Sulfide solid electrolyte, method for producing same, and lithium ion-conductive crystal

Abstract

The present invention relates to a sulfide solid electrolyte containing a crystalline phase and a glass phase, wherein: the glass phase contains a phase comprising a sulfide-based glass containing Li, P, S, and Ha as constituent elements; the Ha comprises at least one selected from the group consisting of F, Cl, Br, and I; the crystalline phase includes a highly ion-conductive crystalline phase derived from the sulfide-based glass; the highly ion-conductive crystalline phase has diffraction peaks at least at 2θ = 20.2 ± 0.5°, 23.8 ± 0.5°, and 29.7 ± 0.5° in an XRD pattern obtained by powder X-ray diffraction measurement; and the half-value width of the diffraction peak at 2θ = 20.2 ± 0.5° is 0.01-0.4°.

Description

Sulfide solid electrolyte, its manufacturing method, and lithium ion conductive crystal

[0001] The present invention relates to a sulfide solid electrolyte and a method for producing the same, and also to a novel lithium ion conductive crystalline material.

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

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

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

[0005] As a solid electrolyte that is resistant to hydrolysis and has high ionic conductivity, Patent Document 1 discloses a crystallized solid electrolyte that contains lithium, phosphorus, sulfur, and Br as constituent components and has a specific crystal structure.

[0006] Japanese Patent Application Publication No. 2013-201110

[0007] The crystallized solid electrolyte described in Patent Document 1 is crystallized by heat treating a sulfide-based glass obtained by mechanical milling. However, the crystallized solid electrolyte after the crystallization has low crystallinity, and it is desired to achieve a higher lithium ion conductivity.

[0008] Therefore, an object of the present invention is to provide a sulfide solid electrolyte having excellent lithium ion conductivity and a method for producing the same, as well as a novel crystalline body having excellent lithium ion conductivity.

[0009] As a result of extensive research, the present inventors have come up with the idea of ​​performing the heating and cooling under normal pressure conditions and at a very fast cooling rate when obtaining a sulfide-based glass phase by heating and melting raw materials and then cooling them. They have also found that by partially crystallizing the glass phase thus obtained, a sulfide solid electrolyte with high crystallinity and high lithium-ion conductivity can be obtained.

[0010] That is, the present invention relates to the following items [1] to [8]. [1] A sulfide solid electrolyte comprising a crystalline phase and a glassy phase, wherein the glassy phase comprises a phase made of a sulfide-based glass containing Li, P, S, and Ha as constituent elements, wherein the Ha is at least one element selected from the group consisting of F, Cl, Br, and I, and the crystalline phase comprises a highly ion-conductive crystalline phase derived from the sulfide-based glass, wherein the highly ion-conductive crystalline phase has diffraction peaks at least at 2θ=20.2±0.5°, 23.8±0.5°, and 29.7±0.5° in an XRD pattern obtained by powder X-ray diffraction measurement, and the half-width of the diffraction peak at 2θ=20.2±0.5° is 0.01 to 0.4°. [2] A sulfide solid electrolyte comprising: a sulfide solid electrolyte having a peak intensity of the diffraction peak at 2θ=20.2±0.5° in the XRD pattern of the highly ion-conductive crystalline phase, the peak intensity being I Ａ The peak intensity of the diffraction peak at 2θ=29.7±0.5° is defined as I Ｂ When I Ａ / I Ｂ

[0023] The sulfide solid electrolyte according to any one of [1] to [3], wherein the peak intensity ratio represented by the formula (I) is greater than 1.0. [3] The sulfide solid electrolyte according to any one of [1] to [2], wherein the content of the high ion-conductive crystalline phase in the sulfide solid electrolyte is 50 mass% or more. [4] The sulfide solid electrolyte according to any one of [1] to [3], wherein the sulfide-based glass phase and the high ion-conductive crystalline phase have compositions satisfying Li: 30 to 50 at%, P: 5 to 15 at%, S: 30 to 60 at%, and Ha: 1 to 12 at%. [5] The sulfide solid electrolyte according to any one of [1] to [4], wherein the high ion-conductive crystalline phase further has a diffraction peak at at least one selected from the group consisting of 2θ = 12.4 ± 0.5°, 14.4 ± 0.5°, and 31.4 ± 0.5° in the XRD pattern.

[0011] [6] A powder containing Li, P, S, and Ha as constituent elements, wherein the Ha is at least one selected from the group consisting of F, Cl, Br, and I, and wherein an XRD pattern obtained by powder X-ray diffraction measurement has diffraction peaks at at least 2θ=12.4±0.5°, 14.4±0.5°, 20.2±0.5°, 23.8±0.5°, 29.7±0.5°, and 31.4±0.5°, and the peak intensity of the diffraction peak at 2θ=20.2±0.5° is I Ａ The peak intensity of the diffraction peak at 2θ=29.7±0.5° is defined as I Ｂ When I Ａ / I Ｂ The lithium ion conductive crystal has a peak intensity ratio of more than 1.0.

[0012] [7] A method for producing a sulfide solid electrolyte comprising: mixing raw materials to obtain a raw material mixture containing Li, P, and S; heating the raw material mixture to obtain a melt; cooling and solidifying the melt to obtain the glass phase; and heating the glass phase to obtain a high ion-conductive crystalline phase by crystallizing a portion of the glass phase, wherein the heating to obtain the melt and the cooling and solidifying are performed under atmospheric pressure, the cooling rate in the cooling and solidifying is 100°C / second or more, and the heating to obtain the high ion-conductive crystalline phase is performed at a temperature equal to or higher than the crystallization temperature of the glass phase minus 15°C for one minute or more. [8] The method for producing a sulfide solid electrolyte according to [7], wherein the raw material mixture further contains Ha, and the Ha is at least one element selected from the group consisting of F, Cl, Br, and I.

[0013] According to the present invention, a sulfide solid electrolyte having high crystallinity and excellent lithium ion conductivity can be obtained. Therefore, when the sulfide solid electrolyte is used in an all-solid-state lithium secondary battery, good battery characteristics can be achieved. Furthermore, the lithium ion conductive crystalline material obtained by the present invention has high conductivity and is suitable for use in sulfide solid electrolytes.

[0014] Fig. 1 is a flow diagram showing a method for producing a sulfide solid electrolyte according to the present embodiment. Fig. 2 is an XRD pattern of the sulfide solid electrolyte obtained in Example 2. Fig. 3 is an XRD pattern of the sulfide solid electrolyte obtained in Example 5.

[0015] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be modified as desired without departing from the spirit of the present invention. Furthermore, the term "to" indicating a range of values ​​is used to mean that the values ​​before and after it are included as the lower and upper limits.

[0016] <<Sulfide Solid Electrolyte>> The sulfide solid electrolyte according to this embodiment includes a crystalline phase and a glassy phase. The glassy phase includes a phase made of sulfide-based glass containing Li, P, S, and Ha as constituent elements (hereinafter, sometimes simply referred to as the "sulfide-based glassy phase"). The crystalline phase includes a highly ion-conductive crystalline phase derived from the sulfide-based glass. Here, Ha is at least one element selected from the group consisting of F, Cl, Br, and I.

[0017] The high ion-conductive crystalline phase derived from sulfide-based glass refers to a crystalline phase obtained by crystallizing the sulfide-based glass through heat treatment, and its constituent elements and composition ratios are considered to be substantially identical. Here, "substantially identical" means that the difference in composition determined from structural analysis of the XRD pattern of the high ion-conductive crystalline phase relative to the overall composition is within a range of ±20% for each component.

[0018] The high ion conductive crystalline phase has diffraction peaks at least at 2θ=20.2±0.5°, 23.8±0.5°, and 29.7±0.5° in an XRD pattern obtained by powder X-ray diffraction measurement. The half width of the peak at 2θ=20.2±0.5° is 0.01 to 0.4°.

[0019] <Sulfide-based glass phase and high ion-conductive crystalline phase> The sulfide-based glass phase and high ion-conductive crystalline phase in this embodiment contain Li, P, S, and Ha as constituent elements. Here, Ha is at least one selected from the group consisting of F, Cl, Br, and I. From the viewpoint of obtaining good oxidation resistance and water resistance, it is more preferable to contain at least one selected from the group consisting of Cl, Br, and I, even more preferable to contain at least one of Cl and Br, and even more preferable to contain Br. It is also even more preferable to contain both Cl and Br.

[0020] The high ion conductive crystalline phase in this embodiment has diffraction peaks at least at 2θ=20.2±0.5°, 23.8±0.5°, and 29.7±0.5° in an XRD pattern obtained by powder XRD measurement. Of these diffraction peaks, the half width of the peak at 2θ=20.2±0.5° is 0.01 to 0.4°.

[0021] The XRD measurement is performed using CuKα radiation (λ=1.5418 Å) as a radiation source, and the detailed measurement conditions are as described in detail in the Examples section below. Furthermore, the half-width of a peak in this specification refers to the width of a diffraction line at half the height of the diffraction line intensity, also known as the full width at half maximum (FWHM). In other words, the half-width refers to the width where the peak intersects with half the peak intensity of the corresponding peak when an XRD spectrum is drawn.

[0022] Here, even in the crystallized solid electrolyte described in Patent Document 1, diffraction peaks are observed at 2θ = 20.2 ± 0.5°, 23.8 ± 0.5°, and 29.7 ± 0.5° (see Patent Document 1, [Figure 6], Example 12, etc.). However, among these diffraction peaks, the half-width of the peak at 2θ = 20.2 ± 0.5° is about 0.5 to 0.6°, and higher crystallinity has not been achieved. Furthermore, their lithium ion conductivity is about 2 mS / cm.

[0023] In contrast, the highly ion-conductive crystalline phase of this embodiment exhibits high crystallinity with a peak half-width of 0.01 to 0.4° at 2θ=20.2±0.5°, and also has a high lithium ion conductivity of approximately 3 mS / cm.

[0024] The reason for this is unclear, but it is thought to be as follows: When sulfide-based glass is obtained using a conventional mechanical milling method, as in the crystallized solid electrolyte described in Patent Document 1, the crystal structure derived from the raw materials becomes disordered due to the physical energy of a ball mill, etc., and the resulting glass is in an amorphous state without a regular atomic arrangement. Therefore, even if such sulfide-based glass is subjected to heat treatment to crystallize it, high crystallinity cannot be achieved, and the improvement in lithium ion conductivity also reaches a plateau.

[0025] In contrast, the sulfide solid electrolyte according to this embodiment employs a melt-quenching method to obtain the glass phase. Furthermore, the heating and cooling to melt the raw materials are performed under atmospheric pressure, and the cooling is performed at a very fast cooling rate. It is therefore speculated that the glass phase in this embodiment has a certain degree of order, i.e., a periodic structure, although not to the extent observed in the XRD pattern. Furthermore, it is believed that crystallization of such a glass phase by heat treatment may improve crystallinity and achieve high lithium ion conductivity.

[0026] In the high ion conductive crystalline phase of this embodiment, the half-width of the diffraction peak at 2θ = 20.2 ± 0.5° is 0.01 to 0.4°, and if the half-width is 0.4° or less, it can be determined that the crystallinity is high. The half-width is preferably 0.05° to 0.35°, and more preferably 0.1° to 0.3°. Here, from the viewpoint of high lithium ion conductivity associated with high crystallinity, the half-width is preferably 0.35° or less, and more preferably 0.3° or less. There is no particular limitation on the lower limit of the half-width, and the smaller the better. However, from the viewpoint of the detection accuracy of the device, it may be 0.05° or more, or 0.1° or more.

[0027] In the present embodiment, the high ion conductive crystalline phase preferably has, in an XRD pattern obtained by powder X-ray diffraction measurement, a diffraction peak at at least one selected from the group consisting of 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 at least two, and more preferably at all three.

[0028] In the XRD pattern of the highly ion-conductive crystalline phase in this embodiment, the peak intensity of the diffraction peak at 2θ=20.2±0.5° is expressed as I Ａ The peak intensity of the diffraction peak at 2θ = 29.7 ± 0.5° is defined as I Ｂ When I Ａ / I ＢThe peak intensity ratio represented by the formula (1) is preferably greater than 1.0, more preferably greater than 1.0 but not greater than 2.0, even more preferably from 1.05 to 1.8, even more preferably from 1.05 to 1.5, particularly preferably from 1.1 to 1.45, and most preferably from 1.1 to 1.4.

[0029] Regarding the peak intensity ratio, when the sulfide-based glass obtained by the mechanical milling method is crystallized, I Ａ / I Ｂ The peak intensity ratio represented by is 1.0 or less, that is, the peak intensity I of the diffraction peak at 2θ = 20.2 ± 0.5 ° is Ａ The peak intensity I of the diffraction peak at 2θ=29.7±0.5° is Ｂ On the other hand, according to the study by the present inventors, when sulfide-based glass obtained by a melt quenching method under specific conditions is crystallized, I Ａ / I Ｂ The peak intensity ratio represented by is greater than 1.0, that is, the peak intensity I of the diffraction peak at 2θ = 20.2 ± 0.5 ° Ａ The peak intensity I of the diffraction peak at 2θ = 29.7 ± 0.5° is Ｂ This is a characteristic of the crystalline phase that was first obtained by employing the above-mentioned melt-quenching method.

[0030] Based on the above, I Ａ / I Ｂ The peak intensity ratio represented by the formula (1) may be more than 1.0, but from the viewpoint of lithium ion conductivity, it is preferably 1.05 or more, more preferably 1.1 or more, and is preferably 2.0 or less, more preferably 1.8 or less, even more preferably 1.5 or less, still more preferably 1.45 or less, and particularly preferably 1.4 or less.

[0031] In addition, when the XRD pattern has diffraction peaks at 2θ=20.2±0.5°, 23.8±0.5°, and 29.7±0.5°, it can be determined that the high ion-conducting crystalline phase has a thiolisicon-type or LGPS-type crystalline structure, which has high lithium ion conductivity.

[0032] In this embodiment, the compositions of the sulfide-based glass phase and the high ion-conductive crystalline phase more preferably satisfy the following: Li: 30 to 50 at%, P: 5 to 15 at%, S: 30 to 60 at%, and Ha: 1 to 12 at%. In this specification, at% means atomic %. As mentioned above, the sulfide-based glass and the high ion-conductive crystalline phase derived therefrom are considered to have substantially the same constituent elements and composition ratios, but this does not mean that they are strictly the same. It is preferable that the compositions of the sulfide-based glass phase and the high ion-conductive crystalline phase each satisfy the above ranges.

[0033] In the sulfide-based glass phase and the highly ion-conductive crystalline phase of this embodiment, Li is an element responsible for ionic conduction as a solid electrolyte. In the compositions of the sulfide-based glass phase and the highly ion-conductive crystalline phase, the Li content is preferably 30 to 50 at%. 35 to 45 at% is preferred, and 37 to 43 at% is more preferred. From the viewpoint of increasing lithium ion conductivity, the Li content is preferably 30 at% or more, more preferably 35 at% or more, and even more preferably 37 at% or more. Furthermore, from the viewpoint of widening the vitrification range, the Li content is preferably 50 at% or less, more preferably 45 at% or less, and even more preferably 43 at% or less.

[0034] In the sulfide-based glass phase and the high ion-conductive crystalline phase of this embodiment, P is an element that forms a glass network, and among sulfides, the P-S bond is highly resistant to both oxidation and reduction. Therefore, as a solid electrolyte, it has a wide potential window and excellent electrochemical stability. In the composition of the sulfide-based glass phase and the high ion-conductive crystalline phase, the P content is preferably 5 to 15 at%, more preferably 6 to 13 at%, and more preferably 7 to 12 at%. Here, from the viewpoint of widening the vitrification range, the P content is preferably 5 at% or more, more preferably 6 at% or more, and even more preferably 7 at% or more. Furthermore, from the viewpoint of increasing lithium ion conductivity, the P content is preferably 15 at% or less, more preferably 13 at% or less, and even more preferably 12 at% or less.

[0035] In the sulfide-based glass phase and the high ion-conductive crystalline phase of this embodiment, S is an element that forms P—S bonds with P and is an essential element for forming the glass phase. In the composition of the sulfide-based glass phase and the high ion-conductive crystalline phase, the S content is preferably 30 to 60 at%. 33 to 50 at% is more preferable, and 35 to 47 at% is even more preferable. From the viewpoint of widening the vitrification range, the S content is preferably 30 at% or more, more preferably 33 at% or more, and even more preferably 35 at% or more. Furthermore, from the viewpoint of increasing the lithium ion conductivity, the S content is preferably 60 at% or less, more preferably 50 at% or less, and even more preferably 47 at% or less.

[0036] In the sulfide-based glass phase and the highly ion-conductive crystalline phase of this embodiment, Ha is an element that contributes to high lithium ion conductivity. In the compositions of the sulfide-based glass phase and the highly ion-conductive crystalline phase, the Ha content is preferably 1 to 12 at%; more preferably 3 to 10 at%; and even more preferably 3.5 to 8 at%. Here, from the viewpoint of obtaining high lithium ion conductivity, the Ha content is preferably 1 at% or more, more preferably 3 at% or more, and even more preferably 3.5 at% or more. Furthermore, from the viewpoint of preventing precipitation of lithium halide crystals, the Ha content is preferably 12 at% or less, more preferably 10 at% or less, and even more preferably 8 at% or less. Here, the Ha content refers to the total content of F, Cl, Br, and I.

[0037] Ha is at least one element selected from the group consisting of F, Cl, Br, and I. As described above, from the viewpoint of obtaining good oxidation resistance and water resistance, it is more preferable that at least one of Cl and Br is contained, and it is even more preferable that Br is contained. It is also more preferable that both Cl and Br are contained. For example, of the Ha content, the total content of Cl and Br preferably accounts for 50 at% or more, more preferably 70 at% or more, and may be 100 at%, i.e., it may consist only of Cl and Br. Furthermore, the atomic ratio of the content represented by 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.

[0038] The sulfide-based glass phase and the highly ion-conductive crystalline phase in this embodiment may contain elements other than the above-mentioned Li, P, S, and Ha as constituent elements. Examples of the other elements that may be contained include Si, B, Ge, Al, O, Na, K, Mg, Ca, Sr, Ba, Y, Zr, Cr, Zn, Ga, Sn, and Sb. However, if the other elements are SiO ２ Or B ２ O ３ , P ２ O ５ , Al ２ O ３ In the case of forming oxides such as those mentioned above, it is preferable that such oxides are not contained because they become crystal nuclei. The total content of oxides is preferably 1 mol% or less, more preferably 0.1 mol% or less, and even more preferably 0.05 mol% or less, expressed in mol% based on the oxides, and may be zero, i.e., not contained.

[0039] The sulfide-based glass phase and the highly ion-conductive crystalline phase in this embodiment may contain, among the other elements, Si, B, Ge, Al, Sn, and Sb, which are elements that can occupy the position of P when the sulfide-based glass phase is crystallized.

[0040] When the sulfide-based glass phase and the highly ion-conductive crystalline phase in this embodiment contain Si as a constituent element, Si has the effect of increasing the viscosity of the melt and promoting vitrification. The Si content is preferably 0 to 15 at%, more preferably 0.1 to 10 at%, and even more preferably 1 to 5 at%. Here, from the viewpoint of optimally obtaining the effect of Si, the Si content is preferably 0.1 at% or more, and more preferably 1 at% or more. Furthermore, from the viewpoint of electrochemical stability, the Si content is preferably 15 at% or less, more preferably 10 at% or less, and even more preferably 5 at% or less. However, if Si has a Si—O bond or SiO ２ When Si is contained as an oxide, the Si content is appropriately adjusted so that the total content of oxides is 1 mol % or less, or so that the total content of oxides that become network formers of glass is 3 to 20 mol %, as described above.

[0041] When the sulfide-based glass phase and the highly ion-conductive crystalline phase in this embodiment contain B as a constituent element, B has the effect of increasing the viscosity of the melt and promoting vitrification. The B content is preferably 0 to 15 at %, more preferably 0.1 to 10 at %, and even more preferably 1 to 5 at %. Here, from the viewpoint of optimally obtaining the effect of B, the B content is preferably 0.1 at % or more, and more preferably 1 at % or more. Furthermore, from the viewpoint of lithium ion conductivity, the B content is preferably 15 at % or less, more preferably 10 at % or less, and even more preferably 5 at % or less. However, if B has a B-O bond or B ２ O ３ When B is contained as an oxide, the B content is appropriately adjusted so that the total content of oxides is 1 mol % or less, or so that the total content of oxides that become network formers of the glass is 3 to 20 mol %, as described above.

[0042] When the sulfide-based glass phase and the high ion-conducting crystalline phase in this embodiment contain Ge as a constituent element, Ge has the effect of promoting an improvement in lithium ion conductivity. The Ge content is preferably 0 to 15 at %, more preferably 0.1 to 10 at %, and even more preferably 1 to 5 at %. Here, from the viewpoint of lithium ion conductivity, the Ge content is preferably 0.1 at % or more, and more preferably 1 at % or more. Furthermore, from the viewpoint of ease of glass formation, the Ge content is preferably 15 at % or less, more preferably 10 at % or less, and even more preferably 5 at % or less. However, if Ge has a Ge—O bond or is a GeO ２ When Ge is contained as an oxide, the Ge content is appropriately adjusted so that the total content of the oxides is 1 mol % or less, as described above.

[0043] When the sulfide-based glass phase and the high ion-conductive crystalline phase in this embodiment contain Al as a constituent element, Al has the effect of increasing the viscosity of the melt and promoting vitrification. The Al content is preferably 0 to 15 at %, more preferably 0.1 to 10 at %, and even more preferably 1 to 5 at %. Here, from the viewpoint of optimally obtaining the effect of Al, the Al content is preferably 0.1 at % or more, and more preferably 1 at % or more. Furthermore, from the viewpoint of lithium ion conductivity, the Al content is preferably 15 at % or less, more preferably 10 at % or less, and even more preferably 5 at % or less. However, if Al has an Al—O bond or Al ２ O ３ When Al is contained as an oxide, the Al content is appropriately adjusted so that the total content of oxides is 1 mol % or less, or so that the total content of oxides that become network formers of glass is 3 to 20 mol %, as described above.

[0044] When the sulfide-based glass phase and the highly ion-conductive crystalline phase in this embodiment contain Sn as a constituent element, Sn has the effect of increasing the viscosity of the melt and promoting vitrification. The Sn content is preferably 0 to 15 at%, more preferably 0.1 to 10 at%, and even more preferably 1 to 5 at%. Here, from the viewpoint of optimally obtaining the effects of Sn, the Sn content is preferably 0.1 at% or more, and more preferably 1 at% or more. Furthermore, from the viewpoint of achieving high lithium ion conductivity, the Sn content is preferably 15 at% or less, more preferably 10 at% or less, and even more preferably 5 at% or less. However, if Sn has an Sn—O bond or SnO ２ When Sn is contained as an oxide, the Sn content is appropriately adjusted so that the total content of the oxides is 1 mol % or less, as described above.

[0045] When the sulfide-based glass phase and the highly ion-conductive crystalline phase in this embodiment contain Sb as a constituent element, Sb has the effect of increasing the viscosity of the melt and promoting vitrification. The Sb content is preferably 0 to 15 at %, more preferably 0.1 to 10 at %, and even more preferably 1 to 5 at %. Here, from the viewpoint of optimally obtaining the effects of Sb, the Sb content is preferably 0.1 at % or more, and more preferably 1 at % or more. Furthermore, from the viewpoint of lithium ion conductivity, the Sb content is preferably 15 at % or less, more preferably 10 at % or less, and even more preferably 5 at % or less. However, if Sb has an Sb—O bond or Sb ２ O ３ When Sb is contained as an oxide, the Sb content is appropriately adjusted so that the total content of oxides is 1 mol % or less, or so that the total content of oxides that become network formers of glass is 3 to 20 mol %, as described above.

[0046] In the compositions of the sulfide-based glass phase and the high ion-conductive crystalline phase in this embodiment, the composition ratio represented by Li / P is preferably 2.5 or more, more preferably 2.5 to 7.0, even more preferably 3.0 to 6.5, and even more preferably 3.2 to 6.2. From the viewpoint of obtaining high lithium ion conductivity, the composition ratio is preferably 2.5 or more, more preferably 3.0 or more, and even more preferably 3.2 or more. Furthermore, from the viewpoint of widening the vitrification range, the composition ratio is preferably 7.0 or less, more preferably 6.5 or less, and even more preferably 6.2 or less. In this specification, the composition ratio refers to the ratio of the content (at %) of each element in the sulfide-based glass phase and the high ion-conductive crystalline phase.

[0047] In the compositions of the sulfide-based glass phase and the highly ion-conductive crystalline phase in this embodiment, the composition ratio represented by S / P is preferably 3.0 to 5.0, more preferably 3.5 to 4.5, and even more preferably 3.8 to 4.2. From the viewpoint of lithium ion conductivity, the composition ratio is preferably 3.0 or more, more preferably 3.5 or more, and even more preferably 3.8 or more. From the viewpoint of water resistance, the composition ratio is preferably 5.0 or less, more preferably 4.5 or less, and even more preferably 4.2 or less.

[0048] In the compositions of the sulfide-based glass phase and the high ion-conductive crystalline phase, the composition ratio represented by [(F + Cl + Br) / Ha] is preferably 0.5 or more, more preferably 0.5 to 1.0, even more preferably 0.6 to 1.0, and particularly preferably 0.8 to 1.0. From the viewpoint of oxidation resistance, the composition ratio is preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.8 or more. The upper limit of the composition ratio is not particularly limited, and may be 1.0. The composition ratio of 1.0 means that I is not contained as Ha. When the sulfide-based glass phase and the high ion-conductive crystalline phase contain I as Ha, from the viewpoint of obtaining the effect of I, the composition ratio may be 0.8 or less, or even 0.6 or less.

[0049] In the compositions of the sulfide-based glass phase and the high ion-conducting crystalline phase, the composition ratio represented by 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. From the viewpoint of water resistance, the composition ratio is preferably 0.01 or more, more preferably 0.1 or more, and even more preferably 0.2 or more. Furthermore, from the viewpoint of lithium halide crystal precipitation, the composition ratio is preferably 1.5 or less, more preferably 1.2 or less, and even more preferably 1.0 or less. Here, Ha refers to the sum of F, Cl, Br, and I.

[0050] The constituent elements and their respective contents in the sulfide-based glass phase and the highly ion-conductive crystalline phase are determined by comparing the results of measuring the constituent elements and their respective contents (composition ratios) in the entire sulfide solid electrolyte with the element ratios constituting the crystal structure determined from the XRD pattern. The methods for determining the constituent elements and their respective contents in the entire sulfide solid electrolyte vary depending on the element. For example, P and S can be determined by ICP atomic emission spectroscopy, Li by atomic absorption spectroscopy, and Ha by ion chromatography. Details of each analysis are described in the Examples section below.

[0051] The sulfide-based glass phase in this embodiment is partially crystallized by heat treatment to become the highly ion-conductive crystalline phase in this embodiment. This highly ion-conductive crystalline phase can have a thio-lisicon or LGPS crystalline structure. The highly ion-conductive crystalline phases of the thio-lisicon and LGPS types have high lithium ion conductivity and are useful as solid electrolytes.

[0052] The total proportion of the sulfide-based glass phase and the high ion-conductive crystalline phase in the sulfide solid electrolyte according to this embodiment is preferably 50 to 100% by mass, more preferably 70 to 95% by mass, and even more preferably 80 to 90% by mass. From the viewpoint of lithium ion conductivity, the total proportion is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. The total proportion may be 100% by mass, i.e., the sulfide-based glass phase and the high ion-conductive crystalline phase alone. On the other hand, when obtaining the sulfide-based glass phase, both crystalline phases may be obtained, and obtaining only the sulfide-based glass phase and the high ion-conductive crystalline phase requires time and cost. Therefore, from the viewpoint of the manufacturability of the sulfide solid electrolyte, the total proportion is more preferably 95% by mass or less, and even more preferably 90% by mass or less. The proportions of the sulfide-based glass phase and the highly ion-conductive crystalline phase are determined by powdering the sulfide solid electrolyte, performing powder X-ray diffraction (XRD) measurement together with a crystalline powder serving as an internal standard, and then performing Rietveld analysis. The proportion of the sulfide-based glass phase is determined by subtracting the proportion of the crystalline phase from 100% by mass.

[0053] The content of the high ion-conducting crystalline phase in the sulfide solid electrolyte according to 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 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 optimally obtaining the effects of the sulfide-based glass phase, the content is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less.

[0054] The sulfide solid electrolyte according to this embodiment preferably contains a sulfide-based glass phase in an amount of 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 the softness of the glass phase that facilitates the formation of an interface between the active material and the solid electrolyte, the 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 optimally obtaining the effects of the highly ion-conductive crystalline phase, the content is preferably 70% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0055] <Other Phases> The sulfide solid electrolyte according to this embodiment may contain phases other than the sulfide-based glass phase and the highly ion-conductive crystalline phase. Examples of other phases include crystalline phases obtained during the production of the sulfide-based glass phase. The proportion of such other 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. From the viewpoint of fully utilizing the properties of the sulfide-based glass phase and the highly ion-conductive crystalline phase, the total proportion of the other phases is 40% by mass or less, preferably 35% by mass or less, and even more preferably 30% by mass or less. Furthermore, while the other phases may not be present, from the viewpoint of the manufacturability of the sulfide solid electrolyte, the total proportion of the other phases is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 5% by mass or more.

[0056] <Physical Properties of Sulfide Solid Electrolyte> The sulfide solid electrolyte according to this embodiment preferably has a lithium ion conductivity of 2.5 mS / cm or more at 25°C when compacted under 380 MPa. This is due to the high lithium ion conductivity of the sulfide-based glass phase and the high ion-conductive crystalline phase derived therefrom. However, since it is difficult to extract only the sulfide-based glass phase or the high ion-conductive crystalline phase from the sulfide solid electrolyte, the lithium ion conductivity of the sulfide-based glass phase or the high ion-conductive crystalline phase is evaluated based on the lithium ion conductivity of the sulfide solid electrolyte.

[0057] The lithium ion conductivity of the sulfide solid electrolyte according to this embodiment is preferably 2.5 mS / cm or more, and the higher the better. However, this value varies depending on the composition and the proportion of the sulfide glass phase and the highly ion-conductive crystalline phase. For example, when the Br content of the Ha composition is 90 at% or more, the lithium ion conductivity is preferably 3.0 mS / cm or more. Furthermore, when the Cl content of the Ha composition is 90 at% or more, the lithium ion conductivity is preferably 2.5 mS / cm or more. Note that the lithium ion conductivity in this specification is determined by AC impedance measurement using a measurement sample obtained by compacting a sulfide solid electrolyte powder at 380 MPa. Specifically, AC impedance measurement of the measurement sample is performed at a measurement frequency of 100 Hz to 1 MHz, a measurement voltage of 100 mV, and a measurement temperature of 25°C, and the value obtained from the resulting Nyquist plot is taken as the lithium ion conductivity.

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

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

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

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

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

[0063] <Lithium Ion Conductive Crystal> The lithium ion conductive crystal according to this embodiment contains Li, P, S, and Ha as constituent elements, where Ha is at least one element selected from the group consisting of F, Cl, Br, and I.

[0064] The lithium ion conductive crystalline material according to this embodiment has diffraction peaks at least at 2θ=12.4±0.5°, 14.4±0.5°, 20.2±0.5°, 23.8±0.5°, 29.7±0.5°, and 31.4±0.5° in an XRD pattern obtained by powder X-ray diffraction measurement. The peak intensity of the diffraction peak at 2θ=20.2±0.5° is expressed as I Ａ The peak intensity of the diffraction peak at 2θ = 29.7 ± 0.5° is defined as I Ｂ When I Ａ / I Ｂ The peak intensity ratio represented by is greater than 1.0.

[0065] The lithium ion conductive crystalline material according to this embodiment is one aspect of the crystals constituting the high ion conductive crystalline phase in the sulfide solid electrolyte. Specifically, among the crystals constituting the high ion conductive crystalline phase, those containing Ha as a constituent element are included. Furthermore, among the crystals constituting the high ion conductive crystalline phase, those having diffraction peaks at 2θ = 12.4 ± 0.5 °, 14.4 ± 0.5 °, and 31.4 ± 0.5 ° in the XRD pattern obtained by powder X-ray diffraction measurement, in addition to 2θ = 20.2 ± 0.5 °, 23.8 ± 0.5 °, and 29.7 ± 0.5 °.

[0066] The lithium ion conductive crystalline material according to this embodiment has a peak intensity of a diffraction peak at 2θ=20.2±0.5° of I Ａ The peak intensity of the diffraction peak at 2θ=29.7±0.5° is defined as I Ｂ When I Ａ / I ＢThe peak intensity ratio expressed by the formula (2θ) is greater than 1.0, and therefore it can be said to be at least a novel crystal. The half width of the diffraction peak at 2θ=20.2±0.5° is preferably 0.01 to 0.4°.

[0067] Other preferred aspects of the lithium ion conductive crystalline material according to this embodiment are the same as the preferred aspects of the highly ion conductive crystalline phase in the above-mentioned <<Sulfide Solid Electrolyte>>.

[0068] The lithium ion conductive crystalline material according to this embodiment has high lithium ion conductivity and is therefore suitable as a sulfide solid electrolyte. In this case, any sulfide solid electrolyte containing the lithium ion conductive crystalline material may be used. For example, the sulfide solid electrolyte may contain a pre-crystallization glass that serves as a precursor to the lithium ion conductive crystalline material and the lithium ion conductive crystalline material, a sulfide solid electrolyte containing the lithium ion conductive crystalline material without the pre-crystallization glass, or a sulfide electrolyte consisting solely of the lithium ion conductive crystalline material.

[0069] <<Method for Producing Sulfide Solid Electrolyte>> The method for producing a sulfide solid electrolyte according to this embodiment includes the following steps 1 to 4 in order as steps S1 to S4, as shown in FIG. 1 : Step S1: Mixing raw materials to obtain a raw material mixture containing Li, P, and S; Step S2: Heating the raw material mixture obtained in step 1 to obtain a melt; Step S3: Cooling and solidifying the melt obtained in step 2 to obtain a glass phase; Step S4: Heating the glass phase obtained in step 3 to obtain a highly ion-conductive crystalline phase in which a portion of the glass phase is crystallized;

[0070] The heating in step 2 and the cooling and solidification in step 3 are carried out under atmospheric pressure conditions, and the cooling rate during the cooling and solidification is 100°C / sec or higher. In addition to the above, the heating for crystallization in step 4 is carried out for 1 minute or longer at a temperature (crystallization temperature -15°C) or higher than the crystallization temperature of the glass phase obtained in step 3. This results in a sulfide solid electrolyte containing a glass phase and a highly ion-conductive crystalline phase derived therefrom. In this specification, "under atmospheric pressure conditions" means a pressure range of approximately (gauge pressure ±15 kPa).

[0071] Furthermore, in the above step 1, the sulfide solid electrolyte described in the above section <<Sulfide Solid Electrolyte>> can be obtained by mixing the raw materials so that the raw material mixture further contains Ha. Here, Ha is at least one element selected from the group consisting of F, Cl, Br, and I.

[0072] Each step will be explained below.

[0073] <Step 1> In this embodiment, step S1 is step 1 in which raw materials are mixed to obtain a raw material mixture containing Li, P, and S. Specifically, a raw material containing Li, a raw material containing P, and a raw material containing S are mixed to obtain a raw material mixture. Furthermore, when it is desired to obtain a glass phase further containing Ha as a constituent element, a raw material containing Ha is further mixed in addition to the raw material containing Li, the raw material containing P, and the raw material containing S to obtain a raw material mixture containing Li, P, S, and Ha. Here, the Ha element refers to at least one element selected from the group consisting of F, Cl, Br, and I.

[0074] Examples of raw materials containing Li include lithium sulfide (Li ２ S), lithium carbonate (Li ２ CO ３ ), lithium sulfate (Li ２ SO ４ ), lithium oxide (Li ２ Examples of the substance containing Li include lithium compounds such as lithium ion (LiO), lithium hydroxide (LiOH), and metallic lithium. The substance containing Li may be used alone or in combination of two or more.

[0075] From the viewpoint of obtaining a sulfide-based glass phase, it is preferable to use lithium sulfide as the raw material containing Li. Furthermore, when the obtained sulfide solid electrolyte contains a halogen element, lithium halide (LiHa, where Ha is a halogen element) is also preferable as the raw material containing Li. Lithium halide will be described later.

[0076] Examples of raw materials containing the P element include diphosphorus pentasulfide (P ２ S ５ ), diphosphorus trisulfide (P ２ S３ ) and other phosphorus sulfides, sodium phosphate (Na ３ P.O. ４ The phosphorus-containing substance may be used singly or in combination of two or more.

[0077] The raw material containing the P element is preferably phosphorus sulfide, and more preferably diphosphorus pentasulfide (P), from the viewpoint of preventing the inclusion of elements other than those constituting the target sulfide solid electrolyte. ２ S ５ ) is more preferred.

[0078] Examples of raw materials containing the S element include lithium sulfide (Li ２ S), diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ), other sulfur compounds containing phosphorus, and compounds containing sulfur. ２ S, CS ２ , iron sulfide (FeS, Fe ２ S ３ , FeS ２ , Fe １－ｘ S, etc.), bismuth sulfide (Bi ２ S ３ ), copper sulfide (CuS, Cu ２ S, Cu １－ｘ The substance containing the S element may be used alone or in combination of two or more.

[0079] The raw material containing the S element is preferably lithium sulfide or phosphorus sulfide from the viewpoint of preventing the inclusion of elements other than those constituting the target sulfide solid electrolyte. As the phosphorus sulfide, diphosphorus pentasulfide (P ２ S ５ Lithium sulfide is a compound that serves as both a raw material containing Li and a raw material containing S, and phosphorus sulfide is a compound that serves as both a raw material containing S and a raw material containing P.

[0080] Examples of raw materials containing Ha element include lithium halides such as lithium fluoride (LiF), lithium chloride (LiCl), lithium bromide (LiBr), and lithium iodide (LiI), phosphorus halides, phosphoryl halides, sulfur halides, sodium halides, and boron halides. One or more substances containing Ha element may be used, or two or more may be used in combination.

[0081] From the viewpoint of reactivity, the raw material containing the Ha element is preferably a lithium halide, more preferably LiCl, LiBr, or LiI, and even more preferably LiCl or LiBr.

[0082] A raw material mixture may be obtained by further mixing raw materials containing other elements according to the desired composition of the sulfide solid electrolyte. As described above, examples of the other elements include Si, B, Ge, Al, O, Na, K, Mg, Ca, Sr, Ba, Y, Zr, Cr, Zn, Ga, Sn, and Sb. Among the other elements, for example, Si, B, Ge, Al, Sn, and Sb may be included. These Si, B, Ge, Al, Sn, and Sb are elements that can occupy the P position when the sulfide-based glass phase is crystallized.

[0083] As raw materials containing these other elements, conventionally known raw materials can be used. For example, as a raw material containing Si element, SiO ２ , SiS ２ Among them, from the viewpoint of lithium ion conductivity, SiO ２ These compounds may be used alone or in combination of two or more. Examples of raw materials containing B element include B ２ O ３ , B ２ S ３ Among them, from the viewpoint of water resistance of glass, B ２ O ３ These compounds may be used alone or in combination of two or more. The raw material containing Ge element is GeO ２ , GeS, GeS ２ , GeCl ２Among them, from the viewpoint of lithium ion conductivity, GeS ２ , GeCl ２ is preferred, and GeS ２ These compounds may be used alone or in combination of two or more. Examples of raw materials containing Al element include Al ２ S ３ , Al ２ O ３ , AlCl ３ Among them, Al is the most suitable from the viewpoint of lithium ion conductivity and water resistance. ２ S ３ , AlCl ３ is preferred, and Al ２ S ３ These compounds may be used alone or in combination of two or more. Examples of raw materials containing Sn include SnS, SnS ２ , SnO, SnO ２ , SnCl ２ Among them, from the viewpoint of lithium ion conductivity, SnS ２ , SnCl ２ is preferred, and SnS ２ These compounds may be used alone or in combination of two or more. Examples of raw materials containing Sb include Sb ２ S ３ , Sb ２ O ３ , Sb ２ O ５ , SbCl ３ , SbCl ５ Among them, from the viewpoint of lithium ion conductivity and water resistance, Sb ２ S ３ , SbCl ３ is preferred, and Sb ２ S ３ These compounds may be used alone or in combination of two or more.

[0084] These raw materials are blended appropriately according to the composition of the sulfide-based glass phase and the resulting high ion-conductive crystalline phase. Specifically, to obtain the sulfide solid electrolyte described above in "Sulfide Solid Electrolyte," the raw materials are mixed so that the raw material mixture further contains Ha. Furthermore, it is preferable to blend the raw materials so that the resulting glass phase and the resulting high ion-conductive crystalline phase have a composition of Li: 30-50 at%; P: 5-15 at%; and S: 30-60 at%. It is even more preferable to blend the raw materials so that, in addition to the above composition, Ha: 1-12 at% is further blended. The blending of the raw materials also determines the crystal structure of the resulting high ion-conductive crystalline phase.

[0085] In addition to the above, preferred embodiments of the resulting glass phase and the highly ion-conductive crystalline phase derived therefrom are the same as preferred embodiments of the "sulfide-based glass phase and the highly ion-conductive crystalline phase" in the "sulfide solid electrolyte" above.

[0086] It is preferable that the particle size of each raw material be small from the viewpoint of shortening the holding time during heating and melting in the subsequent step 2. Furthermore, if the particle size of the raw material is too large, it may affect the homogeneity of the glass phase or sulfide solid electrolyte, and from this viewpoint as well, it is preferable that the particle size of the raw material be small to a certain extent. However, the production method according to this embodiment has excellent composition controllability. Therefore, even if raw materials with particle sizes that may reduce homogeneity in conventional production methods are used, the production method according to this embodiment can produce a more homogeneous glass phase or sulfide solid electrolyte.

[0087] From the above viewpoint, specifically, the particle size of each raw material is preferably 1 mm or less, more preferably 500 μm or less, even more preferably 250 μm or less, even more preferably 100 μm or less, and particularly preferably 50 μm or less. Smaller particle sizes are preferable, but a practical lower limit is about 0.1 μm, and the particle size may be 1 μm or more, or may be 5 μm or more. Furthermore, as described above, according to the manufacturing method of this embodiment, a homogeneous glass phase or sulfide solid electrolyte is easily obtained even when raw materials with relatively large particle sizes are used. In consideration of this, for example, from the viewpoint of reducing manufacturing costs, the particle size of each raw material may be 10 μm or more, 100 μm or more, or 250 μm or more.

[0088] From these, the particle size of each raw material is preferably 0.1 μm to 1 mm, more preferably 1 to 500 μm, even more preferably 5 to 250 μm, even more preferably 5 to 100 μm, and particularly preferably 5 to 50 μm. Furthermore, from the viewpoint of production costs, the particle size of each raw material is preferably 10 μm to 1 mm, more preferably 100 μm to 1 mm, and even more preferably 250 to 500 μm. In this specification, the particle size of each raw material refers to the average particle size (D50) expressed as the median diameter obtained from a volume-based particle size distribution chart obtained by measuring the particle size distribution using a laser diffraction particle size distribution analyzer MT3300EXII manufactured by Microtrac.

[0089] The raw materials can be mixed, for example, by mixing in a mortar, mixing using media such as a planetary ball mill, or medialess mixing such as a pin mill, a powder mixer, or airflow mixing. The raw materials may be made amorphous by mixing before heating.

[0090] <Step 2> Step S2 in this embodiment is step 2 in which the raw material mixture obtained in step 1 is heated to obtain a melt.

[0091] The specific method for heating and melting the raw material mixture is not particularly limited, as long as the heating is performed under atmospheric pressure. In the production method according to this embodiment, the heating for melting the raw material mixture is performed under atmospheric pressure, thereby reducing the compositional difference between the composition of the raw material mixture and the composition of the resulting sulfide-based glass phase and the highly ion-conductive crystalline phase derived therefrom, or the composition of the sulfide solid electrolyte. Furthermore, by performing the heating under a gas atmosphere containing the element S, the compositional difference can be further suppressed. Note that in the production method according to this embodiment, the heating and melting are performed in an atmosphere-controlled environment under atmospheric pressure, and do not need to be performed in a sealed tube. However, this does not in any way exclude the use of a sealed tube.

[0092] Here, the difference between the sealed tube environment and the controlled atmosphere environment under normal pressure conditions is that in the sealed tube environment, the pressure inside the container is a vacuum, i.e., less than (gauge pressure -15 kPa), whereas in the controlled atmosphere environment under normal pressure conditions, the pressure inside the container during heating and melting is within the range of (gauge pressure ±15 kPa).

[0093] That is, in the manufacturing method according to the present embodiment, the heating and melting in step 2 is performed under normal pressure conditions (gauge pressure ±15 kPa). At this time, the composition ratio of the resulting glass phase or highly ion-conductive crystalline phase expressed as [P / Li] relative to the composition ratio of the raw material mixture expressed as [P / Li] is preferably 95 to 105%, for example.

[0094] The pressure during the heat melting may be normal pressure (gauge pressure ±15 kPa), preferably (gauge pressure ±10 kPa), more preferably (gauge pressure ±5 kPa), and even more preferably (gauge pressure ±2 kPa). Furthermore, the composition ratio of the resulting glass phase or highly ion-conductive crystalline phase expressed as [P / Li] relative to the composition ratio expressed as [P / Li] of the raw material mixture is preferably 95 to 105%, more preferably 97 to 103%, even more preferably 99 to 101%, with the closer to 100% being more preferable. Here, the composition ratio is preferably 95% or more, more preferably 97% or more, even more preferably 99% or more, and is preferably 105% or less, more preferably 103% or less, and even more preferably 101% or less.

[0095] With respect to the composition ratio [P / Li] of the raw material mixture relative to the composition ratio [P / Li] of the resulting glass phase or highly ion-conductive crystalline phase, Li is an element that is difficult to volatilize, and P is an element that is easily volatilized. Therefore, comparing the composition ratio [P / Li] of the raw material mixture with that of the glass phase or highly ion-conductive crystalline phase is appropriate as an index of the compositional deviation between the composition of the raw material mixture and the composition of the resulting sulfide-based glass phase or highly ion-conductive crystalline phase or the composition of the sulfide solid electrolyte.

[0096] Examples of heat-resistant containers for containing the raw material mixture include heat-resistant containers made of carbon, heat-resistant containers containing oxides such as quartz, quartz glass, borosilicate glass, aluminosilicate glass, alumina, zirconia, and mullite, heat-resistant containers containing nitrides such as silicon nitride and boron nitride, and heat-resistant containers containing carbides such as silicon carbide. These heat-resistant containers may be formed in bulk from the above-mentioned materials, or may be containers on which a layer of carbon, oxide, nitride, carbide, or the like is formed, such as a carbon-coated quartz tube.

[0097] The melting temperature when the raw material mixture is heated varies depending on the raw materials used and the composition of the raw material mixture, but is, for example, preferably 600 to 950°C, more preferably 630 to 850°C, and even more preferably 650 to 750°C. Here, from the viewpoint of reaction rate, the melting temperature is preferably 600°C or higher, more preferably 630°C or higher, and even more preferably 650°C or higher. Furthermore, from the viewpoint of suppressing composition deviation due to volatilization of components, the melting temperature is preferably 950°C or lower, more preferably 850°C or lower, and even more preferably 750°C or lower.

[0098] The heat-melting time varies depending on the scale, but is preferably 10 minutes to 10 hours, more preferably 30 minutes to 9.5 hours, even more preferably 45 minutes to 9 hours, and particularly preferably 1 to 9 hours. From the viewpoint of smoothly progressing the reaction, the heat-melting time is preferably 10 minutes or more, more preferably 30 minutes or more, even more preferably 45 minutes or more, and particularly preferably 1 hour or more. From the viewpoint of productivity, the heat-melting time is preferably 10 hours or less, more preferably 9.5 hours or less, and even more preferably 9 hours or less.

[0099] The atmosphere in the container during heat melting is not particularly limited. For example, it may be a nitrogen atmosphere, an argon atmosphere, or a gas atmosphere containing an S element. Among these, a gas atmosphere containing an S element is preferred from the viewpoint of more suitably suppressing composition deviation.

[0100] When the gas atmosphere contains S element, examples of the S element source include sulfur gas, hydrogen sulfide gas, sulfur dioxide gas, etc., and sulfur gas is preferred from the viewpoint of reactivity with the raw materials. Alternatively, the gas containing S element may be introduced by adding elemental sulfur powder and vaporizing the elemental sulfur powder by heating during melting. The elemental sulfur powder may be added together with the raw materials when mixing the raw materials to obtain a raw material mixture, or may be added separately after obtaining the raw material mixture. However, when the elemental sulfur powder is added together with the raw materials when obtaining the raw material mixture, the mass of the obtained raw material mixture does not include the mass of the elemental sulfur powder. The gas containing S element may be introduced by adding the above-mentioned sulfur gas, hydrogen sulfide gas, sulfur dioxide gas, etc., and the gas containing S element resulting from the addition of elemental sulfur powder.

[0101] The gas containing S element is preferably used as a mixed gas with, for example, an inert gas, which is the S element source gas. The mixing ratio with the inert gas is arbitrary and is not particularly limited as long as the cumulative amount of S element introduced relative to the mass of the raw material mixture can be set to a desired value.

[0102] Examples of the inert gas include nitrogen gas, argon gas, and helium gas, and these may be used alone or in combination of two or more.

[0103] The dew point during heat melting is preferably −20° C. or lower, and although there is no particular lower limit, it is usually about −80° C. The oxygen concentration is preferably 1000 ppm by volume or lower.

[0104] In step 2, whether the molten mixture of raw materials is completely dissolved can be confirmed by the absence of peaks derived from crystals in high-temperature X-ray diffraction measurement. It can also be confirmed by heating the molten mixture at a predetermined temperature and tilting the molten mixture to check whether it has fluidity.

[0105] <Step 3> Step S3 in this embodiment is step 3 in which the melt obtained in step 2 is cooled and solidified to obtain a glass phase.

[0106] Cooling and solidification are carried out under atmospheric pressure. As mentioned above, "under atmospheric pressure" means an atmosphere under a pressure of about (gauge pressure ±15 kPa). The pressure during cooling and solidification may be under atmospheric pressure conditions of (gauge pressure ±15 kPa), preferably (gauge pressure ±10 kPa), more preferably (gauge pressure ±5 kPa), and even more preferably (gauge pressure ±2 kPa).

[0107] The cooling rate during solidification is 100°C / sec or higher, preferably 100 to 100,000°C / sec, more preferably 500 to 50,000°C / sec, and even more preferably 1,000 to 10,000°C / sec. Here, by using an ultra-rapid cooling rate of 100°C / sec or higher, which is faster than conventional methods, the proportion of a sulfide-based glass phase containing Li, P, and S as constituent elements can be increased to, for example, 60 mass% or more. This sulfide-based glass phase can achieve higher lithium ion conductivity than conventional sulfide-based glasses, thereby also increasing the lithium ion conductivity of the sulfide solid electrolyte. Furthermore, by performing the cooling and solidification under atmospheric pressure conditions, the compositional deviation between the composition of the raw material mixture and the composition of the resulting glass phase and the highly ion-conductive crystalline phase derived therefrom, or the composition of the sulfide solid electrolyte, can be reduced.

[0108] The cooling rate is 100°C / sec or more, but from the viewpoint of ease of glass formation, it is preferably 500°C / sec or more, more preferably 1000°C / sec or more. Furthermore, the upper limit of the cooling rate is not particularly limited, but from the viewpoint of equipment capacity, it is preferably 100,000°C / sec or less, more preferably 50,000°C / sec or less, and even more preferably 10,000°C / sec or less. The above-mentioned ultra-rapid cooling can be achieved, for example, by using a rapid-cooling twin roll.

[0109] This sulfide-based glass phase can achieve higher lithium ion conductivity than conventional sulfide-based glasses. Furthermore, by performing the cooling and solidification under atmospheric pressure, the compositional difference between the raw material mixture and the resulting sulfide-based glass phase and the resulting highly ion-conductive crystalline phase or sulfide solid electrolyte can be reduced.

[0110] <Step 4> Step S4 according to this embodiment is step 4 in which the glass phase obtained in step 3 is heated to obtain a highly ion-conductive crystalline phase in which part of the glass phase is crystallized.

[0111] The heating temperature in step 4, i.e., the temperature at which crystallization to obtain a high ion-conductive crystalline phase occurs, can be determined based on the crystallization temperature at which the glass phase changes to a high ion-conductive crystalline phase. Specifically, from the viewpoint of effectively promoting the crystallization, a temperature of (crystallization temperature - 15°C) or higher is preferred, and may be (crystallization temperature - 10°C) or higher, or may be a temperature higher than the crystallization temperature, or may be (crystallization temperature + 1°C) or higher. It has also been found that heating at high temperatures precipitates crystals with low ion conductivity, next to the high ion-conductive crystalline phase. Therefore, from the viewpoint of preventing the precipitation of crystals with low ion conductivity, the crystallization temperature is preferably lower than the temperature at which crystals with low ion conductivity precipitate, more preferably lower than (crystallization temperature + 20°C), and even more preferably lower than (crystallization temperature + 15°C). That is, the crystallization temperature is preferably higher than (crystallization temperature - 15°C), and more preferably higher than (crystallization temperature - 15°C) and lower than the temperature at which crystals with low ion conductivity precipitate. Alternatively, the temperature may be (crystallization temperature - 10°C) or more and (crystallization temperature + 20°C) or less, or may be (crystallization temperature + 20°C) or more and (crystallization temperature + 1°C) or more and (crystallization temperature + 15°C) or less.

[0112] The crystallization temperature in this specification refers to the peak top temperature of the exothermic peak observed when differential scanning calorimetry (DSC) is performed on the sulfide-based glass phase, which can be said to be a precursor of the sulfide solid electrolyte obtained in step 3, and the temperature is increased at a heating rate of 5°C / min.

[0113] The heating time during crystallization is, for example, 1 minute or more, preferably 1 minute to 6 hours, more preferably 1 minute to 3 hours, even more preferably 5 minutes to 2 hours, and even more preferably 10 minutes to 100 minutes. From the viewpoint of stable quality, the heating time is preferably 1 minute or more, more preferably 5 minutes or more, and even more preferably 10 minutes or more. From the viewpoint of productivity, the heating time is preferably 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. The content ratio of the high ion-conducting crystalline phase can be adjusted by adjusting the heating temperature and heating time during crystallization.

[0114] The heating atmosphere during crystallization may be a nitrogen atmosphere, an argon atmosphere, a dry air atmosphere, etc. Among these, a nitrogen atmosphere or an argon atmosphere is preferred from the viewpoint of not impairing ionic conductivity.

[0115] The dew point during crystallization is preferably −30° C. or lower. The oxygen concentration during crystallization may be a dry air environment, but from the viewpoint of safety, it is preferably 5% by volume or lower.

[0116] After heating, the sulfide solid electrolyte according to this embodiment can be obtained by cooling to room temperature at a rate of, for example, 1 to 10,000° C. / min.

[0117] The sulfide solid electrolyte obtained above may be used as it is for at least one selected from the group consisting of a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, or may be used after being subjected to pulverization, drying, or the like depending on the application.

[0118] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. Examples 1 to 4 are working examples, and Examples 5 to 7 are comparative examples.

[0119] <Test Examples> <Example 1: Melt-quenching method> Li was melted under a dry nitrogen gas atmosphere. ３．４ P １．０ S ４．０ Br ０．３４Lithium sulfide powder (Sigma, purity 99.98%), diphosphorus pentasulfide powder (Sigma, purity 99%), and lithium bromide powder (Sigma, purity 99.995%) were weighed and mixed in a mortar to obtain a raw material mixture (Step 1). The obtained raw material mixture was placed in a carbon container under a nitrogen atmosphere containing sulfur powder (Sigma, purity 99.998%) as an S element source and a dew point of −50° C. or less, and then placed in an electric furnace inside a glove box. The pressure was increased to +1 kPa and the temperature was increased to 750° C. for 1 hour to obtain a completely dissolved molten material (Step 2). Next, the tip of the container was heated to melt the melt, and the molten material was poured onto a twin roll and cooled to room temperature at a cooling rate of 3000°C / s to obtain a glass phase (step 3). The pressure at this time was (gauge pressure + 1 kPa), and the cooling rate was adjusted by the outflow rate of the melt, the roll gap of the twin rolls, and the rotation speed. The glass phase obtained above was heated in a nitrogen atmosphere at 210°C for 10 minutes to crystallize a portion of the glass phase (step 4), and then 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-conductive crystalline phase. DSC measurement of the glass phase obtained above was performed at a heating rate of 5°C / min, and the temperature at the top of the exothermic peak, i.e., the crystallization temperature, was confirmed to be 223°C.

[0120] Examples 2 and 3: Melt-quenching method A sulfide solid electrolyte containing a glass phase and a highly ion-conductive crystalline phase was obtained in the same manner as in Example 1, except that the cooling rate in step 3 was 8,000°C / sec (Example 2) or 10,000°C / sec (Example 3). The crystallization temperature of the glass phase obtained in step 3 was confirmed to be 217°C (Example 2) or 215°C (Example 3).

[0121] Example 4: Melt quenching method: Composition ratio is Li ３．４ P １．０ S ４．０ Cl ０．１ Br ０．２A sulfide solid electrolyte containing a glass phase and a highly ion-conductive crystalline phase was obtained in the same manner as in Example 1, except that lithium sulfide powder (manufactured by Sigma, purity 99.98%), diphosphorus pentasulfide powder (manufactured by Sigma, purity 99%), lithium bromide powder (manufactured by Sigma, purity 99.995%), and lithium chloride powder (manufactured by Sigma, purity 99.995%) were weighed to obtain a raw material mixture so as to have a composition ratio of (Li: 39.1 at%, P: 11.5 at%, S: 46.0 at%, Cl: 1.1 at%, Br: 2.3 at%). The crystallization temperature of the glass phase obtained in step 3 was confirmed to be 219°C.

[0122] Example 5: Mechanical Milling Method Step 1 was performed in the same manner as in Example 1 to obtain a raw material mixture. The resulting raw material mixture was then further mixed using a planetary ball mill (Fritsch, P-7) to obtain a glass phase (Steps 2'+3'). Mixing using the planetary ball mill involved mechanical milling for 20 hours at 400 rpm under a nitrogen atmosphere using zirconia balls with a particle size of 4 mm and a zirconia pot. The dew point during operation was maintained at -70°C or below. The resulting glass phase was heated in a nitrogen atmosphere at 210°C for 10 minutes to crystallize a portion of the glass phase (Step 4), followed by cooling 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-conductive crystalline phase. The crystallization temperature of the glass phase was 207°C.

[0123] Example 6: Mechanical Milling Method A raw material mixture was obtained by carrying out step 1 in the same manner as in Example 4. Then, steps 2'+3' and 4 were carried out in the same manner as in Example 5 to obtain a sulfide solid electrolyte containing a glass phase and a highly ion-conductive crystalline phase. The crystallization temperature of the glass phase was 210°C.

[0124] Example 7: Melt-Quenching Method A sulfide solid electrolyte was obtained in the same manner as in Example 1, except that the cooling rate in step 3 was 50°C / second. In step 3, a crystalline phase of impurities was obtained, and the desired glass phase was not obtained, so the crystallization temperature of the glass phase could not be measured. Therefore, even when heating was performed at 210°C for 10 minutes in the subsequent step 4, a sulfide solid electrolyte containing a glass phase and a highly ion-conductive crystalline phase was not obtained.

[0125] <Evaluation: Glass Phase> In each example, the sulfide solid electrolyte consisting of the glass phase or the crystalline phase of impurities obtained in step 3 or step 2'+3' was weighed in a glove box and dissolved in an alkaline aqueous solution, and composition analysis was performed for each element. Specifically, P and S were analyzed by ICP atomic emission spectroscopy (apparatus: Hitachi High-Tech Science Corporation, model number PS3520UVDDII). Li was analyzed by atomic absorption spectroscopy (apparatus: Hitachi High-Tech Corporation, model number ZA3300; when measuring Li, CsCl was added so that the solution concentration became 0.1%). Br and Cl were analyzed by ion chromatography (apparatus: Thermo Fisher Scientific, model number ICS-2100 (column: AS11HC), H ２ O ２ The composition of the sulfide solid electrolyte, which is composed of a glass phase or a crystalline phase of impurities, was confirmed by the above procedure.

[0126] In addition, for Example 7, the sulfide solid electrolyte was crushed in a mortar and passed through a 100 μm sieve to obtain a solid electrolyte powder with an average particle size D50 of approximately 20 μm. The sample was used. X-ray diffraction (XRD) measurements were performed in a non-exposed environment using an XRD analyzer (Rigaku Corporation, SmartLab) under the following conditions: radiation source: CuKα radiation (λ = 1.5418 Å), tube voltage: 45 kV, tube current: 200 mA, scan angle: 10 to 100°, scan rate: 5° / min, and step number: 0.01° / step. Silicon powder was added as an internal standard during XRD measurements, and the crystallinity (wt%) was determined by Rietveld analysis.

[0127] <Evaluation: Sulfide Solid Electrolyte> <Composition Ratio, Content Ratio> The sulfide solid electrolytes obtained in Examples 1 to 6 were pulverized in a mortar and passed through a 100 μm sieve to obtain a powder of solid electrolyte precursor having an average particle size D50 of approximately 20 μm. This was used as a sample. XRD measurement was then performed under the same conditions as when the sulfide solid electrolyte consisting of the impurity crystalline phase of Example 7 was used as a sample. In the obtained XRD pattern, the value of 2θ at which a diffraction peak was observed was determined. In addition, the half-width of the diffraction peak at 2θ = 20.2 ± 0.5° and the peak intensity of the diffraction peak at 2θ = 20.2 ± 0.5° were calculated as I. Ａ The peak intensity of the diffraction peak at 2θ = 29.7 ± 0.5° is defined as I Ｂ When I Ａ / I Ｂ The peak intensity ratios represented by the formula (2θ) were also determined. Furthermore, the composition ratio and content of the high ion conductive crystalline phase were also determined by analyzing the obtained XRD patterns. Here, the composition ratio of the sulfide-based glass phase can be determined to be the same as the composition ratio of the high ion conductive crystalline phase, but just to be sure, it was compared with the composition ratio determined by evaluation of the glass phase. As a result, it was confirmed that the composition ratio of the glass phase before step 3 was within ±20% of the composition ratio of the high ion conductive crystalline phase for all components. The results are shown in Table 1. In Example 7, a diffraction peak at 2θ = 20.2 ± 0.5° was not observed, and therefore this is indicated as "-" in Table 1. The XRD patterns of the sulfide solid electrolytes obtained in Examples 2 and 5 are shown in Figures 2 and 3, respectively.

[0128] <Lithium ion conductivity> The sulfide solid electrolyte obtained in each example was pulverized in a mortar and then passed through a 100 μm sieve to obtain a powder with an average particle size (D50) of approximately 20 μm, which was used as a sample. The above sample was compressed under a pressure of 380 MPa to obtain a measurement sample, and measured using an AC impedance measurement device (potentiostat / galvanostat VSP, manufactured by Bio-Logic Sciences Instruments). The measurement conditions were a measurement frequency of 100 Hz to 1 MHz, a measurement voltage of 100 mV, and a measurement temperature of 25°C, and the lithium ion conductivity was calculated from the obtained Nyquist plot. The results are shown in Table 1 under "σ" Ｌｉ＋(mS / cm)".

[0129]

[0130] From the above results, it was found that the sulfide solid electrolytes of Examples 1 to 3 were able to achieve high lithium ion conductivity despite having the same composition as the sulfide solid electrolyte of Example 5. The sulfide solid electrolytes of Examples 1 to 3 had narrow half-widths of the diffraction peaks observed at 2θ = 20.2 ± 0.5°, indicating high crystallinity. A good correlation was also confirmed between the half-widths and the lithium ion conductivity. A similar tendency was also confirmed from the results of Examples 4 and 6. Furthermore, although Examples 1 to 3 and Example 5, and Examples 4 and 6 all had the same composition of the highly ion-conductive crystalline phase, the peak intensities I Ａ and peak intensity I Ｂ Relative to I Ａ / I Ｂ The magnitude relationship was reversed, with ρ exceeding 1.0 (Examples 1 to 3, Example 4) and ρ less than 1.0 (Examples 4 and 6). The highly ion-conductive crystalline phase in the sulfide solid electrolyte according to this embodiment is a novel crystalline body not found in the past. Furthermore, Examples 1 to 3 revealed that when the cooling rate is equal to or higher than a certain level, a slower cooling rate results in a higher lithium ion conductivity. This is thought to be because the slow cooling rate results in a certain degree of ordering in the glassy state, resulting in good crystallinity after heating for crystallization, a narrower half-width, and a higher lithium ion conductivity. In Example 7, the cooling rate during cooling and solidification was 100°C / sec or less, so the desired glass phase was not obtained and a crystalline phase of impurities precipitated. As a result, Example 7 had a low lithium ion conductivity for use as a sulfide solid electrolyte.

[0131] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2023-168393) 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 glass phase, wherein the glass phase comprises a phase made of a sulfide-based glass containing Li, P, S, and Ha as constituent elements, and the Ha is at least one element selected from the group consisting of F, Cl, Br, and I, the crystalline phase comprises a highly ion-conductive crystalline phase derived from the sulfide-based glass, and the highly ion-conductive crystalline phase has diffraction peaks at least at 2θ=20.2±0.5°, 23.8±0.5°, and 29.7±0.5° in an XRD pattern obtained by powder X-ray diffraction measurement, and the half-width of the diffraction peak at 2θ=20.2±0.5° is 0.01 to 0.4°.

2. In the XRD pattern of the highly ion-conductive crystalline phase, the peak intensity of the diffraction peak at 2θ=20.2±0.5° is calculated as I Ａ The peak intensity of the diffraction peak at 2θ=29.7±0.5° is I Ｂ When I Ａ / I Ｂ The sulfide solid electrolyte according to claim 1, wherein the peak intensity ratio represented by is greater than 1.

0.

3. The sulfide solid electrolyte according to claim 1 or 2, wherein the content of the highly ion-conductive crystal phase in the sulfide solid electrolyte is 50 mass % or more.

4. The sulfide solid electrolyte according to claim 1 or 2, wherein the composition of the sulfide-based glass phase and the highly ion-conductive crystal phase satisfies Li: 30 to 50 at %, P: 5 to 15 at %, S: 30 to 60 at %, and Ha: 1 to 12 at %.

5. The sulfide solid electrolyte according to claim 1 or 2, wherein the highly ion-conductive crystalline phase further has a diffraction peak at at least one selected from the group consisting of 2θ=12.4±0.5°, 14.4±0.5°, and 31.4±0.5° in the XRD pattern.

6. A powder containing Li, P, S, and Ha as constituent elements, wherein the Ha is at least one selected from the group consisting of F, Cl, Br, and I, and in an XRD pattern obtained by powder X-ray diffraction measurement, the powder has diffraction peaks at least at 2θ=12.4±0.5°, 14.4±0.5°, 20.2±0.5°, 23.8±0.5°, 29.7±0.5°, and 31.4±0.5°, and the peak intensity of the diffraction peak at 2θ=20.2±0.5° is I. Ａ The peak intensity of the diffraction peak at 2θ=29.7±0.5° is I Ｂ When I Ａ / I Ｂ The lithium ion conductive crystal has a peak intensity ratio of more than 1.

0.

7. A method for producing a sulfide solid electrolyte comprising: mixing raw materials to obtain a raw material mixture containing Li, P, and S; heating the raw material mixture to obtain a molten material; cooling and solidifying the molten material to obtain the glass phase; and heating the glass phase to obtain a highly ion-conductive crystalline phase in which a portion of the glass phase is crystallized, wherein the heating to obtain the molten material and the cooling and solidifying are performed under normal pressure conditions, the cooling rate in the cooling and solidifying is 100°C / sec or more, and the heating to obtain the highly ion-conductive crystalline phase is performed at a temperature that is equal to or higher than the crystallization temperature of the glass phase -15°C for one minute or more.

8. The method for producing a sulfide solid electrolyte according to claim 7, wherein the raw material mixture further contains Ha, and the Ha is at least one element selected from the group consisting of F, Cl, Br, and I.

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