Sulfide solid electrolyte with coating layer, and cathode material

Abstract

To provide: a sulfide solid electrolyte with a coating layer that exhibits excellent ionic and electronic conductivity and can suppress reactions with moisture, cathode active materials and the like, and that is particularly suitable for all-solid-state batteries; and a cathode material using the coated sulfide solid electrolyte.SOLUTION: A sulfide solid electrolyte 10 with a coating layer of the present invention is a sulfide solid electrolyte 10 with a coating layer which has a sulfide solid electrolyte 11 with a coating layer 12 formed on its surface. The coating layer 12 contains a lithium-ion-conductive material and an electronically conductive material. The cathode material of the present invention comprises a cathode active material and the sulfide solid electrolyte 10 with the coating layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sulfide-based solid electrolyte with a coating layer and a positive electrode material that are suitable for use in, for example, all-solid-state batteries. [Background technology]

[0002] Lithium-ion batteries are widely used as power sources in vehicles such as EVs (electric vehicles) and HEVs (hybrid electric vehicles), as well as electronic devices such as mobile phones and laptops. Conventional lithium-ion batteries use an organic electrolyte solution, in which a lithium salt such as lithium hexafluorophosphate (LiPF6) is dissolved in an organic solvent. Such organic electrolytes are flammable and may be damaged by excessive heating or impact.

[0003] In recent years, all-solid-state lithium-ion batteries using sulfide-based solid electrolytes have been proposed to improve the safety and durability of lithium-ion batteries. Examples of sulfide-based solid electrolytes include Li2S-P2S5, Li2S-P2S3, Li2S-SiS2, Li2S-Ga2S2, and Li2S-GeS2.

[0004] The all-solid-state lithium ion battery includes a positive electrode, a negative electrode, and an electrolyte layer provided between the positive electrode and the negative electrode, and the sulfide-based solid electrolyte described above is used as the electrolyte layer. However, when sulfide-based solid electrolytes are handled in the air, they react with moisture in the air, resulting in deterioration of performance and generation of hydrogen sulfide, making them difficult to handle. Furthermore, when a sulfide-based solid electrolyte is used as the electrolyte layer, the positive electrode and the sulfide-based solid electrolyte come into contact with each other, and there is a risk of a reaction between them deteriorating performance. For this reason, the surface of the positive electrode has conventionally been coated.

[0005] Therefore, Patent Document 1 proposes a solid electrolyte composition in which a water-impermeable coating layer made of a lithium ion conductive composition is formed on the surface of a sulfide-based solid electrolyte. In this solid electrolyte composition, since the moisture-impermeable coating layer is formed, deterioration of the sulfide-based solid electrolyte due to moisture in the atmosphere, etc. can be suppressed, making it easier to handle. In addition, since the reaction between the positive electrode and the sulfide-based solid electrolyte is suppressed, coating of the positive electrode is not required. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-022546 Summary of the Invention [Problem to be solved by the invention]

[0007] Incidentally, as shown in FIG. 3, when a cathode material 120 of an all-solid-state lithium ion battery is composed of a cathode active material 121 and a sulfide-based solid electrolyte 110, a conductive additive 122 is added in addition to the cathode active material 121 and the sulfide-based solid electrolyte 110 to ensure electronic conductivity. However, when the conductive additive 122 is added to the positive electrode material 120, there is a problem in that the battery capacity decreases.

[0008] The present invention has been made in view of the above-mentioned circumstances, and aims to provide a sulfide-based solid electrolyte with a coating layer that has excellent ionic conductivity and electronic conductivity, is capable of suppressing reactions with moisture, positive electrode active materials, etc., and is particularly suitable for all-solid-state batteries, and a positive electrode material that uses this sulfide-based solid electrolyte with a coating layer. [Means for solving the problem]

[0009] In order to solve the above problems, a sulfide-based solid electrolyte with a coating layer according to a first aspect of the present invention is a sulfide-based solid electrolyte with a coating layer, in which a coating layer is formed on the surface of a sulfide-based solid electrolyte, and the coating layer is characterized by containing a lithium ion conductive material and an electron conductive material.

[0010] According to the sulfide-based solid electrolyte with a coating layer of the first aspect of the present invention, a coating layer is formed on the surface of the sulfide-based solid electrolyte, which makes it possible to inhibit reactions between the sulfide-based solid electrolyte and moisture and the positive electrode active material, thereby stabilizing the properties of the sulfide-based solid electrolyte. The coating layer ensures lithium ion conductivity and electron conductivity because it contains a lithium ion conductive material, an electron conductive material, and anta B. Therefore, even when forming a cathode material, for example, the amount of conductive additive added can be reduced, and battery capacity can be ensured.

[0011] A sulfide-based solid electrolyte with a coating layer according to a second aspect of the present invention is the sulfide-based solid electrolyte with a coating layer according to the first aspect of the present invention, characterized in that the lithium ion conductive material is one or more selected from the group consisting of lithium niobate, lithium tungstate, and lithium tungstate. According to the sulfide-based solid electrolyte with a coating layer of the second aspect of the present invention, the lithium ion conductive material is one or more selected from lithium niobate, lithium tungstate, and lithium tantalate, and therefore the sulfide-based solid electrolyte has sufficiently excellent lithium ion conductivity and is particularly suitable as a material for constituting a lithium ion battery.

[0012] A sulfide-based solid electrolyte with a coating layer according to a third aspect of the present invention is the sulfide-based solid electrolyte with a coating layer according to the first or second aspect of the present invention, characterized in that the electron conductive material is a carbon material. According to the sulfide-based solid electrolyte with a coating layer of the third aspect of the present invention, the electron-conductive material is a carbon material, which has sufficiently excellent electron conductivity and is particularly suitable as a material for constituting a lithium-ion battery. Furthermore, since the carbon material does not react with the sulfide-based solid electrolyte or the positive electrode active material, deterioration of the sulfide-based solid electrolyte or the positive electrode active material is suppressed, and the characteristics are stabilized.

[0013] A cathode material according to a fourth aspect of the present invention is characterized by including a cathode active material and the sulfide-based solid electrolyte with a coating layer according to any one of the first to third aspects of the present invention. The cathode material of the fourth aspect of the present invention contains the sulfide-based solid electrolyte with a coating layer of any one of the first to third aspects of the present invention, and therefore lithium ion conductivity and electronic conductivity are ensured, making it possible to reduce the amount of conductive additive added and ensure battery capacity. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a sulfide-based solid electrolyte with a coating layer that has excellent ionic conductivity and electronic conductivity and is capable of suppressing reactions with moisture, positive electrode active materials, etc., and is particularly suitable for all-solid-state batteries, and a positive electrode material that uses this sulfide-based solid electrolyte with a coating layer. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is an explanatory diagram of a sulfide-based solid electrolyte with a coating layer according to an embodiment of the present invention. [Figure 2] FIG. 1 is an explanatory diagram of a cathode material according to an embodiment of the present invention. [Figure 3] FIG. 1 is an explanatory diagram of a conventional cathode material. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the following embodiments are specifically described to provide a better understanding of the gist of the invention, and do not limit the present invention unless otherwise specified.

[0017] The sulfide-based solid electrolyte with a coating layer according to this embodiment will be described with reference to FIG. The sulfide-based solid electrolyte 10 with a coating layer according to this embodiment is used, for example, as a solid electrolyte constituting an electrolyte layer of an all-solid-state battery and as a solid electrolyte constituting a positive electrode material.

[0018] As shown in FIG. 1 , the sulfide-based solid electrolyte 10 with a coating layer according to this embodiment includes a sulfide-based solid electrolyte 11 and a coating layer 12 formed on the surface of the sulfide-based solid electrolyte 11.

[0019] The sulfide-based solid electrolyte 11 is not particularly limited, and various solid electrolyte materials can be used. The sulfide-based solid electrolyte 11 is, for example, LGPS (Li 10。35 Ge 1.35 P 1.65 S 12 ), LSSPS(Li 10.35 [Sn 0.27 Si 1.08 ]P 1.65 S 12 ), Li5PS5Cl, and Li7P3S 11 etc.

[0020] The coating layer 12 contains a lithium ion conductive material and an electron conductive material. The lithium ion conductive material is preferably one or more selected from the group consisting of lithium niobate (LiNbO3), lithium tungstate (Li2WO4), and lithium tantalate (LiTaO3). The electron conductive material is preferably, for example, a carbon material.

[0021] In this embodiment, the ratio M1 / M2 of the mass M1 of the lithium ion conductive material to the mass M2 of the electron conductive material in the coating layer 12 is preferably 1 or more, and more preferably 3 or more. On the other hand, the ratio M1 / M2 of the mass M1 of the lithium ion conductive material to the mass M2 of the electron conductive material in the coating layer 12 is preferably 90 or less, and more preferably 60 or less.

[0022] In addition, in the cross section of the sulfide-based solid electrolyte 10 with the coating layer, the ratio S2 / S1 of the area S1 of the sulfide-based solid electrolyte 11 to the area S2 of the coating layer 12 is preferably 0.11 or more, and more preferably 0.25 or more. On the other hand, the ratio S2 / S1 of the area S1 of the sulfide-based solid electrolyte 11 to the area S2 of the coating layer 12 is preferably 9 or less, and more preferably 4 or less.

[0023] Furthermore, the thickness of the coating layer 12 is preferably 3 nm or more, more preferably 6 nm or more, while the thickness of the coating layer 12 is preferably 100 nm or less, more preferably 50 nm or less.

[0024] An example of a method for producing the sulfide-based solid electrolyte 10 with a coating layer according to this embodiment will be described below. First, prepare a powder of the sulfide-based solid electrolyte 11. The powder of the sulfide-based solid electrolyte 11 may be one that is appropriately produced by an existing production method.

[0025] Next, a target material of a lithium ion conductive material and a target material of an electron conductive material are prepared. The target material of the lithium ion conductive material and the target material of the electron conductive material are loaded into a barrel sputtering device. Then, the sulfide-based solid electrolyte powder is placed in a barrel sputtering device, and sputtering film formation is carried out in an inert gas atmosphere.

[0026] As described above, the coating layer 12 containing a lithium ion conductive material and an electron conductive material is formed on the surface of the sulfide-based solid electrolyte 11, and the sulfide-based solid electrolyte 10 with a coating layer according to this embodiment is produced.

[0027] Next, the cathode material 20 according to this embodiment will be described with reference to FIG. 2, the cathode material 20 of this embodiment includes the sulfide-based solid electrolyte 10 with the coating layer of this embodiment and a cathode active material 21. That is, this embodiment does not include a conductive additive.

[0028] Here, the ratio M3 / M4 of the mass M3 of the positive electrode active material 21 to the mass M4 of the sulfide-based solid electrolyte 10 with the coating layer is preferably 1.5 or more, and more preferably 2.3 or more. On the other hand, the ratio M3 / M4 of the mass M3 of the positive electrode active material 21 to the mass M4 of the sulfide-based solid electrolyte 10 with the coating layer is preferably 40 or less, and more preferably 20 or less.

[0029] The cathode material 20 of this embodiment can be produced by weighing and mixing the cathode active material 21 and the sulfide-based solid electrolyte 10 with the coating layer of this embodiment in a predetermined ratio.

[0030] According to the sulfide-based solid electrolyte 10 with a coating layer of this embodiment configured as described above, the coating layer 12 is formed on the surface of the sulfide-based solid electrolyte 11, so that the reaction between the sulfide-based solid electrolyte 11 and moisture and the positive electrode active material 21 can be suppressed, and deterioration of the sulfide-based solid electrolyte 11 can be suppressed. Furthermore, since the coating layer 12 contains a lithium ion conductive material and an electron conductive material, lithium ion conductivity and electron conductivity are ensured. Therefore, even when forming the cathode material 20, for example, it is not necessary to add a conductive additive, and the battery capacity can be ensured.

[0031] In the sulfide-based solid electrolyte 10 with a coating layer of this embodiment, when the lithium ion conductive material is one or more selected from lithium niobate, lithium tungstate, and lithium tantalate, the lithium ion conductivity is sufficiently excellent and the sulfide-based solid electrolyte 10 is particularly suitable as a material for constituting a lithium ion battery.

[0032] In the sulfide-based solid electrolyte 10 with a coating layer according to this embodiment, when the electron-conductive material is a carbon material, the carbon material has sufficiently excellent electron conductivity and is particularly suitable as a material for constituting a lithium-ion battery. Furthermore, the carbon material does not react with the sulfide-based solid electrolyte 11 or the positive electrode active material 21, thereby suppressing deterioration of the sulfide-based solid electrolyte 11 and the positive electrode active material 21 and stabilizing their characteristics.

[0033] The cathode material 20 of this embodiment includes the cathode active material 21 and the sulfide-based solid electrolyte 10 with a coating layer of this embodiment, and therefore has lithium ion conductivity and electron conductivity, eliminating the need to add a conductive additive and ensuring battery capacity.

[0034] Although one embodiment of the present invention has been described above, the present invention is not limited to this and can be modified as appropriate within the scope of the technical idea of ​​the invention. In this embodiment, the cathode material is described as not containing a conductive additive, but a small amount may be added as needed. Even in this case, the amount of conductive additive added is extremely small compared to conventional cathode materials, so that sufficient battery capacity can be ensured. [Example]

[0035] A confirmation experiment conducted to confirm the effectiveness of the present invention will be described.

[0036] (Examples 1, 2, 3, and 4 of the present invention) A sulfide-based solid electrolyte powder shown in Table 1 was prepared. Target materials of the ion-conductive material and electron-conductive material shown in Table 1 were loaded into a barrel sputtering device. The sulfide-based solid electrolyte powder was then placed in the barrel sputtering device, and sputtering was carried out in an inert gas atmosphere at 500 W for 5 hours. This produced a sulfide-based solid electrolyte with a coating layer.

[0037] Next, NMC532 was prepared as a positive electrode active material, and the positive electrode active material was mixed with a sulfide-based solid electrolyte with a coating layer in the ratio shown in Table 1 to produce a positive electrode material. A battery was constructed using the above-mentioned positive electrode material, Li-In foil as the negative electrode material, a sulfide-based solid electrolyte (uncoated) shown in Table 1 as the electrolyte layer, and a Hosen cell (KP-SolidCell) as the cell.

[0038] (Comparative Examples 1-1, 2-1, 3-1, 4-1) A sulfide-based solid electrolyte powder shown in Table 1 was prepared. A target material of the ion-conductive material shown in Table 1 was loaded into a barrel sputtering apparatus. The sulfide-based solid electrolyte powder was then placed in the barrel sputtering apparatus, and sputtering film formation was carried out under conditions of 500 W and 5 hours in an inert gas atmosphere. This produced a sulfide-based solid electrolyte coated only with the ion-conductive material.

[0039] Next, NMC532 was prepared as the positive electrode active material and acetylene black as the conductive additive. The positive electrode active material, sulfide-based solid electrolyte coated with only ion-conductive material, and conductive additive were mixed in the ratios shown in Table 1 to produce the positive electrode material. A battery was constructed using the above-mentioned positive electrode material, Li-In foil as the negative electrode material, a sulfide-based solid electrolyte (uncoated) shown in Table 1 as the electrolyte layer, and a Hosen cell (KP-SolidCell) as the cell.

[0040] (Comparative Examples 1-2, 2-2, 3-2, 4-2) NMC532 was prepared as the positive electrode active material. Furthermore, a target material of the ion-conductive material shown in Table 1 was loaded into a barrel sputtering apparatus. The above-described positive electrode active material was then loaded into the barrel sputtering apparatus, and sputtering film formation was carried out under conditions of 500 W and 5 hours in an inert gas atmosphere. This resulted in the production of a positive electrode active material coated only with the ion-conductive material.

[0041] Next, the sulfide-based solid electrolyte powder shown in Table 1 and acetylene black as a conductive additive were prepared, and the positive electrode active material coated with only the ion-conductive material, the sulfide-based solid electrolyte, and the conductive additive were mixed in the ratios shown in Table 1 to produce the positive electrode material. A battery was constructed using the above-mentioned positive electrode material, Li-In foil as the negative electrode material, a sulfide-based solid electrolyte (without an ion-conductive material film) shown in Table 1 as the electrolyte layer, and a Hohsen cell (KP-SolidCell) as the cell.

[0042] The discharge capacity of each battery obtained as described above was evaluated. Charging was performed with CC charging at 0.1 C and CV charging at 3.6 V and 0.01 C. Discharging was performed with CC discharging at 0.5 C and 1.9 V cutoff. The evaluation results are shown in Table 1.

[0043] [Table 1]

[0044] LGPS (Li) as a sulfide-based solid electrolyte 10。35 Ge 1.35 P 1.65 S 12 ), Example 1 of the present invention, in which a coating layer containing an ion conductive material and an electron conductive material was formed, had a larger discharge capacity than Comparative Example 1-1, in which only a lithium ion conductive material was coated on a sulfide-based solid electrolyte, and Comparative Example 1-2, in which only a lithium ion conductive material was coated on a positive electrode active material.

[0045] As a sulfide-based solid electrolyte, LSSPS (Li10.35 [Sn 0.27 Si 1.08 ]P 1.65 S 12 ), Example 2 of the present invention, in which a coating layer containing an ion conductive material and an electron conductive material was formed, had a larger discharge capacity than Comparative Example 2-1, in which only a lithium ion conductive material was coated on a sulfide-based solid electrolyte, and Comparative Example 2-2, in which only a lithium ion conductive material was coated on a positive electrode active material.

[0046] Comparing Inventive Example 3, which used Li5PS5Cl as the sulfide-based solid electrolyte, with Comparative Examples 3-1 and 3-2, Inventive Example 3, in which a coating layer containing an ion conductive material and an electron conductive material was formed, had a larger discharge capacity than Comparative Example 3-1, in which the sulfide-based solid electrolyte was coated with only a lithium ion conductive material, and Comparative Example 3-2, in which the positive electrode active material was coated with only a lithium ion conductive material.

[0047] Li7P3S as a sulfide-based solid electrolyte 11 Comparing Inventive Example 4, which used glass ceramics, with Comparative Examples 4-1 and 4-2, Inventive Example 4, in which a coating layer containing an ion conductive material and an electron conductive material was formed, had a larger discharge capacity than Comparative Example 4-1, in which only a lithium ion conductive material was coated on a sulfide-based solid electrolyte, and Comparative Example 4-2, in which only a lithium ion conductive material was coated on a positive electrode active material.

[0048] As a result of the above confirmatory experiments, it was confirmed that the present invention can provide a sulfide-based solid electrolyte with a coating layer that has excellent ionic conductivity and electronic conductivity, and is capable of suppressing reactions with moisture, positive electrode active materials, etc., and is particularly suitable for all-solid-state batteries, as well as a positive electrode material that uses this sulfide-based solid electrolyte with a coating layer. It was also confirmed that similar effects could be obtained regardless of the material of the sulfide-based solid electrolyte used. [Explanation of symbols]

[0049] 10 Sulfide-based solid electrolyte with coating layer 11 Sulfide solid electrolyte 12 Coating Layer 20 Cathode material 21 Cathode active material

Claims

1. A sulfide-based solid electrolyte with a coating layer, in which a coating layer is formed on a surface of the sulfide-based solid electrolyte, The sulfide-based solid electrolyte with a coating layer, wherein the coating layer contains a lithium ion conductive material and an electron conductive material.

2. 2. The sulfide-based solid electrolyte with a coating layer according to claim 1, wherein the lithium ion conductive material is one or more selected from the group consisting of lithium niobate, lithium tungstate, and lithium tantalate.

3. 2. The sulfide-based solid electrolyte with a coating layer according to claim 1, wherein the electron-conductive material is a carbon material.

4. A cathode material comprising: a cathode active material; and the sulfide-based solid electrolyte with the coating layer according to claim 1 .

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