Sulfide solid electrolyte and method for producing same

Abstract

The present invention relates to a sulfide solid electrolyte comprising a crystal phase and a glass phase, the glass phase comprising a phase comprising a sulfide-based glass containing Li, P, and S as constituent elements, the crystal phase comprising a crystal phase having high ion conductivity derived from the sulfide-based glass and a crystal phase of beta-Li3PS4, the composition of the high ion conduction crystal phase satisfies 30-50 at% of Li, 5-15 at% of P, and 30-60 at% of S, and the content ratio of the beta-Li3PS4 crystal phase in the sulfide solid electrolyte is 0.1-30 mass%.

Description

Technical Field

[0001] This invention relates to sulfide solid electrolytes and methods for their manufacture. Background Technology

[0002] Lithium-ion rechargeable batteries are widely used in portable electronic devices such as mobile phones and laptops, as well as automobiles.

[0003] Previously, liquid electrolytes were used in lithium-ion secondary batteries, but this posed risks such as leakage and fire. To achieve a safer design, the casing needed to be made larger. In addition, the short battery life and narrow operating temperature range also need to be improved.

[0004] In contrast, all-solid-state lithium secondary batteries, which use solid electrolytes as the electrolyte for lithium-ion secondary batteries, have attracted much attention due to the anticipated improvements in safety, high-speed charging and discharging, and miniaturization of the casing.

[0005] Solid electrolytes can be broadly classified into sulfide solid electrolytes and oxide solid electrolytes. Compared to the oxide ions that constitute oxide solid electrolytes, the sulfide ions that constitute sulfide solid electrolytes have greater polarizability, exhibiting higher ionic conductivity. Li is known to be a sulfide solid electrolyte. 10 GeP2S 12 LGPS type crystals, Li6PS5Cl and other silver-germanium sulfide type crystals, Li7P3S 11 Crystallized glass, LPS crystallized glass, etc.

[0006] As a solid electrolyte that is not easily hydrolyzed and has high ionic conductivity, Patent Document 1 discloses a sulfide glass-ceramic solid electrolyte in which a portion of a sulfide glass in which Li2S / P2S5 / LiI = 63 / 21 / 16 or 52 / 17 / 31 is crystallized.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2018-049834 Summary of the Invention

[0010] 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 crystals with low ionic conductivity that are thermodynamically stable at high temperatures. The precipitation of these crystals begins, for example, after maintaining a temperature above the first half of the 200°C range for more than 30 minutes. Therefore, there are challenges in operating batteries using sulfide solid electrolytes containing both a glassy and crystalline phase in high-temperature regions.

[0011] Therefore, the object of the present invention is to provide a sulfide solid electrolyte comprising a crystalline phase and a glassy phase, which not only has excellent lithium-ion conductivity but also excellent heat resistance, and a method for manufacturing the same.

[0012] Through repeated and in-depth research, the inventors discovered that when obtaining a sulfide solid electrolyte precursor by melting and cooling the raw material under heating, performing the heating and cooling under normal pressure and at a very fast cooling rate can yield a sulfide solid electrolyte precursor containing a glass phase and a crystalline phase of β-Li3PS4. Furthermore, by crystallizing a portion of the glass phase, the aforementioned problem can be solved, thus completing the present invention.

[0013] That is, the present invention relates to the following [1] to [9].

[0014] [1] A sulfide solid electrolyte comprising a crystalline phase and a glassy phase,

[0015] The aforementioned glass phase comprises a phase consisting of sulfide-based glasses containing Li, P, and S as constituent elements.

[0016] The aforementioned crystalline phases include a highly ion-conducting crystalline phase from the aforementioned sulfide-based glass and a crystalline phase of β-Li3PS4.

[0017] The phases composed of the aforementioned sulfide-based glasses and the highly ion-conducting crystalline phases have the following compositions: Li: 30–50 at%, P: 5–15 at%, and S: 30–60 at%.

[0018] The content of the crystalline phase of β-Li3PS4 in the above-mentioned sulfide solid electrolyte is 0.1-30% by mass.

[0019] [2] According to the sulfide solid electrolyte described in [1] above, the phase composed of the sulfide-based glass and the high ion conductivity crystalline phase further contain Ha as a constituent element.

[0020] The above-mentioned Ha is selected from at least one of F, Cl, Br and I.

[0021] [3] According to the sulfide solid electrolyte described in [2] above, the Ha, which is a constituent element of the phase composed of the sulfide glass and the high ion conductivity crystalline phase, includes at least one selected from Cl, Br and I.

[0022] [4] According to the sulfide solid electrolyte described in [2] or [3] above, wherein the Ha, which is a constituent element of the phase composed of the sulfide glass and the high ion conductivity crystalline phase, contains Br.

[0023] [5] The sulfide solid electrolyte according to any one of [1] to [4] above, wherein the crystallite diameter of the crystalline phase of the above-mentioned β-Li3PS4 is 400 nm or less.

[0024] [6] The sulfide solid electrolyte according to any one of [1] to [5] above, wherein the content of the high ion conductivity crystalline phase in the sulfide solid electrolyte is 30% by mass or more.

[0025] [7] The sulfide solid electrolyte according to any one of [1] to [6] above, wherein, in the XRD pattern obtained by powder X-ray diffraction, the peak intensity of the diffraction peak at 2θ = 20.2 ± 0.5° representing the above-mentioned high ion conductivity crystalline phase is set as I. A Let the maximum intensity of the diffraction peak at 2θ = 18.2 ± 0.5° representing the crystalline phase of β-Li3PS4 be defined as I. B At that time, by I B / I A The peak intensity ratio is expressed as 0.01 to 2.0.

[0026] [8] The sulfide solid electrolyte according to any one of [1] to [7] above, wherein, in the XRD pattern obtained by powder X-ray diffraction, the peak intensity of the diffraction peak at 2θ = 19.1 ± 0.5° representing the above-mentioned high ion conductivity crystalline phase is set as I. C Let the maximum intensity of the diffraction peak at 2θ = 18.2 ± 0.5° representing the crystalline phase of β-Li3PS4 be defined as I. B At that time, I B / I C The peak intensity ratio is expressed as 0.01 to 10.0.

[0027] [9] A method for manufacturing a sulfide solid electrolyte, wherein the sulfide solid electrolyte comprises a crystalline phase and a glassy phase, and the manufacturing method comprises the following steps in sequence:

[0028] The raw materials are mixed to obtain a raw material mixture containing Li, P and S.

[0029] The above raw material mixture is heated to obtain a melt.

[0030] The above melt was cooled and solidified to obtain a sulfide solid electrolyte precursor containing a glassy phase and a crystalline phase of β-Li3PS4, and

[0031] Heating the above-mentioned sulfide solid electrolyte precursor yields a partially crystallized, highly ion-conducting crystalline phase of the glassy phase.

[0032] The heating and cooling solidification used to obtain the above-mentioned melt are carried out under normal pressure conditions.

[0033] In the above-mentioned cooling and solidification process, after the molten material flows out, it is held at a temperature range of 750 to 210°C for 0.2 to 100 seconds.

[0034] According to the present invention, a sulfide solid electrolyte comprising both a crystalline phase and a glassy phase can be obtained, exhibiting not only excellent lithium-ion conductivity but also excellent heat resistance. Therefore, when the above-mentioned sulfide solid electrolyte is used in an all-solid-state lithium secondary battery, excellent battery characteristics can be achieved. Attached Figure Description

[0035] Figure 1 This is a flowchart illustrating the method for manufacturing the sulfide solid electrolyte of this embodiment.

[0036] Figure 2 This is the XRD pattern of the sulfide solid electrolyte precursor obtained in Example 4.

[0037] Figure 3 The image shows the XRD pattern of the sulfide solid electrolyte obtained in Example 4. Detailed Implementation

[0038] The present invention will now be described in detail. However, the present invention is not limited to the embodiments described below, and can be implemented in any way without departing from the spirit of the invention. Furthermore, the symbol “~” indicating a numerical range is used to mean that the values ​​described before and after it are both lower and upper limits.

[0039] Sulfide Solid Electrolytes

[0040] The sulfide solid electrolyte of this embodiment comprises a crystalline phase and a glassy phase. The glassy phase comprises a phase composed of a sulfide-based glass containing Li, P and S as constituent elements (hereinafter, sometimes simply referred to as "sulfide-based glassy phase"), and the crystalline phase comprises a highly ion-conducting crystalline phase from the sulfide-based glass and a crystalline phase of β-Li3PS4 (hereinafter, sometimes simply referred to as "β-Li3PS4 crystalline phase").

[0041] Here, the high ion conductivity crystalline phase from sulfide-based glasses refers to the crystalline phase obtained by crystallizing the aforementioned sulfide-based glasses through heat treatment, whose constituent elements and composition ratios can be considered almost identical. Here, "almost identical constituent elements and composition ratios" means that the difference between the composition determined by structural analysis based on the XRD pattern of the high ion conductivity crystalline phase and the overall composition is within ±20% in all components.

[0042] The composition of the aforementioned highly ion-conducting crystalline phase satisfies Li: 30–50 at%, P: 5–15 at%, and S: 30–60 at%. Therefore, the composition of the aforementioned sulfide-based glassy phase also satisfies Li: 30–50 at%, P: 5–15 at%, and S: 30–60 at%.

[0043] Furthermore, the content of the β-Li3PS4 crystalline phase in the sulfide solid electrolyte of this embodiment is 0.1% to 30% by mass.

[0044] <Phase composed of sulfide-based glasses and highly ion-conducting crystalline phases>

[0045] The sulfide-based glassy phase and the highly ion-conducting crystalline phase in this embodiment contain Li, P, and S as constituent elements. From the viewpoint of lithium-ion conductivity, it is preferable to contain Ha in addition to these elements. Here, Ha refers to at least one selected from 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 Cl, Br, and I, further preferably to contain at least one of Cl and Br, and even more preferably to contain Br. In addition, it is even more preferable to contain both Cl and Br.

[0046] In this embodiment, the compositions of the sulfide-based glass phase and the highly ion-conducting crystalline phase preferably satisfy Li: 30–50 at%, P: 5–15 at%, and S: 30–60 at%, more preferably Li: 30–50 at%, P: 5–15 at%, S: 30–60 at%, and Ha: 1–12 at%. It should be noted that in this specification, at% refers to atomic%. Furthermore, as mentioned above, although the constituent elements and composition ratios of the sulfide-based glass phase and the highly ion-conducting crystalline phase derived from it can be considered almost identical, they do not mean they are strictly identical. The compositions of the sulfide-based glass phase and the highly ion-conducting crystalline phase preferably satisfy the above-mentioned ranges.

[0047] In the sulfide-based glass phase and the highly ion-conducting crystalline phase of this embodiment, Li is the element responsible for ion conduction as a solid electrolyte.

[0048] In the composition of the sulfide-based glassy phase and the highly ion-conducting crystalline phase, the Li content is preferably 30–50 at%, more preferably 35–45 at%, and even more preferably 37–43 at%. From the viewpoint of improving lithium-ion conductivity, the aforementioned 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 expanding the glass transition range, the Li content is preferably 50 at% or less, more preferably 45 at% or less, and even more preferably 43 at% or less.

[0049] In the sulfide-based glassy phase and the highly ion-conducting crystalline phase of this embodiment, phosphorus (P) is the element that forms the glass network, and the P-S bond in the sulfide exhibits high resistance to both oxidation and reduction. Therefore, as a solid electrolyte, it has a wide potential window and excellent electrochemical stability.

[0050] In the composition of the sulfide-based glassy phase and the highly ion-conducting crystalline phase, the P content is preferably 5 to 15 at%, more preferably 6 to 13 at%, and even more preferably 7 to 12 at%. From the viewpoint of expanding the glass transition range, the above-mentioned 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 improving 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.

[0051] In the sulfide-based glass phase and the highly ion-conducting crystalline phase of this embodiment, S is an element that forms P-S bonds together with P and is an essential element for forming the glass phase.

[0052] In the composition of the sulfide-based glassy phase and the highly ion-conducting crystalline phase, the sulfur content is preferably 30–60 at%, more preferably 33–50 at%, and even more preferably 35–47 at%. From the viewpoint of expanding the glass transition range, the sulfur 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 improving lithium-ion conductivity, the sulfur content is preferably 60 at% or less, more preferably 50 at% or less, and even more preferably 47 at% or less.

[0053] In this embodiment, when the sulfide-based glass phase and the highly ion-conducting crystalline phase contain Ha, Ha is an element that helps improve lithium-ion conductivity.

[0054] In the composition of the sulfide-based glassy phase and the highly ion-conducting 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. In addition, from the viewpoint of preventing the 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. It should be noted that the Ha content here refers to the total content of F, Cl, Br, and I.

[0055] Ha is selected from at least one of F, Cl, Br and I. As mentioned above, from the viewpoint of obtaining good oxidation resistance and water resistance, it is more preferable to contain at least one of Cl and Br, and even more preferable to contain Br. In addition, it is even more preferable to contain both Cl and Br.

[0056] For example, in the above-mentioned Ha content, the total content of Cl and Br is preferably 50% or more, more preferably 70% or more, and may also be 100%, i.e., composed only of Cl and Br. In addition, 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.

[0057] The sulfide-based glassy phase and the highly ion-conducting crystalline phase in this embodiment may contain elements other than Li, P, S, and Ha as constituent elements. Examples of other elements that may be included include Si, B, Ge, Al, O, Na, K, Mg, Ca, Sr, Ba, Y, Zr, Cr, Zn, Ga, Sn, and Sb.

[0058] However, when the other elements mentioned above constitute oxides such as SiO2, B2O3, P2O5, and Al2O3, these oxides are preferably not present because they can form crystal nuclei. The total content of oxides is expressed as mol% based on oxides, preferably 1 mol% or less, more preferably 0.1 mol% or less, even more preferably 0.05 mol% or less, or it may be 0 mol% (i.e., not present).

[0059] In this embodiment, the sulfide-based glass phase and the highly ion-conducting crystalline phase may contain other elements such as Si, B, Ge, Al, Sn, and Sb. These Si, B, Ge, Al, Sn, and Sb are elements that can enter the P position during the crystallization of the sulfide-based glass phase.

[0060] In this embodiment, when the sulfide-based glassy phase and the highly ion-conducting crystalline phase 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 appropriately obtaining the effect of Si, the Si content is preferably 0.1 at% or more, 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.

[0061] However, when Si has Si-O bonds or exists in the form of SiO2 oxides, as described above, the Si content is appropriately adjusted so that the total content of oxides is less than 1 mol% or the total content of oxides as network formations of the glass is 3 to 20 mol%.

[0062] In this embodiment, when the sulfide-based glass phase and the highly ion-conducting crystalline phase contain boron (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%. From the viewpoint of appropriately 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.

[0063] However, when B has B-O bonds or exists in the form of oxides of B2O3, as described above, the B content is appropriately adjusted so that the total content of oxides is less than 1 mol% or the total content of oxides as network formations of glass is 3 to 20 mol%.

[0064] In this embodiment, when the sulfide-based glass phase and the high ion conductivity crystalline phase contain Ge as a constituent element, Ge has the effect of promoting increased 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, 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.

[0065] However, if Ge has Ge-O bonds or exists in the form of GeO2 oxides, as described above, the Ge content should be appropriately adjusted so that the total content of oxides is less than 1 mol%.

[0066] In this embodiment, when the sulfide-based glass phase and the highly ion-conducting crystalline phase 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 appropriately obtaining the effect of Al, the Al content is preferably 0.1 at% or more, 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.

[0067] However, when Al has Al-O bonds or exists in the form of Al2O3 oxides, as described above, the Al content is appropriately adjusted so that the total content of oxides is less than 1 mol% or the total content of oxides as network formations of glass is 3 to 20 mol%.

[0068] In this embodiment, when the sulfide-based glass phase and the high ion conductivity crystalline phase 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 appropriately obtaining the effect of Sn, the Sn content is preferably 0.1 at% or more, 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.

[0069] However, if Sn has Sn-O bonds or exists in the form of SnO2 oxides, as described above, the Sn content should be appropriately adjusted so that the total content of oxides is less than 1 mol%.

[0070] In this embodiment, when the sulfide-based glass phase and the highly ion-conducting crystalline phase 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 appropriately obtaining the effect of Sb, the Sb content is preferably 0.1 at% or more, 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.

[0071] However, when Sb has Sb-O bonds or exists in the form of oxides of SB2O3, as described above, the Sb content is appropriately adjusted so that the total content of oxides is less than 1 mol% or the total content of oxides as network formations of glass is 3 to 20 mol%.

[0072] In this embodiment, the composition ratio of Li / P in the sulfide-based glass phase and the highly ion-conducting crystalline phase 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.

[0073] From the viewpoint of obtaining high lithium-ion conductivity, the above-mentioned 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 expanding the glass transition range, the above-mentioned composition ratio is preferably 7.0 or less, more preferably 6.5 or less, and even more preferably 6.2 or less.

[0074] It should be noted that in this specification, the composition ratio refers to the ratio (at%) of each element in the sulfide-based glassy phase and the highly ion-conducting crystalline phase.

[0075] In this embodiment, the S / P ratio in the composition of the sulfide-based glassy phase and the highly ion-conducting crystalline phase 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 above-mentioned composition ratio is preferably 3.0 or more, more preferably 3.5 or more, and even more preferably 3.8 or more. Furthermore, from the viewpoint of water resistance, the above-mentioned composition ratio is preferably 5.0 or less, more preferably 4.5 or less, and even more preferably 4.2 or less.

[0076] When the sulfide-based glassy phase and the highly ion-conducting crystalline phase further contain Ha, the composition ratio expressed as [(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. Here, from the viewpoint of oxidation resistance, the above composition ratio is preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.8 or more. In addition, the upper limit of the above composition ratio is not particularly limited, and it can also be 1.0. The above composition ratio of 1.0 means that it does not contain I as Ha. When the sulfide-based glassy phase and the highly ion-conducting crystalline phase contain I as Ha, from the viewpoint of obtaining the effect of I, the above composition ratio can be 0.8 or less, or it can be 0.6 or less.

[0077] When the sulfide-based glass phase and the highly ion-conducting crystalline phase further contain Ha, the composition ratio of Ha / P in the sulfide-based glass phase of 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 above 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 precipitating lithium halide crystals, the above composition ratio is preferably 1.5 or less, more preferably 1.2 or less, and even more preferably 1.0 or less. It should be noted that Ha here refers to the total of F, Cl, Br, and I.

[0078] The constituent elements and their contents of the sulfide-based glassy phase and the highly ion-conducting crystalline phase are determined by comparing the results of measuring the constituent elements and their contents (composition ratios) of the sulfide solid electrolyte as a whole with the element ratios of the crystal structure obtained from the XRD pattern.

[0079] It should be noted that the constituent elements and their contents of the above-mentioned sulfide solid electrolytes are determined using different methods depending on the element. For example, P and S are determined by ICP emission spectroscopy, Li by atomic absorption spectroscopy, and Ha by ion chromatography, etc. Details of each analysis are described in the items of the embodiments described later.

[0080] In this embodiment, the sulfide-based glass phase is partially crystallized by heat treatment to form the high ion conductivity crystalline phase of this embodiment. This high ion conductivity crystalline phase can adopt a Thio-Lisicon type or LGPS type crystal structure. Thio-Lisicon type and LGPS type high ion conductivity crystalline phases have high lithium-ion conductivity and are useful as solid electrolytes.

[0081] In this embodiment, the total proportion of the sulfide-based glassy phase and the highly ion-conducting crystalline phase in the sulfide solid electrolyte is 99.9% by mass or less, preferably 50 to 99.9% by mass, more preferably 70 to 95% by mass, and even more preferably 75 to 90% by mass. From the viewpoint of lithium-ion conductivity, the above-mentioned total proportion is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 75% by mass or more. Furthermore, from the viewpoint of appropriately utilizing the effect of the β-Li3PS4 crystalline phase, the above-mentioned total proportion is 99.9% by mass or less, preferably 95% by mass or less, and even more preferably 90% by mass or less.

[0082] It should be noted that the respective proportions of the sulfide-based glassy phase and the highly ion-conducting crystalline phase were determined by powder X-ray diffraction (XRD) of the sulfide solid electrolyte powder together with the crystalline powder used as an internal standard, followed by Rietveld analysis. The proportion of the sulfide-based glassy phase was determined by subtracting the proportion of the crystals from 100% by mass using the above analysis.

[0083] In this embodiment, the content of the high ion conductivity 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 above-mentioned content is preferably 30% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more. Furthermore, from the viewpoint of effectively obtaining a phase composed of sulfide glass and a crystalline phase of β-Li3PS4, the above-mentioned content is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less.

[0084] In this embodiment, the content of the sulfide-based glass phase is preferably 1 to 70% by mass, more preferably 5 to 50% by mass, and even more preferably 8 to 40% by mass. From the viewpoint of achieving a smooth interface between the active material and the solid electrolyte in the glass phase, the above-mentioned content is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 8% by mass or more. Furthermore, from the viewpoint of appropriately obtaining a highly ion-conducting crystalline phase or a β-Li3PS4 crystalline phase, the above-mentioned content is preferably 70% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0085] In this embodiment, the high ion conductivity crystalline phase can be, for example, a lithium thiosulfate superion conductor type or an LGPS type crystal structure. These structures have high lithium ion conductivity.

[0086] In this embodiment, the high ion conductivity crystalline phase exhibits a diffraction peak at least at 2θ = 20.2 ± 0.5° in the XRD pattern obtained by powder X-ray diffraction (XRD), preferably further at 2θ = 23.8 ± 0.5°. Additionally, it is also preferable to further exhibit a diffraction peak at 2θ = 19.1 ± 0.5°. In this case, it can be determined that the aforementioned high ion conductivity crystalline phase adopts a lithium thiocyanate superionic conductor type or LGPS type crystal structure. The XRD measurement was performed using CuKα rays (λ = 1.5418 Å) as the radiation source, and the details of the measurement conditions are described in detail in the items of the embodiments described later.

[0087] The XRD pattern shown above exhibits diffraction peaks at 2θ = 19.1 ± 0.5° and 23.8 ± 0.5°. Furthermore, it can show diffraction peaks at one or more of 2θ = 12.4 ± 0.5°, 29.7 ± 0.5°, and 31.4 ± 0.5°, or even two or more, or all three.

[0088] <Crystall phase of β-Li3PS4>

[0089] In addition to the sulfide-based glass phase and the highly ion-conducting crystalline phase described above, the sulfide solid electrolyte of this embodiment also contains 0.1 to 30% by mass of β-Li3PS4 crystalline phase.

[0090] The β-Li3PS4 crystalline phase is a thermodynamically stable phase that exhibits diffraction peaks at least at 2θ = 18.2 ± 0.5° in the XRD pattern obtained by powder X-ray diffraction (XRD), preferably further at 2θ = 26.0 ± 0.5°. Multiple diffraction peaks may also be observed at 2θ = 18.2 ± 0.5°. The XRD measurements were performed using CuKα rays (λ = 1.5418 Å) as the radiation source, and the detailed measurement conditions are described in detail in the examples described later.

[0091] The above XRD pattern can further show more than one diffraction peak at 2θ = 17.8±0.5°, 20.0±0.5°, 29.8±0.5° and 34.0±0.5°, or more than two diffraction peaks, or more than three diffraction peaks, or diffraction peaks at all four locations.

[0092] It is known that the sulfide solid electrolyte of this embodiment contains a β-Li3PS4 crystalline phase, which prevents the thermal decomposition of the highly ion-conducting crystalline phase even when heat-treated at a temperature exceeding 200°C, thus achieving good heat resistance.

[0093] The reasoning is not yet clear, but it is believed that the β-Li3PS4 crystalline phase precipitated in this embodiment is uniformly precipitated throughout the entire bulk of the sulfide solid electrolyte. Therefore, it is thought that the crystal structure of the highly ion-conducting crystalline phase precipitated from the remaining mother glass will also differ from that of previously known materials. In addition, it is believed that if the β-Li3PS4 crystalline phase is microcrystal, the crystallite diameter of the aforementioned highly ion-conducting crystalline phase will also decrease, and the microscopic thermodynamic properties will change, thus enabling better heat resistance.

[0094] The β-Li3PS4 crystalline phase in the sulfide solid electrolyte of this embodiment contains 0.1 to 30% by mass, preferably 5 to 25% by mass, and more preferably 10 to 20% by mass. From the viewpoint of appropriately obtaining the heat resistance of the β-Li3PS4 crystalline phase, the above-mentioned content is 0.1% by mass or more, preferably 5% by mass or more, and more preferably 10% by mass or more. Furthermore, from the viewpoint of lithium-ion conductivity, the above-mentioned content is 30% by mass or less, preferably 25% by mass or less, and more preferably 20% by mass or less.

[0095] It should be noted that the proportion of the β-Li3PS4 crystalline phase was determined by powder X-ray diffraction (XRD) of the sulfide solid electrolyte in powder form together with the crystalline powder used as an internal standard, followed by Rietveld analysis.

[0096] The crystallite diameter of the β-Li3PS4 crystalline phase is preferably 400 nm or less, more preferably 20–400 nm, even more preferably 20–350 nm, even more preferably 50–300 nm, and particularly preferably 80–260 nm. Here, since the β-Li3PS4 crystalline phase exists in the form of microcrystals, even the precipitation of a highly ion-conductivity crystalline phase can achieve good heat resistance. Therefore, 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. Furthermore, although it is presumed that a smaller crystallite diameter is better, from the viewpoint of crystal growth rate, in practice, the crystallite diameter is preferably 20 nm or more, more preferably 50 nm or more, and even more preferably 80 nm or more.

[0097] It should be noted that the above-mentioned crystallite diameter was determined using the Scherrer formula for the full width at half maximum (FWHM) in the XRD pattern.

[0098] The β-Li3PS4 crystalline phase described above is obtained by performing the above heating and cooling under normal pressure and cooling at a very fast cooling rate when obtaining a sulfide solid electrolyte precursor by melting and cooling the raw material.

[0099] Even when heating was performed to crystallize a portion of the sulfide-based glassy phase in the aforementioned sulfide solid electrolyte precursor to form a highly ion-conducting crystalline phase, no significant crystal growth was observed in the obtained β-Li3PS4 crystalline phase; the content ratio and crystallite diameter remained unchanged.

[0100] In the XRD pattern obtained by powder XRD, the peak intensity of the diffraction peak at 2θ = 20.2 ± 0.5°, representing the above-mentioned highly ion-conducting crystalline phase, is set as I. A Furthermore, the maximum intensity of the diffraction peak at 2θ = 18.2 ± 0.5° representing the aforementioned β-Li3PS4 crystalline phase is designated as I. B At this time, by I B / I AThe indicated peak intensity ratio 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 above-mentioned intensity ratio is preferably 0.01 or higher, more preferably 0.05 or higher, and even more preferably 0.07 or higher. Furthermore, from the viewpoint of lithium-ion conductivity, the above-mentioned ratio is preferably 2.0 or lower, more preferably 1.0 or lower, and even more preferably 0.7 or lower.

[0101] It should be noted that the diffraction peaks representing the β-Li3PS4 crystalline phase sometimes show more than two peaks within the range of 2θ = 18.2 ± 0.5°. In this case, the peak intensity of the most intense peak among these multiple diffraction peaks is set as I. B .

[0102] In the XRD pattern obtained by powder XRD, the peak intensity of the diffraction peak at 2θ = 19.1 ± 0.5°, representing the above-mentioned highly ion-conducting crystalline phase, is set as I. C Furthermore, the maximum intensity among the peak intensities of the diffraction peak representing the β-Li3PS4 crystalline phase at 2θ = 18.2 ± 0.5° is defined as I. B At this time, by I B / I C The indicated peak intensity ratio 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 above-mentioned intensity ratio is preferably 0.01 or higher, more preferably 0.3 or higher, and even more preferably 0.5 or higher. Furthermore, from the viewpoint of lithium-ion conductivity, the above-mentioned ratio is preferably 10.0 or lower, more preferably 5.0 or lower, and even more preferably 2.5 or lower.

[0103] It should be noted that when a peak is observed at 2θ = 18.6–18.7° in the XRD pattern obtained by powder XRD, and a diffraction peak is also observed at an angle lower than 2θ = 18.2 ± 0.5°, this peak is attributed to the diffraction peak at 2θ = 19.1 ± 0.5°, representing a highly ion-conductive crystalline phase. Conversely, in the case described above, if a diffraction peak is observed at an angle higher than 2θ = 19.1 ± 0.5°, this peak is attributed to the diffraction peak at 2θ = 18.2 ± 0.5°, representing the β-Li3PS4 crystalline phase.

[0104] Other phases

[0105] The sulfide solid electrolyte of this embodiment may contain phases other than the sulfide-based glass phase, the highly ion-conducting crystalline phase, and the β-Li3PS4 crystalline phase described above. Examples of such other phases include the crystalline phase obtained simultaneously during the manufacture of the sulfide-based glass phase and the β-Li3PS4 crystalline phase.

[0106] The proportion of such other phases in the sulfide solid electrolyte is preferably 0 to 30% by mass, more preferably 0 to 20% by mass, and even more preferably 0 to 15% by mass. Here, from the viewpoint of appropriately obtaining a sulfide-based glassy phase, a highly ion-conducting crystalline phase, and a β-Li3PS4 crystalline phase, the proportion of other phases is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less. Alternatively, other phases may not be included.

[0107] Properties of Sulfide Solid Electrolytes

[0108] The lithium-ion conductivity of the sulfide solid electrolyte in this embodiment, when formed into powder at 380 MPa, is preferably 1 mS / cm or higher at 25°C. This is because the lithium-ion conductivity of the aforementioned sulfide-based glass phase and the high-ion-conductivity crystalline phase derived from the sulfide-based glass phase is high. However, since it is difficult to extract only the sulfide-based glass phase and the high-ion-conductivity crystalline phase from the sulfide solid electrolyte, the lithium-ion conductivity of the sulfide-based glass phase and the high-ion-conductivity crystalline phase is evaluated using the lithium-ion conductivity of the aforementioned sulfide solid electrolyte.

[0109] The lithium-ion conductivity of the sulfide solid electrolyte in this embodiment is preferably 1 mS / cm or higher, and the higher the better. This value also varies depending on the composition, the proportion of the sulfide-based glass phase, and the high-ion-conductivity crystalline phase.

[0110] For example, when the Br content in Ha is 90 at% or more, the lithium-ion conductivity is preferably 2 mS / cm or more. In addition, when the Cl content in Ha is 90 at% or more, the lithium-ion conductivity is preferably 1.5 mS / cm or more.

[0111] It should be noted that the lithium-ion conductivity in this specification is determined by pressing the powder of the sulfide solid electrolyte into a powder at 380 MPa as the test sample and measuring its AC resistance. Specifically, the AC resistance of the test 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. The value obtained from the Nyquist plot is taken as the lithium-ion conductivity.

[0112] The heat resistance of the sulfide solid electrolyte in this embodiment can be evaluated by the lithium-ion conductivity after heat treatment at 240°C for 1 hour under a nitrogen atmosphere.

[0113] Specifically, the lithium-ion conductivity after the above heat treatment is preferably 0.8 mS / cm or higher, and the higher the better. This value also varies depending on the composition, the proportion of sulfide glass phase, and high ion conductivity crystalline phase.

[0114] If the difference in lithium-ion conductivity before and after the heat treatment is less than 2 mS / cm, it can be said that the sulfide solid electrolyte has good heat resistance. More preferably, the difference is less than 1.8 mS / cm, and even more preferably less than 1.5 mS / cm. The smaller the difference, the better.

[0115] The amount of H2S generated by the sulfide solid electrolyte in this embodiment when kept in an atmosphere with a dew point of -20°C for 5 hours 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 less the better.

[0116] It should be noted that the more specific measurement conditions for the above-mentioned H2S generation are as follows.

[0117] First, the sulfide solid electrolyte was passed through a 100 μm sieve to form a powder with an average particle size of 10–20 μm. Furthermore, the amount of hydrogen sulfide (H2S) generated was monitored when 10 mg of the powder was exposed to nitrogen (N2) gas conditioned to a dew point of -20°C at a flow rate of 0.5 L / min for 5 hours, and the total amount of this exposure was taken as the H2S generation.

[0118] The H2S generation amount mentioned above is an indicator of the hydrolysis resistance, i.e., water resistance, of the sulfide solid electrolyte. This can be achieved by the presence of a sulfide-based glassy phase, a highly ionicly conductive crystalline phase, or by including Ha as a constituent element. It is particularly preferred that Ha contains at least one of Cl and Br, and more preferably Br. Furthermore, it is even more preferable that both Cl and Br are present.

[0119] The average particle size (D50) of the sulfide solid electrolyte in 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. From the viewpoint of reducing the load on the micronization process when using the sulfide solid electrolyte in a secondary battery, the above-mentioned 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 processing, the above-mentioned 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.

[0120] The aforementioned average particle size (D50) can be adjusted by coarsely grinding the obtained sulfide solid electrolyte. Coarse grinding can be performed using conventionally known methods, such as cutting mills, planetary ball mills, and jet mills; dry grinding is preferred. Then, a finer particle size can be produced using wet or dry grinding methods such as bead mills or jet mills to create a solid electrolyte suitable for use as a positive or negative electrode or separator layer in battery materials.

[0121] The sulfide solid electrolyte in this embodiment is preferably an electrolyte for lithium-ion secondary batteries. When used in lithium-ion secondary batteries, the sulfide solid electrolyte is formed into a solid electrolyte layer together with other components such as binders, as needed. Conventionally known substances can be used as binders or other components.

[0122] In this embodiment, the content of sulfide solid electrolyte is preferably 80% by mass or more, and more preferably 90% by mass or more, relative to the entire solid electrolyte layer.

[0123] Furthermore, the sulfide solid electrolyte of this embodiment can be mixed with a positive electrode active material or a negative electrode active material to be used as a positive electrode layer or a negative electrode layer. The positive electrode active material or negative electrode active material, current collector, binder, conductive additive, etc. used in the positive electrode layer or negative electrode layer can be conventionally known substances.

[0124] The lithium-ion secondary battery includes a positive electrode layer, a solid electrolyte layer, and a positive electrode layer. Preferably, at least one layer selected from the above-mentioned positive electrode layer, solid electrolyte layer, and positive electrode layer contains the sulfide solid electrolyte of this embodiment.

[0125] The material used for the outer casing of a lithium-ion secondary battery can also be a previously known substance. The shape of a lithium-ion secondary battery can also be a previously known shape, such as coin-shaped, sheet-like (film-like), folded, wound, bottomed cylindrical, or button-shaped, and can be appropriately selected according to the application.

[0126] Manufacturing Method of Sulfide Solid Electrolytes

[0127] The method for manufacturing the sulfide solid electrolyte in this embodiment is as follows: Figure 1 The steps shown are sequentially comprised of the following processes 1 to 4 in the form of steps S1 to S4.

[0128] Step S1: Process 1 of mixing raw materials to obtain a raw material mixture containing Li, P and S.

[0129] Step S2: Step 2 involves heating the raw material mixture obtained in step 1 to obtain a melt.

[0130] Step S3: Cooling and solidifying the melt obtained in step 2 to obtain a sulfide solid electrolyte precursor containing a glassy phase and a crystalline phase of β-Li3PS4.

[0131] Step S4: Heating the sulfide solid electrolyte precursor obtained in step 3 to obtain a portion of the crystallized, highly ion-conducting crystalline phase of the glassy phase in step 4.

[0132] The heating in step 2 and the cooling and solidification in step 3 are carried out under normal pressure, and during cooling and solidification, the molten material is allowed to flow out and remain at a temperature range of 750–210°C for 0.2–100 seconds. This yields a sulfide solid electrolyte containing a phase composed of a sulfide-based glass, a highly ion-conducting crystalline phase derived from that phase, and a crystalline phase of β-Li3PS4, with the β-Li3PS4 crystalline phase comprising 0.1–30% by mass. It should be noted that in this specification, "normal pressure" refers to a pressure range of approximately (gauge pressure ± 15 kPa).

[0133] In addition, in the above-mentioned step 1, the sulfide solid electrolyte described in the above-mentioned "Sulfide Solid Electrolyte" is obtained by mixing the raw materials in such a way that the composition of the obtained sulfide glass phase and the high ion conductivity crystalline phase satisfies Li: 30-50 at%, P: 5-15 at%, and S: 30-60 at%.

[0134] The following is a description of each process.

[0135] <Process 1>

[0136] Step S1 in this embodiment is process 1, which involves mixing raw materials to obtain a raw material mixture containing Li, P, and S.

[0137] 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, if 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 materials containing Li, P, and S to obtain a raw material mixture containing Li, P, S, and Ha. Here, Ha refers to at least one element selected from F, Cl, Br, and I.

[0138] Examples of raw materials containing lithium include lithium compounds such as lithium sulfide (Li₂S), lithium carbonate (Li₂CO₃), lithium sulfate (Li₂SO₄), lithium oxide (Li₂O), and lithium hydroxide (LiOH), as well as metallic lithium. One type of lithium-containing substance can be used, or two or more can be used in combination.

[0139] From the viewpoint of obtaining a sulfide-based glassy phase, lithium sulfide is the preferred raw material containing Li. Furthermore, if the resulting sulfide solid electrolyte contains halogens, lithium halide (LiHa, where Ha is a halogen) is also preferred as the raw material containing Li. Lithium halide will be discussed later.

[0140] Examples of raw materials containing phosphorus (P) include phosphorus sulfides such as phosphorus pentasulfide (P₂S₅) and phosphorus trisulfide (P₂S₃), phosphorus compounds such as sodium phosphate (Na₃PO₄), and elemental phosphorus. One type of phosphorus-containing substance can be used, or two or more types can be used in combination.

[0141] From the viewpoint of preventing the presence of elements other than those constituting the target sulfide solid electrolyte, the raw material containing P is preferably phosphorus sulfide, and more preferably phosphorus pentasulfide (P2S5).

[0142] Examples of raw materials containing sulfur include lithium sulfide (Li₂S), phosphorus trisulfide (P₂S₃), phosphorus pentasulfide (P₂S₅), other phosphorus-containing sulfur compounds, and sulfur-containing compounds. Examples of sulfur-containing compounds include H₂S, CS₂, and iron sulfide (FeS, Fe₂S₃, FeS₂, Fe...). 1－x Bismuth sulfide (Bi2S3), copper sulfide (CuS, Cu2S, Cu, etc.), bismuth sulfide (Bi2S3), copper sulfide (CuS, Cu2S, Cu... 1－x (S, etc.). Substances containing the element S can use one type or a combination of two or more types.

[0143] From the viewpoint of preventing the presence of elements other than those constituting the target sulfide solid electrolyte, the raw materials containing sulfur are preferably lithium sulfide and phosphorus sulfide, and phosphorus pentasulfide (P2S5) is more preferred as phosphorus sulfide. It should be noted that lithium sulfide is a compound that contains both lithium (Li) and sulfur, and phosphorus sulfide is a compound that contains both sulfur (S) and phosphorus (P).

[0144] Examples of raw materials containing the element Ha include lithium fluoride (LiF), lithium chloride (LiCl), lithium bromide (LiBr), lithium iodide (LiI), lithium halides, phosphorus halides, phosphoryl halides, sulfur halides, sodium halides, and boron halides. Substances containing the element Ha can use one type or a combination of two or more.

[0145] From a reactivity point of view, the raw materials containing Ha are preferably lithium halides, more preferably LiCl, LiBr, or LiI, and even more preferably LiCl or LiBr.

[0146] The raw material mixture can be obtained by further mixing raw materials containing other elements according to the desired composition of the sulfide solid electrolyte.

[0147] As mentioned above, other elements include, for example, Si, B, Ge, Al, O, Na, K, Mg, Ca, Sr, Ba, Y, Zr, Cr, Zn, Ga, Sn, and Sb. Among these other elements, Si, B, Ge, Al, Sn, and Sb may be present. These Si, B, Ge, Al, Sn, and Sb are elements that can enter the P position during the crystallization of the sulfide-based glass phase.

[0148] These raw materials containing other elements can be made from substances that are already known to the public.

[0149] For example, SiO2 and SiS2 are examples of raw materials containing Si. Among them, SiO2 is more preferred from the viewpoint of lithium-ion conductivity. These compounds can be used alone or in combination of two or more.

[0150] Examples of raw materials containing element B include B₂O₃ and B₂S₃. Among these, B₂O₃ is preferred from the viewpoint of water resistance of glass. These compounds can be used alone or in combination of two or more.

[0151] Examples of raw materials containing Ge include GeO2, GeS, GeS2, and GeCl2. From the viewpoint of lithium-ion conductivity, GeS2 and GeCl2 are preferred, with GeS2 being more preferred. These compounds can be used alone or in combination of two or more.

[0152] Examples of raw materials containing Al include Al₂S₃, Al₂O₃, and AlCl₃. From the viewpoint of lithium-ion conductivity and water resistance, Al₂S₃ and AlCl₃ are preferred, and Al₂S₃ is more preferred. These compounds can be used alone or in combination of two or more.

[0153] Examples of raw materials containing the element Sn include SnS, SnS2, SnO, SnO2, and SnCl2. Among these, SnS2 and SnCl2 are preferred from the viewpoint of lithium-ion conductivity, and SnS2 is more preferred. These compounds can be used alone or in combination of two or more.

[0154] Examples of raw materials containing Sb include SB₂S₃, SB₂O₃, SB₂O₅, SbCl₃, and SbCl₅. From the viewpoint of lithium-ion conductivity and water resistance, SB₂S₃ and SbCl₃ are preferred, and SB₂S₃ is more preferred. These compounds can be used alone or in combination of two or more.

[0155] These raw materials are appropriately blended according to the desired composition of the sulfide-based glass phase and the highly ion-conducting crystalline phase derived from that glass phase. Specifically, in order to obtain the sulfide solid electrolyte described in the above-mentioned "Sulfide Solid Electrolytes", the raw materials are mixed such that the composition of the obtained glass phase and the highly ion-conducting crystalline phase derived from that glass phase satisfies Li: 30-50 at%, P: 5-15 at%, and S: 30-60 at%. In addition, the glass phase and the highly ion-conducting crystalline phase further contain Ha as a constitutive element, preferably satisfying Ha: 1-12 at%, in addition to the above composition.

[0156] The combination of these raw materials also determines the crystal structure of the resulting highly ion-conducting crystalline phase.

[0157] In addition to the above, the preferred mode for the obtained glass phase and the highly ion-conducting crystalline phase derived from the glass phase is the same as the preferred mode for "phase composed of sulfide-based glass and highly ion-conducting crystalline phase" in the above-mentioned "Sulfide Solid Electrolytes".

[0158] From the viewpoint of shortening the holding time of heating and melting in subsequent step 2, it is preferable to reduce the particle size of each raw material. Furthermore, if the particle size of the raw material is too large, it may sometimes affect the homogeneity of the sulfide solid electrolyte precursor and the sulfide solid electrolyte; from the above viewpoint, it is also preferable to have a relatively small particle size. However, the manufacturing method of this embodiment offers excellent composition control. Therefore, even if raw materials with particle sizes that would reduce homogeneity in conventional manufacturing methods are used, for example, the manufacturing method of this embodiment can produce more homogeneous sulfide solid electrolyte precursors and sulfide solid electrolytes.

[0159] From the above perspective, specifically, the particle size of each raw material is preferably less than 1 mm, more preferably less than 500 μm, further preferably less than 250 μm, even more preferably less than 100 μm, and particularly preferably less than 50 μm. The smaller the particle size, the better; the lower limit is actually around 0.1 μm, but it can be greater than 1 μm or greater than 5 μm.

[0160] Furthermore, as described above, according to the manufacturing method of this embodiment, even when using raw materials with larger particle sizes, homogeneous sulfide solid electrolyte precursors and sulfide solid electrolytes can be easily obtained. Considering this, for example from the viewpoint of reducing manufacturing costs, the particle size of each raw material can be 10 μm or more, 100 μm or more, or 250 μm or more.

[0161] Therefore, 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 manufacturing cost, 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.

[0162] It should be noted that in this specification, the particle size of each raw material refers to the average particle size (D50) expressed by the median particle size obtained from the volume-based particle size distribution map obtained by measuring the particle size distribution using a Microtrac MT3300EXII laser diffraction particle size distribution measuring machine.

[0163] The mixing of raw materials can be carried out through media-based mixing methods, such as mixing using a mortar and pestle, mixing using a planetary ball mill, media-free mixing using a pin mill or powder mixer, or air-jet mixing. Raw materials can be amorphized through mixing before heating.

[0164] <Process 2>

[0165] In this embodiment, step S2 is step 2, which involves heating the raw material mixture obtained in step 1 to obtain a melt.

[0166] There are no particular limitations on the specific methods for heating and melting the raw material mixture, except that heating is carried out under normal pressure.

[0167] The manufacturing method of this embodiment melts the raw material mixture by heating it under atmospheric pressure, thereby minimizing the compositional deviation between the raw material mixture and the composition of the obtained sulfide-based glass phase and the highly ion-conducting crystalline phase derived from that glass phase, or the composition of the sulfide solid electrolyte. Furthermore, by performing the above heating under a gaseous atmosphere containing sulfur, compositional deviations can be further suppressed. It should be noted that in the manufacturing method of this embodiment, the heating and melting are carried out in an atmosphere-controlled environment under atmospheric pressure, thus eliminating the need for pipe sealing. However, the possibility of using pipe sealing is not excluded.

[0168] Here, the difference between a sealed container and an atmosphere-controlled environment under normal pressure is that a sealed container means that the pressure inside the container is in a vacuum state, that is, less than (gauge pressure - 15 kPa). In contrast, an atmosphere-controlled environment under normal pressure means that the pressure inside the container during heating and melting is within the range of (gauge pressure ± 15 kPa).

[0169] That is, the manufacturing method of this embodiment is carried out under normal pressure (gauge pressure ± 15 kPa) for the heating and melting of step 2. At this time, the composition ratio of the glass phase or the highly ion-conducting crystalline phase obtained by [P / Li] relative to the composition ratio of the raw material mixture is preferably 95 to 105%.

[0170] The pressure during the heating and melting process can be as low as (gauge pressure ± 15 kPa) at normal pressure, preferably (gauge pressure ± 10 kPa), more preferably (gauge pressure ± 5 kPa), and even more preferably (gauge pressure ± 2 kPa).

[0171] Furthermore, the [P / Li] ratio of the obtained glassy phase or highly ion-conducting crystalline phase relative to the [P / Li] ratio of the raw material mixture is more preferably 95-105%, more preferably 97-103%, and even more preferably 99-101%, and the closer to 100%, the better. Here, the above-mentioned composition ratio is preferably 95% or more, more preferably 97% or more, more preferably 99% or more, and preferably 105% or less, more preferably 103% or less, and even more preferably 101% or less.

[0172] It should be noted that, for the [P / Li] ratio of the obtained glassy phase or highly ion-conducting crystalline phase relative to the composition ratio of the raw material mixture, Li represents a non-volatile element, and P represents a highly volatile element. Therefore, comparing the [P / Li] ratio of the raw material mixture with that of the glassy phase or highly ion-conducting crystalline phase is appropriate as an indicator of the compositional deviation between the composition of the raw material mixture and the composition of the obtained sulfide-based glassy phase or highly ion-conducting crystalline phase, or the composition of the sulfide solid electrolyte.

[0173] Examples of heat-resistant containers for containing raw material mixtures include carbon-based heat-resistant containers, heat-resistant containers containing oxides such as quartz, quartz glass, borosilicate glass, aluminosilicate glass, alumina, zirconium oxide, and mullite, heat-resistant containers containing nitrides such as silicon nitride and boron nitride, and heat-resistant containers containing carbides such as silicon carbide. Furthermore, these heat-resistant containers can have the main body formed from the aforementioned materials, or they can be containers with layers of carbon, oxides, nitrides, or carbides, such as carbon-coated quartz tubes.

[0174] The melting temperature when heating the raw material mixture varies depending on the raw materials used and the composition of the raw material mixture. For example, it is preferably 600–950°C, more preferably 630–850°C, and even more preferably 650–750°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. In addition, from the viewpoint of suppressing compositional deviations caused by component volatilization, the above-mentioned melting temperature is preferably 950°C or lower, more preferably 850°C or lower, and even more preferably 750°C or lower.

[0175] The heating and melting time varies depending on the scale, preferably from 10 minutes to 10 hours, more preferably from 30 minutes to 9.5 hours, even more preferably from 45 minutes to 9 hours, and particularly preferably from 1 to 9 hours. Here, from the viewpoint of ensuring a good reaction, the heating and 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. Furthermore, from the viewpoint of productivity, the heating and melting time is preferably 10 hours or less, more preferably 9.5 hours or less, and even more preferably 9 hours or less.

[0176] The atmosphere inside the container during heating and melting is not particularly limited. For example, it can be a nitrogen atmosphere, an argon atmosphere, or a gaseous atmosphere containing sulfur. However, from the viewpoint of more appropriately suppressing compositional deviations, a gaseous atmosphere containing sulfur is preferred.

[0177] In the case of an atmosphere containing sulfur gas, sulfur gas, hydrogen sulfide gas, sulfur dioxide gas, etc. can be used as sources of sulfur. From the viewpoint of reactivity with raw materials, sulfur gas is preferred.

[0178] Alternatively, as a gas containing sulfur, elemental sulfur powder can be introduced by adding it and vaporizing it during the melting process. The elemental sulfur powder can be added together with the raw materials when mixing them to obtain the raw material mixture, or it can 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 is not included in the mass of the elemental sulfur powder.

[0179] As a gas containing sulfur, sulfur gas, hydrogen sulfide gas, sulfur dioxide gas, etc., can be introduced, along with a gas containing sulfur produced by adding elemental sulfur powder.

[0180] The gas containing sulfur is preferably used as the source of sulfur in the form of, for example, a mixture with an inert gas. The mixing ratio with the inert gas is arbitrary, and there is no particular limitation as long as the cumulative amount of sulfur introduced relative to the mass of the raw material mixture is at a desired value.

[0181] Examples of inert gases mentioned above include nitrogen, argon, and helium. They can be used alone or in combination of two or more.

[0182] The dew point during heating and melting is preferably below -20°C, with no particular lower limit, but typically around -80°C. The oxygen concentration is preferably below 1000 ppm by volume.

[0183] In step 2, the complete dissolution of the raw material mixture can be confirmed by the absence of peaks originating from crystals in high-temperature X-ray diffraction measurements. Alternatively, it can be confirmed by heating at a specified temperature and pouring the melt to check for fluidity.

[0184] <Process 3>

[0185] In this embodiment, step S3 is step 3 of cooling and solidifying the melt obtained in step 2 to obtain a sulfide solid electrolyte precursor containing a glass phase and a crystalline phase of β-Li3PS4.

[0186] Cooling and curing are carried out under normal pressure conditions. Here, normal pressure conditions, as mentioned above, refer to an atmosphere at a pressure of approximately (gauge pressure ± 15 kPa).

[0187] The pressure during cooling and curing can be as low as (gauge pressure ± 15 kPa) under normal pressure conditions, preferably (gauge pressure ± 10 kPa), more preferably (gauge pressure ± 5 kPa), and even more preferably (gauge pressure ± 2 kPa).

[0188] During cooling and solidification, the molten material obtained in step 2 is discharged from the container used for heating and melting in step 2. After the molten material is discharged, it is held at a temperature range of 750–210°C for 0.2–100 seconds. It has been found that a sulfide solid electrolyte precursor containing a sulfide-based glassy phase with Li, P, and S as constituent elements and a crystalline phase of β-Li3PS4 can be obtained. Furthermore, in addition to the above, the content of the crystalline phase of β-Li3PS4 in the sulfide solid electrolyte precursor can be appropriately set to, for example, 0.1–30% by mass. That is, the content of the crystalline phase of β-Li3PS4 in the sulfide solid electrolyte obtained through step 4 can also be appropriately set to, for example, 0.1–30% by mass.

[0189] It should be noted that during the cooling process within the temperature range of 750 to 210°C, the molten material becomes a solid instead of a liquid, depending on its composition. For ease of explanation, this temperature will be referred to as the temperature of the molten material.

[0190] During cooling and solidification, the time for which the flowing melt remains at a temperature range of 750–210°C is 0.2–100 seconds, preferably 0.5–60 seconds, and more preferably 1–40 seconds. Here, a time of 0.2 seconds or more is preferred from the viewpoint of precipitation of the β-Li3PS4 crystalline phase, and more preferably 0.5 seconds or more, and more preferably 1 second or more. Furthermore, a time of 100 seconds or less is preferred from the viewpoint of preventing excessive precipitation of the β-Li3PS4 crystalline phase, and more preferably 60 seconds or less, and more preferably 40 seconds or less.

[0191] It should be noted that when the heating temperature used to obtain the melt in step 2 is below 750°C, the time during which the melt remains in the temperature range of 750°C to 210°C can be described as the time during which the melt remains in the temperature range of the heating temperature to 210°C.

[0192] The average cooling rate during the cooling and solidification process, during which the melt remains in the temperature range of 750 to 210°C, is preferably 5.4°C / second or higher, more preferably 5.4 to 2700°C / second, even more preferably 50 to 2000°C / second, and even more preferably 100 to 1000°C / second.

[0193] By rapidly cooling the material within an appropriate range, a sulfide solid electrolyte precursor comprising a sulfide-based glassy phase containing Li, P, and S as constituent elements and a crystalline phase of β-Li3PS4 can be readily obtained. More specifically, from the viewpoint of achieving a smaller crystallite diameter, the average cooling rate is preferably 5.4 °C / s or more, more preferably 50 °C / s or more, and even more preferably 100 °C / s or more. Furthermore, from the viewpoint of allowing appropriate crystal growth, the average cooling rate is preferably 2700 °C / s or less, more preferably 2000 °C / s or less, and even more preferably 1000 °C / s or less.

[0194] During the cooling and solidification process, after the temperature of the flowing melt reaches 210°C, it is further cooled to below 150°C, for example, and then supplied to the next process 4.

[0195] The cooling rate when the molten liquid reaches a temperature of 210°C can be the same as or different from the cooling rate when it is further cooled to below 150°C.

[0196] Furthermore, through the aforementioned cooling, the content of the sulfide-based glassy phase in the sulfide solid electrolyte precursor can be, for example, 60% by mass or more, and the content of the crystalline phase of β-Li3PS4 can be 0.1% to 30% by mass. In addition, the total content of the aforementioned sulfide-based glassy phase and the crystalline phase of β-Li3PS4 can be, for example, 80% by mass or more.

[0197] This sulfide-based glass phase achieves higher lithium-ion conductivity compared to conventional sulfide-based glasses. Furthermore, by performing the aforementioned cooling and solidification under ambient pressure, the compositional deviation between the raw material mixture and the resulting sulfide-based glass phase and the highly ion-conducting crystalline phase derived from that glass phase, or the composition of the sulfide solid electrolyte, can be reduced.

[0198] <Process 4>

[0199] Step S4 of this embodiment is a process 4 in which the sulfide solid electrolyte precursor obtained in step 3 is heated to obtain a highly ion-conducting crystalline phase in which a portion of the glass phase in the sulfide solid electrolyte precursor is crystallized.

[0200] The heating in step 4, i.e. the temperature during crystallization, can be determined by the crystallization temperature at which the glass phase forms a highly ion-conducting crystalline phase.

[0201] Specifically, from the viewpoint of effectively promoting the above-mentioned crystallization, a temperature of (crystallization temperature - 15°C) or higher is preferred, but it can also be (crystallization temperature - 10°C) or higher, or a temperature of (crystallization temperature + 1°C) or higher. Furthermore, it is known that during high-temperature heating, crystals with low ionic conductivity, i.e., other different types of phases, will precipitate after the high-ionic-conductivity crystalline phase. Therefore, from the viewpoint of preventing the precipitation of crystals with low ionic conductivity, the above-mentioned crystallization temperature is preferably below the temperature at which such crystals with low ionic conductivity precipitate, more preferably below (crystallization temperature + 20°C), and even more preferably below (crystallization temperature + 15°C).

[0202] That is, the crystallization temperature is preferably a temperature of (crystallization temperature - 15°C) or higher, more preferably a temperature of (crystallization temperature - 15°C) or higher and below the temperature at which crystals with low ionic conductivity are precipitated. Alternatively, it can be a temperature of (crystallization temperature - 10°C) or higher and below (crystallization temperature + 20°C), or a temperature of (crystallization temperature + 20°C) or higher and below (crystallization temperature + 1°C) or lower. Using the above ranges, a high ionic conductivity crystalline phase is obtained from the glass phase, and other crystalline phases are also obtained.

[0203] It should be noted that the crystallization temperature in this specification refers to the temperature of the peak of the exothermic peak observed when the sulfide solid electrolyte precursor obtained in step 3 is subjected to differential scanning calorimetry (DSC) at a heating rate of 5°C / min.

[0204] The heating time during crystallization is preferably 1 to 180 minutes, more preferably 5 to 120 minutes, and even more preferably 10 to 100 minutes. From the viewpoint of quality stability, the heating time is preferably 1 minute or more, more preferably 5 minutes or more, and even more preferably 10 minutes or more. Furthermore, 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.

[0205] The proportion of highly ion-conducting crystalline phases can be adjusted by changing the heating temperature and time during crystallization.

[0206] Examples of heating atmospheres during crystallization include nitrogen, argon, and dry air. From the perspective of not impairing ion conductivity, nitrogen and argon atmospheres are preferred.

[0207] The dew point during crystallization is preferably below -30°C.

[0208] In addition, the oxygen concentration during crystallization can be in a dry air environment, and from a safety point of view, it is preferably 5% by volume or less.

[0209] After heating, the mixture is cooled to room temperature at a rate of, for example, 1 to 10,000 °C / min, thereby obtaining the sulfide solid electrolyte of this embodiment.

[0210] The sulfide solid electrolyte obtained above can be directly used in at least one of the positive electrode layer, solid electrolyte layer and negative electrode layer, and can be used in the form of pulverization, drying, etc., depending on the application.

[0211] Example

[0212] The following examples illustrate the present invention in detail, but the present invention is not limited thereto.

[0213] Examples 3 to 5 and 7 are examples, while examples 1, 2 and 6 are comparative examples.

[0214] Experimental Examples

[0215] 〈Example 1〉

[0216] Under a dry nitrogen atmosphere, to become Li 3.4 P 1.0 S 4.0 Br0.3 Lithium sulfide powder (Sigma-Aldrich, 99.98% purity), phosphorus pentasulfide powder (Sigma-Aldrich, 99% purity), and lithium bromide powder (Sigma-Aldrich, 99.995% purity) were weighed according to the composition ratio of (Li: 38.9at%, P: 11.4at%, S: 45.9at%, Br: 3.8at%) and mixed in a mortar to obtain the raw material mixture (Step 1).

[0217] The obtained raw material mixture was placed in a carbon container under a nitrogen atmosphere containing sulfur powder (Sigma, purity 99.998%) as the sulfur source and with a dew point below -50°C. The container was then placed in an electric furnace inside a glove box and heated for 1 hour at a pressure of gauge pressure +1 kPa and a temperature of 750°C to obtain a completely melted molten material (step 2).

[0218] Next, the front end of the container is heated and melted, and the molten material flows out onto a double roller and is cooled to room temperature at an average cooling rate of 5400°C / second, thereby obtaining the sulfide solid electrolyte precursor (step 3). The average cooling rate is adjusted according to the outflow rate of the molten material, the roller gap, and the rotation speed. The pressure at this time is (gauge pressure + 1 kPa), and the outflowing molten material remains in the temperature range of 750–210°C for 0.1 seconds.

[0219] The sulfide solid electrolyte precursor obtained above was heated at 210°C for 10 minutes under a nitrogen atmosphere and then cooled to room temperature at a cooling rate of 300°C / min to obtain the sulfide solid electrolyte.

[0220] It should be noted that the sulfide solid electrolyte precursor obtained above was subjected to DSC analysis at a heating rate of 5°C / min, and the temperature of the peak of the exothermic peak, i.e. the crystallization temperature, was confirmed to be 223°C.

[0221] 〈Example 2〉

[0222] Under a dry nitrogen atmosphere, to become Li 3.4 P 1.0 S 4.0 Br 0.3 Lithium sulfide powder (Sigma-Aldrich, 99.98% purity), phosphorus pentasulfide powder (Sigma-Aldrich, 99% purity), and lithium bromide powder (Sigma-Aldrich, 99.995% purity) were weighed according to the composition ratio and mixed using a mortar and pestle to obtain the raw material mixture (step 1).

[0223] The resulting raw material mixture was further mixed using a planetary ball mill (Fritsch, P-7) to obtain a sulfide solid electrolyte precursor (steps 2'+3'). The mixing in the planetary ball mill was performed mechanically at 400 rpm for 20 hours under a nitrogen atmosphere using 4 mm zirconia balls and a zirconia jar. The dew point was maintained below -70°C during operation.

[0224] The sulfide solid electrolyte obtained above was heated at 210°C for 10 minutes under a nitrogen atmosphere, and then cooled to room temperature at a cooling rate of 300°C / min to obtain the sulfide solid electrolyte (step 4). It should be noted that the crystallization temperature of the above sulfide solid electrolyte precursor is 210°C.

[0225] 〈Example 3~Example 6〉

[0226] The cooling rate of the melt obtained by heating and the time the melt remained in the temperature range of 750–210°C were changed to 0.5 seconds (Example 3), 3.2 seconds (Example 4), 15 seconds (Example 5), and 150 seconds (Example 6), respectively. Otherwise, the same procedure as in Example 1 was followed to obtain the sulfide solid electrolyte. It should be noted that the crystallization temperature of the above-mentioned sulfide solid electrolyte precursors is around 225°C.

[0227] 〈Example 7〉

[0228] To become Li 3.4 P 1.0 S 4.0 Br 0.15 I 0.15 The raw materials were weighed according to the composition ratio, mixed to obtain a raw material mixture, and the melt was held at a temperature range of 750–210°C for 55 seconds. Otherwise, the same procedure as in Example 1 was followed to obtain the sulfide solid electrolyte. It should be noted that the crystallization temperature of the above-mentioned sulfide solid electrolyte precursor is 215°C.

[0229] Evaluation: Sulfide Solid Electrolyte Precursors

[0230] In each case, the sulfide solid electrolyte precursor obtained in step 3 or step 2'+3' is weighed in a glove box and dissolved in an alkaline aqueous solution, and the composition of each element is analyzed.

[0231] Specifically, ICP emission spectroscopy analysis was performed on P and S (device: Hitachi Advanced Scientific Corporation, model PS3520UVDDII).

[0232] For Li, atomic absorption spectrometry was used for analysis (apparatus: Hitachi High Technology Co., Ltd., model ZA3300; CsCl was added to make the solution concentration 0.1% during Li determination).

[0233] For Br and I, ion chromatography was used for analysis (Apparatus: Thermo Fisher Scientific, model ICS-2100 (column: AS11HC), and a small amount of H2O2 was added to dilute with ultrapure water for determination).

[0234] The above methods were used to confirm the overall composition of the sulfide solid electrolyte precursor.

[0235] In addition to the above, the sulfide solid electrolyte precursor was further pulverized in a mortar and passed through a 100μm sieve to prepare a solid electrolyte precursor powder with an average particle size D50 of about 20μm. This powder was used as a sample.

[0236] X-ray diffraction (XRD) was performed using a Rigaku SmartLab apparatus under the following conditions: X-ray source: CuKα rays (λ = 1.5418 Å); tube voltage: 45 kV; tube current: 200 mA; scanning angle: 10–100°; scanning speed: 5° / min; step size: 0.01° / step; in a non-exposed atmospheric environment. Silicon powder was added as an internal standard during XRD measurements. Rietveld analysis was performed when peaks were observed in the XRD patterns to determine the crystallinity (wt%).

[0237] The obtained XRD pattern was used to confirm the presence of crystallization peaks and the presence of the β-Li3PS4 crystalline phase. If the β-Li3PS4 crystalline phase was present, its content and crystallite diameter were determined. The crystallite diameter was calculated using the Scherrer formula for the full width at half maximum (FWHM) of the crystallization peak. More specifically, the crystallite diameter was calculated using the PDXL analysis software attached to the device, analyzing the peak at 2θ = 18.2 ± 0.5 (from the 011 crystal plane).

[0238] In addition, the content of the glass phase (by weight) can be calculated by subtracting the crystallinity (by weight) of the sulfide solid electrolyte precursor from 100% by weight.

[0239] These results are shown in Table 1.

[0240] Evaluation: Sulfide Solid Electrolytes

[0241] <Composition ratio, content ratio>

[0242] The sulfide solid electrolytes obtained in each example were pulverized using a mortar and pestle and passed through a 100 μm sieve to prepare a powder of solid electrolyte precursor with an average particle size D50 of about 20 μm. This powder was used as a sample.

[0243] Then, XRD measurements were performed under the same conditions as when the above-mentioned sulfide solid electrolyte precursor was used as the sample.

[0244] The composition ratio and content of the high ion conductivity crystalline phase and the β-Li3PS4 crystalline phase were determined by analyzing the obtained XRD patterns. The content of the phase composed of sulfide glass was also determined based on the crystallinity.

[0245] Here, it can be determined that the composition ratio of the phase composed of sulfide-based glass is the same as that of the highly ion-conducting crystalline phase. To be on the safe side, this is compared with the composition ratio determined in the evaluation of the sulfide solid electrolyte precursor. The results confirm that, relative to the composition ratio of the highly ion-conducting crystalline phase, the composition ratio of the sulfide solid electrolyte precursor is within ±20% of all components.

[0246] In addition, it was confirmed that the crystallinity, content ratio, and crystallite diameter of the β-Li3PS4 crystalline phase remained unchanged in both the sulfide solid electrolyte precursor and the sulfide solid electrolyte obtained by crystallizing the phase composed of sulfide-based glass through heating.

[0247] The results are shown in Table 1. It should be noted that the proportions of the sulfide-based glass phase in Examples 2 and 5–7 and the highly ion-conducting crystalline phase in Examples 2 and 7 were not analyzed, but it was confirmed that at least the sulfide solid electrolytes in Examples 5–7 contained a sulfide-based glass phase and a highly ion-conducting crystalline phase derived from that glass phase.

[0248] In the analysis of XRD patterns, the peak intensity of the diffraction peak at 2θ = 20.2 ± 0.5°, representing a highly ion-conductive crystalline phase, is set as I. A Let the maximum intensity of the peak intensities of the diffraction peak at 2θ = 18.2 ± 0.5° representing the crystalline phase of β-Li3PS4 be defined as I. B At the same time, we also need to find the result of I. B / I A The peak intensity ratio is represented. The results are shown in Table 1.

[0249] Furthermore, the peak intensity of the diffraction peak at 2θ = 19.1 ± 0.5°, representing a highly ion-conducting crystalline phase, is set as I. C Let the maximum intensity of the peak intensities of the diffraction peak at 2θ = 18.2 ± 0.5° representing the crystalline phase of β-Li3PS4 be defined as I. B At the same time, we also need to find the result of I. B / I C The peak intensity ratio is represented. The results are shown in Table 1.

[0250] It should be noted that the XRD patterns of the sulfide solid electrolyte precursor and the sulfide solid electrolyte obtained in Example 4 are shown in [reference to image / image / etc.]. Figure 2 and Figure 3 .

[0251] <Lithium-ion conductivity>

[0252] The obtained sulfide solid electrolyte was pulverized in a mortar and then passed through a 100 μm sieve to produce a powder with an average particle size (D50) of about 20 μm. This powder was used as a sample.

[0253] The above samples were pressed into powder at a pressure of 380 MPa and used as test samples. The AC resistance was measured using an AC resistance measuring device (Bio-Logic Sciences Instruments, potentiostat / galvanostat VSP). The measurement conditions were: measurement frequency: 100 Hz–1 MHz, measurement voltage: 100 mV, and measurement temperature: 25 °C. The lithium-ion conductivity was calculated based on the obtained Nyquist plot. The results are shown in Table 1 under "Heat Resistance" and "Before Heat Treatment" with the σ value. Li＋ (mS / cm)

[0254] <Heat resistance>

[0255] The obtained sulfide solid electrolyte was heat-treated at 240°C for 1 hour under a nitrogen atmosphere. The lithium-ion conductivity of the heat-treated sulfide solid electrolyte was determined using the same method described in the section on "Lithium-ion Conductivity". The results are shown in Table 1 under "Heat Resistance" and "After Heat Treatment" with the σ value. Li＋ (mS / cm)”, the difference in lithium-ion conductivity before and after heat treatment is expressed as “Δσ” in “heat resistance”. Li＋ (mS / cm)

[0256] Here, as long as the difference between the lithium-ion conductivity after heat treatment and the lithium-ion conductivity before heat treatment is less than 2 mS / cm, the heat resistance can be considered good. Furthermore, the smaller the difference in lithium-ion conductivity before and after heat treatment, the better.

[0257]

[0258] Based on the above results, it can be seen that the sulfide solid electrolyte of this embodiment has high lithium-ion conductivity due to the presence of a phase composed of sulfide-based glass and a highly ion-conducting crystalline phase derived from that phase. Furthermore, although the crystalline phase of β-Li3PS4 is considered to be preferable due to its low lithium-ion conductivity, its presence in the range of 0.1 to 30% by mass enables good heat resistance without significantly reducing the lithium-ion conductivity of the sulfide solid electrolyte.

[0259] Although the present invention has been described in detail 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 invention. This application is based on Japanese 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, The glass phase comprises a phase consisting of sulfide-based glasses containing Li, P, and S as constituent elements. The crystalline phase comprises a highly ion-conducting crystalline phase from the sulfide-based glass and a crystalline phase of β-Li3PS4. The phase composed of the sulfide-based glass and the highly ion-conducting crystalline phase have the following compositions: Li: 30–50 at%, P: 5–15 at%, and S: 30–60 at%. The content of the β-Li3PS4 crystalline phase in the sulfide solid electrolyte is 0.1-30% by mass.

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

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

5. The sulfide solid electrolyte according to claim 1 or 2, wherein, The crystallite diameter of the β-Li3PS4 crystalline phase is less than 400 nm.

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

7. The sulfide solid electrolyte according to claim 1 or 2, wherein, In the XRD pattern obtained by powder X-ray diffraction, the peak intensity of the diffraction peak at 2θ = 20.2 ± 0.5°, representing the highly ion-conducting crystalline phase, is set as I. A Let the maximum intensity of the peak intensities of the diffraction peak at 2θ = 18.2 ± 0.5° representing the crystalline phase of β-Li3PS4 be defined as I. B At that time, by I B / I A The peak intensity ratio is expressed as 0.01 to 2.

0.

8. The sulfide solid electrolyte according to claim 1 or 2, wherein, In the XRD pattern obtained by powder X-ray diffraction, the peak intensity of the diffraction peak at 2θ = 19.1 ± 0.5°, representing the highly ion-conducting crystalline phase, is set as I. C Let the maximum intensity of the peak intensities of the diffraction peak at 2θ = 18.2 ± 0.5° representing the crystalline phase of β-Li3PS4 be defined as I. B At that time, by I B / I C The peak intensity ratio is expressed as 0.01 to 10.

0.

9. A method for manufacturing a sulfide solid electrolyte, wherein the sulfide solid electrolyte comprises a crystalline phase and a glassy phase, the manufacturing method comprising the following steps in sequence: The raw materials are mixed to obtain a raw material mixture containing Li, P and S. The raw material mixture is heated to obtain a melt. The melt was cooled and solidified to obtain a sulfide solid electrolyte precursor containing a glassy phase and a crystalline phase of β-Li3PS4, and Heating the sulfide solid electrolyte precursor yields a portion of the glassy phase crystallized into a highly ion-conducting crystalline phase. The heating and cooling solidification used to obtain the melt are carried out under normal pressure conditions. During the cooling and solidification process, the molten material is allowed to flow out and then remain at a temperature range of 750–210°C for 0.2–100 seconds.

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