WO2024121684A1 - 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
WO2024121684A1
WO2024121684A1 PCT/IB2023/062044 IB2023062044W WO2024121684A1 WO 2024121684 A1 WO2024121684 A1 WO 2024121684A1 IB 2023062044 W IB2023062044 W IB 2023062044W WO 2024121684 A1 WO2024121684 A1 WO 2024121684A1
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positive electrode
active material
electrode active
lithium
magnesium
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English (en)
French (fr)
Japanese (ja)
Inventor
山崎舜平
門馬洋平
福島邦宏
高橋辰義
黒澤奈緒
川月惇史
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Semiconductor Energy Laboratory Co Ltd
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Semiconductor Energy Laboratory Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G51/00—Compounds of cobalt
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G53/00—Compounds of nickel
    • 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
    • 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

Definitions

  • 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.
  • high-output, high-capacity lithium-ion secondary batteries has rapidly expanded 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. Research is also being conducted on the crystal structure of positive electrode active materials (Non-Patent Documents 1 to 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 steelmaking and other processes, and their physical properties have been studied (Non-Patent Document 14).
  • Non-Patent Document 14 describes the thermal stability of positive electrode active materials and electrolytes.
  • Lithium-ion secondary batteries have room for improvement in many areas, including discharge capacity, cycle characteristics, reliability, safety, and cost.
  • the positive electrode active materials to be able to improve issues such as discharge capacity, cycle characteristics, reliability, safety, and cost when used in secondary batteries.
  • 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 embodiment of the present invention is a positive electrode having a positive electrode active material, the positive electrode active material having magnesium, nickel, fluorine, and lithium cobalt oxide, the positive electrode active material having a surface portion, the maximum value of a magnesium concentration observed in EDX-ray analysis of the surface portion being 10 atomic% or more when the sum of carbon, oxygen, fluorine, magnesium, aluminum, silicon, phosphorus, sulfur, calcium, titanium, iron, cobalt, nickel, and gallium is taken as 100 atomic%, and a battery having a positive electrode and lithium as a counter electrode, the positive electrode active material has diffraction peaks at 2 ⁇ of 19.13° or more and less than 19.37° and at 2 ⁇ of 45.37° or more and less than 45.57° when the positive electrode is analyzed by X-ray diffraction using CuK ⁇ 1 ray in a state where the battery is charged to 4.6 V.
  • the magnesium present in the surface layer is dissolved in lithium cobalt oxide.
  • Another embodiment of the present invention is a positive electrode having a positive electrode active material, the positive electrode active material including magnesium, nickel, and fluorine, and lithium cobalt oxide.
  • the positive electrode has a positive electrode and lithium as a counter electrode.
  • the positive electrode active material has diffraction peaks at 2 ⁇ of 19.00° or more and 19.20° or less, and at 2 ⁇ of 19.13° or more and less than 19.37°.
  • I O3 the area of the diffraction peak having a maximum value in the range of 2 ⁇ from 19.00° to 19.20°
  • I O3' the area of the diffraction peak having a maximum value in the range of 2 ⁇ from 19.13° to 19.37°
  • I O3 /(I O3 +I O3' ) is 15% or more and 60% or less.
  • Another aspect of the present invention is a lithium ion secondary battery having a positive electrode, the positive electrode having a positive electrode active material, the positive electrode active material having magnesium, nickel, and lithium cobalt oxide, and in EDX ray analysis, the ratio of the number of atoms of magnesium (Mg) to cobalt (Co) is 0.3 or more and 2.0 or less at the measurement point where the maximum value of magnesium is detected in the surface layer of the positive electrode active material, and the ratio of the number of atoms of nickel (Ni) to cobalt (Co) is 0 or more and 1 or less at the measurement point where the maximum value of nickel is detected in the surface layer of the positive electrode active material.
  • Another aspect of the present invention is a lithium ion secondary battery having a positive electrode, the positive electrode having a positive electrode active material, the positive electrode active material having magnesium, nickel, and lithium cobalt oxide, and in EDX ray analysis, the maximum value of the ratio of the number of atoms of magnesium Mg in the surface layer of the positive electrode active material to the average value of cobalt Co inside (Mg/Co) is 0.05 or more and 0.6 or less, the maximum value of the ratio of the number of atoms of nickel Ni in the surface layer to the average value of cobalt Co inside (Ni/Co) is 0 or more and 0.2 or less, and the maximum value of the ratio of the number of atoms of the sum of magnesium and nickel in the surface layer to the average value of cobalt inside ((Mg+Ni)/Co)) is 0.05 or more and 0.8 or less.
  • the surface portion has an edge region and a basal region, and that the amount of magnesium detected in the edge region is greater than the amount of magnesium detected in the basal region, and that the amount of nickel detected in the edge region is greater than the amount of nickel detected on the basal surface.
  • Another aspect of the present invention is a lithium ion secondary battery having a positive electrode, the positive electrode having a positive electrode active material, the positive electrode active material having magnesium and lithium cobalt oxide, the maximum magnesium concentration in the surface layer of the positive electrode active material observed by EDX ray analysis being 3 atomic% or more and 20 atomic% or less when the sum of cobalt, oxygen, magnesium, nickel, aluminum and carbon is 100 atomic%, and the average magnesium concentration in the positive electrode active material (positive electrode active material particles including the surface layer 100a and the interior 100b) observed by ICP-MS or GD-MS is 0.03 atomic% or more and 1 atomic% or less.
  • the positive electrode active material contains lithium cobalt oxide containing nickel in addition to magnesium, and it is preferable that the average concentration of nickel inside the positive electrode active material is 0.0042 atomic% or more and 0.0126 atomic% or less.
  • the lithium cobalt oxide contains fluorine.
  • Another aspect of the present invention is a method for producing a positive electrode active material, comprising a step of mixing a lithium source, a cobalt source, and an additive element source to produce a mixture, and a step of heating the mixture, the method comprising a first heating step of heating the mixture at a first temperature for a first time, and a second heating step, which is performed after the first heating step, of heating the mixture at a second temperature for a second time, the first temperature being higher than the second temperature and the first time being shorter than the second time.
  • the first heating step has a function of reducing crystal defects in the positive electrode active material
  • the second heating step has a function of uniformly diffusing the additive element into the surface layer of the positive electrode active material while allowing the additive element to remain in the surface layer.
  • the source of the added element is preferably one or more selected from a magnesium source, a nickel source, and a fluorine source.
  • Another aspect of the present invention is a method for producing a positive electrode active material, comprising a first step of heating a container containing one or more selected from a magnesium source, a fluorine source, and a lithium source, and a second step of containing a lithium source, a cobalt source, and an additive element source in the container and heating the container.
  • 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 and 1B are cross-sectional views of a positive electrode active material.
  • FIG. 2 is a diagram illustrating the phase change of the positive electrode active material.
  • FIG. 3 is a diagram illustrating the charge depth and lattice constant of the positive electrode active material.
  • Fig. 4A is a diagram illustrating an example of a method for manufacturing a positive electrode active material
  • Fig. 4B and Fig. 4C are diagrams illustrating an example of a heating method in the manufacturing method.
  • 5A and 5B are diagrams illustrating an example of a method for producing a positive electrode active material.
  • 6A and 6B are diagrams illustrating an example of a method for manufacturing a positive electrode active material.
  • FIG. 7 is a diagram illustrating an example of a method for producing a positive electrode active material.
  • FIG. 8 is a diagram illustrating an example of a method for producing a positive electrode active material.
  • FIG. 9 is a diagram illustrating an example of a method for producing a positive electrode active material.
  • FIG. 10 is a phase diagram showing the relationship between the composition of lithium fluoride and magnesium fluoride and the temperature.
  • FIG. 11 is a phase diagram showing the relationship between the composition of lithium fluoride and aluminum fluoride and the temperature.
  • FIG. 12 is an example of a TEM image in which the crystal orientations are roughly consistent.
  • Fig. 13A is an example of an STEM image in which the crystal orientations are roughly consistent
  • Fig. 13B is an FFT pattern of a region of the rock-salt crystal RS, and Fig.
  • FIG. 13C is an FFT pattern of a region of the layered rock-salt crystal LRS.
  • FIG. 14 is a diagram illustrating the crystal structure of the positive electrode active material.
  • FIG. 15 is a diagram illustrating the crystal structure of a conventional positive electrode active material.
  • FIG. 16 is a diagram showing an XRD pattern calculated from the crystal structure.
  • FIG. 17 shows an XRD pattern calculated from the crystal structure.
  • 18A and 18B show XRD patterns calculated from the crystal structure.
  • FIG. 19 is a diagram showing the external appearance of a secondary battery.
  • 20A to 20C are diagrams illustrating a method for manufacturing a secondary battery.
  • 21A to 21H are diagrams illustrating an example of an electronic device.
  • 22A to 22D are diagrams illustrating an example of an electronic device.
  • 23A to 23C are diagrams illustrating an example of an electronic device.
  • 24A to 24C are diagrams illustrating an example of a vehicle.
  • 25A and 25B are EDX ray analysis profiles of the positive electrode active material.
  • 26A and 26B are EDX analysis profiles of the positive electrode active material.
  • 27A and 27B are EDX ray analysis profiles of the positive electrode active material.
  • 28A and 28B are EDX analysis profiles of the positive electrode active material.
  • 29A and 29B are EDX ray analysis profiles of the positive electrode active material.
  • 30A and 30B are EDX ray analysis profiles of the positive electrode active material.
  • 31A to 31C are cross-sectional STEM images of the positive electrode active material.
  • FIG. 32A is a cross-sectional STEM image of the positive electrode active material
  • FIG. 32A is a cross-sectional STEM image of the positive electrode active material
  • FIG. 32B is a mapping image of cobalt
  • FIG. 32C is a mapping image of nickel
  • FIG. 33A is a cross-sectional STEM image of a positive electrode active material and a diagram showing an analyzed portion
  • FIG. 33B is a graph showing the cobalt and nickel concentrations.
  • FIG. 34 shows the XRD pattern of the positive electrode during charging.
  • 35A and 35B are enlarged XRD patterns of a portion of FIG. 36A to 36D are graphs showing the results of ICP-MS.
  • 37A to 37D are graphs showing the results of ICP-MS.
  • 38A to 38C are graphs showing the results of STEM-EELS.
  • 39A and 39B are graphs showing the results of STEM-EELS.
  • FIG. 40A and 40B are SEM images showing the EPMA analysis points.
  • FIG. 41 is a HAADF-STEM image of the positive electrode active material.
  • FIG. 42A is a schematic diagram of a layered rock-salt type crystal structure, and FIGS. 42B and 42C are HAADF-STEM images of a region having a layered rock-salt type crystal structure.
  • FIG. 43A is a schematic diagram of a spinel crystal structure, and FIGS. 43B and 43C are HAADF-STEM images of a region having a spinel crystal structure.
  • FIG. 44A is a schematic diagram of a rock-salt type crystal structure, and FIGS. 44B and 44C are HAADF-STEM images of a region having a rock-salt type crystal structure.
  • 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.
  • LiCoO 2 LiCoO 2
  • 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, etc., "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.
  • the positive electrode active material to which an additive element has been added may be expressed as a composite oxide, a positive electrode material, a positive electrode material, a positive electrode material for secondary batteries, etc.
  • the positive electrode active material of one embodiment of the present invention preferably has a compound.
  • the positive electrode active material of one embodiment of the present invention preferably has a composition.
  • the positive electrode active material of one embodiment of the present invention preferably has a composite.
  • 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.
  • the short circuit current is suppressed even at a high charging voltage.
  • the positive electrode active material of one embodiment of the present invention suppresses the short circuit current even at a high charging voltage. 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.
  • FIG. 1A and 1B are cross-sectional views of a positive electrode active material 100 according to one embodiment of the present invention.
  • the positive electrode active material 100 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 figures indicates the (001) plane of lithium cobalt oxide (LiCoO 2 ).
  • LiCoO 2 belongs to the space group R-3m.
  • the positive electrode active material 100 has lithium, cobalt, oxygen, and an additive element.
  • the positive electrode active material 100 has lithium cobalt oxide to which an additive element has been added.
  • edge region 100a the area around A-B in FIG. 1B above can be called edge region 100a1.
  • the area around C-D in FIG. 1B above can be called basal region 100a2.
  • the straight line marked (00l) represents the (00l) plane.
  • the edge region has a surface exposed in a direction intersecting with the (00l) plane, and the edge region is a region that is perpendicular or approximately perpendicular from the surface, 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.
  • intersecting means that the angle between the perpendicular line to the first surface ((00l) plane) and the normal line to the second surface (surface of the positive electrode active material 100) is 10 degrees or more and 90 degrees or less, more preferably 30 degrees or more and 90 degrees or less.
  • the basal region has a surface parallel to the (00l) plane, and is referred to as 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 perpendicular or nearly perpendicular from the surface toward the inside.
  • "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 100) is 0 degrees or more and less than 10 degrees, more preferably 0 degrees or more and 5 degrees or less.
  • the additive elements contained in the positive electrode active material 100 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 100, it can be considered that the charge/discharge capacity of the positive electrode active material 100 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.
  • 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, iron, cobalt, nickel, and gallium is 100 atomic %. Details of EDX analysis will be described later.
  • 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 wt ppm or more and 300 wt ppm or less, that is, 0.0042 atomic % or more and 0.0126 atomic % or less.
  • At least magnesium and nickel preferably have a small amount of elution even after a charge-discharge cycle test in a high-voltage charging (eg, 4.7 V vs. Li/Li + ) and a measurement environment (eg, 45° C.) higher than room temperature.
  • a high-voltage charging eg, 4.7 V vs. Li/Li +
  • a measurement environment eg, 45° C.
  • the Mg/Co atomic ratio
  • the Ni/Co is 0.005 ⁇ 0.001 (0.004 or more and 0.006 or less).
  • the positive electrode active material 100 has a more stable composition and crystal structure during charging due to the presence of the additive elements in the surface layer 100a and the interior 100b as described above. Therefore, the positive electrode active material 100 can have an O3' type crystal structure during charging.
  • the positive electrode active material 100 having an O3' type crystal structure during charging has extremely good charge/discharge cycle characteristics when used in a secondary battery. It is also expected to be highly safe.
  • O3 on the left side is a schematic diagram of the crystal structure of the interior 100b of the positive electrode active material 100 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 to the right of O3 is a schematic diagram of the crystal structure of the inside 100b of the positive electrode active material 100 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 at the cobalt site suppresses the desorption of lithium nearby.
  • magnesium and nickel are present at some of the lithium sites as in the discharge state. Therefore, it is believed that lithium present at the inside 100b exists randomly at 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 100. 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.
  • H1-3 shown to the right of O3' 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.
  • 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 to change to the H1-3 phase (Non-Patent Document 5).
  • Non-Patent Document 4 the c-axis length of lithium cobalt oxide changes with the phase change.
  • the change in the c-axis length of conventional lithium cobalt oxide described in Non-Patent Document 4 is shown in Figure 3.
  • the round markers are hexagonal phases, and the diamond markers are monoclinic phases.
  • the c-axis length shrinks as shown by the diamond marker in Figure 3. Since the phase transition from O3 to the H1-3 phase is a phase transition associated with the desorption of lithium ions, it is thought that the phase transition occurs from the surface of the positive electrode active material, which is the region where lithium ions are first removed, but it may eventually extend to the entire positive electrode active material.
  • the phase transition to spinel is a phase transition accompanied by the desorption of oxygen, so it is considered to occur from the surface from which oxygen is easily desorbed.
  • Lithium cobalt oxide that becomes H1-3 when x in Li x CoO 2 is about 0.2 does not have an additive element in the surface layer part, or the distribution of the additive element in the surface layer part is insufficient, so oxygen is easily desorbed from the surface and it may be easily phase-changed to a spinel type crystal structure.
  • the spinel type crystal structure may be more likely to phase-change to a rock salt type crystal structure. These phase changes may be particularly likely to propagate in the direction perpendicular to the c-axis. When the region of the spinel type crystal structure and the rock salt type crystal structure increases, the charge/discharge capacity of the positive electrode active material decreases.
  • the 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.
  • the positive electrode active material 100 can be produced, for example, by the flow shown in Figure 4A.
  • Step S11 First, in step S11 shown in FIG. 4A, a lithium source (Li source) and a cobalt source (Co source) are prepared as starting materials, that is, lithium and transition metal materials, respectively.
  • Li source Li source
  • Co source cobalt source
  • the lithium source it is preferable to use a compound containing lithium, such as lithium carbonate, lithium hydroxide, lithium nitrate, or lithium fluoride. It is preferable that the lithium source has high purity, for example, a material with a purity of 99.99% or more.
  • cobalt source it is preferable to use a compound containing cobalt, such as cobalt oxide or cobalt hydroxide.
  • the cobalt source has high crystallinity, for example, single crystal grains.
  • the crystallinity of the cobalt source can be evaluated using TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope) images, ABF-STEM (annular bright-field scanning transmission electron microscope) images, etc., or evaluation using X-ray diffraction (XRD), electron beam diffraction, neutron beam diffraction, etc.
  • XRD X-ray diffraction
  • step S12 the lithium source and the cobalt source are pulverized and mixed to prepare a mixed material.
  • the pulverization and mixing can be performed in a dry or wet manner.
  • the wet method is preferable because it can be crushed into smaller pieces.
  • a solvent is prepared.
  • ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. can be used. It is more preferable to use an aprotic solvent that is less likely to react with lithium.
  • dehydrated acetone with a purity of 99.5% or more is used. It is preferable to mix the lithium source and the cobalt source with dehydrated acetone with a purity of 99.5% or more, in which the moisture content is suppressed to 10 ppm or less, and then pulverize and mix them.
  • dehydrated acetone with the above-mentioned purity it is possible to reduce impurities that may be mixed in.
  • a ball mill, a bead mill, or the like can be used as a means for grinding and mixing.
  • a ball mill it is 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, diameter of ball mill container 40 mm).
  • step S13 shown in Fig. 4A 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 elements uniformly into the surface layer of the positive electrode active material while allowing them to remain in the surface layer.
  • 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 100.
  • 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 100 of one embodiment of the present invention by a single heat treatment as shown in Figures 4A to 4C is highly productive and is preferable.
  • additive elements such as magnesium and fluorine
  • the container which may be called a sheath
  • additive elements such as magnesium and fluorine
  • an additive element source such as a magnesium source or a fluorine source and/or a lithium source and undergoes a heating process.
  • Step S34 Through the above steps, the positive electrode active material 100 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.
  • 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.
  • Method 4 for preparing the positive electrode active material can be used as a reference.
  • 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.
  • 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 elements. This heating is sometimes called initial heating.
  • Step S15> 7 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 rock-salt type. Therefore, by performing initial heating, it is possible to make it easier for divalent additive elements such as nickel to remain in the surface layer 100a.
  • the effect of this initial heating is particularly large on the surface other than the (001) orientation of the positive electrode active material 100 and on its surface layer 100a.
  • the Me-O distance in rock salt Ni0.5Mg0.5O is 2.09 ⁇
  • the Me-O distance in rock salt MgO is 2.11 ⁇ .
  • the Me-O distance in spinel NiAl2O4 is 2.0125 ⁇
  • the bond distance between metals other than lithium and oxygen is shorter than the above.
  • the Al-O distance in layered rock salt type LiAlO2 is 1.905 ⁇ (Li-O distance is 2.11 ⁇ ).
  • the Co-O distance in layered rock salt type LiCoO2 is 1.9224 ⁇ (Li-O distance is 2.0916 ⁇ ).
  • Non-Patent Document 16 the ionic radius of hexacoordinated aluminum is 0.535 ⁇ , and the ionic radius of hexacoordinated oxygen is 1.4 ⁇ , the sum of which is 1.935 ⁇ .
  • 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.
  • 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 cathode active material 100 having O3′ type and/or 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.
  • the surface layer 100a of the positive electrode active material 100 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 perpendicular or approximately perpendicular from the surface toward the inside. Note that approximately perpendicular is defined as 80° or more and 100° or less. Surfaces caused by cracks and/or fissures may also be referred to as the surface.
  • the surface layer 100a is synonymous with the surface vicinity, surface vicinity region, or 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 to the first surface (the (00l) plane) and the normal line to the second surface (the surface of the positive electrode active material 100) 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 100) 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.
  • 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 detection amount of fluorine in the surface layer 100a is greater than the detection amount inside. It is also preferable that the detection amount peak is located closer to the surface of the surface layer 100a. For example, it is preferable that the detection amount peak is located on the surface or within 3 nm from the reference point. Similarly, it is preferable that the detection amount of titanium, silicon, phosphorus, boron and/or calcium is greater than the detection amount inside the surface layer 100a. It is also preferable that the detection amount peak is located closer to the surface of the surface layer 100a. For example, it is preferable that the detection 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 100.
  • Arrows C-D are shown in FIG. 1 as an example of the depth direction of the (001) surface of lithium cobalt oxide in the positive electrode active material 100.
  • the (001) oriented surface crossed by the arrows C-D may have a different distribution of the additive element from the other surfaces.
  • the (001) oriented surface and its surface layer 100a may have a lower detection amount of one or more selected from the 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 the additive elements not detected or the detection amount may be 1 atomic % or less. Specifically, nickel may not be detected or the detection amount may be 1 atomic % or less.
  • the (001) oriented surface and its surface layer 100a may have a peak of the detection amount of one or more selected from the additive elements 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 100 to have a (001) orientation. The main diffusion path of lithium ions during charge and discharge is not exposed on the (001) plane.
  • the diffusion paths of lithium ions are exposed on surfaces other than those with the (001) orientation. Therefore, the surfaces and surface layer 100a other than those with the (001) orientation are important regions for maintaining the diffusion paths of lithium ions, and at the same time, they are prone to becoming unstable because they are the regions from which lithium ions are first desorbed. Therefore, reinforcing the surfaces and surface layer 100a other than those with the (001) orientation is extremely important for maintaining the crystal structure of the entire positive electrode active material 100.
  • the profile of the added element on the surface other than the (001) oriented surface and on the surface layer 100a thereof is the distribution described above.
  • the concentration of the added element on the (001) oriented surface and on 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 surface other than the (001) oriented surface and its surface layer 100a preferably has a half-width of more than 200 nm to 500 nm, more preferably more than 200 nm to 300 nm, and even more preferably 230 nm to 270 nm.
  • the nickel distribution in the surface other than the (001) orientation and in the surface layer 100a thereof preferably has a half-width of 30 nm or more and 150 nm or less, more preferably 50 nm or more and 130 nm or less, and even more preferably 70 nm or more and 110 nm or less.
  • 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 100.
  • 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 an adverse 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, unnecessary magnesium compounds (oxides, fluorides, etc.) that do not substitute for either the lithium site or the cobalt site may segregate on the surface of the positive electrode active material, and may become resistance components in 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 100 is appropriate.
  • the number of magnesium atoms is preferably 0.002 to 0.06 times the number of cobalt atoms, more preferably 0.005 to 0.03 times, and even more preferably about 0.01 times.
  • the amount of magnesium contained in the entire positive electrode active material 100 here may be a value obtained by performing an elemental analysis of the entire positive electrode active material 100 using, for example, GD-MS, 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 100.
  • 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, aluminum, cobalt, and nickel (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 range of temperature and time 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 positive electrode active material 100 as a whole contains an appropriate amount of nickel.
  • the number of nickel atoms contained in the positive electrode active material 100 is preferably more than 0% and not more than 7.5% of the number of cobalt atoms, 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.
  • Or 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 an 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 100 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 charging depth or charging rate, deterioration of the positive electrode active material 100 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 100 in a secondary battery. Furthermore, it is possible to obtain a positive electrode active material 100 whose crystal structure is less likely to collapse even when repeatedly charged and discharged.
  • 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 100 is appropriate.
  • the number of aluminum atoms contained in the entire positive electrode active material 100 is preferably 0.05% to 4% of the number of cobalt atoms, preferably 0.1% to 2%, and more preferably 0.3% to 1.5%.
  • 0.05% to 2% is preferable.
  • 0.1% to 4% is preferable.
  • the amount contained in the entire positive electrode active material 100 here may be, for example, a value obtained by performing elemental analysis of the entire positive electrode active material 100 using GD-MS, ICP-MS, or the like, or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material 100.
  • fluorine The presence of fluorine in the surface layer portion 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 100 and the electrolyte, and can effectively improve corrosion resistance to hydrofluoric acid.
  • fluorides such as lithium fluoride can function as a fluxing agent that lowers the melting point of other additive element sources.
  • the fluxing effect causes at least a portion of the surface layer of the lithium cobalt oxide and at least a portion of the additive element source to melt and 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 100.
  • 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. 11 (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 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 reduce the oxidation number of cobalt in lithium cobalt oxide, thereby stabilizing the crystal structure.
  • 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 short circuits can be suppressed 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 hydrogen fluoride generated by the 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 100 When the positive electrode active material 100 has phosphorus together with magnesium, the stability in the state where x in Li x CoO 2 is 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. Or 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.
  • concentrations of phosphorus and magnesium shown here may be values obtained by performing elemental analysis of the entire positive electrode active material 100 using, for example, GD-MS, ICP-MS, or the like, or may be based on values of the composition of raw materials in the process of producing the positive electrode active material 100.
  • the 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.
  • the positive electrode active material 100 has additive elements with different distributions, it is preferable because it can stabilize the crystal structure in a wider region.
  • the positive electrode active material 100 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 can 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 distributed widely in a deeper region.
  • aluminum is continuously detected in a region from 1 nm to 25 nm in the depth direction from the surface. It is preferable 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 can stabilize the crystal structure in a wider region.
  • the effects of the respective additive elements are synergistic and can contribute to further stabilization of the surface layer 100a.
  • the presence of magnesium, nickel, and aluminum is highly effective in providing a stable composition and crystal structure, 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 characteristics of the rock salt type or both the rock salt type and the layered rock salt type. It is also preferable that the orientation of the surface layer 100a, which has characteristics of the rock salt type or both the rock salt type and the layered rock salt type, and the interior 100b of the layered rock salt type are roughly consistent.
  • 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
  • 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 structure that has a cubic crystal structure, such as the space group Fm-3m, in which cations and anions are arranged alternately. Note that there may be a deficiency of cations or anions.
  • 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 diffraction pattern corresponding to the crystal planes forming this two-dimensional plane is set as the origin 000
  • the bright spot closest to the central spot is, for example, the (111) plane in the rock salt type in an ideal state, and, for example, the (003) plane in the layered rock salt type.
  • the distance between the bright spots on the (003) plane of LiCoO 2 is observed to be about half the distance between the bright spots on the (111) plane of MgO. Therefore, when the analysis 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 12 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 bright bands (bright strips) and dark bands (dark strips). Therefore, when a repetition of bright lines and dark lines is observed in a TEM image and the angle between the bright lines (for example, L RS and L LRS shown in FIG.
  • 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 13A 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 13B
  • the FFT pattern of the area of the layered rock-salt crystal LRS is shown in Figure 13C.
  • the composition, JCPDS card number, d value calculated from these, angle, and incidence are shown on the left of Figures 13B and 13C.
  • 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 13B is due to the 11-1 reflection of the cubic crystal.
  • the spot marked A in Figure 13C is due to the 0003 reflection of the layered rock salt type. From Figures 13B and 13C, 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 13B is roughly parallel to the line passing through AO in Figure 13C. 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. 13C is due to the 1014 reflection of the layered rock salt type. This may be observed at an angle of 52° to 56° (i.e., ⁇ AOB is 52° to 56°) from the orientation of the reciprocal lattice point (A in FIG.
  • spots not originating from the 11-1 reflection of a cubic crystal may be observed in a reciprocal lattice space other than the orientation where the 11-1 reflection of a cubic crystal is observed.
  • the spot marked B in Figure 13B 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 13B) 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 are prone to have 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 so that the (0003) plane can be easily observed.
  • FIB Flucused Ion Beam
  • the positive electrode active material 100 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. 15.
  • the conventional positive electrode active material shown in Fig. 15 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 as 1/2 of the unit cell in order to make it easier to compare with other crystal structures.
  • 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 the change in the angle at which the peak of, for example, the (003) plane of lithium cobalt oxide appears in the XRD pattern. It is known that in XRD using CuK ⁇ 1 radiation, the peak of the (003) plane of lithium cobalt oxide appears at 2 ⁇ of approximately 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 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 between 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 between the state where x is 1 and the state where x is 0.24 or less can be reduced. Also, the change in volume compared per cobalt atom can be reduced. Therefore, the positive electrode active material 100 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 100 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, the positive electrode active material 100 of one embodiment of the present invention is less likely to cause a short circuit when the state where x in Li x CoO 2 is 0.24 or less is maintained. In such a case, the safety of the secondary battery is further improved, which is preferable.
  • the interior 100b of the positive electrode active material 100 when x in Li x CoO 2 is 1, approximately 0.2, and approximately 0.15.
  • the interior 100b occupies most of the volume of the positive electrode active material 100 and is the part that contributes greatly to charge and discharge, so it can be said that the displacement of the CoO 2 layer and the change in volume are the most problematic parts.
  • the positive electrode active material 100 has the same crystal structure as conventional lithium cobalt oxide, R-3m O3.
  • the positive electrode active material 100 has a different crystal structure from that of conventional lithium cobalt oxide when x is 0.24 or less, for example, about 0.2 and about 0.15, in which case the lithium cobalt oxide has an H1-3 type crystal structure.
  • the symmetry of the CoO2 layer is the same as that of O3. Therefore, this crystal structure is called an O3'-type crystal structure.
  • This crystal structure is shown in FIG. 14 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 100 at this time is about 15 atomic % in the discharged state. Therefore, this crystal structure is called a monoclinic O1(15) type crystal structure. This crystal structure is shown in FIG. 14 with P2/m monoclinic O1(15) attached.
  • the monoclinic O1(15) crystal structure has the coordinates of cobalt and oxygen in the unit cell as follows: Co1(0.5,0,0.5), Co2(0,0.5,0.5), O1(X O1 , 0, Z O1 ), 0.23 ⁇ XO1 ⁇ 0.24, 0.61 ⁇ ZO1 ⁇ 0.65, O2(X O2 , 0.5, Z O2 ),
  • the lattice constant of the unit cell can be expressed as follows: 0.75 ⁇ X O2 ⁇ 0.78, 0.68 ⁇ Z O2 ⁇ 0.71.
  • a 4.880 ⁇ 0.05 ⁇
  • b 2.817 ⁇ 0.05 ⁇
  • this crystal structure can show the lattice constant even in the space group R-3m if a certain degree of error is allowed.
  • the coordinates of cobalt and oxygen in the unit cell are as follows: Co(0,0,0.5), O(0,0,Z O ), The range of Z O can be expressed as 0.21 ⁇ Z O ⁇ 0.23.
  • the difference in volume per the same number of cobalt atoms between R-3m O3 in a discharged state and the O3' type crystal structure is 2.5% or less, more specifically 2.2% or less, typically 1.8%.
  • the difference in volume per the same number of cobalt atoms between R-3m O3 in a discharged state and the monoclinic O1(15) crystal structure is 3.3% or less, more specifically 3.0% or less, typically 2.5%.
  • Table 1 shows the difference in volume per cobalt atom between R-3m O3 in a discharged state, O3', monoclinic O1(15), H1-3 type, and trigonal O1.
  • 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.
  • reference values can be referred to for R-3m O3 in a discharged state and trigonal O1 (ICSDcoll.code.172909 and 88721).
  • H1-3 reference can be made to Non-Patent Document 3.
  • O3' and monoclinic O1(15) the values can be calculated from experimental values obtained by XRD.
  • the positive electrode active material 100 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 100 does not easily lose its crystal structure even when charging and discharging are repeated such that x is 0.24 or less. Therefore, the positive electrode active material 100 suppresses a decrease in charge and discharge capacity in the charge and discharge cycle. In addition, since more lithium can be stably used than in the conventional positive electrode active material, the positive electrode active material 100 has a large discharge capacity per weight and per volume. Therefore, by using the positive electrode active material 100, a secondary battery with a high discharge capacity per weight and per volume can be manufactured.
  • the positive electrode active material 100 may have an O3' type crystal structure when x in Li x CoO 2 is 0.15 or more and 0.24 or less, and it is estimated that the positive electrode active material 100 may have an O3' type crystal structure even when x is more than 0.24 and 0.27 or less. It has also been confirmed that the positive electrode active material 100 may have a monoclinic O1 (15) type crystal structure when x in Li x CoO 2 is more than 0.1 and 0.2 or less, typically when x is 0.15 or more and 0.17 or less.
  • the crystal structure is not necessarily limited to the above range of x because it is affected 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 100 may have only O3' type, may have only monoclinic O1 (15) type, or may have both crystal structures. Also, all of the particles in the inside 100b of the positive electrode active material 100 may not have O3' type and/or monoclinic O1 (15) type crystal structures. They may contain other crystal structures, or may be partially amorphous.
  • the state in which x in Li x CoO 2 is small can be said to be a state in which it is charged at a high charging voltage.
  • a charging voltage of 4.6 V or more based on the potential of lithium metal can be said to be a high charging voltage.
  • the charging voltage is expressed based on the potential of lithium metal.
  • the positive electrode active material 100 of one embodiment of the present invention is preferable because it can maintain a crystal structure with R-3m O3 symmetry even when charged at a high charging voltage, for example, a voltage of 4.6 V or more at 25°C. It can also be said that it is preferable because it can adopt an O3' type crystal structure when charged at a higher charging voltage, for example, a voltage of 4.65 V or more and 4.7 V or less at 25°C. It can also be said that it is preferable because it can adopt a monoclinic O1(15) type crystal structure when charged at an even higher charging voltage, for example, a voltage of more than 4.7 V and 4.8 V or less at 25°C.
  • the positive electrode active material 100 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 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 100 of one embodiment of the present invention may be able to have 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 able to be formed.
  • 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 the voltage obtained by subtracting the graphite potential from the above voltage.
  • 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. 15.
  • 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 100 of one embodiment of the present invention is distributed as described above, and 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 100 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 100 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 in the positive electrode active material after cracks have occurred, the corrosion resistance to hydrofluoric acid can be improved. Also, even in the positive electrode active material after cracks have occurred, 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 100 with a relatively small particle size is expected to have high charge/discharge rate characteristics.
  • Positive electrode active material 100 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 100 of one embodiment of the present invention having an O3′ type and/or monoclinic O1(15) type crystal structure when x in Li x CoO 2 is small can be determined by analyzing a positive electrode having a positive electrode active material with a small x in Li x CoO 2 using XRD, electron beam diffraction, neutron beam diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), or the like.
  • XRD is particularly preferred because it can analyze 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 periodic distortion of the lattice and the crystallite size, and it can obtain sufficient accuracy even when measuring the positive electrode obtained by dismantling the secondary battery as is.
  • powder XRD can obtain diffraction peaks that reflect the crystal structure of the interior 100b of the positive electrode active material 100, which occupies the majority of the volume of the positive electrode active material 100.
  • the positive electrode active material from the positive electrode obtained by dismantling a secondary battery, prepare a powder sample, and then measure it.
  • the positive electrode active material 100 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 the crystal structure when charged at a high voltage is not preferable because it cannot withstand high-voltage charging and discharging.
  • the O3' or monoclinic O1(15) crystal structure is not obtained by simply adding an additive element.
  • lithium cobalt oxide having magnesium and fluorine, or lithium cobalt oxide having magnesium and aluminum is common, depending on the concentration and distribution of the additive element, there are cases where x in Li x CoO 2 is 0.24 or less and the O3' and/or monoclinic O1(15) crystal structure is 60% or more, and cases where the H1-3 crystal structure is 50% or more.
  • the positive electrode active material 100 of one embodiment of the present invention Even in the case of the positive electrode active material 100 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 positive electrode active material 100 of one embodiment of the present invention is present, 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 100.
  • 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.
  • 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 XRD measurement apparatus and conditions are not particularly limited.
  • the measurement can be performed using the following apparatus and conditions.
  • XRD device Bruker AXS, D8 ADVANCE
  • X-ray source Cu Output: 40kV, 40mA 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.
  • Figures 18A and 18B 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 18A showing an enlarged view of the region in which 2 ⁇ is between 18° (degree) and 21°, and Figure 18B showing an enlarged view of the region in which 2 ⁇ is between 42° and 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 positive electrode active material 100 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 50% or less. 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 small.
  • 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 100 is reduced to only 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 in the positive electrode active material 100 according to one embodiment of the present invention.
  • the positive electrode active material 100 may contain transition metals such as nickel and manganese as additive elements in addition to cobalt.
  • 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 100 in a state where no charging or discharging is performed or in a discharged state, which can be estimated from the XRD pattern, the a-axis lattice constant is preferably greater than 2.814 ⁇ 10 ⁇ 10 m and smaller than 2.817 ⁇ 10 ⁇ 10 m, and the c-axis lattice constant is preferably greater than 14.05 ⁇ 10 ⁇ 10 m and smaller than 14.07 ⁇ 10 ⁇ 10 m.
  • the state where no charging or discharging is performed may be, for example, a powder state before the positive electrode of a secondary battery is prepared.
  • the value obtained by dividing the lattice constant of the a-axis by the lattice constant of the c-axis is greater than 0.20000 and less than 0.20049.
  • a first peak may be observed at 2 ⁇ of 18.50° or more and 19.30° or less, and a second peak may be observed at 2 ⁇ of 38.00° or more and 38.80° or less.
  • XPS X-ray photoelectron spectroscopy
  • 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.
  • narrow scan analysis can be used to analyze the bonding state of 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 100. 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 100 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 100.
  • the nickel concentration of at least a part of the surface layer 100a is higher than the average nickel concentration of the entire positive electrode active material 100.
  • 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 100.
  • the fluorine concentration in at least a portion of the surface layer 100a is higher than the average fluorine concentration in the entire positive electrode active material 100.
  • the surface and surface layer 100a of the positive electrode active material 100 do not contain carbonates, hydroxyl groups, etc. that are chemically adsorbed after the preparation of the positive electrode active material 100. They also do not contain electrolyte, binder, conductive material, or compounds derived from these that are attached to the surface of the positive electrode active material 100. Therefore, when quantifying the elements contained in the positive electrode active material, corrections may be made to exclude carbon, hydrogen, excess oxygen, excess fluorine, etc. that can be detected by surface analysis such as XPS. For example, XPS makes it possible to separate the types of bonds by analysis, and corrections may be made to exclude C-F bonds derived from the binder.
  • the 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 with 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 100 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.
  • 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 value is different from both the bond energy of lithium fluoride, 685 eV, and the bond energy of magnesium fluoride, 686 eV.
  • the peak showing the bond energy between magnesium and other elements is preferably equal to or greater than 1302 eV and less than 1304 eV, and more preferably about 1303 eV. This is a different value from the bond energy of magnesium fluoride, which is 1305 eV, and is close to the bond energy of magnesium oxide.
  • ⁇ EDX> It is preferable that one or more selected from the additive elements contained in the positive electrode active material 100 have a concentration gradient. It is more preferable that the depth from the surface of the concentration peak of the positive electrode active material 100 differs 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 100 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 100.
  • EDX ray analysis can analyze the concentration distribution and maximum value of the added element. Analysis using a thinned sample such as STEM-EDX is more suitable because it can analyze the concentration distribution in the depth direction from the surface to the center of the positive electrode active material in a specific region without being affected by the distribution in the depth direction.
  • the positive electrode active material 100 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 detection amount of the characteristic X-ray of the transition metal M is 50% of the sum of the average value M AVE of the detection amount of the characteristic X-ray of the transition metal M in the interior and the average value M BG of the detection amount of the characteristic X-ray of the transition metal M in the background, or a point where the detection amount of the characteristic X-ray of oxygen is 50% of the sum of the average value O AVE of the detection amount of the characteristic X-ray of the oxygen in the interior and the average value O BG of the detection amount of the characteristic X-ray of the oxygen in the background.
  • the point where the amount of detection of the characteristic X-rays of the transition metal M is 50% of the sum of the average amount of detection of the characteristic X-rays of the transition metal M inside and the average amount of detection of the characteristic X-rays of the transition metal M in the background is different from the point where the amount of detection of the characteristic X-rays of oxygen is 50% of the sum of the average amount of detection of the characteristic X-rays of oxygen inside and the average amount of detection of the characteristic X-rays of oxygen in the background, it is considered that this is due to the influence of metal oxides, carbonates, etc.
  • the point where the amount of detection of the characteristic X-rays of the transition metal M is 50% of the sum of the average amount M AVE of the detection of the characteristic X-rays of the transition metal M inside and the average amount M BG of the detection of the characteristic X-rays of the transition metal M in the background can be adopted as the position of the surface of the positive electrode active material.
  • the surface can be obtained using the M AVE and M BG of the element with the largest amount of detection of characteristic X-rays inside.
  • the average background value M BG 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, for example, avoiding the vicinity where the detected amount of the transition metal M starts to increase.
  • the average internal detected amount M AVE 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 transition metal M and oxygen are saturated and stable, for example, a portion that is 30 nm or more, preferably 50 nm deep from the region where the detected amount of the transition metal M starts to increase.
  • the average background value O BG of oxygen and the average internal detected amount of oxygen O AVE can also be obtained in the same manner.
  • the surface of the positive electrode active material 100 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 a larger atomic number than lithium among the metal elements that make up the positive electrode active material are observed. Alternatively, it is the intersection of a tangent drawn to the brightness profile from the surface to the bulk in the STEM image and the axis in the depth direction.
  • the surface in a STEM image or the like may be determined in conjunction with an analysis with higher spatial resolution.
  • the spatial resolution of STEM-EDX is about 1 nm. Therefore, the maximum value of the additive element profile can deviate by about 1 nm. For example, even if the maximum value of the additive element profile of magnesium or the like is outside the surface determined above, if the difference between the maximum value and the surface is less than 1 nm, this can be considered an error.
  • a peak in STEM-ED X-ray analysis refers to the detection intensity in each element profile, or the maximum value of the 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 values measured over six scans can be used as the profile for each element.
  • the number of scans is not limited to six, and more scans can be performed and the average can be used as the profile for each element.
  • STEM-EDX analysis can be performed, for example, as follows.
  • a protective film is deposited on the surface of the positive electrode active material.
  • carbon can be deposited 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 using, for example, a STEM device (Hitachi High-Tech HD-2700) and an EDAX Octane T Ultra W (two-wire) 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 100 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 top.
  • the magnesium concentration decays to 30% or less of the peak at a point 2 nm deep from the peak top.
  • the peak concentration 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 100 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 up to 3 nm from the surface or reference point of the positive electrode active material 100 toward the center, more preferably at a depth of up to 1 nm, and even more preferably at a depth of up to 0.5 nm.
  • the distribution of nickel preferably overlaps with the distribution of magnesium.
  • the difference in depth between the peak of nickel concentration and the peak of 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 100, 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 and cobalt atoms (Mg/Co) in the vicinity of the grain boundary is preferably 0.020 or more and 0.50 or less. More preferably, it is 0.025 or more and 0.30 or less. Even more preferably, it is 0.030 or more and 0.20 or less. Or it is preferably 0.020 or more and 0.30 or less. Or it is preferably 0.020 or more and 0.20 or less. Or it is preferably 0.025 or more and 0.50 or less. Or it is preferably 0.025 or more and 0.20 or less. Or it is preferably 0.030 or more and 0.50 or less.
  • the ratio is within the above range at multiple locations, for example, three or more locations, of the positive electrode active material 100, it can be said that this indicates that the additive element is not attached to a narrow area on the surface of the positive electrode active material 100, but is widely distributed at a preferred concentration in the surface layer portion 100a of the positive electrode active material 100.
  • EPMA concentration of the additive element contained in the positive electrode active material 100 can be analyzed using EDX, but can also be analyzed using EPMA.
  • EPMA has a higher detection capability (also called a lower detection limit) than EDX in analyzing elements present in trace amounts in a sample. Therefore, it is preferable to use EPMA when analyzing a region where a trace amount of the additive element is present.
  • EPMA uses a wavelength-dispersive detector, so it has a higher ability to detect trace elements than EDX, which uses an energy-dispersive detector.
  • the spatial resolution of EPMA analysis is inferior to EDX (especially STEM-EDX). Therefore, STEM-EDX is suitable for analysis focusing on the detailed distribution of added elements in the surface layer 100a of the positive electrode active material 100, while EPMA analysis is suitable for analysis of trace amounts of added elements in the interior 100b.
  • EPMA and EDX are different analytical methods, so the concentration values obtained when the same region is analyzed using each analytical method may not match.
  • a cross section of the positive electrode active material 100 is exposed by mechanical polishing, ion polishing, FIB, or the like, and the cross section is analyzed.
  • an EPMA device for example, an electron probe microanalyzer JXA-iHP200F manufactured by JEOL Ltd. can be used.
  • ⁇ Raman spectroscopy> As described above, it is preferable that at least a part of the surface layer 100a of the positive electrode active material 100 of one embodiment of the present invention has a rock salt type crystal structure. Therefore, when the positive electrode active material 100 and a positive electrode having the same are analyzed by Raman spectroscopy, it is preferable that a cubic crystal structure such as a rock salt type is also observed along with the layered rock salt crystal structure.
  • peaks are observed at 470 cm -1 to 490 cm -1 and 580 cm -1 to 600 cm - 1 in layered rock salt LiCoO2
  • a peak is observed at 665 cm -1 to 685 cm -1 in cubic CoOx (0 ⁇ x ⁇ 1) (rock salt Co1 - yO (0 ⁇ y ⁇ 1) or spinel Co3O4 ).
  • the integrated intensity of each peak is defined as I1 from 470 cm -1 to 490 cm -1 , I2 from 580 cm -1 to 600 cm - 1, and I3 from 665 cm -1 to 685 cm -1 , it is preferable that the value of I3/I2 is 1% or more and 10% or less, and more preferably 3% or more and 9% or less.
  • the surface layer 100a of the positive electrode active material 100 has a rock-salt type crystal structure within a preferred range.
  • the characteristics of the rock salt type crystal structure are observed in the electron microbeam diffraction pattern as well as the layered rock salt crystal structure.
  • the characteristics of the rock salt type crystal structure are not too strong in the surface layer 100a, especially in the outermost surface (for example, 1 nm deep from the surface), taking into account the above-mentioned difference in sensitivity. This is because the presence of an additive element such as magnesium in the lithium layer while maintaining the layered rock salt type crystal structure can ensure a diffusion path for lithium and has a stronger function of stabilizing the crystal structure than when the outermost surface is covered with a rock salt type crystal structure.
  • a micro-electron beam diffraction pattern is obtained from a region having a depth of 1 nm or less from the surface, and a micro-electron beam diffraction pattern is obtained from a region having a depth of 3 nm to 10 nm, it is preferable that the difference in the lattice constant calculated from these patterns is small.
  • the difference in lattice constant calculated from a measurement point at a depth of 1 nm or less from the surface and a measurement point at a depth of 3 nm to 10 nm is preferably 0.1 ⁇ or less for the a-axis, and 1.0 ⁇ or less for the c-axis. It is more preferable that the difference is 0.05 ⁇ or less for the a-axis, and more preferably 0.6 ⁇ or less for the c-axis. It is even more preferable that the difference is 0.04 ⁇ or less for the a-axis, and even more preferably 0.3 ⁇ or less for the c-axis.
  • the positive electrode active material 100 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 100, the specific surface area of the positive electrode active material 100, etc.
  • the surface smoothness can be quantified from a cross-sectional SEM image of the positive electrode active material 100 as follows:
  • the cathode active material 100 is processed by FIB or the like to expose the cross section. At this time, it is preferable to cover the cathode active material 100 with a protective film, a protective agent, or the like.
  • an SEM image of the interface between the protective film or the like and the cathode active material 100 is taken.
  • the interface is extracted using the image processing software.
  • the interface line between the protective film or the like and the cathode active material 100 is selected using an automatic selection tool or the like, and 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 100 of this embodiment preferably has a root mean square (RMS) surface roughness, which is an index of roughness, of less than 3 nm, preferably less than 1 nm, and more preferably less than 0.5 nm.
  • RMS root mean square
  • the image processing software used for noise processing, interface extraction, etc. is not particularly limited, but for example, "ImageJ" described in Non-Patent Documents 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 100 can also be quantified from the ratio of the actual specific surface area S R measured by a constant volume gas adsorption method to the ideal specific surface area S i .
  • the ideal specific surface area S i is calculated assuming that all particles have the same diameter D50, the same weight, and an ideal spherical shape.
  • the median diameter D50 can be measured using a particle size distribution 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 100 by the following method.
  • a surface SEM image of the positive electrode active material 100 is obtained.
  • a conductive coating may be applied as a pretreatment before observation. 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 above 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.
  • This embodiment can be used in combination with other embodiments.
  • Example of secondary battery configuration The following description will be given taking as an example a secondary battery shown in FIG. 19 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 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 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 have a sheet-like shape.
  • Graphene compounds may have a curved surface, enabling surface contact with low contact resistance.
  • the graphene compound may cover 80% or more of the area of the active material. It is preferable that the graphene compound is wrapped around at least a part of the active material particles.
  • 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.
  • 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 used in the form of a foil, plate, sheet, net, punched metal, or expanded metal. It is preferable to use a current collector having a thickness of 5 ⁇ m or more and 30 ⁇ m or less.
  • the negative electrode includes a negative electrode active material layer and a negative electrode current collector.
  • the negative electrode active material layer may include a conductive material and a binder.
  • Negative electrode active material for example, an alloy-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 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.
  • the conversion reaction can also occur in 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 for example, 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, sulfolane,
  • DMC
  • the ionic liquid is composed of a cation and an anion, and includes an organic cation and an 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 materials improves oxidation resistance, suppressing the deterioration of the separator during high-voltage charging and discharging, and improving the reliability of the secondary battery.
  • Coating with fluorine-based materials also makes it easier for the separator and electrodes to adhere to each other, improving output characteristics.
  • Coating with polyamide-based materials, especially aramid improves heat resistance, improving the safety of the secondary battery.
  • both sides of a polypropylene film may be coated with a mixture of aluminum oxide and aramid.
  • the surface of the polypropylene film that comes into contact with the positive electrode may be coated with a mixture of aluminum oxide and aramid, and the surface that comes into contact with the negative electrode may be coated with a fluorine-based material.
  • the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, so the discharge capacity per volume of the secondary battery can be increased.
  • the exterior body of the secondary battery can be made of, for example, a metal material such as aluminum and/or a resin material.
  • a film-shaped exterior body can also be used.
  • 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. 19 and Fig. 20 An example of an external view of a laminated secondary battery 500 is shown in Fig. 19 and Fig. 20.
  • Fig. 19 and Fig. 20 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. 20A to 20C.
  • FIG. 20B 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 or the like may be used for the joining.
  • the tab regions of the negative electrodes 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.
  • the negative electrode 506, separator 507, and positive electrode 503 are placed on the exterior body 509 shown in FIG. 20C.
  • 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. 21A to 21G 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. 21A to 21G.
  • 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. 21A 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 21B shows the mobile phone 7400 in a bent state.
  • the secondary battery 7407 installed inside is also bent.
  • Figure 21C 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 the current collector.
  • the current collector is copper foil, and a part of it is alloyed with gallium to improve adhesion with the active material layer in contact with the current collector, resulting in a configuration with high reliability when the secondary battery 7407 is bent.
  • FIG. 21D 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. 21E 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. 21F 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. 21E 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.
  • FIG. 21G 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. 21H 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. 22A 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. 22A.
  • 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-savings 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 22B shows an oblique view of the wristwatch device 4005 removed from the wrist.
  • FIG. 22C shows a state in which a secondary battery 913 is built in.
  • the secondary battery 913 is the secondary battery described in embodiment 4.
  • the secondary battery 913 is provided in a position overlapping with the display portion 4005a, and is small and lightweight.
  • FIG. 22D 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 bodies 4100a and 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 units 4100a and 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 units 4100a and 4100b. Furthermore, if main units 4100a and 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 units 4100a and 4100b for playback. This allows them to be used as, for example, a translation machine.
  • 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 1 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.
  • FIG. 23A 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. 23B shows an example of a robot.
  • the robot 6400 shown in FIG. 23B 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. 23C shows an example of an aircraft.
  • the aircraft 6500 shown in FIG. 23C 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. 24 illustrates an example of a vehicle using a secondary battery according to one embodiment of the present invention.
  • the automobile 8400 illustrated in FIG. 24A is an electric automobile using 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.
  • 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. 24B 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. 24B 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. 24C is an example of a two-wheeled vehicle using a secondary battery of one embodiment of the present invention.
  • a scooter 8600 shown in FIG. 24C 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. 24C 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.
  • a positive electrode active material was produced and its characteristics were evaluated.
  • step S14 of the flow in FIG. 6B lithium cobalt oxide (Cellseed C-10N, manufactured by Nippon Chemical Industry Co., Ltd.) with no particular added elements was prepared.
  • step S21b nickel hydroxide was prepared by pulverizing and mixing in dehydrated acetone and then sieving through a 300 ⁇ m sieve, and weighed to be 0.5 mol% relative to the cobalt in the lithium cobalt oxide.
  • step S21c aluminum hydroxide was prepared by pulverizing and mixing in dehydrated acetone and then sieving through a 300 ⁇ m sieve, and weighed to be 0.5 mol% relative to the cobalt in the lithium cobalt oxide. No magnesium source or fluorine source was used. Then, lithium cobalt oxide, nickel hydroxide, and aluminum hydroxide were mixed in a dry manner. The mixing conditions were 150 rpm and 20 minutes.
  • step S21 lithium fluoride was prepared and weighed out so that it was 1.17 mol% relative to the cobalt in the lithium cobalt oxide. No magnesium source, nickel source, or aluminum source was used. Then, the lithium cobalt oxide and magnesium hydroxide were dry mixed.
  • sample 2 The mixture obtained above was placed in an aluminum oxide crucible and heated in a muffle furnace. The heating conditions were 850°C for 60 hours. Oxygen was passed through at a flow rate of 10 L/min. The mixture was then cooled to room temperature to obtain a positive electrode active material. This was designated sample 2.
  • step S21c aluminum hydroxide was prepared by grinding and mixing in dehydrated acetone, then sieving through a 300 ⁇ m mesh sieve, and weighed out to be 0.5 mol% relative to the cobalt in the lithium cobalt oxide. No fluorine source, magnesium source, or nickel source was used. The lithium cobalt oxide and aluminum hydroxide were then dry mixed. The mixing conditions were 150 rpm and 20 minutes.
  • the mixture obtained above was placed in an aluminum oxide crucible and heated in a muffle furnace. The heating conditions were 850°C for 10 hours. Oxygen was passed through at a flow rate of 5 L/min. The mixture was then cooled to room temperature to obtain a positive electrode active material. This was designated sample 3.
  • nickel hydroxide was prepared by grinding and mixing in dehydrated acetone, then sieving through a 300 ⁇ m mesh sieve, and weighed out to be 0.5 mol% relative to the cobalt in the lithium cobalt oxide. No fluorine source, magnesium source, or aluminum source was used. The lithium cobalt oxide and aluminum hydroxide were then dry mixed. The mixing conditions were 150 rpm and 20 minutes.
  • sample 4 The mixture obtained above was heated in the same manner as sample 3 to obtain a positive electrode active material. This was designated sample 4.
  • magnesium hydroxide was prepared in place of lithium fluoride and magnesium fluoride.
  • the magnesium hydroxide was weighed out so that it was 0.5 mol% relative to the cobalt in the lithium cobalt oxide.
  • the lithium cobalt oxide and magnesium hydroxide were then mixed in a dry manner. The mixing conditions were 150 rpm and 1 hr.
  • the mixture obtained above was placed in an aluminum oxide crucible and heated in a muffle furnace. The heating conditions were 850°C for 60 hours. Oxygen was passed through at a flow rate of 10 L/min. The mixture was then cooled to room temperature to obtain a positive electrode active material. This was designated sample 5.
  • lithium cobalt oxide with no added elements was prepared.
  • step S21 lithium fluoride was prepared as the fluorine source and lithium source, and was weighed out to be 0.17 mol% relative to the cobalt in the lithium cobalt oxide.
  • Magnesium fluoride was prepared as the magnesium source and fluorine source, and was weighed out to be 0.5 mol% relative to the cobalt.
  • the lithium cobalt oxide, lithium fluoride, and magnesium fluoride were mixed in a dry manner. The mixing conditions were 150 rpm and 1 hr.
  • the mixture obtained above was placed in an aluminum oxide crucible and heated in a muffle furnace. The heating conditions were 850°C for 60 hours. Oxygen was passed through at a flow rate of 10 L/min. The mixture was then cooled to room temperature to obtain a positive electrode active material. This was designated sample 6.
  • lithium fluoride was weighed out to be 0.17 mol% and magnesium fluoride was weighed out to be 0.5 mol%.
  • LiF and MgF2 adjusted to the above molar ratio were pulverized and mixed in dehydrated acetone, and then sieved through a sieve with an opening of 300 ⁇ m.
  • Nickel hydroxide was weighed out to be 0.5 mol% relative to the cobalt of lithium cobalt oxide. For this, nickel hydroxide was pulverized and mixed in dehydrated acetone, and then sieved through a sieve with an opening of 300 ⁇ m.
  • lithium cobalt oxide, lithium fluoride, magnesium fluoride and nickel hydroxide were mixed in a dry state, and then sieved through a sieve with an opening of 300 ⁇ m.
  • the mixing conditions were 150 rpm and 1 hr.
  • Sample 7-11 was prepared in the same manner as sample 7, except that nickel fluoride was used instead of nickel hydroxide as the nickel source.
  • step S15 of the flow in FIG. 7 lithium cobalt oxide with no added elements was heated in a muffle furnace.
  • the heating conditions were 850°C and 2 hours. Heating was performed in an oxygen atmosphere, and no flow occurred.
  • steps S21 to S23 in the flow chart in Figure 7 were carried out in the same manner as for sample 2.
  • Lithium cobalt oxide, lithium fluoride, and magnesium fluoride were then mixed in a dry state and sieved through a sieve with 300 ⁇ m openings.
  • the mixing conditions were 150 rpm and 1 hr.
  • the mixture obtained above was placed in a square container made of aluminum oxide and heated in a muffle furnace.
  • the heating conditions were 900°C for 20 hours.
  • the heating was performed in an oxygen atmosphere, and no flow occurred. It was then cooled to room temperature to obtain a composite oxide.
  • step S41 of the flow in Figure 7 nickel hydroxide and aluminum hydroxide were weighed out so that the ratio of nickel hydroxide to cobalt in lithium cobalt oxide was 0.5 mol % and 0.5 mol %, respectively.
  • nickel hydroxide or aluminum hydroxide was crushed and mixed in dehydrated acetone, and then sieved through a sieve with 300 ⁇ m openings.
  • Lithium cobalt oxide, lithium fluoride, magnesium fluoride, nickel hydroxide, and aluminum hydroxide were then dry mixed, and then sieved through a sieve with 300 ⁇ m openings.
  • the mixing conditions were 150 rpm and 1 hr.
  • sample 8 The mixture obtained above was then placed in a square container made of aluminum oxide and heated in a muffle furnace. The heating conditions were 850°C for 10 hours. The heating was performed in an oxygen atmosphere, and no flow occurred. The mixture was then cooled to room temperature to obtain a positive electrode active material. This was designated sample 8.
  • FIG. 25A shows the edge region of Sample 3, and FIG. 25B shows the profile of the basal region of Sample 3.
  • FIG. 26A shows the edge region of Sample 4, and FIG. 26B shows the profile of the basal region of Sample 4.
  • FIG. 27A shows the edge region of Sample 5, and FIG. 27B shows the profile of the basal region of Sample 5.
  • FIG. 28A shows the edge region of Sample 6, and FIG. 28B shows the profile of the basal region of Sample 6.
  • FIG. 29A shows the edge region of Sample 7, and FIG. 29B shows the profile of the basal region of Sample 7.
  • FIG. 30A shows the edge region of Sample 8, and FIG. 30B shows the profile of the basal region of Sample 8.
  • the reference point in the EDX-ray analysis i.e., the point where cobalt is 50% of the sum of the average internal detection amount M AVE and the average background amount M BG , is indicated by a dashed dotted line.
  • nickel was distributed not only on the surface of the lithium cobalt oxide particles but also inside.
  • the maximum value of the nickel profile was 2.1 atomic% at a point 40 nm from the reference point in the basal region. In the edge region, no decrease in the nickel profile was observed up to a depth of 60 nm from the reference point. Magnesium and aluminum were not detected, and more specifically, the magnesium concentrations were all 0.3 atomic% or less, and the aluminum concentrations were all 0.3 atomic% or less.
  • a comparison with sample 3 suggests that nickel in lithium cobalt oxide is more diffusible than aluminum, and that it is more diffusible in the direction perpendicular to the c-axis than in the c-axis direction.
  • magnesium, nickel, and aluminum were detected in the surface layer.
  • the maximum value of the magnesium profile was 12.8 atomic% at 0 nm from the reference point in the edge region, and 4.6 atomic% at -1 nm from the reference point in the basal region.
  • the maximum value of the aluminum profile was 1.5 atomic% at 1 nm from the reference point in the edge region, and 2.5 atomic% at 21 nm from the reference point in the basal region.
  • the maximum value of the nickel profile was 2.5 atomic% at 1 nm from the reference point in the edge region, and was not detected in the basal region, being 0.5 atomic% or less.
  • nickel was below the detection limit, but in sample 8, in which the process of adding the additive element sources and heating was divided into two steps and nickel was added in the latter process, nickel was detected in the edge region. In this way, it was shown that by carefully selecting the combination of added elements and the timing of their addition, it is possible to make more of the added elements present in the surface layer.
  • the atomic ratio Mg/Co of magnesium to cobalt at the measurement point where the maximum value of the magnesium profile was detected was 0.3 to 2.0, more specifically 0.4 to 1.0. Specifically, Mg/Co was 0.48 in the basal region and 0.85 in the edge region.
  • FIG. 31A A cross-sectional STEM image of Sample 4 is shown in Fig. 31A.
  • An enlarged view of the basal region surrounded by a dashed line and labeled 1 is shown in Fig. 31B.
  • An enlarged view of the edge region surrounded by a dashed line and labeled 2 is shown in Fig. 31C.
  • the brightness of the region about 1.5 nm from the surface was different from that of other regions.
  • Figure 32A shows a cross-sectional STEM image (HAADF-STEM image) of the basal region of Sample 4.
  • Figure 32B shows a cobalt mapping image of the same region, and
  • Figure 32C shows a nickel mapping image.
  • the cobalt mapping image a striped pattern similar to that in the cross-sectional STEM image was observed.
  • no particular regularity was observed in the nickel mapping image.
  • Figure 33A shows the same cross-sectional STEM image as Figure 32A.
  • EDX point analysis was performed on multiple areas along the dark and bright lines in the STEM image in Figure 33A.
  • the analysis area was approximately 11 nm wide and 0.2 nm long, with the analysis areas along the dark lines indicated by black arrows and the analysis areas along the bright lines indicated by open arrows.
  • the EDX point analysis results for the areas indicated by the black arrows are shown as "dark” in the graph in Figure 33B.
  • the EDX point analysis results for the areas indicated by the open arrows are shown as "bright” in the graph in Figure 33B.
  • the black circle markers indicate the cobalt concentration and refer to the right axis.
  • the open square markers indicate the nickel concentration and refer to the left axis.
  • NMP N-methyl-2-pyrrolidone
  • test battery (referred to as a half cell) was made using the above positive electrode and lithium metal as the counter electrode.
  • a coin-type cell was used for the test battery.
  • the electrolyte for the half-cell was prepared by dissolving lithium hexafluorophosphate (LiPF 6 ) at 1 mol/L in a mixed organic solvent containing EC (ethylene carbonate) and DEC (diethyl carbonate) at a volume ratio of 3: 7 .
  • VC lithium hexafluorophosphate
  • a 25 ⁇ m thick porous polypropylene film was used as the half-cell separator.
  • a coin-shaped half cell containing samples 1 to 8 was fabricated using a positive electrode can and a negative electrode can made of stainless steel (SUS316).
  • Half cells containing samples 1 to 8 were charged for XRD measurement.
  • the charging method was CC (10 mA/g, charge cut-off voltage 4.60 V) with a 10-minute rest period for samples 1 to 3, 5, and 7.
  • Sample 4 was the same as sample 1, etc., except that no rest period was provided.
  • Sample 6 was CCCV (4.6 V, 68.5 mA/g, charge cut-off current 1.37 mA/g) with a 30-minute rest period.
  • the half cell containing sample 8 was charged and discharged once, and then charged for XRD measurement.
  • the first charge and discharge was CCCV (4.5 V, 40 mA/g, charge cut-off current 4 mA/g) and CC (40 mA/g, discharge cut-off voltage 3.0 V) for charging and CCCV (4.6 V, 40 mA/g, charge cut-off current 4 mA/g) for discharging, and CCCV (4.6 V, 40 mA/g, charge cut-off current 4 mA/g) for charging for XRD measurement.
  • Table 3 shows the charge/discharge capacity per weight of the positive electrode active material for Samples 1 to 8.
  • the cell was disassembled in an argon atmosphere glove box within 1 hour after charging was completed and sealed in an airtight cell.
  • the airtight cell was tightly fastened, and XRD measurement was started within 2 minutes of removing it from the glove box.
  • the XRD measurement conditions were as follows: XRD device: Bruker AXS, D8 ADVANCE X-ray source: CuK ⁇ Output: 40kV, 40mA Divergence angle: Div. Slit, 0.5° Detector: LynxEye Scan method: 2 ⁇ / ⁇ continuous scan Measurement range (2 ⁇ ): 15° to 75° (100 min) Step width (2 ⁇ ): 0.01° Setting counting time: 1 second/step Sample stage rotation: 15 rpm
  • Figure 34 shows the powder XRD patterns of the positive electrode active materials of Samples 1 to 7-1, and Sample 8. For comparison, the XRD patterns of O3, H1-3, and O3' are also shown. Enlarged patterns of a portion of Figure 34 are shown in Figures 35A and 35B.
  • Samples 1, 3, 4, and 5 which have aluminum, nickel, and/or magnesium as additive elements but no fluorides that can function as fluxes, were primarily in the H1-3 phase when charged at 4.6 V. The same was true for Sample 2, which contains only fluorides and no other additive elements.
  • sample 6 having magnesium and fluoride was mainly in the O3' phase when charged at 4.6 V.
  • Sample 7-1 having nickel in addition to magnesium and fluoride, and sample 8 having aluminum were also mainly in the O3' phase when charged at 4.6 V.
  • fluoride that can function as a flux the distribution of additive elements such as magnesium in the positive electrode active material becomes good, and it was shown that when x in Li x CoO 2 is, for example, 0.1 ⁇ x ⁇ 0.24, an O3' type crystal structure is formed.
  • a coin-shaped half cell was prepared in the same manner as above using sample 8 as the positive electrode active material, and a charge-discharge cycle test was performed with charge: CCCV (100 mA/g, 4.7 V, charge cut-off current 10 mA/g) and discharge: CC (100 mA/g, discharge cut-off voltage 2.5 V). A rest period of 10 minutes was provided between charge and discharge. The temperature of the measurement environment was 25°C or 45°C. After 1, 5, 15, and 50 cycles, the coin cell was disassembled, and the positive electrode active material was scraped off from the positive electrode and analyzed by ICP-MS.
  • the Li/Co (atomic ratio) tends to decrease as the charge/discharge cycle progresses, and this is more pronounced at 45°C. This indicates that the positive electrode active material is losing lithium as it deteriorates.
  • Mg/Co was in the range of 0.01 ⁇ 0.002 (0.008 to 0.012) after each cycle, specifically 0.0096 to 0.011. This is similar to the Mg mixing ratio of 0.01 in the manufacturing process of sample 8.
  • Ni/Co was in the range of 0.005 ⁇ 0.001 (0.004 or more and 0.006 or less) after each cycle, specifically 0.0050 or more and 0.00568 or less. This is similar to the Ni mixture ratio of 0.005 in the manufacturing process of sample 8.
  • the STEM-EELS measurement apparatus and conditions were as follows. Equipment: NEOARM (manufactured by JEOL Ltd.) Acceleration voltage: 200 kV Cs-STEM mode Measurement pitch: 0.25 nm Measurement sample thickness: about 50 nm
  • Figure 38A shows a HAADF-STEM image of the measurement area
  • Figure 38B shows a cobalt valence mapping image by STEM-EELS.
  • Valence peak shift
  • Figure 38C shows a graph of the average cobalt valence at the same depth, superimposed with graphs of magnesium and aluminum distribution by EDX-ray analysis.
  • Figure 39A shows the same mapping image as Figure 38B
  • Figure 39B shows the EELS spectrum of CoL2.3 edge in area 1 (part of the surface layer) and area 2 (part of the interior) shown here.
  • Figure 40A is an SEM image of the cross section of the S52 mixture
  • Figure 40B is an SEM image of sample 8, both of which were subjected to EPMA analysis. Both samples were embedded in resin and processed using the ion polishing method. The area where the EPMA analysis was performed is indicated by a white cross in the figure. As shown in these figures, the measurement area in both cases was the inside of the positive electrode active material. Note that these cross sections are not thin slices, and EPMA analysis was performed using characteristic X-rays obtained from an area extending to a depth of about 1 ⁇ m from the surface of the analyzed sample.
  • nickel was not detected in the mixture from step S52, but was detected in sample 8 after heating. This indicates that nickel diffuses easily into lithium cobalt oxide, and that the mixed nickel diffused to the inside due to heating.
  • aluminum was not detected in sample 8 after heating. This suggests that aluminum does not diffuse easily into lithium cobalt oxide, and that even when heated, it remains in the surface layer and in shallow regions inside.
  • ⁇ HAADF-STEM> a coin cell was prepared in the same manner as above for Sample 8. After multiple cycles of charge and discharge as an aging treatment, a charge and discharge cycle test was performed 50 times at 45° C. and a charge voltage of 4.55 V or more and 4.65 V or less to deteriorate the positive electrode active material, and then the coin cell was observed using a HAADF-STEM.
  • the equipment used was a Hitachi High-Tech HF5000, with an accelerating voltage of 200 kV.
  • the magnification accuracy was ⁇ 3%.
  • Figure 41 shows a HAADF-STEM image of the surface layer of deteriorated sample 8.
  • a region 1001 with a layered rock-salt crystal structure, a region 1002 with a spinel crystal structure, and a region 1003 with a rock-salt crystal structure were observed. Both rock-salt crystal structures and spinel crystal structures were observed on the surface.
  • the white dotted lines are a guide to the boundaries of each region, and do not indicate that any region consists of only one type of crystal structure. Any region may have characteristics of two or more types of crystal structures.
  • FIG. 42A is a schematic diagram of lithium cobalt oxide (LiCoO 2 ) having a layered rock salt type crystal structure. Oxygen is cubic close-packed, and cobalt and lithium are present in alternating layers at the oxygen 6-coordinated positions.
  • FIG. 42C is a HAADF-STEM image of lithium cobalt oxide, and FIG. 42B shows an enlarged view of the area surrounded by the dashed line in the figure. In both cases, a layered arrangement of cobalt was observed. In the HAADF-STEM image, contrast is obtained that is approximately proportional to the square of the atomic number, so the brightness of cobalt (atomic number 27) is much higher than that of lithium (atomic number 3) and oxygen (atomic number 8).
  • FIG. 43A is a schematic diagram of Co 3 O 4 having a spinel type crystal structure.
  • Oxygen is cubic close-packed, and cobalt is present at oxygen hexahedral and tetrahedral positions.
  • cobalt is present at 4-coordinate positions and 6-coordinate positions in a deformed hexagon on the (001) plane, with cobalt at the 6-coordinate position at the center.
  • FIG. 43C is a HAADF-STEM image of Co 3 O 4 , and an enlarged view of the area surrounded by the dashed line in the figure is shown in FIG. 43B.
  • FIG. 43B As shown by the dashed line in FIG. 43B, a deformed hexagon with high brightness centered on cobalt was observed, as in the schematic diagram.
  • Figure 44A is a schematic diagram of CoO with a rock-salt crystal structure. The oxygen is cubic close-packed, with cobalt at the 6-coordination site of oxygen.
  • Figure 44C is a HAADF-STEM image of CoO, and an enlarged view of the area enclosed by the dashed line in the figure is shown in Figure 44B. Cobalt arrangement was observed in both cases.
  • 100a Surface layer
  • 100b Interior
  • 503 Positive electrode
  • 506 Negative electrode
  • 507 Separator
  • 509 Exterior body
  • 510 Positive electrode lead electrode
  • 511 Negative electrode lead electrode
  • 903 Mixture
  • 913 Secondary battery

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