WO2023276479A1 - 非水電解質二次電池用正極および非水電解質二次電池 - Google Patents
非水電解質二次電池用正極および非水電解質二次電池 Download PDFInfo
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- WO2023276479A1 WO2023276479A1 PCT/JP2022/020613 JP2022020613W WO2023276479A1 WO 2023276479 A1 WO2023276479 A1 WO 2023276479A1 JP 2022020613 W JP2022020613 W JP 2022020613W WO 2023276479 A1 WO2023276479 A1 WO 2023276479A1
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- single particles
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Images
Classifications
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- 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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- 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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
- H01M4/366—Composites as layered products
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- 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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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- 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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
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- H01M2004/021—Physical characteristics, e.g. porosity, surface area
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- H—ELECTRICITY
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- 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
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- 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
Definitions
- the present disclosure relates to a positive electrode for nonaqueous electrolyte secondary batteries and a nonaqueous electrolyte secondary battery using the positive electrode.
- the positive electrode active material that makes up the positive electrode greatly affects battery performance such as input/output characteristics, capacity, and durability.
- the positive electrode active material is a lithium-transition metal composite oxide that contains a metal element such as Ni, Co, Mn, and Al, and is composed of secondary particles formed by agglomeration of primary particles. . Since the properties of positive electrode active materials vary greatly depending on their composition, particle shape, and the like, various studies have been conducted on various positive electrode active materials.
- Patent Document 1 discloses a positive electrode active material containing a lithium-nickel composite oxide having a hexagonal layered structure and consisting of a single primary particle or a single primary particle and secondary particles in which a plurality of primary particles are aggregated. Materials are disclosed.
- the positive electrode active material is particles having a predetermined composition and X-ray diffraction pattern and a circularity of 0.93 to 1.00.
- Patent Document 1 describes the effect of improving the cycle characteristics of the battery by using the positive electrode active material.
- Patent Document 1 By the way, in a non-aqueous electrolyte secondary battery, it is an important issue to suppress the decrease in capacity due to charging and discharging and to improve the durability. Note that the technology disclosed in Patent Document 1 still has room for improvement in terms of improving battery durability.
- a positive electrode for a non-aqueous electrolyte secondary battery which is one aspect of the present disclosure, is for a non-aqueous electrolyte secondary battery having a positive electrode core and a positive electrode mixture layer containing a positive electrode active material provided on the positive electrode core.
- the positive electrode, the positive electrode active material is composed of single particles having no grain boundaries in the particles, and the single particles include first single particles having a particle size of 4 ⁇ m or more and is small, and includes second single particles adjacent to the first single particles, and the particle with the smallest particle size among the second single particles has a particle size of 1/5 or less of the particle size of the adjacent first single particles and the content of the first single particles is 3 to 30% of the total number of particles of the positive electrode active material.
- a non-aqueous electrolyte secondary battery includes the positive electrode, the negative electrode, and the non-aqueous electrolyte.
- a non-aqueous electrolyte secondary battery using a positive electrode according to the present disclosure has, for example, a high capacity retention rate after charge-discharge cycles and excellent cycle characteristics.
- FIG. 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery that is an example of an embodiment
- FIG. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically the cross section of the positive mix layer which is an example of embodiment.
- 1 is a scanning electron microscope (SEM) image of a cross section of a positive electrode mixture layer that is an example of an embodiment.
- FIG. 4 is a diagram showing changes in capacity retention rate with charge/discharge cycles in non-aqueous electrolyte secondary batteries of Examples and Comparative Examples.
- the present inventors have made intensive studies to develop a positive electrode that contributes to improving the durability of non-aqueous electrolyte secondary batteries. found that the durability of the battery is greatly improved by using a positive electrode having a positive electrode mixture layer in which second single particles with a small particle size are arranged around the first single particles with a large particle size. rice field. When the smallest second single particle has a particle size of 1/5 or less of the particle size of the adjacent first single particles, the effect of improving the durability appears remarkably.
- the content of the first single particles is preferably 3 to 30% of the total number of particles of the positive electrode active material. In this case, the effect of improving durability becomes more pronounced. Further, by using the positive electrode according to the present disclosure, durability can be improved while ensuring high discharge capacity, for example.
- a cylindrical battery in which the wound electrode body 14 is housed in a bottomed cylindrical outer can 16 will be exemplified. It may be a can (square battery), a coin-shaped exterior can (coin-shaped battery), or an exterior body (laminate battery) composed of a laminate sheet including a metal layer and a resin layer. Further, the electrode body may be a laminated electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated with separators interposed therebetween.
- FIG. 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery 10 that is an example of an embodiment.
- the non-aqueous electrolyte secondary battery 10 includes a wound electrode body 14, a non-aqueous electrolyte, and an outer can 16 that accommodates the electrode body 14 and the non-aqueous electrolyte.
- the electrode body 14 has a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween.
- the outer can 16 is a bottomed cylindrical metal container that is open on one side in the axial direction. In the following description, for convenience of explanation, the side of the sealing member 17 of the battery will be referred to as the upper side, and the bottom side of the outer can 16 will be referred to as the lower side.
- the non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.
- non-aqueous solvents include esters, ethers, nitriles, amides, and mixed solvents of two or more thereof.
- the non-aqueous solvent may contain a halogen-substituted product obtained by substituting at least part of the hydrogen atoms of these solvents with halogen atoms such as fluorine.
- non-aqueous solvents include ethylene carbonate (EC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC), mixed solvents thereof, and the like.
- Lithium salts such as LiPF 6 are used, for example, as electrolyte salts.
- the non-aqueous electrolyte is not limited to a liquid electrolyte, and may be a solid electrolyte.
- the positive electrode 11, the negative electrode 12, and the separator 13, which constitute the electrode assembly 14, are all strip-shaped elongated bodies, and are spirally wound to be alternately laminated in the radial direction of the electrode assembly 14. .
- the negative electrode 12 is formed with a size one size larger than that of the positive electrode 11 in order to prevent deposition of lithium. That is, the negative electrode 12 is formed longer than the positive electrode 11 in the longitudinal direction and the width direction (transverse direction).
- the separator 13 is at least one size larger than the positive electrode 11, and two separators 13 are arranged so as to sandwich the positive electrode 11, for example.
- a positive electrode lead 20 is connected to the positive electrode 11 of the electrode body 14 by welding or the like
- a negative electrode lead 21 is connected to the negative electrode 12 by welding or the like.
- Insulating plates 18 and 19 are arranged above and below the electrode body 14, respectively.
- the positive electrode lead 20 extends through the through hole of the insulating plate 18 toward the sealing member 17
- the negative electrode lead 21 extends through the outside of the insulating plate 19 toward the bottom of the outer can 16 .
- the positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the cap 27, which is the top plate of the sealing body 17 electrically connected to the internal terminal plate 23, serves as the positive electrode terminal.
- the negative electrode lead 21 is connected to the inner surface of the bottom of the outer can 16 by welding or the like, and the outer can 16 serves as a negative electrode terminal.
- a gasket 28 is provided between the outer can 16 and the sealing member 17 to ensure hermeticity inside the battery and insulation between the outer can 16 and the sealing member 17 .
- the outer can 16 is formed with a grooved portion 22 that supports the sealing member 17 and has a portion of the side surface projecting inward.
- the grooved portion 22 is preferably annularly formed along the circumferential direction of the outer can 16 and supports the sealing member 17 on its upper surface.
- the sealing member 17 is fixed to the upper portion of the outer can 16 by the grooved portion 22 and the open end of the outer can 16 crimped to the sealing member 17 .
- the sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are layered in order from the electrode body 14 side.
- Each member constituting the sealing member 17 has, for example, a disk shape or a ring shape, and each member except for the insulating member 25 is electrically connected to each other.
- the lower valve body 24 and the upper valve body 26 are connected at their central portions, and an insulating member 25 is interposed between their peripheral edge portions.
- the positive electrode 11, the negative electrode 12, and the separator 13 that make up the electrode body 14 will be described in detail below, and in particular, the configurations of the positive electrode active material and the positive electrode mixture layer that make up the positive electrode 11 will be described in detail.
- the positive electrode 11 has a positive electrode core and a positive electrode mixture layer provided on the surface of the positive electrode core.
- the positive electrode core is a sheet-like current collector having higher conductivity than the positive electrode mixture layer.
- a foil of a metal such as aluminum or an aluminum alloy that is stable in the potential range of the positive electrode 11, a film in which the metal is arranged on the surface layer, or the like can be used.
- the positive electrode material mixture layer contains a positive electrode active material, a binder, and a conductive agent, and is preferably provided on both sides of the positive electrode core.
- the thickness of the positive electrode material mixture layer is thicker than that of the positive electrode core, and is, for example, 50 ⁇ m to 150 ⁇ m on one side of the core.
- binder contained in the positive electrode mixture layer examples include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. be done.
- the positive electrode mixture layer preferably further contains cellulose derivatives such as carboxymethyl cellulose (CMC) or salts thereof, polyethylene oxide (PEO), and the like.
- the conductive agent contained in the positive electrode mixture layer include carbon materials such as carbon black, acetylene black, ketjen black, and graphite.
- FIG. 2 is a schematic diagram showing a cross section of the positive electrode mixture layer 11A, which is an example of the embodiment
- FIG. 3 is a cross-sectional SEM image of the positive electrode mixture layer 11A.
- the first single particles 31 are hatched with low-density dots
- the particles 32X having the smallest particle size among the second single particles 32 adjacent to the first single particles 31 are hatched with high-density dots.
- the positive electrode active material 30 is composed of single particles. and second single particles 32 having a smaller particle size.
- the second single particles 32 are present around the first single particles 31, and among the second single particles 32 adjacent to the first single particles 31, the particles 32X having the smallest particle size are adjacent to each other. It has a particle size of 1 ⁇ 5 or less of the particle size of the first single particles 31 .
- the first single particles 31 and the second single particles 32 preferably have no grain boundaries inside the particles, but may have 5 or less crystal planes in the single particles.
- the positive electrode active material 30 is substantially composed only of the first single particles 31 and the second single particles 32, but the positive electrode mixture layer 11A contains particles other than single particles, such as a large number of particles. Secondary particles formed by agglomeration of primary particles may also be included.
- the content of the single particles in the positive electrode active material 30 is preferably 50% or more, more preferably 70% or more, and particularly preferably 80% or more based on the number.
- a single particle may not be a single crystal, but may be an aggregate containing 5 or less crystal planes in a primary particle, and the voids at the particle interface within the particle are at most 1%.
- a crystal plane can be identified by a difference in contrast observed when a cross section of a particle is observed with a scanning ion microscope (SIM) at a magnification of 3000.
- the content of the first single particles 31 is preferably 30% or less, more preferably 25% or less, of the total number of particles of the positive electrode active material 30 .
- a preferable example of the content of the first single particles 31 is 3 to 30% or 5 to 25% based on number.
- the content of the second single particles 32 is, for example, 70 to 97% based on number. If the contents of the first single particles 31 and the second single particles 32 are within this range, the durability of the battery can be improved more effectively.
- the first single particles 31 and the second single particles 32 contain, for example, 90 mol % of at least one metal element selected from Ni, Mn, Fe, and Al with respect to the total molar amount of metal elements excluding Li. It is composed of the lithium-transition metal composite oxide containing the above.
- the lithium-transition metal composite oxide may contain elements other than Li, Ni, Mn, Fe and Al in an amount of 10 mol % or less with respect to the total molar amount of the elements excluding Li and O.
- Other elements include Co, B, Mg, Ti, V, Cr, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, W, Si, Ca, etc., especially divalent ions. is preferred.
- the above lithium-transition metal composite oxide preferably contains 30 mol % or more of Ni with respect to the total molar amount of metal elements excluding Li.
- Ni is the most contained metal element other than Li, which constitutes the lithium-transition metal composite oxide.
- the content of Ni is more preferably 50 mol % or more, particularly preferably 70 mol % or more, relative to the total molar amount of metal elements excluding Li.
- the upper limit of the Ni content may be 95 mol%, preferably 90 mol%.
- a preferred example of the Ni content is 50 to 90 mol %, or 70 to 90 mol % with respect to the total molar amount of metal elements excluding Li. If the Ni content is within this range, it becomes easy to increase the capacity while ensuring good durability.
- the lithium-transition metal composite oxide preferably contains Al.
- the content of Al is preferably 10 mol % or less, more preferably 5 mol % or less, relative to the total molar amount of metal elements excluding Li.
- a preferred example of the Al content is 1 to 10 mol % or 1 to 5 mol % with respect to the total molar amount of metal elements excluding Li. If the Al content is within this range, it becomes easy to increase the capacity while ensuring good durability.
- the lithium-transition metal composite oxide may contain at least one of Mn and Fe.
- Mn and Fe When Mn and Fe are contained, the content of each is preferably 1 to 60 mol %, more preferably 10 to 50 mol %, relative to the total molar amount of metal elements excluding Li.
- the lithium-transition metal composite oxide may contain Co, but since Co is an expensive metal element, the content thereof is, for example, 10 mol with respect to the total molar amount of the metal elements excluding Li. % or less, more preferably 5 mol % or less, or substantially 0%.
- An example of a suitable lithium-transition metal composite oxide has a composition formula of Li ⁇ NixMyAlzO2 (where 0.9 ⁇ ⁇ ⁇ 1.2, 0.70 ⁇ x ⁇ 0.90, 0.90 ⁇ x ⁇ 0.90, 0.9 ⁇ 1.2, 0.70 ⁇ x ⁇ 0.90, 01 ⁇ y ⁇ 0.3, 0 ⁇ z ⁇ 0.10, and M is at least one metal element selected from cobalt, manganese, and iron).
- the Li site occupancy rate in the first composite oxide particles 31 is preferably 80% or more, more preferably 90% or more, and particularly preferably 95% or more. If the Li site occupancy is within this range, it is easy to achieve a high capacity.
- the Li site occupancy means the ratio of Li to the Li sites in the crystal structure, and is determined by Rietveld analysis of the X-ray diffraction pattern of the lithium-transition metal composite oxide.
- the Li site occupancy may be 98% or more in the manganese-free lithium-transition metal composite oxide, and may be 94% or more in the manganese-containing lithium-transition metal composite oxide, and may be substantially 100%. %.
- the proportion of metal elements other than Li present in the Li layer can be obtained from Rietveld analysis of an X-ray diffraction pattern obtained by X-ray diffraction measurement of the lithium-transition metal composite oxide.
- the X-ray diffraction pattern is obtained by a powder X-ray diffraction method under the following conditions using a powder X-ray diffractometer (manufactured by Rigaku Co., Ltd., trade name "RINT-TTR", radiation source Cu-K ⁇ ).
- the particle cross section of each single particle has, for example, a polygonal shape including sides with a length of 1.5 ⁇ m or more, and at least three interior angles ⁇ of the polygon are 45 to 160°.
- the length of the longest long side is, for example, 3 to 20 ⁇ m, preferably 3 to 15 ⁇ m. All interior angles ⁇ of the polygon may be 45 to 160°, 60 to 150°, or 70 to 130°, and three or more interior angles ⁇ of 90° or less may exist.
- the positive electrode active material 30 contains, for example, 50% or more of angular particles satisfying the length of the long side and the internal angle ⁇ .
- the average porosity of the first single particles 31 and the second single particles 32 is preferably 1% or less, more preferably 0.3% or less.
- the average porosity means the average ratio of voids in each single particle, and is measured by the method described later.
- Each single particle may be a dense particle with few voids and an average porosity of less than 1%.
- the average porosities of the first single particles 31 and the second single particles 32 are measured by the following method.
- the SEM image of the cross section of the positive electrode mixture layer 11A was taken into a computer, and the image analysis software was used to classify the image into two colors based on the contrast.
- the first single particles 31 are large particles with a particle size of 4 ⁇ m or more, as described above.
- the second single particles 32 are particles with a particle size of less than 4 ⁇ m.
- the particle diameter of a single particle means the diameter of the circumscribed circle of the particle in the cross-sectional SEM image of the positive electrode mixture layer 11A.
- the positive electrode active material 30 may have, for example, a particle size distribution with peaks in the particle size range of 4 ⁇ m or more and less than 4 ⁇ m.
- the average particle diameter of the first single particles 31 is preferably 5-20 ⁇ m, more preferably 6-15 ⁇ m.
- the average particle size of the second single particles 32 is preferably 0.5 to 3.5 ⁇ m, more preferably 1 to 3 ⁇ m.
- the average particle diameter can be calculated by averaging the particle diameters of arbitrary 100 particles from the SEM image, but when the particle size distribution of each particle can be measured, D50 can be substituted.
- the second single particles 32 are arranged around the first single particles 31 in the positive electrode mixture layer 11A. That is, the first single particles 31 are surrounded by the plurality of second single particles 32, and the first single particles 31 are hardly in contact with each other. In the positive electrode mixture layer 11A, for example, 80 to 100% of the first single particles 31 are arranged without contacting other first single particles 31, and the second single particles are arranged between the first single particles 31. 32 intervenes.
- the second single particles 32 may be in direct contact with the first single particles 31, but a binder and a conductive agent are present between the first single particles 31 and the second single particles 32. is preferred.
- a particle 32X having the smallest particle size among the second single particles 32 adjacent to the first single particles 31 has a particle size of 1/5 or less of the particle size of the adjacent first single particles 31. That is, the difference in particle size between the adjacent first single particles 31 and second single particles 32 is five times or more.
- a plurality of second single particles 32 are present around the first single particles 31, and at least one of the second single particles 32 has a particle size of 1 ⁇ 5 or less of the particle size of the first single particles 31. , preferably plural.
- the number of second single particles 32 surrounding the first single particles 31 is, for example, 5 to 30, preferably 8 to 20.
- the average value of the ratio of the particle size of the particles 32X to the particle size of the first single particles 31 is preferably 1/5 to 1/30, more preferably 1/8 to 1/20. That is, the average value of the difference in particle size between the adjacent first single particles 31 and the particles 32X is preferably 5 to 30 times, more preferably 8 to 20 times.
- the positive electrode mixture layer 11A includes the first single particles 31 and the second single particles 32 having such a large difference in particle size, and the plurality of second single particles 32 are arranged around the first single particles 31. According to the positive electrode 11, the polarization of the first single particles 31, which are large single particles, is reduced, and thus the durability of the nonaqueous electrolyte secondary battery 10 is considered to be improved.
- the positive electrode mixture layer 11A contains a positive electrode active material as a main component, and the total content of the binder and the conductive agent is 0.5 to 5.0 mass with respect to the mass of the positive electrode mixture layer. %, more preferably 0.8 to 4.0% by mass.
- the positive electrode 11 is produced by coating the surface of a positive electrode core with a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive agent, etc., drying the coating film, and then compressing the positive electrode mixture layer to form a positive electrode core. It can be made by forming on both sides of the body. It is believed that increasing the amount of the binder and the conductive agent added increases the viscosity of the slurry, making it easier for the second single particles 32, which are small particles, to gather around the first single particles 31, which are large particles. .
- the first single particles 31 and the second single particles 32 can be synthesized, for example, by mixing a transition metal compound containing at least Ni, an aluminum compound, and a lithium compound, firing the mixture at a high temperature, and then firing the mixture at a low temperature.
- the first firing is performed at a temperature 100 to 150° C. higher than the firing temperature of a conventional general positive electrode active material
- the second firing is performed at a temperature 100 to 150° C. lower than the first firing temperature, that is, the conventional temperature. It is carried out at the baking temperature of a general positive electrode active material.
- An example of a specific firing temperature is that the temperature for the first firing is 720 to 1000°C, the temperature for the second firing is 600 to 800°C, and there is a temperature difference of 50°C or more in each firing process. is preferred.
- the first single particles 31 and the second single particles 32 can be produced by separately synthesizing and mixing them, but they can also be synthesized at the same time, for example, by utilizing abnormal particle growth.
- the temperature is increased for a short period of time, the grain size of single particles tends to increase.
- the particle size, sintering temperature, temperature rise speed, and specific surface area of the composite oxide as a raw material large single particles and small particles coexist in one aggregated particle, and this is crushed. By doing so, the first single particles 31 and the second single particles 32 can be produced.
- the positive electrode material mixture layer 11A having the above configuration can be produced based on the description of the specification of the present application.
- the negative electrode 12 has a negative electrode core and a negative electrode mixture layer provided on the surface of the negative electrode core.
- the negative electrode core is a sheet-like current collector having higher conductivity than the negative electrode mixture layer.
- a foil of a metal such as copper or a copper alloy that is stable in the potential range of the negative electrode 12, a film in which the metal is arranged on the surface layer, or the like can be used.
- the negative electrode mixture layer contains a negative electrode active material and a binder, and is preferably provided on both sides of the negative electrode core.
- the thickness of the negative electrode mixture layer is thicker than that of the negative electrode core, for example, 50 ⁇ m to 150 ⁇ m on one side of the core.
- the negative electrode mixture layer contains a negative electrode active material as a main component.
- the content of the negative electrode active material is preferably 90% by mass or more, and a preferred example is 90 to 98% by mass, based on the mass of the negative electrode mixture layer.
- the content of the binder is, for example, 0.5 to 5% by mass with respect to the mass of the negative electrode mixture layer.
- the negative electrode 12 is produced by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, etc. to the surface of the negative electrode core, drying the coating film, and then compressing the negative electrode mixture layer on both sides of the negative electrode core. It can be produced by forming.
- the negative electrode mixture layer generally contains a carbon-based active material that reversibly absorbs and releases lithium ions as a negative electrode active material.
- Suitable carbon-based active materials are graphite such as natural graphite such as flake graphite, massive graphite and earthy graphite, artificial graphite such as massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB).
- a Si-based active material composed of at least one of Si and a Si-containing compound may be used as the negative electrode active material, or a carbon-based active material and a Si-based active material may be used in combination.
- the binder contained in the negative electrode mixture layer may be fluororesin, PAN, polyimide, acrylic resin, polyolefin, or the like, but styrene-butadiene rubber (SBR) is preferably used. is preferred.
- the negative electrode mixture layer preferably further contains a cellulose derivative such as CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like.
- the negative electrode mixture layer may contain a conductive agent. As the conductive agent, the same conductive agent as that applied to the positive electrode 11 can be used.
- a porous sheet having ion permeability and insulation is used for the separator 13 .
- porous sheets include microporous thin films, woven fabrics, and non-woven fabrics.
- Suitable materials for the separator 13 include polyolefins such as polyethylene, polypropylene, copolymers of ethylene and ⁇ -olefin, and cellulose.
- the separator 13 may have either a single layer structure or a laminated structure.
- a heat-resistant layer containing inorganic particles, a heat-resistant layer made of a highly heat-resistant resin such as aramid resin, polyimide, polyamideimide, or the like may be formed on the surface of the separator 13 .
- Example 1 [Synthesis of positive electrode active material] Lithium hydroxide and nickel-cobalt-aluminum composite oxide were mixed at a predetermined mass ratio, raised from 650° C. to 780° C. in 0.5 hours, fired at 780° C. for 30 hours, and then fired at 700° C. for 30 hours. Thereafter, the fired product was pulverized and classified to obtain a lithium transition metal composite oxide (positive electrode active material) represented by the composition formula LiNi 0.91 Co 0.45 Al 0.45 O 2 . The lithium site occupancy in this lithium transition metal composite oxide was 98.5%, and the lattice constant a-axis was 2.87536 ⁇ .
- the content of the first single particles is 14% with respect to all particles of the positive electrode active material.
- a positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed at a solid content mass ratio of 100:2:1.3, and N-methyl-2-pyrrolidone (NMP) was used as a dispersion medium to form a positive electrode mixture.
- NMP N-methyl-2-pyrrolidone
- An agent slurry was prepared.
- the positive electrode mixture slurry was applied onto a positive electrode core made of aluminum foil, the coating film was dried and compressed, and then cut into a predetermined electrode size to obtain a positive electrode A1.
- FIG. 3 shows a cross-sectional SEM image of the mixture layer of positive electrode A1. From this image, the second single particles are arranged around the first single particles having a particle size of 4 ⁇ m or more, and the particle size of the smallest particle among the second single particles is larger than the particle size of the adjacent first single particles. It was confirmed to be 1/5 or less. Second single particles having a particle size of 1 ⁇ 5 or less of the particle size of the first single particles were found around substantially all of the first single particles.
- the particle size of the positive electrode active material was uniform, and the first single particles were 1.5% in the cross-sectional SEM image of the positive electrode mixture layer.
- the lithium site occupancy in this lithium transition metal composite oxide was 99.3%, and the lattice constant a-axis was 2.87272 ⁇ .
- the particle size of the positive electrode active material was uniform, and the first single particles were not included in the cross-sectional SEM image of the positive electrode mixture layer.
- Low BET graphite refers to graphite particles having a pore diameter of 2 nm or less determined by the DFT method from the nitrogen adsorption isotherm and a volume per mass of pores of 0.3 mm 3 /g or less, and a specific surface area of 1 by the BET method. .5 m 2 /g or less.
- Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a predetermined volume ratio. LiPF 6 was added to the mixed solvent to obtain a non-aqueous electrolyte.
- a non-aqueous electrolyte secondary battery for evaluation was produced using the positive electrodes A1, B1, and B2.
- the positive electrode with the positive electrode lead made of aluminum and the negative electrode with the negative electrode lead made of nickel are spirally wound with a separator made of polyethylene interposed therebetween, and formed into a flat shape to form a wound electrode assembly. made.
- This electrode assembly was housed in an outer package made of an aluminum laminate, and after the non-aqueous electrolyte was injected, the opening of the outer package was sealed to produce a non-aqueous electrolyte secondary battery for evaluation.
- Capacity retention rate (discharge capacity after 800 and 1500 cycles/initial discharge capacity) x 100 Charging and discharging conditions: Under a temperature environment of 45 ° C., charge to a battery voltage of 4.2 V at a constant current of 0.5 C, after additional charging to 0.02 C at 4.2 V, rest for 30 minutes, 0.5 E The battery was discharged to a battery voltage of 2.5 V at a constant capacity.
- the battery using the positive electrode A1 of the example has a higher capacity retention rate and excellent durability (cycle characteristics) than the batteries using the positive electrodes B1 and B2 of the comparative example. .
- Non-aqueous electrolyte secondary battery 11 Positive electrode 11A Positive electrode mixture layer 12 Negative electrode 13 Separator 14 Electrode body 16 Outer can 17 Sealing body 18, 19 Insulating plate 20 Positive electrode lead 21 Negative electrode lead 22 Grooved portion 23 Internal terminal plate 24 Lower valve body 25 Insulating member 26 Upper valve body 27 Cap 28 Gasket 30 Positive electrode active material 31 First single particle 32 Second single particle
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Abstract
Description
正極11は、正極芯体と、正極芯体の表面に設けられた正極合剤層とを有する。正極芯体は、正極合剤層よりも導電性の高いシート状の集電体である。正極芯体には、アルミニウム又はアルミニウム合金などの正極11の電位範囲で安定な金属の箔、当該金属を表層に配置したフィルム等を用いることができる。正極合剤層は、正極活物質、結着剤、および導電剤を含み、正極芯体の両面に設けられることが好ましい。正極合剤層の厚みは、正極芯体より厚く、一例としては芯体の片側で50μm~150μmである。
Li層に存在するLi以外の金属元素の割合は、リチウム遷移金属複合酸化物のX線回折測定により得られるX線回折パターンのリートベルト解析から求められる。X線回折パターンは、粉末X線回折装置(株式会社リガク製、商品名「RINT-TTR」、線源Cu-Kα)を用いて、以下の条件による粉末X線回折法によって得られる。
測定範囲:15-120°
スキャン速度:4°/min
解析範囲:30-120°
バックグラウンド:B-スプライン
プロファイル関数:分割型擬Voigt関数
束縛条件:Li(3a)+Ni(3a)=1
Ni(3a)+Ni(3b)=β(βは各々のNi含有割合)
ICSD No.:98-009-4814
また、X線回折パターンのリートベルト解析には、リートベルト解析ソフトであるPDXL2(株式会社リガク製)が使用される。
(1)イオンミリング装置(例えば、日立ハイテク社製、IM4000PLUS)を用いて、正極合剤層11Aの断面を露出させる。
(2)走査型電子顕微鏡(SEM)を用いて、露出させた正極合剤層11Aの断面の反射電子像を撮影する。反射電子像を撮影する際の倍率は、1000~10000倍である。
(3)正極合剤層11Aの断面のSEM画像をコンピュータに取り込み、画像解析ソフトを用いて、コントラストから2色に色分けし、コントラストが低い方の色を空隙とした。
(4)処理画像からランダムに選択した100個の粒子の空隙面積を求め、粒子の断面積に占める空隙面積の割合(気孔率)を算出して平均化する。
負極12は、負極芯体と、負極芯体の表面に設けられた負極合剤層とを有する。負極芯体は、負極合剤層よりも導電性の高いシート状の集電体である。負極芯体には、銅又は銅合金などの負極12の電位範囲で安定な金属の箔、当該金属を表層に配置したフィルム等を用いることができる。負極合剤層は、負極活物質および結着剤を含み、負極芯体の両面に設けられることが好ましい。負極合剤層の厚みは、負極芯体より厚く、一例としては芯体の片側で50μm~150μmである。
セパレータ13には、イオン透過性および絶縁性を有する多孔性シートが用いられる。多孔性シートの具体例としては、微多孔薄膜、織布、不織布等が挙げられる。セパレータ13の材質としては、ポリエチレン、ポリプロピレン、エチレンとαオレフィンの共重合体等のポリオレフィン、セルロースなどが好適である。セパレータ13は、単層構造、積層構造のいずれであってもよい。セパレータ13の表面には、無機粒子を含む耐熱層、アラミド樹脂、ポリイミド、ポリアミドイミド等の耐熱性の高い樹脂で構成される耐熱層などが形成されていてもよい。
[正極活物質の合成]
水酸化リチウム、およびニッケルコバルトアルミニウム複合酸化物を所定の質量比で混合し、650℃から780℃へ0.5時間で上げ780℃で30時間焼成した後、さらに700℃で30時間焼成した。その後、焼成物の粉砕、分級処理を行い、組成式LiNi0.91Co0.45Al0.45O2で表されるリチウム遷移金属複合酸化物(正極活物質)を得た。このリチウム遷移金属複合酸化物中のリチウム席占有率は98.5%、格子定数a軸は2.87536Åであった。
第1単粒子の含有量は、正極活物質の全粒子に対して14%である。正極活物質と、アセチレンブラックと、ポリフッ化ビニリデンとを、100:2:1.3の固形分質量比で混合し、分散媒としてN-メチル-2-ピロリドン(NMP)を用いて、正極合剤スラリーを調製した。次に、アルミニウム箔からなる正極芯体上に正極合剤スラリーを塗布し、塗膜を乾燥、圧縮した後、所定の電極サイズに切断して正極A1を得た。
[正極B1の作製]
水酸化リチウム、およびニッケルコバルトアルミニウム複合酸化物(D50=7μm))を所定の質量比で混合し、720℃で30時間焼成した後、さらに700℃で30時間焼成した。その後、焼成物の粉砕、分級処理を行い、組成式LiNi0.91Co0.45Al0.45O2で表されるリチウム遷移金属複合酸化物として、正極B1を作製した。このリチウム遷移金属複合酸化物中のリチウム席占有率は99.5%、格子定数a軸は2.87313Åであった。正極B1では、正極活物質の粒径が揃っており、正極合剤層の断面SEM画像において、第一単粒子は1.5%であった。
<比較例2>
[正極B2の作製]
水酸化リチウム、およびニッケルコバルトアルミニウム複合酸化物(D50=5μm)を所定の質量比で混合し、720℃で30時間焼成した後、さらに700℃で30時間焼成した。その後、焼成物の粉砕、分級処理を行い、組成式LiNi0.91Co0.04Al0.05O2で表されるリチウム遷移金属複合酸化物として、正極B1を作製した。このリチウム遷移金属複合酸化物中のリチウム席占有率は99.3%、格子定数a軸は2.87272Åであった。正極B1では、正極活物質の粒径が揃っており、正極合剤層の断面SEM画像において、第一単粒子は含まれていなかった。
低BET黒鉛と、スチレン-ブタジエンゴム(SBR)のディスパージョンと、カルボキシメチルセルロースナトリウム(CMC-Na)とを、所定の固形分質量比で混合し、分散媒として水を用いて、負極合剤スラリーを調製した。次に、この負極合剤スラリーを銅箔からなる負極芯体の両面に塗布し、塗膜を乾燥、圧縮した後、所定の電極サイズに切断し、負極芯体の両面に負極合剤層が形成された負極を作製した。低BET黒鉛とは、窒素吸着等温線からDFT法により求めた細孔径が2nm以下である細孔の質量当たりの体積が0.3mm3/g以下である黒鉛粒子でBET法による比表面積が1.5m2/g以下ものである。
エチレンカーボネート(EC)と、エチルメチルカーボネート(EMC)と、ジメチルカーボネート(DMC)とを、所定の体積比で混合した。当該混合溶媒に、LiPF6を添加して非水電解液を得た。
正極A1、B1、B2を用いて評価用の非水電解質二次電池を作製した。アルミニウム製の正極リードを取り付けた上記正極、およびニッケル製の負極リードを取り付けた上記負極を、ポリエチレン製のセパレータを介して渦巻状に巻回し、扁平状に成形して巻回型の電極体を作製した。この電極体をアルミニウムラミネートで構成される外装体内に収容し、上記非水電解液を注入後、外装体の開口部を封止して評価用の非水電解質二次電池を作製した。
作製した各電池について、下記充放電を800、1500サイクル(B1を用いて作製した電池については800サイクルのみ)行い、下記式により容量維持率を算出した。評価結果を表1に示す。また、1500サイクル(B1を用いて作製した電池については800サイクル)までの容量維持率の変化を図4に示す。
容量維持率=(800、1500サイクル後の放電容量/初期放電容量)×100
充放電条件:45℃の温度環境下、0.5Cの定電流で電池電圧4.2Vまで充電し、4.2Vで0.02Cまで追充電をした後、30分間休止し、0.5Eの定容量で電池電圧2.5Vまで放電を行った。
Claims (3)
- 正極芯体と、前記正極芯体上に設けられた、正極活物質を含む正極合剤層とを有する非水電解質二次電池用正極であって、
前記正極活物質は、単粒子で構成され、
前記単粒子には、粒径が4μm以上である第1単粒子と、前記第1単粒子よりも粒径が小さな第2単粒子とが含まれ、
前記正極合剤層において、前記第2単粒子は、前記第1単粒子の周囲に配置され、前記第1単粒子に隣接する前記第2単粒子のうち最も粒径が小さな粒子は、隣接する前記第1単粒子の粒径の1/5以下の粒径を有し、
前記第1単粒子の含有量は、前記正極活物質の全粒子数に対して3~30%である、非水電解質二次電池用正極。 - 前記単粒子は、Liを除く金属元素の総モル量に対して、Ni、Mn、Fe、およびAlから選択される少なくとも1種の金属元素を90モル%以上含有するリチウム遷移金属複合酸化物で構成されている、請求項1に記載の非水電解質二次電池用正極。
- 請求項1又は2のいずれか一項に記載の正極と、
負極と、
非水電解質と、
を備える、非水電解質二次電池。
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JP2018045998A (ja) * | 2016-09-18 | 2018-03-22 | 貴州振華新材料有限公司 | 球形又は類球形リチウムイオン電池の正極材料、製造方法及び応用 |
WO2019163483A1 (ja) * | 2018-02-22 | 2019-08-29 | 三洋電機株式会社 | 非水電解質二次電池 |
WO2020110260A1 (ja) * | 2018-11-29 | 2020-06-04 | 株式会社 東芝 | 電極、電池、及び電池パック |
WO2021004033A1 (zh) | 2019-07-11 | 2021-01-14 | 电子科技大学 | 量化的边缘计算侧终端安全接入策略选择方法 |
JP6857752B1 (ja) * | 2020-01-09 | 2021-04-14 | 住友化学株式会社 | リチウム金属複合酸化物、リチウム二次電池用正極活物質、リチウム二次電池用正極、リチウム二次電池及びリチウム金属複合酸化物の製造方法 |
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JP2018045998A (ja) * | 2016-09-18 | 2018-03-22 | 貴州振華新材料有限公司 | 球形又は類球形リチウムイオン電池の正極材料、製造方法及び応用 |
WO2019163483A1 (ja) * | 2018-02-22 | 2019-08-29 | 三洋電機株式会社 | 非水電解質二次電池 |
WO2020110260A1 (ja) * | 2018-11-29 | 2020-06-04 | 株式会社 東芝 | 電極、電池、及び電池パック |
WO2021004033A1 (zh) | 2019-07-11 | 2021-01-14 | 电子科技大学 | 量化的边缘计算侧终端安全接入策略选择方法 |
JP6857752B1 (ja) * | 2020-01-09 | 2021-04-14 | 住友化学株式会社 | リチウム金属複合酸化物、リチウム二次電池用正極活物質、リチウム二次電池用正極、リチウム二次電池及びリチウム金属複合酸化物の製造方法 |
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