Method for recovering monocrystalline silicon or polycrystalline silicon from solar panel, and method for producing raw material for all-solid-state lithium ion battery negative electrode active material using recovered silicon

Abstract

[Problem] To provide a method for reusing, by a simple method, a silicon cell separated from a solar panel. [Solution] Provided is a method for recovering monocrystalline silicon or polycrystalline silicon from a solar panel, the method being characterized by: separating monocrystalline silicon or polycrystalline silicon from a waste solar panel; thereafter, washing the surface of the separated monocrystalline silicon or polycrystalline silicon with an acid; and crushing the monocrystalline silicon or polycrystalline silicon, of which the surface has been washed with an acid, to an average particle diameter of 0.5-5.0 μm in the presence of a dispersion medium containing an alcohol.

Description

Method for recovering single-crystal silicon or polycrystalline silicon from solar panels, and method for producing raw material for negative electrode active material of all-solid-state lithium-ion batteries using the recovered silicon

[0001] The present invention relates to a method for recovering single-crystal silicon or polycrystalline silicon from solar panels, and a method for producing a raw material for a negative electrode active material of an all-solid-state lithium-ion battery using the recovered silicon.

[0002] Toward the realization of a low-carbon society, CO2 reduction through the utilization of renewable energy sources, including solar power generation, is accelerating. A typical solar cell module for solar power generation has a three-layer structure: a tempered glass surface, an encapsulating resin layer inside, and a backsheet on the back. Solar cells made of monocrystalline or polycrystalline silicon are arranged within the encapsulating resin layer and connected by electrical wires (interconnectors). The encapsulating resin must have transparency, flexibility, adhesiveness, tensile strength, and weather resistance. Ethylene-vinyl acetate copolymer (EVA) is commonly used, and it bonds the tempered glass, cells, and backsheet together by applying heat and pressure. While the adoption of solar power generation has progressed significantly, recycling solar cell modules at the time of disposal has become an issue.

[0003] When this solar cell module is heated in an electric furnace or the like under an oxidizing atmosphere, the EVA melts at 80 to 120° C., a deacetylation reaction of the EVA occurs at around 350° C., and a thermal decomposition reaction of the polyethylene main chain occurs rapidly at around 450° C. Technologies for recycling solar cell modules by such thermal decomposition have been disclosed (see Patent Documents 1 and 2).

[0004] Furthermore, in order to prevent the EVA contained in solar cell modules from burning too quickly, a method has been proposed in which the resin components are slowly and steadily burned and removed, rather than lowering the oxygen concentration in the heating furnace, thereby recovering valuable resources efficiently and simply (see Patent Document 3).

[0005] By the above method, resin components such as the back sheet and sealing resin layer can be removed from the solar cell module, and the glass, cells, aluminum frame, etc. can be separated and recovered.

[0006] Japanese Patent Publication No. 11-165150 Japanese Patent Publication No. 2007-59793 International Publication No. WO2020 / 031661 Korean Patent Publication No. 20230033968 Chinese Patent Publication No. 115353111

[0007] The glass, aluminum frames, etc. recovered by the above method can be reused for solar cell modules and other uses. On the other hand, although the recovered cells are mainly composed of polycrystalline silicon or single crystal silicon, they contain metal components such as wiring materials and resin components used in adhesives that were used to construct the solar cell module, and therefore require further purification measures before they can be used as cell materials as they are.

[0008] For example, proposed methods include a primary acid leaching step in which an acid leaching solution is added to crushed waste solar silicon to leach and stir impurities contained in the waste solar silicon (see Patent Document 4), and a method in which recovered solar panels are disassembled, immersed in an FeCl3 solution, and pickled with hydrochloric acid, and a portion of the organic material is thermally decomposed at 330°C to 380°C, crushed into powder, melt-refined to purify, and then solidified to obtain recycled silicon (see Patent Document 5).

[0009] These methods involve purifying silicon cells recovered from solar cell modules and reusing them for use in solar cell modules, but they require numerous purification steps, and a simpler recycling method has been desired.

[0010] Therefore, an object of the present invention is to provide a simple method for reusing silicon cells recovered from solar cell modules.

[0011] The present inventors conducted extensive research to address the above-mentioned problems. Analysis of impurities in polycrystalline silicon and single-crystalline silicon recovered from solar panels using known purification methods revealed the presence of metal components derived from wiring materials such as aluminum and organic substances derived from resins. However, the quality of the silicon recovered was confirmed to be equivalent to that of silicon produced from conventional silicon sources such as high-purity polycrystalline silicon or silicon metal, demonstrating its applicability as a raw material for the negative electrode active material of all-solid-state lithium-ion secondary batteries. The inventors then investigated methods for efficiently producing silicon for the negative electrode active material of all-solid-state lithium-ion batteries from polycrystalline silicon and single-crystalline silicon separated from solar panels. They discovered that by acid-washing the surface of the separated silicon and then crushing it in the presence of a dispersion medium containing alcohol, it was possible to efficiently produce silicon for the negative electrode active material of all-solid-state lithium-ion batteries, and that this could be achieved at a level that would not cause any problems in terms of characteristics, leading to the completion of the present invention.

[0012] That is, the first invention is a method for recovering single crystal silicon or polycrystalline silicon from solar panels, comprising separating single crystal silicon or polycrystalline silicon from waste solar panels, then washing the surface of the separated single crystal silicon or polycrystalline silicon with an acid, and crushing the single crystal silicon or polycrystalline silicon whose surface has been washed with acid to particles having an average particle size of 0.5 to 5.0 μm in the presence of a dispersion medium containing alcohol.

[0013] The second invention is a method for producing a raw material for a negative electrode active material of an all-solid-state lithium-ion secondary battery, comprising: separating single crystal silicon or polycrystalline silicon from waste solar panels; subsequently, washing the surface of the separated single crystal silicon or polycrystalline silicon with an acid; and crushing the single crystal silicon or polycrystalline silicon whose surface has been washed with acid in the presence of a dispersion medium containing an alcohol to particles with an average particle size of 0.5 to 5.0 μm.

[0014] Furthermore, a third aspect of the present invention is a material for forming an anode of an all-solid-state lithium-ion secondary battery, the material comprising: a negative electrode active material layer formed on a current collector to a thickness of 10 μm or more, the negative electrode active material layer being made of a composition containing a raw material for the anode active material of the all-solid-state lithium-ion secondary battery according to the second aspect of the present invention. In the third aspect of the present invention, it is preferable that the layer made of the raw material for the anode active material of the all-solid-state lithium-ion secondary battery is patterned on the current collector to form island-shaped protrusions spaced apart from each other, and that a connection layer made of a composition containing the raw material for the anode active material of the all-solid-state lithium-ion secondary battery is formed on the bottom surface of a groove formed between the island-shaped protrusions, the connection layer being continuous with the island-shaped protrusions.

[0015] Furthermore, a fourth aspect of the present invention is an all-solid-state lithium ion secondary battery having a positive electrode, a negative electrode, and a solid electrolyte layer, characterized in that the above-mentioned material for forming an all-solid-state lithium ion secondary battery negative electrode is disposed as the negative electrode.

[0016] According to the manufacturing method of the present invention, polycrystalline silicon and single crystal silicon separated from solar panels can be efficiently used as raw materials (i.e., silicon sources) for producing silicon for use as a negative electrode active material in all-solid-state lithium-ion batteries. To use the polycrystalline silicon and single crystal silicon for use in cells of solar cell modules, it is necessary to thoroughly purify and remove metal components derived from wiring materials and organic substances derived from resins. In contrast, according to the present invention, these can be removed using known purification methods, and therefore the polycrystalline silicon and single crystal silicon can be used as silicon sources for producing silicon for use as a negative electrode active material in all-solid-state lithium-ion batteries without thorough purification.

[0017] Fig. 1 is a schematic cross-sectional view showing one embodiment of a material for forming an all-solid-state lithium-ion battery (LiB) negative electrode according to the present invention. Fig. 2 is a schematic plan view showing one embodiment of a material for forming an all-solid-state LiB negative electrode according to the present invention. Fig. 3 is a plan view showing another embodiment of a material for forming an all-solid-state LiB negative electrode according to the present invention. Fig. 4 is a plan view showing another embodiment of a material for forming an all-solid-state LiB negative electrode according to the present invention. Fig. 5 is a schematic cross-sectional view showing one embodiment of a state before charge and discharge of an all-solid-state LiB according to the present invention.

[0018] The method for recovering single crystal silicon or polycrystalline silicon of the present invention is characterized by washing the surface of single crystal silicon or polycrystalline silicon separated from waste solar panels with acid, and then crushing the acid-washed single crystal silicon or polycrystalline silicon to an average particle size of 0.5 to 5.0 μm in the presence of a dispersion medium containing alcohol. As described above, silicon cells separated from solar panels are primarily composed of polycrystalline silicon and single crystal silicon. However, the polycrystalline silicon and single crystal silicon contain impurities such as metal components such as aluminum used as wiring materials and organic components derived from resin materials. Therefore, when using the silicon cells as silicon for solar cell modules, these impurities must be thoroughly removed. When removing the wiring material and resin material, the solar panel cracks and breaks into small pieces. If the separated silicon pieces are too large, they can be coarsely crushed to a size suitable for cleaning, as described below. The size of the small pieces is not particularly limited, but they are usually small enough to pass through a sieve with a mesh size of 30 mm.

[0019] On the other hand, when producing silicon for use as an anode active material in an all-solid-state lithium-ion battery (hereinafter also referred to as an all-solid-state LiB), high-purity polycrystalline silicon or metallic silicon is generally crushed to about 10 μm in a dry manner to obtain silicon for use as an anode active material in an all-solid-state lithium-ion battery. Therefore, by using polycrystalline silicon or single-crystalline silicon separated from a solar panel instead of the metallic silicon, silicon for use as an anode active material in an all-solid-state lithium-ion battery can be obtained.

[0020] Generally, high-purity silicon is insulating. Therefore, to impart conductivity during crushing, carbon sources such as acetylene black or dopant components such as boron and phosphorus are mixed into the silicon to improve its properties as a negative electrode active material for all-solid-state lithium-ion batteries. However, it is also known that the presence of these components in excess can actually degrade the properties of silicon as a negative electrode active material for all-solid-state lithium-ion batteries. Meanwhile, polycrystalline silicon or single-crystalline silicon separated from solar panels contains aluminum derived from the wiring material on its surface, but contains no or very low amounts of dopant components such as boron and phosphorus. Therefore, when polycrystalline silicon or single-crystalline silicon separated from solar panels is used as a silicon source for producing silicon for a negative electrode active material for all-solid-state lithium-ion batteries without undergoing advanced purification, it can be treated in the same way as conventional high-purity silicon, allowing for efficient production of silicon for a negative electrode active material for all-solid-state lithium-ion batteries.

[0021] Unless otherwise specified, in this specification, the notation "A to B" for numerical values ​​A and B means "greater than or equal to A and less than or equal to B." In such notation, when a unit is added only to numerical value B, the unit also applies to numerical value A. The method for producing silicon for use as a negative electrode active material in an all-solid-state lithium-ion battery of the present invention will be described in detail below. In this specification, all-solid-state LiB refers to a lithium-ion secondary battery that does not contain a liquid such as a non-aqueous electrolyte or an ionic liquid as an electrolyte.

[0022] <Silicon Source> The manufacturing method of the present invention is characterized in that the silicon source contains at least one of monocrystalline silicon and polycrystalline silicon (hereinafter collectively referred to as "separated silicon") separated from solar panels. Known methods can be used to separate monocrystalline silicon and polycrystalline silicon from solar panels. Among these, it is preferable to use polycrystalline silicon separated from solar panels in view of the characteristics of the all-solid-state lithium-ion secondary battery. Specific examples of the method for separating monocrystalline silicon and polycrystalline silicon include the method described in Patent Document 3, in which a waste solar panel containing monocrystalline silicon or polycrystalline silicon is heated to heat and melt the resin in the waste solar panel, the heat-melted resin is burned, and then the monocrystalline silicon or polycrystalline silicon is separated from the waste solar panel.

[0023] When the wiring material and resin material are removed from the separated solar panels, the solar panels are cracked and broken into small pieces. If the separated silicon pieces are too large, they may be coarsely crushed to a size suitable for cleaning, as described below. The size of the pieces is not particularly limited, but they are usually crushed to a size small enough to pass through a sieve with 30 mm openings.

[0024] The silicon can be roughly crushed by known methods, such as a manual hammer, a hammer crusher, a chain crusher, a single-shaft crusher, a double-shaft crusher, a four-shaft crusher, a roll crusher, and a jaw crusher.

[0025] <Pickling of Silicon> The separated silicon contains impurities such as metal components such as aluminum and organic components derived from the resin material. Because metal components are sometimes present on the surface of the separated silicon, the surface of the separated silicon is pickled to remove some of the metal components. In the recovery method of the present invention, examples of acids used for pickling include hydrochloric acid, nitric acid, sulfuric acid, and hydrofluoric acid. Pickling can be carried out by using an aqueous solution with a concentration of 5 to 35% by mass, immersing the silicon at a reaction temperature of 10 to 40°C for 30 minutes to 4 hours. The cleaning solution may be stirred with a stirring rod, rotating blades, or the like to promote the reaction. The content of at least one impurity in the separated silicon after pickling is preferably one of the following. Note that the content in the following description is the content per 100 parts by mass of the at least one impurity of the separated silicon.

[0026] Aluminum: preferably 300,000 ppm by mass or less, more preferably 10,000 ppm by mass or less, and particularly preferably 1,000 ppm by mass or less. Iron: preferably 300,000 ppm by mass or less, more preferably 10,000 ppm by mass or less, and particularly preferably 1,000 ppm by mass or less. Oxygen: preferably 500 to 100,000 ppm by mass, more preferably 1,000 to 50,000 ppm by mass, and particularly preferably 5,000 to 40,000 ppm by mass.

[0027] Among the impurity components of the silicon source or the separated silicon, the aluminum and iron contents can be measured by X-ray fluorescence spectroscopy (XRF). The oxygen content of the silicon source or the separated silicon can be determined by measuring CO and CO by non-dispersive infrared absorption spectroscopy.

[0028] <Crushing of Silicon> The acid-washed separated silicon is crushed to an average particle size of 0.5 to 5.0 μm in the presence of an alcohol-containing dispersion medium to be used as a negative electrode active material for all-solid-state lithium-ion secondary batteries. Crushing the silicon in an alcohol-containing dispersion medium can produce silicon suitable for use as a raw material for the negative electrode active material of all-solid-state lithium-ion secondary batteries. During the crushing of the separated silicon, a mechanochemical reaction occurs, causing alkoxy groups generated from the alcohol to bond to the silicon particle surface. This is thought to increase the ionic and / or electronic conductivity when used as a raw material for the negative electrode active material of all-solid-state lithium-ion secondary batteries, thereby contributing to improved battery performance. On the other hand, in the presence of a dispersion medium other than alcohol, the alkoxy groups are not bonded, and no improvement in battery performance is observed. Furthermore, in the presence of water alone, oxidation reactions proceed, which is thought to reduce the silicon's properties and prevent any improvement in battery performance.

[0029] The method for pulverizing the separated silicon may be any method that uses a pulverizer that applies shear to the extent that the dispersion medium present during pulverization causes a mechanochemical reaction on the silicon particle surfaces. Specific examples include pulverization methods using pulverizers such as jet mills, planetary ball mills, vibration mills, hammer mills, and stamp mills. The amount of the dispersion medium present is 0.1 to 10 times, preferably 0.2 to 5.0 times, by mass relative to the silicon powder. The pulverization temperature is preferably in the range of 10 to 70°C, preferably 20 to 50°C. The pulverization time is preferably 5 to 120 minutes, preferably 10 to 60 minutes.

[0030] Specific examples of alcohols used in the dispersion medium include methanol, ethanol, normal propyl alcohol, isopropyl alcohol, normal butyl alcohol, isobutyl alcohol, pentyl alcohol, hexyl alcohol, heptyl alcohol, octyl alcohol, 2-ethylhexyl alcohol, and benzyl alcohol. These alcohols may be used alone or in combination with two or more. A mixture of alcohol and another organic solvent may also be used. In this case, it is preferable to contain 50 to 99 parts by mass of alcohol per 100 parts by mass of the dispersion medium.The organic solvent to be mixed and used is appropriately selected from aldehydes, ketones, ethers, esters, amides, imides, aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, heterocycles, and the like, and examples thereof include ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monoisopropyl ether, triethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol butyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, ethyl acetate, normal propyl acetate, isopropyl acetate, normal butyl acetate, isobutyl acetate, hexyl acetate, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether acetate, ethylene glycol monoisopropyl ether, Propyl ether acetate, diethylene glycol monoisopropyl ether acetate, triethylene glycol monoisopropyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether acetate, triethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, hexane, nonane, decane, isodecane, dodecane, isododecane, terpene oil solvents, naphthene solvents, isoparaffin solvents, cyclohexane, methylcyclohexane, dimethylcyclohexane, ethylcyclohexane, alkylcyclohexane, toluene, xylene, aromatic high-boiling solvents, acetone, methyl ethyl ketone, methyl pentyl ketone, methyl isobutyl ketone, cyclohexanone, terpineol, dihydroterpineol, and dihydroterpineol acetate, NMP (N-methylpyrrolidone), methoxybenzene, diethyl ether, dipropyl ether, dibutyl ether, and the like can be mentioned. After the treatment, the free dispersion medium may be removed by drying, if necessary.The silicon powder has an average particle size of preferably 0.8 to 2.5 μm, particularly preferably 1.0 to 1.5 μm, from the viewpoint of improving the cycle characteristics of the negative electrode active material layer after energization when used in an all-solid-state LiB battery. The average particle size means the 50% cumulative diameter (D50) in the particle size distribution measurement results obtained by a laser scattering method.

[0031] (Raw material for negative electrode active material of all-solid-state lithium-ion secondary battery) The silicon recovered by the method of the present invention can be used as a raw material for negative electrode active material of all-solid-state lithium-ion secondary battery. As a silicon source used as a raw material for negative electrode active material of all-solid-state lithium-ion secondary battery, silicon recovered by the method of the present invention may be used alone or in combination with silicon obtained by another production method.

[0032] Examples of silicon obtained by other production methods include polycrystalline silicon rods obtained by the so-called Siemens process, silicon obtained by pulverizing and classifying single-crystal silicon obtained by the so-called Czochralski process, and silicon obtained by pulverizing and classifying metallic silicon obtained by a silica reduction method.

[0033] (Composition for forming a negative electrode of an all-solid-state lithium-ion secondary battery) The raw material for the negative electrode active material is mixed with components constituting a negative electrode to form a composition for forming a negative electrode, and a layer made of the negative electrode active material is formed on a negative electrode current collector, thereby obtaining a negative electrode.

[0034] Furthermore, when a battery is assembled using the above-mentioned negative electrode active material and charged and discharged, as described above, some or all of the silicon crystal particles become amorphous, fuse into blocks, and densify in each block. The blocked negative electrode active material layer is dense and adheres closely to the negative electrode current collector, exhibiting excellent electronic conductivity. It has been confirmed that the carbon-containing functional groups present on the surfaces of the silicon particles constituting the silicon powder remain in a state that does not affect the densification. Therefore, charging at a high current density is possible even after the second charge / discharge.

[0035] The composition for forming an all-solid-state LiB negative electrode contains the above-described negative electrode active material, and the content of the electronic conductivity imparting agent is 2 parts by mass or less per 100 parts by mass of the negative electrode active material particles. In the most preferred embodiment, the composition is substantially free of the electronic conductivity imparting agent. According to the present invention, the proportion of the electronic conductivity imparting agent can be reduced, thereby increasing the relative amount of the active material particles and contributing to an improvement in battery capacity.

[0036] The composition for forming an all-solid-state LiB negative electrode can contain an ion-conductivity imparting agent to improve ion conductivity. The solid electrolyte described below can be used as such an ion-conductivity imparting agent. If the blending amount of the ion-conductivity imparting agent is too large, the relative amount of active material particles decreases, and the cycle characteristics also decrease. Therefore, the content of the ion-conductivity imparting agent in the composition for forming an all-solid-state LiB negative electrode is preferably 30% by mass or less, more preferably 20% by mass or less, and more preferably substantially free of the ion-conductivity imparting agent.

[0037] The composition for forming an all-solid-state LiB negative electrode can contain a binder, a plasticizer, etc., to form the raw material for the negative electrode into a layer. These components are preferably used in as small an amount as possible within the range that allows the above-mentioned forming, and the total amount is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, per 100 parts by mass of the negative electrode active material particles. If the amount of binder or plasticizer is too large, the amount of active material in the negative electrode active material layer will relatively decrease, which is undesirable in terms of increasing battery capacity.

[0038] Examples of binders include thermosetting resins such as thermosetting polyimide, phenolic resin, epoxy resin, urea resin, melamine resin, unsaturated polyester resin, and polyurethane; water-soluble polymers such as cellulose derivatives such as carboxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxypropyl cellulose, ethyl cellulose, hydroxyethyl cellulose, and hydroxymethyl cellulose, and polyvinyl alcohol; polycarbonate resins such as polypropylene carbonate; polyvinylidene fluoride; styrene-butadiene copolymers (so-called SBR rubber-based), styrene-propylene copolymers, styrene-ethylene-propylene copolymers (so-called SES-based and SEPS-based), copolymers of acrylic acid derivatives such as polymethyl acrylate and polymethyl methacrylate, and copolymers of modified acrylic acid derivatives.

[0039] The all-solid-state LiB negative electrode composition may contain a dispersion medium for forming island-shaped protrusions made of the all-solid-state LiB negative electrode composition described later on the negative electrode current collector. The dispersion medium may be appropriately selected from alcohols, aldehydes, ketones, ethers, esters, amides, imides, aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, heterocycles, and the like. Examples of the dispersion medium include methanol, ethanol, normal propyl alcohol, isopropyl alcohol, normal butyl alcohol, isobutyl alcohol, pentyl alcohol, hexyl alcohol, heptyl alcohol, octyl alcohol, 2-ethylhexyl alcohol, benzyl alcohol, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monoisopropyl ether, triethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol butyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, and ethyl acetate. , normal propyl acetate, isopropyl acetate, normal butyl acetate, isobutyl acetate, hexyl acetate, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether acetate, ethylene glycol monoisopropyl ether acetate, diethylene glycol monoisopropyl ether acetate, triethylene glycol monoisopropyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether acetate, triethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, hexane, nonane, decane, isodecane, dodecane, isododecane, terpene, naphthenic solvents, isoparaffinic solvents, cyclohexane, methylcyclohexane, dimethylcyclohexane, ethylcyclohexane, alkylcyclohexane, toluene,Examples of the dispersion medium include xylene, aromatic high-boiling solvents, acetone, methyl ethyl ketone, methyl pentyl ketone, methyl isobutyl ketone, cyclohexanone, terpineol, dihydroterpineol, dihydroterpineol acetate, NMP (N-methylpyrrolidone), methoxybenzene, diethyl ether, dipropyl ether, and dibutyl ether. These may be used alone or in combination. The amount of the dispersion medium used may be determined appropriately so that the viscosity of the paste containing the all-solid-state LiB negative electrode composition is optimal for the method of forming the negative electrode active material layer. The dispersion medium is removed by drying after coating the paste containing the all-solid-state LiB negative electrode composition.

[0040] (All-solid-state LiB anode-forming material) An anode active material layer made of the all-solid-state LiB anode-forming composition is formed on an anode current collector to obtain an all-solid-state LiB anode-forming material. The anode-forming material is one of the components constituting a battery and functions as an anode itself, but when an LiB is assembled and charged / discharged, the silicon crystals become amorphous, resulting in a crystal structure different from that of the anode in the battery after charging / discharging.

[0041] The packing rate of silicon, the active material in the negative electrode active material layer, is preferably in the range of 35 to 55% by volume, more preferably 40 to 50% by volume. Because the packing rate of the active material is low and voids exist in the negative electrode active material layer, lithium ions are absorbed into the silicon active material during charge and discharge, making it possible to mitigate volume expansion during amorphization (lithium-silicon alloying). The packing rate of the active material can be adjusted by the particle size or particle size distribution of the silicon particles, the amount of binder added, and the like. The packing rate of the active material in the negative electrode active material layer refers to the ratio of the volume of silicon to the volume of the negative electrode.

[0042] When using the anode active material raw material made of the specific silicon powder of the present invention, even if the thickness of the anode active material layer is increased to increase the battery capacity, it is possible to set a high current density at the initial stage of charging. Therefore, in the present invention, it is possible to form the anode active material layer with a thickness of 10 μm or more, particularly 15 μm or more, and even 20 μm or more. The upper limit of the thickness is not particularly limited, but is generally about 200 μm, particularly about 100 μm.

[0043] In an embodiment in which island-shaped convex portions are formed in the negative electrode active material layer described below, the above thickness refers to the thickness of the connection portion in the groove portion when the area ratio of the groove portion is 10% or more of the total area of ​​the negative electrode active material layer, and refers to the thickness of the convex portion when the area ratio of the groove portion is less than 10%.

[0044] Copper foil, nickel foil, or SUS foil is generally used as the negative electrode current collector, but other conductive metal foils may also be used. The negative electrode current collector may be electrolytic copper with a rust-proofing treatment applied to the surface. The thickness of the negative electrode current collector is not particularly limited, but from the viewpoint of battery miniaturization and handling, a thickness of 3 μm to 100 μm is usually used, and when a roll-to-roll manufacturing method is used, a thickness of 5 μm to 50 μm is preferably used. The shape of the negative electrode current collector may be a non-perforated sheet, or a perforated sheet such as a two-dimensional mesh, a three-dimensional net, or a punched metal. The surface of the negative electrode current collector may be subjected to a known surface treatment, such as mechanical surface processing, etching, chemical conversion treatment, anodizing, wash primer, corona discharge, or glow discharge.

[0045] When a negative electrode active material layer containing silicon crystals undergoes charging and discharging, the silicon crystal particles, which are the negative electrode active material, become amorphous and fuse into blocks, densifying them. However, because the blocking of the negative electrode active material layer occurs spontaneously during charging and discharging, the size, shape, and gaps between the blocks tend to become nonuniform. When the size, shape, and gaps between the blocks are nonuniform, adjacent blocks may come into contact with each other due to expansion and contraction during charging and discharging, generating compressive forces that can cause the blocks to crack. This can result in the negative electrode active material becoming more granular and isolated, potentially leading to a decrease in capacity. Furthermore, many of the grooves formed between the blocks reach the negative electrode current collector. The penetration of solid electrolyte into the interface between the blocks and the negative electrode current collector creates gaps, promoting block delamination and silicon isolation.

[0046] In order to solve the above problem, we have thoroughly investigated means for controlling the size, shape, and spacing of the spontaneously generated blocks. As a result, we have found that it is preferable to form the negative electrode active material layer of the all-solid-state LiB negative electrode forming material before charging and discharging into a pattern of island-shaped convex portions with spacing between them, and to form a connection layer that covers the bottom of the grooves formed between the island-shaped convex portions.

[0047] That is, as shown in a cross-sectional view in FIG. 1 and a plan view in FIG. 2 , an all-solid-state LiB anode-forming material 10 of this embodiment has an anode active material layer 2 made of an all-solid-state LiB anode-forming composition on an anode current collector 1, and the anode active material layer 2 has island-shaped protrusions 11 formed in a pattern at intervals, and grooves 12 formed between the island-shaped protrusions have connection layers 13 made of the all-solid-state lithium-ion secondary battery anode-forming composition formed on the bottom surfaces of the island-shaped protrusions so as to be continuous with the island-shaped protrusions.

[0048] The shape of the island-shaped protrusions 11 is not particularly limited. While Figures 1 and 2 show the case where the island-shaped protrusions 11 are truncated quadrangular pyramids, they may be cylindrical (Figure 3), elliptical cylindrical, or polygonal prisms such as triangular, quadrangular, pentagonal, or hexagonal prisms. They may also be truncated cones or elliptical cones. They may also be truncated polygonal pyramids such as triangular, quadrangular, pentagonal, or hexagonal pyramids (Figure 4). They may also be cones, elliptical cones, or polygonal pyramids, or combinations thereof. Furthermore, when an all-solid-state LiB is constructed, the island-shaped protrusions 11 may be covered with the solid electrolyte, and the solid electrolyte may also penetrate into the grooves 12.

[0049] Referring to FIG. 1 , the dimensions of each portion of the negative electrode active material layer 2 formed on the negative electrode current collector are described. The width (W) of the island-shaped protrusions 11 is preferably in the range of 10 μm to 100 μm, particularly 15 to 50 μm, and even more preferably 15 to 30 μm. By setting the width of the island-shaped protrusions 11 within this range, the blocks can be formed in a state in which the outer shape of the island-shaped protrusions is substantially maintained even during charge and discharge of the all-solid-state LiB after formation, thereby enabling stable performance. Furthermore, if the width of the island-shaped protrusions 11 is formed within the above range and is larger than the average size of blocks naturally formed during charge and discharge of the all-solid-state LiB, specifically, a width of approximately 15 to 25 μm, cracks may occur within the blocks originating from the island-shaped protrusions. However, these cracks do not reach the negative electrode current collector, and the effect of forming the blocks more uniformly remains unchanged compared to when the negative electrode active material layer is formed over the entire surface of the negative electrode current collector.

[0050] The size of the island-shaped convex portions is 100 to 10,000 μm. 2 , especially 225 to 2500 μm 2 , and further 225 to 900 μm 2 It is preferable that the range is set as follows: Specifying the size of the island-shaped convex portion by area is particularly effective when the shape to be patterned is complex.

[0051] The height (H) of the island-shaped protrusions 11 is preferably set to a height corresponding to the thickness of the layer made of the raw material for the negative electrode active material. The height (H) of the island-shaped protrusions 11 refers to the distance from the surface of the current collector to the highest point of the island-shaped protrusions 11. Furthermore, the spacing (P) between the island-shaped protrusions 11 is preferably in the range of 10 to 50%, particularly 15 to 30%, of the width (W) of the island-shaped protrusions 11, in order to suppress the effects of expansion and contraction between the island-shaped protrusions during charge and discharge after the all-solid-state LiB is formed. Furthermore, the thickness (t) of the connection layer 13 only needs to be smaller than the height of the island-shaped protrusions, and is preferably in the range of 1 to 50%, particularly 10 to 30%, of the height of the island-shaped protrusions, and is patterned so as not to exceed 15 μm. This is preferable because blocking in such portions is unlikely to occur during charge and discharge after the all-solid-state LiB is formed, and exposure of the negative electrode current collector to the bottom of the grooves 12 is reliably prevented.

[0052] The width (W) of an island-shaped protrusion refers to the length measured from the rising portion of the island-shaped protrusion as shown in Figure 1. Furthermore, the above length refers to the distance between opposing sides in the case of a rectangle having opposing sides, the diameter in the case of a circle, and the equivalent diameter in the case of a polygon having an odd number of sides. The spacing (P) between the island-shaped protrusions 11 refers to the distance between the rising portions of opposing island-shaped protrusions. The thickness (t) of the connection layer 13 refers to the average thickness of the negative electrode active material layer present between the rising portions.

[0053] In addition, when the side-to-side length and diameter vary depending on the measurement location, it is preferable that each measured value falls within the above-mentioned range. When the island-shaped protrusion and the connection layer are connected by a gentle curve, the width of the island-shaped protrusion 11 can be measured by taking the part of the rising portion that exceeds 50% of the height of the island-shaped protrusion as the rising portion. An angle of about 60 to 90 degrees is preferable, as this allows a large amount of silicon to be secured per island-shaped protrusion.

[0054] To form a negative electrode active material layer made of an all-solid-state LiB negative electrode composition on a negative electrode current collector, a method is recommended in which the all-solid-state LiB negative electrode composition is made into a paste with a solvent, a pattern is formed on the negative electrode current collector, and then the solvent is dried. The application method is not particularly limited as long as it can form a pattern of island-shaped convex portions described below. Examples include screen printing and 3D printing. Drying can be performed at a temperature sufficient to volatilize the solvent used.

[0055] Another method is to apply the composition for forming an all-solid-state LiB negative electrode to the entire surface of the negative electrode current collector, and then press a mold such as a mesh against the negative electrode active material layer in a dry or semi-dry state, thereby forming island-shaped protrusions 11 and grooves 12 in a mesh pattern, as shown in Fig. 5. In this case, the width of the island-shaped protrusions can be adjusted by the mesh opening spacing, the spacing between the island-shaped protrusions can be adjusted by the mesh thickness, and the height of the island-shaped protrusions and the thickness of the connection layer can be adjusted by the pressing depth.

[0056] As described above, when an LiB is assembled using an all-solid-state LiB negative electrode forming material having island-shaped protrusions 11 formed in a predetermined pattern on an anode current collector and then charged and discharged, the shape of the island-shaped protrusions 11 is generally maintained, although complete control is difficult. Therefore, the size and shape of each block derived from the island-shaped protrusions 11 and the grooves between the blocks are uniform, suppressing contact between adjacent blocks even with repeated expansion and contraction due to charge and discharge. As a result, the anode active material is less likely to become granular or isolated, preventing capacity loss. Furthermore, the presence of the connection layer 13 prevents the anode current collector 1 from being exposed at the bottom of the grooves 12, even after charge and discharge. When the negative electrode current collector 1 is exposed at the bottom of the groove 12, the solid electrolyte penetrates into the interface between the negative electrode current collector 1 and the block through the exposed portion, creating a gap and isolating the negative electrode active material, but such isolation can be effectively prevented by providing the connection 13. Furthermore, by providing the connection 13, the thickness of the layer made of the negative electrode active material can be partially reduced, further promoting the effect of increasing the initial current density obtained by using the negative electrode active material of the present invention.

[0057] The material for forming an all-solid-state LiB negative electrode has the above-mentioned negative electrode active material layer 2 on the negative electrode current collector 1, and a solid electrolyte layer may be further formed on the negative electrode active material layer. The solid electrolyte is not particularly limited, but examples include commonly used sulfide-based solid electrolytes and oxide-based solid electrolytes. Sulfide-based solid electrolytes are advantageous in terms of high lithium ion conductivity. Oxide-based solid electrolytes are advantageous in terms of being relatively chemically stable and having high voltage resistance. When an oxide-based solid electrolyte is used for the solid electrolyte layer, a commonly used ion-conducting material may be used in combination as needed to improve lithium ion conductivity.

[0058] The sulfide-based solid electrolyte contains, for example, lithium, phosphorus, and sulfur, and may further contain elements such as O, Al, B, Si, Ge, and I. Specifically, amorphous Li3PS4, amorphous 40LiI.60Li3PS4 (mol %), β-Li3PS4, α-Li3PS4, and Li7P3S 11 Crystals, etc., are used. Argyrodite-based solid electrolytes may also be used.

[0059] Such sulfide-based solid electrolytes can be obtained by known methods, such as preparing lithium sulfide (LiS) and diphosphorus pentasulfide (P2S5) as starting materials, mixing LiS and P2S5 in a molar ratio of about 50:50 to 80:20, melting the mixture, and rapidly cooling it, or mechanically milling it, or by known wet methods such as the suspension method, solution method, and sol-gel method.

[0060] The sulfide-based solid electrolyte obtained by the above method is amorphous. It can be used in this amorphous state, but it can also be heat-treated to become a crystalline sulfide-based solid electrolyte. Crystallization is expected to improve lithium ion conductivity.

[0061] The oxide-based solid electrolyte is, for example, Li 5+X La3(Zr X , A 2-X ) O 12 (wherein A is one or more elements selected from the group consisting of Sc, Ti, C, Y, Nb, Hf, Ta, Al, Si, Ga, Ge, and Sn, and X is 1.4≦X≦2), Li1+X Al X Ti 2-X (PO4)3 (where 0≦X≦1), Li 3X La 2 / 3-X TiO3 (where x is 0≦x≦2 / 3), etc. These have high ionic conductivity at room temperature and high electrochemical stability.

[0062] From the viewpoint of electrochemical stability, the oxide-based solid electrolyte may contain insulating particles such as silica (SiO2) particles, γ-alumina (Al2O3) particles, ceria (CeO2) particles, zirconia (ZrO2) particles, etc. Other known metal oxide particles may also be used.

[0063] The solid electrolyte preferably has a Young's modulus (25°C) of 10 to 70 GPa, more preferably 15 to 30 GPa, because when the negative electrode active material is densified into blocks, the solid electrolyte can easily fill the gaps that form between the blocks, thereby maintaining high ionic conductivity. Examples of solid electrolytes having a Young's modulus (25°C) of 10 to 70 GPa include amorphous Li3PS4, LiX-Li3PS4 (X = I, Br, Cl)-based glass, β-Li3PS4, α-Li3PS4, and Li7PS 11 Crystal, Li 10 GeP2S 12 and argyrodite-based crystals such as Li6PS5X (X=I, Br, Cl).

[0064] The thickness of the solid electrolyte layer is preferably 500 nm to 1000 μm, and more preferably 1 μm to 500 μm. If the thickness is 500 nm or more, a solid battery with stable performance can be produced without chipping or cracking. If the thickness is 1000 μm or less, a solid battery with sufficiently low resistance can be produced.

[0065] When a battery is assembled using the above-mentioned material for forming an all-solid-state LiB negative electrode and is charged and discharged, as described above, some or all of the silicon crystal particles, which are the negative electrode active material, become amorphous and densify into blocks while substantially maintaining the pattern of the island-shaped protrusions, thereby exhibiting the unique effects of the present invention described above.

[0066] Generally, when silicon is used as the negative electrode active material, the theoretical maximum charge capacity of an all-solid-state LiB is approximately 3600 mAhg, but the practical charge / discharge range is approximately 1000 to 3000 mAhg. That is, it is presumed that the reason why the all-solid-state LiB exhibits stable battery performance with good cycle characteristics over a long period of time is that the blocks generated by charge / discharge are uniformly controlled by the island-shaped protrusions 11, and that grooves reaching the negative electrode current collector 1 are unlikely to be formed due to the interaction with the connection layer 13, and further that the volume change of the generated blocks is small.

[0067] (All-Solid-State LiB) As shown in FIG. 6, the all-solid-state LiB of the present invention has a positive electrode current collector 5, a positive electrode active material layer 4, a negative electrode active material layer 2, a negative electrode current collector 1, and a solid electrolyte layer 3, and the negative electrode is formed using an all-solid-state LiB negative electrode-forming material. When an LiB is assembled using the all-solid-state LiB negative electrode-forming material and charged / discharged, some or all of the silicon crystals contained in the all-solid-state LiB negative electrode-forming material become amorphous. Furthermore, as a result of the charge / discharge, some or all of the silicon forms an alloy with lithium. That is, after the LiB is assembled and charged / discharged, the crystal structure of the negative electrode active material layer differs from the silicon crystals before assembly and is partially or entirely composed of amorphous silicon. In this specification, the negative electrode active material after charge / discharge may be simply referred to as "amorphous silicon," but the amorphous silicon may contain silicon crystals or may be alloyed with lithium.

[0068] When the battery is charged, the silicon particles in the anode layer expand in volume by absorbing lithium, causing the silicon particles to fuse together and become amorphous. The tiny voids between the silicon particles are pushed out, forming dense blocks of island-like protrusions isolated by grooves (depending on the size of the island-like protrusions, grooves may form within the block that do not reach the anode current collector). This limits the increase in thickness of the anode layer itself to about 1.5 times, even if the silicon particles themselves expand by about 300% during charging. Furthermore, during discharge, the silicon attempts to return to its original volume due to the release of lithium, but the solid electrolyte, which is relatively softer than the silicon blocks, is drawn into the voids around the blocks, resulting in almost no reduction in the thickness of the anode layer itself.

[0069] The solid electrolyte layer 3 is made of the solid electrolyte.

[0070] In the all-solid-state LiB of the present invention, the configuration other than the negative electrode can be the same as that of a known all-solid-state LiB and is not particularly limited. The positive electrode is composed of a positive electrode active material layer 4 and a positive electrode current collector 5, and known positive electrode active materials and current collectors may be used.

[0071] The present invention will be further explained below with reference to examples, but the present invention is not limited to these examples in any way.

[0072] <Silicon Source> In the following examples, the following silicon sources were used. Unwashed separated silicon: silicon obtained by heating a waste solar panel containing single crystal silicon to heat-melt the resin in the waste solar panel, burning the heat-melted resin, and then separating it from the waste solar panel. Washed separated silicon: silicon obtained by acid-washing the unwashed separated silicon and then drying. The acid-washing conditions for the separated silicon are shown in Table 1. Polycrystalline silicon: commercially available product

[0073] <Crushing of silicon> The silicon source was crushed in the presence of the dispersion medium shown in Table 2 using a planetary ball mill under the following conditions, and the dispersion medium was filtered off and then dried to obtain the target silicon powder. Crushing conditions: planetary ball mill rotation speed - crushing time Crushing condition A: 450 rpm - 60 minutes Crushing condition B: 450 rpm - 15 minutes Crushing condition C: 300 rpm - 60 minutes Crushing condition D: 300 rpm - 30 minutes

[0074] The average particle size of each silicon powder was determined from the laser diffraction / scattered light intensity using an LA-950S2 (manufactured by Horiba, Ltd.). The aluminum and iron contents in the silicon powder were measured by X-ray fluorescence spectroscopy (XRF) (ZSX Primus IV (manufactured by Rigaku Corporation)). The oxygen content was determined by measuring CO and CO2 using an oxygen / nitrogen concentration analyzer (TC-600 manufactured by LECO Corporation). The particle size and content of each element of each silicon particle are shown in Table 2.

[0075] Each silicon powder was evaluated as a material for an all-solid-state battery by fabricating a half-cell and conducting a charge-discharge test. The experimental conditions are as follows: (1) Silicon powder: Each silicon powder obtained by acid washing and crushing the silicon source described above. (2) Battery materials (Counter electrode) Lithium (Li) foil: 0.1 mm thick (manufactured by Honjo Metals Co., Ltd.) Indium (In) foil: 0.127 mm thick (manufactured by Aldrich Chemicals) (Negative electrode) Negative electrode current collector: CF-T7F-35 (manufactured by Fukuda Metal Foil and Powder Co., Ltd.) Negative electrode active material layer: A mixture of 90 parts by mass of raw material for the negative electrode active material and 10 parts by mass of a thermosetting polyimide resin (DreamBond (trade name) manufactured by IST Co., Ltd.) (Solid electrolyte) a-40LiI.60Li3PS3 (prepared by mechanical milling)

[0076] (All-solid-state LiB anode forming material) 360 mg of silicon powder and a polyimide solution (27.2 wt% NMP solution) were mixed in an amount to give a solid content of 40 mg, and NMP (N-methylpyrrolidone) was further added to obtain a composition for forming an all-solid-state LiB anode. The composition was stirred for 2 hours (rotation 1056 rpm, revolution 1600 rpm) and degassed for 6 minutes (rotation 290 rpm, revolution 1360 rpm) to obtain a coating solution.

[0077] The resulting coating solution was applied onto a negative electrode current collector using a doctor blade (feed rate: 1.0 mm / sec). After drying at room temperature for more than half a day, the coating solution was heated under vacuum with a heater (250°C, 30 minutes) to harden the polyimide, thereby obtaining a negative electrode current collector having a negative electrode active material layer made of the negative electrode-forming material. The thickness of the negative electrode active material layer after drying was adjusted to 40 μm by adjusting the blade gap.

[0078] (Production of Half Cell) A negative electrode current collector having a negative electrode active material layer was punched to 9 mm diameter and placed in an insulating die with the negative electrode active material layer facing up. 65 mg of solid electrolyte powder was uniformly loaded onto the negative electrode active material layer, and uniaxial pressing was performed at a molding pressure of 560 MPa. After the upper punch was temporarily removed, a counter electrode made of In and Li metal foils punched to 6 mm diameter and stacked in the order In / Li / In was placed on top of the solid electrolyte layer, and uniaxial pressing was performed again at a pressure of about 50 MPa to produce an all-solid-state half cell. The assembly of the above half cell was performed in an argon atmosphere in a glove box that was sealed off from the outside air to eliminate the effects of oxygen, nitrogen, moisture, etc.

[0079] (3) Initial charging characteristics The charge-discharge test of the battery using the half cell prepared in (2) was carried out using HJ1001SD8 (manufactured by Meiden Hokuto Co., Ltd.) at a measurement temperature of 25°C and a current density of 0.2 mAcm. -2 In the first charge, a cutoff voltage of −0.62 V was set as the termination condition.

[0080] (4) Cycle Characteristics For the batteries that were initially chargeable in (3), charge and discharge were further repeated, and the change in charge and discharge capacity was monitored for each cycle. The cycle performance was evaluated based on the number of cycles at which the charge and discharge capacity retention rate became less than 90%.

[0081]

[0082]

[0083] Example 1 Silicon powder-1, which was prepared by washing and separating silicon as the silicon source, was used as a raw material for the negative electrode active material of an all-solid-state LiB to prepare a material for forming an all-solid-state LiB negative electrode. Further, an all-solid-state LiB half cell incorporating this was prepared, and the initial charge characteristics and cycle characteristics were evaluated. The results are shown in Table 3.

[0084] Examples 2 to 12 Silicon powders 2 to 12 were used as raw materials for the negative electrode active material of all-solid-state LiB, and half cells of all-solid-state LiB were fabricated in the same manner as in Example 1, and the initial charge characteristics and cycle characteristics were evaluated. The results are shown in Table 3.

[0085] <Comparative Examples 1 to 3> Silicon powders 13 to 15 were used as raw materials for the negative electrode active material of all-solid-state LiB, and half cells of all-solid-state LiB were produced in the same manner as in Example 1, and the initial charge characteristics and cycle characteristics were evaluated. The results are shown in Table 3.

[0086] Comparative Example 4 A half-cell of an all-solid-state LiB was produced in the same manner as in Example 1, except that washed and separated silicon was used as the silicon source and silicon powder-16 obtained under conditions in which no dispersant was entrained during crushing was used, and the initial charge characteristics and cycle characteristics were evaluated. The results are shown in Table 3.

[0087] Comparative Example 5 A half-cell of an all-solid-state LiB was produced in the same manner as in Example 1, except that unwashed separated silicon silicon powder-17 was used as the silicon source, and the initial charge characteristics and cycle characteristics were evaluated. The results are shown in Table 3.

[0088] <Comparative Example 6> A half-cell of an all-solid-state LiB was produced in the same manner as in Example 1, except that silicon powder-18, which was polycrystalline silicon obtained by the Siemens process, was used as the silicon source, and the initial charge characteristics and cycle characteristics were evaluated. The results are shown in Table 3.

[0089] Example 12: Using the all-solid-state LiB anode active material obtained in Example 2, a cathode active material layer was dried at room temperature, heated to 80°C, and pressed against a Ni mesh with a square pattern for 30 minutes to obtain an anode-forming material having prismatic island-shaped protrusions with a thickness of 50 μm. The mesh pattern was a square with a side length of 30 μm. A pattern of grooves (groove ratio: 64%) with a width of approximately 20 μm and a depth of approximately 35 μm (active material layer thickness: 15 μm) was transferred to the active material layer.

[0090] A half-cell for evaluation was prepared using the above-mentioned negative electrode material. The behavior of the resulting battery during initial charging and cycle performance were evaluated.

[0091] As a result, the current density was 0.2 mA cm -2 The battery was capable of being charged and discharged at the initial charge of 100 cycles, and the cycle characteristics were 500 cycles or more (no deterioration in charge / discharge capacity after 500 cycles).

[0092]

[0093] <Evaluation of initial charge / discharge characteristics> A: Current density 0.2 mA / cm -2 D: Current density 0.2 mA / cm or more -2 In charging, the cutoff voltage was set to −0.62 V, but fell below this value during the first charge.

[0094] F: A short circuit occurred during the initial charge, and the charge / discharge test was terminated.

[0095] <Evaluation of cycle characteristics> Good: Current density 0.2 mA / cm -2 Can be continuously charged and discharged for 100 cycles or more. -2 Unable to achieve 100 consecutive cycles

[0096] DESCRIPTION OF SYMBOLS 1... Negative electrode current collector 2... Negative electrode active material layer 3... Solid electrolyte layer 4... Positive electrode active material layer 5... Positive electrode current collector 10... All-solid-state lithium ion secondary battery negative electrode forming material 11... Negative electrode active material layer (island-shaped convex portion) 12... Groove portion 13... Connection layer 20... All-solid-state lithium ion secondary battery

Claims

1. A method for recovering single-crystalline silicon or polycrystalline silicon from a solar panel, comprising separating single-crystalline silicon or polycrystalline silicon from a waste solar panel, then washing the surface of the separated single-crystalline silicon or polycrystalline silicon with an acid, and crushing the single-crystalline silicon or polycrystalline silicon with a washed surface to an average particle size of 0.5 to 5.0 μm in the presence of a dispersion medium containing alcohol.

2. A method for producing a raw material for a negative electrode active material of an all-solid-state lithium-ion secondary battery, comprising separating single-crystalline silicon or polycrystalline silicon from a waste solar panel, then washing the surface of the separated single-crystalline silicon or polycrystalline silicon with an acid, and crushing the single-crystalline silicon or polycrystalline silicon with a washed surface to an average particle size of 0.5 to 5.0 μm in the presence of a dispersion medium containing alcohol.

3. A material for forming a negative electrode of an all-solid-state lithium-ion secondary battery, comprising a negative electrode active material layer formed on a current collector with a thickness of 10 μm or more, the negative electrode active material layer being composed of a composition containing the raw material for the negative electrode active material of the all-solid-state lithium-ion secondary battery according to claim 2.

4. The material for forming a negative electrode of an all-solid-state lithium-ion secondary battery according to claim 3, wherein a layer made of the raw material for the negative electrode active material of the all-solid-state lithium-ion secondary battery is patterned to form island-shaped protrusions with intervals, and a connection layer made of a composition containing the raw material for the negative electrode active material of the all-solid-state lithium-ion secondary battery is formed continuously with the island-shaped protrusions on the bottom surface of the groove formed between the island-shaped protrusions.

5. An all-solid-state lithium-ion secondary battery having a positive electrode, a negative electrode, and a solid electrolyte layer, wherein the negative electrode is arranged with the material for forming a negative electrode of an all-solid-state lithium-ion secondary battery according to claim 3 or 4.

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