Cathode materials, cathodes, and batteries

Abstract

This positive electrode active material 10 comprises a positive electrode active material 100, a first solid electrolyte 101 and a second solid electrolyte 102. The first solid electrolyte 101 contains Li, Zr, M and X. M represents at least one element that is selected from the group consisting of metal elements other than Li and semimetal elements. X represents at least one element that is selected from the group consisting of F, Cl, Br and I. The second solid electrolyte 102 has a composition that is different from the composition of the first solid electrolyte 101. The ratio of the volume of the first solid electrolyte 101 to the total volume of the first solid electrolyte 101 and the second solid electrolyte 102 is not less than 3% but not more than 60%.

Description

[Technical Field]

[0001] The present disclosure relates to positive electrode materials, positive electrodes, and batteries. [Background technology]

[0002] Patent Document 1 discloses a method for producing an active material in which a positive electrode active material is coated with an oxide-based solid electrolyte and further coated with a sulfide-based solid electrolyte, and a battery using the same. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-18735 Summary of the Invention

[0004] There is a desire in the art to improve battery safety.

[0005] The positive electrode material of the present disclosure comprises: a positive electrode active material; a first solid electrolyte; a second solid electrolyte; Equipped with the first solid electrolyte comprises Li, Zr, M, and X; M is at least one selected from the group consisting of metal elements and metalloid elements other than Li, X is at least one selected from the group consisting of F, Cl, Br, and I; the second solid electrolyte has a different composition from the first solid electrolyte; The ratio of the volume of the first solid electrolyte to the total volume of the first solid electrolyte and the second solid electrolyte is 3% or more and 60% or less.

[0006] According to the present disclosure, the safety of the battery can be improved. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of a positive electrode material according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a modified example of the positive electrode material according to the first embodiment. [Figure 3] FIG. 3 is a cross-sectional view showing a schematic configuration of a battery according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] (Findings that formed the basis of this disclosure) Although batteries using solid electrolytes are generally recognized as safe, this is not always the case. For example, oxygen may be generated from the positive electrode active material. The generated oxygen oxidizes the solid electrolyte and raises the battery temperature. As a result, the battery container may deteriorate or be damaged, or the battery may malfunction. Therefore, further improvements in the safety of batteries using solid electrolytes are expected.

[0009] (Summary of one aspect of the present disclosure) The positive electrode material according to the first aspect of the present disclosure is a positive electrode active material; a first solid electrolyte; a second solid electrolyte; Equipped with the first solid electrolyte comprises Li, Zr, M, and X; M is at least one selected from the group consisting of metal elements and metalloid elements other than Li, X is at least one selected from the group consisting of F, Cl, Br, and I; the second solid electrolyte has a different composition from the first solid electrolyte; The ratio of the volume of the first solid electrolyte to the total volume of the first solid electrolyte and the second solid electrolyte is 3% or more and 60% or less.

[0010] The positive electrode material of the first aspect can improve the safety of the battery.

[0011] In a second aspect of the present disclosure, for example, in the cathode material according to the first aspect, the ratio of the volume of the first solid electrolyte to the total volume of the first solid electrolyte and the second solid electrolyte may be 3.3% or more and 50% or less. The cathode material of the second aspect can further improve the safety of the battery.

[0012] In a third aspect of the present disclosure, for example, in the cathode material according to the second aspect, the ratio of the volume of the first solid electrolyte to the total volume of the first solid electrolyte and the second solid electrolyte may be 6.7% or more and 50% or less. The cathode material of the third aspect can further improve the safety of the battery.

[0013] In a fourth aspect of the present disclosure, for example, in the positive electrode material according to the third aspect, the ratio of the volume of the first solid electrolyte to the total volume of the first solid electrolyte and the second solid electrolyte may be 33% or more and 50% or less. The positive electrode material of the fourth aspect can further improve the safety of the battery.

[0014] In a fifth aspect of the present disclosure, for example, in the cathode material according to the second aspect, the ratio of the volume of the first solid electrolyte to the total volume of the first solid electrolyte and the second solid electrolyte may be 3.3% or more and 8.0% or less. The cathode material of the fifth aspect can further improve the safety of the battery.

[0015] In a sixth aspect of the present disclosure, for example, in the cathode material according to any one of the first to fifth aspects, the second solid electrolyte may contain Li and S. The sulfide solid electrolyte has high ionic conductivity and can improve the charge / discharge efficiency of the battery. On the other hand, the sulfide solid electrolyte may have poor oxidation resistance. When the sulfide solid electrolyte is included in the battery as the second solid electrolyte, applying the technology of the present disclosure can significantly improve the safety of the battery.

[0016] In a seventh aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to sixth aspects, M may contain aluminum. When M contains aluminum, the first solid electrolyte exhibits high ionic conductivity.

[0017] In an eighth aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to seventh aspects, the first solid electrolyte may be represented by the following composition formula (1), where α, β, γ, and δ may each independently be a value greater than 0. When the halide solid electrolyte represented by composition formula (1) is used in a battery, the output characteristics of the battery can be improved. Li α Zr β M γ X δ ...Equation (1)

[0018] In the ninth aspect of the present disclosure, for example, the positive electrode active material according to any one of the first to eighth aspects may have a coating layer on at least a part of its surface, which can improve the charge / discharge efficiency of the battery.

[0019] In a tenth aspect of the present disclosure, for example, in the positive electrode material according to the ninth aspect, the coating layer may contain an oxide solid electrolyte having lithium ion conductivity. By using an oxide solid electrolyte as the coating layer, the charge / discharge efficiency of the battery can be further improved.

[0020] In an eleventh aspect of the present disclosure, for example, in the positive electrode material according to the ninth or tenth aspect, the coating layer may contain lithium niobate. This configuration can improve the charge / discharge efficiency of the battery.

[0021] A positive electrode according to a twelfth aspect of the present disclosure includes the positive electrode material according to any one of the first to eleventh aspects. With this configuration, the safety of the battery can be improved.

[0022] A battery according to a thirteenth aspect of the present disclosure includes the positive electrode according to the twelfth aspect. According to the present disclosure, the safety of the battery can be improved.

[0023] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings, but the present disclosure is not limited to the following embodiments.

[0024] (Embodiment 1) 1 is a cross-sectional view showing a schematic configuration of a positive electrode material according to Embodiment 1. The positive electrode material 10 includes a positive electrode active material 100, a first solid electrolyte 101, and a second solid electrolyte .

[0025] The first solid electrolyte contains Li, Zr, M, and X. M is at least one selected from the group consisting of metal elements and semimetal elements other than Li and Zr. X is at least one selected from the group consisting of F, Cl, Br, and I. In the positive electrode material 10, the ratio V1 / Vt of the volume V1 of the first solid electrolyte to the total volume Vt of the first solid electrolyte 101 and the second solid electrolyte 102 is, expressed as a percentage, 3% or more and 60% or less.

[0026] "Metalloid elements" include B, Si, Ge, As, Sb, and Te.

[0027] "Metal elements" include all elements in groups 1 to 12 of the periodic table except hydrogen, and all elements in groups 13 to 16 except B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. In other words, metal elements are a group of elements that can become cations when forming inorganic compounds with halogen elements.

[0028] The first solid electrolyte may be a solid electrolyte containing a halogen, a so-called halide solid electrolyte. Halide solid electrolytes have excellent oxidation resistance. Therefore, by mixing the first solid electrolyte, oxidation of the positive electrode (for example, oxidation of the second solid electrolyte) can be suppressed. This suppresses heat generation in a battery using the positive electrode material 10, and ultimately improves the safety of the battery using the positive electrode material 10.

[0029] If the ratio V1 / Vt is too low, the first solid electrolyte may not sufficiently suppress the oxidation reaction between the positive electrode active material 100 and the second solid electrolyte, and the above-mentioned effect may not be fully achieved. The ratio V1 / Vt may be 3.3% or more, 6% or more, or even 6.7% or more. If the ratio V1 / Vt is too high, there is a concern that the ionic conductivity of the positive electrode material 10 may be insufficient. The ratio V1 / Vt may desirably be 50% or less, or even 40% or less.

[0030] To improve the safety of the battery, the ratio V1 / Vt may be, for example, not less than 3.3% and not more than 50%.

[0031] To further improve the safety of the battery, the ratio V1 / Vt may be 6.7% or more and 50% or less, or 33% or more and 50% or less.

[0032] To further improve the safety of the battery, the ratio V1 / Vt may be 3.3% or more and 8.0% or less.

[0033] The total volume Vt of the first solid electrolyte 101 and the second solid electrolyte 102 is the sum of the volume V1 of the first solid electrolyte 101 and the volume V2 of the second solid electrolyte 102. The volume V1 of the first solid electrolyte 101 is the total volume of the first solid electrolyte 101 in the powder of the positive electrode material 10. The volume V2 of the second solid electrolyte 102 is the total volume of the second solid electrolyte 102 in the powder of the positive electrode material 10. In other words, the ratio V1 / Vt is a value determined from a certain amount of the entire powder of the positive electrode material 10.

[0034] The ratio V1 / Vt can be calculated from the amounts of materials charged, or by the method described below. Specifically, a cross section of a positive electrode using the positive electrode material 10 is observed with a scanning electron microscope (SEM-EDX) to obtain a two-dimensional mapping image of the elements. The measurement conditions for the scanning electron microscope to obtain the two-dimensional mapping image are, for example, a magnification of 1000 to 3000 times and an acceleration voltage of 5 kV. The two-dimensional mapping image is obtained at a resolution of 1280 × 960. The two-dimensional mapping image of the elements is analyzed, and the volume of the positive electrode active material 100, the volume V1 of the first solid electrolyte 101, and the volume V2 of the second solid electrolyte 102 can be determined from the number of pixels of the elements contained in each of the positive electrode active material 100, the first solid electrolyte 101, and the second solid electrolyte 102.

[0035] In the positive electrode material 10, the ratio "v1:100-v1" of the volume of the positive electrode active material 100 to the volume of the solid electrolyte may satisfy 30≦v1≦95. When 30≦v1 is satisfied, the battery energy density is sufficiently ensured. When v1≦95 is satisfied, the battery can operate at high power. The "volume of the solid electrolyte" is the total volume of the first solid electrolyte 101 and the second solid electrolyte 102.

[0036] <Cathode active material> The positive electrode active material 100 includes a material capable of absorbing and releasing metal ions (e.g., lithium ions). Examples of the positive electrode active material 100 that can be used include lithium-containing transition metal oxides, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. In particular, when a lithium-containing transition metal oxide is used as the positive electrode active material 100, 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 Li(NiCoAl)O2, Li(NiCoMn)O2, and LiCoO2.

[0037] The positive electrode active material 100 has, for example, a particle shape. There are no particular limitations on the shape of the particles of the positive electrode active material 100. The shape of the particles of the positive electrode active material 100 can be spherical, oval, scaly, or fibrous.

[0038] The median diameter of the positive electrode active material 100 may be 0.1 μm or more and 100 μm or less. When the median diameter of the positive electrode active material 100 is 0.1 μm or more, the positive electrode active material 100, the first solid electrolyte 101, and the second solid electrolyte 102 can be well dispersed in the positive electrode material 10. As a result, the charge / discharge characteristics of the battery are improved. When the median diameter of the positive electrode active material 100 is 100 μm or less, the diffusion rate of lithium within the positive electrode active material 100 is sufficiently ensured. This allows the battery to operate at high power.

[0039] The median diameter of the positive electrode active material 100 may be larger than the median diameters of the first solid electrolyte 101 and the second solid electrolyte 102. This allows the positive electrode active material 100, the first solid electrolyte 101, and the second solid electrolyte 102 to form a well-dispersed state.

[0040] As used herein, the term "median diameter" refers to the particle size when the cumulative volume in the volume-based particle size distribution is equal to 50%. The volume-based particle size distribution is measured, for example, by a laser diffraction measurement device or an image analysis device.

[0041] <First solid electrolyte> The first solid electrolyte 101 has, for example, ion conductivity. The ion conductivity is typically lithium ion conductivity. The raw materials of the first solid electrolyte 101, by-products generated during the production of the first solid electrolyte 101, and the like are included in the inevitable impurities. The mass ratio of the inevitable impurities to the total mass of the first solid electrolyte 101 may be 5% or less, 3% or less, 1% or less, or 0.5% or less.

[0042] The first solid electrolyte 101 is a material containing Li, Zr, M, and X. M and X are as described above. Such a material has excellent ionic conductivity and oxidation resistance. Therefore, a battery using a positive electrode material containing the first solid electrolyte 101 improves the charge / discharge efficiency and thermal stability of the battery.

[0043] The halide solid electrolyte serving as first solid electrolyte 101 is represented, for example, by the following composition formula (1): In composition formula (1), α, β, γ, and δ are each independently a value greater than zero. Li α Zr β M γ X δ ...Equation (1)

[0044] The halide solid electrolyte represented by composition formula (1) has higher ionic conductivity than halide solid electrolytes such as LiI, which are composed only of Li and halogen elements. Therefore, when the halide solid electrolyte represented by composition formula (1) is used in a battery, the charge / discharge efficiency of the battery can be improved.

[0045] M may contain Al (=aluminum). That is, the halide solid electrolyte may contain Al as a metal element. When M contains Al, the halide solid electrolyte exhibits high ionic conductivity.

[0046] The halide solid electrolyte may consist essentially of Li, Zr, Al, and X. Here, "the halide solid electrolyte consists essentially of Li, Zr, Al, and X" means that the ratio of the total amount of substance of Li, Zr, Al, and X to the total amount of substance of all elements constituting the halide solid electrolyte (i.e., molar fraction) is 90% or more. As an example, the molar ratio (i.e., molar fraction) may be 95% or more. The halide solid electrolyte may consist only of Li, Zr, Al, and X.

[0047] In order to further enhance the ionic conductivity of the solid electrolyte, in the halide solid electrolyte, the ratio of the amount of substance of Li to the total amount of substances of Zr and Al may be 1.12 or more and 5.07 or less.

[0048] The halide solid electrolyte may be represented by the following compositional formula (2). Li 6-(4-x)b (Zr 1-x Al x ) b F6 ··· Formula (2)

[0049] In formula (2), the mathematical formulas: 0 < x < 1 and 0 < b ≤ 1.5 are satisfied. Such a halide solid electrolyte has high ionic conductivity.

[0050] In order to enhance the ionic conductivity of the halide solid electrolyte, in formula (2), the mathematical formula: 0.01 ≤ x ≤ 0.99 may be satisfied. Desirably, the mathematical formula: 0.2 ≤ x ≤ 0.95 may be satisfied.

[0051] The upper and lower limit values of the range of x in formula (2) can be defined by any combination selected from the numerical values of 0.01, 0.2, 0.4, 0.5, 0.5, 0.7, 0.8, 0.95, and 0.99.

[0052] In order to enhance the ionic conductivity of the halide solid electrolyte, in formula (2), the mathematical formula:

[0053] The upper and lower limit values of the range of b in formula (2) can be defined by any combination selected from the numerical values of 0.7, 0.8, 0.9, 0.96, 1, 1.04, 1.1, 1.2, and 1.3.

[0054] The halide solid electrolyte may be crystalline or amorphous.

[0055] The shape of the halide solid electrolyte is not limited. Examples of the shape include needles, spheres, and ellipsoids. The halide solid electrolyte may be in the form of particles.

[0056] When the halide solid electrolyte is particulate (e.g., spherical), the solid electrolyte may have a median diameter of 0.1 μm or more and 100 μm or less. The median diameter refers to the particle size when the cumulative volume in the volume-based particle size distribution is equal to 50%. The volume-based particle size distribution is measured, for example, using a laser diffraction measurement device or an image analyzer.

[0057] The halide solid electrolyte may be a sulfur-free solid electrolyte. In this case, generation of sulfur-containing gases such as hydrogen sulfide gas from the solid electrolyte can be avoided. A sulfur-free solid electrolyte refers to a solid electrolyte represented by a composition formula that does not contain elemental sulfur. Therefore, a solid electrolyte containing a very small amount of sulfur, for example, a solid electrolyte having a sulfur content of 0.1 mass % or less, is classified as a sulfur-free solid electrolyte. The halide solid electrolyte may further contain oxygen as an anion other than the halogen element.

[0058] <Method for manufacturing halide solid electrolyte> The halide solid electrolyte as the first solid electrolyte can be produced, for example, by the following method.

[0059] Raw material powders are prepared and mixed to obtain a desired composition. The raw material powders may be, for example, halides.

[0060] As an example, if the target composition is Li 2.64 Zr 0.48 Al 0.48 In the case of F6, LiF, ZrF4, and AlF3 are mixed in a molar ratio of about 2.64:0.48:0.48. The raw material powders may be mixed in a pre-adjusted molar ratio to offset compositional changes that may occur during the synthesis process.

[0061] The raw material powders are reacted with each other mechanochemically (i.e., using a mechanochemical milling method) in a mixing device such as a planetary ball mill to obtain a reactant. The reactant may be fired in a vacuum or in an inert atmosphere. Alternatively, a mixture of the raw material powders may be fired in a vacuum or in an inert atmosphere to obtain a reactant. The firing is preferably carried out, for example, at a temperature of 100°C or higher and 400°C or lower for one hour or longer. In order to suppress compositional changes during firing, the raw material powders are preferably fired in a sealed container such as a quartz tube.

[0062] These methods provide a halide solid electrolyte.

[0063] <Second solid electrolyte> The second solid electrolyte 102 may include at least one selected from the group consisting of a halide solid electrolyte, a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte.

[0064] Examples of halide solid electrolytes include the materials previously described as the first solid electrolyte 101. However, the second solid electrolyte 102 has a different composition from that of the first solid electrolyte 101. Here, a different composition means a composition in which the constituent elements do not match, or a composition in which the constituent elements are the same but in different ratios.

[0065] The oxide solid electrolyte is a solid electrolyte containing oxygen. The oxide solid electrolyte may further contain anions other than sulfur and halogen elements as anions other than oxygen.

[0066] Examples of oxide solid electrolytes include NASICON-type solid electrolytes, such as LiTi2(PO4)3 and its elemental substitution products, (LaLi)TiO3-based perovskite-type solid electrolytes, and Li 14 ZnGeO 16 , Li4SiO4, LiGeO4 and their element-substituted LISICON-type solid electrolytes, Li7La3Zr2O 12Garnet-type solid electrolytes, such as those substituted with these elements, Li3PO4 and its N-substituted compounds, and glass or glass ceramics containing a base material containing Li-BO compounds such as LiBO2 and Li3BO3 to which a material such as Li2SO4 or Li2CO3 has been added can be used.

[0067] As the polymer solid electrolyte, for example, a compound of a polymer compound and a lithium salt can be used. The polymer compound may have an ethylene oxide structure. A polymer compound having an ethylene oxide structure can contain a large amount of lithium salt. This can further increase ionic conductivity. Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), and LiC(SO2CF3)3. One type of lithium salt selected from these may be used alone, or a mixture of two or more types of lithium salts selected from these may be used.

[0068] Examples of the complex hydride solid electrolyte that can be used include LiBH4-LiI and LiBH4-P2S5.

[0069] The second solid electrolyte 102 may contain Li and S. In other words, the second solid electrolyte 102 may contain a sulfide solid electrolyte. The sulfide solid electrolyte has high ionic conductivity and can improve the charge / discharge efficiency of the battery. On the other hand, the sulfide solid electrolyte may have poor oxidation resistance. When a battery contains a sulfide solid electrolyte as the second solid electrolyte 102, applying the technology of the present disclosure can provide significant benefits.

[0070] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, and Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12These include LiX, LiO, MO q , Li p MO q etc. may be added. Here, X in "LiX" is at least one selected from the group consisting of F, Cl, Br, and I. q " and "Li p MO q "The element M is at least one selected from the group consisting of P, Si, Ge, B, Al, Ga, In, Fe, and Zn. q " and "Li p MO q " p and q in this expression are independent natural numbers.

[0071] The second solid electrolyte 102 may contain two or more of the materials listed as solid electrolytes, for example, a halide solid electrolyte and a sulfide solid electrolyte.

[0072] The second solid electrolyte 102 may have a higher lithium ion conductivity than the lithium ion conductivity of the first solid electrolyte 101 .

[0073] The second solid electrolyte 102 may contain inevitable impurities such as starting materials, by-products, decomposition products, etc. used in synthesizing the solid electrolyte. This also applies to the first solid electrolyte 101.

[0074] <Other ingredients> The positive electrode material 10 may contain a binder to improve adhesion between particles. The binder is used to improve the binding properties of the materials that make up the positive electrode. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyhexyl acrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polycarbonate, polyethersulfone, polyetherketone, polyetheretherketone, polyphenylene sulfide, hexafluoropolypropylene, styrene-butadiene rubber, carboxymethyl cellulose, and ethyl cellulose. Copolymers of two or more monomers selected from the group consisting of tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, butadiene, styrene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid ester, acrylic acid, and hexadiene may also be used. One selected from these may be used alone, or two or more may be used in combination.

[0075] The binder may be an elastomer because it has excellent binding properties. An elastomer is a polymer having rubber elasticity. The elastomer used as the binder may be a thermoplastic elastomer or a thermosetting elastomer. The binder may contain a thermoplastic elastomer. Examples of thermoplastic elastomers include styrene-ethylene-butylene-styrene (SEBS), styrene-ethylene-propylene-styrene (SEPS), styrene-ethylene-ethylene-propylene-styrene (SEEPS), butylene rubber (BR), isoprene rubber (IR), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), styrene-butylene rubber (SBR), styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), hydrogenated isoprene rubber (HIR), hydrogenated butyl rubber (HIIR), hydrogenated nitrile rubber (HNBR), hydrogenated styrene-butylene rubber (HSBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), etc. One selected from these may be used alone, or two or more may be used in combination.

[0076] The positive electrode material 10 may contain a conductive additive to enhance electronic conductivity. Examples of conductive additives include graphites (natural or artificial graphite), carbon blacks (acetylene black, ketjen black, etc.), conductive fibers (carbon fiber, metal fiber, etc.), metal powders (carbon fluoride, aluminum, etc.), conductive whiskers (zinc oxide, potassium titanate, etc.), conductive metal oxides (titanium oxide, etc.), and conductive polymer compounds (polyaniline, polypyrrole, polythiophene, etc.). Using a carbon conductive additive can reduce costs.

[0077] <Method of manufacturing positive electrode material> The cathode material 10 is obtained by mixing the cathode active material 100, the first solid electrolyte 101, and the second solid electrolyte 102. The method for mixing the cathode active material 100, the first solid electrolyte 101, and the second solid electrolyte 102 is not particularly limited. The cathode active material 100, the first solid electrolyte 101, and the second solid electrolyte 102 may be mixed using a tool such as a mortar, or may be mixed using a mixing device such as a ball mill.

[0078] (Variation) 2 is a cross-sectional view showing a schematic configuration of a modified example of the cathode material according to Embodiment 1. In this modified example, the cathode active material is a coated active material having a coating layer on at least a portion of its surface. That is, the cathode material 20 includes a coated active material 220, a first solid electrolyte 201, and a second solid electrolyte 202. The coated active material 220 includes a cathode active material 200 and a coating layer 203.

[0079] The coating layer 203 may contain a material with low electron conductivity, such as an oxide material or an oxide solid electrolyte.

[0080] Examples of oxide materials include SiO2, Al2O3, TiO2, B2O3, Nb2O5, WO3, and ZrO2. Examples of oxide solid electrolytes include Li-Nb-O compounds such as LiNbO3, Li-BO compounds such as LiBO2 and Li3BO3, Li-Al-O compounds such as LiAlO2, Li-Si-O compounds such as Li4SiO4, Li2SO4, and Li4Ti5O. 12 Li-Ti-O compounds such as Li2ZrO3, Li-Zr-O compounds such as Li2MoO3, Li-VO compounds such as LiV2O5, and Li-WO compounds such as Li2WO4. The underlayer material may be one selected from these, or a mixture of two or more.

[0081] The coating layer 203 may be a solid electrolyte having lithium ion conductivity. The coating layer 203 is typically an oxide solid electrolyte having lithium ion conductivity. The oxide solid electrolyte has high ion conductivity and is excellent in high potential stability. By using an oxide solid electrolyte as the coating layer 203, the charge / discharge efficiency of the battery can be improved.

[0082] The material of the coating layer 203 may be a material containing Nb. The coating layer 203 typically contains lithium niobate (LiNbO3). With such a configuration, the charge / discharge efficiency of the battery can be improved. As the oxide solid electrolyte material of the coating layer 203, the materials described above can also be used.

[0083] The thickness of coating layer 203 is, for example, 1 nm or more and 500 nm or less. When the thickness of coating layer 203 is appropriately adjusted, contact between positive electrode active material 200 and second solid electrolyte 202 can be sufficiently suppressed.

[0084] The thickness of the coating layer 203 can be determined by slicing the coated active material 220 into thin slices by a method such as ion milling and observing the cross section of the coated active material 220 with a transmission electron microscope. The average value of thicknesses measured at any number of positions (for example, five points) can be regarded as the thickness of the coating layer 203.

[0085] The coated active material 220 can be manufactured by the following method.

[0086] First, the coating layer 203 is formed on the surface of the positive electrode active material 200. There are no particular limitations on the method for forming the coating layer 203. Methods for forming the coating layer 203 include a liquid-phase coating method and a vapor-phase coating method.

[0087] For example, in the liquid-phase coating method, a precursor solution of the base material is applied to the surface of the positive electrode active material 100. When forming a coating layer 203 containing LiNbO3, the precursor solution can be a mixed solution (sol solution) of a solvent, lithium alkoxide, and niobium alkoxide. Examples of lithium alkoxide include lithium ethoxide. Examples of niobium alkoxide include niobium ethoxide. The solvent is, for example, an alcohol such as ethanol. The amounts of lithium alkoxide and niobium alkoxide are adjusted depending on the target composition of the coating layer 203. Water may be added to the precursor solution as needed. The precursor solution may be acidic or alkaline.

[0088] The method for applying the precursor solution to the surface of the positive electrode active material 200 is not particularly limited. For example, the precursor solution can be applied to the surface of the positive electrode active material 200 using a tumbling fluidized granulation coating device. With the tumbling fluidized granulation coating device, the precursor solution can be sprayed onto the positive electrode active material 200 while tumbling and fluidizing the positive electrode active material 200, thereby applying the precursor solution to the surface of the positive electrode active material 200. In this way, a precursor coating is formed on the surface of the positive electrode active material 200. Thereafter, the positive electrode active material 200 coated with the precursor coating is heat-treated. The heat treatment promotes gelation of the precursor coating, and a coating layer 203 is formed.

[0089] Vapor-phase coating methods include pulsed laser deposition (PLD), vacuum evaporation, sputtering, thermal chemical vapor deposition (CVD), and plasma chemical vapor deposition. For example, in the PLD method, a target made of an ion-conductive material is irradiated with a high-energy pulse laser (e.g., KrF excimer laser, wavelength: 248 nm), and the sublimated ion-conductive material is deposited on the surface of the positive electrode active material 100. When forming the second coating layer 103 of LiNbO3, highly sintered LiNbO3 is used as the target.

[0090] However, the method for forming the coating layer 203 is not limited to the above, and the coating layer 203 may be formed by various methods such as a spray method, a spray dry coating method, an electrodeposition method, a dipping method, or a mechanical mixing method using a disperser.

[0091] (Embodiment 2) 3 is a cross-sectional view showing a schematic configuration of a battery according to embodiment 2. Battery 300 includes a positive electrode 301, a separator layer 302, and a negative electrode 303. Separator layer 302 is disposed between positive electrode 301 and negative electrode 303. Positive electrode 301 includes at least one of positive electrode material 10 and positive electrode material 20 described in embodiment 1. This configuration improves the safety of battery 300.

[0092] The thickness of each of the positive electrode 301 and the negative electrode 303 may be 10 μm or more and 500 μm or less. When the thickness of the positive electrode 301 and the negative electrode 303 is 10 μm or more, a sufficient energy density of the battery can be ensured. When the thickness of the positive electrode 301 and the negative electrode 303 is 500 μm or less, high-power operation of the battery 300 can be achieved.

[0093] The separator layer 302 is a layer containing an electrolyte material. The separator layer 302 may contain at least one solid electrolyte selected from the group consisting of a sulfide solid electrolyte, an oxide solid electrolyte, a halide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte. Details of each solid electrolyte are as described in the first embodiment.

[0094] The thickness of the separator layer 302 may be 1 μm or more and 300 μm or less. When the thickness of the separator layer 302 is 1 μm or more, the positive electrode 301 and the negative electrode 303 can be more reliably separated. When the thickness of the separator layer 302 is 300 μm or less, the battery 300 can operate at high power.

[0095] The negative electrode 303 contains, as a negative electrode active material, a material that has the property of absorbing and releasing metal ions (for example, lithium ions).

[0096] Examples of the negative electrode active material that can be used include metal materials, carbon materials, oxides, nitrides, tin compounds, and silicon compounds. The metal material may be a single metal. Alternatively, the metal material may be an alloy. Examples of the metal material include lithium metal and lithium alloys. Examples of the carbon material include natural graphite, coke, partially graphitized carbon, carbon fiber, spherical carbon, artificial graphite, and amorphous carbon. From the viewpoint of capacity density, silicon (Si), tin (Sn), silicon compounds, and tin compounds can be preferably used.

[0097] The median diameter of the particles of the negative electrode active material may be 0.1 μm or more and 100 μm or less.

[0098] The negative electrode 303 may contain other materials such as a solid electrolyte. As the solid electrolyte, the materials described in the first embodiment can be used. [Example]

[0099] The present disclosure will be described in detail below using examples and comparative examples, but the positive electrode material and battery of the present disclosure are not limited to the following examples.

[0100] Example 1 [Preparation of coated active material] In an argon glove box, 5.95 g of ethoxylithium (manufactured by Kojundo Chemical Co., Ltd.) and 36.43 g of pentaethoxyniobium (manufactured by Kojundo Chemical Co., Ltd.) were dissolved in 500 mL of ultra-dehydrated ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) to prepare a coating solution.

[0101] Li(NiCoAl)O2 (hereafter referred to as NCA) powder was prepared as the positive electrode active material. A fluidized bed granulation coating system (Powrex Corporation, FD-MP-01E) was used to form a LiNbO3 coating layer on the NCA surface. The NCA loading, stirring speed, and coating solution delivery rate were 1 kg, 400 rpm, and 6.59 g / min, respectively. The loading amount of the coating solution was adjusted to achieve a LiNbO3 film thickness of 10 nm. The loading amount of the coating solution was calculated using the specific surface area of ​​the active material and the density of LiNbO3. The entire process using the fluidized bed granulation coating system was carried out in a dry atmosphere with a dew point below -30°C. After the LiNbO3 coating layer was formed, the resulting powder was placed in an alumina crucible and heat-treated in air at 300°C for 1 hour. The heat-treated powder was then re-ground in an agate mortar. This resulted in an NCA with a LiNbO3 coating layer. The coating layer was made of lithium niobate (LiNbO3). Hereafter, the NCA with a LiNbO3 coating layer will be referred to as "Nb-NCA."

[0102] [Preparation of the first solid electrolyte] In an argon glove box with a dew point of -60°C or less, raw material powders of LiF, ZrF4, and AlF3 were weighed out in a molar ratio of LiF:ZrF4:AlF3 = 2.5:0.5:0.5. These were ground and mixed in a mortar to obtain a mixture. The obtained mixed powder was milled for 12 hours at 500 rpm using a planetary ball mill. In this way, a halide solid electrolyte powder according to Example 1 was obtained. The first solid electrolyte according to Example 1 contained Li 2.5 Zr 0.5 Al 0.5 F6 (hereinafter referred to as "LZAF").

[0103] [Preparation of second solid electrolyte] In an argon glove box with a dew point below -60°C, the raw material powders Li2S and P2S5 were weighed out to a molar ratio of Li2S:P2S5 = 75:25. These were crushed and mixed in a mortar to obtain a mixture. The mixture was then milled for 10 hours at 510 rpm using a planetary ball mill (Fritsch, P-7 model). This yielded a glassy solid electrolyte. The glassy solid electrolyte was then heat-treated in an inert atmosphere at 270°C for 2 hours. This yielded a glass-ceramic solid electrolyte, Li2S-P2S5 (hereinafter referred to as "LPS").

[0104] [Preparation of cathode material] In an argon glove box, the positive electrode active material of Example 1, LZAF, and LPS were weighed out so that the volume ratio of Nb-NCA to the solid electrolyte (i.e., Nb-NCA:solid electrolyte) was 70:30 and the volume ratio of the first solid electrolyte (i.e., LZAF) to the second solid electrolyte (i.e., LPS) (i.e., LZAF:LPS) was 6.7:93.3. These were mixed in an agate mortar to produce the positive electrode material of Example 1. In the volume ratio of Nb-NCA to the solid electrolyte, "solid electrolyte" refers to the total volume of LZAF and LPS.

[0105] <Example 2> The positive electrode material of Example 2 was obtained in the same manner as in Example 1, except that the volume ratio of LZAF to LPS (ie, LZAF:LPS) was changed to 15:75.

[0106] Example 3 The positive electrode material of Example 3 was obtained in the same manner as in Example 1, except that the volume ratio of LZAF to LPS (ie, LZAF:LPS) was changed to 23.3:76.7.

[0107] Example 4 The positive electrode material of Example 4 was obtained in the same manner as in Example 1, except that the volume ratio of LZAF to LPS (ie, LZAF:LPS) was changed to 33.3:66.7.

[0108] <Example 5> The positive electrode material of Example 5 was obtained in the same manner as in Example 1, except that the volume ratio of LZAF to LPS (ie, LZAF:LPS) was changed to 50:50.

[0109] <Comparative Example 1> The positive electrode material of Comparative Example 1 was obtained without using LZAF as the first solid electrolyte, and using only the second solid electrolyte, that is, only LPS as the solid electrolyte.

[0110] In the positive electrode materials of the Examples and Comparative Examples, the ratio of the LZAF volume to the total volume of LZAF and LPS was as shown in Table 1.

[0111] [Battery construction] The positive electrode material was weighed to contain 14 mg of Nb-NCA. The LPS and positive electrode material were stacked in this order inside an insulating outer cylinder. The resulting laminate was press-molded at a pressure of 720 MPa. Next, metallic lithium was placed in contact with the LPS layer, and the laminate was again press-molded at a pressure of 40 MPa. This produced a laminate consisting of a positive electrode, a solid electrolyte layer, and a negative electrode. Next, stainless steel current collectors were placed on the top and bottom of the laminate. Current collector leads were attached to each current collector. Next, the outer cylinder was sealed using an insulating ferrule to isolate the interior of the outer cylinder from the outside atmosphere. Through these processes, the batteries of Examples 1 to 6 and Comparative Example 1 were fabricated. The battery was constrained from above and below with four bolts, and a surface pressure of 150 MPa was applied to the battery.

[0112] [Preparation of thermal analysis samples] The battery was placed in a thermostatic chamber at 25°C. The battery was charged at a constant current of 147 μA, which corresponds to a 0.05C rate (20-hour rate) relative to the theoretical capacity of the battery, until the voltage reached 4.3 V. The battery was then charged at a constant voltage of 4.3 V until the current reached 2.9 μA.

[0113] The charged battery was disassembled in an argon glove box, and only the positive electrode material was removed. 2 mg of the positive electrode material was sealed in a stainless steel closed pan. This gave thermal analysis samples for Examples 1 to 5 and Comparative Example 1.

[0114] [Thermal analysis] Using the thermal analysis samples of Examples 1 to 5 and Comparative Example 1, thermal analysis was carried out under the following conditions.

[0115] A differential scanning calorimeter (Q1000 manufactured by TA Instruments) was used for the thermal analysis. The temperature was increased from 0°C to 400°C at a rate of 10°C / min. The temperature at which the peak rose in the thermal analysis curve was regarded as the exothermic onset temperature. The results are shown in Table 1.

[0116] [Table 1]

[0117] <Consideration> As shown in Table 1, in the batteries of Examples 1 to 5 in which the ratio V1 / Vt of the volume V1 of the first solid electrolyte to the total volume Vt of the first and second solid electrolytes in the positive electrode material was within the range of 3% or more and 60% or less, the heat generation initiation temperature was higher than that of the battery of Comparative Example 1. In other words, it was suggested that by including the first solid electrolyte in the positive electrode material within the above volume range, the reaction between oxygen released from the positive electrode active material and the sulfide solid electrolyte was suppressed, thereby improving the safety of the battery.

[0118] It is estimated that if the volume of LZAF relative to the volume of Nb-NCA is less than 1%, it is difficult to suppress oxygen release from the positive electrode active material. Therefore, the ratio of the volume of LZAF relative to the volume of Nb-NCA is preferably 1% or more. The upper limit of the ratio of the volume of LZAF relative to the volume of Nb-NCA is, for example, 15%. [Industrial Applicability]

[0119] The technology of the present disclosure is useful, for example, in all-solid-state lithium secondary batteries. [Explanation of symbols]

[0120] 10,20 Cathode materials 100,200 Cathode active material 101,201 1st solid electrolyte 102,202 Second solid electrolyte 203 Covering layer 220 Coated active material 300 batteries 301 Positive electrode 302 Separator layer 303 Negative electrode

Claims

1. a positive electrode active material; a first solid electrolyte; a second solid electrolyte; Equipped with the first solid electrolyte comprises Li, Zr, M, and X; M is at least one selected from the group consisting of metal elements and metalloid elements other than Li, X is at least one selected from the group consisting of F, Cl, Br, and I; the second solid electrolyte has a different composition from the first solid electrolyte; a ratio of the volume of the first solid electrolyte to the total volume of the first solid electrolyte and the second solid electrolyte is 3% or more and 60% or less; Positive electrode material.

2. a ratio of the volume of the first solid electrolyte to the total volume of the first solid electrolyte and the second solid electrolyte is 3.3% or more and 50% or less; The positive electrode material according to claim 1 .

3. a ratio of the volume of the first solid electrolyte to the total volume of the first solid electrolyte and the second solid electrolyte is 6.7% or more and 50% or less; The positive electrode material according to claim 2 .

4. a ratio of the volume of the first solid electrolyte to the total volume of the first solid electrolyte and the second solid electrolyte is 33% or more and 50% or less; The positive electrode material according to claim 3 .

5. a ratio of the volume of the first solid electrolyte to the total volume of the first solid electrolyte and the second solid electrolyte is 3.3% or more and 8.0% or less; The positive electrode material according to claim 2 .

6. The second solid electrolyte contains Li and S. The positive electrode material according to any one of claims 1 to 5.

7. M comprises aluminum; The positive electrode material according to any one of claims 1 to 6.

8. The first solid electrolyte is represented by the following composition formula (1): Li α Zr β M γ X δ ... Formula (1) where α, β, γ, and δ are each independently a value greater than 0. The positive electrode material according to any one of claims 1 to 7.

9. The positive electrode active material has a coating layer on at least a part of its surface. The positive electrode material according to any one of claims 1 to 8.

10. the coating layer contains an oxide solid electrolyte having lithium ion conductivity; The positive electrode material according to claim 9.

11. The coating layer contains lithium niobate. The positive electrode material according to claim 9 or 10.

12. A positive electrode comprising the positive electrode material of any one of claims 1 to 11.

13. A battery comprising the positive electrode according to claim 12.

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