Method for producing lithium halide

Abstract

Provided is a method for producing lithium halide by a method for producing lithium halide that includes mixing lithium carbonate and ammonium halide, in which the method does not involve a step for directly removing moisture, does not use elemental halogens which are difficult to handle, and does not require excessive energy for production.

Description

Lithium halide manufacturing method

[0001] The present invention relates to a method for producing a lithium halide compound.

[0002] With the recent rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, the development of batteries to be used as their power sources has become increasingly important. Conventionally, batteries used for such applications have used electrolytes containing flammable organic solvents, but by making batteries all-solid-state, flammable organic solvents are not used in the battery, safety devices can be simplified, and manufacturing costs and productivity can be improved. Therefore, all-solid-state batteries in which the electrolyte is replaced with a solid electrolyte layer are being developed.

[0003] Sulfide solid electrolytes have been known for some time as solid electrolytes used in solid electrolyte layers, and it is known that a glass-ceramic electrolyte having high ionic conductivity can be obtained by, for example, reacting lithium sulfide with phosphorus sulfide to produce sulfide glass and then subjecting the sulfide glass to heat treatment (see, for example, Patent Document 1). In addition, in response to demands for higher ionic conductivity, a manufacturing method using lithium halide as a sulfide solid electrolyte containing halogen atoms has also been known (see, for example, Patent Document 2).

[0004] Lithium halides used as raw materials in the production of sulfide solid electrolytes containing halogen atoms are generally produced as hydrates because aqueous solutions of the raw materials are used or the materials are reacted in water during the synthesis process (see, for example, Patent Documents 3 and 4). Since the ionic conductivity of the sulfide solid electrolyte may be reduced if the lithium halide contains water, it is necessary to remove water from the lithium halide. Methods such as azeotropic distillation with an organic solvent or drying have been investigated (see, for example, Patent Document 4). However, in either case, removing water from lithium halide hydrate is not easy. Also disclosed is a method for producing lithium halide using lithium sulfide and ammonium halide as raw materials (see, for example, Patent Document 5). Furthermore, a method for obtaining anhydrous lithium halide by reacting lithium carbonate with hydrochloric acid is also known (see, for example, Patent Document 6).

[0005] Japanese Patent Application Publication No. 2005-228570 Japanese Patent Application Publication No. 2013-201110 Japanese Patent Application Publication No. 2013-103851 Japanese Patent Application Publication No. 2013-256416 International Publication No. 2022 / 158422 Pamphlet U.S. Patent No. 2,968,526

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing lithium halide which does not involve a step of directly removing moisture, does not use an elemental halogen which is difficult to handle, and does not require excessive energy for production.

[0007] The method for producing a lithium halide compound according to the present invention is a method for producing a lithium halide compound, which comprises mixing lithium carbonate and ammonium halide.

[0008] According to the present invention, it is possible to provide a method for producing lithium halide which does not involve a step of directly removing moisture, does not use an elemental halogen which is difficult to handle, and does not require excessive energy for production.

[0009] 1 is an X-ray diffraction spectrum of the powder obtained in Example 1.

[0010] Hereinafter, an embodiment of the present invention (hereinafter, sometimes referred to as "the present embodiment") will be described. In this specification, the upper and lower limit values ​​of a range expressed as "greater than or equal to," "less than or equal to," and "to" can be arbitrarily combined, and the numerical values ​​in the examples can also be used as the upper and lower limit values.

[0011] (Findings Obtained by the Inventors to Achieve the Present Invention) The present inventors conducted extensive research to solve the above-mentioned problems, and as a result, discovered the following and completed the present invention. As described above, the methods of Patent Documents 1 to 4 require the removal of moisture, which is not easy. On the other hand, the production method described in Patent Document 5 does not require the removal of moisture as in the methods of Patent Documents 1 to 4, but it uses expensive lithium sulfide as a raw material. In order to advance the mass production of sulfide solid electrolytes, it is necessary to expand the options for lithium sources in the production of lithium halides used as raw materials, and a production method with better cost performance is desired. Furthermore, the method of obtaining anhydrous lithium halide by reacting lithium carbonate with hydrochloric acid, disclosed as a conventional technique in Patent Document 6, has the problem of requiring a great deal of effort for dehydration. Therefore, the present inventors investigated methods for producing lithium halide using other relatively inexpensive lithium compounds as raw materials, and discovered that lithium halide can be produced using lithium carbonate as a raw material.

[0012] [Method for Producing Lithium Halide] A method for producing lithium halide according to a first aspect of the present embodiment is a method for producing lithium halide that includes mixing lithium carbonate and ammonium halide.

[0013] According to the first aspect, since ammonium halide is used as a raw material for supplying a halogen element, it is not necessary to use an elemental halogen as a raw material, which is difficult to handle. Furthermore, since the by-products generated by using these raw materials are gaseous ammonia, water, and carbon dioxide, they can be very easily removed.

[0014] A method for producing a lithium halide according to a second aspect of the present embodiment is the same as the method for producing a lithium halide according to the first aspect, except that the mixing ratio of the lithium carbonate and the ammonium halide is 1.50 to 2.50 moles of ammonium halide per 1 mole of lithium carbonate. According to the second aspect, it becomes possible to efficiently convert lithium carbonate, which is a raw material, into lithium halide.

[0015] A method for producing lithium halide according to a third aspect of the present embodiment is the method for producing lithium halide according to the first or second aspect, except that the lithium carbonate and ammonium halide are premixed and then heated and mixed. By premixing the lithium carbonate and ammonium halide and then heating and mixing, the reaction can be efficiently promoted.

[0016] A method for producing lithium halide according to a fourth aspect of the present embodiment is the method for producing lithium halide according to the third aspect, wherein the temperature condition for the heating and mixing is 90 to 400° C. By setting the temperature condition for the heating and mixing within the above range, the reaction can be promoted and lithium halide can be obtained efficiently.

[0017] A fifth aspect of the present embodiment is a method for producing a lithium halide according to the third or fourth aspect, wherein the heating and mixing is carried out under reduced pressure or in an inert gas atmosphere, which is preferable from the viewpoint of suppressing side reactions.

[0018] A method for producing a sulfide solid electrolyte according to a sixth aspect of the present embodiment includes reacting the lithium halide obtained by any of the production methods of the first to fifth aspects with a phosphorus compound. This method makes it possible to produce a sulfide solid electrolyte using lithium carbonate as a lithium source.

[0019] A seventh aspect of the present embodiment is a method for producing a sulfide solid electrolyte according to the sixth aspect, wherein a lithium compound other than lithium halide is further reacted. The lithium compound other than lithium halide to be reacted in this embodiment is prepared separately from the lithium halide and the phosphorus compound described above.

[0020] The manufacturing method of this embodiment will be described in more detail below in accordance with the above-described embodiment.

[0021] [Lithium Carbonate] The lithium carbonate used in the production method of this embodiment is usually in particulate form, and may be a commercially available product, or one produced by a known method may also be used.

[0022] The average particle size (D ５０ ) is preferably 0.1 μm or more and 200 μm or less, more preferably 0.3 μm or more and 150 μm or less, and even more preferably 0.5 μm or more and 100 μm or less. ５０ ) is the particle size at which 50% of the total particle size is reached when the particle size distribution integral curve is drawn and the integral is calculated from the smallest particle size, and the volume distribution is an average particle size that can be measured using, for example, a laser diffraction / scattering particle size distribution measuring device.

[0023] Lithium carbonate preferably contains a small amount of water as an impurity, in order to reduce the amount of water in the resulting lithium halide, and further, when using lithium halide as a raw material for a sulfide solid electrolyte, to reduce the amount of water in the solid electrolyte and suppress a decrease in ionic conductivity and a decrease in battery performance due to water. The amount of water contained in lithium carbonate is preferably 1.5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less. The lower limit is not particularly limited, as the lower the better, but is typically about 0.1% by mass. In this specification, the water content in lithium carbonate is a value measured using a Karl Fischer moisture meter under conditions of vaporization at 280°C.

[0024] [Ammonium Halide] The ammonium halide used in the production method of this embodiment may be selected according to the desired lithium halide, and may be selected from ammonium fluoride (NH ４ F), ammonium chloride (NH ４ Cl), ammonium bromide (NH ４ Br) and ammonium iodide (NH ４ It is preferable to use one or more selected from the group consisting of ammonium bromide (NH ４ Br) and ammonium iodide (NH ４It is more preferable to use at least one selected from I).

[0025] In the production method of this embodiment, lithium carbonate and ammonium halide react according to the following reaction formulas (1) to (3). Therefore, the mixing ratio of lithium carbonate and ammonium halide is preferably 1.50 to 2.50 mol, more preferably 1.70 to 2.30 mol, and even more preferably 1.80 to 2.20 mol of ammonium halide per 1 mol of lithium carbonate.

[0026] Li ２ CO ３ +2NH ４ X→2LiX+(NH ４ ) ２ CO ３ (1) Li ２ CO ３ +2NH ４ X → 2LiX + NH ４ HCO ３ +NH ３ (2) Li ２ CO ３ +2NH ４ X → 2LiX + H ２ O+CO ２ +2NH ３ (3) (In formulas (1) to (3), X is a halogen atom.)

[0027] As is clear from the above reaction formulas (1) to (3), in the production method of this embodiment, lithium halide is produced by the reaction of lithium carbonate with ammonium halide, and at the same time, water, carbon dioxide, and ammonia are generated as by-products, but carbon dioxide and ammonia are gaseous and therefore easy to remove. Furthermore, it is preferable to remove water generated as a by-product by, for example, mixing lithium carbonate with ammonium halide under heating conditions.

[0028] [Mixing] In the production method of this embodiment, the lithium carbonate and ammonium halide are mixed. The temperature conditions for the mixing are not particularly limited, and the mixing may be performed at room temperature. However, it is preferable to mix the materials while heating them, in order to promote the reaction between the lithium carbonate and the ammonium halide and to remove the water generated as a by-product, as described above. The temperature conditions for the heated mixing are preferably 90°C or higher, more preferably 150°C or higher, even more preferably 180°C or higher, and particularly preferably 200°C or higher. Furthermore, in order to reduce the energy required for producing the lithium halide, the temperature is preferably 400°C or lower, more preferably 350°C or lower, even more preferably 300°C or lower, and particularly preferably 280°C or lower. Specifically, the temperature is preferably 90 to 400°C, more preferably 150 to 350°C, even more preferably 180 to 300°C, and particularly preferably 200 to 280°C.

[0029] The mixing treatment can be carried out in the absence of a solvent or using a solvent to react lithium carbonate with ammonium halide. The mixing treatment is preferably carried out under an inert gas such as nitrogen or argon, since this effectively removes by-products such as ammonia, water, and carbon dioxide, thereby accelerating the reaction. In the production method of this embodiment, the lithium halide produced may form a complex with ammonia, which is generated as a by-product. By carrying out the mixing treatment, the ammonia can be removed.

[0030] In the production method of this embodiment, by mixing the lithium carbonate and ammonium halide, the lithium carbonate and ammonium halide react to produce lithium halide, and the by-products, ammonia and carbon dioxide, are removed as gases, thereby preventing reverse reactions and promoting the reaction. When mixing the lithium carbonate, ammonium halide, and optional solvent, there are no particular limitations on the mixing method. The lithium carbonate, ammonium halide, and optional solvent may be mixed in an apparatus capable of mixing these materials, and the materials may be mixed while being heated to the predetermined temperature. When mixing the lithium carbonate and ammonium halide in the absence of a solvent, they may be mixed by, for example, mechanical milling, which involves the use of a grinder such as a ball mill or a bead mill to cause the materials to react. When mixing the lithium carbonate and ammonium halide in a solvent, these raw materials may be added to a large excess of solvent and stirred, or a small amount of solvent may be added to an apparatus or grinder capable of mixing the raw materials and mixed together with the lithium carbonate and ammonium halide.

[0031] The equipment used to mix lithium carbonate and ammonium halide, optionally with a small amount of solvent, may be selected appropriately depending on the scale. For example, for small-scale operations, an apparatus such as a Schlenk mixer with a stirrer may be used, while for medium to large-scale operations, a mechanical stirring mixer equipped with stirring blades in a tank may be used. Examples of mechanical stirring mixers include high-speed stirring mixers and double-arm mixers, with high-speed stirring mixers being preferred from the viewpoint of improving the uniformity of the raw material mixture. Examples of high-speed stirring mixers include vertical-axis rotary mixers and horizontal-axis rotary mixers, and either type of mixer may be used.

[0032] Examples of the shape of the stirring blade used in the mechanical stirring mixer include blade type, arm type, anchor type, paddle type, full zone type, ribbon type, multi-stage blade type, double arm type, shovel type, double-shaft blade type, flat blade type, and C-type blade type.

[0033] The mixing time for the above mixing treatment is usually about 0.1 to 500 hours, but from the viewpoint of allowing the reaction between lithium carbonate and ammonium halide to proceed sufficiently, it is preferably 0.5 to 100 hours, more preferably 1.0 to 50 hours, and even more preferably 1.5 to 20 hours.

[0034] In the production method of the present embodiment, it is preferable to premix the lithium carbonate and the ammonium halide and then perform the heating and mixing, from the viewpoint of promoting the reaction. The mixing method and solvent used in the premixing are the same as those used in the mixing step.

[0035] [Solvent] Preferred examples of the solvent used in this embodiment include hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents; and solvents containing carbon atoms, such as solvents containing carbon atoms and heteroatoms. Examples of aliphatic hydrocarbon solvents include hexane, pentane, 2-ethylhexane, heptane, octane, decane, undecane, dodecane, and tridecane. Examples of alicyclic hydrocarbon solvents include cyclohexane and methylcyclohexane. Examples of aromatic hydrocarbon solvents include benzene, toluene, xylene, mesitylene, ethylbenzene, tert-butylbenzene, chlorobenzene, trifluoromethylbenzene, and nitrobenzene. Examples of solvents containing carbon atoms and heteroatoms include carbon disulfide, diethyl ether, dibutyl ether, and tetrahydrofuran. Among these solvents, alicyclic hydrocarbon solvents or solvents containing carbon atoms and heteroatoms are preferred. Among alicyclic hydrocarbon solvents, cyclohexane is preferred. Among solvents containing carbon atoms and heteroatoms, solvents containing oxygen atoms are preferred, with tetrahydrofuran being more preferred. Among the above solvents, tetrahydrofuran is particularly preferred. It is not preferable to use water as a solvent, as this reduces the performance of the solid electrolyte.

[0036] The amount of the solvent used is preferably such that the total amount of lithium carbonate and ammonium halide used per liter of solvent is 0.1 to 1 kg, more preferably 0.05 to 0.8 kg, and even more preferably 0.2 to 0.7 kg. When the amount of the solvent used is within the above range, the raw materials can be reacted more smoothly, and the solvent can be easily removed when it becomes necessary.

[0037] [Removal of Solvent] When a solvent is used in the production method of this embodiment, lithium halide can be obtained by removing the solvent. To remove the solvent, a solid-liquid separation method such as filtration, decantation, or centrifugation may be used, or a drying method may be used. These methods will be described later.

[0038] Filtration is a method used to remove solvents present as a liquid, and can be carried out using, for example, a glass filter, and the glass filter used may have a pore size of, for example, about 10 to 200 μm, preferably 20 to 150 μm. Decantation can be carried out by removing the supernatant solvent after the solid has settled. Centrifugation can be carried out using a centrifuge.

[0039] Drying can be carried out by drying under reduced pressure, drying by heating, or the like. For example, drying under reduced pressure can be followed by drying by heating, or drying by heating under reduced pressure can also be carried out.

[0040] Drying under reduced pressure can be carried out using, for example, a vacuum pump, and drying under reduced pressure is preferred from the viewpoint of shortening the drying time. When drying is carried out by heating, the temperature can be determined depending on the type of solvent, for example, at a temperature equal to or higher than the boiling point of the solvent. In this case, the heating temperature is usually 30 to 140°C, preferably 40 to 130°C, more preferably 50 to 120°C, and even more preferably 60 to 100°C, although it cannot be generalized because it depends on the degree of reduced pressure.

[0041] As described above, the lithium halide compound obtained by the production method of this embodiment contains a lithium halide complex in addition to lithium halide. The water content of the lithium halide obtained by the production method of this embodiment is 1% by mass or less, further 0.5% by mass or less, or 0.3% by mass or less. The lower limit is usually about 0.01% by mass. In this specification, the water content of the lithium halide compound is a value measured using a Karl Fischer moisture meter under the vaporization method at 280°C, similar to the water content in lithium carbonate.

[0042] <Method for Producing Sulfide Solid Electrolyte> The lithium halide obtained by the method for producing lithium halide according to the present embodiment is suitably used as a raw material for sulfide solid electrolytes, as described above. The method for producing the sulfide solid electrolyte according to the present embodiment includes reacting the lithium halide with a phosphorus compound, and preferably includes reacting the lithium halide with a lithium compound other than lithium halide and a phosphorus compound. The production method including reacting the lithium halide with a lithium compound other than lithium halide and a phosphorus compound is a known method, and specific treatments, operations, and the like may be performed according to known methods.

[0043] Examples of lithium halides include lithium fluoride, lithium chloride, lithium bromide, and lithium iodide, and lithium bromide and lithium iodide are preferred. Examples of lithium compounds other than lithium halides include lithium sulfide (Li ２ S), lithium oxide (Li ２ O), lithium carbonate (Li ２ CO ３ Among these, lithium sulfide is preferred from the viewpoint of ionic conductivity.

[0044] Examples of phosphorus compounds include diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ) and other phosphorus sulfides, sodium phosphate (Na ３ P.O. ４ ), lithium phosphate (Li３ P.O. ４ Among them, phosphorus sulfide is preferred, and diphosphorus pentasulfide (P ２ S ５ ) is more preferred. ２ S ５ The phosphorus compounds may be any of those commercially available and industrially produced. These phosphorus compounds may be used alone or in combination.

[0045] In addition, halogen atoms other than lithium halide include halogen molecules, such as fluorine (F ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ ), preferably chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ ), more preferably bromine (Br ２ ), iodine (I ２ ) can also be used.

[0046] Among the above, a combination of lithium sulfide, diphosphorus pentasulfide and lithium halide, and a combination of lithium sulfide, diphosphorus pentasulfide, lithium halide and halogen molecules are preferred.

[0047] When a combination of lithium sulfide, diphosphorus pentasulfide, and lithium halide is used as the raw materials, the ratio of lithium sulfide to the total of lithium sulfide and diphosphorus pentasulfide is preferably 70 to 80 mol%, more preferably 72 to 78 mol%, and even more preferably 74 to 78 mol%, from the viewpoint of obtaining higher chemical stability and higher ionic conductivity. Furthermore, when a combination of lithium bromide and lithium iodide is used as the lithium halide, the ratio of lithium bromide to the total of lithium bromide and lithium iodide is preferably 1 to 99 mol%, more preferably 20 to 90 mol%, even more preferably 40 to 80 mol%, and particularly preferably 50 to 70 mol%, from the viewpoint of improving ionic conductivity.

[0048] When lithium sulfide, diphosphorus pentasulfide, an elemental halogen, and a lithium halide are used, the content of the elemental halogen (α mol %) and the content of the lithium halide (β mol %) relative to the total amount thereof preferably satisfy the following formula (2), more preferably satisfy the following formula (3), even more preferably satisfy the following formula (4), and even more preferably satisfy the following formula (5): 2≦2α+β≦100 (2) 4≦2α+β≦80 (3) 6≦2α+β≦50 (4) 6≦2α+β≦30 (5)

[0049] In reacting lithium halide, a lithium compound other than lithium halide, and a phosphorus compound, the reaction can be carried out by treating these raw materials by methods such as mixing, stirring, pulverization, etc. For example, when mixing or stirring is performed, a mechanical stirring mixer used in mixing in the production method of this embodiment may be used, and when pulverization is performed, equipment generally referred to as a pulverizer, such as a media-type pulverizer such as a ball mill or a bead mill, may be used.

[0050] Furthermore, when reacting the raw materials, a complexing agent or a solvent may be further added as necessary. In this case, a slurry containing an electrolyte precursor composed of the raw materials and the complexing agent, a liquid complexing agent, and a solvent is obtained. This slurry is dried to remove the liquid complexing agent and solvent, and then heated to obtain a sulfide solid electrolyte. The drying can be performed by any of the methods capable of performing drying in the production method of this embodiment. The temperature conditions, etc., when performing drying by heating are the same as those for drying by heating in the production method of this embodiment, since the solvent used is the same as the solvent used in the production method of this embodiment. The solvent used in the production method of the sulfide solid electrolyte of this embodiment is the same as that used in the production method of the lithium halide of this embodiment.

[0051] [Complexing Agent] The complexing agent is capable of coordinating (bonding) with the lithium atom, sulfur atom, and halogen atom, particularly lithium atom, contained in the lithium sulfide or lithium halide to form a complex. The complexing agent can be used without any particular limitation as long as it has such properties, and is particularly preferably a compound containing an atom having a high affinity with the lithium atom, such as a heteroatom such as a nitrogen atom, an oxygen atom, or a chlorine atom, and more preferably a compound having a group containing these heteroatoms.

[0052] The heteroatom is preferably a nitrogen atom or an oxygen atom. The nitrogen atom-containing group is preferably an amino group, an amide group, a nitro group, or a nitrile group, more preferably an amino group. The oxygen atom-containing group is preferably an ester group or an ether group, more preferably an ester group.

[0053] Examples of the complexing agent having an amino group include amine compounds such as aliphatic amines, alicyclic amines, heterocyclic amines, and aromatic amines, and these can be used alone or in combination.

[0054] Representative and preferred examples of the aliphatic amine include aliphatic primary diamines such as ethylenediamine, diaminopropane, and diaminobutane; aliphatic secondary diamines such as N,N'-dimethylethylenediamine, N,N'-diethylethylenediamine, N,N'-dimethyldiaminopropane, and N,N'-diethyldiaminopropane; and aliphatic tertiary diamines such as N,N,N',N'-tetramethyldiaminomethane, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetraethylethylenediamine, N,N,N',N'-tetramethyldiaminopropane, N,N,N',N'-tetraethyldiaminopropane, N,N,N',N'-tetramethyldiaminobutane, N,N,N',N'-tetramethyldiaminopentane, and N,N,N',N'-tetramethyldiaminohexane. In the examples given in this specification, for example, in the case of diaminobutane, unless otherwise specified, all isomers of butane, such as linear and branched isomers, are included in addition to isomers relating to the position of the amino group, such as 1,2-diaminobutane, 1,3-diaminobutane, and 1,4-diaminobutane.

[0055] The number of carbon atoms in the aliphatic amine is preferably 2 or more, more preferably 4 or more, and even more preferably 6 or more, and the upper limit is preferably 10 or less, more preferably 8 or less, and even more preferably 7 or less. The number of carbon atoms in the aliphatic hydrocarbon group in the aliphatic amine is preferably 2 or more, and the upper limit is preferably 6 or less, more preferably 4 or less, and even more preferably 3 or less.

[0056] Representative preferred examples of the alicyclic amine include alicyclic primary diamines such as cyclopropanediamine and cyclohexanediamine; alicyclic secondary diamines such as bisaminomethylcyclohexane; and alicyclic tertiary diamines such as N,N,N',N'-tetramethyl-cyclohexanediamine and bis(ethylmethylamino)cyclohexane. Representative preferred examples of the heterocyclic amine include heterocyclic primary diamines such as isophoronediamine; heterocyclic secondary diamines such as piperazine and dipiperidylpropane; and heterocyclic tertiary diamines such as N,N-dimethylpiperazine and bismethylpiperidylpropane. The number of carbon atoms in the alicyclic amine and heterocyclic amine is preferably 3 or more, more preferably 4 or more, and preferably 16 or less, more preferably 14 or less.

[0057] Representative preferred examples of aromatic amines include aromatic primary diamines such as phenyldiamine, tolylenediamine, and naphthalenediamine; aromatic secondary diamines such as N-methylphenylenediamine, N,N'-dimethylphenylenediamine, N,N'-bismethylphenylphenylenediamine, N,N'-dimethylnaphthalenediamine, and N-naphthylethylenediamine; and aromatic tertiary diamines such as N,N-dimethylphenylenediamine, N,N,N',N'-tetramethylphenylenediamine, N,N,N',N'-tetramethyldiaminodiphenylmethane, and N,N,N',N'-tetramethylnaphthalenediamine. The number of carbon atoms in the aromatic amine is preferably 6 or more, more preferably 7 or more, and even more preferably 8 or more, with the upper limit being preferably 16 or less, more preferably 14 or less, and even more preferably 12 or less.

[0058] The amine compound used in this embodiment may be substituted with a substituent such as an alkyl group, an alkenyl group, an alkoxyl group, a hydroxyl group, or a cyano group, or with a halogen atom. Although diamines have been given as specific examples, it goes without saying that the amine compounds that can be used in this embodiment are not limited to diamines, and examples thereof include aliphatic monoamines corresponding to various diamines such as trimethylamine, triethylamine, ethyldimethylamine, and the above-mentioned aliphatic diamines; piperidine compounds such as piperidine, methylpiperidine, and tetramethylpiperidine; pyridine compounds such as pyridine and picoline; morpholine compounds such as morpholine, methylmorpholine, and thiomorpholine; imidazole compounds such as imidazole and methylimidazole; and the above-mentioned alicyclic diamines. In addition to monoamines such as alicyclic monoamines such as the corresponding monoamines; heterocyclic monoamines corresponding to the above heterocyclic diamines; and aromatic monoamines corresponding to the above aromatic diamines, polyamines having three or more amino groups such as diethylenetriamine, N,N',N''-trimethyldiethylenetriamine, N,N,N',N'',N''-pentamethyldiethylenetriamine, triethylenetetramine, N,N'-bis[(dimethylamino)ethyl]-N,N'-dimethylethylenediamine, hexamethylenetetramine, and tetraethylenepentamine can also be used.

[0059] Among the above, a tertiary amine having a tertiary amino group as the amino group is preferred, a tertiary diamine having two tertiary amino groups is more preferred, a tertiary diamine having two tertiary amino groups at both ends is even more preferred, and an aliphatic tertiary diamine having tertiary amino groups at both ends is even more preferred. Among the above amine compounds, the aliphatic tertiary diamine having tertiary amino groups at both ends is preferably tetramethylethylenediamine, tetraethylethylenediamine, tetramethyldiaminopropane, or tetraethyldiaminopropane, and in consideration of ease of availability, tetramethylethylenediamine (also referred to as "TMEDA") or tetramethyldiaminopropane (also referred to as "TMPDA") is preferred.

[0060] Although not specifically exemplified, compounds having a nitrogen atom as a heteroatom and a group other than an amino group, such as an amide group, a nitro group, or a nitrile group, can also provide the same effects as compounds containing an amino group.

[0061] Next, examples of the complexing agent having an ether group include ether compounds such as aliphatic ethers, alicyclic ethers, heterocyclic ethers, and aromatic ethers, and these can be used alone or in combination of two or more kinds.

[0062] Examples of aliphatic ethers include monoethers such as dimethyl ether, diethyl ether, diisopropyl ether, dibutyl ether, and tert-butyl methyl ether; diethers such as dimethoxymethane, dimethoxyethane, diethoxymethane, and diethoxyethane; polyethers having three or more ether groups such as diethylene glycol dimethyl ether (diglyme) and triethylene oxide glycol dimethyl ether (triglyme); and ethers containing hydroxyl groups such as diethylene glycol and triethylene glycol. The number of carbon atoms in the aliphatic ether is preferably 2 or more, more preferably 3 or more, and even more preferably 4 or more, with the upper limit being preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. The number of carbon atoms in the aliphatic hydrocarbon group in the aliphatic ether is preferably 1 or more, and the upper limit is preferably 6 or less, more preferably 4 or less, and even more preferably 3 or less.

[0063] Examples of alicyclic ethers include ethylene oxide, propylene oxide, tetrahydrofuran, tetrahydropyran, dimethoxytetrahydrofuran, cyclopentyl methyl ether, dioxane, dioxolane, etc., and examples of heterocyclic ethers include furan, benzofuran, benzopyran, dioxene, dioxine, morpholine, methoxyindole, hydroxymethyldimethoxypyridine, etc. The number of carbon atoms in the alicyclic ether and heterocyclic ether is preferably 3 or more, more preferably 4 or more, and the upper limit is preferably 16 or less, more preferably 14 or less.

[0064] Examples of aromatic ethers include methyl phenyl ether (anisole), ethyl phenyl ether, dibenzyl ether, diphenyl ether, benzyl phenyl ether, naphthyl ether, etc. The number of carbon atoms in the aromatic ether is preferably 7 or more, more preferably 8 or more, and the upper limit is preferably 16 or less, more preferably 14 or less, and even more preferably 12 or less.

[0065] The ether compound used in this embodiment may be substituted with a substituent such as an alkyl group, an alkenyl group, an alkoxyl group, a hydroxyl group, or a cyano group, or with a halogen atom.

[0066] The ether compound used in this embodiment is preferably an aliphatic ether, and more preferably dimethoxyethane or tetrahydrofuran.

[0067] Examples of the complexing agent having an ester group include ester compounds such as aliphatic esters, alicyclic esters, heterocyclic esters, and aromatic esters, and these can be used alone or in combination.

[0068] Examples of aliphatic esters include formate esters such as methyl formate, ethyl formate, and triethyl formate; acetate esters such as methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, and isobutyl acetate; propionate esters such as methyl propionate, ethyl propionate, propyl propionate, and butyl propionate; oxalate esters such as dimethyl oxalate and diethyl oxalate; malonate esters such as dimethyl malonate and diethyl malonate; and succinate esters such as dimethyl succinate and diethyl succinate. The number of carbon atoms in the aliphatic ester is preferably 2 or more, more preferably 3 or more, and even more preferably 4 or more, with the upper limit being preferably 10 or less, more preferably 8 or less, and even more preferably 7 or less. The number of carbon atoms in the aliphatic hydrocarbon group in the aliphatic ester is preferably 1 or more, more preferably 2 or more, and the upper limit being preferably 6 or less, more preferably 4 or less, and even more preferably 3 or less.

[0069] Examples of alicyclic esters include methyl cyclohexanecarboxylate, ethyl cyclohexanecarboxylate, dimethyl cyclohexanedicarboxylate, dibutyl cyclohexanedicarboxylate, and dibutyl cyclohexenedicarboxylate, while examples of heterocyclic esters include methyl pyridinecarboxylate, ethyl pyridinecarboxylate, propyl pyridinecarboxylate, methyl pyrimidinecarboxylate, ethyl pyrimidinecarboxylate, and lactones such as acetolactone, propiolactone, butyrolactone, and valerolactone. The number of carbon atoms in the alicyclic esters and heterocyclic esters is preferably 3 or more, more preferably 4 or more, and the upper limit is preferably 16 or less, more preferably 14 or less.

[0070] Examples of aromatic esters include benzoic acid esters such as methyl benzoate, ethyl benzoate, propyl benzoate, and butyl benzoate; phthalic acid esters such as dimethyl phthalate, diethyl phthalate, dibutyl phthalate, butyl benzyl phthalate, and dicyclohexyl phthalate; and trimellitic acid esters such as trimethyl trimellitate, triethyl trimellitate, tripropyl trimellitate, tributyl trimellitate, and trioctyl trimellitate. The number of carbon atoms in the aromatic ester is preferably 8 or more, more preferably 9 or more, and the upper limit is preferably 16 or less, more preferably 14 or less, and even more preferably 12 or less.

[0071] The ester compound used in this embodiment may be substituted with a substituent such as an alkyl group, an alkenyl group, an alkoxyl group, a hydroxyl group, or a cyano group, or with a halogen element.

[0072] The ester compound used in this embodiment is preferably an aliphatic ester, more preferably an acetate ester, and particularly preferably ethyl acetate.

[0073] In the production method of this embodiment, the amount of the complexing agent used is preferably 100 mL or more, more preferably 200 mL or more, even more preferably 250 mL or more, and still more preferably 300 mL or more, relative to 1 kg of the total amount of lithium sulfide and lithium halide, and the upper limit is preferably 30,000 mL or less, more preferably 25,000 mL or less, even more preferably 20,000 mL or less, and still more preferably 10,000 mL or less.

[0074] When a complexing agent is used in producing a sulfide solid electrolyte, it is preferable to include removing the complexing agent from the resulting complex (electrolyte precursor). By removing the complexing agent from the complex (electrolyte precursor), an amorphous sulfide solid electrolyte is obtained. The complexing agent can be removed from the complex (electrolyte precursor), for example, by heating.

[0075] The sulfide solid electrolyte obtained by the manufacturing method of this embodiment contains lithium, sulfur, phosphorus, and a halogen element, and is basically an amorphous sulfide solid electrolyte. In this specification, the amorphous sulfide solid electrolyte refers to an X-ray diffraction pattern in X-ray diffraction measurement that shows a halo pattern in which peaks other than those derived from the material are substantially not observed, regardless of whether or not peaks derived from the raw materials of the solid electrolyte are present. Representative examples of amorphous sulfide solid electrolytes obtained using lithium halide compounds obtained by the manufacturing method of this embodiment include, for example, Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５ -LiI-LiBr, etc., a solid electrolyte composed of lithium sulfide, phosphorus sulfide, and lithium halide; ２ S-P ２ S ５ -Li ２ O-LiI, Li２ S-SiS ２ -P ２ S ５ In order to obtain higher ionic conductivity, a solid electrolyte such as Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５ A solid electrolyte composed of lithium sulfide, phosphorus sulfide, and a lithium halide, such as LiI-LiBr, is preferred. The types of elements constituting the amorphous solid electrolyte can be confirmed, for example, by an ICP emission spectrometer.

[0076] In the amorphous sulfide solid electrolyte obtained by the production method of this embodiment, the compounding ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms is preferably 1.0 to 1.8: 1.0 to 2.0: 0.1 to 0.8: 0.01 to 0.6, more preferably 1.1 to 1.7: 1.2 to 1.8: 0.2 to 0.6: 0.05 to 0.5, and even more preferably 1.2 to 1.6: 1.3 to 1.7: 0.25 to 0.5: 0.08 to 0.4. Further, when bromine and iodine are used in combination as halogen atoms, the compounding ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, bromine, and iodine is preferably 1.0 to 1.8: 1.0 to 2.0: 0.1 to 0.8: 0.01 to 0.3: 0.01 to 0.3, more preferably 1.1 to 1.7: 1.2 to 1.8: 0.2 to 0.6: 0.02 to 0.25: 0.02 to 0.25, more preferably 1.2 to 1.6: 1.3 to 1.7: 0.25 to 0.5: 0.03 to 0.2: 0.03 to 0.2, and even more preferably 1.35 to 1.45: 1.4 to 1.7: 0.3 to 0.45: 0.04 to 0.18: 0.04 to 0.18. By setting the compounding ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms within the above range, it becomes easier to obtain a solid electrolyte with higher ionic conductivity having a thiolisiconregion II type crystal structure, an argyrodite type crystal structure, or the like, which will be described later.

[0077] Furthermore, the above-mentioned amorphous sulfide solid electrolyte can be converted into a crystalline sulfide solid electrolyte by further heating. In this specification, a crystalline solid electrolyte refers to a solid electrolyte in which a peak derived from the solid electrolyte is observed in an X-ray diffraction pattern in X-ray diffraction measurement, regardless of whether or not a peak derived from the raw material of the solid electrolyte is present. That is, the crystalline solid electrolyte includes a crystalline structure derived from the solid electrolyte, and a portion of the crystalline structure may be derived from the solid electrolyte, or the entire crystalline structure may be derived from the solid electrolyte. Furthermore, as long as the crystalline solid electrolyte has the above-mentioned X-ray diffraction pattern, it may also contain an amorphous solid electrolyte in part. Therefore, the crystalline solid electrolyte includes so-called glass ceramics obtained by heating an amorphous solid electrolyte to a temperature equal to or higher than the crystallization temperature.

[0078] The heating temperature can be appropriately selected depending on the structure of the amorphous sulfide solid electrolyte, so it cannot be generalized. For example, using a differential thermal analyzer (DTA device), differential thermal analysis (DTA) is performed under a heating condition of 10 ° C. / min. Starting from the peak top temperature of the exothermic peak observed on the lowest temperature side, the temperature is preferably 5 ° C. or higher, more preferably 10 ° C. or higher, and even more preferably 20 ° C. or higher. There is no particular limit on the upper limit, but it may be about 40 ° C. or lower. Specifically, usually, 130 ° C. or higher is preferred, 135 ° C. or higher is more preferred, and 140 ° C. or higher is even more preferred. There is no particular limit on the upper limit, but it is preferably 300 ° C. or lower, more preferably 280 ° C. or lower, and even more preferably 250 ° C. or lower.

[0079] The heating time is not particularly limited as long as it is a time that allows a desired crystalline sulfide solid electrolyte to be obtained, but is preferably 1 minute or more, more preferably 10 minutes or more, even more preferably 30 minutes or more, and even more preferably 1 hour or more. The upper limit of the heating time is not particularly limited, but is preferably 24 hours or less, more preferably 10 hours or less, even more preferably 5 hours or less, and even more preferably 3 hours or less.

[0080] Furthermore, heating is preferably carried out in an inert gas atmosphere (e.g., a nitrogen atmosphere or an argon atmosphere) or a reduced pressure atmosphere (particularly in a vacuum). This is because deterioration (e.g., oxidation) of the crystalline solid electrolyte can be prevented. The heating method is not particularly limited, and examples thereof include methods using a hot plate, a vacuum heating device, an argon gas atmosphere furnace, and a baking furnace. Furthermore, industrially, a horizontal dryer or a horizontal vibration fluidized dryer having a heating means and a feeding mechanism can also be used, and the method may be selected depending on the amount of heat to be processed.

[0081] The crystalline sulfide solid electrolyte obtained using the lithium halide compound obtained by the production method of this embodiment includes Li ３ P.S. ４ Crystal structure, Li ４ P ２ S ６ Crystal structure, Li ７ P.S. ６ Crystal structure, Li ７ P ３ S １１ Examples of such sulfide solid electrolytes include those having a crystalline structure, such as a crystalline structure having peaks at 2θ=approximately 20.2° and 23.6° (for example, JP 2013-16423 A).

[0082] Also, Li ４－ｘ Ge １－ｘ P ｘ S ４ Thio-LISICON Region II crystal structure (Kanno et al., Journal of the Electrochemical Society, 148(7)A742-746(2001)), Li ４－ｘ Ge １－ｘ P ｘ S ４ Also included are crystal structures similar to the thio-LISICON Region II type (see Solid State Ionics, 177 (2006), 2721-2725). From the viewpoint of ionic conductivity, the thio-LISICON Region II type crystal structure is preferred. Here, the "thio-LISICON Region II type crystal structure" refers to a structure in which Li ４－ｘ Ge１－ｘ P ｘ S ４ Thio-LISICON Region II crystal structure, Li ４－ｘ Ge １－ｘ P ｘ S ４ This indicates that the thio-LISICON region II type has a similar crystal structure to that of the thio-LISICON region II type. ４－ｘ Ge １－ｘ P ｘ S ４ The notation of the crystal structure "thio-LISICON Region II type" means that the crystal structure was composed of the atoms in question, namely, Li, Ge, P, and S atoms, at the time of discovery in the above document. The fact that the sulfide solid electrolyte obtained by the production method of this embodiment has a thio-LISICON Region II type crystal structure means that the above "Li ４－ｘ Ge １－ｘ P ｘ S ４ This means that a crystal structure exhibiting the same diffraction peaks as those of the "thio-LISICON Region II type" crystal structure (including the above-mentioned similar crystal structures) is formed by the atoms (Li, P, S, and halogen atoms) contained in the raw material inclusions. The same applies to the argyrodite-type crystal structure described below.

[0083] Furthermore, the atomic composition ratios contained in the crystalline sulfide solid electrolyte are preferably those according to the composition formulas corresponding to the various crystal structures, and are within the range of the atomic composition ratios of the amorphous sulfide solid electrolyte. When the atomic composition ratios are within the range, it is easy to form a thiosilicon region II type crystal structure or an argyrodite type crystal structure, among the above crystal structures.

[0084] The sulfide solid electrolyte obtained in this manner is obtained from a lithium halide compound containing almost no water or hydrates, and therefore has high ionic conductivity and excellent battery performance. Therefore, the sulfide solid electrolyte obtained using the lithium halide compound obtained by the manufacturing method of this embodiment can be used in any application requiring Li ion conductivity, and is particularly suitable for use in batteries. The sulfide solid electrolyte may be used in the positive electrode layer, the negative electrode layer, or the electrolyte layer. Each layer can be manufactured by a known method. Furthermore, the battery preferably uses a current collector in addition to the positive electrode layer, the electrolyte layer, and the negative electrode layer, and known current collectors can be used. For example, a layer in which a material that reacts with the sulfide solid electrolyte, such as Au, Pt, Al, Ti, or Cu, is coated with Au or the like can be used.

[0085] The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples in any way.

[0086] (Example 1) Lithium carbonate (Li ２ CO ３ ) 0.274 g (3.7 mmol) and ammonium bromide (NH ４0.726 g (7.4 mmol) of ammonium bromide (Br) was weighed and mixed, and visual observation confirmed that deliquescence had not occurred. Next, the resulting mixture was placed in a Schlenk tube (volume: 100 mL) equipped with a stirrer, and the mixture was heated to 250°C under vacuum while continuing mixing with the stirrer for 2 hours, yielding a white powder. Powder X-ray diffraction (XRD) measurement was performed on the resulting powder using the following method. The results are shown in Figure 1. Furthermore, XRD measurement was also performed on the lithium carbonate and ammonium bromide used as raw materials using the same method. It was confirmed that strong peaks due to lithium carbonate appeared near 2θ = 21.4°, 30.7°, and 31.8°, strong peaks due to ammonium bromide appeared near 2θ = 21.9° and 31.2°, and strong peaks due to lithium bromide appeared near 2θ = 28.3°, 32.7°, 46.9°, and 55.6°. As shown in FIG. 1 , it was confirmed that the powder obtained in Example 1 had the strongest peak due to lithium bromide, and that although some peaks due to the raw materials lithium carbonate and ammonium bromide remained, most of them had disappeared.

[0087] In this specification, powder X-ray diffraction (XRD) measurements were carried out as follows. A sample powder was filled into a groove 20 mm in diameter and 0.2 mm deep, and leveled with glass to prepare a sample. This sample was sealed with Kapton film for XRD and measured under the following conditions without being exposed to air. Measurement equipment: D2 PHASER, manufactured by Bruker Corporation Tube voltage: 30 kV Tube current: 10 mA X-ray wavelength: Cu-Kα ray (1.5418 Å) Optical system: focusing method Slit configuration: Soller slit 4°, divergence slit 1 mm, Kβ filter (Ni plate) used Detector: semiconductor detector Measurement range: 2θ = 10-60 deg Step width, scan speed: 0.05 deg, 0.05 deg / sec

[0088] Comparative Example 1: Lithium hydroxide monohydrate (LiOH·H ２ 0.300 g (7.1 mmol) of ammonium bromide (NH ４When 0.700 g (7.1 mmol) of lithium halide was weighed out and mixed, it was found to be in a state that appeared to be deliquescent when visually observed, and even if it was recovered and dried in vacuum, it would adhere to the wall surface of the container, and it was clear that a powdery lithium halide could not be obtained.

[0089] The production method of the present invention does not involve a step of directly removing moisture, does not use elemental halogens that are difficult to handle, and does not require excessive energy for production. The obtained lithium halide compound has a low moisture content and can therefore be suitably used as a raw material for sulfide solid electrolytes.

Claims

1. A method for producing lithium halide comprising mixing lithium carbonate with ammonium halide.

2. The method for producing lithium halide according to claim 1, wherein the mixing ratio of the lithium carbonate and the ammonium halide is 1.50 to 2.50 moles of the ammonium halide per 1 mole of lithium carbonate.

3. The method for producing lithium halide according to claim 1 or 2, wherein the lithium carbonate and ammonium halide are premixed and then further mixed under heating.

4. The method for producing lithium halide according to claim 3, wherein the temperature condition for the heating and mixing is 90 to 400°C.

5. The method for producing lithium halide according to claim 3 or 4, wherein the heating and mixing is carried out under reduced pressure or in an inert gas atmosphere.

6. A method for producing a sulfide solid electrolyte, comprising reacting the lithium halide obtained by the method according to any one of claims 1 to 5 with a phosphorus compound.

7. The method for producing a sulfide solid electrolyte according to claim 6, further comprising reacting a lithium compound other than lithium halide.

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