Manufacturing method of energy storage element

Abstract

To provide a power storage element in which particles of a sulfide solid electrolyte are satisfactorily bonded to each other by fluorine resin particles, and deterioration in the sulfide solid electrolyte in production is suppressed, and a method for manufacturing the same.SOLUTION: A power storage element includes an electrolyte-containing layer obtained by drying a coated matter of a solid electrolyte-containing slurry containing a low polar solvent, particles of a fluorine resin and particles of a sulfide solid electrolyte, wherein the low polar solvent is at least one of a hydrocarbon compound, and a compound having only a hydrocarbon group and an ether group in the molecule, an average particle diameter of the particles of the fluorine resin is 200 nm or less, and the fluorine resin exists between the particles of the sulfide solid electrolyte in the electrolyte-containing layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a dispersion, a method for producing a dispersion, a slurry, a method for producing an electric storage element, and an electric storage element. [Background technology]

[0002] Patent Document 1 describes a method for producing an all-solid-state battery, which includes a step of forming an electrolyte-containing layer using a slurry containing a sulfide solid electrolyte containing Li, P, and S elements, a PVDF-based binder, and a solvent, wherein the solvent contains 50% by volume or more of a ketone solvent represented by a specific molecular structural formula as a first solvent. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-091632 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide an electric storage element in which particles of a sulfide solid electrolyte are well bound to each other by fluororesin particles and in which deterioration of the sulfide solid electrolyte during production is suppressed, and a method for producing the electric storage element. Another object of the present invention is to provide a dispersion that can satisfactorily bond sulfide solid electrolyte particles together using fluororesin particles and that can suppress deterioration of the sulfide solid electrolyte in the production of an energy storage element, a solid electrolyte-containing slurry that includes the dispersion, and a method for producing the dispersion. [Means for solving the problem]

[0005] A dispersion according to one aspect of the present invention includes a low-polarity solvent and fluororesin particles dispersed in the low-polarity solvent, the low-polarity solvent is at least one of a hydrocarbon compound and a compound having only a hydrocarbon group and an ether group in the molecule; The particles have an average particle size of 200 nm or less.

[0006] A method for producing a dispersion liquid according to another aspect of the present invention includes preparing a stock solution containing a highly polar solvent containing water and fluororesin particles having an average particle size of 200 nm or less dispersed in the highly polar solvent; and subjecting the raw liquid to a substitution treatment in which the water is substituted with a low-polarity solvent having a lower polarity than the high-polarity solvent, thereby obtaining a dispersion liquid of the fluororesin particles, The low polarity solvent is at least one of a hydrocarbon compound and a compound having only a hydrocarbon group and an ether group in the molecule.

[0007] A slurry according to yet another aspect of the present invention comprises the above-described dispersion and The battery contains at least one of particles of a sulfide solid electrolyte, particles of a lithium transition metal composite oxide, and particles of a carbon material.

[0008] A method for producing an electric storage element according to another aspect of the present invention includes preparing a solid electrolyte-containing slurry containing a low-polarity solvent, fluororesin particles, and sulfide solid electrolyte particles; and preparing an electrolyte-containing layer containing fluororesin and sulfide solid electrolyte particles from the coated material of the solid electrolyte-containing slurry, In preparing the solid electrolyte-containing slurry, the low-polarity solvent is at least one of a hydrocarbon compound and a compound having only a hydrocarbon group and an ether group in the molecule, and the particles have an average particle size of 200 nm or less; In preparing the electrolyte-containing layer, the coating is subjected to a drying treatment for volatilizing the low-polarity solvent.

[0009] According to yet another aspect of the present invention, there is provided an electric storage element including an electrolyte-containing layer formed by drying an applied material of a solid electrolyte-containing slurry including a low-polarity solvent, fluororesin particles, and sulfide solid electrolyte particles; the low-polarity solvent is at least one of a hydrocarbon compound and a compound having only a hydrocarbon group and an ether group in the molecule, and the average particle size of the fluororesin particles is 200 nm or less; In the electrolyte-containing layer, the fluororesin is present between particles of the sulfide solid electrolyte. [Effects of the Invention]

[0010] In the energy storage element according to one aspect of the present invention, the particles of the sulfide solid electrolyte are well bound together by the fluororesin particles, and deterioration of the sulfide solid electrolyte during production is suppressed. Furthermore, by the method for producing an electric storage element according to another aspect of the present invention, the particles of the sulfide solid electrolyte can be well bound together by the fluororesin particles, and deterioration of the sulfide solid electrolyte can be suppressed. Furthermore, according to the dispersion liquid or the solid electrolyte-containing slurry containing the dispersion liquid according to another aspect of the present invention, in the production of an electric storage element, the particles of the sulfide solid electrolyte can be well bound together by the fluororesin particles, and deterioration of the sulfide solid electrolyte can be suppressed. Furthermore, by a method for producing a dispersion according to yet another aspect of the present invention, it is possible to obtain a dispersion that can be used for producing an energy storage element, in which the particles of the sulfide solid electrolyte can be well bound together by the fluororesin particles and deterioration of the sulfide solid electrolyte during production can be suppressed. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view of the energy storage device according to this embodiment. [Figure 2] FIG. 2 is a perspective view of a structural unit housed in the energy storage device of FIG. [Figure 3] FIG. 3 is a schematic cross-sectional view of an electrode body that constitutes the energy storage element according to this embodiment. [Figure 4] FIG. 4 is a schematic diagram showing an example of the process for producing a positive electrode active material layer. [Figure 5] FIG. 5 is a schematic diagram showing an example of the process for producing a solid electrolyte layer. [Figure 6] FIG. 6 is a schematic diagram of an energy storage device including a plurality of energy storage elements according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] An overview of the energy storage element 1 and a method for manufacturing the energy storage element disclosed in this specification will be described. Also, an overview of the dispersion and a method for manufacturing the dispersion disclosed in this specification will be described. Also, an overview of the slurry disclosed in this specification will be described.

[0013] An energy storage device 1 according to one aspect of the present invention includes: The electrochemical cell has an electrolyte-containing layer formed by drying an applied layer of a solid electrolyte-containing slurry containing a low-polarity solvent, fluororesin particles, and sulfide solid electrolyte particles, the low-polarity solvent is at least one of a hydrocarbon compound and a compound having only a hydrocarbon group and an ether group in the molecule, and the average particle size of the fluororesin particles is 200 nm or less; In the electrolyte-containing layer, the fluororesin is present between particles of the sulfide solid electrolyte. In an energy storage element having such a configuration, the fluororesin particles are relatively small during production, and therefore the particles of the sulfide solid electrolyte are well bound together by the fluororesin particles, and deterioration of the sulfide solid electrolyte during production is suppressed.

[0014] A method for manufacturing an energy storage element according to another aspect of the present invention includes: preparing a stock solution containing a highly polar solvent containing water and fluororesin particles having an average particle size of 200 nm or less dispersed in the highly polar solvent; and subjecting the raw liquid to a substitution treatment in which the water is substituted with a low-polarity solvent having a lower polarity than the high-polarity solvent, thereby obtaining a dispersion liquid of the fluororesin particles, The low polarity solvent is at least one of a hydrocarbon compound and a compound having only a hydrocarbon group and an ether group in the molecule. In the manufacturing method having such a configuration, since the fluororesin particles are relatively small, the particles of the sulfide solid electrolyte can be well bound together by the fluororesin particles, and deterioration of the sulfide solid electrolyte can be suppressed.

[0015] A dispersion according to yet another aspect of the present invention comprises: A low-polarity solvent and fluororesin particles dispersed in the low-polarity solvent, the low-polarity solvent is at least one of a hydrocarbon compound and a compound having only a hydrocarbon group and an ether group in the molecule; The particles have an average particle size of 200 nm or less. By using a dispersion liquid having such a configuration, in the production of an electricity storage element, the fluororesin particles are relatively small, so that the particles of the sulfide solid electrolyte can be well bound together by the fluororesin particles, and deterioration of the sulfide solid electrolyte can be suppressed.

[0016] A method for producing a dispersion according to another aspect of the present invention includes the steps of: preparing a stock solution containing a highly polar solvent containing water and fluororesin particles having an average particle size of 200 nm or less dispersed in the highly polar solvent; and subjecting the raw liquid to a substitution treatment in which the water is substituted with a low-polarity solvent having a lower polarity than the high-polarity solvent, thereby obtaining a dispersion liquid of the fluororesin particles, The low polarity solvent is at least one of a hydrocarbon compound and a compound having only a hydrocarbon group and an ether group in the molecule. By using the method for producing a dispersion having such a configuration, it is possible to obtain a dispersion in which the fluororesin particles are relatively small, so that the particles of the sulfide solid electrolyte can be well bound together by the fluororesin particles, and further, deterioration of the sulfide solid electrolyte during production can be suppressed. The obtained dispersion can be used for producing an energy storage element.

[0017] A slurry according to yet another aspect of the present invention comprises: The dispersion liquid, The battery contains at least one of particles of a sulfide solid electrolyte, particles of a lithium transition metal composite oxide, and particles of a carbon material. In the production of an electric storage element using a slurry having such a configuration, the fluororesin particles are relatively small, so that the particles of the sulfide solid electrolyte can be well bound together by the fluororesin particles, and deterioration of the sulfide solid electrolyte can be suppressed.

[0018] Conventionally, electrodes of nonaqueous electrolyte batteries (energy storage elements), such as lithium-ion secondary batteries, often contain a fluororesin, such as polyvinylidene fluoride (PVDF), as a binder. In the process of fabricating such electrodes, the fluororesin is generally used in the form of a solution dissolved in a polar solvent, such as N-methylpyrrolidone (NMP), a slurry containing the solution, or a powder. However, polar solvents containing polar groups, such as carbonyl groups, such as NMP, may deteriorate the sulfide solid electrolyte in the solid electrolyte during the electrode fabrication process. Meanwhile, when fluororesin powder is dry-mixed with an electrode material in a dry state, the fluororesin particles aggregate, and even if a solvent is added, the fluororesin particles may be unevenly distributed in the electrode, potentially limiting the binding ability of the fluororesin particles. Increasing the blending ratio of the fluororesin particles in order to fully exert the binding performance not only affects the charge / discharge reaction by inhibiting electronic conduction between the active material particles, ionic conduction between the active material particles and the solid electrolyte particles, and ionic conduction between the solid electrolyte particles, but also reduces the energy density of the electrode. Therefore, when producing an electrode using a sulfide solid electrolyte as the solid electrolyte, it has been desired to fully utilize the binding properties of the fluororesin without using the above-mentioned polar solvents that deteriorate the sulfide solid electrolyte.

[0019] In this regard, the present inventors believed that the sulfide solid electrolyte deteriorated because the polar solvent contained in the slurry as described above has the property of dissolving the fluororesin. Therefore, the present inventors focused on preparing a slurry from a fluororesin dispersion prepared in a solvent that does not easily dissolve the fluororesin, instead of preparing a slurry from a fluororesin solution prepared in a solvent that dissolves the fluororesin. They then discovered an electric storage element containing a sulfide solid electrolyte prepared using such a slurry, and a method for producing an electric storage element using such a slurry.

[0020] As described above, in one aspect of the present invention, the average particle diameter of the fluororesin particles in the slurry or dispersion is sufficiently small, at 200 nm or less. Therefore, in any electrolyte-containing layer prepared using the slurry, the number of fluororesin particles is sufficiently large if the fluororesin content is the same on a volume basis. Therefore, while the fluororesin is sufficiently dispersed in the electrolyte-containing layer, uneven distribution of the fluororesin particles between sulfide solid electrolyte particles can be suppressed. This allows the fluororesin particles to bond well to each other. Furthermore, since the average particle diameter of the fluororesin particles is small, the amount of fluororesin required to achieve sufficient bonding is reduced. Therefore, the total area of ​​the contact interfaces between sulfide solid electrolyte particles can be increased. Therefore, the adverse effect of ionic conduction between sulfide solid electrolyte particles being inhibited by the fluororesin particles can be reduced. Furthermore, since the average particle diameter of the fluororesin particles is sufficiently small, settling of the fluororesin when the slurry is applied can be suppressed. Therefore, a more uniform electrolyte-containing layer can be prepared.

[0021] The configuration of the energy storage element 1 according to one embodiment of the present invention, the configuration of the energy storage device 100, and a method for manufacturing the energy storage element 1, as well as 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.

[0022] <Configuration of energy storage element> As shown in FIGS. 1 to 3 , an energy storage element 1 according to one embodiment of the present invention includes an electrode assembly 2 having a positive electrode 40, a negative electrode 50, and a solid electrolyte layer 60, and a container 3 that houses the electrode assembly 2. Because the energy storage element 1 according to this embodiment substantially does not contain an electrolyte solution, it may be referred to as an “all-solid-state energy storage element” hereinafter. In this embodiment, the electrode assembly 2 is a stacked electrode assembly in which the positive electrode 40, the negative electrode 50, and the solid electrolyte layer 60 are stacked. The container 3 houses the electrode assembly 2 such that the electrode assembly 2 is sandwiched between two sheets. In other words, the container 3 is a so-called flat pouch container. The positive electrode 40 has a positive electrode active material layer 42 containing a solid electrolyte and a positive electrode active material, and the negative electrode 50 has a negative electrode active material layer 52 containing a solid electrolyte and a negative electrode active material. The solid electrolyte layer 60 is disposed between the positive electrode 40 and the negative electrode 50 and mainly contains a solid electrolyte. As an example of the all-solid-state energy storage element, an all-solid-state lithium ion secondary battery (hereinafter also simply referred to as "secondary battery") will be described.

[0023] 1 to 3, the energy storage device 1 of this embodiment includes a stacked electrode assembly 2 in which a positive electrode 40 and a negative electrode 50 are stacked with a solid electrolyte layer 60 interposed therebetween, the container 3 that houses the electrode assembly 2, and two external terminals (a positive electrode terminal 4 and a negative electrode terminal 5). The positive electrode terminal 4 is configured as a tab portion formed by a portion of a positive electrode substrate 41 (described later) of the positive electrode 40 extending outward. Similarly, the negative electrode terminal 5 is configured as a tab portion formed by a portion of a negative electrode substrate 51 (described later) of the negative electrode 50 extending outward. The energy storage element 1 is configured so that electricity flows between the electrode assembly 2 and any external device via a positive electrode terminal 4 and a negative electrode terminal 5 during charging and discharging. In the energy storage element 1 of this embodiment, one electrode assembly 2 is housed in a container 3, and the electrode assembly 2 is configured to undergo a charging and discharging reaction. Furthermore, the container 3 is preferably in a state where a compressive force is applied from the outside to the inside in the thickness direction, which can further reduce the interfacial resistance between the positive electrode 40 and the negative electrode 50 and the solid electrolyte layer 60. The container 3 may accommodate one or more electrode bodies 2.

[0024] The electrode assembly 2 is formed by stacking a rectangular sheet-shaped positive electrode 40 and a rectangular sheet-shaped negative electrode 50 with a solid electrolyte layer 60 interposed therebetween. As shown in FIG. 3 , the solid electrolyte layer 60 is arranged so as to electrically insulate the positive electrode 40 and the negative electrode 50. The solid electrolyte layer 60 does not contain either a positive electrode active material or a negative electrode active material. In this embodiment, the electrode assembly 2 and the container 3 both have a flat shape. The electrode assembly 2 is arranged in the container 3 so that the stacking direction of the electrodes in the electrode assembly 2 and the thickness direction of the container 3 are the same.

[0025] In the electrode assembly 2 of this embodiment, at least one of the positive electrode active material layer 42 of the positive electrode 40, the negative electrode active material layer 52 of the negative electrode 50, and the solid electrolyte layer 60 contains a solid electrolyte. Specifically, in this embodiment, at least one of the positive electrode active material layer 42, the negative electrode active material layer 52, and the solid electrolyte layer 60 contains, as the solid electrolyte, particles of a sulfide solid electrolyte, which will be described in detail later. In one example of this embodiment, the positive electrode active material layer 42, the negative electrode active material layer 52, and the solid electrolyte layer 60 all contain a sulfide solid electrolyte. Therefore, hereinafter, as shown in FIG. 3 , the positive electrode active material layer 42, the negative electrode active material layer 52, and the solid electrolyte layer 60 are referred to as an electrolyte-containing layer A. Note that, in one aspect of the present invention, it is sufficient that a fluororesin (described later) is present between particles of the sulfide solid electrolyte in at least one layer of the electrolyte-containing layer A (at least one of the positive electrode active material layer 42, the negative electrode active material layer 52, and the solid electrolyte layer 60). In the following description, a detailed description will be given of an embodiment in which at least in the positive electrode active material layer 42, a fluororesin (described later) is present between particles of the sulfide solid electrolyte.

[0026] (positive electrode) The positive electrode 40 has a positive electrode substrate 41 and a positive electrode active material layer 42 that overlaps the positive electrode substrate 41 directly or via a predetermined layer. In this embodiment, the positive electrode substrate 41 and the positive electrode active material layer 42 overlap directly in the positive electrode 40. In this embodiment, the positive electrode active material layer 42 is overlapped on one surface (one side) of the positive electrode substrate 41. The positive electrode active material layer 42 and the negative electrode active material layer 52 undergo a charge / discharge reaction between each other.

[0027] The positive electrode substrate 41 has electrical conductivity. Whether or not the positive electrode substrate 41 has electrical conductivity is determined by whether or not the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 7 The threshold value is Ω·cm. The material of the positive electrode substrate 41 may be a metal such as aluminum, titanium, tantalum, or stainless steel, or an alloy thereof. Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high conductivity, and cost. The positive electrode substrate 41 may be a foil, a vapor-deposited film, or the like, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or an aluminum alloy foil is preferred as the positive electrode substrate 41. Examples of aluminum or aluminum alloys include A1085 and A3003 specified in JIS-H-4000 (2014).

[0028] The average thickness of the positive electrode substrate 41 is preferably 1 μm or more and 50 μm or less, more preferably 30 μm or less, and even more preferably 15 μm or less. By setting the average thickness of the positive electrode substrate 41 within the above range, the strength of the positive electrode substrate 41 can be increased while increasing the energy density per volume of the secondary battery.

[0029] The positive electrode active material layer 42 contains a positive electrode active material, particles of a sulfide solid electrolyte, and a fluororesin. The fluororesin is present at least between the particles of the sulfide solid electrolyte. The positive electrode active material layer 42 may contain optional components such as a conductive agent, a binder (binding agent) other than the fluororesin, and a thickener, as needed.

[0030] The positive electrode active material can be appropriately selected from known positive electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the positive electrode active material for a lithium ion secondary battery. Examples of the positive electrode active material include lithium transition metal composite oxides having an α-NaFeO2 crystal structure, lithium transition metal composite oxides having a spinel crystal structure, polyanion compounds, chalcogen compounds, and sulfur. Examples of lithium transition metal composite oxides having an α-NaFeO2 crystal structure include Li[Li x Ni (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Co (1-x-γ) ]O2(0≦x<0.5, 0<γ<1), Li[Li x Co (1-x) ]O2(0≦x<0.5), Li[LiNiMn (1-x-γ) ]O2(0≦x<0.5, 0<γ<1), Li[Li x Ni γ Mn β Co (1-x-γ-β) ]O2(0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1), Li[Li x Ni γ Co β Al (1-x-γ-β) ]O2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1). Lithium transition metal composite oxides with spinel crystal structure include Li x Mn2O4, Li x Ni γ Mn (2-γ) Examples of polyanion compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, and Li2CoPO4F. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, iron sulfide, cobalt sulfide, copper sulfide, nickel sulfide, and copper Chevrel. Note that sulfur, bismuth oxide, bismuth plumbate, copper oxide, vanadium oxide, and the like can also be used as the positive electrode active material. The atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer 42, one of these materials may be used alone, or two or more may be used in combination. Among these materials, lithium transition metal composite oxides are preferred as the positive electrode active material. It is preferable to select a positive electrode active material that is coated with a coating layer containing a material such as a lithium ion conductive oxide. Examples of lithium ion conductive oxides include LiNbO3, Li2WO4, and Li4Ti5O. 12 , Li3PO4, etc. Among these, it is preferable to select LiNbO3. The coating layer may cover the entire surface of the positive electrode active material, or may cover only a portion of the surface.

[0031] The positive electrode active material is usually particulate. The average particle diameter of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. When the average particle diameter of the positive electrode active material is equal to or greater than the above-mentioned lower limit, the positive electrode active material is easily manufactured and handled. When the average particle diameter of the positive electrode active material is equal to or less than the above-mentioned upper limit, the electronic conductivity of the positive electrode active material layer 42 is improved. When a composite of the positive electrode active material and another material is used (e.g., when the surface of the positive electrode active material is coated with a coating layer), the average particle diameter of the composite is taken as the average particle diameter of the positive electrode active material. The term "average particle diameter" 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).

[0032] To obtain a powder of the positive electrode active material 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 as needed for both dry and wet methods.

[0033] The content of the positive electrode active material in the positive electrode active material layer 42 is preferably 10% by mass to 95% by mass, more preferably 20% by mass to 90% by mass, and even more preferably 30% by mass to 80% by mass. When the content of the positive electrode active material is within the above range, it is possible to achieve both a high energy density of the positive electrode active material layer 42 and a relatively simple production of the positive electrode active material layer 42.

[0034] The solid electrolyte of the positive electrode active material layer 42 includes at least a sulfide solid electrolyte. The solid electrolyte of the positive electrode active material layer 42 may further include a solid electrolyte other than the sulfide solid electrolyte, which will be described in detail later, but preferably includes only a sulfide solid electrolyte. The solid electrolyte included in the positive electrode active material layer 42 may be the same type as the solid electrolyte included in the solid electrolyte layer 60, or may be a different type. The content of the solid electrolyte in the positive electrode active material layer 42 is preferably 5% by mass or more and 90% by mass or less, more preferably 10% by mass or more and 80% by mass or less, and even more preferably 15% by mass or more and 70% by mass or less. When the content of the solid electrolyte in the positive electrode active material layer 42 is within the above range, the energy storage device can have a relatively large electric capacity.

[0035] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbon materials, metals, conductive ceramics, etc. Carbon materials include graphitized carbon, non-graphitized carbon, graphene-based carbon, etc. Non-graphitized carbon includes carbon fiber, pitch-based carbon fiber, carbon black, etc. Carbon black includes furnace black, acetylene black, ketjen black, etc. Graphene-based carbon includes graphene, carbon nanotubes (CNT), fullerene, etc. The conductive agent may be in the form of particles or fibers. One type of conductive agent may be used alone, or two or more types may be mixed and used. The above materials may also be used in combination. For example, a composite material of carbon black and CNT may be used. Of the above conductive agents, carbon fiber is preferred from the viewpoint of electronic conductivity.

[0036] When the positive electrode active material layer 42 contains a conductive agent, the content of the conductive agent in the positive electrode active material layer 42 is preferably 1 mass % or more and 10 mass % or less, and more preferably 3 mass % or more and 9 mass % or less. When the content of the conductive agent is in the above range, the energy density of the secondary battery can be increased.

[0037] Examples of fluororesins include polytetrafluoroethylene (PTFE) and vinylidene fluoride polymers. Examples of vinylidene fluoride polymers include polyvinylidene fluoride (PVDF) and copolymers of vinylidene fluoride and compounds other than vinylidene fluoride. Examples of monomers copolymerizable with vinylidene fluoride include vinyl fluoride, trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, and perfluoroalkyl vinyl ether. As the fluororesin, vinylidene fluoride polymers are preferred, and polyvinylidene fluoride (PVDF) is more preferred, in that they have a wider potential window. The shape of the fluororesin present between particles of the sulfide solid electrolyte is not particularly limited. The shape may be, for example, particulate or an unspecified, amorphous shape.

[0038] Examples of binders other than fluororesin that may be further contained in the positive electrode active material layer 42 include thermoplastic resins such as polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0039] The content of the binder (total amount of binder including fluororesin) in the positive electrode active material layer 42 is preferably 0.01 mass % or more and 10 mass % or less, and more preferably 0.1 mass % or more and 7.0 mass % or less. When the binder content is in the above range, the active material can be stably held.

[0040] The positive electrode active material layer 42 may contain only a fluororesin as a binder. The positive electrode active material layer 42 may contain only polyvinylidene fluoride (PVDF) as a binder. The proportion of the fluororesin (particularly PVDF) in the binder may be 95 mass % or more.

[0041] When the positive electrode active material layer 42 contains a thickener, examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) 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.

[0042] In this embodiment, at least the positive electrode active material layer 42 of the electrolyte-containing layer A is formed by drying an applied solid electrolyte-containing slurry containing a low-polarity solvent, fluororesin particles having an average particle size of 200 nm or less, and sulfide solid electrolyte particles, as will be described later in the manufacturing method of an energy storage device. As described above, since the fluororesin particles are relatively small during manufacturing, the sulfide solid electrolyte particles are well bonded together by the fluororesin particles, and deterioration of the sulfide solid electrolyte during manufacturing is suppressed.

[0043] As described above, the solid electrolyte-containing slurry contains fluororesin particles with a sufficiently small average particle diameter of 200 nm or less. Therefore, in a positive electrode active material layer 42 fabricated using the above slurry, the number of fluororesin particles is sufficiently large, assuming the same volumetric content of fluororesin. Therefore, while the fluororesin is sufficiently dispersed within the positive electrode active material layer, uneven distribution of the fluororesin particles among the sulfide solid electrolyte particles can be suppressed. This allows the fluororesin particles to effectively bind the sulfide solid electrolyte particles together. Furthermore, since the average particle diameter of the fluororesin particles is small, a smaller amount of fluororesin is required to achieve sufficient binding. This allows the total area of ​​the contact interfaces between the sulfide solid electrolyte particles to be increased. This reduces the adverse effect of ionic conduction between the sulfide solid electrolyte particles being inhibited by the fluororesin particles. Furthermore, since the average particle diameter of the fluororesin particles is sufficiently small, settling of the fluororesin during application of the slurry can be suppressed. This allows for the fabrication of a more uniform positive electrode active material layer 42.

[0044] In the positive electrode active material layer 42 prepared using the solid electrolyte-containing slurry as described above, the fluororesin particles are arranged between the sulfide solid electrolyte particles. The fluororesin particles in this state do not necessarily maintain a particle shape, such as a spherical shape, making it difficult to measure their average particle diameter. Therefore, it is nearly impossible and impractical to specify the average particle diameter of the fluororesin particles contained in the positive electrode active material layer 42.

[0045] (Negative electrode) The negative electrode 50 has a negative electrode substrate 51 and a negative electrode active material layer 52 that overlaps the negative electrode substrate 51 directly or via a predetermined layer. In this embodiment, the negative electrode substrate 51 and the negative electrode active material layer 52 overlap directly in the negative electrode 50. In this embodiment, the negative electrode active material layer 52 is overlapped on one surface (one side) of the negative electrode substrate 51.

[0046] The negative electrode substrate 51 is conductive. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof, are used as the material for the negative electrode substrate 51. Among these, stainless steel, nickel or nickel alloys, or copper or copper alloys are preferred. Examples of the negative electrode substrate 51 include metal foils and vapor-deposited films, with metal foils being preferred from the viewpoint of cost. Examples of the negative electrode substrate 51 include stainless steel foils, nickel foils or nickel alloy foils, and copper foils or copper alloy foils. Examples of copper foils include rolled copper foils and electrolytic copper foils.

[0047] The average thickness of the negative electrode substrate 51 is preferably 1 μm or more and 50 μm or less, more preferably 30 μm or less, and even more preferably 15 μm or less. By setting the average thickness of the negative electrode substrate 51 within the above range, the strength of the negative electrode substrate 51 can be increased while increasing the energy density per volume of the secondary battery.

[0048] The negative electrode active material layer 52 includes a negative electrode active material and particles of a solid electrolyte. The negative electrode active material layer 52 includes optional components such as a conductive agent, a binder, a thickener, and a filler as needed. The optional components such as the conductive agent, the binder, the thickener, and the filler can be selected from the materials exemplified for the positive electrode 40. The negative electrode active material layer 52 may include only a fluororesin or only polyvinylidene fluoride (PVDF) as the binder, similar to the positive electrode active material layer 42. The proportion of the fluororesin (particularly PVDF) in the binder may be 95 mass % or more.

[0049] The negative electrode active material layer 52 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.

[0050] The negative electrode active material can be appropriately selected from known negative electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the negative electrode active material for lithium ion secondary batteries. Examples of the negative electrode active material include metallic Li; 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.

[0051] "Graphite" refers to graphite 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.

[0052] "Non-graphitic carbon" refers to the 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.

[0053] 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, in a single-electrode battery using a negative electrode containing a carbonaceous material as a negative electrode active material as a working electrode and metallic Li as a counter electrode, this refers to a state in which the open circuit voltage is 0.7 V or higher.

[0054] "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.

[0055] "Graphitizable carbon" refers to the above d002 This refers to carbon materials with a particle size of 0.34 nm or more and less than 0.36 nm.

[0056] The negative electrode active material is usually in the form of particles (powder). The average particle diameter of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is a carbon material, a titanium-containing oxide, or a polyphosphate compound, the average particle diameter may be 1 μm or more and 100 μm or less. When the negative electrode active material is Si, Sn, Si oxide, Sn oxide, or the like, the average particle diameter may be 1 nm or more and 1 μm or less. By setting the average particle diameter of the negative electrode active material to the above lower limit or more, the negative electrode active material can be easily produced or handled. By setting the average particle diameter of the negative electrode active material to the above upper limit or less, the electronic conductivity of the active material layer is improved. To obtain powder with a predetermined particle size, a pulverizer, a classifier, or the like is used. The pulverization method and the powder classification method can be selected, for example, from the methods exemplified for the positive electrode. When the negative electrode active material is a metal such as metallic Li, the negative electrode active material may be in the form of a foil.

[0057] The content of the negative electrode active material in the negative electrode active material layer 52 is preferably 10% by mass to 95% by mass, more preferably 20% by mass to 90% by mass, and even more preferably 30% by mass to 80% by mass. When the content of the negative electrode active material is within the above range, it is possible to achieve both a high energy density of the negative electrode active material layer 52 and a relatively simple production of the negative electrode active material layer 52.

[0058] The solid electrolyte of the anode active material layer 52 can be appropriately selected from the solid electrolytes exemplified in the description of the solid electrolyte layer 60, which will be described in detail later. The solid electrolyte contained in the anode active material layer 52 may be the same type as the solid electrolyte contained in the solid electrolyte layer 60, or may be a different type. In one example of this embodiment, the solid electrolyte contained in the anode active material layer 52 is a sulfide solid electrolyte. The content of the solid electrolyte in the anode active material layer 52 is preferably 5% by mass to 90% by mass, more preferably 10% by mass to 80% by mass, and even more preferably 15% by mass to 70% by mass. When the content of the solid electrolyte in the anode active material layer 52 is within the above range, the energy storage device can have a relatively large electric capacity. The anode active material layer 52 may contain multiple different types of solid electrolytes.

[0059] The negative electrode active material layer 52, like the above-described positive electrode active material layer 42, may be formed by drying an applied material of a solid electrolyte-containing slurry containing a low-polarity solvent, fluororesin particles having an average particle diameter of 200 nm or less, and sulfide solid electrolyte particles.

[0060] In the electrode body 2, the positive electrode active material layer 42 and the negative electrode active material layer 52 face each other with the solid electrolyte layer 60 interposed therebetween. When the electrode body 2 is viewed from one side in the stacking direction (thickness direction), the area of ​​the negative electrode active material layer 52 may be larger than the area of ​​the positive electrode active material layer 42. In other words, at least a part of the peripheral edge of the negative electrode active material layer 52 does not have to face the positive electrode active material layer 42 in the thickness direction.

[0061] (Solid electrolyte layer) In the electrode body 2 of this embodiment, a solid electrolyte layer 60 containing a solid electrolyte but no active material is disposed between the positive electrode 40 and the negative electrode 50. The thickness of the solid electrolyte layer 60 may be 5 μm or more and 200 μm or less, or 10 μm or more and 100 μm or less.

[0062] The solid electrolyte layer 60 may further contain, as a binder, the fluororesin mentioned above in the description of the positive electrode active material layer 42. In other words, the solid electrolyte layer 60 may contain a binder similar to the binder that may be contained in the positive electrode active material layer 42, and specifically, may contain the above-mentioned fluororesin as a binder.

[0063] The solid electrolyte is an ion-conductive material that conducts ions such as lithium, sodium, potassium, magnesium, and calcium, and is a compound that remains solid even in a nitrogen atmosphere at 1 atmosphere pressure and 25°C. Examples of the solid electrolyte include a sulfide solid electrolyte (described in detail later) and a solid electrolyte other than a sulfide solid electrolyte (described in detail later). In one example of this embodiment, the solid electrolyte layer 60 includes at least a sulfide solid electrolyte. It is preferable that the solid electrolyte layer 60 includes only a sulfide solid electrolyte as the solid electrolyte.

[0064] The use of a sulfide solid electrolyte as the solid electrolyte has the advantage of increasing the conductivity of ions such as lithium in the solid electrolyte layer. Furthermore, since sulfide solid electrolyte particles are more easily deformed, the contact area between the solid electrolyte particles and the contact area between the solid electrolyte and the active material can be increased. This has the advantage of reducing the interfacial resistance between the solid electrolyte particles and between the solid electrolyte and the active material.

[0065] The sulfide solid electrolyte is a compound that contains sulfur element as an essential component and remains solid even in a nitrogen atmosphere at 1 atmosphere pressure and 25°C. When used in lithium ion secondary batteries, examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-GeS2, LiI-Li2S-P2S5, and Li 10 Ge-P2S 12 , Li6PS5X (X = Cl, Br, I), etc. 10 Ge-P2S 12 is called the LGPS type, and Li6PS5X is called the argyrodite type.

[0066] Other solid electrolytes that can be included in the solid electrolyte layer 60 include an oxide solid electrolyte, an oxynitride solid electrolyte, or a polymer solid electrolyte. In the solid electrolyte layer 60, the proportion of the sulfide solid electrolyte in the solid electrolyte may be 95 mass % or more.

[0067] An oxide solid electrolyte is a compound that contains oxygen as an essential component and remains solid even in a nitrogen atmosphere at 1 atmosphere pressure and 25° C. Examples of oxide solid electrolytes include perovskite-type oxides, NASICON-type oxides, LISICON-type oxides, and garnet-type oxides. Examples of perovskite oxides include Li x La 1-x Examples of such oxides include oxides represented by TiO3 (Li-La-Ti-O perovskite oxides). 0.29 La 0.57 TiO3, Li 0.35 La 0.55 Examples include TiO3. Examples of NASICON-type oxides include Li 1.3 Al 0.3 Ti 1.7 (PO4)3, etc. Examples of LISICON-type oxides include Li4SiO4-Li3PO4 and Li3BO3-Li3PO4. Garnet-type oxides include, for example, Li7La3Zr2O 12 Li-La-Zr-O based oxides such as those mentioned above can be cited.

[0068] An example of the oxynitride solid electrolyte is Li3N.

[0069] The polymer solid electrolyte may be an ion-conductive polymer, such as a chemically modified or crosslinked polyether-, polyester-, polyamine-, or polysulfide-based polymer.

[0070] Similarly to the above-described positive electrode active material layer 42, the solid electrolyte layer 60 may be formed by drying an applied material (not including an active material) of a solid electrolyte-containing slurry containing a low-polarity solvent, fluororesin particles having an average particle diameter of 200 nm or less, and sulfide solid electrolyte particles.

[0071] <Method of manufacturing all-solid-state energy storage element> The method for manufacturing the energy storage element of this embodiment includes, for example, the steps of producing an electrode body and housing the electrode body in a container 3 to assemble an energy storage element. By fabricating the electrode body, the positive electrode 40, the negative electrode 50, and the solid electrolyte layer 60 are fabricated.

[0072] The step of preparing the electrode body is preparing a solid electrolyte-containing slurry containing a low-polarity solvent, fluororesin particles, and sulfide solid electrolyte particles; and preparing an electrolyte-containing layer A containing fluororesin and sulfide solid electrolyte particles from the applied solid electrolyte-containing slurry. In the step of preparing the solid electrolyte-containing slurry, the low-polarity solvent is at least one of a hydrocarbon compound and a compound having only a hydrocarbon group and an ether group in the molecule, and the particles have an average particle size of 200 nm or less. In the step of producing the electrolyte-containing layer A, the coating is subjected to a drying treatment to volatilize the low-polarity solvent.

[0073] In the electrode assembly fabrication step, a dispersion containing a low-polarity solvent and fluororesin particles dispersed in the low-polarity solvent is prepared to fabricate at least one of the electrolyte-containing layers A. Next, the prepared dispersion is mixed with at least one of sulfide solid electrolyte particles, lithium transition metal composite oxide particles, and carbon material particles to prepare a slurry. Subsequently, the applied slurry is dried to volatilize the low-polarity solvent from the slurry, thereby fabricating at least one of the positive electrode active material layer 42, the negative electrode active material layer 52, and the solid electrolyte layer.

[0074] Each of the above steps will be described in detail below. In the following, an example in which each of the layers constituting the electrolyte-containing layer A (the positive electrode active material layer 42, the negative electrode active material layer 52, and the solid electrolyte layer 60) is produced using the above-mentioned slurry and dispersion will be described in detail.

[0075] (Step of producing electrode body) In the process of producing an electrode assembly, first, the above-described dispersion liquid is prepared. The dispersion liquid includes a low-polarity solvent and fluororesin particles dispersed in the low-polarity solvent. The low-polarity solvent is at least one of a hydrocarbon compound and a compound having only a hydrocarbon group and an ether group in the molecule, and the particles have an average particle size of 200 nm or less. In this embodiment, the above-described dispersion liquid is a dispersion liquid for producing an electrode assembly of an energy storage element, as described below.

[0076] The dispersion can be prepared as follows: A method for preparing the dispersion includes preparing a stock solution containing a highly polar solvent containing water and fluororesin particles having an average particle size of 200 nm or less dispersed in the highly polar solvent; and subjecting the raw liquid to a substitution treatment in which the water is substituted with the low-polarity solvent having a lower polarity than the high-polarity solvent, thereby obtaining a dispersion liquid of the fluororesin particles.

[0077] [Preparation of stock solution for preparing dispersion] The highly polar solvent is a solvent containing at least water. The highly polar solvent may further contain a solvent other than water (an organic solvent). The content of the organic solvent in the highly polar solvent is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less.

[0078] A highly polar solvent has a higher polarity than the aforementioned low-polarity solvent. In other words, the polarity of the solvent contained in the original solution is higher than the polarity of the solvent contained in the dispersion liquid prepared by the substitution process. The level of polarity can be determined by the Hildebrand solubility parameter (δ SP value), even if the high-polarity solvent or the low-polarity solvent is a mixed solvent. The larger the SP value, the higher the polarity.

[0079] The highly polar solvent may be a solvent that further contains, in addition to water, an organic solvent that dissolves in water, such as acetonitrile, isopropanol, or N-methylpyrrolidone.

[0080] The stock solution can be prepared, for example, as follows: A commercially available fluororesin (e.g., polyvinylidene fluoride powder) is mixed with acetonitrile under heating so that the fluororesin concentration is, for example, 1% by mass, to obtain a solution in which the fluororesin is dissolved. Water, for example, 10 times the mass of the fluororesin (solid content equivalent), is added to this solution to obtain a fluororesin solution. The fluororesin solution, heated to approximately 70 to 80°C, is continuously added to water in an amount 100 times the mass of the fluororesin (solid content equivalent), to obtain a dispersion in which fluororesin particles are dispersed in water and acetonitrile. Most of the acetonitrile and water contained in this dispersion are volatilized by vacuum concentration. An appropriate amount of water is then added to prepare a stock solution with a concentration of, for example, 5% to 10% by mass. This stock solution contains the fluororesin in particulate form.

[0081] [Preparation of dispersion liquid (replacement process)] The stock solution prepared as described above is subjected to a substitution treatment to substitute at least the water contained in the high-polarity solvent with the low-polarity solvent. The substitution treatment results in a dispersion in which fluororesin particles are dispersed. The substitution treatment can be carried out by a general substitution treatment method, including a dispersion operation using ultrasonic irradiation, a volatilization operation, a centrifugal separation operation, and a solvent removal operation by decantation.

[0082] The low polarity solvent is at least one of a hydrocarbon compound and a compound having only a hydrocarbon group and an ether group in the molecule.

[0083] Examples of hydrocarbon compounds include aliphatic hydrocarbons such as octane, nonane, and decane, and aromatic hydrocarbons such as benzene, toluene, xylene, mesitylene, and tetralin. On the other hand, examples of compounds having only hydrocarbon groups and ether groups in the molecule include aliphatic ethers such as dihexyl ether, diheptyl ether, and dibutyl ether, and aromatic ethers such as anisole (methoxybenzene), methoxytoluene, methoxyxylene, methoxymesitylene, and ethoxybenzene.

[0084] The low-polarity solvent is preferably at least one selected from the group consisting of octane, nonane, decane, benzene, toluene, xylene, mesitylene, tetralin, dihexyl ether, diheptyl ether, dibutyl ether, anisole (methoxybenzene), methoxytoluene, methoxyxylene, methoxymesitylene, and ethoxybenzene.

[0085] In the replacement treatment, various commonly known operations can be employed. For example, in the replacement treatment, a dispersion operation using ultrasonic irradiation can be performed to thoroughly disperse the fluororesin particles. In addition, in the replacement treatment, after the dispersion operation, a volatilization operation can be performed using an evaporator or the like to volatilize the water in the stock solution. The volatilization operation can be performed under reduced pressure while the stock solution is heated to 100°C or less. In addition, in the replacement treatment, after the volatilization operation, a centrifugation operation can be performed to precipitate the fluororesin particles, and a solvent removal operation can be performed to remove the supernatant liquid after centrifugation by decantation. This series of operations can be repeated multiple times.

[0086] In the substitution treatment, if necessary, an intermediate solvent (e.g., isopropanol) that is less polar than water but more polar than the low-polarity solvent may be used. Specifically, after the above-mentioned series of operations for substituting the water in the raw solution with the intermediate solvent is performed, a series of operations for substituting the intermediate solvent with a low-polarity solvent may be performed. In this case, the operation for volatilizing water may volatilize not only the water but also the intermediate solvent.

[0087] The intermediate solvent is preferably an organic solvent that dissolves in both water and low-polarity solvents. In other words, the intermediate solvent is preferably a protic organic solvent that has good solubility in both water and low-polarity solvents. Examples of the intermediate solvent include monohydric alcohols having 3 or less carbon atoms, such as methyl alcohol, ethyl alcohol, and isopropanol.

[0088] The dispersion obtained through the substitution treatment contains the above-mentioned low-polarity solvent as a solvent. The solvent of the dispersion may contain a solvent other than the above-mentioned low-polarity solvent. The proportion of the low-polarity solvent in the solvent of the dispersion is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more. Furthermore, the proportion of solvents other than the above-mentioned low-polarity solvent in the solvent of the dispersion is preferably 1% by mass or less. For example, the proportion of carbonyl group-containing solvents (compounds having a carbonyl group in the molecule) in the solvent of the dispersion is 1% by mass or less.

[0089] The average particle size of the fluororesin particles contained in the dispersion is 200 nm or less. This average particle size may be 180 nm or less, 120 nm or less, or 100 nm or less. Furthermore, this average particle size may be 10 nm or more. Because the average particle size is relatively small, 200 nm or less, when this dispersion is used to manufacture an energy storage element (including a solid electrolyte), the fluororesin particles are likely to penetrate between the solid electrolyte particles. Therefore, the fluororesin particles can effectively bond the sulfide solid electrolyte particles together.

[0090] The average particle size of the fluororesin particles contained in the dispersion is directly reflected by the average particle size of the fluororesin particles contained in the stock solution for preparing the dispersion. Therefore, when preparing the stock solution for preparing the dispersion, for example, if the entire amount of the fluororesin solution is added to water in a shorter time to prepare an aqueous dispersion of fluororesin particles, fusion between the fluororesin particles can be promoted, thereby making the average particle size of the fluororesin particles in the dispersion larger. On the other hand, when preparing the stock solution for preparing the dispersion, for example, if the addition rate of the fluororesin solution is slower (for example, 20 mass% / min or less), fusion between the fluororesin particles can be suppressed, thereby making the average particle size of the fluororesin particles in the dispersion smaller.

[0091] The average particle size of fluororesin particles is measured as follows. A laser diffraction / scattering particle size distribution analyzer is used as the measuring instrument. A 0.5 mass% aqueous solution of polyoxyethylene-p-cumylphenyl ether (trade name "Nonal 912A" manufactured by Toho Chemical Industry Co., Ltd.) is used as the dispersion medium. A cumulative curve is calculated by analyzing the scattered laser light, with the total volume of the particles being 100%, and the particle size (median diameter: d50) at the point where the cumulative curve reaches 50% is taken as the average particle size of the fluororesin particles.

[0092] In the step of producing the electrode body, a slurry is next prepared.

[0093] [Preparation of slurry] The slurry contains the dispersion liquid prepared as described above and at least one of sulfide solid electrolyte particles, lithium transition metal composite oxide particles, and carbon material particles. The solid electrolyte-containing slurry containing the dispersion liquid, sulfide solid electrolyte particles, and lithium transition metal composite oxide particles (positive electrode active material particles) can be used to prepare, for example, a positive electrode active material layer 42. The solid electrolyte-containing slurry containing the dispersion liquid, sulfide solid electrolyte particles, and carbon material particles (negative electrode active material particles) can be used to prepare, for example, a negative electrode active material layer 52. The solid electrolyte-containing slurry containing the dispersion liquid and sulfide solid electrolyte particles but not containing either a positive electrode active material or a negative electrode active material can be used to prepare, for example, a solid electrolyte layer 60.

[0094] For example, the solid electrolyte-containing slurry can be prepared by mixing the above-mentioned dispersion with at least one of sulfide solid electrolyte particles, lithium transition metal composite oxide particles, and carbon material particles. As the lithium transition metal composite oxide, the lithium transition metal composite oxides listed in the above description of the positive electrode active material can be used. As the carbon material particles, the carbon material particles listed in the above description of the negative electrode active material can be used.

[0095] Alternatively, a pre-prepared (commercially available) slurry may be used. For example, the slurry may contain the dispersion liquid and at least one of lithium transition metal composite oxide particles and carbon material particles, but may not contain sulfide solid electrolyte particles. A solid electrolyte-containing slurry can be prepared by adding sulfide solid electrolyte particles to the slurry.

[0096] For example, in the slurry (solid electrolyte-containing slurry), the total content of solvents other than the above-mentioned low-polarity solvent is 1% by mass or less. The slurry (solid electrolyte-containing slurry) preferably does not substantially contain solvents other than the above-mentioned low-polarity solvent (e.g., carbonyl group-containing solvents, protic organic solvents, etc.). For example, the slurry (solid electrolyte-containing slurry) does not substantially contain any of ester group-containing solvents, ketone group-containing solvents, protic organic solvents, etc. This can more sufficiently suppress deterioration of the sulfide solid electrolyte.

[0097] The average particle size of the fluororesin particles in the slurry is 200 nm or less, similar to the average particle size in the dispersion liquid. Therefore, as described above, when such a slurry is used in the production of an electric storage device (including a solid electrolyte), the fluororesin particles can effectively bind the sulfide solid electrolyte particles together. Furthermore, because the solvent contained in the slurry (solid electrolyte-containing slurry) is the specific solvent described above, deterioration of the sulfide solid electrolyte can be suppressed during storage of the solid electrolyte-containing slurry and during the production of an electric storage device as described below.

[0098] In the slurry, the average particle size of the fluororesin particles is preferably smaller than the average particle size of the sulfide solid electrolyte particles. That is, the ratio of the average particle size of the fluororesin particles to the average particle size of the sulfide solid electrolyte particles is preferably less than 1.0. This ratio may be 0.9 or less, or even 0.5 or less. Furthermore, this ratio may be 0.1 or more. A ratio of less than 1.0 allows the fluororesin particles to more easily penetrate between the sulfide solid electrolyte particles. Therefore, in the electrolyte-containing layer A, such as the positive electrode active material layer 42, the sulfide solid electrolyte particles can be more fully bound together. Furthermore, since this can be more fully bound, the amount of fluororesin particles can be reduced to achieve the same binding properties.

[0099] The average particle size of solid electrolyte particles is measured as follows. A laser diffraction / scattering particle size distribution analyzer is used as the measuring device. Tetralin is used as the dispersion medium. A cumulative curve is calculated by analyzing the scattered laser light, with the total volume of the particles set to 100%, and the particle size at the point where the cumulative curve reaches 50% (median diameter: d50) is taken as the average particle size of the solid electrolyte particles.

[0100] [Preparation of electrolyte-containing layers (positive electrode active material layer, solid electrolyte layer, negative electrode active material layer)] The electrolyte-containing layers A, such as the solid electrolyte-containing positive electrode active material layer 42, the solid electrolyte layer 60, and the solid electrolyte-containing negative electrode active material layer 52, can each be prepared using a solid electrolyte-containing slurry. Specifically, the positive electrode active material layer 42 can be prepared using a solid electrolyte-containing slurry (slurry for the positive electrode active material layer) containing at least a low-polarity solvent, fluororesin particles, sulfide solid electrolyte particles, and lithium transition metal composite oxide particles (positive electrode active material particles). The solid electrolyte layer 60 can be prepared using a solid electrolyte-containing slurry (slurry for the solid electrolyte layer) containing a low-polarity solvent, fluororesin particles, and sulfide solid electrolyte particles, but not positive electrode active material particles or negative electrode active material particles. The negative electrode active material layer 52 can be prepared using a solid electrolyte-containing slurry (slurry for the negative electrode active material layer) containing at least a low-polarity solvent, fluororesin particles, sulfide solid electrolyte particles, and carbon material particles (negative electrode active material particles).

[0101] Preparation of the positive electrode active material layer For example, the above-mentioned metal foil or alloy foil is prepared as the positive electrode substrate 41. As shown in Fig. 4, the positive electrode active material layer 42 can be produced by carrying out the following operations. (I) A slurry for a positive electrode active material layer (denoted as SL) is applied to the metal foil or alloy foil of the positive electrode substrate 41. In this way, the applied material is superimposed on the positive electrode substrate 41. A conventional general method can be used as the application method (coating method). (II) The coated material is subjected to a drying treatment to volatilize the low-polarity solvent contained in the coated slurry. For example, the solvent is volatilized and removed from the coated material by a heat treatment. The set temperature during the heat treatment may be, for example, 40°C or higher and 150°C or lower. The heat treatment may be carried out under reduced pressure. (III) After the low-polarity solvent has evaporated, the coated product (positive electrode active material layer 42) is subjected to a pressing process (indicated by the dashed arrow). If necessary, the pressing process is carried out while heating. (IV) A pressed positive electrode active material layer 42 is formed.

[0102] - Preparation of solid electrolyte layer As shown in FIG. 5, the solid electrolyte layer 60 can be fabricated by carrying out the following operations. (i) A slurry for a solid electrolyte layer (denoted as SL′) is applied to the positive electrode active material layer 42. In this way, the applied material is superimposed on the positive electrode active material layer 42. A conventional general method can be used as the application method (coating method). (ii) The coated material is subjected to a drying treatment to volatilize the low-polarity solvent contained in the coated slurry. For example, the solvent is volatilized and removed from the coated material by a heat treatment. The set temperature during the heat treatment may be within the temperature range employed when fabricating the positive electrode active material layer 42, for example. (iii) After the low-polarity solvent has evaporated, the coated material (solid electrolyte layer 60) is subjected to a pressing process (indicated by the dashed arrow). If necessary, the pressing process is performed while heating. (iv) A pressed solid electrolyte layer 60 is formed.

[0103] - Preparation of negative electrode active material layer Although not shown, the negative electrode active material layer 52 can be produced by the same method as the above-mentioned production of the positive electrode active material layer or the production of the solid electrolyte layer.

[0104] In the process of producing the electrode body, after producing a laminate of the positive electrode active material layer 42, the solid electrolyte layer 60, and the negative electrode active material layer 52 as described above, the negative electrode substrate 51 is further stacked on top of the laminate and pressed from both sides in the thickness direction, thereby producing the electrode body 2. In the process of producing the electrode body, the positive electrode 40 may be produced by superposing the positive electrode active material layer 42 on the positive electrode substrate 41, and the negative electrode 50 may be produced by superposing the negative electrode active material layer 52 on the negative electrode substrate 51, and a laminate of the negative electrode 50 and the solid electrolyte layer 60 may be produced. Thereafter, the laminate and the positive electrode 40 may be superposed, and further, a pressing process may be performed from both sides in the thickness direction to produce the electrode body 2.

[0105] (Process for assembling the energy storage element) In this step, the produced electrode body 2 is housed in a container 3, and the energy storage element 1 is assembled so that the positive electrode 40 and negative electrode 50 of the electrode body 2 are electrically connected to the external terminals of the energy storage element 1. A general method can be used to assemble the energy storage element.

[0106] In this manner, the energy storage device 1 of this embodiment can be manufactured.

[0107] <Configuration of the power storage device> The energy storage element 1 of this embodiment can be mounted as an energy storage device 100 (battery module) configured by assembling a plurality of energy storage elements 1 in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), or a plug-in hybrid electric vehicle (PHEV), a power source for electronic devices such as a personal computer or a communication terminal, or a power source for power storage, etc. In this case, it is sufficient that the technology of the present invention is applied to at least one energy storage element 1 included in the energy storage device 100. 6 shows an example of an energy storage device 100 in which energy storage units 10, each of which is an assembly of two or more electrically connected energy storage elements 1, are further assembled. The energy storage device 100 may include a bus bar (not shown) that electrically connects two or more energy storage elements 1, a bus bar (not shown) that electrically connects two or more energy storage units 10, etc. The energy storage unit 10 or the energy storage device 100 may include a status monitoring device (not shown) that monitors the status of one or more energy storage elements.

[0108] <Other embodiments> The energy storage device of the present invention is 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.

[0109] In the above embodiment, the case where the energy storage device 1 is used as a chargeable and dischargeable all-solid-state secondary battery (for example, an all-solid-state lithium ion secondary battery) has been described, but the type, shape, size, capacity, etc. of the energy storage device are arbitrary.

[0110] In the above embodiment, the positive electrode 40 in which the positive electrode active material layer 42 is superimposed on one side of the positive electrode substrate 41 and the negative electrode 50 in which the negative electrode active material layer 52 is superimposed on one side of the negative electrode substrate 51 have been described. However, in the positive electrode, the positive electrode active material layer 42 may be superimposed on both sides of the positive electrode substrate 41, and in the negative electrode, the negative electrode active material layer 52 may be superimposed on both sides of the negative electrode substrate.

[0111] According to the manufacturing method of the energy storage element of the above embodiment, the fluororesin particles are relatively small, so that the particles of the sulfide solid electrolyte can be well bound together by the fluororesin particles, and deterioration of the sulfide solid electrolyte can be suppressed. According to the dispersion liquid of the above embodiment or the solid electrolyte-containing slurry containing the dispersion liquid, in the production of an energy storage element, the fluororesin particles are relatively small, so that the particles of the sulfide solid electrolyte can be well bound together by the fluororesin particles, and deterioration of the sulfide solid electrolyte can be suppressed. According to the method for producing a dispersion liquid of the above embodiment, since the fluororesin particles are relatively small, the particles of the sulfide solid electrolyte can be well bound together by the fluororesin particles, and a dispersion liquid can be obtained that can suppress deterioration of the sulfide solid electrolyte during production. This dispersion liquid can be used for producing an energy storage element.

[0112] Conventionally, when preparing an electrolyte-containing layer (such as a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer in an electrode assembly) in which sulfide solid electrolyte particles are bound with a binder, for example, fluororesin particles, which have good oxidation resistance, are used as the binder. However, fluororesin particles tend to aggregate, and therefore do not necessarily exhibit sufficient binding properties as a binder. Therefore, in order to sufficiently bind the sulfide solid electrolyte particles with the fluororesin, it is preferable to prepare an electrolyte-containing layer by drying a solid electrolyte-containing slurry prepared from a fluororesin solution in which the fluororesin is first dissolved in a solvent. However, fluororesins (such as PVDF) are soluble only in certain polar solvents (such as carbonyl group-containing solvents) that can deteriorate the sulfide solid electrolyte. Therefore, when attempting to sufficiently bind the sulfide solid electrolyte particles with the fluororesin binder, there is a problem that the sulfide solid electrolyte may deteriorate during production. In contrast, in the above embodiment, while using fluororesin particles (such as PVDF particles) as a binder, it is possible to suppress deterioration of the sulfide solid electrolyte particles during production, and also to satisfactorily bind the sulfide solid electrolyte particles together with the fluororesin.

[0113] In the above embodiment, it is preferable that the specific low-polarity solvent is used, and the fluororesin particles contained in the slurry are polyvinylidene fluoride particles, and the average particle diameter of such particles is 200 nm or less. When the solvent contained in the slurry is the specific low-polarity solvent, deterioration of the sulfide solid electrolyte particles can be sufficiently suppressed during the production of an energy storage device. Furthermore, when the average particle diameter of polyvinylidene fluoride contained in the slurry is sufficiently small, the sulfide solid electrolyte particles can be more effectively bound together.

[0114] The energy storage element 1 of the above embodiment is preferably an all-solid-state energy storage element, that is, the positive electrode active material layer 42, the negative electrode active material layer 52, and the solid electrolyte layer 60 of the energy storage element 1 of the above embodiment preferably do not contain an electrolytic solution.

[0115] In the above embodiment, the all-solid-state energy storage element among the energy storage elements has been described in detail, but the energy storage element of the present invention is not limited to the all-solid-state energy storage element. The positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer constituting the energy storage element of the present invention may contain an electrolytic solution. The electrolytic solution can be appropriately selected from known electrolytic solutions. When the energy storage element of the present invention is a lithium ion secondary battery, for example, the electrolytic solution can be one in which LiPF6 is dissolved as an electrolyte salt in a solvent containing a mixture of a cyclic carbonate and a chain carbonate. [Example]

[0116] 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.

[0117] <Production of dispersion liquid> Example 1 594 parts by mass of acetonitrile and 6 parts by mass of polyvinylidene fluoride powder (PVDF, model number #9100, manufactured by Kureha) were mixed and dissolved by heating to 80°C to obtain a fluororesin acetonitrile solution. 66 parts by mass of water was added to this solution to obtain a fluororesin solution. 0.08 dm of the above fluororesin solution maintained at 80°C was added to 600 parts by mass of stirred water at 20°C. 3 A dispersion liquid in which fluororesin particles were dispersed in water and acetonitrile was obtained by dripping at a drip rate of 1 / min for a drip time of 10 minutes. Most of the acetonitrile and water contained in this dispersion liquid were volatilized by vacuum concentration treatment. Water was then added so that the PVDF concentration was 5% by mass, and a stock solution of Example 1 in which PVDF was dispersed was prepared. The particle size distribution of the fluororesin particles contained in this stock solution was measured by the method described above, and the average particle diameter was found to be 70 nm. In this way, a stock solution according to Example 1 was prepared, containing PVDF particles with an average particle diameter of 70 nm and water, and in which the PVDF particles were dispersed in water at a concentration of 5% by mass.

[0118] Next, a sufficient amount of isopropanol (IPA) was added to the above stock solution, and the mixture was dispersed using an ultrasonic vibrator. The solid (PVDF) was then precipitated using a centrifuge, and most of the supernatant was removed by decantation. This series of steps, including the addition of IPA, dispersion using an ultrasonic vibrator, settling of the solid using a centrifuge, and removal of the supernatant by decantation, was repeated three times. Next, a sufficient amount of anisole was added as a low-polarity solvent, and dispersion was performed using an ultrasonic vibrator. The solid (PVDF) was then precipitated using a centrifuge, and most of the supernatant was removed by decantation. This series of steps, including the addition of a low-polarity solvent, dispersion using an ultrasonic vibrator, settling of the solid using a centrifuge, and removal of the supernatant by decantation, was repeated three times. Finally, a predetermined amount of anisole was added to produce a dispersion of Example 1 in which PVDF having an average particle size of 70 nm was dispersed in anisole at a concentration of 4.5% by mass.

[0119] Example 2 The drip rate is 0.4 dm 3 A stock solution according to Example 2 was produced in the same manner as in Example 1, except that the dropwise addition rate was set to 1 / min and the dropping time was set to 2 min. The particle size distribution of the fluororesin particles contained in the stock solution was measured by the method described above, and the average particle diameter was found to be 172 nm. In this manner, a stock solution according to Example 2 was prepared in which PVDF having an average particle diameter of 172 nm was dispersed in water at a concentration of 5% by mass. A dispersion according to Example 2 was produced in which PVDF having an average particle diameter of 172 nm was dispersed in anisole at a concentration of 10% by mass, in the same manner as in Example 1, except that the stock solution was used.

[0120] (Comparative Example 1) The particle size distribution of polyvinylidene fluoride powder (PVDF #9100 manufactured by Kureha) was measured using the method described above, and the average particle diameter was found to be 140 μm. Water was added to the PVDF to prepare a stock solution of Comparative Example 1 in which 140 μm PVDF was dispersed in water at a concentration of 5 mass%. Except for using the stock solution, a dispersion of Comparative Example 1 in which PVDF with an average particle diameter of 140 μm was dispersed in anisole at a concentration of 10 mass% was produced in the same manner as in Example 1.

[0121] (Comparative Example 2) Polyvinylidene fluoride powder (PVDF #9100 manufactured by Kureha) was dispersed in a mixed solvent (methyl isobutyl ketone 90 parts by mass / decane 10 parts by mass) to a concentration of 1% by mass, and then stirred at 80°C for 24 hours to produce a dispersion liquid according to Comparative Example 2.

[0122] <Visual evaluation of dispersion liquid dispersibility> The dispersions of Examples 1 and 2 and Comparative Examples 1 and 2 were each placed in a 20 ml reagent bottle with a lid and allowed to stand. As a result, it was visually observed that the dispersions of Examples 1 and 2 maintained good dispersibility even after one month. On the other hand, it was visually observed that the dispersions of Comparative Examples 1 and 2 lost uniformity after a few seconds, and after about 90 seconds lost dispersibility and completely separated.

[0123] Example 3 An energy storage element (all-solid-state lithium ion secondary battery) of Example 3 was manufactured as follows. The manufactured energy storage element is also referred to as an all-solid-state secondary battery. In the all-solid-state secondary battery described below, only the positive electrode active material layer was manufactured using the dispersion liquid of Example 1 described above.

[0124] <Preparation of solid electrolyte-containing slurry A> A sulfide solid electrolyte having an argyrodite structure and containing lithium, phosphorus, sulfur, and chlorine was prepared as the solid electrolyte. The dispersion liquid of Example 1 was mixed with the solid electrolyte powder, and the mixture was stirred using a planetary centrifugal mixer to prepare a solid electrolyte-containing slurry A.

[0125] <Preparation of solid electrolyte-containing slurry B (positive electrode mixture paste)> The solid electrolyte-containing slurry A contains an α-NaFeO2-type crystal structure and LiNi 0.5 Co 0.2 Mn 0.3 A lithium transition metal composite oxide (particulate active material) represented by O2 and carbon fiber as a conductive agent were added and stirred with a planetary mixer to prepare solid electrolyte-containing slurry B (positive electrode mixture paste).

[0126] <Preparation of positive electrode> The solid electrolyte-containing slurry B, which is a cathode mixture paste, was applied to the carbon coating layer side of a 20 μm-thick aluminum foil (cathode substrate) that had previously been provided with a carbon coating layer on one side. The resulting mixture was then dried to volatilize and remove the solvent from the slurry B. In this way, a cathode was fabricated in which a 60 μm-thick cathode active material layer was formed on the cathode substrate.

[0127] <Fabrication of all-solid-state secondary batteries> The positive electrode prepared as described above was punched out in the thickness direction to a predetermined size. A solid electrolyte was poured into one side of the Macol tube. Next, a SUS jig was used to press the tube at 100 MPa to form a solid electrolyte layer with a thickness of 800 μm. The punched cathode was then inserted into the Macol tube and pressed at 580 MPa. This bonded the cathode's solid electrolyte layer and the solid electrolyte layer inside the Macol tube. Next, a lithium-indium counter electrode was inserted from the other side of the Macol tube. This caused the inserted lithium-indium counter electrode to face the positive electrode inside the Macol tube with the solid electrolyte layer interposed between them. Then, inside the Macol tube, the positive electrode, the solid electrolyte layer, and the counter electrode were sandwiched between SUS jigs. Thereafter, the SUS jigs on both sides were fastened with bolts, and leads were connected to the SUS jigs on both sides as external terminals, thereby producing a half cell (all-solid-state secondary battery) of Example 3.

[0128] <Performance evaluation> (Float charge test) The all-solid-state secondary battery of Example 3, which had a positive electrode active material layer fabricated using the dispersion of Example 1, was subjected to constant current charging at a charge current of 0.1 C and a cut-off voltage of 3.93 V at a temperature of 25°C, and constant current discharging at a discharge current of 0.1 C and a cut-off voltage of 2.38 V. A 30-minute rest period was provided after each charge and discharge. Next, as a float charge test, constant current charging at a charge current of 0.1 C and a cut-off voltage of 3.93 V was performed at a temperature of 60°C for 120 hours. Subsequently, constant current discharging at a discharge current of 0.1 C and a cut-off voltage of 2.38 V was performed at 25°C. A 30-minute rest period was provided after each charge and discharge. As a result, the discharge capacity retention rate, which is the percentage of the discharged amount of electricity after the float charge test relative to the discharged amount of electricity before the float charge test, was 75%, confirming good float life performance.

[0129] The reason why the all-solid-state secondary battery of Example 3 exhibited good float life performance is that deterioration of the sulfide solid electrolyte during production was suppressed because a solvent that deteriorates the sulfide solid electrolyte was not used in the dispersion liquid of Example 1. Furthermore, because a fluororesin (PVDF) that has higher oxidation resistance than rubber-based binders and the like was used as the binder, the fluororesin was present not only between the sulfide solid electrolytes but also between the positive electrode active material or conductive agent and the sulfide solid electrolyte, which suppressed oxidative decomposition of the binder and the solid electrolyte.

[0130] (Comparative Example 3) Except for using the dispersion liquid of Comparative Example 2, a solid electrolyte-containing slurry C (positive electrode mixture paste) was prepared in the same procedure as for the solid electrolyte-containing slurry A prepared in the production of the energy storage element of Example 3. The presence of many coarse lumps was observed in this solid electrolyte-containing slurry C.

[0131] A 20 μm thick aluminum foil (positive electrode substrate) was prepared with a carbon coating layer on one side. The solid electrolyte-containing slurry C, which is a positive electrode mixture paste, was applied to the carbon coating layer side. After application, streaks that significantly impaired the appearance were observed on the applied surface. A drying treatment was then performed to volatilize and remove the solvent from the slurry C. As a result, the positive electrode active material layer peeled off from the positive electrode substrate, and a positive electrode and the all-solid-state secondary battery of Comparative Example 3 using this positive electrode could not be manufactured. [Explanation of symbols]

[0132] 1: Energy storage element (all-solid-state lithium-ion secondary battery), 2: Electrode body, 3: Container, 4: Positive terminal, 5: Negative terminal, 40: Positive electrode, 41: positive electrode base material, 42: positive electrode active material layer, 50: negative electrode, 51: negative electrode base material, 52: negative electrode active material layer, 60: solid electrolyte layer, 10: Power storage unit, 100: Power storage device.

Claims

[Claim 1] preparing a solid electrolyte-containing slurry containing a low-polarity solvent, fluororesin particles, and sulfide solid electrolyte particles; preparing an electrolyte-containing layer containing particles of the fluororesin and particles of the sulfide solid electrolyte from the applied material of the solid electrolyte-containing slurry, In preparing the solid electrolyte-containing slurry, the low-polarity solvent is at least one selected from the group consisting of methoxybenzene, methoxytoluene, methoxyxylene, methoxymesitylene, and ethoxybenzene, and the average particle size of the fluororesin particles is 200 nm or less; The method for producing an electric storage element includes, in forming the electrolyte-containing layer, subjecting the applied material to a drying treatment for volatilizing the low-polarity solvent.

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