Composition for electrode, method for manufacturing electrode, and method for manufacturing all-solid-state battery

Abstract

This composition for an electrode comprises an active material, a solid electrolyte, fibrous carbon, and a cyclic siloxane. This method for manufacturing an electrode includes: a step for applying the composition for an electrode to a support; and a step for volatilizing the cyclic siloxane from the composition for an electrode. This method for manufacturing an all-solid-state battery includes said method for manufacturing an electrode.

Description

Electrode composition, electrode manufacturing method, and all-solid-state battery manufacturing method

[0001] The present invention relates to an electrode composition, a method for manufacturing an electrode, and a method for manufacturing an all-solid-state battery. This application claims priority based on Japanese Patent Application No. 2024-045934, filed on March 22, 2024, the contents of which are incorporated herein by reference.

[0002] With the remarkable development of electronics technology, portable electronic devices are becoming smaller, lighter, thinner, and more multifunctional. There is also a strong demand for batteries, which serve as the power source for electronic devices, to be smaller, lighter, thinner, more reliable, and safer. All-solid-state batteries, which use solid electrolytes, are attracting attention because they are safer than lithium-ion secondary batteries, which use liquid electrolytes.

[0003] An all-solid-state battery has a positive electrode, a negative electrode, and a solid electrolyte layer sandwiched between the positive electrode and the negative electrode. The positive electrode and the negative electrode contain active materials that are responsible for charge and discharge reactions. The positive electrode and the negative electrode often contain a conductive additive that helps conduct electricity generated by the active material. For example, Patent Document 1 discloses the use of fibrous carbon such as carbon nanotubes and carbon nanofibers as a conductive additive.

[0004] Furthermore, Patent Document 2 discloses that by using one or more selected from aliphatic hydrocarbons, cyclic organic compounds, chain ethers having two long-chain hydrocarbon groups each having four or more carbon atoms, and cyclic ethers as a dispersion medium for a halide solid electrolyte (halide-based solid electrolyte) that is prone to decomposition, it is possible to prevent the solid electrolyte from decomposing and generating LiX.

[0005] JP 2022-168747 A JP 2023-21918 A

[0006] Electrodes for all-solid-state batteries are fabricated by applying a paste containing an electrode composition to a current collector and drying the paste. Fibrous carbon, such as carbon nanotubes and carbon nanofibers, tends to aggregate and may aggregate within the paste. Dispersants can be used to suppress the aggregation of fibrous carbon. Meanwhile, sulfide-based solid electrolytes and halide-based solid electrolytes are prone to chemical reactions and may react with dispersants.

[0007] The present disclosure has been made in view of the above-mentioned problems, and aims to provide an electrode composition that has excellent dispersibility of fibrous carbon and is less likely to react with a solid electrolyte, and also aims to provide a method for manufacturing an electrode and a method for manufacturing an all-solid-state battery using the electrode composition.

[0008] In order to solve the above problems, the following means are provided.

[0009] The electrode composition according to the first aspect includes an active material, a solid electrolyte, fibrous carbon, and a cyclic siloxane.

[0010] The electrode composition according to the above embodiment has excellent dispersibility of fibrous carbon and is less likely to react with the solid electrolyte.

[0011] FIG. 1 is a cross-sectional view of an all-solid-state battery according to an embodiment of the present invention.

[0012] The present embodiment will be described in detail below with reference to the accompanying drawings. The drawings used in the following description may show characteristic portions enlarged for the sake of clarity, and the dimensional proportions of each component may differ from the actual proportions. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present disclosure is not limited thereto. Appropriate modifications may be made within the scope of the present disclosure.

[0013] The electrode composition according to this embodiment includes an active material, a solid electrolyte, fibrous carbon, and a cyclic siloxane. The electrode composition is a mixture of the active material, the solid electrolyte, the fibrous carbon, and the cyclic siloxane, which are formed into a paste.

[0014] Electrode compositions are used when producing positive or negative electrodes of all-solid-state batteries. Electrode compositions include positive electrode compositions used to produce positive electrodes and negative electrode compositions used to produce negative electrodes. Electrode compositions are a general term for positive electrode compositions and negative electrode compositions.

[0015] The active material is a substance that is responsible for the charge / discharge reaction of a battery. The active material differs between the positive electrode composition and the negative electrode composition. The active material contained in the positive electrode composition is the positive electrode active material, and the active material contained in the negative electrode composition is the negative electrode active material. The positive electrode active material and the negative electrode active material are collectively referred to as the active material. The battery composition contains either the positive electrode active material or the negative electrode active material.

[0016] The positive electrode active material is not particularly limited as long as it can reversibly absorb and release lithium ions and insert and extract them (intercalate and deintercalate), and any positive electrode active material used in known all-solid-state batteries can be used. Examples of the positive electrode active material include lithium-containing metal oxides and lithium-containing metal phosphates.

[0017] The lithium-containing metal oxide is, for example, LiMO ２ , LiM ２ O ４ (wherein M includes one or more of Co, Ni, Mn, Al, Fe, and P). For example, the lithium-containing metal oxide is LiCoO ２ , LiNiO ２ , LiNi Ｏ．８ Co ０．１５ Al ０．０５ O ２ , LiNi １／３ Mn １／３ Co １／３ O ２ , LiMn ２ O ４ , LiMn １．９ Co ０．１ O ４ The lithium-containing metal phosphate can be, for example, represented by the general formula LiMPO ４ (wherein M represents at least one element selected from Co, Ni, Mn, and Fe). The lithium-containing metal phosphate is, for example, an olivine-type oxide represented by LiFePO ４ is.

[0018] The positive electrode active material may not contain lithium. Examples of such a positive electrode active material include lithium-free metal oxides (MnO ２ , V ２ O ５etc.), lithium-free metal sulfides (MoS ２ etc.), lithium-free fluorides (FeF ３ , V.F. ３ When a positive electrode active material that does not contain lithium is used, the negative electrode is doped with lithium ions in advance, or a negative electrode containing lithium ions is used.

[0019] The negative electrode active material may be any compound capable of absorbing and releasing ions, and active materials used in known batteries may be used. Examples of the negative electrode active material include carbon materials, metals, alloys, semimetals, or compounds capable of combining with lithium or sodium, composite materials of these metals, alloys, or semimetals with carbon materials, oxides, sulfur-modified polyacrylonitrile, metallic lithium, metallic sodium, etc. Examples of carbon materials include natural graphite, artificial graphite, mesocarbon microbeads, mesocarbon fiber (MCF), cokes, glassy carbon, organic compound sintered bodies, and hard carbon. Examples of metals, alloys, semimetals, or compounds capable of combining with lithium or sodium include Si, SiO ｘ , Sn, aluminum, etc. The oxides include lithium titanate (Li ４ Ti ５ O １２ ), SnO ２ And so on.

[0020] The surface of the active material may be surface-treated. For example, an organic substance may be added to the surface of the active material. For example, trimethoxymethylsilane or trimethoxyphenylsilane may be hydrolyzed, mixed with the active material, and heated as necessary to add the organic substance to the surface of the active material. By making a portion of the surface of the active material organic, the dispersibility of the active material in a non-polar dispersion medium is improved.

[0021] The solid electrolyte is, for example, a halide-based solid electrolyte or a sulfide-based solid electrolyte. The halide-based solid electrolyte and the sulfide-based solid electrolyte can ensure adhesion between solid electrolytes and between the solid electrolyte and the active material by applying pressure, making it possible to eliminate the need for heating such as firing in electrode formation.

[0022] Li ２ S-SiS ２ , Li２ S-P ２ S ５ , Li ２ S-GeS ２ , Li ２ S-B ２ S ３ , Li ２ S-Ga ２ S ３ , Li ２ S-Al ２ S ３ , Li ２ S-GeS ２ -P ２ S ５ , Li ２ S-Al ２ S ３ -P ２ S ５ , Li ２ S-P ２ S ３ , Li ２ S-P ２ S ３ -P ２ S ５ , LiX-Li ２ S-P ２ S ５ , LiX-Li ２ S-SiS ２ , LiX-Li ２ S-B ２ S ３ are examples of sulfide-based solid electrolytes. ２ ZrCl ６ , Li ２ ZrSO ４ Cl ４ , Li ２ MgX ４ , Li ２ FeX ４ , Li(Al,Ga,In)X ４ , Li ３ (Al,Ga,In)X ６ Examples of halide-based solid electrolytes include: X is a halogen element, and is at least one element selected from the group consisting of F, Cl, Br, and I.

[0023] Sulfide-based solid electrolytes and halide-based solid electrolytes are prone to chemical reactions with other substances. Sulfide-based solid electrolytes and halide-based solid electrolytes may react with water, for example, resulting in performance degradation. Halide-based solid electrolytes also react with some organic substances, resulting in a decrease in ionic conductivity. Furthermore, decomposition of sulfide-based solid electrolytes and halide-based solid electrolytes may produce toxic gases. Therefore, there is a need to suppress the decomposition of solid electrolytes. To prevent the reaction between water and the solid electrolyte, it is preferable to fabricate all-solid-state batteries in a rare gas atmosphere such as argon, or in a low-humidity atmosphere with a dew point of, for example, −70°C or lower.

[0024] The particle size of the solid electrolyte may be appropriately selected taking into consideration constraints such as the thickness of the solid electrolyte layer. The particle size of the solid electrolyte is, for example, preferably 10 nm or more and 100 μm or less, more preferably 30 nm or more and 20 μm or less, and even more preferably 50 nm or more and 10 μm or less. If the particle size of the solid electrolyte is larger than the thickness of the solid electrolyte layer, the film thickness of the solid electrolyte layer will be non-uniform. The particle size of the solid electrolyte is preferably smaller than the thickness of the solid electrolyte layer.

[0025] The fibrous carbon functions as both a conductive additive and a binder. The conductive additive provides electrical conductivity between active materials. The binder maintains the shape of the coating film obtained by applying the electrode composition while enhancing adhesion to the current collector. The viscosity of the electrode composition can be adjusted by the ratio and type of fibrous carbon present.

[0026] The fibrous carbon is a carbon compound having an aspect ratio, calculated by dividing the fiber length by the fiber diameter, of 100 or more. The aspect ratio, calculated by dividing the fiber length by the fiber diameter, of the fibrous carbon is preferably 500 or more, and more preferably 1000 or more.

[0027] Examples of fibrous carbon include carbon nanotubes (CNT) and carbon nanofibers. Carbon nanotubes are particularly preferred as fibrous carbon because they are thin and have high electronic conductivity. Carbon nanotubes may be single-walled carbon nanotubes (SWCNT) or multi-walled carbon nanotubes (MWCNT). SWCNTs tend to have smaller fiber diameters than MWCNTs, and it is more preferable to use SWCNTs as fibrous carbon. SWCNTs include metallic CNTs and semiconducting CNTs, and either may be used.

[0028] The fiber diameter and fiber length of the fibrous carbon can be selected appropriately. For example, the fiber diameter of the fibrous carbon is preferably 1 nm or more and 10 nm or less. The fiber length of the fibrous carbon is preferably 1 μm or more and 1000 μm or less, and more preferably 5 μm or more and 500 μm or less. An electrode composition using fibrous carbon with a short fiber length tends to have low viscosity. Fibrous carbon with a long fiber length tends to be difficult to disperse in the electrode composition. In order to sufficiently increase the viscosity of the electrode composition with a small amount of fibrous carbon, thin fibrous carbon is preferred.

[0029] The fibrous carbon is preferably dispersed in the electrode composition. Fibrous carbon such as CNT has a bundle structure and is prone to aggregation. The dispersibility of the fibrous carbon such as CNT is enhanced by the cyclic siloxane, and aggregation in the electrode composition is suppressed.

[0030] Cyclic siloxanes are one of the dispersion media for fibrous carbon. They help disperse fibrous carbon within electrode compositions. Cyclic siloxane is a general term for cyclic organic compounds with a cyclic molecular structure skeleton formed by siloxane bonds. Cyclic siloxanes have excellent dispersibility for fibrous carbon. Cyclic siloxanes also have low reactivity with solid electrolytes. Therefore, electrode compositions containing cyclic siloxanes suppress the generation of toxic gases due to decomposition of solid electrolytes and are less likely to cause a decrease in ionic conductivity.

[0031] The boiling point of the cyclic siloxane is preferably 260°C or lower. The dispersion medium such as the cyclic siloxane is preferably removed after the electrode composition is applied. If the boiling point of the cyclic siloxane is 260°C or lower, the cyclic siloxane can be easily volatilized when the electrode composition is dried. Furthermore, cyclic siloxanes that satisfy the above conditions have little effect on sulfide-based solid electrolytes or halide-based solid electrolytes when the cyclic siloxane is volatilized. Sulfide-based solid electrolytes and halide-based solid electrolytes may decompose due to high heat.

[0032] The cyclic siloxane is, for example, a cyclic product of dimethylsiloxane. Examples of the cyclic siloxane include hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and dodecamethylcyclohexasiloxane. The type of cyclic siloxane may be appropriately selected depending on the properties of the type of solid electrolyte, and hexamethylcyclotrisiloxane is preferred. Hexamethylcyclotrisiloxane is easily volatilized by reducing pressure even at room temperature. This makes it easy to remove the cyclic siloxane from the electrode composition after application.

[0033] The mass ratios of the active material, solid electrolyte, fibrous carbon, and cyclic siloxane contained in the electrode composition are not particularly limited. For example, the mass ratio of the active material contained in the electrode composition is 10 mass% or more and 65 mass% or less. For example, the mass ratio of the solid electrolyte contained in the electrode composition is 4 mass% or more and 50 mass% or less. For example, the mass ratio of the fibrous carbon contained in the electrode composition is 0.05 mass% or more and 4 mass% or less. For example, the mass ratio of the cyclic siloxane contained in the electrode composition is 2 mass% or more and 70 mass% or less.

[0034] The electrode composition may contain materials other than the active material, solid electrolyte, fibrous carbon, and cyclic siloxane.

[0035] For example, the electrode composition may contain a conductive additive, which is used when sufficient conductivity cannot be ensured by the fibrous carbon alone.

[0036] The conductive additive is a fine particle having electrical conductivity. Examples of the conductive additive include carbon powder, carbon material, metal fine powder, a mixture of carbon material and metal fine powder, and conductive oxide. Examples of the carbon powder include carbon black such as acetylene black and ketjen black. Examples of the carbon material include vapor grown carbon fiber (VGCF), graphite, graphene, etc. Examples of the metal fine powder include powder of copper, nickel, stainless steel, iron, etc. The conductive additive is preferably a substance containing carbon.

[0037] The electrode composition may also contain a dispersion medium other than cyclic siloxane. Examples of the dispersion medium that can be used include saturated hydrocarbons such as hexane, aromatic hydrocarbons such as toluene and xylene, alcohols such as methanol, ethanol, propanol, and butanol, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone, esters such as ethyl acetate and butyl acetate, ethers such as tetrahydrofuran, dioxane, and diethyl ether, amides such as N,N-dimethylformamide, N-methylpyrrolidone (NMP), and N,N-dimethylacetamide, halogenated hydrocarbons such as ethylene chloride and chlorobenzene, siloxane-based liquids such as dimethyl silicone oil and methylphenyl silicone oil, and fluorine-based liquids such as hydrofluoroethers.

[0038] Furthermore, for example, when the electrode composition contains a dispersion medium other than cyclic siloxane, the dispersion medium can be appropriately selected depending on the type of solid electrolyte. For example, when the solid electrolyte is a halide-based solid electrolyte, the electrode composition preferably contains a hydrocarbon, and the hydrocarbon is more preferably an aliphatic hydrocarbon. Hydrocarbons are insoluble in water, preventing water from entering the electrode composition and suppressing the reaction between water and the solid electrolyte. Hydrocarbons also dissolve hexamethylcyclotrisiloxane. Hexamethylcyclotrisiloxane is a solid at room temperature but dissolves in hydrocarbons. By including a hydrocarbon in the electrode composition, hexamethylcyclotrisiloxane dissolves in the hydrocarbon, and the electrode composition is made into a homogeneous paste.

[0039] The aliphatic hydrocarbon is preferably at least one selected from, for example, heptane, octane, nonane, and decane. These have moderate volatility. Therefore, the electrode composition can be applied to these dispersion media under conditions that suppress volatility, such as room temperature and normal pressure, and then the hydrocarbon can be volatilized together with the cyclic siloxane by reducing the pressure or drying with hot air.

[0040] The electrode composition may also contain a binder, for example, polyvinylidene fluoride (PVDF) or a copolymer thereof, polytetrafluoroethylene (PTFE), polyamide (PA), polyimide (PI), polyamideimide (PAI), polybenzimidazole (PBI), polyethersulfone (PES), polyacrylic acid (PA) and a copolymer thereof, a metal ion crosslinked product of polyacrylic acid (PA) and a copolymer thereof, maleic anhydride-grafted polypropylene (PP), maleic anhydride-grafted polyethylene (PE), or a mixture thereof.

[0041] On the other hand, since a binder does not contribute to the charge / discharge reaction, it is preferable not to include a binder in the electrode composition. If the electrode composition can ensure sufficient viscosity with only the fibrous carbon and can ensure adhesion between the electrode composition and other layers, there is no need to include a binder in the electrode composition.

[0042] The electrode composition according to this embodiment can be produced, for example, by preparing a dispersion containing fibrous carbon and a cyclic siloxane, and then adding and dispersing the active material and solid electrolyte in the dispersion. If a water-insoluble hydrocarbon-based dispersion medium is used for the dispersion, the dehydration process of the dispersion medium can be simplified.

[0043] The method for preparing the dispersion is not particularly limited. For example, a high-speed shear disperser, an ultrasonic disperser, or the like can be used to prepare the dispersion. When dispersing fibrous carbon, it is also preferable to select a disperser depending on the degree of aggregation of the fibrous carbon. For example, when SWCNT is used as the fibrous carbon, the secondary aggregated SWCNT may be dispersed using a high-speed shear disperser to form primary aggregates, and then the bundle structure of the SWCNT may be broken down using an ultrasonic disperser.

[0044] Regarding the cyclic siloxane, the fibrous carbon may be dispersed in a different dispersion medium and then the cyclic siloxane may be added, or the fibrous carbon and the cyclic siloxane may be mixed from the beginning. When the fibrous carbon is dispersed in a different dispersion medium from the cyclic siloxane and then the cyclic siloxane is added, it is preferable to subject the solution to which the cyclic siloxane has been added to the disperser again.

[0045] The active material and the solid electrolyte are added to the dispersion liquid prepared by the above procedure. Preferably, after the active material and the solid electrolyte are added, the solution is then subjected to a dispersing machine again. In this manner, the electrode composition according to this embodiment can be prepared.

[0046] The electrode composition according to this embodiment contains a cyclic siloxane, which suppresses aggregation of the fibrous carbon. Furthermore, because the cyclic siloxane has poor reactivity with the solid electrolyte, the electrode composition according to this embodiment suppresses the generation of toxic gases associated with the decomposition of the solid electrolyte and is less likely to experience a decrease in ionic conductivity. Furthermore, the electrode composition according to this embodiment has sufficient viscosity because the fibrous carbon functions as a binder. Furthermore, in the electrode composition according to this embodiment, the fibrous carbon functions as a binder, which suppresses the sedimentation of active materials and the like within the electrode composition. In other words, the electrode composition according to this embodiment can be satisfactorily used as a paint.

[0047] The electrode composition according to this embodiment is used in the production of an all-solid-state battery. Specifically, the electrode composition according to this embodiment is used in the production of an electrode for the all-solid-state battery. The method for producing an electrode according to this embodiment includes the steps of applying the electrode composition according to this embodiment to a support, and volatilizing the cyclic siloxane from the electrode composition. The support is a positive electrode current collector 22 or a negative electrode current collector 32, which will be described later. The method for producing an all-solid-state battery according to this embodiment includes the method for producing an electrode according to this embodiment.

[0048] Fig. 1 is a cross-sectional view of an all-solid-state battery 100 according to this embodiment. The all-solid-state battery 100 shown in Fig. 1 includes a power generating element 40 and an exterior body 50. The exterior body 50 covers the periphery of the power generating element 40. The exterior body 50 is, for example, a metal laminate film in which a metal foil 52 is coated on both sides with a resin layer 54. The power generating element 40 is connected to the outside via a pair of terminals 60, 62 connected to the power generating element 40.

[0049] Although a laminated battery is shown in Fig. 1, a wound battery may also be used. The all-solid-state battery 100 is used, for example, in laminated batteries, prismatic batteries, cylindrical batteries, coin batteries, button batteries, etc. Furthermore, although Fig. 1 shows an example in which the power generation element is composed of one unit of a positive electrode, a negative electrode, and a solid electrolyte layer, the all-solid-state battery may also be a bipolar type in which multiple units are stacked while sharing the positive electrode or the negative electrode between the units.

[0050] The power generating element 40 includes a solid electrolyte layer 10, a positive electrode 20, and a negative electrode 30. The solid electrolyte layer 10 is sandwiched between the positive electrode 20 and the negative electrode 30. The power generating element 40 is charged or discharged by the exchange of ions between the positive electrode 20 and the negative electrode 30 via the solid electrolyte layer 10 and the exchange of electrons via an external circuit.

[0051] The solid electrolyte layer 10 includes a solid electrolyte that can move ions by an externally applied voltage. The solid electrolyte is, for example, the above-mentioned halide-based solid electrolyte or sulfide-based solid electrolyte. In addition to the solid electrolyte, the solid electrolyte layer 10 may also include a binder or the like.

[0052] 1, the positive electrode 20 has a plate-shaped (foil-shaped) positive electrode current collector 22 and a positive electrode active material layer 24. The positive electrode active material layer 24 is in contact with at least one surface of the positive electrode current collector 22.

[0053] The positive electrode current collector 22 may be made of any electron-conductive material that is resistant to oxidation during charging and corrosion. The material for the positive electrode current collector 22 can be appropriately selected taking into consideration the materials of the solid electrolyte and active material. For example, aluminum, copper, nickel, titanium, and stainless steel can be used for the positive electrode current collector 22. The positive electrode current collector 22 may be a conductive foil or mesh. For example, metal foil, expanded metal, punched metal, graphite sheet, carbon cloth, etc. can be used for the positive electrode current collector 22.

[0054] The thickness of the metal foil is preferably 3 μm to 100 μm, and more preferably 7 μm to 20 μm. If it is less than 3 μm, the foil is easily damaged, and if it is more than 100 μm, the energy density of the all-solid-state battery will be low.

[0055] Furthermore, to improve the adhesion between the positive electrode current collector 22 and the positive electrode active material layer 24, one surface of the positive electrode current collector 22 may be roughened or an adhesion layer may be formed. The roughness may be formed by blasting, etching, or the like. The adhesion layer preferably contains, for example, an organic substance. For example, polyvinylidene fluoride (PVDF), acrylic resin, cellulose-based resin, silicone resin, various rubbers, or the like may be used for the adhesion layer.

[0056] The positive electrode active material layer 24 is produced using the above-described electrode composition. The positive electrode active material layer 24 includes the above-described positive electrode active material, a solid electrolyte, and fibrous carbon. The cyclic siloxane in the battery composition is volatilized and removed during production of the positive electrode active material layer 24.

[0057] 1, the negative electrode 30 has a plate-shaped (foil-shaped) negative electrode current collector 32 and a negative electrode active material layer 34. The negative electrode active material layer 34 is in contact with at least one surface of the negative electrode current collector 32.

[0058] The negative electrode current collector 32 may be made of the same material as the positive electrode current collector 22. The negative electrode current collector 32 may have an uneven surface formed thereon, or may have an adhesive layer.

[0059] The negative electrode active material layer 34 is produced using the above-described electrode composition. The negative electrode active material layer 34 includes the above-described negative electrode active material, a solid electrolyte, and fibrous carbon. The cyclic siloxane in the battery composition is volatilized and removed when the negative electrode active material layer 34 is produced.

[0060] The positive electrode active material layer 24 can be produced by applying a positive electrode composition to one surface of the positive electrode current collector 22 and volatilizing cyclic siloxane from the positive electrode composition. The negative electrode active material layer 34 can be produced by applying a negative electrode composition to one surface of the negative electrode current collector 32 and volatilizing cyclic siloxane from the negative electrode composition. The positive electrode current collector 22 and the negative electrode current collector 32 are examples of supports.

[0061] There are no particular limitations on the method for applying the electrode composition to the positive electrode current collector 22 and the negative electrode current collector 32. For example, application methods such as a reverse roll method, a direct roll method, a blade method, a knife method, an extrusion nozzle method, a curtain method, a gravure roll method, a bar coating method, a dip method, a kiss coating method, and a squeeze method can be used.

[0062] The electrode composition can be dried by hot air drying, infrared drying, vacuum drying, or the like. When heating in the drying step, the composition is maintained at a temperature of, for example, 50°C or higher and 150°C or lower for 10 seconds to 10 minutes to volatilize the dispersion medium. If it is desired to lower the drying temperature, the composition may be dried under reduced pressure using a vacuum dryer or the like. This volatilizes the cyclic siloxane from the electrode composition.

[0063] The solid electrolyte layer 10 can be produced by applying a dispersion of a solid electrolyte to a carrier film and drying it. The positive electrode 20 and the negative electrode 30 are stacked so as to sandwich the solid electrolyte layer 10. The stack is then pressed to obtain the power generating element 40. The power generating element 40 is then covered with an exterior body 50 to obtain the all-solid-state battery 100.

[0064] According to the electrode manufacturing method of this embodiment, an electrode layer with very few defects such as fading of the coating film can be obtained. This is thought to be because the fibrous carbon is uniformly dispersed in the electrode composition, which is a paint, and the viscosity of the paint is appropriately adjusted. Furthermore, according to the electrode manufacturing method of this embodiment, the dispersion medium, such as cyclic siloxane, can be easily removed during drying.

[0065] Furthermore, according to the method for producing an all-solid-state battery according to this embodiment, it is possible to produce an all-solid-state battery that has a small amount of binder that does not contribute to charge and discharge, a large charge and discharge capacity, and excellent rate characteristics.

[0066] The above describes the embodiments of the present disclosure in detail with reference to the drawings. However, each configuration and combination thereof in each embodiment is an example, and addition, omission, substitution, and other modifications of the configuration are possible within the scope that does not deviate from the technical requirements of the present disclosure.

[0067] "Example 1" (Preparation of solid electrolyte) Li ２ SO ４ 32 parts by mass of (lithium sulfate) powder, ZrCl ４ 68 parts by mass of (zirconium chloride) powder and zirconia balls as media were placed in a zirconia container and the container was closed with a lid. This container was placed in a planetary ball mill and rotated. ２ SO ４ and ZrCl ４ is converted to Li by mechanochemical reaction ２ ZrSO ４ Cl ４ It became. ２ ZrSO ４ Cl ４ is a powder material with partial crystallinity and is a solid electrolyte with Li ion conductivity. ２ ZrSO ４ Cl ４ The powder was sieved to remove coarse particles, and a solid electrolyte was obtained.

[0068] It was confirmed that hexamethylcyclotrisiloxane does not reduce the ionic conductivity of the solid electrolyte. 50 parts by mass of hexamethylcyclotrisiloxane was dissolved in 50 parts by mass of heptane to prepare a dispersion medium. 100 parts by mass of the solid electrolyte (Li ２ ZrSO ４ Cl ４ ) was added and stirred. Then, the dispersion medium was dried under reduced pressure, and the solid electrolyte was recovered and its ionic conductivity was measured.

[0069] For comparison, a solid electrolyte was dispersed in 100 parts by mass of heptane, the dispersion medium was dried, the solid electrolyte was recovered, and the ionic conductivity was measured. There was no difference in ionic conductivity between these solid electrolytes. In other words, it was confirmed that hexamethylcyclotrisiloxane, like heptane, does not reduce the ionic conductivity of the solid electrolyte.

[0070] Next, a dispersion of carbon nanotubes was prepared. Carbon nanotubes correspond to fibrous carbon. The dispersion of carbon nanotubes was prepared by a first dispersion step and a second dispersion step. In the first dispersion step, 0.2 parts by mass of single-walled carbon nanotubes and 80 parts by mass of heptane were mixed and dispersed using a high-speed rotation homogenizer. In the second dispersion step, 20 parts by mass of hexamethylcyclotrisiloxane was added to the solution prepared in the first dispersion step, and the mixture was dispersed again using an ultrasonic homogenizer.

[0071] Next, a positive electrode composition was prepared using the dispersion. First, lithium cobalt oxide (LCO) was surface-treated using a hydrolyzate of trimethoxyphenylsilane. This surface-treated LCO was used as a positive electrode active material. 70 parts by mass of the positive electrode active material and 1.8 parts by mass of flake graphite were added to the dispersion, and the mixture was dispersed again using an ultrasonic homogenizer. Then, 30 parts by mass of Li ２ ZrSO ４ Cl ４ The mixture was further added and dispersed again using an ultrasonic homogenizer to prepare a positive electrode composition.

[0072] Next, an aluminum foil was prepared as a positive electrode current collector. The positive electrode composition was then applied to the positive electrode current collector using a knife coater. The applied product was glossy and free of defects such as pinholes and smudges.

[0073] Next, the positive electrode composition applied to the positive electrode current collector was dried using a hot plate. The heptane and hexamethylsiloxane were evaporated from the positive electrode composition by drying. The surface after application was inspected, and no pinholes or smudges were found. The coating did not fall off even when the composition was removed from the hot plate.

[0074] Comparative Example 1 differs from Example 1 in that, when preparing the carbon nanotube dispersion, only heptane was used without using hexamethylcyclotrisiloxane. Specifically, in the second dispersion step when preparing the carbon nanotube dispersion, 20 parts by mass of heptane was used instead of hexamethylcyclotrisiloxane. The other conditions were the same as in Example 1, and the positive electrode composition was applied to one surface of the positive electrode current collector.

[0075] The coated surface of Comparative Example 1 had no gloss. Also, fading was observed in part of the coated surface, and coating voids were observed in part of the coated surface.

[0076] The coated positive electrode composition was then dried. In the areas where coating voids were confirmed before drying, aluminum was exposed in the dried coating film. Furthermore, when the coating film was removed from the hot plate, a portion of the coating film fell off from the aluminum foil.

[0077] Example 2 Example 2 differs from Example 1 in that an etched aluminum foil was used as the positive electrode current collector. The other conditions were the same as those of Example 1.

[0078] In Example 2, the coated surface was glossy and no smearing, pinholes, etc. were observed. Furthermore, the coating did not come off when it was removed from the hot plate.

[0079] The electrode composition of the present embodiment is suitably applied to the manufacturing process of an electrode for an all-solid-state battery.

[0080] REFERENCE SIGNS LIST 10 solid electrolyte layer 20 positive electrode 22 positive electrode current collector 24 positive electrode active material layer 30 negative electrode 32 negative electrode current collector 34 negative electrode active material layer 40 power generating element 50 exterior body 52 metal foil 54 resin layer 100 all-solid-state battery.

Claims

1. An electrode composition comprising an active material, a solid electrolyte, fibrous carbon, and a cyclic siloxane.

2. The electrode composition according to claim 1, wherein the boiling point of the cyclic siloxane is 260°C or lower.

3. The electrode composition according to claim 1, wherein the cyclic siloxane is hexamethylcyclotrisiloxane.

4. The electrode composition according to claim 1, further comprising a hydrocarbon.

5. The electrode composition according to claim 4, wherein the hydrocarbon is at least one selected from the group consisting of heptane, octane, nonane, and decane.

6. A method for manufacturing an electrode, comprising the steps of: applying the electrode composition according to claim 1 to a support; and volatilizing the cyclic siloxane from the electrode composition.

7. A method for producing an all-solid-state battery, comprising the method for producing an electrode according to claim 6.

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