Sulfide solid electrolyte

Abstract

To provide a sulfide solid electrolyte capable of reducing the amount of generation of hydrogen sulfide gas caused by reaction with moisture in the atmosphere while achieving high Li ion conductivity.SOLUTION: A sulfide solid electrolyte characterized in that, when X-ray diffraction measurement using a CuKα ray is performed at room temperature, in a diffraction pattern, a diffraction intensity of the strongest peak is defined as IX, a diffraction intensity of a peak at 2θ=25.50°±0.5° is defined as IA, and a diffraction intensity of a peak at 2θ=32.46°±0.5° is defined as IB, a peak intensity ratio IA / IX of IA relative to IX is 0.5 or less, and a peak intensity ratio IB / IX of IB relative to IX is 0.5 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a sulfide solid electrolyte that is suitable for use in, for example, all-solid-state batteries. [Background technology]

[0002] Currently available lithium-ion batteries use flammable organic electrolytes as the electrolyte material, making it necessary to install safety devices to prevent temperature rises in the event of a short circuit, as well as to improve the structure and materials to prevent short circuits. In contrast, all-solid-state lithium-ion batteries use a solid electrolyte as the electrolyte material, which simplifies the safety devices that are associated with flammable organic electrolytes, and is therefore superior in terms of manufacturing cost and productivity. In addition, by stacking batteries in a bipolar configuration in series within the same cell, there is also the potential for development to achieve high voltage and high output.

[0003] As a solid electrolyte suitable for all-solid-state batteries, sulfide solid electrolytes with high ionic conductivity are known, as described in Patent Document 1. However, sulfide-based solid electrolytes have the disadvantage of easily reacting with moisture in the atmosphere, generating toxic hydrogen sulfide gas and producing oxides that also reduce Li-ion conductivity. This has led to increased costs associated with managing the dew point temperature during the production of solid electrolytes and all-solid-state batteries, as well as the need for safety measures to prevent the generation of hydrogen sulfide gas.

[0004] Therefore, Patent Documents 2 to 4 propose several techniques for suppressing the amount of hydrogen sulfide gas generated. Furthermore, Patent Document 5 describes a method for producing a sulfide solid electrolyte by heat treating a raw material composition containing elemental sulfur or a sulfur compound. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2011 / 118801 [Patent Document 2] Japanese Patent Application Publication No. 2019-160625 [Patent Document 3] International Publication No. 2021 / 029315 [Patent Document 4] International Publication No. 2021 / 117869 [Patent Document 5] Japanese Patent Publication No. 2022-022955 Summary of the Invention [Problem to be solved by the invention]

[0006] However, Patent Documents 2 to 4 disclose techniques for suppressing the amount of hydrogen sulfide gas generated, but they have the problem of reducing Li-ion conductivity, making it impossible to construct a high-power solid-state battery. That is, in Patent Documents 2 to 4, it was difficult to achieve both high Li-ion conductivity, for example, exceeding 5.0 mS / cm, and suppression of the amount of hydrogen sulfide gas generated. Furthermore, Patent Document 5 has the problem that by-products (impurity phases) other than the target sulfide solid electrolyte are generated, and these by-products have adverse effects on the generation of hydrogen sulfide gas and the decrease in ionic conductivity.

[0007] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a sulfide solid electrolyte that has high Li ion conductivity while suppressing the amount of hydrogen sulfide gas generated by reaction with moisture in the atmosphere. [Means for solving the problem]

[0008] To solve the above problems, the present inventors conducted extensive research and found that, in an LGPS-type sulfide solid electrolyte, compounds that have a diffraction peak at 2θ=25.50°±0.5° or 2θ=32.46°±0.5° when measured by X-ray diffraction are responsible for the generation of hydrogen sulfide gas and the decrease in ionic conductivity. Therefore, the inventors discovered that by reducing the content of at least one or both of these compounds in an LGPS-type sulfide solid electrolyte, it is possible to provide a sulfide solid electrolyte that has high Li-ion conductivity while suppressing the amount of hydrogen sulfide gas generated by reaction with moisture in the air.

[0009] The present invention has been made based on the above findings, and the sulfide solid electrolyte of the first aspect of the present invention has a diffraction intensity of the strongest peak in a diffraction pattern of I when X-ray diffraction measurement using CuKα radiation is performed at room temperature. X The diffraction intensity of the peak at 2θ = 25.50° ± 0.5° is I A The diffraction intensity of the peak at 2θ = 32.46° ± 0.5° is I B As, I X I against A Peak intensity ratio I A / I X is less than or equal to 0.5, and I X I against B Peak intensity ratio I B / I X is 0.5 or less.

[0010] According to the sulfide solid electrolyte of the first aspect of the present invention, when X-ray diffraction measurement using CuKα radiation is performed at room temperature, the diffraction intensity of the strongest peak in the diffraction pattern is I X The diffraction intensity of the peak at 2θ = 25.50° ± 0.5° is I A The diffraction intensity of the peak at 2θ = 32.46° ± 0.5° is I B As, I X I against A Peak intensity ratio I A / I X is less than or equal to 0.5, and I X I against B Peak intensity ratio IB / I X is set to 0.5 or less, the content of the compound having a peak at 2θ=32.46°±0.5° and the content of the compound having a peak at 2θ=32.46°±0.5° are sufficiently reduced, making it possible to suppress the generation of hydrogen sulfide gas and to suppress the decrease in ionic conductivity.

[0011] The sulfide solid electrolyte of the second aspect of the present invention is the sulfide solid electrolyte of the first aspect of the present invention, which is the same as the sulfide solid electrolyte of the first aspect of the present invention except that the sulfide solid electrolyte is LGPS (Li 10 GeP2S 12 ) type crystal structure.

[0012] The sulfide solid electrolyte of the second aspect of the present invention has an LGPS-type crystal structure belonging to the space group P42 / nmc, and is therefore particularly suitable as a solid electrolyte for use in all-solid-state batteries and the like. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a sulfide solid electrolyte that has high Li ion conductivity while suppressing the amount of hydrogen sulfide gas generated by reaction with moisture in the atmosphere. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a flow chart showing an example of a method for producing a sulfide solid electrolyte according to an embodiment of the present invention. [Figure 2] FIG. 1 is a diagram showing an example of the results of XRD measurement of the sulfide solid electrolyte of Example 1 in the Examples. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the following embodiments are specifically described to provide a better understanding of the gist of the invention, and do not limit the present invention unless otherwise specified.

[0016] The sulfide solid electrolyte according to this embodiment is a sulfide used as a solid electrolyte for constituting, for example, an all-solid-state battery. Sulfide solid electrolyte materials have high ionic conductivity, are non-flammable, and are highly safe, and are therefore applied to electric vehicles and the like.

[0017] In the sulfide solid electrolyte according to this embodiment, when X-ray diffraction measurement using CuKα radiation is performed at room temperature, the diffraction intensity of the strongest peak in the diffraction pattern is I X The diffraction intensity of the peak at 2θ = 25.50° ± 0.5° is I A The diffraction intensity of the peak at 2θ = 32.46° ± 0.5° is I B As, I X I against A Peak intensity ratio I A / I X is less than or equal to 0.5, and I X I against B Peak intensity ratio I B / I X is set to be 0.5 or less.

[0018] That is, in the sulfide solid electrolyte according to this embodiment, the above-mentioned peak intensity ratio I A / I X , and peak intensity ratio I B / I X Both of these are considered to be 0.5 or less, and the content of both the compound having a peak at 2θ=25.50°±0.5° and the compound having a peak at 2θ=32.46°±0.5° is considered to be sufficiently reduced.

[0019] In the sulfide solid electrolyte of this embodiment, LGPS (Li 10 GeP2S 12 ) type crystal structure, and when X-ray diffraction measurement is performed at room temperature using CuKα radiation, the following diffraction peaks of formulas (C1) to (C6) are detected. 2θ=17.38°±0.5° (C1) 2θ=20.18°±0.5° (C2) 2θ=20.44°±0.5° (C3) 2θ=23.96°±0.5° (C4) 2θ=26.96°±0.5° (C5) 2θ=29.58°±0.5° (C6)

[0020] Next, an example of a method for producing the sulfide solid electrolyte according to this embodiment will be described with reference to the flow chart of FIG. As shown in FIG. 1, this embodiment includes a raw material mixing step S01 and a production step S02.

[0021] (Raw material mixing process S01) First, raw materials containing the elements that constitute the sulfide solid electrolyte are mixed to obtain a mixed raw material. In this embodiment, the amount of P element in the mixed raw material is set to a range of -2.5% to 2.0% of the stoichiometric amount of P element in the LGPS crystal. By setting the amount of P element in the mixed raw material in this manner, it is possible to prevent the formation of a compound having a peak at 2θ=25.50°±0.5° and a compound having a peak at 2θ=32.46°±0.5° in the formation step S02.

[0022] In this embodiment, elemental sulfur is preferably used as the raw material. In order to utilize a solid-liquid reaction between each raw material and liquid sulfur to produce a sulfide solid electrolyte, excess elemental sulfur exceeding the stoichiometric composition of the sulfide solid electrolyte may be added to the mixed raw material. Furthermore, in order to promote elemental diffusion and chemical reaction in the subsequent production step S02, it is preferable that each raw material and excess elemental sulfur be in the form of powder or granules (powder-like powder, particulate granules, or an aggregate of powder and granules), and among these, powder is more preferable.

[0023] Elemental sulfur refers to sulfur that does not contain elements other than sulfur, except for inevitable impurities. Unless otherwise specified, in other descriptions of this embodiment, each raw material may contain inevitable impurities. Furthermore, the elemental sulfur to be added may be any of sulfur allotropes, such as α sulfur (orthorhombic sulfur), β sulfur (monoclinic sulfur), γ sulfur (monoclinic sulfur), or rubber sulfur, or may contain multiple allotropes.

[0024] The mixing method in the raw material mixing step S01 is not particularly limited as long as it can uniformly mix the raw materials, and examples of various existing methods include a mortar, a general mixer, a blender, a ball mill, a bead mill, a vibration mill, a V-type mixer, etc. Furthermore, instead of the general mixing process, mechanical milling may be performed using a planetary ball mill, a vibration mill, a ball mill, etc.

[0025] Furthermore, when raw material 11 contains sulfides or the like, the mixing treatment in raw material mixing step S01 is preferably carried out in a gas atmosphere that does not react with the raw material, and therefore is preferably carried out in an inert atmosphere such as nitrogen, argon, or other rare gases. In addition, it is preferable that the atmospheric gas used does not contain moisture and oxygen gas, and in particular, the moisture content in the atmospheric gas is preferably 500 ppm or less, more preferably 100 ppm or less, and even more preferably 10 ppm or less. By keeping the moisture content in the atmospheric gas within this range, oxidation due to moisture is suppressed, and a high-quality sulfide solid electrolyte can be produced.

[0026] (Generation process S02) In the production step S02, the mixed raw materials placed in a firing vessel such as a crucible or a sagger are heated to produce a sulfide solid electrolyte. Regarding the material of the firing container, it is preferable that the inner wall of the container is made of a material that is unlikely to react with the melt, such as elemental sulfur or sulfides, in other words, a material that is unlikely to be corroded by sulfurization, and examples thereof include alumina, zirconia, carbon, and silicon carbide.

[0027] The heating temperature in the generating step S02 is preferably 400° C. or higher, more preferably 450° C. or higher, and even more preferably 500° C. or higher. On the other hand, the heating temperature is preferably 1000° C. or lower, and more preferably 650° C. or higher. The holding time at the heating temperature is preferably 30 minutes or more, more preferably 60 minutes or more, while the holding time at the heating temperature is preferably 12 hours or less, more preferably 6 hours or less.

[0028] The heat treatment in the production step S02 is preferably carried out in a gas atmosphere that does not react with the mixed raw materials, the intermediate product, or the sulfide solid electrolyte, and is therefore preferably carried out in an inert atmosphere such as nitrogen, argon, or other rare gases. In addition, it is preferable that the atmospheric gas used does not contain moisture and oxygen gas, and in particular, the moisture content in the atmospheric gas is preferably 500 ppm or less, more preferably 100 ppm or less, and even more preferably 10 ppm or less. By keeping the moisture content in the atmospheric gas within this range, reaction with moisture is suppressed, and a high-quality sulfide solid electrolyte can be produced.

[0029] According to the sulfide solid electrolyte of the present embodiment configured as described above, when X-ray diffraction measurement using CuKα rays is performed at room temperature, the diffraction intensity of the strongest peak in the diffraction pattern is I X The diffraction intensity of the peak at 2θ = 25.50° ± 0.5° is I A The diffraction intensity of the peak at 2θ = 32.46° ± 0.5° is I B As, I X I against A Peak intensity ratio I A / I X , and I X I against B Peak intensity ratio I B / I Xare both 0.5 or less, and the contents of both the compound having a peak at 2θ=25.50°±0.5° and the compound having a peak at 2θ=32.46°±0.5° are considered to be sufficiently reduced, so that it is possible to suppress the generation of hydrogen sulfide gas and to suppress the decrease in ionic conductivity.

[0030] In addition, in the sulfide solid electrolyte of this embodiment, LGPS (Li 10 GeP2S 12 ) type crystal structure, and when X-ray diffraction measurement using CuKα radiation is performed at room temperature, the peaks of the above formulas (C1) to (C6) are detected as diffraction peaks. In this case, the solid electrolyte is particularly suitable for use in all-solid-state batteries and the like.

[0031] Although one embodiment of the present invention has been described above, the present invention is not limited to this and can be modified as appropriate within the scope of the technical idea of ​​the invention. [Example]

[0032] A confirmation experiment conducted to confirm the effectiveness of the present invention will be described.

[0033] The raw materials Li2S, Ge, P, and S were prepared, weighed out to a predetermined ratio, and mixed in a mortar. At this time, the amount of P element in the mixed raw materials was adjusted to the ratio shown in Table 1 relative to the stoichiometric amount of P element in the target LGPS-type crystal. The mixed raw materials were placed in an alumina firing container and then placed in a firing furnace. Then, firing was performed under the conditions of an Ar atmosphere, a heating temperature of 550°C, and a holding time of 6 hours. In this way, sulfide solid electrolytes of the present invention and comparative examples were produced.

[0034] The obtained sulfide solid electrolyte was subjected to X-ray diffraction measurement (XRD measurement) using CuKα radiation. The ionic conductivity of the sulfide solid electrolyte was also measured. Furthermore, the amount of hydrogen sulfide generated was evaluated. The XRD measurement method, ionic conductivity, and evaluation methods for the amount of hydrogen sulfide generated are described below.

[0035] <XRD measurement> XRD measurement was performed in the range of 10° ≤ 2θ ≤ 55° using an XRD instrument "D8 ADVANCE" manufactured by Bruker, with a step width of 0.01° and an integration time of 1.2 seconds / step under the θ-2θ measurement condition. The measurement sample was prepared in a glove box under an argon atmosphere. The solid electrolyte member pulverized with an agate mortar was sealed in a sealable measurement cell, and powder X-ray diffraction measurement was performed while maintaining a state of not being exposed to the atmosphere. The XRD measurement results of Example 1 of the present invention are shown in FIG. 2.

[0036] <Ionic conductivity measurement> After each of the solid electrolyte members obtained as described above was taken out in a glove box under an argon atmosphere, it was pulverized with an agate mortar, 0.200 g was weighed, filled into a ceramic insulating tube (cylindrical with an inner diameter of 10.2 mm) under an applied pressure of 30 MPa, and the insulating tube was sealed with a stainless steel ionic conductivity measurement cell. Then, using a measurement device "Potentiostat / Galvanostat SP-300" manufactured by Biologic, the ionic conductivity (mS / cm) was measured by the alternating current impedance method under the conditions of a measurement temperature of 25°C and a measurement frequency of 1 Hz to 1 MHz.

[0037] <Measurement of hydrogen sulfide gas generation amount> In a glove box with a dew point of -30°C, 10 mg of the measurement sample and a digital hydrogen sulfide meter were placed, and they were loaded into a 1 L sealed container in the glove box and left standing, and the hydrogen sulfide concentration after 1 hour was measured.

[0038]

Table 1

[0039] In Comparative Example 1, when X-ray diffraction measurement using CuKα radiation was performed at room temperature, the diffraction intensity of the strongest peak in the diffraction pattern was I X and the diffraction intensity of the peak at 2θ = 25.50° ± 0.5° was IA As, I X I against A Peak intensity ratio I A / I X The ionic conductivity was low at 4.8 mS / cm, and the amount of hydrogen sulfide generated was high at 36.3 ppm.

[0040] In Comparative Example 2, when X-ray diffraction measurement using CuKα rays was performed at room temperature, the diffraction intensity of the strongest peak in the diffraction pattern was I X The diffraction intensity of the peak at 2θ = 32.46° ± 0.5° is I B As, I X I against B Peak intensity ratio I B / I X The ionic conductivity was low at 7.2 mS / cm, and the amount of hydrogen sulfide generated was high at 14.9 ppm.

[0041] In Comparative Example 3, when X-ray diffraction measurement using CuKα radiation was performed at room temperature, the diffraction intensity of the strongest peak in the diffraction pattern was I X The diffraction intensity of the peak at 2θ = 32.46° ± 0.5° is I B As, I X I against B Peak intensity ratio I B / I X The ionic conductivity was 0.705, the ionic conductivity was low at 6.8 mS / cm, and the amount of hydrogen sulfide generated was high at 16.3 ppm.

[0042] In contrast, in Examples 1-3 of the present invention, when X-ray diffraction measurement using CuKα radiation was performed at room temperature, the diffraction intensity of the strongest peak in the diffraction pattern was I X The diffraction intensity of the peak at 2θ = 25.50° ± 0.5° is I A The diffraction intensity of the peak at 2θ = 32.46° ± 0.5° is I B As, I X I against A Peak intensity ratio I A / I X is less than or equal to 0.5, and IX I against B Peak intensity ratio I B / I X The ionic conductivity was 9.3 mS / cm or more, which was sufficiently higher than that of the comparative example, and the amount of hydrogen sulfide generated was less than that of the comparative example.

[0043] As a result of the above confirmatory experiments, it was confirmed that the present invention can provide a sulfide solid electrolyte having high Li-ion conductivity while suppressing the amount of hydrogen sulfide gas generated by reaction with moisture in the atmosphere.

Claims

【Request Item 1】 When X-ray diffraction measurement using CuKα radiation was performed at room temperature, the diffraction intensity of the strongest peak in the diffraction pattern was determined as I Ｘ The diffraction intensity of the peak at 2θ = 25.50° ± 0.5° is I Ａ The diffraction intensity of the peak at 2θ = 32.46° ± 0.5° is I Ｂ As, I Ｘ I against Ａ Peak intensity ratio I Ａ / I Ｘ is 0.5 or less, and I Ｘ I against Ｂ Peak intensity ratio I Ｂ / I Ｘ A sulfide solid electrolyte characterized in that: 【Request Item 2】 LGPS (Li) belonging to the space group P42 / nmc １０ GeP ２ S １２ 2. The sulfide solid electrolyte according to claim 1, characterized in that it has a crystalline structure of the sulphide-based solid electrolyte.

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