Cathode materials, cathodes and batteries

Abstract

A positive electrode material 10 contains: a positive electrode active substance 101; a coating layer 102 that contains a first solid electrolyte and coats at least a part of the surface of the positive electrode active substance 101; and a second solid electrolyte 105, wherein the first solid electrolyte contains Li, M, and X, M is at least one element selected from the group consisting of the metalloid elements and the metallic elements other than Li, X is at least one element selected from the group consisting of F, Cl, Br, and I, the second solid electrolyte 105 abuts the positive electrode active substance 101 with the coating layer 102 therebetween, and the ratio of the volume of the first solid electrolyte to the total volume of the first solid electrolyte and the second solid electrolyte 105 is 4% to 60%, inclusive.

Description

[Technical Field]

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

[0002] Patent Document 1 describes a method for producing a composite active material by coating a positive electrode active material with an oxide solid electrolyte and then coating it with a sulfide solid electrolyte. [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 present disclosure provides: a positive electrode active material; a coating layer including a first solid electrolyte and coating at least a portion of the surface of the positive electrode active material; a second solid electrolyte; Equipped with the first solid electrolyte comprises Li, 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 is in contact with the positive electrode active material via the coating layer, 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 4% or more and 60% or less; A positive electrode material is provided.

[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 positive electrode material according to a modified example. [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 coating layer including a first solid electrolyte and coating at least a portion of the surface of the positive electrode active material; a second solid electrolyte; Equipped with the first solid electrolyte comprises Li, 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 is in contact with the positive electrode active material via the coating layer, 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 4% 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 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 as the second solid electrolyte in a battery, the application of the technology of the present disclosure can provide significant benefits.

[0012] In the third embodiment of the present disclosure, for example, in the positive electrode material according to the first or second embodiment, M may contain yttrium. When M contains Y, the halide solid electrolyte exhibits high ionic conductivity.

[0013] In a fourth aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to third aspects, the first solid electrolyte may be represented by the following composition formula (1), where α, β, and γ 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 M β X γ ...Equation (1)

[0014] In a fifth aspect of the present disclosure, for example, in the cathode material according to any one of the first to fourth aspects, the coating layer may include a first coating layer containing the first solid electrolyte and a second coating layer containing a base material, and the first coating layer may be located outside the second coating layer. This configuration can further improve the safety of the battery.

[0015] In a sixth aspect of the present disclosure, for example, in the positive electrode material according to the fifth aspect, the base material may include an oxide solid electrolyte having lithium ion conductivity. By using the oxide solid electrolyte as the base material, the charge / discharge efficiency of the battery can be improved.

[0016] In a seventh aspect of the present disclosure, for example, in the positive electrode material according to the fifth or sixth aspect, the base material may contain lithium niobate, which can improve the charge / discharge efficiency of the battery.

[0017] A positive electrode according to an eighth aspect of the present disclosure includes the positive electrode material according to any one of the first to seventh aspects. With this configuration, the safety of the battery can be improved.

[0018] A battery according to a ninth aspect of the present disclosure includes the positive electrode according to the eighth aspect. According to the present disclosure, the safety of the battery can be improved.

[0019] 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.

[0020] (Embodiment 1) FIG. 1 is a cross-sectional view showing a schematic configuration of a cathode material according to embodiment 1. The cathode material 10 includes a cathode active material 101, a coating layer 102 containing a first solid electrolyte, and a second solid electrolyte 105. The coating layer 102 coats at least a portion of the surface of the cathode active material 101. The coating layer 102 may coat only a portion of the surface of the cathode active material 101, or may coat the entire surface of the cathode active material 101. The cathode active material 101 and the coating layer 102 constitute a coated active material 100. The second solid electrolyte 105 is in contact with the cathode active material 101 via the coating layer 102.

[0021] In the coating layer 102, the first solid electrolyte contains Li, M, and X. M is at least one selected from the group consisting of metal elements and semi-metal elements other than Li. 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 and the second solid electrolyte 105 is, expressed as a percentage, 4% or more and 60% or less.

[0022] "Metalloid elements" include B, Si, Ge, As, Sb, and Te.

[0023] "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 compounds.

[0024] 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 covering the cathode active material 101 with the first solid electrolyte, oxidation of the second solid electrolyte 105 can be suppressed. This suppresses heat generation in a battery using the cathode material 10, and ultimately improves the safety of the battery using the cathode material 10.

[0025] If the ratio V1 / Vt is too low, the coverage of the positive electrode active material 101 with the first solid electrolyte may be insufficient, and the above-mentioned effects may not be fully achieved. If the ratio V1 / Vt is too high, there is a concern that the electron conductivity or ionic conductivity of the positive electrode material 10 may be insufficient. The ratio V1 / Vt may desirably be 40% or less.

[0026] The total volume Vt of the first solid electrolyte and the second solid electrolyte 105 is the sum of the volume V1 of the first solid electrolyte and the volume V2 of the second solid electrolyte 105. The volume V1 of the first solid electrolyte is the total volume of the first solid electrolyte in the powder of the positive electrode material 10. The volume V2 of the second solid electrolyte 105 is the total volume of the second solid electrolyte 105 in the powder of the positive electrode material 10. In other words, the ratio V1 / Vt is a value determined from the entirety of a certain amount of the powder of the positive electrode material 10.

[0027] 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 can be analyzed to determine the volume of the positive electrode active material 101, the volume V1 of the first solid electrolyte, and the volume V2 of the second solid electrolyte 105 from the number of pixels of the elements contained in each of the positive electrode active material 101, the first solid electrolyte, and the second solid electrolyte 105.

[0028] In the positive electrode material 10, the second solid electrolyte 105 and the coated active material 100 may be in contact with each other. In this case, the first solid electrolyte and the second solid electrolyte 105 are in contact with each other. The positive electrode material 10 may include a plurality of particles of the second solid electrolyte 105 and a plurality of particles of the coated active material 100.

[0029] In the positive electrode material 10, the ratio "v1:100-v1" of the volume of the positive electrode active material 101 to the volume of the solid electrolyte may satisfy 30≦v1≦95. When 30≦v1 is satisfied, the battery's 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 and the second solid electrolyte 105.

[0030] <Cathode active material> The positive electrode active material 101 includes a material having the property of absorbing and releasing metal ions (e.g., lithium ions). Examples of the positive electrode active material 101 that can be used include lithium-containing transition metal oxides, transition metal fluorides, polyanion materials, fluorinated polyanion 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 101, 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.

[0031] The positive electrode active material 101 has, for example, a particle shape. There are no particular limitations on the particle shape of the positive electrode active material 101. The particle shape of the positive electrode active material 101 can be spherical, oval, scaly, or fibrous.

[0032] The median diameter of the coated active material 100 may be 0.1 μm or more and 100 μm or less. When the median diameter of the coated active material 100 is 0.1 μm or more, the coated active material 100 and the second solid electrolyte 105 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 coated active material 100 is 100 μm or less, the diffusion rate of lithium inside the coated active material 100 is sufficiently ensured. This allows the battery to operate at high power.

[0033] The median diameter of coated active material 100 may be larger than the median diameter of second solid electrolyte 105. This allows coated active material 100 and second solid electrolyte 105 to form a well-dispersed state.

[0034] 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.

[0035] <Coating layer> The coating layer 102 includes a first solid electrolyte. The first solid electrolyte has ion conductivity. The ion conductivity is typically lithium ion conductivity. The coating layer 102 is provided on the surface of the positive electrode active material 101. The coating layer 102 may include the first solid electrolyte as a main component, or may include only the first solid electrolyte. "Main component" refers to the component that is most abundant by mass. "Includes only the first solid electrolyte" means that, with the exception of inevitable impurities, no materials other than the first solid electrolyte are intentionally added. For example, the inevitable impurities include raw materials for the first solid electrolyte and by-products generated during the production of the first solid electrolyte. The mass ratio of the inevitable impurities to the total mass of the coating layer 102 may be 5% or less, 3% or less, 1% or less, or 0.5% or less.

[0036] The first solid electrolyte is a material containing Li, M, and X. M and X are as described above. Such a material has excellent ionic conductivity and oxidation resistance. Therefore, the coated active material 100 having the coating layer 102 of the first solid electrolyte improves the charge / discharge efficiency and thermal stability of the battery.

[0037] The halide solid electrolyte as the first solid electrolyte is represented, for example, by the following composition formula (1): In composition formula (1), α, β, and γ are each independently a value greater than 0. γ may be 4 or 6.

[0038] Li α M β X γ ...Equation (1)

[0039] 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.

[0040] M may contain Y (=yttrium). That is, the halide solid electrolyte may contain Y as a metal element. When M contains Y, the halide solid electrolyte exhibits high ionic conductivity.

[0041] The halide solid electrolyte containing Y is represented by, for example, the following composition formula (2).

[0042] Li a Me b Y c X6...Formula (2)

[0043] Composition formula (2) satisfies a + mb + 3c = 6 and c > 0. In composition formula (2), Me includes at least one element selected from the group consisting of metal elements and metalloid elements other than Li and Y. m is the valence of Me. When Me includes multiple elements, mb is equal to the sum of the values ​​obtained by multiplying the composition ratio of each element by the valence of the element. For example, when Me includes element Me1 and element Me2, and the composition ratio of element Me1 is b1, the valence of element Me1 is m1, the composition ratio of element Me2 is b2, and the valence of element Me2 is m2, then mb = m1b1 + m2b2 holds. In composition formula (2), X is at least one element selected from the group consisting of F, Cl, Br, and I.

[0044] Me may be at least one selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, Gd and Nb.

[0045] The halide solid electrolyte may be the following material. The following halide solid electrolyte exhibits high ionic conductivity. Therefore, the ionic conductivity of the positive electrode material 10 is also improved. This also improves the charge / discharge efficiency of a battery using the positive electrode material 10.

[0046] The halide solid electrolyte may be a material represented by the following compositional formula (A1). Here, in the compositional formula (A1), X is at least one selected from the group consisting of Cl, Br, and I. In the compositional formula (A1), 0 < d < 2 is satisfied.

[0047] Li 6-3d Y d X6 ··· Formula (A1)

[0048] The halide solid electrolyte may be a material represented by the following compositional formula (A2). Here, in the compositional formula (A2), X is at least one selected from the group consisting of Cl, Br, and I.

[0049] Li3YX6 ··· Formula (A2)

[0050] The halide solid electrolyte may be a material represented by the following compositional formula (A3). Here, in the compositional formula (A3), 0 < δ ≦ 0.15 is satisfied.

[0051] Li 3-3δ Y 1+δ Cl6 ··· Formula (A3)

[0052] The halide solid electrolyte may be a material represented by the following compositional formula (A4). Here, in the compositional formula (A4), 0 < δ ≦ 0.25 is satisfied.

[0053] Li 3-3δ Y 1+δ Br6 ··· Formula (A4)

[0054] The halide solid electrolyte may be a material represented by the following compositional formula (A5). Here, in the compositional formula (A5), Me is at least one selected from the group consisting of Mg, Ca, Sr, Ba, and Zn. In the compositional formula (A5), -1 < δ < 2, 0 < a < 3, 0 < (3 - 3δ + a), 0 < (1 + δ - a), 0 ≦ x ≦ 6, 0 ≦ y ≦ 6, and (x + y) ≦ 6 are satisfied.

[0055] Li 3-3δ+a Y 1+δ-a Me a Cl 6-x-y Br x I y ··· Formula (A5)

[0056] The halide solid electrolyte may be a material represented by the following compositional formula (A6). Here, in compositional formula (A6), Me is at least one selected from the group consisting of Al, Sc, Ga, and Bi. In compositional formula (A6), -1 < δ < 1, 0 < a < 2, 0 < (1 + δ - a), 0 ≦ x ≦ 6, 0 ≦ y ≦ 6, and (x + y) ≦ 6 are satisfied.

[0057] Li 3-3δ Y 1+δ-a Me a Cl 6-x-y Br x I y ··· Formula (A6)

[0058] The halide solid electrolyte may be a material represented by the following compositional formula (A7). Here, in compositional formula (A7), Me is at least one selected from the group consisting of Zr, Hf, and Ti. In compositional formula (A7), -1 < δ < 1, 0 < a < 1.5, 0 < (3 - 3δ - a), 0 < (1 + δ - a), 0 ≦ x ≦ 6, 0 ≦ y ≦ 6, and (x + y) ≦ 6 are satisfied.

[0059] Li 3-3δ-a Y 1+δ-a Me a Cl 6-x-y Br x I y ··· Formula (A7)

[0060] The halide solid electrolyte may be a material represented by the following compositional formula (A8). Here, in compositional formula (A8), Me is at least one selected from the group consisting of Ta and Nb. In compositional formula (A8), -1 < δ < 1, 0 < a < 1.2, 0 < (3 - 3δ - 2a), 0 < (1 + δ - a), 0 ≦ x ≦ 6, 0 ≦ y ≦ 6, and (x + y) ≦ 6 are satisfied.

[0061] Li 3-3δ-2a Y 1+δ-a Me a Cl 6-x-y Br x I y ...Formula (A8)

[0062] Specific examples of halide solid electrolytes that can be used include Li3YX6, Li2MgX4, Li2FeX4, Li(Al,Ga,In)X4, and Li3(Al,Ga,In)X6, where X is at least one selected from the group consisting of F, Cl, Br, and I.

[0063] In the present disclosure, when an element in a formula is expressed as "(Al, Ga, In)", this notation indicates at least one element selected from the group of elements in the parentheses. That is, "(Al, Ga, In)" is synonymous with "at least one selected from the group consisting of Al, Ga, and In". The same applies to other elements.

[0064] A typical composition of Li3YX6 is, for example, Li3YBr2Cl4. The halide solid electrolyte may be Li3YBr2Cl4.

[0065] The halide solid electrolyte is Li 2.7 Y 1.1 Cl6, Li3YBr6 or Li 2.5 Y 0.5 Zr 0.5 It may also be Cl6.

[0066] The thickness of the coating layer 102 is, for example, 1 nm or more and 500 nm or less. When the thickness of the coating layer 102 is appropriately adjusted, contact between the positive electrode active material 101 and the second solid electrolyte 105 can be sufficiently suppressed. The thickness of the coating layer 102 can be determined by slicing the coated active material 100 by a method such as ion milling and observing the cross section of the coated active material 100 with a transmission electron microscope. The average value of thicknesses measured at any multiple positions (for example, five points) can be considered to be the thickness of the coating layer 102.

[0067] 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.

[0068] The shape of the halide solid electrolyte is not particularly limited and may be, for example, needle-like, spherical, oval-spherical, etc. For example, the shape of the halide solid electrolyte may be particulate.

[0069] The halide solid electrolyte can be produced by the following method, which will be exemplified below by a method for producing the halide solid electrolyte represented by composition formula (1).

[0070] Halide raw material powders are prepared according to the desired composition. The halide may be a compound consisting of two elements, including a halogen element. For example, to produce Li3YCl6, LiCl and YCl3 are prepared as raw material powders in a molar ratio of 3:1. By appropriately selecting the type of raw material powder, the element types of "M" and "X" in composition formula (1) can be determined. The values ​​of "α", "β", and "γ" in composition formula (1) can be adjusted by adjusting the type of raw material powder, the compounding ratio of the raw material powders, and the synthesis process.

[0071] After mixing and pulverizing the raw material powders, the raw material powders are reacted with each other using mechanochemical milling. Alternatively, after mixing and pulverizing the raw material powders, the raw material powders may be fired in a vacuum or in an inert atmosphere. The firing is carried out, for example, at 100°C to 550°C for at least one hour. Through these steps, a halide solid electrolyte is obtained.

[0072] The constitution of the crystalline phase (i.e., the crystalline structure) of the halide solid electrolyte can be adjusted and determined by the reaction method and reaction conditions of the raw material powders.

[0073] <Second solid electrolyte> The second solid electrolyte 105 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.

[0074] Examples of the halide solid electrolyte include the materials previously described as the first solid electrolyte. That is, the composition of the second solid electrolyte 105 may be the same as or different from that of the first solid electrolyte.

[0075] 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.

[0076] 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 12 Garnet-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.

[0077] 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.

[0078] Examples of the complex hydride solid electrolyte that can be used include LiBH4-LiI and LiBH4-P2S5.

[0079] The second solid electrolyte 105 may contain Li and S. In other words, the second solid electrolyte 105 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 105, applying the technology of the present disclosure can provide significant benefits.

[0080] 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 12 These include LiX, Li2O, 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.

[0081] The second solid electrolyte 105 may contain two or more of the materials listed as solid electrolytes, for example, a halide solid electrolyte and a sulfide solid electrolyte.

[0082] The second solid electrolyte 105 may have a lithium ion conductivity higher than the lithium ion conductivity of the first solid electrolyte.

[0083] The second solid electrolyte 105 may contain inevitable impurities such as starting materials, by-products, decomposition products, etc. used in synthesizing the solid electrolyte, and this also applies to the first solid electrolyte.

[0084] <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.

[0085] 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.

[0086] The coating layer 102 may contain a conductive additive to enhance electronic conductivity. Examples of conductive additives that can be used include graphites such as natural graphite or artificial graphite, carbon blacks such as acetylene black and ketjen black, conductive fibers such as carbon fiber or metal fiber, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, and conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene. Using a carbon conductive additive can reduce costs.

[0087] The positive electrode material 10 may contain the above-mentioned conductive additives for the purpose of increasing electronic conductivity.

[0088] <Method of manufacturing coated active material> The coated active material 100 can be produced by the following method.

[0089] A powder of the positive electrode active material 101 and a powder of the first solid electrolyte are mixed in an appropriate ratio to obtain a mixture. The mixture is then milled to impart mechanical energy to the mixture. A mixing device such as a ball mill can be used for the milling process. To prevent oxidation of the materials, the milling process may be performed in a dry and inert atmosphere.

[0090] The coated active material 100 may be manufactured by a dry particle compounding method. The treatment by the dry particle compounding method includes applying at least one mechanical energy selected from the group consisting of impact, compression, and shear to the positive electrode active material 101 and the first solid electrolyte. The positive electrode active material 101 and the first solid electrolyte are mixed in an appropriate ratio.

[0091] The apparatus used in producing the coated active material 100 is not particularly limited and may be an apparatus capable of applying mechanical energy such as impact, compression, and shear to a mixture of the positive electrode active material 101 and the first solid electrolyte. Examples of apparatus capable of applying mechanical energy include a ball mill and a compression shear processing apparatus (particle composite apparatus) such as "Mechanofusion" (manufactured by Hosokawa Micron Corporation) or "Nobilta" (manufactured by Hosokawa Micron Corporation).

[0092] "Mechanofusion" is a particle compounding device that uses a dry mechanical compounding technology by applying strong mechanical energy to multiple different raw material powders. In mechanofusion, raw material powders are placed between a rotating container and a press head, and mechanical energy of compression, shear, and friction is applied to them. This causes the particles to compound.

[0093] "Nobilta" is a particle compounding device that uses dry mechanical compounding technology, an advanced form of particle compounding technology, to compound nanoparticles as raw materials. Nobilta produces composite particles by applying mechanical energy of impact, compression, and shear to multiple types of raw material powders.

[0094] In the Nobilta, a rotor positioned at a predetermined gap between itself and the inner wall of a horizontal cylindrical mixing vessel rotates at high speed, forcing the raw material powder through the gap, a process that is repeated multiple times. This applies impact, compression, and shear forces to the mixture, producing composite particles of the positive electrode active material 101 and the first solid electrolyte. By adjusting conditions such as the rotor rotation speed, processing time, and feed amount, it is possible to control the thickness of the coating layer 102 and the coverage rate of the positive electrode active material 101 with the first solid electrolyte.

[0095] However, processing using the above-mentioned apparatus is not essential. The coated active material 100 may be produced by mixing the positive electrode active material 101 and the first solid electrolyte using a mortar, a mixer, or the like. The first solid electrolyte may be deposited on the surface of the positive electrode active material 101 by various methods, such as a spray method, a spray-dry coating method, an electrodeposition method, an immersion method, or a mechanical mixing method using a disperser.

[0096] <Method of manufacturing positive electrode material> The positive electrode material 10 is obtained by mixing the coated active material 100 and the second solid electrolyte 105. The method for mixing the coated active material 100 and the second solid electrolyte 105 is not particularly limited. The coated active material 100 and the second solid electrolyte 105 may be mixed using a tool such as a mortar, or may be mixed using a mixing device such as a ball mill.

[0097] (Variation) FIG. 2 is a cross-sectional view showing a schematic configuration of a cathode material 20 according to a modified example. The cathode material 20 includes a coated active material 110 and a second solid electrolyte 105. The coated active material 110 includes a cathode active material 101 and a coating layer 104. The coating layer 104 includes a first coating layer 102 and a second coating layer 103. The first coating layer 102 is a layer containing the first solid electrolyte. The second coating layer 103 is a layer containing a base material. The first coating layer 102 is located outside the second coating layer 103. This configuration can further improve the safety of the battery.

[0098] The first coating layer 102 is a layer corresponding to the coating layer 102 described with reference to FIG.

[0099] The second coating layer 103 is located between the first coating layer 102 and the positive electrode active material 101. In this modification, the second coating layer 103 is in direct contact with the positive electrode active material 101. The second coating layer 103 may contain, as a base material, a material with low electronic conductivity, such as an oxide material or an oxide solid electrolyte.

[0100] 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.

[0101] The base material may be a solid electrolyte having lithium ion conductivity. The base material 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 the oxide solid electrolyte as the base material, the charge / discharge efficiency of the battery can be improved.

[0102] The underlayer material may be a material containing Nb. The underlayer material typically contains lithium niobate (LiNbO3). With this configuration, the charge / discharge efficiency of the battery can be improved. The above-described materials can also be used as the oxide solid electrolyte underlayer material.

[0103] In one example, the ionic conductivity of the halide solid electrolyte contained in the first coating layer 102 is higher than the ionic conductivity of the base material contained in the second coating layer 103. With this configuration, oxidation of the second solid electrolyte 105 can be further suppressed without sacrificing ionic conductivity.

[0104] The thickness of the first coating layer 102 is, for example, 1 nm or more and 500 nm or less. The thickness of the second coating layer 103 is, for example, 1 nm or more and 100 nm or less. When the thicknesses of the first coating layer 102 and the second coating layer 103 are appropriately adjusted, contact between the positive electrode active material 101 and the second solid electrolyte 105 can be sufficiently suppressed. The thickness of each layer can be determined by the method described above.

[0105] The coated active material 110 can be produced by the following method.

[0106] First, the second coating layer 103 is formed on the surface of the positive electrode active material 101. There are no particular limitations on the method for forming the second coating layer 103. Methods for forming the second coating layer 103 include a liquid-phase coating method and a vapor-phase coating method.

[0107] For example, in a liquid-phase coating method, a precursor solution of the base material is applied to the surface of the positive electrode active material 101. When forming the second coating layer 103 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 second coating layer 103. Water may be added to the precursor solution if necessary. The precursor solution may be acidic or alkaline.

[0108] The method for applying the precursor solution to the surface of the positive electrode active material 101 is not particularly limited. For example, the precursor solution can be applied to the surface of the positive electrode active material 101 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 101 while tumbling and fluidizing the positive electrode active material 101, thereby applying the precursor solution to the surface of the positive electrode active material 101. In this way, a precursor coating is formed on the surface of the positive electrode active material 101. Thereafter, the positive electrode active material 101 coated with the precursor coating is heat-treated. The heat treatment promotes gelation of the precursor coating, and a second coating layer 103 is formed.

[0109] 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 101. When forming the second coating layer 103 of LiNbO3, highly sintered LiNbO3 is used as the target.

[0110] However, the method for forming the second coating layer 103 is not limited to the above. The second coating layer 103 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.

[0111] After the second coating layer 103 is formed, the first coating layer 102 is formed by the method described above, thereby obtaining the coated active material 110.

[0112] (Embodiment 2) 3 is a cross-sectional view showing a schematic configuration of a battery according to embodiment 2. Battery 200 includes a positive electrode 201, a separator layer 202, and a negative electrode 203. Separator layer 202 is disposed between positive electrode 201 and negative electrode 203. Positive electrode 201 includes at least one of positive electrode material 10 and positive electrode material 20 described in embodiment 1. This configuration can improve the safety of battery 200.

[0113] The thickness of each of the positive electrode 201 and the negative electrode 203 may be 10 μm or more and 500 μm or less. When the thickness of the positive electrode 201 and the negative electrode 203 is 10 μm or more, a sufficient energy density of the battery can be ensured. When the thickness of the positive electrode 201 and the negative electrode 203 is 500 μm or less, high-power operation of the battery 200 can be achieved.

[0114] The separator layer 202 is a layer containing an electrolyte material. The separator layer 202 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.

[0115] The thickness of the separator layer 202 may be 1 μm or more and 300 μm or less. When the thickness of the separator layer 202 is 1 μm or more, the positive electrode 201 and the negative electrode 203 can be more reliably separated. When the thickness of the separator layer 202 is 300 μm or less, high-power operation of the battery 200 can be achieved.

[0116] The negative electrode 203 contains, as a negative electrode active material, a material that has the property of absorbing and releasing metal ions (for example, lithium ions).

[0117] 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.

[0118] The median diameter of the particles of the negative electrode active material may be 0.1 μm or more and 100 μm or less.

[0119] The negative electrode 203 may contain other materials such as a solid electrolyte. As the solid electrolyte, the materials described in the first embodiment can be used. [Example]

[0120] Hereinafter, the present disclosure will be described in detail using examples and comparative examples. Note that the electrodes and batteries of the present disclosure are not limited to the following examples.

[0121] Example 1 [Preparation of the first solid electrolyte] In an argon glove box with a dew point below -60°C, the raw material powders YCl3, LiCl, and LiBr were weighed in a molar ratio of YCl3:LiCl:LiBr = 1:1:2. These were ground and mixed in a mortar to obtain a mixture. The mixture was fired in an electric furnace at 520°C for 2 hours. This yielded the halide solid electrolyte Li3YBr2Cl4 (hereinafter referred to as "LYBC"). p-Chlorotoluene was added to LYBC, and the LYBC was pulverized using a wet mill / disperser and then dried. This yielded LYBC powder (median diameter D50 = 0.4 μm) as the first solid electrolyte.

[0122] [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.

[0123] 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."

[0124] Next, a first coating layer made of LYBC was formed on the surface of Nb-NCA. The first coating layer was formed by compressive shear treatment using a particle composite device (NOB-MINI, manufactured by Hosokawa Micron Corporation). Specifically, Nb-NCA and LYBC were weighed to have a volume ratio of 85:15, and treated under the following conditions: blade clearance: 2 mm, rotation speed: 6000 rpm, treatment time: 50 min. This produced the coated active material of Example 1.

[0125] <Example 2> A coated active material of Example 2 was obtained in the same manner as in Example 1, except that the volume ratio of Nb-NCA to LYBC was changed to 90:10.

[0126] Example 3 A coated active material of Example 3 was obtained in the same manner as in Example 1, except that the volume ratio of Nb-NCA to LYBC was changed to 92:8.

[0127] Example 4 A coated active material of Example 4 was obtained in the same manner as in Example 1, except that the volume ratio of Nb-NCA to LYBC was changed to 95:5.

[0128] <Example 5> A coated active material of Example 5 was obtained in the same manner as in Example 1, except that the volume ratio of Nb-NCA to LYBC was changed to 97:3.

[0129] Example 6 Nb-NCA and LYBC were weighed out to a volume ratio of 90:10. Nb-NCA and LYBC were mixed in an agate mortar for 30 minutes. This gave a coated active material of Example 6.

[0130] <Comparative Example 1> Nb-NCA was used as the coated active material in Comparative Example 1.

[0131] [Preparation of sulfide 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").

[0132] [Preparation of cathode material] The coated active material of Example 1 and LPS were weighed in an argon glove box so that the volume ratio of Nb-NCA to solid electrolyte was 75:25. These were mixed in an agate mortar to prepare the positive electrode material of Example 1. In the volume ratio of Nb-NCA to solid electrolyte, "solid electrolyte" refers to the total volume of LYBC and LPS.

[0133] The positive electrode materials of Examples 2 to 6 and Comparative Example 1 were prepared by the same method as in Example 1. In the positive electrode materials of the Examples and Comparative Example, the ratio of the volume of LYBC to the total volume of LYBC and LPS was as shown in Table 1.

[0134] [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.

[0135] [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.

[0136] 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 6 and Comparative Example 1.

[0137] [Thermal analysis] Using the thermal analysis samples of Examples 1 to 6 and Comparative Example 1, thermal analysis was carried out under the following conditions.

[0138] 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.

[0139] [Table 1]

[0140] <Consideration> As shown in Table 1, the heat generation initiation temperature increased as the volume ratio of the halide solid electrolyte in the positive electrode material increased. This suggests that the reaction between oxygen released from the positive electrode active material and the sulfide solid electrolyte is suppressed, thereby improving the safety of the battery.

[0141] If the volume of LYBC relative to the volume of Nb-NCA is less than 1%, it is expected that it will be difficult to coat Nb-NCA with LYBC. Therefore, the ratio of the volume of LYBC to the volume of Nb-NCA is preferably 1% or more. The upper limit of the ratio of the volume of LYBC to the volume of Nb-NCA is, for example, 15%.

[0142] The thermal analysis sample of Example 2 showed a higher heat generation onset temperature than the thermal analysis sample of Example 6. In other words, the coated active material obtained by mixing Nb-NCA and LYBC in a particle composite device is more likely to realize a battery with higher safety than the coated active material obtained by mixing Nb-NCA and LYBC in an agate mortar. This is thought to be because the particle composite device enabled the surfaces of the Nb-NCA particles to be uniformly coated with LYBC. [Industrial Applicability]

[0143] The technology of the present disclosure is useful, for example, in all-solid-state lithium secondary batteries. [Explanation of symbols]

[0144] 10,20 Cathode materials 100,110 Coated active material 101 Cathode active material 102 1st coating layer 103 Second coating layer 104 Covering layer 105 Second solid electrolyte 200 batteries 201 Positive electrode 202 separator layer 203 Negative electrode

Claims

1. a positive electrode active material; a coating layer that coats at least a portion of the surface of the positive electrode active material; a second solid electrolyte; Equipped with the coating layer includes a first coating layer including a first solid electrolyte and a second coating layer including a base material; the first coating layer is located outside the second coating layer, the first solid electrolyte comprises Li, 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 is in contact with the positive electrode active material via the coating layer, 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 4% or more and 60% or less; Positive electrode material.

2. The second solid electrolyte contains Li and S. The positive electrode material according to claim 1 .

3. M comprises yttrium; The positive electrode material according to claim 1 .

4. The first solid electrolyte is represented by the following composition formula (1): Li α M β X γ ... Equation (1) where α, β, and γ are each independently a value greater than 0. The positive electrode material according to claim 1 .

5. The base material includes an oxide solid electrolyte having lithium ion conductivity. The positive electrode material according to claim 1 .

6. the underlayer material comprises lithium niobate; The positive electrode material according to claim 1 .

7. A positive electrode comprising the positive electrode material according to any one of claims 1 to 6.

8. A battery comprising the positive electrode according to claim 7.

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