Solid electrolyte material, method for producing solid electrolyte material, positive electrode material, and battery

Abstract

This solid electrolyte material comprises Li, Al, and X. X is an anion containing F, and the specific surface area of the solid electrolyte material is at least 16 m2 / g. This method for producing the solid electrolyte material includes a wet pulverization step for pulverizing a mixture containing a solvent and a raw material composition containing constituent components of the solid electrolyte material. This positive electrode material includes the positive electrode active material coated with a solid electrolyte material.

Description

Solid electrolyte material, method for producing solid electrolyte material, positive electrode material and battery

[0001] The present disclosure relates to a solid electrolyte material, a method for producing a solid electrolyte material, a positive electrode material, and a battery.

[0002] Patent Document 1 discloses an all-solid-state battery using a sulfide solid electrolyte.

[0003] Patent Document 2 discloses coating the surface of lithium nickel oxide with lithium fluoride.

[0004] JP 2011-129312 A JP 2012-84547 A

[0005] An object of the present disclosure is to provide a solid electrolyte material that is suitable for lithium ion conduction and has improved contact with other materials.

[0006] The present disclosure provides a solid electrolyte material comprising Li, Al, and X, wherein X is an anion containing F, and wherein the specific surface area of ​​the solid electrolyte material is 16 m 2 / g or more.

[0007] The present disclosure provides a solid electrolyte material that is suitable for lithium ion conduction and has improved contact with other materials.

[0008] FIG. 1 shows a cross-sectional view of a battery 1000 according to a second embodiment. FIG. 2 shows a schematic diagram of a pressure forming die 300 used to evaluate the ionic conductivity of a solid electrolyte material. FIG. 3 is a graph showing a Cole-Cole plot obtained by measuring the impedance of the solid electrolyte material according to Example 1. FIG. 4 is a graph showing the initial discharge characteristics of the battery according to Example 1.

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0010] First Embodiment A solid electrolyte material according to a first embodiment is composed of Li, Al, and X. X is an anion containing F. The specific surface area of ​​the solid electrolyte material according to the first embodiment is 16 m 2 / g. Here, the specific surface area of ​​the solid electrolyte material in the present disclosure means the specific surface area determined by the BET (Brunauer-Emmett-Teller) method.

[0011] "Consisting of Li, Al, and X" means that elements other than Li, Al, and X are not actively used in the raw materials of the solid electrolyte material. The solid electrolyte material is allowed to contain inevitable impurities. Examples of elements contained as inevitable impurities are hydrogen, oxygen, or nitrogen. These elements are present in the raw material powder of the solid electrolyte material or in the atmosphere used for producing or storing the solid electrolyte material. Impurities may also be mixed into the solid electrolyte material from the container used to synthesize the solid electrolyte material.

[0012] The solid electrolyte material according to the first embodiment is suitable for lithium ion conduction and has good contact with other materials, such as active materials, and therefore can reduce the resistance at the interface with the other materials.

[0013] Polycrystalline materials are commonly used as active materials in lithium-ion secondary batteries. The surface of an active material is often uneven, with small grooves or depressions. When coating the surface of an active material with a solid electrolyte, it is desirable to improve the contact between the active material and the solid electrolyte to reduce battery resistance. To achieve this, the solid electrolyte must be deformed, for example by compression, to conform to the uneven shape of the active material. However, if the surface of the solid electrolyte is flat and the particle size of the solid electrolyte is large, the pressure during pressing is concentrated on the protrusions on the surface of the active material. As a result, good contact between the active material and the solid electrolyte cannot be achieved inside the depressions. On the other hand, if the particle size of the solid electrolyte is smaller than the depressions on the surface of the active material, pressure is applied to the solid electrolyte while it is embedded in the depressions, resulting in good contact between the active material and the solid electrolyte. Furthermore, when the surface of a solid electrolyte is uneven, the solid electrolyte can more easily penetrate into the depressions on the surface of the active material than when the surface is flat, making it easier to achieve good contact between the active material and the solid electrolyte. Small particle size and an uneven surface mean a large specific surface area. In other words, a solid electrolyte with a large specific surface area can easily achieve good contact with the active material, which can reduce the resistance of the battery and improve, for example, the charge-discharge characteristics of the battery.

[0014] The solid electrolyte material according to the first embodiment can be used, for example, to obtain a battery with excellent charge / discharge characteristics. An example of such a battery is a solid-state battery. The solid electrolyte material according to the first embodiment is suitable as a material for a solid-state battery. The solid-state battery may be a primary battery or a secondary battery. The solid-state battery may be an all-solid-state battery.

[0015] The solid electrolyte material according to the first embodiment desirably does not contain sulfur. A sulfur-free solid electrolyte material does not generate hydrogen sulfide even when exposed to the atmosphere, and is therefore highly safe. The sulfide solid electrolyte disclosed in Patent Document 1 may generate hydrogen sulfide when exposed to the atmosphere.

[0016] The solid electrolyte material according to the first embodiment contains F, and therefore can have high oxidation resistance. This is because F has a high redox potential. On the other hand, F has a high electronegativity, and therefore the bond between F and Li is relatively strong. As a result, the lithium ion conductivity of a solid electrolyte material containing Li and F is usually low. For example, the conductivity of LiF disclosed in Patent Document 2 is so high that it cannot be measured by the AC impedance method. In contrast, the solid electrolyte material according to the first embodiment contains Al in addition to Li and F, and therefore has a lithium ion conductivity of, for example, 1.2 × 10 -10 The solid electrolyte material according to the first embodiment can have an ionic conductivity of 1000 S / cm or more. This value is a conductivity sufficient for lithium ions to move over a very short distance. For example, when the surface of the active material is coated with the solid electrolyte material according to the first embodiment, lithium ions can permeate the layer of the solid electrolyte material.

[0017] The specific surface area of ​​the solid electrolyte material according to the first embodiment is 100 m 2 / g, and may be less than 60m 2 / g, and may be less than 44.6m 2 / g or less. With this configuration, the above-mentioned effects can be sufficiently obtained.

[0018] The specific surface area of ​​the solid electrolyte material according to the first embodiment is 32.4 m 2 / g or more. With this configuration, the above-mentioned effects can be sufficiently obtained.

[0019] In order to increase the ionic conductivity of the solid electrolyte material, the solid electrolyte material according to the first embodiment may further contain at least one anion other than F. Examples of the anion include Cl, Br, I, O, and Se.

[0020] In order to enhance the oxidation resistance of the solid electrolyte material, the ratio of the amount of substance of F to the total amount of substance of the anions constituting the solid electrolyte material according to the first embodiment may be 0.50 or more and 1.0 or less.

[0021] In order to improve the oxidation resistance of the solid electrolyte material, the anion constituting the solid electrolyte material according to the first embodiment may be only F. That is, the ratio of the amounts of substances may be 1.0.

[0022] The solid electrolyte material according to the first embodiment has a composition formula (1): Li 6-3a Al a F6 (1) (wherein 0<a≦1.5 is satisfied) A solid electrolyte material containing a phase having such a composition has high ionic conductivity.

[0023] In order to increase the ionic conductivity of the solid electrolyte material, in formula (1), 0.7≦a≦1.3 may be satisfied, or 0.9≦a≦1.04 may be satisfied.

[0024] The upper and lower limits of the range of a in formula (1) can be defined by any combination selected from the following numerical values: 0.7, 0.8, 0.9, 0.96, 1, 1.04, 1.1, 1.2, and 1.3.

[0025] The solid electrolyte material according to the first embodiment may contain Li3AlF6 or may be Li3AlF6. Li3AlF6 has excellent oxidation resistance.

[0026] The solid electrolyte material according to the first embodiment may be crystalline or amorphous.

[0027] The solid electrolyte material according to the first embodiment may include a phase represented by formula (1).

[0028] The shape of the solid electrolyte material according to the first embodiment is not limited. Examples of the shape include a needle shape, a sphere shape, or an oval sphere shape. The solid electrolyte material according to the first embodiment may be in the form of particles. The solid electrolyte material according to the first embodiment may have the shape of a pellet or a plate.

[0029] <Method for Producing Solid Electrolyte Material> The solid electrolyte material according to the first embodiment is produced, for example, by the following method.

[0030] A plurality of halide raw material powders weighed to have a desired composition are mixed with an organic solvent in a mixer while being pulverized.

[0031] For example, if the desired composition is LiAlF, LiF and AlF are prepared in a molar ratio of approximately 3:1. The raw material powders may be prepared in a pre-adjusted molar ratio to compensate for any compositional changes that may occur during the synthesis process. The raw material powders and an organic solvent are placed in a mixing device such as a planetary ball mill and mixed while being pulverized. In other words, a wet ball mill process is performed. The raw material powders may be mixed before being placed in the mixing device.

[0032] After mixing, the balls are separated to obtain a slurry with dispersed particles. The slurry is dried at a temperature depending on the boiling point of the organic solvent used to obtain a solid. The reaction product is obtained by crushing this solid in a mortar.

[0033] By carrying out the wet pulverization, it is possible to realize a reduction in particle size of the product by pulverization, that is, it is possible to increase the specific surface area of ​​the solid electrolyte material.

[0034] The solid obtained by drying the slurry can be expected to have a further reduced particle size by dissolving it in an organic solvent and recrystallizing it. Alternatively, the raw material powder of the solid electrolyte material may be dissolved in an organic solvent and recrystallized to reduce the particle size, and then the resulting powder may be treated with a wet ball mill.

[0035] The solid obtained by drying the slurry may be calcined in a vacuum or in an inert atmosphere. The calcination is carried out, for example, at a temperature of 100°C or higher and 300°C or lower for 1 hour or longer. To prevent compositional changes during calcination, the calcination may be carried out in a sealed container such as a quartz tube.

[0036] As described above, the solid electrolyte material according to the first embodiment can be obtained by wet-pulverizing a mixture containing a raw material composition containing the constituent components of the solid electrolyte material and a solvent. The raw material composition containing the constituent components of the solid electrolyte material is raw material powder of a plurality of halides. The solvent is typically an organic solvent.

[0037] To increase the specific surface area of ​​the solid electrolyte material, the particle size of the balls used in the wet ball mill may be reduced, the amount of balls used in the wet ball mill may be increased, or the treatment time in the wet ball mill may be extended.

[0038] The solvent used in the wet ball mill may include at least one selected from the group consisting of γ-butyrolactone, propylene carbonate, butyl acetate, ethanol, dimethyl sulfoxide, and tetralin. By using these solvents, the solid electrolyte material according to the first embodiment can be produced. From the viewpoint of the dielectric constant of the solvent, N-methyl-2-pyrrolidone (NMP) may be used as the solvent.

[0039] Second Embodiment A second embodiment will be described below, and the matters described in the first embodiment will be omitted as appropriate.

[0040] The battery according to the second embodiment includes a positive electrode, an electrolyte layer, and a negative electrode. The electrolyte layer is disposed between the positive electrode and the negative electrode.

[0041] At least one selected from the group consisting of the positive electrode, the electrolyte layer, and the negative electrode contains the solid electrolyte material according to the first embodiment.

[0042] The battery according to the second embodiment contains the solid electrolyte material according to the first embodiment, and therefore has excellent charge / discharge characteristics.

[0043] FIG. 1 shows a cross-sectional view of a battery 1000 according to a second embodiment.

[0044] The battery 1000 according to the second embodiment includes a positive electrode 201, an electrolyte layer 202, and a negative electrode 203. The electrolyte layer 202 is provided between the positive electrode 201 and the negative electrode 203.

[0045] The positive electrode 201 contains a positive electrode active material 204 and a solid electrolyte 100 .

[0046] The electrolyte layer 202 contains an electrolyte material.

[0047] The negative electrode 203 contains a negative electrode active material 205 and a solid electrolyte 100 .

[0048] The solid electrolyte 100 includes, for example, the solid electrolyte material according to the first embodiment. The solid electrolyte 100 may be particles containing the solid electrolyte material according to the first embodiment as a main component. Particles containing the solid electrolyte material according to the first embodiment as a main component refer to particles in which the component contained most abundantly in terms of molar ratio is the solid electrolyte material according to the first embodiment. The solid electrolyte 100 may be particles made of the solid electrolyte material according to the first embodiment.

[0049] The positive electrode 201 contains a material capable of absorbing and releasing metal ions (e.g., lithium ions). The material is, for example, a positive electrode active material 204.

[0050] Examples of the positive electrode active material 204 include lithium-containing metal oxides such as lithium-containing transition metal oxides, lithium-containing transition metal phosphates, transition metal fluorides, polyanions, fluorinated polyanion materials, transition metal sulfides, transition metal oxyfluorides, transition metal oxysulfides, or transition metal oxynitrides. Here, the transition metal is defined as, for example, d according to the definitions set forth in the IUPAC "Gold Book" and "Red Book." 10 Elements (Zn, Cd, Hg of group 12), lanthanides (La (5d 1 6s 2 ) and actinides (Ac(6d l 7S 2 Examples of lithium-containing transition metal oxides include Li(Ni, Co, Mn)O, Li(Ni, Co, Al)O, and LiCoO.

[0051] In the present disclosure, "(A, B, C)" means "at least one selected from the group consisting of A, B, and C."

[0052] The shape of the positive electrode active material 204 is not limited to a specific shape. The positive electrode active material 204 may be particles. The positive electrode active material 204 may have a median diameter of 0.1 μm or more and 100 μm or less. When the positive electrode active material 204 has a median diameter of 0.1 μm or more, the positive electrode active material 204 and the solid electrolyte 100 can be well dispersed in the positive electrode 201. This improves the charge / discharge characteristics of the battery 1000. When the positive electrode active material 204 has a median diameter of 100 μm or less, the lithium diffusion rate within the positive electrode active material 204 improves. This allows the battery 1000 to operate at a high output.

[0053] The positive electrode active material 204 may have a larger median diameter than the solid electrolyte 100. This allows the positive electrode active material 204 and the solid electrolyte 100 to be dispersed well in the positive electrode 201.

[0054] In order to improve the energy density and output of the battery 1000, in the positive electrode 201, the ratio of the volume of the positive electrode active material 204 to the sum of the volume of the positive electrode active material 204 and the volume of the solid electrolyte 100 may be 0.30 or more and 0.95 or less.

[0055] A coating layer may be formed on at least a portion of the surface of the positive electrode active material 204. The coating layer may be formed on the surface of the positive electrode active material 204, for example, before mixing with the conductive additive and the binder. Examples of coating materials included in the coating layer include a sulfide solid electrolyte, an oxide solid electrolyte, or a halide solid electrolyte. When the solid electrolyte 100 contains a sulfide solid electrolyte, the coating material may contain the solid electrolyte material according to the first embodiment to suppress oxidative decomposition of the sulfide solid electrolyte. When the solid electrolyte 100 contains the solid electrolyte material according to the first embodiment, the coating material may contain an oxide solid electrolyte to suppress oxidative decomposition of the solid electrolyte material. Lithium niobate, which has excellent stability at high potentials, may be used as the oxide solid electrolyte. By suppressing oxidative decomposition, an increase in overvoltage of the battery 1000 can be suppressed.

[0056] The sulfide solid electrolyte is a solid electrolyte containing Li and S. When the solid electrolyte 100 contains a sulfide solid electrolyte, a material described below, such as LiS-P2S5, can be used as the sulfide solid electrolyte. When the positive electrode active material 204 is coated with the solid electrolyte material according to the first embodiment, oxidative decomposition of the solid electrolyte 100 containing Li and S can be suppressed.

[0057] To improve the energy density and output of the battery 1000, the positive electrode 201 may have a thickness of 10 μm or more and 500 μm or less.

[0058] The electrolyte layer 202 contains an electrolyte material. The electrolyte material is, for example, a solid electrolyte material. The solid electrolyte material may include the solid electrolyte material according to the first embodiment. The electrolyte layer 202 may be a solid electrolyte layer.

[0059] The electrolyte layer 202 may contain 50 mass % or more of the solid electrolyte material according to the first embodiment. The electrolyte layer 202 may contain 70 mass % or more of the solid electrolyte material according to the first embodiment. The electrolyte layer 202 may contain 90 mass % or more of the solid electrolyte material according to the first embodiment. The electrolyte layer 202 may be made of only the solid electrolyte material according to the first embodiment.

[0060] Hereinafter, the solid electrolyte material according to the first embodiment will be referred to as a first solid electrolyte material, and a solid electrolyte material different from the first solid electrolyte material will be referred to as a second solid electrolyte material.

[0061] The electrolyte layer 202 may contain not only the first solid electrolyte material but also the second solid electrolyte material. The first solid electrolyte material and the second solid electrolyte material may be uniformly dispersed in the electrolyte layer 202. A layer made of the first solid electrolyte material and a layer made of the second solid electrolyte material may be stacked along the stacking direction of the battery 1000.

[0062] The battery according to the second embodiment may include a cathode 201, a second electrolyte layer, a first electrolyte layer, and an anode 203, in this order. The solid electrolyte material contained in the first electrolyte layer may have a lower reduction potential than the solid electrolyte material contained in the second electrolyte layer. This allows the solid electrolyte material contained in the second electrolyte layer to be used without being reduced. As a result, the charge / discharge efficiency of the battery 1000 can be improved. For example, when the second electrolyte layer contains the first solid electrolyte material, the first electrolyte layer may contain a sulfide solid electrolyte to suppress reductive decomposition of the solid electrolyte material. This allows the charge / discharge efficiency of the battery 1000 to be improved. The second electrolyte layer may contain the first solid electrolyte material. The first solid electrolyte material has high oxidation resistance, thereby achieving a battery with excellent charge / discharge characteristics.

[0063] The electrolyte layer 202 may be made of only the second solid electrolyte material.

[0064] The electrolyte layer 202 may have a thickness of 1 μm or more and 1000 μm or less. When the electrolyte layer 202 has a thickness of 1 μm or more, the cathode 201 and the anode 203 are less likely to short-circuit. When the electrolyte layer 202 has a thickness of 1000 μm or less, the battery 1000 can operate at high power.

[0065] Examples of the second solid electrolyte material are LiMgX, LiFeX, Li(Al,Ga,In)X, Li(Al,Ga,In)X, or LiI, where X is at least one selected from the group consisting of F, Cl, Br, and I.

[0066] To improve the energy density and power output of the battery 1000, the electrolyte layer 202 may have a thickness of 1 μm or more and 1000 μm or less.

[0067] The negative electrode 203 contains a material capable of absorbing and releasing metal ions (e.g., lithium ions). The material is, for example, a negative electrode active material 205.

[0068] Examples of the negative electrode active material 205 include a metal material, a carbon material, an oxide, a nitride, a tin compound, or a silicon compound. The metal material may be a simple metal or an alloy. An example of the metal material is lithium metal or a lithium alloy. Examples of the carbon material are natural graphite, coke, partially graphitized carbon, carbon fiber, spherical carbon, artificial graphite, or amorphous carbon. From the viewpoint of capacity density, suitable examples of the negative electrode active material are silicon (i.e., Si), tin (i.e., Sn), a silicon compound, or a tin compound.

[0069] The anode active material 205 may be selected taking into consideration the reduction resistance of the solid electrolyte material contained in the anode 203. For example, when the anode 203 contains a first solid electrolyte material, the anode active material 205 may be a material capable of absorbing and releasing lithium ions at 0.27 V or more relative to lithium. Examples of such anode active materials include titanium oxide, indium metal, or a lithium alloy. An example of titanium oxide is Li4Ti5O 12 , LiTiO, or TiO. By using the above-mentioned negative electrode active material, it is possible to suppress the reductive decomposition of the first solid electrolyte material contained in the negative electrode 203. As a result, it is possible to improve the charge / discharge efficiency of the battery 1000.

[0070] The shape of the negative electrode active material 205 is not limited to a specific shape. The negative electrode active material 205 may be particles. The negative electrode active material 205 may have a median diameter of 0.1 μm or more and 100 μm or less. When the negative electrode active material 205 has a median diameter of 0.1 μm or more, the negative electrode active material 205 and the solid electrolyte 100 can be well dispersed in the negative electrode 203. This improves the charge / discharge characteristics of the battery 1000. When the negative electrode active material 205 has a median diameter of 100 μm or less, the lithium diffusion rate within the negative electrode active material 205 improves. This allows the battery 1000 to operate at high power.

[0071] The negative electrode active material 205 may have a larger median diameter than the solid electrolyte 100. This allows the negative electrode active material 205 and the solid electrolyte 100 to be dispersed well in the negative electrode 203.

[0072] In order to improve the energy density and output of the battery 1000, in the negative electrode 203, the ratio of the volume of the negative electrode active material 205 to the sum of the volume of the negative electrode active material 205 and the volume of the solid electrolyte 100 may be 0.30 or more and 0.95 or less.

[0073] To improve the energy density and output of the battery 1000, the negative electrode 203 may have a thickness of 10 μm or more and 500 μm or less.

[0074] At least one selected from the group consisting of the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 may contain a second solid electrolyte material for the purpose of increasing ionic conductivity, chemical stability, and electrochemical stability.

[0075] The second solid electrolyte material may be a sulfide solid electrolyte.

[0076] 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, or Li 10 GeP2S 12 is.

[0077] When the electrolyte layer 202 contains a first solid electrolyte material, the anode 203 may contain a sulfide solid electrolyte to suppress reductive decomposition of the solid electrolyte material. The electrochemically stable sulfide solid electrolyte covers the anode active material, thereby suppressing contact between the first solid electrolyte material and the anode active material. As a result, the internal resistance of the battery 1000 can be reduced.

[0078] The second solid electrolyte material may be an oxide solid electrolyte.

[0079] Examples of oxide solid electrolytes include: (i) NASICON-type solid electrolytes such as LiTi2(PO4)3 or its elemental substitutions; (ii) perovskite-type solid electrolytes such as (LaLi)TiO3; (iii) Li 14 ZnGeO 16LISICON-type solid electrolytes such as LiSiO, LiGeO or elemental substitutions thereof; (iv) LiLaZrO 12 or an element-substituted product thereof, or (v) a garnet-type solid electrolyte such as Li3PO4 or an N-substituted product thereof.

[0080] As mentioned above, the second solid electrolyte material may be a halide solid electrolyte.

[0081] Examples of halide solid electrolytes are LiMgX, LiFeX, Li(Al,Ga,In)X, Li(Al,Ga,In)X, or LiI, where X is at least one selected from the group consisting of F, Cl, Br, and I.

[0082] Other examples of halide solid electrolytes include Li a Me b Y c Z6, where a + mb + 3c = 6 and c > 0 are satisfied. Me is at least one selected from the group consisting of metal elements and metalloid elements other than Li and Y. Z is at least one selected from the group consisting of F, Cl, Br, and I. m represents the valence of Me. "Metalloid elements" are B, Si, Ge, As, Sb, and Te. "Metal elements" are all elements included in Groups 1 to 12 of the periodic table (excluding hydrogen) and all elements included in Groups 13 to 16 of the periodic table (excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se).

[0083] In order to improve the ionic conductivity of the halide solid electrolyte, 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, and Nb.

[0084] The halide solid electrolyte may be Li3YCl6 or Li3YBr6.

[0085] The second solid electrolyte material may be an organic polymer solid electrolyte.

[0086] An example of the organic polymer solid electrolyte is a compound of a polymer compound and a lithium salt.

[0087] 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, and therefore can further increase ionic conductivity.

[0088] Examples of lithium salts include LiPF, LiBF, LiSbF, LiAsF, LiSOCF, LiN(SOCF), LiN(SOCF), LiN(SOCF)(SOCF), or LiC(SOCF). One lithium salt selected from these may be used alone. Alternatively, a mixture of two or more lithium salts selected from these may be used.

[0089] At least one selected from the group consisting of the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 may contain a non-aqueous electrolyte solution, a gel electrolyte, or an ionic liquid to facilitate the exchange of lithium ions and improve the output characteristics of the battery.

[0090] The non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent.

[0091] Examples of non-aqueous solvents are cyclic carbonate ester solvents, chain carbonate ester solvents, cyclic ether solvents, chain ether solvents, cyclic ester solvents, chain ester solvents, or fluorine-containing solvents. Examples of cyclic carbonate ester solvents are ethylene carbonate, propylene carbonate, or butylene carbonate. Examples of chain carbonate ester solvents are dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate. Examples of cyclic ether solvents are tetrahydrofuran, 1,4-dioxane, or 1,3-dioxolane. Examples of chain ether solvents are 1,2-dimethoxyethane or 1,2-diethoxyethane. An example of a cyclic ester solvent is γ-butyrolactone. An example of a chain ester solvent is methyl acetate. Examples of fluorine-containing solvents are fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, or fluorodimethylene carbonate. One non-aqueous solvent selected from these may be used alone, or two or more non-aqueous solvents selected from these may be used in combination.

[0092] Examples of lithium salts include LiPF, LiBF, LiSbF, LiAsF, LiSOCF, LiN(SOCF), LiN(SOCF), LiN(SOCF)(SOCF), or LiC(SOCF). A single lithium salt selected from these may be used alone. Alternatively, a mixture of two or more lithium salts selected from these may be used. The concentration of the lithium salt is, for example, in the range of 0.5 mol / L or more and 2 mol / L or less.

[0093] The gel electrolyte may be a polymer material impregnated with a non-aqueous electrolyte, such as polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, or a polymer having an ethylene oxide bond.

[0094] Examples of cations contained in the ionic liquid are: (i) aliphatic chain quaternary salts such as tetraalkylammonium or tetraalkylphosphonium; (ii) aliphatic cyclic ammoniums such as pyrrolidiniums, morpholiniums, imidazoliniums, tetrahydropyrimidiniums, piperaziniums, or piperidiniums; or (iii) nitrogen-containing heterocyclic aromatic cations such as pyridiniums or imidazoliums.

[0095] An example of an anion contained in an ionic liquid is PF6 - , BF4 - , SbF6 - , AsF6 - , SO3CF3 - , N(SO2CF3)2 - , N(SO2C2F5)2 - , N(SO2CF3)(SO2C4F9) - , or C(SO2CF3)3 - is.

[0096] The ionic liquid may contain a lithium salt.

[0097] At least one selected from the group consisting of the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 may contain a binder to improve adhesion between particles.

[0098] Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl ester of acrylic acid, polyethyl ester of acrylic acid, polyhexyl ester of acrylic acid, polymethacrylic acid, polymethyl ester of methacrylic acid, polyethyl ester of methacrylic acid, polyhexyl ester of methacrylic acid, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadiene rubber, and carboxymethyl cellulose. Copolymers can also be used as binders. Examples of such binders include copolymers of two or more materials selected from the group consisting of tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene. Mixtures of two or more materials selected from these may also be used as binders.

[0099] At least one selected from the positive electrode 201 and the negative electrode 203 may contain a conductive additive to improve electronic conductivity.

[0100] Examples of the conductive additive include: (i) graphites such as natural graphite or artificial graphite, (ii) carbon blacks such as acetylene black or ketjen black, (iii) conductive fibers such as carbon fiber or metal fiber, (iv) carbon fluoride, (v) metal powders such as aluminum, (vi) conductive whiskers such as zinc oxide or potassium titanate, (vii) conductive metal oxides such as titanium oxide, or (viii) conductive polymer compounds such as polyaniline, polypyrrole, or polythiophene. To reduce costs, the conductive additives (i) or (ii) above may be used.

[0101] Examples of the shape of the battery according to the second embodiment include a coin type, a cylindrical type, a square type, a sheet type, a button type, a flat type, and a laminate type.

[0102] The battery according to the second embodiment may be manufactured, for example, by preparing a material for forming a positive electrode, a material for forming an electrolyte layer, and a material for forming a negative electrode, and by using a known method to fabricate a laminate in which the positive electrode, the electrolyte layer, and the negative electrode are arranged in this order.

[0103] (Additional Note) From the above description, the following techniques are disclosed.

[0104] (Technology 1) A solid electrolyte material comprising Li, Al, and X, wherein X is an anion containing F, and the specific surface area of ​​the solid electrolyte material is 16 m 2 / g or more.

[0105] According to the present disclosure, it is possible to provide a solid electrolyte material that is suitable for lithium ion conduction and has improved contact with other materials.

[0106] (Technology 2) The solid electrolyte material is represented by the composition formula (1): Li 6-3x Al x The solid electrolyte material according to Technology 1 includes a phase represented by the formula: F6 (1) (wherein 0<x≦1.5 is satisfied). The solid electrolyte material including a phase having such a composition has high ionic conductivity.

[0107] (Technology 3) The solid electrolyte material according to Technology 1 or 2, wherein a ratio of the amount of substance of F to the total amount of substance of the anions constituting the solid electrolyte material is 0.50 or more and 1.0 or less. With this configuration, the oxidation resistance of the solid electrolyte material can be improved.

[0108] (Technology 4) The solid electrolyte material according to any one of Technologies 1 to 3, wherein the solid electrolyte material contains Li3AlF6. According to this configuration, the oxidation resistance of the solid electrolyte material can be improved.

[0109] (Technology 5) The specific surface area is 100 m 2 / g or less. / g. According to this configuration, the above-mentioned effects can be sufficiently obtained.

[0110] (Technology 6) The specific surface area is 60 m 2 / g or less. According to this configuration, the above-mentioned effects can be sufficiently obtained.

[0111] (Technology 7) The specific surface area is 32.4 m 2 / g or more. According to this configuration, the above-mentioned effects can be sufficiently obtained.

[0112] (Technology 8) A method for producing a solid electrolyte material according to any one of Technologies 1 to 7, comprising a wet-pulverization step of pulverizing a mixture containing a raw material composition containing constituent components of the solid electrolyte material and a solvent. With this configuration, the solid electrolyte material according to the present disclosure can be obtained.

[0113] (Technology 9) The method for producing a solid electrolyte material according to Technology 8, wherein the solvent contains at least one selected from the group consisting of γ-butyrolactone, propylene carbonate, butyl acetate, ethanol, dimethyl sulfoxide, and tetralin. By using these solvents, the solid electrolyte material according to the present disclosure can be produced.

[0114] (Technology 10) A positive electrode material comprising the solid electrolyte material according to any one of Technologies 1 to 7 and a positive electrode active material coated with the solid electrolyte material. With this configuration, it is possible to suppress contact between the positive electrode active material and other materials such as the solid electrolyte, and to suppress decomposition of the other materials.

[0115] (Technology 11) A battery comprising an electrolyte layer and a positive electrode containing the positive electrode material according to Technology 10. According to the present disclosure, a battery in which an increase in overvoltage is suppressed can be obtained.

[0116] (Technology 12) The battery according to Technology 11, wherein the battery is a solid-state battery. The solid electrolyte material according to the present disclosure is suitable as a material for solid-state batteries.

[0117] (Technology 13) The battery according to Technology 11 or 12, wherein the electrolyte layer contains a solid electrolyte containing Li and S. According to the technology of the present disclosure, oxidative decomposition of the solid electrolyte containing Li and S can be suppressed.

[0118] Hereinafter, the present disclosure will be described in more detail with reference to examples and comparative examples.

[0119] Example 1 (Preparation of Solid Electrolyte Material) In an argon atmosphere with a dew point of −60°C or lower (hereinafter referred to as a “dry argon atmosphere”), raw material powders of LiF and AlF were prepared in a molar ratio of LiF:AlF=3:1. These raw material powders were loaded into a 45 cc planetary ball mill pod along with 1 mm diameter balls (25 g). An organic solvent, γ-butyrolactone (GBL), was added dropwise to the pod to achieve a solids content of 30%. The solids content is calculated as {(mass of input raw materials) / (mass of input raw materials + mass of input solvent)} × 100. Milling was performed for 12 hours at 500 rpm using a planetary ball mill. After milling, the balls were separated to obtain a slurry. The resulting slurry was dried at 270°C for 1 hour under a nitrogen flow using a mantle heater. The obtained solid was pulverized in a mortar to obtain a powder of the solid electrolyte material according to Example 1. The solid electrolyte material according to Example 1 had a composition represented by Li3AlF6.

[0120] (Evaluation of Ionic Conductivity) FIG. 2 shows a schematic diagram of a pressure forming die 300 used to evaluate the ionic conductivity of the solid electrolyte material.

[0121] The pressure molding die 300 had an upper punch 301, a frame 302, and a lower punch 303. The frame 302 was made of insulating polycarbonate, and the upper punch 301 and the lower punch 303 were made of electronically conductive stainless steel.

[0122] The ionic conductivity of the solid electrolyte material of Example 1 was evaluated by the following method using the pressure molding die 300 shown in FIG.

[0123] In a dry atmosphere having a dew point of −30° C. or less, the powder of the solid electrolyte material according to Example 1 was filled into the inside of the pressure molding die 300. Inside the pressure molding die 300, a pressure of 400 MPa was applied to the solid electrolyte material according to Example 1 using the upper punch 301 and the lower punch 303.

[0124] While the pressure was still applied, the upper punch 301 and the lower punch 303 were connected to a potentiostat (VSP300, manufactured by BioLogic) equipped with a frequency response analyzer. The upper punch 301 was connected to a working electrode and a potential measurement terminal. The lower punch 303 was connected to a counter electrode and a reference electrode. The impedance of the solid electrolyte material was measured at room temperature by electrochemical impedance measurement.

[0125] FIG. 3 is a graph showing a Cole-Cole plot obtained by measuring the impedance of the solid electrolyte material according to Example 1.

[0126] In Fig. 3, the real value of the impedance at the measurement point where the absolute value of the phase of the complex impedance is smallest was considered to be the resistance value for ion conduction of the solid electrolyte material. SE Using the resistance value, the equation (i) σ = (R SE × S / t) -1 The ionic conductivity was calculated based on the following equation (i).

[0127] Here, σ represents ionic conductivity, and S represents the contact area of ​​the solid electrolyte material with the punch upper portion 301. In other words, S is equal to the cross-sectional area of ​​the hollow portion of the frame mold 302 in FIG. 3. R SE represents the resistance value of the solid electrolyte material in impedance measurement. t represents the thickness of the solid electrolyte material. That is, t represents the thickness of the layer formed from the powder 101 of the solid electrolyte material in FIG. 3 .

[0128] The ionic conductivity of the solid electrolyte material according to Example 1 measured at 25°C was 1.4 × 10 -10 S / cm.

[0129] (Measurement of Specific Surface Area) The specific surface area was measured using a specific surface area / pore distribution measuring device (BELSORP MINI X, manufactured by Microtrackbell Co., Ltd.) Hereinafter, the specific surface area obtained using this device will be referred to as the BET specific surface area.

[0130] In an air atmosphere having a dew point of −40° C. or less, powder (about 1 g) of the solid electrolyte material according to Example 1 was placed in a dedicated test tube.

[0131] As a pretreatment, the substrate was dried in a vacuum at 80° C. for 1 hour.

[0132] The added mass was calculated from the difference between the weight of the test tube containing the sample after pretreatment and the weight of the test tube before the sample was added.

[0133] The BET specific surface area was measured using the pretreated test tube, and the specific surface area of ​​the solid electrolyte material according to Example 1 was found to be 16.0 m 2 / g.

[0134] (Preparation of Coated Active Material) A powder of Li(Ni, Co, Al)O2 (hereinafter referred to as NCA) was prepared as the positive electrode active material. A coating layer made of LAF was formed on the surface of the NCA. The coating layer was formed by a compressive shear treatment using a particle compositer (NOB-MINI, manufactured by Hosokawa Micron Corporation). Specifically, the NCA and LAF were weighed to have a volume ratio of 98.9:1.1, and treated under the following conditions: blade clearance: 2 mm, rotation speed: 8000 rpm, and treatment time: 30 min. This resulted in the production of the coated active material of Example 1.

[0135] (Preparation of sulfide solid electrolyte) In an argon glove box with a dew point of −60°C or less, raw material powders LiS and P2S5 were weighed out to a molar ratio of LiS:P2S5 = 75:25. These were pulverized 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 resulted in a glassy solid electrolyte. The glassy solid electrolyte was then heat-treated in an inert atmosphere at 270°C for 2 hours. This resulted in a glass-ceramic solid electrolyte, Li2S-P2S5 (hereinafter referred to as "LPS").

[0136] (Fabrication of Battery) In a dry argon atmosphere, the positive electrode active material of Example 1 and LPS were weighed out so that the volume ratio of the coated active material to the sulfide solid electrolyte was 7: 3. These were mixed in an agate mortar to prepare the positive electrode material mixture of Example 1.

[0137] In an insulating cylinder having an inner diameter of 9.5 mm, LPS (50 mg) and the above-mentioned positive electrode mixture (10 mg) were stacked in this order. A pressure of 300 MPa was applied to the resulting stack to form an electrolyte layer and a positive electrode. The thickness of the electrolyte layer was 400 μm.

[0138] Next, metallic Li (thickness: 200 μm) was laminated on the first electrolyte layer, and a pressure of 80 MPa was applied to the resulting laminate to form a negative electrode.

[0139] Next, current collectors made of stainless steel were attached to the positive and negative electrodes, and current collecting leads were attached to the current collectors.

[0140] Finally, the inside of the insulating cylinder was isolated from the outside atmosphere using an insulating ferrule, and the inside of the cylinder was sealed. In this way, the battery according to Example 1 was obtained.

[0141] (Charge / Discharge Test) Fig. 4 is a graph showing the initial discharge characteristics of the battery according to Example 1. The initial charge / discharge characteristics were measured by the following method.

[0142] The battery according to Example 1 was placed in a thermostatic chamber at 25°C.

[0143] 125 μA / cm 2 The battery according to Example 1 was charged at a current density of 0.1 C until a voltage of 4.3 V was reached. The current density corresponds to a 0.1 C rate.

[0144] Next, 125 μA / cm 2 The battery according to Example 1 was discharged at a current density of 0.1 V until a voltage of 3.1 V was reached.

[0145] As a result of the charge-discharge test, the battery according to Example 1 had an initial discharge capacity of 1340 μAh.

[0146] <Examples 2 to 4> (Preparation of Solid Electrolyte Material) In Examples 2 to 4, as in Example 1, LiF and AlF3 were prepared as raw material powders in a molar ratio of LiF:AlF3 = 3:1.

[0147] The solvent, solid content ratio, ball diameter, ball amount, processing time, and drying conditions used in the milling treatment are shown in Table 1.

[0148] Except for the conditions shown in Table 1, the solid electrolyte materials of Examples 2 to 4 were obtained in the same manner as in Example 1.

[0149] (Evaluation of Ionic Conductivity) The ionic conductivity of the solid electrolyte materials according to Examples 2 to 4 was measured in the same manner as in Example 1. The measurement results are shown in Table 1.

[0150] (Measurement of Specific Surface Area) Using the solid electrolyte materials of Examples 2 to 4, the BET specific surface area was measured in the same manner as in Example 1. The measurement results are shown in Table 1.

[0151] (Charge-Discharge Test) Using the solid electrolyte materials of Examples 2 to 4, the batteries of Examples 2 to 4 were obtained in the same manner as in Example 1.

[0152] A charge / discharge test was carried out using the batteries of Examples 2 to 4 in the same manner as in Example 1. As a result, the batteries of Examples 2 to 4 were successfully charged and discharged, similar to the battery of Example 1.

[0153] Reference Example 1 In a dry argon atmosphere, LiF and AlF were prepared as raw material powders in a molar ratio of LiF:AlF = 3:1. These raw material powders were pulverized and mixed in a mortar. The resulting mixed powder was placed in a 45 cc planetary ball mill pod together with 5 mm diameter balls (25 g). Milling was performed for 12 hours at 500 rpm using the planetary ball mill. In this way, a solid electrolyte material according to Reference Example 1 was obtained.

[0154] As described above, the solid electrolyte material according to Reference Example 1 was produced by a dry ball mill without using an organic solvent.

[0155] Using the solid electrolyte material of Reference Example 1, the ionic conductivity and the specific surface area were measured in the same manner as in Example 1.

[0156] The ionic conductivity measured at 25°C was 8.3 x 10 -8 S / cm.

[0157] The measured specific surface area is 3.1 m 2 / g.

[0158] Comparative Example 1 LiF was used as the solid electrolyte material, and the ionic conductivity was measured in the same manner as in Example 1. As a result, it was not possible to measure the ionic conductivity at 25°C.

[0159]

[0160] <Discussion> The solid electrolyte materials according to Examples 1 to 4 had a melting point of 1.2 × 10 at room temperature. -10 S / cm or more ionic conductivity and 2 On the other hand, the specific surface area of ​​the solid electrolyte material according to Reference Example 1 produced by a dry ball mill is 3.1 m 2 The value was as small as / g.

[0161] The batteries according to Examples 1 to 4 were all charged and discharged at 25°C.

[0162] As described above, the solid electrolyte material according to the present disclosure is suitable for providing a battery that has high lithium ion conductivity and can be charged and discharged well.

[0163] The results shown in this example are believed to be obtainable even when a positive electrode active material other than NCA, particularly a lithium-containing transition metal oxide, is used. A solid electrolyte material with a high specific surface area penetrates into the recesses on the surface of the active material, improving the contact between the solid electrolyte material and the active material. This effect is obtained regardless of the composition of the positive electrode active material. This effect is particularly pronounced when the particles of the positive electrode active material are secondary particles.

[0164] The solid electrolyte material of the present disclosure is used, for example, in lithium ion secondary batteries.

[0165] REFERENCE SIGNS LIST 100 Solid electrolyte 101 Powder of solid electrolyte material 201 Positive electrode 202 Electrolyte layer 203 Negative electrode 204 Positive electrode active material 205 Negative electrode active material 300 Pressure molding die 301 Upper punch 302 Frame 303 Lower punch 1000 Battery

Claims

1. A solid electrolyte material comprising Li, Al, and X, where X is an anion containing F, and the specific surface area of ​​the solid electrolyte material is 16 m 2 / g or more.

2. The solid electrolyte material has the composition formula (1): Li 6-3x A x The solid electrolyte material according to claim 1 , comprising a phase represented by the formula: F6 (1) (wherein 0<x≦1.5 is satisfied).

3. The solid electrolyte material according to claim 1, wherein a ratio of the amount of substance of F to the total amount of substances of the anions constituting the solid electrolyte material is 0.50 or more and 1.0 or less.

4. The solid electrolyte material according to claim 1, wherein the solid electrolyte material comprises Li3AlF6.

5. The specific surface area is 100 m 2 The solid electrolyte material according to claim 1 , wherein the MnO 2 content is less than 1 / g.

6. The specific surface area is 60 m 2 The solid electrolyte material according to claim 1 , wherein the MnO 2 content is less than 1 / g.

7. The specific surface area is 32.4 m 2 The solid electrolyte material according to claim 1 , wherein the Mo content is 1 / g or more.

8. A method for producing a solid electrolyte material according to claim 1, comprising a wet-grinding step of grinding a mixture containing a raw material composition containing components of the solid electrolyte material and a solvent.

9. The method for producing a solid electrolyte material according to claim 8, wherein the solvent contains at least one selected from the group consisting of γ-butyrolactone, propylene carbonate, butyl acetate, ethanol, dimethyl sulfoxide, and tetralin.

10. A positive electrode material comprising: the solid electrolyte material according to any one of claims 1 to 7; and a positive electrode active material coated with the solid electrolyte material.

11. A battery comprising: a positive electrode containing the positive electrode material according to claim 10; and an electrolyte layer.

12. The battery according to claim 11, wherein the battery is a solid-state battery.

13. The battery according to claim 11, wherein the electrolyte layer comprises a solid electrolyte containing Li and S.