Sulfide solid electrolyte powder and all-solid-state lithium ion secondary battery

Abstract

The present invention relates to a sulfide solid electrolyte powder having a specific surface area of 5 m2 / g or more, and having a chromaticity x and a chromaticity y in the range of 0.32-0.36 when reflected light is represented by the CIE 1931 color system when powder particles are irradiated with simulated white light under specific conditions, and compressed particles obtained by molding the sulfide solid electrolyte powder at a pressure of 300 MPa.

Description

Technical Field

[0001] The present invention relates to a sulfide solid electrolyte powder and an all-solid-state lithium-ion secondary battery containing the sulfide solid electrolyte powder. Background Art

[0002] Lithium-ion secondary batteries are widely used in portable electronic devices such as mobile phones and laptop computers.

[0003] Conventionally, liquid electrolytes have been used in lithium-ion secondary batteries, but there are concerns such as leakage and ignition, and the housing needs to be enlarged for safety design. In addition, the battery life is short and the operating temperature range is narrow, which also need to be improved urgently.

[0004] On the other hand, all-solid-state lithium-ion secondary batteries using a solid electrolyte as the electrolyte of a lithium-ion secondary battery have attracted attention in terms of expected improvement in safety, high-speed charge and discharge, and miniaturization of the housing.

[0005] Solid electrolytes can be roughly classified into sulfide solid electrolytes and oxide solid electrolytes. Sulfide ions constituting the sulfide solid electrolyte have a larger polarizability than oxide ions constituting the oxide solid electrolyte, and exhibit higher lithium-ion conductivity. As the sulfide solid electrolyte, Li 10 GeP 2 S 12 and other LGPS-type crystals, Li 6 PS 5 Cl and other argyrodite-type crystals, Li 7 P 3 S 11 Crystallized glass such as LPS crystallized glass, etc.

[0006] As an example of disclosing an argyrodite-type sulfide solid electrolyte, Patent Document 1 can be cited. According to Patent Document 1, it is described that by containing lithium, phosphorus, sulfur, and chlorine, the molar ratio c(Cl / P) of chlorine to phosphorus is greater than 1.0 and 1.9 or less, and the lattice constant of the argyrodite-type crystal structure is It is possible to improve the lithium-ion conductivity.

[0007] By applying such a sulfide solid electrolyte with excellent lithium-ion conductivity to a lithium-ion secondary battery, good battery characteristics can be expected.

[0008] Prior Art Documents

[0009] Patent Documents

[0010] Patent Document 1: International Publication No. 2018 / 092366 Summary of the Invention

[0011] However, when the sulfide solid electrolyte is in the form of submicron-sized powder, during packaging, weighing, etc. at the time of factory shipment, the sulfide solid electrolyte powder scatters due to static electricity.

[0012] When manufacturing a lithium-ion battery, resin containers or containers with resin-coated surfaces are used in view of preventing metal contamination. In such cases, the above-mentioned scattering is more likely to occur.

[0013] The scattering of the sulfide solid electrolyte powder directly causes losses. In addition, if the scattered sulfide solid electrolyte powder adheres to the equipment, it will also cause equipment failures.

[0014] Therefore, it is desired to suppress the above-mentioned scattering. As one of the scattering suppression methods, it is desired to develop a sulfide solid electrolyte powder with suppressed surface charging.

[0015] Therefore, an object of the present invention is to provide a sulfide solid electrolyte powder with suppressed surface charging and an all-solid-state lithium-ion secondary battery containing the sulfide solid electrolyte powder.

[0016] In response to the above problems, the present inventors repeatedly conducted in-depth research and found that: the hue of the sulfide solid electrolyte powder reflects the surface charging state. Specifically, it is considered that: the sulfide solid electrolyte powder with a yellow color has sulfur attached to its surface, which inhibits the lithium-ion conduction on the surface of the sulfide solid electrolyte, and as a result, it is in a state where it is easily charged. In addition, it is considered that: the sulfide solid electrolyte powder with a gray color is the color presented along with lattice defects, and the lithium-ion conductivity on the surface of the sulfide solid electrolyte powder becomes low, and as a result, it is in a state where it is easily charged.

[0017] In response to the above situation, it was found that by making a white sulfide solid electrolyte powder with chromaticity x and chromaticity y within a specific range, the above problems can be solved, and thus the present invention was completed.

[0018] That is, the present invention relates to the following [1] to [9].

[0019] [1] A sulfide solid electrolyte powder having a specific surface area of 5 m 2 / g or more,

[0020] When the reflected light when irradiating the pressed powder particles with simulated white light under the following conditions is represented by the CIE 1931 colorimetric system, both chromaticity x and chromaticity y are in the range of 0.32 to 0.36, and the pressed powder particles are obtained by molding the above sulfide solid electrolyte powder under a pressure of 300 MPa.

[0021] (Conditions)

[0022] The above-mentioned simulated white light has light intensity in the wavelength range of 420 to 680 nm, and the light intensity of each wavelength in the range of 440 to 650 nm is more than half of the light intensity of the wavelength with the highest light intensity.

[0023] [2] The sulfide solid electrolyte powder according to [1] above, wherein the specific surface area is 8 m 2 / g or more.

[0024] [3] The sulfide solid electrolyte powder according to [1] or [2] above, wherein both the chromaticity x and the chromaticity y are in the range of 0.325 to 0.355.

[0025] [4] The sulfide solid electrolyte powder according to any one of [1] to [3] above, wherein the lithium ion conductivity is 2 mS / cm or more.

[0026] [5] The sulfide solid electrolyte powder according to any one of [1] to [4] above, which has a thiogermanate-type crystal structure.

[0027] [6] The sulfide solid electrolyte powder according to [5] above, wherein the thiogermanate-type crystal structure is represented by the composition formula Li a PS b Ha c wherein,

[0028] the above-mentioned Ha is at least one selected from F, Cl, Br, and I,

[0029] a, b, and c in the above composition formula satisfy the relationship of 5 ≤ a ≤ 7, 4 ≤ b ≤ 6, and 1.3 ≤ c ≤ 2.

[0030] [7] The sulfide solid electrolyte powder according to [6] above, wherein, as the above-mentioned Ha, Cl and Br are contained,

[0031] when the content of Cl in the above thiogermanate-type crystal structure is set as α (at%), and the content of Br is set as β (at%), the content ratio represented by (α / β) is 0.1 to 10.

[0032] [8] The sulfide solid electrolyte powder according to any one of [1] to [7] above, which is used in a lithium ion secondary battery.

[0033] [9] A all-solid-state lithium ion secondary battery, containing the sulfide solid electrolyte powder according to any one of [1] to [8] above.

[0034] The sulfide solid electrolyte powder according to the present invention suppresses the charging on the powder surface, and thus can suppress scattering caused by static electricity during packaging, shipping, etc., and has excellent processability. Therefore, it is possible to reduce the scattering loss of the sulfide solid electrolyte powder, and in addition, it is also possible to prevent equipment failures caused by adhesion to equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram showing a measurement system for irradiating a compacted granule of a sulfide solid electrolyte powder with simulated white light and measuring the reflected light.

[0036] Figure 2 It is a flowchart showing a method for manufacturing the sulfide solid electrolyte powder of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0037] Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following embodiments, and can be arbitrarily modified and implemented without departing from the gist of the present invention. In addition, "~" indicating a numerical range is used to mean including the values described before and after it as the lower limit value and the upper limit value.

[0038] <Sulfide Solid Electrolyte Powder>

[0039] The sulfide solid electrolyte powder of the present embodiment is a powder having a specific surface area of 5 m 2 / g or more. Moreover, when the reflected light when irradiating the compacted granule of the sulfide solid electrolyte powder with simulated white light under the following conditions is represented by the CIE1931 colorimetric system, both the chromaticity x and the chromaticity y are in the range of 0.32 to 0.36. The compacted granule of the sulfide solid electrolyte powder is a pellet obtained by molding the sulfide solid electrolyte powder at a pressure of 300 MPa.

[0040] The specific surface area of the sulfide solid electrolyte powder is related to its particle size. That is, when the particle size of the sulfide solid electrolyte powder is small enough to reach a specific surface area of 5 m 2 / g or more, it can be said that the light scattering on the powder surface is large, which contributes to its hue and reflects the surface state of the particles. In addition, the smaller the particle size, the easier the powder is to scatter during packaging, shipping, etc., and thus the problems of the present invention are likely to occur.

[0041] The specific surface area of the sulfide solid electrolyte powder of the present embodiment is 5 m 2 / g or more, and from the viewpoint of increasing the contact area with the active material, it is preferably 8 m 2 / g or more, more preferably 10 m 2 / g or more. In addition, the upper limit of the specific surface area is not particularly limited, and from the viewpoint of processing, it is preferably 40 m 2 / g or less.

[0042] It should be noted that in this specification, the specific surface area refers to the BET specific surface area analyzed by the BET (Brunauer Emmett Teller) formula based on the results of nitrogen adsorption and desorption measurement.

[0043] The average particle size of the sulfide solid electrolyte powder of this embodiment is not particularly limited as long as the specific surface area is within the above range. The average particle size is preferably 2 μm or less, more preferably 1 μm or less, and still more preferably 0.8 μm or less. In addition, from the viewpoint of processing, the average particle size is preferably 0.1 μm or more.

[0044] It should be noted that in this specification, the average particle size refers to the median particle size, which is the particle size at which 50% by volume of the particles obtained by measuring the particle size distribution using a particle size distribution meter based on laser diffraction method and from the resulting volume-based particle size distribution diagram is below this value.

[0045] The hue of the sulfide solid electrolyte powder of this embodiment is represented by the chromaticity x and chromaticity y when the reflected light when irradiating the pressed powder particles of the sulfide solid electrolyte with simulated white light using simulated white light as the light source is represented by the CIE 1931 colorimetric system. Both the above chromaticity x and chromaticity y are in the range of 0.32 to 0.36. First, the method for obtaining the chromaticity will be described.

[0046] The sample uses pressed powder particles composed of sulfide solid electrolyte powder.

[0047] The diameter of the pressed powder particles is 20 mm, and the pressed powder particles are made by molding 0.5 g of the sulfide solid electrolyte powder at a pressure of 300 MPa. The thickness of the pressed powder particles is about 0.8 mm.

[0048] Figure 1 It is a schematic diagram showing the measurement system when irradiating the pressed powder particles of the sulfide solid electrolyte powder with simulated white light and detecting the reflected light. First, the above-obtained pressed powder particles are used as sample 1, and the arrow-indicated simulated white light is irradiated by the light source 2. The light source 2 uses simulated white light that satisfies the following conditions: it has light intensity in the wavelength range of 420 to 680 nm, and the light intensity of each wavelength in the wavelength range of 440 to 650 nm is more than half of the light intensity of the wavelength with the highest light intensity.

[0049] As the light source 2, a light source that emits only the above-described simulated white light can be used, or a light source 2 that also includes light other than the simulated white light can be used. For example, a standard light source D50, a standard light source D65, a standard light source C light source, a simulated sunlight illumination (manufactured by Kamban Electric Co., Ltd., SOL-1000-24A27), etc. can be used as the light source 2. In this case, light can be made incident on the scatterer 3 to produce simulated white light that satisfies the above conditions, and it can be irradiated onto the specimen 1 as shown by the arrow. The above-exemplified light sources are light sources in which the light intensity at each wavelength in the visible region is uniform, such as sunlight, that is, light sources that exhibit a light intensity of a certain level or more in a wavelength region with high sensitivity when converted to the xyz coordinate system represented by the CIE 1931 colorimetric system.

[0050] In this way, simulated white light that satisfies the above conditions is irradiated onto the specimen 1, and the reflected light (not shown) thereof is measured using the two-dimensional spectro-radiometer 4.

[0051] Specifically, the incident angle of the simulated white light with respect to the specimen 1 is 2 to 45°, and the reflected light mainly composed of diffuse reflection light is measured using the two-dimensional spectro-radiometer 4. As the two-dimensional spectro-radiometer 4, for example, SR-5000 manufactured by TOPCON TECHNOHOUSE Co., Ltd. can be used.

[0052] The obtained reflected light (reflection spectrum) is converted to the CIE 1931 colorimetric system, and the chromaticity x, chromaticity y, and chromaticity z are obtained. In addition, when the light intensity of the used simulated white light fluctuates greatly at each wavelength, correction can also be performed.

[0053] Specifically, correction can be performed by dividing the light intensity at each wavelength of the obtained reflection spectrum by the light intensity at each wavelength of the light source spectrum. By performing the correction, the deviation of the apparent hue from the hue when the values of the chromaticity x and chromaticity y before correction are plotted in the CIE 1931 colorimetric system can be corrected.

[0054] Both the chromaticity x and chromaticity y obtained for the sulfide solid electrolyte powder of the present embodiment are in the range of 0.32 to 0.36.

[0055] The relationship between the above-described chromaticity x and chromaticity y and the charging of the powder surface will be described below.

[0056] It is known that conventional sulfide solid electrolyte powders are prone to sulfur deficiency as described in International Publication No. 2013 / 14580. In particular, sulfide solid electrolyte powders having a thiogermanate-type crystal structure are prone to sulfur deficiency. Moreover, coloring is generally observed when a defect structure is generated.

[0057] If there are lattice defects such as sulfur deficiency, the sulfide solid electrolyte powder turns gray, and it is considered that the lithium ion conductivity on the surface of the sulfide solid electrolyte powder becomes low. As a result, it is in a state where it is easily charged.

[0058] Regarding the decrease in lithium ion conductivity, in Japanese Patent Publication No. 5957144, sulfur deficiency is suppressed by treating with H 2 S gas in the manufacturing process.

[0059] However, it is difficult to achieve a balance between the sulfur deficiency rate and the sulfidation rate with treatments using gases containing sulfur elements such as H 2 S gas and sulfur gas. In order to prevent sulfur deficiency, an excessive amount of gas needs to be supplied.

[0060] By supplying an excessive amount of gas containing sulfur elements, sulfur is more likely to precipitate and adhere to the surface of the sulfide solid electrolyte powder. In addition, there are also cases where the desorbed sulfur adheres to the surface of the sulfide solid electrolyte powder. If sulfur adheres to the surface of the sulfide solid electrolyte powder along with such desorption and precipitation of sulfur, the powder turns yellow. Moreover, it is considered that the ion conduction on the surface of the sulfide solid electrolyte powder is suppressed, and as a result, the powder surface becomes easily charged.

[0061] In contrast, the present invention has found that in the sulfide solid electrolyte powder, both the chromaticity x and the chromaticity y in the CIE 1931 colorimetric system being in the range of 0.32 to 0.36 means that both lattice defects and the adhesion of sulfur to the powder surface can be suppressed. Thus, the sulfide solid electrolyte powder of the present embodiment with chromaticity x and chromaticity y in the above range can suppress charging caused by lattice defects and sulfur adhesion to the powder surface.

[0062] The chromaticity x is 0.32 to 0.36, preferably 0.325 to 0.355, and more preferably 0.330 to 0.350. Here, from the viewpoint of further suppressing the charging on the surface of the sulfide solid electrolyte powder, the chromaticity x is preferably 0.325 or more, more preferably 0.330 or more, and preferably 0.355 or less, more preferably 0.350 or less.

[0063] The chromaticity y is 0.32 to 0.36, preferably 0.325 to 0.355, and more preferably 0.330 to 0.350. Here, from the viewpoint of further suppressing the charging on the surface of the sulfide solid electrolyte powder, the chromaticity y is preferably 0.325 or more, more preferably 0.330 or more, and preferably 0.355 or less, more preferably 0.350 or less.

[0064] In addition, both the chromaticity x and the chromaticity y are preferably 0.325 to 0.355, and more preferably 0.330 to 0.350.

[0065] From the viewpoints of lithium ion conductivity and battery characteristics, the sulfide solid electrolyte powder of the present embodiment preferably has a thiogermanate crystal structure. Here, the thiogermanate crystal structure refers to the crystal structure possessed by the compound group of minerals represented by the composition formula Ag 8 GeS 6 The crystal structure possessed by the compound group of minerals represented by the composition formula Ag

[0066] For example, when the thiogermanate crystal structure is represented by the composition formula Li a PS b Ha c It has: a PS 4 tetrahedron formed by the P element as the central element and the S element as the four vertices, and a tetrahedron formed by the Li element as the central element and at least one selected from the S element and the Ha element as the four vertices.

[0067] The above-mentioned Ha is at least one selected from F, Cl, Br, and I, preferably at least one selected from Cl, Br, and I, more preferably at least one of Cl and Br. In addition, as Ha, it is also more preferably to contain Cl and Br.

[0068] When Ha is composed of two or more elements, c in the above composition formula refers to the total of these elements.

[0069] When Cl and Br are included as Ha, when the content of Cl in the thiogermanate crystal structure is α (at%), and the content of Br is β (at%), the content ratio represented by (α / β) is preferably 0.1 to 10, more preferably 0.3 to 3, and further preferably 0.5 to 1.6. By satisfying the above range, the interaction between lithium ions and halide ions is weakened, and the lithium ion conductivity of the sulfide solid electrolyte is likely to become good. It is considered that this is due to the influence of the mixed anion effect of weakening the interaction between cations and anions by mixing bromide ions with a larger ionic radius than chloride ions. In addition, the cycle characteristics of the lithium ion secondary battery are also likely to be improved.

[0070] From the above viewpoints, the content ratio represented by (α / β) is preferably 0.1 or more, more preferably 0.3 or more, further preferably 0.5 or more. In addition, it is preferably 10 or less, more preferably 3 or less, and further preferably 1.6 or less.

[0071] In the above composition formula, a, b, and c preferably satisfy the relationship of 5 ≤ a ≤ 7, 4 ≤ b ≤ 6, and 1.3 ≤ c ≤ 2. The above element ratio more preferably satisfies the relationship of 5.1 < a < 6.3, 4 < b < 5.3, and 1.4 ≤ c ≤ 1.9, and further preferably satisfies the relationship of 5.2 < a < 6.2, 4.1 < b < 5.2, and 1.5 ≤ c ≤ 1.8.

[0072] That is, a is preferably 5 or more, more preferably greater than 5.1, and still more preferably greater than 5.2. Additionally, it is preferably 7 or less, more preferably less than 6.3, and still more preferably less than 6.2. b is preferably 4 or more, more preferably greater than 4, and still more preferably greater than 4.1. Additionally, it is preferably 6 or less, more preferably less than 5.3, and still more preferably less than 5.2. c is preferably 1.3 or more, more preferably 1.4 or more, and still more preferably 1.5 or more. Additionally, it is preferably 2 or less, more preferably 1.9 or less, and still more preferably 1.8 or less.

[0073] In the case where the argyrodite crystal structure is represented by the composition formula Li a PS b Ha c Among a plurality of PS 4 tetrahedra T 1 In a part of them, as the central element, the P element can be replaced by at least one element selected from the group consisting of Si element, Al element, Sn element, In element, Cu element, Sb element, B element, and Ge element.

[0074] From the viewpoint of further improving the lithium ion conductivity, it is preferable to replace the P element with the Si element.

[0075] In addition, whether or not the Al element, Sn element, In element, Cu element, Sb element, B element, and Ge element other than the Si element are intentionally included in the raw materials used in the production of the sulfide solid electrolyte powder or are mixed in during the production process, they can be replaced by the P element.

[0076] The proportion of the replacement of the P element with the Si element is preferably 0.01 to 50%, more preferably 0.1 to 40%. Here, from the viewpoint of obtaining higher lithium ion conductivity, the above-mentioned replacement proportion is preferably 0.01% or more, more preferably 0.1% or more. On the other hand, from the viewpoint of crystallinity, the above-mentioned proportion is preferably 50% or less, more preferably 40% or less. However, the replacement proportion can also be 0%, that is, not replaced with the Si element.

[0077] When the P element is also replaced with an element other than the Si element, the total proportion including the above-mentioned replacement with the Si element is preferably 50% or less.

[0078] It should be noted that in this specification, the replacement proportion of the elements constituting the crystal structure is obtained by performing X-ray diffraction (XRD) measurement and performing Rietveld analysis on the obtained XRD pattern.

[0079] In addition, among a plurality of PS 4 tetrahedra T 1In a part of the [tetrahedron], at least a part of the S element as a vertex can be replaced with at least one element selected from the O element and the Ha element. From the viewpoint of maintaining high lithium ion conductivity, PS is preferred. 4 tetrahedron, and from the viewpoint of improving water resistance, PS is preferred. 4 P(S + O) obtained by replacing at least a part of the S element of the [tetrahedron] with the O element. 4 tetrahedron.

[0080] In the above PS 4 tetrahedron T 1 When at least a part of the P element as the central element is replaced with at least one element selected from the Si element, the Al element, the Sn element, the In element, the Cu element, the Sb element, the B element, and the Ge element in a part of the [tetrahedron], at least a part of the S element as a vertex can also be replaced with at least one element selected from the O element and the Ha element. From the viewpoint of maintaining high lithium ion conductivity, a tetrahedron with 4 S elements as vertices is preferred, and from the viewpoint of improving water resistance, a tetrahedron in which at least a part of the above S element is replaced with the O element is preferred.

[0081] The total proportion of the S element replaced with the O element and the Ha element is preferably 0.01 to 25%, more preferably 0.1 to 20%. Here, from the viewpoint of obtaining the effect brought by the replacement, the above proportion is preferably 0.01% or more, more preferably 0.1% or more. On the other hand, from the viewpoint of maintaining high lithium ion conductivity, the above proportion is preferably 25% or less, more preferably 20% or less. However, the case where all the tetrahedrons are those with the central element being the P element and all the elements as vertices being the S elements, that is, the above proportion is 0%, is not excluded.

[0082] It should be noted that for the composition formula Li a PS b Ha c When a part of the P element is replaced by the X element, it is preferable to set the total of the P element and the X element to 1, and a, b, and c thereof are respectively within the above ranges. In addition, when a part of the S element is replaced by the O element, it is preferable that the total of the S element and the O element is within the above range of b.

[0083] The lithium ion conductivity of the sulfide solid electrolyte powder of this embodiment at 25 °C is preferably 1 × 10 －3 S / cm or more, more preferably 1.5 × 10 －3 S / cm or more, and further preferably 2 × 10 －3 S / cm or more, and the higher the better. The upper limit of the lithium ion conductivity is not particularly limited, and is usually 1 × 10 －1 S / cm or less.

[0084] It should be noted that the lithium ion conductivity can be measured by the AC impedance method.

[0085] The sulfide solid electrolyte powder of the present embodiment is preferably used for a lithium ion secondary battery. In addition to being used as the solid electrolyte layer of a lithium ion secondary battery, the sulfide solid electrolyte powder can also be mixed with a positive electrode active material or a negative electrode active material to be used as a positive electrode layer or a negative electrode layer.

[0086] In addition, the above-mentioned sulfide solid electrolyte powder can also be used together with other solid electrolyte powders.

[0087] There is no particular limitation on other solid electrolyte powders. For example, solid electrolytes having a thiogermanate-type crystal structure known in the past, Li 3 PS 4 、Li 4 P 2 S 6 、Li 2 S, LiHa, etc. can be cited.

[0088] For the positive electrode active material, negative electrode active material, current collector, binder, conductive assistant, etc. used in the positive electrode layer or negative electrode layer in a lithium ion secondary battery, materials known in the past can be used.

[0089] A lithium ion secondary battery using the sulfide solid electrolyte powder of the present embodiment includes a solid electrolyte layer, a positive electrode layer, and a negative electrode layer.

[0090] For the material of the outer package of the lithium ion secondary battery, materials known in the past can also be used. In addition, for the shape of the lithium ion secondary battery, shapes known in the past can also be used. For example, coin type, sheet (film) type, folded type, wound type, bottomed cylindrical type, button type, etc. can be cited and can be appropriately selected according to the use.

[0091] The present invention also relates to an all-solid-state lithium ion secondary battery including the sulfide solid electrolyte powder of the present embodiment.

[0092] The sulfide solid electrolyte powder contained in the all-solid-state lithium ion secondary battery can be contained in the form of a compact, for example. The above-mentioned compact refers to a compact obtained by dry-mixing and molding an active material and a sulfide solid electrolyte powder, a compact obtained by mixing with an organic solvent, etc., wet-mixing and coating an active material and a sulfide solid electrolyte powder, and molding after drying.

[0093] <Manufacturing method of sulfide solid electrolyte powder>

[0094] The manufacturing method of the sulfide solid electrolyte powder of the present embodiment is not particularly limited as long as the powder described in the above <sulfide solid electrolyte powder> can be obtained.

[0095] As an embodiment of the manufacturing method, for example, as Figure 2 shown, it sequentially includes the following steps S1 to S5.

[0096] Step S1: A step of mixing raw materials containing Li element, P element, and S element to obtain a raw material mixture.

[0097] Step S2: A step of heating the raw material mixture obtained in Step S1 to obtain a synthesized compound.

[0098] Step S3: A step of cooling the synthesized compound obtained in Step S2 to precipitate an S-excess sulfide solid electrolyte.

[0099] Step S4: A step of heat-treating the precipitated S-excess sulfide solid electrolyte obtained in Step S3 at 350 to 480 °C in an inert atmosphere to obtain a sulfide solid electrolyte.

[0100] Step S5: A step of pulverizing the sulfide solid electrolyte obtained in Step S4 to obtain a sulfide solid electrolyte powder.

[0101] Each step will be described.

[0102] In Step S1, in the step of mixing raw materials containing Li element, P element, and S element to obtain a raw material mixture, raw materials containing each element constituting the sulfide solid electrolyte powder are used. Therefore, when the sulfide solid electrolyte powder contains the Ha element, a raw material containing the Ha element is further used. In addition, when a part of the Li element, P element, and S element is replaced by other elements, a raw material containing the above other elements is further used. As the elements contained in other raw materials, for example, Si element, Al element, Sn element, In element, Cu element, Sb element, Ge element, B element, and O element can be cited.

[0103] As the raw materials containing Li element, P element, S element, and, if necessary, Ha element and other elements, conventionally known raw materials can be used.

[0104] Specifically, Li metal or a Li-containing compound, P metal or a P-containing compound, S metal or an S-containing compound, any Ha-containing compound, etc. can be appropriately combined and used. When the sulfide solid electrolyte powder contains O element, an oxide can be used as the above compound. In addition, the above compound can also be a compound containing two or more of Li, P, and S, and any other elements such as Ha. For example, as a compound that serves as both an S-containing compound and a P-containing compound, phosphorus pentasulfide (P 2 S5 ) etc. In addition, as a compound that also serves as a compound containing a Li compound and a Ha compound, lithium halide can be cited.

[0105] As a raw material containing the Li element, in addition to metallic lithium, as a compound containing Li, for example, lithium sulfide (Li 2 S), lithium carbonate (Li 2 CO 3 ), lithium sulfate (Li 2 SO 4 ), lithium oxide (Li 2 O) and lithium hydroxide (LiOH) and other lithium compounds etc.

[0106] From the viewpoints of ease of synthesis and ease of handling of the intermediate described later, the raw material containing the Li element is preferably lithium sulfide. On the other hand, since lithium sulfide is expensive, from the viewpoint of suppressing manufacturing costs, lithium compounds, metallic lithium, etc. other than lithium sulfide are preferred. Specifically, it is preferable to use one or more selected from metallic lithium, lithium carbonate (Li 2 CO 3 ), lithium sulfate (Li 2 SO 4 ), lithium oxide (Li 2 O) and lithium hydroxide (LiOH). These can be used alone or in combination of two or more.

[0107] As a raw material containing the S element, in addition to elemental sulfur, as a compound containing S, for example, diphosphorus trisulfide (P 2 S 3 ), diphosphorus pentasulfide (P 2 S 5 ) and other phosphorus sulfides, other sulfur compounds containing phosphorus, and compounds containing sulfur etc. As a compound containing sulfur, H 2 S, CS 2 , FeS, Fe 2 S 3 , FeS 2 , Fe 1－x S and other iron sulfides, bismuth sulfide (Bi 2 S 3 ), CuS, Cu 2 S, Cu 1－x S and other copper sulfides etc.

[0108] From the viewpoints of ease of reaction when synthesizing the intermediate and preventing elements other than the elements constituting the target sulfide solid electrolyte powder, the raw material containing the S element is preferably phosphorus sulfide, more preferably diphosphorus pentasulfide (P 2 S 5)。They can be used alone or in combination of two or more. It should be noted that phosphorus sulfide is a compound that serves as both a substance containing S and a substance containing P.

[0109] As a raw material containing the P element, in addition to elemental phosphorus, as a compound containing P, for example, diphosphorus trisulfide (P 2 S 3 ), phosphorus pentasulfide (P 2 S 5 ), etc. phosphorus sulfides, sodium phosphate (Na 3 PO 4 ), lithium thiophosphate (Li 3 PS 4－x O x ), etc. phosphorus compounds, etc.

[0110] From the viewpoints of the ease of reaction when synthesizing intermediates and preventing elements other than the elements constituting the target sulfide solid electrolyte powder, the raw material containing the P element is preferably phosphorus sulfide, and more preferably phosphorus pentasulfide (P 2 S 5 ). They can be used alone or in combination of two or more.

[0111] In addition, as a raw material containing the P element, in the case of containing an oxide, for example, P 2 O 5 , Li 3 PO 4 , Li 4 P 2 O 7 etc. Among them, from the viewpoint of ease of manufacture, P 2 O 5 is preferred. These compounds can be used alone or in combination of two or more.

[0112] As an optional component, for a raw material containing the Ha element, that is, a compound containing Ha, for example, lithium halides such as lithium fluoride (LiF), lithium chloride (LiCl), lithium bromide (LiBr), lithium iodide (LiI), phosphorus halides, phosphoryl halides, sulfur halides, sodium halides, boron halides, etc.

[0113] From the viewpoint of preventing elements other than the elements constituting the target sulfide solid electrolyte powder, the raw material containing the Ha element is preferably a lithium halide, and more preferably LiCl, LiBr, LiI. These compounds can be used alone or in combination of two or more.

[0114] It should be noted that lithium halide is also a compound containing Li. When the raw material contains lithium halide, part or all of the Li in the raw material can come from the lithium halide.

[0115] When there are also other elements other than Li, S, P, and Ha as the elements constituting the sulfide solid electrolyte powder, raw materials containing the above other elements are also mixed to obtain a raw material mixture.

[0116] As an optional component, for raw materials containing Si element, for example, SiO 2 , SiS 2 can be cited. Among them, from the viewpoints of lithium ion conductivity and water resistance, SiO 2 is more preferred. These compounds can be used alone or in combination of two or more.

[0117] As an optional component, for raw materials containing Al element, for example, Al 2 S 3 , Al 2 O 3 , AlCl 3 can be cited. Among them, from the viewpoint of lithium ion conductivity, Al 2 S 3 , AlCl 3 are preferred, and Al 2 S 3 is more preferred. These compounds can be used alone or in combination of two or more.

[0118] As an optional component, for raw materials containing Sn element, for example, SnS, SnS 2 , SnO, SnO 2 , SnCl 2 can be cited. Among them, from the viewpoint of lithium ion conductivity, SnS 2 , SnCl 2 are preferred, and SnS 2 is more preferred. These compounds can be used alone or in combination of two or more.

[0119] As an optional component, for raw materials containing In element, for example, In 2 O 3 , In 2 S 3 , InCl 3 can be cited. Among them, from the viewpoint of lithium ion conductivity, In 2 S 3 , InCl 3 are preferred, and In 2 S 3 is more preferred. These compounds can be used alone or in combination of two or more.

[0120] As an optional component, for raw materials containing a Cu element, for example, Cu 2 O, CuO, Cu 2 S, CuS, CuCl 2 can be cited. Among them, from the viewpoint of lithium ion conductivity, CuS and CuCl are preferred 2 , and CuS is more preferred. These compounds can be used alone or in combination of two or more.

[0121] As an optional component, for raw materials containing an Sb element, for example, Sb 2 O 3 , Sb 2 S 3 , SbCl 3 can be cited. Among them, from the viewpoint of lithium ion conductivity, Sb 2 S 3 , SbCl 3 are preferred, and Sb 2 S 3 is more preferred. These compounds can be used alone or in combination of two or more.

[0122] As an optional component, for raw materials containing a Ge element, for example, GeO 2 , GeS, GeS 2 , GeCl 2 can be cited. Among them, from the viewpoint of lithium ion conductivity, GeS 2 , GeCl 2 are preferred, and GeS 2 is more preferred. These compounds can be used alone or in combination of two or more.

[0123] As an optional component, for raw materials containing a B element, for example, B 2 S 3 , B 2 O 3 , BCl 3 can be cited. Among them, from the viewpoint of lithium ion conductivity, B 2 S 3 , BCl 3 are preferred, and B 2 S 3 is more preferred. These compounds can be used alone or in combination of two or more.

[0124] The mixing of raw materials is carried out, for example, by mixing using a mortar, mixing using a medium such as a planetary ball mill, a needle mill, a powder mixer, or medium-free mixing such as air flow mixing. The raw materials can be mixed and then amorphousized before heating.

[0125] In subsequent step S2, the raw material mixture obtained in step S1 is heated to obtain a synthetic compound.

[0126] There is no particular limitation on the specific method of heating the raw material mixture. The raw materials are placed in a heat-resistant container and heated using a heating furnace. The mixture of raw materials can also be sealed in a heat-resistant container.

[0127] As the heat-resistant container, a carbon heat-resistant container, quartz, quartz glass, borosilicate glass, aluminosilicate glass, a heat-resistant container containing oxides such as alumina, zirconia, and mullite, a heat-resistant container containing nitrides such as silicon nitride and boron nitride, a heat-resistant container containing carbides such as silicon carbide, etc. can be used. In addition, these heat-resistant containers can be formed entirely of the above materials, or can be containers such as a carbon-coated quartz tube having layers of carbon, oxides, nitrides, carbides, etc.

[0128] The heating temperature when heating the raw material mixture is preferably 200 to 900 °C, more preferably 350 to 850 °C, and further preferably 550 to 850 °C. Here, from the viewpoint of promoting the reaction, the heating temperature is preferably 200 °C or higher, more preferably 350 °C or higher, and further preferably 550 °C or higher. In addition, from the viewpoints of suppressing deterioration, decomposition, etc. caused by heating, the heating temperature is preferably 900 °C or lower, more preferably 850 °C or lower.

[0129] The heating time is preferably 10 minutes to 10 hours, more preferably 30 minutes to 9.5 hours, further preferably 45 minutes to 9 hours, and particularly preferably 1 to 9 hours. Here, from the viewpoint of enabling the reaction to proceed well, the heating time is preferably 10 minutes or longer, more preferably 30 minutes or longer, further preferably 45 minutes or longer, and particularly preferably 1 hour or longer. In addition, from the viewpoints of suppressing deterioration, decomposition, etc. caused by heating, the heating time is preferably 10 hours or shorter, more preferably 9.5 hours or shorter, and further preferably 9 hours or shorter.

[0130] Since the raw material mixture obtained contains raw materials containing S element, the heating atmosphere can be an inert atmosphere. From the viewpoint of appropriately suppressing sulfur deficiency, that is, adjusting the chromaticity x and chromaticity y of the obtained sulfide solid electrolyte powder, a gas atmosphere containing sulfur element is preferred.

[0131] As the gas containing sulfur element, sulfur gas (S x (x = 2 to 8) gas), hydrogen sulfide gas (H 2 S gas), sulfur dioxide gas (SO 2 gas), carbon disulfide gas (CS 2 gas), etc. can be cited. From the viewpoint of promoting the reaction, sulfur gas is preferred.

[0132] The gas containing sulfur element may be composed only of gas compounds containing sulfur element such as the above-mentioned sulfur gas, hydrogen sulfide gas, sulfur dioxide gas, carbon disulfide gas, etc. From the viewpoints of cost inhibition and use as a carrier gas in the transportation of sulfur components, etc., it is also preferable to contain inert gases such as nitrogen, argon, and helium. From the viewpoint of production cost, the inert gas as the carrier gas is preferably nitrogen.

[0133] The gas containing sulfur element may also contain impurities from a sulfur source or the like as long as it is within a range that does not hinder the effects of this manufacturing method.

[0134] When using sulfur gas as the gas containing sulfur element, the content of sulfur gas (S x (x = 2 - 8)) in the gas containing sulfur element is preferably 0.01 - 100% by volume, more preferably 0.1 - 50% by volume, and further preferably 0.2 - 25% by volume. Here, from the viewpoints of having a sufficient amount of sulfur element and promoting the reaction of introducing sulfur, the content of sulfur gas is preferably 0.01% by volume or more, more preferably 0.1% by volume or more, and further preferably 0.2% by volume or more. In addition, the content of sulfur gas is 100% by volume or less, and from the viewpoints of cost inhibition and using an inert gas as the carrier gas, it is preferably 50% by volume or less, more preferably 25% by volume or less. The content of sulfur gas (S x (x = 2 - 8)) can be measured by mass spectrometry gas chromatography.

[0135] The gas containing sulfur element is obtained by heating a sulfur source. Therefore, the sulfur source is not particularly limited as long as it is an elemental sulfur or sulfur compound that can obtain a gas containing sulfur element by heating. For example, elemental sulfur, hydrogen sulfide, sulfur dioxide, organic sulfur compounds such as carbon disulfide, FeS, Fe 2 S 3 、FeS 2 、Fe 1－x S and other iron sulfides, bismuth sulfide (Bi 2 S 3 ), copper sulfide such as CuS, Cu 2 S, Cu 1－x S, polysulfides such as lithium polysulfide and sodium polysulfide, polysulfide ethers, rubber subjected to sulfur vulcanization treatment, etc.

[0136] For example, by heating the above-mentioned sulfur source using a separately provided sulfur source heating unit to generate a gas containing sulfur element, and transporting an inert gas such as nitrogen, argon, or helium as a carrier gas into the heating furnace to obtain a gas atmosphere containing sulfur element.

[0137] By separating the sulfur source heating section and the section where the heating process is carried out, even if the gas introduced into the heating furnace contains oxygen and moisture, it can react with the gas containing sulfur element before introduction to remove them. Thus, a sulfide solid electrolyte with good quality and high purity with few impurities is obtained, which is therefore preferred.

[0138] The temperature for heating the sulfur source can be appropriately selected according to the type of sulfur source used. For example, when using elemental sulfur as the sulfur source, the heating temperature is preferably 250 °C or higher and preferably 750 °C or lower.

[0139] The elemental sulfur, H 2 S, Bi 2 S 3 , iron sulfide, copper sulfide, CS 2 and other solid sulfur sources in a fine state such as powder are pneumatically transported into the heating furnace by a carrier gas to obtain a gas atmosphere containing sulfur element.

[0140] In addition, the dew point during heating is preferably -20 °C or lower, and the lower limit is not particularly limited and is usually around -80 °C. The oxygen concentration is preferably 1000 ppm or lower.

[0141] In the subsequent step S3, the synthetic compound obtained in step S2 is cooled to obtain an S-excess sulfide solid electrolyte containing an excessive amount of S element.

[0142] The cooling rate is preferably 1 to 1,000,000 °C / second, more preferably 10 to 100,000 °C / second, and further preferably 100 to 10,000 °C / second. Thus, the crystal structure at high temperature can be maintained. Here, from the viewpoint of maintaining the stability during the heat treatment in the subsequent process, the cooling rate is preferably 1 °C / second or higher, more preferably 10 °C / second or higher, and further preferably 100 °C / second or higher. In addition, the upper limit value of the cooling rate is not particularly limited. If considering the cooling rate of the twin roll which is generally considered to have the fastest quenching rate, the upper limit value is 1,000,000 °C / second or lower. From the viewpoint of actual production, the cooling rate is more preferably 100,000 °C / second or lower, and further preferably 10,000 °C / second or lower.

[0143] The atmosphere during cooling is preferably a low moisture content and inert atmosphere as in the heating in step S2.

[0144] In step S4, the S-excess sulfide solid electrolyte precipitated in step S3 is heat-treated at 350 to 480 °C in an inert atmosphere to obtain a sulfide solid electrolyte.

[0145] By passing through step S4 based on step S2, the chromaticity x and chromaticity y of the finally obtained sulfide solid electrolyte powder can both be in the range of 0.32 to 0.36.

[0146] The heat treatment temperature is 350 to 480 °C, preferably 380 to 460 °C, more preferably 400 to 450 °C. In order to evaporate and remove the excess sulfur in the sulfide solid electrolyte, the heat treatment temperature is 350 °C or higher. Thus, not only can the excess sulfur be removed from the surface of the sulfide solid electrolyte, but also the excess sulfur can be removed from the inside, and the chromaticity x and chromaticity y of the sulfide solid electrolyte powder can be within the preferred range. Here, the excess sulfur does not refer to the sulfur (S) in the composition ratio of the crystal structure showing the sulfide solid electrolyte, but refers to the sulfur attached to the surface of the sulfide solid electrolyte, the sulfur attached to the part that becomes the surface when the sulfide solid electrolyte is pulverized into powder, and the sulfur present at the grain boundaries.

[0147] From the above viewpoints, the heat treatment temperature is 350 °C or higher, preferably 380 °C or higher, more preferably 400 °C or higher. In addition, from the viewpoint of preventing the decomposition of the sulfide solid electrolyte, the heat treatment temperature is 480 °C or lower, preferably 460 °C or lower, more preferably 450 °C or lower.

[0148] The atmosphere for heat treatment is an inert atmosphere. For example, a nitrogen atmosphere, an argon atmosphere, a helium atmosphere, etc. can be cited.

[0149] The dew point during heat treatment is preferably -20 °C or lower, and the lower limit is not particularly limited and is usually around -80 °C.

[0150] A small amount of oxygen can be contained in the atmosphere for heat treatment. Thereby, the desorption of excess sulfur from the surface of the sulfide solid electrolyte is promoted. The oxygen concentration in the atmosphere for heat treatment is, for example, preferably 0.1 to 1000 ppm, more preferably 1 to 500 ppm, and further preferably 5 to 250 ppm. Here, the oxygen concentration is preferably 0.1 ppm or higher, more preferably 1 ppm or higher, and further preferably 5 ppm or higher. In addition, from the viewpoint of preventing oxidative decomposition, the oxygen concentration is preferably 1000 ppm or lower, more preferably 500 ppm or lower, and further preferably 250 ppm or lower. It should be noted that ppm here refers to the volume basis.

[0151] In step S5, the sulfide solid electrolyte obtained in the above step S4 is pulverized to obtain a sulfide solid electrolyte powder.

[0152] Through the above pulverization, the sulfide solid electrolyte can be made into a powder with a specific surface area of 5 m 2 / g or more.

[0153] The pulverization method can adopt, for example, medium pulverization such as a ball mill and a bead mill, jet mill pulverization without using a medium, cavity pulverization, cutting mill pulverization, etc. Among them, from the viewpoint of obtaining fine particles, ball mill and bead mill pulverization are preferred.

[0154] The pulverization can be either wet pulverization or dry pulverization. From the perspective of obtaining fine particles, wet pulverization is preferred. Both wet pulverization and dry pulverization can adjust the specific surface area of the obtained sulfide solid electrolyte powder according to the pulverization conditions.

[0155] The solvent used in wet pulverization is not particularly limited. For example, hydrocarbon solvents, organic solvents containing hydroxyl groups, organic solvents containing ether groups, organic solvents containing carbonyl groups, organic solvents containing ester groups, organic solvents containing amino groups, organic solvents containing formyl groups, organic solvents containing carboxyl groups, organic solvents containing amide groups, organic solvents containing benzene rings, organic solvents containing mercapto groups, organic solvents containing thioether groups, organic solvents containing thioester groups, organic solvents containing disulfide groups, halogenated alkanes, etc. can be cited.

[0156] As hydrocarbon solvents, for example, cyclohexane, heptane, octane, and toluene can be cited. From the perspective of low saturated water concentration, cyclohexane, heptane, and octane are preferred. From the perspective of adjusting the water concentration, it is preferred to mix them with toluene, dibutyl ether, etc.

[0157] After wet pulverization, in order to remove solvents, additives, etc., drying is preferably performed.

[0158] The drying temperature is not particularly limited. For example, it is preferably 50 - 300 °C, more preferably 100 - 250 °C, and further preferably 150 - 200 °C. Here, from the perspective of shortening the drying time, the drying temperature is preferably 50 °C or higher, more preferably 100 °C or higher, and further preferably 150 °C or higher. In addition, from the perspective of suppressing the decomposition of the sulfide solid electrolyte, the drying temperature is preferably 300 °C or lower, more preferably 250 °C or lower, and further preferably 200 °C or lower.

[0159] The drying time is not particularly limited. For example, it is preferably 10 - 480 minutes, more preferably 30 - 240 minutes, and further preferably 60 - 120 minutes. Here, from the perspective of suppressing poor solvent drying, the drying time is preferably 10 minutes or longer, more preferably 30 minutes or longer, and further preferably 60 minutes or longer. In addition, from the perspective of productivity, the drying time is preferably 480 minutes or shorter, more preferably 240 minutes or shorter, and further preferably 120 minutes or shorter.

[0160] The atmosphere during drying is not particularly limited. For example, from the perspective of obtaining good quality, an inert atmosphere such as nitrogen or argon is preferred.

[0161] The pressure during drying is not particularly limited. It can be vacuum drying, atmospheric drying, weak vacuum drying, or weak pressure drying. Here, weak vacuum drying during drying means that the differential pressure is preferably 0.1 to 50 kPa, for example, and weak pressure drying means that the differential pressure is preferably 0.1 to 50 kPa, for example.

[0162] When the sulfide solid electrolyte powder obtained through the above step S5 or subsequent drying process is used for the electrode mixture or solid electrolyte layer of a lithium-ion secondary battery, it is supplied to a conventionally well-known process together with other components as needed.

[0163] Examples

[0164] The following presents examples for a specific description of the present invention, but the present invention is not limited thereto.

[0165] Examples 1 and 2 are examples, and Examples 3 to 5 are comparative examples.

[0166] [Example 1]

[0167] In a dry nitrogen atmosphere, lithium sulfide powder (manufactured by Sigma, purity 99.98%), phosphorus pentasulfide powder (manufactured by Sigma, purity 99%), and lithium chloride powder (manufactured by Sigma, purity 99.99%) were weighed in a composition ratio to become Li 5.5 PS 4.5 Cl 1.5 , and mixed using a mortar. The obtained raw material mixture was placed in a heat-resistant container and heated at 750 °C for 60 minutes in a gas atmosphere containing sulfur element to obtain a melt in which the raw material mixture was heated and melted as a synthetic compound. The above-mentioned gas containing sulfur element used sulfur gas (S x (x = 2 to 8)) and nitrogen gas as a carrier gas, and the content of sulfur gas was 10% by volume.

[0168] Next, it was cooled to room temperature at 5 °C / second to precipitate crystals of the S-excess sulfide solid electrolyte. The obtained S-excess sulfide solid electrolyte was mixed and pulverized using a mortar, and heat-treated at 440 °C for 1 hour in a nitrogen atmosphere to obtain a sulfide solid electrolyte.

[0169] Then, a planetary ball mill (manufactured by Ito Seisakusho, LP-M2) was used, and wet pulverization was performed using a medium with a particle size of 1 mm and a mixed solvent of heptane and dibutyl ether as a solvent, and dried at 180 °C for 3 hours to obtain a sulfide solid electrolyte powder.

[0170] [Example 2]

[0171] Weigh lithium sulfide powder (manufactured by Sigma, purity 99.98%), phosphorus pentasulfide powder (manufactured by Sigma, purity 99%), lithium chloride powder (manufactured by Sigma, purity 99.99%), and lithium bromide powder (manufactured by Sigma, purity 99.995%) so that the composition ratio is Li 5.4 PS 4.4 Cl 0.8 Br 0.8 , and in other respects, obtain sulfide solid electrolyte powder in the same manner as in Example 1.

[0172] [Example 3]

[0173] Change the atmosphere during the heat melting of the raw material mixture from a sulfur element-containing gas atmosphere to a nitrogen atmosphere. Additionally, do not perform heat treatment after crystal precipitation. In other respects, obtain sulfide solid electrolyte powder in the same manner as in Example 1.

[0174] [Example 4]

[0175] Do not perform heat treatment after crystal precipitation. In other respects, obtain sulfide solid electrolyte powder in the same manner as in Example 1.

[0176] [Example 5]

[0177] In a dry nitrogen atmosphere, weigh lithium sulfide powder (manufactured by Sigma, purity 99.98%), phosphorus pentasulfide powder (manufactured by Sigma, purity 99%), and lithium chloride powder (manufactured by Sigma, purity 99.99%) so as to achieve a composition ratio of Li 5.5 PS 4.5 Cl 1.5 . After mixing for 1 minute using a stirrer, further mix using a planetary ball mill (manufactured by Ito Seisakusho, LP-M2). The planetary ball mill uses grinding balls with a diameter of 4 mm and mixes at 400 rpm for 50 hours. Place the obtained intermediate compound in a heat-resistant container and heat it at 450° for 5 hours in an atmosphere of a gas containing sulfur gas. The gas containing sulfur gas used is a mixture of sulfur gas, hydrogen sulfide gas, and nitrogen as a carrier gas. The content of sulfur gas is 4 vol%, and the content of hydrogen sulfide gas is 20 vol%.

[0178] Then, perform pulverization and drying under the same conditions as in Example 1 to obtain sulfide solid electrolyte powder.

[0179] Summarize the differences in the synthesis conditions of the above Examples 1 to 5 in the "Synthesis Conditions" of Table 1. It should be noted that, compared with Examples 1 and 2, Examples 3 to 5 did not perform the heat treatment corresponding to Step S4.

[0180] [Evaluation: Appearance Observation]

[0181] Visually observe the hue of the obtained sulfide solid electrolyte powder. The results are shown in the "Appearance" of "Sulfide Solid Electrolyte Powder" in Table 1. It should be noted that regarding the definition of hue, for example, it can be determined according to the color card described in JIS Z 8102:2001 Color Names of Object Colors.

[0182] [Evaluation: Chromaticity]

[0183] For the obtained sulfide solid electrolyte powder, use the Figure 1 measurement system shown below, and obtain the chromaticity x and chromaticity y represented by the CIE 1931 colorimetric system by the following method.

[0184] Apply a pressure of 300 MPa to 0.5 g of the sulfide solid electrolyte powder to form a pressed powder pellet with a diameter of 20 mm, and use this pressed powder pellet as Specimen 1. The thickness of the pressed powder pellet is 0.8 mm. Place this Specimen 1 in a transparent jig (not shown) that is not exposed to the atmosphere for fixation.

[0185] Use simulated sunlight illumination (manufactured by Kamban Electric Co., Ltd., SOL-1000-24A27) as Light Source 2. As shown by the arrow, shine the light emitted from the simulated sunlight illumination onto the diffuser 3, extract only the simulated white light, and shine it onto Specimen 1. The incident angle of the simulated white light with respect to Specimen 1 as shown by the arrow is 10°. This simulated white light has a light intensity in the wavelength range of 420 - 680 nm, and the light intensity of each wavelength in the wavelength range of 440 - 650 nm is more than half of the light intensity of the wavelength with the highest light intensity.

[0186] Set a two-dimensional spectroradiometer 4 (manufactured by TOPCON TECHNOHOUSE Co., Ltd., SR-5000) at a position directly opposite to Specimen 1, detect the reflected light reflected from Specimen 1 when the simulated white light is shone on it, and obtain the reflection spectrum.

[0187] Convert the obtained reflection spectrum to the CIE 1931 colorimetric system to obtain the chromaticity x and chromaticity y.

[0188] Show the results in the "CIE 1931 Colorimetric System" of "Sulfide Solid Electrolyte Powder" in Table 1.

[0189] [Evaluation: Electrostatic adhesion amount]

[0190] The surface of a small tray (manufactured by AS ONE Corporation, Balance Tray Natural 10ml) for weighing powders made of polystyrene was electrostatically removed using an ion generator (AD-1683), thereby temporarily removing static electricity. Subsequently, 1 g of the obtained sulfide solid electrolyte powder was placed on the above small tray, and then the powder was removed, thereby conditioning the surface of the small tray. When removing the powder, a wiping paper made of polypropylene (manufactured by CRECIA Corporation, WYPALL) was used until the remaining amount of the powder was less than 0.01 mg.

[0191] Then, 1 g of the sulfide solid electrolyte powder was placed on the small tray again, and the small tray was tilted 90° to cause the sulfide solid electrolyte powder to slide off the small tray. Then, the sulfide solid electrolyte powder remaining on the small tray was weighed.

[0192] The results are shown in the "electrostatic adhesion amount" of "sulfide solid electrolyte powder" in Table 1, showing the residual ratio on the small tray when the amount of the initial sulfide solid electrolyte powder, i.e., 1 g, is set to 100 wt%.

[0193] The smaller the electrostatic adhesion amount, the more the charging on the powder surface is suppressed.

[0194] [Evaluation: Lithium ion conductivity]

[0195] The obtained sulfide solid electrolyte powder was made into a pellet under a pressure of 380 kPa as a measurement sample, and was measured using an alternating current impedance measurement device (manufactured by Bio-Logic Sciences Instruments Corporation, potentiostat / galvanostat VSP) to obtain the lithium ion conductivity. The measurement conditions were measurement frequency: 100 Hz to 1 MHz, measurement voltage: 100 mV, and measurement temperature: 25 °C. The results are shown in the "σ Li+ " of "sulfide solid electrolyte powder" in Table 1.

[0196] [Evaluation: Specific surface area]

[0197] Regarding the specific surface area of the obtained sulfide solid electrolyte powder, a specific surface area and pore size distribution measurement device (manufactured by Micromeritics Corporation, pore size distribution measurement device ASAP-2020) was used, and based on the adsorption and desorption isotherm based on nitrogen adsorption and desorption, the BET (Brunauer Emmett Teller) formula was used for analysis to obtain the BET specific surface area. The measurement was carried out in a manner that did not contact the atmosphere from sampling including the measurement.

[0198] Specifically, as a pretreatment, reduced pressure is applied at room temperature for 12 hours or more. The sample weight is 0.15 g, the analysis temperature is -196°C, and measurements are made at 5 or more points in the range where the relative pressure (P / P 0 ) is 0.1 to 0.25 to prepare a BET curve. The specific surface area is calculated from the obtained curve. The results are shown in the "specific surface area" of "sulfide solid electrolyte powder" in Table 1.

[0199] [Table 1]

[0200]

[0201] Based on the above results, both the chromaticity x and chromaticity y of the sulfide solid electrolyte powder of this embodiment are in the range of 0.32 to 0.36, and different from the conventional yellowish sulfide solid electrolyte powder and grayish sulfide solid electrolyte powder, it is achromatic and highly bright white. The sulfide solid electrolyte powder of this embodiment is a submicron powder with a specific surface area of 5 m 2 / g or more, but the charging on the powder surface is suppressed. Therefore, it is possible to suppress scattering caused by static electricity during packaging, weighing, etc. at the time of shipment, achieve a reduction in scattering loss, and prevent equipment failures caused by powder adhering to the equipment.

[0202] In addition, compared with the conventional yellowish sulfide solid electrolyte powder and grayish sulfide solid electrolyte powder, a high lithium ion conductivity result is obtained in the sulfide solid electrolyte powder of this embodiment. It is considered that this is because in addition to suppression of lattice defects such as sulfur deficiency and suppression of reduction in lithium ion conductivity on the powder surface, hindrance to lithium ion conduction caused by sulfur adhering to the powder surface is also suppressed.

[0203] The present invention has been described in detail with reference to specific embodiments, but those skilled in the art can of course make various changes and modifications without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application filed on October 17, 2022 (Japanese Patent Application No. 2022-166400), the content of which is incorporated herein by reference.

Claims

1. A sulfide solid electrolyte powder having a specific surface area of 5 m 2 / g or more, When the reflected light when irradiating the pressed powder particles with simulated white light under the conditions shown below is expressed in the CIE 1931 colorimetric system, both the chromaticity x and the chromaticity y are in the range of 0.32 to 0.

36. The pressed powder particles are obtained by molding the sulfide solid electrolyte powder at a pressure of 300 MPa. Conditions: The simulated white light has a light intensity in the wavelength range of 420 to 680 nm, and the light intensity of each wavelength in the wavelength range of 440 to 650 nm is more than half of the light intensity of the wavelength with the highest light intensity.

2. The sulfide solid electrolyte powder according to claim 1, wherein, The specific surface area is 8 m 2 / g or more.

3. The sulfide solid electrolyte powder according to claim 1, wherein, both the chromaticity x and the chromaticity y are in the range of 0.325 to 0.

355.

4. The sulfide solid electrolyte powder according to claim 1, wherein, the lithium ion conductivity is 2 mS / cm or more.

5. The sulfide solid electrolyte powder according to claim 1, wherein, it has a thioargentite-type crystal structure.

6. The sulfide solid electrolyte powder according to claim 5, wherein, The argyrodite crystal structure is represented by the composition formula Li a PS b Ha c as follows the Ha is at least one selected from F, Cl, Br, and I, and a, b, and c in the composition formula satisfy the relationship of 5 ≤ a ≤ 7, 4 ≤ b ≤ 6, and 1.3 ≤ c ≤ 2.

7. The sulfide solid electrolyte powder according to claim 6, wherein, as the Ha, it contains Cl and Br. When the content of Cl in the thioargentite-type crystal structure is set as α and the content of Br is set as β, the content ratio represented by α / β is 0.1 to 10, and the units of α and β are at%.

8. The sulfide solid electrolyte powder according to claim 1, which is used in a lithium ion secondary battery.

9. A all-solid-state lithium ion secondary battery, which comprises the sulfide solid electrolyte powder according to any one of claims 1 to 8.

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