Cathode mix for all-solid-state battery

Abstract

To provide a cathode mix capable of improving the discharge capacity of a battery.SOLUTION: A cathode mix for an all-solid-state battery comprises: a sulfur-containing cathode active material; a first sulfur-containing compound including cobalt; a second sulfur-containing compound including phosphorus; and a conductive additive.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] With the recent electrification of means of transportation such as electric vehicles, the development of batteries used as their power sources has attracted attention, and the development of high-output and high-capacity batteries has been underway.

[0003] All-solid-state batteries have attracted attention as next-generation batteries capable of improving safety. Among them, the development of all-solid-state lithium-sulfur batteries using sulfur, which has a very high theoretical capacity of 1675 mAh / g, as a positive electrode active material has been underway. In addition, in the field of sulfur batteries, attempts have been made to improve the utilization rate of sulfur and increase the charge-discharge capacity of sulfur batteries.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] Increasing the capacity of batteries is required. The present disclosure has been made in view of the above circumstances, and the main object is to provide a positive electrode composite material capable of improving the discharge capacity of a battery.

Means for Solving the Problems

[0006] To achieve the above object, the present disclosure provides a positive electrode active material containing sulfur, and A first sulfur-containing compound containing cobalt, a second sulfur-containing compound containing phosphorus, a conductive assistant, and a positive electrode composite material for an all-solid-state battery containing the same are provided.

[0007] In one embodiment, the mass ratio of the first sulfur-containing compound to the total mass of the positive electrode active material, the first sulfur-containing compound, the second sulfur-containing compound, and the conductive assistant may be greater than 0 and not more than 0.25.

[0008] In one embodiment, the molar ratio (Co / P) of cobalt contained in the first sulfur-containing compound to phosphorus contained in the second sulfur-containing compound may be greater than 0 and not more than 3.

[0009] In one embodiment, the positive electrode active material may contain one or more selected from the group consisting of elemental sulfur and Li2S.

[0010] In one embodiment, the first sulfur-containing compound may contain one or more selected from the group consisting of CoS, CoS2, Co3S4, and Co9S8.

[0011] In one embodiment, the second sulfur-containing compound may contain one or more selected from the group consisting of P2S5, P2S4, P4S7, P4S5, and P4S3.

[0012] In one embodiment, it may not contain Li element.

Advantages of the Invention

[0013] The present disclosure can provide a positive electrode composite material capable of improving the discharge capacity of a battery.

Brief Description of the Drawings

[0014]

Figure 1

Mode for Carrying Out the Invention

[0015] In the present disclosure, a positive electrode composite material for an all-solid-state battery is provided, which includes a sulfur-containing positive electrode active material, a first sulfur-containing compound containing cobalt, a second sulfur-containing compound containing phosphorus, and a conductive assistant.

[0016] Among sulfur batteries, lithium-sulfur batteries assume a normal operating voltage with an upper limit voltage of 3.1V - a lower limit voltage of 1.5V. However, due to variations in the battery voltage during charging and discharging, etc., the battery voltage may reach 1.5V or less. There is a need for a positive electrode composite material that does not deteriorate even at 1.5V or less and has a high capacity.

[0017] As a positive electrode composite material for an all-solid-state battery, a positive electrode composite material containing a sulfur-containing positive electrode active material as an alternative to expensive lithium sulfide (Li2S), a second sulfur-containing compound having P and S elements, and a conductive assistant has problems such as low electron conductivity and low adhesion between components in the positive electrode composite material, and the discharge capacity decreases (the irreversible capacity increases) with each charge and discharge of the battery. This is considered to be because side reactions occur when the battery voltage is 1.5V or less, the second sulfur-containing compound is reduced, and the adhesion between components in the positive electrode composite material decreases.

[0018] Also, as a positive electrode composite material for an all-solid-state battery, a positive electrode composite material containing a sulfur-containing positive electrode active material, a first sulfur-containing compound having Co and S elements, and a conductive assistant shows good cycle characteristics even when the lower limit voltage is set to 1V, but there is a problem that the discharge capacity of the battery is low. This is considered to be because in order to increase the capacity, it is necessary for the sulfur-containing positive electrode active material and the sulfur-containing compound to react and form a composite, but the amount of the first sulfur-containing compound containing cobalt required for the composite formation is larger than that of the second sulfur-containing compound containing phosphorus.

[0019] The present inventors have found that by using a positive electrode composite material containing a first sulfur-containing compound containing cobalt and a second sulfur-containing compound containing phosphorus in a battery, the electron conductivity of the positive electrode composite material in the charge and discharge reaction of the battery and the adhesion between the components in the positive electrode composite material can be improved, and the discharge capacity of the battery (especially the discharge capacity when the lower limit voltage is set to 1.5 V) can be improved.

[0020] 1. Positive electrode active material The positive electrode active material has an S element. Various materials can be adopted as the positive electrode active material containing sulfur. For example, the positive electrode active material may contain one or more selected from the group consisting of elemental sulfur and Li2S. Examples of elemental sulfur include S8 sulfur. S8 sulfur can have three crystal forms, namely α-sulfur (orthorhombic sulfur), β-sulfur (monoclinic sulfur), and γ-sulfur (monoclinic sulfur), and any crystal form may be used.

[0021] The amount of the positive electrode active material contained in the positive electrode composite material is not particularly limited and may be appropriately determined according to the intended battery performance. For example, the positive electrode composite material may contain 10% by mass or more and 80% by mass or less of the positive electrode active material. The lower limit may be 15% by mass or more, 20% by mass or more, or 25% by mass or more. The upper limit may be 70% by mass or less, 60% by mass or less. If the content of the positive electrode active material is too large, the ion conductivity and electron conductivity in the positive electrode layer of the battery may be insufficient.

[0022] Part or all of the positive electrode active material may be dissolved in the sulfur-containing compound described later. In other words, the positive electrode composite material may contain a solid solution of the positive electrode active material and the sulfur-containing compound. Further, the S element in the positive electrode active material and the S element in the sulfur-containing compound may have a chemical bond (S-S bond).

[0023] 2. Sulfur-containing compound The positive electrode composite material in the present disclosure contains, as sulfur-containing compounds, at least a first sulfur-containing compound containing cobalt and a second sulfur-containing compound containing phosphorus. The first sulfur-containing compound containing cobalt may be a semiconductor and can have higher electron conductivity than elemental sulfur, which is an insulator used as a positive electrode active material. Further, the first sulfur-containing compound containing cobalt has mechanical flexibility and can improve the adhesion between components in the positive electrode composite material. The second sulfur-containing compound containing phosphorus can form a compound with lithium during the first discharge of the all-solid-state battery and have ion conductivity.

[0024] In the positive electrode composite material in the present disclosure, the mass ratio of the first sulfur-containing compound to the total mass of the positive electrode active material, the first sulfur-containing compound, the second sulfur-containing compound, and the conductive assistant {for example, CoS / (S + CoS + P2S5 + VGCF)} may be greater than 0 and less than or equal to 0.25. Preferably, the above mass ratio may be greater than 0 and less than or equal to 0.15. More preferably, the above mass ratio may be 0.01 or more and 0.1 or less. Even more preferably, the above mass ratio may be 0.03 or more and 0.075 or less. When the above mass ratio is within the above range, the electron conductivity of the positive electrode composite material and the adhesion between components in the positive electrode composite material can be improved, and the discharge capacity of the battery can be improved.

[0025] In the positive electrode composite material in the present disclosure, the molar ratio of cobalt contained in the first sulfur-containing compound to phosphorus contained in the second sulfur-containing compound (Co / P) may be greater than 0 and less than or equal to 3. Preferably, the above molar ratio may be greater than 0 and less than or equal to 2. More preferably, the above molar ratio may be greater than 0 and less than or equal to 1. Even more preferably, the above molar ratio may be greater than 0 and less than or equal to 0.5. Most preferably, the above molar ratio may be 0.1 or more and 0.35 or less. When the above molar ratio is within the above range, the balance between the ion conductivity and the electron conductivity of the positive electrode composite material can be improved, and the discharge capacity of the battery can be improved.

[0026] During the discharge of the battery, carrier ions conduct from the negative electrode layer through the solid electrolyte layer to the positive electrode layer. However, the carrier ions reaching the positive electrode layer react with the positive electrode active material, generating discharge products with low ionic conductivity (e.g., Li2S). Therefore, when there is no second sulfur-containing compound having P element and S element in the positive electrode layer, due to the low ionic conductivity of the discharge products, the ionic conduction path in the positive electrode layer is insufficient, and the discharge reaction may be difficult to proceed. On the contrary, when there is a second sulfur-containing compound containing phosphorus in the positive electrode layer, even if the ionic conductivity of the discharge products is low, the second sulfur-containing compound containing phosphorus ensures the ionic conduction path in the positive electrode layer, so the discharge reaction is likely to proceed. In addition, the first sulfur-containing compound having Co element and S element exhibits high electronic conductivity in the positive electrode composite material and adhesion between components in the positive electrode composite material, so it can also suppress the deterioration of the positive electrode composite material due to side reactions and detachment between components. Therefore, by using a positive electrode composite material containing a first sulfur-containing compound containing cobalt and a second sulfur-containing compound containing phosphorus in the battery, the electronic conductivity of the positive electrode composite material and the adhesion between components in the positive electrode composite material in the charge and discharge reaction of the battery can be improved, and the discharge capacity of the battery (especially the discharge capacity when the lower limit voltage is set to 1.5 V) can be improved.

[0027] The positive electrode composite material may contain a first sulfur-containing compound containing cobalt and a second sulfur-containing compound containing phosphorus, and may further contain a third sulfur-containing compound having other elements (e.g., Ge, Sn, Si, or Al) and S element. In the latter case, the positive electrode composite material may contain a first sulfur-containing compound containing cobalt and a second sulfur-containing compound containing phosphorus as the main components of the sulfur-containing compounds. Specifically, taking the total of the sulfur-containing compounds contained in the positive electrode composite material as 100% by mass, the first sulfur-containing compound containing cobalt and the second sulfur-containing compound containing phosphorus may be contained in a total amount of 50% by mass or more and 100% by mass or less.

[0028] The positive electrode composite material may contain a sulfide as a sulfur-containing compound. That is, the first sulfur-containing compound may have a sulfide of Co element. The first sulfur-containing compound may include one or more selected from the group consisting of CoS, CoS2, Co3S4, and Co9S8. Preferably, the first sulfur-containing compound may be CoS. On the other hand, the second sulfur-containing compound containing phosphorus may have a sulfide of P element. The second sulfur-containing compound may include one or more selected from the group consisting of P2S5, P2S4, P4S7, P4S5, and P4S3. Preferably, the second sulfur-containing compound may be P2S5.

[0029] In addition, the sulfur-containing compound may have a sulfide of M element (M x S y ). Here, x and y are integers that give electrical neutrality with S according to the type of M. Examples of the sulfide (M x S y ) include, for example, GeS2, SnS2, SiS2, and Al2S3. Also, these sulfides may be, for example, residues of starting materials.

[0030] As long as the positive electrode composite material of the present disclosure contains a first sulfur-containing compound containing cobalt and a second sulfur-containing compound containing phosphorus as sulfur-containing compounds, the amount of the sulfur-containing compound contained in the positive electrode composite material is not particularly limited and may be appropriately determined according to the intended battery performance. For example, the positive electrode composite material may contain 10% by mass or more and 80% by mass or less of the sulfur-containing compound. The lower limit may be 15% by mass or more, 20% by mass or more, or 25% by mass or more. The upper limit may be 70% by mass or less, 60% by mass or less. If the content of the sulfur-containing compound is too large, the content of the positive electrode active material will be relatively small, and a positive electrode composite material having sufficient capacity may not be obtained.

[0031] 3. Conductive aid The conductive additive has a function of improving the electronic conductivity of the positive electrode composite material. Also, it is presumed that the conductive additive functions as a reducing agent that reduces elemental sulfur (the positive electrode active material), for example, when mechanical milling is performed on the raw material mixture. The conductive additive may be dispersed and present in the positive electrode composite material.

[0032] Examples of the conductive additive include carbon materials and metal materials. Examples of the carbon materials include vapor-grown carbon fiber (VGCF), acetylene black, activated carbon, furnace black, carbon nanotubes, ketjen black, and graphene, etc. In the positive electrode composite material, two or more kinds of conductive additives may be mixed and used.

[0033] The amount of the conductive additive contained in the positive electrode composite material is not particularly limited and may be appropriately determined according to the intended battery performance. For example, the positive electrode composite material may contain 5% by mass or more and 50% by mass or less of the conductive additive. The lower limit may be 10% by mass or more. The upper limit may be 40% by mass or less. If the content of the conductive additive is too much, the content of the positive electrode active material will relatively decrease, and it may not be possible to obtain a positive electrode composite material having sufficient capacity.

[0034] 4. Elements not substantially contained 4-1. Li element As a conventional technique, a positive electrode composite material containing an ion conductor (solid electrolyte) having Li element is known. For example, an ion conductor using Li2S as a raw material is known. However, since Li2S has low water resistance, a battery using such a positive electrode composite material tends to have a low capacity. On the other hand, since the positive electrode composite material of the present disclosure may not substantially contain Li element, the above-described decrease in capacity can be suppressed.

[0035] "Substantially free of Li element" means that the proportion of Li element in all elements contained in the positive electrode composite material is 20 mol% or less. The proportion of Li element may be 16 mol% or less, 8 mol% or less, 4 mol% or less, 1 mol% or less, or 0 mol% (below the detection limit).

[0036] In the present disclosure, the positive electrode composite material means a material in a state before being incorporated into all-solid-state battery and performing the first Li insertion (first discharge). Therefore, the positive electrode layer of the all-solid-state battery after the first discharge may substantially contain Li element.

[0037] 5. Positive Electrode Composite Material The positive electrode composite material in the present disclosure may contain only a positive electrode active material, a sulfur-containing compound containing a first sulfur-containing compound containing cobalt and a second sulfur-containing compound containing phosphorus, and a conductive assistant, and may further contain other materials such as a binder.

[0038] Examples of the binder include acrylonitrile-butadiene rubber (ABR), butadiene rubber (BR), polyvinylidene fluoride (PVdF), styrene-butadiene rubber (SBR), etc. The content of the binder in the positive electrode composite material is not particularly limited.

[0039] The shape of the positive electrode composite material may be in powder form, may be in a lump form in which a plurality of particles are aggregated and bonded, or may be in other shapes. Depending on the form of the target battery, etc., various shapes can be adopted.

[0040] 6. Manufacturing Method of Positive Electrode Composite Material The manufacturing method of the positive electrode composite material in the present disclosure has at least (1) a preparation step of preparing a raw material containing a positive electrode active material containing sulfur, a sulfur-containing compound containing a first sulfur-containing compound containing cobalt and a second sulfur-containing compound containing phosphorus, and a conductive assistant, and (2) a mixing step of mixing the raw material to obtain a positive electrode composite material.

[0041] (1) Preparation Step The preparation process is a process of preparing a raw material containing a cathode active material containing sulfur, a sulfur-containing compound containing a first sulfur-containing compound containing cobalt and a second sulfur-containing compound containing phosphorus, and a conductive assistant. The raw material may be prepared by oneself or purchased from others.

[0042] The raw material may contain only the cathode active material, the sulfur-containing compound, and the conductive assistant, or may further contain other materials. Also, the raw material may not substantially contain Li element.

[0043] As described above, the cathode active material may be elemental sulfur. The elemental sulfur preferably has high purity.

[0044] Examples of the first sulfur-containing compound containing cobalt include CoS. Examples of the second sulfur-containing compound containing phosphorus include P2S5. The raw material may contain only the first sulfur-containing compound and the second sulfur-containing compound as the sulfur-containing compound, or may further contain sulfur-containing compounds of other elements. Examples of the sulfur-containing compounds of other elements include GeS2, SnS2, SiS2, and Al2S3.

[0045] Regarding the conductive assistant, it is as described above, and the description is omitted here.

[0046] The contents of the cathode active material, the sulfur-containing compound, and the conductive assistant in the raw material can be the same as the contents of the cathode active material, the sulfur-containing compound, and the conductive assistant in the above-described cathode composite material.

[0047] (2) Mixing process The mixing process is a process of mixing the raw material to obtain a cathode composite material. The means for mixing the raw material is not particularly limited. For example, the raw material may be mixed by mechanical milling. By mechanical milling, the raw material can be more easily amorphized.

[0048] Mechanical milling is not particularly limited as long as it is a method of mixing the positive electrode composite material while applying mechanical energy. Examples thereof include a ball mill, a vibration mill, a turbo mill, mechanofusion, and a disk mill. From the viewpoint of further facilitating the amorphization of the raw material, a planetary ball mill may be employed.

[0049] Mechanical milling may be dry mechanical milling or wet mechanical milling. Examples of the liquid used in wet mechanical milling include aprotic liquids that do not generate hydrogen sulfide. Specifically, aprotic liquids such as polar aprotic liquids and nonpolar aprotic liquids can be mentioned. Mechanical milling may be either dry mechanical milling or wet mechanical milling. Examples of the liquid used in wet mechanical milling include those having aprotic properties to such an extent that hydrogen sulfide is not generated. Specifically, aprotic liquids such as polar aprotic liquids and nonpolar aprotic liquids can be mentioned.

[0050] The conditions of mechanical milling are appropriately set so as to obtain a desired positive electrode composite material. For example, when using a planetary ball mill, a raw material mixture and grinding balls are added to a container, and the treatment is performed at a predetermined base rotation speed and time. The base rotation speed is, for example, 200 rpm or more, may be 300 rpm or more, and may be 500 rpm or more. On the other hand, the base rotation speed is, for example, 800 rpm or less, and may be 600 rpm or less. Also, the treatment time of the planetary ball mill is, for example, 30 minutes or more, and may be 5 hours or more. On the other hand, the treatment time of the planetary ball mill is, for example, 100 hours or less, and may be 60 hours or less. Examples of the materials for the container and grinding balls used in the planetary ball mill include ZrO2 and Al2O3. The diameter of the grinding balls is, for example, 1 mm or more and 20 mm or less. Mechanical milling is preferably performed in an inert gas atmosphere (for example, an Ar gas atmosphere).

[0051] 7. All-solid-state battery An all-solid-state battery includes a positive electrode including a positive electrode layer and a positive electrode current collector, a negative electrode including a negative electrode layer and a negative electrode current collector, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer.

[0052] The positive electrode layer contains the positive electrode composite material described above. The positive electrode layer may contain the solid electrolyte mentioned below.

[0053] The positive electrode layer may contain a solid electrolyte, if necessary. The solid electrolyte may be appropriately selected from the solid electrolytes that can be included in the solid electrolyte layer described later.

[0054] The thickness of the positive electrode layer is not particularly limited, but may be, for example, 0.1 μm or more and 1000 μm or less.

[0055] Also, the basis weight of the positive electrode layer is not particularly limited, but may be, for example, 3 mg / cm 2 or more, or 4 mg / cm 2 or more, or 5 mg / cm 2 or more.

[0056] The positive electrode layer can be easily formed, for example, by pressing the above positive electrode composite material.

[0057] The negative electrode layer is a layer containing at least a negative electrode active material.

[0058] The negative electrode active material may contain Li element. Examples of such negative electrode active materials include lithium metal or a lithium alloy. Examples of the lithium alloy include a Li-In alloy.

[0059] The negative electrode layer may contain at least one of a solid electrolyte, a conductive assistant, and a binder, if necessary. The solid electrolyte may be appropriately selected from the solid electrolytes that can be included in the solid electrolyte layer described later. The conductive assistant and the binder may be appropriately selected from the conductive assistant and the binder that can be included in the above positive electrode composite material.

[0060] The thickness of the negative electrode layer is not particularly limited, but may be, for example, 0.1 μm or more and 1000 μm or less.

[0061] The negative electrode layer can be easily formed, for example, by pressing the above-described negative electrode active material or the like. Alternatively, a foil made of the above material may be employed as the negative electrode layer.

[0062] The solid electrolyte layer is a layer containing at least a solid electrolyte, and may contain a binder as required.

[0063] Examples of the solid electrolyte include sulfide-based solid electrolytes, oxide-based solid electrolytes, nitride-based solid electrolytes, and halide-based solid electrolytes. Among them, sulfide-based solid electrolytes are preferred.

[0064] The sulfide-based solid electrolyte preferably has an Li element, an A element (A is at least one of P, Ge, Si, Sn, B, and Al), and an S element. The sulfide-based solid electrolyte may further have a halogen element. Examples of the halogen element include an F element, a Cl element, a Br element, and an I element. Further, the sulfide-based solid electrolyte may further have an O element.

[0065] Examples of the sulfide-based solid electrolyte include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-GeS2, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-P2S5-LiI-LiBr, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (where m and n are positive numbers. Z is either Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers. M is either P, Si, Ge, B, Al, Ga, or In). Desirably, it may include Li6PS5Cl, which is a sulfide-based solid electrolyte having an argyrodite structure.

[0066] The solid electrolyte can be used alone or in combination of two or more kinds. When using two or more kinds of solid electrolytes, they may be mixed, or layers of two or more kinds of solid electrolytes may be formed respectively to form a multilayer structure.

[0067] The proportion of the solid electrolyte contained in the solid electrolyte layer is not particularly limited. For example, it may be 50% by volume or more, 70% by volume or more, or 90% by volume or more. The binder used in the solid electrolyte layer may be appropriately selected from the binders that can be contained in the above-described positive electrode composite material.

[0068] The thickness of the solid electrolyte layer is not particularly limited. For example, it may be 0.1 μm or more and 1000 μm or less. The solid electrolyte layer can be easily formed, for example, by pressing the above-described solid electrolyte or the like.

[0069] Examples of the material of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon.

[0070] On the other hand, examples of the material of the negative electrode current collector include SUS, copper, nickel, and carbon.

[0071] The positive electrode current collector and the negative electrode current collector may be, for example, in the form of a foil or a mesh.

[0072] The all-solid-state battery may include an exterior body that houses the positive electrode, the negative electrode, and the solid electrolyte layer as needed.

[0073] The shape of the exterior body is not particularly limited, and examples thereof include a laminate type.

[0074] The material of the exterior body is not particularly limited as long as it is stable to the electrolyte, and examples thereof include resins such as polypropylene, polyethylene, and acrylic resin.

[0075] The all-solid-state battery in the present disclosure may be a sulfur battery. The sulfur battery means a battery using a positive electrode active material containing sulfur. The all-solid-state battery in the present disclosure may be a lithium-sulfur battery (LiS battery). The all-solid-state battery may be a primary battery or a secondary battery, but a secondary battery is preferred. This is because it can be repeatedly charged and discharged and is useful, for example, as an in-vehicle battery. Note that the use of a secondary battery as a primary battery (use for only one discharge after charging) is also included in the secondary battery.

[0076] Examples of the shape of the all-solid-state battery include coin type, laminate type, cylindrical type, and rectangular type.

[0077] The manufacturing method of the all-solid-state battery of the present disclosure is not particularly limited, and a conventionally known method can be adopted.

[0078] (Example 1) (Preparation of positive electrode composite material) Elemental sulfur S (positive electrode active material, high-purity chemical product), CoS (first sulfur-containing compound containing cobalt), P2S5 (second sulfur-containing compound containing phosphorus), and VGCF (conductive aid) were prepared. These were weighed so that the mass ratio of S / CoS / P2S5 / VGCF was 45 / 3 / 32 / 20, and each raw material was kneaded in an agate mortar for 15 minutes to obtain a raw material. The obtained raw material was put into a container (45 cc, made of ZrO2) of a planetary ball mill, and further ZrO2 balls (φ = 5 mm, 70 g) were put in, and the container was completely sealed. This container was attached to a planetary ball mill machine (P7 made by Fritsch), and a cycle of 1 hour of mechanical milling (table rotation speed 500 rpm), 15 minutes of stop, 1 hour of mechanical milling in reverse rotation (table rotation speed 500 rpm), and 15 minutes of stop was repeated, and a total of 20 hours of mechanical milling was performed. Thereby, a positive electrode composite material was obtained.

[0079] (Manufacture of all-solid-state battery) 1 cm 280 mg of the sulfide-based solid electrolyte Li6PS5Cl with an argyrodite-type structure was placed in a ceramic mold and pressed at 100 MPa to obtain a solid electrolyte layer. 5 mg of the positive electrode composite material (coating weight: 5 mg / cm 2 ) was placed on one side and pressed at 550 MPa to form a positive electrode layer. A lithium metal foil, which is the negative electrode layer, was placed on the opposite side and pressed at 20 MPa to obtain a power generation element. A SUS foil (positive electrode current collector) was placed on the positive electrode layer side, and a SUS foil (negative electrode current collector) was placed on the negative electrode layer side. Thereby, an all-solid-state battery was obtained.

[0080] (Example 2) A positive electrode composite material and an all-solid-state battery were obtained in the same manner as in Example 1, except that the ratio was changed so that the mass ratio of S / CoS / P2S5 / VGCF was 45 / 5 / 30 / 20.

[0081] (Example 3) A positive electrode composite material and an all-solid-state battery were obtained in the same manner as in Example 1, except that the ratio was changed so that the mass ratio of S / CoS / P2S5 / VGCF was 45 / 10 / 25 / 20.

[0082] (Example 4) A positive electrode composite material and an all-solid-state battery were obtained in the same manner as in Example 1, except that the ratio was changed so that the mass ratio of S / CoS / P2S5 / VGCF was 45 / 20 / 15 / 20.

[0083] A positive electrode composite material and an all-solid-state battery were obtained in the same manner as in Example 1, except that CoS was not used and the ratio was changed so that the mass ratio of S / P2S5 / VGCF was 45 / 35 / 20.

[0084]

Table 1

[0085] As shown in Table 1, the discharge capacity of Example 1 was 290 mAh, the discharge capacity of Example 2 was 337 mAh, the discharge capacity of Example 3 was 300 mAh, and the discharge capacity of Example 4 was 251 mAh, while the discharge capacity of Comparative Example 1 was 207 mAh.

[0086] (Charge and Discharge Test) All-solid-state batteries obtained in Examples 1 to 4 and Comparative Example 1 were subjected to a charge and discharge test. The charge and discharge test was performed according to the following procedure. The temperature environment was 25°C, and 1C corresponded to 3.09 mA / cm 2 corresponding thereto. (1) Discharge to 1.5 V at 0.1C and rest for 10 minutes (2) Charge to 3.1 V at 0.1C, rest for 10 minutes, discharge to 1.5 V at 0.1C, and rest for 10 minutes. This was repeated for a total of 2 cycles (3) Charge to 3.1 V at 0.1C, rest for 10 minutes, discharge to 1.5 V at 0.2C, and rest for 10 minutes (4) Charge to 3.1 V at 0.1C, rest for 10 minutes, discharge to 1.5 V at 0.5C, and rest for 10 minutes (5) Charge to 3.1 V at 0.1C, rest for 10 minutes, and discharge to 1.5 V at 1C

[0087] Figure 1 shows the relationship between the mass ratio of the first sulfur-containing compound containing cobalt in the positive electrode composite material {CoS / (S + CoS + P2S5 + VGCF)} and the discharge capacity obtained during the discharge process of the above procedure (5).

[0088] As shown in Figure 1, Examples 1 to 4 containing CoS in the mass ratios shown in Table 1 have a higher discharge capacity at a lower limit voltage of 1.5 V than Comparative Example 1 that does not contain CoS. This is presumably because the positive electrode composite material of the examples contains CoS, which improves the electron conductivity and the adhesion between the components in the positive electrode composite material.

[0089] Also, as shown in Figure 1, Examples 1 to 4 containing CoS and P2S5 in the mass ratios shown in Table 1 have a higher discharge capacity of the battery even at a lower limit voltage of 1.5 V than Comparative Example 1 that contains only P2S5. This is presumably because including a specific amount of CoS in addition to P2S5 improves the balance between the ion conductivity and the electron conductivity of the positive electrode composite material.

[0090] Therefore, it has been clarified that a positive electrode composite material containing a first sulfur-containing compound containing cobalt in the positive electrode composite material improves the electron conductivity and the adhesion between components in the positive electrode composite material, and a all-solid-state battery using the positive electrode composite material can improve the discharge capacity at a lower limit voltage of 1.5V.

[0091] In addition, it has been clarified that a positive electrode composite material containing a first sulfur-containing compound containing cobalt and a second sulfur-containing compound containing phosphorus in the positive electrode composite material improves the balance between the ion conductivity and the electron conductivity of the positive electrode composite material, and a all-solid-state battery using the positive electrode composite material can improve the discharge capacity at a lower limit voltage of 1.5V.

Claims

1. a positive electrode active material containing sulfur, a first sulfur-containing compound containing cobalt, a second sulfur-containing compound containing phosphorus, a conductive assistant, and a positive electrode composite material for an all-solid-state battery containing the same.

2. The positive electrode composite material for an all-solid-state battery according to Claim 1, wherein a mass ratio of the first sulfur-containing compound to a total mass of the positive electrode active material, the first sulfur-containing compound, the second sulfur-containing compound, and the conductive assistant is more than 0 and 0.25 or less.

3. The positive electrode composite material for an all-solid-state battery according to Claim 1, wherein a molar ratio (Co / P) of cobalt contained in the first sulfur-containing compound to phosphorus contained in the second sulfur-containing compound is more than 0 and 3 or less.

4. The positive electrode active material contains one or more selected from the group consisting of elemental sulfur and Li ２ The positive electrode composite material for an all-solid-state battery according to claim 1, which contains one or more selected from the group consisting of S.

5. The first sulfur-containing compound is one or more selected from the group consisting of CoS, CoS ２ , Co ３ S ４ and Co ９ S ８ The positive electrode composite material for an all-solid-state battery according to claim 3, comprising one or more selected from the group consisting of

6. The second sulfur-containing compound is P ２ S ５ 、P ２ S ４ 、P ４ S ７ 、P ４ S ５ and P ４ S ３ The positive electrode composite material for an all-solid-state battery according to claim 3, comprising one or more selected from the group consisting of.

7. The positive electrode composite material for an all-solid-state battery according to Claim 1, which does not contain Li element.

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