JP2023147557A - Method for manufacturing solid electrolyte having argyrodite-type crystal structure - Google Patents

Abstract

To provide a method for manufacturing a solid electrolyte having an argyrodite-type crystal structure which is excellent in mass productivity and reproducibility of synthesis, generates no by-product of the synthesis, and causes no deterioration of conductivity and charge/discharge capacity.SOLUTION: The method includes: mixing a first dispersion liquid for a precursor in which a material including Li element, P element and S element is dispersed in a solvent containing an aprotic polar solvent containing no ether linkage, and a second dispersion liquid for a precursor in which at least LiX is dispersed in a solvent containing a thiol-based solvent; followed by desolvation and heat treatment.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing a solid electrolyte having an argyrodite crystal structure suitable for use in solid-state batteries, and more specifically, the present invention relates to a method for producing a solid electrolyte having an argyrodite crystal structure, which is suitably used in solid-state batteries. The present invention relates to a method for producing a solid electrolyte having an argyrodite crystal structure containing element X (X is a halogen).

A lithium ion battery is a secondary battery that has a structure in which lithium ions are desorbed from the positive electrode as ions and moved to the negative electrode and inserted therein during charging, and lithium ions are inserted from the negative electrode to the positive electrode and returned during discharging. Lithium-ion batteries have characteristics such as high energy density and long life, so they have traditionally been used in home appliances such as computers and cameras, portable electronic devices such as mobile phones, communication devices, and power tools. It is widely used as a power source for power tools, etc., and recently, it has also been applied to large batteries installed in electric vehicles (EVs), hybrid electric vehicles (HEVs), etc. In such lithium ion batteries, using a solid electrolyte instead of an electrolyte containing a flammable organic solvent not only simplifies the safety device, but also improves manufacturing costs and productivity. Research into various materials is actively underway. Among these, solid electrolytes containing sulfides have high electrical conductivity (lithium ion conductivity) and are said to be useful in increasing the output of batteries. In particular, solid electrolytes having an argyrodite crystal structure that provide high electrical conductivity have attracted attention, and various manufacturing methods are known.

For example, Non-Patent Document 1 discloses that a solid electrolyte having an argyrodite crystal structure having a conductivity on the order of 10 ⁻⁴ S/cm at room temperature is produced by heat treatment after mechanical milling treatment. Patent Document 1 discloses a method for producing a solid electrolyte using a solution method without a milling step, and specifically, a mixed solution is prepared by placing a mixed powder of raw material powder and acetonitrile in a reaction container, and the acetonitrile is removed by vacuum drying. It is disclosed that a solid electrolyte having an argyrodite-type crystal structure is produced by performing a heat treatment at 550° C. for 5 hours to crystallize the solid electrolyte. Non-Patent Document 2 describes that Li ₂ S and P ₂ S ₅ are dispersed in THF (tetrahydrofuran) and stirred for 24 hours to obtain Li ₃ PS _4. Li ₂ S and LiX are added to ethanol at a predetermined ratio. A precursor solution is obtained by mixing the dissolved solutions. It is disclosed that a solid electrolyte having an argyrodite crystal structure is produced by drying the obtained precursor and then firing and crystallizing it.

JP2020-064838A

R. P. Rao, S. Adams Phys. Status Solidi A, 208, 8, 1804-1807 (2011). “Studies of lithium argyrodite solid electrolytes for all-solid-state batteries” Laidong Zhou, Kern-Ho Park, Xiaoqi Sun, Fabien Lalere, Torben Adermann, Pascal Hartmann, and Linda F. Nazar, ACS Energy Lett. 4, 1, 265-270 (2019). X = Cl, Br, I) Solid Electrolytes with High Ionic Conductivity”

However, the method using milling described in Non-Patent Document 1 is difficult to scale up, and recovery of the composite is complicated, making it unsuitable for mass production. Furthermore, it has been found that all-solid-state lithium batteries that use electrolytes made by milling have problems with robustness, as sudden short circuits can occur during repeated charging and discharging between lithium metal plates. The method of Patent Document 1 has problems with uniformity and reproducibility of synthesis because multi-step synthesis reactions are processed in one solution, and the produced electrolyte has an argyrodite-type crystal structure produced by a method such as a milling process. The conductivity is inferior to that of solid electrolytes. The solid electrolyte having an argyrodite crystal structure produced by the method of Non-Patent Document 2 has a problem of producing by-products (Li ₃ PO ₄ ). Therefore, it has been found that the conductivity is poor and the charge/discharge capacity when an all-solid-state battery is constructed is also reduced. Furthermore, it has been found that repeated charging and discharging between lithium metal particles forms an insulating reaction layer, resulting in a significant increase in applied voltage.

The purpose of the present invention is to achieve easy scale-up and recovery of the composite, excellent mass productivity, good synthesis reproducibility, no synthesis by-products, and no reduction in conductivity or charge/discharge capacity. It is an object of the present invention to provide a method for producing a solid electrolyte having an argyrodite crystal structure, which has high robustness and is free from sudden short circuits and increases in applied voltage due to the formation of an insulating reaction layer even during repeated charging and discharging.

The above-mentioned problems of the present invention are solved by the following means.
[1] A method for producing a solid electrolyte having an argyrodite crystal structure containing Li element, P element, S element and X element (X is a halogen) in a liquid phase, comprising:
a precursor liquid preparation step of preparing a raw material precursor liquid for solid electrolyte production; a desolution step of desoluting the raw material precursor liquid for solid electrolyte production prepared by the precursor liquid preparation step; and a step of heat-treating the dry matter,
The precursor liquid preparation step includes:
A solvent containing an aprotic polar solvent that does not contain at least an ether bond contains Li element, P element, and S element, and the molar ratio of each element is (3+a):1:(4+b) (0≦a≦2, A first precursor dispersion preparation step of preparing a first precursor dispersion in which a material satisfying 0≦b≦1) is dispersed;
a second precursor dispersion preparation step of preparing a second precursor dispersion in which at least LiX is dispersed in a solvent containing at least a thiol-based solvent;
A method for producing a solid electrolyte having an argyrodite crystal structure, comprising a mixing step of mixing the first precursor dispersion and the second precursor dispersion.
[2] The method according to [1], wherein the solvent used in either or both of the first precursor dispersion preparation step and the second precursor dispersion preparation step contains pyridine. A method for producing a solid electrolyte having an argyrodite crystal structure.
[3] The first precursor dispersion preparation step involves dispersing P2S5 in a solvent containing at least pyridine and dispersing Li2S in a solvent containing at least an aprotic polar solvent that does not contain an ether bond. The method for producing a solid electrolyte having an argyrodite crystal structure according to [1] or [2], which comprises a step of mixing with a dispersion liquid.
[4] Either or both of the first precursor dispersion preparation step and the second precursor dispersion preparation step is performed at a temperature of 40° C. or higher and below the boiling point of the solvent with the lowest boiling point among the solvents contained. The method for producing a solid electrolyte having an argyrodite crystal structure according to [1], which comprises a step of stirring at a temperature.
[5] Each step included in the precursor liquid preparation step is characterized in that none of the steps includes a material having an ether bond and a solvent, and neither a material having an alcoholic OH group nor a solvent [1] The method for producing a solid electrolyte having an argyrodite crystal structure according to [4].

According to the present invention, it is easy to scale up and recover the synthesized product, and it is excellent in mass production, and the reproducibility of the synthesis is good.In addition, it does not produce synthesis by-products, and there is no decrease in conductivity or charge/discharge capacity. Provided is a method for producing a solid electrolyte having an argyrodite crystal structure that is highly robust and free from sudden short circuits or increases in applied voltage due to the formation of an insulating reaction layer even during repeated charging and discharging.

X-ray diffraction images of SE2 (550), SE2 (600), SE3 (550), SE3 (600) Temperature dependence of conductivity of SE2 (550), SE2 (600), SE3 (550), SE3 (600) Schematic cross-sectional diagram showing a measurement cell for charging test Charge and discharge measurement of SE2 (550) and SE3 (550) Constant current charge/discharge cycle measurement of SE1 (550), SE2 (550), SE3 (550) X-ray diffraction images of SE4 (600-10), SE4 (600-2), SE5 (600-10), SE5 (600-2) Temperature dependence of conductivity of SE4 (600-10), SE4 (600-2), SE5 (600-10), SE5 (600-2) X-ray diffraction images of SE5 (550) and SE6 (550) Temperature dependence of conductivity of SE5 (550) and SE6 (550)

Embodiments of the present invention will be described in detail below. In addition, in the following description, "~" is used to include the numerical values described before and after it as a lower limit value and an upper limit value.

First, the present invention relates to a method for manufacturing a solid electrolyte having an argyrodite crystal structure containing Li element, P element, S element, and X element (X is a halogen) using a liquid phase. That the produced solid electrolyte has an argyrodite crystal structure can be confirmed by, for example, X-ray diffraction measurement (hereinafter also referred to as XRD) using CuKα radiation. The argyrodite crystal structure has strong diffraction peaks at 2θ=25.2±1.0 deg and 29.7±1.0 deg. Note that the diffraction peak of the argyrodite crystal structure is, for example, 2θ=15. It may also appear at 3±1.0deg, 17.7±1.0deg, 31.1±1.0deg, 44.9±1.0deg or 47.7±1.0deg. The argyrodite solid electrolyte of the present invention may have these peaks.

The argyrodite solid electrolyte of the present invention contains Li element, P element, S element, and X element (X is halogen). Examples of the X element include F element, Cl element, Br element, and I element. The number of X elements may be one or two or more. As a compositional formula, for example, distinguishing the type of X element and assuming X ¹ element (halogen 1) and X ² element (halogen 2), Li _7-y-z PS _6-y-z X ¹ _y X ² _z ( y≧0, Z≧0, 1≦y+z≦1.8). Specifically, Li ₆ PS ₅ Cl, Li ₆ PS ₅ Br, Li ₆ PS ₅ I, Li ₆ PS ₅ Cl _0.75 Br _0.25 , Li ₆ PS ₅ Cl _0.5 Br _0.5 , Li ₅ Examples include, but are not limited to, _.75 PS _4.75 Cl _1.25 and Li _5.5 PS _4.5 Cl _1.5 .

The method for producing a solid electrolyte of the present invention includes a precursor liquid preparation step of preparing a raw material precursor liquid for solid electrolyte production, and a desolvation step of dissolving the raw material precursor liquid for solid electrolyte production prepared by the precursor liquid preparation step. and a step of heat-treating the dried product obtained by the desolvation step.

In addition, in the method for producing a solid electrolyte of the present invention, it is preferable that a material having an ether bond and a solvent and a material having an alcoholic OH group and a solvent are not included in any step.

The precursor liquid preparation process will be explained. The precursor liquid preparation step includes Li element, P element, and S element in a solvent containing at least an aprotic polar solvent that does not contain an ether bond, and the molar ratio of each element is (3+a):1:(4+b)( 0≦a≦2, 0≦b≦1) A first precursor dispersion preparation step of preparing a first precursor dispersion in which the material of 0≦a≦2, 0≦b≦1) is dispersed; a second precursor dispersion preparation step of preparing a second precursor dispersion in which LiX is dispersed; and mixing the first precursor dispersion and the second precursor dispersion. and a mixing step.

In Patent Document 1, the raw materials are mixed all at once for synthesis, but in the present invention, the dispersion is prepared separately in a first precursor dispersion preparation step and a second precursor dispersion preparation step. Then mix. Using Li ₂ S, P ₂ S ₅ and LiCl as raw materials, this synthesis can be expressed as 5Li ₂ S+P ₂ S ₅ +2LiCl→2Li ₆ PS ₅ Cl, but after 2Li ₃ PS ₄ +2Li ₂ S+2LiCl , Li ₆ PS ₅ Cl have been synthesized. In the present invention, by forming Li ₃ PS ₄ or its precursor in advance in the first precursor dispersion preparation step, the stability of the synthesis is significantly improved compared to the method of synthesizing by mixing all at once. are doing.

In the first precursor dispersion preparation step, an aprotic polar solvent containing at least no ether bond is used. Other solvents may be used in combination as long as they do not inhibit the production of the argyrodite solid electrolyte, but in that case, it is preferable not to include a solvent having an ether bond or a solvent having an alcoholic OH group. In the present invention, an aprotic polar solvent that does not contain an ether bond refers to a solvent that does not contain an ether bond in its molecule, does not have proton donating properties, and has a dielectric constant of 20 or more, such as acetonitrile, propionitrile, benzonitrile, etc. , dimethylformamide, dimethyl sulfoxide and the like. Among these, acetonitrile is preferred. In Non-Patent Document 2, tetrahydrofuran containing an ether bond is used, but the ether bond opens and reacts with P ₂ S ₅ to generate PO ₄ ^3- . In the present invention, by using an aprotic polar solvent that does not contain an ether bond, Li ₃ PS ₄ or its precursor is formed without generating PO ₄ ^3- . The aprotic polar solvent that does not contain an ether bond preferably accounts for 30% by mass or more of the solvent used in the first precursor dispersion, and should preferably account for 60% by mass or more except when pyridine, which will be described later, is used in combination. More preferably, it is 80% by mass or more.

In the first precursor dispersion preparation step, the solvent containing at least an aprotic polar solvent containing no ether bond contains Li element, P element, and S element, and the molar ratio of each element is (3+a): A material satisfying 1:(4+b) (0≦a≦2, 0≦b≦1) is dispersed. As mentioned above, in the first precursor dispersion liquid, Li ₃ PS ₄ or its precursor is formed, so the molar ratio of each element of Li element, P element, and S element is 3:1: However, since the second precursor dispersion liquid also contains Li elements and P elements, a part of it is added to the first dispersion liquid to the extent that it does not inhibit the formation of Li ₃ PS ₄ or its precursor. It may be included in the precursor dispersion preparation process. The range is 0≦a≦2, 0≦b≦1.

Raw materials used for materials containing Li, P, and S elements include lithium (Li), sulfur (S), phosphorus (P), lithium sulfide (Li ₂ S), and diphosphorus pentasulfide (P ₂ S ₅ ), Li ₃ PS ₄ , but are not limited to these. However, it is preferable that materials having ether bonds and materials having alcoholic OH groups are not included. Among them, it is preferable to use lithium sulfide (Li ₂ S) and diphosphorus pentasulfide (P ₂ S ₅ ). Further, materials containing other elements may be included as long as they do not inhibit the production of the argyrodite solid electrolyte. The concentration of the raw material in the first precursor dispersion is not particularly limited, but it is preferably in the range of 0.1 to 30% by mass, more preferably in the range of 0.5 to 15% by mass. If the concentration is low, productivity will be poor. If the concentration is high, unreacted substances may be produced.

In the first precursor dispersion preparation step, it is preferable to use pyridine as a solvent or to heat and stir the mixture in order to improve the stability of the synthesis.

The case where pyridine is used in combination as a solvent will be explained. We believe that the combined use of pyridine improves the solubility of the raw materials and further improves the stability of the synthesis. When pyridine is used in combination in the first precursor dispersion preparation step, a dispersion in which P ₂ S ₅ is dispersed in a solvent containing at least pyridine and a solvent containing at least an aprotic polar solvent that does not contain an ether bond. It is more preferable to use a step of mixing with a dispersion liquid in which Li ₂ S is dispersed. The concentration of the raw materials in each dispersion is not particularly limited, but is preferably in the range of 0.1 to 30% by mass, more preferably in the range of 0.5 to 15% by mass. Further, the amount of pyridine and the aprotic polar solvent used in each dispersion is preferably 60% by mass or more, more preferably 80% by mass or more of the total solvent in each dispersion.

The case of heating and stirring in the first precursor dispersion preparation step will be described. We believe that heating and stirring improves the solubility of the raw materials and further improves the stability of the synthesis. As the stirring method, conventionally known methods can be used, such as a method using a magnetic stirrer or a method in which a stirring blade such as a propeller, paddle, or disk turbine is attached to a shaft and rotated by a motor. The heating temperature is preferably 40° C. or higher and lower than the boiling point of the solvent with the lowest boiling point among the solvents contained. In the case of acetonitrile, the temperature is preferably 40°C or more and 80°C or less, more preferably 60°C or more and 80°C or less. The stirring time is preferably 1 to 100 hours, more preferably 12 to 72 hours.

The second precursor dispersion preparation step is a step of dispersing at least LiX in a solvent containing at least a thiol solvent. The thiol solvent is a solvent having a structure represented by R-SH (R is an organic group), and includes, for example, ethanethiol, 1-propanethiol, 2-propanethiol, 1-butanethiol, and 2-butanethiol. be able to. Among these, 1-propanethiol and 2-propanethiol are preferred. In Non-Patent Document 2, an alcohol-based solvent is used, and the alcohol-based solvent reacts with P ₂ S ₅ to generate PO ₄ ^3- . Thiol-based solvents have properties similar to alcohol-based solvents, but in the present invention, even when a thiol-based solvent reacts with P ₂ S ₅ , PS ₄ ^3- is produced, and this is the argyrodite produced in the present invention. It is a component of a solid electrolyte with a type crystal structure and has no adverse effects. Further, other solvents may be used in combination as long as they do not inhibit the production of the argyrodite solid electrolyte, but in that case, it is preferable not to include a solvent having an ether bond or a solvent having an alcoholic OH group.

The raw materials used in the second precursor dispersion preparation step include LiX and, if necessary, Li ₂ S, lithium, and sulfur. Note that other materials may be included as long as they do not inhibit the production of the argyrodite solid electrolyte, but in that case, it is preferable not to include materials having ether bonds and materials having alcoholic OH groups. The amount added is determined by the dispersion obtained in the first precursor dispersion preparation step and the second precursor dispersion preparation step so that the composition of the solid electrolyte having the desired argyrodite crystal structure is obtained. It is prepared by taking into consideration the mixing ratio when mixing with the dispersion liquid and the concentration of each element contained in the dispersion liquid obtained in the first precursor dispersion preparation step. At this time, the concentration of the dispersion obtained in the second precursor dispersion preparation step is not particularly limited, but it is preferably 0.1 to 30% by mass, and preferably in the range of 0.5 to 15% by mass. It is more preferable. If the concentration is low, productivity will be poor. If the concentration is high, unreacted substances may be produced. The thiol solvent preferably accounts for 30% by mass or more of the solvent used in the second precursor dispersion, and more preferably 60% by mass or more, and 80% by mass or more, except when pyridine is used in combination as described below. Most preferably.

In the second precursor dispersion preparation step, it is preferable to use pyridine as a solvent or to heat and stir the mixture in order to improve the stability of the synthesis.

The case where pyridine is used in combination as a solvent will be explained. We believe that the solubility of raw materials may be improved by using pyridine in combination, or that pyridine's basicity may trap halogen atoms, contributing to synthesis stability. When pyridine is used in combination, the pyridine solvent and the thiol solvent are each preferably at least 30% by mass, more preferably at least 40% by mass, based on the entire solvent of the second precursor dispersion.

The case of heating and stirring in the second precursor dispersion preparation step will be described. We believe that heating and stirring improves the solubility of the raw materials and further improves the stability of the synthesis. As the stirring method, conventionally known methods can be used, such as a method using a magnetic stirrer or a method in which a stirring blade such as a propeller, paddle, or disk turbine is attached to a shaft and rotated by a motor. The heating temperature is preferably 40° C. or higher and lower than the boiling point of the solvent with the lowest boiling point among the solvents contained. In the case of 1-propanethiol, the temperature is preferably 40°C or more and 65°C or less, more preferably 45°C or more and 55°C or less. The stirring time is preferably 1 to 100 hours, more preferably 12 to 72 hours.

A mixing step of mixing the dispersion obtained in the first precursor dispersion preparation step and the dispersion obtained in the second precursor dispersion preparation step will be described. The dispersion obtained in the first precursor dispersion preparation step and the dispersion obtained in the second precursor dispersion preparation step are mixed in a ratio that provides a composition of a solid electrolyte having a desired argyrodite crystal structure. Mix. The mixed liquid is preferably stirred in order to uniformly mix both dispersions. As the stirring method, the method described in the stirring method in the first precursor dispersion preparation step can be used. If pyridine is not used in combination in either the first precursor dispersion preparation step or the second precursor dispersion preparation step, it is preferable to heat during stirring in the mixing step, and the temperature is 40°C. The temperature is preferably at least 0.degree. C. and below the boiling point of the solvent with the lowest boiling point among the solvents included. When 1-propanethyl is used, the temperature is preferably 40°C or more and 65°C or less, more preferably 45°C or more and 55°C or less. The stirring time is preferably 1 to 100 hours, more preferably 12 to 72 hours.

The desolvation process of desoluting the solid electrolyte manufacturing raw material precursor liquid prepared in the precursor liquid preparation process will be described. The desolvation step is a step of removing the solvent contained in the raw material composition for producing a solid electrolyte, and heating, reduced pressure, etc. can be used. The temperature when heating is preferably 60°C to 180°C, more preferably 70°C to 150°C. For reducing the pressure, a method using a conventionally known vacuum drying device can be used. A method that uses both heating and reduced pressure can also be preferably used.

The process of heat-treating the dried product obtained by the desolvation process will be described. This is a step of crystallizing the dry solid obtained by heat-treating the dry solid obtained by the desolvation step to obtain a solid electrolyte having an argyrodite crystal structure. In addition, it is also preferable to subject the dried product obtained by the desolvation step to pressure molding before performing the heat treatment. The pressurizing conditions are, for example, 20 to 150 MPa. The heat treatment conditions can be any conditions as long as they can produce a solid electrolyte having an argyrodite crystal structure, but the temperature is preferably 400 to 700°C, more preferably 500 to 650°C, and the heat treatment time is preferably 0.5°C. ~24 hours, more preferably 1 to 15 hours.

Although the atmosphere in each step in the manufacturing method of the present invention is not particularly limited, it is preferably composed of dry inert gas such as dry nitrogen gas or dry argon gas, dry air, or the like.

The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples.
1. Manufacturing raw materials The raw materials used for manufacturing the solid electrolyte are as follows.
1-1. Diphosphorus pentasulfide (P ₂ S ₅ ) powder “P ₂ S ₅ ” (trade name) manufactured by Merck was used. Purity is 99%.
1-2. Lithium sulfide (Li ₂ S) powder "Li ₂ S" (trade name) manufactured by Mitsuwa Chemical Co., Ltd. was used. Purity is 99.9%.
1-3. Lithium chloride (LiCl) powder "LiCl" (trade name) manufactured by Sigma-Aldrich was used. Purity is 99%.
1-4. Acetonitrile "Acetonitrile (super dehydration)" (trade name) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. was used. Purity is 99.9%.
1-5. Tetrahydrofuran "Tetrahydrofuran (anhydrous)" (trade name) manufactured by Sigma-Aldrich was used. Purity is 99.9%.
1-6. Ethanol "Ethanol (super dehydrated)" (trade name) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. was used. Purity is 99.5%.
1-7.1-Propanethiol “1-Propanethiol” (trade name) manufactured by Tokyo Kasei Kogyo Co., Ltd. was used. Purity is 98%.
1-8. Pyridine "Pyridine (anhydrous)" (trade name) manufactured by Sigma-Aldrich was used. Purity is 99.8%.

(Comparative Example 1; Production of solid electrolyte SE1 by milling treatment)
Lithium sulfide powder, diphosphorus pentasulfide powder, and lithium chloride powder were weighed out in a molar ratio of 5:1:2, totaling 1 g, and mixed using an agate mortar. Next, the mixed powder was placed in a planetary ball mill manufactured by Frisch (container: made of zirconia) together with zirconia balls having a diameter of 10 mm, and mechanical milling was performed (rotation speed: 600 rpm, 20 hours). The milled powder was collected. At this time, it took a great deal of effort to recover the powder that adhered strongly to the zirconia balls and containers, and the entire amount could not be completely recovered. The collected powder was uniaxially pressed at 127 MPa and pelletized. The obtained pellets were heat-treated at 550° C. for 10 hours to obtain solid electrolyte SE1 (550). The solid electrolyte of this example was produced in a dry argon gas atmosphere.

(Comparative Example 2; Production of solid electrolyte SE2 by liquid phase method using tetrahydrofuran and ethanol)
Weighed 0.275 g of lithium sulfide powder and 0.141 g of diphosphorus pentasulfide powder so that the molar ratio of Li, P, and S was 3:1:4, and added them to 10 ml of tetrahydrofuran solvent. The mixture was stirred at 25° C. for 24 hours using a magnetic stirrer to obtain a first precursor dispersion. Next, 0.171 g of lithium sulfide powder and 0.158 g of lithium chloride powder were weighed and added to 10 ml of ethanol solvent, and then stirred using a magnetic stirrer at 25°C for 24 hours. A precursor dispersion liquid was obtained. The obtained first precursor dispersion liquid and second precursor dispersion liquid were mixed and then stirred at 50° C. for 24 hours to obtain a raw material precursor liquid for solid electrolyte production.

Thereafter, the raw material precursor liquid for solid electrolyte production was dried under reduced pressure (80° C., 12 hours) using a diaphragm pump (manufactured by Buchi, V-700 vacuum pump) to remove the solvent and obtain a dry solid. The obtained dried product was uniaxially pressed at 127 MPa to form pellets. The obtained pellets were heat-treated at 550° C. for 10 hours to obtain solid electrolyte SE2 (550). Solid electrolyte SE2 (600) was obtained in the same manner except that the heat treatment temperature was 600°C. The solid electrolyte of this example was produced in a dry argon gas atmosphere.

(Example 1; Present invention; Production of solid electrolyte SE3 by liquid phase method using acetonitrile and 1-propanethiol)
Weighed 0.275 g of lithium sulfide powder and 0.141 g of diphosphorus pentasulfide powder so that the molar ratio of Li, P and S was 3:1:4, and added them to 10 ml of acetonitrile solvent. The mixture was stirred at 75° C. for 24 hours using a magnetic stirrer to obtain a first precursor dispersion. Next, 0.171 g of lithium sulfide powder and 0.158 g of lithium chloride powder were weighed and added to 10 ml of 1-propanethiol solvent, and then stirred using a magnetic stirrer at 50 ° C. for 24 hours. A second precursor dispersion was obtained. The obtained first precursor dispersion liquid and second precursor dispersion liquid were mixed and then stirred at 50° C. for 24 hours to obtain a raw material precursor liquid for solid electrolyte production.

Thereafter, the raw material precursor liquid for solid electrolyte production was dried under reduced pressure (80° C., 12 hours) using a diaphragm pump (manufactured by Buchi, V-700 vacuum pump) to remove the solvent and obtain a dry solid. The obtained dried product was uniaxially pressed at 127 MPa to form pellets. The obtained pellets were heat treated at 550° C. for 10 hours to obtain solid electrolyte SE3 (550). Solid electrolyte SE3 (600) was obtained in the same manner except that the heat treatment temperature was 600°C. The solid electrolyte of this example was produced in a dry argon gas atmosphere.

(X-ray diffraction measurement)
For SE2 (550), SE2 (600), SE3 (550), and SE3 (600), X-ray diffraction measurement (diffraction angle 2θ = 10° to 70 1, sampling width 0.02°, and scanning speed 5°/min) to obtain the X-ray diffraction image shown in FIG. It can be seen that both have an argyrodite crystal structure of Li ₆ PS ₄ Cl, but while SE2 (550) and SE2 (600) also include a Li ₃ PO ₄ structure, SE3 (by the manufacturing method of the present invention) It can be seen that Li ₃ PO ₄ is not included in SE3 (600) and SE3 (600).

(Conductivity measurement)
SE2 (550), SE2 (600), SE3 (550), and SE3 (600) were made into disk-shaped test pieces (size: radius 5 mm x height 0.6 mm) using a uniaxial hydraulic press machine, and argon In a gas atmosphere, a ribbon heater connected to a temperature controller and a heat insulator are wrapped around the measurement unit (glass container) while it is placed in the measurement unit (glass container). The conductivity was measured at 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 110°C, and 130°C by gradually heating from room temperature (25°C). The conductivity was measured after the test piece was kept at each of the above temperatures starting from the low temperature side and allowed to stand for 1 hour.

A graph of the temperature dependence of conductivity is shown in FIG. The conductivity at room temperature (25° C.) was 1.80 mS/cm for SE2 (550) and 1.47 mS/cm for SE2 (600). On the other hand, SE3 (550) had a conductivity of 2.75 mS/cm, and SE3 (600) had a conductivity of 2.13 mS/cm, indicating that SE3 produced by the manufacturing method of the present invention had a higher conductivity than SE2.

(Charge/discharge test)
As a positive electrode composite, titanium sulfide (TiS ₂ ) and SE2 (550) were weighed at a mass ratio of 1:1 and mixed using an agate mortar to obtain a positive electrode composite.

Next, SE2 (550) was pressure-molded using a uniaxial hydraulic press machine to obtain a disk-shaped preform (radius: 5 mm, thickness: 0.5 mm). Then, while this preformed body for the electrolyte layer was housed inside a cylindrical body made of polyetheretherketone (PEEK), about the entirety of one surface side of the preformed body for the positive electrode obtained above was applied. 5 mg was filled, and pressure molding was performed using a uniaxial hydraulic press machine. Furthermore, a Li-In alloy foil (thickness 0.1 mm, diameter 5 mm) was pasted on the other surface of the preformed body for electrolyte layer, and a positive electrode 21 (thickness approximately 30 μm) consisting of a positive electrode composite and SE2 were attached. An all-solid-state lithium-sulfur battery 20 was obtained, including an electrolyte layer 25 made of (550) and a negative electrode 23 made of a Li--In alloy.

Thereafter, conductive parts made of stainless steel and nickel were inserted from both sides of the cylindrical body housing this lithium-sulfur battery 20, and fixed with a jig to obtain the measurement cell 10 shown in FIG. 3. Then, this measurement cell 10 was sealed in a glass container (not shown), the gas in the glass container was replaced with argon gas, and a charging test was conducted. The charging test was conducted using a charge/discharge device "BTS-2004H" (model name) manufactured by NAGANO under conditions of 1.0-2.4V vs. Li-In, C rate: 0.1C. A similar test was conducted on SE3 (550). The results are shown in FIG.

The charge capacity of SE2 (550) was 182.8 mAh·g ⁻¹ per unit weight of TiS ₂ , and the discharge capacity was 197.86 mAh·g ⁻¹ . On the other hand, the charging capacity of SE3 (550) is 221.73 mAh g ^-1 and the discharging capacity is 222.38 mAh g ^-1 , and SE3 produced by the manufacturing method of the present invention is higher than SE2, with a theoretical capacity of 236 mAh g -1. It exhibited a charge/discharge capacity close to g ⁻¹ .

(Constant current charge/discharge cycle test)
Using electrode SE2 (550), a symmetrical structure was obtained in the same manner except that Li foil was used for both the positive electrode 21 made of the positive electrode composite and the negative electrode 23 made of Li-In alloy in the charge/discharge test. I got a cell. Using the charge/discharge device "BTS-2004H" (model name) manufactured by NAGANO, the current intensity is ±0.1 mA cm ^-2 up to 100 cycles, 1 hour each for charging and discharging, and ±0.2 mA cm ^-2 after 100 cycles. The test was conducted as follows. Similar tests were conducted on SE1 (550) and SE3 (550). The results are shown in FIG.

SE1 (550) was shorted in 10 hours. SE2 (550) had an initial voltage of 21 mV, which increased to 154 mV in 200 hours. This seems to be due to the formation of an insulating reaction layer. SE3 (550) manufactured by the manufacturing method of the present invention had an initial voltage of 6 mV, and the voltage increased only to 13 mV even after 150 hours.

(Example 2; Present invention; Production of solid electrolytes SE4 and SE5 by liquid phase method using acetonitrile, 1-propanethol, and pyridine in combination)
0.141 g of diphosphorus pentasulfide powder was weighed out, added to 5 ml of pyridine solvent, and stirred at room temperature (25° C.) for 1 hour using a magnetic stirrer. 0.428 g of lithium sulfide powder was weighed out, added to 5 ml of acetonitrile solvent, and stirred at room temperature (25° C.) for 1 hour using a magnetic stirrer. These were mixed and further stirred at room temperature (25°C) for 24 hours using a magnetic stirrer to obtain a first precursor dispersion. The molar ratio of Li, P and S in the first precursor dispersion is 5:1:5. Next, 0.158 g of lithium chloride powder was weighed out, added to a mixed solvent of 5 ml of pyridine solvent and 5 ml of 1-propanethiol solvent, and stirred using a magnetic stirrer at room temperature (25° C.) for 24 hours. , a second precursor dispersion was obtained. The obtained first precursor dispersion liquid and second precursor dispersion liquid were mixed and then stirred at room temperature (25° C.) for 24 hours to obtain a raw material precursor liquid for producing a solid electrolyte. The molar ratio of Li, P, S, and Cl in the raw material precursor liquid for solid electrolyte production is 6:1:5:1.

Thereafter, the raw material precursor liquid for solid electrolyte production was dried under reduced pressure (80° C., 12 hours) using a diaphragm pump (manufactured by Buchi, V-700 vacuum pump) to remove the solvent and obtain a dry solid. The obtained dried product was uniaxially pressed at 127 MPa to form pellets. The obtained pellets were heat treated at 600° C. for 10 hours to obtain solid electrolyte SE4 (600-10). Solid electrolyte SE4 (600-2) was obtained in the same manner except that the heat treatment time was changed to 2 hours. The solid electrolyte of this example was produced in a dry argon gas atmosphere.

Furthermore, a solid was prepared in the same manner except that the weight of the raw materials was adjusted so that the molar ratio of Li, P, S, and Cl in the raw material precursor liquid for solid electrolyte production was 5.5:1:4.5:1.5. Electrolyte SE5 (600-10) was obtained. Furthermore, a solid electrolyte SE5 (600-2) was obtained in the same manner except that the heat treatment time was changed to 2 hours.

(X-ray diffraction measurement)
X-ray diffraction measurement ( Diffraction angle 2θ=10° to 70°, sampling width 0.02°, scanning speed 5°/min) was performed to obtain the X-ray diffraction image shown in FIG. It can be seen that both electrolytes have an argyrodite crystal structure and do not contain Li ₃ PO ₄ .

(Conductivity measurement)
Ionic conductivity measurements were performed on SE4 (600-10), SE4 (600-2), SE5 (600-10), and SE5 (600-2) in the same manner as SE2 (550). A graph of the temperature dependence of conductivity is shown in FIG. The conductivity at room temperature (25°C) is 4.76 mS/cm for SE4 (600-10), 2.11 mS/cm for SE4 (600-2), 5.41 mS/cm for SE5 (600-10), and 5.41 mS/cm for SE5 ( 600-2) was 1.82 mS/cm, showing higher conductivity than SE2. Note that in these examples, in addition to ionic conduction, some electronic conduction behavior was also observed. It is possible that some of the solvent remained during the desolvation process and was carbonized.

(Example 3; Present invention; Production of solid electrolytes SE5 and SE6 in which the addition of lithium sulfide was changed from Example 1)
In Example 1, the amount of lithium sulfide added was 0.324 g so that the molar ratio of Li, P, and S in the first precursor dispersion was 4:1:4.5, and the amount of lithium sulfide added was 0.324 g. Same as above except that the amount of lithium sulfide added in the dispersion for solid electrolyte production was 0.086 g (the molar ratio of Li, P, S and Cl in the raw material precursor liquid for solid electrolyte production was 6:1:5:1). The conditions for the heat treatment step were 550° C. for 10 hours) to obtain solid electrolyte SE5 (550).

Furthermore, in Example 1, the amount of lithium sulfide added was set to 0.428 g so that the molar ratio of Li, P, and S in the first precursor dispersion was 5:1:5, and the second precursor dispersion was Same as above except that the amount of lithium sulfide added in the dispersion for solid electrolyte production was 0 g (the molar ratio of Li, P, S and Cl in the raw material precursor liquid for solid electrolyte production was 6:1:5:1). The process conditions were 550° C. for 10 hours) to obtain solid electrolyte SE6 (550).

(X-ray diffraction measurement)
For SE5 (550) and SE6 (550), X-ray diffraction measurement (diffraction angle 2θ = 10° to 70°, sampling width 0.02°, scan The X-ray diffraction image shown in FIG. 8 was obtained. It can be seen that both electrolytes have an argyrodite crystal structure and do not contain Li ₃ PO ₄ .

(Conductivity measurement)
Regarding SE5 (550) and SE6 (550), ionic conductivity measurements were performed in the same manner as SE2 (550) and the like. A graph of the temperature dependence of conductivity is shown in FIG. The conductivity at room temperature (25° C.) was 2.21 mS/cm for SE5 (550) and 2.37 mS/cm for SE6 (550), which showed higher conductivity than SE2.

10: Charging test measurement cell 20: Lithium sulfur battery 21: Positive electrode 23: Negative electrode 25: Electrolyte layer 27: PEEK cylindrical body 31: Holding plate 33: Holding pin 35: Tightening screw 37: Kapton (registered trademark) tape

Claims (5)

A method for producing a solid electrolyte having an argyrodite crystal structure containing Li element, P element, S element and X element (X is a halogen) in a liquid phase, the method comprising:
a precursor liquid preparation step of preparing a raw material precursor liquid for solid electrolyte production; a desolution step of desoluting the raw material precursor liquid for solid electrolyte production prepared by the precursor liquid preparation step; and a step of heat treating the dry matter,
The precursor liquid preparation step includes:
A solvent containing an aprotic polar solvent that does not contain at least an ether bond contains Li element, P element, and S element, and the molar ratio of each element is (3+a):1:(4+b) (0≦a≦2, A first precursor dispersion preparation step of preparing a first precursor dispersion in which a material satisfying 0≦b≦1) is dispersed;
a second precursor dispersion preparation step of preparing a second precursor dispersion in which at least LiX is dispersed in a solvent containing at least a thiol-based solvent;
A method for producing a solid electrolyte having an argyrodite crystal structure, comprising a mixing step of mixing the first precursor dispersion and the second precursor dispersion.
The argyrodite-type crystal according to claim 1, wherein the solvent used in either or both of the first precursor dispersion preparation step and the second precursor dispersion preparation step contains pyridine. A method for producing a solid electrolyte having a structure.
The first precursor dispersion preparation step includes dispersing P ₂ S ₅ in a solvent containing at least pyridine and dispersing Li ₂ S in a solvent containing at least an aprotic polar solvent that does not contain an ether bond. 3. The method for producing a solid electrolyte having an argyrodite-type crystal structure according to claim 1 or 2, further comprising the step of mixing the solid electrolyte with a dispersion liquid obtained by preparing a solid electrolyte.
Either or both of the first precursor dispersion preparation step and the second precursor dispersion preparation step is performed at a temperature of 40°C or higher and below the boiling point of the solvent with the lowest boiling point among the solvents contained. The method for producing a solid electrolyte having an argyrodite crystal structure according to claim 1, further comprising the step of:
According to claims 1 to 4, each step included in the precursor liquid preparation step does not contain a material having an ether bond or a solvent, and does not contain a material having an alcoholic OH group or a solvent. A method for producing a solid electrolyte having an argyrodite crystal structure as described above.

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