Sulfide solid electrolyte and method for producing sulfide solid electrolyte

Abstract

To provide a sulfide solid electrolyte excellent in ionic conductivity and particularly suitable for high output solid state battery, and a method for producing the sulfide solid electrolyte.SOLUTION: The sulfide solid electrolyte of the present invention has a crystal structure of the LGPS type belonging to the space group P42 / nmc, and has a full width at half maximum of the peak at 2θ=29.58°±1.0° of 0.1 or less in X-ray diffraction measurements using CuKα radiation. The producing method of the sulfide solid electrolyte of the present invention uses elemental sulfur as a raw material, and the volume ratio of the elemental sulfur in the entire mixed raw material when heated at 120°C is set to be 20% or more. Furthermore, when the heating temperature is T°C, and the holding time is h hours, T×h is 1000 or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a sulfide solid electrolyte suitably used, for example, in all-solid-state batteries and the like, and a method for producing the sulfide solid electrolyte.

Background Art

[0002] In recent years, as an electrolyte for lithium-ion secondary batteries, sulfide-based solid electrolytes having high ionic conductivity and being safer than electrolytic solutions have attracted attention. As a method for producing a sulfide solid electrolyte, a process is widely adopted in which first, mechanical milling is performed on a mixture of raw materials to vitrify or amorphize it, and then heat treatment is performed to synthesize the sulfide solid electrolyte by a solid-phase reaction.

[0003] For example, Patent Document 1 describes a process for producing a sulfide glass and glass ceramics, which are one type of sulfide-based solid electrolyte, in which a mixture of metallic lithium, elemental sulfur, and elemental phosphorus is vitrified by mechanical milling and then heat treatment is performed. Further, 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 amorphized by mechanical milling, then heat treated, and crystallized by a solid-phase reaction. That is, a method of performing mechanical milling on a mixture of electrolyte raw materials to diffuse and mix the contained elements and homogenize the chemical composition of the entire mixture before heat treatment has become common as a method for producing a solid electrolyte having sufficient ionic conductivity.

[0004] Further, Patent Document 4 describes that as a method for producing a crystalline sulfide-based solid electrolyte, 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

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] By the way, in all-solid-state batteries using sulfide solid electrolytes, if the ionic conductivity of the sulfide solid electrolyte is low, the resistance will increase. The sulfide solid electrolytes produced by the production methods described in Patent Documents 1-4 have insufficient ionic conductivity and cannot be used as sulfide solid electrolytes for constructing high-output batteries.

[0007] This invention has been made in view of the above-described circumstances, and an object thereof is to provide a sulfide solid electrolyte having excellent ionic conductivity and particularly suitable for high-output solid-state batteries, and a method for producing this sulfide solid electrolyte.

Means for Solving the Problems

[0008] As a result of intensive studies by the present inventors to solve the above problems, it has been found that by increasing the crystallinity of the sulfide solid electrolyte, the ionic conductivity is significantly improved.

[0009] This invention has been made based on the above findings. The sulfide solid electrolyte of Aspect 1 of this invention has an LGPS-type crystal structure belonging to the space group P42 / nmc, and in X-ray diffraction measurement using CuKα rays, the half-value width of the peak at 2θ = 29.58° ± 1.0° is 0.1 or less.

[0010] According to the sulfide solid electrolyte of Embodiment 1 of the present invention, it has an LGPS-type crystal structure belonging to the space group P42 / nmc, and in the X-ray diffraction measurement using CuKα rays, the half-value width of the peak at 2θ = 29.58° ± 1.0° is 0.1 or less, the crystallinity is sufficiently high, and it is excellent in ionic conductivity. Therefore, it is possible to construct a high-output solid battery.

[0011] The method for producing a sulfide solid electrolyte according to Embodiment 2 of the present invention is a method for producing a sulfide solid electrolyte, which includes a raw material mixing step of mixing raw materials containing each element constituting the sulfide solid electrolyte to obtain a mixed raw material, and a production step of heat-treating the mixed raw material to produce the sulfide solid electrolyte. In the raw material mixing step, elemental sulfur is used as a raw material, and the volume ratio of the elemental sulfur in the entire mixed raw material when the mixed raw material is heated to 120°C is 20% or more. In the production step, the heating temperature is T °C and the holding time is h hours, and it is characterized in that T×h is 1000 or more.

[0012] According to the method for producing a sulfide solid electrolyte according to Embodiment 2 of the present invention, since elemental sulfur is used as a raw material, the volume ratio of the elemental sulfur in the entire mixed raw material when the mixed raw material is heated to 120°C is 20% or more, and in the production step, the heating temperature is T °C and the holding time is h hours, and T×h is 1000 or more, it is possible to produce a sulfide solid electrolyte having high crystallinity and excellent ionic conductivity.

Effects of the Invention

[0013] According to the present invention, it is possible to provide a sulfide solid electrolyte excellent in ionic conductivity and particularly suitable for a high-output solid battery, and a method for producing this sulfide solid electrolyte.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that each of the embodiments shown below is specifically described to better understand the gist of the invention, and does not limit the present invention unless otherwise specified.

[0016] The sulfide solid electrolyte according to this embodiment is used, for example, as a solid electrolyte constituting an all-solid-state battery. Since the sulfide solid electrolyte has a relatively high ionic conductivity, is non-flammable, and has high safety, it is applied to electric vehicles and the like. Here, in order to constitute a high-output solid battery, a sulfide solid electrolyte with even more excellent ionic conductivity is required.

[0017] Therefore, the sulfide solid electrolyte according to this embodiment has a LGPS-type crystal structure belonging to the space group P42 / nmc, and in X-ray diffraction measurement using CuKα rays, the full width at half maximum of the peak at 2θ = 29.58° ± 1.0° is 0.1 or less. That is, in the sulfide solid electrolyte of this embodiment, the intensity height of the maximum peak (the peak at 2θ = 29.58° ± 1.0°) of the X-ray diffraction pattern of the sulfide solid electrolyte having a LGPS-type crystal structure is high, and the full width at half maximum is small. Therefore, the sulfide solid electrolyte according to this embodiment has sufficiently progressed crystallization.

[0018] In the sulfide solid electrolyte of this embodiment, as described above, it has an LGPS-type crystal structure belonging to the space group P42 / nmc. When measured by X-ray diffraction measurement using CuKα rays, the peaks of the following formulas (A) to (F) are detected as diffraction peaks. Regarding the peak of formula (G), either the peak is not detected, or when the diffraction intensity of the peak of formula (F) is IA and the diffraction intensity of the peak of formula (G) is IB, the peak of formula (G) is detected at a diffraction intensity IB such that the peak intensity ratio of IB to IA is less than 50%. 2θ = 17.38° ± 1.0° ··· (A) 2θ = 20.18° ± 1.0° ··· (B) 2θ = 20.44° ± 1.0° ··· (C) 2θ = 23.96° ± 1.0° ··· (D) 2θ = 26.96° ± 1.0° ··· (E) 2θ = 29.58° ± 1.0° ··· (F) 2θ = 27.33° ± 1.0° ··· (G)

[0019] Next, the manufacturing method of the sulfide solid electrolyte of this embodiment will be described with reference to the flowchart of FIG. 1. In this embodiment, as shown in FIG. 1, it has a raw material mixing step S01 and a generation step S02.

[0020] (Raw material mixing step S01) First, raw materials containing each element constituting the sulfide solid electrolyte are mixed to obtain a mixed raw material. Here, elemental sulfur is used as the raw material. This elemental sulfur is mixed such that the volume ratio of elemental sulfur in the entire mixed raw material when the mixed raw material is heated to 120°C is 20% or more. In order to utilize the solid-liquid reaction between each raw material and liquid sulfur for the generation of the sulfide solid electrolyte, an excess of elemental sulfur exceeding the stoichiometric ratio composition of the sulfide solid electrolyte is added to the mixed raw material. In addition, in order to promote element diffusion and chemical reactions in the subsequent generation step S02, each raw material and excess elemental sulfur are preferably in the form of powder particles (powdered powders, particulate granules, or aggregates of powders and granules), and among them, powders are more preferable.

[0021] Elemental sulfur refers to sulfur that contains no elements other than sulfur excluding inevitable impurities. In other descriptions of this embodiment as well, unless otherwise specified, each raw material may contain inevitable impurities. Also, the added elemental sulfur may be any of sulfur allotropes such as α-sulfur (orthorhombic sulfur), β-sulfur (monoclinic sulfur), γ-sulfur (monoclinic sulfur), rubbery sulfur, etc., or may contain a plurality of allotropes.

[0022] The mixing method in the raw material mixing step S01 is not particularly limited as long as it can uniformly mix each raw material. As existing various methods, general mixers, blenders, ball mills, bead mills, vibration mills, V-type mixers, etc. can be mentioned. In addition, when the raw material 11 contains sulfides or the like in the mixing process of the raw material mixing step S01, it is preferably carried out in a gas atmosphere that does not react with the raw material. Therefore, it is preferably carried out in an inert atmosphere such as nitrogen, argon, or other noble gases. In addition, it is preferable that the atmosphere gas used does not contain moisture and oxygen gas. In particular, regarding the moisture content in the atmosphere gas, it is preferably 500 ppm or less, more preferably 100 ppm or less, and even more preferably 10 ppm or less. By setting the moisture content in the atmosphere gas within this range, oxidation by moisture is suppressed, and it is possible to manufacture a high-quality sulfide solid electrolyte.

[0023] (Generation Step S02) In the generation step S02, the mixed raw materials charged into a firing container such as a crucible or a box furnace are heated to generate a sulfide solid electrolyte. Regarding the material of the firing container, it is preferable to use a material for the inner wall of the container that is less likely to react with the melt such as elemental sulfur or sulfides, in other words, a material that is less likely to be corroded by sulfidation. For example, alumina, zirconia, carbon, silicon carbide, etc. can be mentioned.

[0024] And in the production step S02, the heating temperature is set to T °C and the holding time is set to h hours, and T×h is set to 1000 or more. Note that T×h is preferably 2000 or more, and more preferably 3000 or more. Also, there is no particular limitation on the upper limit of T×h, but from the viewpoints of productivity and economy, it is preferably 20000 or less, and more preferably 15000 or less.

[0025] Also, the heating temperature in the production step S02 is preferably 400 °C or more, more preferably 450 °C or more, and even more preferably 500 °C or more. On the other hand, the heating temperature is preferably 1000 °C or less, and more preferably 650 °C or less. Furthermore, the holding time at the heating temperature is preferably set as appropriate so as to satisfy T×h≥1000 described above.

[0026] Also, the heat treatment in the production step S02 is preferably carried out in a gas atmosphere that does not react with the mixed raw material, intermediate product, or sulfide solid electrolyte. Therefore, it is preferably carried out in an inert atmosphere such as nitrogen, argon, or other rare gases. In addition, it is preferable that the atmosphere gas used does not contain moisture and oxygen gas. In particular, regarding the moisture content in the atmosphere gas, it is preferably 500 ppm or less, more preferably 100 ppm or less, and even more preferably 10 ppm or less. By setting the moisture content in the atmosphere gas within this range, the reaction with moisture is suppressed, and it is possible to manufacture a high-quality sulfide solid electrolyte.

[0027] According to the sulfide solid electrolyte of the present embodiment configured as described above, it has an LGPS-type crystal structure belonging to the space group P42 / nmc. In the X-ray diffraction measurement using CuKα rays, the full width at half maximum of the peak at 2θ = 29.58° ± 1.0° is 0.1 or less, indicating that the crystallinity is sufficiently high and the ionic conductivity is excellent. Therefore, it is possible to construct a high-output solid battery.

[0028] Also, according to the method for manufacturing the sulfide solid electrolyte of the present embodiment, elemental sulfur is used as a raw material, and the volume ratio of the elemental sulfur in the entire mixed raw material when the mixed raw material is heated to 120°C is 20% or more. In the production step, with the heating temperature being T °C and the holding time being h hours, since T × h is 1000 or more, it is possible to manufacture a sulfide solid electrolyte with high crystallinity and excellent ionic conductivity.

[0029] As described above, one embodiment of the present invention has been described. However, the present invention is not limited thereto, and can be appropriately modified without departing from the technical idea of the invention.

Example

[0030] A confirmation experiment conducted to confirm the effectiveness of the present invention will be described.

[0031] (Example 1-1, 1-2 of the present invention) As raw materials, Li 2 S, Ge, P, and S were prepared, weighed in a predetermined ratio, and mixed in a mortar. Here, the volume ratio of the elemental sulfur in the entire mixed raw material when the mixed raw material was heated to 120°C was 40%. The mixed raw material was placed in a firing container made of alumina and loaded into a firing furnace. Then, it was fired under the conditions of an Ar atmosphere, a heating temperature of T °C, a holding time of h hours, and T × h = 3000, thereby producing a sulfide solid electrolyte made of an LGPS material.

[0032] (Example 2-1, 2-2 of the present invention) As raw materials, Li 2S, Ge, P, and S were prepared, weighed in a predetermined ratio, and mixed in a mortar. Here, for elemental sulfur, the volume ratio of the elemental sulfur in the whole mixed raw material when the mixed raw material was heated to 120 °C was set to 40%. The mixed raw material was placed in a fired container made of alumina and loaded into a firing furnace. Then, it was fired under the condition that in an Ar atmosphere, the heating temperature was T °C, the holding time was h hours, and T×h = 1000, thereby producing a sulfide solid electrolyte made of LGPS material.

[0033] (Comparative Example 1) As raw materials, Li 2 S, Ge, P, and S were prepared, weighed in a predetermined ratio, and mixed in a mortar. Here, for elemental sulfur, the volume ratio of the elemental sulfur in the whole mixed raw material when the mixed raw material was heated to 120 °C was set to 40%. The mixed raw material was placed in a fired container made of alumina and loaded into a firing furnace. Then, it was fired under the condition that in an Ar atmosphere, the heating temperature was T °C, the holding time was h hours, and T×h = 500, thereby producing a sulfide solid electrolyte made of LGPS material.

[0034] (Examples 3-1 and 3-2 of the present invention) As raw materials, Li 2 S, Si, Sn, P, and S were prepared, weighed in a predetermined ratio, and mixed in a mortar. Here, for elemental sulfur, the volume ratio of the elemental sulfur in the whole mixed raw material when the mixed raw material was heated to 120 °C was set to 40%. The mixed raw material was placed in a fired container made of alumina and loaded into a firing furnace. Then, it was fired under the condition that in an Ar atmosphere, the heating temperature was T °C, the holding time was h hours, and T×h = 3000, thereby producing a sulfide solid electrolyte made of LSSPS material.

[0035] (Examples 4-1 and 4-2 of the present invention) As raw materials, Li 2S, Si, Sn, P, and S were prepared, weighed so as to have a predetermined ratio, and mixed in a mortar. Here, for elemental sulfur, the volume ratio of the elemental sulfur in the whole mixed raw material when the mixed raw material was heated to 120°C was set to 40%. The mixed raw material was placed in a fired container made of alumina and loaded into a firing furnace. Then, under an Ar atmosphere, with the heating temperature being T °C and the holding time being h hours, firing was carried out under the condition that T×h = 1000. Thereby, a sulfide solid electrolyte made of LSSPS material was produced.

[0036] (Comparative Example 2) As raw materials, Li 2 S, Si, Sn, P, and S were prepared, weighed so as to have a predetermined ratio, and mixed in a mortar. Here, for elemental sulfur, the volume ratio of the elemental sulfur in the whole mixed raw material when the mixed raw material was heated to 120°C was set to 40%. The mixed raw material was placed in a fired container made of alumina and loaded into a firing furnace. Then, under an Ar atmosphere, with the heating temperature being T °C and the holding time being h hours, firing was carried out under the condition that T×h = 500. Thereby, a sulfide solid electrolyte made of LSSPS material was produced.

[0037] Regarding the obtained sulfide solid electrolyte, the half-value width of the peak at 2θ = 29.58° ± 1.0° was measured by X-ray diffraction measurement (XRD measurement) using CuKα radiation. 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.

[0038] <XRD Measurement> X-ray diffraction measurement (XRD measurement) using CuKα radiation was performed. The XRD measurement was carried out using an XRD device "D8 ADVANCE" manufactured by Bruker in the range of 10° ≤ 2θ ≤ 55° under the conditions of a step width of 0.01° and an integration time of 1.2 seconds / step for θ-2θ measurement, and the half-value width of the peak at 2θ = 29.58° ± 1.0° was evaluated. The measurement sample was prepared in a glove box under an argon atmosphere. The sulfide solid electrolyte 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.

[0039] <Ionic conductivity> After taking out the obtained solid electrolyte in a glove box under an argon atmosphere, it was pulverized in an agate mortar, 0.3 g was weighed, and it was filled into a stainless-steel ion conductivity measurement cell (cylindrical with an inner diameter of 17 mm). Then, using a measurement device "Potentiostat / Galvanostat SP-300" manufactured by Biologic, under the conditions of a measurement temperature of 25°C, a measurement frequency of 1 Hz to 1 MHz, and an applied pressure to the measurement cell of 360 MPa, the ionic conductivity (mS / cm) was measured by the alternating current impedance method.

[0040]

Table 1

[0041] Examples 1-1, 1-2, 2-1, 2-2 and Comparative Example 1 of the present invention are LGPS materials. In Examples 1-1, 1-2, 2-1, 2-2 of the present invention, the volume ratio of the elemental sulfur in the total mixed raw materials when the mixed raw materials are heated to 120°C is 40% or more, the product T×h of the heating temperature T°C and the holding time h hours is 1000 or more, and the half-value width of the peak at 2θ = 29.58° ± 1.0° is 0.096 or less. On the other hand, in Comparative Example 1, the volume ratio of the elemental sulfur in the total mixed raw materials when the mixed raw materials are heated to 120°C is 40%, the product T×h of the heating temperature T°C and the holding time h hours is 500, and the half-value width of the peak at 2θ = 29.58° ± 1.0° is 0.105. It can be seen that Examples 1-1, 1-2, 2-1, 2-2 of the present invention have higher crystallinity than Comparative Example 1. And in Examples 1-1, 1-2, 2-1, 2-2 of the present invention, the ionic conductivity is 9.6 mS / cm or more, and in Comparative Example 1, the ionic conductivity is 8.0 mS / cm. Examples 1 and 2 of the present invention were superior in ionic conductivity to Comparative Example 1.

[0042] Examples 3-1, 3-2, 4-1, and 4-2 of the present invention and Comparative Example 2 are LSSPS materials. In Examples 3-1, 3-2, 4-1, and 4-2 of the present invention, the volume ratio of the elemental sulfur in the total mixed raw materials when the mixed raw materials are heated to 120°C is 40% or more, the product of the heating temperature T°C and the holding time h hours, T×h, is 1000 or more, and the half-value width of the peak at 2θ = 29.58° ± 1.0° is 0.096 or less. On the other hand, in Comparative Example 2, the volume ratio of the elemental sulfur in the total mixed raw materials when the mixed raw materials are heated to 120°C is 40%, the product of the heating temperature T°C and the holding time h hours, T×h, is 500, and the half-value width of the peak at 2θ = 29.58° ± 1.0° is 0.103. It can be seen that Examples 3-1, 3-2, 4-1, and 4-2 of the present invention have higher crystallinity than Comparative Example 2. And in Examples 3-1, 3-2, 4-1, and 4-2 of the present invention, the ionic conductivity is 7.6 mS / cm or more, while in Comparative Example 2, the ionic conductivity is 6.1 mS / cm. Examples 3-1, 3-2, 4-1, and 4-2 of the present invention were superior in ionic conductivity to Comparative Example 2.

[0043] As a result of the above confirmation experiments, it was confirmed that according to the examples of the present invention, it is possible to provide a sulfide solid electrolyte excellent in ionic conductivity and particularly suitable for a high-output solid battery, and a method for manufacturing this sulfide solid electrolyte.

Claims

1. A sulfide solid electrolyte having an LGPS-type crystal structure belonging to the space group P42 / nmc, wherein in an X-ray diffraction measurement using CuKα radiation, the full width at half maximum of the peak at 2θ = 29.58° ± 1.0° is 0.1 or less.

2. A method for producing a sulfide solid electrolyte, comprising a raw material mixing step of mixing raw materials containing each element constituting the sulfide solid electrolyte to obtain a mixed raw material, and a production step of heat-treating the mixed raw material to produce the sulfide solid electrolyte, wherein in the raw material mixing step, elemental sulfur is used as a raw material, and the volume ratio of the elemental sulfur in the entire mixed raw material when the mixed raw material is heated to 120°C is 20% or more, and in the production step, the heating temperature is T °C and the holding time is h hours, and T × h is 1000 or more. A method for producing a sulfide solid electrolyte, characterized in that.

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