RU2787019C2 - Lgps-based solid electrolyte and its production method - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to a solid electrolyte including Li, Sn, P, S, and halogen and to a method for its production. The solid electrolyte has a composition of Li_uSn_vP₂S_yX_z, where 6≤u≤14, 0.8≤v≤2.1, 9≤y≤16, 0<z≤1.6; X is Cl, Br, or I and has, in X-ray beam diffraction, CuKα: λ=1.5405

, peaks in at least following positions 2θ=19.80°±0.50°, 20.10°±0.50°, 26.60°±0.50°, and 29.10°±0.50°.

EFFECT: provision of a solid electrolyte having high ionic conductivity, wherein SnS₂ is used as raw material for it, which is not affected by moisture so easily.

8 cl, 4 dwg, 4 ex, 1 tbl

Description

FIELD OF TECHNOLOGY

[0001] The present invention relates to a solid electrolyte based on LGPS (Li-Ge-P-S) and to a method for its manufacture. It should be noted that the LGPS-based solid electrolyte refers to a solid electrolyte having a specific crystal structure that includes Li, P and S, however, the present invention relates to a solid electrolyte including Li, Sn, P, S and halogen.

BACKGROUND OF THE INVENTION

[0002] Recently, there has been an increased demand for secondary lithium ion batteries in applications including portable data terminals, portable electronic equipment, electric vehicles, hybrid electric vehicles, and stationary energy storage systems. However, at present, a flammable organic solvent is used as the electrolyte solution in secondary lithium-ion batteries, and a strong case is required to prevent this organic solvent from escaping. In addition, for example, in the case of portable personal computers, it is necessary to use a structure that prevents risks from leakage of the electrolytic solution. Thus, there is a restriction on the design of the devices.

[0003] Moreover, their range of application has been extended to mobile devices such as vehicles and aircraft, and high capacity is desirable for stationary secondary lithium ion batteries. In such circumstances, there is usually more attention than before to safety, and efforts are focused on the development of an all-solid state secondary lithium-ion battery that does not use toxic substances such as organic solvents.

[0004] For example, studies have been conducted on the use of an oxide, a phosphate compound, an organic polymer, a sulfide, or the like. as a solid electrolyte in an all-solid secondary lithium-ion battery.

Among these solid electrolytes, sulfide has the characteristics of high ionic conductivity, relative softness, and ease of forming an interface between solid particles. Sulfide is stable towards active materials and has been developed as a practical solid electrolyte.

[0005] Among the sulfide solid electrolytes, there is an LGPS-based solid electrolyte having a special crystal structure (non-patent literature [1] and patent literature [1]). Among the sulfide solid electrolytes, the LGPS composition has a very high ionic conductivity and can work stably at -30°C to 100°C, so its practical use is highly expected.

[0006] The development of solid electrolyte compositions based on LGPS without using expensive Ge has been developed, and among them, compositions including Si and halogen are known to have high ionic conductivity (patent literature [2]-[4]). However, since SiS ₂ , which is one of the raw materials, has a very high reactivity with water (non-patent literature [2]), toxic H ₂ S is immediately generated in the atmosphere, and SiS ₂ is partially converted to SiO ₂ . In addition, when an LGPS-based solid electrolyte is produced using SiS ₂ whose quality varies as a raw material, there is a problem that the ion conductivity is greatly reduced.

LIST OF CITATIONS

PATENT LITERATURE

[0007] Patent Literature 1: International Publication Brochure WO 2011/118801.

Patent Literature 2: Japanese Patent No. 6044587.

Patent Literature 3: Japanese Patent No. 6044588.

Patent Literature 4: Japanese Patent No. 6222134.

NON-PATENT LITERATURE

[0008] Non-Patent Literature 1: Nature Energy 1, Article Number: 16030 (2016).

Non-Patent Literature 2: THE SANTAFE SYMPOSIUM, May 2010, "The Tarnishing of Silver Alloys: Causes and Possibilities".

DISCLOSURE OF THE INVENTION

TECHNICAL PROBLEMS

[0009] Under the above circumstances, it is desirable to provide an LGPS-based solid electrolyte that is not easily affected by changing the quality of raw materials during production and has a high ionic conductivity without using an expensive element such as Ge.

SOLUTION OF PROBLEMS

[0010] The inventors of the present invention have made careful studies in view of the above problems, and have found that the present invention described below provides an LGPS-based solid electrolyte having a high ionic conductivity, using SnS ₂ as a raw material, which is not easily affected by moisture.

[0011] In particular, the present invention is described below.

).<1> Solid electrolyte based on LGPS (Li-Ge-PS) which has the composition of Li _u Sn _v P ₂ S _y X _z (6≤u≤14, 0.8≤v≤2.1, 9≤y≤ 16, 0<z≤1.6; X is Cl, Br, or I) and which peaks at at least 2θ=19.80°±0.50°, 20.10°±0.50°, 26.60°±0.50° and 29.10°±0.50° by X-ray diffraction (CuKα: λ=1.5405

).

<2> The LGPS-based solid electrolyte according to <1>, wherein the intensity of the diffraction peak at 2θ=29.10°±0.50° is designated I _A and the intensity of the diffraction peak at 2θ=27.33°±0, 50° is denoted as I _B , and I _B /I _A is less than 0.50.

<3> The LGPS-based solid electrolyte according to <1> or <2>, which has an O octahedron consisting of the Li element and an S element, a T ₁ tetrahedron consisting of at least one element selected from the group consisting of the elements P and Sn and the S element, and the T ₂ tetrahedron, consisting of the P element and the S element, and mainly includes a crystal structure in which the T ₁ tetrahedron and the O octahedron share an edge, and the T ₂ tetrahedron and the O octahedron share a vertex, in this case, part of the S elements in the O octahedron, T ₁ tetrahedron, and T ₂ tetrahedron can be replaced by Cl, Br, or I.

<4> An all-solid-state battery obtained using the LGPS-based solid electrolyte according to any one of <1> to <3>.

<5> The LGPS solid electrolyte manufacturing method according to any one of <1> to <3>, comprising:

a solution preparation step in which a homogeneous solution is prepared by mixing and reacting Li ₂ S and P ₂ S ₅ in an organic solvent, wherein the molar ratio of Li ₂ S/P ₂ S ₅ is 0.75 to 1.85;

a precipitation step in which LiX (where X is Cl, Br or I) is added to and dissolved in said homogeneous solution, followed by adding SnS ₂ and Li ₂ S thereto and performing mixing to form a precipitate;

a drying step in which the organic solvent is removed from the precipitate to obtain a precursor; and

a heat treatment step in which the precursor is heated at a temperature of 200° C. to 700° C. to form a solid electrolyte based on LGPS.

<6> The method of <5>, wherein the organic solvent is at least one selected from the group consisting of tetrahydrofuran, acetonitrile, ethyl acetate, and methyl acetate.

<7> The method according to <5> or <6>, wherein the temperature in the drying step is 60 to 280°C.

<8> The method according to any one of <5> to <7>, wherein the heat treatment step is carried out in an inert gas atmosphere.

POSITIVE EFFECTS OF THE INVENTION

[0012] According to the present invention, it is possible to provide an LGPS-based solid electrolyte that is not easily affected by moisture during production.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a schematic view showing the crystal structure of an LGPS-based solid electrolyte according to one embodiment of the present invention.

In FIG. 2 is a schematic sectional view of an all solid state battery in accordance with one embodiment of the present invention.

In FIG. 3 is a graph showing the measurement results of X-ray diffraction of the ionic conductors obtained in Examples 1 to 3 and Comparative Example 1.

In FIG. 4 is a graph showing the Raman spectroscopy results of the ionic conductors obtained in Examples 1-3 and Comparative Example 1.

IMPLEMENTATION OF THE INVENTION

[0014] Next, the LGPS-based solid electrolyte of the present invention, the manufacturing method thereof, and the all-solid-state battery obtained using said LGPS-based solid electrolyte will be described in detail. It should be noted that the materials, compositions, etc. described below do not limit the present invention and may be modified in various ways within the spirit of the present invention.

[0015] <LPGS-Based Solid Electrolyte>

The LGPS solid electrolyte of the present invention has the composition Li _u Sn _v P ₂ S _y X _z (6≤u≤14, 0.8≤v≤2.1, 9≤y≤16, 0<z≤1.6 ; X is Cl, Br or I).

Preferably, 6.5≤u≤12.0, 0.85≤v≤1.70, 9.5≤y≤14.5 and 0.1≤z≤1.5. More preferably, 7.0 ≤ u ≤ 12.0, 0.85 ≤ v ≤ 1.60, 10.0 ≤ y ≤ 14.5, and 0.1 ≤ z ≤ 1.0. It is particularly preferred that 8.0 ≤ u ≤ 11.5, 0.90 ≤ v ≤ 1.60, 10.0 ≤ y ≤ 14.0 and 0.1 ≤ z ≤ 0.7. In addition, it is preferred that X is Br.

It should be noted that the element ratio is an important factor for designing a particular LGPS crystal, and within the above-described range, a desired LGPS crystal can generally exist. In addition, the LGPS crystal may have a composition in which some of the S atoms are replaced by O atoms, in which case the ratio of u, v, y, and z may be outside the range described above.

). Следует отметить, что более предпочтительно, чтобы твердый электролит имел пики при 2θ=17,00±0,50°, 19,80°±0,50°, 20,10°±0,50°, 23,50°±0,50°, 26,60°±0,50°, 28,60°±0,50° и 29,10°±0,60° (более предпочтительно 29,10°±0,50°).[0016] The above solid electrolyte based on LGPS preferably has peaks at at least 2θ=19.80°±0.50°, 20.10°±0.50°, 26.60°±0.50° and 29, 10°±0.60° (more preferably 29.10°±0.50°) in x-ray diffraction (CuKα: λ=1.5405

). It should be noted that it is more preferable that the solid electrolyte has peaks at 2θ=17.00±0.50°, 19.80°±0.50°, 20.10°±0.50°, 23.50°±0 .50°, 26.60°±0.50°, 28.60°±0.50° and 29.10°±0.60° (more preferably 29.10°±0.50°).

[0017] With regard to the above LGPS-based solid electrolyte, if the intensity of the diffraction peak at 2θ=29.10°±0.50° is denoted as I _A , and the intensity of the diffraction peak at 2θ=27.33°±0.50° is denoted as I _B , I _B /I _A is preferably less than 0.50. More preferably, the I _B /I _A ratio is less than 0.40. This is due to the fact that the peak of the LGPS crystal corresponds to I _A , and the crystalline phase, which has a low ionic conductivity, corresponds to I _B .

[0018] Moreover, it is preferable that the LGPS-based solid electrolyte has an O octahedron consisting of the element Li and the element S, a tetrahedron T ₁ consisting of at least one element selected from the group consisting of the elements P and Sn and the element S, and a T ₂ tetrahedron composed of a P element and an S element, and mainly included a crystal structure in which a T ₁ tetrahedron and an O octahedron share an edge, and a T ₂ tetrahedron and an O octahedron share a vertex, as shown in FIG. 1. It should be noted that some of the S elements in the O octahedron, T ₁ tetrahedron and T ₂ tetrahedron can be replaced by Cl, Br or I.

[0019] <Method of manufacturing solid electrolyte based on LGPS>

The method for manufacturing an LGPS-based solid electrolyte of the present invention includes a step of mixing raw materials and a step of heat treating the mixed raw materials.

The mixing method of the raw materials is not particularly limited. Examples thereof include: the method of using mechanical grinding, such as through planetary ball mill, vibratory mill and bead mill; and a method of stirring and mixing raw materials in a solvent. For mass production, the mixing and solvent mixing method is more preferable.

[0020] 1. Raw materials

The raw materials are not particularly limited, and Li ₂ S, P ₂ S ₅ , SnS or SnS ₂ and LiX (X is Cl, Br or I) can be used. In addition, Li ₃ PS ₄ obtained by the reaction of Li ₂ S and P ₂ S ₅ and Li ₄ SnS ₄ obtained by the reaction of SnS ₂ and Li ₂ S can be used as raw materials.

As Li ₂ S, a commercially available product or a synthesized product can be used. Since the purity of Li ₂ S significantly affects the LGPS-based solid electrolyte obtained by synthesis, the purity is preferably 95% or more, and more preferably 98% or more. In particular, when carbonate (CO ₃ ^2- ) is present in the electrolyte, the ionic conductivity of the LGPS-based solid electrolyte decreases.

P ₂ S ₅ may contain a small number of O atoms. P ₂ S ₅ reacts with Li ₂ S to form Li ₃ PS ₄ , but even when some of the PS bonds in PS ₄ ^3- are replaced by O atoms and P-O bonds exist, ionic conductivity of the LGPS-based solid electrolyte finally obtained is not significantly reduced. Considering the stability of the PS bonds, the case where the P-O bonds partially exist is more stable, in which case the reactivity with water is suppressed, and as a result, the effect of suppressing the formation of hydrogen sulfide is achieved.

[0021] The purity of SnS ₂ is preferably high. It is believed that the ionic conductivity of the eventually obtained solid electrolyte based on LGPS tends to decrease due to Sn-O bonds in the case of Li ₄ SnS ₄ , which is formed by the reaction of SnS ₂ and Li ₂ S, in contrast to the case with Li _{3 PS4} . Accordingly, the purity of SnS ₂ should preferably be 95% or more, and more preferably 98% or more. Because SnS ₂ does not readily react with water, it can be used as a raw material for an LGPS-based solid electrolyte in a manufacturing process without reducing the purity of SnS ₂ .

As LiX (X is Cl, Br or I), a commercially available product or a synthesized product can be used. Its purity is preferably 95% or more, and more preferably 98% or more. The moisture content of LiX (X is Cl, Br or I) is preferably less than 50 ppm (parts per million), and more preferably less than 10 ppm. This is because moisture from the raw materials causes the formation of a by-product during the production of the solid electrolyte based on LGPS. Since the LiI hydrate is stable, the humidity must be strictly controlled.

[0022] 2. Mixing method

The mixing method is not particularly limited as long as the raw materials can be uniformly distributed. Examples of this include mechanical grinding using a bead mill, vibratory mill or planetary ball mill, either a wet process or a dry process can be used. Preferably, the raw materials are amorphized, but it is not necessary to amorphize all the raw materials, and this is sufficient when the fine particles of the respective raw materials are a few µm or less in size and sufficiently mixed. It should be noted that mechanical grinding is preferably carried out in an inert gas atmosphere.

As a mixing method for mass production, the solvent mixing and mixing method described below is more preferable than the mechanical grinding described above.

[0023] The mixing and mixing method in a solvent will be described in detail.

In one embodiment of the present invention we have:

a solution preparation step in which a homogeneous solution is prepared by mixing and reacting Li ₂ S and P ₂ S ₅ in an organic solvent, wherein the molar ratio of Li ₂ S/P ₂ S ₅ is 0.75 to 1.85;

a precipitation step in which LiX (where X is Cl, Br or I) is added and suspended in said homogeneous solution, followed by adding SnS ₂ and Li ₂ S thereto and performing stirring to form a precipitate;

a drying step in which the organic solvent is removed from the precipitate to obtain a precursor.

Preferably, SnS ₂ is added in the precipitation step, followed by further addition of Li ₂ S.

Next, the respective steps will be described in detail.

[0024] A. Solution preparation step

In the solution preparation step according to the present invention, Li ₂ S and P ₂ S ₅ are mixed and reacted in an organic solvent at a molar ratio of Li ₂ S/P ₂ S ₅ =0.75-1.85 to obtain a homogeneous solution. According to the present invention, the expression "homogeneous solution" means a solution in which there is no undissolved precipitate. In this regard, the Li ₂ S/P ₂ S ₅ molar ratio described above is preferably 0.85-1.5, and more preferably 0.9-1.4. When the molar ratio of Li ₂ S/P ₂ S ₅ is from 0.75 to 1.85, a solution can be prepared using Li ₂ S and P ₂ S ₅ at room temperature. When the molar ratio is outside the range described above, precipitation may occur. It should be noted that when the undissolved precipitate is separated from the solution by filtration or the like, the composition in the solution becomes the same as that obtained in the solution preparation step performed at a molar ratio within the range described above.

[0025] Li ₂ S can be a synthesized product or a commercially available product. The lower the moisture content, the better, because mixing with moisture degrades other raw materials and the precursor. More preferably, the moisture content is 300 ppm or less, particularly preferably 50 ppm or less. The smaller the particle diameter of Li ₂ S, the better, since a faster reaction rate is achieved. The particle diameter is preferably 10 nm to 100 µm, more preferably 100 nm to 30 µm, and even more preferably 300 nm to 10 µm. It should be noted that the particle diameter can be measured by an SEM (Scanning Election Microscope; scanning electron microscope), a particle size distribution measuring device using laser scattering, or the like.

[0026] As P ₂ S ₅ you can use a synthesized product or a commercially available product. The higher the purity of P ₂ S ₅ , the better, because the amount of impurities mixed into the solid electrolyte becomes smaller. The smaller the P ₂ S ₅ particle diameter, the better, since a faster reaction rate is achieved. The particle diameter is preferably 10 nm to 100 µm, more preferably 100 nm to 30 µm, and even more preferably 300 nm to 10 µm. The lower the moisture content, the better, because mixing with moisture degrades other raw materials and the precursor. More preferably, the moisture content is 300 ppm or less, particularly preferably 50 ppm or less.

[0027] The organic solvent is not particularly limited as long as it does not react with Li ₂ S or P ₂ S ₅ . Examples of the solvent include an ether-based solvent, an ester-based solvent, a hydrocarbon-based solvent, and a nitrile-based solvent. Specific examples include tetrahydrofuran, cyclopentyl methyl ether, diisopropyl ether, diethyl ether, dimethyl ether, dioxane, methyl acetate, ethyl acetate, butyl acetate, and acetonitrile. Especially preferred are tetrahydrofuran and acetonitrile. In order to prevent deterioration of the composition of the raw material, it is preferable to remove oxygen and water from the organic solvent in advance. In particular, with regard to the moisture content, it should preferably be 100 ppm or less, more preferably 50 ppm or less, and particularly preferably 10 ppm or less.

[0028] The total concentration of Li ₂ S and P ₂ S ₅ in the organic solvent is preferably 1 to 40% by weight, more preferably 5 to 30% by weight, and particularly preferably 10 to 20% by weight. When the total concentration of Li ₂ S and P ₂ S ₅ in the organic solvent exceeds 40% by weight, the viscosity of the slurry increases and mixing may be difficult. Meanwhile, when the total concentration of Li ₂ S and P ₂ S ₅ in the organic solvent is lower than 1% by weight, it becomes necessary to use a large amount of the organic solvent and increase the solvent recovery load. In addition, this leads to an excessive increase in the size of the reactor.

[0029] With regard to the reaction mechanism in the step of preparing the solution according to the present invention, Li ₂ S gradually reacts with P ₂ S ₅ suspended in an organic solvent, leading to the preparation of a solution. However, it is preferable that Li ₂ S is first added to the organic solvent and suspended in it, and then P ₂ S ₅ is gradually added. This is because when Li ₂ S is added in a state where P ₂ S ₅ is in excess, a condensed polymer may be generated.

[0030] During mixing in the solution preparation step, the substrate is dispersed to provide a slurry state, but it eventually reacts to become a homogeneous solution. It is not necessary to carry out a special mixing operation for pulverizing the particles, and this is sufficient when a mixing power is provided that can suspend and disperse the slurry.

As for the reaction temperature in the solution preparation step, the reaction proceeds slowly even at room temperature, but heating can be carried out to increase the reaction rate. When performing heating, it is sufficient to provide a temperature equal to or lower than the boiling point of the organic solvent. The temperature varies depending on the organic solvent used, but is usually below 120°C. Heating can also be carried out under pressure using an autoclave or the like. However, when the mixing is carried out at a high temperature (120° C. or higher), there is a possibility that a side reaction will occur.

[0031] The reaction time in the solution preparation step varies depending on the type of organic solvent, the particle diameter and the concentration of raw materials, but for example, if the reaction is carried out for 0.1 to 24 hours, the reaction is completed and the solution can be prepared.

A small amount of sediment may form in the prepared solution, depending on the ratio of the composition to be added and the mixing conditions of the raw material impurities. In this case, it is desirable to remove the precipitate by filtration or centrifugation.

[0032] B. Deposition step

LiX (X is Cl, Br or I) is added to the homogeneous solution obtained in the solution preparation step, and stirring is carried out to dissolve LiX therein. LiX is added because it is believed that the interaction between S and Li can be reduced when a part of the S elements in the LGPS crystal is replaced by X, and it has been found that ionic conductivity is improved due to this. It should be noted that when the amount of added LiX is too large, a crystal other than an LGPS crystal, such as an argyrodite type crystal, is formed, and the ionic conductivity decreases. The amount of LiX added is preferably 0.01-1.6 times, and more preferably 0.1-1.5 times the molar amount of P ₂ S ₅ in a homogeneous solution.

Thereafter, SnS ₂ is added thereto and suspended therein by stirring. The amount of SnS ₂ added is preferably 0.8-2.1 times, and more preferably 0.85-1.70 times the molar amount of P ₂ S ₅ in the homogeneous solution. Then additional Li ₂ S is added and stirred until a precipitate forms. With regard to the additionally added Li ₂ S, the total amount of added Li ₂ S is preferably 3.0 to 7.0 times, and more preferably 3.2 to 6.0 times the molar amount of P ₂ S ₅ in a homogeneous solution.

As a mixing method, it is sufficient to use mixing using a conventional paddle mixer. To grind the added particles of SnS ₂ and Li ₂ S, it is preferable to carry out grinding by stirring. Moreover, a homogenizer or an ultrasonic disperser can also be used.

[0033] With regard to SnS ₂ , usually the valency of the element is preferably 4. In particular, SnS ₂ can be used either as a commercially available product or as a synthesized product. SnS ₂ is preferably in the form of small particles, because then better compatibility is achieved. The particle diameter is preferably 10 nm to 100 µm, more preferably 100 nm to 30 µm, and even more preferably 300 nm to 10 µm. The particle diameter can be measured by an SEM, a particle size distribution measuring device using laser scattering, or the like. It should be noted that problems do not occur even when a part of the raw materials used as described above are amorphous. The lower the moisture content, the better, since mixing with moisture degrades other raw materials and the precursor. More preferably, the moisture content is 300 ppm or less, particularly preferably 50 ppm or less.

[0034] When additionally adding Li ₂ S to the suspension obtained by suspending SnS ₂ in a homogeneous solution, the precipitate gradually increases. The precipitate may be a solvate. For example, it is believed that when using tetrahydrofuran (THF) as an organic solvent, a Li ₃ PS ₄ ⋅3THF crystal is obtained. The Li ₂ S added may be the same as the Li ₂ S used in the solution preparation step.

[0035] A precipitate is formed when the reaction proceeds to form Li ₃ PS ₄ . The reaction mechanism is unknown, but it is believed that the substance dissolves in solution in the -(PSPS)n- state. It is believed that Li ₂ S added to it disperses into a suspended state and cleaves PS, thereby forming Li ₃ PS ₄ .

[0036] The mixing time for suspending SnS ₂ in a homogeneous solution is preferably from 0.1 to 24 hours. By carrying out stirring to such an extent, a state is obtained in which SnS ₂ is sufficiently suspended. The mixing time after additional addition of Li ₂ S may be from 0.1 to 48 hours, and more preferably from 4 to 36 hours. It should be noted that since the additionally added Li ₂ S reacts with Li ₂ SP ₂ S ₅ in the solution state, when the reaction time is short, the desired Li ₃ PS ₄ is formed in insufficient quantity, and the unreacted Li ₂ S is mixed with the precipitate.

[0037] The temperature during mixing may be room temperature. Heating can be performed, but if the temperature is too high, there is a possibility of a side reaction. When performing heating, it is sufficient to provide a temperature equal to or lower than the boiling point of the organic solvent. The temperature varies depending on the organic solvent used, but is usually below 120°C.

[0038] The mixing in the precipitation step is preferably carried out under an inert gas atmosphere. Examples of the inert gas include nitrogen, helium and argon, and argon is particularly preferred. Also, by removing oxygen and moisture in the inert gas, deterioration of the composition of the raw material can be prevented. The concentration of oxygen and moisture in the inert gas is preferably 1000 ppm or less, more preferably 100 ppm or less, and particularly preferably 10 ppm or less.

[0039] C. Drying step

The resulting precipitate is dried to remove the organic solvent, thereby obtaining a precursor. Drying can be carried out by drying with heated air or vacuum drying in an inert gas atmosphere.

The drying temperature is preferably 60 to 280°C, more preferably 100 to 250°C. The optimum temperature range varies slightly depending on the type of organic solvent, but the temperature range is important. If the drying temperature is too high in a state in which an organic solvent is present, the quality of the precursor changes in almost all cases. In addition, when the drying temperature is too low, the amount of residual solvent is larger, and when the next heat treatment step is carried out directly, the organic solvent is carbonized, and the resulting LGPS-based solid electrolyte will have high electronic conductivity. It may be preferable for the solid electrolyte to be electronically conductive depending on the method of use, but the solid electrolyte to be used for pos. 2 in FIG. 2 should have a sufficiently low electronic conductivity. If a solid electrolyte is used for such applications, the amount of residual solvent should be reduced as much as possible.

[0040] The drying time varies slightly depending on the type of organic solvent and the drying temperature, but the organic solvent can be sufficiently removed by drying for 1 to 24 hours. It should be noted that by removing the organic solvent under reduced pressure, as in the case of vacuum drying, and by passing an inert gas such as nitrogen and argon in which the moisture content is sufficiently low, the temperature during removal of the organic solvent can be reduced and the required time can be shortened.

It should be noted that the heat treatment step described below and the drying step may be performed simultaneously.

[0041] D. Heat treatment step

In the manufacturing method of the present invention, the precursor obtained in the drying step is subjected to heat treatment, resulting in a solid electrolyte based on LGPS. The heating temperature varies depending on the type of precursor and is usually 200 to 700°C, more preferably 350 to 650°C and particularly preferably 400 to 600°C. When the temperature is lower than the above-described range, desired crystals are not easily obtained, and when the temperature is higher than the above-described range, other than desired crystals are formed.

[0042] The heating time varies slightly depending on the heating temperature, but usually crystallization becomes sufficient when the heating time is from 0.1 to 24 hours. Heating is not allowed to be carried out at a high temperature for a long period of time that exceeds the range described above, since there is a possibility of changing the quality of the LGPS-based solid electrolyte.

The heating can be carried out in a vacuum or in an inert gas atmosphere, but is preferably carried out in an inert gas atmosphere. As the inert gas, nitrogen, helium, argon or the like can be used, and among them, argon is preferable. The content of oxygen and moisture is preferably low, and the conditions for them are the same as during mixing in the precipitation stage.

[0043] The solid electrolyte based on LGPS of the present invention, obtained by the above described method, can be formed into a body of the desired shape by various means and can be used for various applications, including the all-solid state battery described below. The forming method is not particularly limited. For example, a method similar to the method of forming the respective layers constituting an all-solid-state battery described below in <All-solid-state battery> can be used.

[0044] <Full Solid State Battery>

The LGPS-based solid electrolyte of the present invention can be used, for example, as a solid electrolyte for all-solid-state batteries. In addition, according to another embodiment of the present invention, an all-solid-state battery containing the above-described solid electrolyte for all-solid-state batteries is provided.

[0045] In this regard, the expression "all-solid state battery" means "all-solid state lithium-ion secondary battery." Fig. 2 is a schematic sectional view of an all solid state battery according to one embodiment of the present invention. The all-solid battery 10 has a structure in which the solid electrolyte layer 2 is interposed between the positive electrode layer 1 and the negative electrode layer 3. The solid state battery 10 can be used in a variety of applications including mobile phones, personal computers, and automobiles.

The LGPS-based solid electrolyte of the present invention 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. In the case where the LGPS solid electrolyte of the present invention is contained in the positive electrode layer 1 or the negative electrode layer 3, the LGPS solid electrolyte of the present invention is used in combination with a well-known positive electrode active material or a lithium negative electrode active material. ion secondary battery. The ratio of the LGPS-based solid electrolyte of the present invention contained in the positive electrode layer 1 or the negative electrode layer 3 is not particularly limited.

[0046] In the case where the LGPS-based solid electrolyte of the present invention is contained in the solid electrolyte layer 2, the solid electrolyte layer 2 may only be composed of the LGPS-based solid electrolyte of the present invention and, if necessary, an oxide solid electrolyte (for example, Li ₇ La ₃ Zr ₂ O ₁₂ ), sulfide-based solid electrolyte (eg Li ₂ SP ₂ S ₅ ), other complex hydride solid electrolytes (eg LiBH ₄ and 3LiBH ₄ -LiI), and the like. may suitably be used in combination. When using a material exhibiting strong reducing ability such as Li metal for the negative electrode active material, a reaction occurs at the interface between the LGPS-based solid electrolyte of the present invention and the active material, and an irreversible increase in capacitance and resistance can occur. In order to prevent this phenomenon, it is preferable to provide a solid electrolyte having a reduction resistance, a complex hydride solid electrolyte, an argyrodite-type solid sulfide electrolyte, a sulfide glass ceramic or the like on the side of the negative electrode layer or on the surface of the negative electrode active material.

[0047] An all-solid-state battery is manufactured by forming and layering the above-described layers, and the forming method and the layering method for the respective layers are not particularly limited.

Examples of methods include: a method in which a solid electrolyte and/or an active material of an electrode is dispersed in a solvent to obtain a slurry mixture, which is applied by a doctor blade, centrifugation, and the like, and subjected to rolling to form a film; a gas phase method in which film formation and layering are performed using a vacuum deposition method, an ion deposition method, a sputtering method, a laser ablation method, or the like; and a pressing method in which the powder is formed by hot or cold pressing (without heating) to perform layering.

[0048] Since the LGPS-based solid electrolyte of the present invention is relatively soft, it is particularly preferable to manufacture an all-solid-state battery by forming appropriate layers through a pressing and layering method. As the pressing method, there are hot pressing in which heating is performed and cold pressing in which heating is not performed, but the formation of layers can be sufficiently performed even by cold pressing.

It should be noted that the present invention includes a shaped body obtained by heating and forming an LGPS-based solid electrolyte of the present invention. The shaped body is suitable for use as a fully solid state battery. In addition, the present invention includes a method for manufacturing an all-solid-state battery, which includes the step of heating and forming a solid electrolyte based on the LGPS of the present invention.

EXAMPLES

[0049] Hereinafter, embodiments of the present invention will be more specifically described by way of examples, but the embodiments are not limited to these examples.

[0050] (Example 1)

<Stage of solution preparation>

Li ₂ S (manufactured by Sigma-Aldrich, purity: 99.8%) and P ₂ S ₅ (manufactured by Sigma-Aldrich, purity: 99%) were weighed in a glove box under an argon atmosphere so that the molar ratio of Li ₂ S:P ₂ S ₅ was 1:1. Then, Li ₂ S and P ₂ S ₅ were added to acetonitrile (manufactured by Wako Pure Chemical Industries, Ltd., super dehydrated grade) in such order that the concentration of (Li ₂ S+P ₂ S ₅ ) was 10% by weight, and mixing was performed at room temperature for 12 hours. The mixture was gradually dissolved and a homogeneous solution was obtained.

<Deposition stage>

LiBr (manufactured by Sigma-Aldrich, purity: 99.8%) was added to the resulting homogeneous solution with stirring and dissolution in an amount equal to 0.29 molar amount of P ₂ S ₅ in the homogeneous solution. Then, SnS ₂ (GEI04PB, manufactured by Kojundo Chemical Laboratory Co., Ltd.) was added with stirring in an amount equal to 1.09 molar amount of P ₂ S ₅ in a homogeneous solution, and mixing was performed at room temperature for 12 hours. Li ₂ S was then added with stirring in an amount equal to 3.2 molar amounts of P ₂ S ₅ in a homogeneous solution (that is, based on the total amount, the molar ratio of Li ₂ S:SnS ₂ :P ₂ S ₅ :LiBr=4, 18:1.09:1:0.29), and mixing was performed at room temperature for 24 hours to obtain a slurry solution.

[0051] <Drying Stage>

The resulting weighed solution was dried in vacuum at 200°C for 3 hours to obtain a precursor. A series of operations was carried out in a glove box in an argon atmosphere.

<Heating stage>

In the glove box, the obtained precursor was placed in a glass reaction tube, which was placed in an electric tube furnace so that the precursor was not exposed to the atmosphere. Argon (grade G3) was introduced into the reaction tube, the temperature was raised to 475°C for 3 hours, and then firing was performed at 475°C for 8 hours, as a result of which a Li _8.66 Sn _1.09 P ₂ S _11.36 Br _0.29 crystal was synthesized .

[0052] (Example 2)

The Li _8.66 Sn _1.09 P ₂ S _11.36 Cl _0.29 crystal was synthesized in the same way as in Example 1, except that LiCl was used instead of LiBr. (Example 3)

The Li _8.66 Sn _1.09 P ₂ S _11.36 Cl _0.29 crystal was synthesized in the same way as in Example 1, except that LiI was used instead of LiBr.

[0053] (Comparative Example 1)

The Li _9.81 Sn _0.81 P _2.19 S ₁₂ crystal was synthesized in the same manner as in Example 1, except that no LiBr was added in the <deposition step> in Example 1; SnS ₂ was added in an amount equal to 0.74 molar amount of P ₂ S ₅ ; a Li ₂ S was added in an amount equal to 4.48 molar amount of P ₂ S ₅ .

[0054] <X-ray diffraction measurement>

).The ionic conductor powders obtained in Examples 1-3 and Comparative Example 1 were examined by measuring X-ray diffraction in an Ar atmosphere at room temperature (25°C) ("X' Pert3 Powder" manufactured by PANalytical, CuKα: λ=1, 5405

).

The results of the X-ray diffraction measurements of the ionic conductors obtained in Examples 1 to 3 and Comparative Example 1 are shown in FIG. 3.

As shown in FIG. 3, in examples 1-3, diffraction peaks were observed at least at 2θ=19.80°±0.50°, 20.10°±0.50°, 26.60°±0.50° and 29.10° ±0.50°, and the pattern corresponded to Li ₁₀ GeP ₂ S ₁₂ from the ICSD database (Inorganic Crystal Structure Database; database of inorganic crystal structures).

If the intensity of the diffraction peak at 2θ=29.10°±0.50° is designated as I _A , and the intensity of the diffraction peak at 2θ=27.33°±0.50° is designated as I _B , I _B was very small and in all Examples 1-3, the I _B /I _A ratio was 0.1 or less.

[0055] <Lithium Ion Conductivity Measurement>

Each of the ionic conductors obtained in Examples 1 to 3 and Comparative Example 1 was subjected to uniaxial molding (420 MPa) to obtain a disk having a thickness of about 1 mm and a diameter of 10 mm. Using an all-solid-state battery evaluation cell (manufactured by Hohsen Corporation), the AC impedance was measured by the four-terminal method using an indium electrode at room temperature (25°C) ("SI1260 IMPEDANCE/GAIN-PHASE ANALYZER" manufactured by Solartron), and the conductivity was calculated by lithium ions.

Specifically, the sample was placed in a thermostated bath set at 25° C. and kept for 30 minutes, after which the lithium ion conductivity was measured. The measurement frequency range was from 0.1 Hz to 1 MHz, and the amplitude was 50 mV. The results of lithium ion conductivity measurements are shown in Table 1 below.

[0056] <Raman spectroscopy>

(1) Sample preparation

The measurement sample was prepared using a sealed container having a quartz glass (φ: 60 mm, thickness: 1 mm) at the top as an optical window. In a glove box in an argon atmosphere, the sample was glued to quartz glass, then the container was hermetically sealed and removed from the glove box, and then Raman spectroscopy was performed.

(2) Measurement conditions

Using an NRS-5100 laser Raman spectrometer (manufactured by JASCO Corporation), measurement was performed at an excitation wavelength of 532.15 nm for an exposure time of 5 seconds. The results of Raman spectroscopy of the ionic conductors obtained in Examples 1-3 and Comparative Example 1 are shown in FIG. four.

LIST OF REFERENCE NUMBERS IN THE DRAWINGS

[0057] 1 - positive electrode layer

2 - solid electrolyte layer

3 - negative electrode layer

10 - full solid state battery

Claims (12)

1. A solid electrolyte for an all-solid battery, which has the composition Li _u Sn _v P ₂ S _y X _z , where 6≤u≤14, 0.8≤v≤2.1, 9≤y≤16, 0<z≤ 1.6; X is Cl, Br or I and which has peaks at at least 2θ=19.80°±0.50°, 20.10°±0.50°, 26.60°±0.50° and 29 ,10°±0.50° with CuKα X-ray diffraction: λ=1.5405

. 2. The solid electrolyte according to claim 1, wherein the intensity of the diffraction peak at 2θ=29.10°±0.50° is designated as I _A , and the intensity of the diffraction peak at 2θ=27.33°±0.50° is designated as I _B , with I _B /I _A less than 0.50. 3. A solid electrolyte according to claim 1 or 2, which has an O octahedron consisting of the element Li and an element S, a tetrahedron T ₁ consisting of at least one element selected from the group consisting of the elements P and Sn and the element S, and the T ₂ tetrahedron, consisting of the P element and the S element, and mainly includes a crystal structure in which the T ₁ tetrahedron and the O octahedron have a common edge, and the T ₂ tetrahedron and the O octahedron have a common vertex, while part of the S elements in the octahedron O, T ₁ tetrahedron and T ₂ tetrahedron can be replaced by Cl, Br or I. 4. Fully solid-state battery obtained using a solid electrolyte according to any one of paragraphs. 1-3. 5. A method of manufacturing a solid electrolyte according to any one of paragraphs. 1-3, including a solution preparation step in which a homogeneous solution is prepared by mixing and reacting Li ₂ S and P ₂ S ₅ in an organic solvent, wherein the molar ratio of Li ₂ S/P ₂ S ₅ is 0.75 to 1.85; a precipitation step in which LiX, where X is Cl, Br or I, is added to said homogeneous solution for dissolution, followed by adding SnS ₂ and Li ₂ S thereto and performing mixing to form a precipitate; a drying step in which the organic solvent is removed from the precipitate to obtain a precursor; and a heat treatment step in which the precursor is heated at a temperature of 200° C. to 700° C. to form a solid electrolyte. 6. The method of claim 5 wherein the organic solvent is at least one selected from the group consisting of tetrahydrofuran, acetonitrile, ethyl acetate and methyl acetate. 7. The method according to claim 5 or 6, wherein the temperature in the drying step is between 60 and 280°C. 8. The method according to any one of paragraphs. 5-7, wherein the heat treatment step is carried out under an inert gas atmosphere.

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