Sulfide solid electrolyte and method for manufacturing same

Abstract

The present invention relates to a sulfide solid electrolyte including a crystal phase and a glass phase. The glass phase includes a phase formed of a sulfide-based glass containing Li, P, and S as constituent elements, and the crystal phase includes a highly ion-conductive crystal phase derived from the sulfide-based glass and a crystal phase of β-Li3PS4. The composition of the highly ion-conductive crystal phase satisfies 30-50 at% of Li, 5-15 at% of P, and 30-60 at% of S. The content percentage of the crystal phase of the β-Li3PS4 in the sulfide solid electrolyte is 0.1-30 mass%.

Description

Sulfide solid electrolyte and method for producing same

[0001] The present invention relates to a sulfide solid electrolyte and a method for producing the same.

[0002] Lithium-ion secondary batteries are widely used in portable electronic devices such as mobile phones and laptop computers, as well as in automobiles. Conventionally, liquid electrolytes have been used in lithium-ion secondary batteries, but concerns about leakage and fire have led to the need for larger casings for safety reasons. Furthermore, improvements have been needed to address the short battery life and narrow operating temperature range.

[0003] In response to this, all-solid-state lithium secondary batteries, which use solid electrolytes as the electrolyte for lithium-ion secondary batteries, are attracting attention because they are expected to offer improved safety, high-speed charging and discharging, and smaller cases.

[0004] Solid electrolytes are broadly classified into sulfide solid electrolytes and oxide solid electrolytes. Sulfide ions constituting sulfide solid electrolytes have higher polarizability than oxide ions constituting oxide solid electrolytes, and exhibit high ionic conductivity. As sulfide solid electrolytes, Li １０ GeP ２ S １２ LGPS type crystals such as Li ６ P.S. ５ Argyrodite-type crystals such as Cl, Li ７ P ３ S １１ LPS crystallized glass and the like are known.

[0005] As a solid electrolyte that is resistant to hydrolysis and has high ionic conductivity, Patent Document 1 discloses Li ２ S / P ２ S ５ Sulfide-based glass in which Li / LiI=63 / 21 / 16 or 52 / 17 / 31, ２ S / P ２ S ５ A sulfide-based glass ceramic solid electrolyte is disclosed in which a sulfide-based glass having a composition of Zn / LiBr=64 / 21 / 14 is partially crystallized.

[0006] Japanese Patent Application Publication No. 2018-049834

[0007] However, the sulfide-based glass ceramic solid electrolyte described in Patent Document 1 exhibits a significant decrease in ionic conductivity due to the precipitation of thermodynamically stable crystals with low ionic conductivity at high temperatures. The precipitation of these crystals begins to occur, for example, when the battery is maintained at a temperature in the low 200°C range or higher for 30 minutes or longer. Therefore, batteries using a sulfide solid electrolyte containing a glass phase and a crystalline phase have problems with battery operation at high temperatures.

[0008] Therefore, an object of the present invention is to provide a sulfide solid electrolyte containing a crystalline phase and a glassy phase, which has not only excellent lithium ion conductivity but also excellent heat resistance, and a method for producing the same.

[0009] As a result of extensive research, the present inventors have found that when a sulfide solid electrolyte precursor is obtained by heating and melting raw materials and then cooling them, the heating and cooling are carried out under normal pressure conditions, and the cooling is carried out at a very fast cooling rate, thereby forming a glass phase and a β-Li phase. ３ P.S. ４ The present inventors have found that the above-mentioned problems can be solved by obtaining a sulfide solid electrolyte precursor containing a crystalline phase of the above-mentioned glass phase, and further by crystallizing a part of the glass phase, and have thus completed the present invention.

[0010] That is, the present invention relates to the following [1] to [9]. [1] A sulfide solid electrolyte including a crystalline phase and a glassy phase, wherein the glassy phase includes a phase made of sulfide-based glass containing Li, P, and S as constituent elements, and the crystalline phase includes a highly ion-conductive crystalline phase derived from the sulfide-based glass and a β-Li ３ P.S. ４ and a crystalline phase of the sulfide-based glass, wherein the composition of the sulfide-based glass phase and the highly ion-conductive crystalline phase is Li: 30 to 50 at %, P: 5 to 15 at %, and S: 30 to 60 at %, and the β-Li in the sulfide solid electrolyte ３ P.S. ４The sulfide solid electrolyte according to [1], wherein the sulfide-based glass phase and the highly ion-conductive crystalline phase further contain Ha as a constituent element, and the Ha is at least one element selected from the group consisting of F, Cl, Br, and I. [3] The sulfide solid electrolyte according to [2], wherein the Ha, which is a constituent element of the sulfide-based glass phase and the highly ion-conductive crystalline phase, contains at least one element selected from the group consisting of Cl, Br, and I. [4] The sulfide solid electrolyte according to [2] or [3], wherein the Ha, which is a constituent element of the sulfide-based glass phase and the highly ion-conductive crystalline phase, contains Br. [5] The sulfide solid electrolyte according to [2] or [3], wherein the Ha, which is a constituent element of the sulfide-based glass phase and the highly ion-conductive crystalline phase, contains Br. ３ P.S. ４ [6] The sulfide solid electrolyte according to any one of [1] to [4], wherein the crystallite diameter of the crystalline phase is 400 nm or less. [7] The sulfide solid electrolyte according to any one of [1] to [5], wherein the content of the high ion-conducting crystalline phase in the sulfide solid electrolyte is 30 mass % or more. [8] In an XRD pattern obtained by powder X-ray diffraction measurement, the peak intensity of a diffraction peak at 2θ = 20.2 ± 0.5° indicating the high ion-conducting crystalline phase is I Ａ and the β-Li ３ P.S. ４ The highest intensity of the diffraction peaks at 2θ = 18.2 ± 0.5°, which indicate the crystalline phase of Ｂ When I Ｂ / I Ａ [8] In an XRD pattern obtained by powder X-ray diffraction measurement, the peak intensity of the diffraction peak at 2θ = 19.1 ± 0.5°, which indicates the high ion-conducting crystalline phase, is expressed as I Ｃ and the β-Li ３ P.S. ４ The highest intensity of the diffraction peaks at 2θ = 18.2 ± 0.5°, which indicate the crystalline phase of Ｂ When I Ｂ / I ＣThe sulfide solid electrolyte according to any one of [1] to [7], wherein the peak intensity ratio represented by

[0011] [9] A method for producing a sulfide solid electrolyte containing a crystalline phase and a glassy phase, comprising: mixing raw materials to obtain a raw material mixture containing Li, P, and S; heating the raw material mixture to obtain a melt; and cooling and solidifying the melt to obtain a glassy phase and β-Li. ３ P.S. ４ and heating the sulfide solid electrolyte precursor to obtain a highly ion-conductive crystalline phase in which a portion of the glass phase is crystallized, wherein the heating to obtain the molten material and the cooling and solidification are carried out under normal pressure conditions, and during the cooling and solidification, the molten material is allowed to flow out and then remain at a temperature in the range of 750 to 210°C for 0.2 to 100 seconds.

[0012] According to the present invention, a sulfide solid electrolyte containing a crystalline phase and a glassy phase, which has excellent lithium ion conductivity and heat resistance, can be obtained. Therefore, when the sulfide solid electrolyte is used in an all-solid-state lithium secondary battery, good battery characteristics can be achieved.

[0013] Fig. 1 is a flow diagram showing a method for producing a sulfide solid electrolyte according to the present embodiment. Fig. 2 is an XRD pattern of the sulfide solid electrolyte precursor obtained in Example 4. Fig. 3 is an XRD pattern of the sulfide solid electrolyte obtained in Example 4.

[0014] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be modified as desired without departing from the spirit of the present invention. Furthermore, the term "to" indicating a range of values ​​is used to mean that the values ​​before and after it are included as the lower and upper limits.

[0015] The sulfide solid electrolyte according to this embodiment includes a crystalline phase and a glass phase. The glass phase includes a phase made of sulfide-based glass containing Li, P, and S as constituent elements (hereinafter, sometimes simply referred to as a "sulfide-based glass phase"). The crystalline phase includes a highly ion-conductive crystalline phase derived from the sulfide-based glass and a β-Li crystalline phase. ３ P.S. ４ The crystalline phase (hereinafter simply referred to as "β-Li ３ P.S. ４ Here, the high ion conductive crystalline phase derived from sulfide-based glass refers to a crystalline phase obtained by crystallizing the sulfide-based glass through heat treatment, and its constituent elements and composition ratios are considered to be substantially identical. Here, "substantially identical" means that the proportion of the composition determined from structural analysis of the XRD pattern of the high ion conductive crystalline phase to the overall composition is within a range of ±20% for each component.

[0016] The composition of the high ion-conductive crystalline phase satisfies 30 to 50 at% Li, 5 to 15 at% P, and 30 to 60 at% S. Accordingly, the composition of the sulfide-based glass phase also satisfies 30 to 50 at% Li, 5 to 15 at% P, and 30 to 60 at% S.

[0017] In addition, the β-Li in the sulfide solid electrolyte according to this embodiment ３ P.S. ４ The content of the crystalline phase is 0.1 to 30 mass%.

[0018] <Sulfide-based glass phase and high ion-conductive crystalline phase> The sulfide-based glass phase and high ion-conductive crystalline phase in this embodiment contain Li, P, and S as constituent elements. In addition to these, it is preferable to contain Ha from the viewpoint of lithium ion conductivity. Here, Ha is at least one selected from the group consisting of F, Cl, Br, and I. From the viewpoint of obtaining good oxidation resistance and water resistance, it is more preferable to contain at least one selected from the group consisting of Cl, Br, and I, even more preferable to contain at least one of Cl and Br, and even more preferable to contain Br. It is also even more preferable to contain both Cl and Br.

[0019] In this embodiment, the compositions of the sulfide-based glass phase and the high ion-conductive crystalline phase preferably satisfy Li: 30 to 50 at%, P: 5 to 15 at%, and S: 30 to 60 at%, and more preferably Li: 30 to 50 at%, P: 5 to 15 at%, S: 30 to 60 at%, and Ha: 1 to 12 at%. Note that in this specification, at% means atomic %, i.e., atomic %. Furthermore, as mentioned above, the sulfide-based glass phase and the high ion-conductive crystalline phase derived therefrom can be considered to have substantially the same constituent elements and composition ratios, but this does not mean that they are strictly the same. It is preferable that the compositions of the sulfide-based glass phase and the high ion-conductive crystalline phase satisfy the above ranges.

[0020] In the sulfide-based glass phase and the highly ion-conductive crystalline phase of this embodiment, Li is an element responsible for ionic conduction as a solid electrolyte. In the compositions of the sulfide-based glass phase and the highly ion-conductive crystalline phase, the Li content is preferably 30 to 50 at%. 35 to 45 at% is preferred, and 37 to 43 at% is more preferred. From the viewpoint of increasing lithium ion conductivity, the Li content is preferably 30 at% or more, more preferably 35 at% or more, and even more preferably 37 at% or more. Furthermore, from the viewpoint of widening the vitrification range, the Li content is preferably 50 at% or less, more preferably 45 at% or less, and even more preferably 43 at% or less.

[0021] In the sulfide-based glass phase and the high ion-conductive crystalline phase of this embodiment, P is an element that forms a glass network, and among sulfides, the P-S bond is highly resistant to both oxidation and reduction. Therefore, as a solid electrolyte, it has a wide potential window and excellent electrochemical stability. In the composition of the sulfide-based glass phase and the high ion-conductive crystalline phase, the P content is preferably 5 to 15 at%, more preferably 6 to 13 at%, and more preferably 7 to 12 at%. Here, from the viewpoint of widening the vitrification range, the P content is preferably 5 at% or more, more preferably 6 at% or more, and even more preferably 7 at% or more. Furthermore, from the viewpoint of increasing lithium ion conductivity, the P content is preferably 15 at% or less, more preferably 13 at% or less, and even more preferably 12 at% or less.

[0022] In the sulfide-based glass phase and the high ion-conductive crystalline phase of this embodiment, S is an element that forms P—S bonds with P and is an essential element for forming the glass phase. In the composition of the sulfide-based glass phase and the high ion-conductive crystalline phase, the S content is preferably 30 to 60 at%. 33 to 50 at% is more preferable, and 35 to 47 at% is even more preferable. From the viewpoint of widening the vitrification range, the S content is preferably 30 at% or more, more preferably 33 at% or more, and even more preferably 35 at% or more. Furthermore, from the viewpoint of increasing the lithium ion conductivity, the S content is preferably 60 at% or less, more preferably 50 at% or less, and even more preferably 47 at% or less.

[0023] In the present embodiment, when the sulfide-based glass phase and the high ion-conductive crystalline phase contain Ha, Ha is an element that contributes to high lithium ion conductivity. In the compositions of the sulfide-based glass phase and the high ion-conductive crystalline phase, the Ha content is preferably 1 to 12 at%; more preferably 3 to 10 at%; and even more preferably 3.5 to 8 at%. Here, from the viewpoint of obtaining high lithium ion conductivity, the Ha content is preferably 1 at% or more, more preferably 3 at% or more, and even more preferably 3.5 at% or more. Furthermore, from the viewpoint of preventing precipitation of lithium halide crystals, the Ha content is preferably 12 at% or less, more preferably 10 at% or less, and even more preferably 8 at% or less. Here, the Ha content refers to the total content of F, Cl, Br, and I.

[0024] Ha is at least one element selected from the group consisting of F, Cl, Br, and I. As described above, from the viewpoint of obtaining good oxidation resistance and water resistance, it is more preferable that at least one of Cl and Br is contained, and it is even more preferable that Br is contained. It is also more preferable that both Cl and Br are contained. For example, of the Ha content, the total content of Cl and Br preferably accounts for 50% or more, more preferably 70% or more, and may be 100%, i.e., it may consist only of Cl and Br. Furthermore, the content ratio expressed as Cl:Br is preferably 100:0 to 0:100, more preferably 80:20 to 0:100, and even more preferably 60:40 to 0:100.

[0025] The sulfide-based glass phase and the highly ion-conductive crystalline phase in this embodiment may contain elements other than the above-mentioned Li, P, S, and Ha as constituent elements. Examples of the other elements that may be contained include Si, B, Ge, Al, O, Na, K, Mg, Ca, Sr, Ba, Y, Zr, Cr, Zn, Ga, Sn, and Sb. However, if the other elements are SiO ２ Or B ２ O ３ , P ２ O ５ , Al ２ O ３ In the case of forming oxides such as those mentioned above, it is preferable that such oxides are not contained because they become crystal nuclei. The total content of oxides is preferably 1 mol% or less, more preferably 0.1 mol% or less, and even more preferably 0.05 mol% or less, expressed in mol% based on the oxides, and may be zero, i.e., not contained.

[0026] The sulfide-based glass phase and the highly ion-conductive crystalline phase in this embodiment may contain, among the other elements, Si, B, Ge, Al, Sn, and Sb, which are elements that can occupy the position of P when the sulfide-based glass phase is crystallized.

[0027] When the sulfide-based glass phase and the highly ion-conductive crystalline phase in this embodiment contain Si as a constituent element, Si has the effect of increasing the viscosity of the melt and promoting vitrification. The Si content is preferably 0 to 15 at%, more preferably 0.1 to 10 at%, and even more preferably 1 to 5 at%. Here, from the viewpoint of optimally obtaining the effect of Si, the Si content is preferably 0.1 at% or more, and more preferably 1 at% or more. Furthermore, from the viewpoint of electrochemical stability, the Si content is preferably 15 at% or less, more preferably 10 at% or less, and even more preferably 5 at% or less. However, if Si has a Si—O bond or SiO ２ When Si is contained as an oxide, the Si content is appropriately adjusted so that the total content of oxides is 1 mol % or less, or so that the total content of oxides that become network formers of glass is 3 to 20 mol %, as described above.

[0028] When the sulfide-based glass phase and the highly ion-conductive crystalline phase in this embodiment contain B as a constituent element, B has the effect of increasing the viscosity of the melt and promoting vitrification. The B content is preferably 0 to 15 at %, more preferably 0.1 to 10 at %, and even more preferably 1 to 5 at %. Here, from the viewpoint of optimally obtaining the effect of B, the B content is preferably 0.1 at % or more, and more preferably 1 at % or more. Furthermore, from the viewpoint of lithium ion conductivity, the B content is preferably 15 at % or less, more preferably 10 at % or less, and even more preferably 5 at % or less. However, if B has a B-O bond or B ２ O ３ When B is contained as an oxide, the B content is appropriately adjusted so that the total content of oxides is 1 mol % or less, or so that the total content of oxides that become network formers of the glass is 3 to 20 mol %, as described above.

[0029] When the sulfide-based glass phase and the high ion-conducting crystalline phase in this embodiment contain Ge as a constituent element, Ge has the effect of promoting an improvement in lithium ion conductivity. The Ge content is preferably 0 to 15 at %, more preferably 0.1 to 10 at %, and even more preferably 1 to 5 at %. Here, from the viewpoint of lithium ion conductivity, the Ge content is preferably 0.1 at % or more, and more preferably 1 at % or more. Furthermore, from the viewpoint of ease of glass formation, the Ge content is preferably 15 at % or less, more preferably 10 at % or less, and even more preferably 5 at % or less. However, if Ge has a Ge—O bond or is a GeO ２ When Ge is contained as an oxide, the Ge content is appropriately adjusted so that the total content of the oxides is 1 mol % or less, as described above.

[0030] When the sulfide-based glass phase and the high ion-conductive crystalline phase in this embodiment contain Al as a constituent element, Al has the effect of increasing the viscosity of the melt and promoting vitrification. The Al content is preferably 0 to 15 at %, more preferably 0.1 to 10 at %, and even more preferably 1 to 5 at %. Here, from the viewpoint of optimally obtaining the effect of Al, the Al content is preferably 0.1 at % or more, and more preferably 1 at % or more. Furthermore, from the viewpoint of lithium ion conductivity, the Al content is preferably 15 at % or less, more preferably 10 at % or less, and even more preferably 5 at % or less. However, if Al has an Al—O bond or Al ２ O ３ When Al is contained as an oxide, the Al content is appropriately adjusted so that the total content of oxides is 1 mol % or less, or so that the total content of oxides that become network formers of glass is 3 to 20 mol %, as described above.

[0031] When the sulfide-based glass phase and the highly ion-conductive crystalline phase in this embodiment contain Sn as a constituent element, Sn has the effect of increasing the viscosity of the melt and promoting vitrification. The Sn content is preferably 0 to 15 at%, more preferably 0.1 to 10 at%, and even more preferably 1 to 5 at%. Here, from the viewpoint of optimally obtaining the effects of Sn, the Sn content is preferably 0.1 at% or more, and more preferably 1 at% or more. Furthermore, from the viewpoint of achieving high lithium ion conductivity, the Sn content is preferably 15 at% or less, more preferably 10 at% or less, and even more preferably 5 at% or less. However, if Sn has an Sn—O bond or SnO ２ When Sn is contained as an oxide, the Sn content is appropriately adjusted so that the total content of the oxides is 1 mol % or less, as described above.

[0032] When the sulfide-based glass phase and the highly ion-conductive crystalline phase in this embodiment contain Sb as a constituent element, Sb has the effect of increasing the viscosity of the melt and promoting vitrification. The Sb content is preferably 0 to 15 at %, more preferably 0.1 to 10 at %, and even more preferably 1 to 5 at %. Here, from the viewpoint of optimally obtaining the effects of Sb, the Sb content is preferably 0.1 at % or more, and more preferably 1 at % or more. Furthermore, from the viewpoint of lithium ion conductivity, the Sb content is preferably 15 at % or less, more preferably 10 at % or less, and even more preferably 5 at % or less. However, if Sb has an Sb—O bond or Sb ２ O ３ When Sb is contained as an oxide, the Sb content is appropriately adjusted so that the total content of oxides is 1 mol % or less, or so that the total content of oxides that become network formers of glass is 3 to 20 mol %, as described above.

[0033] In the compositions of the sulfide-based glass phase and the high ion-conductive crystalline phase in this embodiment, the composition ratio represented by Li / P is preferably 2.5 or more, more preferably 2.5 to 7.0, even more preferably 3.0 to 6.5, and even more preferably 3.2 to 6.2. From the viewpoint of obtaining high lithium ion conductivity, the composition ratio is preferably 2.5 or more, more preferably 3.0 or more, and even more preferably 3.2 or more. Furthermore, from the viewpoint of widening the vitrification range, the composition ratio is preferably 7.0 or less, more preferably 6.5 or less, and even more preferably 6.2 or less. In this specification, the composition ratio refers to the ratio of the content (at %) of each element in the sulfide-based glass phase and the high ion-conductive crystalline phase.

[0034] In the compositions of the sulfide-based glass phase and the highly ion-conductive crystalline phase in this embodiment, the composition ratio represented by S / P is preferably 3.0 to 5.0, more preferably 3.5 to 4.5, and even more preferably 3.8 to 4.2. From the viewpoint of lithium ion conductivity, the composition ratio is preferably 3.0 or more, more preferably 3.5 or more, and even more preferably 3.8 or more. From the viewpoint of water resistance, the composition ratio is preferably 5.0 or less, more preferably 4.5 or less, and even more preferably 4.2 or less.

[0035] When the sulfide-based glass phase and the high ion-conductive crystalline phase further contain Ha, the composition ratio represented by [(F + Cl + Br) / Ha] is preferably 0.5 or more, more preferably 0.5 to 1.0, even more preferably 0.6 to 1.0, and particularly preferably 0.8 to 1.0. From the viewpoint of oxidation resistance, the composition ratio is preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.8 or more. The upper limit of the composition ratio is not particularly limited, and may be 1.0. The composition ratio of 1.0 means that I is not included as Ha. When the sulfide-based glass phase and the high ion-conductive crystalline phase contain I as Ha, from the viewpoint of obtaining the effect of I, the composition ratio may be 0.8 or less, or may be 0.6 or less.

[0036] When the sulfide-based glass phase and the high ion-conductive crystalline phase further contain Ha, the composition ratio represented by Ha / P in the composition of the sulfide-based glass phase in this embodiment is preferably 0.01 to 1.5, more preferably 0.1 to 1.2, and even more preferably 0.2 to 1.0. From the viewpoint of water resistance, the composition ratio is preferably 0.01 or more, more preferably 0.1 or more, and even more preferably 0.2 or more. Furthermore, from the viewpoint of lithium halide crystal precipitation, the composition ratio is preferably 1.5 or less, more preferably 1.2 or less, and even more preferably 1.0 or less. Here, Ha refers to the sum of F, Cl, Br, and I.

[0037] The constituent elements and their respective contents in the sulfide-based glass phase and the highly ion-conductive crystalline phase are determined by comparing the results of measuring the constituent elements and their respective contents (composition ratios) in the entire sulfide solid electrolyte with the element ratios constituting the crystal structure determined from the XRD pattern. The methods for determining the constituent elements and their respective contents in the entire sulfide solid electrolyte vary depending on the element. For example, P and S can be determined by ICP atomic emission spectroscopy, Li by atomic absorption spectroscopy, and Ha by ion chromatography. Details of each analysis are described in the Examples section below.

[0038] The sulfide-based glass phase in this embodiment is partially crystallized by heat treatment to become the highly ion-conductive crystalline phase in this embodiment. This highly ion-conductive crystalline phase can have a thio-lisicon or LGPS crystalline structure. The highly ion-conductive crystalline phases of the thio-lisicon and LGPS types have high lithium ion conductivity and are useful as solid electrolytes.

[0039] The total proportion of the sulfide-based glass phase and the highly ion-conductive crystalline phase in the sulfide solid electrolyte according to this embodiment is 99.9 mass% or less, preferably 50 to 99.9 mass%, more preferably 70 to 95 mass%, and even more preferably 75 to 90 mass%. From the viewpoint of lithium ion conductivity, the total proportion is preferably 50 mass% or more, more preferably 70 mass% or more, and even more preferably 75 mass% or more. In addition, the total proportion is β-Li ３ P.S. ４ From the viewpoint of optimally exerting the effects of the crystalline phase, the content is 99.9% by mass or less, preferably 95% by mass or less, and more preferably 90% by mass or less. The respective proportions of the sulfide-based glass phase and the high ion-conducting crystalline phase are determined by powdering the sulfide solid electrolyte, performing powder X-ray diffraction (XRD) measurement together with a crystalline powder serving as an internal standard, and performing Rietveld analysis. The proportion of the sulfide-based glass phase is determined by determining the proportion of crystals by the above analysis and subtracting it from 100% by mass.

[0040] In this embodiment, the content of the high ion conductive crystalline phase is preferably 30% by mass or more, more preferably 30 to 90% by mass, even more preferably 50 to 85% by mass, and even more preferably 60 to 80% by mass. From the viewpoint of lithium ion conductivity, the content is preferably 30% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more. In addition, the content of the high ion conductive crystalline phase is preferably 30% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more. ３ P.S. ４ From the viewpoint of preferably obtaining the effect of the crystalline phase, the content is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less.

[0041] In this embodiment, the content of the sulfide-based glass phase is preferably 1 to 70 mass %, more preferably 5 to 50 mass %, and even more preferably 8 to 40 mass %. Here, from the viewpoint of realizing softness that facilitates the formation of an interface between the active material and the solid electrolyte due to the glass phase, the content is preferably 1 mass % or more, more preferably 5 mass % or more, and even more preferably 8 mass % or more. In addition, the high ion-conducting crystalline phase and β-Li ３ P.S. ４ From the viewpoint of suitably obtaining the effect of the crystalline phase, the content is preferably 70% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0042] The highly ion-conductive crystalline phase in this embodiment may have, for example, a thiolisicone-type or LGPS-type crystalline structure, which has high lithium ion conductivity.

[0043] In this embodiment, the high ion conductive crystalline phase exhibits a diffraction peak at least at 2θ = 20.2 ± 0.5° in an XRD pattern obtained by powder X-ray diffraction (XRD) measurement, and preferably exhibits a diffraction peak at 2θ = 23.8 ± 0.5°. It is also preferable that the high ion conductive crystalline phase exhibits a diffraction peak at 2θ = 19.1 ± 0.5°. In this case, the high ion conductive crystalline phase may be determined to have a thiolisicon-type or LGPS-type crystal structure. The XRD measurement is performed using CuKα radiation (λ = 1.5418 Å) as a radiation source, and the detailed measurement conditions are as described in detail in the Examples section below. The XRD pattern may exhibit diffraction peaks at both 2θ = 19.1 ± 0.5° and 23.8 ± 0.5°. Furthermore, the diffraction peak may be present at one or more of 2θ=12.4±0.5°, 29.7±0.5°, and 31.4±0.5°, or may be present at two or more of these, or may be present at all three.

[0044] <β-Li ３ P.S. ４ The sulfide solid electrolyte according to this embodiment has, in addition to the sulfide-based glass phase and the highly ion-conductive crystal phase, β-Li ３ P.S. ４ Contains 0.1 to 30 mass% of crystalline phase. ３ P.S. ４The crystalline phase is a thermodynamically stable phase, and in an XRD pattern obtained by powder X-ray diffraction (XRD) measurement, it exhibits a diffraction peak at at least 2θ = 18.2 ± 0.5°, preferably at 2θ = 26.0 ± 0.5°. It may also exhibit multiple diffraction peaks at 2θ = 18.2 ± 0.5°. The XRD measurement is performed using CuKα radiation (λ = 1.5418 Å) as a radiation source, and the measurement conditions are described in detail in the Examples section below. The XRD pattern may also exhibit a diffraction peak at one or more of 2θ = 17.8 ± 0.5°, 20.0 ± 0.5°, 29.8 ± 0.5°, and 34.0 ± 0.5°, or may exhibit two or more diffraction peaks, three or more diffraction peaks, or all four diffraction peaks.

[0045] The sulfide solid electrolyte according to this embodiment is β-Li ３ P.S. ４ It was found that the inclusion of the crystalline phase prevents the thermal decomposition of the highly ion-conductive crystalline phase, even when heat treatment is performed at a temperature exceeding 200°C, and good heat resistance can be achieved. Although the reason for this is unclear, the precipitated β-Li in this embodiment ３ P.S. ４ The crystalline phase is thought to be uniformly precipitated throughout the bulk of the sulfide solid electrolyte. This suggests that the highly ionic conductive crystalline phase precipitated from the residual glass may also have a different crystalline structure from that of conventionally known materials. In addition to the above, β-Li ３ P.S. ４ When the crystalline phase becomes microcrystalline, the crystallite size of the highly ionic conductive crystalline phase also becomes smaller, which changes the microscopic thermodynamic properties, and we believe that this will enable the realization of better heat resistance.

[0046] β-Li in the sulfide solid electrolyte according to this embodiment ３ P.S. ４ The content of the crystalline phase is 0.1 to 30 mass%, preferably 5 to 25 mass%, and more preferably 10 to 20 mass%. ３ P.S. ４From the viewpoint of obtaining the heat resistance effect of the crystalline phase, the content is 0.1 mass % or more, preferably 5 mass % or more, and more preferably 10 mass % or more. From the viewpoint of lithium ion conductivity, the content is 30 mass % or less, preferably 25 mass % or less, and more preferably 20 mass % or less. ３ P.S. ４ The proportion of the crystalline phase can be determined by powdering the sulfide solid electrolyte, performing powder X-ray diffraction (XRD) measurement together with a crystalline powder serving as an internal standard, and performing Rietveld analysis.

[0047] β-Li ３ P.S. ４ The crystallite size of the crystalline phase is preferably 400 nm or less, more preferably 20 to 400 nm, even more preferably 20 to 350 nm, even more preferably 50 to 300 nm, and particularly preferably 80 to 260 nm. ３ P.S. ４ The crystalline phase exists in microcrystalline form, so that even if a high ion-conducting crystalline phase is precipitated, good heat resistance can be achieved, so the crystallite diameter is preferably 400 nm or less, more preferably 350 nm or less, even more preferably 300 nm or less, and even more preferably 260 nm or less.In addition, it is assumed that the smaller the crystallite diameter, the more preferable it is, but from the viewpoint of crystal growth rate, in reality, the crystallite diameter is preferably 20 nm or more, more preferably 50 nm or more, and even more preferably 80 nm or more.In addition, the crystallite diameter is calculated by Scherrer's formula using the half-width of the peak in the XRD pattern.

[0048] β-Li as above ３ P.S. ４ The crystalline phase can be obtained in an appropriate amount by performing the heating and cooling under normal pressure conditions and at a very fast cooling rate when obtaining a sulfide solid electrolyte precursor by heating and melting the raw materials and then cooling them. ３ P.S. ４Regarding the crystalline phase, even when the sulfide solid electrolyte precursor was heated to crystallize a part of the sulfide-based glass phase into a highly ion-conductive crystalline phase, no significant crystal growth was observed, and there was no change in the content or crystallite size.

[0049] In the XRD pattern obtained by powder XRD measurement, the peak intensity of the diffraction peak at 2θ=20.2±0.5°, which indicates the high ion-conducting crystalline phase, is defined as I Ａ In addition, the above β-Li ３ P.S. ４ The highest intensity of the diffraction peak at 2θ = 18.2 ± 0.5°, which indicates the crystalline phase, is designated as I Ｂ At this time, I Ｂ / I Ａ The peak intensity ratio represented by the formula (1) is preferably 0.01 to 2.0, more preferably 0.05 to 1.0, and even more preferably 0.07 to 0.7. From the viewpoint of heat resistance, the intensity ratio is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.07 or more. From the viewpoint of lithium ion conductivity, the ratio is preferably 2.0 or less, more preferably 1.0 or less, and even more preferably 0.7 or less. Note that, in the case of β-Li ３ P.S. ４ Two or more diffraction peaks indicating a crystalline phase may be present in the range of 2θ=18.2±0.5°. In this case, the peak intensity of the peak with the greatest intensity among the multiple diffraction peaks is designated as I. Ｂ Let's say.

[0050] In the XRD pattern obtained by powder XRD measurement, the peak intensity of the diffraction peak at 2θ=19.1±0.5°, which indicates the high ion-conducting crystalline phase, is defined as I Ｃ In addition, the above β-Li ３ P.S. ４ The highest intensity of the diffraction peak at 2θ = 18.2 ± 0.5°, which indicates the crystalline phase, is designated as I Ｂ At this time, I Ｂ / I ＣThe peak intensity ratio represented by the formula (1) is preferably 0.01 to 10.0, more preferably 0.3 to 5.0, and even more preferably 0.5 to 2.5. From the viewpoint of heat resistance, the intensity ratio is preferably 0.01 or more, more preferably 0.3 or more, and even more preferably 0.5 or more. From the viewpoint of lithium ion conductivity, the ratio is preferably 10.0 or less, more preferably 5.0 or less, and even more preferably 2.5 or less.

[0051] In addition, when a peak is observed at 2θ=18.6 to 18.7° in the XRD pattern obtained by powder XRD measurement, if there is a diffraction peak within the range of 2θ=18.2±0.5° and on the lower angle side of that peak, that peak is attributed to a diffraction peak at 2θ=19.1±0.5° indicating a high ion-conducting crystalline phase. In addition, in the above case, if there is a diffraction peak within the range of 2θ=19.1±0.5° and on the higher angle side of that peak, that peak is attributed to β-Li ３ P.S. ４ This is attributed to a diffraction peak at 2θ=18.2±0.5°, which indicates a crystalline phase.

[0052] <Other Phases> The sulfide solid electrolyte according to this embodiment includes the sulfide-based glass phase, the highly ion-conductive crystalline phase, and the β-Li ３ P.S. ４ It may contain other phases besides the crystalline phase. Examples of other phases include a sulfide-based glass phase and β-Li ３ P.S. ４ The proportion of such other phases in the sulfide solid electrolyte is preferably 0 to 30 mass%, more preferably 0 to 20 mass%, and even more preferably 0 to 15 mass%. Here, the sulfide-based glass phase, the highly ion-conductive crystalline phase, and the β-Li ３ P.S. ４ From the viewpoint of preferably obtaining the effect of the crystalline phase, the proportion of the other phase is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less. In addition, the other phase may not be contained.

[0053] <Physical Properties of Sulfide Solid Electrolyte> The sulfide solid electrolyte according to this embodiment, when compacted under 380 MPa, preferably has a lithium ion conductivity of 1 mS / cm or more at 25°C. This is due to the high lithium ion conductivity of the sulfide-based glass phase and the high ion-conductive crystalline phase derived therefrom. However, since it is difficult to extract only the sulfide-based glass phase or the high ion-conductive crystalline phase from the sulfide solid electrolyte, the lithium ion conductivity of the sulfide-based glass phase or the high ion-conductive crystalline phase is evaluated based on the lithium ion conductivity of the sulfide solid electrolyte.

[0054] The lithium ion conductivity of the sulfide solid electrolyte according to this embodiment is preferably 1 mS / cm or more, and the higher the better. However, this value varies depending on the composition and the proportion of the sulfide glass phase and the highly ion-conductive crystalline phase. For example, when the Br content of the Ha composition is 90 at% or more, the lithium ion conductivity is preferably 2 mS / cm or more. Furthermore, when the Cl content of the Ha composition is 90 at% or more, the lithium ion conductivity is preferably 1.5 mS / cm or more. The lithium ion conductivity in this specification is determined by AC impedance measurement using a measurement sample obtained by compacting a sulfide solid electrolyte powder at 380 MPa. Specifically, the AC impedance of the measurement sample is measured at a measurement frequency of 100 Hz to 1 MHz, a measurement voltage of 100 mV, and a measurement temperature of 25°C, and the value obtained from the resulting Nyquist plot is taken as the lithium ion conductivity.

[0055] The heat resistance of the sulfide solid electrolyte according to this embodiment can be evaluated by the lithium ion conductivity after heat treatment of the sulfide solid electrolyte in a nitrogen atmosphere at 240° C. for 1 hour. Specifically, the lithium ion conductivity after the heat treatment is preferably 0.8 mS / cm or more, and the higher the better, but the value varies depending on the composition and the proportion of the sulfide-based glass phase and the highly ion-conductive crystalline phase, etc.

[0056] If the difference in lithium ion conductivity before and after the heat treatment is 2 mS / cm or less, it can be said that the heat resistance of the sulfide solid electrolyte is good, and the difference is more preferably 1.8 mS / cm or less, and even more preferably 1.5 mS / cm or less, and the smaller the difference, the more preferable.

[0057] The sulfide solid electrolyte according to this embodiment was kept in an atmosphere with a dew point of −20° C. for 5 hours. ２ The amount of sulfur generated is preferably 10 mL / g or less, more preferably 1 mL / g or less, and even more preferably 0.1 mL / g or less, and the smaller the better. ２ More specific conditions for measuring the amount of sulfur generated are as follows: First, the sulfide solid electrolyte is passed through a 100 μm mesh to obtain powder with an average particle size of 10 to 20 μm. Then, 10 mg of this powder is mixed with nitrogen (N ２ ) gas at a flow rate of 0.5 L / min for 5 hours. ２ S) Monitor the amount of generation and calculate the total amount as H ２ The amount of S generated is the above H ２ The amount of S generated is a value that serves as an index of the hydrolysis resistance, i.e., water resistance, of the sulfide solid electrolyte, and can be achieved by the presence of a sulfide-based glass phase or a highly ion-conductive crystalline phase, or by including Ha as a constituent element. In particular, it is preferable that at least one of Cl and Br is included as Ha, and it is more preferable that Br is included. It is also more preferable that both Cl and Br are included.

[0058] The average particle size (D50) of the sulfide solid electrolyte according to this embodiment is preferably 0.1 to 300 μm, more preferably 0.3 to 50 μm, and even more preferably 0.5 to 5 μm. Here, from the viewpoint of reducing the load of the pulverization process when using the sulfide solid electrolyte in a secondary battery, the average particle size is preferably 300 μm or less, more preferably 50 μm or less, and even more preferably 5 μm or less. Furthermore, from the viewpoint of powder handling, the average particle size is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more. The average particle size (D50) can be adjusted by subjecting the obtained sulfide solid electrolyte to coarse pulverization. Conventional known methods for coarse pulverization can be used, including, for example, a cutter mill, a planetary ball mill, and a jet mill, and dry pulverization is preferred. The resulting solid electrolyte can then be further pulverized to a finer particle size using a wet or dry pulverization method such as a bead mill or a jet mill, and used as a battery material, such as a solid electrolyte for a positive electrode, a negative electrode, or a separator layer.

[0059] The sulfide solid electrolyte according to this embodiment is suitable as an electrolyte for lithium ion secondary batteries. When used in lithium ion secondary batteries, the sulfide solid electrolyte forms a solid electrolyte layer together with other components such as a binder, as necessary. Conventionally known binders and other components can be used. The content of the sulfide solid electrolyte according to this embodiment is preferably 80 mass % or more, and more preferably 90 mass % or more, of the entire solid electrolyte layer.

[0060] The sulfide solid electrolyte according to this embodiment may be mixed with a positive electrode active material or a negative electrode active material to form a positive electrode layer or a negative electrode layer. The positive electrode active material or a negative electrode active material, current collector, binder, conductive additive, and the like used in the positive electrode layer or the negative electrode layer may be conventionally known materials.

[0061] The lithium ion secondary battery includes a positive electrode layer, a solid electrolyte layer, and a positive electrode layer. It is preferable that at least one layer selected from the group consisting of the positive electrode layer, the solid electrolyte layer, and the positive electrode layer contains the sulfide solid electrolyte according to the present embodiment.

[0062] The lithium ion secondary battery may have any of a variety of shapes, including a coin shape, a sheet shape (film shape), a folded shape, a wound bottomed cylindrical shape, and a button shape, and may be appropriately selected depending on the intended use.

[0063] <<Method for Producing Sulfide Solid Electrolyte>> The method for producing a sulfide solid electrolyte according to this embodiment includes the following steps 1 to 4 in order as steps S1 to S4 as shown in FIG. 1. Step S1: Step 1 of mixing raw materials to obtain a raw material mixture containing Li, P, and S. Step S2: Step 2 of heating the raw material mixture obtained in step 1 to obtain a melt. Step S3: Step 4 of cooling and solidifying the melt obtained in step 2 to obtain a glass phase and β-Li. ３ P.S. ４ Step S4: Heating the sulfide solid electrolyte precursor obtained in step S3 to obtain a highly ion-conductive crystalline phase in which a portion of the glass phase is crystallized.

[0064] The heating in step 2 and the cooling and solidification in step 3 are carried out under normal pressure conditions, and in the cooling and solidification, the melt is allowed to flow out and then allowed to remain in a temperature range of 750 to 210°C for 0.2 to 100 seconds. This results in a phase consisting of sulfide-based glass, a highly ion-conductive crystalline phase derived therefrom, and β-Li ３ P.S. ４ and a crystalline phase of β-Li ３ P.S. ４ In this specification, "under normal pressure conditions" means a pressure range of about (gauge pressure ±15 kPa).

[0065] Furthermore, in the above step 1, the raw materials are mixed so that the compositions of the resulting sulfide-based glass phase and highly ion-conductive crystalline phase satisfy Li: 30 to 50 at %, P: 5 to 15 at %, and S: 30 to 60 at %, thereby obtaining the sulfide solid electrolyte described in the above section "Sulfide Solid Electrolyte."

[0066] Each step will be explained below.

[0067] <Step 1> In this embodiment, step S1 is step 1 in which raw materials are mixed to obtain a raw material mixture containing Li, P, and S. Specifically, a raw material containing Li, a raw material containing P, and a raw material containing S are mixed to obtain a raw material mixture. Furthermore, when it is desired to obtain a glass phase further containing Ha as a constituent element, a raw material containing Ha is further mixed in addition to the raw material containing Li, the raw material containing P, and the raw material containing S to obtain a raw material mixture containing Li, P, S, and Ha. Here, the Ha element refers to at least one element selected from the group consisting of F, Cl, Br, and I.

[0068] Examples of raw materials containing Li include lithium sulfide (Li ２ S), lithium carbonate (Li ２ CO ３ ), lithium sulfate (Li ２ SO ４ ), lithium oxide (Li ２ Examples of the substance containing Li include lithium compounds such as lithium ion (LiO), lithium hydroxide (LiOH), and metallic lithium. The substance containing Li may be used alone or in combination of two or more.

[0069] From the viewpoint of obtaining a sulfide-based glass phase, it is preferable to use lithium sulfide as the raw material containing Li. Furthermore, when the obtained sulfide solid electrolyte contains a halogen element, lithium halide (LiHa, where Ha is a halogen element) is also preferable as the raw material containing Li. Lithium halide will be described later.

[0070] Examples of raw materials containing the P element include diphosphorus pentasulfide (P ２ S ５ ), diphosphorus trisulfide (P ２ S ３ ) and other phosphorus sulfides, sodium phosphate (Na ３ P.O. ４ The phosphorus-containing substance may be used singly or in combination of two or more.

[0071] The raw material containing the P element is preferably phosphorus sulfide, and more preferably diphosphorus pentasulfide (P), from the viewpoint of preventing the inclusion of elements other than those constituting the target sulfide solid electrolyte.２ S ５ ) is more preferred.

[0072] Examples of raw materials containing the S element include lithium sulfide (Li ２ S), diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ), other sulfur compounds containing phosphorus, and compounds containing sulfur. ２ S, CS ２ , iron sulfide (FeS, Fe ２ S ３ , FeS ２ , Fe １－ｘ S, etc.), bismuth sulfide (Bi ２ S ３ ), copper sulfide (CuS, Cu ２ S, Cu １－ｘ The substance containing the S element may be used alone or in combination of two or more.

[0073] The raw material containing the S element is preferably lithium sulfide or phosphorus sulfide from the viewpoint of preventing the inclusion of elements other than those constituting the target sulfide solid electrolyte. As the phosphorus sulfide, diphosphorus pentasulfide (P ２ S ５ Lithium sulfide is a compound that serves as both a raw material containing Li and a raw material containing S, and phosphorus sulfide is a compound that serves as both a raw material containing S and a raw material containing P.

[0074] Examples of raw materials containing Ha element include lithium halides such as lithium fluoride (LiF), lithium chloride (LiCl), lithium bromide (LiBr), and lithium iodide (LiI), phosphorus halides, phosphoryl halides, sulfur halides, sodium halides, and boron halides. One or more substances containing Ha element may be used, or two or more may be used in combination.

[0075] From the viewpoint of reactivity, the raw material containing the Ha element is preferably a lithium halide, more preferably LiCl, LiBr, or LiI, and even more preferably LiCl or LiBr.

[0076] A raw material mixture may be obtained by further mixing raw materials containing other elements according to the desired composition of the sulfide solid electrolyte. As described above, examples of the other elements include Si, B, Ge, Al, O, Na, K, Mg, Ca, Sr, Ba, Y, Zr, Cr, Zn, Ga, Sn, and Sb. Among the other elements, for example, Si, B, Ge, Al, Sn, and Sb may be included. These Si, B, Ge, Al, Sn, and Sb are elements that can occupy the P position when the sulfide-based glass phase is crystallized.

[0077] As raw materials containing these other elements, conventionally known raw materials can be used. For example, as a raw material containing Si element, SiO ２ , SiS ２ Among them, from the viewpoint of lithium ion conductivity, SiO ２ These compounds may be used alone or in combination of two or more. Examples of raw materials containing B element include B ２ O ３ , B ２ S ３ Among them, from the viewpoint of water resistance of glass, B ２ O ３ These compounds may be used alone or in combination of two or more. The raw material containing Ge element is GeO ２ , GeS, GeS ２ , GeCl ２ Among them, from the viewpoint of lithium ion conductivity, GeS ２ , GeCl ２ is preferred, and GeS ２ These compounds may be used alone or in combination of two or more. Examples of raw materials containing Al element include Al ２ S ３ , Al ２ O ３ , AlCl ３ Among them, Al is the most suitable from the viewpoint of lithium ion conductivity and water resistance. ２ S ３ , AlCl ３ is preferred, and Al２ S ３ These compounds may be used alone or in combination of two or more. Examples of raw materials containing Sn include SnS, SnS ２ , SnO, SnO ２ , SnCl ２ Among them, from the viewpoint of lithium ion conductivity, SnS ２ , SnCl ２ is preferred, and SnS ２ These compounds may be used alone or in combination of two or more. Examples of raw materials containing Sb include Sb ２ S ３ , Sb ２ O ３ , Sb ２ O ５ , SbCl ３ , SbCl ５ Among them, from the viewpoint of lithium ion conductivity and water resistance, Sb ２ S ３ , SbCl ３ is preferred, and Sb ２ S ３ These compounds may be used alone or in combination of two or more.

[0078] These raw materials are blended appropriately according to the composition of the sulfide-based glass phase and the resulting high ion-conductive crystalline phase. Specifically, to obtain the sulfide solid electrolyte described in the above "Sulfide Solid Electrolyte," the raw materials are mixed so that the resulting glass phase and the resulting high ion-conductive crystalline phase have a composition of Li: 30 to 50 at%; P: 5 to 15 at%; and S: 30 to 60 at%. Furthermore, the glass phase and the high ion-conductive crystalline phase preferably further contain Ha as a constituent element, and in addition to the above composition, the Ha content is preferably 1 to 12 at%. The blending of the raw materials also determines the crystal structure of the resulting high ion-conductive crystalline phase.

[0079] In addition to the above, preferred embodiments of the resulting glass phase and the highly ion-conductive crystalline phase derived therefrom are the same as preferred embodiments of the "sulfide-based glass phase and the highly ion-conductive crystalline phase" in the "sulfide solid electrolyte" above.

[0080] It is preferable that the particle size of each raw material be small from the viewpoint of shortening the holding time during heating and melting in the subsequent step 2. Furthermore, if the particle size of the raw material is too large, it may affect the homogeneity of the sulfide solid electrolyte precursor and the sulfide solid electrolyte, and from this viewpoint as well, it is preferable that the particle size of the raw material be small to a certain extent. However, the production method according to this embodiment has excellent composition controllability. Therefore, even if raw materials with particle sizes that may reduce homogeneity in conventional production methods are used, the production method according to this embodiment can produce more homogeneous sulfide solid electrolyte precursor and sulfide solid electrolyte.

[0081] From the above viewpoints, specifically, the particle size of each raw material is preferably 1 mm or less, more preferably 500 μm or less, even more preferably 250 μm or less, even more preferably 100 μm or less, and particularly preferably 50 μm or less. Smaller particle sizes are preferable, but a practical lower limit is about 0.1 μm, and the particle size may be 1 μm or more, or may be 5 μm or more. Furthermore, as described above, according to the production method of this embodiment, a homogeneous sulfide solid electrolyte precursor and sulfide solid electrolyte are easily obtained even when raw materials with relatively large particle sizes are used. In consideration of this, for example, from the viewpoint of reducing production costs, the particle size of each raw material may be 10 μm or more, 100 μm or more, or 250 μm or more.

[0082] From these, the particle size of each raw material is preferably 0.1 μm to 1 mm, more preferably 1 to 500 μm, even more preferably 5 to 250 μm, even more preferably 5 to 100 μm, and particularly preferably 5 to 50 μm. Furthermore, from the viewpoint of production costs, the particle size of each raw material is preferably 10 μm to 1 mm, more preferably 100 μm to 1 mm, and even more preferably 250 to 500 μm. In this specification, the particle size of each raw material refers to the average particle size (D50) expressed as the median diameter obtained from a volume-based particle size distribution chart obtained by measuring the particle size distribution using a laser diffraction particle size distribution analyzer MT3300EXII manufactured by Microtrac.

[0083] The raw materials can be mixed, for example, by mixing in a mortar, mixing using media such as a planetary ball mill, or medialess mixing such as a pin mill, a powder mixer, or airflow mixing. The raw materials may be made amorphous by mixing before heating.

[0084] <Step 2> Step S2 in this embodiment is step 2 in which the raw material mixture obtained in step 1 is heated to obtain a melt.

[0085] The specific method for heating and melting the raw material mixture is not particularly limited, as long as the heating is performed under atmospheric pressure. In the production method according to this embodiment, the heating for melting the raw material mixture is performed under atmospheric pressure, thereby reducing the compositional difference between the composition of the raw material mixture and the composition of the resulting sulfide-based glass phase and the highly ion-conductive crystalline phase derived therefrom, or the composition of the sulfide solid electrolyte. Furthermore, by performing the heating under a gas atmosphere containing the element S, the compositional difference can be further suppressed. Note that in the production method according to this embodiment, the heating and melting are performed in an atmosphere-controlled environment under atmospheric pressure, and do not need to be performed in a sealed tube. However, this does not in any way exclude the use of a sealed tube.

[0086] Here, the difference between the sealed tube environment and the controlled atmosphere environment under normal pressure conditions is that in the sealed tube environment, the pressure inside the container is a vacuum, i.e., less than (gauge pressure -15 kPa), whereas in the controlled atmosphere environment under normal pressure conditions, the pressure inside the container during heating and melting is within the range of (gauge pressure ±15 kPa).

[0087] That is, in the manufacturing method according to the present embodiment, the heating and melting in step 2 is performed under normal pressure conditions (gauge pressure ±15 kPa). At this time, the composition ratio of the resulting glass phase or highly ion-conductive crystalline phase expressed as [P / Li] relative to the composition ratio of the raw material mixture expressed as [P / Li] is preferably 95 to 105%, for example.

[0088] The pressure during the heat melting may be normal pressure (gauge pressure ±15 kPa), preferably (gauge pressure ±10 kPa), more preferably (gauge pressure ±5 kPa), and even more preferably (gauge pressure ±2 kPa). Furthermore, the composition ratio of the resulting glass phase or highly ion-conductive crystalline phase expressed as [P / Li] relative to the composition ratio expressed as [P / Li] of the raw material mixture is preferably 95 to 105%, more preferably 97 to 103%, even more preferably 99 to 101%, with the closer to 100% being more preferable. Here, the composition ratio is preferably 95% or more, more preferably 97% or more, even more preferably 99% or more, and is preferably 105% or less, more preferably 103% or less, and even more preferably 101% or less.

[0089] With respect to the composition ratio [P / Li] of the raw material mixture relative to the composition ratio [P / Li] of the resulting glass phase or highly ion-conductive crystalline phase, Li is an element that is difficult to volatilize, and P is an element that is easily volatilized. Therefore, comparing the composition ratio [P / Li] of the raw material mixture with that of the glass phase or highly ion-conductive crystalline phase is appropriate as an index of the compositional deviation between the composition of the raw material mixture and the composition of the resulting sulfide-based glass phase or highly ion-conductive crystalline phase or the composition of the sulfide solid electrolyte.

[0090] Examples of heat-resistant containers for containing the raw material mixture include heat-resistant containers made of carbon, heat-resistant containers containing oxides such as quartz, quartz glass, borosilicate glass, aluminosilicate glass, alumina, zirconia, and mullite, heat-resistant containers containing nitrides such as silicon nitride and boron nitride, and heat-resistant containers containing carbides such as silicon carbide. These heat-resistant containers may be formed in bulk from the above-mentioned materials, or may be containers on which a layer of carbon, oxide, nitride, carbide, or the like is formed, such as a carbon-coated quartz tube.

[0091] The melting temperature when the raw material mixture is heated varies depending on the raw materials used and the composition of the raw material mixture, but is, for example, preferably 600 to 950°C, more preferably 630 to 850°C, and even more preferably 650 to 750°C. Here, from the viewpoint of reaction rate, the melting temperature is preferably 600°C or higher, more preferably 630°C or higher, and even more preferably 650°C or higher. Furthermore, from the viewpoint of suppressing composition deviation due to volatilization of components, the melting temperature is preferably 950°C or lower, more preferably 850°C or lower, and even more preferably 750°C or lower.

[0092] The heat-melting time varies depending on the scale, but is preferably 10 minutes to 10 hours, more preferably 30 minutes to 9.5 hours, even more preferably 45 minutes to 9 hours, and particularly preferably 1 to 9 hours. From the viewpoint of smoothly progressing the reaction, the heat-melting time is preferably 10 minutes or more, more preferably 30 minutes or more, even more preferably 45 minutes or more, and particularly preferably 1 hour or more. From the viewpoint of productivity, the heat-melting time is preferably 10 hours or less, more preferably 9.5 hours or less, and even more preferably 9 hours or less.

[0093] The atmosphere in the container during heat melting is not particularly limited. For example, it may be a nitrogen atmosphere, an argon atmosphere, or a gas atmosphere containing an S element. Among these, a gas atmosphere containing an S element is preferred from the viewpoint of more suitably suppressing composition deviation.

[0094] When the gas atmosphere contains S element, examples of the S element source include sulfur gas, hydrogen sulfide gas, sulfur dioxide gas, etc., and sulfur gas is preferred from the viewpoint of reactivity with the raw materials. Alternatively, the gas containing S element may be introduced by adding elemental sulfur powder and vaporizing the elemental sulfur powder by heating during melting. The elemental sulfur powder may be added together with the raw materials when mixing the raw materials to obtain a raw material mixture, or may be added separately after obtaining the raw material mixture. However, when the elemental sulfur powder is added together with the raw materials when obtaining the raw material mixture, the mass of the obtained raw material mixture does not include the mass of the elemental sulfur powder. The gas containing S element may be introduced by adding the above-mentioned sulfur gas, hydrogen sulfide gas, sulfur dioxide gas, etc., and the gas containing S element resulting from the addition of elemental sulfur powder.

[0095] The gas containing S element is preferably used as a mixed gas with, for example, an inert gas, which is the S element source gas. The mixing ratio with the inert gas is arbitrary and is not particularly limited as long as the cumulative amount of S element introduced relative to the mass of the raw material mixture can be set to a desired value.

[0096] Examples of the inert gas include nitrogen gas, argon gas, and helium gas, and these may be used alone or in combination of two or more.

[0097] The dew point during heat melting is preferably −20° C. or lower, and although there is no particular lower limit, it is usually about −80° C. The oxygen concentration is preferably 1000 ppm by volume or lower.

[0098] In step 2, whether the molten mixture of raw materials is completely dissolved can be confirmed by the absence of peaks derived from crystals in high-temperature X-ray diffraction measurement. It can also be confirmed by heating the molten mixture at a predetermined temperature and tilting the molten mixture to check whether it has fluidity.

[0099] <Step 3> In this embodiment, step S3 is a step of cooling and solidifying the melt obtained in step 2 to form a glass phase and β-Li. ３ P.S. ４ and step 3 of obtaining a sulfide solid electrolyte precursor containing the crystalline phase of

[0100] Cooling and solidification are carried out under atmospheric pressure. As mentioned above, "under atmospheric pressure" means an atmosphere under a pressure of about (gauge pressure ±15 kPa). The pressure during cooling and solidification may be under atmospheric pressure conditions of (gauge pressure ±15 kPa), preferably (gauge pressure ±10 kPa), more preferably (gauge pressure ±5 kPa), and even more preferably (gauge pressure ±2 kPa).

[0101] In the cooling and solidification step, the melt obtained in step 2 is poured out from the container used for the heating and melting step in step 2. After the melt is poured out, it is kept in a temperature range of 750 to 210°C for 0.2 to 100 seconds. This allows a sulfide-based glass phase containing Li, P, and S as constituent elements and a β-Li ３ P.S. ４ In addition to the above, it has been found that a sulfide solid electrolyte precursor containing the β-Li crystal phase can be obtained. ３ P.S. ４ The content of the β-Li crystal phase in the sulfide solid electrolyte obtained through step 4 can be set to a suitable amount of, for example, 0.1 to 30 mass %. ３ P.S. ４ The content of the crystalline phase of can be set to a suitable amount of, for example, 0.1 to 30 mass %. Note that, during the cooling to the temperature range of 750 to 210°C, depending on the composition, the melt may already be solid rather than molten (liquid), but for convenience of explanation, the temperature will be referred to as the melt temperature here.

[0102] In the cooling and solidification, the time for which the poured melt is kept in the temperature range of 750 to 210°C is 0.2 to 100 seconds, preferably 0.5 to 60 seconds, and more preferably 1 to 40 seconds. Here, the time is 0.2 seconds or more, and β-Li ３ P.S. ４ From the viewpoint of precipitation of the crystalline phase of β-Li, the time is preferably 0.5 seconds or more, more preferably 1 second or more. ３ P.S. ４From the viewpoint of preventing excessive precipitation of the crystalline phase, the time is preferably 60 seconds or less, and more preferably 40 seconds or less. When the heating temperature for obtaining a melt in step 2 is 750°C or less, the time for which the melt is allowed to stay in the temperature range of 750 to 210°C may be read as the time for which the melt is allowed to stay in the temperature range of the heating temperature to 210°C.

[0103] During cooling and solidification, the average cooling rate while the melt is kept in the temperature range of 750 to 210°C is preferably 5.4°C / sec or more, more preferably 5.4 to 2700°C / sec, even more preferably 50 to 2000°C / sec, and even more preferably 100 to 1000°C / sec. By controlling the cooling rate within a suitable range and performing rapid cooling, a sulfide-based glass phase containing Li, P, and S as constituent elements and a β-Li ３ P.S. ４ This makes it easy to obtain a sulfide solid electrolyte precursor containing the crystalline phase of (I). More specifically, from the viewpoint of realizing a small crystallite diameter, the average cooling rate is preferably 5.4°C / sec or more, more preferably 50°C / sec or more, and even more preferably 100°C / sec or more. Furthermore, from the viewpoint of favorable crystal growth, the average cooling rate is preferably 2700°C / sec or less, more preferably 2000°C / sec or less, and even more preferably 1000°C / sec or less.

[0104] In the cooling and solidification, after the temperature of the poured melt reaches 210°C, it is further cooled, for example, to 150°C or less, and then subjected to the next step 4. The cooling rate until the temperature of the melt reaches 210°C and the cooling rate when further cooling from there to 150°C or less may be the same or different.

[0105] Furthermore, by the cooling, the content of the sulfide-based glass phase in the sulfide solid electrolyte precursor can be increased to, for example, 60 mass % or more, and β-Li ３ P.S. ４ The content of the crystalline phase of the sulfide-based glass phase and β-Li can be set to 0.1 to 30 mass %. ３ P.S. ４ The total content of the crystalline phases can be set to, for example, 80 mass % or more.

[0106] This sulfide-based glass phase can achieve higher lithium ion conductivity than conventional sulfide-based glasses. Furthermore, by performing the cooling and solidification under atmospheric pressure, the compositional difference between the raw material mixture and the resulting sulfide-based glass phase and the resulting highly ion-conductive crystalline phase or sulfide solid electrolyte can be reduced.

[0107] <Step 4> Step S4 according to this embodiment is step 4 in which the sulfide solid electrolyte precursor obtained in step 3 is heated to obtain a highly ion-conductive crystalline phase in which a part of the glass phase in the sulfide solid electrolyte precursor is crystallized.

[0108] The heating temperature in step 4, i.e., the temperature during crystallization, can be determined depending on the crystallization temperature at which the glass phase changes to a high ion-conductivity crystalline phase. Specifically, from the viewpoint of effectively promoting the crystallization, a temperature of (crystallization temperature - 15°C) or higher is preferable, and it may be (crystallization temperature - 10°C) or higher, or a temperature higher than the crystallization temperature, or even (crystallization temperature + 1°C) or higher. Furthermore, it has been found that heating at high temperatures precipitates other heterogeneous phases, which are crystals with low ion conductivity, next to the high ion-conductivity crystalline phase. Therefore, from the viewpoint of preventing the precipitation of crystals with low ion conductivity, the crystallization temperature is preferably lower than the temperature at which crystals with low ion conductivity precipitate, more preferably lower than (crystallization temperature + 20°C), and even more preferably lower than (crystallization temperature + 15°C). That is, the temperature during crystallization is preferably higher than (crystallization temperature - 15°C), and more preferably higher than (crystallization temperature - 15°C) and lower than the temperature at which crystals with low ion conductivity precipitate. Alternatively, the temperature may be (crystallization temperature - 10 ° C) or higher and (crystallization temperature + 20 ° C) or lower, or may be (crystallization temperature + 20 ° C) or higher, or (crystallization temperature + 1 ° C) or higher and (crystallization temperature + 15 ° C) or lower. Within the above range, a highly ion-conductive crystalline phase is obtained from the glass phase, and other crystalline phases are also obtained. Note that the crystallization temperature in this specification refers to the peak top temperature of the exothermic peak observed when differential scanning calorimetry (DSC) is performed on the sulfide solid electrolyte precursor obtained in step 3 and the temperature is increased at a rate of 5 ° C / min.

[0109] The heating time during crystallization is, for example, preferably 1 to 180 minutes, more preferably 5 to 120 minutes, and even more preferably 10 to 100 minutes. From the viewpoint of stable quality, the heating time is preferably 1 minute or more, more preferably 5 minutes or more, and even more preferably 10 minutes or more. From the viewpoint of productivity, the heating time is preferably 180 minutes or less, more preferably 120 minutes or less, and even more preferably 100 minutes or less. The content ratio of the high ion-conducting crystalline phase can be adjusted by adjusting the heating temperature and heating time during crystallization.

[0110] The heating atmosphere during crystallization may be a nitrogen atmosphere, an argon atmosphere, a dry air atmosphere, etc. Among these, a nitrogen atmosphere or an argon atmosphere is preferred from the viewpoint of not impairing ionic conductivity.

[0111] The dew point during crystallization is preferably −30° C. or lower. The oxygen concentration during crystallization may be a dry air environment, but from the viewpoint of safety, it is preferably 5% by volume or lower.

[0112] After heating, the sulfide solid electrolyte according to this embodiment can be obtained by cooling to room temperature at a rate of, for example, 1 to 10,000° C. / min.

[0113] The sulfide solid electrolyte obtained above may be used as it is for at least one selected from the group consisting of a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, or may be used after being subjected to pulverization, drying, or the like depending on the application.

[0114] The present invention will be described in detail below with reference to examples, but is not limited to these. Examples 3 to 5 and 7 are working examples, and Examples 1, 2 and 6 are comparative examples.

[0115] <Test Examples> <Example 1> Li under a dry nitrogen gas atmosphere ３．４ P １．０ S ４．０ Br ０．３Lithium sulfide powder (Sigma, purity 99.98%), diphosphorus pentasulfide powder (Sigma, purity 99%), and lithium bromide powder (Sigma, purity 99.995%) were weighed and mixed in a mortar to obtain a raw material mixture (Step 1). The obtained raw material mixture was placed in a carbon container under a nitrogen atmosphere containing sulfur element (Sigma, purity 99.998%) as an S element source and a dew point of −50° C. or less, and then placed in an electric furnace inside a glove box. The pressure was increased to +1 kPa and the temperature was increased to 750° C. for 1 hour to obtain a completely dissolved molten material (Step 2). Next, the tip of the vessel was heated to melt the melt, and the melt was poured onto a twin roll and cooled to room temperature at an average cooling rate of 5,400°C / s, yielding a sulfide solid electrolyte precursor (Step 3). The average cooling rate was adjusted by adjusting the melt outflow rate, the roll gap between the twin rolls, and the rotation speed. The pressure was (gauge pressure + 1 kPa), and the time the poured melt spent in the temperature range of 750 to 210°C was 0.1 seconds. The sulfide solid electrolyte precursor obtained above was heated to 210°C for 10 minutes in a nitrogen atmosphere and then cooled to room temperature at a cooling rate of 300°C / min, yielding a sulfide solid electrolyte. The sulfide solid electrolyte precursor obtained above was subjected to DSC measurement at a heating rate of 5°C / min, and the temperature at the top of the exothermic peak, i.e., the crystallization temperature, was confirmed to be 223°C.

[0116] Example 2: Li under a dry nitrogen gas atmosphere ３．４ P １．０ S ４．０ Br ０．３Lithium sulfide powder (manufactured by Sigma, purity 99.98%), diphosphorus pentasulfide powder (manufactured by Sigma, purity 99%), and lithium bromide powder (manufactured by Sigma, purity 99.995%) were weighed and mixed in a mortar to obtain a raw material mixture (step 1). The obtained raw material mixture was further mixed using a planetary ball mill (manufactured by Fritsch, P-7) to obtain a sulfide solid electrolyte precursor (steps 2'+3'). Mixing using a planetary ball mill was performed using zirconia balls with a particle size of 4 mm and a zirconia pot, and mechanical milling was performed at 400 rpm for 20 hours under a nitrogen atmosphere. The dew point during operation was maintained below -70 ° C. The sulfide solid electrolyte obtained above was heated in a nitrogen atmosphere at 210 ° C. for 10 minutes, and then cooled to room temperature at a cooling rate of 300 ° C. / min to obtain a sulfide solid electrolyte (step 4). The crystallization temperature of the sulfide solid electrolyte precursor was 210°C.

[0117] Examples 3 to 6 Sulfide solid electrolytes were obtained in the same manner as in Example 1, except that the cooling rate of the melt obtained by heating and the time the melt spent in the temperature range of 750 to 210°C were changed to 0.5 seconds (Example 3), 3.2 seconds (Example 4), 15 seconds (Example 5), and 150 seconds (Example 6), respectively. The crystallization temperatures of the sulfide solid electrolyte precursors were all around 225°C.

[0118] Example 7: Li ３．４ P １．０ S ４．０ Br ０．１５ I ０．１５ A sulfide solid electrolyte was obtained in the same manner as in Example 1, except that the raw materials were weighed and mixed to obtain a raw material mixture having a composition ratio of: and the time during which the melt remained in the temperature range of 750 to 210°C was set to 55 seconds. The crystallization temperature of the sulfide solid electrolyte precursor was 215°C.

[0119] <Evaluation: Sulfide Solid Electrolyte Precursor> In each example, the sulfide solid electrolyte precursor obtained in step 3 or step 2'+3' was weighed in a glove box and dissolved in an alkaline aqueous solution, and composition analysis was performed for each element. Specifically, P and S were analyzed by ICP atomic emission spectroscopy (apparatus: Hitachi High-Tech Science Corporation, model number PS3520UVDDII). Li was analyzed by atomic absorption spectroscopy (apparatus: Hitachi High-Tech Corporation, model number ZA3300; when measuring Li, CsCl was added so that the solution concentration became 0.1%). Br and I were analyzed by ion chromatography (apparatus: Thermo Fisher Scientific, model number ICS-2100 (column: AS11HC)). ２ O ２ The entire composition of the sulfide solid electrolyte precursor was confirmed by the above procedure.

[0120] In addition, the sulfide solid electrolyte precursor was pulverized in a mortar and passed through a 100 μm sieve to obtain a powder of solid electrolyte precursor with an average particle size D50 of approximately 20 μm. This was used as a sample. Using an X-ray diffraction (XRD) device (Rigaku Corporation, SmartLab), measurements were taken in an environment not exposed to the atmosphere under the following conditions: radiation source: CuKα radiation (λ = 1.5418 Å), tube voltage: 45 kV, tube current: 200 mA, scan angle: 10 to 100°, scan rate: 5° / min, step number: 0.01° / step. Furthermore, silicon powder was added as an internal standard during XRD measurement. When a peak was observed in the XRD pattern, the crystallinity (wt%) was determined by Rietveld analysis. The presence or absence of a crystalline peak in the obtained XRD pattern was confirmed, and β-Li ３ P.S. ４ The presence or absence of the β-Li crystal phase was confirmed. ３ P.S. ４When a crystalline phase of the formula (I) was present, its content and crystallite size were determined. The crystallite size was calculated using the Scherrer equation using the half-width of the crystalline peak. More specifically, the crystallite size was calculated using the analysis software PDXL provided with the device, and the peak at 2θ = 18.2 ± 0.5 (derived from the 011 plane) was analyzed. In addition, the content (wt%) of the glass phase can be calculated by subtracting the crystallinity (wt%) of the sulfide solid electrolyte precursor from 100 wt%. These results are shown in Table 1.

[0121] <Evaluation: Sulfide Solid Electrolyte> <Composition Ratio, Content Ratio> The sulfide solid electrolyte obtained in each example was pulverized in a mortar and passed through a 100 μm sieve to obtain a powder of solid electrolyte precursor having an average particle size D50 of about 20 μm, which was used as a sample. XRD measurement was then carried out under the same conditions as when the sulfide solid electrolyte precursor was used as a sample. Analysis of the obtained XRD pattern revealed the presence of a highly ion-conducting crystalline phase and β-Li ３ P.S. ４ The composition ratio and content ratio of each of the crystalline phases were determined, and the content ratio of the phase consisting of sulfide-based glass was also determined from the crystallinity. Here, it can be determined that the composition ratio of the phase consisting of sulfide-based glass is the same as the composition ratio of the highly ion-conductive crystalline phase, but just to be sure, it was compared with the composition ratio determined in the evaluation of the sulfide solid electrolyte precursor. As a result, it was confirmed that the composition ratio of the sulfide solid electrolyte precursor was within a range of ±20% for all components relative to the composition ratio of the highly ion-conductive crystalline phase. In addition, β-Li ３ P.S. ４ It was confirmed that there was no change in the crystallinity, content, or crystallite size between the sulfide solid electrolyte precursor and the sulfide solid electrolyte obtained after heating to crystallize the sulfide-based glass phase. The results are shown in Table 1. While the content ratios of the sulfide-based glass phase and the high ion-conductive crystalline phase in Examples 2 and 7 have not been analyzed, it was confirmed that at least the sulfide solid electrolytes in Examples 5 to 7 contain a sulfide-based glass phase and a high ion-conductive crystalline phase derived therefrom.

[0122] In the analysis of the XRD pattern, the peak intensity of the diffraction peak at 2θ=20.2±0.5°, which indicates a highly ion-conductive crystalline phase, was determined as IＡ and β-Li ３ P.S. ４ The highest intensity of the diffraction peaks at 2θ = 18.2 ± 0.5°, which indicate the crystalline phase of Ｂ When I Ｂ / I Ａ The peak intensity ratio, expressed as I, was also determined. The results are shown in Table 1. The peak intensity of the diffraction peak at 2θ = 19.1 ± 0.5°, which indicates a highly ion-conductive crystalline phase, was also determined. Ｃ and β-Li ３ P.S. ４ The highest intensity of the diffraction peaks at 2θ = 18.2 ± 0.5°, which indicate the crystalline phase of Ｂ When I Ｂ / I Ｃ The peak intensity ratio represented by the following formula was also determined. The results are shown in Table 1. The XRD patterns of the sulfide solid electrolyte precursor obtained in Example 4 and the sulfide solid electrolyte obtained in Example 4 are shown in Figures 2 and 3, respectively.

[0123] <Lithium ion conductivity> The obtained sulfide solid electrolyte was pulverized in a mortar and then passed through a 100 μm sieve to obtain a powder with an average particle size (D50) of approximately 20 μm, which was used as a sample. The above sample was pressed under a pressure of 380 MPa to obtain a measurement sample, and was measured using an AC impedance measuring device (potentiostat / galvanostat VSP, manufactured by Bio-Logic Sciences Instruments). The measurement conditions were a measurement frequency of 100 Hz to 1 MHz, a measurement voltage of 100 mV, and a measurement temperature of 25°C, and the lithium ion conductivity was calculated from the obtained Nyquist plot. The results are shown in the "σ" column of "Before heat treatment" in the "Heat resistance" section of Table 1. Ｌｉ＋ (mS / cm)".

[0124] <Heat Resistance> The obtained sulfide solid electrolyte was subjected to a heat treatment at 240°C for 1 hour in a nitrogen atmosphere. The lithium ion conductivity of the sulfide solid electrolyte after the heat treatment was determined in the same manner as in the above-mentioned <Lithium ion conductivity>. The results are shown in the "σ" column of "After heat treatment" in the "Heat resistance" section of Table 1. Ｌｉ＋(mS / cm)" and the difference in lithium ion conductivity before and after heat treatment is shown as "Δσ" in "Heat resistance". Ｌｉ＋ (mS / cm)" respectively. Here, if the difference in lithium ion conductivity after heat treatment from the lithium ion conductivity before heat treatment is 2 mS / cm or less, it can be said that the heat resistance is good. Furthermore, the smaller the difference in lithium ion conductivity before and after heat treatment, the more preferable it is.

[0125]

[0126] From the above results, the sulfide solid electrolyte according to this embodiment has high lithium ion conductivity due to the presence of a phase made of sulfide-based glass and a highly ion-conductive crystalline phase derived therefrom. ３ P.S. ４ Although it is considered better not to include this crystalline phase due to its low lithium ion conductivity, by including it in the range of 0.1 to 30 mass %, good heat resistance was achieved without significantly decreasing the lithium ion conductivity of the sulfide solid electrolyte.

[0127] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2023-168394) filed on September 28, 2023, the contents of which are incorporated herein by reference.

Claims

1. A sulfide solid electrolyte comprising a crystalline phase and a glassy phase, wherein the glassy phase comprises a phase of sulfide-based glass containing Li, P, and S as constituent elements, and the crystalline phase comprises a highly ion-conducting crystalline phase derived from the sulfide-based glass and a β-Li ３ P.S. ４ The sulfide-based glass phase and the highly ion-conductive crystal phase have a composition of Li: 30 to 50 at%, P: 5 to 15 at%, and S: 30 to 60 at%, and the β-Li in the sulfide solid electrolyte is ３ P.S. ４ The sulfide solid electrolyte has a content of the crystal phase of 0.1 to 30 mass %.

2. The sulfide solid electrolyte according to claim 1, wherein the sulfide-based glass phase and the highly ion-conductive crystal phase further contain Ha as a constituent element, and the Ha is at least one element selected from the group consisting of F, Cl, Br, and I.

3. The sulfide solid electrolyte according to claim 2, wherein the Ha which is a constituent element of the sulfide-based glass phase and the highly ion-conductive crystal phase includes at least one element selected from the group consisting of Cl, Br, and I.

4. The sulfide solid electrolyte according to claim 2, wherein the Ha, which is a constituent element of the sulfide-based glass phase and the highly ion-conductive crystal phase, contains Br.

5. Said β-Li ３ P.S. ４ The sulfide solid electrolyte according to claim 1 or 2, wherein the crystallite diameter of the crystal phase is 400 nm or less.

6. The sulfide solid electrolyte according to claim 1 or 2, wherein the content of the highly ion-conductive crystal phase in the sulfide solid electrolyte is 30 mass % or more.

7. In the XRD pattern obtained by powder X-ray diffraction measurement, the peak intensity of the diffraction peak at 2θ = 20.2 ± 0.5°, which indicates the high ion conductive crystal phase, is determined as I Ａ and the β-Li ３ P.S. ４ The maximum intensity of the diffraction peak at 2θ=18.2±0.5°, which indicates the crystal phase of Ｂ When I Ｂ / I Ａ The sulfide solid electrolyte according to claim 1 or 2, wherein the peak intensity ratio represented by is 0.01 to 2.

0.

8. In the XRD pattern obtained by powder X-ray diffraction measurement, the peak intensity of the diffraction peak at 2θ = 19.1 ± 0.5 °, which indicates the high ion conductive crystal phase, is determined as I Ｃ and the β-Li ３ P.S. ４ The maximum intensity of the diffraction peak at 2θ=18.2±0.5°, which indicates the crystal phase of Ｂ When I Ｂ / I Ｃ The sulfide solid electrolyte according to claim 1 or 2, wherein the peak intensity ratio represented by is 0.01 to 10.

0.

9. A method for producing a sulfide solid electrolyte containing a crystalline phase and a glassy phase, comprising: mixing raw materials to obtain a raw material mixture containing Li, P, and S; heating the raw material mixture to obtain a molten material; and cooling and solidifying the molten material to obtain a glassy phase and β-Li. ３ P.S. ４ and heating the sulfide solid electrolyte precursor to obtain a highly ion-conductive crystal phase in which a portion of the glass phase is crystallized, wherein the heating and cooling and solidifying for obtaining the molten material are performed under normal pressure conditions, and in the cooling and solidifying, the molten liquid is allowed to flow out and then stay in a temperature range of 750 to 210° C. for 0.2 to 100 seconds.

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