Method for manufacturing LGPS-type solid electrolyte

Abstract

An embodiment provides a method for manufacturing a LGPS-type solid electrolyte, the method comprising: bringing a first solution, in which a first compound comprising counterions that are ions or ammonium ions of monovalent or a divalent metal atoms M1 that have a larger ionic radius than Li atoms is dissolved in a solvent, into contact with a cation exchange resin that comprises Li ions, to exchange the M1 ions or the ammonium ions contained in the first compound with Li ions, whereby a second solution in which a Li-containing compound is dissolved in the solvent is obtained; removing the solvent from the second solution to obtain a Li-containing crystal; mixing the Li-containing crystal with a Li3 PS4 crystal to obtain a precursor; and heat-treating the precursor, wherein the first compound comprises the M1 ions or the ammonium ions and an anion containing an S element and a Sn element.

Description

Method for producing LGPS-based solid electrolyte

[0001] In particular, the present invention relates to a method for producing an LGPS-based solid electrolyte containing Sn element.

[0002] In recent years, demand for lithium-ion secondary batteries has been increasing for applications such as personal digital assistants (PDAs), portable electronic devices, electric vehicles (EVs), hybrid electric vehicles (HEVs), and even stationary energy storage systems. However, current lithium-ion secondary batteries use flammable organic solvents as electrolytes, and require robust packaging to prevent leakage of the organic solvent. Furthermore, restrictions on the design of portable personal computers and other devices are being placed on their construction, such as the need to incorporate measures to protect against the risk of electrolyte leakage.

[0003] Furthermore, their use is expanding to mobile vehicles such as automobiles and airplanes, requiring stationary lithium-ion secondary batteries with large capacities. Under these circumstances, safety is becoming more important than ever, and efforts are being made to develop all-solid-state lithium-ion secondary batteries that do not use hazardous substances such as organic solvents.

[0004] The use of oxides, phosphate compounds, organic polymers, sulfides, and other materials as solid electrolytes in all-solid-state lithium-ion secondary batteries is being considered. Among these solid electrolytes, sulfides have the advantage of high ionic conductivity and being relatively soft, making them easy to form solid-solid interfaces. Furthermore, they are stable against active materials, and development is underway to develop them as practical solid electrolytes.

[0005] A useful sulfide-based solid electrolyte is an LGPS-based solid electrolyte having a specific crystal structure (Patent Document 1). Among sulfide-based solid electrolytes, LGPS-based solid electrolytes have extremely high ionic conductivity and can operate stably from low temperatures of -30°C to high temperatures of 100°C, and there are high expectations for their practical application. In particular, LGPS-based solid electrolytes containing Sn have been attracting particular attention in recent years due to their excellent ionic conductivity, water resistance, and low cost (Non-Patent Document 1, Patent Document 2).

[0006] Patent No. 6996553 Patent No. 6998588

[0007] Journal of Power Sources 396, 2018, p.824-830

[0008] Under the above circumstances, there is a demand for efficient production of Sn-containing LGPS-based solid electrolytes with excellent properties.

[0009] Therefore, the present inventors have conducted extensive research and found a method for efficiently producing a solid electrolyte having excellent properties (e.g., ionic conductivity, activation energy, etc.). The present invention is, for example, as follows: [1] A first solution in which a first compound having an ion of a monovalent or divalent metal atom M1 having an ionic radius larger than that of a Li atom or an ammonium ion as a counter ion is dissolved in a solvent is brought into contact with a cation exchange resin containing Li ions to exchange the M1 ion or the ammonium ion contained in the first compound for Li ions, thereby obtaining a second solution in which a Li-containing compound is dissolved in the solvent; removing the solvent from the second solution to obtain Li-containing crystals; and converting the Li-containing crystals into Li. ３ P.S. ４ A method for producing an LGPS-based solid electrolyte, comprising: mixing a crystalline ion with an ammonium ion to obtain a precursor; and heat-treating the precursor, wherein the first compound is composed of the M1 ion or the ammonium ion and an anion containing an S element and an Sn element. [1-2] The method according to [1], wherein the metal atom M1 is selected from the group consisting of a Na atom, a K atom, a Rb atom, a Cs atom, a Ca atom, a Sr atom, and a Ba atom. [1-3] The anion containing an S element and an Sn element is selected from the group consisting of SnS ４ ４－ , Sn ２ S ７ ６－ , Sn ２ S ６ ４－ , SnS ３ ２－ and SnP ２ S １２ １０－ The method according to [1] or [1-2], wherein the first compound is selected from the group consisting of Na ４ SnS ４, Na ６ Sn ２ S ７ , Na ４ Sn ２ S ６ , Na ２ SnS ３ , Na １０ SnP ２ S １２ , Na ９．８１ Sn ０．８１ P ２．１９ S １２ , Na １０ (Ge ０．５ Sn ０．５ ) P ２ S １２ , Na １０ (Si ０．５ Sn ０．５ ) P ２ S １２ , Na ３．４５ [Sn ０．０９ Si ０．３６ ]P ０．５５ S ４ , (NH ４ ) ４ SnS ４ , (NH ４ ) ４ Sn ２ S ６ and (NH ４ ) ２ SnS ３ [2] The method according to any one of [1] to [1-4], wherein the solvent is water or methanol. [3] The method according to [2], wherein the solvent is methanol. [3-1] The Li-containing crystal is ４ SnS ４ , Li ６ Sn ２ S ７ , Li ４ Sn ２ S ６ , Li ２ SnS ３ , Li １０ SnP ２ S １２ , Li ３．８ Sn ０．８ Sb ０．２ S ４ , Li３．２７ Sn ０．２７ P ０．７３ S ４ , Li １０ (Ge ０．５ Sn ０．５ ) P ２ S １２ , Li １０ (Si ０．５ Sn ０．５ ) P ２ S １２ and Li ３．４５ [Sn ０．０９ Si ０．３６ ]P ０．５５ S ４ The method according to any one of [1] to [3], wherein the heat treatment is carried out at a temperature of 300 to 700°C. [5] The method according to any one of [1] to [4], wherein the heat treatment is carried out in an inert gas atmosphere. [6] The method according to any one of [1] to [5], wherein the LGPS-based solid electrolyte has peaks at 2θ = 20.18° ± 0.50°, 20.44° ± 0.50°, 26.96° ± 0.50°, and 29.58° ± 0.50° in X-ray diffraction (CuKα: λ = 1.5405 Å). [7] The LGPS-based solid electrolyte is a tetrahedron composed of an octahedron O composed of Li and S, and a tetrahedron T composed of S and one or more elements selected from the group consisting of P and Sn. １ and a tetrahedron T consisting of P and S elements. ２ and the tetrahedron T １ and the octahedron O shares an edge, and the tetrahedron T ２ and the octahedron O mainly contains a crystal structure sharing vertices. [8] The method according to any one of [1] to [6]. ３ P.S. ４ The crystal is β-Li ３ P.S. ４ [9] The method according to any one of [1] to [7], wherein the Li-containing crystal is Li ４ SnS ４ The method according to any one of [1] to [8], wherein the LGPS-based solid electrolyte has a composition of Li ３．２７ Sn０．２７ P ０．７３ S ４ , Li ３．３３ Sn ０．３３ P ０．６７ S ４ , Li １０ SnP ２ S １２ , Li １０ (Ge ０．５ Sn ０．５ ) P ２ S １２ , Li １０ (Si ０．５ Sn ０．５ ) P ２ S １２ and Li ３．４５ [Sn ０．０９ Si ０．３６ ]P ０．５５ S ４ [9-2] The method according to any one of [1] to [9], wherein the Li-containing crystal is ３ P.S. ４ In the step of mixing with the crystals, ４ SnS ４ :Li ３ P.S. ４ The method according to any one of [1] to [9-1], wherein the first solution and the second solution are mixed at a molar ratio of 1:x (x = 1 to 3). [9-3] The method according to any one of [1] to [9-2], further comprising a step of atomizing the Li-containing crystals after the step of removing the solvent from the second solution. [9-4] The method according to [9-3], wherein the atomized Li-containing crystals have an average particle size (D50) of 0.1 to 10 μm.

[0010] According to the present invention, it is possible to provide a method for efficiently producing a Sn-containing LGPS-based solid electrolyte having excellent properties.

[0011] 1 is a schematic diagram showing the crystal structure of a Sn-containing LGPS-based solid electrolyte according to one embodiment of the present invention; 2 is a schematic cross-sectional view of an all-solid-state battery according to one embodiment of the present invention; 3 is a diagram showing the results of X-ray diffraction measurement of the solid electrolyte powders obtained in Examples 1 and 2 and Comparative Example 1; 4 is a diagram showing the results of Raman spectroscopy measurement of the solid electrolyte powders obtained in Examples 1 and 2 and Comparative Example 1;

[0012] Hereinafter, embodiments of the present invention will be described. Note that the materials, configurations, etc. described below do not limit the present invention, and various modifications can be made within the scope of the present invention.

[0013] A method for producing an LGPS-based solid electrolyte according to one embodiment of the present invention includes contacting a first solution in which a first compound having a counter ion, an ion of a monovalent or divalent metal atom M1 having an ionic radius larger than that of a Li atom, or an ammonium ion, is dissolved in a solvent with a cation exchange resin containing Li ions to exchange the M1 ion or the ammonium ion contained in the first compound for Li ions, thereby obtaining a second solution in which a Li-containing compound is dissolved in the solvent; removing the solvent from the second solution to obtain Li-containing crystals; and converting the Li-containing crystals into Li. ３ P.S. ４ and mixing the first compound with the crystal to obtain a precursor, and heat-treating the precursor, wherein the first compound in the above method is composed of an M ion or an ammonium ion and an anion containing an S element and an Sn element.

[0014] According to the above method, it is possible to obtain an LGPS-based solid electrolyte having properties (ionic conductivity, activation energy, etc.) that are particularly favorable for use in all-solid-state batteries. Although the reason for this is unclear, it is believed that the Li-containing crystals obtained by the ion exchange process can be further treated with Li ３ P.S. ４ It is speculated that the reaction with the crystal is one of the reasons for the improvement of ionic conductivity. ３ P.S. ４ The ion exchange method is also believed to be a key factor in the production of highly ionic conductive LGPS phases.

[0015] SnS, which is conventionally used as a solid electrolyte material ２ and Li ２Sulfides such as S react with oxygen and moisture in the atmosphere, causing deterioration of materials (by-production of oxides) and generation of toxic hydrogen sulfide, and therefore have had to be stored and handled in a low dew point environment. ２ and Li ２ Unlike S, which is expensive and difficult to handle, Na ２ S, SnCl ４ Inexpensive and easily handled materials such as LiOH can be used as raw materials. Therefore, the above method has the advantage of being able to produce an LGPS-based solid electrolyte inexpensively and simply. Furthermore, the above method can be carried out using a reaction vessel and an ion exchange column without using a planetary ball mill, which is not suitable for large-scale production, and therefore, it is possible to mass-produce an LGPS-based solid electrolyte using a large-scale device. Therefore, the above method makes it possible to more efficiently produce an LGPS-based solid electrolyte.

[0016] Furthermore, Sn-containing sulfide solid electrolytes have been confirmed to have high water resistance and are highly safe materials because they suppress the generation of hydrogen sulfide. Therefore, in the production of the Sn-containing LGPS-based solid electrolyte according to an embodiment of the present invention, it is not necessary to prepare a low dew point environment, particularly in the stage leading up to obtaining the Li-containing crystals. In this respect, it can be said that the LGPS-based solid electrolyte can be produced at low cost.

[0017] The components of the present invention will be described below in order. 1. Method for producing an Sn-containing LGPS-based solid electrolyte According to one embodiment of the present invention, a first solution in which a first compound having a counter ion of a monovalent or divalent metal atom M1 having an ionic radius larger than that of a Li atom or an ammonium ion is dissolved in a solvent is brought into contact with a cation exchange resin containing Li ions to exchange the M1 ion or the ammonium ion contained in the first compound for Li ions, thereby obtaining a second solution in which a Li-containing compound is dissolved in the solvent (ion exchange step), the solvent is removed from the second solution to obtain Li-containing crystals (solvent removal step), and the Li-containing crystals are converted into Li ions. ３ P.S. ４and mixing the first compound with a crystal to obtain a precursor (mixing step), and heating the precursor (heating step), wherein the first compound is composed of the M ion or the ammonium ion and anions containing S and Sn. In this specification, an LGPS-based solid electrolyte refers to a solid electrolyte containing Li, P, and S, and the present invention particularly relates to a method for producing an LGPS-based solid electrolyte further containing Sn.

[0018] (1) Ion Exchange Step In the ion exchange step, a first solution is prepared by dissolving a first compound having a counter ion of a monovalent or divalent metal atom M1 or an ammonium ion, the counter ion of which is larger than that of a Li atom, in a solvent. Since the M1 atom has a larger ionic radius than the Li atom, ion exchange between the M1 ion and the Li ion is successfully carried out.

[0019] The first solution used in the ion exchange step is a solution in which a first compound, which is an M1 atom-containing compound or an ammonium salt, is dissolved in a solvent. Examples of M1 atoms include Na atoms, K atoms, Rb atoms, Cs atoms, Ca atoms, Sr atoms, and Ba atoms. Among these, Na atoms are preferred from the viewpoint of versatility. The first compound is mainly composed of M1 ions or ammonium ions and anions containing S and Sn elements, but the first compound may further contain other elements. Examples of such other elements include silicon (Si), germanium (Ge), phosphorus (P), antimony (Sb), halogen elements (fluorine (F), chlorine (Cl), bromine (Br), and iodine (I)), oxygen (O), and the like. These other elements may be contained alone or in combination of two or more. Examples of anions containing S and Sn include SnS ４ ４－ , Sn ２ S ７ ６－ , Sn ２ S ６ ４－ , SnS ３ ２－ , SnP ２ S１２ １０－ etc., and preferably SnS ４ ４－ or Sn ２ S ６ ４－ , more preferably SnS ４ ４－ Specific examples of the first compound containing such an anion include Na ４ SnS ４ , Na ６ Sn ２ S ７ , Na ４ Sn ２ S ６ , Na ２ SnS ３ , Na １０ SnP ２ S １２ , Na ９．８１ Sn ０．８１ P ２．１９ S １２ , Na １０ (Ge ０．５ Sn ０．５ ) P ２ S １２ , Na １０ (Si ０．５ Sn ０．５ ) P ２ S １２ , Na ３．４５ [Sn ０．０９ Si ０．３６ ]P ０．５５ S ４ , (NH ４ ) ４ SnS ４ , (NH ４ ) ４ Sn ２ S ６ , (NH ４ ) ２ SnS ３ Among these, Na ４ SnS ４ and Na ４ Sn ２ S ６ is preferred, and Na ４ SnS ４ is more preferred.

[0020] For example, if the first compound is Na４ SnS ４ If Na ４ SnS ４ can be produced and used by the following reaction: ４ SnS ４ Synthesis of 2Na ２ S + SnCl ４ →SnS ２ + 4NaCl (Reaction Formula 1) SnS ２ +2Na ２ S → Na ４ SnS ４ (Reaction formula 2) In this way, Na ４ SnS ４ is Na ２ S, SnCl ４ It is advantageous to use this as the first compound because it can be produced using inexpensive and easy-to-handle raw materials such as

[0021] The raw materials for producing the first compound are not limited to those mentioned above, and other examples include magnesium sulfide (MgS), strontium sulfide (SrS), elemental sulfur, tin sulfide (SnS), tin (Sn), etc. When the first compound contains an element other than M1 ions or ammonium ions, S element, and Sn element, a raw material containing the other element can be used, and specifically, silicon sulfide (SiS ２ ), silicon (Si), silicon dioxide (SiO ２ Si-containing raw materials such as germanium sulfide (GeS ２ ), germanium (Ge), germanium dioxide (GeO ２ ) and other Ge element-containing raw materials; antimony sulfide (Sb ２ S ３ ), antimony (Sb), antimony oxide (Sb ２ O ３ Sb element-containing raw materials such as elemental phosphorus (P), diphosphorus trisulfide (P) ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ), phosphorus pentachloride (PCl ５ ), phosphorus tribromide (PBr ３ ), phosphorus pentabromide (PBr ５P-element-containing raw materials such as lithium bromide (LiBr), sodium bromide (NaBr), lithium iodide (LiI), sodium iodide (NaI), magnesium iodide (MgI) ２ ), phosphorus pentachloride (PCl ５ ), phosphorus tribromide (PBr ３ ), phosphorus pentabromide (PBr ５ ) and other halogen-containing raw materials; lithium oxide (Li ２ O), lithium oxide (Na ２ O) Phosphorus pentoxide (P ２ O ５ ), silicon dioxide (SiO ２ ), germanium dioxide (GeO ２ ), tin(II) oxide (SnO), tin(IV) oxide (SnO ２ ), tin (IV) oxide (SnO ３ These raw materials may be used alone or in combination of two or more.

[0022] The solvent in the first solution is not particularly limited as long as it dissolves the first compound, but examples thereof include water, alcohols, thiols, acetone, etc., preferably water or alcohols, more preferably alcohols. Examples of alcohols include methanol, ethanol, propanol, etc. Among these, it is preferable to use water, methanol, or ethanol, more preferably water or methanol, and particularly preferably methanol.

[0023] The content of the first compound in the first solution is not particularly limited, but is preferably 1×10 －５ The concentration is preferably 0.001 to 0.5 mol / L, more preferably 0.01 to 0.1 mol / L.

[0024] Next, the first solution prepared as described above is brought into contact with a cation exchange resin containing Li ions to exchange the M1 ions or ammonium ions contained in the first compound for Li ions, thereby obtaining a second solution in which the Li-containing compound is dissolved in the solvent. Either a strong acid cation exchange resin or a weak acid cation exchange resin may be used as the cation exchange resin, but it is preferable to use a strong acid cation exchange resin because it has a small amount of H-type residue or small volume change and is easy to handle. Examples of strong acid cation exchange resins include those containing -SO as the exchange group. ３ Li, -[(SO ３ ) ２ Li ２ In some cases, a chelating resin may also be used. The base structure of the cation exchange resin is not particularly limited, but may be a styrene-based, methacrylic-based, or other base. The average pore size and specific surface area of ​​the cation exchange resin are also not particularly limited.

[0025] The specific operation of the ion exchange step is not particularly limited, and conventionally known methods can be applied. That is, by supplying the first solution to an ion exchange column loaded with a cation exchange resin and passing the first solution through the column, the M1 ions or ammonium ions in the first compound are exchanged for Li ions, and a second solution containing a Li-containing compound can be obtained as a distillate. The temperature at which the ion exchange step is performed is not particularly limited, and is preferably 10°C to 50°C. In addition, the SV value (space velocity: the value obtained by dividing the amount of the first solution passed through by the volume of the cation exchange resin) is preferably 15 or less, more preferably 10 or less, from the viewpoint of exchange efficiency.

[0026] As described above, in the ion exchange step, M ions or ammonium ions in the first compound are exchanged with Li ions on the ion exchange resin. ４ SnS ４ The ion exchange resin is used as an exchange group -SO ３ When a resin containing Li is used, ion exchange occurs through the following reaction: Na ４ SnS ４ +4R-SO ３ Li → Li ４ SnS４ +4R-SO ３ Na By the above ion exchange step, a second solution is obtained in which the Li-containing compound is dissolved in the solvent of the first solution.

[0027] (2) Solvent Removal Step The solvent removal step is performed following the ion exchange step. Other steps may be optionally included between the ion exchange step and the solvent removal step. The solvent is removed from the second solution to obtain Li-containing crystals by the solvent removal step. The specific operation of the solvent removal step is not particularly limited, and conventionally known methods can be applied. For example, the solvent can be removed by freeze-drying (a method in which the second solution is first frozen, and then the boiling point of the frozen dried product is lowered in a vacuum to sublimate the water in the dried product), vacuum drying (a method in which the boiling point is lowered by reducing the pressure inside a heating device to promote solvent removal from the second solution), or spray drying (a method in which the second solution is sprayed into a gas and rapidly dried to obtain a dry powder). Alternatively, the solvent may be removed by heat drying. In this case, the heating temperature can be appropriately set depending on the type of solvent, for example, 50 to 300°C, more preferably 100 to 180°C. Vacuum drying may also be performed together with heat drying. Regardless of which method is used, it is preferable to set appropriate conditions depending on the type of solvent contained in the second solution.

[0028] The constituent elements of the Li-containing crystal obtained by the above process vary depending on the composition of the first compound, which is the raw material, but examples include a crystal consisting of Li, Sn, and S, a crystal consisting of Li, Sn, Si, and S, a crystal consisting of Li, Sn, Sb, and S, a crystal consisting of Li, Sn, P, and S, a crystal consisting of Li, Sn, F, and S, a crystal consisting of Li, Sn, Cl, and S, a crystal consisting of Li, Sn, Br, and S, a crystal consisting of Li, Sn, O, and S, a crystal consisting of Li, Sn, Si, P, and S, and a crystal consisting of Li, Ge, Sn, P, and S. Among these, a crystal consisting of Li, Sn, and S elements, a crystal consisting of Li, Sn, P, and S elements, a crystal consisting of Li, Sn, Si, P, and S elements, and a crystal consisting of Li, Ge, Sn, P, and S elements are preferred, and a crystal consisting of Li, Sn, and S elements is more preferred.

[0029] The composition of the Li-containing crystal is not particularly limited, but Li ４ SnS ４ , Li ６ Sn ２ S ７ , Li ４ Sn ２ S ６ , Li ２ SnS ３ , Li １０ SnP ２ S １２ , Li ３．８ Sn ０．８ Sb ０．２ S ４ , Li ３．２７ Sn ０．２７ P ０．７３ S ４ , Li １０ (Ge ０．５ Sn ０．５ ) P ２ S １２ , Li １０ (Si ０．５ Sn ０．５ ) P ２ S１２ , Li ３．４５ [Sn ０．０９ Si ０．３６ ]P ０．５５ S ４ Among these, Li ４ SnS ４ and Li ４ Sn ２ S ６ is preferred, and Li ４ SnS ４ is more preferred.

[0030] The Li-containing crystals are mainly composed of a Li-containing compound obtained by subjecting the first solution to an ion exchange step, but depending on the treatment conditions in the ion exchange step, an M1 atom-containing component or ammonium salt derived from the first compound contained in the first solution may be mixed in. The content of these impurities in the Li-containing crystals is preferably 3% by mass or less, more preferably 1% by mass or less.

[0031] (3) Micronization Step After the solvent removal step, a micronization step of the Li-containing crystals may be optionally performed. In all-solid-state batteries, the finer the crystal particles of the solid electrolyte, the lower the interfacial resistance between the solid electrolyte layer and the electrode layer, which is expected to result in higher energy density and higher output of the all-solid-state battery. Furthermore, small particles facilitate reactions in the subsequent heating step, suppressing the generation of by-products. For example, the average particle size (D50) of the micronized Li-containing crystals obtained by the micronization step is preferably 0.1 to 10 μm, more preferably 0.1 to 1 μm. The micronization method is not particularly limited, but examples include a method in which the good solvent solution obtained by dissolving the Li-containing crystals in a good solvent is brought into contact with a poor solvent to micronize the good solvent solution. This method is preferably performed under an inert gas atmosphere such as argon.

[0032] The good solvent is not particularly limited, but examples thereof include alcohol solvents, carboxylic acid solvents, lactam solvents, water, etc. Examples of alcohol solvents include methanol (boiling point: 64.7°C), ethanol (boiling point: 78.4°C), propanol (boiling point: 97°C), isopropyl alcohol (boiling point: 82.5°C), and 1-butanol (boiling point: 117.7°C). Examples of carboxylic acid solvents include formic acid (boiling point: 100.8°C) and acetic acid (boiling point: 118°C). Examples of lactam solvents include N-methylpyrrolidone (NMP) (boiling point: 202°C). Of these, the good solvent is preferably an alcohol solvent, and particularly preferably methanol. These good solvents may be used alone or in combination of two or more.

[0033] The content of the Li-containing crystals in the good solvent solution is preferably 1 to 30% by mass, more preferably 5 to 30% by mass, and even more preferably 15 to 30% by mass, relative to the total mass of the good solvent. A content of the Li-containing crystals of 1% by mass or more is preferred from the viewpoints of being able to reduce the amount of solvent used and obtaining finer crystals. On the other hand, a content of the Li-containing crystals of 30% by mass or less is preferred from the viewpoint of being able to reduce the amount of undissolved crystals.

[0034] The poor solvent is not particularly limited, but examples thereof include aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, ketone solvents, ether solvents, ester solvents, nitrile solvents, halogenated solvents, amide solvents, and sulfoxide solvents. Examples of aliphatic hydrocarbon solvents include hexane (boiling point: 69°C), heptane (boiling point: 98.4°C), and octane (boiling point: 125.6°C). Examples of aromatic hydrocarbon solvents include benzene (boiling point: 80.1°C), toluene (boiling point: 110.6°C), and xylene (boiling point: 139°C). Examples of ketone solvents include acetone (boiling point: 56°C) and methyl ethyl ketone (MEK) (boiling point: 79.6°C). Examples of ether solvents include diethyl ether (boiling point: 34.6°C), tetrahydrofuran (THF) (boiling point: 66°C), and 1,4-dioxane (boiling point: 101°C). Examples of ester solvents include methyl acetate (boiling point: 57.1°C), ethyl acetate (boiling point: 77.1°C), propyl acetate (boiling point: 102°C), methyl propionate (boiling point: 79.8°C), and ethyl propionate (boiling point: 99°C). Examples of nitrile solvents include acetonitrile (boiling point: 82°C), isobutyronitrile (boiling point: 108°C), and benzonitrile (boiling point: 191°C). Examples of halogen-based solvents include methylene chloride (boiling point: 39.6°C) and chloroform (boiling point: 61.2°C). Examples of amide solvents include N,N-dimethylformamide (DMF) (boiling point: 153°C). Examples of sulfoxide solvents include dimethyl sulfoxide (DMSO) (boiling point: 189°C).

[0035] Among the above-mentioned solvents, the poor solvent preferably contains at least one of a nitrile solvent and an ester solvent, more preferably a nitrile solvent, and further preferably acetonitrile. The poor solvents may be used alone or in combination of two or more.

[0036] The boiling point of the poor solvent is preferably higher than that of the good solvent. As will be described later, if the boiling point of the poor solvent is higher than that of the good solvent, the temperature of the poor solvent at the time of contact can be made higher than that of the good solvent. This causes part or all of the good solvent to volatilize immediately when the good solvent solution comes into contact with the poor solvent, further increasing the chance of contact between the crystals and the poor solvent, thereby further increasing the crystal precipitation rate. This results in crystals with a smaller average particle size and more finely divided.

[0037] By contacting the good solvent solution with the poor solvent, finely divided Li-containing crystals are precipitated. The contacting method is not particularly limited, but includes adding a poor solvent to a good solvent solution and adding a good solvent solution to a poor solvent. The addition method is not particularly limited, and the mixture may be added dropwise or all at once. Finally, a drying step is performed to remove the remaining poor solvent and good solvent, thereby obtaining finely divided Li-containing crystals. The drying temperature is not particularly limited as long as it is a temperature at which the remaining solvent can be removed, but is preferably 100°C or higher, more preferably 120 to 300°C, and even more preferably 150 to 250°C. The pressure during drying is not particularly limited, but is preferably 500 hPa or less, more preferably 0.1 to 200 hPa, and even more preferably 1 to 50 hPa.

[0038] When the atomization step is performed following the solvent removal step, and the solvent in the second solution is the same as the solvent used in the atomization step, the second solution can be directly subjected to the atomization step without removing the solvent from the second solution. That is, the above-mentioned solvent removal step can be omitted. For example, when the solvent in the second solution is methanol and the Li-containing crystals are dissolved in methanol as a good solvent in the subsequent atomization step, there is no need to perform the solvent removal step. Using the same solvent in both steps is preferable from the viewpoint of simplifying the production method.

[0039] (4) Mixing Step Subsequently, the Li-containing crystals obtained as described above are mixed with Li ３ P.S. ４ The Li-containing crystals are mixed with Li to obtain a precursor. ３ P.S. ４The mixed molar ratio of the crystals may be adjusted to an element ratio that allows the desired LGPS-based solid electrolyte to be obtained. For example, Li ４ SnS ４ :Li ３ P.S. ４ When the molar ratio is 1:x, it is preferable that x is 1 to 3, and more preferably x is 2 to 2.8. ４ SnS ４ :Li ３ P.S. ４ = about 1:2, Li １０ SnP ２ S １２ An LGPS-based solid electrolyte of Li ４ SnS ４ :Li ３ P.S. ４ When the ratio is about 1:2.7, the Li has the highest ionic conductivity. ３．２７ Sn ０．２７ P ０．７３ S ４ is obtained.

[0040] Li ３ P.S. ４ As the crystal, any of α, β, and γ can be used, but β-Li is more preferable. ３ P.S. ４ β-Li ３ P.S. ４ This is because Li is relatively stable in the LGPS synthesis system. ３ P.S. ４ Commercially available crystals may be used. However, as described in the examples below, Li crystals can be prepared by heating under an inert gas atmosphere such as argon. ２ S and P ２ S ５ It can also be synthesized from

[0041] Li-containing crystals and Li ３ P.S. ４The crystals can be mixed in the solid phase or in the presence of a solvent. Mixing methods using a solvent are suitable for large-scale synthesis because they allow uniform mixing. When using a solvent, it is preferable to use a solvent that does not react with the raw materials or the resulting precursor. Examples include ether-based solvents, ester-based solvents, hydrocarbon-based solvents, and nitrile-based solvents. Specific examples include tetrahydrofuran, cyclopentyl methyl ether, diisopropyl ether, diethyl ether, dimethyl ether, dioxane, methyl acetate, ethyl acetate, butyl acetate, and acetonitrile. To prevent deterioration of the raw material composition, it is preferable to remove oxygen and moisture from the solvent. In particular, the moisture content is preferably 100 ppm or less, more preferably 50 ppm or less. Mixing is preferably performed under an inert gas atmosphere. Examples of inert gases that can be used include nitrogen, helium, and argon. Removing oxygen and moisture from the inert gas can also prevent deterioration of the raw material composition. The oxygen and moisture concentrations in the inert gas are preferably 1000 ppm or less, more preferably 100 ppm or less, and particularly preferably 10 ppm or less.

[0042] During mixing, the substrates may be in a uniformly dispersed slurry state, but it is more preferable that a portion of the raw materials (regardless of type) be dissolved. In the case of a slurry, it is preferable to disintegrate the aggregated particles by stirring. Furthermore, a bead mill, homogenizer, or ultrasonic disperser may be used. For solid-phase mixing, a mortar mixer, a mortar and pestle mixer, a ball mill, or the like can be used. These methods do not usually result in amorphization of the crystals. Mixing is preferably performed in a vacuum or in an inert gas atmosphere, and the conditions are similar to those when a solvent is used. The temperature during mixing does not need to be heated, but if a solvent is used, heating can be used to increase the solubility and dissolution rate of the substrates. If heating is required, it is sufficient to perform the mixing below the boiling point of the solvent. However, it is also possible to perform the mixing under pressure using an autoclave, etc. Note that mixing at high temperatures may cause the reaction to proceed before the raw materials are thoroughly mixed, which may lead to the formation of by-products; therefore, it is preferable to perform the mixing at around room temperature.

[0043] The mixing time is sufficient as long as it is long enough to make the mixture homogenous. The time often depends on the scale of production, but homogenization can be achieved by, for example, performing the mixing for 0.1 to 24 hours.

[0044] When a solvent is used, the precursor is obtained by removing the solvent. Solvent removal is performed by heat drying or vacuum drying, and the optimal temperature varies depending on the type of solvent. The solvent removal time can be shortened by applying a temperature sufficiently higher than the boiling point. The temperature when removing the solvent is preferably in the range of 60 to 280°C, more preferably 100 to 250°C. Note that removing the solvent under reduced pressure, such as by vacuum drying, can lower the temperature when removing the solvent and shorten the required time. The time required for solvent removal can also be shortened by flowing an inert gas such as nitrogen or argon that has a sufficiently low moisture content. Note that the subsequent heat treatment step and solvent removal can also be performed simultaneously.

[0045] (5) Heating Step: The precursor obtained in the mixing step is heat-treated to obtain a LGPS-based solid electrolyte having a small particle size. The heating temperature is in the range of 300 to 700°C, preferably 350 to 650°C, and particularly preferably 450 to 600°C. By heating at a temperature within the above range, the desired crystals can be obtained with high purity.

[0046] Although the heating time varies slightly depending on the heating temperature, sufficient crystallization is usually achieved within a range of 0.1 to 24 hours. Heating for a short time is preferable because it is less likely to cause deterioration of the LGPS-based solid electrolyte. Heating can be performed in a vacuum or in an inert gas atmosphere, but an inert gas atmosphere is preferred. Examples of inert gases that can be used include nitrogen, helium, and argon, with argon being preferred. Low concentrations of oxygen and moisture are preferred, and the conditions are the same as those for the mixing step used to synthesize the precursor.

[0047] 2. Sn-containing LGPS-based solid electrolyte The LGPS-based solid electrolyte obtained by the above-described method has peaks at least at 2θ = 20.18° ± 0.50°, 20.44° ± 0.50°, 26.96° ± 0.50°, and 29.58° ± 0.50° in X-ray diffraction (CuKα: λ = 1.5405 Å). Preferably, the LGPS-based solid electrolyte has peaks at least at 2θ = 20.18° ± 0.40°, 20.44° ± 0.40°, 26.96° ± 0.40°, and 29.58° ± 0.40° in X-ray diffraction (CuKα: λ = 1.5405 Å). More preferably, the LGPS-based solid electrolyte has peaks at least at 2θ=20.18°±0.30°, 20.44°±0.30°, 26.96°±0.30°, and 29.58°±0.30° in X-ray diffraction (CuKα: λ=1.5405 Å).

[0048] The LGPS-based solid electrolyte obtained by the method according to the embodiment preferably has an octahedron O composed of Li and S elements, and a tetrahedron T composed of S and one or more elements selected from the group consisting of P and Sn, as shown in FIG. １ and a tetrahedron T consisting of P and S elements. ２and the tetrahedron T １ and the octahedron O shares an edge, and the tetrahedron T ２ The octahedron O mainly contains a crystal structure in which the corners are shared. It is presumed that the crystal has such a structure, which results in higher ionic conductivity.

[0049] The LGPS-based solid electrolyte obtained by the method according to the embodiment can be suitably used as a solid electrolyte material for, for example, a lithium ion secondary battery. －３ S / cm or more (for example, 1.0 × 10 －３ ~5.0 x 10 －３ S / cm, 1.0×10 －３ ~3.0 x 10 －３ S / cm), preferably 1.5×10 －３ S / cm or more (for example, 1.5×10 －３ ~5.0 x 10 －３ S / cm, 1.5×10 －３ ~3.0 x 10 －３ S / cm, 1.6×10 －３ ~3.0 x 10 －３ S / cm), and more preferably 2.0×10 －３ S / cm or more (e.g., 2.0 × 10 －３ ~5.0 x 10 －３ S / cm, 2.0×10 －３ ~3.0 x 10 －３ S / cm, 2.5×10 －３ ~3.0 x 10 －３ The LGPS-based solid electrolyte has a lithium ion conductivity (25°C) of 35.0 kJ / mol or less, and more preferably 30.0 kJ / mol or less. The activation energy is the energy required for lithium ion diffusion calculated by the Arrhenius equation from the lithium ion conductivity at each measurement temperature, and serves as an index of the ease of lithium ion diffusion.

[0050] The composition of the LGPS-based solid electrolyte obtained by the method according to the embodiment is not particularly limited. For example, ３．２７ Sn ０．２７ P ０．７３ S４ , Li ３．３３ Sn ０．３３ P ０．６７ S ４ ,,Li １０ SnP ２ S １２ , Li １０ (Ge ０．５ Sn ０．５ ) P ２ S １２ , Li １０ (Si ０．５ Sn ０．５ ) P ２ S １２ , Li ３．４５ [Sn ０．０９ Si ０．３６ ]P ０．５５ S ４ Li １０ SnP ２ S １２ , Li ３．２７ Sn ０．２７ P ０．７３ S ４ , Li ３．３３ Sn ０．３３ P ０．６７ S ４ is preferred, and Li ３．２７ Sn ０．２７ P ０．７３ S ４ , Li １０ SnP ２ S １２ is particularly preferred.

[0051] The LGPS-based solid electrolyte obtained by the method according to the embodiment can be formed into a desired molded body by various means and used in various applications including the all-solid-state battery described below. The molding method is not particularly limited. For example, the same molding method as the method for forming each layer constituting the all-solid-state battery described later in the all-solid-state battery description can be used.

[0052] 3. All-Solid-State Battery The LGPS-based solid electrolyte obtained by the method according to the embodiment can be used, for example, in a lithium ion secondary battery, particularly an all-solid-state lithium ion secondary battery. Here, the term "all-solid-state battery" refers to an all-solid-state lithium ion secondary battery. FIG. 2 is a schematic cross-sectional view of an all-solid-state battery according to one embodiment of the present invention. The all-solid-state battery 10 has a structure in which a solid electrolyte layer 2 is disposed between a positive electrode layer 1 and a negative electrode layer 3. The all-solid-state battery 10 can be used in various devices, including mobile phones, personal computers, automobiles, etc.

[0053] The LGPS-based solid electrolyte obtained by the method according to the embodiment may be contained as a solid electrolyte in at least one of the positive electrode layer 1, the negative electrode layer 3, and the solid electrolyte layer 2. When the LGPS-based solid electrolyte according to the embodiment is contained in the positive electrode layer 1 or the negative electrode layer 3, the LGPS-based solid electrolyte is used in combination with a known positive electrode active material or negative electrode active material for lithium-ion secondary batteries. The quantitative ratio of the LGPS-based solid electrolyte to other materials contained in the positive electrode layer 1 or the negative electrode layer 3 is not particularly limited.

[0054] When the solid electrolyte layer 2 contains an LGPS-based solid electrolyte obtained by the method according to the embodiment, the solid electrolyte layer 2 may be composed of only the LGPS-based solid electrolyte according to the embodiment, or may contain an oxide solid electrolyte (e.g., Li ７ La ３ Zr ２ O １２ ), sulfide-based solid electrolytes (e.g., Li ２ S-P ２ S ５ ) and other complex hydride solid electrolytes (e.g., LiBH ４ , 3LiBH ４ -LiI) may be used in appropriate combination.

[0055] The all-solid-state battery is produced by molding and laminating the above-mentioned layers, but the molding method and lamination method for each layer are not particularly limited. For example, there are a method in which a solid electrolyte and / or an electrode active material is dispersed in a solvent to form a slurry, which is applied by a doctor blade or spin coating, and then rolled to form a film; a gas phase method in which a film is formed and laminated using a vacuum deposition method, an ion plating method, a sputtering method, a laser ablation method, or the like; and a pressure molding method in which powder is molded by hot pressing or cold pressing without applying heat, and then laminated.

[0056] Since the LGPS-based solid electrolyte obtained by the method according to the embodiment is relatively soft, it is particularly preferable to fabricate an all-solid-state battery by molding and laminating each layer by a pressure molding method. Pressure molding methods include hot pressing, which is performed with heating, and cold pressing, which is not performed with heating, but cold pressing can also be used to sufficiently mold the battery.

[0057] The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited thereto. (Example 1) (1) Li ４ SnS ４ Synthesis of 9 mmol of SnCl ４ ・5H ２ O (Sigma-Aldrich) and 18 mmol of Na ２ S・9H ２ O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was dissolved in 10 mL of ion-exchanged water. ２ S・9H ２ SnCl in O aqueous solution ４ ・5H ２ SnS was slowly added dropwise to the O solution. ２ After the dropwise addition was completed, the slurry was immediately centrifuged to remove the supernatant. The slurry was washed with ion-exchanged water three or more times to remove the by-product NaCl, and SnS ２ A paste was obtained.

[0058] The obtained 9 mmol of SnS ２ The paste contains 18 mmol of Na ２ S・9H ２After adding 10 mL of 0 and ion-exchanged water, 9 mmol of Na was obtained by stirring at room temperature. ４ SnS ４ A small amount of precipitate was removed using a membrane filter (PTFE, pore size 1.0 μm). ４ SnS ４ Ion-exchanged water was added to the aqueous solution to make a total volume of 200 mL. This aqueous solution was passed through an ion-exchange resin column packed with a cation-exchange resin (strong acid cation-exchange resin manufactured by Organo Corporation) that had been previously exchanged for Li ions with an aqueous LiOH solution, and Li was extracted from the distillate. ４ SnS ４ An aqueous solution was obtained. ４ SnS ４ Water was removed from the aqueous solution using an evaporator at 40°C, and then the solution was dried in a glass tube oven at 240°C for 1 hour to obtain Li. ４ SnS ４ This was used as bulk Li powder. ４ SnS ４ It is called.

[0059] (2) Li ４ SnS ４ In a glove box under an argon atmosphere, the bulk Li obtained by the above operation was atomized. ４ SnS ４ 5 mL of methanol (ultra-dehydrated grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added as a good solvent to the powder (400 mg) and mixed at room temperature (25°C) for 24 hours. The powder gradually dissolved. The insoluble matter in the resulting solution was filtered using a membrane filter, and Li ４ SnS ４ A methanol solution in which Li was uniformly dissolved was obtained. 100 mL of acetonitrile (ultra-dehydrated grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to this solution, and the solvent was removed at 40°C under reduced pressure using an evaporator. This was followed by vacuum drying at 180°C for 4 hours to obtain finely divided Li. ４ SnS ４ This powder was used as the finely divided Li ４ SnS ４ It is called.

[0060] (3) β-Li ３ P.S. ４ Synthesis of Li in a glove box under an argon atmosphere ２ S (Sigma-Aldrich, purity 99.8%) and P ２ S ５ (Sigma-Aldrich, purity 99%) ２ S:P ２ S ５ The molar ratio of (Li) was 1.5:1. ２ S+P ２ S ５ ) to tetrahydrofuran (ultra-dehydrated grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) so that the concentration of Li ２ S, P ２ S ５ The mixture was added in this order and mixed at room temperature for 12 hours. The mixture gradually dissolved to give a nearly homogeneous solution containing a small amount of insoluble matter.

[0061] The resulting solution was mixed with the raw material composition containing the above. ２ S:P ２ S ５ Li so that the molar ratio was 3:1 ２ S was further added, and the mixture was mixed at room temperature for 12 hours to obtain a suspension. The solvent was removed from the obtained suspension at 50°C under reduced pressure. Then, the suspension was vacuum dried at 180°C for 4 hours to obtain β-Li ３ P.S. ４ β-Li was obtained. ３ P.S. ４ The resulting slurry was heated to 50°C under reduced pressure to remove the acetonitrile, and the resulting powder was dried at 180°C for 4 hours under vacuum to remove the solvent, resulting in the finely divided β-Li powder. ３ P.S. ４ A series of operations was carried out in a glove box under an argon atmosphere.

[0062] (4) Synthesis of LGPS-based solid electrolyte In a glove box under an argon atmosphere, the above-obtained finely divided β-Li ３ P.S. ４and atomized Li ４ SnS ４ β-Li ３ P.S. ４ :Li ４ SnS ４ The mixture was weighed out so that the molar ratio was 2.7:1, and mixed in an agate mortar. The mixture was fired in an argon atmosphere (550°C, 2 hours) to obtain Li ３．２７ Sn ０．２７ P ０．７３ S ４ Crystals (LGPS-based solid electrolyte) were obtained.

[0063] (Example 2) (1) Li ４ SnS ４ Synthesis of SnS was prepared in the same manner as in Example 1, except that after washing with ion-exchanged water, it was further washed with methanol three times. ２ A paste was obtained. The resulting 9 mmol of SnS ２ To the paste, 18 mmol of anhydrous Na ２ After adding S and 20 mL of ultra-dehydrated methanol, 9 mmol of Na was obtained by stirring at room temperature. ４ SnS ４ A homogeneous methanol solution containing the hydrate was obtained. A small amount of precipitate derived from the hydrate was removed using a membrane filter. ４ SnS ４ The methanol solution was previously exchanged for Li ions with an aqueous LiOH solution, and then passed through an ion exchange resin column packed with a cation exchange resin (the same as in Example 1) that had been substituted with methanol. Li was extracted from the distillate. ４ SnS ４ A methanol solution was obtained. ４ SnS ４ The concentration of the methanol solution was about 1.7 wt %.

[0064] (2) Li ４ SnS ４ In a glove box under an argon atmosphere, the Li obtained by the above operation was atomized. ４ SnS ４100 mL of acetonitrile (ultra-dehydrated grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to 5 mL of the methanol solution. The solvent was then removed at 40°C under reduced pressure using an evaporator. Further, the solution was vacuum dried at 180°C for 4 hours to obtain finely divided Li. ４ SnS ４ A powder was obtained.

[0065] (3) Synthesis of LGPS-based solid electrolyte The finely divided Li obtained above ４ SnS ４ Powder and β-Li synthesized in Example 1 ３ P.S. ４ Using Li as in Example 1 ３．２７ Sn ０．２７ P ０．７３ S ４ Crystals (LGPS-based solid electrolyte) were obtained.

[0066] (Comparative Example 1) (1) Li ４ SnS ４ Synthesis of Li ２ S (Sigma-Aldrich, purity 99.8%) and SnS ２ (Kojundo Chemical Co., Ltd., 99.9%) was used as the raw material. These were heated in a glove box under an argon atmosphere with Li ４ SnS ４ The powder was weighed to a stoichiometric ratio of 1.0 g and mixed for 15 minutes using an agate mortar. 1.0 g of the obtained powder and 15 zirconia balls with a diameter of 10 mm were placed in a 45 mL zirconia pot and sealed. This zirconia pot was fixed to a planetary ball mill (manufactured by Fritsch Japan Co., Ltd.) and subjected to mechanical milling at 500 rpm for 10 hours. The precursor powder obtained by mechanical milling was calcined at 450 ° C for 8 hours to obtain Li. ４ SnS ４ obtained.

[0067] (2) Li ４ SnS ４ In a glove box under an argon atmosphere, the Li obtained by the above operation was atomized. ４ SnS ４ Then, 1 g of the weighed Li ４ SnS ４The mixture was added to 10 mL of methanol (Wako Pure Chemical Industries, Ltd., ultra-dehydrated grade) and mixed at room temperature for 6 hours. The mixture gradually dissolved, and a slurry containing insoluble matter was obtained. The obtained slurry was filtered using a membrane filter to remove Li. ４ SnS ４ A homogeneous solution of the Li obtained above was obtained. ４ SnS ４ The solution was mixed with 200 mL of acetonitrile (Wako Pure Chemical Industries, Ltd., ultra-dehydrated grade) to obtain a methanol-acetonitrile homogeneous solution. Methanol was removed from the obtained homogeneous solution at 50°C under reduced pressure to obtain Li in acetonitrile. ４ SnS ４ Then, the acetonitrile was removed under reduced pressure at 50°C to obtain a powder. The solvent was removed while stirring the homogeneous solution. The powder obtained above was dried under vacuum at 180°C for 4 hours to obtain finely divided Li ４ SnS ４ A powder was obtained.

[0068] (3) Synthesis of LGPS-based solid electrolyte The finely divided Li obtained above ４ SnS ４ Powder and β-Li synthesized in Example 1 ３ P.S. ４ Using Li as in Example 1 ３．２７ Sn ０．２７ P ０．７３ S ４ Crystals (LGPS-based solid electrolyte) were obtained.

[0069] <Lithium Ion Conductivity Measurement> The LGPS-based solid electrolytes obtained in Examples 1 and 2 were subjected to uniaxial molding (380 MPa) to obtain disks with a thickness of approximately 1 mm and a diameter of 10 mm. Using an all-solid-state battery evaluation cell (manufactured by Hosen Co., Ltd.), AC impedance measurements were performed by the four-terminal method (using a Solartron "SI1260 IMPEDANCE / GAIN-PHASE ANALYZER") at room temperature (25°C), and the lithium ion conductivity was calculated. Specifically, the sample was placed in a thermostatic chamber set to 25°C and held there for 30 minutes, after which the lithium ion conductivity was measured. The measurement frequency range was 0.1 Hz to 1 MHz, and the amplitude was 50 mV.

[0070] <Activation Energy Measurement> After measuring the ionic conductivity at 25°C as described above, the temperature of the thermostatic chamber was raised from 30°C to 90°C in 10°C increments, and the ionic conductivity was measured after holding at each temperature for 25 minutes. The activation energy of lithium ion conduction was obtained using the Arrhenius equation from the slope when the natural logarithm of the obtained ionic conductivity was plotted against the reciprocal of absolute temperature. The results of ionic conductivity and activation energy are shown in Table 1.

[0071] <X-ray Diffraction Measurement> X-ray diffraction measurement (PANalytical's "X'Pert3 Powder", CuKα: λ=1.5405 Å) was performed on the solid electrolyte powders obtained in Examples 1 and 2 and Comparative Example 1 under an Ar atmosphere at room temperature (25° C.). The results of the X-ray diffraction measurement are shown in FIG.

[0072] <Raman Spectroscopic Measurement> Samples for Raman spectroscopy were prepared using the solid electrolyte powders obtained in Examples 1 and 2 and Comparative Example 1 and a sealed container having a quartz glass (φ60 mm, thickness 1 mm) on top as an optical window. The solid electrolyte powder was adhered to the quartz glass in an argon atmosphere glove box, and the container was then sealed and removed from the glove box for Raman spectroscopy. A laser Raman spectrophotometer NRS-5100 (manufactured by JASCO Corporation) was used to perform the measurements at an excitation wavelength of 532.15 nm and exposure times of 60 seconds (Example 1), 30 seconds (Example 2), and 50 seconds (Comparative Example 1). The results of the Raman spectroscopy are shown in FIG. 4.

[0073] In both X-ray diffraction measurement and Raman spectroscopy measurement, the crystals of Examples 1 and 2 were found to be similar to Li produced by mechanical milling. ４ SnS ４ A peak was observed at the same position as in the crystals of Comparative Example 1 using the above-mentioned method. According to the method of the present example, an LGPS-based solid electrolyte having properties (ionic conductivity, activation energy, etc.) that are particularly favorable for use in all-solid-state batteries could be obtained. Furthermore, since such an excellent LGPS-based solid electrolyte can be obtained without using a planetary ball mill, it is possible to mass-produce an excellent LGPS-based solid electrolyte using a large-scale device.

[0074] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[0075] DESCRIPTION OF SYMBOLS 1... Positive electrode layer, 2... Solid electrolyte layer, 3... Negative electrode layer, 10... All-solid-state battery.

Claims

1. A first solution in which a first compound having an ion of a monovalent or divalent metal atom M1 having an ionic radius larger than that of a Li atom or an ammonium ion as a counter ion is dissolved in a solvent is contacted with a cation exchange resin containing Li ions to exchange the M1 ion or the ammonium ion contained in the first compound for Li ions to obtain a second solution in which a Li-containing compound is dissolved in the solvent; removing the solvent from the second solution to obtain Li-containing crystals; and converting the Li-containing crystals into Li. ３ P.S. ４ a first compound including the M1 ion or the ammonium ion, and an anion including an S element and an Sn element; and a second compound including the M1 ion or the ammonium ion.

2. The method of claim 1, wherein the solvent is water or methanol.

3. The method of claim 2, wherein the solvent is methanol.

4. The method according to any one of claims 1 to 3, wherein the heat treatment is carried out at a temperature of 300 to 700°C.

5. The method according to any one of claims 1 to 4, wherein the heat treatment is carried out under an inert gas atmosphere.

6. The method according to any one of claims 1 to 5, wherein the LGPS-based solid electrolyte has peaks at least at 2θ = 20.18° ± 0.50°, 20.44° ± 0.50°, 26.96° ± 0.50°, and 29.58° ± 0.50° in X-ray diffraction (CuKα: λ = 1.5405 Å).

7. The LGPS-based solid electrolyte is an octahedron O composed of Li and S elements, and a tetrahedron T composed of one or more elements selected from the group consisting of P and Sn and S elements. １ and a tetrahedron T consisting of P and S elements. ２ and the tetrahedron T １ and the octahedron O shares an edge, and the tetrahedron T ２ and the octahedron O mainly contains a vertex-sharing crystal structure.

8. The Li ３ P.S. ４ The crystal is β-Li ３ P.S. ４ The method according to any one of claims 1 to 7, wherein 9. The Li-containing crystal is Li ４ SnS ４ The method according to any one of claims 1 to 8, wherein the crystal has a composition of

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