All solid state power storage element and method for manufacturing all solid state power storage element

Abstract

To provide an all solid state power storage element comprising a cathode having a cathode active material layer containing sulfur-based active material and binder, and possessing high charge capacity, and a method for manufacturing the all solid state power storage element.SOLUTION: An all solid state power storage element according to one aspect of the present invention comprises a cathode having a cathode active material layer, the cathode active material layer contains sulfur-based active material, conductive carbon, sulfide solid electrolyte, and binder and the content of the binder in the cathode active material layer is 0.1 mass% or more but less than 2.0 mass%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an all-solid-state energy storage element and a method for manufacturing an all-solid-state energy storage element. [Background technology]

[0002] Due to their high energy density, non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. Non-aqueous electrolyte secondary batteries generally have a pair of electrically isolated electrodes and a non-aqueous electrolyte interposed between the electrodes, and are configured to charge and discharge by transferring charge-transporting ions between the electrodes. Capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as energy storage elements other than non-aqueous electrolyte secondary batteries.

[0003] In recent years, all-solid-state energy storage elements have been proposed that use, as the non-aqueous electrolyte, a solid electrolyte such as a sulfide solid electrolyte, an oxide solid electrolyte, or a polymer solid electrolyte instead of a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a liquid such as an organic solvent.

[0004] Meanwhile, positive electrodes using high-capacity sulfur-based active materials have been developed. However, sulfur-based active materials have a problem of easily dissolving in nonaqueous electrolytes. All-solid-state energy storage devices using solid electrolytes do not encounter the problem of sulfur-based active materials dissolving, making them promising as a technology for applying sulfur-based active materials. Considering mass productivity, positive electrodes are preferably manufactured by preparing a positive electrode mixture paste (also referred to as a slurry) and applying it to a substrate. Patent Document 1 describes a method for manufacturing a positive electrode for an all-solid-state lithium-sulfur battery using a positive electrode slurry containing a sulfur-containing positive electrode active material, a solid electrolyte, a binder, and a solvent. Note that a binder may not be used when forming a positive electrode active material layer by pressing a powdered positive electrode mixture, but a binder is usually required when forming a positive electrode active material layer by applying a positive electrode mixture paste. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-119761 Summary of the Invention [Problem to be solved by the invention]

[0006] In an all-solid-state energy storage element including a positive electrode in which a positive electrode active material layer is formed using a positive electrode mixture paste containing a sulfur-based active material and a binder as described above, the charge capacity may be insufficient.

[0007] An object of the present invention is to provide an all-solid-state energy storage element including a positive electrode having a positive electrode active material layer containing a sulfur-based active material and a binder, the all-solid-state energy storage element having a large charging capacity, and a method for manufacturing such an all-solid-state energy storage element. [Means for solving the problem]

[0008] An all-solid-state storage element according to one aspect of the present invention includes a positive electrode having a positive electrode active material layer, the positive electrode active material layer containing a sulfur-based active material, conductive carbon, a sulfide solid electrolyte, and a binder, and the content of the binder in the positive electrode active material layer is 0.1 mass % or more and less than 2.0 mass %.

[0009] A method for manufacturing an all-solid-state energy storage element according to another aspect of the present invention includes applying a positive electrode mixture paste onto a substrate directly or via an intermediate layer, the positive electrode mixture paste containing a sulfur-based active material, conductive carbon, a sulfide solid electrolyte, and a binder, and a content of the binder relative to a total solid content in the positive electrode mixture paste is less than 2.0 mass%. [Effects of the Invention]

[0010] According to any one aspect of the present invention, it is possible to provide an all-solid-state energy storage element including a positive electrode having a positive electrode active material layer containing a sulfur-based active material and a binder, the all-solid-state energy storage element having a large charging capacity, and a method for manufacturing such an all-solid-state energy storage element. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view of an all-solid-state energy storage element according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view of an all-solid-state energy storage element according to an embodiment different from the all-solid-state energy storage element of FIG. [Figure 3] FIG. 3 is a schematic diagram showing an electricity storage device configured by assembling a plurality of all-solid-state electricity storage elements according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] First, an outline of the all-solid-state energy storage element and the method for manufacturing the all-solid-state energy storage element disclosed in this specification will be described.

[0013] [1] An all-solid-state storage element according to one aspect of the present invention includes a positive electrode having a positive electrode active material layer, the positive electrode active material layer containing a sulfur-based active material, conductive carbon, a sulfide solid electrolyte, and a binder, and a content of the binder in the positive electrode active material layer is 0.1 mass % or more and less than 2.0 mass %.

[0014] The all-solid-state storage element described in [1] above is an all-solid-state storage element including a positive electrode having a positive electrode active material layer containing a sulfur-based active material and a binder, and has a large charge capacity. While the reason for this is unclear, the following is presumed. The binder is a component necessary for binding the active materials and other components contained in the coated positive electrode mixture paste. In the case of a non-aqueous electrolyte storage element using a non-aqueous electrolyte, the positive electrode active material layer generally contains at least about 3 mass% of binder to sufficiently bind the active materials and other components. In the case of a non-aqueous electrolyte storage element, even if the binder coats the sulfur-based active material, the non-aqueous electrolyte can penetrate the binder coating, thereby ensuring a sufficient reaction area between the sulfur-based active material and the non-aqueous electrolyte, and thereby achieving good charge / discharge performance. In contrast, in the case of an all-solid-state storage element using a solid electrolyte, the solid electrolyte cannot penetrate the binder coating, and the portion of the sulfur-based active material coated with the binder cannot contribute to charge / discharge. Therefore, even if the binder content is about 3 mass%, the charge capacity is low. In the all-solid-state energy storage element described in [1] above, the binder content in the positive electrode active material layer is 0.1 mass % or more and less than 2.0 mass %, so it is presumed that the area where the sulfur-based active material is covered by the binder is small, resulting in a large charging capacity.

[0015] The term "all-solid-state energy storage element" refers to an energy storage element that is substantially composed of only solid constituent members. In an all-solid-state energy storage element, for example, a volatile component may remain in a positive electrode active material layer formed by coating and drying a positive electrode mixture paste. The all-solid-state energy storage element may be a non-aqueous electrolyte energy storage element that uses only a solid electrolyte as the non-aqueous electrolyte, or may be a non-aqueous electrolyte energy storage element that does not use a non-aqueous electrolyte solution.

[0016] [2] In the all-solid-state storage element according to [1] above, the positive electrode active material layer further contains a volatile component having a boiling point of 220°C or less at 1 atmosphere, and the polar term δ of the Hansen solubility parameter of the volatile component is p is 7.0 (J / cm 3 ) 1 / 2 It may be the following:

[0017] Usually, when a positive electrode active material layer is formed by coating a positive electrode mixture paste, a volatile component, which is a solvent used in the positive electrode mixture paste, remains in the positive electrode active material layer even after drying. In the all-solid-state energy storage element described in [2] above, the polar term δ of the Hansen solubility parameter p is 7.0 (J / cm 3 ) 1 / 2 The positive electrode active material layer is formed from a positive electrode mixture paste using a solvent with low polarity, which is as follows: The positive electrode active material layer has a larger charge capacity. This is presumably because the use of a solvent with low polarity can suppress a decrease in the ionic conductivity of the sulfide solid electrolyte due to a reaction with the solvent.

[0018] The types of volatile components in the positive electrode active material layer are identified by gas chromatography-mass spectrometry (GC-MS), specifically as follows. (1) Collection of volatile components First, the all-solid-state energy storage element is disassembled, and the positive electrode active material layer is removed and immersed in a suitable extraction solvent (e.g., toluene, hexane, etc.). The extraction solvent impregnated with the positive electrode active material layer is stirred by ultrasonic treatment or the like to extract the volatile components contained in the positive electrode active material layer into the extraction solvent. The solid components (active material, binder, etc.) derived from the positive electrode active material layer are then removed by filtration, and the volatile components diluted in the extraction solvent are collected to obtain a measurement solution. (2) GC-MS The GC-MS analysis equipment used was the Shimadzu GCMS-TQ8040, and helium was used as the carrier gas. The measurement sample (volatile components) is subjected to GC-MS analysis. The components contained in the sample are predicted from the MS spectrum of each peak in the obtained gas chromatogram. A known sample of the predicted components is subjected to GC-MS analysis. The retention time and MS spectrum of the peak corresponding to each predicted component in the measurement sample are compared with the retention time and MS spectrum of the peak of a known sample of each predicted component, and if they match, the prediction is assumed to be correct. Note that the extraction solvent is excluded from this analysis.

[0019] Dispersion term δ in Hansen solubility parameters (HSP values) d , polar term δ p , and the hydrogen bond term δ h The value of is calculated as follows: Based on the chemical structure of the target compound (volatile component), the HSP value (dispersion term δ d , polar term δ p , and the hydrogen bond term δ h ) is calculated using the Y-MB method in the DYI program of Hansen Solubility Parameters in Practice (HSPiP) ver. 5.4.03.

[0020] [3] In the all-solid-state energy storage element according to [1] or [2] above, the positive electrode may further include a substrate including a metal aluminum layer at least in part thereof, and an intermediate layer containing a carbon material and disposed between the substrate and the positive electrode active material layer.

[0021] The all-solid-state energy storage element described in [3] above has an intermediate layer containing a carbon material between the substrate and the positive electrode active material layer in the positive electrode, and therefore has high adhesion between the substrate and the positive electrode active material layer despite the small amount of binder in the positive electrode active material layer. In the case of a nonaqueous electrolyte energy storage element, even if such an intermediate layer is provided in the positive electrode, if the binder content in the positive electrode active material layer is small, such as 0.1% by mass or more but less than 2.0% by mass, adhesion between the substrate and the positive electrode active material layer tends to be insufficient. In contrast, the positive electrode active material layer of the all-solid-state energy storage element described in [3] above tends to have a smaller specific surface area than the positive electrode active material layer of a nonaqueous electrolyte energy storage element. Therefore, even with a small amount of binder, sufficient binder can be present on the surface of each particle, providing sufficient bonding between the particles, and is thought to also increase adhesion between the substrate and the positive electrode active material layer. The positive electrode active material layer of the all-solid-state energy storage element described in [3] above contains a sulfide solid electrolyte. This is thought to result in a smaller specific surface area than that of the positive electrode active material layer of a nonaqueous electrolyte energy storage element, due to the fact that the sulfide solid electrolyte itself has a small specific surface area and that the relatively flexible sulfide solid electrolyte fills the pores present in the positive electrode active material layer.

[0022] [4] In the all-solid-state energy storage element described in [2] above, the positive electrode may further comprise a substrate including a metal aluminum layer at least in a portion thereof, and an intermediate layer disposed between the substrate and the positive electrode active material layer and containing a carbon material, the intermediate layer may further comprise a resin, and when the Hansen solubility parameter of the resin is placed in a Hansen space, the Hansen sphere may not include the coordinates of the Hansen solubility parameter of the volatile component.

[0023] In the all-solid-state storage element described in [4] above, an intermediate layer containing a carbon material is provided between the substrate and the positive electrode active material layer in the positive electrode, and therefore, even though the binder content in the positive electrode active material layer is small, the adhesion between the substrate and the positive electrode active material layer is high. Furthermore, in the all-solid-state storage element described in [4] above, when the Hansen solubility parameter of the resin contained in the intermediate layer is arranged in the Hansen space, the Hansen sphere is aligned with the coordinates (δ d ,δ p ,δ h ) is not contained therein. This means that the resin contained in the intermediate layer is difficult to dissolve in the volatile component in the positive electrode active material layer, i.e., in the solvent in the positive electrode mixture paste used. In the all-solid-state energy storage element described in [4] above, such a resin is used in the intermediate layer, so the resin in the intermediate layer is difficult to dissolve when the positive electrode active material layer is provided, and the adhesion between the substrate and the positive electrode active material layer can be further improved.

[0024] The resin Hansen sphere is the center coordinate of the resin's HSP value (δ d ,δ p ,δ h If the HSP value and interaction radius R0 of a resin are unknown, they can be calculated using the following method. d ,δ p ,δ h) in three-dimensional space, the Hansen Solubility Parameter space is identified. Then, multiple pure substances with known HPS values ​​are plotted in the space. The Hansen sphere is identified based on the solubility of the sample in the pure substance. The HSP value of the resin can be calculated by determining the center value of the Hansen sphere. To calculate the HSP value of a resin by determining the center value of the Hansen sphere, use the Sphere program in HSPiP ver. 5.4.03. The interaction radius R0, which is the radius of the Hansen sphere, can also be calculated using the software.

[0025] [5] In the all-solid-state energy storage element described in [4] above, the dispersion term δ in the Hansen solubility parameters of the volatile component d , polar term δ p and the hydrogen bond term δ h The values ​​are 20.0 (J / cm 3 ) 1 / 2 Below, 7.0(J / cm 3 ) 1 / 2 and 7.0 (J / cm 3 ) 1 / 2 It may satisfy any of the following ranges:

[0026] In the all-solid-state storage element described in [5] above, the positive electrode active material layer contains a volatile component that satisfies the above-mentioned Hansen solubility parameters, i.e., the positive electrode active material layer is formed from a positive electrode mixture paste that uses a solvent that satisfies the above-mentioned Hansen solubility parameters. Solvents that satisfy the above-mentioned Hansen solubility parameters are good solvents that have low reactivity with sulfide solid electrolytes and relatively high solubility in binders that are commonly used in positive electrode active material layers containing sulfide solid electrolytes. Therefore, the all-solid-state storage element described in [5] above can exhibit good binding properties even with a small amount of binder in the positive electrode active material layer, thereby enabling the charging capacity to be increased and the adhesion between the substrate and the positive electrode active material layer to be improved.

[0027] [6] In the all-solid-state energy storage element according to the above [4] or [5], the resin may be insoluble in at least one selected from the group consisting of carboxylic acid esters, ketones, trifluoroalkylbenzenes having a terminal CF3 group, and bis(trifluoroalkyl)benzenes having a terminal CF3 group.

[0028] Carboxylic acid esters, ketones, trifluoroalkylbenzenes having a terminal CF3 group, and bis(trifluoroalkyl)benzenes having a terminal CF3 group are solvents that have high solubility for the binder used in the positive electrode active material layer. In the all-solid-state storage element described in [6] above, a resin that has low solubility in the above solvents, which are particularly suitable as solvents for the positive electrode mixture paste, is used for the resin in the intermediate layer, so that dissolution of the resin in the intermediate layer is further suppressed, and adhesion between the substrate and the positive electrode active material layer can be further improved.

[0029] "No solubility" means that the solubility at 20°C (maximum amount that dissolves in 100 g of solvent) is 0.1 g / 100 g or less.

[0030] [7] In the all-solid-state energy storage element according to any one of [2] and [4] to [6] above, the volatile component may contain at least one selected from the group consisting of carboxylic acid esters, ketones, trifluoroalkylbenzenes having a terminal CF3 group, and bis(trifluoroalkyl)benzenes having a terminal CF3 group.

[0031] In the all-solid-state energy storage element described in [7] above, a solvent in which the binder has high solubility is used as the volatile component, i.e., the solvent of the positive electrode mixture paste used. Therefore, even with a small amount of binder, particularly excellent binding properties can be exhibited, and it is possible to further increase the charge capacity and further improve the adhesion between the substrate and the positive electrode active material layer.

[0032] [8] In the all solid state storage element according to any one of [1] to [7] above, the binder may be a polymer having no double bond.

[0033] In the all-solid-state energy storage element described in [8] above, a polymer having no double bonds is used as a binder in the positive electrode active material layer, which can increase the charge capacity, improve the adhesion between the substrate and the positive electrode active material layer, etc. This is presumably because the polymer having no double bonds is less likely to react with the sulfur-based active material, and therefore is less likely to cause a decrease in charge / discharge performance, binding strength, etc.

[0034] [9] In the all-solid-state energy storage element according to [8] above, the binder may be a fluororesin.

[0035] In the all-solid-state electricity storage element described in [9] above, it is possible to increase the charge capacity and further improve the adhesion between the substrate and the positive electrode active material layer.

[0036]

[10] A method for producing an all-solid-state energy storage element according to another aspect of the present invention includes applying a positive electrode mixture paste onto a substrate directly or via an intermediate layer, the positive electrode mixture paste containing a sulfur-based active material, conductive carbon, a sulfide solid electrolyte, and a binder, and a content of the binder relative to a total solid content in the positive electrode mixture paste is less than 2.0 mass%.

[0037] The method for producing an all-solid-state storage element described in

[10] above can produce an all-solid-state storage element having a positive electrode with a positive electrode active material layer containing a sulfur-based active material and a binder, and having a large charging capacity.

[0038]

[11] In the method for producing an all-solid-state storage element according to

[10] above, the positive electrode mixture paste further contains a solvent, and the polar term δ of the Hansen solubility parameter of the solvent is p is 7.0 (J / cm 3 ) 1 / 2 It may be the following:

[0039] In the method for producing an all-solid-state electricity storage element described in

[11] above, it is possible to increase the charge capacity of the obtained all-solid-state electricity storage element, for example.

[0040] An all-solid-state energy storage element according to one embodiment of the present invention, a manufacturing method for an all-solid-state energy storage element, an energy storage device, and other embodiments will be described in detail. Note that the names of the components (elementary components) used in each embodiment may differ from the names of the components (elementary components) used in the background art.

[0041] <All-solid-state energy storage element> An all-solid-state energy storage element according to one embodiment of the present invention includes an electrode assembly having a positive electrode, a negative electrode, and a solid electrolyte layer, and a container that accommodates the electrode assembly. The electrode assembly is typically a laminated type in which the positive electrode and the negative electrode are laminated with the solid electrolyte layer interposed therebetween. The positive electrode has a substrate (hereinafter, the substrate of the positive electrode will also be referred to as the "positive electrode substrate") and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer. The negative electrode has a substrate (hereinafter, the substrate of the negative electrode will also be referred to as the "negative electrode substrate") and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The electrode assembly may be a so-called "bipolar type" in which a positive electrode active material layer is provided on one surface of the substrate and a negative electrode active material layer is provided on the other surface. The all-solid-state energy storage element according to one embodiment of the present invention may be an all-solid-state secondary battery.

[0042] 1 and 2 show an example of the structure of an all-solid-state energy storage element. The all-solid-state energy storage element 10 of FIG. 1 has a structure in which a positive electrode 1 and a negative electrode 2 are stacked with a solid electrolyte layer 3 interposed therebetween. The positive electrode 1 has a positive electrode substrate 4 and a positive electrode active material layer 5. The negative electrode 2 has a negative electrode substrate 7 and a negative electrode active material layer 6. In the all-solid-state energy storage element 10 shown in FIG. 1, the negative electrode active material layer 6, the solid electrolyte layer 3, the positive electrode active material layer 5, and the positive electrode substrate 4 are stacked in this order on the negative electrode substrate 7.

[0043] The all-solid-state energy storage element 20 of FIG. 2 has a structure in which a positive electrode 11 and a negative electrode 2 are stacked with a solid electrolyte layer 3 interposed therebetween. The positive electrode 11 has a positive electrode substrate 4, an intermediate layer 8, and a positive electrode active material layer 5. The negative electrode 2 has a negative electrode substrate 7 and a negative electrode active material layer 6. In the all-solid-state energy storage element 20 shown in FIG. 2, the negative electrode active material layer 6, the solid electrolyte layer 3, the positive electrode active material layer 5, the intermediate layer 8, and the positive electrode substrate 4 are stacked in this order on the negative electrode substrate 7.

[0044] Hereinafter, each of the constituent members of the all-solid-state energy storage element according to one embodiment of the present invention will be described in detail.

[0045] (positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer. The intermediate layer and the positive electrode active material layer may be disposed on only one side or both sides of the positive electrode substrate.

[0046] The positive electrode substrate is electrically conductive. Whether or not it has "electrical conductivity" is determined by whether the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 -2 The threshold value is Ω·cm. The material of the positive electrode substrate is a metal such as aluminum, titanium, tantalum, stainless steel, or an alloy of these. Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high conductivity, and cost. The positive electrode substrate may be a foil, a vapor-deposited film, a mesh, a porous material, or the like, with foil being preferred from the viewpoint of cost.

[0047] The positive electrode substrate preferably includes a metallic aluminum layer at least in part. The metallic aluminum layer may be a layer of aluminum alone or an aluminum alloy. The positive electrode substrate may consist of only one metallic aluminum layer, or may be a laminate having a metallic aluminum layer and other layers. In the positive electrode substrate, the outermost layer on the positive electrode active material layer side, i.e., the layer in contact with the positive electrode active material layer or intermediate layer, is preferably a metallic aluminum layer. By including a metallic aluminum layer in the positive electrode substrate, good conductivity can be exhibited. The positive electrode substrate may be an aluminum foil or an aluminum alloy foil consisting only of a metallic aluminum layer. Examples of aluminum alone or an aluminum alloy include A1085, A3003, and A1N30 specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0048] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be increased while increasing the energy density per volume of the all-solid-state energy storage element. The average thickness of the metal aluminum layer is preferably 1 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. The average thickness is the average value of thicknesses measured at any five locations.

[0049] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer is preferably a layer containing a carbon material. By including the intermediate layer in the positive electrode, it is possible to improve the adhesion between the positive electrode substrate and the positive electrode active material layer and reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer.

[0050] A carbon material is a material other than an uncarbonized polymer compound, whose main constituent element is carbon. The main constituent element refers to the element with the highest content by mass. For example, the carbon content in the carbon material may be 80% by mass or more, 90% by mass or more, 95% by mass or more, 99% by mass or more, or 99.9% by mass or more. The carbon material may contain elements other than carbon, such as oxygen and nitrogen. The carbon material may be conductive (conductive carbon). Examples of carbon materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofiber, pitch-based carbon fiber, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. As the carbon material, a carbon material containing at least one of CNTs and carbon black is preferably used, and a carbon material consisting solely of CNTs is more preferably used. One or more types of carbon materials can be used.

[0051] The content of the carbon material in the intermediate layer is adjusted appropriately depending on the mechanical, electrical, and thermal properties required of the intended intermediate layer, but is preferably 0.1% by mass to 99.9% by mass, more preferably 1% by mass to 99% by mass, and even more preferably 10% by mass to 98% by mass. The lower limit of the content of the carbon material in the intermediate layer may be 10%, 25%, or 60% by mass.

[0052] The intermediate layer preferably further contains a resin. When the intermediate layer contains a resin, the resin functions as a binder, thereby improving adhesion between the carbon materials and between layers (between the positive electrode substrate and the intermediate layer, and between the intermediate layer and the positive electrode active material layer).

[0053] The resin contained in the intermediate layer preferably has low solubility in the solvent (volatile component contained in the positive electrode active material layer) contained in the positive electrode mixture paste used to form the positive electrode active material layer, which will be described in detail later. In other words, it is preferable that the Hansen sphere when the Hansen solubility parameter of the resin is arranged in the Hansen space does not include the coordinates of the Hansen solubility parameter of the volatile component contained in the positive electrode active material layer. In such a case, the dissolution of the resin in the intermediate layer is particularly sufficiently suppressed, thereby further improving the adhesion between the substrate and the positive electrode active material layer.

[0054] In particular, the resin contained in the intermediate layer preferably does not dissolve in at least one selected from the group consisting of carboxylic acid esters, ketones, trifluoroalkylbenzenes having a terminal CF3 group, and bis(trifluoroalkyl)benzenes having a terminal CF3 group. Carboxylic acid esters, ketones, trifluoroalkylbenzenes having a terminal CF3 group, and bis(trifluoroalkyl)benzenes having a terminal CF3 group are solvents with relatively low polarity and are solvents that highly dissolve the binder used in the positive electrode active material layer. Therefore, when a positive electrode mixture paste containing such a solvent is used to form the positive electrode active material layer and the resin contained in the intermediate layer does not dissolve in such a solvent, the adhesion between the substrate and the positive electrode active material layer can be further improved. Specific examples of these solvents that are suitable for use in the positive electrode mixture paste will be described later.

[0055] Since it is preferable to use the above-mentioned solvents with relatively low polarity as the solvent for preparing the positive electrode mixture paste, it is preferable that the resin contained in the intermediate layer has high solubility in solvents with relatively high polarity. In other words, it is preferable to use a solvent with relatively high polarity as the solvent for the intermediate layer forming material (paste for forming the intermediate layer). Examples of such solvents include water; amides such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methyl-2-pyrrolidone (NMP); alcohols such as methanol, ethanol, isopropanol, and n-propanol; glycol ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and propylene glycol monomethyl ether; and glycols such as ethylene glycol and propylene glycol. Among these, water is particularly preferable from the viewpoint of cost. These solvents can be used alone or in combination.

[0056] The resin contained in the intermediate layer is not particularly limited, but is preferably one that does not have solubility in the above-mentioned solvents with relatively low polarity and has high solubility in the above-mentioned solvents with relatively high polarity. Among them, since it is particularly preferable to use water as the solvent for the material for forming the intermediate layer, water-soluble resins such as polyacrylic acid, ammonium polyacrylate, sodium polyacrylate, sodium carboxymethyl cellulose, water-soluble cellulose ether, sodium alginate, polyvinyl alcohol, polystyrene sulfonic acid, polyethylene glycol, etc. are preferred, and polyacrylic acid, ammonium polyacrylate, sodium polyacrylate, sodium carboxymethyl cellulose, etc. are particularly more preferred.

[0057] The resin content in the intermediate layer is adjusted appropriately depending on the mechanical, electrical, thermal properties, etc. required for the intended intermediate layer, but is preferably 0.1% by mass or more and 99% by mass or less, and more preferably 1% by mass or more and 90% by mass or less.

[0058] The intermediate layer preferably contains substantially no sulfur element. The sulfur element content in the intermediate layer is, for example, preferably 0.1 mass % or less, more preferably 0.01 mass % or less, and even more preferably 0.001 mass % or less.

[0059] The intermediate layer may further contain other components besides the carbon material and resin, such as a dispersant and a crosslinking agent. The amount of these other components added can be appropriately adjusted depending on the solvent used in the intermediate layer-forming material, the positive electrode substrate, the viscosity required for the intermediate layer-forming material, the film shape required for the intermediate layer, etc. The total content of the carbon material and resin in the intermediate layer is preferably 80% by mass or more and 100% by mass or less, and more preferably 90% by mass or more and 100% by mass or less.

[0060] The average thickness of one intermediate layer is preferably 1 nm or more and 20 μm or less, more preferably 1 nm or more and 1 μm or less, and even more preferably 1 nm or more and 500 nm or less, in order to sufficiently increase the adhesion between the positive electrode substrate and the positive electrode active material layer and to reduce the internal resistance of the all-solid-state energy storage element.

[0061] The intermediate layer can be obtained by applying an intermediate layer forming material (for example, a paste containing a carbon material and a resin) to the positive electrode substrate and drying it. A commercially available product in which an intermediate layer is laminated on a positive electrode substrate can also be used.

[0062] The positive electrode active material layer contains a sulfur-based active material, conductive carbon, a sulfide solid electrolyte, and a binder. The positive electrode active material layer can be formed from a so-called positive electrode mixture paste containing the sulfur-based active material, etc. The positive electrode active material layer may contain optional components such as a thickener and a filler as needed.

[0063] The sulfur-based active material is a component that functions as a positive electrode active material. The sulfur-based active material may be elemental sulfur, a sulfur compound, or a mixture thereof. Examples of sulfur compounds include metal sulfides such as lithium sulfide, organic disulfide compounds, and organic sulfur compounds such as carbon sulfide compounds. The sulfur-based active material has advantages such as a large theoretical capacity and low cost. One or more sulfur-based active materials can be used.

[0064] The content of the sulfur-based active material in the positive electrode active material layer is preferably 20% by mass to 70% by mass, more preferably 30% by mass to 60% by mass, and even more preferably 35% by mass to 55% by mass. By having the content of the sulfur-based active material in the above range, it is possible to further increase the charge capacity, etc. Note that the content of each component other than the volatile component in the positive electrode active material layer is the content based on the components excluding the volatile component (total solid content).

[0065] The positive electrode active material layer may contain a positive electrode active material other than the sulfur-based active material, provided that the content of the sulfur-based active material relative to the total positive electrode active materials contained in the positive electrode active material layer is preferably 90% by mass or more and 100% by mass or less, and more preferably 99% by mass or more and 100% by mass or less.

[0066] Conductive carbon is a carbon material having electrical conductivity. The conductive carbon is preferably porous, i.e., porous carbon. Porous carbon is generally a porous inorganic material whose main constituent element is carbon. Activated carbon or the like can be used as the porous carbon. Conductive carbon other than porous carbon, such as carbon black or carbon nanotubes, can also be used as the conductive carbon. One or more types of conductive carbon can be used. As the conductive carbon, porous carbon and other conductive carbon such as carbon black may be used in combination.

[0067] The lower limit of the carbon element content in the conductive carbon is preferably 70 mass%, more preferably 80 mass%, 90 mass%, 95 mass%, or 97 mass%. The upper limit of the carbon element content in the conductive carbon may be 100 mass% or 99.9 mass%. The carbon element content in the conductive carbon can be a combination of any of the above lower limits and the above upper limit. The conductive carbon may contain elements other than carbon, such as oxygen and nitrogen.

[0068] The content of conductive carbon in the positive electrode active material layer is preferably 5% by mass to 50% by mass, more preferably 10% by mass to 40% by mass, and even more preferably 15% by mass to 30% by mass. By having the content of conductive carbon in the above range, it is possible to further increase the charge capacity, etc.

[0069] The positive electrode active material layer may contain a conductive agent other than conductive carbon, provided that the content of the conductive carbon relative to all the conductive agents contained in the positive electrode active material layer is preferably 90% by mass or more and 100% by mass or less, and more preferably 99% by mass or more and 100% by mass or less.

[0070] The sulfur-based active material and conductive carbon (typically porous carbon) preferably form a composite. In a composite of a sulfur-based active material and porous carbon, the sulfur-based active material is usually supported in the pores of the porous carbon. Such a composite form ensures sufficient electronic conductivity, and can improve charge / discharge performance. The composite may be in powder form.

[0071] When conductive porous carbon forms a composite with a sulfur-based active material, the pores of the porous carbon are filled with sulfur-based carbon, and the remaining pores are filled with sulfide solid electrolyte. In such cases, the specific surface area of ​​the mixture (a mixture of a sulfur-based active material, porous carbon, and sulfide solid electrolyte) is significantly smaller than that of the porous carbon alone or the composite of the porous carbon and the sulfur-based active material. Therefore, in such cases, the binder can adhere to these surfaces with a high coverage, and even a small amount of binder can exhibit particularly good binding properties.

[0072] The composite of the sulfur-based active material and the conductive carbon can be produced by a conventional method, for example, by heating a mixture of the sulfur-based active material and the conductive carbon to a temperature equal to or higher than the melting point of the sulfur-based active material and then cooling it.

[0073] The sulfide solid electrolyte may be a conventionally known one. Examples of sulfide solid electrolytes include Li3PS4, Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-P2S5-Li3N, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z. m S 2n(where m and n are positive numbers, and Z is Ge, Zn, or Ga.), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, and In.) Li 10 GeP2S 12 The sulfide solid electrolyte may be used alone or in combination of two or more.

[0074] The sulfide solid electrolyte is preferably present in the positive electrode active material layer in the form of a mixed powder mixed with a composite of a sulfur-based active material and conductive carbon, and is also preferably present in the positive electrode active material layer as a composite of a sulfur-based active material, conductive carbon, and sulfide solid electrolyte, and is more preferably present in the positive electrode active material layer in the form of a mixed powder mixed with a composite of a sulfur-based active material, conductive carbon, and sulfide solid electrolyte.

[0075] A composite of a sulfur-based active material, conductive carbon, and a sulfide solid electrolyte can be prepared by physical or chemical methods. Physical methods involve applying compressive force, shear force, impact force, or the like to form a composite. For example, a composite of a sulfur-based active material and conductive carbon and a sulfide solid electrolyte can be subjected to mechanical milling using a ball mill or the like. These processes can be performed dry or wet, but dry milling is preferred. Chemical methods involve chemical reactions, such as reacting raw materials for the sulfide solid electrolyte with the sulfur-based active material, conductive carbon, or the surface of the composite to form a composite of the sulfide solid electrolyte and the sulfur-based active material, conductive carbon, or the surface of the composite. Among the above-mentioned composite methods, physical methods are preferred, and mechanical milling using a ball mill or the like is particularly preferred.

[0076] The BET specific surface area of ​​the mixed powder of the sulfur-based active material, conductive carbon, and sulfide solid electrolyte or the composite of the sulfur-based active material, conductive carbon, and sulfide solid electrolyte is 10 m2 / g or less is preferable, and 7m 2 / g or less is more preferable. When the BET specific surface area of ​​the mixed powder of the sulfur-based active material, conductive carbon, and sulfide solid electrolyte or the composite of the sulfur-based active material, conductive carbon, and sulfide solid electrolyte is relatively small, the binder can cover a relatively high proportion of the surface of the mixed powder or composite, thereby further improving the binding strength of the binder. The lower limit of the BET specific surface area is not particularly limited, and is preferably 1 m 2 / g, and 2m 2 / g.

[0077] The "BET specific surface area" is a value obtained by measuring using the following procedure. 1.00 g of the sample to be measured is placed in a measurement sample tube. Next, an adsorption isotherm is measured using nitrogen gas adsorption with liquid nitrogen within the relative pressure P / P0 (P0 = approximately 770 mmHg) range of 0 to 1. The measurement device used is an "autosorb iQ" manufactured by Quantachrome. Five points are extracted from the region of P / P0 = 0.05 to 0.3 of the obtained adsorption isotherm, and a BET plot is made. The BET specific surface area is calculated from the y-intercept and slope of the line.

[0078] The sulfide solid electrolyte may be crystalline, glassy, ​​or glass-ceramic (glass ceramic). Glassy refers to a case where, in X-ray diffraction measurement, no diffraction peaks derived from crystals are observed, or even if a diffraction peak derived from crystals is observed, the peak intensity is low (the object is mainly amorphous). On the other hand, glass-ceramic (glass ceramic) refers to a case where, in X-ray diffraction measurement, a diffraction peak derived from crystals is observed, and crystalline refers to a case where no halo pattern derived from glass is observed, and only diffraction peaks derived from crystals are observed. Glass-ceramic (glass ceramic) may contain an amorphous portion. In other words, glass-ceramic (glass ceramic) also includes a mixture of glass and crystalline. In one embodiment of the present invention, the sulfide solid electrolyte may be glassy. Glass-ceramic sulfide solid electrolytes have a high proportion of amorphous portions and are therefore relatively flexible. In particular, when preparing a composite of a sulfur-based active material, conductive carbon, and a sulfide solid electrolyte, by using a glassy sulfide solid electrolyte, the pores in the composite of the sulfur-based active material, conductive carbon, and sulfide solid electrolyte are likely to be filled with the sulfide solid electrolyte, and the specific surface area of ​​these components tends to be smaller, and the binding ability tends to be improved.

[0079] The content of the sulfide solid electrolyte in the positive electrode active material layer is preferably 20% by mass to 60% by mass, more preferably 30% by mass to 55% by mass, and even more preferably 35% by mass to 50% by mass. By having the content of the sulfide solid electrolyte in the above range, it is possible to further increase the charge capacity, etc.

[0080] The positive electrode active material layer may contain a solid electrolyte other than the sulfide solid electrolyte, provided that the content of the sulfide solid electrolyte relative to all the solid electrolytes contained in the positive electrode active material layer is preferably 90% by mass or more and 100% by mass or less, and more preferably 99% by mass or more and 100% by mass or less.

[0081] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), etc.), polyolefins (polyethylene (PE), polypropylene (PP), etc.), polyacrylics, and polyimides; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubbers; and polysaccharide polymers. Polymers without double bonds are preferred as binders. Examples of polymers without double bonds include fluororesins such as PTFE, PVDF, and PVDF-HFP, and polyolefins such as PE and PP. Fluororesins are preferred, and PVDF-HFP is particularly preferred. The use of such binders can improve binding properties, etc. One or more binders can be used.

[0082] The content of the binder in the positive electrode active material layer is 0.1% by mass or more and less than 2.0% by mass. The lower limit of the binder content is preferably 0.3% by mass, and may be 0.5% by mass or 0.7% by mass. By setting the binder content to the above lower limit or more, it is possible to improve the adhesion between the positive electrode substrate and the positive electrode active material layer, etc. The upper limit of the binder content is preferably 1.5% by mass, and may be 1.2% by mass or 0.8% by mass. By setting the binder content to the above upper limit or less, it is possible to increase the charge capacity and the ratio of the initial charge capacity to the initial discharge capacity (hereinafter, the ratio of the charge capacity to the discharge capacity is also referred to as the "reverse Coulomb efficiency"), etc. The content of the binder in the positive electrode active material layer can be a combination of any of the above lower limits and the above upper limit.

[0083] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, the functional group may be deactivated in advance by methylation or the like. One or more types of thickeners can be used. When the positive electrode active material layer contains a thickener, the content of the thickener in the positive electrode active material layer is preferably 0.1% by mass or more and 8% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less. The technology disclosed herein can also be implemented in an embodiment in which the positive electrode active material layer does not contain a thickener.

[0084] The filler is not particularly limited. Examples of fillers include polyolefins such as polypropylene and polyethylene; inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide; carbonates such as calcium carbonate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate; nitrides such as aluminum nitride and silicon nitride; mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica; and artificial products thereof. One or more fillers can be used. When the positive electrode active material layer contains a filler, the content of the filler in the positive electrode active material layer can be 0.1% by mass or more and 8% by mass or less, and typically 5% by mass or less is preferred, and 2% by mass or less is more preferred. The technology disclosed herein can also be implemented in an embodiment in which the positive electrode active material layer does not contain a filler.

[0085] The positive electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as solid components other than the sulfur-based active material, other positive electrode active material, conductive carbon, other conductive agents, sulfide solid electrolyte, other solid electrolyte, binder, thickener, and filler.

[0086] The positive electrode active material layer preferably further contains a volatile component having a boiling point of 220°C or lower at 1 atmosphere. When the positive electrode active material layer is formed by coating and drying a positive electrode mixture paste, the solvent used in the positive electrode mixture paste usually remains in the positive electrode active material layer as a volatile component. The boiling point of the volatile component is preferably 50°C or higher and 200°C or lower, more preferably 80°C or higher and 180°C or lower.

[0087] The polarity term δ of the Hansen solubility parameters of the above volatile components p The upper limit is 7.0 (J / cm 3 ) 1 / 2 is preferable, and 6.0 (J / cm 3 ) 1 / 2 When a positive electrode active material layer is formed using a positive electrode mixture paste in which such a solvent with low polarity is used, the charge capacity of the all-solid-state storage element tends to be larger. The polar term δp of the Hansen solubility parameter is 7.0 (J / cm 3 ) 1 / 2 The volatile components (solvents) below include those shown in Table 3 below. p The lower limit is 0.1 (J / cm 3 ) 1 / 2 is preferable, and 1.0 (J / cm 3 ) 1 / 2 More preferably, the polarity term δ p can be a combination of any of the above lower limits and the above upper limits.

[0088] The dispersion term δ in the Hansen solubility parameters of the above volatile components d , polar term δ p and the hydrogen bond term δ h The values ​​of δ d ≦20.0(J / cm 3 ) 1 / 2 , δ p ≦7.0(J / cm 3 ) 1 / 2 and δ h ≦7.0(J / cm 3 ) 1 / 2It is preferable to satisfy both of the above ranges, and 14.8 (J / cm 3 ) 1 / 2 ≦δ d ≦17.5(J / cm 3 ) 1 / 2 , 1.0 (J / cm 3 ) 1 / 2 ≦δ p ≦7.0(J / cm 3 ) 1 / 2 and 1.0 (J / cm 3 ) 1 / 2 ≦δ h ≦7.0(J / cm 3 ) 1 / 2 It is more preferable that both of the above ranges are satisfied. A volatile component, i.e., a solvent, that satisfies such Hansen solubility parameters has high solubility for binders, particularly for fluororesins used as binders. Therefore, when a positive electrode active material layer is formed from a positive electrode mixture paste using such a solvent, even a small amount of binder can exhibit particularly excellent binding properties, thereby making it possible to increase the charge capacity and further improve the adhesion between the substrate and the positive electrode active material layer.

[0089] The volatile components, especially the dispersion term δ in the Hansen solubility parameters d , polar term δ p and the hydrogen bond term δ h The values ​​of δ d ≦20.0(J / cm 3 ) 1 / 2 , δ p ≦7.0(J / cm 3 ) 1 / 2 and δ h ≦7.0(J / cm 3 ) 1 / 2The volatile component satisfying both of the above ranges preferably includes at least one selected from the group consisting of carboxylic acid esters, ketones, trifluoroalkylbenzenes having a terminal CF3 group, and bis(trifluoroalkyl)benzenes having a terminal CF3 group. Such volatile components, i.e., solvents, have high binder solubility, particularly high solubility of fluororesins as binders. Therefore, when a positive electrode active material layer is formed using a positive electrode mixture paste containing such a solvent, even a small amount of binder can exhibit particularly excellent binding properties, thereby enabling the charging capacity to be increased and the adhesion between the substrate and the positive electrode active material layer to be further improved.

[0090] Examples of carboxylic acid esters include alkyl carboxylic acid esters such as butyl butyrate and butyl acetate. Examples of ketones include aliphatic ketones such as diisobutyl ketone. Examples of trifluoroalkylbenzenes having a CF3 group at the terminal include trifluoromethylbenzene and 2,2,2-trifluoroethylbenzene. Examples of bis(trifluoroalkyl)benzenes having a CF3 group at the terminal include 1,2-bis(trifluoromethyl)benzene, 1,3-bis(trifluoromethyl)benzene, and 1,4-bis(trifluoromethyl)benzene.

[0091] The volatile component may be one or more kinds, and may include, for example, a first volatile component which is at least one selected from the group consisting of fluorinated ethers and fluorinated alkanes, and a second volatile component which is at least one selected from the group consisting of carboxylic acid esters, ketones, trifluoroalkylbenzenes having a terminal CF3 group, and bis(trifluoroalkyl)benzenes having a terminal CF3 group.

[0092] Examples of the fluorinated ether that is the first volatile component include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, (1,2,2,2-tetrafluoroethyl)(heptafluoropropyl)ether, ethyl-1,1,2,2-tetrafluoroethyl ether, 1,1,1,2,3,4,4,5,5,5-decafluoro-3-methoxy-2-(trifluoromethyl)pentane, etc. Examples of the fluorinated alkane that is the first volatile component include 2H,3H-decafluoropentane, pentafluorobutane, 1H,6H-dodecafluorohexane, 1H-perfluorohexane, 1H,1H,1H,2H,2H-nonafluorohexane, etc.

[0093] Specific examples of the second volatile component, carboxylic acid ester, ketone, trifluoroalkylbenzene having a terminal CF3 group, and bis(trifluoroalkyl)benzene having a terminal CF3 group, are as described above. The second volatile component has a dispersion term δ d、 polarity term δ p and the hydrogen bond term δ h The values ​​are 14.8(J / cm 3 ) 1 / 2 ≦δ d ≦17.5(J / cm 3 ) 1 / 2 , 1.0 (J / cm 3 ) 1 / 2 ≦δ p ≦7.0(J / cm 3 ) 1 / 2 and 1.0 (J / cm 3 ) 1 / 2 ≦δ h ≦7.0(J / cm 3 ) 1 / 2 It is preferable that both of the above ranges are satisfied.

[0094] The content of the volatile component in the positive electrode active material layer may be, for example, 0.0001% by mass or more and 1% by mass or less, or 0.001% by mass or more and 0.1% by mass or less.

[0095] The average thickness of one positive electrode active material layer is preferably 30 μm or more and 1,000 μm or less, and more preferably 60 μm or more and 500 μm or less. By setting the average thickness of one positive electrode active material layer to the above lower limit or more, an all-solid-state energy storage element having a high energy density can be obtained. By setting the average thickness of one positive electrode active material layer to the above upper limit or less, the all-solid-state energy storage element can be made smaller.

[0096] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The intermediate layer and the negative electrode active material layer may be disposed on only one side of the negative electrode substrate or on both sides. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the positive electrode, for example.

[0097] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, alloys thereof, and carbonaceous materials are used as the material for the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foils, vapor-deposited films, meshes, and porous materials, with foils being preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0098] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate and to increase the energy density per volume of the all-solid-state energy storage element.

[0099] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer can be formed from a so-called negative electrode mixture paste containing the negative electrode active material. The negative electrode active material layer may contain a solid electrolyte. The negative electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler as needed. The types of binder, thickener, and filler in the negative electrode active material layer are the same as those of the above-mentioned components of the positive electrode active material layer. One or more of these optional components may not be substantially contained in the negative electrode active material layer.

[0100] The negative electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, solid electrolyte, conductive agent, binder, thickener, and filler.

[0101] The negative electrode active material can be appropriately selected from known negative electrode active materials. Materials capable of absorbing and releasing lithium ions are typically used as negative electrode active materials for lithium ion secondary batteries. Examples of negative electrode active materials include metallic lithium; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 , LiTiO 2、 Examples of the material include titanium-containing oxides such as TiNbO; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphitic carbon (easily graphitizable carbon or non-graphitizable carbon). Among these materials, graphite and non-graphitic carbon are preferred. In the negative electrode active material layer, one of these materials may be used alone, or two or more may be used in combination.

[0102] "Graphite" refers to a graphite material that has an average lattice spacing (d 002) is 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the viewpoint of being able to obtain a material with stable physical properties.

[0103] "Non-graphitic carbon" refers to carbon that has an average lattice spacing (d 002 ) is 0.34 nm or more and 0.42 nm or less. Non-graphitic carbon includes non-graphitizable carbon and graphitizable carbon. Examples of non-graphitic carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

[0104] Here, the "discharged state" refers to a state in which the negative electrode active material, a carbonaceous material, is discharged so that lithium ions capable of being absorbed and desorbed during charging and discharging are sufficiently released. For example, this refers to a state in which the open circuit voltage of a half cell using a negative electrode containing a carbonaceous material as a negative electrode active material as a working electrode and metallic lithium as a counter electrode is 0.7 V or higher.

[0105] "Non-graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.36 nm or more and 0.42 nm or less.

[0106] "Graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.34 nm or more and less than 0.36 nm.

[0107] The negative electrode active material is typically in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm to 100 μm. When the negative electrode active material is a carbon material, a titanium-containing oxide, or a polyphosphate compound, the average particle size may be 1 μm to 100 μm. When the negative electrode active material is Si, Sn, Si oxide, Sn oxide, or the like, the average particle size may be 1 nm to 1 μm. Setting the average particle size of the negative electrode active material to be equal to or greater than the above-mentioned lower limit facilitates the production and handling of the negative electrode active material. Setting the average particle size of the negative electrode active material to be equal to or less than the above-mentioned upper limit improves the electronic conductivity of the negative electrode active material layer. "Average particle size" refers to the value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50% based on the particle size distribution measured by laser diffraction / scattering in a diluted solution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013).

[0108] In order to obtain powder with a predetermined particle size, a pulverizer, a classifier, or the like is used. Examples of pulverization methods include methods using a mortar, a ball mill, a sand mill, a vibration ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling airflow jet mill, or a sieve. Wet pulverization in the presence of water or an organic solvent such as hexane can also be used during pulverization. As a classification method, a sieve, an air classifier, or the like is used in both dry and wet methods as needed. When the negative electrode active material is a metal such as metallic lithium, the negative electrode active material layer may be in the form of a foil.

[0109] The content of the negative electrode active material in the negative electrode active material layer is preferably 10% by mass or more and 100% by mass or less, more preferably 30% by mass or more and 95% by mass or less, with the lower limit being 50% by mass, and even more preferably 70% by mass. When the negative electrode active material is a metal such as metallic lithium, the lower limit of the content of the negative electrode active material in the negative electrode active material layer may be 95% by mass or even 99% by mass. By setting the content of the negative electrode active material within the above range, it is possible to further increase the discharge capacity of the all-solid-state energy storage element, for example.

[0110] The solid electrolyte contained in the negative electrode active material layer can be a conventionally known solid electrolyte. Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, dry polymer electrolytes, gel polymer electrolytes, and pseudo-solid electrolytes, with sulfide solid electrolytes being preferred. Specific examples of sulfide solid electrolytes include the materials exemplified for the positive electrode active material layer. One or more solid electrolytes can be used. The solid electrolyte used in the negative electrode active material layer may be the same as or different from the solid electrolytes contained in other layers.

[0111] When the negative electrode active material layer contains a solid electrolyte, the content of the solid electrolyte is preferably 5% by mass or more and 90% by mass or less, more preferably 20% by mass or more and 70% by mass or less, and in some cases the upper limit is even more preferably 50% by mass. By setting the content of the solid electrolyte within the above range, the discharge capacity of the all-solid-state energy storage element can be further increased.

[0112] The conductive agent is not particularly limited as long as it is a material having conductivity. Examples of such conductive agents include conductive carbon, as shown in the positive electrode, as well as metals and conductive ceramics. The conductive agent may be in the form of powder or fiber. As the conductive agent, one of these materials may be used alone, or two or more may be mixed and used. These materials may also be used in combination. For example, a composite material of carbon black and carbon nanotubes may be used.

[0113] When the negative electrode active material layer contains a conductive agent, the content of the conductive agent in the negative electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. The content of the conductive agent in the negative electrode active material layer may be 5% by mass or less, or may be 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a conductive agent.

[0114] When the negative electrode active material layer contains a binder, the content of the binder in the negative electrode active material layer is preferably 0.1% by mass to 10% by mass, more preferably 0.5% by mass to 8% by mass. The content of the binder in the negative electrode active material layer may be 5% by mass or less, or may be 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a binder.

[0115] When the negative electrode active material layer contains a thickener, the content of the thickener in the negative electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 8% by mass or less. The content of the thickener in the negative electrode active material layer may be 5% by mass or less, or may be 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a thickener.

[0116] When the negative electrode active material layer contains a filler, the content of the filler in the negative electrode active material layer can be 0.1 mass % or more and 8 mass % or less, and usually 5 mass % or less is preferable, and 2 mass % or less is more preferable. The technology disclosed herein can also be implemented in an embodiment in which the negative electrode active material layer does not contain a filler.

[0117] The average thickness of one negative electrode active material layer is preferably 30 μm or more and 1,000 μm or less, and more preferably 60 μm or more and 500 μm or less. By setting the average thickness of the negative electrode active material layer to the above lower limit or more, an all-solid-state energy storage element having a high energy density can be obtained. By setting the average thickness of the negative electrode active material layer 6 to the above upper limit or less, it is possible to achieve miniaturization of the all-solid-state energy storage element.

[0118] (solid electrolyte layer) The solid electrolyte layer contains a solid electrolyte. A conventionally known solid electrolyte can be used as the solid electrolyte contained in the solid electrolyte layer. Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, dry polymer electrolytes, gel polymer electrolytes, and pseudo-solid electrolytes, with sulfide solid electrolytes being preferred. Specific examples of sulfide solid electrolytes include the materials exemplified for the positive electrode active material layer. One or more solid electrolytes can be used. The solid electrolyte used in the solid electrolyte layer may be the same as or different from the solid electrolytes contained in other layers.

[0119] The content of the solid electrolyte in the solid electrolyte layer is preferably 70% by mass or more and 100% by mass or less, and more preferably 90% by mass or more and 99.9% by mass or less.

[0120] The solid electrolyte layer may contain optional components such as a binder, a filler, and other additives (for example, a phosphate compound such as LiPO, an oxide, a halogen compound, etc.) The optional components such as the binder and the filler can be selected from the materials exemplified for the positive electrode active material layer.

[0121] The average thickness of the solid electrolyte layer is preferably 1 μm or more and 300 μm or less, and more preferably 3 μm or more and 50 μm or less. By setting the average thickness of the solid electrolyte layer to the above lower limit or more, it is possible to reliably insulate the positive electrode active material layer and the negative electrode active material layer. By setting the average thickness of the solid electrolyte layer to the above upper limit or less, it is possible to increase the energy density of the all-solid-state energy storage element.

[0122] The shape of the all-solid-state energy storage element of this embodiment is not particularly limited, and examples thereof include a cylindrical shape, a square shape, a flat shape, a coin shape, and a button shape.

[0123] <Method of manufacturing all-solid-state energy storage element> A method for manufacturing an all-solid-state energy storage element according to one embodiment of the present invention includes applying a positive electrode mixture paste directly onto a substrate (positive electrode substrate) or via an intermediate layer. The manufacturing method may include preparing a positive electrode, preparing a negative electrode, preparing a solid electrolyte layer, and stacking the positive electrode and the negative electrode with the solid electrolyte layer interposed therebetween. Applying the positive electrode mixture paste may be one step in preparing the positive electrode.

[0124] The positive electrode mixture paste contains a sulfur-based active material, conductive carbon, a sulfide solid electrolyte, and a binder. The positive electrode mixture paste usually further contains a solvent. The positive electrode mixture paste may further contain other optional components that constitute the positive electrode active material layer. The content of the binder relative to the total solid content in the positive electrode mixture paste is less than 2.0 mass%. The preferred range of the content of the binder relative to the total solid content in the positive electrode mixture paste is the same as the preferred range of the content of the binder in the positive electrode active material layer described above.

[0125] The solvent used for the positive electrode mixture paste has a polarity term δ p is 7.0 (J / cm 3 ) 1 / 2 The following is preferred. The preferred form of the solvent used in the positive electrode mixture paste is the same as the preferred form of the volatile component contained in the positive electrode active material layer. As the solvent, the second solvent, which is the second volatile component described above, may be used alone, but it is preferred to use it in combination with the first solvent, which is the first volatile component described above.

[0126] The positive electrode mixture paste can be prepared by kneading each component constituting the positive electrode active material layer with a solvent. The positive electrode mixture paste can be applied by a known method such as a doctor blade method, a die coating method, a gravure coating method, a spray coating method, an electrostatic coating method, or a bar coating method. The positive electrode mixture paste can be applied, and then dried and pressed as necessary to obtain a positive electrode.

[0127] The positive electrode active material layer may be a coating layer. In an embodiment different from the above, the positive electrode active material layer may be formed by dry coating. A positive electrode active material layer formed by dry coating usually does not contain a volatile component. In a further embodiment, the positive electrode active material layer may be formed by a method other than coating.

[0128] The negative electrode may be prepared by fabricating a negative electrode. The negative electrode can be obtained, for example, by applying a negative electrode mixture paste directly or via an intermediate layer to a negative electrode substrate, as in the case of a positive electrode, and then drying and pressing the resulting mixture as necessary. The negative electrode can also be obtained by laminating a foil-shaped negative electrode active material layer on the negative electrode substrate.

[0129] Preparing a solid electrolyte layer may mean fabricating a solid electrolyte layer. The solid electrolyte layer can be obtained, for example, by applying a paste for forming a solid electrolyte layer, and optionally drying and pressing the paste. The solid electrolyte layer can also be obtained by pressing a powdered material for forming a solid electrolyte layer.

[0130] Stacking a positive electrode and a negative electrode with a solid electrolyte layer interposed therebetween can be performed, for example, by the following procedure. A positive electrode is placed on a solid electrolyte layer formed on a release substrate so that the positive electrode active material layer is in contact with the solid electrolyte layer. The solid electrolyte layer and positive electrode in this stacked state are subjected to cold isostatic pressing (CIP). This is then followed by warm isostatic pressing (WIP) to obtain a stack of the solid electrolyte layer and positive electrode. The release substrate is then removed, and a negative electrode is placed on the side of the solid electrolyte layer opposite the positive electrode so that the negative electrode active material layer is in contact with the solid electrolyte layer. By performing WIP on the negative electrode, solid electrolyte layer, and positive electrode in this stacked state, an electrode body in which the positive electrode and negative electrode are stacked with the solid electrolyte layer interposed therebetween is obtained.

[0131] Alternatively, an electrode assembly may be obtained by first forming a laminate of a solid electrolyte layer and a negative electrode, and then laminating a positive electrode on the laminate. Alternatively, the positive electrode, solid electrolyte, and negative electrode may be pressed in a stacked state to integrate the positive electrode, solid electrolyte layer, and negative electrode in a single press, thereby obtaining an electrode assembly. After obtaining the electrode assembly, an all-solid-state energy storage element can be obtained by performing a known process, such as inserting the electrode assembly into a container.

[0132] In addition, when a positive electrode having a positive electrode active material layer with a binder content of 0.1% by mass or more but less than 2.0% by mass laminated on a positive electrode substrate and a solid electrolyte layer are arranged so that the positive electrode active material layer and the solid electrolyte layer are in contact with each other and then integrated by a pressure treatment such as CIP, the positive electrode substrate and the positive electrode active material layer tend to peel off after the pressure treatment. This is thought to be due to the low adhesion between the positive electrode substrate and the positive electrode active material layer due to the small amount of binder in the positive electrode active material layer. In contrast, by using a positive electrode having an intermediate layer containing a carbon material between the positive electrode substrate and the positive electrode active material layer, the peeling between the positive electrode substrate and the positive electrode active material layer after the pressure treatment can be suppressed.

[0133] <Electricity storage device> The all-solid-state energy storage element of this embodiment can be mounted as an energy storage unit (battery module) comprising a plurality of all-solid-state energy storage elements in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), etc., a power source for electronic devices such as a personal computer or a communication terminal, or a power storage power source, etc. In this case, the technology of the present invention may be applied to at least one all-solid-state energy storage element included in the energy storage unit.

[0134] 3 shows an example of an energy storage device 40 in which energy storage units 30, each of which is an assembly of two or more electrically connected all-solid-state energy storage elements 10, are further assembled. The energy storage device 40 may include a bus bar (not shown) that electrically connects two or more all-solid-state energy storage elements 10, a bus bar (not shown) that electrically connects two or more energy storage units 30, etc. The energy storage unit 30 or the energy storage device 40 may include a status monitoring device (not shown) that monitors the status of one or more all-solid-state energy storage elements 10.

[0135] <Other embodiments> The all-solid-state energy storage element and the manufacturing method of the all-solid-state energy storage element of the present invention are not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0136] In the above embodiment, the all-solid-state energy storage element is used as a chargeable and dischargeable all-solid-state secondary battery, but the all-solid-state energy storage element may be of any type, shape, size, capacity, etc. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors.

[0137] <Example> The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0138] [Example 1] (Preparation of sulfur-porous carbon composites) Sulfur (manufactured by Aldrich) and activated porous carbon ("MH-00" manufactured by Toyo Tanso) were mixed in a mass ratio of 70:30. This mixture was placed in a sealed electric furnace. The furnace was heated to 150°C at a rate of 5°C / min and held for 5 hours. After that, the mixture was allowed to cool to 80°C, the temperature at which sulfur solidifies. The temperature was then increased again to 300°C at a rate of 5°C / min and held for 2 hours. This heat treatment was then carried out, and the mixture was allowed to cool to room temperature, yielding a sulfur-porous carbon composite.

[0139] (Preparation of mixed powder (sulfur-porous carbon-solid electrolyte composite)) The sulfur-porous carbon composite obtained above and a sulfide solid electrolyte (Li3PS4 glass) were mixed in a mass ratio of 60:40. This mixture was placed in a sealed 80 mL zirconia pot containing 100 g of 4 mm diameter zirconia balls. These steps were carried out in an argon atmosphere with a dew point of -50°C or less. Next, the mixture was mechanically milled for 15 minutes using a planetary ball mill (FRITSCH, Model Premium line PL-7) at a revolution speed of 300 rpm to obtain a mixed powder (sulfur-porous carbon-solid electrolyte composite).

[0140] (Preparation of Positive Electrode Mixture Paste) A mixed solvent was prepared by mixing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and trifluoromethylbenzene in a mass ratio of 70:30. PVDF-HFP (soluble in trifluoromethylbenzene), which serves as a binder, was dissolved in the mixed solvent to obtain a binder solution. The binder solution prepared above was mixed with 99.5 parts by mass of the mixed powder (sulfur-porous carbon-solid electrolyte composite) prepared above so that the PVDF-HFP content was 0.5 parts by mass (solid content equivalent), and the mixture was kneaded in a planetary centrifugal mixer. The mixed solvent of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and trifluoromethylbenzene prepared above was added to the resulting mixture, and the mixture was further kneaded in a planetary centrifugal mixer to obtain a positive electrode mixture paste (solid content ratio: 35% by mass).

[0141] (Preparation of positive electrode) The positive electrode mixture paste obtained above was mixed with a paste having a solid content of 6 mg / cm 2 Over 8mg / cm 2 The resulting coating was applied to an aluminum foil serving as a positive electrode substrate, followed by drying at normal pressure for 30 minutes at 80°C and then drying under reduced pressure for 30 minutes at 80°C to form a positive electrode active material layer. This resulted in a positive electrode having a binder content of 0.5% by mass in the positive electrode active material layer.

[0142] (Fabrication of all-solid-state energy storage elements) The positive electrode obtained above was punched out to a diameter of 10 mm. 80 mg of argyrodite-type solid electrolyte (Li6PS5Cl) was inserted into a ceramic powder molding machine with an inner diameter of 10 mm and pressure-molded using a uniaxial press at a pressure of 50 MPa for several seconds to form a solid electrolyte layer. After releasing the pressure, the positive electrode was laminated on one side of the solid electrolyte layer so that the positive electrode active material layer faced the solid electrolyte layer, and then pressed using a uniaxial press at 400 MPa for 5 minutes. After releasing the pressure, In foil (manufactured by Nilaco, average thickness 100 μm, diameter 10 mm) and Li foil (manufactured by Honjo Metal, average thickness 100 μm, diameter 8 mm) were laminated on the side opposite the laminated surface of the positive electrode, and then pressed using a uniaxial press at a pressure of 50 MPa for several seconds. The resulting product was removed from the ceramic powder molding machine to obtain the all-solid-state energy storage element of Example 1.

[0143] [Example 2] An all-solid-state energy storage element of Example 2 including a positive electrode in which the binder content in the positive electrode active material layer was 1.0 mass % was obtained in the same manner as in Example 1, except that, when preparing the positive electrode mixture paste, 99.0 mass parts of the mixed powder (sulfur-porous carbon-solid electrolyte composite) was mixed with a binder solution so that 1.0 mass part of PVDF-HFP (converted to solid content) was used.

[0144] [Comparative Example 1] An all-solid-state energy storage element of Comparative Example 1 including a positive electrode in which the binder content in the positive electrode active material layer was 3.0 mass % was obtained in the same manner as in Example 1, except that, when preparing the positive electrode mixture paste, 97.0 parts by mass of the mixed powder (sulfur-porous carbon-solid electrolyte composite) was mixed with 3.0 parts by mass of PVDF-HFP (converted to solid content).

[0145] [Evaluation] (Charge / discharge test) A charge / discharge test was carried out for each of the all-solid-state energy storage elements of Examples 1 and 2 and Comparative Example 1. Discharge was performed at a constant current of 0.1 C, with a lower limit voltage of 0.7 V. Charging was performed at a constant current of 0.1 C, with an upper limit voltage of 2.4 V. A 10-minute rest period was provided after discharge. 1 C represents a current per unit mass of sulfur, which was 1675 mA / g. The initial discharge capacity, initial charge capacity, and initial reverse Coulomb efficiency (the percentage of charge capacity relative to discharge capacity) were determined. The results are shown in Table 1. The discharge capacity and charge capacity shown in Table 1 are both discharge capacities per unit mass of sulfur.

[0146] [Table 1]

[0147] As shown in Table 1, the all-solid-state energy storage elements of Examples 1 and 2, in which the binder content in the positive electrode active material layer was 0.1 mass % or more and less than 2.0 mass %, had a large initial charge capacity of 600 mAh / g or more. Furthermore, the all-solid-state energy storage elements of Examples 1 and 2 had a high initial reverse coulombic efficiency of 70% or more.

[0148] [Example 3] (Preparation of sulfur-porous carbon composites) A sulfur-porous carbon composite was obtained in the same manner as in Example 1.

[0149] (Preparation of mixed powder (sulfur-porous carbon-solid electrolyte composite)) A mixed powder (sulfur-porous carbon-solid electrolyte composite) was obtained in the same manner as in Example 1, except that the sulfur-porous carbon composite and the sulfide solid electrolyte (LiPS glass) were mixed in a mass ratio of 65:35.

[0150] (Preparation of Positive Electrode Mixture Paste) A positive electrode mixture paste was obtained in the same manner as in Example 1, except that 99.0 parts by mass of the mixed powder (sulfur-porous carbon-solid electrolyte composite) prepared above was mixed with 1.0 part by mass of PVDF-HFP (converted to solid content).

[0151] (Preparation of positive electrode) A laminate (manufactured by Nissan Chemical Industries, Ltd.) was prepared, in which an aluminum foil serving as a positive electrode substrate was provided with a carbon coating layer serving as an intermediate layer containing a carbon material and a resin. The positive electrode mixture paste obtained above was applied to the carbon coating layer of the laminate, and the resultant was dried at 80°C for 30 minutes under normal pressure, followed by drying at 80°C for 30 minutes under reduced pressure to form a positive electrode active material layer. This resulted in a positive electrode having a binder content of 1.0% by mass in the positive electrode active material layer.

[0152] (Fabrication of frame materials) A saturated polyester (Elite® UE-3500, manufactured by Unitika Ltd.) with a softening point of 80°C and exhibiting fluidity at temperatures below 200°C was dissolved in N-methyl-2-pyrrolidone (NMP) to prepare a 25% by mass solution. The resulting solution was applied to a 25 μm-thick polyimide substrate and then dried to obtain a 45 μm-thick substrate. The resulting substrate was cut into a 25 mm x 25 mm square, and a 20.2 mm x 20.2 mm opening was formed in the center to form a frame material. The saturated polyester does not exhibit tackiness at 25°C.

[0153] (Fabrication of all-solid-state energy storage elements) The positive electrode obtained above was punched out into a square having a side of 20 mm. A solid electrolyte layer was provided on a release substrate and punched out into a square with sides of 25 mm to form laminate A. The solid electrolyte layer was formed by mixing an argyrodite-type solid electrolyte (Li6PS5Cl) and an SBR-based binder in a mass ratio of 95:5 using butyl butyrate as a solvent, and then applying the resulting paste for forming the solid electrolyte layer to the release substrate and drying it. A negative electrode having a side length of 25 mm was prepared, in which a metallic lithium foil serving as a negative electrode active material layer was provided on a copper foil serving as a negative electrode substrate. In a glove box under an argon atmosphere, the saturated polyester-coated surface of the frame material was placed on top of the solid electrolyte layer of the laminate A, and the positive electrode was placed in the opening of the frame material so that the positive electrode active material layer was in contact with the solid electrolyte layer to form laminate B. The resulting laminate B was then sealed in a flexible sealant under reduced pressure in a glove box under an argon atmosphere. The sealed laminate B was then removed from the glove box and subjected to CIP at 25°C and 200 MPa to temporarily bond the solid electrolyte layer, frame material, and positive electrode. After the temporary bonding, the sealed laminate B was removed from the glove box and re-sealed in a flexible sealant under reduced pressure. Subsequently, WIP was performed at 120°C and 1000 MPa to permanently bond the solid electrolyte layer, frame material, and positive electrode. Thereafter, in a glove box under an argon atmosphere, the sealant was opened to remove the laminate B, the release substrate was peeled off from the laminate B, and the negative electrode was placed so that the surface of the solid electrolyte layer on which the release substrate had been provided was in contact with the negative electrode active material layer, to obtain a laminate C. The laminate C was then encapsulated in a flexible sealant under reduced pressure. Thereafter, the laminate C encapsulated in the sealant was removed from the glove box, and CIP was performed on the laminate C under conditions of 25°C and 100 MPa, to obtain an all-solid-state energy storage element of Example 3 in which the positive electrode and the negative electrode were stacked via the solid electrolyte layer.

[0154] The BET specific surface areas of the porous carbon, the sulfur-porous carbon composite, the sulfide solid electrolyte, and the mixed powder (sulfur-porous carbon-solid electrolyte composite) used in or prepared for the production of the positive electrode of Example 3 were measured, and the results were as follows. Porous carbon: 1519m 2 / g Sulfur-porous carbon composite: 36.49m 2 / g Sulfide solid electrolyte: 1.354m 2 / g Mixed powder (sulfur-porous carbon-solid electrolyte composite): 4.577m 2 / g It was confirmed that the mixed powder (sulfur-porous carbon-solid electrolyte composite) had a significantly smaller specific surface area than the sulfur-porous carbon composite without a solid electrolyte.

[0155] [Example 4] An all-solid-state energy storage element of Example 4 including a positive electrode in which the binder content in the positive electrode active material layer was 0.5 mass % was obtained in the same manner as in Example 3, except that, when preparing the positive electrode mixture paste, 99.5 mass parts of the mixed powder (sulfur-porous carbon-solid electrolyte composite) was mixed with 0.5 mass parts of PVDF-HFP (converted to solid content).

[0156] [Example 5] An all-solid-state energy storage element of Example 5 including a positive electrode in which the binder content in the positive electrode active material layer was 0.3 mass % was obtained in the same manner as in Example 3, except that, when preparing the positive electrode mixture paste, 99.7 parts by mass of the mixed powder (sulfur-porous carbon-solid electrolyte composite) was mixed with 0.3 parts by mass of PVDF-HFP (converted to solid content).

[0157] [Example 6] An all-solid-state electricity storage element of Example 6 was obtained in the same manner as in Example 3, except that when preparing the positive electrode, aluminum foil was used instead of the laminate in which the aluminum foil was provided with a carbon coating layer (intermediate layer).

[0158] [Example 7] An all-solid-state electricity storage element of Example 7 was obtained in the same manner as in Example 4, except that when preparing the positive electrode, aluminum foil was used instead of the laminate in which the aluminum foil was provided with a carbon coating layer (intermediate layer).

[0159] [Evaluation] (Adhesion) For each of the all-solid-state energy storage elements of Examples 3 to 7, the adhesion between the positive electrode substrate and the positive electrode active material layer after CIP for laminate B in the production stage was evaluated as follows. For laminate B after CIP, the positive electrode substrate was held with suction tweezers and lifted up. If laminate B was lifted up without peeling between the positive electrode substrate and the positive electrode active material layer, it was rated A, and if peeling occurred between the positive electrode substrate and the positive electrode active material layer, it was rated B. The results are shown in Table 2.

[0160] [Table 2]

[0161] As shown in Table 2, in each of the all-solid-state energy storage elements of Examples 3 to 5, in which an intermediate layer was provided between the positive electrode substrate and the positive electrode active material layer, adhesion between the positive electrode substrate and the positive electrode active material layer was high and no peeling occurred between the positive electrode substrate and the positive electrode active material layer, despite the low binder content in the positive electrode active material layer. In contrast, in each of the all-solid-state energy storage elements of Examples 6 and 7, in which no intermediate layer was provided between the positive electrode substrate and the positive electrode active material layer, adhesion between the positive electrode substrate and the positive electrode active material layer was low and peeling occurred between the positive electrode substrate and the positive electrode active material layer.

[0162] The results of Examples 1 to 5 suggest that in an all-solid-state energy storage element in which the binder content in the positive electrode active material layer is 0.1 mass % or more and less than 2.0 mass % and an intermediate layer is provided between the positive electrode substrate and the positive electrode active material layer, both a large discharge capacity and high adhesion between the positive electrode substrate and the positive electrode active material layer can be achieved.

[0163] (Binder solubility) The relationship between binder solubility and the HSP and SP values ​​of the solvent was investigated as follows. To investigate binder solubility, 0.2g of the binder fluororesin (PVDF-HFP) and 3.8g of each solvent were placed in a glass container and stirred with a magnetic stirrer for more than 12 hours. The binder solutions obtained were rated A if no residual binder was found, and B if residual binder was found or if the binder was barely dissolved. The HSP and SP values ​​of the solvents were calculated by structural calculation based on the chemical structure of each solvent. d、 polarity term δ p , and the hydrogen bond term δ h ) and SP value σ t The calculation was performed using the Y-MB method in the DYI program of Hansen Solubility Parameters in Practice (HSPiP) ver. 5.4.03. The SP value σ t and HSP value (variance term δ d , polarity term δ p , and the hydrogen bond term δ h ) is expressed by the following formula (1). σ t 2 =δ d 2 +δ p 2 +δ h 2 ···(1) HSP value of the solvent (dispersion term δ d , polarity term δ p , and the hydrogen bond term δ h The relationship between the SP value and the solubility of the binder is shown in Table 3. The unit of the value is (J / cm 3 ) 1 / 2 is.

[0164] [Table 3]

[0165] From Table 3, we can see the following: Variance term δ d , polarity term δ p and the hydrogen bond term δ h The values ​​are 14.8(J / cm 3 ) 1 / 2 ≦δ d ≦17.5(J / cm 3 ) 1 / 2 , 1.0 (J / cm 3 ) 1 / 2 ≦δ p ≦7.0(J / cm 3 ) 1 / 2 , and 1.0 (J / cm3 ) 1 / 2 ≦δ h ≦7.0(J / cm 3 ) 1 / 2 The solvents 1,3-bis(trifluoromethyl)benzene, (trifluoromethyl)benzene, butyl butyrate, and butyl acetate, which satisfy all of the above ranges, showed good binder solubility (A). In contrast, the fluorinated ethers 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether showed good dispersion terms δ d is 14.8(J / cm 3 ) 1 / 2 m-xylene, mesitylene, toluene, tetralin and anisole have a dispersion term δ d is 17.5 (J / cm 3 ) 1 / 2 and heptane and decane have polar terms δ p and the hydrogen bond term δ h is 1.0 (J / cm 3 ) 1 / 2 The results were less than 100%, and solvents that did not satisfy any of the above ranges did not have good binder solubility (B). Furthermore, it was found that even solvents with similar SP values, such as decane and 1,3-bis(trifluoromethyl)benzene, had different binder solubility. [Industrial Applicability]

[0166] The present invention can be applied to all-solid-state energy storage devices used as power sources for electronic devices such as personal computers and communication terminals, automobiles, and the like. [Explanation of symbols]

[0167] 1, 11 positive electrode 2 negative electrode 3 Solid electrolyte layer 4. Positive electrode substrate (substrate) 5 Cathode active material layer 6 Negative electrode active material layer 7. Negative electrode substrate 8. Middle Class 10, 20 All-solid-state energy storage element 30 Energy Storage Unit 40 Power storage device

Claims

1. a positive electrode having a positive electrode active material layer, the positive electrode active material layer contains a sulfur-based active material, conductive carbon, a sulfide solid electrolyte, and a binder, The content of the binder in the positive electrode active material layer is 0.1% by mass or more and less than 2.0% by mass.

2. The positive electrode active material layer further contains a volatile component having a boiling point of 220° C. or less at 1 atmosphere, and the polar term δ of the Hansen solubility parameter of the volatile component is ｐ is 7.0 (J / cm ３ ) １／２ The all-solid-state energy storage element according to claim 1 , wherein:

3. The positive electrode is a substrate including at least a portion of a metal aluminum layer; and an intermediate layer containing a carbon material, which is disposed between the substrate and the positive electrode active material layer; The all-solid-state energy storage element according to claim 1 or 2, further comprising:

4. The positive electrode is a substrate including at least a portion of a metal aluminum layer; and an intermediate layer containing a carbon material, which is disposed between the substrate and the positive electrode active material layer; Furthermore, the intermediate layer further comprises a resin; 3. The all-solid-state energy storage element according to claim 2, wherein when the Hansen solubility parameter of the resin is arranged in the Hansen space, the Hansen sphere does not include the coordinates of the Hansen solubility parameter of the volatile component.

5. The dispersion term δ in the Hansen solubility parameters of the above volatile components ｄ , polarity term δ ｐ and the hydrogen bond term δ ｈ The values ​​of 20.0 (J / cm ３ ) １／２ Below, 7.0 (J / cm ３ ) １／２ and 7.0 (J / cm ３ ) １／２ The all-solid-state energy storage element according to claim 4 , which satisfies any of the following ranges:

6. The resin is a carboxylic acid ester, a ketone, and a CF ３ Trifluoroalkylbenzene having a group and a CF group at the end ３ 6. The all-solid-state electricity storage element according to claim 4, which has no solubility in at least one selected from the group consisting of bis(trifluoroalkyl)benzenes having a group.

7. The volatile components are carboxylic acid esters, ketones, and CF terminals. ３ Trifluoroalkylbenzene having a group and a CF group at the end ３ The all-solid-state electricity storage element according to claim 2 or 4, comprising at least one selected from the group consisting of bis(trifluoroalkyl)benzenes having a group.

8. 3. The all-solid-state energy storage element according to claim 1, wherein the binder is a polymer having no double bonds.

9. The all-solid-state energy storage element according to claim 8 , wherein the binder is a fluororesin.

10. The method comprises applying the positive electrode mixture paste directly onto a substrate or via an intermediate layer, the positive electrode mixture paste contains a sulfur-based active material, conductive carbon, a sulfide solid electrolyte, and a binder; The method for producing an all-solid-state energy storage element, wherein the content of the binder relative to the total solid content in the positive electrode mixture paste is less than 2.0 mass %.

11. The positive electrode mixture paste further contains a solvent, and the polarity term δ of the Hansen solubility parameter of the solvent ｐ is 7.0 (J / cm ３ ) １／２ The method for producing an all-solid-state energy storage element according to claim 10, wherein:

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