Methods for manufacturing sulfide solid electrolytes, all-solid-state batteries, and sulfide solid electrolytes

Abstract

The main objective of this disclosure is to provide a sulfide solid electrolyte with good water resistance. This disclosure addresses the aforementioned problem by providing a sulfide solid electrolyte containing Li, Ge, P, and S, and exhibiting an LGPS-type crystal phase. When X-ray photoelectron spectroscopy is performed on the surface of the aforementioned sulfide solid electrolyte, Ge... 2+ It accounts for more than 20% of the total amount of Ge.

Description

Technical Field

[0001] This disclosure relates to sulfide solid electrolytes. Background Technology

[0002] All-solid-state batteries are batteries with a solid electrolyte layer between the positive and negative electrode active material layers. Compared to liquid-based batteries with electrolytes containing flammable organic solvents, they offer the advantage of simplified safety devices. Sulfide solid electrolytes are known as solid electrolytes used in all-solid-state batteries. Among sulfide solid electrolytes, LGPS-based sulfide solid electrolytes are known as materials with high Li-ion conductivity.

[0003] For example, Patent Document 1 discloses a method for manufacturing an LGPS-based solid electrolyte, which includes a step of mixing Li3PS4 crystals and Li4MS4 crystals (M = Ge, Si, Sn) in a crystalline state to synthesize a precursor; and a step of heat-treating the precursor at 300–700°C. Additionally, Patent Documents 2–4 also disclose LGPS-based sulfide solid electrolytes.

[0004] Existing technical documents

[0005] Patent Document 1: International Publication No. 2018 / 173939

[0006] Patent Document 2: Japanese Patent Application Publication No. 2017-021965

[0007] Patent Document 3: Japanese Patent Application Publication No. 2019-501105

[0008] Patent Document 4: International Publication No. 2019 / 044517 Summary of the Invention

[0009] While LGPS-based sulfide solid electrolytes are materials with high Li-ion conductivity, this conductivity decreases due to moisture content in the atmosphere. Therefore, improved water resistance is desirable. This disclosure was made in view of the above, and its main objective is to provide a sulfide solid electrolyte with good water resistance.

[0010] This disclosure provides a sulfide solid electrolyte, which is a sulfide solid electrolyte containing Li, Ge, P, and S and having an LGPS-type crystal phase. When X-ray photoelectron spectroscopy is performed on the surface of the above-mentioned sulfide solid electrolyte, Ge... 2+ It accounts for more than 20% of the total amount of Ge.

[0011] According to this disclosure, due to Ge 2+ The ratio relative to the total amount of Ge is specified, thus a sulfide solid electrolyte with good water resistance can be produced.

[0012] In the aforementioned disclosure, the aforementioned Ge 2+ The proportion can also be below 92%.

[0013] In the aforementioned disclosure, the aforementioned Ge 2+ The proportion can also be above 49%.

[0014] In the aforementioned disclosure, the aforementioned Ge 2+ The proportion can also be above 55% and below 90%.

[0015] In the aforementioned disclosure, the aforementioned Ge 2+ The proportion can also be over 94%.

[0016] In the aforementioned disclosure, the aforementioned Ge 2+ The proportion can also be 100%.

[0017] In addition, this disclosure provides an all-solid-state battery having a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, wherein at least one of the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer contains the sulfide solid electrolyte.

[0018] According to this disclosure, by using the above-described sulfide solid electrolyte, an all-solid-state battery that can maintain its output characteristics can be manufactured even in environments such as high humidity.

[0019] In addition, this disclosure provides a method for manufacturing a sulfide solid electrolyte, which includes a preparation step and a calcination step. The preparation step is a step of preparing a precursor containing Li, Ge, P and S. The calcination step is a step of calcining the precursor in an atmosphere containing at least one of nitrogen and a rare gas to form the LGPS type crystal phase.

[0020] According to this disclosure, a sulfide solid electrolyte with good water resistance can be obtained by firing under a specified gas atmosphere.

[0021] In the above disclosure, the gas may also contain the nitrogen gas.

[0022] In the above disclosure, the gas may also contain argon as the rare gas.

[0023] In the above disclosure, the gas may also contain oxidizing gases.

[0024] In the above disclosure, the gas may also contain reducing gases.

[0025] In the above disclosure, the firing process may also include a first firing treatment and a second firing treatment. The first firing treatment fires the precursor in an atmosphere containing argon as a first gas, and the second firing treatment fires the precursor after the first firing treatment in an atmosphere containing nitrogen as a second gas.

[0026] In the aforementioned disclosure, the precursor may also be a sulfide glass.

[0027] In this disclosure, there is an effect of providing a sulfide solid electrolyte with good water resistance. Attached Figure Description

[0028] Figure 1 This is a schematic cross-sectional view illustrating the all-solid-state battery of this disclosure.

[0029] Figure 2 This is a flowchart illustrating a method for manufacturing a sulfide solid electrolyte according to the present disclosure.

[0030] Figure 3 The results are obtained by XPS measurement of the sulfide solid electrolyte prepared in Example 2.

[0031] Figure 4 It means Ge 2+ A graph showing the relationship between the proportion of Li and the conductivity of Li ions after exposure tests.

[0032] Explanation of reference numerals in the attached figures

[0033] 1…Positive electrode active material layer

[0034] 2…Negative electrode active material layer

[0035] 3… Solid electrolyte layer

[0036] 4…Positive current collector

[0037] 5… Negative current collector

[0038] 6…battery casing

[0039] 10… All-solid-state batteries Detailed Implementation

[0040] The following provides a detailed description of the sulfide solid electrolyte, all-solid-state battery, and manufacturing method of the sulfide solid electrolyte disclosed herein.

[0041] A. Sulfide solid electrolytes

[0042] The sulfide solid electrolyte disclosed herein is a sulfide solid electrolyte containing Li, Ge, P, and S, and having an LGPS-type crystal phase. When X-ray photoelectron spectroscopy is performed on the surface of the above-mentioned sulfide solid electrolyte, Ge...2+ It accounts for more than 20% of the total amount of Ge.

[0043] According to this disclosure, Ge 2+ By maintaining a specified proportion relative to the total Ge content, a sulfide solid electrolyte with good water resistance can be produced. While sulfide solid electrolytes with an LGPS-type crystal phase are materials with high Li-ion conductivity, this conductivity decreases due to moisture content in the atmosphere. Therefore, improving water resistance is desirable. In this disclosure, Ge... 2+ By maintaining a predetermined ratio relative to the total amount of Ge, a sulfide solid electrolyte with good water resistance can be produced. Here, as described in the examples below, when the sulfide glass is sintered under vacuum, all Ge present on the particle surface is converted to Ge. 4+ . That is, Ge 2+ The proportion relative to the total amount of Ge (Ge 2+ The presence rate is 0%. In contrast, in this disclosure, for example, the Ge content can be controlled by adjusting the type of gas used during firing. 2+ The ratio. Specifically, a highly water-resistant reducing layer (Ge) is formed on the particle surface through the gas used during firing. 2+ By adjusting the type of gas, the reducing layer (Ge) can be controlled. 2+ The proportion of (layers). In this disclosure, by making Ge 2+ When the proportion is above the specified ratio, a sulfide solid electrolyte with good water resistance can be obtained. The reason for this good water resistance is presumably due to Ge... 2+ With Ge 4+ The better water resistance of GeS can also be attributed to the fact that GeS is less soluble in water than GeS2.

[0044] The sulfide solid electrolyte disclosed herein contains Li, Ge, P, and S. The total proportion of Li, Ge, P, and S relative to all elements contained in the sulfide solid electrolyte is, for example, 70 mol% or more, 80 mol% or more, or 90 mol% or more. Furthermore, the sulfide solid electrolyte may or may not contain halogens. In the former case, the sulfide solid electrolyte may contain only one halogen or two or more halogens. Examples of halogens include Cl, Br, and I.

[0045] The sulfide solid electrolyte of this disclosure has an LGPS-type crystalline phase. In this disclosure, the LGPS-type crystalline phase is a crystalline phase containing Li, Ge, P, and S. The LGPS-type crystalline phase exhibits typical peaks at 2θ = 20.18°±0.50°, 20.44°±0.50°, 26.96°±0.50℃, and 29.58°±0.50℃ in X-ray diffraction using CuKα rays. Additionally, the LGPS-type crystalline phase also exhibits peaks at 2θ = 17.38°±0.50°, 23.56°±0.50°, 23.96°±0.50℃, 24.93°±0.50℃, 29.07°±0.5℃, 31.71°±0.5℃, 32.66°±50℃, and 33.39°±0.50°. Furthermore, the positions of these peaks can vary depending on the composition of, for example, sulfide solid electrolytes, and are therefore specified within a range of ±0.50°. The positions of each peak can be within the range of ±0.30° or ±0.10°.

[0046] In addition, the LGPS type crystal phase typically has an octahedral O composed of Li and S elements (e.g., LiS6 octahedron) and a M-type crystal phase. 2a Element (M) 2a Tetrahedral T1 (e.g., GeS4 and PS4) composed of at least one of P and Ge and S elements, and tetrahedral T1 composed of M 2b Element (M) 2b It is a crystal phase consisting of tetrahedron T2 (e.g., PS4) and S elements (at least one of P and Ge), and tetrahedron T1 and octahedron O share an edge, while tetrahedron T2 and octahedron O share a vertex.

[0047] The sulfide solid electrolyte of this disclosure preferably contains an LGPS-type crystalline phase as the main phase. "Contains as the main phase" means that the LGPS-type crystalline phase has the largest proportion relative to all crystalline phases contained in the sulfide solid electrolyte. The proportion of the LGPS-type crystalline phase is, for example, 50% by weight or more, 70% by weight or more, or 90% by weight or more. Furthermore, the proportion of the aforementioned crystalline phase can be determined, for example, by radiometric XRD.

[0048] Furthermore, in this disclosure, when X-ray photoelectron spectroscopy is performed on the surface of the sulfide solid electrolyte, Ge 2+ It accounts for more than 20% of the total Ge content. 2+ The proportion relative to the total Ge can be above 49%, above 50%, above 55%, or above 60%. If Ge 2+ If the proportion of Ge relative to the total Ge is too small, the Li ion conductivity after moisture exposure may be lower. Additionally, Ge... 2+The ratio relative to the total amount of Ge can be 92% or less, 90% or less, or 85% or less. By making the ratio of Ge 2+ within the above range, the Li ion conductivity after moisture exposure becomes higher. As shown in the embodiments described later, when the ratio of Ge 2+ relative to the total amount of Ge is 49% or more and 92% or less (preferably 55% or more and 90% or less), the Li ion conductivity after moisture exposure is particularly high. Regarding the calculation method of the ratio of Ge 2+ relative to the total amount of Ge, it is described in the embodiments described later.

[0049] In addition, in the present disclosure, when performing X-ray photoelectron spectroscopy measurement on the surface of the sulfide solid electrolyte, the ratio of Ge 2+ relative to the total amount of Ge can be 77% or more, 92% or more, 94% or more, 96% or more, or 100%. By increasing the ratio of Ge 2+ the retention rate of the Li ion conductivity before and after moisture exposure becomes higher.

[0050] In addition, in the present disclosure, when performing X-ray photoelectron spectroscopy measurement on the surface of the sulfide solid electrolyte, the ratio of Ge 2+ relative to the total amount of Ge can be 45% or less. By making the ratio of Ge 2+ within the above range, the Li ion conductivity before moisture exposure becomes higher.

[0051] The composition of the sulfide solid electrolyte of the present disclosure is not particularly limited. The sulfide solid electrolyte can, for example, have a composition represented by αLiX·(1-α)(Li 4-x Ge 1-x P x S4) (X is one or more halogens, α satisfies 0≤α<1, and x satisfies 0<x<1). As X, for example, Cl, Br, and I can be cited. α can be 0 or greater than 0. In the latter case, α can be 0.1 or more, or 0.2 or more. In addition, α can be 0.5 or less, or 0.4 or less. x can be 0.5 or more, or 0.6 or more. In addition, x can be 0.8 or less, or 0.75 or less.

[0052] The sulfide solid electrolyte of the present disclosure preferably has a high Li ion conductivity. The Li ion conductivity (25°C) of the sulfide solid electrolyte is, for example, 1×10 -4 S / cm or more, or can also be 1×10 -3 S / cm or more. In addition, the sulfide solid electrolyte preferably has a high Li ion conductivity after a specified exposure test. The Li ion conductivity (25°C) after the exposure test is, for example, 1×10-4 S / cm or higher, or 1×10 -3 S / cm or higher.

[0053] The exposure test, as described in the examples below, involves placing a sulfide solid electrolyte in a glove box with the dew point controlled at -30°C for 6 hours, exposing the atmospheric moisture to the sulfide solid electrolyte. When the Li-ion conductivity before the exposure test is set as IC1, and the Li-ion conductivity after the exposure test is set as IC2, the IC2 / IC1 (the maintenance rate of Li-ion conductivity before and after the exposure test) is, for example, 27% or more, 56% or more, or 95% or more.

[0054] Examples of shapes for sulfide solid electrolytes include granular forms. The average particle size (D) of sulfide solid electrolytes... 50 For example, the particle size can be 0.1 μm or larger, 0.5 μm or larger, or 1 μm or larger. On the other hand, the average particle size (D) of sulfide solid electrolytes... 50 For example, it can be below 50 μm, or below 30 μm. Average particle size (D) 50 For example, it can be determined from the results of particle size distribution measurements using laser diffraction scattering.

[0055] The sulfide solid electrolyte of this disclosure has good Li-ion conductivity, and therefore can be used in any application requiring Li-ion conductivity. The sulfide solid electrolyte of this disclosure is preferably used in all-solid-state batteries. Furthermore, the manufacturing method of the sulfide solid electrolyte of this disclosure is not particularly limited, and an example can be found in "C. Manufacturing Method of Sulfide Solid Electrolyte" described later.

[0056] B. All-solid-state batteries

[0057] Figure 1 This is a schematic cross-sectional view illustrating the all-solid-state battery of this disclosure. Figure 1 The all-solid-state battery 10 shown includes: a positive electrode active material layer 1 containing a positive electrode active material, a negative electrode active material layer 2 containing a negative electrode active material, a solid electrolyte layer 3 disposed between the positive electrode active material layer 1 and the negative electrode active material layer 2, a positive electrode current collector 4 for collecting current from the positive electrode active material layer 1, a negative electrode current collector 5 for collecting current from the negative electrode active material layer 2, and a battery casing 6 housing these components. In this disclosure, one characteristic is that at least one of the positive electrode active material layer 1, the negative electrode active material layer 2, and the solid electrolyte layer 3 contains the aforementioned sulfide solid electrolyte.

[0058] According to this disclosure, by using the above-described sulfide solid electrolyte, it is possible to manufacture an all-solid-state battery that can maintain output characteristics even under conditions such as high humidity.

[0059] 1. Positive electrode active material layer

[0060] The positive electrode active material layer is a layer containing at least a positive electrode active material, and may also contain at least one of a solid electrolyte, a conductive material, and a binder, depending on the need. In particular, in this disclosure, the positive electrode active material layer preferably contains the aforementioned sulfide solid electrolyte. The proportion of the sulfide solid electrolyte contained in the positive electrode active material layer is, for example, 0.1% by volume or more, 1% by volume or more, or 10% by volume or more. On the other hand, the proportion of the sulfide solid electrolyte contained in the positive electrode active material layer is, for example, 80% by volume or less, 60% by volume or less, or 50% by volume or less. Furthermore, examples of positive electrode active materials include LiCoO2, LiMnO2, LiNiO2, and LiNiO2. 1 / 3 Co 1 / 3 Mn 1 / 3 Oxide active substances such as O2, LiVO2, LiCrO2, Li2NiMn3O8, LiFePO4, and LiCoPO4.

[0061] The positive electrode active material layer may contain a conductive material. Adding a conductive material can improve the electronic conductivity of the positive electrode active material layer. Examples of conductive materials include carbon materials such as acetylene black, Ketjen black, and carbon fiber. Additionally, the positive electrode active material layer may contain a binder. Examples of binders include fluorine-based binders such as polyvinylidene fluoride (PVDF). Furthermore, the thickness of the positive electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

[0062] 2. Negative electrode active material layer

[0063] The negative electrode active material layer is a layer containing at least a negative electrode active material, and may also contain at least one of a solid electrolyte, a conductive material, and a binder, depending on the need. In particular, in this disclosure, the negative electrode active material layer preferably contains the aforementioned sulfide solid electrolyte. The proportion of the sulfide solid electrolyte contained in the negative electrode active material layer is, for example, 0.1 vol% or more, 1 vol% or more, or 10 vol% or more. On the other hand, the proportion of the sulfide solid electrolyte contained in the negative electrode active material layer is, for example, 80 vol% or less, 60 vol% or less, or 50 vol% or less. Furthermore, examples of negative electrode active materials include, for example, metallic active materials and carbon active materials. Examples of metallic active materials include, for example, In, Al, Si, and Sn. On the other hand, examples of carbon active materials include, for example, mesophase carbon microspheres (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon.

[0064] Furthermore, the conductive materials and adhesives used in the negative electrode active material layer are the same as those used in the positive electrode active material layer. Additionally, the thickness of the negative electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

[0065] 3. Solid electrolyte layer

[0066] The solid electrolyte layer is disposed between the positive electrode active material layer and the negative electrode active material layer. Furthermore, the solid electrolyte layer is a layer containing at least a solid electrolyte, and may also contain a binder if necessary. In particular, in this disclosure, the solid electrolyte layer preferably contains the aforementioned sulfide solid electrolyte. The proportion of sulfide solid electrolyte contained in the solid electrolyte layer is, for example, 50% by volume or more, 70% by volume or more, or 90% by volume or more. Moreover, the binder used in the solid electrolyte layer is the same as that used in the positive electrode active material layer. Additionally, the thickness of the solid electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less.

[0067] 4. Other structures

[0068] The all-solid-state battery disclosed herein has at least the aforementioned positive electrode active material layer, solid electrolyte layer, and negative electrode active material layer. Furthermore, it typically includes a positive electrode current collector for collecting current from the positive electrode active material layer and a negative electrode current collector for collecting current from the negative electrode active material layer. Examples of materials for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. Examples of materials for the negative electrode current collector include SUS, copper, nickel, and carbon.

[0069] 5. All-solid-state batteries

[0070] The all-solid-state battery disclosed herein is typically an all-solid-state lithium-ion battery. Furthermore, an all-solid-state battery can be a primary battery or a secondary battery, but the latter is preferred. This is because it can be repeatedly charged and discharged, making it useful, for example, as a battery for automotive applications.

[0071] C. Manufacturing methods of sulfide solid electrolytes

[0072] Figure 2 This is a flowchart illustrating a method for manufacturing a sulfide solid electrolyte according to the present disclosure. Figure 2 First, a precursor containing Li, Ge, P, and S is prepared (preparation step). Next, the prepared precursor is calcined in a gas atmosphere containing at least one of nitrogen and a rare gas to form an LGPS-type crystalline phase (calcination step). This yields the aforementioned sulfide solid electrolyte.

[0073] According to this disclosure, a sulfide solid electrolyte with good water resistance can be obtained by firing under a specified gas atmosphere.

[0074] 1. Preparation process

[0075] The preparation process of the present disclosure is a process of preparing a precursor containing Li, Ge, P, and S. The precursor can be a raw material mixture, can be a sulfide glass, or can have an LGPS-type crystal phase.

[0076] First, the case where the precursor is a raw material mixture will be described. The precursor usually contains a Li source, a Ge source, a P source, and a S source. As the Li source, for example, Li单质 and lithium sulfide (such as Li2S) can be cited. As the Ge source, for example, Ge单质 and germanium sulfide (such as GeS2) can be cited. As the P source, for example, P单质 and phosphorus sulfide (such as P2S5) can be cited. As the S source, for example, S单质, lithium sulfide, germanium sulfide, and phosphorus sulfide can be cited. In addition, the raw material mixture can contain LiX (X is a halogen), or can not contain LiX.

[0077] The composition of the raw material mixture is not particularly limited. For example, the raw material mixture can have a composition represented by αLiX·(1-α)(Li 4- x Ge 1-x P x S4) (X is one or more than two kinds of halogens, α satisfies 0≤α<1, x satisfies 0<x<1). Regarding X, α, and x, the content is the same as that described in the above "A. Sulfide solid electrolyte". In addition, the raw material mixture can be obtained by mixing each raw material in a mixing device (such as an agate mortar).

[0078] Next, the case where the precursor is a sulfide glass will be described. The sulfide glass can be obtained, for example, by mechanically grinding the raw material mixture. As the mechanical grinding, for example, a ball mill, a vibration mill, a turbo mill, and a disk mill can be cited. In addition, the sulfide glass can be obtained, for example, by melt quenching the raw material mixture. The sulfide glass usually has an amorphous property. That is, a halo pattern is observed in the X-ray diffraction measurement of the sulfide glass. In addition, in the X-ray diffraction measurement of the sulfide glass, it can have peaks from the raw materials, or can not have peaks from the raw materials, but the latter is preferred because its amorphous property is higher.

[0079] Next, the case where the precursor has an LGPS-type crystal phase will be described. Such a precursor can be obtained, for example, by heat-treating the raw material mixture or the sulfide glass. The heat treatment temperature is, for example, 300°C or higher, can be 400°C or higher, and can also be 500°C or higher. In addition, the heat treatment temperature is, for example, 1000°C or lower, and can also be 700°C or lower. As the heat treatment atmosphere, for example, a reduced pressure atmosphere such as vacuum can be cited. The heat treatment time is, for example, 1 hour or more and 20 hours or less.

[0080] 2. Firing process

[0081] The sintering process of this disclosure involves sintering the aforementioned precursor in a gas atmosphere containing at least one of nitrogen and a rare gas to form the aforementioned LGPS-type crystal phase. In this disclosure, a specified gas is used to sinter the Ge on the particle surface. 4+ Restore to Ge 2+ , obtain Ge 2+ A high proportion of sulfide solid electrolytes. Furthermore, by adjusting the gas composition used during firing, the Ge... 2+ The proportion relative to the total amount of Ge.

[0082] The gas used during firing (atmosphere gas) contains at least one of nitrogen and a rare gas. Examples of rare gases include argon and helium. Nitrogen, compared to rare gases, will... 4+ Restore to Ge 2+ The reducing power is weak. Furthermore, in this disclosure, nitrogen and rare gases are referred to as reference gases. The proportion of the reference gas in the atmosphere gas is, for example, 90% by volume or more, 95% by volume or more, or 99% by volume or more.

[0083] In addition, the atmospheric gas may contain oxidizing gases. By adding oxidizing gases, the reducing power of the reference gas can be suppressed. Examples of oxidizing gases include oxygen, dry air, and carbon dioxide. Furthermore, the proportion of the oxidizing gas in the atmospheric gas is, for example, 0.01% by volume or more and 1% by volume or less.

[0084] In addition, the atmospheric gas may also contain a reducing gas. By adding a reducing gas, the reducing power of the reference gas can be enhanced. Examples of reducing gases include hydrogen, carbon monoxide, methane, propane, butane, and other hydrocarbon gases. Furthermore, the proportion of the reducing gas in the atmospheric gas is, for example, 0.01% by volume or more and 1% by volume or less.

[0085] Furthermore, in this disclosure, it is preferable to allow gas to circulate during firing. This is because it facilitates the removal of Ge particles from the particle surface. 4+ Restore to Ge 2+ The firing temperature is, for example, above 300°C, above 400°C, or above 500°C. Alternatively, the firing temperature is, for example, below 1000°C, or below 700°C. The firing time is, for example, between 1 hour and 20 hours.

[0086] Furthermore, in this disclosure, the firing process may include a first firing treatment and a second firing treatment. The first firing treatment fires the precursor under a first gas atmosphere containing argon, and the second firing treatment fires the precursor after the first firing treatment under a second gas atmosphere containing nitrogen. By performing the first and second firing treatments, a sulfide solid electrolyte with high Li-ion conductivity after exposure testing and high retention rate before and after exposure testing can be obtained. The first and second firing treatments can be performed continuously, or the first firing treatment can be followed by cooling, and then the second firing treatment can be performed. In the latter case, the first firing treatment can be followed by cooling to room temperature. Furthermore, the firing temperature and firing time in the first and second firing treatments are the same as described above.

[0087] 3. Sulfide solid electrolytes

[0088] Regarding the sulfide solid electrolyte obtained through the above processes, the content described in "A. Sulfide Solid Electrolyte" is the same, so it is omitted here.

[0089] This disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and any technical solution having a structure that is substantially the same as the technical concept described in the claims of this disclosure and achieving the same effect is included within the technical scope of this disclosure.

[0090]

Example

[0091] [Comparative Example 1]

[0092] As raw materials, Li₂S, P₂S₅, and GeS₂ are prepared to form Li. 10 GeP2S 12 They were weighed and added to a zirconia jar along with zirconia balls. Then, they were mechanically ground (mechanical alloying) using a planetary ball mill at 380 rpm for 40 hours to obtain sulfide glass. The obtained sulfide glass was granulated, vacuum-sealed in a quartz tube, and sintered at 550°C for 8 hours to obtain a sulfide solid electrolyte.

[0093] [Example 1]

[0094] Sulfide glass was obtained in the same manner as in Comparative Example 1. The obtained sulfide glass was placed on an alumina plate and fired in a tubular furnace at 550°C for 8 hours while a gas containing 0.2% oxygen by volume in nitrogen was passed through it, to obtain a sulfide solid electrolyte.

[0095] [Example 2]

[0096] Sulfide glass was obtained in the same manner as in Comparative Example 1. The obtained sulfide glass was placed on an alumina plate and fired in a tubular furnace at 550°C for 8 hours while nitrogen was flowing through it, to obtain a sulfide solid electrolyte.

[0097] [Example 3]

[0098] Sulfide glass was obtained in the same manner as in Comparative Example 1. The obtained sulfide glass was placed on an alumina plate and fired in a tube furnace at 550°C for 8 hours while argon gas was flowing through it. After cooling to room temperature, it was fired again in a tube furnace at 550°C for 8 hours while nitrogen gas was flowing through it to obtain a sulfide solid electrolyte.

[0099] [Example 4]

[0100] Sulfide glass was obtained in the same manner as in Comparative Example 1. The obtained sulfide glass was placed on an alumina plate and fired in a tubular furnace at 550°C for 8 hours while argon gas was flowing through it, to obtain a sulfide solid electrolyte.

[0101] [Example 5]

[0102] Sulfide glass was obtained in the same manner as in Comparative Example 1. The obtained sulfide glass was placed on an alumina plate and fired in a tubular furnace at 550°C for 8 hours while a gas containing 0.2% hydrogen by volume in argon was passed through it, to obtain a sulfide solid electrolyte.

[0103] [evaluate]

[0104] (XRD measurement)

[0105] X-ray diffraction (XRD) was performed on the sulfide solid electrolytes obtained in Examples 1-5 and Comparative Example 1. The results confirmed that the sulfide solid electrolytes obtained in Examples 1-5 and Comparative Example 1 all had the LGPS type crystal phase.

[0106] (XPS measurement)

[0107] X-ray photoelectron spectroscopy (XPS) was performed on the sulfide solid electrolytes obtained in Examples 1-5 and Comparative Example 1 to evaluate their structure. The XPS apparatus used was a ULVACPHI PHI-5800. The sample was placed in an XPS support within an argon-atmosphere glove box, and the support was evacuated in a pre-exhaust chamber for at least 30 minutes before being introduced into the analysis chamber. A monochromatic AlKα (1487 eV) X-ray source was used to obtain information about the outermost surface of the sample. The measurement area was approximately 100 μm Φ, and Ar was used for charge neutralization. +Electron beam neutralization gun.

[0108] Peak separation was performed on the Ge3d spectrum obtained by XPS measurement to calculate the equivalent high-energy Ge. 4+ The peak area A and the equivalent low-energy Ge 2+ The peak area B. Using the calculated peak area, determine Ge. 2+ There exists a ratio (B / (A+B)), which serves as "Ge 2+ The proportion relative to the total Ge content. Peak separation was performed using the analysis software (MULTIPACK (ULVACPHI)) accompanying the X-ray photoelectron spectroscopy apparatus. Background processing was performed using the Shirley method, and peak separation was achieved using curve fitting based on the nonlinear least squares method. As a typical result, Figure 3 This represents the results of Example 2. Specifically, as... Figure 3 As shown, the Ge3d spectrum obtained by XPS measurement is separated into Ge... 4+ peak and Ge 2+ The peaks are calculated by determining Ge from the areas of each peak. 2+ The proportion exists. The results are shown in Table 1.

[0109] (Determination of Li ion conductivity)

[0110] The Li-ion conductivity of the sulfide solid electrolytes obtained in Examples 1-5 and Comparative Example 1 was determined. Specifically, 100 mg of the sulfide solid electrolyte was weighed in a glove box at a dew point of -80°C and placed in a MACOR cylinder. 2 The particles were compressed under pressure. Both ends of the obtained particles were clamped with SUS pins, and the particles were tightened with bolts to apply constraint pressure, resulting in evaluation single cells. For the evaluation single cells, the Li ion conductivity at 25°C was calculated using the AC impedance method. A Solartron 1260 frequency response analyzer was used for the measurements, with an applied voltage of 5 mV and a measurement frequency range of 0.01 MHz to 1 MHz. The results (Li ion conductivity before exposure testing) are shown in Table 1.

[0111] (Exposure test)

[0112] Exposure tests were conducted on the sulfide solid electrolytes obtained in Examples 1-5 and Comparative Example 1. Specifically, the sulfide solid electrolytes were left to stand for 6 hours in a glove box with the dew point controlled at -30°C, exposing the sulfide solid electrolytes to moisture contained in the atmosphere. The Li-ion conductivity after the exposure test was measured in the same manner as above. The results are shown in Table 1 and Figure 4 .

[0113] Table 1

[0114]

[0115] As shown in Table 1, under vacuum firing conditions as in Comparative Example 1, Ge 2+ The presence rate is 0%. That is, all Ge present on the particle surface of sulfide solid electrolytes is Ge. 4+ In contrast, in Examples 1-5, Ge 2+ The presence rate is above 20% for all cases. Additionally, as shown in Table 1 and... Figure 4 As shown, Examples 1-5 exhibited higher Li-ion conductivity after the exposure test compared to Comparative Example 1. Specifically, Examples 2-4 showed higher Li-ion conductivity after the exposure test, with Example 3 showing the highest conductivity. This demonstrates that there is a maximum value between Examples 2 and 4.

[0116] Furthermore, from the viewpoint of maintaining the Li ion conductivity before and after the exposure test, Example 2 is higher than Example 1, and Examples 3-5 are significantly higher than Example 2. Moreover, comparing Examples 3, 4, and 5, the Li ion conductivity after the exposure test is higher in Examples 3 and 4 than in Example 5, while the maintenance rate of Li ion conductivity before and after the exposure test is the same in Examples 3-5. Furthermore, it is clear from the results of Examples 1-5 and Comparative Example 1 that Ge 2+ The presence ratio affects the water resistance of the sulfide solid electrolyte. Therefore, from the viewpoint of water resistance over time, Example 5 is superior.

[0117] Furthermore, the results of Examples 1-5 were examined in detail. First, Examples 2 and 4 were compared, confirming that nitrogen, compared to argon, significantly reduced the efficiency of Ge... 4+ Restore to Ge 2+ Its reducing power is weak. Nitrogen and argon are generally known to be low-reactivity gases, but it has been found that Ge... 2+ There are unexpected results, such as significant differences in the proportions. The reasons for these significant differences are not entirely clear, but since nitrogen itself is classified as a neutral gas, it may be less reactive than argon. In addition, since it is assumed that the sulfur contained in the precursors volatilizes during calcination, it is also assumed that some kind of interaction occurs between the volatilized sulfur and nitrogen and argon, and the strength of this interaction may produce significant differences.

[0118] Next, comparing Example 2 and Example 1, it was confirmed that by adding oxygen as an oxidizing gas to nitrogen, Ge... 4+ Restore to Ge 2+ The reducing power was suppressed. Similarly, comparing Examples 4 and 5, it was confirmed that by adding hydrogen as a reducing gas to argon, the reducing power of Ge was reduced. 4+ Restore to Ge 2+The reducing power of Ge is enhanced. Thus, it is confirmed that by using oxidizing and reducing gases, the reducing power of Ge can be controlled. 2+ A certain proportion exists. Furthermore, although no specific experiments were conducted, the addition of an oxidizing gas to argon gas suggests that Ge... 2+ The proportion is the same as in Example 3. Similarly, with the addition of a reducing gas in nitrogen, Ge can be expected to... 2+ The proportion of presence is the same as in Example 3.

[0119] Next, in Example 3, a first firing process with argon gas flowing through it and a second firing process with nitrogen gas flowing through it were performed. At the end of the first firing process, Ge was presumed to be... 2+ The presence rate was 92%, but during the second firing process, Ge 2+ The proportion of presence dropped to 77%. While the reason is not yet clear, it is hypothesized that Ge diffuses from within the particle. 4 + The ratio of nitrogen to Ge 4+ Restore to Ge 2+ The possibility of a large quantity.

Claims

1. A sulfide solid electrolyte that is a sulfide solid electrolyte containing Li, Ge, P, and S, and having an LGPS-type crystal phase. In the case where the surface of the sulfide solid electrolyte is subjected to X-ray photoelectron spectroscopy measurement, Ge 2+ The proportion with respect to the total amount of Ge is 55% or more and 90% or less.

2. A sulfide solid electrolyte that is a sulfide solid electrolyte containing Li, Ge, P, and S, and having an LGPS-type crystal phase. In the case where the surface of the sulfide solid electrolyte is subjected to X-ray photoelectron spectroscopy measurement, Ge 2+ The proportion with respect to the total amount of Ge is 94% or more.

3. The sulfide solid electrolyte according to claim 2, wherein the proportion of Ge 2+ is 100%.

4. An all-solid battery that is an all-solid battery having a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, at least one of the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer contains the sulfide solid electrolyte according to any one of claims 1 to 3.

5. A method for manufacturing a sulfide solid electrolyte that is a method for manufacturing a sulfide solid electrolyte containing Li, Ge, P, and S, and having an LGPS-type crystal phase, In the case where the surface of the sulfide solid electrolyte is subjected to X-ray photoelectron spectroscopy measurement, Ge 2+ the proportion with respect to the total amount of Ge is 20% or more, the manufacturing method has a preparation step and a firing step, the preparation step is a step of preparing a precursor containing Li, Ge, P, and S, the firing step is a step of firing the precursor in an atmosphere of a gas containing at least one of nitrogen gas and a rare gas, thereby forming the LGPS-type crystal phase, the gas contains an oxidizing gas.

6. A method for manufacturing a sulfide solid electrolyte that is a method for manufacturing a sulfide solid electrolyte containing Li, Ge, P, and S, and having an LGPS-type crystal phase, In the case where the surface of the sulfide solid electrolyte is subjected to X-ray photoelectron spectroscopy measurement, Ge 2+ the proportion with respect to the total amount of Ge is 20% or more, the manufacturing method has a preparation step and a firing step, the preparation step is a step of preparing a precursor containing Li, Ge, P, and S, the firing step is a step of firing the precursor in an atmosphere of a gas containing at least one of nitrogen gas and a rare gas, thereby forming the LGPS-type crystal phase, the gas contains a reducing gas.

7. A method for manufacturing a sulfide solid electrolyte that is a method for manufacturing a sulfide solid electrolyte containing Li, Ge, P, and S, and having an LGPS-type crystal phase, In the case where the surface of the sulfide solid electrolyte is subjected to X-ray photoelectron spectroscopy measurement, Ge 2+ the proportion with respect to the total amount of Ge is 20% or more, the manufacturing method has a preparation step and a firing step, the preparation step is a step of preparing a precursor containing Li, Ge, P, and S, the firing step is a step of firing the precursor in an atmosphere of a gas containing at least one of nitrogen gas and a rare gas, thereby forming the LGPS-type crystal phase, the firing step has a first firing process and a second firing process, the first firing process is a step of firing the precursor in an atmosphere of a first gas containing argon gas, the second firing process is a step of firing the precursor after the first firing process in an atmosphere of a second gas containing nitrogen gas.

8. The method for manufacturing a sulfide solid electrolyte according to any one of claims 5 to 7, wherein the precursor is a sulfide glass.

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