Coated positive electrode active material and battery using same

Abstract

This coated positive electrode active material (13) is provided with: a first positive electrode active material (10) containing lithium and a transition metal; and a coating layer (11) that covers the first positive electrode active material (10), the coating layer (11) containing: a first material (14) that contains a halide; and a second material (15) containing at least one selected from the group consisting of a second positive electrode active material capable of absorbing and releasing lithium and a compound containing a transition metal. A battery (100) according to the present invention is provided with a positive electrode (23), a negative electrode (26), and an electrolyte layer disposed between the positive electrode (23) and the negative electrode (26). The positive electrode (23) contains the coated positive electrode active material (13) according to the present invention.

Description

Technical Field

[0001] The present invention relates to a coated positive electrode active material and a battery using the same. Background Art

[0002] As those skilled in the art are aware, in existing batteries, the electrolyte can sometimes decompose due to the active material. This decomposition can form a film of the decomposed electrolyte within the electrodes. This can lead to adverse consequences such as increased battery internal resistance and decreased battery cycle performance.

[0003] Coating the active material with an appropriate coating material can suppress electrolyte decomposition caused by the active material. For example, Patent Document 1 discloses coating the positive electrode active material with lithium niobate. Patent Document 2 discloses coating the positive electrode active material with a solid electrolyte containing Li, Ti, Al, and F.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2009-193940

[0007] Patent Document 2: International Publication No. 2021 / 187391 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] From the viewpoints of discharge capacity and resistance value, the existing technology has room for improvement.

[0010] Solutions for solving problems

[0011] The present invention provides a coated positive electrode active material having:

[0012] a first positive electrode active material comprising lithium and a transition metal; and

[0013] a coating layer covering the first positive electrode active material,

[0014] The coating layer includes a first material including a halide and a second material including at least one selected from the group consisting of a second positive electrode active material capable of occluding and releasing lithium and a compound containing the transition metal.

[0015] Effects of the Invention

[0016] According to the technology of the present invention, the discharge capacity and resistance value of the battery can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a cross-sectional view showing a schematic structure of the coated positive electrode active material according to the first embodiment.

[0018] Figure 2 This is a cross-sectional view showing a schematic structure of a battery according to Embodiment 2.

[0019] Figure 3 These are diagrams showing the STEM image and elemental mapping of the coated positive electrode active material of Example 1.

[0020] Figure 4 These are diagrams showing the STEM image and elemental mapping of the coated positive electrode active material of Example 2. DETAILED DESCRIPTION

[0021] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments.

[0022] (Implementation Method 1)

[0023] Figure 1 This is a cross-sectional view schematically illustrating the structure of a coated positive electrode active material 13 according to Embodiment 1. The coated positive electrode active material 13 includes a first positive electrode active material 10 and a coating layer 11. The first positive electrode active material 10 is, for example, granular. The coating layer 11 covers at least a portion of the surface of the particles of the first positive electrode active material 10.

[0024] The first positive electrode active material 10 contains lithium and a transition metal, and is a material capable of occluding and releasing lithium. The coating layer 11 contains a first material 14 and a second material 15. The composition of the first material 14 and the composition of the second material 15 are different. The first material 14 contains a halide. The second material 15 contains at least one member selected from the group consisting of a second positive electrode active material and a compound A. The second positive electrode active material is capable of occluding and releasing lithium. The compound A contains the same transition metal as that contained in the first positive electrode active material 10.

[0025] The coating layer 11 can prevent other materials such as the electrolyte and the solid electrolyte from directly contacting the first positive electrode active material 10. As a result, the decomposition of other materials such as the electrolyte and the solid electrolyte is suppressed. The halide contained in the first material 14 is difficult to be decomposed by the first positive electrode active material 10 due to its excellent oxidation resistance or reduction resistance. The second material 15 improves the electronic conductivity of the coating layer 11 and reduces the possibility of isolation of the first positive electrode active material 10 in the battery electrode. As a result, the discharge capacity of the battery using the coated positive electrode active material 13 is improved, and the resistance value of the battery using the coated positive electrode active material 13 is reduced.

[0026] Examples of the first positive electrode active material 10 include lithium-containing transition metal oxides, lithium-containing transition metal phosphates, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. In particular, when lithium-containing transition metal oxides or lithium-containing transition metal phosphates are used as the positive electrode active material, the manufacturing cost of the battery can be reduced and the average discharge voltage can be increased. Examples of lithium-containing transition metal oxides include lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide. Examples of lithium-containing transition metal phosphates include lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate. At least one selected from these positive electrode active materials can be used.

[0027] The particles of the first positive electrode active material 10 may be either primary particles or secondary particles. The particles of the first positive electrode active material 10 have an average particle size of, for example, 1 μm or more and 10 μm or less. The average particle size refers to the particle diameter (median particle size) at which the cumulative volume in the volume-based particle size distribution is 50%. The volume-based particle size distribution is measured, for example, using a laser diffraction particle size distribution analyzer.

[0028] When the thickness of the coating layer 11 is on the nanometer order, the average particle size of the first positive electrode active material 10 is substantially equal to the average particle size of the coating positive electrode active material 13 .

[0029] The first material 14 and the second material 15 may each be in the form of particles. The particles of the second material 15 may be dispersed in the coating layer 11. With this configuration, the effect of the second material 15 can be easily exhibited uniformly in the coating layer 11.

[0030] The ratio of the first material 14 to the second material 15 in the coating layer 11 is not particularly limited. The ratio of the first material 14 to the second material 15 can be determined so that the first material 14 is contained as the main component in the coating layer 11. In this case, the effect of suppressing the decomposition of other materials such as the electrolyte is improved. In one example, the ratio of the amount m2 of the second material 15 to the amount m1 of the first material 14 (m2 / m1) is 0.05 to 0.4, preferably 0.1 to 0.3. "Main component" refers to the component that is contained in the largest amount by weight.

[0031] The first material 14 may also have lithium ion conductivity. With this structure, the first positive electrode active material 10 can smoothly absorb and release lithium ions.

[0032] From the viewpoint of chemical stability, the halide as the first material 14 may be an inorganic compound.

[0033] Since halogens have high electronegativity, halides can improve the oxidation resistance of the coating layer 11. From the viewpoint of oxidation resistance, fluorides can be used as halides. Halides also include oxyhalides.

[0034] The halide contains, for example, Li, M1, M2, and F. M1 is at least one member selected from the group consisting of Ti and Nb. M2 is at least one member selected from the group consisting of Ca, Mg, Al, Y, and Zr. This halide is called a halide solid electrolyte and has excellent lithium ion conductivity.

[0035] The halide may be composed of Li, M1, M2, and F except for unavoidable impurities.

[0036] M1 may be Ti, and M2 may be Al. In this case, the halide has excellent lithium ion conductivity.

[0037] The ratio of the amount of Li to the total amount of M1 and M2 is, for example, 0.5 to 4.5. When the ratio falls within this range, the halide has excellent lithium ion conductivity.

[0038] The halide may have a composition represented by the following formula (1). In formula (1), M is at least one member selected from the group consisting of Ca, Mg, Al, Y, and Zr. x, y, and b respectively satisfy 0 < x < 1, 0 < y < 1, 0 < x + y ≤ 1, and 0.8 ≤ b ≤ 1.1. When having the composition represented by formula (1), the halide has excellent lithium ion conductivity.

[0039] Li 6-(5-x-2y)b (Nb 1-x-y Ti x M y ) b F6···Formula (1)

[0040] The halide as the first material 14 preferably does not contain sulfur. In this case, the first material 14 can be prevented from becoming a source of hydrogen sulfide.

[0041] The second material 15 may include compound A. In this case, compound A may also be a compound capable of occluding and releasing lithium. In other words, compound A may also function as an active material. This configuration is advantageous for increasing the battery's discharge capacity and reducing its resistance.

[0042] Compound A may be composed of the same element group as that constituting the first positive electrode active material 10. Specifically, compound A may have the same composition as that of the first positive electrode active material 10. This composition is advantageous in increasing the discharge capacity of the battery and reducing the resistance value of the battery.

[0043] The second material 15 may include a second positive electrode active material. The second positive electrode active material may be an active material capable of occluding and releasing lithium and having a composition different from that of the first positive electrode active material 10. Examples of the second positive electrode active material include the materials previously exemplified as the first positive electrode active material 10. For example, when the first positive electrode active material 10 includes lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, or the like may be used as the second positive electrode active material.

[0044] The first material 14 and the second material 15 may be a halide and a compound A, respectively.

[0045] The average thickness of the coating layer 11 is, for example, 1 nm or more and 150 nm or less, preferably 100 nm or less, and more preferably 50 nm or less. By appropriately adjusting the average thickness of the coating layer 11, the effect of increasing the discharge capacity of the battery and reducing the resistance value of the battery can be enhanced. The average thickness of the coating layer 11 can be calculated based on a STEM image obtained using a scanning transmission electron microscope (STEM). The average thickness can be the average value of the thicknesses of any number of locations (e.g., 5 locations).

[0046] The particles of compound A and the particles of the second positive electrode active material can be nanoparticles respectively. Preferably, the particles of compound A and / or the particles of the second positive electrode active material exist in the form of dispersion in the coating layer 11. Therefore, the particles of compound A and the particles of the second positive electrode active material preferably have a particle diameter smaller than the thickness of the coating layer 11. That is, particles of the second material 15 having a particle diameter smaller than the thickness of the coating layer 11 may exist in the coating layer 11. According to this structure, the effect of suppressing the decomposition of other materials such as the electrolyte can be balanced with the effect of increasing the discharge capacity of the battery and reducing the resistance value of the battery. The particle diameter of the particles of the second material 15 is the diameter of a circle having an area equal to the area of the particles of the second material 15 calculated based on the transmission electron microscope image. The average particle size of the particles of compound A and the particles of the second positive electrode active material can be smaller than the thickness of the coating layer 11.

[0047] The covering layer 11 may cover the entire surface of the particles of the first positive electrode active material 10 or may cover only a portion thereof.

[0048] The coating layer 11 may contain a material other than the first material 14 and the second material 15. Examples of such a material include conductive carbon materials. The coating layer 11 may contain only the first material 14 and the second material 15, excluding unavoidable impurities.

[0049] The presence of the second material 15 in the coating layer 11 can be confirmed by elemental mapping of the particles coating the positive electrode active material 13. The elemental mapping can be obtained by combining energy dispersive X-ray spectroscopy (STEM-EDX) with a scanning transmission electron microscope.

[0050] The coated positive electrode active material 13 is obtained by attaching a coating material to the surface of particles of the first positive electrode active material 10. The coating material includes a first material 14 and a second material 15. For example, the coating material is prepared by mixing the first material 14 and the second material 15. The coating material is then attached to the surface of the first positive electrode active material 10 to form the coating layer 11. This method allows for efficient production of the coated positive electrode active material 13 of Embodiment 1.

[0051] The method for attaching the coating material to the surface of the first positive electrode active material 10 is not particularly limited. As described in Patent Document 2, for example, a powder of the first positive electrode active material 10 and a powder of the coating material are mixed in an appropriate ratio to form a mixture. The mixture is then subjected to a grinding process to impart mechanical energy to the mixture. The grinding process can be performed using a mixing device such as a ball mill. To suppress oxidation of the material, the grinding process can also be performed in a dry and inert atmosphere.

[0052] The coated positive electrode active material 13 can be produced by a dry particle composite method. The dry particle composite method includes applying at least one mechanical energy selected from the group consisting of impact, compression, and shear to the first positive electrode active material 10 and the coating material.

[0053] Examples of devices capable of imparting mechanical energy to the mixture of the first positive electrode active material 10 and the coating material include processing devices (particle compounding devices) such as a ball mill, "MECHANOFUSION" (manufactured by Hosokawa Micron Corporation), "NOBILTA" (manufactured by Hosokawa Micron Corporation), and "BALANCE GRAN" (manufactured by FREUND-TURBO CORPORATION).

[0054] In any device, the thickness of the coating layer 11 can be controlled by adjusting conditions such as the rotation speed, processing time, and feed amount. It should be noted that the treatment using the above-mentioned device is not necessary. The coated positive electrode active material 13 can also be manufactured by mixing the first positive electrode active material 10 with the coating material using a mortar, a mixer, etc. The coating material can also be deposited on the surface of the first positive electrode active material 10 by various methods such as spraying, spray dry coating, electrodeposition, impregnation, and mechanical mixing using a disperser.

[0055] (Implementation Method 2)

[0056] Figure 2 This is a cross-sectional view of a battery 100 according to Embodiment 2. The battery 100 includes a positive electrode 23, a negative electrode 26, a nonaqueous electrolyte 29, a separator 27, and an outer package 28. The positive electrode 23 includes a positive electrode collector 21 and a positive electrode active material layer 22. The positive electrode active material layer 22 is disposed on the positive electrode collector 21. The negative electrode 26 includes a negative electrode collector 24 and a negative electrode active material layer 25. The negative electrode active material layer 25 is disposed on the negative electrode collector 24. A separator 27 is disposed between the positive electrode 23 and the negative electrode 26. The positive electrode 23 and the negative electrode 26 face each other with the separator 27 interposed therebetween. The positive electrode 23, the negative electrode 26, the separator 27, and the nonaqueous electrolyte 29 are housed in the outer package 28. The battery 100 is typically a secondary battery.

[0057] The positive electrode 23 includes the coated positive electrode active material 13 of Embodiment 1. This configuration suppresses decomposition of other materials such as the electrolyte in the positive electrode 23. As a result, the discharge capacity can be increased and the resistance value can be reduced.

[0058] The positive electrode current collector 21 is a sheet or film made of a metal material such as aluminum, an aluminum alloy, stainless steel, titanium, or a titanium alloy. The sheet or film may be porous or non-porous. Examples of the sheet or film include metal foil and metal mesh. The surface of the positive electrode current collector 21 may also be coated with a carbon material as an auxiliary conductive material.

[0059] The positive electrode active material layer 22 may contain other materials such as a conductive additive, an ion conductor, and a binder.

[0060] Conductive additives and ion conductors are used to reduce the resistance of the positive electrode 23. Examples of conductive additives include carbon materials and conductive polymer compounds. Examples of carbon materials include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide. Examples of conductive polymer compounds include polyaniline, polypyrrole, and polythiophene. At least one selected from these conductive additives may be used.

[0061] Examples of ion conductors include polymethyl methacrylate, gel electrolytes such as polymethyl methacrylate, organic solid electrolytes such as polyethylene oxide, Li7La3Zr2O 12 Inorganic solid electrolytes such as the above. At least one selected from these ion conductors can be used.

[0062] The binder is used to improve the binding properties of the materials constituting negative electrode 26. Examples of the binder include polymer materials such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethyl cellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, polyethylene, and polyimide. At least one selected from these binders may be used.

[0063] The negative electrode current collector 24 is a sheet or film made of a metal material such as stainless steel, nickel, a nickel alloy, copper, or a copper alloy. The sheet or film may be porous or non-porous. Examples of the sheet or film include metal foil and metal mesh. The surface of the negative electrode current collector 24 may also be coated with a carbon material as an auxiliary conductive material.

[0064] The negative electrode active material layer 25 may contain a negative electrode active material capable of occluding and releasing lithium. Examples of negative electrode active materials capable of occluding and releasing lithium include lithium titanate, graphite, silicon, silicon-containing oxides, zinc alloys, lithium metal, and lithium alloys. At least one selected from these negative electrode active materials may be used.

[0065] The negative electrode active material layer 25 may contain other materials such as a conductive additive, an ion conductor, and a binder. The materials used for the conductive additive, ion conductor, and binder in the positive electrode active material layer 22 may also be used in the negative electrode active material layer 25 .

[0066] The positive electrode 23, the negative electrode 26, and the separator 27 may also contain a non-aqueous electrolyte 29. The non-aqueous electrolyte 29 may fill the interior space of the outer packaging 28. The non-aqueous electrolyte 29 allows lithium ions to move between the positive electrode 23 and the negative electrode 26. The non-aqueous electrolyte 29 may include a non-aqueous electrolyte solution, a gel electrolyte, or an ionic liquid.

[0067] The non-aqueous electrolyte solution contains, for example, a non-aqueous solvent and a lithium salt.

[0068] As non-aqueous solvents, cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, cyclic esters, chain esters, fluorinated solvents, and nitriles can be used. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, and butylene carbonate. Examples of chain carbonates include dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Examples of cyclic ethers include tetrahydrofuran, 1,4-dioxane, and 1,3-dioxolane. Examples of chain ethers include 1,2-dimethoxyethane and 1,2-diethoxyethane. Examples of cyclic esters include γ-butyrolactone. Examples of chain esters include methyl acetate. Examples of fluorinated solvents include fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, ethyl fluoromethyl carbonate, and fluorodimethylene carbonate. Examples of nitriles include acetonitrile. At least one selected from these non-aqueous solvents can be used.

[0069] Examples of lithium salts include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(perfluoroethylsulfonyl)imide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, and lithium difluorooxalatoborate. At least one selected from these lithium salts may be used.

[0070] The gel electrolyte may be a material obtained by impregnating a polymer material with a non-aqueous electrolyte. Examples of the polymer material include polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, and polymers having oxyethylene bonds.

[0071] Examples of cations constituting ionic liquids include: aliphatic chain quaternary cations, aliphatic cyclic ammonium, nitrogen-containing heterocyclic aromatic cations, etc. Examples of aliphatic chain quaternary cations include: tetraalkylammonium, tetraalkylphosphine, etc. Examples of aliphatic cyclic ammonium include: pyrrolidinium, morpholinium, imidazolinium, tetrahydropyrimidinium, piperazinium, piperidinium, etc. Examples of nitrogen-containing heterocyclic aromatic cations include: pyridinium, imidazolium, etc. Examples of anions constituting ionic liquids include: PF6 - 、BF4 - 、SbF6 - 、AsF6 - 、SO3CF3 - 、N(SO2F)2 - 、N(SO2CF3)2 - 、N(SO2C2F5)2 - 、N(SO2CF3)(SO2C4F9) - 、C(SO2CF3)3- etc. Ionic liquids may also contain lithium salts.

[0072] The separator 27 is an electrolyte layer having lithium ion conductivity. The material of the separator 27 is not particularly limited as long as it allows lithium ions to pass through. The material of the separator 27 can be at least one selected from the group consisting of a solid electrolyte, a gel electrolyte, an ion exchange resin membrane, a semipermeable membrane, and a porous membrane. If the separator 27 is made of these materials, the safety of the battery 100 can be fully ensured. Examples of the solid electrolyte include sulfide solid electrolytes such as Li2S-P2S5, Li7La3Zr2O 12 Examples of the electrolyte include oxide solid electrolytes such as (LLZ). Examples of gel electrolytes include gel electrolytes containing fluororesins such as PVdF. Examples of ion exchange resin membranes include cation exchange membranes and anion exchange membranes. Examples of porous membranes include porous membranes made of polyolefin resins and porous membranes made of cellophane obtained by weaving glass fibers into non-woven fabrics.

[0073] The outer package 28 is made of a material obtained by laminating a metal foil such as aluminum foil with a resin film such as a PET film, etc. The outer package 28 may be a container made of resin or metal.

[0074] The shape of the battery 100 is not limited to a laminated type, and other shapes of the battery 100 include a coin shape, a cylindrical shape, a square shape, a sheet shape, a button shape, and a flat shape.

[0075] The battery 100 may also be a solid-state battery.

[0076] When the battery 100 is a solid-state battery, a solid electrolyte is used in the positive electrode 23, the negative electrode 26, and the separator 27 instead of the non-aqueous electrolyte 29. Examples of solid electrolytes include halide solid electrolytes, sulfide solid electrolytes, oxide solid electrolytes, polymer solid electrolytes, and complex hydride solid electrolytes. The positive electrode 23, the negative electrode 26, and the separator 27 can each use at least one selected from these solid electrolytes.

[0077] (Other embodiments)

[0078] (Note)

[0079] The following technology is disclosed through the description of the above embodiments.

[0080] (Technique 1)

[0081] A coated positive electrode active material comprising:

[0082] a first positive electrode active material comprising lithium and a transition metal; and

[0083] a coating layer covering the first positive electrode active material,

[0084] The coating layer includes a first material including a halide and a second material including at least one selected from the group consisting of a second positive electrode active material capable of occluding and releasing lithium and a compound containing the transition metal.

[0085] According to this configuration, the discharge capacity and resistance value of the battery can be improved.

[0086] (Technique 2)

[0087] According to the coated positive electrode active material of technique 1, particles of the second material are dispersed in the coating layer. With this configuration, the effect of the second material can be easily exerted uniformly in the coating layer.

[0088] (Technique 3)

[0089] In the coated positive electrode active material according to Technique 1 or 2, particles of the second material having a particle diameter smaller than the thickness of the coating layer are present within the coating layer. This allows for a balance between suppressing the decomposition of other materials, such as the electrolyte, and improving the battery's discharge capacity and reducing its resistance.

[0090] (Technique 4)

[0091] The coated positive electrode active material according to any one of Techniques 1 to 3, wherein the second material comprises the compound containing the transition metal, and the compound containing the transition metal is a compound capable of occluding and releasing lithium. This configuration is advantageous for increasing the discharge capacity of the battery and reducing the resistance of the battery.

[0092] (Technique 5)

[0093] According to the coated positive electrode active material of technique 4, the compound containing the transition metal is composed of the same element group as the element group constituting the first positive electrode active material. This configuration is advantageous in increasing the discharge capacity of the battery and reducing the resistance value of the battery.

[0094] (Technique 6)

[0095] In the coated positive electrode active material according to technology 4 or 5, the compound containing the transition metal has the same composition as that of the first positive electrode active material. This configuration is advantageous in increasing the discharge capacity of the battery and reducing the resistance of the battery.

[0096] (Technique 7)

[0097] The coated positive electrode active material according to any one of techniques 1 to 6, wherein the first material has lithium ion conductivity. With this configuration, the first positive electrode active material can smoothly absorb and release lithium ions.

[0098] (Technique 8)

[0099] The coated positive electrode active material according to any one of Techniques 1 to 7, wherein the first material comprises the halide, the halide comprises Li, M1, M2, and F, M1 is at least one member selected from the group consisting of Ti and Nb, and M2 is at least one member selected from the group consisting of Ca, Mg, Al, Y, and Zr. Such a halide is known as a halide solid electrolyte and has excellent lithium ion conductivity.

[0100] (Technique 9)

[0101] The coated positive electrode active material according to the eighth aspect, wherein the M1 is Ti and the M2 is Al. In this case, the halide has excellent lithium ion conductivity.

[0102] (Technique 10)

[0103] The coated positive electrode active material according to any one of Techniques 1 to 7, wherein the halide has a composition represented by the following formula (1), wherein M is at least one member selected from the group consisting of Ca, Mg, Al, Y, and Zr, and x, y, and b respectively satisfy 0 < x < 1, 0 < y < 1, 0 < x + y ≤ 1, and 0.8 ≤ b ≤ 1.1. When the halide has the composition represented by formula (1), it has excellent lithium ion conductivity.

[0104] Li 6-(5-x-2y)b (Nb 1-x-y Ti x M y ) b F6···Formula (1)

[0105] (Technology 11)

[0106] A battery comprising:

[0107] A positive electrode comprising the coated positive electrode active material according to any one of techniques 1 to 10;

[0108] a negative electrode; and

[0109] The electrolyte layer is disposed between the positive electrode and the negative electrode.

[0110] According to this structure, decomposition of other materials such as the electrolyte solution in the positive electrode or the negative electrode is suppressed, resulting in an effect of increasing discharge capacity and reducing resistance.

[0111] Example

[0112] (Example 1)

[0113] [Preparation of coating material]

[0114] In an argon atmosphere with a dew point below -60°C, LiF, TiF4 and AlF3 as raw material powders were weighed in a molar ratio of LiF:TiF4:AlF3=2.7:0.3:0.7. These were crushed and mixed in a mortar to obtain a mixture. Thereafter, the mixture was ground using 5mm φ zirconia balls and a planetary ball mill (Fritsch, P-7 model) for 12 hours at 500 rpm. Thus, a Li 2.7 Ti 0.3 Al 0.7 A powdery halide solid electrolyte (hereinafter referred to as "LTAF") having a composition of F6.

[0115] A coating material is obtained by grinding a mixture of LTAF (the first material) and lithium cobalt oxide (average particle size 4 μm) (the second material). The LTAF and lithium cobalt oxide are finely ground by grinding. A mixing device such as a ball mill can be used for grinding. Hereinafter, lithium cobalt oxide may be referred to as "LCO."

[0116] [Preparation of coated positive electrode active material]

[0117] As a positive electrode active material, LCO powder (average particle size 4 μm) was prepared. A coating material was attached to the surface of the LCO particles to form a coating layer. The coating layer was formed by compression shearing using a particle composite device (NOB-MINI, manufactured by Hosokawa Micron Corporation). Specifically, LCO and the coating material were mixed at a mass ratio of 100:3, and the mixture was treated under the conditions of a rotation speed of 6000 rpm and a treatment time of 50 minutes. Thus, the coated positive electrode active material of Example 1 was obtained. The target thickness of the coating layer was 40 nm.

[0118] (Example 2)

[0119] The coating material of Example 2 was obtained by grinding LTAF (the first material) and lithium nickel cobalt manganese oxide (Ni:Co:Mn = 6:2:2, average particle size 5 μm) (the second material). LTAF and lithium nickel cobalt manganese oxide were finely ground by grinding. Hereinafter, lithium nickel cobalt manganese oxide may be referred to as "NCM."

[0120] NCM powder (average particle size 5 μm) was prepared as the first positive electrode active material. A coated positive electrode active material of Example 2 was prepared under the same conditions as in Example 1 except that the coating material and NCM particles of Example 2 were used.

[0121] (Comparative Example 1)

[0122] The LCO used in Example 1 was regarded as the active material in Comparative Example 1.

[0123] (Comparative Example 2)

[0124] A coated positive electrode active material of Comparative Example 2 was prepared by the same method as in Example 1, except that only LTAF as the first material was used as the coating material instead of the second material.

[0125] [STEM-EDX measurement]

[0126] STEM images and elemental mapping of the active materials of Examples 1 and 2 were obtained using a scanning transmission electron microscope (JEM-F200, manufactured by JEOL Ltd., accelerating voltage: 200 kV) and an attached energy dispersive X-ray analyzer (System 7, manufactured by Thermo Fisher Scientific).

[0127] Figure 3 These are diagrams showing the STEM image and elemental mapping of the coated positive electrode active material of Example 1. Figure 3 The upper left image is a STEM image. Figure 3 The remaining images are element mappings of O, F, Al, Ti, and Co. Figure 3 As shown in the STEM image, the dense white areas are particles of LCO, the first positive electrode active material. A coating layer containing LTAF surrounds the LCO particles. In particular, elemental mapping of Co reveals the presence of Co and O in the region corresponding to the coating layer. This indicates that the coating layer also contains LCO.

[0128] Figure 4 These are diagrams showing the STEM image and elemental mapping of the coated positive electrode active material of Example 2. Figure 4 The upper left image is a STEM image. Figure 4 The remaining images are element mappings of O, F, Al, Ti, Mn, Co, and Ni. Figure 4As shown in the STEM image, the dense white areas are particles of NCM, the first positive electrode active material. A coating layer containing LTAF surrounds the NCM particles. In particular, elemental mapping of Mn, Co, and Ni reveals the presence of Mn, Co, Ni, and O in the region corresponding to the coating layer. This indicates that the coating layer also contains NCM.

[0129] [Fabrication of non-aqueous electrolyte batteries]

[0130] Coin-type non-aqueous electrolyte batteries were produced using the active materials of Example 1, Comparative Example 1, and Comparative Example 2.

[0131] [Production of positive electrode]

[0132] A positive electrode slurry was prepared by mixing the coating positive electrode active material, acetylene black, polyvinylidene fluoride, and N-methyl-2-pyrrolidone. The mass ratio of the coating positive electrode active material, acetylene black, and polyvinylidene fluoride was 90:7:3. The positive electrode slurry was applied to one side of an aluminum foil to form a coating film. After the coating film was dried, it was rolled to obtain a positive electrode comprising an aluminum foil and a positive electrode active material layer.

[0133] [Production of negative electrode]

[0134] Lithium titanate (Li4Ti5O 12 A negative electrode slurry was prepared by mixing lithium titanate (LiTiO2), acetylene black, polyvinylidene fluoride (PVDF), and N-methyl-2-pyrrolidone (N-Methyl-2-pyrrolidone). The mass ratio of lithium titanate, acetylene black, and polyvinylidene fluoride was 90:7:3. The negative electrode slurry was applied to one side of aluminum foil to form a coating. After drying, the coating was rolled to obtain a negative electrode comprising aluminum foil and a negative electrode active material layer.

[0135] [Preparation of non-aqueous electrolyte]

[0136] LiBF4 was dissolved in γ-butyrolactone to obtain a non-aqueous electrolyte solution having a LiBF4 concentration of 1.5 mol / L.

[0137] [Fabrication of non-aqueous electrolyte secondary battery]

[0138] In a low dew point atmosphere at -50°C, the positive and negative electrodes were punched into a 10.8 mm diameter. The positive electrode, polyolefin film, and negative electrode were placed in a 1616 coin case, and a nonaqueous electrolyte solution was injected into the coin case. The coin case was sealed with a lid to produce a coin-type nonaqueous electrolyte battery.

[0139] [Measurement of initial discharge capacity]

[0140] The initial discharge capacity of the batteries of Example 1, Comparative Example 1, and Comparative Example 2 was measured by the following method. Constant current charging was performed at a current of 0.01 C until the voltage reached 2.5 V, and then constant current discharge was performed at a current of 0.01 C until the voltage reached 1.5 V. The discharge capacity measured at this time was considered the initial discharge capacity. The pause time between charging and discharging was 60 minutes. Charging and discharging were performed at a temperature of 25°C (ambient temperature). The results are shown in Table 1.

[0141] [Measurement of resistance]

[0142] The initial resistance of the batteries of Example 1, Comparative Example 1, and Comparative Example 2 was measured using the following method. The batteries were charged to a state of charge (SOC) of 50%, and the voltage drop ΔV was measured when constant current discharge was initiated at a current I of 0.1C. The value of ΔV / I was considered the battery resistance. The results are shown in Table 1.

[0143] [High temperature storage test]

[0144] High-temperature storage testing was conducted on the batteries of Example 1, Comparative Example 1, and Comparative Example 2 using the following method. Continuous charging was performed at 100°C (ambient temperature) for 500 hours. Charging was then stopped, and the batteries were stored at 100°C for 100 hours. Afterwards, the temperature was returned to 25°C, and charge and discharge measurements were repeated. The discharge capacity measured at this point was considered the recovery discharge capacity. The results are shown in Table 1.

[0145] [Table 1]

[0146] coating layer Initial discharge capacity resistance value Restore discharge capacity Example 1 LTAF+LCO 0.95 1.26 0.91 Comparative Example 1 none 1.00 1.00 0.56 Comparative Example 2 LTAF 0.88 1.54 0.84

[0147] In Table 1, the initial discharge capacity and resistance value of Example 1 and Comparative Example 2 are values normalized by the initial discharge capacity and resistance value of Comparative Example 1. The recovery discharge capacity is a value normalized by the initial discharge capacity of Comparative Example 1.

[0148] As shown in Table 1, the initial discharge capacity of the battery of Example 1 is equivalent to the initial discharge capacity of the battery of Comparative Example 1, and far exceeds the initial discharge capacity of the battery of Comparative Example 2.

[0149] The resistance value of the battery of Example 1 is slightly higher than that of the battery of Comparative Example 1, but much lower than that of the battery of Comparative Example 2. The reduction in resistance means advantages in improving rate characteristics and low-temperature operation.

[0150] The battery of Example 1 showed excellent discharge capacity after the high-temperature storage test, i.e., recovery discharge capacity. The battery of Comparative Example 1 showed significantly lower recovery discharge capacity than the initial discharge capacity. This indicates that the battery of Example 1 exhibited excellent durability in a charged state and under high-temperature storage.

[0151] [Production of solid-state batteries]

[0152] Solid-state batteries were fabricated using the coated positive electrode active materials of Example 2, Comparative Example 3, and Comparative Example 4.

[0153] (Fabrication of Solid Electrolyte Materials)

[0154] Under a dry argon atmosphere, raw material powders (LiBr, YBr₃, LiCl, and YCl₃) were weighed at a molar ratio of Li:Y:Br:Cl = 3:1:2:4. These were ground and mixed in a mortar to form a mixture. The mixture was then milled in a planetary ball mill at 600 rpm for 25 hours. This yielded a powdered solid electrolyte with the composition of Li₃YBr₂Cl₄.

[0155] LiCl and YCl3 were weighed in a specified molar ratio, and the same method as Li3YBr2Cl4 was used to obtain Li x Powdered solid electrolyte composed of YCl6.

[0156] (Preparation of positive electrode composite material)

[0157] In a dry argon atmosphere, Li x YCl6, the coated positive electrode active material, and a conductive additive were mixed in an agate mortar to prepare a positive electrode composite material. The volume ratio of the solid electrolyte to the coated positive electrode active material was 50:50. Carbon nanofiber (VGCF, manufactured by Showa Denko Co., Ltd.) was used as the conductive additive. The ratio of the conductive additive mass to the combined mass of the solid electrolyte and the coated positive electrode active material was 1 wt%. "VGCF" is a registered trademark of Showa Denko Co., Ltd.

[0158] (Preparation of negative electrode composite material)

[0159] In a dry argon atmosphere, Li3YBr2Cl4 as a solid electrolyte and Li4Ti5O as a negative electrode active material were added. 12 (average particle size 2.5 μm) and a conductive additive were mixed in an agate mortar to prepare a negative electrode composite material. The volume ratio of the solid electrolyte to the negative electrode active material was 40:60. Carbon nanofibers (VGCF, manufactured by Showa Denko K.K.) were used as the conductive additive. The ratio of the conductive additive to the total mass of the solid electrolyte and negative electrode active material was 1 wt%.

[0160] (Manufacturing of Secondary Batteries)

[0161] In an insulating outer cylinder with an inner diameter of 9.4 mm, 20.5 mg of the positive electrode composite material, 50 mg of Li xYCl6, 60 mg of Li3YBr2Cl4, and 28.8 mg of the negative electrode composite material. The positive electrode composite material, solid electrolyte, and negative electrode composite material are press-formed at a pressure of 720 MPa. Thus, a laminate having a positive electrode, an electrolyte layer, and a negative electrode is produced. Next, stainless steel collectors are placed above and below the laminate, and current collector leads are installed on the collectors. Finally, an insulating hoop is used to seal the insulating outer cylinder to isolate the interior of the insulating outer cylinder from the external atmosphere. Thus, the solid-state battery of Example 2 is obtained.

[0162] (Comparative Example 3)

[0163] A lithium niobate coating layer with a target thickness of 5 nm was formed on the surface of NCM particles (average particle size 5 μm). The lithium niobate coating layer was formed using lithium ethoxide and niobium ethoxide by a liquid phase method in a dry air environment with a dew point of -50°C.

[0164] A solid-state battery of Comparative Example 3 was produced by the same method as in Example 2 except that the coated positive electrode active material of Comparative Example 3 was used.

[0165] The ionic conductivity of LTAF and lithium niobate is 7×10 -6 S / cm and 2×10 -7 S / cm. LTAF has a much higher ionic conductivity than lithium niobate. Therefore, even if the thickness of the LTAF coating layer is at least 10 times that of the lithium niobate coating layer, a battery using an active material coated with an LTAF coating layer exhibits a resistance value comparable to that of a battery using an active material coated with a lithium niobate coating layer. Therefore, the target thickness of the active material coating layer in Example 2 was set to 40 nm, while the target thickness of the active material coating layer in Comparative Example 3 was set to 5 nm.

[0166] (Comparative Example 4)

[0167] A coated positive electrode active material of Comparative Example 4 was produced in the same manner as in Example 2, except that only LTAF was used as the first material instead of the second material as the coating material. A solid-state battery of Comparative Example 4 was produced in the same manner as in Example 2, except that the coated positive electrode active material of Comparative Example 4 was used.

[0168] [Measurement of resistance]

[0169] The resistance of the solid-state batteries of Example 2, Comparative Example 3, and Comparative Example 4 was measured using the following method. Continuous charging at 2.75 V was performed for 500 hours at 100°C (ambient temperature). Charging was then stopped, and the batteries were stored at 100°C for 100 hours. Impedance measurements were then performed at 0°C, measuring resistance at 1 kHz and 1 Hz. The results are shown in Table 2. The resistance values shown in Table 2 are standardized using the resistance values of Comparative Example 4.

[0170] [Table 2]

[0171] coating layer Resistance value (1KHz) Resistance value (1Hz) Example 2 LTAF+NCM 0.90 0.90 Comparative Example 3 lithium niobate 1.75 1.91 Comparative Example 4 LTAF 1.00 1.00

[0172] The resistance value is the lowest in the solid-state battery of Example 2. The resistance value of the solid-state battery of Example 2 is lower than the resistance value of the solid-state battery of Comparative Example 4.

[0173] As shown in the results of Comparative Example 3, when the coating layer material was changed to lithium niobate, the resistance of the solid-state battery showed a significant increase. It should be noted that when the target thickness of the coating layer covering the active material in Comparative Example 3 was set to the same as that in Example 2, the resistance of the solid-state battery increased further.

[0174] Industrial applicability

[0175] The technology of the present invention is useful for batteries such as lithium secondary batteries.

Claims

1. A coated positive electrode active material comprising: a first positive electrode active material comprising lithium and a transition metal; and a coating layer covering the first positive electrode active material, The coating layer includes: a first material including a halide; and a second material including at least one selected from the group consisting of a second positive electrode active material capable of occluding and releasing lithium and a compound containing the transition metal.

2. The coated positive electrode active material according to claim 1, wherein Particles of the second material are dispersed in the coating layer.

3. The coated positive electrode active material according to claim 1, wherein Particles of the second material having a particle diameter smaller than the thickness of the coating layer exist in the coating layer.

4. The coated positive electrode active material according to claim 1, wherein The second material includes the compound containing the transition metal, The compound containing the transition metal is a compound capable of occluding and releasing lithium.

5. The coated positive electrode active material according to claim 4, wherein The compound containing the transition metal is composed of the same element group as the element group constituting the first positive electrode active material.

6. The coated positive electrode active material according to claim 4, wherein The compound containing the transition metal has the same composition as that of the first positive electrode active material.

7. The coated positive electrode active material according to claim 1, wherein The first material has lithium ion conductivity.

8. The coated positive electrode active material according to claim 1, wherein The halide comprises Li, M1, M2 and F, The M1 is at least one selected from the group consisting of Ti and Nb, The M2 is at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr.

9. The coated positive electrode active material according to claim 8, wherein The M1 is Ti, The M2 is Al.

10. The coated positive electrode active material according to claim 1, wherein The halide has a composition represented by the following formula (1), Li 6-(5-x-2y)b (Nb 1-x-y Ti x M y ) b F6···Formula (1) The M is at least one selected from the group consisting of Ca, Mg, Al, Y and Zr, and x, y and b respectively satisfy 0<x<1, 0<y<1, 0<x+y≤1, and 0.8≤b≤1.

1.

11. A battery comprising: A positive electrode comprising the coated positive electrode active material according to claim 1; a negative electrode; and The electrolyte layer is disposed between the positive electrode and the negative electrode.

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