Cathode mix for all-solid-state battery

Abstract

The present disclosure aims to provide a cathode mix capable of improving the discharge capacity of a battery. The cathode mix for all-solid-state batteries 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.

Description

Cathode composites for all-solid-state batteries

[0001] The present invention relates to a cathode composite for an all-solid-state battery.

[0002] This application claims priority to Japanese Application No. 2023-221545, filed December 27, 2023, the entire disclosure of which is incorporated herein by reference.

[0003] Recently, with the electrification of transportation vehicles such as electric vehicles, the development of batteries used as power sources has been attracting attention, and the development of high-output, high-capacity batteries is underway.

[0004] All-solid-state batteries are attracting attention as next-generation batteries with improved safety. Among these, development is underway for all-solid-state lithium-sulfur batteries utilizing sulfur as the cathode active material, which boasts a very high theoretical capacity of 1,675 mAh / g. Furthermore, efforts are being made to improve sulfur utilization and thereby increase the charge-discharge capacity of sulfur batteries.

[0005] Higher battery capacity is demanded. The present invention was developed in consideration of this situation, and its primary purpose is to provide a positive electrode composite that can improve the discharge capacity of a battery.

[0006] To achieve the above purpose, the present invention,

[0007] Cathode active material containing sulfur,

[0008] A first sulfur-containing compound containing cobalt,

[0009] Secondary sulfur-containing compounds containing phosphorus, and

[0010] A cathode composite for an all-solid-state battery including a challenge agent is provided.

[0011] 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 agent may be greater than 0 and less than or equal to 0.25.

[0012] 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 less than or equal to 3.

[0013] In one embodiment, the positive electrode active material may contain at least one selected from the group consisting of simple sulfur and Li2S.

[0014] In one embodiment, the first sulfur-containing compound may contain at least one selected from the group consisting of CoS, CoS2, Co3S4, and Co9S8.

[0015] In one embodiment, the second sulfur-containing compound may contain at least one selected from the group consisting of P2S5, P2S4, P4S7, P4S5, and P4S3.

[0016] In one embodiment, it may not contain the Li element.

[0017] The present invention can provide a cathode composite that can improve the discharge capacity of a battery.

[0018] Figure 1 is a graph showing the relationship between the mass ratio of the first sulfur-containing compound containing cobalt in the positive electrode composite (CoS / (S+CoS+P2S5+VGCF)) and the discharge capacity of the all-solid-state battery when the lower limit voltage is set to 1.5 V.

[0019] In the present invention, a positive electrode composite for an all-solid-state battery is provided, which includes a positive electrode active material containing sulfur, a first sulfur-containing compound containing cobalt, a second sulfur-containing compound containing phosphorus, and a conductive additive.

[0020] Among sulfur batteries, lithium sulfur batteries are generally assumed to have an upper voltage limit of 3.1 V and a lower voltage limit of 1.5 V as their operating voltages. However, due to voltage deviations during battery charging and discharging, there is a possibility that the battery voltage may reach below 1.5 V. Therefore, a high-capacity cathode composite that does not deteriorate even below 1.5 V is required.

[0021] As a positive electrode composite for an all-solid-state battery, a positive electrode composite containing a sulfur-containing positive electrode active material that replaces expensive lithium sulfide (Li2S), a secondary sulfur-containing compound having P and S elements, and a conductive additive has a problem in that the electronic conductivity and adhesion between the components in the positive electrode composite are low, resulting in a lower discharge capacity (increased irreversible capacity) with each charge and discharge of the battery. This is thought to be because a side reaction occurs when the battery voltage is 1.5 V or lower, reducing the secondary sulfur-containing compound, and thus lowering the adhesion between the components in the positive electrode composite.

[0022] In addition, as a positive electrode composite for an all-solid-state battery, a positive electrode composite containing a positive electrode active material containing sulfur, a first sulfur-containing compound having Co and S elements, and a conductive additive exhibits good cycle characteristics even when the lower limit voltage is set to 1 V, but has the problem of low discharge capacity of the battery. This is thought to be because, although high capacity requires a reaction and complexation of the sulfur-containing positive electrode active material and the sulfur-containing compound, the amount of the first sulfur-containing compound containing cobalt required for complexation is greater than that of the second sulfur-containing compound containing phosphorus.

[0023] The inventor of the present invention found that by using a positive electrode composite containing a first sulfur-containing compound containing cobalt and a second sulfur-containing compound containing phosphorus in a battery, the electronic conductivity of the positive electrode composite and the adhesion between components of the positive electrode composite can be improved in the charge / discharge reaction of the battery, thereby improving the discharge capacity of the battery (particularly, the discharge capacity when the lower limit voltage is set to 1.5 V).

[0024] 1. Positive active material

[0025] The positive electrode active material contains the element S. Various materials can be employed as the positive electrode active material containing sulfur. For example, the positive electrode active material can contain at least one selected from the group consisting of elemental sulfur and Li2S. An example of the elemental sulfur is S8 sulfur. S8 sulfur can have three crystal forms: α sulfur (orthorhombic sulfur), β sulfur (monoclinic sulfur), and γ sulfur (monoclinic sulfur), but any crystal form is acceptable.

[0026] The amount of positive electrode active material contained in the positive electrode composite is not particularly limited and may be appropriately determined depending on the intended battery performance. For example, the positive electrode composite may contain 10 mass% or more and 80 mass% or less of the positive electrode active material. The lower limit may be 15 mass% or more, 20 mass% or more, or 25 mass% or more. The upper limit may be 70 mass% or less, or 60 mass% or less. If the content of the positive electrode active material is too high, ion conductivity and electron conductivity in the positive electrode layer of the battery may be insufficient.

[0027] Part or all of the positive electrode active material may be solid-dissolved in the sulfur-containing compound described below. In other words, the positive electrode composite may contain a solid-solution of the positive electrode active material and the sulfur-containing compound. Furthermore, 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).

[0028] 2. Sulfur-containing compounds

[0029] The positive electrode composite of the present invention contains at least a first sulfur-containing compound containing cobalt as a sulfur-containing compound, and a second sulfur-containing compound containing phosphorus. The first sulfur-containing compound containing cobalt may be a semiconductor and may have higher electronic conductivity than the elemental sulfur of an insulator used as the positive electrode active material. Furthermore, the first sulfur-containing compound containing cobalt has mechanical flexibility, which may improve the adhesion between components in the positive electrode composite. The second sulfur-containing compound containing phosphorus may form a compound with lithium during the first discharge of an all-solid-state battery, thereby having ionic conductivity.

[0030] In the positive electrode composite of the present invention, 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 additive (e.g., CoS / (S+CoS+P2S5+VGCF)) may be greater than 0 and less than or equal to 0.25. Preferably, the mass ratio may be greater than 0 and less than or equal to 0.15. More preferably, the mass ratio may be greater than or equal to 0.01 and less than or equal to 0.1. Even more preferably, the mass ratio may be greater than or equal to 0.03 and less than or equal to 0.075. When the mass ratio is within the above range, the electronic conductivity of the positive electrode composite and the adhesion between components in the positive electrode composite are improved, thereby improving the discharge capacity of the battery.

[0031] In the positive electrode composite of the present invention, 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 less than or equal to 3. Preferably, the molar ratio may be greater than 0 and less than or equal to 2. More preferably, the molar ratio may be greater than 0 and less than or equal to 1. Even more preferably, the molar ratio may be greater than 0 and less than or equal to 0.5. Most preferably, the molar ratio may be greater than or equal to 0.1 and less than or equal to 0.35. When the molar ratio is within the above range, the balance of ionic conductivity and electronic conductivity of the positive electrode composite is improved, thereby improving the discharge capacity of the battery.

[0032] When the battery is discharged, carrier ions are conducted from the cathode layer to the anode layer through the solid electrolyte layer. The carrier ions that reach the anode layer can react with the cathode active material to generate discharge products with low ionic conductivity (e.g., Li2S). Therefore, if the second sulfur-containing compound having P and S elements is not present in the anode layer, the ionic conductivity of the discharge product is low, so there are cases where the ionic conduction path within the anode layer is insufficient, making it difficult for the discharge reaction to proceed. In contrast, if the second sulfur-containing compound containing phosphorus is present in the anode layer, even if the ionic conductivity of the discharge product is low, the discharge reaction easily proceeds because the second sulfur-containing compound containing phosphorus secures the ionic conduction path within the anode layer. In addition, the first sulfur-containing compound having Co and S elements exhibits high electron conductivity in the cathode composite and adhesion between components in the cathode composite, so that it can suppress deterioration of the cathode composite due to side reactions and separation of components. Therefore, by using a positive electrode composite containing a first sulfur-containing compound containing cobalt and a second sulfur-containing compound containing phosphorus in a battery, the electronic conductivity of the positive electrode composite and the adhesion between components in the positive electrode composite in the charge / discharge reaction of the battery can be improved, thereby improving the discharge capacity of the battery (particularly, the discharge capacity when the lower limit voltage is set to 1.5 V).

[0033] The positive electrode composite 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 another element (e.g., Ge, Sn, Si, or Al) and the element S. In the latter case, the positive electrode composite may contain the first sulfur-containing compound containing cobalt and the second sulfur-containing compound containing phosphorus as the main sulfur-containing compounds. Specifically, the positive electrode composite may contain a combined amount of 50 mass% or more and 100 mass% or less of the first sulfur-containing compound containing cobalt and the second sulfur-containing compound containing phosphorus, with the total sulfur-containing compounds contained in the positive electrode composite being 100 mass%.

[0034] The cathode composite may contain a sulfide as a sulfur-containing compound. That is, the first sulfur-containing compound may contain a sulfide of Co element. The first sulfur-containing compound may contain at least one selected from the group consisting of CoS, CoS2, Co3S4, and Co9S8. Preferably, the first sulfur-containing compound may be CoS. Meanwhile, the second sulfur-containing compound containing phosphorus may contain a sulfide of P element. The second sulfur-containing compound may contain at least one selected from the group consisting of P2S5, P2S4, P4S7, P4S5, and P4S3. Preferably, the second sulfur-containing compound may be P2S5.

[0035] Additionally, sulfur-containing compounds are sulfides of element M (M x S y ) may contain. Here, x and y are integers that impart electrical neutrality with S depending on the type of M. Sulfide (M x S y ) include, for example, GeS2, SnS2, SiS2, and Al2S3. In addition, these sulfides may be, for example, residues of starting materials.

[0036] If the positive electrode composite of the present invention contains a first sulfur-containing compound containing cobalt as a sulfur-containing compound and a second sulfur-containing compound containing phosphorus, the amount of the sulfur-containing compound contained in the positive electrode composite is not particularly limited and may be appropriately determined depending on the desired battery performance. For example, the positive electrode composite may contain the sulfur-containing compound in an amount of 10 mass% or more and 80 mass% or less. The lower limit may be 15 mass% or more, 20 mass% or more, or 25 mass% or more. The upper limit may be 70 mass% or less, or 60 mass% or less. If the content of the sulfur-containing compound is too high, the content of the positive electrode active material becomes relatively low, and in some cases, a positive electrode composite having sufficient capacity may not be obtained.

[0037] 3. Challenge preparation

[0038] The conductive additive has the function of improving the electronic conductivity of the cathode composite. Furthermore, it is believed that the conductive additive will function as a reducing agent, reducing elemental sulfur (the cathode active material), for example, during mechanical milling of the raw material mixture. The conductive additive may be dispersed within the cathode composite.

[0039] Examples of conductive additives include carbon materials and metal materials. Examples of carbon materials include vapor-grown carbon fiber (VGCF), acetylene black, activated carbon, furnace black, carbon nanotubes, Ketjen black, and graphene. In cathode composites, two or more conductive additives may be mixed and used.

[0040] The amount of conductive additive contained in the cathode composite is not particularly limited and may be appropriately determined based on the desired battery performance. For example, the cathode composite may contain 5 mass% or more and 50 mass% or less of the conductive additive. The lower limit may be 10 mass% or more, and the upper limit may be 40 mass% or less. If the content of the conductive additive is excessive, the content of the cathode active material may be relatively low, making it difficult to obtain a cathode composite with sufficient capacity.

[0041] 4. Elements that are practically not contained

[0042] 4-1. Li element

[0043] Conventionally, a cathode composite containing an ion conductor (solid electrolyte) containing Li element is known. For example, an ion conductor using Li2S as a raw material is known. However, due to the low water resistance of Li2S, a battery using such a cathode composite tends to have a low capacity. In contrast, the cathode composite of the present invention can suppress the aforementioned decrease in capacity by substantially not containing Li element.

[0044] “Substantially free of Li element” means that the proportion of Li element with respect to all elements included in the positive electrode composite 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).

[0045] Meanwhile, in the present invention, the positive electrode composite refers to a material introduced into an all-solid-state battery before the first Li insertion (first discharge). Therefore, the positive electrode layer of the all-solid-state battery after the first discharge may substantially contain the Li element.

[0046] 5. Bipolar composite

[0047] The positive electrode composite of the present invention may contain only a positive electrode active material, a sulfur-containing compound including a first sulfur-containing compound containing cobalt and a second sulfur-containing compound containing phosphorus, and a conductive agent, or may further contain other materials such as a binder.

[0048] Examples of binders include acrylonitrile butadiene rubber (ABR), butadiene rubber (BR), polyvinylidene fluoride (PVdF), and styrene butadiene rubber (SBR). The binder content in the positive electrode composite is not particularly limited.

[0049] The shape of the cathode composite may be powder, a lump formed by the agglomeration and bonding of multiple particles, or any other shape. Various shapes can be adopted depending on the desired battery type.

[0050] 6. Method for manufacturing anode composite

[0051] The method for manufacturing a positive electrode composite of the present invention comprises at least (1) a preparation step of preparing a raw material containing a positive electrode active material containing sulfur, a sulfur-containing compound including a first sulfur-containing compound containing cobalt and a second sulfur-containing compound containing phosphorus, and a conductive agent, and (2) a mixing step of mixing the raw materials to obtain a positive electrode composite.

[0052] (1) Preparation process

[0053] The preparation process involves preparing a raw material containing a sulfur-containing cathode active material, a sulfur-containing compound including a first sulfur-containing compound containing cobalt, and a second sulfur-containing compound containing phosphorus, and a conductive additive. The raw materials can be manufactured in-house or purchased from other sources.

[0054] The raw material may contain only a positive electrode active material, a sulfur-containing compound, and a conductive additive, or may contain additional materials. Furthermore, the raw material need not substantially contain lithium element.

[0055] As mentioned above, the positive electrode active material may be elemental sulfur. Elemental sulfur preferably has a high purity.

[0056] 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 sulfur-containing compounds, 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.

[0057] The challenge preparation is as described above, and its explanation is omitted here.

[0058] The content of the positive electrode active material, sulfur-containing compound, and conductive agent in the raw material may be the same as the content of the positive electrode active material, sulfur-containing compound, and conductive agent in the positive electrode composite described above.

[0059] (2) Mixing process

[0060] The mixing process involves mixing the above raw materials to obtain a cathode composite. The method for mixing the raw materials is not particularly limited. For example, the raw materials may be mixed by mechanical milling. Mechanical milling can more easily de-crystallize the raw materials.

[0061] Mechanical milling is not particularly limited to any method that mixes the anode composite while applying mechanical energy. Examples include ball mills, vibratory mills, turbo mills, mechanofusion mills, and disk mills. From the perspective of further facilitating the amorphization of the raw material, a planetary ball mill may also be employed.

[0062] Mechanical milling can be either dry or wet. Liquids used in wet milling include those that are aprotic to the extent that they do not generate hydrogen sulfide. Specifically, these liquids include polar aprotic liquids and nonpolar aprotic liquids.

[0063] The conditions for mechanical milling are appropriately set to obtain the desired anode composite. For example, when using a planetary ball mill, the raw material mixture and grinding balls are placed in a container and processed at a predetermined base rotation speed and time. The base rotation speed may be, for example, 200 rpm or more, 300 rpm or more, or 500 rpm or more. Meanwhile, the base rotation speed may be, for example, 800 rpm or less, or 600 rpm or less. In addition, the processing time of the planetary ball mill may be, for example, 30 minutes or more, or 5 hours or more. Meanwhile, the processing time of the planetary ball mill may be, for example, 100 hours or less, or 60 hours or less. Materials for the container and grinding balls used in the planetary ball mill include, for example, ZrO2 and Al2O3. The diameter of the grinding balls is, for example, 1 mm or more and 20 mm or less. It is preferable that mechanical milling be performed in an inert gas atmosphere (e.g., Ar gas atmosphere).

[0064] 7. All-solid-state batteries

[0065] An all-solid-state battery comprises 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.

[0066] The anode layer comprises the anode composite material described above. The anode layer may also contain a solid electrolyte as described below.

[0067] The anode 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 below.

[0068] The thickness of the anode layer is not particularly limited, but may be, for example, 0.1 ㎛ or more and 1000 ㎛ or less.

[0069] In addition, the basic weight of the bipolar layer is not particularly limited, but may be, for example, 3 mg / cm2 or more, 4 mg / cm2 or more, or 5 mg / cm2 or more.

[0070] The anode layer can be easily formed, for example, by pressing the above anode composite.

[0071] The cathode layer is a layer containing at least a cathode active material.

[0072] The negative electrode active material may contain lithium. Examples of such negative electrode active materials include lithium alone or a lithium alloy. Examples of lithium alloys include a Li-In alloy.

[0073] The cathode layer may optionally contain at least one of a solid electrolyte, a conductive additive, and a binder. The solid electrolyte may be appropriately selected from the solid electrolytes that can be included in the solid electrolyte layer described below. The conductive additive and binder may be appropriately selected from the conductive additives and binders that can be included in the aforementioned cathode composite.

[0074] The thickness of the cathode layer is not particularly limited, but may be, for example, 0.1 ㎛ or more and 1000 ㎛ or less.

[0075] The negative electrode layer can be easily formed, for example, by pressing the aforementioned negative electrode active material. Alternatively, a foil made of the above material may be used as the negative electrode layer.

[0076] The solid electrolyte layer is a layer containing at least a solid electrolyte, and may contain a binder if necessary.

[0077] Examples of the solid electrolyte include a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a nitride-based solid electrolyte, and a halide-based solid electrolyte, and among these, a sulfide-based solid electrolyte is preferable.

[0078] The sulfide-based solid electrolyte preferably contains Li element, A element (A is at least one of P, Ge, Si, Sn, B, and Al), and S element. The sulfide-based solid electrolyte may further contain a halogen element. Examples of the halogen element include F element, Cl element, Br element, and I element. In addition, the sulfide-based solid electrolyte may further contain O element.

[0079] As sulfide-based solid electrolytes, for example, 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 (wherein m and n are positive numbers, and Z is any one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (wherein x and y are positive numbers, and M is any one of P, Si, Ge, B, Al, Ga, or In). Preferably, it may include Li6PS5Cl, which is a sulfide-based solid electrolyte having an argyrodite structure.

[0080] The solid electrolyte may be used singly or in combination of two or more types. Furthermore, when two or more types of solid electrolytes are used, the two or more types of solid electrolytes may be mixed, or two or more layers of solid electrolytes may be formed to form a multilayer structure.

[0081] The proportion of the solid electrolyte contained in the solid electrolyte layer is not particularly limited, but may be, for example, 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 aforementioned positive electrode composite.

[0082] The thickness of the solid electrolyte layer is not particularly limited, but may be, for example, 0.1 μm or more and 1000 μm or less. The solid electrolyte layer can be easily formed, for example, by pressing the solid electrolyte described above.

[0083] Examples of materials for the positive electrode collector include SUS, aluminum, nickel, iron, titanium, and carbon.

[0084] Meanwhile, examples of materials for the negative electrode collector include SUS, copper, nickel, and carbon.

[0085] The positive electrode current collector and the negative electrode current collector may be, for example, in the shape of a foil or a mesh.

[0086] The all-solid-state battery has an outer body that accommodates a positive electrode, a negative electrode, and a solid electrolyte layer as needed.

[0087] The shape of the outer body is not particularly limited, but examples include laminate type.

[0088] The material of the outer body is not particularly limited as long as it is stable in electrolyte, but examples thereof include resins such as polypropylene, polyethylene, and acrylic resin.

[0089] The all-solid-state battery of the present invention may be a sulfur battery. A sulfur battery refers to a battery that uses a positive electrode active material containing sulfur. The all-solid-state battery of the present invention may also 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 allows for repeated charging and discharging and is useful, for example, as a battery mounted on a vehicle. Meanwhile, the term "secondary battery" also includes the use of a secondary battery as a primary battery (use intended for only one discharge after charging).

[0090] Examples of the shape of the all-solid-state battery include coin-shaped, laminated, cylindrical, and square shapes.

[0091] The method for manufacturing the all-solid-state battery of the present invention is not particularly limited, and a conventionally known method can be adopted.

[0092] (Example 1)

[0093] (Production of bipolar composite)

[0094] Group sulfur S (positive electrode active material, Japan Pure Chemical product), CoS (primary sulfur-containing compound containing cobalt), P2S5 (secondary sulfur-containing compound containing phosphorus), and VGCF (conductive agent) 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 the raw material. The obtained raw material was placed in the container (45 cc, made of ZrO2) of a planetary ball mill, and ZrO2 balls (φ=5 mm, 70 g) were further added, and the container was completely sealed. This vessel was mounted on a planetary ball mill (Fritsch product P7), and a cycle of mechanical milling (pedestal rotation speed 500 rpm) for 1 hour, stopping for 15 minutes, and then mechanical milling with reverse rotation for 1 hour (pedestal rotation speed 500 rpm), stopping for 15 minutes was repeated, for a total of 20 hours of mechanical milling. As a result, a positive electrode composite was obtained.

[0095] (Manufacturing of all-solid-state batteries)

[0096] 80 mg of Li6PS5Cl, a sulfide-based solid electrolyte with an argyrodite structure, was placed in a 1㎠ ceramic mold and pressed at 100 MPa to obtain a solid electrolyte layer. 5 mg of a cathode composite (basic weight: 5 mg / ㎠) was placed on one side of the mold and pressed at 550 MPa to form a cathode layer. A lithium metal foil, which serves as an anode layer, was placed on the opposite side and pressed at 20 MPa to obtain a power generation element. A SUS foil (anode current collector) was placed on the cathode layer side, and a SUS foil (anode current collector) was placed on the cathode layer side. As a result, an all-solid-state battery was obtained.

[0097] (Example 2)

[0098] A positive electrode composite and an all-solid-state battery were obtained in the same manner as in Example 1, except that the mass ratio of S / CoS / P2S5 / VGCF was changed to 45 / 5 / 30 / 20.

[0099] (Example 3)

[0100] A positive electrode composite and an all-solid-state battery were obtained in the same manner as in Example 1, except that the mass ratio of S / CoS / P2S5 / VGCF was changed to 45 / 10 / 25 / 20.

[0101] (Example 4)

[0102] A positive electrode composite and an all-solid-state battery were obtained in the same manner as in Example 1, except that the mass ratio of S / CoS / P2S5 / VGCF was changed to 45 / 20 / 15 / 20.

[0103] A cathode composite and an all-solid-state battery were obtained in the same manner as in Example 1, except that CoS was not used and the mass ratio of S / P2S5 / VGCF was changed to 45 / 35 / 20.

[0104]

[0105] 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, whereas the discharge capacity of Comparative Example 1 was 207 mAh.

[0106] (charge / discharge test)

[0107] Charge-discharge tests were conducted on the all-solid-state batteries obtained in Examples 1 to 4 and Comparative Example 1. The charge-discharge tests were performed in the following order. The temperature environment was set to 25°C, and 1C corresponds to 3.09 mA / cm2.

[0108] (1) Discharge to 1.5 V at 0.1 C, rest for 10 minutes

[0109] (2) Charge to 3.1 V at 0.1 C, rest for 10 minutes, discharge to 1.5 V at 0.1 C, rest for 10 minutes, this is a total of 2 cycles.

[0110] (3) Charge to 3.1 V at 0.1 C, rest for 10 minutes, discharge to 1.5 V at 0.2 C, rest for 10 minutes

[0111] (4) Charge to 3.1 V at 0.1 C, rest for 10 minutes, discharge to 1.5 V at 0.5 C, rest for 10 minutes

[0112] (5) Charge to 3.1 V at 0.1 C, rest for 10 minutes, discharge to 1.5 V at 1 C.

[0113] The relationship between the mass ratio of the first sulfur-containing compound containing cobalt in the positive electrode composite (CoS / (S+CoS+P2S5+VGCF)) and the discharge capacity obtained in the discharge process of the above sequence (5) is shown in Figure 1.

[0114] As shown in Fig. 1, Examples 1 to 4 containing CoS in the mass ratios shown in Table 1 have higher discharge capacities at a lower voltage of 1.5 V than Comparative Example 1 not containing CoS. This is thought to be because the positive electrode composite of the examples contains CoS, thereby improving electronic conductivity and adhesion between components in the positive electrode composite.

[0115] In addition, as shown in Fig. 1, Examples 1 to 4 containing CoS and P2S5 in the mass ratios shown in Table 1 have higher discharge capacities of the batteries even at a lower voltage of 1.5 V than Comparative Example 1 containing only P2S5. This is thought to be because the balance of ionic and electronic conductivity of the positive electrode composite is improved by containing a specific amount of CoS in addition to P2S5.

[0116] Therefore, it has become clear that the cathode composite including the first sulfur-containing compound containing cobalt among the cathode composites can improve the electronic conductivity and adhesion between components in the cathode composite, and thus the all-solid-state battery using this cathode composite can improve the discharge capacity at a lower limit voltage of 1.5 V.

[0117] In addition, it was revealed that the positive electrode composite including a first sulfur-containing compound containing cobalt and a second sulfur-containing compound containing phosphorus among the positive electrode composites improved the balance of ionic conductivity and electronic conductivity of the positive electrode composite, and thus an all-solid-state battery using this positive electrode composite could improve the discharge capacity at a lower limit voltage of 1.5 V.

Claims

1. Cathode active material containing sulfur, A first sulfur-containing compound containing cobalt, Secondary sulfur-containing compounds containing phosphorus, and A cathode composite for an all-solid-state battery, comprising a challenge agent.

2. In paragraph 1, A positive electrode composite for an all-solid-state battery, wherein a 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 agent is greater than 0 and less than or equal to 0.

25.

3. In paragraph 1, A positive electrode composite for an all-solid-state battery, wherein the molar ratio (Co / P) of cobalt contained in the first sulfur-containing compound to phosphorus contained in the second sulfur-containing compound is greater than 0 and less than or equal to 3.

4. In paragraph 1, A positive electrode composite for an all-solid-state battery, wherein the positive electrode active material contains at least one selected from the group consisting of elemental sulfur and Li2S.

5. In paragraph 3, An all-solid-state battery positive electrode composite, wherein the first sulfur-containing compound contains at least one selected from the group consisting of CoS, CoS2, Co3S4, and Co9S8.

6. In paragraph 3, An all-solid-state battery positive electrode composite, wherein the second sulfur-containing compound contains at least one selected from the group consisting of P2S5, P2S4, P4S7, P4S5, and P4S3.

7. In paragraph 1, A cathode composite for all-solid-state batteries that does not contain Li element.

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