Sulfide solid electrolyte

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, and the crystal phase comprising a high-ion-conductivity crystal phase derived from the sulfide-based glass and another crystal phase, the composition of the phase comprising the sulfide-based glass and the high-ion-conductivity crystal phase satisfies 30-50 at% of Li, 5-15 at% of P, and 30-60 at% of S, and the other crystal phases exhibit two or more diffraction peaks different from the diffraction peak representing the high-ion-conductivity crystal phase in the range of 2 [theta] = 18.0-22.5 degrees in an XRD pattern obtained by powder X-ray diffraction measurement.

Description

Technical Field

[0001] This invention relates to a sulfide solid electrolyte. 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 a known example of 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 crystallized solid electrolyte containing lithium, phosphorus, sulfur and Br as constituent components and having a specific crystal structure.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2013-201110 Summary of the Invention

[0010] The crystallized solid electrolyte described in Patent Document 1 is obtained by heat treatment of a sulfide-based glass obtained by mechanical grinding to crystallize it.

[0011] However, the reduction in hydrogen sulfide generation by the crystallized solid electrolyte after crystallization is limited, and higher water resistance is desired.

[0012] Therefore, the object of the present invention is to provide a sulfide solid electrolyte that inhibits the generation of hydrogen sulfide and has excellent water resistance.

[0013] Through repeated and in-depth research, the inventors conceived of obtaining a sulfide-based glass phase by melting and cooling raw materials under heating conditions, performing the heating and cooling at atmospheric pressure and at a very rapid cooling rate. They discovered that when a portion of the resulting glass phase is crystallized, in addition to the precipitation of a highly ion-conducting crystalline phase with excellent ion conductivity, a different crystalline phase also precipitates. These sulfide solid electrolytes containing multiple crystalline phases achieve excellent water resistance, thus completing this invention.

[0014] That is, the present invention relates to the following [1] to [5].

[0015] [1] A sulfide solid electrolyte comprising a crystalline phase and a glassy phase,

[0016] The aforementioned glass phase comprises a phase consisting of sulfide-based glasses containing Li, P, and S as constituent elements.

[0017] The aforementioned crystalline phases include highly ion-conducting crystalline phases and other crystalline phases derived from the aforementioned sulfide-based glasses.

[0018] The compositions of the sulfide-based glass phase and the highly ion-conducting crystalline phase described above satisfy Li: 30–50 at%, P: 5–15 at%, and S: 30–60 at%.

[0019] In the XRD patterns obtained by powder X-ray diffraction, the other crystalline phases mentioned above show more than two diffraction peaks in the range of 2θ = 18.0 to 22.5° that are different from the diffraction peaks representing the high ion conductivity crystalline phases mentioned above.

[0020] [2] According to the sulfide solid electrolyte described in [1] above, the high ion conductivity crystalline phase has diffraction peaks at least at 2θ = 20.2 ± 0.5°, 23.8 ± 0.5° and 29.7 ± 0.5° in the XRD pattern obtained by powder X-ray diffraction.

[0021] [3] According to the sulfide solid electrolyte described in [2] above, wherein the peak intensity of the diffraction peak at 2θ = 20.2 ± 0.5° of the high ion conductivity crystalline phase is set as I. A Among the two or more diffraction peaks appearing in the range of 2θ = 18.0 to 22.5° for the other crystalline phases mentioned above, the peak intensity of the diffraction peak located on the lowest angle side is set as I. α At that time, by I α / I A The peak intensity ratio is greater than 0.01 and less than 0.6.

[0022] [4] The sulfide solid electrolyte according to any one of [1] to [3] above, wherein the above-mentioned high ion conductivity crystalline phase has at least one diffraction peak selected from 2θ = 12.4 ± 0.5°, 14.4 ± 0.5° and 31.4 ± 0.5° in the XRD pattern obtained by powder X-ray diffraction.

[0023] [5] The sulfide solid electrolyte according to any one of [1] to [4] above, wherein the phase composed of the sulfide-based glass and the high ion conductivity crystalline phase further contain Ha as a constituent element.

[0024] The above-mentioned Ha is selected from at least one of F, Cl, Br and I.

[0025] The composition of the phase composed of the above-mentioned sulfide-based glass and the above-mentioned highly ion-conducting crystalline phase further satisfies Ha: 1-12 at%.

[0026] According to the present invention, a sulfide solid electrolyte with excellent water resistance is obtained. Therefore, when the above-mentioned sulfide solid electrolyte is used in an all-solid-state lithium secondary battery, good battery characteristics can be achieved. Attached Figure Description

[0027] Figure 1 This is a flowchart illustrating the method for manufacturing the sulfide solid electrolyte of this embodiment.

[0028] Figure 2 The image shows the XRD pattern of the sulfide solid electrolyte obtained in Example 2.

[0029] Figure 3 The image shows the XRD pattern of the sulfide solid electrolyte obtained in Example 5. Detailed Implementation

[0030] The present invention will now be described in detail, but the 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.

[0031] Sulfide Solid Electrolytes

[0032] The sulfide solid electrolyte of this embodiment comprises a crystalline phase and a glassy phase. The glassy phase comprises a phase composed of sulfide-based glasses containing Li, P, and S as constituent elements (hereinafter, sometimes simply referred to as "sulfide-based glassy phase"). In addition, the crystalline phase comprises a highly ion-conducting crystalline phase derived from the sulfide-based glass and other crystalline phases different from it.

[0033] 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.

[0034] The compositions of the above-mentioned sulfide-based glassy phase and highly ion-conducting crystalline phase satisfy Li: 30–50 at%, P: 5–15 at%, and S: 30–60 at%.

[0035] Furthermore, in the XRD patterns obtained by powder X-ray diffraction, the aforementioned other crystalline phases exhibit two or more diffraction peaks in the range of 2θ = 18.0–22.5° that are different from the diffraction peaks representing the aforementioned high ion conductivity crystalline phase. Here, the aforementioned other crystalline phases may consist of only one crystalline phase or two or more crystalline phases. Therefore, the aforementioned two or more diffraction peaks appearing in the range of 2θ = 18.0–22.5° can be peaks of one other crystalline phase or peaks of two or more other crystalline phases.

[0036] <Phase composed of sulfide-based glasses and highly ion-conducting crystalline phases>

[0037] 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.

[0038] The compositions of the aforementioned sulfide-based glassy phase and highly ion-conducting crystalline phase satisfy Li: 30–50 at%, P: 5–15 at%, and S: 30–60 at%, preferably satisfying 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%.

[0039] 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 the sulfide-based glass phase can be considered to be almost identical, they do not mean that 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.

[0040] In this embodiment, Li is the element responsible for ion conduction in the sulfide-based glass phase and the highly ion-conducting crystalline phase.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] For example, in the above-mentioned Ha content, the total content of Cl and Br is preferably 50 at% or more, more preferably 70 at% or more, and may also be 100 at% (i.e., composed only of Cl and Br). Furthermore, the atomic ratio of 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.

[0050] 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.

[0051] 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).

[0052] 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.

[0053] 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.

[0054] 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%.

[0055] 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.

[0056] 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%.

[0057] 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.

[0058] 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%.

[0059] 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.

[0060] 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%.

[0061] 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.

[0062] 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%.

[0063] 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.

[0064] However, when Sb has Sb-O bonds or exists in the form of SB2O3 oxides, 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 the glass is 3 to 20 mol%.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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 can 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 0.6 or less.

[0070] When the composition of the sulfide-based glassy phase and the highly ion-conducting crystalline phase further contains Ha, the composition ratio expressed as Ha / P is preferably 0.01 to 1.5, more preferably 0.1 to 1.2, and even more preferably 0.2 to 1.0. Here, 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. In addition, 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.

[0071] 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.

[0072] 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 or S is 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.

[0073] 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.

[0074] In this embodiment, the highly ion-conducting crystalline phase preferably has diffraction peaks at least at 2θ = 20.2 ± 0.5°, 23.8 ± 0.5°, and 29.7 ± 0.5° in the XRD pattern obtained by powder X-ray diffraction (XRD).

[0075] The above 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 following examples.

[0076] In this embodiment, the high ion conductivity crystalline phase, in the XRD pattern obtained by powder X-ray diffraction, preferably has at least one diffraction peak selected from 2θ = 12.4 ± 0.5°, 14.4 ± 0.5°, and 31.4 ± 0.5°, in addition to 2θ = 20.2 ± 0.5°, 23.8 ± 0.5°, and 29.7 ± 0.5°, more preferably at least two diffraction peaks, and more preferably at all three diffraction peaks.

[0077] When diffraction peaks are observed as described above, it can be determined that the high ion conductivity crystalline phase employs a lithium thiosulfate superionic conductor type or LGPS type crystal structure. These structures exhibit high lithium-ion conductivity.

[0078] In this embodiment, the total ratio of the sulfide-based glassy phase and the highly ion-conducting crystalline phase in the sulfide solid electrolyte is preferably 50-100% by mass, more preferably 70-95% by mass, and even more preferably 80-90% by mass. From the viewpoint of lithium-ion conductivity, the above-mentioned total ratio is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. Alternatively, the above-mentioned total ratio can be 100% by mass, i.e., consisting only of the sulfide-based glassy phase and the highly ion-conducting crystalline phase. On the other hand, when obtaining the sulfide-based glassy phase, a crystalline phase is sometimes obtained simultaneously. Obtaining only the sulfide-based glassy phase and the highly ion-conducting crystalline phase requires time and cost. Therefore, from the viewpoint of manufacturability of the sulfide solid electrolyte, the above-mentioned total ratio is more preferably 95% by mass or less, and even more preferably 90% by mass or less.

[0079] 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 crystalline phase from 100% by mass using the above analysis.

[0080] The content of the highly ion-conducting crystalline phase in the sulfide solid electrolyte of this embodiment is preferably 30% by mass or more, more preferably 50% by mass or more, or 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 appropriately obtaining a phase composed of sulfide-based glass, 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.

[0081] The content of the sulfide-based glass phase in the sulfide solid electrolyte of this embodiment is preferably 1 to 70% by mass, more preferably 5 to 50% by mass, and even more preferably 8 to 40% by mass. Here, from the viewpoint of achieving a smooth interface between the glass phase and the active material and the solid electrolyte, 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. In addition, from the viewpoint of appropriately obtaining a crystalline phase with high ion conductivity, 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.

[0082] Other crystalline phases

[0083] 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 includes other crystalline phases.

[0084] In the XRD patterns obtained by powder X-ray diffraction, the aforementioned other crystalline phases exhibit at least two diffraction peaks that differ from the diffraction peaks representing the highly ion-conducting crystalline phase, within the range of 2θ = 18.0–22.5°. Here, as described above, the aforementioned other crystalline phases may consist of only one crystalline phase or two or more crystalline phases.

[0085] The crystal structure of the crystalline phase exhibiting more than two diffraction peaks in the aforementioned 2θ = 18.0–22.5° range has not yet been analyzed. However, the aforementioned diffraction peaks are not indicative of lithium phosphate, as determined by Raman spectroscopy or... 31 This was confirmed by the absence of P-O bond peaks observed in the P-NMR spectrum. Furthermore, the specific manufacturing conditions are described in the examples described later; however, even with heating to 210°C for crystallization, it is difficult to conclude that the aforementioned lithium phosphate would precipitate. Therefore, the crystalline phase exhibiting two or more diffraction peaks in the range of 2θ = 18.0–22.5° is considered to be a novel crystalline phase.

[0086] The sulfide solid electrolyte of this embodiment has significantly improved water resistance by including other crystalline phases in addition to the highly ion-conducting crystalline phase.

[0087] The reason for this is not yet clear, but it is speculated that during heat treatment, the aforementioned other crystalline phases precipitate near the surface of the particles composed of highly ion-conducting crystalline phases. Moreover, it is believed that these other crystalline phases may inhibit the reaction between the highly ion-conducting crystalline phases and water, resulting in a decrease in the amount of hydrogen sulfide generated by the highly ion-conducting crystalline phases, thereby improving the water resistance of the sulfide solid electrolyte.

[0088] The other crystalline phases mentioned above only need to show more than two diffraction peaks in the range of 2θ = 18.0 to 22.5°. The number of diffraction peaks is preferably 2 to 5, more preferably 2 to 4, and even more preferably 2 to 3.

[0089] Diffraction peaks in the range of 2θ = 18.0 to 22.5° preferably appear at one or more positions among, for example, 2θ = 18.2 ± 0.5°, 19.2 ± 0.5°, 21.4 ± 0.5° and 21.8 ± 0.5°, more preferably at two or more positions, and may appear at three or more positions, or may appear at all four positions.

[0090] Furthermore, the diffraction peaks are more preferably located at one or more of the following positions: 2θ = 18.2 ± 0.5°, 19.2 ± 0.5°, and 21.8 ± 0.5°, and even more preferably at two or more positions, or at all three positions.

[0091] The peak intensity of the diffraction peak at 2θ = 20.2 ± 0.5° of the above-mentioned highly ion-conducting crystalline phase is set as I. A Among two or more diffraction peaks appearing in the range of 2θ = 18.0–22.5° for other crystalline phases, the peak intensity of the diffraction peak located on the lowest angle side is set as I. α At that time, by I α / I A The peak intensity ratio is preferably greater than 0.01 and less than 0.6, more preferably 0.05 to 0.5, and even more preferably 0.1 to 0.4. From the viewpoint of appropriately improving the water resistance of the sulfide solid electrolyte, the above-mentioned peak intensity ratio is preferably greater than 0.01, more preferably 0.05 or more, and even more preferably 0.1 or more. Furthermore, from the viewpoint of lithium-ion conductivity, the above-mentioned peak intensity ratio is preferably less than 0.6, more preferably 0.5 or less, and even more preferably 0.4 or less.

[0092] The proportion of the aforementioned other crystalline phases in the sulfide solid electrolyte is preferably 1 to 40% by mass, more preferably 3 to 30% by mass, and even more preferably 5 to 20% by mass. Here, from the viewpoint of fully utilizing the characteristics of the sulfide-based glassy phase and the highly ion-conducting crystalline phase, the proportion of the other crystalline phases is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less. Furthermore, from the viewpoint of water resistance, the other crystalline phases are preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more.

[0093] <Other Different Types of Phases>

[0094] The sulfide solid electrolyte of this embodiment may also include other types of phases besides the sulfide-based glass phase, the highly ion-conducting crystalline phase, and other crystalline phases described above. For example, other types of phases may include crystalline phases other than those obtained during the manufacture of the sulfide-based glass phase.

[0095] The proportion of these other different types of phases in the sulfide solid electrolyte is 40% by mass or less, preferably 1 to 40% by mass, more preferably 2 to 35% by mass, and even more preferably 5 to 30% by mass. Here, from the viewpoint of fully utilizing the characteristics of the sulfide-based glassy phase, the highly ion-conducting crystalline phase, and other crystalline phases, the total proportion of the other different types of phases is 40% by mass or less, preferably 35% by mass or less, and even more preferably 30% by mass or less. Alternatively, the other different types of phases may not be included. From the viewpoint of the manufacturability of the sulfide solid electrolyte, the total proportion of the other different types of phases is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 5% by mass or more.

[0096] Properties of Sulfide Solid Electrolytes

[0097] The lithium-ion conductivity of the sulfide solid electrolyte of this embodiment, when formed into powder at 380 MPa, is preferably 2.0 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.

[0098] The lithium-ion conductivity of the sulfide solid electrolyte in this embodiment is preferably 2.0 mS / cm or higher, and the higher the better. Its value also varies depending on the composition, the proportion of sulfide-based glass phase, and high-ion-conductivity crystalline phase.

[0099] For example, when the Br content in Ha is 90 at% or more, the lithium-ion conductivity is preferably 2.5 mS / cm or more. In addition, when the Cl content in Ha is 90 at% or more, the lithium-ion conductivity is preferably 2.0 mS / cm or more.

[0100] 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.

[0101] 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.

[0102] It should be noted that the more specific measurement conditions for the above-mentioned H2S generation are as follows.

[0103] 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.

[0104] The H2S generation amount mentioned above is an indicator of the hydrolysis resistance, i.e., water resistance, of sulfide solid electrolytes. This can be achieved by the presence of a sulfide-based glassy phase, a highly ionicly conductive crystalline phase, and 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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 ball mills or jet mills for use as a battery material, i.e., as a positive or negative electrode, or as a separator layer.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] Manufacturing Method of Sulfide Solid Electrolytes

[0116] The method for manufacturing the sulfide solid electrolyte in this embodiment is as follows: Figure 1 The steps shown are S1 to S4, which sequentially include the following steps 1 to 4.

[0117] Step S1: Process 1 of mixing raw materials to obtain a raw material mixture containing Li, P and S.

[0118] Step S2: Step 2 involves heating the raw material mixture obtained in step 1 to obtain a melt.

[0119] Step S3: Cooling and solidifying the melt obtained in step 2 to obtain the glass phase (step 3).

[0120] Step S4: Heating the glass phase obtained in step 3 to obtain a portion of the glass phase, crystallizing it to obtain a high ion conductivity crystalline phase and other crystalline phases.

[0121] The heating in step 2 and the cooling and solidification in step 3 are carried out under normal pressure, and the cooling rate during cooling and solidification is 100°C / second or higher. This yields a sulfide solid electrolyte containing a glass phase, a highly ion-conducting crystalline phase derived from the glass phase, and other crystalline phases. It should be noted that in this specification, "normal pressure" refers to a pressure range of approximately (gauge pressure ± 15 kPa).

[0122] In addition, in the above-mentioned step 1, the sulfide solid electrolyte described in the above-mentioned "Sulfide Solid Electrolyte" is obtained by mixing 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%.

[0123] The following is a description of each process.

[0124] <Process 1>

[0125] Step S1 in this embodiment is process 1, which involves mixing raw materials to obtain a raw material mixture containing Li, P, and S.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] Examples of raw materials containing phosphorus 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.

[0130] 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).

[0131] 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.

[0132] 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).

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] These raw materials containing other elements can be made from substances that are already known to the public.

[0138] For example, SiO2 and SiS2 are examples of raw materials containing Si. Among them, SiO2 is preferred from the viewpoint of lithium-ion conductivity. These compounds can be used alone or in combination of two or more.

[0139] 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.

[0140] Examples of raw materials containing Ge include GeO2, GeS, GeS2, and GeCl2. From the perspective 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.

[0141] Examples of raw materials containing Al include Al₂S₃, Al₂O₃, and AlCl₃. Among these, Al₂S₃ and AlCl₃ are preferred, and Al₂S₃ is more preferred, considering lithium-ion conductivity and water resistance. These compounds can be used alone or in combination of two or more.

[0142] 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, with SnS2 being more preferred. These compounds can be used alone or in combination of two or more.

[0143] Examples of raw materials containing Sb include SB₂S₃, SB₂O₃, SB₂O₅, SbCl₃, and SbCl₅. Among these, SB₂S₃ and SbCl₃ are preferred, and SB₂S₃ is more preferred, considering lithium-ion conductivity and water resistance. These compounds can be used alone or in combination of two or more.

[0144] 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.

[0145] The combination of these raw materials also determines the crystal structure of the resulting highly ion-conducting crystalline phase.

[0146] In addition to the above, the preferred methods for obtaining the glass phase and the highly ion-conducting crystalline phase derived from the glass phase are the same as those for the preferred methods in "Sulfide-based Glass Phases and Highly Ion-Conducting Crystalline Phases" of the above-mentioned "Sulfide Solid Electrolytes".

[0147] 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 glass phase or 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, a more homogeneous glass phase or sulfide solid electrolyte can be manufactured using the manufacturing method of this embodiment.

[0148] 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.

[0149] Furthermore, as described above, according to the manufacturing method of this embodiment, even when using raw materials with larger particle sizes, it is easy to obtain a homogeneous glass phase or sulfide solid electrolyte. 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.

[0150] 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.

[0151] 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 chart determined by measuring the particle size distribution using a Microtrac MT3300EXII laser diffraction particle size distribution measuring machine.

[0152] 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.

[0153] <Process 2>

[0154] In this embodiment, step S2 is step 2, which involves heating the raw material mixture obtained in step 1 to obtain a melt.

[0155] 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.

[0156] The manufacturing method of this embodiment melts the raw material mixture by heating it under atmospheric pressure, thereby minimizing the deviation between the composition of 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.

[0157] 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).

[0158] 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%.

[0159] 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).

[0160] 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.

[0161] 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.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] In the case of a gaseous atmosphere containing sulfur, 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-containing gas is preferred.

[0167] 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.

[0168] As a gas containing sulfur, sulfur gas, hydrogen sulfide gas, sulfur dioxide gas, etc. can be introduced simultaneously with the addition of elemental sulfur powder to produce a gas containing sulfur.

[0169] The gas containing sulfur is preferably a gas used as the source of sulfur, for example, in 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.

[0170] Examples of inert gases mentioned above include nitrogen, argon, and helium. They can be used alone or in combination of two or more.

[0171] 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.

[0172] In step 2, the complete melting 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 the mixture at a specified temperature and then pouring the melt to check for fluidity.

[0173] <Process 3>

[0174] In this embodiment, step S3 is step 3, which involves cooling and solidifying the melt obtained in step 2 to obtain a glass phase.

[0175] 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).

[0176] 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).

[0177] The cooling rate during cooling and solidification is 100°C / second or higher, preferably 100 to 100,000°C / second, more preferably 500 to 50,000°C / second, and even more preferably 1,000 to 10,000°C / second. Here, by using ultra-rapid cooling at a rate of 100°C / second or higher, which is faster than before, the proportion of the sulfide-based glass phase containing Li, P, and S as constituent elements can be, for example, 60% by mass or higher.

[0178] This sulfide-based glass phase achieves higher lithium-ion conductivity compared to conventional sulfide-based glasses, thus improving the lithium-ion conductivity of the sulfide solid electrolyte. Furthermore, by performing the aforementioned cooling and solidification under ambient pressure, the compositional deviation between the raw material mixture and the resulting glass phase and the high-ion-conductivity crystalline phase derived from that glass phase, or the composition of the sulfide solid electrolyte, can be reduced.

[0179] The aforementioned cooling rate is 100°C / second or higher. From the viewpoint of facilitating glass formation, it is preferably 500°C / second or higher, and more preferably 1000°C / second or higher. Furthermore, there is no particular upper limit to the cooling rate. From the viewpoint of equipment capacity, it is preferably 100,000°C / second or lower, more preferably 50,000°C / second or lower, and even more preferably 10,000°C / second or lower.

[0180] The ultra-rapid cooling described above can be achieved by using, for example, a chilling twin roller.

[0181] This sulfide-based glass phase achieves higher lithium-ion conductivity compared to conventional sulfide-based glasses. Furthermore, by performing the aforementioned cooling and curing under ambient pressure, the compositional deviation between the raw material mixture and the resulting sulfide-based glass phase and the high-ion-conductivity crystalline phase derived from that glass phase, or the composition of the sulfide solid electrolyte, can be reduced.

[0182] <Process 4>

[0183] Step S4 of this embodiment is step 4, which involves heating the glass phase obtained in step 3 to obtain a partially crystallized glass phase with high ion conductivity and other crystalline phases.

[0184] The heating in step 4, i.e. the temperature at which crystallization is carried out to obtain a highly ion-conducting crystalline phase and other crystalline phases, can be determined based on the crystallization temperature at which the glass phase transforms into a highly ion-conducting crystalline phase.

[0185] 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, following the precipitation of a highly ionicly conductive crystalline phase, crystals with low ionic conductivity, i.e., other different types of phases, will precipitate. 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).

[0186] 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 precipitate. Alternatively, it can be a temperature of (crystallization temperature - 10°C) or higher and below (crystallization temperature + 20°C), a temperature of (crystallization temperature) or higher and below (crystallization temperature + 20°C), or a temperature of (crystallization temperature + 1°C) or higher and below (crystallization temperature + 15°C). Using the above ranges, a highly ionicly conductive crystalline phase is obtained from the glassy phase, and other crystalline phases are also obtained.

[0187] It should be noted that the crystallization temperature in this specification refers to the temperature at the peak of the exothermic peak observed when the sulfide-based glass phase, which can be called the precursor of the sulfide solid electrolyte obtained in step 3, is heated at a rate of 5°C / min using differential scanning calorimetry (DSC).

[0188] The heating time during crystallization is, for example, 1 minute to 6 hours, preferably 1 minute to 3 hours, more preferably 5 minutes to 2 hours, and even more preferably 10 minutes to 100 minutes. From the viewpoint of quality stability, the above 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 above heating time is preferably 6 hours or less, more preferably 3 hours or less, even more preferably 2 hours or less, and even more preferably 100 minutes or less.

[0189] The proportion of highly ion-conducting crystalline phases can be adjusted by changing the heating temperature and time during crystallization.

[0190] 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.

[0191] The dew point during crystallization is preferably below -30°C.

[0192] 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.

[0193] 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.

[0194] 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 after being crushed, dried or otherwise processed according to the intended use.

[0195] Example

[0196] The following examples illustrate the present invention in detail, but the present invention is not limited thereto.

[0197] Examples 1-4 are examples, and Examples 5 and 6 are comparative examples.

[0198] Experimental Examples

[0199] <Example 1: Melt quenching method>

[0200] Under a dry nitrogen atmosphere, to become Li 3.4 P 1.0 S 4.0 Br 0.34 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: 45.8at%, Br: 3.9at%) and mixed in a mortar to obtain the raw material mixture (Step 1).

[0201] 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).

[0202] Next, the front end of the container is heated and melted, and the molten material flows out onto the twin rollers and is cooled to room temperature at a cooling rate of 3000°C / second, thereby obtaining the glass phase (step 3). The pressure at this time is (gauge pressure + 1 kPa), and the cooling rate is adjusted according to the outflow rate of the molten material, the gap between the twin rollers, and the rotation speed.

[0203] The glass phase obtained above is heated at 210°C for 10 minutes under a nitrogen atmosphere to crystallize a portion of the glass phase (step 4). Then, it is cooled to room temperature at a cooling rate of 300°C / min to obtain a sulfide solid electrolyte containing a glass phase, a highly ion-conducting crystalline phase, and other crystalline phases.

[0204] It should be noted that the glass phase obtained above was subjected to DSC measurement 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.

[0205] <Examples 2 and 3: Melt quenching method>

[0206] The cooling rate in step 3 is set to 8000°C / second (Example 2) or 10000°C / second (Example 3). Otherwise, the process is repeated in the same manner as in Example 1 to obtain a sulfide solid electrolyte containing a glassy phase, a highly ion-conducting crystalline phase, and other crystalline phases. The crystallization temperature of the glassy phase obtained in step 3 is confirmed to be 217°C (Example 2) or 215°C (Example 3).

[0207] <Example 4: Melt quenching method>

[0208] With the composition ratio of Li 3.4 P 1.0 S4.0 Cl 0.1 Br 0.2 A mixture of raw materials was obtained by weighing lithium sulfide powder (99.98% purity, manufactured by Sigma-Aldrich), phosphorus pentasulfide powder (99% purity, manufactured by Sigma-Aldrich), lithium bromide powder (99.995% purity, manufactured by Sigma-Aldrich), and lithium chloride powder (99.995% purity, manufactured by Sigma-Aldrich) in the manner of composition ratio (Li: 39.1at%, P: 11.5at%, S: 46.0at%, Cl: 1.1at%, Br: 2.3at%). Otherwise, the same procedure as in Example 1 was followed to obtain a sulfide solid electrolyte containing a glassy phase, a highly ion-conducting crystalline phase, and other crystalline phases.

[0209] It should be noted that the crystallization temperature of the glass phase obtained in step 3 is confirmed to be 219°C.

[0210] Example 5: Mechanical Grinding Method

[0211] Perform step 1 in the same manner as in Example 1 to obtain a mixture of raw materials.

[0212] Next, the obtained raw material mixture was further mixed using a planetary ball mill (Fritsch, P-7) to obtain the glass phase (steps 2'+3'). The mixing process was carried out using 4mm zirconia balls and a zirconia jar in a planetary ball mill at 400 rpm for 20 hours under a nitrogen atmosphere. The dew point was maintained below -70°C during operation.

[0213] The glass phase obtained above is heated at 210°C for 10 minutes under a nitrogen atmosphere to crystallize a portion of the glass phase (step 4). Then, it is cooled to room temperature at a cooling rate of 300°C / min to obtain a sulfide solid electrolyte containing a glass phase and a highly ion-conducting crystalline phase.

[0214] It should be noted that the crystallization temperature of the glass phase mentioned above is 207°C.

[0215] Example 6: Mechanical Grinding Method

[0216] Perform step 1 in the same manner as in Example 4 to obtain a mixture of raw materials.

[0217] Next, processes 2'+3' and 4 are performed in the same manner as in Example 5 to obtain a sulfide solid electrolyte containing a glassy phase and a highly ion-conducting crystalline phase.

[0218] It should be noted that the crystallization temperature of the aforementioned glass phase is 210℃.

[0219] Evaluation: Glassy Phase

[0220] In each example, the glass phase 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.

[0221] Specifically, ICP emission spectroscopy analysis was performed on P and S (device: Hitachi Advanced Scientific Corporation, model PS3520UVDDII).

[0222] 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).

[0223] For Br and Cl, ion chromatography was used for analysis (Apparatus: Thermo Fisher Scientific, model ICS-2100 (column: AS11HC), a small amount of H2O2 was added and diluted with ultrapure water for determination).

[0224] The composition of the glass phase was confirmed using the methods described above.

[0225] Evaluation: Sulfide Solid Electrolytes

[0226] <Composition ratio, content ratio>

[0227] The sulfide solid electrolytes obtained in Examples 1 to 6 were pulverized using a mortar and pestle and passed through a 100 μm sieve to obtain a powder of solid electrolyte precursor with an average particle size D50 of about 20 μm. This powder was used as a sample.

[0228] Then, 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. Additionally, silicon powder was added as an internal standard during XRD measurements, and Rietveld analysis was performed to obtain the crystallinity (wt%).

[0229] The 2θ value of the observed diffraction peak was determined from the obtained XRD pattern.

[0230] In addition, the peak intensity of the diffraction peak at 2θ = 20.2 ± 0.5° is set as I. A For diffraction peaks appearing in the range of 2θ = 18.0–22.5°, among the diffraction peaks that differ from those indicating a highly ion-conducting crystalline phase, the peak intensity of the diffraction peak located on the lowest angle side is set as I. α Find them separately, and use them to find the results of I separately. A / Iα The peak intensity ratio is represented.

[0231] 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. For the sake of caution, this is compared with the composition ratio obtained in the evaluation relative to the glass phase. The results confirm that, relative to the composition ratio of the highly ion-conducting crystalline phase, the composition ratio of the glass phase prior to step 3 is within ±20% of all components.

[0232] It should be noted that the XRD patterns of the sulfide solid electrolytes obtained in Examples 2 and 5 are shown in [the figures]. Figure 2 and Figure 3 .

[0233] <Water resistance>

[0234] 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.

[0235] A 10 mg sample was exposed to humidified N2 gas with a dew point of -20°C for 5 hours. The concentration of hydrogen sulfide in the gas was monitored, and the total amount of hydrogen sulfide generated was calculated. The humidified N2 gas was supplied at a rate of 0.5 L / min.

[0236] Thus, the evaluation of hydrolysis resistance is based on the detection of the total amount of hydrogen sulfide generated, which serves as an assessment of water resistance. A hydrogen sulfide concentration meter (TEKHNE, Model 3000RS) was used for the detection tube.

[0237] The results are shown in Table 1, “Water Resistance H2S Generation (mL / g)”.

[0238] <Lithium-ion conductivity>

[0239] The sulfide solid electrolytes obtained in each example were pulverized in a mortar and then passed through a 100 μm sieve to produce powder with an average particle size (D50) of about 20 μm. This powder was used as a sample.

[0240] The above samples were pressed into powder at a pressure of 380 MPa and used as the 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, measurement temperature: 25 °C. The lithium-ion conductivity was calculated based on the obtained Nyquist plot. The results are shown in Table 1, “σ”. Li＋ (mS / cm)

[0241]

[0242] Based on the above results, it can be seen that the sulfide solid electrolytes of Examples 1 to 3, despite having the same composition of sulfide-based glassy phase and highly ion-conducting crystalline phase as the sulfide solid electrolyte of Example 5, can achieve high water resistance. Similarly, the sulfide solid electrolyte of Example 4 achieves higher water resistance compared to the sulfide solid electrolyte of Example 6. This is believed to be because, in the manufacture of the sulfide solid electrolytes of Examples 1 to 4, a glassy phase was obtained using a melt-quenching method under specific conditions, followed by crystallization by heating. This precipitated other crystalline phases with two or more diffraction peaks in the range of 2θ = 18.0 to 22.5° that differed from the diffraction peaks of the highly ion-conducting crystalline phase, thus suppressing the reaction with water.

[0243] Furthermore, based on the results of the water resistance of the sulfide solid electrolytes in Examples 1 to 3, the peak intensity was higher than that of I. α / I A The higher the concentration of the other crystalline phases mentioned above, the more pronounced the water resistance effect.

[0244] 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. 2023-168391, 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 other crystalline phases. The phase composed of the sulfide-based glass and the highly ion-conducting crystalline phase have compositions satisfying Li: 30–50 at%, P: 5–15 at%, and S: 30–60 at%. The other crystalline phases, in the XRD pattern obtained by powder X-ray diffraction, show more than two diffraction peaks in the range of 2θ = 18.0 to 22.5° that are different from the diffraction peaks representing the high ion conductivity crystalline phase.

2. The sulfide solid electrolyte according to claim 1, wherein, The highly ion-conducting crystalline phase exhibits diffraction peaks at at least 2θ = 20.2 ± 0.5°, 23.8 ± 0.5°, and 29.7 ± 0.5° in the XRD pattern obtained by powder X-ray diffraction.

3. The sulfide solid electrolyte according to claim 2, wherein, The peak intensity of the diffraction peak at 2θ = 20.2 ± 0.5° of the highly ion-conducting crystalline phase is set as I. A Among the two or more diffraction peaks appearing in the range of 2θ = 18.0 to 22.5° of the other crystalline phases, the peak intensity of the diffraction peak located on the lowest angle side is set as I. α At that time, by I α / I A The peak intensity ratio is greater than 0.01 and less than 0.

6.

4. The sulfide solid electrolyte according to claim 1 or 2, wherein, The highly ion-conducting crystalline phase also has a diffraction peak at at least one location selected from 2θ = 12.4 ± 0.5°, 14.4 ± 0.5°, and 31.4 ± 0.5° in the XRD pattern obtained by powder X-ray diffraction.

5. The sulfide solid electrolyte according to claim 1 or 2, 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. The composition of the phase composed of the sulfide-based glass and the highly ion-conducting crystalline phase further satisfies Ha: 1–12 at%.

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