Solid state battery fibrous conductive auxiliary agent

Abstract

To provide a solid state battery fibrous conductive auxiliary agent capable of improving dispersibility in a solid state battery electrode active material layer, especially a positive electrode active material layer, in view of the possibility that using a sufficiently dehydrated fibrous conductive auxiliary agent for the electrode active material layer of a solid state battery may increase the resistance of the solid state battery owing to insufficient dispersion of the dehydrated fibrous conductive auxiliary agent in the electrode active material layer and inability to form an electronic path by the fibrous conductive auxiliary agent in the electrode active material layer, thereby increasing the electronic resistance of the electrode active material layer.SOLUTION: The solid state battery fibrous conductive auxiliary agent has a moisture content of 17-200 ppm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a fibrous conductive additive for a solid state battery. [Background technology]

[0002] Conductive additives are materials used in electrode active material layers of solid-state batteries and the like. Moisture can reduce the ionic conductivity of the solid electrolyte contained in the solid-state battery and can cause hydrolysis of other components of the battery, so conductive additives used in solid-state batteries are required to contain as little moisture as possible. For this reason, the following methods for dehydrating carbonaceous material dispersions (conductive additives) are known.

[0003] Patent Document 1 discloses a method for removing moisture from a carbonaceous material dispersion in which carbonaceous material particles are dispersed in an organic dispersion medium, the method comprising the steps of blowing 6 to 30 L of dry inert gas per 100 g of the dispersion into the dispersion held at 20 to 120°C, and bringing the dispersion into contact with the dry inert gas to evaporate the moisture in the dispersion.

[0004] According to the dehydration method for a carbonaceous material dispersion in Patent Document 1, low-polarity or non-polar solvents used as solvents for electrode slurries for producing solid electrolyte electrodes, such as ester-based substances typified by butyl butyrate, ketone-based substances typified by methyl isobutyl ketone, water-insoluble aromatic substances such as xylene and toluene, and hydrocarbon substances such as heptane and cyclohexane, almost always have an azeotropic point with water, and therefore water can be evaporated along with them when they evaporate. Furthermore, even for solvents that do not have an azeotropic point, solvents with a boiling point higher than that of water are often used for reasons of the working environment, and therefore sufficient dehydration can be achieved by aeration with a dry gas. This method does not require a pretreatment step or additives or consumables that are difficult to separate and remove, and is said to make it possible to provide a low-moisture carbonaceous material dispersion quickly by a simple method without compromising the stability of the dispersion.

[0005] Furthermore, according to the method for dehydrating a carbonaceous material dispersion in Patent Document 1, it is said that reducing the moisture content of the carbonaceous material dispersion contributes to improving the stability and characteristics of the dispersion. Furthermore, when the low-moisture carbonaceous material dispersion obtained in this manner is used as a conductive additive for an all-solid-state lithium-ion secondary battery, it is said that deterioration of the solid electrolyte can be suppressed, the carbonaceous material is dispersed uniformly at a high concentration, and when mixed with an electrode active material, the solid content can be dispersed at a high concentration with low viscosity, making it possible to produce a secondary battery with excellent performance such as charge / discharge characteristics, cycle characteristics, and electrode conductivity, and with stable characteristics. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2022-186527 Summary of the Invention [Problem to be solved by the invention]

[0007] From the description in Patent Document 1, it is considered preferable to prepare an electrode active material layer of a solid battery using a sufficiently dehydrated fibrous conductive additive. However, the present inventors have found that preparing an electrode active material layer of a solid battery using a sufficiently dehydrated fibrous conductive additive may increase the resistance of the solid battery.

[0008] Therefore, an object of the present disclosure is to provide a fibrous conductive additive for solid state batteries that can improve dispersibility in electrode active material layers, particularly positive electrode active material layers, of solid state batteries. [Means for solving the problem]

[0009] The present disclosure achieves the above object by the following means.

[0010] <Aspect 1> A fibrous conductive additive for solid-state batteries, having a moisture content of 17 to 200 ppm. <Aspect 2> The fibrous conductive additive for a solid state battery according to aspect 1, wherein the conductive additive is a multi-walled carbon nanotube. <Aspect 3> The fibrous conductive additive for a solid state battery according to aspect 1 or 2. a positive electrode active material, and sulfide solid electrolyte, A positive electrode active material layer comprising: <Aspect 4> The positive electrode active material layer according to aspect 3, a solid electrolyte layer, and negative electrode active material layer, A solid-state battery having, in this order: <Aspect 5> A method for producing a composite slurry for a positive electrode active material layer, the method comprising dispersing the fibrous conductive additive for a solid battery according to aspect 1 or 2, a positive electrode active material, and a sulfide solid electrolyte in a non-polar solvent. [Effects of the Invention]

[0011] The fibrous conductive additive for a solid battery according to the present disclosure can improve dispersibility in an electrode active material layer, particularly a positive electrode active material layer, of a solid battery. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating a solid state battery according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the present disclosure.

[0014] In the context of the present disclosure, a "solid-state battery" refers to a battery that uses at least a solid electrolyte as the electrolyte, and thus a solid-state battery may use a combination of a solid electrolyte and a liquid electrolyte as the electrolyte. Also, in the context of the present disclosure, a solid-state battery may be an all-solid-state battery, i.e., a battery that uses only a solid electrolyte as the electrolyte.

[0015] In the present disclosure, a "composite" refers to a composition that can constitute an electrode active material layer, etc., either as it is or by further containing other components. Also, in the present disclosure, a "composite slurry" refers to a slurry that contains a dispersion medium in addition to a "composite" and can be applied and dried to form a positive electrode active material layer, etc.

[0016] <<Fiber-like conductive additive for solid-state batteries>> The fibrous conductive additive for a solid state battery according to the present disclosure comprises: The moisture content is 17 to 200 ppm.

[0017] The fibrous conductive additive for a solid battery according to the present disclosure can improve dispersibility in an electrode active material layer, particularly a positive electrode active material layer, of a solid battery.

[0018] Without being limited by theory, it is believed that the adsorption of a predetermined amount of moisture on the surface of the fibrous conductive additive suppresses aggregation of the fibrous conductive additives, allowing the fibrous conductive additives to be well dispersed during preparation of the electrode mixture slurry, thereby improving dispersibility in the electrode active material layer, particularly the positive electrode active material layer. In contrast, an excessively dehydrated fibrous conductive additive does not disperse sufficiently in the electrode active material layer, preventing the formation of an electronic path by the fibrous conductive additive in the electrode active material layer, thereby increasing the electronic resistance of the electrode active material layer.

[0019] <Fibrous conductive additive> The fibrous conductive additive is not particularly limited as long as it is a fibrous conductive additive. Here, the fibrous conductive additive is, for example, a conductive additive having an aspect ratio (ratio of fiber length to fiber diameter) of 5 or more. The aspect ratio of the fibrous conductive additive is not particularly limited, but may be 5 or more, 10 or more, or 20 or more, or may be 100,000 or less, 10,000 or less, 1,000 or less, or 100 or less.

[0020] Examples of the fibrous conductive additive include, but are not limited to, fibrous carbon materials, particularly multi-walled carbon nanotubes (MWCNTs), carbon nanofibers (CNFs), vapor-grown carbon fibers (VGCFs), single-walled carbon nanotubes (SWCNTs), etc. In the present disclosure, the fibrous conductive additive is not particularly limited, but is preferably multi-walled carbon nanotubes (MWCNTs), and more preferably vapor-grown carbon fibers (VGCFs).

[0021] In the present disclosure, the water content of the fibrous conductive additive for solid state batteries is 17 to 200 ppm, preferably 20 to 60 ppm, and more preferably 30 to 50 ppm. The water content of the fibrous conductive additive for solid state batteries is not particularly limited, but from the viewpoint of dispersibility, it may be 17 ppm or more, 20 ppm or more, 25 ppm or more, 30 ppm or more, 35 ppm or more, 40 ppm or more, or 45 ppm or more, and may be 200 ppm or less, 150 ppm or less, 100 ppm or less, 80 ppm or less, 60 ppm or less, or 50 ppm or less. The water content of the fibrous conductive additive for solid state batteries can be determined by heating the material to 25°C to 200°C using a Karl Fischer moisture meter (water content measuring device CA-310, manufactured by Nitto Analytech Co., Ltd.) and measuring the amount of water vaporized during the heating process. It is presumed that the moisture that evaporates at temperatures between 25°C and 200°C is moisture that is physically adsorbed on the surface of the fibrous conductive additive.

[0022] The fibrous conductive additive for a solid battery of the present disclosure can be produced, for example, by leaving it in a constant temperature and humidity environment. The humidity in the constant temperature and humidity environment is not particularly limited, but may be 70% or more, 80% or more, or 90% or more, or 100% or less. The temperature in the constant temperature and humidity environment is not particularly limited, but may be 10°C or more, 15°C or more, or 20°C or more, and may be 40°C or less, 35°C or less, 30°C or less, or 25°C or less. The time for leaving it in the constant temperature and humidity environment may be 1 hour or more, 6 hours or more, 12 hours or more, or 24 hours or more, or may be 60 hours or less, or 48 hours or less.

[0023] 《Cathode active material layer》 The positive electrode active material layer of the present disclosure comprises: the fibrous conductive additive for a solid-state battery, a positive electrode active material, and sulfide solid electrolyte, Includes:

[0024] The positive electrode active material layer of the present disclosure can reduce the DC resistance of a solid-state battery.

[0025] Without being limited by theory, it is believed that by having a predetermined amount of moisture adsorbed on the surface of the fibrous conductive additive, the dispersibility of the fibrous conductive additive in the electrode active material layer, particularly the positive electrode active material layer, can be improved, and the electron path and ion path of the fibrous conductive additive in the electrode active material layer can be optimized, thereby reducing the DC resistance of the solid-state battery.

[0026] In addition, unlike fibrous conductive additives, particulate conductive additives have good dispersibility in the electrode active material layer to begin with, so even if moisture is adsorbed onto the surface of the particulate conductive additive, the dispersibility of the particulate conductive additive in the electrode active material layer does not improve, and the reduction in DC resistance of the solid-state battery is small. Here, the particulate conductive additive is, for example, a conductive additive with an aspect ratio of less than 5.

[0027] The positive electrode active material layer contains at least the fibrous conductive additive for solid batteries of the present disclosure, a positive electrode active material, and a sulfide solid electrolyte, and may further contain, optionally, a solid electrolyte, a conductive additive, a binder, and the like. The positive electrode active material layer may also contain various other additives. The contents of the positive electrode active material, the fibrous conductive additive for solid batteries, the sulfide solid electrolyte, the binder, and the like in the positive electrode active material layer may be appropriately determined depending on the desired battery performance. For example, when the entire positive electrode active material layer (total solid content) is taken as 100 mass%, the content of the positive electrode active material may be 40 mass% or more, 50 mass% or more, or 60 mass% or more, or may be 100 mass% or less, or 90 mass% or less.

[0028] <Fibrous conductive additive for solid-state batteries> For the fibrous conductive additive for solid state batteries, the above description of "<Fibrous conductive additive for solid state batteries>" can be referred to.

[0029] <Cathode active material> The material of the positive electrode active material is not particularly limited as long as it can absorb and release lithium ions. Examples of the positive electrode active material include lithium cobalt oxide (LiCoO), lithium nickel oxide (LiNiO), lithium manganese oxide (LiMnO), and nickel-cobalt-manganese oxide (NCM:LiCO x Ni y Mn z O2), lithium nickel-cobalt-aluminate (LiNi 0.8 (CoAl) 0.2 O2), etc., but are not limited to these.

[0030] The positive electrode active material may have a coating layer, although it is not particularly limited. The coating layer is a layer containing a substance that has lithium ion conductivity, low reactivity with the positive electrode active material and the solid electrolyte, and can maintain the shape of the coating layer without flowing even when in contact with the active material and the solid electrolyte. Specific examples of materials that constitute the coating layer include LiNbO3 and Li4Ti5O 12 , Li3PO4, Li-Ti-Al-F based materials, etc., but are not limited to these.

[0031] The shape of the positive electrode active material is not particularly limited as long as it is a general shape for a positive electrode active material of a solid-state battery. The positive electrode active material may be, for example, in the form of particles. The positive electrode active material may be in the form of primary particles or secondary particles formed by agglomeration of a plurality of primary particles. The average particle diameter D of the positive electrode active material 50 The average particle size D may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. 50 is the particle size (median size) at 50% cumulative value in the volume-based particle size distribution determined by laser diffraction / scattering method.

[0032] <Sulfide solid electrolyte> Examples of sulfide solid electrolytes include, but are not limited to, sulfide-based amorphous solid electrolytes, sulfide-based crystalline solid electrolytes, and argyrodite-type solid electrolytes. Specific examples of sulfide solid electrolytes include Li2S-P2S5-based (Li7P3S 11 , Li3PS4, Li8P2S9, etc.), Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-P2S5-GeS2(Li 13 GeP3S 16 , Li 10 GeP2S 12 ), LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li 7-x PS 6-x Cl x or a combination thereof. The sulfide solid electrolyte is not particularly limited, but may be glass or crystallized glass (glass ceramics).

[0033] <Optional component - solid electrolyte> The material of the solid electrolyte is not particularly limited and may be, for example, a sulfide solid electrolyte, an oxide solid electrolyte, a polymer electrolyte, etc. For the sulfide solid electrolyte, the above description of "Sulfide Solid Electrolyte" can be referred to.

[0034] An example of an oxide solid electrolyte is Li7La3Zr2O 12 , Li 7-x La3Zr 1-x Nb x O 12 , Li 7-3x La3Zr2Al x O 12 , Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, or Li 3+x PO4-x N x Examples of the oxide solid electrolyte include, but are not limited to, glass and crystallized glass (glass ceramics).

[0035] Examples of polymer electrolytes include, but are not limited to, polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof.

[0036] <Optional ingredient - conductive additive> The conductive additive is not particularly limited. The conductive additive may be, for example, vapor grown carbon fiber (VGCF), acetylene black (AB), ketjen black (KB), carbon nanotube (CNT), carbon nanofiber (CNF), etc., but is not limited thereto. The conductive additive may be, for example, particulate or fibrous, and its size is not particularly limited. The conductive additive is not particularly limited, and one type may be used alone, or two or more types may be used in combination.

[0037] <Optional Component - Binder> The binder is not particularly limited. The binder may be, for example, polyvinylidene fluoride (PVdF), butadiene rubber (BR), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), or other materials, but is not limited to these. The binder is not particularly limited, and one type may be used alone, or two or more types may be used in combination.

[0038] The shape of the positive electrode active material layer is not particularly limited, and may be, for example, a substantially flat sheet-like positive electrode active material layer. The thickness of the positive electrode active material layer is not particularly limited, and may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, and may be 2 mm or less, 1 mm or less, or 500 μm or less.

[0039] The positive electrode active material layer can be produced by applying a known method. For example, the positive electrode active material layer can be easily formed by dry or wet molding a positive electrode composite containing the above-mentioned various components. The positive electrode active material layer may be formed together with the positive electrode current collector layer or may be formed separately from the positive electrode current collector layer.

[0040] <<Method for producing composite slurry for positive electrode active material layer>> The method for producing a composite slurry for a positive electrode active material layer according to the present disclosure includes: The method includes dispersing the above-mentioned fibrous conductive additive for a solid-state battery, the positive electrode active material, and the sulfide solid electrolyte in a non-polar solvent.

[0041] According to the method for producing a mixture slurry for a positive electrode active material layer of the present disclosure, a mixture slurry for a positive electrode active material layer in which a fibrous conductive additive is dispersed can be obtained.

[0042] The dispersion method can be, for example, by using a small ultrasonic homogenizer, but is not limited to this.

[0043] <Nonpolar solvent> The non-polar solvent is not particularly limited. Examples of the non-polar solvent include, but are not limited to, tetralin (1,2,3,4-tetrahydronaphthalene), anisole, xylene, octane, hexane, decalin, butyl acetate, and ethyl propionate. The non-polar solvent is not particularly limited, and one type may be used alone, or two or more types may be used in combination.

[0044] For the fibrous conductive additive for solid-state batteries, the description in "<<Fibrous conductive additive for solid-state batteries>>" above can be referenced, and for the positive electrode active material and the sulfide solid electrolyte, the description in "<<Positive electrode active material layer>>" above can be referenced.

[0045] 《Solid-state battery》 The solid-state battery of the present disclosure comprises: The positive electrode active material layer, a solid electrolyte layer, and negative electrode active material layer, in this order.

[0046] According to the solid-state battery of the present disclosure, the direct current resistance of the solid-state battery can be reduced.

[0047] 1 is a schematic cross-sectional view showing one embodiment of a solid-state battery according to the present disclosure, but is not limited to this example. The solid-state battery 100 includes a positive electrode active material layer 110, a solid electrolyte layer 120, and a negative electrode active material layer 130, in this order.

[0048] The solid-state battery of the present disclosure has at least the cathode active material layer, solid electrolyte layer, and anode active material layer of the present disclosure, in this order, and may further include an optional cathode current collector layer and an anode current collector layer. For the cathode active material layer, please refer to the description above in "<<Cathode Active Material Layer>>".

[0049] <Positive electrode current collector layer> The material used for the positive electrode current collector layer is not particularly limited, and any material commonly used for positive electrode current collectors in solid-state batteries can be appropriately used. Examples of materials used for the positive electrode current collector layer include, but are not limited to, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. The positive electrode current collector layer may have a coating layer on its surface for purposes such as adjusting resistance. The positive electrode current collector layer may also be a metal foil or a substrate on which the above metals are plated or vapor-deposited.

[0050] The shape of the positive electrode current collector layer is not particularly limited, but examples thereof include foil, plate, and mesh. Among these, foil is preferred. The thickness of the positive electrode current collector layer is not particularly limited, but may be 0.1 μm or more, or 1 μm or more, or 1 mm or less, or 100 μm or less.

[0051] <Solid electrolyte layer> The solid electrolyte layer contains at least a solid electrolyte, and may contain, as necessary, a conductive additive, a binder, etc. For the solid electrolyte, the conductive additive, and the binder, reference can be made to the description above in "<<Positive Electrode Active Material Layer>>".

[0052] The thickness of the solid electrolyte layer is not particularly limited, but may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, and may be 2 mm or less, 1 mm or less, or 500 μm or less.

[0053] The solid electrolyte layer can be easily formed, for example, by dry or wet molding a solid electrolyte mixture containing the above-mentioned solid electrolyte and a binder.

[0054] <Negative electrode active material layer> The negative electrode active material layer contains at least a negative electrode active material and may further contain, optionally, a solid electrolyte, a conductive additive, a binder, and the like. The solid electrolyte, conductive additive, and binder that may be contained in the negative electrode active material layer are described above in "<Positive Electrode Active Material Layer>". The negative electrode active material layer may also contain various additives. The contents of the negative electrode active material, solid electrolyte, conductive additive, binder, and the like in the negative electrode active material layer may be appropriately determined depending on the desired battery performance. For example, the content of the negative electrode active material may be 40% by mass or more, 50% by mass or more, or 60% by mass or more, or 100% by mass or less, or 90% by mass or less, where the total amount (total solid content) of the negative electrode active material layer is taken as 100% by mass.

[0055] (Negative electrode active material) As the negative electrode active material, various materials can be used that have a potential (charge / discharge potential) at which they absorb and release lithium ions that is lower than that of the positive electrode active material. The material for the negative electrode active material is not particularly limited, and may be metallic lithium or a material capable of absorbing and releasing metal ions such as lithium ions. Examples of materials capable of absorbing and releasing metal ions such as lithium ions include alloy-based negative electrode active materials, carbon materials, and lithium titanate (Li4Ti5O 12 ) and the like can be mentioned, but are not limited to these.

[0056] The alloy-based negative electrode active material is not particularly limited, and examples thereof include Si alloy-based negative electrode active materials and Sn alloy-based negative electrode active materials. Examples of Si alloy-based negative electrode active materials include silicon, silicon oxide, silicon carbide, silicon nitride, and solid solutions thereof. The Si alloy-based negative electrode active material may contain metal elements other than silicon, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, and Ti. Examples of Sn alloy-based negative electrode active materials include tin, tin oxide, tin nitride, and solid solutions thereof. The Sn alloy-based negative electrode active material may contain metal elements other than tin, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Ti, and Si.

[0057] The carbon material is not particularly limited, and examples thereof include hard carbon, soft carbon, graphite, and the like.

[0058] The shape of the negative electrode active material is not particularly limited, and may be any shape commonly used for negative electrode active materials in solid-state batteries. The negative electrode active material may be, for example, in the form of particles or a sheet.

[0059] The shape of the negative electrode active material layer is not particularly limited, and may be, for example, a substantially flat sheet-like negative electrode active material layer. The thickness of the negative electrode active material layer is not particularly limited, and may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, and may be 2 mm or less, 1 mm or less, or 500 μm or less.

[0060] The negative electrode active material layer can be produced by applying a known method. For example, the negative electrode active material layer can be easily formed by dry or wet molding a negative electrode composite containing the above-mentioned various components. The negative electrode active material layer may be formed together with the negative electrode current collector layer or may be formed separately from the negative electrode current collector layer.

[0061] <Negative electrode current collector layer> The material used for the negative electrode current collector layer is not particularly limited, and any material commonly used for negative electrode current collectors in solid-state batteries can be appropriately used. Examples of materials used for the negative electrode current collector layer include, but are not limited to, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, and carbon sheet. The negative electrode current collector layer may have a coating layer on its surface for the purpose of adjusting resistance, etc.

[0062] The shape of the negative electrode current collector layer is not particularly limited, but examples thereof include foil, plate, and mesh. Of these, foil is preferred. The thickness of the negative electrode current collector layer is not particularly limited, but may be 0.1 μm or more, or 1 μm or more, or 1 mm or less, or 100 μm or less.

[0063] <<Applications of solid-state batteries>> The solid-state battery in the present disclosure may be, for example, an in-vehicle battery, or may be used as a power source for moving objects other than vehicles (for example, trains, ships, and aircraft), or may be used as a power source for electrical appliances such as information processing devices. [Example]

[0064] The present disclosure will be described in more detail with reference to the following examples, but the scope of the present disclosure is not limited to these examples.

[0065] Example 1 <Preparation of fibrous conductive additive A1 for solid state batteries> Vapor grown carbon fiber (aspect ratio: 26.7) as a fibrous conductive additive was vacuum dried at a temperature of 150° C. for 8 hours to prepare a fibrous conductive additive A1 for solid state batteries.

[0066] <Measurement of moisture content of fibrous conductive additive A1 for solid state batteries> The moisture content of the fibrous conductive additive A1 for solid state batteries was determined by a Karl Fischer moisture meter (moisture measuring device CA-310, manufactured by Nitto Analytech Co., Ltd.) by heating the material from 25° C. to 200° C. and measuring the amount of moisture evaporated during the heating process. The moisture content of the fibrous conductive additive A1 for solid state batteries was 17 ppm.

[0067] <Preparation of Positive Electrode Active Material Layer Composite Slurry B1> Fibrous conductive additive A1 for solid-state batteries and LiNi surface-treated with Li-Ti-Al-F-based material as a positive electrode active material 0.8 (CoAl) 0.2 O2, a sulfide solid electrolyte, a particulate conductive additive, a binder, a dispersant, and tetralin as a non-polar solvent were mixed and dispersed using a small ultrasonic homogenizer to prepare a composite slurry B1 for the positive electrode active material layer.

[0068] <Formation of Positive Electrode Active Material Layer C1> The positive electrode active material layer mixture slurry B1 was applied onto an aluminum foil by die coating and dried to form a positive electrode active material layer C1 on the aluminum foil.

[0069] <Formation of solid electrolyte layer D1> A Li2S-P2S5-based glass ceramic solid electrolyte, a conductive additive, a binder, a dispersant, and a solvent were mixed and dispersed using a small ultrasonic homogenizer to prepare a solid electrolyte composite slurry. The solid electrolyte composite slurry was then die-coated onto an aluminum foil and dried to form a solid electrolyte layer D1 on the aluminum foil.

[0070] <Formation of Negative Electrode Active Material Layer E1> Li4Ti5O as a negative electrode active material 12The particles, solid electrolyte, fibrous conductive additive A1 for solid-state batteries, particulate conductive additive, binder, dispersant, and solvent were mixed and dispersed using a small ultrasonic homogenizer to prepare a negative electrode composite slurry. The negative electrode composite slurry was then die-coated onto both sides of an aluminum foil serving as a negative electrode current collector, and dried to form a negative electrode active material layer E1 on both sides of the aluminum foil. The basis weight of the negative electrode active material layer was adjusted so that the charge specific capacity of the negative electrode active material layer was 1x the charge specific capacity of the positive electrode active material layer, which was 200 mAh / g.

[0071] <Fabrication of solid-state battery F1> A solid electrolyte layer D1 was placed on each surface of the negative electrode active material layer E1 formed on both sides of an aluminum foil serving as a negative electrode current collector, and pressed to transfer the solid electrolyte layer D1 to the surface of the negative electrode active material layer E1. The aluminum foil in contact with the solid electrolyte layer D1 was peeled off, and the solid electrolyte layer D1 was laminated on the negative electrode active material layer E1. Next, a positive electrode active material layer C1 was placed on each surface of the solid electrolyte layer D1 formed on both sides of the negative electrode active material layer E1, and pressed to transfer the positive electrode active material layer C1 to the surface of the solid electrolyte layer D1. The aluminum foil in contact with the positive electrode active material layer C1 was peeled off, and the positive electrode active material layer C1 was laminated on the solid electrolyte layer D1. The fabricated laminate was roll-pressed at 175°C and 5 ton / cm to obtain a densified laminate. Then, carbon-coated aluminum foil serving as a positive electrode current collector was placed on each surface of the densified laminate, and pressed at 140°C and 5 MPa for 5 minutes to obtain a power generating element. The power generating element was formed by laminating a carbon-coated aluminum foil, a positive electrode active material layer C1, a solid electrolyte layer D1, a negative electrode active material layer E1, an aluminum foil, a negative electrode active material layer E1, a solid electrolyte layer D1, a positive electrode active material layer C1, and a carbon-coated aluminum foil in this order. The resulting power generating element was sealed with a laminate and constrained at 5 MPa to obtain a solid battery F1.

[0072] <DC resistance measurement of solid-state battery F1> Solid battery F1 was charged at a constant current of 0.3 C until it reached a voltage corresponding to a charge depth of 40%, and then charged at a constant voltage of 0.01 C until it reached a current value of 0.01 C. Solid battery F1 was then discharged at a constant current of 20 C for 10 seconds. The potential difference between the voltage before constant current discharge and the voltage after 10 seconds of constant current discharge was determined, and the DC resistance was calculated by dividing this potential difference by the current value at 20 C. The DC resistance of solid battery F1 was 13.2 Ω.

[0073] Example 2 <Preparation of fibrous conductive additive A2 for solid state batteries> Vapor grown carbon fiber (aspect ratio 26.7) as a fibrous conductive additive was not treated and used as fibrous conductive additive A2 for solid state batteries. The water content of fibrous conductive additive A2 for solid state batteries was measured in the same manner as in Example 1 and was as shown in Table 1.

[0074] Example 3 <Preparation of fibrous conductive additive A3 for solid-state batteries> Vapor grown carbon fiber (aspect ratio 26.7) as a fibrous conductive additive was left to stand for 12 hours in an environment at a temperature of 23°C and a humidity of 85%, and then left to stand for 12 hours in a dry box at a temperature of 23°C and a dew point of -65°C or less to produce fibrous conductive additive A3 for solid state batteries. The water content of fibrous conductive additive A3 for solid state batteries was measured in the same manner as in Example 1 and was as shown in Table 1.

[0075] Example 4 <Preparation of fibrous conductive additive A4 for solid-state batteries> Vapor-grown carbon fiber (aspect ratio 26.7) as a fibrous conductive additive was left to stand for 12 hours in an environment at a temperature of 23°C and a humidity of 85%, and then left to stand for 1 hour in a dry box at a temperature of 23°C and a dew point of -65°C or less to produce fibrous conductive additive A4 for solid state batteries. The water content of fibrous conductive additive A4 for solid state batteries was measured in the same manner as in Example 1 and was as shown in Table 1.

[0076] Example 5 <Preparation of fibrous conductive additive A5 for solid-state batteries> A vapor-grown carbon fiber (aspect ratio 26.7) serving as a fibrous conductive additive was left standing for 12 hours in an environment of 85% humidity and 23°C temperature to produce a fibrous conductive additive A5 for solid state batteries. The water content of the fibrous conductive additive A5 for solid state batteries was measured in the same manner as in Example 1 and was as shown in Table 1.

[0077] Example 6 <Preparation of fibrous conductive additive A6 for solid-state batteries> Vapor grown carbon fiber (aspect ratio 26.7) as a fibrous conductive additive was immersed in pure water and then left to stand in an atmospheric environment at a temperature of 23°C for 8 hours to produce fibrous conductive additive A6 for solid state batteries. The water content of fibrous conductive additive A6 for solid state batteries was measured in the same manner as in Example 1 and was as shown in Table 1.

[0078] <Formation of Positive Electrode Active Material Layers C2 to C6, and Fabrication of Solid-State Batteries F2 to F6> Positive electrode active material layers C2 to C6 were formed in the same manner as in Example 1, except that fibrous conductive additives A2 to A6 were used instead of fibrous conductive additive A1 for solid state batteries. Solid batteries F2 to F6 were produced in the same manner as in Example 1, except that positive electrode active material layers C2 to C6 were used instead of positive electrode active material layer C1. The DC resistances of solid batteries F2 to F6 were measured in the same manner as in Example 1, and were as shown in Table 1.

[0079] Comparative Example 1 <Preparation of fibrous conductive additive a1 for solid state batteries> Vapor grown carbon fiber (aspect ratio 26.7) as a fibrous conductive additive was vacuum dried at a temperature of 500°C for 24 hours to prepare a fibrous conductive additive a1 for solid state batteries. The water content of the fibrous conductive additive a1 for solid state batteries was measured in the same manner as in Example 1 and was as shown in Table 1.

[0080] <Formation of Positive Electrode Active Material Layer c1 and Fabrication of Solid State Battery f1> A positive electrode active material layer c1 was produced in the same manner as in Example 1, except that a fibrous conductive additive a1 for solid state batteries was used instead of a fibrous conductive additive A1 for solid state batteries. A solid battery f1 was produced in the same manner as in Example 1, except that a positive electrode active material layer c1 was used instead of a positive electrode active material layer C1. The DC resistance of the solid battery f1 was measured in the same manner as in Example 1, and was as shown in Table 1.

[0081] [Table 1]

[0082] When the fibrous conductive additives A1 to A6 for solid state batteries of Examples 1 to 6 were used in the solid state batteries, the DC resistance of the solid state batteries was reduced compared to when an excessively dehydrated fibrous conductive additive was used as in Comparative Example 1. This is presumably because a predetermined amount of moisture was adsorbed on the surface of the fibrous conductive additive, improving the dispersibility of the fibrous conductive additive in the positive electrode active material layer, thereby optimizing the electron path and ion path of the fibrous conductive additive in the electrode active material layer.

[0083] Although preferred embodiments of the fibrous conductive additive for a solid battery, the positive electrode active material layer, the solid battery, and the method for producing a composite slurry for a positive electrode active material layer according to the present disclosure have been described, those skilled in the art will understand that modifications are possible without departing from the scope of the claims. [Explanation of symbols]

[0084] 100 solid state battery 110 Cathode active material layer 120 Solid electrolyte layer 130 Negative electrode active material layer

Claims

1. A fibrous conductive additive for a solid state battery, having a water content of 17 to 200 ppm.

2. The fibrous conductive additive for a solid state battery according to claim 1 , which is a multi-walled carbon nanotube.

3. The fibrous conductive additive for a solid battery according to claim 1 or 2, a positive electrode active material, and sulfide solid electrolyte, A positive electrode active material layer comprising:

4. The positive electrode active material layer according to claim 3 . a solid electrolyte layer, and negative electrode active material layer, A solid-state battery having, in this order:

5. A method for producing a composite slurry for a positive electrode active material layer, comprising dispersing the fibrous conductive additive for a solid battery according to claim 1 or 2, a positive electrode active material, and a sulfide solid electrolyte in a non-polar solvent.

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