WO2024003663A1 - 二次電池 - Google Patents

二次電池 Download PDF

Info

Publication number
WO2024003663A1
WO2024003663A1 PCT/IB2023/056238 IB2023056238W WO2024003663A1 WO 2024003663 A1 WO2024003663 A1 WO 2024003663A1 IB 2023056238 W IB2023056238 W IB 2023056238W WO 2024003663 A1 WO2024003663 A1 WO 2024003663A1
Authority
WO
WIPO (PCT)
Prior art keywords
positive electrode
active material
electrode active
tab
lithium
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/IB2023/056238
Other languages
English (en)
French (fr)
Japanese (ja)
Inventor
山崎舜平
神保安弘
和田理人
比嘉麻子
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Semiconductor Energy Laboratory Co Ltd
Original Assignee
Semiconductor Energy Laboratory Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Semiconductor Energy Laboratory Co Ltd filed Critical Semiconductor Energy Laboratory Co Ltd
Priority to JP2024530067A priority Critical patent/JPWO2024003663A1/ja
Priority to US18/872,382 priority patent/US20250293408A1/en
Priority to CN202380045088.6A priority patent/CN119318054A/zh
Priority to KR1020247038995A priority patent/KR20250028250A/ko
Publication of WO2024003663A1 publication Critical patent/WO2024003663A1/ja
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Images

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/50—Current conducting connections for cells or batteries
    • H01M50/531—Electrode connections inside a battery casing
    • H01M50/538—Connection of several leads or tabs of wound or folded electrode stacks
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/26—Electrodes characterised by their structure, e.g. multi-layered, porosity or surface features
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H01G11/46—Metal oxides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/66—Current collectors
    • H01G11/70—Current collectors characterised by their structure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/74—Terminals, e.g. extensions of current collectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/04—Construction or manufacture in general
    • H01M10/0431—Cells with wound or folded electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/50—Current conducting connections for cells or batteries
    • H01M50/531—Electrode connections inside a battery casing
    • H01M50/533—Electrode connections inside a battery casing characterised by the shape of the leads or tabs
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • One embodiment of the present invention relates to a secondary battery.
  • One embodiment of the present invention relates to a lithium ion secondary battery.
  • One embodiment of the present invention relates to an electronic device having a secondary battery.
  • one embodiment of the present invention is not limited to the above technical field.
  • the technical fields of one embodiment of the present invention disclosed in this specification etc. include semiconductor devices, display devices, light emitting devices, power storage devices, storage devices, electronic devices, lighting devices, input devices, input/output devices, and driving methods thereof. , or their manufacturing method.
  • Semiconductor devices refer to all devices that can function by utilizing semiconductor characteristics.
  • lithium ion secondary batteries lithium ion capacitors
  • air batteries air batteries
  • all-solid-state batteries lithium ion secondary batteries
  • demand for high-output, high-capacity lithium-ion secondary batteries is rapidly expanding along with the development of the semiconductor industry, and they have become indispensable in today's information society as a source of rechargeable energy. .
  • Non-Patent Document 6 describes the thermal stability of a positive electrode active material and an electrolyte.
  • An object of one embodiment of the present invention is to provide a highly safe secondary battery.
  • An object of one embodiment of the present invention is to provide a secondary battery that can be charged and discharged at high speed.
  • An object of one embodiment of the present invention is to provide a secondary battery that can achieve both high safety and shortened charging and discharging time.
  • An object of one embodiment of the present invention is to provide a high-capacity secondary battery.
  • the present invention is a wound-type secondary battery having a positive electrode and a negative electrode.
  • the positive electrode includes a positive electrode current collector and a positive electrode active material.
  • the positive electrode current collector has a first tab and a second tab.
  • the negative electrode includes a negative electrode current collector and a negative electrode active material.
  • the negative electrode current collector has a third tab and a fourth tab.
  • the first tab is located closer to the center of the winding than the second tab.
  • the third tab is located closer to the center of the winding than the fourth tab.
  • the first tab and the second tab are joined at the first joint, and the third tab and the fourth tab are joined at the second joint.
  • the positive electrode active material has a first region and a second region located on the surface side of the positive electrode active material.
  • the first region has lithium, cobalt and oxygen.
  • the second region has lithium, cobalt, magnesium and oxygen.
  • the present invention is a wound-type secondary battery having a positive electrode and a negative electrode.
  • the positive electrode includes a positive electrode current collector and a positive electrode active material.
  • the positive electrode current collector has a first tab, a second tab, and a fifth tab.
  • the negative electrode includes a negative electrode current collector and a negative electrode active material.
  • the negative electrode current collector has a third tab, a fourth tab, and a sixth tab.
  • the first tab, the second tab, and the fifth tab are located in this order from the side closer to the center of the winding, and are joined at the first joint.
  • the third tab, fourth tab, and sixth tab are located in this order from the side closer to the center of the winding, and are joined at the second joint.
  • the positive electrode active material has a first region and a second region located on the surface side of the positive electrode active material.
  • the first region has lithium, cobalt and oxygen.
  • the second region has lithium, cobalt, magnesium and oxygen.
  • the present invention is a wound-type secondary battery having a positive electrode and a negative electrode.
  • the positive electrode includes a positive electrode current collector and a positive electrode active material.
  • the positive electrode current collector has a first tab, a second tab, and a fifth tab.
  • the negative electrode includes a negative electrode current collector and a negative electrode active material.
  • the negative electrode current collector has a third tab, a fourth tab, and a sixth tab.
  • the first tab, the second tab, and the fifth tab are located in this order from the side closer to the center of the winding, and are joined at the first joint.
  • the third tab, fourth tab, and sixth tab are located in this order from the side closer to the center of the winding, and are joined at the second joint.
  • the positive electrode active material has a first region and a second region located on the surface side of the positive electrode active material.
  • the first region has lithium, cobalt and oxygen.
  • the second region has lithium, cobalt, magnesium and oxygen.
  • the thickness of the second region is preferably 2 nm or more and 5 nm or less.
  • the second region further contains nickel.
  • the second region further contains fluorine.
  • the first region further contains aluminum.
  • the second region is preferably located within a range of 5 nm from the surface of the positive electrode active material.
  • the volume resistivity of the powder of the positive electrode active material at a temperature of 15° C. or more and 30° C. or less is 1.0 ⁇ 10 5 ⁇ cm or more at a pressure of 64 MPa.
  • the volume resistivity of the powder of the positive electrode active material at a temperature of 15° C. or more and 30° C. or less is 2.0 ⁇ 10 5 ⁇ cm or more at a pressure of 13 MPa.
  • the volume resistivity of the powder of the positive electrode active material at a temperature of 15° C. to 30° C. is 1.0 ⁇ 10 5 ⁇ cm or more at a pressure of 64 MPa, and It is preferable that the resistance is 2.0 ⁇ 10 5 ⁇ cm or more.
  • a highly safe secondary battery can be provided.
  • a secondary battery capable of high-speed charging and discharging can be provided.
  • a high capacity secondary battery can be provided.
  • FIG. 1 is a diagram showing an example of the configuration of a secondary battery.
  • FIG. 2A and FIG. 2B are diagrams showing an example of the configuration of a secondary battery.
  • FIG. 3 is a diagram showing a configuration example of a secondary battery.
  • FIG. 4 is a diagram showing a configuration example of a secondary battery.
  • FIG. 5 is a diagram showing a configuration example of a secondary battery.
  • FIG. 6 is a diagram showing a configuration example of a secondary battery.
  • FIGS. 7A and 7B are diagrams illustrating an example of the configuration of a positive electrode active material.
  • 8A and 8B are graphs showing the internal temperature of the secondary battery.
  • FIGS. 9A and 9B are diagrams illustrating a nail penetration test.
  • FIG. 10A to 10F are diagrams showing configuration examples of positive electrode active materials.
  • FIG. 11 is a diagram showing a configuration example of a positive electrode active material.
  • FIG. 12 is a diagram showing a configuration example of a positive electrode active material.
  • FIG. 13 is an example of a TEM image of a crystal.
  • FIG. 14A is an example of a STEM image, and FIGS. 14B and 14C are examples of FFT patterns.
  • FIG. 15 is an XRD pattern.
  • FIG. 16 is an XRD pattern.
  • 17A and 17B are XRD patterns.
  • 18A to 18C are graphs showing lattice constants.
  • FIG. 19 is a diagram showing a configuration example of a positive electrode active material.
  • 20A to 20C are diagrams illustrating a method for manufacturing a positive electrode active material.
  • FIGS. 21A to 21C are diagrams illustrating a method for manufacturing a positive electrode active material.
  • FIG. 22 is a diagram illustrating a method for producing a positive electrode active material.
  • 23A to 23C are diagrams illustrating a method for producing a positive electrode active material.
  • FIG. 24 is a diagram illustrating a heating furnace and a heating method.
  • 25A to 25D are diagrams showing configuration examples of electronic equipment.
  • 26A to 26C are diagrams illustrating configuration examples of electronic equipment.
  • 27A to 27C are diagrams showing configuration examples of a vehicle.
  • 28A to 28C are configuration examples of a measuring device.
  • FIG. 29 shows the measurement results of volume resistivity according to the example.
  • FIG. 30 shows the measurement results of volume resistivity according to the example.
  • space groups are expressed using short notation in international notation (or Hermann-Mauguin symbol).
  • crystal planes and crystal directions are expressed using Miller indices.
  • Space groups, crystal planes, and crystal directions are expressed in terms of crystallography by adding a superscript bar to the number, but in this specification, etc., due to formatting constraints, instead of adding a bar above the number, they are written in front of the number. It is sometimes expressed by adding a - (minus sign) to it.
  • the individual orientation that indicates the direction within the crystal is [ ]
  • the collective orientation that indicates all equivalent directions is ⁇ >
  • the individual plane that indicates the crystal plane is ( )
  • the collective plane that has equivalent symmetry is ⁇ ⁇ .
  • the trigonal crystal represented by the space group R-3m is generally represented by a complex hexagonal lattice of hexagonal crystals for ease of understanding the structure, and unless otherwise mentioned in this specification, the space group R-3m is It is expressed as a complex hexagonal lattice.
  • the space group R-3m is It is expressed as a complex hexagonal lattice.
  • hkl but also (hkil) may be used as the Miller index.
  • i is -(h+k).
  • particles is not limited to only spherical shapes (circular cross-sectional shapes), but also includes particles whose cross-sectional shapes are elliptical, rectangular, trapezoidal, triangular, square with rounded corners, and asymmetrical. Examples include shape, and further, individual particles may be amorphous.
  • the theoretical capacity of the positive electrode active material refers to the amount of electricity when all the lithium that can be intercalated and desorbed from the positive electrode active material is desorbed.
  • the theoretical capacity of LiCoO 2 is 274 mAh/g
  • the theoretical capacity of LiNiO 2 is 274 mAh/g
  • the theoretical capacity of LiMn 2 O 4 is 148 mAh/g.
  • the amount of lithium that can be intercalated and desorbed remaining in the positive electrode active material is indicated by x in the composition formula, for example, x in Li x CoO 2 .
  • x (theoretical capacity ⁇ charge capacity)/theoretical capacity.
  • LiCoO 2 charge capacity
  • x 0.2 CoO 2
  • x in Li x CoO 2 is small, for example, 0.1 ⁇ x ⁇ 0.24.
  • the termination of the discharge refers to a state where the voltage is 3.0 V or 2.5 V or less at a current of, for example, 100 mA/g or less.
  • the charging capacity and/or discharging capacity used to calculate x in Li x CoO 2 is preferably measured under conditions where there is no or little influence of short circuits and/or decomposition of the electrolytic solution. For example, data from a lithium ion secondary battery that has undergone a sudden change in capacity that appears to be a short circuit should not be used to calculate x.
  • the space group of a lithium ion secondary battery is identified by XRD, electron beam diffraction, neutron beam diffraction, etc. Therefore, in this specification and the like, belonging to a certain space group, belonging to a certain space group, or being a certain space group can be rephrased as identifying with a certain space group.
  • the structure is called a cubic close-packed structure. Therefore, the anions do not need to form a strictly cubic lattice. Furthermore, since real crystals always have defects, analysis results do not necessarily match theory. For example, in an FFT (fast Fourier transform) pattern such as an electron diffraction pattern or a TEM image, a spot may appear at 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 that the structure has a cubic close-packed structure.
  • FFT fast Fourier transform
  • the distribution of an element refers to a region where the element is continuously detected at a level higher than background noise when analyzed using an analysis method that allows spatially continuous analysis.
  • a positive electrode active material to which additive elements are added may be expressed as a composite oxide, a positive electrode material, a positive electrode material, a positive electrode material for lithium ion secondary batteries, etc.
  • the positive electrode active material of one embodiment of the present invention preferably contains one or more of a compound, a composition, and a composite.
  • all particles do not necessarily have to have the characteristics. For example, if 50% or more, preferably 70% or more, more preferably 90% or more of three or more randomly selected positive electrode active material particles have the characteristic, it is sufficient to have the positive electrode active material and the same. It can be said that this has the effect of improving the characteristics of lithium ion secondary batteries.
  • internal short circuits and external short circuits of the lithium ion secondary battery not only cause problems in at least one of the charging operation and discharging operation of the lithium ion secondary battery, but also may cause heat generation and ignition. Therefore, in order to realize a safe lithium ion secondary battery, it is preferable that internal short circuits and external short circuits be suppressed even at high charging voltages.
  • internal short circuits are suppressed even at high charging voltage. Therefore, a lithium ion secondary battery that has both high discharge capacity and safety can be obtained.
  • an internal short circuit in a lithium ion secondary battery refers to contact between a positive electrode and a negative electrode inside the battery.
  • an external short circuit of a lithium ion secondary battery is assumed to occur due to misuse, and refers to contact between the positive electrode and the negative electrode outside the battery.
  • the materials included in the lithium ion secondary battery will be described in terms of their state before deterioration.
  • a decrease in discharge capacity due to aging treatment and burn-in treatment during the manufacturing stage of a lithium ion secondary battery is not called deterioration.
  • a lithium ion secondary battery consisting of a single cell or an assembled battery has a discharge capacity of 97% or more of the rated capacity, it can be said to be in a state before deterioration.
  • the rated capacity is based on JIS C 8711:2019 for lithium ion secondary batteries for portable devices. In the case of other lithium ion secondary batteries, they comply with not only the JIS standards mentioned above but also JIS and IEC standards for electric vehicle propulsion, industrial use, etc.
  • the state of the material of a lithium ion secondary battery before deterioration is referred to as the initial product or initial state, and the state after deterioration (discharge of less than 97% of the rated capacity of the lithium ion secondary battery)
  • the state in which the product has a capacity is sometimes referred to as a used product or in-use state, or a used product or used state.
  • a lithium ion secondary battery refers to a battery using lithium ions as carrier ions, but the carrier ions of the present invention are not limited to lithium ions.
  • an alkali metal ion or an alkaline earth metal ion can be used as a carrier ion in the present invention, and specifically, a sodium ion or the like can be used.
  • the present invention can be understood by reading lithium ions as sodium ions, etc.
  • the battery may be referred to as a secondary battery.
  • FIG. 1 shows a schematic diagram of a secondary battery 10 according to one embodiment of the present invention.
  • the secondary battery 10 has a wound body in which a laminate in which a positive electrode 11, a negative electrode 12, and two separators 13 are laminated is wound. That is, the secondary battery 10 is a wound type secondary battery.
  • the secondary battery 10 is housed in an exterior body (not shown), and is sealed after being injected with an electrolytic solution in which a salt containing carrier ions is dissolved.
  • Lithium ions can typically be used as carrier ions included in the electrolytic solution.
  • a secondary battery containing lithium ions is called a lithium ion secondary battery.
  • the exterior body is preferably film-shaped from the viewpoint of weight reduction, and a secondary battery having a film-like exterior body can be referred to as a laminate-type secondary battery. Further, from the viewpoint of excellent cooling function, a laminated film of polymer and metal having excellent thermal conductivity may be used for the exterior body. Specifically, it is preferable to use polypropylene as the polymer and aluminum as the metal, and furthermore, nylon or the like may be provided on the outside of the exterior body. Note that a metal can may be used as the exterior body, and when a circular can case is used, it is called a coin-shaped secondary battery.
  • the cathode 11 has a cathode current collector, and both surfaces of the cathode 11 are coated with a cathode composition containing a cathode active material.
  • the negative electrode 12 has a negative electrode current collector, and both sides of the negative electrode current collector are coated with a negative electrode composition containing a negative electrode active material.
  • the separator 13 is provided between the positive electrode 11 and the negative electrode 12, and has a function of preventing electrical short circuit between them.
  • the positive electrode 11 is preferably located outside the negative electrode 12. Further, one surface of the positive electrode 11 is preferably located at the outermost surface of the wound body. At this time, it is preferable that a part or all of the outermost surface of the wound body of the positive electrode 11 is not coated with the positive electrode composition.
  • aluminum foil can be used for the positive electrode current collector
  • copper foil can be used for the negative electrode current collector.
  • a laminate of aluminum foil and a resin film is used for the exterior body, there is a risk that a portion of the resin film may be damaged and the aluminum foil of the exterior body and the wound body may come into contact with each other.
  • different metals come into contact with each other, they may corrode, so it is preferable that the metal used for the exterior body and the metal located on the outermost surface of the wound body be the same metal (aluminum in this case).
  • the negative electrode 12 is wider than the positive electrode 11. Furthermore, it is preferable that the separator 13 is wider than the negative electrode 12 and the positive electrode 11. Thereby, since the positive electrode 11 is provided so as to be wrapped around the negative electrode 12 via the separator 13, internal short circuit between the positive electrode 11 and the negative electrode 12 can be prevented.
  • the positive electrode 11 has two or more tabs 21. Further, the negative electrode 12 has two or more tabs 22. Tab 21 is part of the positive electrode current collector, and tab 22 is part of the negative electrode current collector. Tab 21 and tab 22 contain different metals.
  • the plurality of tabs 21 are protrusions provided on the positive electrode current collector of the positive electrode 11, respectively.
  • a plurality of tabs 21 are provided on the positive electrode current collector so that the tabs 21 overlap each other when it becomes a wound body through a winding process.
  • the negative electrode current collector of the negative electrode 12 is provided with a plurality of tabs 22 so as to overlap each other when the tab is formed into a wound body through the winding process.
  • the plurality of tabs 21 are bundled and joined at their overlapping parts.
  • a region including a portion where a plurality of tabs 21 are bundled and joined is defined as a joint portion 31.
  • the plurality of tabs 22 are similarly bundled and joined at their overlapping parts, and this joined part is referred to as a joint part 32.
  • the bonding method for example, ultrasonic bonding can be used.
  • the bonding portions 31 and 32 have a plurality of bonding marks. This allows for excellent mechanical strength and low electrical resistance.
  • a lead may be connected to each of the plurality of tabs 21 and the plurality of tabs 22.
  • the lead connected to the positive electrode 11 may be joined to the plurality of tabs 21 at the same joint portion 31, or may be joined to the plurality of tabs 21 at a different position from the joint portion 31. The same applies to the lead connected to the negative electrode 12.
  • the positive electrode active material of the positive electrode 11 the positive electrode active material of one embodiment of the present invention is used, which has a high resistance region in a region closer to the surface than the center or in a surface layer including the surface. It is preferable.
  • a positive electrode active material even if the positive electrode 11 and the negative electrode 12 are short-circuited, the current flowing into the positive electrode active material can be reduced, and ignition or smoke generation can be suppressed, which is preferable. That is, a secondary battery according to one embodiment of the present invention having such a positive electrode active material can realize a secondary battery that is difficult to burn or does not burn even if an internal short circuit or an external short circuit occurs.
  • FIG. 2A is a schematic perspective view of the secondary battery 10a at a stage before the tabs are joined. Further, FIG. 2B is an enlarged view of a portion including the tabs 22 and 21 in FIG. 2A. Note that although the separator 13 is not clearly shown in FIGS. 2A and 2B so that the positions and shapes of the positive electrode 11 and the negative electrode 12 are easily understood, the separator 13 is actually provided between the positive electrode 11 and the negative electrode 12.
  • the positive electrode 11 has four tabs (tabs 21_1 to 21_4)
  • the negative electrode 12 also has four tabs (tabs 22_1 to 22_4). Note that the number of tabs is not limited to this, and each tab may be two or more.
  • the two ends (end 11a, end 11b) of the positive electrode 11 and the two ends (end 12a, end 12b) of the negative electrode 12 are shown by arrows.
  • the end portion 11a and the end portion 12a are each located on the center side of the winding, and the end portion 11b and the end portion 12b are each located on the outside of the winding.
  • the center of the winding can also be expressed as the center of the spiral, and here can be a region including the end portions 11a and 12a. Note that since the secondary battery illustrated here has a flat shape rather than a cylindrical shape, the cross section of the wound body does not have a simple spiral shape.
  • tabs are provided on the positive electrode 11 in the order of tab 21_1, tab 21_2, tab 21_3, and tab 21_4 from the end 11a to the end 11b.
  • the four tabs are arranged in the order of tab 21_1, tab 21_2, tab 21_3, and tab 21_4 from the side closest to the center of the winding.
  • tabs are provided on the negative electrode 12 in the order of tab 22_1, tab 22_2, tab 22_3, and tab 22_4 from the end 12a to the end 12b.
  • the four tabs are arranged in the order of tab 22_1, tab 22_2, tab 22_3, and tab 22_4 from the side closest to the center of the winding.
  • FIG. 3 shows an enlarged view of the secondary battery 10a after bonding.
  • the tabs 21_1 to 21_4 of the positive electrode 11 are joined at a joining portion 31.
  • the tabs 22_1 to 22_4 of the negative electrode 12 are joined at a joint portion 32.
  • the joint portion 31 includes a portion where all the tabs of the positive electrode 11 overlap
  • the joint portion 32 includes a portion where all the tabs of the negative electrode overlap.
  • a plurality of bonding marks 35 are provided in each of the bonding portion 31 and the bonding portion 32.
  • tab 21_2 is located between tabs 21_1 and 21_3, and tab 21_3 is located between tabs 21_2 and 21_4.
  • tab 22_2 is located between tabs 22_1 and 22_3, and tab 22_3 is located between tabs 22_2 and 22_4.
  • the configuration shown in FIG. 3 is an example in which one tab is arranged for each circumference of both the positive electrode 11 and the negative electrode 12. Therefore, since the tab is provided only on one side with the center of the wound body as a reference, the thickness of the joint portion 31 and the joint portion 32 can be reduced.
  • the secondary battery 10b shown in FIG. 4 shows an example in which one tab is arranged on each of the positive electrode 11 and the negative electrode 12 every half circumference.
  • the positive electrode 11 has seven tabs (tabs 21_1 to 21_7), and the negative electrode 12 also has seven tabs (tabs 22_1 to 22_7).
  • Seven tabs are provided on the positive electrode 11 from the end 11a to the end 11b in the order of tabs 21_1 to 21_7 along the winding direction. Further, the tab 21_1 is located between the tab 21_2 and the tab 21_3. Further, the seven tabs are stacked in the order of tab 21_4, tab 21_2, tab 21_1, tab 21_3, tab 21_5, and tab 21_7 from tab 21_6 to tab 21_7. That is, there is a portion where even-numbered tabs are stacked and a portion where odd-numbered tabs are stacked, centering on the tab 21_1.
  • the negative electrode 12 is also provided in the order of tabs 22_1 to 22_7 along the winding direction from the end 12a toward the end 12b. Further, the tab 22_1 is located between the tab 22_2 and the tab 22_3. Further, the seven tabs are stacked in the order of tab 22_4, tab 22_2, tab 22_1, tab 22_3, tab 22_5, and tab 22_7 from tab 22_6 to tab 22_7.
  • the intervals between the tabs are narrower than in the secondary battery 10a, so in addition to being able to more effectively reduce internal resistance, it is also possible to more effectively suppress heat generation. .
  • the secondary battery 10c shown in FIG. 5 is mainly different from the secondary battery 10a illustrated in FIG. 3 in that the positions of the plurality of tabs included in the negative electrode 12 are different.
  • the tabs 22_2 to 22_4 of the negative electrode 12 are provided on the opposite side of the wound body from the tabs of the positive electrode 11 across the center of the wound body. With this configuration, the physical distance between the tab of the positive electrode 11 and the tab of the negative electrode 12 can be increased, and it is possible to effectively suppress the occurrence of an external short circuit due to contact between them. can.
  • FIG. 6 shows how the stacked body of the positive electrode 11 and the negative electrode 12 changes from the state before winding to the state after winding.
  • FIG. 6 shows six states arranged in chronological order from the upper left to the lower right.
  • the laminate has two separators to insulate the positive electrode 11 and the negative electrode 12.
  • the laminate before winding may have a structure in which the first separator, the positive electrode 11, the second separator, and the negative electrode 12 are laminated in this order, and the positive electrode 11 is sandwiched between the two separators.
  • one separator long in the longitudinal direction of the laminate is folded in half, and the positive electrode is 11 may be sandwiched therebetween.
  • the positive electrode 11, the first separator, the negative electrode 12, and the second separator may be laminated in this order, and the negative electrode 12 may be sandwiched between the two separators. Further, at this time, the negative electrode 12 may be sandwiched between long separators as described above so that the crease is located on the end 12a side of the negative electrode.
  • the positive electrode 11 has five tabs (tabs 21_1 to 21_5) from the end 11a to the end 11b.
  • the negative electrode 12 has five tabs (tabs 22_1 to 22_5) from the end 12a to the end 12b.
  • the 10 tabs that the laminate has are, from the end 11a (end 12a) side, tab 22_1, tab 21_1, tab 21_2, tab 22_2, tab 22_3, tab 21_3, tab 21_4, tab 22_4, tab 22_5, tab 21_5. They are arranged in this order.
  • the distance between two adjacent tabs is arranged such that the closer it is to the center of the winding, the shorter it is, and the closer it is to the outside of the winding, the wider it is.
  • X1 and 21_2 are X1
  • X3 and 21_4 are X2
  • Y2 is larger than Y1.
  • FIG. 7A shows an example of a cross-sectional view of the positive electrode 11 used in the secondary battery 10 and the like.
  • the positive electrode 11 has a positive electrode active material layer 502 on a positive electrode current collector 501 .
  • the positive electrode active material layer 502 includes a positive electrode active material 561 , a positive electrode active material 562 , a conductive material 553 , a conductive material 554 , and an electrolyte 530 .
  • the positive electrode active material layer 502 also has a binder (not shown).
  • the secondary battery may have a configuration including either one of the conductive material 553 and the conductive material 554.
  • positive electrode active materials with different median diameters (D50).
  • D50 median diameters
  • the median diameter (D50) of the positive electrode active material 561 is 1 ⁇ m or more and 50 ⁇ m or less, preferably 5 ⁇ m or more and 30 ⁇ m or less.
  • the median diameter (D50) of the positive electrode active material 562 is preferably 1/6 or more and 1/10 or less of the median diameter (D50) of the positive electrode active material 561.
  • both the positive electrode active material 561 and the positive electrode active material 562 have a shell.
  • a positive electrode active material having a shell can have high insulation properties and is less likely to cause thermal runaway.
  • the boundary between the surface layer and the interior is marked with a dotted line, but the boundary is not necessarily as clear as in FIG. 7A.
  • the positive electrode active material is not limited to that shown in FIG. 7A, and for example, either one of the positive electrode active material 561 and the positive electrode active material 562 may have a shell.
  • the active material of the positive electrode active material 561 may be the same as or different from the active material of the positive electrode active material 562.
  • Identical active materials include active materials whose main raw materials are the same, and may differ in the presence or absence of additive elements.
  • Different active material materials include those in which the main raw materials of the active materials are different.
  • the positive electrode active material 561 and the positive electrode active material 562 preferably have an additive element, and in particular, the additive element is preferably included in the shell.
  • the additive element that the shell has may be unevenly distributed or may be thinly distributed inside. Uneven distribution refers to the fact that the additive element is present non-uniformly or unevenly. Therefore, a state in which the concentration of the additive element is higher toward the shell than the inside is sometimes referred to as the additive element being unevenly distributed in the shell. Uneven distribution may also be described as segregation or precipitation.
  • the positive electrode active material 561 and the positive electrode active material 562 are called positive electrode active material particles.
  • the shape of the positive electrode active material can take various shapes other than particulate.
  • FIG. 7A shows an example in which the positive electrode active material is spherical and its cross section is circular.
  • FIG. 7B shows an example in which the cross section is not circular.
  • the positive electrode active material 561 and the positive electrode active material 562 shown in FIGS. 7A and 7B are primary particles, they may be secondary particles.
  • primary particles refer to the smallest unit particles (agglomerates) that do not have grain boundaries when observed at a magnification of, for example, 5000 times using an SEM (scanning electron microscope) or the like. In other words, primary particles are the smallest unit particles.
  • secondary particles refers to particles (independent particles) in which the above-mentioned primary particles aggregate so as to share a part of the above-mentioned grain boundaries (such as the outer periphery of the primary particles). That is, the secondary particles have grain boundaries.
  • the surface layer portion of the secondary particle may be the surface layer portion of the entire secondary particle. Further, the surface layer portion of the secondary particles may be the surface layer portion of the primary particles constituting the secondary particles.
  • positive electrode active material and other positive electrode active materials may be used in combination.
  • Examples of other positive electrode active materials include oxides having an olivine crystal structure, a layered rock salt crystal structure, or a spinel crystal structure. Examples include compounds such as LiFePO 4 , LiFeO 2 , LiNiO 2 , LiMn 2 O 4 , V 2 O 5 , Cr 2 O 5 and MnO 2 .
  • a lithium manganese composite oxide that can be represented by the composition formula Li a Mn b M c O d can be used.
  • the element M is preferably a metal element selected from lithium or manganese, silicon, or phosphorus, and more preferably nickel.
  • the composition of metal, silicon, phosphorus, etc. of the entire particle of the lithium manganese composite oxide can be measured using, for example, ICP-MS (inductively coupled plasma mass spectrometer).
  • the oxygen composition of the entire particle of the lithium manganese composite oxide can be measured using, for example, EDX (energy dispersive X-ray analysis). Further, it can be determined by using valence evaluation of melted gas analysis and XAFS (X-ray absorption fine structure) analysis in combination with ICP-MS analysis.
  • the lithium-manganese composite oxide refers to an oxide containing at least lithium and manganese, including chromium, cobalt, aluminum, nickel, iron, magnesium, molybdenum, zinc, indium, gallium, copper, titanium, niobium, silicon, and phosphorus, and the like.
  • the conductive material functions to assist the current path between the active material and the current collector, or between a plurality of active materials. In order to perform such a function, the conductive material preferably has a lower resistance than the active material.
  • the conductive material is also called a conductive aid or a conductive imparting agent due to its role.
  • a carbon material or a metal material is typically used as the conductive material.
  • granular conductive materials include carbon black (furnace black, acetylene black, graphite, etc.). Carbon black often has a smaller particle size than the positive electrode active material.
  • the conductive material may be fibrous.
  • carbon nanotubes (CNT) and VGCF (registered trademark) are examples of fibrous conductive materials.
  • the conductive material may be in the form of a sheet, such as multilayer graphene. The sheet-like conductive additive may appear thread-like in the cross section of the positive electrode.
  • the granular conductive material can get into the gaps of the positive electrode active material, etc., and is likely to aggregate. Therefore, the granular conductive material can assist in forming a conductive path between the cathode active materials disposed nearby.
  • the fibrous conductive material also has a bent region, but it is larger than the positive electrode active material. Therefore, the fibrous conductive material can assist the conductive path not only between adjacent positive electrode active materials but also between distant positive electrode active materials. In this way, it is preferable to mix two or more shapes of conductive materials.
  • the positive electrode active material layer 502 includes sheet-like graphene or a graphene compound as the conductive material 554.
  • the conductive material 553 carbon black can be used, for example.
  • the conductive material 554 is schematically represented by a thick line in FIGS. 7A and 7B, it is actually an extremely thin film having a thickness of a single layer or multiple layers of carbon molecules.
  • the plurality of graphenes or graphene compounds are formed so as to partially cover the plurality of positive electrode active materials or to adhere to the surfaces of the plurality of positive electrode active materials. Thereby, a conductive path can be efficiently formed even with a small amount, so that internal resistance can be reduced.
  • the binder functions as a binding agent that ensures the adhesion of the powdered active material without covering the surface of the active material. Considering the expansion of the active material, the binder should preferably exhibit sufficient flexibility and be able to respond to changes in the state of the active material. The binder also needs to exhibit compatibility with the electrolyte. Furthermore, since extremely strong oxidation and reduction reactions occur in secondary batteries, a binder that does not deteriorate or has low reactivity with respect to these reactions is desired.
  • the binder it is preferable to use rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene-propylene-diene copolymer.
  • SBR styrene-butadiene rubber
  • fluororubber can be used as the binder.
  • the binder it is preferable to use, for example, a water-soluble polymer.
  • a water-soluble polymer for example, polysaccharides can be used.
  • the polysaccharide one or more of cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, regenerated cellulose, starch, etc. can be used. Further, it is more preferable to use these water-soluble polymers in combination with the above-mentioned rubber material.
  • CMC carboxymethyl cellulose
  • ethyl cellulose methyl cellulose
  • hydroxypropyl cellulose diacetyl cellulose
  • regenerated cellulose starch, etc.
  • polystyrene polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride
  • PVA polyvinyl alcohol
  • PEO polyethylene oxide
  • PEO polypropylene oxide
  • polyimide polyvinyl chloride
  • materials such as polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, nitrocellulose, etc.
  • the positive electrode current collector As the positive electrode current collector, highly conductive materials such as metals such as stainless steel, gold, platinum, copper, aluminum, and titanium, and alloys thereof can be used. Further, it is preferable that the material used for the positive electrode current collector does not elute at the potential of the positive electrode. Furthermore, an aluminum alloy to which an element that improves heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum is added, can be used.
  • the current collector may have a foil shape, a plate shape, a sheet shape, a net shape, a punched metal shape, an expanded metal shape, or the like as appropriate.
  • the current collector preferably has a thickness of 5 ⁇ m or more and 30 ⁇ m or less.
  • the negative electrode has a negative electrode active material layer and a negative electrode current collector. Further, the negative electrode active material layer may include a conductive material and a binder. As the negative electrode active material, for example, alloy-based materials, carbon-based materials, etc. can be used.
  • an element capable of performing a charge/discharge reaction through an alloying/dealloying reaction with lithium can be used.
  • a material containing one or more 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. Further, compounds having these elements may also be used.
  • an element that can perform a charge/discharge reaction by alloying/dealloying reaction with lithium, a compound having the element, etc. may be referred to as an alloy-based material.
  • graphite graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, carbon black, etc. may be used.
  • titanium dioxide TiO 2
  • lithium titanium oxide Li 4 Ti 5 O 12
  • lithium graphite intercalation compound Li x C 6
  • niobium pentoxide Nb 2 O 5
  • tungsten oxide tungsten oxide
  • WO 2 molybdenum oxide
  • MoO 2 molybdenum oxide
  • Li 2.6 Co 0.4 N 3 is preferable because it has a large charge/discharge capacity (900 mAh/g, 1890 mAh/cm 3 ).
  • the negative electrode active material contains lithium ions, it can be combined with materials such as V 2 O 5 and Cr 3 O 8 that do not contain lithium ions as the positive electrode active material, which is preferable. Note that even when a material containing lithium ions is used as the positive electrode active material, a nitride of lithium and a transition metal can be used as the negative electrode active material by removing the lithium ions contained in the positive electrode active material in advance.
  • a material that causes a conversion reaction can also be used as the negative electrode active material.
  • transition metal oxides that do not form an alloy with lithium such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO)
  • Materials that cause conversion reactions include oxides such as Fe 2 O 3 , CuO, Cu 2 O, RuO 2 , and Cr 2 O 3 , sulfides such as CoS 0.89 , NiS, and CuS, and Zn 3 N 2 , nitrides such as Cu 3 N and Ge 3 N 4 , phosphides such as NiP 2 , FeP 2 and CoP 3 , and fluorine compounds such as FeF 3 and BiF 3 .
  • the same materials as the conductive material and binder that the positive electrode active material layer can have can be used.
  • ⁇ Negative electrode current collector ⁇ The same material as the positive electrode current collector can be used for the negative electrode current collector. Note that it is preferable to use a material that does not form an alloy with carrier ions such as lithium for the negative electrode current collector.
  • the electrolyte includes a solvent and a lithium salt.
  • aprotic organic solvents are preferred, such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, ⁇ -butyrolactone, ⁇ -valerolactone, and dimethyl carbonate.
  • DMC diethyl carbonate
  • DEC diethyl carbonate
  • EMC ethyl methyl carbonate
  • methyl formate methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4 -
  • DME dimethoxyethane
  • DME dimethyl sulfoxide
  • diethyl ether methyl diglyme
  • acetonitrile benzonitrile
  • tetrahydrofuran sulfolane
  • sultone etc., or any combination and ratio of two or more of these. It can be used in
  • a mixed organic solvent containing a fluorinated cyclic carbonate (sometimes referred to as fluorinated cyclic carbonate) or a fluorinated chain carbonate (sometimes referred to as fluorinated chain carbonate) can be used.
  • fluorinated cyclic carbonate sometimes referred to as fluorinated cyclic carbonate
  • fluorinated chain carbonate sometimes referred to as fluorinated chain carbonate
  • fluorinated cyclic carbonate fluoroethylene carbonate (fluoroethylene carbonate, FEC, F1EC), difluoroethylene carbonate (DFEC, F2EC), trifluoroethylene carbonate (F3EC), or tetrafluoroethylene carbonate (F4EC) can be used.
  • FEC fluoroethylene carbonate
  • F1EC fluoroethylene carbonate
  • DFEC difluoroethylene carbonate
  • F3EC trifluoroethylene carbonate
  • F4EC tetrafluoroethylene carbonate
  • F4EC tetrafluoroethylene carbonate
  • Ionic liquids are composed of cations and anions, and include organic cations and anions.
  • Examples of the organic cation used in the electrolytic solution 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 electrolytic solution include monovalent amide anions, monovalent methide anions, fluorosulfonic acid anions, perfluoroalkylsulfonic acid anions, tetrafluoroborate anions, perfluoroalkylborate anions, and hexafluorophosphate anions. , or perfluoroalkyl phosphate anion.
  • lithium salt also called electrolyte
  • examples of the lithium salt (also called electrolyte) to be dissolved in the above solvent include LiPF 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiAlCl 4 , LiSCN, LiBr, LiI, Li 2 SO 4 , Li 2 B 10 Cl 10 , Li 2B12Cl12 , LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3 , LiC ( C2F5SO2 ) 3 , LiN ( CF3SO2 ) 2 , LiN ( C One type of lithium salt such as 4F9SO2 ) ( CF3SO2 ), LiN( C2F5SO2 ) 2 , or two or more of these may be used in any combination and ratio.
  • the amount of the lithium salt relative to the solvent is preferably 0.5 mol/L or more and 3.0 mol/L or less.
  • Use of fluorides such as LiPF 6 and LiBF 4 improves the
  • a solid electrolyte having an inorganic material such as a sulfide-based or oxide-based material, a solid electrolyte having a polymeric material such as a PEO (polyethylene oxide)-based material, etc. can be used.
  • a solid electrolyte it is not necessary to install a separator and/or spacer. Additionally, since the entire battery can be solidified, there is no risk of leakage, dramatically improving safety.
  • ⁇ Separator ⁇ for example, one made of paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyolefin, polyurethane, etc. can be used. Can be done.
  • the separator may have a multilayer structure.
  • a film of an organic material such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture thereof.
  • the ceramic material for example, aluminum oxide particles, silicon oxide particles, etc. can be used.
  • the fluorine-based material for example, PVDF, polytetrafluoroethylene, etc. can be used.
  • the polyamide material for example, nylon, aramid (meta-aramid, para-aramid), etc. can be used.
  • a metal material such as aluminum and a resin material
  • a film-like exterior body can also be used.
  • a film for example, a highly flexible metal thin film such as aluminum, stainless steel, copper, or nickel is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an exterior coating is further applied on the metal thin film.
  • a three-layered film having an insulating synthetic resin film such as polyamide resin or polyester resin can be used as the outer surface of the body.
  • FIG. 8A is a graph of the temperature of the secondary battery versus time. For example, when the temperature of the secondary battery reaches or near 100° C., (1) SEI (Solid Electrolyte Interphase) of the negative electrode collapses and heat is generated.
  • SEI Solid Electrolyte Interphase
  • the temperature of the secondary battery exceeds 100°C
  • (2) the electrolyte is reduced and heat generated by the negative electrode if graphite is used, the negative electrode becomes C 6 Li
  • the temperature of the secondary battery reaches 180°C or around 180°C
  • (4) thermal decomposition of the electrolyte occurs, and (5) oxygen is released from the positive electrode and thermal decomposition occurs (the thermal decomposition involves a structural change in the positive electrode active material). ) occurs.
  • the temperature of the secondary battery exceeds 200° C.
  • the secondary battery 500 is fully charged (States of Charge: equivalent to 100% SOC), and a nail 1003 having a predetermined diameter selected from 2 mm to 10 mm is inserted into the secondary battery at a predetermined speed.
  • the speed at which the nail is inserted can be, for example, 1 mm/s or more and 20 mm/s or less.
  • FIG. 9A shows a cross-sectional view of the secondary battery 500 with a nail 1003 inserted therein.
  • the secondary battery 500 has a structure in which a positive electrode 503, a separator 508, a negative electrode 506, and an electrolyte 530 are housed in an exterior body 531.
  • the positive electrode 503 has a positive electrode current collector 501 and positive electrode active material layers 502 formed on both surfaces thereof
  • the negative electrode 506 has a negative electrode current collector 504 and negative electrode active material layers 505 formed on both surfaces thereof.
  • FIG. 9B shows an enlarged view of the nail 1003 and the positive electrode current collector 501, and also clearly shows the positive electrode active material 561 and the conductive material 553 included in the positive electrode active material layer 502.
  • the temperature of the secondary battery 500 may rise due to Joule heat.
  • a change in the crystal structure of the lithium cobalt oxide may occur, and further heat generation may occur.
  • the electrons (e - ) flowing to the positive electrode 503 reduce the tetravalent Co in the charged lithium cobalt oxide to become trivalent or divalent, and this reduction reaction releases oxygen from the lithium cobalt oxide. be done.
  • the electrolytic solution 530 is decomposed by an oxidation reaction caused by the oxygen. This is one of the electrochemical reactions and is called the oxidation reaction of the electrolyte by the positive electrode.
  • the speed at which current flows into the positive electrode active material 561 and the like varies depending on the insulation properties of the positive electrode active material, and it is also considered that the speed at which the current flows affects the electrochemical reaction.
  • FIG. 8B is a partially revised diagram based on the graph shown on page 70 [FIG. 2-12] of Non-Patent Document 6, and shows the temperature (specifically, internal temperature) of the secondary battery versus time. It is a graph.
  • P0 the temperature of the secondary battery increases over time.
  • P1 if heat generation due to Joule heat continues until the temperature of the secondary battery reaches around 100°C, it will exceed the standard temperature (Ts) of the secondary battery, which is the limit temperature that does not lead to thermal runaway. I end up.
  • the temperature rise of the secondary battery must be suppressed, and the components that make up the secondary battery (negative electrode, positive electrode, electrolyte, etc.) must be stable at high temperatures. is considered important.
  • the positive electrode active material has a stable structure that does not release oxygen even when exposed to high temperatures.
  • the positive electrode active material preferably has a structure in which the speed of current flowing into the active material is slow.
  • the positive electrode active material 100 which is one embodiment of the present invention, can have both the stable structure described above and a structure that slows down the current speed.
  • the positive electrode active material 100 which is one embodiment of the present invention, will be described.
  • a compound containing a transition metal and oxygen that can insert and extract carrier ions typically lithium ions (Li + )
  • the transition metal one or more selected from cobalt (Co), nickel (Ni), manganese (Mn), iron (Fe), etc.
  • Co cobalt
  • Ni nickel
  • Mn manganese
  • Fe iron
  • the positive electrode active material 100 illustrated below can be used for the positive electrode of the above-mentioned secondary battery.
  • the positive electrode active material 100 preferably has an insulating region or a high resistance region. It can be said that the positive electrode active material 100 including the region has a structure in which rapid current does not easily flow. Note that this area may be referred to as a first area in order to distinguish it from other areas.
  • the above region preferably exists in a narrow width such as 1 nm or more and 20 nm or less, preferably 2 nm or more and 10 nm or less, and more preferably 2 nm or more and 5 nm or less in cross-sectional view, and the above numerical value is the thickness or width of the first region in cross-sectional view. I can say that.
  • the narrow region is sometimes referred to as a "shell" in this specification and the like.
  • a cross-sectional STEM image can be used as the cross-sectional view.
  • the shell is preferably included in the surface layer of the positive electrode active material 100.
  • the positive electrode active material 100 having such a shell is preferable because even when a nail penetration test is performed, the current flowing into the positive electrode active material can be reduced, and ignition, smoking, etc. can be suppressed.
  • the shell is located outside or on the surface side of the surface layer portion of the positive electrode active material 100.
  • the shell preferably has an additive element added to the positive electrode active material 100.
  • Additive elements include magnesium, fluorine, nickel, and aluminum, and in addition to these, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, bromine, and beryllium. can be mentioned.
  • Magnesium is one of the elements suitable for the shell, and fluorine is considered to be one of the elements preferable for adding magnesium to the positive electrode active material 100.
  • it is also suitable to include the additive element in the surface layer portion. Specifically, the crystal structure of the positive electrode active material 100 can be stabilized.
  • the structure of the shell will be explained using magnesium. It is preferable that magnesium exists in a narrow width of 1 nm or more and 20 nm or less, preferably 2 nm or more and 10 nm or less, and more preferably 2 nm or more and 5 nm or less in a cross-sectional view of the surface layer of the positive electrode active material 100, and the narrow region is used as a shell. call.
  • the shell may also contain cobalt, and the shell makes it possible to insert and extract lithium ions (Li + ) while slowing down the current flow rate due to internal short circuits.
  • the surface layer of the positive electrode active material 100 has a first region and a second region, and at least the first region may contain magnesium, and the second region may not contain magnesium.
  • the first region is preferably located on the outer side or surface side of the positive electrode active material 100 than the second region. Furthermore, it is considered that the presence of cobalt in the first region and the second region makes it possible to insert and extract lithium ions (Li + ).
  • the shell described above may be provided so as to sufficiently cover the entire positive electrode active material 100, or may be provided so that a specific region of the positive electrode active material 100 is thicker. For example, it can be provided thickly along a plane other than the (00l) plane of layered rock salt type lithium cobalt oxide.
  • the shell may be positioned in any position with respect to the positive electrode active material 100, and the shell can be positioned in any position relative to the positive electrode active material 100, allowing insertion and extraction of lithium ions (Li + ) while reducing the current flow rate due to internal short circuit.
  • Li + lithium ions
  • Magnesium may be present throughout the surface layer as long as it can be made moderate.
  • lithium cobalt oxide having one or more selected from the above-mentioned additive elements for the positive electrode active material 100.
  • the additive element has a function of further stabilizing the positive electrode active material 100, oxygen release from lithium cobalt oxide can be suppressed and thermal stability can be improved.
  • the crystal structure becomes stable, oxygen release is suppressed, and thermal stability becomes high.
  • insulation can be increased and thermal runaway is less likely to occur.
  • F may be included as an additive element, which suppresses oxygen release from surfaces other than the (00l) plane, improves thermal stability, and provides a structure that is unlikely to cause thermal runaway.
  • the additive element Mg may be added to the surface layer of lithium cobalt oxide in an amount of 0.5 at% to 30 at%, preferably 1.5 at% to 10 at%.
  • the above Mg concentration can be determined by EDX line analysis or the like. If Mg is present in the entire surface layer at a high concentration, the insulation properties will be high, making it difficult to obtain favorable battery characteristics in charge/discharge cycle tests and the like.
  • the presence of Mg in an appropriate area like a shell in the surface layer and at an appropriate concentration can stabilize lithium cobalt oxide, suppressing heat generation and smoke generation in the nail penetration test etc. mentioned above. This is preferable because it can be done.
  • the presence of Mg in the surface layer at an appropriate concentration is expected to increase the hardness of lithium cobalt oxide.
  • Mg and the like exist in a high concentration in the surface layer. If Mg is present in a higher concentration inside than in the surface layer, the discharge capacity may decrease. Therefore, for example, Mg is preferably present at least in the surface layer portion or in the shell. That is, Mg is preferably located on the surface side compared to other additive elements.
  • FIG. 10A is a cross-sectional view of a positive electrode active material 100 that is one embodiment of the present invention.
  • the positive electrode active material 100 which is one embodiment of the present invention, preferably has a shell 100s.
  • the shell 100s is preferably narrow in width. Further, it is more preferable that the width of the shell 100s is thicker on a surface where lithium can be inserted and extracted, that is, on a surface other than the (00l) surface than on the (00l) surface. In other words, by providing the shell 100s on a surface other than the (00l) surface, desorption of oxygen from the surface other than the (00l) surface may be suppressed.
  • the (001) plane, the (003) plane, etc. are sometimes collectively referred to as the (00l) plane.
  • the (00l) plane may be referred to as a C-plane, a basal plane, or the like.
  • lithium cobalt oxide lithium has a two-dimensional diffusion path. In other words, it can be said that the diffusion path of lithium exists along the basal plane.
  • a surface where a lithium diffusion path is exposed that is, a surface where lithium is intercalated and deintercalated, specifically, a surface other than the (001) plane may be referred to as an edge surface.
  • the positive electrode active material 100 which is an embodiment of the present invention, further contains Ni as an additive element, a region having Mg and a region having Mg on a surface where lithium can be inserted and extracted, that is, a surface other than (001), It is preferable that the area having the area overlap, connect, or connect with each other. In other words, it is preferable that Ni is also present in the shell. With this configuration, desorption of oxygen from the positive electrode active material or structural change of the positive electrode active material can be suppressed.
  • FIGS. 10B to 10D are conceptual diagrams in which a region B with squares in FIG. 10A is enlarged.
  • the positive electrode active material 100 lithium cobalt oxide containing Mg is illustrated.
  • Mg which is one of the additive elements, is preferably bonded to oxygen in the shell.
  • the shell preferably contains Co, and the Co is preferably bonded to oxygen. According to the shell shown in FIG. 10B, it is considered that it is possible to suppress the sudden flow of current due to an internal short circuit while making it possible to insert and extract lithium ions (Li + ).
  • the positive electrode active material 100 lithium cobalt oxide containing Mg and F is illustrated.
  • F which is one of the additive elements, does not need to be present in the shell and may be adsorbed on the surface of the positive electrode active material 100.
  • Fluorine is highly electronegative and is known to easily form stable compounds with many elements.
  • the positive electrode active material 100 is impregnated with an electrolytic solution, and since fluorine is adsorbed on the surface of the positive electrode active material, it can react with the electrolytic solution near fluorine, and the internal Even if a short circuit occurs, thermal decomposition of the electrolytic solution, etc. can be suppressed.
  • lithium cobalt oxide containing Mg and F may have a fluorine compound 100f adsorbed on the surface of the positive electrode active material 100, as shown in FIG. 10D.
  • Fluorine is highly electronegative and is known to easily form stable compounds with many elements.
  • the positive electrode active material 100 is impregnated with an electrolytic solution, and since the fluorine compound 100f is adsorbed on the surface of the positive electrode active material, it can react with the electrolyte near the fluorine compound 100f, causing an internal short circuit. Even if this occurs, thermal decomposition of the electrolytic solution, etc. can be suppressed.
  • the adsorption mentioned above includes chemical adsorption or physical adsorption.
  • Chemical adsorption is the formation of a chemical bond by a chemical reaction between at least one of the additive elements and the surface of the positive electrode active material 100
  • physical adsorption is the formation of a chemical bond between at least one of the additive elements and the surface of the positive electrode active material 100. This means that they are adsorbed by intermolecular forces (van der Waals forces) that act on them.
  • the positive electrode active material 100 may contain fluorine in solid solution, for example, fluorine may substitute for a portion of the oxygen in lithium cobalt oxide.
  • fluorine may substitute for a portion of the oxygen in lithium cobalt oxide.
  • the solid-dissolved fluorine only needs to be present in the surface layer of the lithium cobalt oxide, and may be present in the shell. If there is sufficient fluorine in the positive electrode active material 100, both fluorine adsorbed on the surface and fluorine partially substituted for oxygen exist.
  • FIGS. 10E and 10F are examples of positive electrode active materials in which the boundary between the surface layer 100a and the bulk 100b is indicated by a broken line.
  • the surface layer portion is distinguished from the interior, and the surface layer portion includes the surface.
  • the surface layer portion of the positive electrode active material 100 refers to a region within 20 nm or a region within 50 nm perpendicularly or substantially perpendicularly from the surface toward the inside from the surface.
  • the surface layer portion has the same meaning as near-surface and near-surface region.
  • vertical or substantially vertical specifically refers to a range of 80° or more and 100° or less from the surface.
  • a region deeper than the surface layer of the positive electrode active material is called the inside. Internal is synonymous with bulk or core.
  • a grain boundary 101 is further added as indicated by a dashed line.
  • a crystal with a layered crystal structure such as a layered rock salt type, has a characteristic that cleavage tends to occur along a plane parallel to the layers (basal plane in this case). Therefore, the grain boundaries 101 are likely to be formed parallel to the basal plane.
  • FIG. 10F shows a crack formed and an embedded portion 102 formed to fill the crack. In a portion of the positive electrode active material 100 where a crack is formed, a cleavage plane (that is, a plane parallel to the basal plane) is likely to be exposed.
  • the positive electrode active material 100 may have magnesium in the entire surface layer.
  • more magnesium may be present in the surface layer than in the inside of the lithium cobalt oxide.
  • Lithium cobalt oxide containing magnesium has the characteristic that its crystal structure does not easily collapse when charged at high voltage.
  • the positive electrode active material 100 may include nickel. Nickel may be present inside lithium cobalt oxide. If fluorine and magnesium exist inside lithium cobalt oxide, the discharge capacity of the positive electrode active material may decrease, but even if nickel exists inside lithium cobalt oxide, the discharge capacity is unlikely to decrease. Therefore, lithium cobalt oxide having nickel inside can exhibit the effect that the crystal structure is less likely to collapse when charged at a high voltage without lowering the discharge capacity.
  • lithium cobalt oxide containing an additive element such as fluorine is applied to the positive electrode of a lithium ion secondary battery, heat generation is suppressed even when an internal short circuit occurs, so thermal runaway is less likely to occur.
  • Lithium cobalt oxide is composed of a lithium layer (sometimes referred to as a lithium site) and an octahedron of oxygen atoms.
  • the octahedron of oxygen atoms can be said to be an octahedral structure in which six oxygen atoms are coordinated with cobalt, and is sometimes referred to as a CoO 2 layer.
  • the lithium layer of lithium cobalt oxide forms a plane, and lithium ions can move along the plane as the battery is charged and discharged. (001) in the figure indicates the (001) plane of lithium cobalt oxide.
  • LiCoO 2 belongs to space group R-3m.
  • fluorides used in lithium ion secondary batteries include LiPF 6 and LiBF 4 as lithium salts, and polyvinylidene fluoride (PVDF) as binders, which will be described later. Fluorine from such fluorides may be adsorbed onto the surface of the positive electrode active material 100.
  • the surface of the positive electrode active material 100 refers to the surface of the composite oxide including the surface layer portion 100a and the bulk 100b. Such a surface can be confirmed in a cross-sectional view. Therefore, the surface of the positive electrode active material 100 may be made of metal oxides such as aluminum oxide (Al 2 O 3 ) that do not have lithium sites that can contribute to charging and discharging, or carbonic acid chemically adsorbed after the production of the positive electrode active material. Does not contain salts, hydroxy groups, etc. Note that the deposited metal oxide refers to, for example, a metal oxide whose crystal orientation does not match that of the bulk 100b.
  • the positive electrode active material 100 is a compound containing a transition metal and oxygen that can intercalate and deintercalate lithium, the transition metal M (for example, Co, Ni, Mn, Fe, etc.) and oxygen that are redoxed as lithium intercalates and deintercalates.
  • the interface between the region where is present and the region where is not is defined as the surface of the positive electrode active material.
  • a protective film is sometimes attached to the surface, but the protective film is not included in the positive electrode active material.
  • the protective film a single layer film or a multilayer film of carbon, metal, oxide, resin, etc. may be used.
  • the surface of the positive electrode active material in STEM-EDX-ray analysis, etc. is the point at which the transition metal M is 50% of the sum of the average value MAVE of the detected amount inside and the average value MBG of the background; and oxygen becomes 50% of the sum of the average value O AVE of the internal detection amount and the average value O BG of the background.
  • the transition metal M and oxygen differ in the 50% point of the sum of the interior and background, this is considered to be due to the influence of oxygen-containing metal oxides, carbonates, etc. attached to the surface.
  • a point that is 50% of the sum of the average value M AVE of the detected amount inside M and the average value M BG of the background can be adopted.
  • the surface can be determined using M AVE and M BG of the elements having the largest number of counts in the bulk 100b.
  • the average value MBG of the background of the transition metal M can be determined by averaging the outer range of 2 nm or more, preferably 3 nm or more, avoiding the vicinity where the detected amount of the transition metal M starts to increase, for example.
  • the average value M AVE of the detected amounts inside is determined at a depth of 30 nm or more, preferably more than 50 nm, from a region where the counts of transition metal M and oxygen are saturated and stable, for example, a region where the detected amount of transition metal M starts to increase. 2 nm or more, preferably 3 nm or more can be determined on average.
  • the average background value OBG of oxygen and the average value OAVE of the internal detected amount of oxygen can also be determined in the same manner.
  • the surface of the positive electrode active material 100 in a cross-sectional STEM (scanning transmission electron microscope) image, etc. is the boundary between a region where an image derived from the crystal structure of the positive electrode active material is observed and a region where it is not observed. This is the outermost region in which an atomic column originating from the nucleus of a metal element with a higher atomic number than lithium among the metal elements constituting the substance is confirmed. Alternatively, it is the intersection of a tangent drawn to the brightness profile from the surface toward the bulk of the STEM image and the axis in the depth direction. Surfaces in STEM images and the like may be determined in conjunction with analysis with higher spatial resolution.
  • the spatial resolution of STEM-EDX is approximately 1 nm. Therefore, the maximum value of the additive element profile may deviate by about 1 nm. For example, even if the maximum value of the profile of an additive element such as magnesium exists outside the surface determined above, if the difference between the maximum value and the surface is less than 1 nm, it can be considered as an error.
  • the peak in STEM-EDX-ray analysis refers to the detection intensity in each element profile or the maximum value of characteristic X-rays for each element.
  • noise in STEM-EDX-ray analysis can be considered to be a measured value of a half-width that is less than the spatial resolution (R), for example, less than R/2.
  • the effects of noise can be reduced by scanning the same location multiple times under the same conditions.
  • the integrated value obtained by measuring six scans can be used as the profile of each element.
  • the number of scans is not limited to six, and it is also possible to perform more scans and use the average as the profile for each element.
  • STEM-EDX-ray 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 vapor-deposited using an ion sputtering device (MC1000 manufactured by Hitachi High-Tech).
  • the positive electrode active material is cut into thin pieces to prepare a STEM cross-sectional sample.
  • thinning processing can be performed using a FIB-SEM device (XVision 200TBS manufactured by Hitachi High-Technology).
  • the pickup is performed using an MPS (micro probing system), and the finishing conditions can be, for example, an accelerating voltage of 10 kV.
  • STEM-EDX-ray analysis for example, a STEM device (HD-2700 manufactured by Hitachi High-Tech) may be used, and an EDAX Octane T Ultra W (two-piece) may be used as the EDX detector.
  • the emission current of the STEM device is set to be 6 ⁇ A or more and 10 ⁇ A or less, and the depth and portions of the thin sectioned sample with few irregularities are measured.
  • the magnification is, for example, about 150,000 times.
  • the conditions for the EDX-ray analysis may include drift correction, line width of 42 nm, pitch of 0.2 nm, and number of frames of 6 or more.
  • the crystal grain boundaries 101 are, for example, areas where particles of the positive electrode active material 100 are fixed to each other, areas where the crystal orientation changes inside the positive electrode active material 100, in other words, the repetition of bright lines and dark lines in a STEM image etc. is discontinuous. This refers to areas where the crystal structure is disordered, areas with many crystal defects, areas where the crystal structure is disordered, etc.
  • crystal defects refer to defects that can be observed in a cross-sectional TEM (transmission electron microscope) image or a cross-sectional STEM image, that is, a structure in which other atoms enter between lattices, cavities, etc.
  • the grain boundary 101 can be said to be one of the planar defects.
  • the vicinity of the grain boundary 101 refers to a region within 10 nm from the grain boundary 101.
  • the positive electrode active material 100 includes lithium, cobalt, oxygen, and additional elements.
  • the positive electrode active material 100 may include lithium cobalt oxide (LiCoO 2 ) to which an additive element is added.
  • the positive electrode active material of a lithium ion secondary battery must contain a transition metal capable of redox in order to maintain charge neutrality even when lithium ions are intercalated and desorbed. It is preferable that the positive electrode active material 100 of one embodiment of the present invention mainly uses cobalt as the transition metal responsible for the redox reaction. In addition to cobalt, at least one or two selected from nickel and manganese may be used.
  • the transition metals contained in the positive electrode active material 100 if cobalt accounts for 75 atomic % or more, preferably 90 atomic % or more, and more preferably 95 atomic % or more, it is relatively easy to synthesize, easy to handle, and has excellent cycle characteristics. It is preferable as it has many advantages.
  • nickel such as lithium nickelate (LiNiO 2 ) accounts for the majority of the transition metals.
  • the stability is better when x in Li x CoO 2 is small compared to complex oxides in which the amount of x in Li x CoO 2 is small. This is thought to be because cobalt is less affected by distortion due to the Jahn-Teller effect than nickel.
  • the strength of the Jahn-Teller effect in transition metal compounds differs depending on the number of electrons in the d orbital of the transition metal.
  • Layered rock-salt complex oxides, such as lithium nickelate, in which octahedral-coordinated low-spin nickel (III) accounts for the majority of the transition metal, are strongly influenced by the Jahn-Teller effect, and are separated from the octahedral structure of nickel and oxygen.
  • the additive elements of the positive electrode active material 100 are listed again, and include magnesium, fluorine, nickel, aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, bromine, and It is preferable to use one or more selected from beryllium. Moreover, the sum of transition metals among the additional elements is preferably less than 25 atom %, more preferably less than 10 atom %, and even more preferably less than 5 atom %.
  • the positive electrode active material 100 includes lithium cobalt oxide to which magnesium and fluorine are added, lithium cobalt oxide to which magnesium, fluorine and titanium are added, lithium cobalt oxide to which magnesium, fluorine and aluminum are added, magnesium, fluorine and nickel. It can have added lithium cobalt oxide, lithium cobalt oxide added with magnesium, fluorine, nickel and aluminum, and the like.
  • the additive element may be solidly dissolved in the positive electrode active material 100, for example, it is preferable to be solidly dissolved in the surface of the positive electrode active material 100. Therefore, for example, when performing STEM-EDX line analysis, the depth at which the amount of added elements increases is deeper than the depth at which the amount of transition metal M is detected, that is, the positive electrode active area. Preferably, it is located inside the substance 100.
  • the depth at which the amount of a certain element detected in STEM-EDX line analysis increases is defined as the depth at which measurement values that can be determined not to be noise from the viewpoint of intensity, spatial resolution, etc. are continuously obtained. This refers to the depth at which it becomes like this.
  • additive element has the same meaning as a mixture or a part of raw materials.
  • additive elements do not necessarily include magnesium, fluorine, nickel, aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, bromine, or beryllium. .
  • the positive electrode active material 100 is made substantially free of manganese, the above-mentioned advantages such as being relatively easy to synthesize, easy to handle, and having excellent cycle characteristics are further enhanced. It is preferable that the weight of manganese contained in the positive electrode active material 100 is, for example, 600 ppm or less, more preferably 100 ppm or less.
  • Layered rock salt type composite oxides have high discharge capacity, have two-dimensional lithium ion diffusion paths, are suitable for lithium ion insertion/extraction reactions, and are excellent as positive electrode active materials for secondary batteries. Therefore, it is particularly preferable that the bulk 100b, which occupies most of the volume of the positive electrode active material 100, has a layered rock salt crystal structure.
  • FIG. 11 shows the layered rock salt type crystal structure with R-3m O3 attached.
  • the surface layer portion 100a of the positive electrode active material 100 of one embodiment of the present invention even if a large amount of lithium is removed from the positive electrode active material 100 due to charging, the layered structure consisting of the octahedron of transition metal M and oxygen in the bulk 100b does not break. It is preferable to have a reinforcing function. Alternatively, it is preferable that the surface layer portion 100a functions as a barrier film for the positive electrode active material 100. Alternatively, it is preferable that the surface layer portion 100a, which is the outer peripheral portion of the positive electrode active material 100, reinforces the positive electrode active material 100.
  • Reinforcement here refers to suppressing structural changes in the surface layer 100a and bulk 100b of the positive electrode active material 100, including desorption of oxygen, and preventing the electrolyte from being oxidized and decomposed on the surface of the positive electrode active material 100. Refers to at least one of the following:
  • the surface layer portion 100a has a composition and crystal structure different from those of the bulk 100b. Further, the surface layer portion 100a preferably has a composition and crystal structure that are more stable at room temperature (25° C.) than the bulk 100b. For example, it is preferable that at least a portion of the surface layer portion 100a of the positive electrode active material 100 according to one embodiment of the present invention has a rock salt crystal structure. Alternatively, the surface layer portion 100a preferably has both a layered rock salt type crystal structure and a rock salt type crystal structure. Alternatively, the surface layer portion 100a preferably has characteristics of both a layered rock salt type and a rock salt type crystal structure.
  • the surface layer portion 100a is a region where lithium ions are first desorbed during charging, and is a region where the lithium concentration tends to be lower than that of the bulk 100b. Further, it can be said that the atoms on the surface of the positive electrode active material 100 that the surface layer portion 100a has have some bonds broken. Therefore, the surface layer portion 100a tends to become unstable, and can be said to be a region where the crystal structure tends to deteriorate. On the other hand, if the surface layer 100a can be made sufficiently stable, even when x in Li x CoO 2 is small, for example, even if x is 0.24 or less, the layered structure consisting of the octahedron of the transition metal M and oxygen in the bulk 100b will be difficult to break. can do. Furthermore, it is possible to suppress misalignment of the octahedral layer of transition metal M and oxygen in the bulk 100b.
  • the bulk 100b of the positive electrode active material 100 has a low density of defects such as dislocations. Further, it is preferable that the positive electrode active material 100 has a large crystallite size as measured by XRD. In other words, it is preferable that the bulk 100b has high crystallinity. Further, it is preferable that the surface of the positive electrode active material 100 is smooth. These characteristics are important elements that support the reliability of the positive electrode active material 100 when used in a secondary battery. If the reliability of the positive electrode active material is high, the upper limit of the charging voltage of the secondary battery can be increased, and the secondary battery can have a high charge/discharge capacity.
  • Dislocations in the bulk 100b can be observed using a TEM, for example.
  • defects such as dislocations may not be observed in a specific 1 ⁇ m square of the observation sample. Note that a dislocation is a type of crystal defect and is different from a point defect.
  • the crystallite size measured by XRD is preferably 300 nm or more, for example. As described later, the larger the crystallite size, the easier it is to maintain the O3' type crystal structure in a state where x in Li x CoO 2 is small, and the easier it is to suppress the shortening of the c-axis length.
  • the particles of the positive electrode active material may be oriented such that the crystal planes of the particles of the positive electrode active material are aligned in one direction due to the influence of pressure etc. during the manufacturing process. If the orientation is strong, the crystallite size may not be calculated accurately, so take out the positive electrode active material layer from the positive electrode, remove some of the binder, etc.
  • Bruker D8 ADVANCE is used, CuK ⁇ is used as the X-ray source, 2 ⁇ is 15° or more and 90° or less, increment 0.005, and the diffraction pattern obtained using LYNXEYE XE-T as the detector and cobalt.
  • ICSD coll. code. 172909 can be used.
  • DIFFRAC. crystal structure analysis software.
  • TOPAS ver. 6 can be used for analysis, and for example, the following settings can be made.
  • Emission Profile CuKa5.
  • LVol-IB which is the crystallite size calculated by the above method, as the crystallite size. Note that if the calculated Preferred Orientation is less than 0.8, too many particles in the sample have the same orientation, and the sample may not be suitable for determining the crystallite size.
  • the surface layer portion 100a preferably contains an additive element, and more preferably contains a plurality of additive elements. Further, it is preferable that the surface layer portion 100a has a higher concentration of one or more selected additive elements than the bulk 100b. Further, it is preferable that one or more selected from the additive elements included in the positive electrode active material 100 have a concentration gradient. Further, it is more preferable that the positive electrode active material 100 has a different distribution depending on the added element. For example, it is more preferable that the depth of the concentration peak from the surface differs depending on the added element.
  • the concentration peak here refers to the maximum value of the detected amount in the surface layer portion 100a or at a distance of 50 nm or less from the surface.
  • additive elements such as magnesium, fluorine, nickel, titanium, silicon, phosphorus, boron, calcium, etc.
  • concentration gradient that increases from the bulk 100b toward the surface.
  • An element having such a concentration gradient will be referred to as an additive element X.
  • another additive element such as aluminum or manganese
  • the concentration peak may exist in the surface layer portion 100a or may be deeper than the surface layer portion 100a.
  • An element having such a concentration gradient will be referred to as an additive element Y.
  • magnesium which is one of the additive elements X, is divalent, and since magnesium ions are more stable in the lithium site than in the transition metal M site in the layered rock salt crystal structure, they easily enter the lithium site.
  • the presence of magnesium at an appropriate concentration in the lithium sites of the surface layer 100a makes it easier to maintain the layered rock salt crystal structure. This is presumed to be because the magnesium present at the lithium site functions as a pillar that supports the two CoO layers.
  • the presence of magnesium can suppress desorption 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 in the surface layer portion 100a is high, it can be expected that the corrosion resistance against hydrofluoric acid produced by decomposition of the electrolytic solution will be improved.
  • magnesium is at an appropriate concentration, it will not adversely affect the insertion and desorption of lithium during charging and discharging, and the above benefits can be enjoyed.
  • an excess of magnesium may have an adverse effect on lithium intercalation and deintercalation.
  • the effect on stabilizing the crystal structure may be reduced. This is considered to be because magnesium enters the transition metal M site in addition to the lithium site.
  • unnecessary magnesium compounds oxides, fluorides, etc.
  • the discharge capacity of the positive electrode active material may decrease. This is thought to be because too much magnesium enters the lithium site, reducing the amount of lithium that contributes to charging and discharging.
  • the entire positive electrode active material 100 has an appropriate amount of magnesium.
  • the ratio of magnesium to the sum of transition metals M (Mg/Co) in the positive electrode active material 100 of one embodiment of the present invention is preferably 0.25% or more and 5% or less, and 0.5% or more and 2% or less. More preferably, about 1% is even more preferable.
  • the amount of magnesium contained in the entire positive electrode active material 100 herein may be a value obtained by elemental analysis of the entire positive electrode active material 100 using, for example, GD-MS, ICP-MS, etc. It may be based on the value of the composition of raw materials in the process of producing the substance 100.
  • nickel which is one of the additive elements X, can exist at both the transition metal M site and the lithium site.
  • the redox potential becomes lower than that of cobalt, which leads to an increase in discharge capacity, which is preferable.
  • the entire positive electrode active material 100 has an appropriate amount of nickel.
  • the number of nickel atoms contained in the positive electrode active material 100 is preferably more than 0% and less than 7.5% of the number of cobalt atoms, preferably 0.05% or more and 4% or less, and preferably 0.1% or more and 2% or less. is preferable, and more preferably 0.2% or more and 1% or less.
  • it is preferably more than 0% and 4% or less.
  • it is preferably more than 0% and 2% or less.
  • preferably 0.05% or more and 2% or less Or preferably 0.1% or more and 7.5% or less.
  • the amount of nickel shown here may be, for example, a value obtained by elemental analysis of the entire positive electrode active material using GD-MS, ICP-MS, etc., or a value obtained by mixing raw materials in the process of producing the positive electrode active material. may be based on the value of
  • aluminum which is one of the additive elements Y
  • aluminum can exist at the transition metal M site in the layered rock salt crystal structure.
  • Aluminum is a typical trivalent element and its valence does not change, so lithium around aluminum is difficult to move during charging and discharging. Therefore, aluminum and the lithium surrounding it function as pillars and can suppress changes in the crystal structure. Furthermore, aluminum has the effect of suppressing the elution of surrounding transition metal M and improving continuous charging resistance. Furthermore, since the Al--O bond is stronger than the Co--O bond, desorption of oxygen around aluminum can be suppressed. These effects improve thermal stability. Therefore, when aluminum is included as the additive element Y, safety can be improved when used in a secondary battery. Moreover, the positive electrode active material 100 can be made such that the crystal structure does not easily collapse even after repeated charging and discharging.
  • the entire positive electrode active material 100 has an appropriate amount of aluminum.
  • the number of aluminum atoms contained in the entire positive electrode active material 100 is preferably 0.05% or more and 4% or less of the number of cobalt atoms, preferably 0.1% or more and 2% or less, and 0.3% or more and 1.5% or less. % or less is more preferable. Or preferably 0.05% or more and 2% or less. Or preferably 0.1% or more and 4% or less.
  • the amount that the entire positive electrode active material 100 has here may be, for example, a value obtained by elemental analysis of the entire positive electrode active material 100 using GD-MS, ICP-MS, etc. It may also be based on the value of the composition of raw materials during the production process.
  • fluorine which is one of the additive elements X
  • fluorine is a monovalent anion
  • fluorine is a monovalent anion
  • the lithium desorption energy becomes small.
  • the valence of cobalt ions changes from trivalent to tetravalent when fluorine is not present, and from divalent to trivalent when fluorine is present, resulting in a difference in redox potential. Therefore, if part of the oxygen in the surface layer 100a of the positive electrode active material 100 is replaced with fluorine, it can be said that desorption and insertion of lithium ions near fluorine tend to occur smoothly. Therefore, when the positive electrode active material 100 is used in a secondary battery, charging/discharging characteristics, current characteristics, etc.
  • the melting point of fluoride such as lithium fluoride is lower than the melting point of other additive element sources, it can function as a fluxing agent (also referred to as a fluxing agent) that lowers the melting point of the other additive element sources.
  • titanium oxide which is one of the additive elements X, has superhydrophilicity. Therefore, by using the positive electrode active material 100 having titanium oxide in the surface layer portion 100a, the wettability with respect to a highly polar solvent may be improved. When used as a secondary battery, the interface between the positive electrode active material 100 and the highly polar electrolytic solution becomes good, and there is a possibility that an increase in internal resistance can be suppressed.
  • phosphorus which is one of the additive elements X
  • the positive electrode active material 100 contains phosphorus because the phosphorus reacts with hydrogen fluoride generated by decomposition of the electrolyte, and there is a possibility that the hydrogen fluoride concentration in the electrolyte can be reduced.
  • hydrogen fluoride may be generated due to hydrolysis. Furthermore, there is a possibility that hydrogen fluoride may be generated due to the reaction between polyvinylidene fluoride (PVDF) used as a component of the positive electrode and an alkali.
  • PVDF polyvinylidene fluoride
  • the positive electrode active material 100 contains phosphorus together with magnesium because stability in a state where x in Li x CoO 2 is small is extremely high.
  • 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 preferably 1% or more and 10% or less. Or preferably 1% or more and 8% or less. Or preferably 2% or more and 20% or less. Or preferably 2% or more and 8% or less. Or preferably 3% or more and 20% or less. Or preferably 3% or more and 10% or less.
  • 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 preferably 0.1% or more and 5% or less. Or preferably 0.1% or more and 4% or less. Or preferably 0.5% or more and 10% or less. Or preferably 0.5% or more and 4% or less. Or preferably 0.7% or more and 10% or less. Or preferably 0.7% or more and 5% or less.
  • concentrations of phosphorus and magnesium shown here may be, for example, values obtained by elemental analysis of the entire positive electrode active material 100 using GC-MS, ICP-MS, etc., or values obtained during the manufacturing process of the positive electrode active material 100. It may be based on the value of the raw material composition in .
  • the positive electrode active material 100 has a crack
  • the presence of phosphorus, or more specifically, a compound containing phosphorus and oxygen, in the vicinity of the center of the positive electrode active material with the crack as the surface, for example, in the buried portion 102, may cause the crack to occur. Progress may be inhibited.
  • the surface layer portion 100a contains both magnesium and nickel, there is a possibility that divalent magnesium can exist more stably near divalent nickel. Therefore, elution of magnesium can be suppressed even when x in Li x CoO 2 is small. Therefore, it can contribute to stabilization of the surface layer portion 100a.
  • additive element X and additive element Y additional elements having different distributions, such as additive element X and additive element Y, because the crystal structure can be stabilized over a wider region.
  • the positive electrode active material 100 contains both magnesium and nickel, which are part of the additive element X, and aluminum, which is one of the additive elements Y
  • the positive electrode active material 100 has a higher It is possible to stabilize the crystal structure in a wide range.
  • the positive electrode active material 100 has both the additive element X and the additive element Y, the additive element do not have.
  • each additive element can be synergized and contribute to further stabilization of the surface layer portion 100a.
  • magnesium, nickel and aluminum are highly effective in providing a stable composition and crystal structure.
  • the surface layer portion 100a is occupied only by the compound of the additive element and oxygen, it is not preferable because it becomes difficult to insert and extract lithium.
  • the surface layer portion 100a is occupied only by MgO, a structure in which MgO and NiO(II) are dissolved in solid solution, and/or a structure in which MgO and CoO(II) are dissolved in solid solution. Therefore, the surface layer portion 100a must contain at least cobalt, also contain lithium in the discharge state, and have a path for inserting and extracting lithium.
  • the surface layer portion 100a has a higher concentration of cobalt than magnesium.
  • the ratio Mg/Co of the number of atoms of magnesium, Mg, and the number of atoms of cobalt, Co is preferably 0.62 or less.
  • the surface layer portion 100a has a higher concentration of cobalt than nickel.
  • the surface layer portion 100a has a higher concentration of cobalt than aluminum.
  • the surface layer portion 100a has a higher concentration of cobalt than fluorine.
  • the surface layer portion 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 additive elements particularly magnesium, nickel, and aluminum, have a higher concentration in the surface layer portion 100a than in the bulk 100b, it is preferable that they also exist randomly and dilutely in the bulk 100b.
  • magnesium and aluminum are present at appropriate concentrations in the lithium sites of the bulk 100b, there is an effect that the layered rock salt type crystal structure can be easily maintained, similar to the above.
  • nickel is present in the bulk 100b at an appropriate concentration, the shift of the layered structure consisting of the octahedron of the transition metal M and oxygen can be suppressed in the same way as described above.
  • divalent magnesium may exist more stably near divalent nickel, so a synergistic effect of suppressing the elution of magnesium can be expected.
  • the crystal structure changes continuously from the bulk 100b toward the surface due to the concentration gradient of the additive element as described above.
  • the crystal orientations of the surface layer portion 100a and the bulk 100b are approximately the same.
  • the crystal structure changes continuously from the layered rock salt bulk 100b toward the surface and surface layer portion 100a that has the characteristics of the rock salt type or both the rock salt type and the layered rock salt type.
  • the orientations of the surface layer portion 100a, which has characteristics of rock salt type or both rock salt type and layered rock salt type, and the layered rock salt type bulk 100b are approximately the same.
  • the layered rock-salt crystal structure belonging to space group R-3m which a composite oxide containing a transition metal M such as lithium and cobalt has, is defined as a structure in which cations and anions alternate. It has a rock salt-type ion arrangement, and the transition metal M and lithium are regularly arranged to form a two-dimensional plane, so it is a crystal structure that allows two-dimensional diffusion of lithium. Note that there may be defects such as cation or anion deficiency. Strictly speaking, the layered rock salt crystal structure may have a structure in which the lattice of the rock salt crystal is distorted.
  • rock salt type crystal structure refers to a structure having a cubic crystal structure including a space group Fm-3m, in which cations and anions are arranged alternately. Note that there may be a deficiency of cations or anions.
  • the presence of both layered rock salt type and rock salt type crystal structure characteristics can be determined by electron beam diffraction, TEM images, cross-sectional STEM images, etc.
  • the rock salt type has no distinction in cation sites, but the layered rock salt type has two types of cation sites in its crystal structure, one mostly occupied by lithium and the other occupied by the transition metal M.
  • the layered structure in which two-dimensional planes of cations and two-dimensional planes of anions are arranged alternately is the same for both the rock salt type and the layered rock salt type.
  • the central spot transparent spot
  • the bright spot closest to the central spot is the ideal one.
  • a state rock salt type has a (111) plane
  • a layered rock salt type has a (003) plane, for example.
  • the distance between the bright spots on the (003) plane of LiCoO 2 is approximately half the distance between the bright spots on the (111) plane of MgO. observed at the position of Therefore, when the analysis region has two phases, for example, rock salt type MgO and layered rock salt type LiCoO2 , in the electron diffraction image, there is a plane orientation in which bright spots with strong brightness and bright spots with weak brightness are arranged alternately. do. Bright spots common to the halite type and layered halite type have strong brightness, and bright spots that occur only in the layered halite type have weak brightness.
  • Layered rock salt crystals and anions of rock salt crystals have a cubic close-packed structure (face-centered cubic lattice structure).
  • the anions are also presumed to have a cubic close-packed structure. Therefore, when a layered rock salt crystal and a rock salt crystal come into contact, there is a crystal plane in which the cubic close-packed structure composed of anions is oriented in the same direction.
  • Anions in the ⁇ 111 ⁇ plane of the cubic crystal structure have a triangular lattice.
  • the layered rock salt type has a space group R-3m and has a rhombohedral structure, but to facilitate understanding of the structure, it is generally expressed as a complex hexagonal lattice, and the (0001) plane of the layered rock salt type has a hexagonal lattice.
  • the triangular lattice of the cubic ⁇ 111 ⁇ plane has an atomic arrangement similar to the hexagonal lattice of the (0001) plane of the layered rock salt type. When both lattices are consistent, it can be said that the orientations of the cubic close-packed structures are 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 of rock salt crystals (the space group of general rock salt crystals), so the above conditions are
  • the Miller index of the crystal planes to be satisfied is different between a layered rock salt type crystal and an O3' type crystal and a rock salt type crystal.
  • layered rock salt type crystals, O3' type crystals, and rock salt type crystals when the directions of the cubic close-packed structures constituted by anions are aligned, the orientation of the crystals approximately coincides, or the orientation of the crystals is topotaxy. Sometimes referred to as epitaxy.
  • Topotaxis refers to having three-dimensional structural similarity such that the crystal orientations roughly match, or having the same crystallographic orientation.
  • epitaxy refers to the structural similarity of two-dimensional interfaces.
  • HAADF-STEM High-angle Annular Dark Field Scanning TEM (high-angle scattering annular dark-field scanning transmission electron microscope) image
  • ABF-STEM annular bright-field scanning transmission electron microscope
  • eHCI-TEM enhanced Hollow-Cone Illumination-TEM
  • FIG. 13 shows an example of a TEM image in which the orientations of the layered rock salt crystal LRS and the rock salt crystal RS are approximately the same.
  • a TEM image, a STEM image, a HAADF-STEM image, an ABF-STEM image, etc. provide images that reflect the crystal structure.
  • contrast derived from crystal planes is obtained. Due to electron beam diffraction and interference, for example, when an electron beam is incident perpendicularly to the c-axis of a layered rock-salt complex hexagonal lattice, the contrast originating from the (0003) plane is divided into bright bands (bright strips) and dark bands (dark strips). ) is obtained by repeating. Therefore, if repeating bright lines and dark lines are observed in the TEM image, and the angle between the bright lines (for example, LRS and LLRS shown in FIG.
  • lithium cobalt oxide which has a layered rock salt crystal structure
  • the arrangement of cobalt atoms perpendicular to the c-axis is observed as a bright line or an arrangement of strong bright points, and lithium atoms and oxygen atoms are observed perpendicularly to the c-axis.
  • the arrangement is observed as a dark line or region of low brightness.
  • lithium cobalt oxide contains fluorine (atomic number 9) and magnesium (atomic number 12) as additive elements.
  • FIG. 14A shows an example of a STEM image in which the orientations of the layered rock salt crystal LRS and the rock salt crystal RS are approximately the same.
  • FIG. 14B shows the FFT of the region of the rock salt crystal RS
  • FIG. 14C shows the FFT of the region of the layered rock salt crystal LRS.
  • the left side of FIGS. 14B and 14C shows the composition, the JCPDS (Joint Committee Powder Diffraction Standard) card number, and the d value and angle calculated from this. Actual measurements are shown on the right.
  • the spot marked with O is the 0th order of diffraction, and the center position of the spot is marked with an X.
  • the spots labeled A in FIG. 14B originate from the 11-1 reflection of the cubic crystal.
  • the spots labeled A in FIG. 14C originate from layered rock salt type 0003 reflection. It can be seen from FIGS. 14B and 14C 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 match. That is, it can be seen that the straight line passing through AO in FIG. 14B and the straight line passing through AO in FIG. 14C are approximately parallel.
  • the terms “approximately coincident” and “approximately parallel” here mean that the angle is 0 degrees or more and 5 degrees or less, or 0 degrees or more and 2.5 degrees or less.
  • the direction of the 11-1 reflection of the cubic crystal and the direction of the 0003 reflection of the layered rock salt type may vary.
  • a spot that is not derived from layered rock salt type 0003 reflection may be observed.
  • the spot labeled B in FIG. 14C is derived from a layered rock salt type 10-14 reflection.
  • ⁇ AOB is 52° or more and 56° or less
  • d may be observed at a location of 0.19 nm or more and 0.21 nm or less.
  • this index is just an example, and does not necessarily have to match this index.
  • equivalent reciprocal lattice points in each may be used.
  • a spot that is not derived from the 11-1 reflection of the cubic crystal may be observed on a reciprocal lattice space different from the direction in which the 11-1 reflection of the cubic crystal was observed.
  • the spot labeled B in FIG. 14B is derived from 200 reflections of a cubic crystal. This is a diffraction spot at a location that is at an angle of 54° or more and 56° or less (that is, ⁇ AOB is 54° or more and 56° or less) from the direction of the reflection derived from cubic crystal 11-1 (A in Figure 14B). may be observed. Note that this index is just an example, and does not necessarily have to match this index. For example, equivalent reciprocal lattice points in each may be used.
  • the positive electrode active material 100 of one embodiment of the present invention has the above-mentioned distribution of additive elements and crystal structure in a discharge state, so that the crystal structure in a state where x in Li x CoO 2 is small is as follows. Different from conventional positive electrode active materials. Note that x is small here, which means 0.1 ⁇ x ⁇ 0.24.
  • FIG. 12 shows changes in the crystal structure of a conventional positive electrode active material.
  • the conventional positive electrode active material shown in FIG. 12 is lithium cobalt oxide (LiCoO 2 ) without any particular additive element.
  • changes in the crystal structure of lithium cobalt oxide without additive elements are described in Non-Patent Documents 1 to 4.
  • this crystal structure three two CoO layers exist in the unit cell, and lithium is located between the two CoO layers. Further, lithium occupies octahedral sites in which six oxygen atoms are coordinated. 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 six oxygen atoms are coordinated with cobalt is continuous in a plane in a shared edge state. This is sometimes referred to as a layer consisting of an octahedron of cobalt and oxygen.
  • R-3m O3 can express the coordinates of lithium, cobalt and oxygen in the unit cell as Li(0,0,0)Co(0,0,0.5)O(0,0,0.23951) .
  • one CoO 2 layer exists 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 trigonal space group P-3m1, and one CoO 2 layer is also present in the unit cell. Therefore, this crystal structure is sometimes called O1 type or trigonal O1 type.
  • the trigonal crystal is sometimes converted into a complex hexagonal lattice and is called the hexagonal O1 type.
  • This structure can also be said to be a structure in which a CoO 2 structure like trigonal O1 type and a LiCoO 2 structure like R-3m O3 are stacked alternately. Therefore, this crystal structure is sometimes called an H1-3 type crystal structure.
  • the H1-3 type crystal structure has twice the number of cobalt atoms per unit cell as other structures.
  • the c-axis of the H1-3 type crystal structure is shown as 1/2 of the unit cell.
  • the coordinates of cobalt and oxygen in the unit cell are Co(0, 0, 0.42150 ⁇ 0.00016), O1(0, 0, 0.27671 ⁇ 0.00045), O2 (0, 0, 0.11535 ⁇ 0.00045).
  • O1 and O2 are each oxygen atoms.
  • Which unit cell should be used to represent the crystal structure of the positive electrode active material can be determined, for example, by Rietveld analysis of the XRD pattern. In this case, a unit cell with a small GOF (goodness of fit) value may be used.
  • conventional lithium cobalt oxide has an H1-3 type crystal structure, an R-3m O3 structure in a discharged state, The crystal structure changes (that is, non-equilibrium phase changes) repeatedly between the two.
  • the crystal structure of conventional lithium cobalt oxide collapses.
  • the collapse of the crystal structure causes deterioration of cycle characteristics. This is because as the crystal structure collapses, the number of sites where lithium can exist stably decreases, and insertion and extraction of lithium becomes difficult.
  • FIG. 11 shows a crystal structure of a positive electrode active material 100 according to one embodiment of the present invention.
  • the crystal structure that the bulk 100b of the positive electrode active material 100 has when x in Li x CoO 2 is approximately 1 and 0.2 is shown. Since the bulk 100b occupies most of the volume of the positive electrode active material 100 and is a part that greatly contributes to charging and discharging, it can be said that the displacement of the CoO 2 layer and the change in volume are the part that poses the most problems.
  • the crystal structure changes less in the discharge state where x in Li x CoO 2 is 1 and in the state where x is 0.24 or less than in conventional positive electrode active materials. More specifically, the deviation between the two CoO layers between the state where x is 1 and the state where x is 0.24 or less can be reduced. Further, the change in volume when compared per cobalt atom can be reduced. Therefore, in the positive electrode active material 100 of one embodiment of the present invention, the crystal structure does not easily collapse even after repeated charging and discharging such that x becomes 0.24 or less, and excellent cycle characteristics can be achieved.
  • the positive electrode active material 100 of one embodiment of the present invention can have a more stable crystal structure than conventional positive electrode active materials when x in Li x CoO 2 is 0.24 or less. Therefore, in the cathode active material 100 of one embodiment of the present invention, short circuits are unlikely to occur when x in Li x CoO 2 is maintained at 0.24 or less. In such a case, the safety of the secondary battery is further improved, which is preferable.
  • the positive electrode active material 100 has the same R-3mO3 crystal structure as conventional lithium cobalt oxide. However, when x is 0.24 or less, for example, about 0.2 or 0.12, where conventional lithium cobalt oxide has an H1-3 type crystal structure, the positive electrode active material 100 forms a crystal with a different structure.
  • the crystal structure of the O3' type has the coordinates of cobalt and oxygen in the unit cell within the range of Co(0,0,0.5), O(0,0,x), 0.20 ⁇ x ⁇ 0.25. It can be shown as
  • ions such as cobalt, nickel, and magnesium occupy six oxygen coordination positions. Note that a light element such as lithium may occupy the 4-coordination position of oxygen.
  • the difference in volume per same number of cobalt atoms between R-3m(O3) in the discharge state and the O3' type crystal structure is 2.5% or less, more specifically 2.2% or less, typically 1. It is 8%.
  • the cathode active material 100 of one embodiment of the present invention changes in the crystal structure when x in Li x CoO 2 is small, that is, when a large amount of lithium is released, are suppressed more than in conventional cathode active materials. has been done.
  • changes in volume are also suppressed when comparing the same number of cobalt atoms. Therefore, the crystal structure of the positive electrode active material 100 does not easily collapse even after repeated charging and discharging such that x becomes 0.24 or less. Therefore, in the positive electrode active material 100, a decrease in charge/discharge capacity during charge/discharge cycles is suppressed.
  • 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 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 when x exceeds 0.24 and 0. It is estimated that even if it is less than .27, it has an O3' type crystal structure.
  • the crystal structure is influenced not only by x in Li x CoO 2 but also by the number of charge/discharge cycles, charge/discharge current, temperature, electrolyte, etc., it is not necessarily limited to the above range of x.
  • the entire bulk 100b of the positive electrode active material 100 does not need to have an O3' type crystal structure. It may contain other crystal structures, or may be partially amorphous.
  • a state in which x in Li x CoO 2 is small can be rephrased as a state in which the battery is charged at a high charging voltage.
  • a charging voltage of 4.6 V or more can be said to be a high charging voltage with reference to the potential of lithium metal.
  • 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 can maintain a crystal structure having R-3mO3 symmetry even when charged at a high charging voltage, for example, 4.6 V or higher at 25° C., and therefore is preferable. It can be rephrased as In addition, it can be said that it is preferable because an O3' type crystal structure can be obtained 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.
  • the H1-3 type crystal structure may be finally observed when the charging voltage is further increased. Furthermore, as mentioned above, the crystal structure is affected by the number of charge/discharge cycles, charge/discharge current, temperature, electrolyte, etc., so if the charging voltage is lower, for example, if the charging voltage is 4.5 V or more and less than 4.6 V at 25°C, In some cases, the positive electrode active material 100 of one embodiment of the present invention can have an O3' type crystal structure.
  • the voltage of the secondary battery is lowered by the difference between the potential of graphite and the potential of lithium metal 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 a negative electrode active material, it has a similar crystal structure when the voltage obtained by subtracting the potential of graphite from the above voltage is applied.
  • lithium is shown to exist at all lithium sites with equal probability, but the present invention is not limited to this. It may be concentrated in some lithium sites, or it may have a symmetry such as monoclinic O1 (Li 0.5 CoO 2 ) shown in FIG. 12, for example.
  • the distribution of lithium can be analyzed, for example, by neutron beam diffraction.
  • the O3' type crystal structure is similar to the CdCl2 type crystal structure, although it has lithium randomly between the layers.
  • This crystal structure similar to CdCl type 2 is close to the crystal structure when lithium nickelate is charged to Li 0.06 NiO 2 , but pure lithium cobalt oxide or a layered rock salt type positive electrode active material containing a large amount of cobalt is It is known that CdCl does not normally have a type 2 crystal structure.
  • the concentration gradient of the additive element be the same at a plurality of locations in the surface layer portion 100a of the positive electrode active material 100.
  • the barrier film derived from the additive element exists homogeneously in the surface layer portion 100a. Even if a portion of the surface layer portion 100a is reinforced, if there is a portion without reinforcement, stress may be concentrated on the portion without reinforcement. When stress is concentrated on a portion of the positive electrode active material 100, defects such as cracks may occur there, leading to cracking of the positive electrode active material and a decrease in discharge capacity.
  • maldistribution refers to the concentration of an element in a certain region being different from that in other regions. It has the same meaning as segregation, precipitation, non-uniformity, deviation, or a mixture of areas with high concentration and areas with low concentration.
  • the magnesium concentration at and near the grain boundaries 101 of the positive electrode active material 100 is higher than in other regions of the bulk 100b.
  • the fluorine concentration at the grain boundary 101 and its vicinity is also higher than that in other regions of the bulk 100b.
  • the nickel concentration in the grain boundaries 101 and the vicinity thereof is also higher than in other regions of the bulk 100b.
  • the aluminum concentration in the grain boundaries 101 and the vicinity thereof is also higher than in other regions of the bulk 100b.
  • the grain boundary 101 is one of the planar defects. Therefore, like the particle surface, it tends to become unstable and the crystal structure tends to change. Therefore, if the concentration of the additive element at and near the grain boundaries 101 is high, changes in the crystal structure can be suppressed more effectively.
  • the magnesium concentration and fluorine concentration at the grain boundary 101 and the vicinity thereof are high, even if a crack occurs along the grain boundary 101 of the positive electrode active material 100 of one embodiment of the present invention, the surface Magnesium and fluorine concentrations increase in the vicinity. Therefore, the corrosion resistance against hydrofluoric acid can be improved even in the positive electrode active material after cracks have occurred.
  • the median diameter (D50) is preferably 1 ⁇ m or more and 100 ⁇ m or less, more preferably 2 ⁇ m or more and 40 ⁇ m or less, and even more preferably 5 ⁇ m or more and 30 ⁇ m or less.
  • the thickness is preferably 1 ⁇ m or more and 40 ⁇ m or less.
  • the thickness is preferably 1 ⁇ m or more and 30 ⁇ m or less.
  • the thickness is preferably 2 ⁇ m or more and 100 ⁇ m or less. Or preferably 2 ⁇ m or more and 30 ⁇ m or less. Alternatively, the thickness is preferably 5 ⁇ m or more and 100 ⁇ m or less. Alternatively, the thickness is preferably 5 ⁇ m or more and 40 ⁇ m or less.
  • the positive electrode active material 100 having a relatively small particle size is expected to have high charge/discharge rate characteristics.
  • the positive electrode active material 100 having 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, which has an O3' type and/or monoclinic O1 (15) type crystal structure when x in Li x CoO 2 is small.
  • XRD can analyze the symmetry of transition metals such as cobalt contained in positive electrode active materials with high resolution, compare the height of crystallinity and crystal orientation, and analyze periodic lattice distortion and crystallite size. This is preferable because sufficient accuracy can be obtained even if the positive electrode obtained by disassembling the secondary battery is directly measured.
  • powder XRD provides a diffraction peak that reflects the crystal structure of the bulk 100b of the positive electrode active material 100, which occupies most of the volume of the positive electrode active material 100.
  • the positive electrode active material when analyzing the crystallite size by powder XRD, it is preferable to perform the measurement without the influence of orientation due to pressurization or the like. For example, it is preferable to take out the positive electrode active material from a positive electrode obtained by disassembling a secondary battery and use it as a powder sample before measurement.
  • the positive electrode active material 100 of one embodiment of the present invention is characterized by a small change in crystal structure between when x in Li x CoO 2 is 1 and when x is 0.24 or less.
  • a material in which 50% or more of the crystal structure changes significantly when charged at a high voltage is not preferable because it cannot withstand repeated high voltage charging and discharging.
  • the O3' type or monoclinic O1 (15) type crystal structure is not achieved simply by adding additional elements.
  • x in Li x CoO 2 may be 0.24 or less.
  • the O3' type and/or monoclinic O1(15) type crystal structure accounts for 60% or more, and in other cases, the H1-3 type crystal structure accounts for 50% or more.
  • 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, the crystal structure of the H1-3 type or trigonal O1 type will change. This may occur in some cases. Therefore, in order to determine whether the positive electrode active material 100 of one embodiment of the present invention is used, analysis of the crystal structure such as XRD, and information such as charging capacity or charging voltage are required.
  • the positive electrode active material in a state where x is small may undergo a change in crystal structure when exposed to the atmosphere.
  • the O3' type and monoclinic O1(15) type crystal structures may change to the H1-3 type crystal structure. Therefore, it is preferable that all samples subjected to crystal structure analysis be handled in an inert atmosphere such as an argon atmosphere.
  • whether the distribution of additive elements in a certain positive electrode active material is in the state described above can be determined by, for example, XPS, energy dispersive X-ray spectroscopy (EDX), EPMA ( This can be determined by analysis using methods such as electronic probe microanalysis.
  • the crystal structure of the surface layer 100a, grain boundaries 101, etc. can be analyzed by electron beam diffraction of a cross section of the positive electrode active material 100.
  • the positive electrode active material 100 of one embodiment of the present invention has a stable crystal structure even at high voltage. Since the crystal structure of the positive electrode active material is stable in the charged state, it is possible to suppress a decrease in charge/discharge capacity due to repeated charging/discharging.
  • the volume resistivity of the powder of the positive electrode active material 100 is preferably 1.0 ⁇ 10 4 ⁇ cm or more at a pressure of 64 MPa, and 1.0 It is more preferably ⁇ 10 5 ⁇ cm or more, and more preferably 1.0 ⁇ 10 6 ⁇ cm or more. Moreover, at a pressure of 64 MPa, it is preferably 1.0 ⁇ 10 9 ⁇ cm or less, more preferably 1.0 ⁇ 10 8 ⁇ cm or less, and 1.0 ⁇ 10 7 ⁇ cm or less It is more preferable that there be.
  • the positive electrode active material 100 having the above-mentioned volume resistivity has a stable crystal structure even at high voltage, and has a good surface layer portion 100a, which is important for the crystal structure of the positive electrode active material to be stable in a charged state. It can be used as an indicator to show that the formation has been completed. That is, it is preferable that the surface layer portion 100a has high resistance.
  • a high-resistance region exists thickly from the surface of the positive electrode active material 100 toward the inside, the battery reaction may be inhibited. Therefore, it is more preferable that only a thin region near the surface of the surface layer portion 100a has high resistance. That is, in the surface layer portion 100a, it is preferable that a high resistance region exist thinly from the surface toward the inside. For example, a region where Mg is present at a high concentration in the surface layer portion 100a can be a region with high resistance. Therefore, it is preferable that Mg be located in the surface layer portion 100a.
  • a method for measuring the volume resistivity of the powder of the positive electrode active material 100 according to one embodiment of the present invention will be described.
  • a device part that has a terminal for resistance measurement and a mechanism that applies pressure to the powder that is the object of measurement.
  • MCP-PD51 manufactured by Mitsubishi Chemical Analytech can be used as a measuring device having a terminal for resistance measurement and a mechanism for applying pressure to the powder (sample) to be measured.
  • Lorestar GP or Hirestar GP can be used as the resistance meter. Lorestar-GP can be used to measure low-resistance samples using the four-probe method, and Hirestar-UP can be used to measure high-resistance samples using the two-probe method.
  • the measurement environment is preferably a stable environment such as a dry room, but may be a general laboratory environment.
  • the environment of the dry room is preferably, for example, a temperature environment of 20° C. or higher and 25° C. or lower, and a dew point environment of ⁇ 40° C. or lower.
  • a general laboratory environment may be a temperature environment of 15° C. or more and 30° C. or less, and a humidity environment of 30% or more and 70% or less.
  • a powder sample is set in the measuring section.
  • the powder sample and the terminal for resistance measurement are in contact with each other, and the structure is such that pressure can be applied to the powder sample. It also has a structure for measuring the thickness of the powder sample in the measuring section.
  • the measurement section described above has a cylindrical space, and a powder sample is set in the space.
  • the thickness resistivity of the powder measure the electrical resistance of the powder and the thickness of the powder while applying pressure to the powder.
  • the pressure applied to the powder can be applied under multiple conditions.
  • the electrical resistance of the powder and the thickness of the powder can be measured under pressure conditions of 13 MPa, 25 MPa, 38 MPa, 51 MPa, and 64 MPa.
  • the volume resistivity of the powder can be calculated from the measured electrical resistance of the powder and the thickness of the powder.
  • volume resistivity When measuring with the two-terminal method using Hirestar-UP, the volume resistivity can be found by multiplying the electrical resistance of the powder by the area of the electrode pressing the powder and dividing by the thickness of the powder.
  • the volume resistivity can be determined by multiplying the electrical resistance of the powder by a correction coefficient and by the thickness of the powder.
  • the correction coefficient is a value that changes depending on the sample shape, dimensions, and measurement position, and can be determined by the calculation software built into Lorestar GP.
  • the volume resistivity of the powder of the positive electrode active material 100 of one embodiment of the present invention is preferably 1.0 ⁇ 10 4 ⁇ cm or more at a pressure of 64 MPa, and 1 It is more preferably .0 ⁇ 10 5 ⁇ cm or more, and more preferably 1.0 ⁇ 10 6 ⁇ cm or more. Moreover, at a pressure of 64 MPa, it is preferably 1.0 ⁇ 10 9 ⁇ cm or less, more preferably 1.0 ⁇ 10 8 ⁇ cm or less, and 1.0 ⁇ 10 7 ⁇ cm or less It is more preferable that there be.
  • a battery having the positive electrode active material 100 exhibiting such a volume resistivity exhibits favorable cycle characteristics in a charge/discharge cycle test under high voltage conditions. Furthermore, the battery can be made less likely to catch fire in an internal short circuit test such as a nail penetration test.
  • ⁇ Charging method Charging to determine whether a certain composite oxide is the positive electrode active material 100 of one embodiment of the present invention is performed using, for example, a coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) using lithium metal as a counter electrode. ) can be created and charged.
  • a coin cell CR2032 type, diameter 20 mm, height 3.2 mm
  • lithium metal as a counter electrode.
  • the positive electrode may be prepared by coating a positive electrode current collector made of aluminum foil with a slurry containing a positive electrode active material, a conductive material, and a binder.
  • lithium metal can be used for the counter electrode, but materials other than lithium metal may also be used. When a material other than lithium metal is used, the potential of the secondary battery and the potential of the positive electrode are different. Voltages and potentials in this specification and the like are the potentials of the positive electrode unless otherwise mentioned.
  • LiPF 6 lithium hexafluorophosphate
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • VC vinylene carbonate
  • a polypropylene porous film with a thickness of 25 ⁇ m can be used as the separator.
  • the positive electrode can and the negative electrode can may be made of stainless steel (SUS).
  • the coin cell produced under the above conditions is charged at an arbitrary 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 amount of time.
  • the current in CC charging can be 20 mA/g or more and 100 mA/g or less.
  • CV charging can be completed at 2 mA/g or more and 10 mA/g or less.
  • the temperature of 25° C. is an example.
  • the coin cell is disassembled in a glove box with an argon atmosphere and the positive electrode is taken out, thereby obtaining a positive electrode active material with an arbitrary charging capacity.
  • XRD can be performed in a sealed container with an argon atmosphere.
  • the conditions for charging and discharging the multiple times may be different from the above-mentioned charging conditions.
  • charging is performed by constant current charging to an arbitrary voltage (for example, 4.6V, 4.65V, 4.7V, 4.75V, or 4.8V) at a current value of 20 mA/g or more and 100 mA/g or less, and then Constant voltage charging can be performed until the voltage is 2 mA/g or more and 10 mA/g or less, and discharging can be performed at a constant current of 2.5 V and 20 mA/g or more and 100 mA/g or less.
  • an arbitrary voltage for example, 4.6V, 4.65V, 4.7V, 4.75V, or 4.8V
  • constant current discharge can be performed at, for example, 2.5 V and a current value of 20 mA/g or more and 100 mA/g or less.
  • the equipment and conditions for XRD measurements are not particularly limited. For example, it can be measured using the following equipment and conditions.
  • XRD device Bruker AXS, D8 ADVANCE X-ray: CuK ⁇ 1 Output: 40kV, 40mA Divergence angle: Div. Slit, 0.5° Detector: LynxEye Scan method: 2 ⁇ / ⁇ continuous scan Measurement range (2 ⁇ ): 15° or more and 90° or less Step width (2 ⁇ ): 0.01°
  • Setting Counting time 1 second/step Sample table rotation: 15 rpm
  • a standard sample used for adjustment and calibration for example, a standard aluminum oxide sintered plate SRM 1976 from NIST (National Institute of Standards and Technology) can be used.
  • the sample to be measured is a powder, it can be set by placing it on a glass sample holder or by sprinkling the sample on a greased silicone non-reflective plate.
  • the positive electrode can be attached to the substrate with double-sided tape, and the positive electrode active material layer can be set according to the measurement surface required by the apparatus.
  • a filter or the like may be used to make the characteristic X-rays monochromatic, or it may be performed using XRD data analysis software after obtaining an XRD pattern.
  • XRD data analysis software For example, DEFFRAC.
  • EVA XRD data analysis software manufactured by Bruker
  • the software can also be used to remove backgrounds.
  • crystal structure analysis software used for fitting is not particularly limited, but for example, TOPASver. 3 (crystal structure analysis software manufactured by Bruker) can be used.
  • FIG. 15 shows the diffraction profiles of the O3 type crystal structure, the O3' type crystal structure, and the monoclinic O1 (15) type crystal structure when CuK ⁇ 1 is used for X-rays.
  • FIGS. 17A and 17B show all of the above-mentioned XRD patterns. However, the 2 ⁇ range is 18° or more and 21° or less, and the 2 ⁇ range is 42° or more and 46° or less.
  • the pattern of the H1-3 type crystal structure was similarly created from the crystal structure information described in Non-Patent Document 3.
  • the crystal structure patterns of the O3' type and the monoclinic O1 (15) type were estimated from the XRD pattern of the positive electrode active material 100 of one embodiment of the present invention, and were determined using TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker).
  • 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; however, all of the particles are O3' type and/or monoclinic O1 (15) type crystal structure. It may contain other crystal structures, or may be partially amorphous. However, when performing Rietveld analysis on the XRD pattern, the O3' type and/or monoclinic O1 (15) type crystal structure is preferably 50% or more, more preferably 60% or more, More preferably, it is 66% or more. If the 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, the positive electrode active material has sufficiently excellent cycle characteristics. be able to.
  • the O3' type and/or monoclinic O1(15) type crystal structure remains 35% or more when Rietveld analysis is performed. % or more, more preferably 43% or more.
  • the H1-3 type and O1 type crystal structures are 50% or less. Alternatively, it is preferably 34% or less. Or, it is more preferable that it is substantially not observed.
  • each diffraction peak after charging be sharp, that is, have a narrow half-width, for example, a full width at half-maximum.
  • the half width varies depending on the XRD measurement conditions and the 2 ⁇ value even for peaks generated from the same crystal phase.
  • the full width at half maximum is preferably 0.2° or less, more preferably 0.15° or less, and 0.12° or less. More preferred. Note that not all peaks necessarily satisfy this requirement. If some peaks satisfy this requirement, it can be said that the crystallinity of the crystal phase is high. Such high crystallinity contributes to sufficient stabilization of the crystal structure after charging.
  • the crystallite size is small and the peak is 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 as described above.
  • transition metals such as nickel and manganese may be included as additive elements, as long as the influence of the Jahn-Teller effect is small.
  • FIG. 18 shows the results of calculating the a-axis and c-axis lattice constants using XRD when the positive electrode active material 100 according to one embodiment of the present invention has a layered rock salt crystal structure and contains cobalt and nickel. show.
  • FIG. 18A shows the results for the a-axis
  • FIG. 18B shows the results for the c-axis. Note that the XRD pattern used for these calculations is the powder after the synthesis of the positive electrode active material, but before it is incorporated into the positive electrode.
  • the nickel concentration on the horizontal axis indicates the nickel concentration when the sum of the numbers of cobalt and nickel atoms is taken as 100%.
  • FIG. 18C shows the value obtained by dividing the a-axis lattice constant by the c-axis lattice constant (a-axis/c-axis) for the positive electrode active materials whose lattice constant results are shown in FIGS. 18A and 18B.
  • nickel concentration does not necessarily apply to the surface layer portion 100a. That is, in the surface layer portion 100a, the concentration may be higher than the above concentration.
  • the a-axis lattice constant is greater than 2.814 ⁇ 10 ⁇ 10 m and smaller than 2.817 ⁇ 10 ⁇ 10 m
  • the c-axis lattice constant is less than 14.05 ⁇ 10 ⁇ 10 m. It was found that it is preferable that the diameter be larger than 14.07 ⁇ 10 ⁇ 10 m.
  • the state where charging and discharging are not performed may be, for example, the state of the powder before producing the positive electrode of the secondary battery.
  • the value obtained by dividing the a-axis lattice constant by the c-axis lattice constant is It is preferably greater than 0.20000 and smaller than 0.20049.
  • XRD analysis is performed on the layered rock salt crystal structure of the cathode active material 100 in a state where no charging/discharging is performed or in a discharged state, a first peak is observed at 2 ⁇ of 18.50° or more and 19.30° or less. is observed, 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 if monochromatic aluminum K ⁇ rays are used as the X-rays, it is possible to analyze a region from the surface to a depth of about 2 to 8 nm (usually 5 nm or less). Therefore, the concentration of each element can be quantitatively analyzed in a region that is approximately half the depth of the surface layer 100a. Additionally, narrow scan analysis allows the bonding state of elements to be analyzed. Note that the quantitative accuracy of XPS is about ⁇ 1 atomic % in most cases, and the lower limit of detection is about 1 atomic %, although it depends on the element.
  • the concentration of one or more selected additive elements is higher in the surface layer portion 100a than in the bulk 100b.
  • concentration of one or more selected additive elements in the surface layer portion 100a is preferably higher than the average of the entire positive electrode active material 100. Therefore, for example, the concentration of one or more additive elements selected from the surface layer 100a measured by It can be said that it is preferable that the concentration of the added element be higher than the average concentration of the added element of the entire positive electrode active material 100 measured by .
  • the magnesium concentration in at least a portion of the surface layer portion 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 portion of the surface layer portion 100a is higher than the average nickel concentration of the entire positive electrode active material 100.
  • the aluminum concentration of at least a portion of the surface layer portion 100a is higher than the average aluminum concentration of the entire positive electrode active material 100.
  • the fluorine concentration in at least a portion of the surface layer portion 100a is higher than the average fluorine concentration of the entire positive electrode active material 100.
  • the surface and surface layer portion 100a of the positive electrode active material 100 do not contain carbonate, hydroxyl groups, etc. that were chemically adsorbed after the positive electrode active material 100 was produced. It is also assumed that the electrolytic solution, binder, conductive material, or compounds derived from these adhered to the surface of the positive electrode active material 100 are not included. Therefore, when quantifying the elements contained in the positive electrode active material, correction may be made to exclude carbon, hydrogen, excess oxygen, excess fluorine, etc. that can be detected by surface analysis such as XPS. For example, in XPS, it is possible to separate the types of bonds by analysis, and correction may be performed to exclude binder-derived C-F bonds.
  • samples such as the positive electrode active material and the positive electrode active material layer are washed to remove the electrolyte, binder, conductive material, or compounds derived from these that have adhered to the surface of the positive electrode active material. You may do so. At this time, lithium may dissolve into the solvent used for cleaning, but even in that case, the additive elements are difficult to dissolve, so the atomic ratio of the additive elements is not affected.
  • the concentration of the added element may also be compared in terms of its ratio to cobalt.
  • the ratio to cobalt it is possible to reduce the influence of carbonate, etc. chemically adsorbed after the positive electrode active material is produced, and to make a comparison, which is preferable.
  • the ratio Mg/Co of the number of atoms of magnesium and cobalt as determined by XPS analysis is preferably 0.4 or more and 1.5 or less.
  • Mg/Co as determined by ICP-MS analysis is preferably 0.001 or more and 0.06 or less.
  • the positive electrode active material 100 preferably has a higher concentration of lithium and cobalt than each additive element in the surface layer portion 100a in order to sufficiently secure a path for insertion and desorption of lithium.
  • concentration of lithium and cobalt in the surface layer 100a is preferably higher than the concentration of one or more of the additive elements selected from the additive elements contained in the surface layer 100a, which is measured by XPS or the like. can.
  • concentration of cobalt in at least a portion of the surface layer portion 100a measured by XPS or the like is higher than the concentration of magnesium in at least a portion of the surface layer portion 100a measured by XPS or the like.
  • the concentration of lithium is higher than the concentration of magnesium.
  • the concentration of cobalt is higher than the concentration of nickel.
  • the concentration of lithium is higher than the concentration of nickel.
  • the concentration of cobalt is higher than that of aluminum.
  • the concentration of lithium is higher than the concentration of aluminum.
  • the concentration of cobalt is higher than that of fluorine.
  • the concentration of lithium is higher than that of fluorine.
  • the additive element Y including aluminum is widely distributed in a deep region, for example, in a region with a depth of 5 nm or more and 50 nm or less from the surface. Therefore, although additive elements Y such as aluminum are detected in the analysis of the entire cathode active material 100 using ICP-MS, GD-MS, etc., if the concentration of this element is below the detection limit using XPS etc. preferable.
  • the number of magnesium atoms is preferably 0.4 times or more and 1.2 times or less, and 0.65 times or more and 1 times or less, relative to the number of cobalt atoms. More preferably, it is .0 times or less.
  • the number of nickel atoms is preferably 0.15 times or less, more preferably 0.03 times or more and 0.13 times or less 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 times or more and 0.9 times or less, more preferably 0.1 times or more and 1.1 times or less, relative to the number of cobalt atoms.
  • the above range indicates that these additive elements are not attached to a narrow area on the surface of the positive electrode active material 100, but are widely distributed in the surface layer 100a of the positive electrode active material 100 at a preferable concentration. It can be said that it shows.
  • the take-out angle may be, for example, 45°.
  • the take-out angle may be, for example, 45°.
  • it can be measured using the following equipment and conditions.
  • the peak indicating 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 binding energy of lithium fluoride, 685 eV, and the binding energy of magnesium fluoride, 686 eV.
  • the peak indicating the bond energy between magnesium and other elements is preferably 1302 eV or more and less than 1304 eV, and more preferably about 1303 eV. This value is different from the binding energy of magnesium fluoride, 1305 eV, and is close to the binding energy of magnesium oxide.
  • concentration gradient of the additive element can be determined by, for example, exposing a cross section of the positive electrode active material 100 using FIB (Focused Ion Beam) or the like, and then using the cross section by energy dispersive X-ray spectroscopy (EDX) or EPMA (electronic electron beam). It can be evaluated by analysis using probe microanalysis).
  • EDX surface analysis measuring while scanning the area and evaluating the area two-dimensionally. Also, measuring while scanning linearly and evaluating the distribution of atomic concentration within the positive electrode active material is called line analysis. Furthermore, data on a linear region extracted from the EDX surface analysis is sometimes called line analysis. Also, measuring a certain area without scanning it is called point analysis.
  • the concentration of added elements in the surface layer 100a, bulk 100b, near the grain boundaries 101, etc. of the positive electrode active material 100 can be quantitatively analyzed. Further, the concentration distribution and maximum value of the added element can be analyzed by EDX-ray analysis. In addition, analysis in which the sample is sliced into thin sections, such as STEM-EDX, can analyze the concentration distribution in the depth direction from the surface of the positive electrode active material toward the center in a specific region without being affected by the distribution in the depth direction. More suitable.
  • the concentration of each additive element, especially the additive element X, in the surface layer portion 100a is higher than that in the bulk 100b.
  • the magnesium concentration in the surface layer portion 100a is higher than the magnesium concentration in the bulk 100b.
  • the peak of the magnesium concentration in the surface layer 100a preferably exists within a depth of 3 nm from the surface of the positive electrode active material 100 toward the center, and more preferably exists within a depth of 1 nm. Preferably, it is more preferable to exist at a depth of 0.5 nm.
  • the magnesium concentration attenuates to 60% or less of the peak at a depth of 1 nm from the peak top. Further, it is preferable that the attenuation decreases to 30% or less of the peak at a depth of 2 nm from the peak top.
  • the peak of concentration herein refers to the maximum value of concentration.
  • the distribution of fluorine preferably overlaps with the distribution of magnesium.
  • the difference in the depth direction between the peak of fluorine concentration and the peak of magnesium concentration is preferably within 10 nm, more preferably within 3 nm, and even more preferably within 1 nm.
  • the peak of fluorine concentration in the surface layer 100a preferably exists within a depth of 3 nm from the surface of the positive electrode active material 100 toward the center, and more preferably exists within a depth of 1 nm. Preferably, it is more preferable to exist at a depth of 0.5 nm. Further, it is more preferable that the peak of the fluorine concentration be present slightly closer to the surface than the peak of the magnesium concentration, since this increases resistance to hydrofluoric acid. For example, the peak of fluorine concentration is more preferably 0.5 nm or more closer to the surface than the peak of magnesium concentration, and even more preferably 1.5 nm or more closer to the surface.
  • the peak of nickel concentration in the surface layer 100a preferably exists within a depth of 3 nm from the surface of the positive electrode active material 100 toward the center, and preferably within a depth of 1 nm from the surface of the positive electrode active material 100 toward the center. It is more preferable that it exists, and even more preferably that it exists within a depth of 0.5 nm. Further, in the positive electrode active material 100 containing magnesium and nickel, the distribution of nickel preferably overlaps with the distribution of magnesium. For example, the difference in the depth direction between the peak of nickel concentration and the peak of magnesium concentration is preferably within 10 nm, more preferably within 3 nm, and even more preferably within 1 nm.
  • the peak of the concentration of magnesium, nickel, or fluorine is closer to the surface than the peak of the aluminum concentration in the surface layer portion 100a.
  • the peak of aluminum concentration preferably exists at a depth of 0.5 nm or more and 50 nm or less from the surface of the positive electrode active material 100 toward the center, and more preferably exists at a depth of 5 nm or more and 50 nm or less.
  • the ratio of the number of atoms of magnesium Mg and cobalt Co (Mg/Co) at the peak of magnesium concentration is preferably 0.05 or more and 0.6 or less. , more preferably 0.1 or more and 0.4 or less.
  • the ratio of the number of atoms of aluminum Al and cobalt Co (Al/Co) at the peak of the aluminum concentration is preferably 0.05 or more and 0.6 or less, more preferably 0.1 or more and 0.45 or less.
  • the ratio of the number of atoms of nickel Ni and cobalt Co (Ni/Co) at the peak of the nickel concentration is preferably 0 or more and 0.2 or less, more preferably 0.01 or more and 0.1 or less.
  • the ratio of the number of atoms of fluorine F and cobalt Co (F/Co) at the peak of the fluorine concentration is preferably 0 or more and 1.6 or less, more preferably 0.1 or more and 1.4 or less.
  • the surface of the positive electrode active material 100 in the EDX-ray analysis results can be estimated as follows, for example.
  • an element that is uniformly present in the bulk 100b of the positive electrode active material 100 such as oxygen or cobalt
  • the point at which the amount detected in the bulk 100b is 1/2 is defined as the surface.
  • the surface can be estimated using the detected amount of oxygen. Specifically, first, the average value O ave of oxygen concentration is determined from a region where the detected amount of oxygen in the bulk 100b is stable. At this time, if oxygen O bg , which is considered to be due to chemical adsorption or background, is detected in an area that can be clearly judged to be outside the surface, O bg can be subtracted from the measured value to obtain the average value of oxygen concentration O ave. can.
  • the measurement point showing the value of 1/2 of this average value O ave that is, the measurement value closest to 1/2 O ave , can be estimated to be the surface of the positive electrode active material.
  • the surface can also be estimated using the detected amount of cobalt in the same way as above. Alternatively, similar estimation can be made using the sum of detected amounts of multiple transition metals.
  • the detected amounts of transition metals such as cobalt are not easily affected by chemisorption, making them suitable for surface estimation.
  • the ratio of the number of atoms of the additive element A to cobalt Co (A/Co) in the vicinity of the grain boundary 101 is preferably 0.020 or more and 0.50 or less. More preferably, it is 0.025 or more and 0.30 or less. More preferably, it is 0.030 or more and 0.20 or less. Or preferably 0.020 or more and 0.30 or less. Or preferably 0.020 or more and 0.20 or less. Or preferably 0.025 or more and 0.50 or less. Or preferably 0.025 or more and 0.20 or less. Or preferably 0.030 or more and 0.50 or less. Or preferably 0.030 or more and 0.30 or less.
  • the ratio of the number of magnesium and cobalt atoms (Mg/Co) near the grain boundary 101 is 0.020 or more and 0.50.
  • the following are preferred. More preferably, it is 0.025 or more and 0.30 or less. More preferably, it is 0.030 or more and 0.20 or less. Or preferably 0.020 or more and 0.30 or less. Or preferably 0.020 or more and 0.20 or less. Or preferably 0.025 or more and 0.50 or less. Or preferably 0.025 or more and 0.20 or less. Or preferably 0.030 or more and 0.50 or less. Or preferably 0.030 or more and 0.30 or less.
  • the additive element will not adhere to a narrow range on the surface of the positive electrode active material 100, but will preferably be applied to the surface layer 100a of the positive electrode active material 100. This can be said to indicate that the concentration is widely distributed.
  • ⁇ EPMA ⁇ EPMA Electro Probe Microanalysis
  • one or more selected additive elements have a concentration gradient, similar to the EDX analysis results. Further, it is more preferable that the depth of the concentration peak from the surface differs depending on the added element. The preferred range of the concentration peak of each additive element is also the same as in the case of EDX.
  • EPMA analyzes a region from the surface to a depth of about 1 ⁇ m. Therefore, the quantitative value of each element may differ from the measurement results using other analysis methods. For example, when the surface of the positive electrode active material 100 is analyzed by EPMA, the concentration of each additive element present in the surface layer portion 100a may be lower than the result of XPS.
  • the positive electrode active material 100 of one embodiment of the present invention at least a portion of the surface layer portion 100a preferably has a rock salt crystal structure. Therefore, when the positive electrode active material 100 and the positive electrode containing the same are analyzed by Raman spectroscopy, it is preferable that not only the layered rock salt crystal structure but also the cubic crystal structure including the rock salt type is observed.
  • the STEM image and the ultrafine electron beam diffraction pattern described below the STEM image and the ultrafine electron beam diffraction pattern will be different if there is no cobalt substituted at the lithium position with a certain frequency in the depth direction at the time of observation, and cobalt present at the 4-coordination position of oxygen.
  • Raman spectroscopy is an analysis that captures the vibrational mode of bonds such as Co-O, even if the amount of the corresponding Co-O bond is small, it may be possible to observe the wavenumber peak of the corresponding vibrational mode. be. Furthermore, since Raman spectroscopy can measure a surface area of several ⁇ m 2 and a depth of about 1 ⁇ m, it is possible to sensitively capture states that exist only on the particle surface.
  • the integrated intensity of each peak is 470 cm -1 to 490 cm -1 as I1, 580 cm -1 to 600 cm -1 as I2, and 665 cm -1 to 685 cm -1 as I3, the value of I3/I2 is 1% or more. It is preferably 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 in a preferable range.
  • the difference in the lattice constants calculated from these is small. is preferable.
  • 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 or more and 10 nm or less is preferably 0.01 nm or less for the a-axis, and 0.1 nm for the c-axis. It is preferable that it is below. Moreover, it is more preferable that the a-axis is 0.005 nm or less, and the c-axis is more preferably 0.06 nm or less. Further, it is more preferable that the a-axis is 0.004 nm or less, and even more preferable that the c-axis is 0.03 nm or less.
  • the positive electrode active material 100 may have a recess, a crack, a depression, a V-shaped cross section, or the like. These are one type of defects, and when charging and discharging are repeated, cobalt may be eluted, the crystal structure may collapse, the positive electrode active material 100 may be cracked, and oxygen may be eliminated. However, if a buried portion 102 as shown in FIG. 10F exists to bury these, elution of cobalt, etc. can be suppressed. Therefore, the positive electrode active material 100 can have excellent reliability and cycle characteristics.
  • the additive element contained in the positive electrode active material 100 is in excess, there is a risk that insertion and desorption of lithium will be adversely affected. Furthermore, when the positive electrode active material 100 is used in a secondary battery, there is a possibility that an increase in internal resistance, a decrease in charge/discharge capacity, etc. may occur. On the other hand, if it is insufficient, it may not be distributed throughout the surface layer portion 100a, and the effect of suppressing the deterioration of the crystal structure may become insufficient. As described above, it is necessary that the additive element has an appropriate concentration in the positive electrode active material 100, but it is not easy to adjust the concentration.
  • the positive electrode active material 100 has a region where the additive element is unevenly distributed, some of the atoms of the excessive additive element are removed from the bulk 100b of the positive electrode active material 100, and the concentration of the additive element is adjusted to an appropriate concentration in the bulk 100b. can do.
  • This can suppress an increase in internal resistance, a decrease in charge/discharge capacity, etc. when used as a secondary battery.
  • Being able to suppress an increase in internal resistance of a secondary battery is an extremely desirable characteristic, particularly in charging and discharging at a large current, for example, at 400 mA/g or more.
  • the positive electrode active material 100 having a region where the additive element is unevenly distributed it is permissible to mix the additive element in a certain amount of excess during the manufacturing process. Therefore, the production margin is wide, which is preferable.
  • a coating portion may be attached to at least a portion of the surface of the positive electrode active material 100.
  • FIG. 19 shows an example of the positive electrode active material 100 to which the coating portion 104 is attached.
  • a covering portion 104 is provided to cover the surface layer portion 100a. Note that when the surface of the positive electrode active material 100 has an uneven portion, a crack, or an embedded portion 102 illustrated in FIG. It's okay.
  • the covering portion 104 is preferably formed by, for example, depositing decomposition products such as lithium salt and organic electrolyte during charging and discharging.
  • decomposition products such as lithium salt and organic electrolyte
  • having a coating derived from an organic electrolyte on the surface of the positive electrode active material 100 can improve charge-discharge cycle characteristics. Be expected. This is for reasons such as suppressing an increase in impedance on the surface of the positive electrode active material or suppressing elution of cobalt.
  • the covering portion 104 contains carbon, oxygen, and fluorine, for example.
  • the coating portion 104 containing one or more selected from boron, nitrogen, sulfur, and fluorine may be a high-quality coating portion and is therefore preferable. Further, the covering portion 104 does not need to cover all of the positive electrode active material 100. For example, it is sufficient to cover 50% or more of the surface of the positive electrode active material 100, more preferably 70% or more, and even more preferably 90% or more. Fluorine may be adsorbed on the surface of the positive electrode active material 100 in areas where there is no coating.
  • This embodiment can be implemented by appropriately combining at least a part of it with other embodiments described in this specification.
  • lithium cobalt oxide is synthesized, and then an additional element source is mixed and a heat treatment is performed.
  • a method may be used in which lithium cobalt oxide having an additive element is synthesized by mixing a cobalt source, a lithium source, and an additive element source at the same time.
  • heat treatment after mixing the additive element source is important.
  • the heat treatment after mixing the additive element source is sometimes called firing or annealing.
  • a flux is a substance with a melting point lower than that of lithium cobalt oxide, and the substance functions as a flux.
  • fluorine compounds such as lithium fluoride are suitable as the fluxing agent. Addition of the flux lowers the melting point of the additive element source and the lithium cobalt oxide. By lowering the melting point, it becomes easier to distribute the additive element well at a temperature at which cation mixing is less likely to occur.
  • lithium is desorbed from a part of the surface layer 100a of lithium cobalt oxide, so that the distribution of the added elements becomes even better.
  • the initial heating makes it easier to vary the distribution depending on the added element through the following mechanism.
  • lithium is desorbed from a portion of the surface layer portion 100a due to initial heating.
  • this lithium cobalt oxide having the surface layer portion 100a deficient in lithium and additional element sources including a nickel source, an aluminum source, and a magnesium source are mixed and heated.
  • magnesium is a typical divalent element
  • nickel is a transition metal but tends to become a divalent ion. Therefore, a rock salt-type phase containing Mg 2+ , Ni 2+ , and Co 2+ reduced due to lithium deficiency is formed in a part of the surface layer 100a.
  • this phase is formed in a part of the surface layer portion 100a, it may not be clearly visible in an electron microscope image such as STEM or in an electron beam diffraction pattern.
  • nickel tends to form a solid solution when the surface layer 100a is layered rock salt type lithium cobalt oxide and diffuses to the bulk 100b, but when a part of the surface layer 100a is rock salt type, it tends to stay in the surface layer 100a. . Therefore, by performing initial heating, divalent additive elements such as nickel can be easily retained in the surface layer portion 100a. The effect of this initial heating is particularly large on the surface of the positive electrode active material 100 other than the (001) orientation and the surface layer portion 100a thereof.
  • the Me-O distance in rock salt type Ni 0.5 Mg 0.5 O is 0.209 nm
  • the Me-O distance in rock salt type MgO is 0.211 nm.
  • the Me-O distance of spinel type NiAl 2 O 4 is 0.20125 nm
  • the Me-O distance of spinel type MgAl 2 O 4 is 0.20125 nm. It is 202 nm. In both cases, the Me-O distance exceeds 0.2 nm.
  • the bond distance between metals other than lithium and oxygen is shorter than the above.
  • the Al-O distance in layered rock salt type LiAlO 2 is 0.1905 nm (Li-O distance is 0.211 nm).
  • the Co-O distance in layered rock salt type LiCoO 2 is 0.19224 nm (Li-O distance is 0.20916 nm).
  • the ionic radius of six-coordinated aluminum is 0.0535 nm
  • the ionic radius of six-coordinated oxygen is 0.14 nm, and the sum of these is It is 0.1935 nm.
  • the effect of increasing the crystallinity of the layered rock salt type crystal structure of the bulk 100b can also be expected by the initial heating.
  • the positive electrode active material 100 having a monoclinic O1 (15) type crystal structure especially when x in Li x CoO 2 is, for example, 0.15 or more and 0.17 or less this initial heating is required. It is preferable.
  • initial heating does not necessarily have to be performed.
  • the positive electrode active material 100 having an O3' type and/or a monoclinic O1 (15) type can be formed. It may be possible to make one.
  • a method 1 for producing the positive electrode active material 100 that undergoes initial heating will be described with reference to FIGS. 20A to 20C.
  • Step S11 In step S11 shown in FIG. 20A, a lithium source (Li source) and a cobalt source (Co source) are prepared as starting materials for lithium and transition metal materials, respectively.
  • a lithium source Li source
  • a cobalt source Co 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 may be used.
  • cobalt source it is preferable to use a compound containing cobalt, and for example, cobalt oxide (typically tricobalt tetroxide), cobalt hydroxide (typically cobalt hydroxide), etc. can be used.
  • cobalt oxide typically tricobalt tetroxide
  • cobalt hydroxide typically cobalt hydroxide
  • the cobalt source preferably has a high purity, for example, the purity is 3N (99.9%) or higher, preferably 4N (99.99%) or higher, more preferably 4N5 (99.995%) or higher, and even more preferably 5N (99%) or higher. .999%) or more is preferably used.
  • the purity is 3N (99.9%) or higher, preferably 4N (99.99%) or higher, more preferably 4N5 (99.995%) or higher, and even more preferably 5N (99%) or higher. .999%) or more is preferably used.
  • impurities in the positive electrode active material can be controlled. As a result, the capacity of the secondary battery increases and/or the reliability of the secondary battery improves.
  • the cobalt source has high crystallinity, for example, it may have single crystal grains.
  • TEM transmission electron microscope
  • STEM scanning transmission electron microscope
  • HAADF-STEM high angle scattering annular dark field scanning transmission electron microscope
  • ABF-STEM annular bright field scanning electron microscope
  • Evaluations include scanning transmission electron microscopy) images, X-ray diffraction (XRD), electron diffraction, neutron diffraction, and the like. Note that the above method for evaluating crystallinity can be applied not only to cobalt sources but also to evaluating other crystallinities.
  • a lithium source and a cobalt source are ground and mixed to produce a mixed material. Grinding and mixing can be done dry or wet. The wet method is preferable because it can be crushed into smaller pieces. If using a wet method, prepare a solvent.
  • the solvent ketones such as acetone, alcohols such as ethanol and isopropanol, ethers, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. can be used. It is more preferable to use an aprotic solvent that hardly reacts with lithium. In this embodiment, dehydrated acetone with a purity of 99.5% or more is used.
  • dehydrated acetone of the purity described above possible impurities can be reduced.
  • a ball mill, bead mill, or the like can be used as a means for grinding and mixing.
  • aluminum oxide balls or zirconium oxide balls may be used as the grinding media.
  • Zirconium oxide balls are preferable because they emit fewer impurities.
  • the peripheral speed is preferably 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 838 mm/s (rotation speed 400 rpm, ball mill diameter 40 mm).
  • step S13 shown in FIG. 20A the mixed material is heated.
  • the heating is preferably performed at a temperature of 800°C or more and 1100°C or less, more preferably 900°C or more and 1000°C or less, and even more preferably about 950°C. If the temperature is too low, the lithium source and cobalt source may be insufficiently decomposed and melted. On the other hand, if the temperature is too high, defects may occur due to evaporation of lithium from the lithium source and/or excessive reduction of cobalt. For example, cobalt changes from trivalent to divalent, which may induce oxygen defects.
  • the heating time is preferably 1 hour or more and 100 hours or less, and more preferably 2 hours or more and 20 hours or less.
  • the temperature increase rate depends on the temperature reached by the heating temperature, but is preferably 80°C/h or more and 250°C/h or less. For example, when heating at 1000°C for 10 hours, the temperature increase rate is preferably 200°C/h.
  • Heating is preferably carried out in an atmosphere with little water such as dry air, for example an atmosphere with a dew point of -50°C or less, more preferably -80°C or less. In this embodiment, heating is performed in an atmosphere with a dew point of -93°C. Further, in order to suppress impurities that may be mixed into the material, the concentration of impurities such as CH 4 , CO, CO 2 , H 2 , etc. in the heating atmosphere is preferably set to 5 ppb (parts per billion) or less.
  • An atmosphere containing oxygen is preferable as the heating atmosphere.
  • the heating atmosphere there is a method of continuously introducing dry air into the reaction chamber.
  • the flow rate of dry air is preferably 10 L/min.
  • the method in which oxygen is continuously introduced into the reaction chamber and the oxygen flows within the reaction chamber is called flow.
  • a method without flow may be used.
  • a method may be used in which the reaction chamber is depressurized and then filled with oxygen (also referred to as purging) to prevent the oxygen from entering or exiting the reaction chamber.
  • the reaction chamber may be depressurized to -970 hPa and then filled with oxygen to 50 hPa.
  • Cooling after heating may be allowed to cool naturally, but it is preferable that the cooling time from the specified temperature to room temperature falls within 10 hours or more and 50 hours or less, for example, 80 ° C / h or more and 250 ° C / h or less, preferably 180 ° C / h.
  • the temperature is more preferably 210° C./h or less.
  • cooling to room temperature is not necessarily required, and cooling to a temperature permitted by the next step is sufficient.
  • Heating in this step may be performed using a rotary kiln or a roller hearth kiln. Heating with a rotary kiln can be carried out while stirring in either a continuous type or a batch type.
  • the crucible used during heating is preferably an aluminum oxide crucible.
  • An aluminum oxide crucible is a material that does not easily release impurities. In this embodiment, an aluminum oxide crucible with a purity of 99.9% is used. It is preferable to heat the crucible with a lid on. Volatilization or sublimation of the material can be prevented. It is sufficient to cover the crucible as long as it can prevent volatilization or sublimation of the material from the time of temperature rise to the time of temperature fall in this step, and the crucible does not necessarily need to be sealed with a lid. For example, by filling the reaction chamber with oxygen as described above, it is also possible to carry out this step without sealing the crucible.
  • a used crucible refers to one in which a material containing lithium, a transition metal M, and/or an additive element is charged and heated twice or less.
  • a used crucible is defined as one that has undergone the step of charging and heating materials containing lithium, transition metal M, and/or additive elements three or more times. This is because if a new crucible is used, there is a risk that some of the material, including lithium fluoride, will be absorbed, diffused, moved and/or attached to the sheath during heating.
  • step S13 After heating is completed, it may be crushed and further sieved if necessary. When recovering the heated material, it may be transferred from the crucible to the mortar and then recovered. Further, it is preferable to use an aluminum oxide mortar as the mortar.
  • Aluminum oxide mortar is a material that does not easily release impurities. Specifically, an aluminum oxide mortar with a purity of 90% or more, preferably 99% or more is used. Note that the same heating conditions as in step S13 can be applied to heating steps other than step S13, which will be described later.
  • lithium cobalt oxide (LiCoO 2 ) shown in step S14 shown in FIG. 20A can be synthesized.
  • the median diameter (D50) is used as the particle size of lithium cobalt oxide, in order to obtain the positive electrode active material 100 having a relatively small median diameter (D50), lithium cobalt oxide is preferably pulverized.
  • the composite oxide may also be produced by a coprecipitation method.
  • the composite oxide may be produced by a hydrothermal method.
  • step S15 shown in FIG. 20A lithium cobalt oxide is heated. Since the lithium cobalt oxide is first heated, the heating in step S15 may be referred to as initial heating. Alternatively, since it is heated before step S20 described below, it may be called preheating or pretreatment. The crucible and/or lid used in this step are the same as those in step S13. Although the following effects are expected from the initial heating, the initial heating is not essential to obtain the positive electrode active material that is one embodiment of the present invention.
  • lithium is desorbed from a part of the surface layer portion 100a of lithium cobalt oxide as described above. Moreover, the effect of increasing the crystallinity of the bulk 100b can be expected. Further, impurities may be mixed in the lithium source and/or cobalt source prepared in step S11 and the like. It is possible to reduce impurities from the lithium cobalt oxide completed in step S14 by initial heating.
  • initial heating has the effect of smoothing the surface of lithium cobalt oxide.
  • a smooth surface means that there are few irregularities, that the composite oxide is rounded overall, and that the corners are rounded. Furthermore, a state in which there are few foreign substances attached to the surface is called smooth. Foreign matter is considered to be a cause of unevenness, and it is preferable that it does not adhere to the surface.
  • the heating conditions can be selected from the heating conditions explained in step S13. Adding to the heating conditions, the heating temperature in this step is preferably lower than the temperature in step S13 in order to maintain the crystal structure of the composite oxide. Further, the heating time in this step is preferably shorter than the time in step S13 in order to maintain the crystal structure of the composite oxide. For example, heating is preferably performed at a temperature of 700° C. or more and 1000° C. or less for 2 hours or more and 20 hours or less.
  • the effect of increasing the crystallinity of the bulk 100b is, for example, the effect of alleviating distortion, displacement, etc. resulting from the shrinkage difference of the lithium cobalt oxide produced in step S13.
  • a temperature difference may occur between the surface and the inside of the lithium cobalt oxide due to the heating in step S13. Temperature differences can induce differential shrinkage. It is also thought that the temperature difference causes a difference in shrinkage due to the difference in fluidity between the surface and the inside.
  • the energy associated with differential shrinkage imparts differential internal stress to lithium cobalt oxide.
  • the difference in internal stress is also called strain, and the energy is sometimes called strain energy. It is considered that the internal stress is removed by the initial heating in step S15, and in other words, the strain energy is homogenized by the initial heating in step S15. When the strain energy is homogenized, the strain in lithium cobalt oxide is relaxed. As a result, the surface of lithium cobalt oxide may become smooth. It is also said that the surface has been improved. In other words, it is considered that after step S15, the shrinkage difference that occurs in the lithium cobalt oxide is alleviated, and the surface of the composite oxide becomes smooth.
  • the difference in shrinkage may cause microscopic shifts in the lithium cobalt oxide, such as crystal shifts.
  • This step may also be carried out in order to reduce the deviation. Through this step, it is possible to equalize the deviation of the composite oxide. If the misalignment is made uniform, the surface of the composite oxide may become smooth. It is also said that crystal grains have been aligned. In other words, it is considered that after step S15, the displacement of crystals, etc. that occurs in the composite oxide is alleviated, and the surface of the composite oxide becomes smooth.
  • lithium cobalt oxide with a smooth surface is used as a positive electrode active material, there will be less deterioration during charging and discharging as a secondary battery, and cracking of the positive electrode active material can be prevented.
  • lithium cobalt oxide synthesized in advance may be used in step S14.
  • steps S11 to S13 can be omitted.
  • step S15 By performing step S15 on lithium cobalt oxide synthesized in advance, lithium cobalt oxide with a smooth surface can be obtained.
  • step S20 it is preferable to add additive element A to the lithium cobalt oxide that has undergone initial heating.
  • the additive element A can be added evenly. Therefore, it is preferable to add the additive element A after the initial heating.
  • the step of adding additive element A will be explained using FIG. 20B and FIG. 20C.
  • step S21 shown in FIG. 20B an additive element A source (A source) to be added to lithium cobalt oxide is prepared.
  • a lithium source may be prepared together with the additive element A source.
  • the additive elements described in the previous embodiment such as the additive element X and the additive element Y, can be used.
  • one or more selected from magnesium, fluorine, nickel, aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, and boron can be used.
  • one or two selected from bromine and beryllium can also be used.
  • the additive element source can be called a magnesium source.
  • magnesium source magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, or the like can be used. Further, a plurality of the above-mentioned magnesium sources may be used.
  • the additive element source can be called a fluorine source.
  • the fluorine source include lithium fluoride (LiF), magnesium fluoride (MgF 2 ), aluminum fluoride (AlF 3 ), titanium fluoride (TiF 4 ), cobalt fluoride (CoF 2 , CoF 3 ), and fluorine.
  • lithium fluoride is preferable because it has a relatively low melting point of 848° C. and is easily melted in the heating step described below.
  • Magnesium fluoride can be used both as a fluorine source and as a magnesium source. Lithium fluoride can also be used as a lithium source. Another lithium source used in step S21 is lithium carbonate.
  • the fluorine source may be a gas, such as fluorine (F 2 ), fluorocarbon, sulfur fluoride, or fluorinated oxygen (OF 2 , O 2 F 2 , O 3 F 2 , O 4 F 2 , O 5 F 2 , O 6 F 2 , O 2 F) or the like may be used and mixed in the atmosphere in the heating step described later. Further, a plurality of the above-mentioned fluorine sources may be used.
  • lithium fluoride (LiF) is prepared as a fluorine source
  • magnesium fluoride (MgF 2 ) is prepared as a fluorine source and a magnesium source.
  • LiF lithium fluoride
  • MgF 2 magnesium fluoride
  • the effect of lowering the melting point is maximized.
  • the amount of lithium fluoride increases, there is a concern that the amount of lithium will be too much and the cycle characteristics will deteriorate.
  • the term “near” means a value greater than 0.9 times and less than 1.1 times that value.
  • step S22 shown in FIG. 20B the magnesium source and the fluorine source are ground and mixed. This step can be carried out by selecting from the pulverization and mixing conditions described in step S12.
  • step S23 shown in FIG. 20B the materials crushed and mixed above can be recovered to obtain an additive element A source (A source).
  • a source an additive element A source
  • the additive element A source shown in step S23 has a plurality of starting materials and can be called a mixture.
  • the particle size of the above mixture preferably has a median diameter (D50) of 600 nm or more and 10 ⁇ m or less, more preferably 1 ⁇ m or more and 5 ⁇ m or less. Even when one type of material is used as the additive element source, the median diameter (D50) is preferably 600 nm or more and 10 ⁇ m or less, more preferably 1 ⁇ m or more and 5 ⁇ m or less.
  • Step S21 A process different from that in FIG. 20B will be explained using FIG. 20C.
  • step S21 shown in FIG. 20C four types of additive element sources to be added to lithium cobalt oxide are prepared. That is, FIG. 20C is different from FIG. 20B in the type of additive element source.
  • a lithium source may be prepared together with the additive element source.
  • a magnesium source (Mg source), a fluorine source (F source), a nickel source (Ni source), and an aluminum source (Al source) are prepared as four types of additional element sources. Note that the magnesium source and the fluorine source can be selected from the compounds described in FIG. 20B.
  • the nickel source nickel oxide, nickel hydroxide, etc. can be used.
  • the aluminum source aluminum oxide, aluminum hydroxide, etc. can be used.
  • Step S22 and Step S23 are similar to the steps described in FIG. 20B.
  • step S31 shown in FIG. 20A lithium cobalt oxide and an additive element A source (A source) are mixed.
  • the mixing in step S31 is preferably performed under milder conditions than the mixing in step S12 so as not to destroy the shape of the lithium cobalt oxide particles.
  • the rotational speed is lower or the time is shorter than the mixing in step S12.
  • the dry method has milder conditions than the wet method.
  • a ball mill, a bead mill, etc. can be used for mixing.
  • zirconium oxide balls it is preferable to use, for example, zirconium oxide balls as the media.
  • dry mixing is performed at 150 rpm for 1 hour using a ball mill using zirconium oxide balls with a diameter of 1 mm. Further, the mixing is performed in a dry room with a dew point of -100°C or more and -10°C or less.
  • Step S32 of FIG. 20A the materials mixed above are collected to obtain a mixture 903. During recovery, sieving may be performed after crushing if necessary.
  • FIGS. 20A to 20C describe a manufacturing method in which additive elements are added after initial heating
  • the present invention is not limited to the above method.
  • the additive element may be added at other timings or may be added multiple times. The timing may be changed depending on the added element.
  • the additive element may be added to the lithium source and the cobalt source at the stage of step S11, that is, at the stage of the starting material of the composite oxide.
  • FIG. 21A shows a flow for adding a magnesium source to a lithium source and a cobalt source.
  • FIG. 21B shows a flow for adding a magnesium source and an aluminum source to a lithium source and a cobalt source.
  • FIG. 21C shows a flow for adding a magnesium source and a nickel source to a lithium source and a cobalt source.
  • the additive element sources shown in FIGS. 21A to 21C are exemplary.
  • step S12 lithium cobalt oxide having additive elements can be obtained. It is also possible to control the distribution of additive elements according to the timing of adding the additive elements.
  • the additive elements added as shown in FIGS. 21A to 21C are expected to be located inside the positive electrode active material 100. Further, in the case of the flow shown in FIGS. 21A to 21C, it is not necessary to separate the steps S11 to S14 and the steps S21 to S23, so it can be said that the method is simple and highly productive. Of course, even in the flow shown in FIGS. 21A to 21C, a new additive element may be added in step S20.
  • lithium cobalt oxide having some of the additive elements in advance may be used.
  • steps S11 to S14 and a part of step S20 can be omitted. It can be said that this is a simple and highly productive method.
  • a magnesium source and a fluorine source or a magnesium source, a fluorine source, a nickel source, and an aluminum source are added as in step S20. may be added.
  • step S33 shown in FIG. 20A the mixture 903 is heated.
  • the heating conditions can be selected from the heating conditions explained in step S13.
  • the heating time is preferably 2 hours or more.
  • the pressure inside the furnace may exceed atmospheric pressure in order to increase the oxygen partial pressure in the heating atmosphere. This is because if the oxygen partial pressure in the heating atmosphere is insufficient, cobalt and the like are reduced, and lithium cobalt oxide and the like may not be able to maintain a layered rock salt crystal structure.
  • the lower limit of the heating temperature in step S33 needs to be equal to or higher than the temperature at which the reaction between lithium cobalt oxide and the additive element source progresses.
  • the temperature at which the reaction proceeds may be any temperature at which interdiffusion of the elements of the lithium cobalt oxide and the additional element source occurs, and may be lower than the melting temperature of these materials. This will be explained using an oxide as an example, and it is known that solid phase diffusion occurs from 0.757 times the melting temperature T m (Tammann temperature T d ). Therefore, the heating temperature in step S33 may be 650° C. or higher.
  • the temperature is higher than the temperature at which one or more of the materials selected from the mixture 903 melts, the reaction will more easily proceed.
  • the eutectic point of LiF and MgF 2 is around 742°C, so the lower limit of the heating temperature in step S33 is preferably 742°C or higher.
  • a higher heating temperature is preferable because the reaction progresses more easily, heating time is shorter, and productivity is higher.
  • the upper limit of the heating temperature is lower than the decomposition temperature of lithium cobalt oxide (1130°C). At temperatures near the decomposition temperature, there is concern that lithium cobalt oxide will decompose, albeit in a small amount. Therefore, the temperature is more preferably 1000°C or lower, even more preferably 950°C or lower, and even more preferably 900°C or lower.
  • the heating temperature in step S33 is preferably 650°C or more and 1130°C or less, more preferably 650°C or more and 1000°C or less, even more preferably 650°C or more and 950°C or less, and even more preferably 650°C or more and 900°C or less.
  • the temperature is preferably 742°C or more and 1130°C or less, more preferably 742°C or more and 1000°C or less, even more preferably 742°C or more and 950°C or less, and even more preferably 742°C or more and 900°C or less.
  • the temperature is preferably 800°C or more and 1100°C or less, 830°C or more and 1130°C or less, more preferably 830°C or more and 1000°C or less, even more preferably 830°C or more and 950°C or less, and even more preferably 830°C or more and 900°C or less.
  • the heating temperature in step S33 is preferably lower than that in step S13.
  • a heating furnace 220 shown in FIG. 24 includes a heating furnace interior space 202, a hot plate 204, a pressure gauge 221, a heater section 206, and a heat insulating material 208. More preferably, a container 216 corresponding to a crucible or a pod is heated with a lid 218 on. With this configuration, an atmosphere containing fluoride can be created in the space 219 formed by the container 216 and the lid 218. During heating, if the concentration of gasified fluoride in the space 219 is kept constant or maintained by covering it so that it does not decrease, fluorine and magnesium can be contained near the particle surface.
  • the space 219 has a smaller volume than the heating furnace interior space 202, a small amount of fluoride evaporates, making it possible to create an atmosphere containing fluoride. That is, the reaction system can be made into an atmosphere containing fluoride without significantly reducing the amount of fluoride contained in the mixture 903. Therefore, LiMO 2 can be generated efficiently. Further, by using the lid 218, the mixture 903 can be heated easily and inexpensively in an atmosphere containing fluoride.
  • a step of making the heating furnace space 202 an atmosphere containing oxygen and a step of installing the container 216 containing the mixture 903 in the heating furnace space 202 are performed before heating in the heating furnace space 202.
  • the mixture 903 can be heated in an atmosphere containing oxygen and fluoride.
  • heating is performed while gas is flowing (flow).
  • Gas can be introduced from the lower surface of the heating furnace interior space 202 and exhausted to the upper surface.
  • the heating furnace interior space 202 can be sealed to be a closed space so that gas is not carried to the outside (purge).
  • an oxygen-containing atmosphere in the heating furnace interior space 202 there are no particular restrictions on the method of creating an oxygen-containing atmosphere in the heating furnace interior space 202, but one example is a method in which a gas containing oxygen, such as oxygen gas or dry air, is introduced after the heating furnace interior space 202 is exhausted. Alternatively, there may be a method in which a gas containing oxygen, such as dry air, is flowed in for a certain period of time. Among these, it is preferable to introduce oxygen gas (oxygen replacement) after exhausting the space 202 in the heating furnace. Note that the atmosphere in the heating furnace interior space 202 may be regarded as an atmosphere containing oxygen.
  • fluoride and the like that have adhered to the inner walls of the container 216 and the lid 218 can be blown off again by heating and adhered to the mixture 903.
  • Heating may be performed using a heating mechanism provided in the heating furnace 220.
  • the heating in step S31 is performed while controlling the pressure inside the furnace using the pressure gauge 221.
  • the inside of the furnace is preferably at atmospheric pressure or pressurized.
  • the surface of lithium cobalt oxide melts when exposed to pressurized conditions. That is, the surface of lithium cobalt oxide heated together with LiF and MgF 2 can be melted by applying pressure.
  • the cooling after heating in step S33 above may be allowed to cool naturally, but it is preferable that the temperature drop time from the specified temperature to room temperature falls within 10 hours or more and 50 hours or less, for example, the temperature drop rate (hereinafter also referred to as cooling rate) is 80 ° C. /h or more and 250°C/h or less, more preferably 180°C/h or more and 210°C/h or less. It is preferable that the cooling rate in this step S33 is faster than that in step S13. A fast cooling rate is called rapid cooling. By performing rapid cooling after the above-mentioned melting, a shell can be appropriately produced. Specifically, it becomes possible to produce a narrow shell. Note that the temperature at the end of the cooling process does not necessarily have to be room temperature, and it is sufficient if the temperature is cooled to a temperature that is allowed by the next step.
  • the lid can prevent the material from volatilizing or sublimating. Therefore, it is only necessary to prevent volatilization or sublimation of the material from the time of temperature rise to the time of temperature fall in this step, and the crucible does not necessarily need to be sealed with a lid. For example, by filling the reaction chamber in which the crucible is placed with oxygen, it is also possible to carry out this step without sealing the crucible.
  • a positive electrode active material containing an appropriate amount of fluorine or a fluorine compound is preferable because it can suppress heat generation and smoke generation even when an internal short circuit occurs.
  • some materials for example, LiF, which is a fluorine source, may function as a flux.
  • the heating temperature can be lowered to below the decomposition temperature of lithium cobalt oxide, for example, from 742°C to 950°C, and additive elements such as magnesium are distributed in the surface layer, creating a positive electrode active material with good characteristics. can.
  • LiF has a lower specific gravity than oxygen in a gas state
  • LiF will volatilize due to heating, and if it volatilizes, LiF in the mixture 903 will decrease. This weakens its function as a flux. Therefore, it is necessary to heat LiF while suppressing its volatilization.
  • LiF is not used as a fluorine source
  • Li on the surface of LiCoO 2 and F of the fluorine source react to generate LiF and volatilize. Therefore, even if a fluorine compound having a higher melting point than LiF is used, it is necessary to suppress volatilization in the same way.
  • the mixture 903 in an atmosphere containing LiF, that is, to heat the mixture 903 in a state where the partial pressure of LiF in the heating furnace is high.
  • Such heating can suppress volatilization of LiF in the mixture 903. It is also recommended to cover the crucible in order to suppress volatilization of LiF.
  • the heating in this step is preferably performed so that the particles of the mixture 903 do not stick to each other. If mixture 903 particles stick to each other during heating, the contact area with oxygen in the atmosphere will be reduced, and the diffusion path of additive elements (e.g. fluorine) will be inhibited. ) distribution may deteriorate. In order to promote the reaction with oxygen in the atmosphere, it is not necessary to seal the crucible with a lid.
  • additive elements e.g. fluorine
  • the additive element for example, fluorine
  • a positive electrode active material that is smooth and has few irregularities can be obtained. Therefore, in order for the surface to remain smooth or to become even smoother after the heating in step S15 in this process, it is better that the particles of the mixture 903 do not stick to each other.
  • the flow rate of the atmosphere containing oxygen in the kiln it is preferable to control the flow rate of the atmosphere containing oxygen in the kiln. For example, it is preferable to reduce the flow rate of the atmosphere containing oxygen, to purge the atmosphere first, and to not allow the atmosphere to flow after introducing the oxygen atmosphere into the kiln. Flowing oxygen may cause the fluorine source to evaporate, which is not preferable for maintaining surface smoothness.
  • the mixture 903 can be heated in an atmosphere containing LiF by placing a lid on the container containing the mixture 903, for example. This is similar to the case of putting a lid on a crucible.
  • heating time varies depending on conditions such as the heating temperature, the size of the lithium cobalt oxide in step S14, and the composition. If the lithium cobalt oxide is small, lower temperatures or shorter times may be more preferred than if it is larger.
  • the heating temperature is preferably, for example, 650° C. or higher and 950° C. or lower.
  • the heating time is preferably 3 hours or more and 60 hours or less, more preferably 10 hours or more and 30 hours or less, and even more preferably about 20 hours.
  • the time for cooling down after heating is preferably 10 hours or more and 50 hours or less, for example.
  • the heating temperature is preferably, for example, 650° C. or higher and 950° C. or lower.
  • the heating time is preferably 1 hour or more and 10 hours or less, and more preferably about 5 hours. Note that the time for cooling down after heating is preferably 10 hours or more and 50 hours or less, for example.
  • step S34 shown in FIG. 20A the heated material is collected and crushed if necessary to obtain the positive electrode active material 100. At this time, it is preferable to further sieve the collected particles.
  • the positive electrode active material 100 of one embodiment of the present invention can be manufactured.
  • the positive electrode active material of one embodiment of the present invention has a smooth surface.
  • Method 2 for manufacturing a positive electrode active material which is one embodiment of the present invention and is different from method 1 for manufacturing a positive electrode active material, will be described with reference to FIGS. 22 to 23C.
  • Manufacturing method 2 of the positive electrode active material differs from manufacturing method 1 mainly in the number of times of addition of additive elements and the mixing method. For other descriptions, the description of production method 1 can be referred to.
  • steps S11 to S15 are performed in the same manner as in FIG. 20A to prepare lithium cobalt oxide that has undergone initial heating.
  • step S20a it is preferable to add additive element A1 to the lithium cobalt oxide that has undergone initial heating.
  • a first additive element source is prepared.
  • the first additive element source can be selected from the additive elements A described in step S21 shown in FIG. 20B.
  • the additive element A1 one or more selected from magnesium, fluorine, and calcium can be suitably used.
  • FIG. 23A illustrates a case where a magnesium source (Mg source) and a fluorine source (F source) are used as the first additive element sources.
  • Steps S21 to S23 shown in FIG. 23A can be performed under the same conditions as steps S21 to S23 shown in FIG. 20B.
  • an additive element source (A1 source) can be obtained in step S23.
  • steps S31 to S33 shown in FIG. 22 can be performed in the same steps as steps S31 to S33 shown in FIG. 20A.
  • Step S34a Next, the material heated in step S33 is recovered, and lithium cobalt oxide having the additive element A1 is produced. It is also referred to as a second composite oxide to distinguish it from the composite oxide in step S14.
  • step S40 In step S40 shown in FIG. 22, an additive element A2 is added. This will be explained with reference to FIGS. 23B and 23C as well.
  • a second additive element source is prepared.
  • the second additive element source can be selected from among the additive elements A described in step S21 shown in FIG. 20B.
  • the additive element A2 one or more selected from nickel, titanium, boron, zirconium, and aluminum can be suitably used.
  • FIG. 23B illustrates a case where a nickel source (Ni source) and an aluminum source (Al source) are used as the second additive element source.
  • Steps S41 to S43 shown in FIG. 23B can be performed under the same conditions as steps S21 to S23 shown in FIG. 20B.
  • an additive element source (A2 source) can be obtained in step S43.
  • FIG. 23C shows a modification of the steps described using FIG. 23B.
  • step S41 shown in FIG. 23C a nickel source (Ni source) and an aluminum source (Al source) are prepared, and in step S42a, they are each pulverized independently.
  • step S43 a plurality of second additive element sources (A2 sources) are prepared.
  • the step in FIG. 23C differs from that in FIG. 23B in that the added element is independently pulverized in step S42a.
  • steps S51 to S53 shown in FIG. 22 can be performed under the same conditions as steps S31 to S34 shown in FIG. 20A.
  • the conditions for step S53 regarding the heating process may be lower temperature and shorter time than step S33.
  • step S54 the positive electrode active material 100 of one embodiment of the present invention can be manufactured.
  • the positive electrode active material of one embodiment of the present invention has a smooth surface.
  • the additive elements to lithium cobalt oxide are introduced separately into additive element A1 and additive element A2.
  • the profile of each additive element in the depth direction can be changed. For example, it is also possible to profile the additive element A1 so that it has a higher concentration in the surface layer than in the inside, and to profile the additive element A2 so that it has a higher concentration inside than in the surface layer.
  • the initial heating shown in this embodiment mode is performed on lithium cobalt oxide. Therefore, the conditions for the initial heating are preferably lower than the heating temperature for obtaining lithium cobalt oxide and shorter than the heating time for obtaining lithium cobalt oxide.
  • the step of adding additional elements to lithium cobalt oxide is preferably performed after initial heating. The addition step can be divided into two or more steps. It is preferable to follow this process order because the smoothness of the surface obtained by the initial heating is maintained.
  • a positive electrode active material 100 with a smooth surface may be more resistant to physical destruction due to pressure or the like than a positive electrode active material with a smooth surface.
  • the positive electrode active material 100 is less likely to be destroyed in a test involving pressurization such as a nail penetration test, which may result in increased safety.
  • This embodiment can be implemented by appropriately combining at least a part of it with other embodiments described in this specification.
  • FIG. 25A shows an example of a wearable device.
  • Wearable devices use secondary batteries as a power source.
  • wearable devices that can be charged wirelessly in addition to wired charging with exposed connectors are being developed to improve splash-proof, water-resistant, and dust-proof performance when used in daily life or outdoors. desired.
  • a secondary battery which is one embodiment of the present invention, can be mounted on a glasses-type device 4000 as shown in FIG. 25A.
  • Glasses-type device 4000 includes a frame 4000a and a display portion 4000b.
  • the eyeglass-type device 4000 can be lightweight, have good weight balance, and can be used for a long time.
  • a secondary battery which is one embodiment of the present invention, a configuration that can save space due to downsizing of the housing can be realized.
  • a secondary battery which is one embodiment of the present invention, can be mounted on the headset type device 4001.
  • the headset type device 4001 includes at least a microphone section 4001a, a flexible pipe 4001b, and an earphone section 4001c.
  • a secondary battery can be provided within the flexible pipe 4001b and/or within the earphone portion 4001c.
  • a secondary battery which is one embodiment of the present invention, can be mounted on the device 4002 that can be directly attached to the body.
  • a secondary battery 4002b can be provided in a thin housing 4002a of the device 4002.
  • a secondary battery which is one embodiment of the present invention, can be mounted on the device 4003 that can be attached to clothing.
  • a secondary battery 4003b can be provided in a thin housing 4003a of the device 4003.
  • a secondary battery which is one embodiment of the present invention, can be mounted on the belt-type device 4006.
  • the belt-type device 4006 includes a belt portion 4006a and a wireless power receiving portion 4006b, and a secondary battery can be mounted inside the belt portion 4006a.
  • a secondary battery which is one embodiment of the present invention, a configuration that can save space due to downsizing of the housing can be realized.
  • a secondary battery which is one embodiment of the present invention, can be mounted on the wristwatch type device 4005.
  • the wristwatch type device 4005 has a display portion 4005a and a belt portion 4005b, and a secondary battery can be provided in the display portion 4005a or the belt portion 4005b.
  • a secondary battery which is one embodiment of the present invention, a configuration that can save space due to downsizing of the housing can be realized.
  • the display section 4005a can display not only the time but also various information such as incoming mail and telephone calls.
  • the wristwatch-type device 4005 is a wearable device that is worn directly around the arm, it may be equipped with a sensor that measures the user's pulse, blood pressure, and the like. Data on the amount of exercise and health of the user can be accumulated to manage the user's health.
  • FIG. 25B shows a perspective view of the wristwatch type device 4005 removed from the wrist.
  • FIG. 25C shows a state in which a secondary battery 913 is built inside.
  • Secondary battery 913 is the secondary battery shown in Embodiment 4.
  • the secondary battery 913 is provided at a position overlapping the display portion 4005a, and is small and lightweight.
  • FIG. 25D shows an example of wireless earphones. Although a wireless earphone having a pair of main bodies 4100a and 4100b is illustrated here, the pair does not necessarily have to be a pair.
  • the main bodies 4100a and 4100b have a driver unit 4101, an antenna 4102, and a secondary battery 4103. It may also include a display section 4104. Further, it is preferable to have a board on which a circuit such as a wireless IC is mounted, a charging terminal, and the like. It may also have a microphone.
  • the case 4110 includes a secondary battery 4111. Further, it is preferable to have 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 section, buttons, etc.
  • the main bodies 4100a and 4100b can wirelessly communicate with other electronic devices such as smartphones. This allows the main bodies 4100a and 4100b to reproduce sound data and the like sent from other electronic devices. Furthermore, if the main bodies 4100a and 4100b have microphones, the sound acquired by the microphones can be sent to another electronic device, and the sound data processed by the electronic device can be sent again to the main bodies 4100a and 4100b for playback. . This allows it to be used, for example, as a translator.
  • the secondary battery 4111 included in the case 4110 can charge the secondary battery 4103 included in the main body 4100a.
  • the coin type secondary battery, the cylindrical secondary battery, etc. of the previous embodiment can be used.
  • a secondary battery using the positive electrode active material 100 obtained in Embodiment 1 as a positive electrode has a high energy density, and by using it for the secondary battery 4103 and the secondary battery 4111, it can save space as the wireless earphone becomes smaller. It is possible to realize a configuration that can accommodate.
  • FIG. 26A shows an example of a cleaning robot.
  • the cleaning robot 6300 includes a display portion 6302 placed on the top surface of a housing 6301, a plurality of cameras 6303 placed on the side, a brush 6304, an operation button 6305, a secondary battery 6306, various sensors, and the like.
  • the cleaning robot 6300 is equipped with tires, a suction port, and the like.
  • the cleaning robot 6300 is self-propelled, can detect dirt 6310, and can suck the dirt from a suction port provided on the bottom surface.
  • the cleaning robot 6300 can analyze the image taken by the camera 6303 and determine the presence or absence of obstacles such as walls, furniture, or steps. Furthermore, if an object such as wiring that is likely to become entangled with the brush 6304 is detected through image analysis, the rotation of the brush 6304 can be stopped.
  • the cleaning robot 6300 includes therein a secondary battery 6306 according to one embodiment of the present invention, and a semiconductor device or an electronic component. 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 a long operating time and high reliability.
  • FIG. 26B shows an example of a robot.
  • the robot 6400 shown in FIG. 26B includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display portion 6405, a lower camera 6406, an obstacle sensor 6407, a movement mechanism 6408, a calculation device, and the like.
  • the microphone 6402 has a function of detecting the user's speaking voice, environmental sounds, and the like. Furthermore, the speaker 6404 has a function of emitting sound. Robot 6400 can communicate with a user using microphone 6402 and 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 section 6405.
  • the display unit 6405 may include a touch panel. Further, the display unit 6405 may be a removable information terminal, and by installing it at a fixed position on the robot 6400, charging and data exchange are possible.
  • the upper camera 6403 and the lower camera 6406 have a function of capturing images around the robot 6400. Further, the obstacle sensor 6407 can detect the presence or absence of an obstacle in the direction of movement of the robot 6400 when the robot 6400 moves forward using the moving mechanism 6408.
  • the robot 6400 uses an upper camera 6403, a lower camera 6406, and an obstacle sensor 6407 to recognize the surrounding environment and can move safely.
  • the robot 6400 includes therein a secondary battery 6409 according to one embodiment of the present invention, and a semiconductor device or an electronic component.
  • the robot 6400 can be an electronic device with a long operating time and high reliability.
  • FIG. 26C shows an example of a flying object.
  • the flying object 6500 shown in FIG. 26C includes a propeller 6501, a camera 6502, a secondary battery 6503, and the like, 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 made into an electronic device with a long operating time and high reliability.
  • This embodiment can be implemented by appropriately combining at least a part of it with other embodiments described in this specification.
  • next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV) can be realized.
  • HV hybrid vehicles
  • EV electric vehicles
  • PSV plug-in hybrid vehicles
  • FIG. 27 illustrates a vehicle using a secondary battery, which is one embodiment of the present invention.
  • a car 8400 shown in FIG. 27A is an electric car that uses an electric motor as a power source for driving. Alternatively, it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as a power source for driving. By using one embodiment of the present invention, a vehicle with a long cruising distance can be realized.
  • the automobile 8400 has a secondary battery.
  • the secondary battery may be used by arranging the secondary battery modules shown in FIGS. 25C and 25D on the floor of the vehicle. Further, a battery pack in which a plurality of secondary batteries shown in FIG. 26 are combined may be installed on the floor of the vehicle.
  • 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 a room light (not shown).
  • the secondary battery can supply power to display devices such as a speedometer and a tachometer that the automobile 8400 has. Further, the secondary battery can supply power to a semiconductor device such as a navigation system included in the automobile 8400.
  • the automobile 8500 shown in FIG. 27B can be charged by receiving power from an external charging facility using a plug-in method, a non-contact power supply method, etc. to a secondary battery of the automobile 8500.
  • FIG. 27B shows a state in which a ground-mounted charging device 8021 is charging a secondary battery 8024 mounted on an automobile 8500 via a cable 8022.
  • a predetermined method such as CHAdeMO (registered trademark) or combo may be used as the charging method and the connector standard.
  • the charging device 8021 may be a charging station provided at a commercial facility, or may be a home power source.
  • the secondary battery 8024 mounted on the automobile 8500 can be charged by external power supply. Charging can be performed by converting AC power into DC power via a conversion device such as an ACDC converter.
  • a power receiving device can be mounted on a vehicle, and power can be supplied from a ground power transmitting device in a non-contact manner for charging.
  • this contactless power supply method by incorporating a power transmission device into the road and/or the outer wall, charging can be performed not only while the vehicle is stopped but also while the vehicle is running. Further, electric power may be transmitted and received between vehicles using this non-contact power feeding method.
  • a solar cell may be provided on the exterior of the vehicle, and the secondary battery may be charged when the vehicle is stopped and/or when the vehicle is running.
  • an electromagnetic induction method and/or a magnetic resonance method can be used.
  • FIG. 27C is an example of a two-wheeled vehicle using the secondary battery of one embodiment of the present invention.
  • a scooter 8600 shown in FIG. 27C includes a secondary battery 8602, a side mirror 8601, and a direction indicator light 8603.
  • the secondary battery 8602 can supply electricity to the direction indicator light 8603.
  • the scooter 8600 shown in FIG. 27C can store a secondary battery 8602 in an 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 driving.
  • the cycle characteristics of the secondary battery can be 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 improve its cruising range. Further, a secondary battery mounted on a vehicle can also be used as a power supply source other than the vehicle. In this case, it is possible to avoid using a commercial power source, for example, at times of peak power demand. If it is possible to avoid using a commercial power source during times of 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, so the amount of rare metals such as cobalt used can be reduced.
  • This embodiment can be implemented by appropriately combining at least a part of it with other embodiments described in this specification.
  • a positive electrode active material according to one embodiment of the present invention was prepared, and the results of powder resistance measurement will be described.
  • a positive electrode active material was manufactured based on the manufacturing method illustrated in FIGS. 22 and 23.
  • step S14 in FIG. 22 commercially available lithium cobalt oxide (Cellseed C-10N, manufactured by Nihon Kagaku Kogyo Co., Ltd.) having cobalt as the transition metal M and no particular additive element was prepared.
  • the initial heating in step S15 was not performed.
  • LiF was prepared as an F source and MgF 2 was prepared as an Mg source.
  • step S31 the A1 source was weighed so that the number of magnesium atoms contained in the source A1 was 0.5% of the number of cobalt atoms contained in the lithium cobalt oxide, and mixed with the lithium cobalt oxide in a dry manner.
  • step S33 in FIG. 22 the mixture 903 was heated.
  • the heating conditions were 850° C. for 60 hours.
  • the crucible containing mixture 903 was covered.
  • the crucible and lid were made of alumina.
  • Oxygen was supplied at a flow rate of 10 L/min (flow) in the furnace used for heating so that the inside of the crucible became an oxygen-containing atmosphere.
  • sample 1-1 was obtained as lithium cobalt oxide containing magnesium and fluorine (step S34a). In this example, no A2 source was added.
  • Sample 1-2 and Sample 1-3 were prepared in which the mixing ratio of the A1 source was different from that of Sample 1-1.
  • Sample 1-2 is obtained by weighing and mixing so that the number of magnesium atoms in the A1 source is 1.0% of the number of cobalt atoms in the lithium cobalt oxide.
  • Sample 1-3 was prepared by weighing and mixing so that the number of magnesium atoms in the A1 source was 6.0% of the number of cobalt atoms in the lithium cobalt oxide.
  • Sample 2 was produced as a comparative example.
  • lithium cobalt oxide (Cellseed C-10N, manufactured by Nihon Kagaku Kogyo Co., Ltd.) was used, and no treatment such as heat treatment was performed.
  • the volume resistivity of the powder was measured for the prepared sample.
  • a method for measuring the volume resistivity of the powder the method described in ⁇ Powder resistance measurement ⁇ of Embodiment 1 was used.
  • MCP-PD51 manufactured by Mitsubishi Chemical Analytech was used, and as a resistance meter, Lorestar GP or Hirestar UP was used. Each resistance meter has a different measurement range with high accuracy, so the optimum resistance meter was selected and used depending on the resistivity of the sample.
  • the measurement was performed in a general laboratory environment (that is, a temperature environment of 15° C. or higher and 30° C. or lower).
  • FIG. 28A shows a schematic diagram of a measuring device that can measure the volume resistivity of powder. Further, FIG. 28B shows a conceptual diagram of the four-probe method, and FIG. 28C shows a conceptual diagram of the two-terminal method.
  • the powder was set in the measuring section, and the electrical resistance of the powder and the volume of the powder were measured under pressure conditions of 13 MPa, 25 MPa, 38 MPa, 51 MPa, and 64 MPa. and were measured to obtain the volume resistivity of the powder of each sample. The results are shown in FIG. 29.
  • the powder resistance increases as the amount of A1 source mixed increases. was found to be large. It is thought that magnesium and other substances are located in the shell, increasing the powder resistance of the positive electrode active material.
  • a secondary battery using the positive electrode active material of one embodiment of the present invention can be said to be a secondary battery with excellent safety.
  • the susceptibility to thermal runaway, ignition, and smoke generation due to an internal short circuit can be evaluated by the above-mentioned nail insertion test or the like.
  • the positive electrode and the negative electrode each have a plurality of tabs, the internal resistance of the secondary battery is reduced compared to conventional secondary batteries. Therefore, even if a material with high powder resistance is used as the positive electrode active material, the influence on charge/discharge time can be minimized. Therefore, it is possible to realize a secondary battery that can easily charge and discharge at high speed, has excellent safety, and has suppressed deterioration.
  • a positive electrode active material was manufactured based on the manufacturing method illustrated in FIGS. 22 and 23.
  • Lithium cobalt oxide (Cellseed C-10N, manufactured by Nihon Kagaku Kogyo Co., Ltd.) was prepared as LiCoO 2 in step S14 in FIG. 22.
  • the initial heating in step S15 lithium cobalt oxide was placed in a crucible, the crucible was covered, and the crucible was heated at 850° C. for 2 hours in a muffle furnace. After creating an oxygen atmosphere in the muffle furnace, no flow occurred ( O2 purge).
  • LiF was prepared as an F source and MgF 2 was prepared as an Mg source.
  • MgF 2 was weighed so that LiF:MgF 2 was 1:3 (mole ratio).
  • LiF and MgF 2 were mixed in dehydrated acetone and stirred at a rotational speed of 400 rpm for 12 hours to prepare an additive element source (A1 source).
  • a ball mill was used for mixing, and zirconium oxide balls were used as the grinding media.
  • a total of about 9 g of an F source and a Mg source were added to a 45 mL container of a mixing ball mill and mixed together with 20 mL of dehydrated acetone and 22 g of zirconium oxide balls (1 mm diameter). After that, it was sieved with a sieve having openings of 300 ⁇ m to obtain an A1 source.
  • step S31 the A1 source was weighed to be 1 mol % of cobalt, and was dry mixed with the initially heated lithium cobalt oxide. At this time, the mixture was stirred for 1 hour at a rotational speed of 150 rpm, which was slower than the stirring used to obtain the A1 source. Finally, the mixture was sieved through a sieve having openings of 300 ⁇ m to obtain a mixture 903 with uniform particle size (step S32).
  • step S33 the mixture 903 was heated.
  • the heating conditions were 900° C. and 20 hours.
  • the crucible containing mixture 903 was covered.
  • the inside of the crucible was made to have an oxygen-containing atmosphere, and entry and exit of the oxygen was blocked (purge).
  • a composite oxide containing Mg and F was obtained by heating (step S34a).
  • step S51 the composite oxide and the additive element source (A2 source) were mixed.
  • nickel hydroxide that underwent a pulverization process was prepared as a nickel source
  • aluminum hydroxide that underwent a pulverization process was prepared as an aluminum source.
  • Nickel hydroxide and aluminum hydroxide were weighed so that both amounted to 0.5 mol % of lithium cobalt oxide, and mixed with the composite oxide in a dry manner. At this time, the mixture was stirred for 1 hour at a rotational speed of 150 rpm.
  • a ball mill was used for mixing, and zirconium oxide balls were used as the grinding media.
  • a total of about 7.5 g of the composite oxide, a nickel source, and an aluminum source were mixed together with 22 g of zirconium oxide balls (1 mm diameter) into a 45 mL container of a mixing ball mill. This is a milder stirring condition than when obtaining the A1 source. Finally, the mixture was sieved through a sieve having openings of 300 ⁇ m to obtain a mixture 904 with uniform particle size (step S52).
  • step S53 the mixture 904 was heated. Heating was performed at 850° C. for 10 hours. During heating, the crucible containing mixture 904 was covered. The inside of the crucible was made to have an oxygen-containing atmosphere, and entry and exit of the oxygen was blocked (purge). By heating, lithium cobalt oxide containing Mg, F, Ni, and Al was obtained (step S54).
  • the LiCoO 2 that had undergone the initial heating in step S15 was designated as sample 3-1.
  • step S34a the composite oxide obtained in step S34a above was designated as sample 3-2.
  • the positive electrode active material obtained in step S54 was designated as sample 3-3.
  • FIG. 30 shows the measurement results.
  • FIG. 30 also shows Sample 2 in Example 1.
  • the volume resistivity increased in the order of sample 2, sample 3-1, sample 3-3, and sample 3-2 from the lowest. Furthermore, a large difference of two or more orders of magnitude was observed in the volume resistivity values between Sample 3-1, Sample 3-2, and Sample 3-3. Sample 3-1 was subjected to only initial heating, whereas sample 3-2 and sample 3-3 both contained Mg and F.
  • the volume resistivity is preferably 5.0 ⁇ 10 3 ⁇ cm or more, more preferably 1.0 ⁇ 10 4 ⁇ cm or more, It is more preferably 1.0 ⁇ 10 5 ⁇ cm or more, more preferably 5.0 ⁇ 10 5 ⁇ cm or more, and more preferably 1.0 ⁇ 10 6 ⁇ cm or more. .
  • the volume resistivity is preferably 2.0 ⁇ 10 4 ⁇ cm or more, and more preferably 2.0 ⁇ 10 5 ⁇ cm or more. It is preferably 5.0 ⁇ 10 5 ⁇ cm or more, more preferably 1.0 ⁇ 10 6 ⁇ cm or more, and preferably 2.0 ⁇ 10 6 ⁇ cm or more. More preferred.
  • the volume resistivity is preferably 1.0 ⁇ 10 4 ⁇ cm or more when the pressure is 64 MPa, and preferably 2.0 ⁇ 10 4 ⁇ cm or more when the pressure is 13 MPa. Moreover, it is preferable that it is 1.0 ⁇ 10 5 ⁇ cm or more when the pressure is 64 MPa, and 2.0 ⁇ 10 5 ⁇ cm or more when the pressure is 13 MPa. Furthermore, it can be said that it is preferable that it is 5.0 ⁇ 10 5 ⁇ cm or more when the pressure is 64 MPa, and 1.0 ⁇ 10 6 ⁇ cm or more when the pressure is 13 MPa.
  • the positive electrode active material of one embodiment of the present invention has a high-resistance shell portion, thereby increasing the volume resistivity of the powder.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • General Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Power Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Inorganic Chemistry (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Secondary Cells (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Connection Of Batteries Or Terminals (AREA)
PCT/IB2023/056238 2022-06-29 2023-06-16 二次電池 Ceased WO2024003663A1 (ja)

Priority Applications (4)

Application Number Priority Date Filing Date Title
JP2024530067A JPWO2024003663A1 (https=) 2022-06-29 2023-06-16
US18/872,382 US20250293408A1 (en) 2022-06-29 2023-06-16 Secondary battery
CN202380045088.6A CN119318054A (zh) 2022-06-29 2023-06-16 二次电池
KR1020247038995A KR20250028250A (ko) 2022-06-29 2023-06-16 이차 전지

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
JP2022104268 2022-06-29
JP2022-104268 2022-06-29
JP2022-110196 2022-07-08
JP2022110196 2022-07-08

Publications (1)

Publication Number Publication Date
WO2024003663A1 true WO2024003663A1 (ja) 2024-01-04

Family

ID=89381888

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/IB2023/056238 Ceased WO2024003663A1 (ja) 2022-06-29 2023-06-16 二次電池

Country Status (5)

Country Link
US (1) US20250293408A1 (https=)
JP (1) JPWO2024003663A1 (https=)
KR (1) KR20250028250A (https=)
CN (1) CN119318054A (https=)
WO (1) WO2024003663A1 (https=)

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2009043477A (ja) * 2007-08-07 2009-02-26 Sony Corp 正極活物質、これを用いた正極および非水電解質電池
CN101714624A (zh) * 2009-09-11 2010-05-26 广州丰江电池新技术股份有限公司 一种螺旋线多极耳锂离子电池及其制造方法
JP2010118315A (ja) * 2008-11-14 2010-05-27 Toshiba Corp 非水電解質電池
JP2010129471A (ja) * 2008-11-28 2010-06-10 Sony Corp 正極活物質および非水電解質電池
WO2011108106A1 (ja) * 2010-03-04 2011-09-09 株式会社 東芝 非水電解質電池、電池パック及び自動車
JP2011187193A (ja) * 2010-03-05 2011-09-22 Hitachi Ltd リチウム二次電池用正極材料、リチウム二次電池及びそれを用いた二次電池モジュール
JP2014167890A (ja) * 2013-02-28 2014-09-11 Toshiba Corp 電池
JP2022071154A (ja) * 2016-11-18 2022-05-13 株式会社半導体エネルギー研究所 リチウムイオン二次電池

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112201844A (zh) 2017-06-26 2021-01-08 株式会社半导体能源研究所 正极活性物质的制造方法及二次电池
JP6933149B2 (ja) 2018-01-22 2021-09-08 トヨタ自動車株式会社 非水電解質二次電池
CN115863743A (zh) 2018-08-03 2023-03-28 株式会社半导体能源研究所 锂离子二次电池
US20220029159A1 (en) 2018-12-13 2022-01-27 Semiconductor Energy Laboratory Co., Ltd. Positive electrode active material, method for manufacturing the same, and secondary battery

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2009043477A (ja) * 2007-08-07 2009-02-26 Sony Corp 正極活物質、これを用いた正極および非水電解質電池
JP2010118315A (ja) * 2008-11-14 2010-05-27 Toshiba Corp 非水電解質電池
JP2010129471A (ja) * 2008-11-28 2010-06-10 Sony Corp 正極活物質および非水電解質電池
CN101714624A (zh) * 2009-09-11 2010-05-26 广州丰江电池新技术股份有限公司 一种螺旋线多极耳锂离子电池及其制造方法
WO2011108106A1 (ja) * 2010-03-04 2011-09-09 株式会社 東芝 非水電解質電池、電池パック及び自動車
JP2011187193A (ja) * 2010-03-05 2011-09-22 Hitachi Ltd リチウム二次電池用正極材料、リチウム二次電池及びそれを用いた二次電池モジュール
JP2014167890A (ja) * 2013-02-28 2014-09-11 Toshiba Corp 電池
JP2022071154A (ja) * 2016-11-18 2022-05-13 株式会社半導体エネルギー研究所 リチウムイオン二次電池

Also Published As

Publication number Publication date
CN119318054A (zh) 2025-01-14
JPWO2024003663A1 (https=) 2024-01-04
US20250293408A1 (en) 2025-09-18
KR20250028250A (ko) 2025-02-28

Similar Documents

Publication Publication Date Title
US20230402601A1 (en) Battery
JP2022173119A (ja) 正極活物質
JP7764465B2 (ja) 電池、電子機器および車両
US20240063387A1 (en) Positive electrode active material and secondary battery
WO2023281346A1 (ja) 正極活物質
WO2023242676A1 (ja) リチウムイオン二次電池
WO2024023625A1 (ja) 電池
WO2024003664A1 (ja) 正極活物質の作製方法
WO2023209477A1 (ja) リチウムイオン電池、及び電子機器
WO2023209474A1 (ja) 正極活物質、リチウムイオン電池、電子機器、および車両
WO2024003663A1 (ja) 二次電池
US20240038985A1 (en) Battery
EP4546463A1 (en) Positive electrode active material, secondary battery, electronic device, and vehicle
US20250343221A1 (en) Method for manufacturing secondary battery
US20250105291A1 (en) Battery
US20250357481A1 (en) Secondary battery
WO2025083507A1 (ja) 正極、二次電池および電子機器
KR20250158785A (ko) 양극 활물질 및 전지
US20240097194A1 (en) Ionic liquid, secondary battery, electronic device, and vehicle
KR20260058213A (ko) 양극 활물질 입자 및 양극 활물질 입자의 제작 방법
JP2025025701A (ja) 二次電池、電子機器および車両
WO2025046417A1 (ja) 正極活物質粒子および正極活物質粒子の作製方法
KR20250167577A (ko) 이차 전지
JP2025035979A (ja) 正極活物質粒子の製造方法
JP2024136700A (ja) 電池

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 23830585

Country of ref document: EP

Kind code of ref document: A1

WWE Wipo information: entry into national phase

Ref document number: 2024530067

Country of ref document: JP

WWE Wipo information: entry into national phase

Ref document number: 202380045088.6

Country of ref document: CN

WWP Wipo information: published in national office

Ref document number: 202380045088.6

Country of ref document: CN

NENP Non-entry into the national phase

Ref country code: DE

WWP Wipo information: published in national office

Ref document number: 1020247038995

Country of ref document: KR

122 Ep: pct application non-entry in european phase

Ref document number: 23830585

Country of ref document: EP

Kind code of ref document: A1

WWP Wipo information: published in national office

Ref document number: 18872382

Country of ref document: US