface layer 100a thereof are distributed as described above.
  • the concentration of the additive elements in the (001) oriented surface and in the surface layer 100a thereof may be low or absent.
  • 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 200 nm to 300 nm, and even more preferably 230 nm to 270 nm.
  • the half-width of the nickel distribution in the surface that is not (001) oriented and in the surface layer 100a thereof is preferably 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.
  • Magnesium is divalent, and magnesium ions are more stable at the lithium site than at the cobalt site in the layered rock salt crystal structure, so they tend to enter the lithium site.
  • the presence of magnesium at an appropriate concentration at the lithium site of the surface layer 100a makes it easier to maintain the layered rock salt crystal structure. This is presumably because the magnesium present at the lithium site functions as a pillar supporting the CoO 2 layers.
  • 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.
  • the presence of magnesium can be expected to increase the density of the positive electrode active material 100A1.
  • the magnesium concentration of the surface layer 100a is high, it can be expected that the corrosion resistance to hydrofluoric acid generated by the decomposition of the electrolyte will be improved.
  • magnesium is present at an appropriate concentration, it does not adversely affect the insertion and desorption of lithium during charging and discharging, and the above benefits can be enjoyed. However, if there is an excess of magnesium, it may have a negative effect on the insertion and desorption of lithium. Furthermore, the effect of stabilizing the crystal structure may be reduced. This is thought to be because magnesium enters the cobalt site in addition to the lithium site. In addition, excess 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 a resistance component of the secondary battery. Furthermore, 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 much magnesium enters 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 100A1 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 100A1 here may be a value obtained by performing an elemental analysis of the entire positive electrode active material 100A1 using, for example, GD-MS, ICP-MS, etc., or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material 100A1.
  • nickel can exist in both the cobalt site and the lithium site.
  • it has a lower redox potential than cobalt, so it can be said that it is easy to release lithium and electrons during charging. Therefore, it is expected that the charge and discharge speed will be faster. Therefore, even at the same charging voltage, a larger charge and discharge capacity can be obtained when the transition metal M is nickel than when it is cobalt.
  • LiNiO2 is less likely to undergo phase changes to the H1-3 phase and O1 even when the charge depth is increased. Therefore, nickel existing in the cobalt site has the effect of further stabilizing the O3 structure.
  • nickel present at the lithium site when nickel is 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. Therefore, nickel present at the lithium site, like magnesium, also functions as a pillar supporting the CoO2 layers, suppressing the phase change to the H1-3 phase. In addition, in a high-voltage charging state, nickel present at the cobalt site may move to the lithium site. Therefore, it is expected that the crystal structure will be more stable, particularly in a charging state at a high temperature, for example, 45°C or higher, which is preferable.
  • NiO nickel oxide
  • the order of ionization tendency is lowest for magnesium (Mg), aluminum (Al), cobalt (Co), and nickel (Ni) (Mg>Al>Co>Ni). Therefore, nickel is thought to be less likely to dissolve into the electrolyte during charging than the other elements listed above. Therefore, it is thought to be highly effective in stabilizing the crystal structure of the surface layer when in a charged state.
  • 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. Excessive nickel may also have a negative effect on the insertion and removal of lithium. If the nickel concentration is too high, the heat resistance may decrease when used in a secondary battery. In addition, the allowable temperature and time ranges in the manufacturing process, especially the heating process, may become narrow. This is because once nickel becomes NiO(II) during the heating process, it does not return to the layered rock salt type crystal structure.
  • the amount of nickel contained in the entire positive electrode active material 100A1 is appropriate.
  • the number of nickel atoms contained in the positive electrode active material 100A1 is preferably more than 0% and not more than 7.5% of the number of cobalt atoms, more preferably 0.05% to 4%, more 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.
  • more than 0.05% to 7.5% is preferable.
  • 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, 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.
  • Aluminum can be present at the cobalt site in the layered rock salt crystal structure. Since aluminum is a typical trivalent element and its valence does not change, lithium around the aluminum is unlikely to move even during charging and discharging. Therefore, aluminum and its surrounding lithium function as columns, and can suppress changes in the crystal structure. Therefore, as described below, even if the positive electrode active material 100A1 is subjected to a force that causes it to expand and contract in the c-axis direction due to the insertion and desorption of lithium ions, that is, even if a force that causes it to expand and contract in the c-axis direction is applied by changing the charge depth or charge rate, deterioration of the positive electrode active material 100A1 can be suppressed.
  • Aluminum also has the effect of suppressing the dissolution of surrounding cobalt and improving continuous charging resistance. Furthermore, since the Al-O bond is stronger than the Co-O bond, it can suppress the desorption of oxygen from around the aluminum. These effects improve thermal stability. Therefore, by having aluminum as an added element, it is possible to improve safety when using the positive electrode active material 100A1 in a secondary battery. Furthermore, it is possible to obtain a positive electrode active material 100A1 whose crystal structure is less likely to collapse even when repeatedly charged and discharged.
  • excess aluminum can have a negative effect on the insertion and removal of lithium. Also, because lithium around the aluminum is less mobile, the discharge capacity of the positive electrode active material can decrease.
  • the amount of aluminum contained in the entire positive electrode active material 100A1 is appropriate.
  • the number of aluminum atoms contained in the entire positive electrode active material 100A1 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 100A1 here may be, for example, a value obtained by performing elemental analysis of the entire positive electrode active material 100A1 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 100A1.
  • fluorine The presence of fluorine in the surface layer 100a having a surface that is in contact with the electrolyte, or the attachment of fluoride to the surface, can suppress excessive reaction between the positive electrode active material 100A1 and the electrolyte, and can effectively improve corrosion resistance against hydrofluoric acid.
  • lithium fluoride and other fluorides can function as a flux (also called a fluxing agent) that lowers the melting point of other additive element sources.
  • a flux also called a fluxing agent
  • the heating step it is believed that due to the fluxing effect, at least a portion of the surface layer of the lithium cobalt oxide and at least a portion of the additive element source melt to form a mixed layer.
  • This fluxing effect can increase the replacement efficiency of other additive elements.
  • liquid phase sintering can begin at a lower temperature, which may increase the crystallinity of the positive electrode active material 100A1.
  • the eutectic point of LiF and MgF2 is around 742°C, so in the heating step after mixing the additive element, it is preferable to set the heating temperature to 742°C or higher.
  • LiF and AlF3 also have two eutectic points, both of which are around 720° C., as shown in FIG. 18 (cited from Non-Patent Document 15). Therefore, when the fluoride contains LiF and AlF3 , it is preferable to set the heating temperature to 725° C. or higher in the heating step after mixing the additive element.
  • titanium additive elements The presence of titanium in the surface layer 100a is expected to promote the diffusion of lithium ions during charging and discharging. On the other hand, if there is an excess of titanium, it may extract magnesium from the lithium cobalt oxide and form a heterogeneous phase such as MgTiO3 on the surface.
  • phosphorus is present in the surface layer portion 100a, it is preferable because it may be possible to suppress short circuits when x in Li x CoO 2 is kept small.
  • phosphorus is preferably present in the surface layer portion 100a as a compound containing phosphorus and oxygen.
  • the positive electrode active material 100A1 contains phosphorus, the hydrogen fluoride generated by decomposition of the electrolyte or electrolyte reacts with the phosphorus, which may reduce the hydrogen fluoride concentration in the electrolyte, which is preferable.
  • hydrogen fluoride When the electrolyte contains LiPF 6 , hydrogen fluoride may be generated by hydrolysis. In addition, hydrogen fluoride may be generated by the reaction of polyvinylidene fluoride (PVDF), which is used as a component of the positive electrode, with an alkali.
  • PVDF polyvinylidene fluoride
  • the positive electrode active material 100A1 has phosphorus together with magnesium, the stability in the state where x in Li x CoO 2 is small becomes 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. Alternatively, 0.5% or more and 4% or less is preferable. Alternatively, 0.7% or more and 10% or less is preferable. Alternatively, 0.7% or more and 5% or less is preferable.
  • the phosphorus and magnesium concentrations shown here may be values obtained by performing elemental analysis of the entire positive electrode active material 100A1 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 100A1.
  • the progression of the cracks can be suppressed by the presence of phosphorus, or more specifically, a compound containing phosphorus and oxygen, inside the positive electrode active material with the cracks on its surface, for example, in the embedded portion.
  • 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 are present, it is preferable because it is possible to stabilize the crystal structure in a wider region.
  • the positive electrode active material 100A1 has both magnesium and nickel distributed in a region closer to the surface of the surface layer 100a and aluminum distributed in a deeper region, it is possible to stabilize the crystal structure in a wider region than if it had only one of them.
  • aluminum is not essential on the surface because the stabilization of the surface can be sufficiently achieved by magnesium, nickel, etc. Rather, it is preferable for aluminum to be widely distributed 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 to distribute aluminum 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, the effects of each additive element are synergistic and can contribute to further stabilization of the surface layer 100a.
  • the effect of achieving a stable composition and crystal structure is high and is therefore preferable.
  • the surface layer 100a is occupied only by compounds of the added element and oxygen, it is not preferable because it makes it difficult to insert and remove lithium.
  • the surface layer 100a 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.
  • 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.
  • the surface layer 100a has a higher cobalt concentration than magnesium.
  • the ratio Mg/Co of the number of magnesium atoms Mg to the number of cobalt atoms Co is preferably 0.62 or less. It is also preferable that the surface layer 100a has a higher cobalt concentration than nickel. It is also preferable that the surface layer 100a has a higher cobalt concentration than aluminum. It is also preferable that the surface layer 100a has a higher cobalt concentration than fluorine.
  • the surface layer 100a has a higher concentration of magnesium than nickel.
  • the number of nickel atoms is preferably 1/6 or less of the number of magnesium atoms.
  • some of the added elements particularly magnesium, nickel and aluminum
  • they are present randomly and dilutely in the interior 100b.
  • magnesium and aluminum are present at appropriate concentrations in the lithium sites of 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 cobalt and oxygen octahedra, 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 due to the concentration gradient of the added element as described above.
  • the crystal orientation of the surface layer 100a and the interior 100b are roughly the same.
  • the crystal structure changes continuously from the interior 100b of the layered rock salt type toward the surface and surface layer 100a, which has a rock salt type or both a rock salt type and a layered rock salt type crystal structure.
  • the crystal orientation of the surface layer 100a, which has the characteristics of the rock salt type or both the rock salt type and the layered rock salt type crystal structure, and the interior 100b of the layered rock salt type are roughly the same.
  • a 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, nickel, manganese, or iron, 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.
  • a rock-salt crystal structure is a cubic crystal structure, including those belonging to the space group Fm-3m, in which cations and anions are arranged alternately. Note that there may be a deficiency of cations or anions.
  • the fact that it has both the characteristics of layered rock salt type and rock salt type crystal structure 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 beam diffraction pattern corresponding to the crystal planes forming this two-dimensional plane is taken 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 region has two phases, for example, rock salt type MgO and layered rock salt type LiCoO2 , 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, and 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 comes into contact with a rock salt crystal, there are crystal faces on which 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 type is in space group R-3m and has a rhombohedral structure, but is generally represented as a compound hexagonal lattice to make the structure easier to understand, and the (0001) plane of the layered rock salt type has a hexagonal lattice.
  • the triangular lattice of the cubic ⁇ 111 ⁇ plane has the same atomic arrangement as the hexagonal lattice of the (0001) plane of the layered rock salt type. When the two lattices are compatible, it can be said that the orientation of the cubic close-packed structure is aligned.
  • the space group of layered rock salt crystals and O3' type crystals is R-3m, which is different from the space group Fm-3m (the space group of general rock salt crystals) of rock salt crystals, so the Miller indices of the crystal planes that satisfy the above conditions are different between layered rock salt crystals and O3' type crystals and rock salt crystals.
  • the crystal orientations are roughly the same.
  • the three-dimensional structural similarity in which the crystal orientations are roughly the same, or the same crystallographic orientation is called topotaxis.
  • the fact 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, etc. It can also be judged from the FFT patterns of TEM images and STEM images. Furthermore, XRD (X-ray diffraction), neutron diffraction, etc. can also be used as materials for judgment.
  • Figure 19 shows an example of a TEM image in which the orientation of the layered rock salt crystals LRS and the rock salt crystals RS roughly coincides.
  • Images reflecting the crystal structure can be 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 a bright band (bright strip) and a dark band (dark strip). 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.
  • the crystal planes are roughly aligned, that is, the crystal orientations are roughly aligned.
  • 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.
  • lithium cobalt oxide with 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 arrangements of the lithium atoms and oxygen atoms are observed as dark lines or low-brightness areas.
  • fluorine (atomic number 9) and magnesium (atomic number 12) are added to the lithium cobalt oxide.
  • Figure 20A shows an example of an STEM image in which the orientations of the layered rock-salt crystal LRS and the rock-salt crystal RS roughly match.
  • the FFT pattern of the area of the rock-salt crystal RS is shown in Figure 20B
  • the FFT pattern of the area of the layered rock-salt crystal LRS is shown in Figure 20C.
  • the composition, JCPDS card number, and the d-value and angle calculated from these are shown on the left of Figures 20B and 20C.
  • the actual measured values are shown on the right.
  • the spot marked with an O is the zeroth order diffraction.
  • the spot marked A in Figure 20B is due to the 11-1 reflection of the cubic crystal.
  • the spot marked A in Figure 20C is due to the 0003 reflection of the layered rock salt type. From Figures 20B and 20C, 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 20B is roughly parallel to the line passing through AO in Figure 20C. 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 that is not due to 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. 20C is due to the 10-14 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 Figure 20B 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 Figure 20B) originating from the 11-1 of a cubic crystal.
  • ⁇ AOB is 54° to 56°
  • this index is just an example, and does not necessarily have to match this.
  • a reciprocal lattice point equivalent to 11-1 and 200 may be used.
  • layered rock-salt type positive electrode active materials such as lithium cobalt oxide
  • the (0003) plane and equivalent planes as well as the (10-14) plane and equivalent planes, as crystal planes. Therefore, when observing the (0003) plane with a TEM or the like, first select a particle of the positive electrode active material in which a crystal plane expected to be the (0003) plane is observed with a SEM or the like, and then slice the particle of the positive electrode active material 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.
  • FIB Flucused Ion Beam
  • the positive electrode active material 100A1 has the above-described distribution of additive elements and/or crystal structure in a discharged state, and therefore has a crystal structure in which x in Li x CoO 2 is small, which is different from that of conventional positive electrode active materials.
  • small x here means that 0.1 ⁇ x ⁇ 0.24.
  • the positive electrode active material 100A1 has the above-described distribution of additive elements and/or crystal structure in a discharged state, and therefore has a crystal structure in which x in Li x CoO 2 is small, which is different from that of conventional positive electrode active materials.
  • small x here means that 0.1 ⁇ x ⁇ 0.24.
  • the change in the crystal structure of a conventional positive electrode active material is shown in Fig. 22.
  • the conventional positive electrode active material shown in Fig. 22 is lithium cobalt oxide (LiCoO 2 ) 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 4, 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 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 O1 type.
  • the trigonal crystal may be converted to a composite hexagonal lattice and called 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.
  • 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 diagram 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 crystal structure and the volume of the unit cell of lithium cobalt oxide change with the change in the charge depth, i.e., with the change in x in Li x CoO 2 .
  • the change in the c-axis length of lithium cobalt oxide corresponds to a change in the angle at which a peak appears in the XRD pattern, for example, of the (003) plane of lithium cobalt oxide.
  • the peak of the (003) plane of lithium cobalt oxide appears at 2 ⁇ of around 19° to 20°.
  • 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.
  • 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 highly 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.
  • the change in the crystal structure in the discharged 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 a 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. In addition, the change in volume compared per cobalt atom can be reduced. Therefore, the positive electrode active material 100A1 of one embodiment of the present invention is less likely to collapse in crystal structure even when charging and discharging are repeated so that x is 0.24 or less, and excellent cycle characteristics can be realized.
  • the positive electrode active material 100A1 of one embodiment of the present invention can have a more stable crystal structure than a conventional positive electrode active material in the state where x in Li x CoO 2 is 0.24 or less. Therefore, in the positive electrode active material 100A1 of one embodiment of the present invention, a short circuit is unlikely to occur when x in Li x CoO 2 is kept at 0.24 or less. In such a case, the safety of the secondary battery is further improved, which is preferable.
  • FIG. 21 shows the crystal structure of the interior 100b of the positive electrode active material 100A1 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 100A1 and is the part that contributes greatly to charge and discharge, so it can be said that the shift of the CoO 2 layer and the change in volume are the most problematic parts.
  • the positive electrode active material 100A1 has the same crystal structure as conventional lithium cobalt oxide, R-3m O3.
  • the positive electrode active material 100A1 has a different crystal structure from that of conventional lithium cobalt oxide, which has an H1-3 type crystal structure when x is 0.24 or less, for example, about 0.2 and about 0.15.
  • 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. 21 with R-3m O3'.
  • the coordinates of cobalt and oxygen in the unit cell can be expressed in the range of Co(0,0,0.5), O(0,0,x), 0.20 ⁇ x ⁇ 0.25.
  • one CoO2 layer exists in the unit cell.
  • the amount of lithium present in the positive electrode active material 100A1 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. 21 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 ⁇ X O1 ⁇ 0.24, 0.61 ⁇ Z O1 ⁇ 0.65, O2( XO2,0.5 , ZO2 ),
  • the lattice constant of the unit cell can be expressed as follows: 0.75 ⁇ X O2 ⁇ 0.78, 0.68 ⁇ Z O2 ⁇ 0.71.
  • 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 type Non-Patent Document 3 can be referred to.
  • the positive electrode active material 100A1 of one embodiment of the present invention 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. In addition, the change in volume is also suppressed when compared per the same number of cobalt atoms. Therefore, the positive electrode active material 100A1 does not easily collapse in crystal structure even when charging and discharging are repeated such that x is 0.24 or less. Therefore, the positive electrode active material 100A1 suppresses a decrease in charge and discharge capacity in the charge and discharge cycle.
  • the positive electrode active material 100A1 since more lithium can be stably used than in the conventional positive electrode active material, the positive electrode active material 100A1 has a large discharge capacity per weight and per volume. Therefore, by using the positive electrode active material 100A1, a secondary battery with a high discharge capacity per weight and per volume can be manufactured.
  • the positive electrode active material 100A1 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 100A1 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 100A1 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 not only by x in Li x CoO 2 but also by the number of charge and discharge cycles, charge and discharge current, temperature, electrolyte, etc.
  • the positive electrode active material 100A1 may have only O3' type, may have only monoclinic O1 (15) type, or may have both crystal structures. Furthermore, all of the particles in the inside 100b of the positive electrode active material 100A1 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 100A1 of one embodiment of the present invention 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 100A1 when the charging voltage is further increased, the H1-3 type crystal structure may finally be observed.
  • the crystal structure is affected by the number of charge/discharge cycles, the charge/discharge current, the temperature, the electrolyte, etc., so that when the charging voltage is lower, for example, even when the charging voltage is 4.5 V or more and less than 4.6 V at 25° C., the positive electrode active material 100A1 of one embodiment of the present invention may be able to adopt the O3' type crystal structure.
  • the monoclinic O1(15) type crystal structure when charging at a voltage of 4.65 V or more and 4.7 V or less at 25° C., the monoclinic O1(15) type crystal structure may be adopted.
  • the voltage of the secondary battery drops by the amount of the graphite potential compared to the above.
  • the potential of graphite is about 0.05V to 0.2V 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 a similar crystal structure at a voltage obtained by subtracting the potential of graphite from the voltage when lithium metal is used as the negative electrode active material.
  • 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. 22.
  • 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.
  • the additive element contained in the positive electrode active material 100A1 of one embodiment of the present invention is distributed as described above, and that at least a part of the additive element is unevenly distributed in and near the crystal grain boundaries.
  • uneven distribution refers to the concentration of an element in one area being 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 magnesium concentration at and near the grain boundaries of the positive electrode active material 100A1 is higher than other regions of the interior 100b. It is also preferable that the fluorine concentration at and near the grain boundaries is higher than other regions of the interior 100b. It is also preferable that the nickel concentration at and near the grain boundaries is higher than other regions of the interior 100b. It is also preferable that the aluminum concentration at and near the grain boundaries is higher than other regions of the interior 100b.
  • Grain boundaries are a type of planar defect. As a result, they are prone to become unstable, just like particle surfaces, and changes in the crystal structure are likely to occur. Therefore, if the concentration of added elements at and near the grain boundaries 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, even if cracks occur along the grain boundaries of the positive electrode active material 100A1 of one embodiment of the present invention, the magnesium concentration and fluorine concentration will be high near the surface created by the cracks. Therefore, even after cracks have occurred in the positive electrode active material, the corrosion resistance to hydrofluoric acid can be improved. Also, even after cracks have occurred in the positive electrode active material, side reactions between the electrolyte and the positive electrode active material can be suppressed.
  • 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 preferably 1 ⁇ m or more and 40 ⁇ m or less. Or preferably 1 ⁇ m or more and 30 ⁇ m or less.
  • Positive electrode active material 100A1 with a relatively small particle size is expected to have high charge/discharge rate characteristics.
  • Positive electrode active material 100A1 with a relatively large particle size is expected to have high charge/discharge cycle characteristics and maintain a high discharge capacity.
  • a certain positive electrode active material is the positive electrode active material 100A1 of one embodiment of the present invention, which has 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 with high resolution the symmetry of transition metals such as cobalt contained in the positive electrode active material, it can compare the degree of crystallinity and the orientation of the crystals, it can analyze the lattice periodicity, distortion and crystallite size, and it can provide sufficient accuracy even when measuring the positive electrode obtained by dismantling a secondary battery.
  • powder XRD can provide diffraction peaks that reflect the crystal structure of the interior 100b of the positive electrode active material 100A1, which occupies the majority of the volume of the positive electrode active material 100A1.
  • the positive electrode active material When analyzing crystallite size using powder XRD, it is preferable to perform the measurement without 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 dismantling a secondary battery, prepare a powder sample, and then perform the measurement.
  • the positive electrode active material 100A1 of one embodiment of the present invention 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.
  • a material in which 50% or more of the crystal structure exhibits a large change in crystal structure when charged at a high voltage is not preferred because it cannot withstand repeated charging and discharging at a high voltage.
  • 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% or more, and cases where the H1-3 crystal structure is 50% or more.
  • the positive electrode active material 100A1 of one embodiment of the present invention Even in the case of the positive electrode active material 100A1 of one embodiment of the present invention, 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 a material is the positive electrode active material 100A1 of one embodiment of the present invention, analysis of the crystal structure, such as XRD, and information such as the charging capacity or charging voltage are required.
  • Whether the distribution of added elements in a certain positive electrode active material is as described above can be determined by analysis using, for example, XPS, energy dispersive X-ray spectroscopy (EDX), electron probe microanalysis (EPMA), etc.
  • the crystal structure of the surface layer 100a, grain boundaries, etc. can be analyzed by electron beam diffraction of a cross section of the positive electrode active material 100A1.
  • a coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) using the composite oxide for the positive electrode and lithium metal for the counter electrode can be fabricated and charged to determine whether a certain composite oxide is the positive electrode active material 100A1 of one embodiment of the present invention.
  • the coin cell includes an electrolyte, a separator, a positive electrode can, and a negative electrode can.
  • charging to determine whether the complex oxide is the positive electrode active material 100A1 of one embodiment of the present invention can be performed by dismantling the lithium ion secondary battery, removing the positive electrode having the complex oxide, and preparing a coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) with a lithium counter electrode in the same manner as above, and charging the coin cell.
  • a coin cell CR2032 type, diameter 20 mm, height 3.2 mm
  • the reason for performing such a process before charging is that, since the battery voltage is the difference between the positive electrode potential and the negative electrode potential, it is difficult to accurately determine the potential of the positive electrode in a lithium ion secondary battery using a material other than lithium metal for the negative electrode.
  • the positive electrode can be made 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 will differ. Unless otherwise specified, voltages and potentials in this specification refer to the potential of the positive electrode.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • 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 cell prepared under the above conditions is charged at any voltage (for example, 4.5V, 4.55V, 4.6V, 4.65V, 4.7V, 4.75V, or 4.8V).
  • the charging method is not particularly limited as long as it can be charged at any voltage for a sufficient 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 current does not become 2mA/g or more and 10mA/g or less even after CV charging for a long time, it is considered that the current is consumed not for charging the positive electrode active material but for decomposing the electrolyte, so CV charging may be terminated when a sufficient time has passed since the start.
  • the sufficient time can be, for example, 1.5 hours or more and 3 hours or less.
  • the temperature is 25°C or 45°C.
  • XRD can be performed by sealing the cell 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 can be performed at a constant current discharge of 2.5 V and 20 mA/g to 100 mA/g.
  • an arbitrary voltage e.g., 4.6 V, 4.65 V, 4.7 V, 4.75 V, or 4.8 V
  • constant current discharge can be performed at, for example, 2.5 V and a current value of 20 mA/g or more and 100 mA/g or less.
  • 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: CuK ⁇ 1 -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 measurement sample is a powder, it can be set up by placing it in a glass sample holder or sprinkling the sample on a greased silicone anti-reflective plate. If the measurement sample is a positive electrode, the positive electrode can be attached to the substrate with double-sided tape, and the positive electrode active material layer can be set to match the measurement surface required by the device.
  • Ideal powder XRD 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 CuK ⁇ 1 radiation are shown in Figures 23, 24, 25A, and 25B.
  • Figures 25A and 25B show the XRD patterns of the O3' type crystal structure, the monoclinic O1(15) type crystal structure, and the H1-3 type crystal structure, with Figure 25A showing an enlarged view of the region in which 2 ⁇ is in the range of 18° to 21°, and Figure 25B showing an enlarged view of the region in which 2 ⁇ is in the range of 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 pattern of the H1-3 type crystal structure was similarly created from the crystal structure information described in Non-Patent Document 3.
  • the crystal structure patterns of the O3′ type and monoclinic O1(15) type were estimated from the XRD pattern of the positive electrode active material of one embodiment of the present invention, and fitting was performed using TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker Corporation), and XRD patterns were created in the same manner as for the others.
  • the positive electrode active material 100A1 of one embodiment of the present invention has an O3' type and/or monoclinic O1 (15) type crystal structure when x in Li x CoO 2 is small, but not all of the particles may have an O3' type and/or monoclinic O1 (15) type crystal structure. It may contain other crystal structures including O3 type, or may be partially amorphous. However, when Rietveld analysis is performed on the XRD pattern, it is preferable that the O3 type, O3' type and/or monoclinic O1 (15) type crystal structure is 50% or more, more preferably 60% or more, and even more preferably 66% or more. If the O3 type, O3' type and/or monoclinic O1 (15) type crystal structure is 50% or more, more preferably 60% or more, and even more preferably 66% or more, it can be a positive electrode active material with sufficiently excellent cycle characteristics.
  • the H1-3 type and O1 type crystal structures are less than 50%. Or, it is preferable that they are 34% or less. Or, more preferably, they are not substantially observed.
  • the O3' type and/or monoclinic O1(15) type crystal structure is preferably 35% or more, more preferably 40% or more, and even more preferably 43% or more.
  • the (003) diffraction peak of O3 has a maximum value at, for example, 19.10 ⁇ 0.10°
  • the abundance ratio of each crystal structure can be estimated by determining the area intensity ratio of specific peaks. For example, using TOPAS as analysis software, fitting can be performed using a Pseudo Voigt function in the range of 2 ⁇ from 15° to 25° to determine the area intensity ratio of each peak.
  • the number of background terms can be set to, for example, 20. It is known that in the range of 2 ⁇ from 15° to 25°, a peak corresponding to the (003) plane of lithium cobalt oxide and a peak corresponding to the (006) plane of the H1-3 crystal structure are observed.
  • the area intensity ratio of the O3 peak to the sum of O3 and O3', I O3 /(I O3 +I O3' ), is preferably 1% or more and 60% or less, more preferably 15% or more and 60% or less, and even more preferably 30% or more and 60% or less.
  • the H1-3 type crystal structure is less in terms of the area intensity ratio.
  • the area intensity ratio of the H1-3 peak to the sum of O3' and H1-3, I H1-3 / (I O3' + I H1-3 ) is preferably 50% or less, more preferably 30% or less, and even more preferably 20% or less.
  • each diffraction peak after charging is sharp, i.e., has a narrow full width at half maximum.
  • 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 that 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 100A1 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, a clear peak of the O3' type and/or monoclinic O1 (15) crystal structure can be confirmed when x in Li x CoO 2 is small.
  • 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 influence of the Jahn-Teller effect is small.
  • transition metals such as nickel and manganese may be added as long as the influence of the Jahn-Teller effect is small.
  • a nickel concentration of less than 7.5% is preferable because it results in an excellent positive electrode active material with small Jahn-Teller distortion.
  • a manganese concentration of, for example, 4% or less is preferable.
  • 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 stated 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 100A1 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. The quantitative accuracy of XPS is often about ⁇ 1 atomic %, with a lower limit of about 1 atomic %, depending on the element.
  • the concentration of one or more selected from the additive elements is preferably higher in the surface layer 100a than in the interior 100b.
  • concentration of one or more selected from the additive elements in the surface layer 100a is preferably higher than the average of the entire positive electrode active material 100A1. Therefore, for example, it can be said that the concentration of one or more selected additive elements in 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 100A1 measured by ICP-MS (inductively coupled plasma mass spectrometry) or GD-MS (glow discharge mass spectrometry).
  • 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 100A1.
  • 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 100A1.
  • the aluminum concentration in at least a portion of the surface layer 100a is higher than the average aluminum concentration in the entire positive electrode active material 100A1.
  • 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 100A1.
  • the surface and surface layer 100a of the positive electrode active material 100A1 of one embodiment of the present invention do not contain carbonates, hydroxyl groups, etc. that are chemically adsorbed after the preparation of the positive electrode active material 100A1. 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 100A1. 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 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 this does not affect the atomic ratio of the added element.
  • the concentration of the added element may also be compared in terms of its ratio to cobalt.
  • Using the ratio to cobalt 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 atoms to 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 100a are higher than the concentrations of one or more additive elements selected from the additive elements contained in the surface layer 100a measured by XPS or the like.
  • the concentration of at least a part of the cobalt in the surface layer 100a measured by XPS or the like is higher than the concentration of at least a part of the magnesium in the surface layer 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 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 fluorine. It is also preferable that the concentration of lithium is higher than fluorine.
  • aluminum is widely distributed in a deep region, for example, on the surface, or in a region having a depth of 5 nm to 50 nm from the reference point. Therefore, although aluminum is detected in an analysis of the entire positive electrode active material 100A1 using ICP-MS, GD-MS, etc., it is more preferable that the concentration of aluminum is not detected by XPS, etc., or is 1 atomic % or less.
  • the number of magnesium atoms is 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 is 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 is 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 is 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 range on the surface of the positive electrode active material 100A1, but are widely distributed in the surface layer 100a of the positive electrode active material 100A1 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 100A1 have a concentration gradient. It is more preferable that the positive electrode active material 100A1 has a concentration peak at a different depth from the surface depending on the additive element.
  • the concentration gradient of the additive element can be evaluated, for example, by exposing a cross section of the positive electrode active material 100A1 using a focused ion beam (FIB) or the like and analyzing the cross section using energy dispersive X-ray spectroscopy (EDX), electron probe microanalysis (EPMA), or the like.
  • FIB focused ion beam
  • EDX energy dispersive X-ray spectroscopy
  • EPMA electron probe microanalysis
  • 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 boundaries of the positive electrode active material 100A1.
  • EDX ray analysis can also 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 positive electrode active material 100A1 is a compound containing oxygen and a transition metal capable of inserting and removing lithium
  • 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 and oxygen are present and the region where they are not present is defined as the surface of the positive electrode active material.
  • a protective film may be attached to the surface, but the protective film is not included in the positive electrode active material.
  • the protective film a single layer or multilayer film of carbon, metal, oxide, resin, etc. may be used.
  • the reference points are the point where the detection amount of the characteristic X-rays of the transition metal M is 50% of the sum of the average detection amount M AVE of the inside and the average detection amount M BG of the background, and the point where oxygen is 50% of the sum of the average detection amount O AVE of the inside and the average detection amount O BG of the background. If the 50% points of the sum of the inside and the background are different for the transition metal M and oxygen, this is considered to be due to the influence of metal oxides, carbonates, etc.
  • the 50% point of the sum of the average detection amount M AVE of the inside of the transition metal M and the average detection amount M BG of the background can be adopted.
  • the reference point can be determined using the M AVE and M BG of the element having the largest count number in the interior 100b.
  • the average value M BG of the background detection amount of the characteristic X-rays of the transition metal M can be obtained by averaging a range of 2 nm or more, preferably 3 nm or more, outside the positive electrode active material, avoiding the vicinity where the detection amount of the characteristic X-rays of the transition metal M starts to increase.
  • the average value M AVE of the internal detection amount can be obtained by averaging a range of 2 nm or more, preferably 3 nm or more, in a region where the counts of the characteristic X-rays of the transition metal M and the characteristic X-rays of oxygen are saturated and stable, for example, a portion that is 30 nm or more, preferably 50 nm deep from the region where the detection amount of the transition metal M starts to increase.
  • the average value O BG of the background of the characteristic X-rays of oxygen and the average value O AVE of the internal detection amount of oxygen can also be obtained in the same manner.
  • the surface of the positive electrode active material 100A1 in a cross-sectional STEM (scanning transmission electron microscope) image or the like is the boundary between an area where an image originating 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 originating from the atomic nuclei of metal elements having atomic numbers larger than that of lithium among the metal elements constituting the positive electrode active material are observed.
  • the spatial resolution of STEM-EDX is about 1 nm. Therefore, the maximum value of the intensity distribution of characteristic X-rays corresponding to the added element may deviate by about 1 nm. For example, even if the maximum value of the intensity distribution of characteristic X-rays corresponding to an added element such as magnesium is located outside the surface determined above, it can be considered an error as long as 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 detected intensity in the intensity distribution of characteristic X-rays corresponding to each element, or the maximum value of characteristic X-rays for each element.
  • noise in STEM-ED X-ray analysis can be measured values 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 value measured over six scans can be used as the detection intensity of the characteristic X-rays corresponding to 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 detection intensity of the characteristic X-rays corresponding to 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 using an ion sputtering device (Hitachi High-Tech MC1000).
  • the positive electrode active material is sliced to prepare a STEM cross-sectional sample.
  • the slice processing can be performed using a FIB-SEM device (Hitachi High-Tech XVision 200TBS).
  • the pickup is performed using an MPS (micro-probing system), and the finishing processing conditions can be, for example, an acceleration voltage of 10 kV.
  • STEM-EDX-ray analysis can be performed, for example, using a STEM device (Hitachi High-Tech HD-2700) and an EDAX Octane T Ultra W EDX detector.
  • the emission current of the STEM device is set to 6 ⁇ A or more and 10 ⁇ A or less, 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 concentration of each added element, particularly added element X, in the surface layer portion 100a is higher than that 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 on the surface of the positive electrode active material 100A1 or at a depth of 3 nm from the reference point toward the center, more preferably at a depth of 1 nm, and even more preferably at a depth of 0.5 nm.
  • the magnesium concentration decays to 60% or less of the peak at a point 1 nm deep from the peak.
  • the magnesium concentration decays to 30% or less of the peak at a point 2 nm deep from the peak.
  • the concentration peak also called peak top
  • the concentration peak here refers to the maximum value of the concentration.
  • the magnesium concentration in the surface layer 100a (detected amount of magnesium/(sum of detected amounts of magnesium, oxygen, cobalt, fluorine, aluminum, and silicon) is preferably 0.5 atomic % or more and 10 atomic % or less, and more preferably 1 atomic % or more and 5 atomic % or less.
  • 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 peak of the fluorine concentration in the surface layer 100a is preferably present on the surface of the positive electrode active material 100A1 or at a depth of 3 nm from the reference point toward the center, more preferably at a depth of 1 nm, and even more preferably at a depth of 0.5 nm.
  • the fluorine concentration peak 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.
  • 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 peak of the nickel concentration in the surface layer 100a is preferably present at a depth of 3 nm from the surface or reference point of the positive electrode active material 100A1 toward the center, more preferably at a depth of 1 nm, and even more preferably at a depth of 0.5 nm.
  • the distribution of nickel preferably overlaps with the distribution of magnesium.
  • the difference in depth between the peak of the nickel concentration and the peak of the magnesium concentration is preferably within 3 nm, and 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 present on the surface of the positive electrode active material 100A1, or at a depth of 0.5 nm to 50 nm from the reference point toward the center, and more preferably at a depth of 5 nm to 50 nm.
  • the ratio of the number of atoms of magnesium Mg to the average value of internal cobalt Co at the peak of the magnesium concentration (Mg/Co) is preferably 0.05 to 0.6, more preferably 0.1 to 0.4.
  • the ratio of the number of atoms of aluminum Al to the average value of internal cobalt Co at the peak of the aluminum concentration (Al/Co) is preferably 0.05 to 0.6, more preferably 0.1 to 0.45.
  • the ratio of the number of atoms of nickel Ni to the average value of internal cobalt Co at the peak of the nickel concentration (Ni/Co) is preferably 0 to 0.2, more preferably 0.01 to 0.1.
  • the ratio of the number of atoms of fluorine F to cobalt Co at the peak of the fluorine concentration (F/Co) is preferably 0 to 1.6, more preferably 0.1 to 1.4.
  • the ratio of the number of atoms of the added element A to the cobalt Co in the vicinity of the grain boundary is preferably 0.020 or more and 0.50 or less. Further, it is more preferably 0.025 or more and 0.30 or less. Further, it is more preferably 0.030 or more and 0.20 or less. Or it is more preferably 0.020 or more and 0.30 or less. Or it is more preferably 0.020 or more and 0.20 or less. Or it is more preferably 0.025 or more and 0.50 or less. Or it is more preferably 0.025 or more and 0.20 or less. Or it is more preferably 0.030 or more and 0.50 or less. Or it is more preferably 0.030 or more and 0.30 or less.
  • the ratio of the number of magnesium atoms to cobalt atoms (Mg/Co) near the grain boundaries is preferably 0.020 or more and 0.50 or less. Further preferably 0.025 or more and 0.30 or less. Further preferably 0.030 or more and 0.20 or less. Or preferably 0.020 or more and 0.30 or less. Or preferably 0.020 or more and 0.20 or less. Or preferably 0.025 or more and 0.50 or less. Or preferably 0.025 or more and 0.20 or less. Or preferably 0.030 or more and 0.50 or less. Or preferably 0.030 or more and 0.30 or less.
  • the above-mentioned range is present at multiple locations, for example, three or more locations, of the positive electrode active material 100A1, it can be said that this indicates that the added element is not attached to a narrow area on the surface of the positive electrode active material 100A1, but is widely distributed at a preferred concentration in the surface layer 100a of the positive electrode active material 100A1.
  • ⁇ Raman spectroscopy> As described above, it is preferable that at least a part of the surface layer 100a of the positive electrode active material 100A1 of one embodiment of the present invention has a rock salt type crystal structure. Therefore, when the positive electrode active material 100A1 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 100A1 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 ⁇ 10 ⁇ 1 nm or less for the a-axis, and preferably 1.0 ⁇ 10 ⁇ 1 nm or less for the c-axis. Also, it is more preferably 0.05 ⁇ 10 ⁇ 1 nm or less for the a-axis, and more preferably 0.6 ⁇ 10 ⁇ 1 nm or less for the c-axis. Also, it is more preferably 0.04 ⁇ 10 ⁇ 1 nm or less for the a-axis, and more preferably 0.3 ⁇ 10 ⁇ 1 nm or less for the c-axis.
  • the positive electrode active material 100A1 preferably has a smooth surface with few irregularities.
  • a smooth surface with few irregularities indicates that the effect of the flux described below is sufficiently exerted to melt the surfaces of the additive element source and the lithium cobalt oxide. 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 100A1, the specific surface area of the positive electrode active material 100A1, etc.
  • the surface smoothness can be quantified from a cross-sectional SEM image of the positive electrode active material 100A1 as follows:
  • the cathode active material 100A1 is processed by FIB or the like to expose the cross section. At this time, it is preferable to cover the cathode active material 100A1 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 100A1 is taken.
  • the interface is extracted using the image processing software.
  • the interface line between the protective film or the like and the cathode active material 100A1 is selected using an automatic selection tool or the like, and the 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 100A1 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 9 to 11 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 100A1 can also be quantified from the ratio between the actual specific surface area S R measured by a constant volume gas adsorption method and 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 meter that uses the laser diffraction/scattering method.
  • the specific surface area can be measured using a specific surface area measuring device that uses the gas adsorption method by the constant volume method, for example.
  • the 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 is preferably 2.1 or less.
  • the surface smoothness can be quantified from a cross-sectional SEM image of the positive electrode active material 100A1 by the following method.
  • a surface SEM image of the positive electrode active material 100A1 First, obtain a surface SEM image of the positive electrode active material 100A1. At this time, a conductive coating may be applied as a pretreatment before observation. It is preferable that the observation surface is perpendicular to the electron beam. When comparing multiple samples, the measurement conditions and observation area should be the same.
  • 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 brightness histogram. Obtaining a brightness histogram makes it possible to visually evaluate the unevenness of the positive electrode active material in an easily understandable way.
  • the difference between the maximum and minimum values of the grayscale value is preferably 120 or less, more preferably 115 or less, and even more preferably 70 to 115.
  • the standard deviation of the grayscale value is preferably 11 or less, more preferably 8 or less, and even more preferably 4 to 8.
  • conditioning can be performed to change the crystal structure of the positive electrode active material 100A1 of the battery to an O3' structure.
  • conditioning is preferably performed when the shape of the battery is complete or close to complete.
  • a discharged state refers to a state in which the open circuit voltage of a lithium ion secondary battery is 3.5 V or less, for example, in a lithium ion secondary battery that uses lithium cobalt oxide for the positive electrode.
  • the lithium cobalt oxide has a value of x smaller than 0.5.
  • a hump sometimes called a plateau
  • the charging curve (a graph with the horizontal axis being capacity and the vertical axis being voltage).
  • the positive electrode active material 100A1 goes through a crystal structure with the longest c-axis length and then becomes the O3' structure during the conditioning charge.
  • the charging current should be 1C or less, preferably 0.5C or less, and more preferably 0.3C or less. This is because if the charging current is large, there is a risk that the change in the crystal structure of the positive electrode active material 100A1 during charging for conditioning will be uneven, for example, there will be a difference in the amount of lithium ions released between the positive electrode active material 100A1 located close to the positive electrode current collector and the positive electrode active material 100A1 located farther away, resulting in a difference in the change in the crystal structure.
  • 1C can be 200mA/g per weight of the positive electrode active material. If charging for conditioning with such a sufficiently small current is performed, the above-mentioned hump may be seen in the charging curve.
  • the effect of using the above-mentioned conditioning method is effective even when the device (see embodiment 5 or 6) equipped with a battery having the positive electrode active material 100A1 does not use the positive electrode active material 100A1 to a charge depth (charge rate) at which the positive electrode active material 100A1 has an O3' structure, and it is possible to use the positive electrode active material 100A1 without bias and to suppress bias in the deterioration of the characteristics of the positive electrode active material 100A1.
  • the above-mentioned conditioning may also be performed in a device (see embodiment 5 or 6) that is equipped with a battery having the positive electrode active material 100A1. However, it is preferable to perform the conditioning as early as possible.
  • a positive electrode active material 100A2 which is lithium nickel-cobalt-manganese oxide as an example of the positive electrode active material 100A of Embodiment 1 and a manufacturing method thereof will be described with reference to FIGS.
  • FIG. 27A shows a schematic cross-sectional view of a particle of the positive electrode active material 100A2.
  • the positive electrode active material 100A2 is nickel-cobalt-manganese lithium oxide, which is also called a lithium composite oxide having nickel, cobalt, and manganese.
  • the nickel-cobalt-manganese lithium has a layered rock salt type crystal structure of space group R-3m.
  • the value in the vicinity of the composition refers to the range in which the composition is obtained when the significant digit is one digit. In this case, the last digit of the significant digit is rounded off.
  • the particles of the positive electrode active material 100A2 are preferably primary particles (single particles). Alternatively, if the particles of the positive electrode active material 100A2 are secondary particles, it is preferable that the number of primary particles contained in the secondary particles is small, for example, preferably 2 to 20, more preferably 2 to 15, more preferably 2 to 10, more preferably 2 to 5, and more preferably 2.
  • the particle size of the positive electrode active material 100A2 is preferably such that the median diameter (D50) measured by the laser diffraction/scattering method is 0.5 ⁇ m or more and 10 ⁇ m or less, and more preferably 1 ⁇ m or more and 5 ⁇ m or less.
  • FIG. 27B is a schematic cross-sectional view of a particle of the positive electrode active material 100A3 having an inner portion 100A3b and a shell layer 100A3s.
  • the inner portion 100A3b may be the same lithium nickel-cobalt-manganese oxide as the positive electrode active material 100A2 described above, and may have a mixed composition layer at the boundary with the shell layer 100A3s.
  • the shell layer 100A3s may have one or more selected from metal oxides such as aluminum oxide and titanium oxide, and lithium composite oxides such as lithium niobate and lithium titanate.
  • the mixed composition layer refers to a region in which one or more elements contained in the inner portion 100A3b and one or more elements contained in the shell layer 100A3s are both detected by elemental analysis means such as STEM-EDX.
  • the shell layer 100A3s is preferably formed uniformly on the surface of the positive electrode active material 100A3, but it may be formed at least on the surface layer portion having a surface other than the (00l) plane where the insertion and desorption of carrier ions occurs.
  • the carrier ions are lithium ions.
  • the particles of the positive electrode active material are prepared by mixing a nickel-cobalt-manganese hydroxide obtained by a coprecipitation method using an aqueous solution of a nickel source, a cobalt source, and a manganese source with lithium hydroxide, performing a first heat treatment, and then mixing the resulting mixture with lithium hydroxide once more and performing a second heat treatment.
  • a transition metal M source i.e., a nickel source (Ni source), a cobalt source (Co source), and a manganese source (Mn source) are prepared. It is preferable that the mixture ratio of nickel, cobalt, and manganese is within a range that allows the product to have a layered rock-salt type crystal structure.
  • a positive electrode active material containing a large amount of nickel as the transition metal M is preferable because the raw materials may be cheaper than those containing a large amount of cobalt, and the charge/discharge capacity per weight may be increased.
  • nickel among the transition metals M is preferably more than 25 atomic %, more preferably 60 atomic % or more, and even more preferably 80 atomic % or more.
  • the proportion of nickel is too high, there is a risk of reduced chemical stability and heat resistance. For this reason, it is preferable that nickel among the transition metals M is 95 atomic % or less.
  • Secondary batteries that have cobalt as the transition metal M of the positive electrode active material are preferable because they have a high average discharge voltage and are highly reliable because cobalt contributes to stabilizing the layered rock salt structure.
  • cobalt is more expensive than nickel and manganese and is unstable, if the proportion of cobalt is too high, there is a risk that the cost of manufacturing the secondary battery will increase. Therefore, for example, it is preferable that cobalt be 2.5 atomic % or more and 34 atomic % or less of the transition metal M.
  • Positive electrode active materials containing manganese as the transition metal M are preferred because they improve heat resistance and chemical stability. However, if the proportion of manganese is too high, the discharge voltage and discharge capacity tend to decrease. Therefore, for example, it is preferable that manganese among the transition metals M is 2.5 atomic % or more and 34 atomic % or less.
  • the transition metal M source is prepared as an aqueous solution of a compound containing the transition metal M.
  • An aqueous solution of a nickel salt can be used as the nickel source.
  • nickel sulfate, nickel chloride, nickel nitrate, or hydrates of these can be used as the nickel salt.
  • Nickel acetate or other nickel organic acid salts, or hydrates of these can also be used.
  • An aqueous solution of nickel alkoxide or an organic nickel complex can also be used as the nickel source.
  • organic acid salts refer to compounds of metals and organic acids such as acetic acid, citric acid, oxalic acid, formic acid, and butyric acid.
  • an aqueous solution of a cobalt salt can be used as the cobalt source.
  • a cobalt salt for example, cobalt sulfate, cobalt chloride, cobalt nitrate, or a hydrate of these can be used.
  • an organic acid salt of cobalt such as cobalt acetate, or a hydrate of these can be used.
  • an aqueous solution of a cobalt alkoxide or an organic cobalt complex can be used as the cobalt source.
  • an aqueous solution of a manganese salt can be used as the manganese source.
  • the manganese salt for example, an aqueous solution of manganese sulfate, manganese chloride, manganese nitrate, or a hydrate of these can be used.
  • an organic acid salt of manganese such as manganese acetate, or a hydrate of these can be used.
  • an aqueous solution of a manganese alkoxide or an organic manganese complex can be used as the manganese source.
  • an aqueous solution in which nickel sulfate, cobalt sulfate, and manganese sulfate are dissolved in pure water is prepared as a source of transition metal M.
  • the aqueous solution is acidic.
  • a chelating agent may be prepared.
  • the chelating agent include glycine, oxine, 1-nitroso-2-naphthol 2-mercaptobenzothiazole, and EDTA (ethylenediaminetetraacetic acid).
  • a plurality of types selected from glycine, oxine, 1-nitroso-2-naphthol, and 2-mercaptobenzothiazole may be used. At least one of these is dissolved in pure water and used as a chelating aqueous solution.
  • the chelating agent is a complexing agent that creates a chelating compound, and is preferable to a general complexing agent.
  • a complexing agent may be used instead of a chelating agent, and ammonia water may be used as the complexing agent.
  • the use of a chelating aqueous solution is preferable because it can suppress the unnecessary generation of crystal nuclei and promote growth. When the generation of unnecessary nuclei is suppressed, the generation of fine particles is suppressed, and therefore a composite hydroxide with a good particle size distribution can be obtained.
  • an ammonia salt may be generated.
  • the use of a chelating aqueous solution can delay the acid-base reaction, and the reaction proceeds gradually to obtain secondary particles that are close to spherical.
  • Glycine has the effect of maintaining the pH value constant at or near a pH of 9 or more and 10 or less, and it is preferable to use a glycine aqueous solution as the chelate aqueous solution since it makes it easier to control the pH in the reaction tank when obtaining the composite hydroxide 98.
  • the glycine concentration is preferably 0.05 mol/L or more and 0.3 mol/L or less, and more preferably 0.07 mol/L or more and 0.32 mol/L or less.
  • Step S114 Next, in step S114 of FIG. 28, a transition metal M source and a chelating agent are mixed to prepare an acid solution.
  • an alkaline solution is prepared.
  • an aqueous solution containing sodium hydroxide, potassium hydroxide, lithium hydroxide, or ammonia can be used.
  • This aqueous solution is preferably prepared using pure water.
  • the aqueous solution may be prepared by dissolving a plurality of types selected from sodium hydroxide, potassium hydroxide, lithium hydroxide, and ammonia in pure water.
  • the pure water that is preferably used for the transition metal M source and alkaline solution is water with a resistivity of 1 M ⁇ cm or more, more preferably water with a resistivity of 10 M ⁇ cm or more, and even more preferably water with a resistivity of 15 M ⁇ cm or more. Water that satisfies this resistivity has high purity and contains very few impurities.
  • Step S122 As shown in step S122 of FIG. 28, it is preferable to prepare water in the reaction tank.
  • This water may be an aqueous solution of a chelating agent, but it is more preferable to use pure water.
  • the use of pure water promotes nucleation, and allows the production of composite hydroxides with small particle sizes.
  • the water prepared in the reaction tank can be called a filling liquid or an adjustment liquid for the reaction tank.
  • the description of step S113 can be referred to.
  • step S131 of Fig. 28 the acid solution and the alkaline solution are mixed and reacted with each other.
  • This reaction can be called a coprecipitation reaction, a neutralization reaction, or an acid-base reaction.
  • step S131 it is preferable to maintain the pH of the reaction system at 9.0 or higher and 13.0 or lower.
  • the acid solution delivery rate is provided in the tank that stores the acid solution, and the acid solution can be added to the reaction tank through a tube by using this pump.
  • the amount of acid solution added i.e. the amount of solution delivered, can be controlled by the pump.
  • the alkaline solution is added to keep the pH of the aqueous solution in the reaction tank constant.
  • the reaction tank includes a reaction vessel, etc.
  • the aqueous solution in the reaction tank may be stirred using a stirring means.
  • the stirring means may have a stirrer or stirring blades. Between two and 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.
  • the rotation speed of the stirring means may be between 800 rpm and 1200 rpm.
  • Baffle plates may also be provided in the reaction tank to change the stirring direction and flow rate. The provision of baffle plates improves mixing efficiency, allowing the synthesis of more uniform composite hydroxide particles.
  • the temperature of the reaction tank prefferably be between 50°C and 90°C. Addition of the alkaline or acidic solution should begin after the reaction tank has reached that temperature.
  • nitrogen or argon can be used as the inert atmosphere.
  • nitrogen gas it is advisable to introduce nitrogen gas at a flow rate of 0.5 L/min or more and 2 L/min or less.
  • the reflux condenser allows the nitrogen gas to be released from the reaction vessel and the water vapor to be returned to the reaction vessel.
  • Step S132> In order to recover the composite hydroxide 98, it is preferable to perform filtration as shown in step S132 of Fig. 28.
  • the filtration is preferably suction filtration.
  • the reaction product precipitated in the reaction tank may be washed with pure water, and then filtered using an organic solvent (e.g., acetone, etc.).
  • the composite hydroxide 98 after filtration may be dried.
  • it may be dried under vacuum at 60°C to 200°C for 0.5 hours to 20 hours.
  • it may be dried for 12 hours.
  • composite hydroxide 98 having a transition metal M can be obtained.
  • composite hydroxide 98 refers to a hydroxide of multiple types of metals.
  • Composite hydroxide 98 can be said to be a precursor of a positive electrode active material.
  • a lithium source is prepared.
  • the step of adding the lithium source is performed multiple times, so that an amount of lithium less than the final amount is prepared in step S141.
  • the lithium atoms can be 0.5 to 0.9 (atomic ratio), and more preferably 0.7 (atomic ratio).
  • lithium hydroxide lithium carbonate, or lithium nitrate
  • a material with a low melting point among lithium compounds such as lithium hydroxide (melting point 462°C).
  • Positive electrode active materials with a high proportion of nickel are more susceptible to cation mixing than lithium cobalt oxide, etc., so heating in step S43, etc. must be performed at a low temperature. For this reason, it is preferable to use a material with a low melting point.
  • the smaller the particle size of the lithium source the easier it is for the reaction to proceed, and this is preferable.
  • a lithium source that has been pulverized using a fluidized bed jet mill can be used.
  • the particle size referred to here is the median diameter.
  • step S142 of FIG. 28 the composite hydroxide 98 and the lithium source are mixed.
  • the mixing can be performed in a dry or wet manner.
  • a ball mill, a bead mill, or a kneader can be used for mixing.
  • zirconia balls it is preferable to use zirconia balls as the media.
  • the peripheral speed it is preferable to 100 mm/sec or more and 2000 mm/sec or less in order to suppress contamination from the media or materials.
  • the composite hydroxide 98 and the lithium compound may be pulverized at the same time as mixing.
  • Step S143 Next, the mixture of composite hydroxide 98 and the lithium source is heated.
  • step S143 may be referred to as the first heating, step S153 as the second heating, and step S155 as the third heating.
  • the firing equipment used for these heating processes can be an electric furnace or a rotary kiln.
  • the crucible, scabbard, setter, and container used during heating are preferably made of materials that do not easily release impurities. For example, it is recommended to use a crucible made of aluminum oxide with a purity of 99.9%. It is also preferable to heat these containers with their lids on.
  • the heating temperature in step S143 is preferably 400°C or higher and 750°C or lower, and more preferably 650°C or higher and 750°C or lower.
  • the heating time in step S143 is preferably 1 hour or higher and 30 hours or lower, and more preferably 2 hours or higher and 20 hours or lower.
  • the heating atmosphere is preferably an oxygen-containing atmosphere or a so-called dry air atmosphere containing oxygen with little water (e.g., a dew point of -50°C or less, more preferably a dew point of -80°C or less).
  • step S144 it is preferable to have a crushing step after heating as step S144.
  • Crushing can be performed, for example, in a mortar.
  • classification may be performed using a sieve.
  • the particle size and/or shape of the positive electrode active material 100A2 can be made more uniform.
  • step S151 a lithium source is prepared.
  • the amount of lithium to be the final amount is prepared in combination with step S141.
  • step S141 when the sum of the atomic numbers of nickel, cobalt, and manganese is set to 1, if the atomic number of lithium is set to 0.7 (atomic number ratio), it is preferable to prepare, for example, 0.31 (atomic number ratio) in step S151.
  • the final amount of lithium atoms when the sum of the atomic numbers of nickel, cobalt, and manganese is set to 1 is set to 1.01, but one aspect of the present invention is not limited to this.
  • step S141 When the sum of the atomic numbers of nickel, cobalt, and manganese is set to 1, the final amount of lithium is preferably 0.95 to 1.25, and more preferably 1.00 to 1.05. Other than the amount to be prepared, the description of step S141 can be referred to.
  • the lithium source is added twice, in steps S141 and S151, and each step is heated, but this is not a limitation of one aspect of the present invention.
  • the lithium source may be added three or more times, and each step may be heated.
  • Step S152> the composite oxide 99 obtained in step S144 is mixed with the lithium source.
  • the mixing see the description of step S142.
  • Step S153 the mixture of the composite oxide 99 and the lithium source is heated.
  • the heating in step S153 is preferably performed at a sufficiently high temperature to increase the crystallite size of the positive electrode active material 100A2, but the range may differ depending on the composition of the transition metal M.
  • the heating temperature in step S153 is preferably, for example, 750°C or higher, more preferably 800°C or higher, and even more preferably 850°C or higher, when the proportion of nickel in the transition metal M is high, for example 70% or higher.
  • a temperature of 950°C or lower is preferable, more preferably 920°C or lower, and even more preferably 900°C or lower.
  • the proportion of nickel in the transition metal M is 40% or more and 60% or less, for example, 900°C or more is preferable, 950°C or more is more preferable, and around 970°C is even more preferable.
  • the temperature is too high, there is a risk of the same disadvantages as mentioned above occurring, so 1020°C or less is preferable, and 990°C or less is more preferable. For other heating conditions, see the description in step S143.
  • step S154 it is preferable to have a crushing step after heating as step S154.
  • a crushing step after heating the description of step S144 can be referred to.
  • Step S155 Furthermore, it is more preferable to perform heating in step S155. By performing the heating, the residue of the lithium source and the like can be reduced.
  • the heating temperature in step S155 is preferably 400° C. or more and 900° C. or less, and more preferably 750° C. or more and 850° C. or less.
  • the heating time in step S152 is preferably 1 hour or more and 30 hours or less, and more preferably 2 hours or more and 20 hours or less. However, the heating in step S155 does not have to be performed. For other heating conditions, refer to the description in step S143.
  • step S156 it is preferable to have a crushing step after heating as step S156.
  • a crushing step after heating the description of step S144 can be referred to.
  • FIG. 28 a method is described in which the lithium source is mixed in step S151 and then heated twice in steps S153 and S155, but this is not a limitation of one aspect of the present invention. Heating may be performed three or more times.
  • the mixture ratio of the metals contained in the positive electrode active material 100A2 can be measured by analysis using X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MS), or energy dispersive X-ray spectroscopy (TEM-EDX).
  • XPS X-ray photoelectron spectroscopy
  • ICP-MS inductively coupled plasma mass spectrometry
  • TEM-EDX energy dispersive X-ray spectroscopy
  • the crystallite size of the resulting positive electrode active material 100A2 calculated from the XRD pattern is 150 nm or more. In order to synthesize lithium nickel-manganese-cobalt oxide with a large crystallite size, it is effective to perform the process of adding a lithium source and heating multiple times.
  • the positive electrode active material 100 is not limited to lithium nickel-cobalt-manganese oxide such as the above-mentioned positive electrode active material 100A2, but may be lithium nickel-cobalt-manganese-aluminate with added aluminum (positive electrode active material 100A4).
  • nickel-cobalt-manganese-lithium aluminum oxide for example, when mixing the composite hydroxide 98 and the lithium source in step S142 of the method for producing the above-mentioned positive electrode active material 100A2, it is advisable to also add and mix the aluminum source.
  • Such a method for producing nickel-cobalt-manganese-lithium aluminum oxide is shown in FIG. 29.
  • Step S134 As step S134 in Fig. 29, a process of preparing an aluminum source will be described.
  • the aluminum source aluminum hydroxide, aluminum sulfate, aluminum chloride, and aluminum nitrate can be used.
  • the amount of aluminum atoms to be added is within a range of 0.005 to 0.05 (atomic ratio) when the sum of the atoms of nickel, cobalt, and manganese is 1, for example.
  • the method for producing the nickel-cobalt-manganese-lithium aluminate in FIG. 29 can be the same as the method for producing the nickel-cobalt-manganese-lithium aluminate in FIG. 28, except for the step of preparing the aluminum source in step S134 and the step of mixing the composite hydroxide 98, the lithium source, and the aluminum source in step S142B.
  • the nickel-cobalt-manganese-lithium aluminate produced in this manner is used as the positive electrode active material 100A4.
  • the positive electrode active material 100A4 produced by the method described in FIG. 29 contains aluminum at a substantially uniform concentration inside the particles, which can increase the storage capacity of the lithium ion secondary battery and improve the cycle characteristics.
  • Example of secondary battery configuration The following description will be given taking as an example a secondary battery shown in FIG. 30 in which a positive electrode, a negative electrode, and an electrolyte are enclosed in an exterior body.
  • the positive electrode includes a positive electrode active material layer and a positive electrode current collector.
  • the positive electrode active material layer includes a positive electrode active material, and may include a conductive material (synonymous with a conductive additive) and a binder.
  • the positive electrode active material is prepared by the method described in the above embodiment.
  • the positive electrode active material described in the previous embodiment may 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
  • This configuration can improve the characteristics of the secondary battery.
  • Carbon-based materials such as acetylene black can be used as conductive materials.
  • Carbon nanotubes, graphene, or graphene compounds can also be used as conductive materials.
  • graphene compounds include multi-layer graphene, multi-graphene, graphene oxide, multi-layer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multi-layer graphene oxide, reduced multi-graphene oxide, graphene quantum dots, etc.
  • Graphene compounds have carbon, have a shape such as a plate or sheet, and have a two-dimensional structure formed of six-membered carbon rings. The two-dimensional structure formed of six-membered carbon rings is sometimes called a carbon sheet.
  • the graphene compound may have a functional group. It is also preferable that the graphene compound has a curved shape.
  • the graphene compound may also be rolled up to resemble a carbon nanofiber.
  • 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 material even in small amounts. In addition, reduced graphene oxide preferably has an intensity ratio G/D of the G band and 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 material even in small amounts.
  • Graphene compounds may have excellent electrical properties, such as high electrical conductivity, and excellent physical properties, such as high flexibility and high mechanical strength. Graphene compounds also have a sheet-like shape. Graphene compounds may have curved surfaces, allowing for surface contact with low contact resistance. Even if the graphene compound is thin, it may have very high electrical conductivity, and a small amount of the compound can efficiently form a conductive path in the active material layer. Therefore, by using the graphene compound as a conductive material, the contact area between the active material and the conductive material can be increased. It is preferable that the graphene compound covers 80% or more of the area of the active material.
  • 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 multiple graphenes or graphene compounds are formed so as to partially cover the multiple granular positive electrode active materials or to be attached to the surfaces of the multiple granular positive electrode active materials, and therefore are preferably 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 an active material
  • the graphene net can also function as a binder that bonds the active materials together. This allows the amount of binder to be reduced or not used at all, thereby improving the ratio of active material to the electrode volume and electrode weight. In other words, the discharge capacity of the secondary battery can be increased.
  • a material used in forming the graphene compound may be mixed with the graphene compound and used in the active material layer.
  • particles used as a catalyst in forming the graphene compound may be mixed with the graphene compound.
  • catalysts used 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 particles preferably have a median diameter (D50) of 1 ⁇ m or less, more preferably 100 nm or less.
  • Binder 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, ethylene-propylene-diene copolymer, etc. Furthermore, as the binder, fluororubber can be used.
  • 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
  • the current collector As the current collector, a material having high electrical 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 shaped in a foil, plate, sheet, mesh, punched metal, or expanded metal form. 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-based material and/or a carbon-based 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 alloy-based 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.
  • Carbon-based materials that can be used include 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 charge/discharge capacity per unit volume, a relatively small volume expansion, low cost, and high safety compared to lithium metal.
  • oxides such as titanium dioxide ( TiO2 ), lithium titanium oxide ( Li4Ti5O12 ), lithium-graphite intercalation compound ( LixC6 ), niobium pentoxide ( Nb2O5 ), tungsten oxide ( WO2 ), and molybdenum oxide ( MoO2 ) can be used.
  • Li2.6Co0.4N3 is preferable because it shows a large charge/discharge capacity (900mAh/g, 1890mAh/ cm3 ).
  • the composite nitride of lithium and a transition metal When a composite 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 composite nitride of lithium and a transition metal can be 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 composite 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 fluorides 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
  • fluorides such as FeF3 and BiF3 .
  • the conductive material and binder that the negative electrode active material layer can have can be the same materials as the conductive material and binder that the positive electrode active material layer can have.
  • 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 electrolytic solution has a solvent and an electrolyte.
  • the solvent of the electrolytic solution is preferably an aprotic organic solvent, and can be, for example, one 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, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, s
  • DMC
  • the ionic liquid is composed of a cation and an anion, and includes an organic cation and an organic anion.
  • Examples of organic cations used in the electrolyte 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 anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.
  • Examples of electrolytes dissolved in the above-mentioned solvent include 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 ) , LiN ( C2F5SO2 ) . 2 or any combination and ratio of two or more of these lithium salts can be used.
  • the electrolyte used in the secondary battery is preferably a highly purified electrolyte with a low content of granular waste or elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities"). Specifically, it is preferable that the weight ratio of impurities to the electrolyte be 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.
  • Additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate)borate (LiBOB), dinitrile compounds such as succinonitrile and adiponitrile, fluorobenzene, and ethyleneglycol bis(propionitrile) ether may also be added to the electrolyte.
  • concentration of each of the added materials may be, for example, 0.1 wt % or more and 5 wt % or less relative to the total solvent.
  • VC and LiBOB are particularly preferred as they are easy to form a good coating portion.
  • a polymer gel electrolyte made by swelling a polymer with an electrolyte solution may be used.
  • polymer gel electrolytes increases safety against leakage and other issues. It also makes it possible to make secondary batteries 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 also have a porous shape.
  • a solid electrolyte containing an inorganic material such as a sulfide or oxide, or a solid electrolyte containing a polymer material such as a PEO (polyethylene oxide) can be used.
  • an inorganic material such as a sulfide or oxide
  • a solid electrolyte containing a polymer material such as a PEO (polyethylene oxide)
  • PEO polyethylene oxide
  • the secondary battery preferably has a separator.
  • the separator may be made of, for example, paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers such as 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.
  • ceramic materials that can be used include aluminum oxide particles and silicon oxide particles.
  • fluorine materials that can be used include PVDF and polytetrafluoroethylene.
  • polyamide materials that can be used include nylon and aramid (meta-aramid and para-aramid).
  • Coating with ceramic-based materials improves oxidation resistance, suppressing the deterioration of the separator during high-voltage charging 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.
  • 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.
  • Fig. 30 and Fig. 31 An example of an external view of a laminated secondary battery 500 is shown in Fig. 30 and Fig. 31.
  • Fig. 30 and Fig. 31 have a positive electrode 503, a negative electrode 506, a separator 507, an exterior body 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.
  • the laminated secondary battery has a flexible structure, and is mounted in an electronic device having at least a part having flexibility, the secondary battery can also be bent in accordance with the deformation of the electronic device.
  • An example of a method for manufacturing the laminated secondary battery will be described with reference to Figs. 31A to 31C.
  • the negative electrode 506, separator 507, and positive electrode 503 are laminated.
  • Figure 31B shows the laminated negative electrode 506, separator 507, and positive electrode 503.
  • an example is shown in which five sets of negative electrodes and four sets of positive electrodes are used.
  • 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.
  • ultrasonic welding 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.
  • the negative electrode 506, separator 507, and positive electrode 503 are placed on the exterior body 509.
  • 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.
  • an electrolyte (not shown) 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, a laminated secondary battery 500 can be produced.
  • FIGs. 32A to 32G An example of mounting a secondary battery having the positive electrode active material described in the previous embodiment in an electronic device is shown in Figs. 32A to 32G.
  • Examples of electronic devices to which secondary batteries are applied include television devices (also called televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game machines, personal digital assistants, audio playback devices, and large game machines such as pachinko machines.
  • secondary batteries with a flexible shape can be incorporated into the interior or exterior walls of houses and buildings, and along the curved surfaces of the interior or exterior of automobiles.
  • FIG. 32A shows an example of a mobile phone.
  • the mobile phone 7400 includes a display portion 7402 built into a housing 7401, operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like.
  • the mobile phone 7400 includes a secondary battery 7407.
  • the secondary battery of one embodiment of the present invention as the secondary battery 7407, a lightweight mobile phone with a long life can be provided.
  • Figure 32B shows the mobile phone 7400 in a bent state.
  • the secondary battery 7407 installed inside is also bent.
  • Figure 32C shows the state of the bent secondary battery 7407 at that time.
  • the secondary battery 7407 is a thin storage battery.
  • the secondary battery 7407 is fixed in a bent state.
  • the secondary battery 7407 has a lead electrode electrically connected to a current collector.
  • FIG. 32D shows an example of a bangle-type display device.
  • the portable display device 7100 includes a housing 7101, a display unit 7102, an operation button 7103, and a secondary battery 7104.
  • FIG. 32E shows a bent state of the secondary battery 7104.
  • the housing deforms, and the curvature of part or all of the secondary battery 7104 changes.
  • the degree of bending at any point of the curve expressed by the value of the radius of the corresponding circle is called the radius of curvature, and the reciprocal of the radius of curvature is called the curvature.
  • part or all of the main surface of the housing or the secondary battery 7104 changes within a range of 40 mm to 150 mm. If the radius of curvature of the main surface of the secondary battery 7104 is within a range of 40 mm to 150 mm, high reliability can be maintained.
  • a secondary battery of one embodiment of the present invention as the secondary battery 7104, a lightweight and long-life portable display device can be provided.
  • FIG 32F shows an example of a wristwatch-type mobile information terminal.
  • the mobile information terminal 7200 includes a housing 7201, a display portion 7202, a band 7203, a buckle 7204, operation buttons 7205, an input/output terminal 7206, and the like.
  • the portable information terminal 7200 can execute various applications such as mobile phone calls, e-mail, text browsing and creation, music playback, Internet communications, and computer games.
  • the display surface of the display unit 7202 is curved, and display can be performed along the curved display surface.
  • the display unit 7202 also has a touch sensor, and can be operated by touching the screen with a finger or a stylus. For example, an application can be started by touching an icon 7207 displayed on the display unit 7202.
  • the operation button 7205 can have various functions, such as time setting, power on/off operation, wireless communication on/off operation, silent mode activation/cancellation, and power saving mode activation/cancellation.
  • the functions of the operation button 7205 can be freely set by an operating system built into the mobile information terminal 7200.
  • the mobile information terminal 7200 is also capable of performing standardized short-range wireless communication. For example, it can communicate hands-free by communicating with a wireless headset.
  • the portable information terminal 7200 also includes an input/output terminal 7206, and can directly exchange data with other information terminals via a connector. Charging can also be performed via the input/output terminal 7206. Note that charging can also be performed by wireless power supply without using the input/output terminal 7206.
  • the display portion 7202 of the mobile information terminal 7200 includes a secondary battery of one embodiment of the present invention.
  • a lightweight mobile information terminal with a long life can be provided.
  • the secondary battery 7104 shown in FIG. 32E can be incorporated in a curved state inside the housing 7201 or in a bendable state inside the band 7203.
  • the mobile information terminal 7200 preferably has a sensor.
  • the mobile information terminal 7200 is equipped with a fingerprint sensor, a pulse sensor, a body temperature sensor or other human body sensor, a touch sensor, a pressure sensor, an acceleration sensor, etc.
  • Figure 32G shows an example of an armband-type display device.
  • the display device 7300 has a display portion 7304 and a secondary battery of one embodiment of the present invention.
  • the display device 7300 can also be provided with a touch sensor in the display portion 7304 and can also function as a portable information terminal.
  • the display surface of the display unit 7304 is curved, and display can be performed along the curved display surface.
  • the display device 7300 can change the display status by using standardized short-range wireless communication, etc.
  • the display device 7300 also has an input/output terminal, and can directly exchange data with other information terminals via a connector. Charging can also be performed via the input/output terminal. Note that charging can also be performed by wireless power supply without using the input/output terminal.
  • a lightweight display device with a long life can be provided.
  • a secondary battery according to one embodiment of the present invention as a secondary battery in everyday electronic devices, it is possible to provide products that are lightweight and have a long life.
  • examples of everyday electronic devices include electric toothbrushes, electric shavers, and electric beauty devices.
  • the secondary batteries used in these products it is desirable to have a stick-shaped secondary battery that is easy for users to hold, is small, lightweight, and has a large discharge capacity.
  • the electronic cigarette 7500 is composed of an atomizer 7501 including a heating element, a secondary battery 7504 that supplies power to the atomizer, and a cartridge 7502 including a liquid supply bottle and a sensor.
  • a protection circuit that prevents overcharging and/or over-discharging of the secondary battery 7504 may be electrically connected to the secondary battery 7504.
  • the secondary battery 7504 shown in FIG. 32H has an external terminal so that it can be connected to a charging device. Since the secondary battery 7504 is the tip part when held, it is desirable that the total length is short and the weight is light.
  • the secondary battery of one embodiment of the present invention has a high discharge capacity and good cycle characteristics, so that a small and lightweight electronic cigarette 7500 that can be used for a long period of time can be provided.
  • Fig. 33A shows an example of a wearable device.
  • Wearable devices use secondary batteries as a power source. Furthermore, when used by a user at home or outdoors, there is a demand for wearable devices that can be charged wirelessly as well as via wired charging with an exposed connector in order to improve splash-proof, water-resistant, or dust-proof performance.
  • a secondary battery according to one embodiment of the present invention can be mounted on a glasses-type device 4000 as shown in FIG. 33A.
  • the glasses-type device 4000 has a frame 4000a and a display unit 4000b.
  • the glasses-type device 4000 can be made lightweight, well-balanced in weight, and capable of long continuous use.
  • a configuration can be realized that can accommodate space-saving features that accompany a smaller housing.
  • the headset type device 4001 can be equipped with a secondary battery which is one embodiment of the present invention.
  • the headset type device 4001 has at least a microphone unit 4001a, a flexible pipe 4001b, and an earphone unit 4001c.
  • a secondary battery can be provided in the flexible pipe 4001b and/or the earphone unit 4001c.
  • the secondary battery according to one embodiment of the present invention can be mounted on the device 4002 that can be directly attached to the body.
  • the secondary battery 4002b can be provided inside the thin housing 4002a of the device 4002.
  • the secondary battery according to one embodiment of the present invention can be mounted on the device 4003 that can be attached to clothing.
  • the secondary battery 4003b can be provided inside the thin housing 4003a of the device 4003.
  • the belt-type device 4006 can be equipped with a secondary battery according to one embodiment of the present invention.
  • the belt-type device 4006 has a belt portion 4006a and a wireless power receiving portion 4006b, and a secondary battery can be mounted inside the belt portion 4006a.
  • a configuration that can accommodate space saving associated with a smaller casing can be realized.
  • the secondary battery of one embodiment of the present invention can be mounted on the wristwatch device 4005.
  • the wristwatch device 4005 has a display portion 4005a and a belt portion 4005b, and a secondary battery can be provided on the display portion 4005a or the belt portion 4005b.
  • the display unit 4005a can display not only the time, but also various other information such as incoming emails and phone calls.
  • the wristwatch type device 4005 is a wearable device that is worn directly on the arm, it may be equipped with sensors that measure the user's pulse, blood pressure, etc. It can accumulate data on the user's amount of exercise and health, and manage the user's health.
  • Figure 33B shows an oblique view of the wristwatch device 4005 removed from the wrist.
  • FIG. 33C shows how a secondary battery 913 is built in.
  • the secondary battery 913 is the secondary battery described in embodiment 6.
  • the secondary battery 913 is provided in a position that overlaps with the display portion 4005a, and is small and lightweight.
  • FIG. 33D shows an example of a wireless earphone.
  • a wireless earphone having a pair of main bodies 4100a and 4100b is illustrated, but this does not necessarily have to be a pair.
  • the main body 4100a and the main body 4100b each have a driver unit 4101, an antenna 4102, and a secondary battery 4103. They may also have a display unit 4104. They also preferably have a substrate on which a circuit such as a wireless IC is mounted, a charging terminal, and the like. They may also have a microphone.
  • the case 4110 has a secondary battery 4111. It also preferably has a board on which circuits such as a wireless IC and a charging control IC are mounted, and a charging terminal. It may also have a display unit, buttons, etc.
  • Main body 4100a and main body 4100b can wirelessly communicate with other electronic devices such as smartphones. This allows sound data and the like sent from other electronic devices to be played on main body 4100a and main body 4100b. Furthermore, if main body 4100a and main body 4100b have a microphone, sound picked up by the microphone can be sent to the other electronic device, and the sound data after processing by the electronic device can be sent back to main body 4100a and main body 4100b for playback. This allows it to be used as a translation machine, for example.
  • the secondary battery 4103 in the main body 4100a can be charged from the secondary battery 4111 in the case 4110.
  • the coin-type secondary battery, cylindrical secondary battery, or the like in the previous embodiment can be used as the secondary battery 4111 and the secondary battery 4103.
  • a secondary battery using the positive electrode active material 100 obtained in embodiment 2 as the positive electrode has a high energy density, and by using it for the secondary battery 4103 and the secondary battery 4111, a configuration that can accommodate space saving associated with miniaturization of wireless earphones can be realized.
  • Figure 34A shows an example of a cleaning robot.
  • the cleaning robot 6300 has a display unit 6302 arranged on the top surface of a housing 6301, multiple cameras 6303 arranged on the side, brushes 6304, operation buttons 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 dirt 6310, and suck up the dirt from a suction port arranged on the bottom surface.
  • the cleaning robot 6300 can analyze an 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 therein. By using the secondary battery 6306 according to one embodiment of the present invention in the cleaning robot 6300, the cleaning robot 6300 can be an electronic device with long operating time and high reliability.
  • FIG. 34B shows an example of a robot.
  • the robot 6400 shown in FIG. 34B 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. Furthermore, 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.
  • a secondary battery according to one embodiment of the present invention in the robot 6400, the robot 6400 can be an electronic device with long operating time and high reliability.
  • FIG. 34C shows an example of an aircraft.
  • the aircraft 6500 shown in FIG. 34C has a propeller 6501, a camera 6502, a secondary battery 6503, etc., and has the ability to fly autonomously.
  • the flying object 6500 includes therein a secondary battery 6503 according to one embodiment of the present invention.
  • the flying object 6500 can be an electronic device with a long operating time and high reliability.
  • next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs) can be realized.
  • HVs hybrid vehicles
  • EVs electric vehicles
  • PVs plug-in hybrid vehicles
  • FIG. 35 illustrates an example of a vehicle using a secondary battery according to one embodiment of the present invention.
  • the automobile 8400 illustrated in FIG. 35A is an electric automobile that uses an electric motor as a power source for running. Alternatively, it is a hybrid automobile that can use an electric motor and an engine as a power source for running. By using one embodiment of the present invention, a vehicle with a long driving range can be realized.
  • the automobile 8400 also has a secondary battery.
  • secondary battery modules can be arranged on the floor of the vehicle interior. The secondary battery not only drives the electric motor 8406, but can also supply power to light-emitting devices such as the headlight 8401 and room light (not shown).
  • the secondary battery can also supply power to display devices such as a speedometer and a tachometer that the automobile 8400 has.
  • the secondary battery can also supply power to semiconductor devices such as a navigation system that the automobile 8400 has.
  • the automobile 8500 shown in FIG. 35B can charge the secondary battery of the automobile 8500 by receiving power supply from an external charging facility by a plug-in method and/or a non-contact power supply method.
  • FIG. 35B shows a state in which a secondary battery 8024 mounted on the automobile 8500 is being charged from a ground-mounted charging device 8021 via a cable 8022.
  • the charging method and connector standards may be appropriately performed using a predetermined method such as CHAdeMO (registered trademark) or Combo.
  • the charging device 8021 may be a charging station installed in a commercial facility or a home power source.
  • the secondary battery 8024 mounted on the automobile 8500 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 power can be supplied contactlessly from a ground power transmission device for charging.
  • this contactless power supply method by incorporating a power transmission device into the road and/or 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 send and receive power between vehicles.
  • solar cells can be provided on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped and/or moving. Electromagnetic induction and/or magnetic field resonance methods can be used for such contactless power supply.
  • FIG. 35C shows an example of a two-wheeled vehicle using a secondary battery of one embodiment of the present invention.
  • a scooter 8600 shown in FIG. 35C includes a secondary battery 8602, a side mirror 8601, and a turn signal light 8603.
  • the secondary battery 8602 can supply electricity to the turn signal light 8603.
  • the scooter 8600 shown in FIG. 35C can store a secondary battery 8602 in the under-seat storage 8604.
  • the secondary battery 8602 can be stored in the under-seat storage 8604 even if the under-seat storage 8604 is small.
  • the secondary battery 8602 is removable, and when charging, the secondary battery 8602 can be carried indoors, charged, and stored before riding.
  • the cycle characteristics of the secondary battery are improved, and the discharge capacity of the secondary battery can be increased. Therefore, the secondary battery itself can be made smaller and lighter. If the secondary battery itself can be made smaller and lighter, it will contribute to reducing the weight of the vehicle, and the cruising distance can be improved.
  • the secondary battery installed in the vehicle can be used as a power supply source for something other than the vehicle. In this case, for example, it is possible to avoid using a commercial power source during peak power demand. If it is possible to avoid using a commercial power source during peak power demand, it can contribute to energy conservation and reduction of carbon dioxide emissions. Furthermore, if the cycle characteristics are good, the secondary battery can be used for a long period of time, and the amount of rare metals used, including cobalt, can be reduced.

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