Sulfide solid electrolyte, method for producing sulfide solid electrolyte, and all-solid-state battery

Abstract

The invention relates to a sulfide solid electrolyte, a method for producing the sulfide solid electrolyte, and an all-solid-state battery. The sulfide solid electrolyte of the present disclosure is a sulfide solid electrolyte used in an all-solid-state battery, the sulfide solid electrolyte having a composition represented by (100-x) [yLi2S (1-y) P2S5] xLiBH4. In the formula, x is a number satisfying 50 < x < 75, and y is a number satisfying 0.72 < = y < = 0.78. The ionic conductivity of the sulfide solid electrolyte at 25 DEG C is 5.0 mS / cm or more.

Description

Technical Field

[0001] The present disclosure relates to a sulfide solid electrolyte, a method for manufacturing the sulfide solid electrolyte, and an all-solid-state battery. Background Art

[0002] An all-solid-state battery is a battery having a solid electrolyte layer between a positive electrode active material layer and a negative electrode active material layer. Compared with a liquid-based battery having an electrolyte containing a flammable organic solvent, an all-solid-state battery has the advantage of being easy to simplify safety devices. As a solid electrolyte for an all-solid-state battery, a sulfide solid electrolyte is known.

[0003] For example, International Publication No. 2016 / 103894 discloses a method for producing an ion conductor (sulfide solid electrolyte), comprising: mixing LiBH4 and P2S5 at a molar ratio of LiBH4:P2S5=x:(1-x) [wherein x is greater than 0.85 and less than 0.98] to obtain a mixture; and heating the mixture. In addition, International Publication No. 2016 / 103894 discloses an ion conductor (sulfide solid electrolyte) produced by the above method.

[0004] In addition, Mechanochemically Prepared Li2S P2S5 LiBH4 Solid Electrolytes with an Argyrodite Structure (ACS Omega 2018, 3, 54535458) discloses a sulfide solid electrolyte represented by (100-x)(0.75Li2S·0.25P2S5)·xLiBH4. Summary of the invention

[0005] From the viewpoint of improving battery performance, a solid electrolyte with good ion conductivity is required.

[0006] The present disclosure has been made in view of the above-mentioned actual situation, and a main object of the present disclosure is to provide a sulfide solid electrolyte having good ion conductivity.

[0007] [1] A sulfide solid electrolyte is a sulfide solid electrolyte for an all-solid-state battery, having a composition represented by (100-x)[yLi2S·(1-y)P2S5]·xLiBH4, wherein x satisfies 50<x<75, y satisfies 0.72≤y≤0.78, and the ionic conductivity of the sulfide solid electrolyte at 25°C is greater than 5.0 mS / cm.

[0008] [2] The sulfide solid electrolyte according to [1], wherein the ion conductivity is 8.0 mS / cm or more.

[0009] [3] The sulfide solid electrolyte according to [1] or [2], which has one peak in the range of 2θ=13° to 16° in X-ray diffraction measurement using CuKα rays.

[0010] [4] The method for producing a sulfide solid electrolyte according to any one of [1] to [3], comprising: a first mechanical polishing step, in which a mixture containing Li2S and P2S5 is mechanically polished to obtain a first sulfide glass; and a second mechanical polishing step, in which a mixture of the first sulfide glass and LiBH4 is mechanically polished to obtain a second sulfide glass, wherein in the first mechanical polishing step and the second mechanical polishing step, each of the mechanical polishing is performed in such a way that the gravity Gn1 calculated by the following formula (1) becomes 6G or more,

[0011]

[0012] In the formula (1), rs represents the orbital radius, rp1 represents the radius of the container used in the mechanical grinding, iw represents the ratio of rotation to revolution, π represents the circumference, and rpm represents the revolution speed.

[0013] [5] The method for producing a sulfide solid electrolyte according to [4], wherein the gravity Gn1 is 15 G or more.

[0014] [6] The method for producing a sulfide solid electrolyte according to [4] or [5], comprising a heat treatment step of heat treating the sulfide glass, wherein the heat treatment temperature is 190° C. or less.

[0015] [7] An all-solid-state battery comprising: a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer arranged between the positive electrode active material layer and the negative electrode active material layer, wherein at least one of the positive electrode active material layer, the negative electrode active material layer and the solid electrolyte layer contains a sulfide solid electrolyte according to any one of [1] to [3].

[0016] The present disclosure achieves the effect of being able to provide a sulfide solid electrolyte having good ion conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, wherein like reference numerals represent like elements, and wherein:

[0018] Figure 1 is a flow chart illustrating a method for producing a sulfide solid electrolyte disclosed herein;

[0019] Figure 2A schematic cross-sectional view illustrating an all-solid-state battery of the present disclosure;

[0020] Figure 3 is a graph showing the measurement results of ion conductivity of the example;

[0021] Figure 4 (a) is a graph showing the measurement results of X-ray diffraction of the example;

[0022] Figure 4 (b) is a graph showing the measurement results of X-ray diffraction of the example;

[0023] Figure 5 is a graph showing the measurement results of the discharge capacity retention rate of the examples; and

[0024] Figure 6 It is a graph showing the measurement results of ion conductivity in Examples. DETAILED DESCRIPTION

[0025] The sulfide solid electrolyte, the method for producing the sulfide solid electrolyte, and the all-solid-state battery disclosed in the present invention are described in detail below.

[0026] A. Sulfide solid electrolyte

[0027] The sulfide solid electrolyte disclosed in the present invention is a sulfide solid electrolyte for an all-solid-state battery. The sulfide solid electrolyte has a composition represented by (100-x)[yLi2S·(1-y)P2S5]·xLiBH4. In the formula, x satisfies 50<x<75. y satisfies 0.72≤y≤0.78. The ionic conductivity of the sulfide solid electrolyte at 25°C is 5.0 mS / cm or more.

[0028] In the present disclosure, the sulfide solid electrolyte exhibits an ion conductivity of 5.0 mS / cm or more within a predetermined composition range, and thus has excellent ion conductivity.

[0029] Among them, the sulfide solid electrolyte disclosed in the above-mentioned International Publication No. 2016 / 103894 does not use Li2S, and the maximum ionic conductivity is 2.0mS / cm (measured at 27°C). In addition, the sulfide solid electrolyte disclosed in the above-mentioned Mechanochemically Prepared Li2SP2S5 LiBH4 Solid Electrolytes with an Argyrodite Structure (ACS Omega 2018, 3, 5453 5458) has a maximum ionic conductivity of 1.8mS / cm (measured at 25°C). The sulfide solid electrolyte disclosed in the present invention shows an ionic conductivity of more than 5.0mS / cm in the prescribed composition. The sulfide solid electrolyte disclosed in the present invention has significantly better ionic conductivity than the sulfide solid electrolytes in the above-mentioned documents.

[0030] The sulfide solid electrolyte disclosed in the present invention has a composition represented by (100-x)[yLi2S·(1-y)P2S5]·xLiBH4. In the above composition, x is a number greater than 50, and may be a number greater than 52, a number greater than 55, or a number greater than 60. On the other hand, x is a number smaller than 75, and may be a number less than 70, a number less than 67, a number less than 65, or a number less than 63. In addition, in the above composition, y is a number greater than 0.72, and may be a number greater than 0.73. On the other hand, y is a number less than 0.78, and may be a number less than 0.75. In particular, y is preferably a number that mainly obtains a Li3PS4 structure in the first mechanical grinding step described later. In particular, it is preferred that y is 0.75, that is, the ratio of Li2S to P2S5 is preferably 75:25.

[0031] The sulfide solid electrolyte disclosed herein has an ion conductivity of 5.0 mS / cm or more at 25° C. The ion conductivity may be 5.3 mS / cm or more, 5.5 mS / cm or more, 6.0 mS / cm or more, 8.0 mS / cm or more, or 10.0 mS / cm or more.

[0032] The sulfide solid electrolyte disclosed herein may be sulfide glass or crystallized sulfide glass (glass ceramic). In addition, the sulfide solid electrolyte disclosed herein may be a crystalline material obtained by subjecting a mixture to a solid phase reaction treatment.

[0033] Sulfide glass can be obtained by subjecting a mixture containing Li2S, P2S5 and LiBH4 to amorphous treatment. As an example of amorphous treatment, mechanical grinding can be cited. Mechanical grinding will be described later.

[0034] In addition, crystallized sulfide glass can be obtained, for example, by heat-treating sulfide glass at a temperature equal to or higher than the crystallization temperature.

[0035] In addition, the sulfide solid electrolyte disclosed in the present invention preferably has one peak in the range of 2θ=13° to 16° in X-ray diffraction measurement using CuKα rays. The so-called "having one peak in the range of 2θ=13° to 16°" means that one peak top is observed in the range of 2θ=13° to 16°. In addition, when a shoulder peak is observed, the shoulder peak itself is regarded as one peak.

[0036] In addition, the sulfide solid electrolyte disclosed in the present invention is used in an all-solid-state battery. The all-solid-state battery will be described later.

[0037] B. Method for producing sulfide solid electrolyte

[0038] Figure 1 The flowchart of the method for producing the sulfide solid electrolyte disclosed in the present invention is shown as an example. The method for producing the sulfide solid electrolyte disclosed in the present invention is the method for producing the sulfide solid electrolyte described above. Figure 1 As shown, the method for producing a sulfide solid electrolyte disclosed in the present invention includes at least a predetermined first mechanical polishing step and a second mechanical polishing step.

[0039] 1. The first mechanical grinding process

[0040] The first mechanical grinding step of the present disclosure is a step of mechanically grinding a mixture containing Li2S and P2S5 to obtain a first sulfide glass.

[0041] The ratio of Li2S to P2S5 in the mixture is not particularly limited as long as the above-mentioned sulfide solid electrolyte is obtained. That is, the ratio (molar ratio) of Li2S to P2S5 is y:1-y (0.72≤y≤0.78) in the above-mentioned composition formula.

[0042] In addition, in the first mechanical grinding step, mechanical grinding is performed in a manner that the gravity Gn1 calculated by the following formula (1) becomes 6G or more. The following formula (1) is a formula for converting the force applied during mechanical grinding into gravity. In addition, Gn1 can also be understood as gravitational acceleration. By performing mechanical grinding in a manner that the gravity conversion is 6G or more, a first sulfide glass with a well-formed Li3PS4 skeleton can be obtained. By using such a first sulfide glass, a sulfide solid electrolyte with good ion conductivity can be obtained.

[0043]

[0044] In formula (1), rs represents the orbital radius. rp1 represents the radius of the container used in mechanical grinding. iw represents the ratio of rotation to revolution. π represents the circumference. rpm represents the revolution speed.

[0045] Gn1 calculated by formula (1) may be 8 G or more, 10 G or more, 15 G or more, or 18 G or more. On the other hand, Gn1 may be, for example, 25 G or less, 22 G or less, or 20 G or less.

[0046] The time for mechanical polishing in the first mechanical polishing step is not particularly limited, and is, for example, 5 hours to 24 hours.

[0047] The type of mechanical grinding may be wet mechanical grinding or dry mechanical grinding. In addition, for example, ball milling such as a planetary ball mill can be cited as an example of mechanical grinding.

[0048] 2. Second mechanical grinding process

[0049] The second mechanical polishing step of the present disclosure is a step of adding LiBH 4 to the first sulfide glass and performing mechanical polishing to obtain the second sulfide glass.

[0050] The ratio of the first sulfide glass to LiBH4 is not particularly limited as long as the above-mentioned sulfide solid electrolyte is obtained. That is, the ratio (molar ratio) of the first sulfide glass to LiBH4 is 100-x:x (50<x<75) in the above-mentioned composition formula.

[0051] In the second mechanical polishing step, mechanical polishing is performed so that the gravity Gn1 calculated by the above formula (1) becomes 6 G or more. The formula (1) and Gn1 are the same as above. In the first mechanical polishing step and the second mechanical polishing step, Gn1 may be the same or different.

[0052] The time and type of mechanical polishing in the second mechanical polishing step are the same as those in the first mechanical polishing step described above.

[0053] 3. Heat treatment process

[0054] The method for producing a sulfide solid electrolyte disclosed herein may include a heat treatment step of heat treating the sulfide glass. The heat treatment temperature is 190° C. or lower.

[0055] If the heat treatment temperature is too high, it is speculated that a different phase may be formed in the obtained sulfide solid electrolyte. On the other hand, it is speculated that by setting the heat treatment temperature to 190°C or less, the formation of a different phase can be suppressed, and a sulfide solid electrolyte with better ion conductivity (sulfide solid electrolyte with good crystallinity) can be obtained. It is speculated that this is because the hydride (LiBH4) used in the sulfide solid electrolyte disclosed in the present invention undergoes a phase transition at around 400K (127°C) to show good ion conductivity as a hexagonal crystal structure as a high-temperature phase.

[0056] The temperature of the heat treatment is, for example, 50° C. or higher, 75° C. or higher, or 100° C. or higher. On the other hand, the temperature of the heat treatment is 190° C. or lower, 160° C. or lower, or 150° C. or lower.

[0057] The time of the heat treatment is not particularly limited and can be appropriately adjusted according to the temperature of the heat treatment. The time of the heat treatment is, for example, 30 minutes to 4 hours.

[0058] 4. Sulfide solid electrolyte

[0059] The sulfide solid electrolyte produced by the above-mentioned method is the same as that described in “A. Sulfide solid electrolyte”, and thus the description thereof is omitted here.

[0060] C. All-solid-state battery

[0061] The sulfide solid electrolyte disclosed in the present invention is used for an all-solid battery. That is, the all-solid battery disclosed in the present invention comprises: a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer. At least one of the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer contains the sulfide solid electrolyte.

[0062] The all-solid-state battery disclosed herein has a good discharge capacity retention rate because at least one of the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer contains the above-mentioned sulfide solid electrolyte.

[0063] Figure 2 This is a schematic cross-sectional view illustrating an all-solid-state battery of the present disclosure. Figure 2 The all-solid battery 10 shown in the figure has a positive electrode active material layer 1, a negative electrode active material layer 2, and a solid electrolyte layer 3 arranged between the positive electrode active material layer 1 and the negative electrode active material layer 2. In addition, the all-solid battery 10 has a positive electrode collector 4 that collects electrons from the positive electrode active material layer 1, and a negative electrode collector 5 that collects electrons from the negative electrode active material layer 2. At least one of the positive electrode active material layer 1, the negative electrode active material layer 2, and the solid electrolyte layer 3 contains the above-mentioned sulfide solid electrolyte.

[0064] 1. Positive electrode active material layer

[0065] The positive electrode active material layer contains at least a positive electrode active material. The positive electrode active material layer preferably contains at least one of a solid electrolyte, a conductive material, and a binder as required. As the positive electrode active material, the conductive material, and the binder, conventionally known materials can be cited. In addition, the positive electrode active material layer preferably contains the above-mentioned sulfide solid electrolyte as a solid electrolyte.

[0066] 2. Negative electrode active material layer

[0067] The negative electrode active material layer contains at least a negative electrode active material. The negative electrode active material layer preferably contains at least one of a solid electrolyte, a conductive material, and a binder as required. As the negative electrode active material, the conductive material, and the binder, conventionally known materials can be cited. In addition, the negative electrode active material layer preferably contains the above-mentioned sulfide solid electrolyte as a solid electrolyte.

[0068] 3. Solid active material layer

[0069] The solid electrolyte layer contains at least a solid electrolyte and may contain a binder as required. The binder is as described above. In addition, the solid electrolyte is preferably the above-mentioned sulfide solid electrolyte.

[0070] 4. Positive electrode collector and negative electrode collector

[0071] The material of the positive electrode current collector and the negative electrode current collector can be, for example, a conventionally known metal material such as Al, SUS, Cu, and Ni.

[0072] 5. All-solid-state batteries

[0073] The all-solid battery in the present disclosure is typically a lithium ion secondary battery. In addition, as the purpose of the all-solid battery, for example, the power supply of vehicles such as hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), electric vehicles (battery-powered vehicles, BEV), gasoline vehicles, and diesel vehicles can be listed. In particular, it is preferably used for the driving power supply of hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV) or electric vehicles (BEV). In addition, the all-solid battery can also be used as a power supply for mobile bodies (such as railways, ships, aircraft) other than vehicles, and can also be used as a power supply for electrical products such as information processing devices.

[0074] The present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are illustrative. Embodiments having substantially the same structure and achieving the same effects as the technical concept described in the patent claims of the present disclosure are all included in the technical scope of the present disclosure.

[0075] Example 1-1

[0076] As raw materials, Li2S (produced by Mitsuwa Chemical) and P2S5 (produced by Melku) were prepared so as to have a molar ratio of 75:25. They were dry-milled under the conditions of a ball diameter of 5 mm, a container of 80 mL, a rotation speed of 510 rpm, and an operation time of 10 hours to obtain a first sulfide glass (0.75Li2S·0.25P2S5) (first mechanical milling step). LiBH4 (produced by Aldrich) was added to the first sulfide glass so that the molar ratio of the first sulfide glass to LiBH4 became 48:52, and dry-milled (ball diameter of 5 mm, container of 80 mL, rotation speed of 510 rpm, and operation time of 15 hours) (second mechanical milling step). Thus, a sulfide solid electrolyte (second sulfide glass) having a composition of 48 (0.75Li2S·0.25P2S5)·52LiBH4 was obtained. The above composition corresponds to the composition of (100-x)[yLi2S·(1-y)P2S5]·xLiBH4 where x=52 and y=0.75. As a mechanical milling device, a planetary ball mill Primeram PL-7 manufactured by Fritsch was used.

[0077] In the mechanical grinding device, the revolution radius rs is 0.07 m, the radius rp1 of the container is 0.0240 m, and the ratio iw of rotation to revolution is -2.0. Substituting these values ​​and the rotation speed into the above formula (1), the gravity Gn1 obtained is 18 G in both the first mechanical grinding step and the second mechanical grinding step.

[0078] Examples 1-2 to 1-5 and Comparative Examples 1-1 to 1-7

[0079] A sulfide solid electrolyte was prepared in the same manner as in Example 1-1 except that the ratios of Li 2 S, P 2 S 5 , and LiBH 4 were changed so that the composition of the sulfide solid electrolyte would have the values ​​shown in Table 1 below.

[0080] Rating 1

[0081] Determination of ionic conductivity

[0082] Each sulfide solid electrolyte of Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-7 was weighed in the range of 0.08 g to 0.1 g, and pressed with a pressure of 6 t to form a pellet. Then, the impedance was measured at 25°C. The obtained resistance value R (Ω), the thickness L (cm) of the pellet, the bottom area A (cm 2 ), the ionic conductivity (σ) was calculated by the following formula. The results are shown in Figure 3 and Table 1.

[0083] σ=L / (RA)

[0084] Table 1

[0085]

[0086] like Figure 3 As shown in Table 1, it was confirmed that the peak of ion conductivity existed in the range of 50<x<75, and good ion conductivity (5.0 ms / cm or more) was exhibited.

[0087] X-ray diffraction measurement

[0088] X-ray diffraction measurements were performed on each of the sulfide solid electrolytes of Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-7 under Ar atmosphere and room temperature. The apparatus used was a fully automatic multi-purpose X-ray diffraction apparatus SmartLab manufactured by Rigaku Corporation, and the X-rays were set to CuKα rays. The results are shown in Figure 4 (a) and Figure 4 (b). Furthermore, Figure 4 (b) Figure 4 (a) is an extracted and enlarged view of Example 1-3 (x=58) and Comparative Example 1-7 (x=83).

[0089] like Figure 4 As shown in (a), if x is too low, no peak is confirmed in the range of 2θ=13° to 16°. Figure 4 As shown in (b), in Example 1-3, there is one peak in the range of 2θ=13° or more and 16° or less, and in Comparative Example 1-7, two peaks including a shoulder peak are confirmed. Although not shown in the figure, in other Comparative Examples, two peaks are confirmed as in Comparative Example 1-7.

[0090] (Determination of discharge capacity maintenance rate)

[0091] Using the sulfide solid electrolytes of Examples 1-3 and Comparative Examples 1-4, evaluation batteries were prepared as described below. First, the sulfide solid electrolyte was mechanically ground in a mixed solvent of heptane and dibutyl ether to be micronized. Secondly, the micronized sulfide solid electrolyte was dried at 100°C for 2 hours. Then, the dried sulfide solid electrolyte was mixed with spherical graphite in a volume ratio of 35:65 to prepare a negative electrode composite. The negative electrode composite, separator layer, and counter electrode (Li-In foil) were stacked in this order. In this way, an evaluation battery (negative electrode half-cell) was prepared. In addition, the separator layer used the sulfide solid electrolyte (second sulfide glass) after the second mechanical grinding step.

[0092] Each evaluation battery was subjected to three cycles of 0.1C CCCV charge and discharge at 25°C. In the CCCV charge and discharge, the cutoff voltage was set to 0.05 V (Li + / Li), and the cut-off current was set to 0.01C. Then, the charge rate was changed from 0.1 to 0.5C, and the discharge rate was fixed at 0.1C, and CC charge and discharge were performed. Furthermore, the cut-off voltage during CC charge and discharge was set to 0.05V (Li + / Li). The capacity during CC charge and discharge was divided by the initial capacity to calculate the discharge capacity retention rate (%). The results are shown in Figure 5 .

[0093] like Figure 5 As shown, the higher the charge rate, the larger the charge-discharge capacity in Example 1-3 is compared with Comparative Example 1-4. In particular, when the charge rate is 0.5C, the capacity retention rate of Example 1-3 is 1.2 times higher than that of Comparative Example 1-4.

[0094] Example 2-1

[0095] A sulfide solid electrolyte was prepared in the same manner as in Example 1-1 except that the ratio of Li2S, P2S5, and LiBH4 was changed so that the composition of the sulfide solid electrolyte became 46(0.75Li2S·0.25P2S5)·54LiBH4. The above composition corresponds to the composition of (100-x)[yLi2S·(1-y)P2S5]·xLiBH4 where x=54 and y=0.75.

[0096] Comparative Example 2-1

[0097] A sulfide solid electrolyte was prepared in the same manner as in Example 2-1 except that in the first mechanical milling step, the ball diameter was 4 mm, the rotation speed was 280 rpm, the gravity Gn1 obtained from the formula (1) was changed to 5.4 G, and the operation time was changed to 45 hours.

[0098] Rating 2

[0099] Determination of ionic conductivity

[0100] The ion conductivity of the sulfide solid electrolytes of Example 2-1 and Comparative Example 2-1 was measured by the same method as in Evaluation 1. The results are shown in Table 2.

[0101] Table 2

[0102]

[0103] As shown in Table 2, it was confirmed that in the first mechanical polishing step and the second mechanical polishing step, the ion conductivity was improved by mechanical polishing in a manner such that Gn1 became 6G or more. It is presumed that this is because the Li3PS4 skeleton was formed more favorably.

[0104] Example 3-1

[0105] In the same manner as in Example 1-3, a sulfide solid electrolyte (sulfide glass) having a composition of 42(0.75Li2S·0.25P2S5)·58LiBH4 was obtained. The obtained sulfide glass was heated at 60°C for 2 hours. The heated sulfide solid electrolyte was used as an evaluation sample.

[0106] Examples 3-2 to 3-4

[0107] A sulfide solid electrolyte (evaluation sample) was obtained in the same manner as in Example 3-1 except that the heat treatment temperature was changed as shown in Table 3.

[0108] Rating 3

[0109] Determination of ionic conductivity

[0110] The ionic conductivity of the sulfide solid electrolytes of Examples 3-1 to 3-4 was measured in the same manner as in Evaluation 1. The results are shown in Tables 3 and 4 together with those of Examples 1-3. Figure 6 In Examples 1-3, it can be considered that no heat treatment was performed, but for the sake of convenience, the heat treatment temperature is recorded as room temperature (25° C.).

[0111] Table 3

[0112]

[0113] like Figure 6 As shown in Table 3, it is confirmed that good ionic conductivity can be obtained by heat treatment below 190°C, and it is confirmed that ionic conductivity is further improved by heat treatment below 160°C. In addition, the ionic conductivity is the highest when heat treated at 100°C. The hydride (LiBH4) used in the sulfide solid electrolyte disclosed in the present invention undergoes a phase change near 400K (127°C). It is known that LiBH4 changes from an orthorhombic structure as a low-temperature phase to a hexagonal structure as a high-temperature phase, thereby improving ionic conductivity. Therefore, it is speculated that even for a sulfide solid electrolyte using LiBH4, the ionic conductivity becomes the highest by heat treatment near the above-mentioned phase change temperature, i.e., 100°C. In addition, for a sulfide solid electrolyte using LiBH4, it is speculated that the ionic conductivity becomes good by good glass ceramicization through heat treatment near 100°C.

Claims

1. A sulfide solid electrolyte, which is a sulfide solid electrolyte for an all-solid-state battery, having a composition represented by (100-x)[yLi2S·(1-y)P2S5]·xLiBH4, wherein x satisfies 50<x<75, y satisfies 0.72≤y≤0.78, and the ionic conductivity of the sulfide solid electrolyte at 25°C is greater than 5.0 mS / cm.

2. The sulfide solid electrolyte according to claim 1, wherein The ionic conductivity is greater than 8.0 mS / cm.

3. The sulfide solid electrolyte according to claim 1, wherein In X-ray diffraction measurement using CuKα rays, there is one peak in the range of 2θ=13° to 16°.

4. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 3, comprising: The first mechanical grinding step, wherein: Mechanically grinding a mixture containing Li2S and P2S5 to obtain a first sulfide glass; and a second mechanical grinding step, wherein the mixture of the first sulfide glass and LiBH4 is mechanically ground to obtain a second sulfide glass, In the first mechanical polishing step and the second mechanical polishing step, each of the mechanical polishing steps is performed so that the gravity Gn1 calculated by the following formula (1) becomes 6G or more. In the formula (1), rs represents the orbital radius, rp1 represents the radius of the container used in the mechanical grinding, iw represents the ratio of rotation to revolution, π represents the circumference, and rpm represents the revolution speed.

5. The method for producing a sulfide solid electrolyte according to claim 4, wherein: The gravity Gn1 is greater than 15G. 6 . The method for producing a sulfide solid electrolyte according to claim 4 , comprising a heat treatment step of heat-treating the sulfide glass, wherein the heat treatment temperature is 190° C. or less.

7. An all-solid-state battery comprising: a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer arranged between the positive electrode active material layer and the negative electrode active material layer, wherein at least one of the positive electrode active material layer, the negative electrode active material layer and the solid electrolyte layer contains the sulfide solid electrolyte according to any one of claims 1 to 3.

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