Positive electrode mixture and all-solid-state battery

Abstract

To provide a positive electrode mixture capable of giving an all-solid-state battery which can achieve higher capacity and suppress capacity reduction even when charging and discharging are repeated.SOLUTION: The positive electrode mixture contains a positive electrode active material, a conductive assistant, and a solid electrolyte. The content of the positive electrode active material is 5 mass% or more and 70 mass% or less, the content of the conductive assistant is 10 mass% or more and 70 mass% or less, and the content of the solid electrolyte is 20 mass% or more and 70 mass% or less based on the total mass of the positive electrode active material, the conductive assistant, and the solid electrolyte.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a positive electrode composite material and a all-solid-state battery.

Background Art

[0002] Recently, organic polysulfides have been synthesized as cathode active materials that exceed the battery performance of sulfur. However, conventional organic polysulfides exhibit a capacity lower than the theoretical capacity of sulfur because the π-organic moiety is not conjugated with the sulfur chain. Non-Patent Document 1 discloses that an organic polysulfide synthesized by inverse vulcanization using a disulfide compound exhibits a higher capacity equal to the theoretical capacity of sulfur due to enhanced electron conductivity based on the conjugation between the organic moiety and the sulfur chain. Furthermore, it has also been disclosed that an organic polysulfide containing a 1,3-dithiol-2-thione moiety exhibits the highest capacity due to enhanced electron conductivity.

Prior Art Documents

Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As described above, according to the lithium metal battery of Non-Patent Document 1, high capacity can be achieved.

[0005] However, in the lithium metal battery of Non-Patent Document 1, there is still room for further improvement in suppressing the capacity degradation after repeated charge and discharge.

[0006] An object of the present disclosure is to provide a positive electrode composite material capable of obtaining an all-solid-state battery that can achieve high capacity and suppress capacity degradation even after repeated charge and discharge, and an all-solid-state battery that can achieve high capacity and suppress capacity degradation even after repeated charge and discharge.

Means for Solving the Problems

[0007] The positive electrode composite material according to one aspect of the present disclosure contains a positive electrode active material, a conductive assistant, and a solid electrolyte. With respect to the total mass of the positive electrode active material, the conductive assistant, and the solid electrolyte, the content of the positive electrode active material is 5% by mass or more and 70% by mass or less, the content of the conductive assistant is 10% by mass or more and 70% by mass or less, and the content of the solid electrolyte is 20% by mass or more and 70% by mass or less.

[0008] The all-solid-state battery according to one aspect of the present disclosure includes a positive electrode, a solid electrolyte layer, and a negative electrode in this order. The positive electrode contains the positive electrode composite material. The solid electrolyte layer contains a sulfide-based solid electrolyte. The negative electrode contains at least one substance selected from the group consisting of lithium, indium, lithium titanate, and lithium silicon.

Advantages of the Invention

[0009] According to the present disclosure, an all-solid-state battery that can achieve high capacity and suppress capacity degradation even after repeated charge and discharge can be obtained.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0011] <Positive Electrode Composite Material> Hereinafter, the positive electrode composite material according to the present embodiment will be described. The positive electrode composite material is in powder form and contains a positive electrode active material, a conductive assistant, and a solid electrolyte. In the positive electrode composite material, the three components of the positive electrode active material, the conductive assistant, and the solid electrolyte are mixed. The mixing ratio of these three components is also one of the features of the present embodiment. In Examples 1 and 2 described later, the mixing ratio (mass ratio) of the three components is approximately positive electrode active material: conductive assistant: solid electrolyte = 15:35:50.

[0012] ≪Positive Electrode Active Material≫ The positive electrode active material is not particularly limited, but preferably contains a sulfide polymer compound having a repeating unit represented by the following formula (1) and / or a sulfide polymer compound having a repeating unit represented by the following formula (2). These sulfide polymer compounds have a high sulfur content and exhibit excellent charge-discharge characteristics, and thus are useful as positive electrode active materials for increasing the capacity of all-solid-state batteries. In this specification, the sulfide polymer compound means a polymer compound having a chemical structure of sulfide, or polysulfide such as disulfide or trisulfide.

[0013]

Chemical Formula

[0014] In the positive electrode composite material, the content of the positive electrode active material is 5% by mass or more and 70% by mass or less, preferably 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more and 50% by mass or less, based on the total mass of the positive electrode active material, the conductive assistant, and the solid electrolyte.

[0015] ≪Conductive Assistant≫ The conductive aid is not particularly limited, but preferably contains a conductive carbon material. Examples of the conductive carbon material include graphite such as natural graphite and artificial graphite; carbon blacks such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers; and carbon fluoride. The conductive carbon material may be used alone or in combination of two or more.

[0016] In the positive electrode composite material, the content of the conductive aid is 10% by mass or more and 70% by mass or less, preferably 20% by mass or more and 70% by mass or less, more preferably 25% by mass or more and 60% by mass or less, based on the total mass of the positive electrode active material, the conductive aid, and the solid electrolyte.

[0017] ≪Solid Electrolyte≫ The solid electrolyte is not particularly limited, but preferably contains a sulfide-based solid electrolyte. Examples of the sulfide-based solid electrolyte include Li3PS4, Li2S-P2S5, Li2S-SiS2, Li2S-P2S5-LiX, Li2S-SiS2-LiX, Li2S-P2S5-LixA, Li2S-P2S5-LixA-LiX, Li2S-P2S5-GeS2, Li7P3S 11 , Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , and Li 10 GeP2S 12 and the like. The sulfide-based solid electrolyte may be used alone or in combination of two or more.

[0018] The solid electrolyte also functions as a binder in the positive electrode composite material. That is, in the positive electrode composite material, the solid electrolyte forms a chemical bond with the positive electrode active material.

[0019] In the positive electrode composite material, the content of the solid electrolyte is 20% by mass or more and 70% by mass or less, preferably 25% by mass or more and 70% by mass or less, more preferably 30% by mass or more and 70% by mass or less, based on the total mass of the positive electrode active material, the conductive assistant, and the solid electrolyte.

[0020] <All-solid-state battery> Next, the all-solid-state battery according to this embodiment will be described. The all-solid-state battery includes a positive electrode, a solid electrolyte layer, and a negative electrode in this order. The all-solid-state battery may further include a container that houses the positive electrode, the solid electrolyte layer, and the negative electrode as needed. The material of the container is not particularly limited, and examples thereof include polyetheretherketone (PEEK), polypropylene (PP), polyethylene (PE), and acrylic resin (PMMA).

[0021] The positive electrode includes a positive electrode composite material. The positive electrode composite material is obtained by mixing the above-described positive electrode active material, conductive assistant, and solid electrolyte. This mixing is preferably performed in two steps. Specifically, it is preferable to mix the positive electrode active material and the conductive assistant (first-step mixing), and then add the solid electrolyte to this mixture and further mix (second-step mixing). It is preferable to perform both mixings in a glove box. The inside of the glove box has little oxygen and moisture and is replaced with an inert gas (for example, argon).

[0022] The solid electrolyte layer is formed by pressing the solid electrolyte into a layer. The solid electrolyte layer includes a sulfide-based solid electrolyte. The positive electrode is disposed by being pressed on one side of the solid electrolyte layer.

[0023] The negative electrode is disposed by being pressed on the other side of the solid electrolyte layer. The negative electrode includes at least one substance selected from the group consisting of lithium, indium, lithium titanate, and lithium silicon. When the negative electrode contains lithium and indium, lithium and indium may be alloyed.

[0024] <Summary> As is clear from the above embodiment, the present disclosure includes the following aspects.

[0025] The first aspect is a positive electrode composite material containing a positive electrode active material, a conductive assistant, and a solid electrolyte. With respect to the total mass of the positive electrode active material, the conductive assistant, and the solid electrolyte, the content of the positive electrode active material is 5% by mass or more and 70% by mass or less, the content of the conductive assistant is 10% by mass or more and 70% by mass or less, and the content of the solid electrolyte is 20% by mass or more and 70% by mass or less.

[0026] According to this aspect, it is possible to obtain an all-solid-state battery that can achieve a higher capacity and suppress a decrease in capacity even when charge and discharge are repeated.

[0027] The second aspect is a positive electrode composite material based on the first aspect. In the second aspect, the positive electrode active material includes a sulfide polymer compound having a repeating unit represented by the following formula (1) and / or a sulfide polymer compound having a repeating unit represented by the following formula (2).

[0028]

Chemical formula

[0029] According to this aspect, it is possible to obtain an all-solid-state battery that can achieve an even higher capacity and further suppress a decrease in capacity even when charge and discharge are repeated.

[0030] The third aspect is a positive electrode composite material based on the first or second aspect. In the third aspect, the conductive assistant includes a conductive carbon material.

[0031] According to this aspect, it is possible to obtain an all-solid-state battery that can achieve an even higher capacity and further suppress a decrease in capacity even when charge and discharge are repeated.

[0032] The fourth aspect is a positive electrode composite material based on any one of the first to third aspects. In the fourth aspect, the solid electrolyte includes a sulfide-based solid electrolyte.

[0033] According to this aspect, it is possible to obtain an all-solid-state battery that can achieve further increased capacity and further suppress capacity degradation even when charge and discharge are repeated.

[0034] A fifth aspect is an all-solid-state battery including a positive electrode, a solid electrolyte layer, and a negative electrode in this order. The positive electrode includes a positive electrode composite material based on any one of the first to fourth aspects. The solid electrolyte layer includes a sulfide-based solid electrolyte. The negative electrode includes at least one substance selected from the group consisting of lithium, indium, lithium titanate, and lithium silicon.

[0035] According to this aspect, it is possible to achieve increased capacity and suppress capacity degradation even when charge and discharge are repeated.

Examples

[0036] Hereinafter, the present disclosure will be specifically described by way of examples. However, the present disclosure is not limited to the following examples.

[0037] <Example 1> ≪Synthesis of Solid Electrolyte≫ The sulfide-based solid electrolyte (Li3PS4) was synthesized as follows. First, 1.3886 g of Li2S and 2.2195 g of P2S5 were weighed in a glove box purged with an inert gas, and these were transferred into a milling pot with a volume of 80 mL. Further, milling balls (made of ZrO, φ5 mm) and 11.7 mL of heptane were added into the above milling pot, and the lid of the milling pot was closed and sealed.

[0038] Next, the above milling pot was set in a ball mill apparatus, and milling treatment was performed under the conditions of a rotation speed of 500 rpm and a stirring time of 20 hours. Thereby, Li3PS4 was obtained.

[0039] ≪Preparation of Positive Electrode Composite Material≫ The positive electrode composite material was prepared as follows. As the positive electrode active material, a sulfide polymer compound having a repeating unit represented by the formula (1) was used. On the other hand, as the conductive assistant, carbon black (Tokablack #5500, manufactured by Tokai Carbon Co., Ltd.) was used. These positive electrode active material and conductive assistant were vacuum dried at room temperature for 24 hours.

[0040] Next, in a glove box replaced with an inert gas, 50 mg of the positive electrode active material, 100 mg of carbon black, and milling balls (made of ZrO, φ5 mm) were placed in a milling pot with a capacity of 50 mL, and the lid was closed and sealed. Then, this milling pot was set in a ball mill apparatus, and milling treatment was performed under the conditions of a rotation speed of 600 rpm and a stirring time of 2 hours.

[0041] Thereafter, the above-mentioned milling pot was returned into the glove box, the lid was opened, and 150 mg of a sulfide-based solid electrolyte (Li3PS4) was put into the milling pot. Again, the sealed milling pot with the lid closed was set in the ball mill apparatus, and milling treatment was performed under the conditions of a rotation speed of 600 rpm and a stirring time of 2 hours. As a result, a positive electrode composite material was obtained. The mixing ratio (mass ratio) of the three components in this positive electrode composite material is approximately positive electrode active material:conductive assistant:solid electrolyte = 15:35:50.

[0042] ≪Fabrication of All-Solid-State Battery≫ The all-solid-state battery was fabricated as follows using the above-mentioned solid electrolyte and positive electrode composite material as raw materials.

[0043] First, 80 mg of the solid electrolyte was weighed and placed in a cylindrical container made of PEEK.

[0044] Next, using a press machine, the solid electrolyte in the cylindrical container was pressed for about 10 seconds for temporary molding. As a result, the solid electrolyte became layered.

[0045] Next, 10 mg of the positive electrode composite material was weighed and placed on one side of the layered solid electrolyte. Thereafter, using a press machine, the positive electrode composite material was pressed against the solid electrolyte side.

[0046] Next, a Li foil (φ4.5 mm), an In foil (φ8 mm), and a stainless steel foil (φ10 mm) were prepared and placed on the other side (opposite to the positive electrode composite material) of the layered solid electrolyte. They were arranged in the order of In foil, Li foil, and stainless steel foil from the side closer to the solid electrolyte. Then, using a press machine, these metal foils were pressed onto the solid electrolyte side. As a result, an all-solid-state battery including a positive electrode, a solid electrolyte layer, and a negative electrode in this order was obtained.

[0047] The all-solid-state battery obtained as described above was fixed to an all-solid cell (battery evaluation cell) by screwing. Further, while pulling out a pair of electric wires from the all-solid-state battery, the all-solid cell was placed in a sealed container and sealed. The entire sealed container was left standing in a constant temperature bath at 60 °C overnight to alloy the Li foil and the In foil. In this way, a test all-solid-state battery was fabricated.

[0048] <Example 2> A test all-solid-state battery was fabricated in the same manner as in Example 1, except that a sulfide polymer compound having a repeating unit represented by formula (2) was used instead of the sulfide polymer compound having a repeating unit represented by formula (1) as the positive electrode active material.

[0049] <Charge and Discharge Cycle Test> For the test all-solid-state batteries of Examples 1 and 2, a charge and discharge cycle test (0.05C, 50 cycles) was carried out at room temperature between a voltage of about 0.6 V and about 2.1 V. Here, C represents the C rate, and the current amount for discharging the total capacity of the battery in 1 hour is defined as 1C rate.

[0050] ≪Test Results of Example 1≫ The test results of Example 1 are shown in FIG. 1. The constant current value is 0.085 mA.

[0051] The charge capacity and the discharge capacity are as shown in Tables 1 and 2.

[0052]

Table 1

[0053]

Table 2

[0054] The charge capacity and discharge capacity are as shown in Table 3 and Table 4.

[0055]

Table 3

[0056]

Table 4

[0057] From the above results, it was confirmed that for all-solid-state batteries of both Examples 1 and 2, high capacity can be achieved and capacity degradation can be suppressed even when charging and discharging are repeated at least 50 times.

Claims

1. A positive electrode composite material containing a positive electrode active material, a conductive assistant, and a solid electrolyte, wherein, with respect to the total mass of the positive electrode active material, the conductive assistant, and the solid electrolyte, the content of the positive electrode active material is 5% by mass or more and 70% by mass or less, the content of the conductive assistant is 10% by mass or more and 70% by mass or less, and the content of the solid electrolyte is 20% by mass or more and 70% by mass or less. Positive electrode composite material.

2. The positive electrode active material includes a sulfide polymer compound having a repeating unit represented by the following formula (1) and / or a sulfide polymer compound having a repeating unit represented by the following formula (2), The positive electrode composite material according to claim 1. 【Chemical 1】

3. The conductive assistant includes a conductive carbon material, The positive electrode composite material according to claim 1.

4. The solid electrolyte includes a sulfide-based solid electrolyte, The positive electrode composite material according to claim 1.

5. An all-solid-state battery including a positive electrode, a solid electrolyte layer, and a negative electrode in this order, wherein the positive electrode includes the positive electrode composite material according to any one of claims 1 to 4, the solid electrolyte layer includes a sulfide-based solid electrolyte, and the negative electrode includes at least one substance selected from the group consisting of lithium, indium, lithium titanate, and lithium silicon. All-solid-state battery.

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