Sulfide solid electrolyte

Abstract

To provide a sulfide solid electrolyte that exhibits sufficiently high ionic conductivity and is especially suitable for a high-output solid-state battery.SOLUTION: A sulfide solid electrolyte characterized in that, when X-ray diffraction measurement using Cu Kα radiation is performed at room temperature, in a diffraction pattern, a diffraction intensity of a strongest peak is defined as IA, a diffraction intensity of a peak at 2θ=26.06°±0.5° derived from a Li3 PS4-type crystal structure belonging to a space group Pnma is defined as IB, and a diffraction intensity of a peak at 2θ=18.24°±0.5° is defined as IC, and either one or both of a peak intensity ratio IB / IA of IB relative to IA and a peak intensity ratio IC / IA of IC relative to IA are 0.500 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 sulfide solid electrolyte as the electrolyte material, which simplifies the safety devices that are associated with flammable organic electrolytes and offers superior manufacturing costs 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] A widely used method for producing sulfide solid electrolytes involves first mechanically milling a mixture of raw materials to vitrify or amorphousize it, then heat treating it to synthesize the sulfide solid electrolyte through a solid-state reaction. For example, Patent Document 1 describes a process for producing sulfide glass and glass ceramics, which are types of sulfide-based solid electrolytes, in which a mixture of metallic lithium, elemental sulfur, and elemental phosphorus is vitrified by mechanical milling, followed by heat treatment.

[0004] Furthermore, Patent Documents 2 and 3 describe a process for producing a sulfide-based solid electrolyte having an LGPS-type crystal structure, in which a mixture of various sulfides is made amorphous by mechanical milling, and then heat-treated to crystallize it through a solid-phase reaction. That is, as disclosed in Patent Documents 1 to 3, a method of subjecting a mixture of electrolyte raw materials to mechanical milling to diffuse and mix the contained elements and homogenize the chemical composition of the entire mixture before heat treatment has become a common method for producing a solid electrolyte with sufficient ionic conductivity.

[0005] Furthermore, Patent Document 4 describes a method for producing a crystalline sulfide-based solid electrolyte, in which elemental sulfur or a sulfur compound is mixed with a solid electrolyte raw material, and the mixture is heat-treated. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-208919 [Patent Document 2] Patent No. 5527673 [Patent Document 3] Patent No. 5888609 [Patent Document 4] Japanese Patent Publication No. 2022-022955 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the manufacturing methods described in Patent Documents 1 to 4 generate impurities (by-products) other than the target sulfide solid electrolyte, and these impurities may cause a decrease in the ionic conductivity of the sulfide solid electrolyte. For this reason, the sulfide solid electrolytes manufactured by the manufacturing methods described in Patent Documents 1 to 4 have insufficient ionic conductivity and cannot be used as sulfide solid electrolytes for forming high-power batteries.

[0008] 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 sufficiently high ionic conductivity and is particularly suitable for high-power solid-state batteries. [Means for solving the problem]

[0009] In order to solve the above problems, the present inventors conducted extensive research and found that β-Li3PS4, a type of impurity (by-product) generated during production, has a significant effect on the ionic conductivity of sulfide solid electrolytes. They also found that the ionic conductivity of sulfide solid electrolytes can be improved by reducing β-Li3PS4.

[0010] 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. A and the space group P nma The diffraction intensity of the peak at 2θ=26.06°±0.5°, which is due to the Li3PS4 type crystal structure, is B , the diffraction intensity of the peak at 2θ = 18.24° ± 0.5° is I C As, I A I against B Peak intensity ratio I B / I A , and I A I against C Peak intensity ratio I C / I A Either one or both of these is 0.500 or less.

[0011] According to the sulfide solid electrolyte of the first aspect of the present invention, when X-ray diffraction measurement is performed at room temperature using CuKα radiation, the diffraction intensity of the strongest peak in the diffraction pattern is I A and the space group P nma The diffraction intensity of the peak at 2θ=26.06°±0.5°, which is due to the Li3PS4 type crystal structure, is B , the diffraction intensity of the peak at 2θ = 18.24° ± 0.5° is I C As, I A I against B Peak intensity ratio I B / I A , and I A I against C Peak intensity ratio I C / I ASince either one or both of these are set to 0.500 or less, the content of β-Li3PS4 is sufficiently reduced, and the ionic conductivity can be significantly improved.

[0012] The sulfide solid electrolyte of the second aspect of the present invention is characterized in that the sulfide solid electrolyte of the first aspect of the present invention has an LGPS-type crystal structure belonging to the space group P42 / nmc. 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.

[0013] The sulfide solid electrolyte of the third aspect of the present invention is characterized in that the sulfide solid electrolyte of the first aspect of the present invention has an Argyrodaite-type crystal structure. The sulfide solid electrolyte of the third aspect of the present invention has an Argyrodaite-type crystal structure, and is therefore particularly suitable as a solid electrolyte for use in all-solid-state batteries and the like. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a sulfide solid electrolyte that has sufficiently high ionic conductivity and is particularly suitable for high-power solid-state batteries. [Brief explanation of the drawings]

[0015] [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

[0016] 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.

[0017] 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.

[0018] In the sulfide solid electrolyte according to this embodiment, the diffraction intensity of the strongest peak in the diffraction pattern is I A and the space group P nma The diffraction intensity of the peak at 2θ=26.06°±0.5°, which is due to the Li3PS4 type crystal structure, is B , the diffraction intensity of the peak at 2θ = 18.24° ± 0.5° is I C As, I A I against B Peak intensity ratio I B / I A , and I A I against C Peak intensity ratio I C / I A Either one or both of these are set to be below 0.500.

[0019] That is, in the sulfide solid electrolyte according to this embodiment, the peak intensity I B , I C It is believed that the content of the impurity β-Li3PS4 is sufficiently reduced.

[0020] The sulfide solid electrolyte of this embodiment may have an LGPS-type crystal structure belonging to the space group P42 / nmc. When X-ray diffraction measurement using CuKα radiation is performed at room temperature, the peaks of the following formulas (C1) to (C6) may be detected as diffraction peaks. 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)

[0021] Alternatively, the sulfide solid electrolyte of this embodiment may have an argyrodaite-type crystal structure.

[0022] 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.

[0023] (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, elemental sulfur is preferably used as the raw material. In addition, in order to utilize a solid-liquid reaction between each raw material and liquid sulfur to generate the 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] (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.

[0028] In this embodiment, the temperature rise rate during heating in the production step S02 is set to a range of 0.5°C / min to 10°C / min. By specifying the temperature rise rate in this manner, it is possible to suppress the production of β-Li3PS4, which is an impurity (by-product). The rate of temperature increase during heating in the production step S02 is preferably 1°C / min or more, more preferably 2°C / min or more, and is preferably 8°C / min or less, more preferably 5°C / min or less.

[0029] Moreover, the heating temperature in the generating step S02 is preferably 300°C or higher, more preferably 350°C or higher, and even more preferably 400°C or higher. Furthermore, 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.

[0030] 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.

[0031] 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 A and the space group P nma The diffraction intensity of the peak at 2θ=26.06°±0.5°, which is due to the Li3PS4 type crystal structure, is B , the diffraction intensity of the peak at 2θ = 18.24° ± 0.5° is I C As, I A I against B Peak intensity ratio I B / I A, and I A I against B Peak intensity ratio I C / I A Since either one or both of these are set to 0.500 or less, the content of β-Li3PS4 is sufficiently reduced, and the ionic conductivity can be significantly improved.

[0032] Furthermore, in the sulfide solid electrolyte of the present embodiment, if it has an LGPS-type crystal structure belonging to the space group P42 / nmc, and if peaks of the above formulas (C1) to (C6) are detected as diffraction peaks when X-ray diffraction measurement using CuKα rays is performed at room temperature, then the sulfide solid electrolyte is particularly suitable as a solid electrolyte for use in all-solid-state batteries and the like. Alternatively, when the sulfide solid electrolyte of this embodiment has an Argyrodaite-type crystal structure, it is particularly suitable as a solid electrolyte for use in all-solid-state batteries and the like.

[0033] 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]

[0034] A confirmation experiment conducted to confirm the effectiveness of the present invention will be described.

[0035] (Example 1 of the present invention) The raw materials, Li2S, Sn, Si, P, and S, were prepared and weighed to the specified ratio and mixed in a mortar. The mixed raw materials were placed in an alumina firing container and loaded into a firing furnace. They were then fired in a vacuum atmosphere at a heating rate of 2.0°C / min, at a heating temperature of 450°C, and held at the heating temperature for 6 hours. This produced a sulfide solid electrolyte made from LSSPS material.

[0036] (Example 2 of the present invention) The raw materials Li2S, Sn, Si, P, and S were prepared, weighed to the specified ratio, and mixed in a mortar. The mixed raw materials were placed in an alumina firing container and loaded into a firing furnace. They were then fired in a vacuum atmosphere at a heating rate of 5.0°C / min, at a heating temperature of 450°C, and held at the heating temperature for 6 hours. This produced a sulfide solid electrolyte made from LSSPS material.

[0037] (Example 3 of the present invention) The raw materials Li2S, Sn, Si, P, and S were prepared, weighed to the specified ratio, and mixed in a mortar. The mixed raw materials were placed in an alumina firing container and loaded into a firing furnace. They were then fired in a vacuum atmosphere at a heating rate of 8.0°C / min, at a heating temperature of 450°C, and held at the heating temperature for 6 hours. This produced a sulfide solid electrolyte made from LSSPS material.

[0038] (Example 4 of the present invention) The raw materials Li2S, Sn, Si, P, and S were prepared, weighed to the specified ratio, and mixed in a mortar. The mixed raw materials were placed in an alumina firing container and placed in a firing furnace. The mixture was then fired at a heating rate of 10.0°C / min, at a heating temperature of 400°C, and held at the heating temperature for 3 hours. This produced a sulfide solid electrolyte made from LSSPS material.

[0039] (Comparative Example 1) The raw materials Li2S, Sn, Si, P, and S were prepared, weighed to the specified ratio, and mixed in a mortar. The mixed raw materials were placed in an alumina firing container and placed in a firing furnace. The materials were then fired in a vacuum atmosphere at a heating rate of 0.1°C / min, at a heating temperature of 400°C, and held at the heating temperature for 6 hours. This produced a sulfide solid electrolyte made from LSSPS material.

[0040] (Comparative Example 2) As raw materials, Li2S, Sn, Si, P, and S were prepared, weighed so as to have a predetermined ratio, and mixed in a mortar. The mixed raw materials were placed in a firing container made of alumina and loaded into a firing furnace. Then, firing was performed under the conditions of a vacuum atmosphere, a heating rate of 20.0 °C / min, a heating temperature of 400 °C, and a holding time at the heating temperature of 6 hours. As a result, a sulfide solid electrolyte made of an LSSPS material was produced.

[0041] Regarding the obtained sulfide solid electrolyte, X-ray diffraction measurement (XRD measurement) using CuKα rays was performed. Furthermore, the ionic conductivity of the obtained sulfide solid electrolyte was measured. The XRD measurement method and the evaluation method of ionic conductivity are shown below.

[0042] <XRD Measurement> The XRD measurement was carried out using an XRD device "SmartLab" manufactured by Rigaku in the range of 10° ≤ 2θ ≤ 40° under the conditions of a step width of 0.02° and a scan speed of 5° / min. The measurement sample was prepared in a glove box under an argon atmosphere, and the solid electrolyte member pulverized in 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 measurement results of Example 1 of the present invention are shown in Figure 2.

[0043] <Ionic Conductivity> After the obtained solid electrolyte was taken out in a glove box under an argon atmosphere, it was pulverized in an agate mortar, 0.200 g was weighed, filled into a ceramic insulating tube (cylindrical with an inner diameter of 10.2 mm) with 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.

[0044]

Table 1

[0045] 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 A and the space group P nma The diffraction intensity of the peak at 2θ=26.06°±0.5°, which is due to the Li3PS4 type crystal structure, is B , the diffraction intensity of the peak at 2θ = 18.24° ± 0.5° is I C As, I A I against B Peak intensity ratio I B / I A , and I A I against C Peak intensity ratio I C / I A All of these values ​​exceeded 0.500, and the ionic conductivity was as low as 3.0 mS / cm.

[0046] 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 A and the space group P nma The diffraction intensity of the peak at 2θ=26.06°±0.5°, which is due to the Li3PS4 type crystal structure, is B , the diffraction intensity of the peak at 2θ = 18.24° ± 0.5° is I C As, I A I against B Peak intensity ratio I B / I A , and I A I against C Peak intensity ratio I C / I A Both values ​​were significantly higher than 0.500, and the ionic conductivity was low at 0.9 mS / cm.

[0047] In contrast, in Inventive Example 1-4, 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 A and the space group P nma The diffraction intensity of the peak at 2θ=26.06°±0.5°, which is due to the Li3PS4 type crystal structure, isB , the diffraction intensity of the peak at 2θ = 18.24° ± 0.5° is I C As, I A I against B Peak intensity ratio I B / I A , and I A I against C Peak intensity ratio I C / I A The ionic conductivity was 5.1 mS / cm or more, which was higher than that of the comparative example.

[0048] As a result of the above confirmatory experiments, it was confirmed that the present invention can provide a sulfide solid electrolyte having sufficiently high ionic conductivity and particularly suitable for high-power solid-state batteries.

Claims

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 Ａ and the space group P ｎｍａ Li belonging to ３ P.S. ４ The diffraction intensity of the peak at 2θ = 26.06° ± 0.5° due to the crystal structure of the I type Ｂ , the diffraction intensity of the peak at 2θ = 18.24° ± 0.5° is I Ｃ As, I Ａ I against Ｂ Peak intensity ratio I Ｂ / I Ａ , and I Ａ I against Ｃ Peak intensity ratio I Ｃ / I Ａ A sulfide solid electrolyte characterized in that either one or both of the above is 0.500 or less.

2. The sulfide solid electrolyte according to claim 1, characterized in that it has an LGPS-type crystal structure belonging to the space group P42 / nmc.

3. 2. The sulfide solid electrolyte according to claim 1, which has an argyrodate-type crystal structure.

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