Slurry for positive electrode, positive electrode, method for producing positive electrode, and battery

Abstract

This slurry for a positive electrode contains: a positive electrode active material containing sulfur; a sulfide-based solid electrolyte; a binder; a first solvent; and a second solvent. The first solvent is one or more compounds selected from fluorinated ethers and fluorinated alkanes. The second solvent is one or more solvents selected from solvents in which the values of the dispersion parameter δd, the polarity parameter δp, and the hydrogen bond parameter δh in Hansen solubility parameters (HSP values) satisfy the ranges 14.8 ≤ δd ≤ 17.5, 1.0 ≤ δp ≤ 7.0, and 1.0 ≤ δh ≤ 7.0, respectively.

Description

Slurry for positive electrode, positive electrode, method for manufacturing positive electrode, and battery

[0001] The present invention relates to a slurry for a positive electrode, a positive electrode using the slurry for a positive electrode, a method for producing a positive electrode, and a battery including the positive electrode.

[0002] In recent years, demand for lithium-ion secondary batteries has been increasing as a power source for electric vehicles, hybrid vehicles, and other vehicles. To simplify systems for ensuring safety, flame-retardant solid electrolytes have been actively developed for use in these batteries. Meanwhile, sulfur positive electrodes using high-capacity sulfur active materials have been developed for positive electrodes, but they suffer from the problem of sulfur active material dissolving in the electrolyte when combined with an electrolyte. All-solid-state secondary batteries using solid electrolytes do not encounter this problem of sulfur active material dissolution, making them promising as a technology for applying sulfur positive electrodes. Furthermore, among solid electrolytes, sulfide-based solid electrolytes are commonly used because they are easily densified by pressing. Considering mass production, it is preferable to prepare a slurry for the positive electrode and apply it to a substrate. Therefore, a technology for fabricating a positive electrode from a slurry containing a sulfur active material and a sulfide-based solid electrolyte has been developed (see, for example, Patent Documents 1 and 2).

[0003] Patent Document 1 describes "a positive electrode material including a conductive material having pores and an active material, wherein the active material is present on at least one of the surface of the conductive material and the pores; solid electrolyte particles containing lithium and sulfur; a binder which is a resin whose molecular skeleton contains a structural unit represented by the following formula (I); a thickener; and a solvent which dissolves part or all of the thickener, wherein the active material is sulfur or a compound containing sulfur, the solvent is one or more selected from a fluorine-based solvent and a hydrocarbon-based solvent, and the conductive material is a particulate conductive material. [Chemical Formula 8] omitted" (Claim 1).

[0004] Furthermore, Patent Document 1 also states that "In the positive electrode composite slurry of the present invention, for example, the binder is preferably dispersed in a solvent. Here, the binder may be partially or completely dissolved in the solvent.", "In addition, in the slurry of the present invention, the binder may be dispersed in the solvent, which allows for a wider range of binder and solvent choices." (paragraph

[0050] ), "The solvent is a solvent that dissolves partially or completely the thickener. Furthermore, the solvent is preferably a solvent that disperses the binder.", "The solvent includes fluorine-based solvents and hydrocarbon-based solvents, and specific examples include fluorine carbonate, fluorobenzene, trifluoromethylbenzene, bistrifluoromethylbenzene, benzene, toluene, xylene, etc.", and "The solvent may be used alone or as a mixed solvent of two or more types." (paragraph

[0053] ).

[0005] Furthermore, in Example 1 of Patent Document 1, it is stated that "1.0 g of a thickener, S-LEC BH-S (manufactured by Sekisui Chemical Co., Ltd.), and 11.5 g of toluene (manufactured by Wako Pure Chemical Industries, Ltd.), were placed in a glass container and stirred on a hot plate at 90°C for 8 hours to dissolve. 2.12 g of the obtained solution, 2.83 g of a binder, PVDF-HFP (KynarLBG, manufactured by Arkema), and 5.22 g of toluene were added, and the mixture was stirred and mixed at 5000 rpm for 1 minute using a small FILMICS (manufactured by Primix Corporation), to obtain thickener-binder mixed solution 1." "(Paragraph

[0082] ) it is stated that "6.20 g of positive electrode mixture 1, 2.12 g of thickener-binder mixed solution 1, and 3.67 g of toluene solvent were added, and the mixture was stirred and mixed in a Filmix at 5000 rpm for 1 minute to obtain a positive electrode slurry.", and in Example 3 it is stated that "A battery was manufactured and evaluated in the same manner as in Example 1, except that the thickener-binder mixed solution and positive electrode mixture slurry were prepared using benzotrifluoride (manufactured by Tokyo Chemical Industry Co., Ltd.) instead of toluene." (Paragraph

[0089] )

[0006] Patent Document 2 describes "a method for manufacturing a positive electrode for an all-solid-state lithium-sulfur battery, comprising a step of applying a positive electrode slurry containing a positive electrode active material, a solid electrolyte, a binder, and a solvent to a positive electrode current collector to form a positive electrode active material layer, wherein the positive electrode active material contains sulfur, and the solvent has a donor number of 19 or less" (Claim 1).

[0007] Furthermore, Patent Document 2 states, "...when butyl butyrate is used as the solvent for the positive electrode slurry, if the positive electrode active material contains sulfur, sulfur-containing components such as sulfur may be unevenly distributed at the edges of the coating surface of the positive electrode slurry." (Paragraph

[0005] ), "Examples of solvents having a donor number of 19 or less include dibutyl ether (donor number: 19), anisole (donor number: 9), and heptane (donor number: 0). The solvent having a donor number of 19 or less used in the positive electrode slurry may be one type, or two or more types." (Paragraph

[0020] ), and "The binder used in the present disclosure is not particularly limited as long as it can be dissolved in the solvent used in the positive electrode slurry. Examples include acrylic binders, fluorine-containing binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), and rubber binders such as butadiene rubber." (Paragraph

[0026] ).

[0008] Patent Document 3 describes "a method for manufacturing an all-solid-state battery, comprising 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 volume % or more of a ketone solvent represented by general formula (1) as a first solvent" (Claim 1), "a method for manufacturing an all-solid-state battery according to claim 1, wherein the slurry further contains a positive electrode active material, and the electrolyte-containing layer is a positive electrode active material layer" (Claim 2), and "a method for manufacturing an all-solid-state battery according to any one of claims 1 to 5, wherein the solvent contains at least one of a saturated hydrocarbon solvent and an aromatic hydrocarbon solvent as a second solvent" (Claim 6).

[0009] Furthermore, Patent Document 3 also states, "In contrast, the above-mentioned ketone solvents can dissolve the PVDF-based binder, allowing the binder to be uniformly dispersed within the layer. This increases the number of bonding points, allowing the inherent performance of the PVDF-based binder to be fully exhibited. As a result, sufficient binding strength can be obtained even with a small amount of binder used. On the other hand, the above-mentioned ketone solvents have relatively low polarity, making it possible to suppress deterioration of the sulfide solid electrolyte." (Paragraph

[0029] ), and "The saturated hydrocarbon solvent is preferably, for example, an alkane. The alkane may be a chain alkane or a cyclic alkane. The saturated hydrocarbon solvent has, for example, 5 or more, 7 or more, or 9 or more carbon atoms. On the other hand, the saturated hydrocarbon solvent has, for example, 15 or less, or 10 or less carbon atoms. Examples of saturated hydrocarbon solvents include isopentane, isohexane, n-hexane, cyclohexane, methylcyclohexane, ethylcyclohexane, n-heptane, isooctane, and n-decane." (Paragraph

[0040] ).

[0010] Japanese Patent No. 5926131 Japanese Patent Application Laid-Open No. 2020-119761 Japanese Patent Application Laid-Open No. 2019-91632

[0011] Conventional positive electrodes using slurries containing solvents such as butyl butyrate, benzotrifluoride (trifluoromethylbenzene), and ketones have had the problem of difficulty in achieving both coatability, adhesiveness, and discharge capacity.

[0012] An object of the present invention is to provide a positive electrode slurry that has good coating properties and binding properties and provides a good discharge capacity, a positive electrode using the positive electrode slurry, a method for manufacturing a positive electrode, and a battery including the positive electrode.

[0013] A positive electrode slurry according to one aspect of the present invention includes a sulfur-containing positive electrode active material, a sulfide-based solid electrolyte, a binder, a first solvent, and a second solvent, the first solvent being at least one selected from a fluorinated ether and a fluorinated alkane, and the second solvent being at least one selected from a dispersion term δ in a Hansen solubility parameter (HSP value). ｄ、 polarity term δ ｐ , and the hydrogen bond term δｈ and the value of δ is 14.8 or less. ｄ ≦17.5, 1.0≦δ ｐ ≦7.0, and 1.0≦δ ｈ The cathode slurry according to another aspect of the present invention includes a sulfur-containing cathode active material, a sulfide-based solid electrolyte, a binder, a first solvent, and a second solvent, the first solvent being at least one solvent selected from a fluorinated ether and a fluorinated alkane, and the second solvent being at least one solvent selected from a carboxylic acid ester and a CF4-terminated alkane. ３ The positive electrode slurry is one or more selected from trifluoroalkylbenzenes or bis(trifluoroalkyl)benzenes having a - group.

[0014] A positive electrode according to yet another aspect of the present invention is a positive electrode using the positive electrode slurry.

[0015] A method for producing a positive electrode according to still another aspect of the present invention is a method for producing a positive electrode, comprising applying the positive electrode slurry to a substrate and drying the applied slurry.

[0016] A battery according to yet another aspect of the present invention is a battery including the above positive electrode.

[0017] The positive electrode slurry according to one aspect and another aspect of the present invention has good coatability and binding properties, and a positive electrode using the positive electrode slurry according to yet another aspect of the present invention and a battery including the positive electrode have good binding properties of the positive electrode active material layer and excellent discharge capacity, and the method for producing a positive electrode according to yet another aspect of the present invention has the effect of being able to provide a positive electrode having good binding properties of the positive electrode active material layer and excellent discharge capacity.

[0018] Fig. 1 is a schematic diagram showing an embodiment of an all-solid-state secondary battery, and Fig. 2 is a schematic diagram showing an embodiment of an electricity storage device configured by assembling a plurality of all-solid-state secondary batteries.

[0019] First, an overview of the positive electrode slurry, positive electrode, and battery disclosed in this specification will be described.

[0020] [1] A positive electrode slurry according to one aspect of the present invention includes a sulfur-containing positive electrode active material, a sulfide-based solid electrolyte, a binder, a first solvent, and a second solvent, wherein the first solvent is at least one selected from a fluorinated ether and a fluorinated alkane, and the second solvent has a dispersion term δ in its Hansen solubility parameter (HSP value). ｄ、 polarity term δ ｐ , and the hydrogen bond term δ ｈ and the value of δ is 14.8 or less. ｄ ≦17.5, 1.0≦δ ｐ ≦7.0, and 1.0≦δ ｈ The solvent is at least one selected from the group consisting of solvents satisfying any of the ranges of ≦7.0.

[0021] The positive electrode slurry described in [1] above has good coating properties and binding properties due to the combination of the first solvent and the second solvent, and by using the positive electrode slurry described in [1] above, a positive electrode and a battery having good binding properties of the positive electrode active material layer as well as excellent discharge capacity can be obtained.

[0022] [2] A positive electrode slurry according to another aspect of the present invention includes a sulfur-containing positive electrode active material, a sulfide-based solid electrolyte, a binder, a first solvent, and a second solvent, wherein the first solvent is at least one selected from a fluorinated ether and a fluorinated alkane, and the second solvent is a carboxylic acid ester and a CF4-terminated alkane. ３ The alkyl benzene compound is at least one selected from trifluoroalkyl benzenes and bis(trifluoroalkyl) benzenes having a - group.

[0023] The positive electrode slurry described in [2] above has good coating properties and binding properties due to the combination of the first solvent and the second solvent, and by using the positive electrode slurry described in [2] above, a positive electrode and a battery having good binding properties of the positive electrode active material layer as well as excellent discharge capacity can be obtained.

[0024] [3] In the positive electrode slurry according to the above [1] or [2], the binder may be a fluororesin.

[0025] The positive electrode slurry described in the above [3] can be a positive electrode slurry having good binding properties.

[0026] [4] In the positive electrode slurry according to any one of [1] to [3], the first solvent may have a boiling point of 50°C or higher and 220°C or lower.

[0027] In the positive electrode slurry described in [4], when the boiling point of the first solvent is equal to or higher than the lower limit, the drying rate of the solvent contained in the positive electrode slurry can be prevented from being too fast, and the positive electrode slurry can have good coatability. When the boiling point of the first solvent is equal to or lower than the upper limit, the amount of residual solvent contained in the positive electrode active material layer after coating and drying the positive electrode slurry can be reduced, and the risk of a decrease in the discharge capacity of the battery due to the influence of the residual solvent can be reduced.

[0028] [5] In the positive electrode slurry according to any one of [1] to [4], the second solvent may have a boiling point of 80° C. or higher and 220° C. or lower.

[0029] In the positive electrode slurry described in [5], when the boiling point of the second solvent is equal to or higher than the lower limit, the drying rate of the solvent contained in the positive electrode slurry can be prevented from being too fast, and the positive electrode slurry can have good coatability. When the boiling point of the second solvent is equal to or lower than the upper limit, the amount of residual solvent contained in the positive electrode active material layer after coating and drying the positive electrode slurry can be reduced, and the risk of a decrease in the discharge capacity of the battery due to the influence of the residual solvent can be reduced.

[0030] [6] In the positive electrode slurry according to any one of [1] to [5], the second solvent may contain a fluorine element in its molecular structure.

[0031] The positive electrode slurry according to the above [6] can suppress the solubility of sulfur in the second solvent, and therefore can reduce the risk of a decrease in the discharge capacity of the battery.

[0032] [7] In the positive electrode slurry according to any one of [1] to [6], the boiling point of the first solvent may be 50°C or higher and 65°C or lower, and the boiling point of the second solvent may be 140°C or higher. Alternatively, the boiling point of the first solvent may be 65°C or higher and 80°C or lower, and the boiling point of the second solvent may be 120°C or higher.

[0033] The positive electrode slurry described in [7] above can be one in which the drying speed of the solvent contained in the positive electrode slurry is not too fast, and can be a positive electrode slurry with good coatability.

[0034] [8] In the positive electrode slurry according to any one of [1] to [7], a mixing ratio (mass %) of the first solvent to the second solvent may be in the range of 99:1 to 10:90.

[0035] The positive electrode slurry described in [8] above can be one in which the drying speed of the solvent contained in the positive electrode slurry is not too fast, and can be a positive electrode slurry with good coatability.

[0036] [9] A positive electrode according to yet another aspect of the present invention is a positive electrode using the positive electrode slurry according to any one of [1] to [8] above.

[0037] The positive electrode described in [9] above has good binding properties of the positive electrode active material layer and also has an excellent discharge capacity by using a positive electrode slurry having good coating properties and binding properties.

[0038]

[10] A method for producing a positive electrode according to yet another aspect of the present invention comprises applying the positive electrode slurry according to any one of [1] to [8] above to a substrate and drying the applied slurry.

[0039] The method for producing a positive electrode according to the above

[10] can provide a positive electrode having good binding properties of the positive electrode active material layer and excellent discharge capacity.

[0040]

[11] A battery according to yet another aspect of the present invention includes the positive electrode according to [9] above.

[0041] The battery described in

[11] above includes a positive electrode using a positive electrode slurry having good coating properties and binding properties, and has an excellent discharge capacity.

[0042] Dispersion term δ in Hansen solubility parameter (HSP value) ｄ、 polarity term δ ｐ , and the hydrogen bond term δ ｈ The value of is calculated as follows: Based on the chemical structure of the compound to be calculated, the HSP value (dispersion term δｄ、 polarity term δ ｐ , and the hydrogen bond term δ ｈ ) and SP value σ ｔ The calculation is performed using the Y-MB method in the DYI program of Hansen Solubility Parameters in Practice (HSPiP) ver. 5.4.03. The SP value σ ｔ and HSP value (variance term δ ｄ、 polarity term δ ｐ , and the hydrogen bond term δ ｈ The relationship between σ and σ is expressed by the following equation (1): ｔ ２ = δ ｄ ２ +δ ｐ ２ +δ ｈ ２ ...(1)

[0043] The configuration of a battery according to one embodiment of the present invention (hereinafter referred to as "the present embodiment"), the positive electrode, the method for manufacturing the positive electrode (including a slurry for the positive electrode), the negative electrode, the method for manufacturing the negative electrode, the solid electrolyte layer, the method for manufacturing the solid electrolyte layer, the method for manufacturing the battery, and the configuration of an electricity storage device, as well as other embodiments, will be described in detail in this order. Note that the names of the components used in each embodiment may differ from the names of the components used in the background art.

[0044] <Battery Configuration, Battery Components (Positive Electrode, Negative Electrode, Solid Electrolyte Layer), and Manufacturing Method> (Battery Configuration) The battery according to this embodiment is preferably an all-solid-state secondary battery. The all-solid-state secondary battery includes an electrode assembly having a positive electrode, a negative electrode, and a solid electrolyte layer, and a container for accommodating the electrode assembly. The electrode assembly is typically a laminated type in which a positive electrode and a negative electrode are laminated with a solid electrolyte layer interposed therebetween. The electrode assembly may also be a so-called "bipolar type" in which a positive electrode active material layer is formed on one side of an electrode substrate and a negative electrode active material layer is formed on the other side. FIG. 1 shows an example of an all-solid-state secondary battery. The all-solid-state secondary battery 10 is a battery in which a positive electrode 1 and a negative electrode 2 are laminated with a solid electrolyte layer 3 interposed therebetween. The positive electrode 1 includes a positive electrode substrate 4 and a positive electrode active material layer 5. The negative electrode 2 includes a negative electrode substrate 7 and a negative electrode active material layer 6. In the all-solid-state secondary battery 10 shown in FIG. 1, an anode active material layer 6, a solid electrolyte layer 3, a cathode active material layer 5, and a cathode substrate 4 are laminated in this order on an anode substrate 7.

[0045] (Positive Electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer.

[0046] The positive electrode substrate has electrical conductivity. Whether or not it has electrical conductivity is determined by whether or not the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 ７ The resistance is determined using Ω cm as a threshold value. Metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof, are used as the material for the positive electrode substrate. Among these, aluminum or aluminum alloys are preferred from the viewpoints of potential resistance, high conductivity, and cost. Examples of the positive electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30, as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0047] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within this range, the strength of the positive electrode substrate can be increased while increasing the energy density per volume of the battery.

[0048] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The configuration of the intermediate layer is not particularly limited, and may contain, for example, a binder and a conductive agent.

[0049] The positive electrode active material layer is formed from a so-called positive electrode mixture containing a positive electrode active material, a sulfide-based solid electrolyte, and a binder. In this embodiment, the positive electrode active material layer preferably contains a conductive agent. The positive electrode active material layer may contain optional components such as a thickener and a filler as needed.

[0050] In this embodiment, the positive electrode active material includes a sulfur-containing positive electrode active material (sulfur active material). Known sulfur active materials can be used, including elemental sulfur and compounds containing sulfur element such as titanium sulfide, molybdenum sulfide, iron sulfide, copper sulfide, nickel sulfide, lithium sulfide, organic disulfide compounds, and carbon sulfide compounds.

[0051] The sulfur active material may be in the form of a composite with a conductive agent (a material with higher conductivity than elemental sulfur or a compound containing sulfur element). Examples of such composites include those in which the sulfur active material is supported on a conductive agent or the like as a carrier. Specific examples include composites of a sulfur active material and porous carbon (sulfur-porous carbon composites: SPCs). The lower limit of the sulfur element content (mass ratio of sulfur atoms to the mass of SPC) in the SPC is preferably 50% by mass, more preferably 60% by mass. Meanwhile, the upper limit of this content is preferably 90% by mass, more preferably 80% by mass. By setting the sulfur element content in the SPC within the above range, it is possible to achieve both high electrical capacity and good conductivity.

[0052] The lower limit of the content of elemental sulfur in the positive electrode active material layer (the mass ratio of sulfur atoms to the mass of the positive electrode active material layer) is preferably 15% by mass, more preferably 25% by mass. Meanwhile, the upper limit of this content is preferably 80% by mass, more preferably 70% by mass. When SPC is used, the lower limit of the content of SPC in the positive electrode active material layer is preferably 30% by mass, more preferably 35% by mass, and even more preferably 40% by mass. Meanwhile, the upper limit of this content is preferably 90% by mass, more preferably 80% by mass. By setting the content of elemental sulfur or SPC within the above range, it is possible to achieve both high electrical capacity and good conductivity, and to increase the energy density, etc.

[0053] The positive electrode active material may contain a positive electrode active material other than the sulfur active material. However, the lower limit of the sulfur element content (mass ratio of sulfur atoms to the mass of the total positive electrode active material) in the total positive electrode active material is preferably 30 mass%, more preferably 50 mass%, and even more preferably 70 mass%. The lower limit of the SPC content in the total positive electrode active material is preferably 80 mass%, more preferably 90 mass%, and even more preferably 99 mass%.

[0054] The conductive agent is not particularly limited as long as it is a material that is conductive. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include graphite and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Among these, carbonaceous materials are preferred from the viewpoints of conductivity and coatability. Acetylene black and ketjen black are particularly preferred. Examples of the conductive agent include powder, sheet, and fiber. The conductive agent may be in the form of a complex with the sulfur active material described above, or may be in a form other than a complex with the sulfur active material. That is, for example, the positive electrode active material layer may contain the conductive agent that constitutes the SPC and other conductive agents.

[0055] The content of the conductive agent (excluding the conductive agent in the SPC) in the positive electrode active material layer is preferably 1% by mass or more and 40% by mass or less, more preferably 3% by mass or more and 30% by mass or less, even more preferably 5% by mass or more and 20% by mass or less, and in some cases even more preferably 10% by mass or more. By setting the content of the conductive agent within the above range, the energy density of the battery can be increased.

[0056] As the positive electrode active material other than the sulfur active material, other known positive electrode active materials capable of absorbing and releasing lithium ions can be used. Examples of other positive electrode active materials include α-NaFeO ２ Examples of suitable chalcogen compounds include lithium transition metal composite oxides having a crystalline structure, lithium transition metal composite oxides having a spinel crystalline structure, polyanion compounds, and chalcogen compounds other than chalcogen compounds containing sulfur element.

[0057] The positive electrode active material is usually in the form of particles (powder). The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the average particle size of the positive electrode active material to the above-mentioned lower limit or more, the positive electrode active material can be easily manufactured or handled. By setting the average particle size of the positive electrode active material to the above-mentioned upper limit or less, the capacity during high-rate discharge can be increased. Note that when a composite of the positive electrode active material and another material is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material. "Average particle size" refers to the value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50% based on the particle size distribution measured by laser diffraction / scattering in a diluted solution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013).

[0058] To obtain a 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. As a classification method, a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

[0059] As the sulfide-based solid electrolyte, Li ６ PS ５ Cl, Li ２ S - P ２ S ５ 、Li ２ S - P ２ S ５ - LiI, Li ２ S - P ２ S ５ - LiCl, Li ２ S - P ２ S ５ - LiBr, Li ２ S - P ２ S ５ - Li ２ O, Li ２ S - P ２ S ５ - Li ２ O - LiI, Li ２ S - P ２ S ５ - Li ３ N, Li ２ S - SiS ２ 、Li ２ S - SiS ２ - LiI, Li ２ S - SiS ２ - LiBr, Li ２ S - SiS ２ - LiCl, Li ２ S - SiS ２ - B ２ S <000007​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​２ -Li ｘ MO ｙ (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga, and In.)

[0060] The content of the sulfide-based solid electrolyte in the positive electrode active material layer is preferably 10% by mass to 70% by mass, more preferably 20% by mass to 65% by mass, and even more preferably 30% by mass to 60% by mass. By setting the content of the sulfide-based solid electrolyte within this range, a high energy density of the positive electrode active material layer can be achieved.

[0061] As the solid electrolyte in the positive electrode active material layer, other solid electrolytes such as known halide-based solid electrolytes and oxide-based solid electrolytes may be used in combination within the range that does not impair the effects of the present invention.

[0062] Examples of binders include thermoplastic resins such as fluororesins, polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers. The binder is preferably a fluororesin. Using a fluororesin as the binder improves binding properties. Examples of fluororesins that can be used include copolymers of vinylidene fluoride monomers, such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), and vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), with one or more fluorine-containing monomers selected from tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, fluorovinyl, and perfluoroalkyl vinyl ether. Among these fluororesins, those that are soluble in the second solvent are preferred.

[0063] The content of the binder in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass, by which the positive electrode active material can be stably maintained.

[0064] Examples of thickeners 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. In this embodiment, the positive electrode active material layer does not need to contain a thickener such as that described in Patent Document 1. Even if the thickener described in Patent Document 1 is not contained, the binding property of the positive electrode active material layer is good.

[0065] The filler is not particularly limited, and examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, substances derived from mineral resources such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and artificial products thereof.

[0066] The positive electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, sulfide-based solid electrolyte, conductive agent, binder, thickener, and filler.

[0067] (Method for Producing Positive Electrode) In the present embodiment, to produce a positive electrode, it is preferable to knead a positive electrode active material, a sulfide-based solid electrolyte, a binder, a first solvent, a second solvent, and, as necessary, optional components such as a conductive agent, a thickener, and a filler to prepare a positive electrode slurry, and then apply the positive electrode slurry to a positive electrode substrate or the like and dry it to form a positive electrode active material layer.

[0068] Specific and preferred embodiments of the cathode active material, sulfide-based solid electrolyte, binder, and optional components such as a conductive agent, thickener, and filler as needed contained in the cathode slurry are the same as those of the cathode active material, sulfide-based solid electrolyte, binder, and optional components such as a conductive agent, thickener, and filler as needed contained in the cathode according to one embodiment of the present invention. The first solvent and second solvent are preferably mixed so that the solid content of the cathode slurry is 10 to 60 mass %.

[0069] (Solvent for Positive Electrode Slurry) In this embodiment, the positive electrode slurry contains a first solvent and a second solvent. The first solvent is at least one selected from a fluorinated ether and a fluorinated alkane, and the second solvent is a solvent containing a carboxylic acid ester and a CF 5 -terminated alkane. ３ The alkyl benzene compound is at least one selected from trifluoroalkyl benzenes and bis(trifluoroalkyl) benzenes having a - group.

[0070] Here, examples of the fluorinated ether that can be used as the first solvent include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, (1,2,2,2-tetrafluoroethyl)(heptafluoropropyl)ether, ethyl-1,1,2,2-tetrafluoroethyl ether, and 1,1,1,2,3,4,4,5,5,5-decafluoro-3-methoxy-2-(trifluoromethyl)pentane. Examples of the fluorinated alkane that can be used include 2H,3H-decafluoropentane, pentafluorobutane, 1H,6H-dodecafluorohexane, 1H-perfluorohexane, and 1H,1H,1H,2H,2H-nonafluorohexane.

[0071] Here, the second solvent is a carboxylic acid ester, and the terminal ３ At least one selected from trifluoroalkylbenzenes or bis(trifluoroalkyl)benzenes having a - group has a dispersion term δ ｄ、 polarity term δ ｐ , and the hydrogen bond term δ ｈ and the value of δ is 14.8 or less. ｄ ≦17.5, 1.0≦δｐ ≦7.0, and 1.0≦δ ｈ It is preferable that the solvent satisfies any of the ranges of ≦7.0.

[0072] As the carboxylic acid ester, butyl butyrate, butyl acetate, etc. can be used. ３ As the trifluoroalkylbenzene having a - group, trifluoromethylbenzene, 2,2,2-trifluoroethylbenzene, etc. can be used, and the terminal ３ As the bis(trifluoroalkyl)benzene having a - group, 1,2-bis(trifluoromethyl)benzene, 1,3-bis(trifluoromethyl)benzene, 1,4-bis(trifluoromethyl)benzene, etc. can be used.

[0073] The first solvent (fluorinated ether, fluorinated alkane) preferably has a boiling point of 50°C or higher and 220°C or lower, more preferably 65°C or higher and 190°C or lower, and even more preferably 80°C or higher and 160°C or lower. The boiling point of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 92°C, the boiling point of 2H,3H-decafluoropentane is 55°C, and the boiling point of 1H,6H-dodecafluorohexane is 84°C. By having the boiling point of the first solvent be higher than the above lower limit, the drying rate of the solvent contained in the positive electrode slurry can be prevented from being too fast, thereby improving the coatability. When a solvent with a relatively low boiling point is used as the first solvent, it is preferable to use a solvent with a relatively high boiling point as the second solvent in terms of coatability. When the boiling point of the first solvent is equal to or lower than the upper limit, the amount of residual solvent contained in the positive electrode active material layer after coating and drying the positive electrode slurry can be reduced, and the risk of the discharge capacity of the battery being reduced due to the influence of the residual solvent can be reduced.

[0074] The proportion of fluorine atoms contained in the molecular structure of the first solvent (fluorinated ether, fluorinated alkane) is preferably not too low, since this can suppress the solubility of sulfur in the first solvent. Also, the proportion of fluorine atoms contained in the molecular structure of the first solvent (fluorinated ether, fluorinated alkane) is preferably not too high, since this can improve compatibility with the second solvent and facilitate the preparation of a positive electrode slurry.

[0075] The boiling point of the second solvent is not particularly limited, but is preferably 80°C or higher and 220°C or lower, more preferably 95°C or higher and 200°C or lower, and even more preferably 110°C or higher and 180°C or lower. The boiling point of butyl butyrate is 160°C, and the boiling point of trifluoromethylbenzene (benzotrifluoride) is 101°C. By having the boiling point of the second solvent be equal to or higher than the lower limit, the drying rate of the solvent contained in the positive electrode slurry can be prevented from being too fast, and good coatability can be achieved. When a solvent with a relatively low boiling point is used as the second solvent, it is preferable to use a solvent with a relatively high boiling point as the first solvent in terms of coatability. By having the boiling point of the second solvent be equal to or lower than the upper limit, the amount of residual solvent contained in the positive electrode active material layer after coating and drying the positive electrode slurry can be reduced, and the risk of the discharge capacity of the battery decreasing due to the influence of the residual solvent can be reduced.

[0076] It is preferable to select a second solvent containing a fluorine element in its molecular structure, since this can suppress the solubility of sulfur in the second solvent. ３ Trifluoroalkylbenzenes and bis(trifluoroalkyl)benzenes containing - groups are particularly preferred.

[0077] More specifically, preferred combinations of the first solvent and the second solvent are as follows. When a first solvent having a boiling point of 50°C or higher and 65°C or lower is used, it is preferable to use a second solvent having a boiling point of 140°C or higher, and more preferably a boiling point of 160°C or higher. When a first solvent having a boiling point of 65°C or higher and 80°C or lower is used, it is preferable to use a second solvent having a boiling point of 120°C or higher, and more preferably a boiling point of 140°C or higher. By combining such a first solvent and a second solvent, the drying rate of the solvent contained in the positive electrode slurry can be prevented from being too fast, and good coatability can be achieved.

[0078] The mixing ratio (mass %) of the first solvent to the second solvent is preferably in the range of 99:1 to 10:90, more preferably 90:10 to 30:70. The positive electrode slurry may also contain an organic solvent other than the first solvent and the second solvent, as long as the effects of the present invention are not impaired.

[0079] (Method for Producing Positive Electrode Slurry) The kneading method for the positive electrode slurry is not particularly limited as long as it can dissolve the binder in the first solvent and the second solvent and can produce a positive electrode slurry with high dispersibility of the positive electrode active material, etc. For example, a general method using a dissolver, a homomixer, a kneader, a roll mill, a sand mill, an attritor, a ball mill, a vibrator mill, a high-speed impeller mill, an ultrasonic homogenizer, a shaker, etc. can be used.

[0080] The solid content of the positive electrode slurry is preferably 10 to 60 mass %, more preferably 25 to 45 mass %. The positive electrode slurry using the first solvent (fluorinated ether or fluorinated alkane) and the second solvent has good coatability even when the solid content is high.

[0081] (Coating method, drying method, etc. of positive electrode slurry) The positive electrode slurry can be coated on the positive electrode substrate, but can also be coated on the solid electrolyte layer. The method for coating the positive electrode slurry is not particularly limited. For example, common methods such as doctor blade method, die coating method, gravure coating method, spray coating method, electrostatic coating method, and bar coating method can be used. The coating thickness of the positive electrode slurry is appropriately selected depending on the desired thickness of the positive electrode active material layer.

[0082] The method for drying the positive electrode slurry after coating is not particularly limited as long as it does not deteriorate the positive electrode active material layer. For example, common methods such as warm air / hot air drying, infrared drying, reduced pressure drying, and dielectric heating drying can be used. Examples of the drying atmosphere include an inert gas atmosphere such as an argon gas atmosphere or a nitrogen gas atmosphere, an air atmosphere, and a reduced pressure atmosphere. Drying conditions are preferably, for example, 60°C to 150°C for 10 minutes to 12 hours.

[0083] The method for producing a positive electrode according to this embodiment may include any other steps in addition to the steps described above. Examples of such steps include a compression step. By including the compression step, a high-density positive electrode active material layer can be obtained, and a high energy density can be achieved by thinning the positive electrode active material layer. By the above method, a positive electrode having a positive electrode active material layer using the positive electrode slurry according to this embodiment can be produced.

[0084] (Negative Electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The intermediate layer may have the same structure as the intermediate layer of the positive electrode.

[0085] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, alloys thereof, and carbonaceous materials are used as the material for the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foils, vapor-deposited films, meshes, and porous materials, with foils being preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0086] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate and also increase the energy density per volume of the battery.

[0087] The negative electrode active material layer contains a negative electrode active material. In this embodiment, the negative electrode active material layer may be formed solely from a negative electrode active material, or may be formed from a negative electrode mixture containing the negative electrode active material. When the negative electrode active material layer is formed from a negative electrode mixture, optional components such as a conductive agent, a solid electrolyte, a binder, a thickener, and a filler may be included as needed. The solid electrolyte included in the negative electrode active material layer may be the same as the sulfide-based solid electrolyte included in the positive electrode active material layer. In addition, the optional components such as the conductive agent, the binder, the thickener, and the filler may be selected from the materials exemplified for the positive electrode. The negative electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, solid electrolyte, conductive agent, binder, thickener, and filler.

[0088] 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 a lithium ion secondary battery. Examples of the negative electrode active material include metal Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; lithium compounds; TiNb ２ O ７ Examples of the negative electrode active material include titanium-containing oxides such as titanium dioxide, polyphosphate compounds, silicon carbide, graphite, non-graphitic carbon (easily graphitizable carbon or non-graphitizable carbon), and other carbon materials. Among these negative electrode active materials, negative electrode active materials containing lithium element, such as metallic Li and lithium compounds, are preferably used. Among these, metallic Li is more preferred as the negative electrode active material. Metallic Li may be pure metallic Li consisting essentially of lithium element alone, or may be a lithium alloy containing other metal elements. Examples of the lithium alloy include lithium silver alloy, lithium zinc alloy, lithium calcium alloy, lithium aluminum alloy, lithium magnesium alloy, and lithium indium alloy. The lithium alloy may contain multiple metal elements other than lithium element. Examples of the lithium compound include Li ４ Ti ５ O １２ , LiTiO ２ In the negative electrode active material layer, one of these materials may be used alone, or two or more of them may be used in combination as needed.

[0089] "Graphite" refers to a graphite material that has an average lattice spacing (d ００２ ) is 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the viewpoint of being able to obtain a material with stable physical properties.

[0090] "Non-graphitic carbon" refers to a carbon material that has an average lattice spacing (d ００２) is 0.34 nm or more and 0.42 nm or less. Examples of non-graphitizable carbon include non-graphitizable carbon and graphitizable carbon. Examples of non-graphitizable 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.

[0091] Here, the "discharged state" refers to a state in which the battery is discharged so that lithium ions capable of being absorbed and desorbed during charging and discharging are sufficiently released from the carbon material serving as the negative electrode active material. For example, this refers to a state in which the open circuit voltage of a half cell using a negative electrode containing a carbon material as the negative electrode active material as the working electrode and metallic Li as the counter electrode is 0.7 V or higher.

[0092] "Non-graphitizable carbon" refers to the above-mentioned d ００２ The term "carbon material" refers to a carbon material having a particle size of 0.36 nm or more and 0.42 nm or less.

[0093] "Graphitizable carbon" refers to the above-mentioned d ００２ The term "carbon material" refers to a carbon material having a particle size of 0.34 nm or more and less than 0.36 nm.

[0094] The negative electrode active material is usually in the form of particles (powder). The average particle size 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 size 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 size may be 1 nm or more and 1 μm or less. By setting the average particle size of the negative electrode active material to the above lower limit or more, the negative electrode active material can be easily manufactured or handled. By setting the average particle size of the negative electrode active material to the above upper limit or less, the capacity during high-rate discharge can be increased. To obtain the negative electrode active material with a predetermined particle size, a pulverizer, a classifier, or the like is used. The pulverization method and classification method can be selected from, for example, 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.

[0095] The content of the negative electrode active material in the negative electrode active material layer is preferably 33% by mass or more and 95% by mass or less, more preferably 50% by mass or more and 90% by mass or less, and even more preferably 60% by mass or more and 80% by mass or less. By setting the content of the negative electrode active material within this range, both high energy density and manufacturability of the negative electrode active material layer can be achieved. When the negative electrode active material is a metal such as metallic Li, the content of the negative electrode active material in the negative electrode active material layer may be 99% by mass or more, or may be 100% by mass.

[0096] (Method for Manufacturing Negative Electrode) The method for manufacturing the negative electrode is not particularly limited, but examples thereof include the following methods. For example, when the negative electrode active material layer is formed from a negative electrode mixture, a negative electrode active material, a solid electrolyte, a binder, an organic solvent (dispersion medium), and, if necessary, optional components such as a conductive agent, a thickener, and a filler are kneaded to prepare a negative electrode slurry, and this negative electrode slurry is applied to the negative electrode substrate or the like and dried to obtain a negative electrode active material layer. The negative electrode slurry may further contain other materials such as a binder, a thickener, and a filler as necessary. The other materials such as the binder, the thickener, and the filler can be selected from the materials exemplified for the positive electrode.

[0097] The content of the solid electrolyte in the negative electrode slurry is preferably in the range of 10% by mass to 90% by mass, and more preferably in the range of 30% by mass to 70% by mass.

[0098] The method for kneading the negative electrode slurry can be the same as the method for kneading the positive electrode slurry described above.

[0099] The negative electrode slurry can be applied to the negative electrode substrate, but can also be applied to the solid electrolyte layer. The method for applying the negative electrode slurry can be the same as the method for applying the positive electrode slurry described above. The coating thickness of the negative electrode slurry can be appropriately selected depending on the purpose.

[0100] The method for drying the negative electrode slurry after application can be the same as the method for drying the positive electrode slurry described above. The thickness of the negative electrode active material layer formed by this step can be appropriately selected depending on the purpose.

[0101] Another method for producing a negative electrode is to form a metal film serving as a negative electrode active material layer on the negative electrode substrate, and the metal contained in the metal film is selected from the metals (pure metals and alloys) exemplified as the negative electrode active material for the negative electrode.

[0102] The method for forming the metal film is not particularly limited, and any known layer or film forming method can be used. For example, methods such as compression bonding, coating, sputtering, and vapor deposition can be used. The thickness of the metal film formed by this process can be appropriately selected depending on the purpose.

[0103] The method for producing a negative electrode according to the present embodiment may include any other steps in addition to the steps described above. Examples of such steps include a compression step. By including the compression step, a high-density negative electrode active material layer can be obtained, and a high energy density can be achieved by reducing the thickness of the negative electrode active material layer.

[0104] (Solid Electrolyte Layer) In this embodiment, the solid electrolyte constituting the solid electrolyte layer is preferably a sulfide-based solid electrolyte. As the sulfide-based solid electrolyte, the same sulfide-based solid electrolyte as that contained in the positive electrode active material layer can be used. Known halide-based solid electrolytes, oxide-based solid electrolytes, etc. may be used together with or instead of the sulfide-based solid electrolyte.

[0105] (Method for Producing Solid Electrolyte Layer) In this embodiment, to produce a solid electrolyte layer, it is preferable to knead a solid electrolyte and an organic solvent (dispersion medium) to prepare a solid electrolyte layer-forming slurry, and then apply the solid electrolyte layer-forming slurry to a substrate and dry it to form a solid electrolyte layer. The solid electrolyte layer-forming slurry may further contain other materials such as a binder, a thickener, a filler, etc. as needed. Of these, it is preferable that the solid electrolyte layer-forming slurry further contains a binder. The other materials such as the binder, the thickener, the filler, etc. can be selected from the materials exemplified for the positive electrode.

[0106] The content of the solid electrolyte in the solid electrolyte layer forming slurry is preferably in the range of 10% by mass to 90% by mass, more preferably in the range of 40% by mass to 70% by mass.

[0107] The solid electrolyte layer-forming slurry can be applied to, for example, a peelable substrate such as a metal foil or a fluorine-based resin sheet, an electrode active material layer, or the like. When applied to an electrode active material layer, it can be applied directly onto a positive electrode active material layer or a negative electrode active material layer. The method for applying the solid electrolyte layer-forming slurry can be the same as the method for applying the positive electrode slurry described above. The coating thickness of the solid electrolyte layer-forming slurry can be appropriately selected depending on the purpose.

[0108] The method for drying the solid electrolyte layer-forming slurry after application can be the same as the method for drying the positive electrode slurry described above. The thickness of the solid electrolyte layer formed by this step is, for example, preferably in the range of 0.01 μm to 1000 μm, more preferably in the range of 0.1 μm to 200 μm.

[0109] The method for producing a solid electrolyte layer in this embodiment may include any other steps in addition to the steps described above. Examples of such steps include a compression step. By including the compression step, a high-density solid electrolyte layer can be obtained, and the ion conductivity can be improved and the energy density can be increased by reducing the thickness of the solid electrolyte layer.

[0110] <Battery Manufacturing Method> The battery manufacturing method of this embodiment can be appropriately selected from known methods. When the battery of this embodiment is an all-solid-state secondary battery, the manufacturing method includes, for example, forming a cathode active material layer by the cathode manufacturing method described above, forming an anode active material layer by the anode manufacturing method, forming a solid electrolyte layer by the solid electrolyte layer manufacturing method, and stacking a cathode having a cathode active material layer and a negative electrode having a negative electrode active material layer via the solid electrolyte layer to form an electrode assembly. In addition, in this manufacturing method, after forming the solid electrolyte layer, a cathode may be formed on the solid electrolyte layer, and an electrode assembly may be formed using the stack of the cathode and solid electrolyte layer and a separately formed negative electrode. For example, a solid electrolyte layer is formed by pressing at room temperature at a pressure of 100 MPa, and then a positive electrode obtained by applying the positive electrode slurry to a positive electrode substrate as described above and drying the positive electrode is placed on the solid electrolyte layer and bonded by pressing at room temperature or 160°C at a pressure of 360 MPa to form a laminate, and this laminate and a negative electrode (In foil and Li foil as negative electrode active materials, and SUS foil as negative electrode substrate) are placed on top of each other and bonded by pressing at room temperature at a pressure of 50 MPa to form an electrode body, thereby obtaining an all-solid-state secondary battery. Conversely to the above manufacturing method, a negative electrode may be formed on a solid electrolyte layer to form a laminate, and then the laminate of the negative electrode and solid electrolyte layer and a separately formed positive electrode may be used to form an electrode body.

[0111] The shape of the battery of this embodiment is not particularly limited. Examples include cylindrical batteries, prismatic batteries, flat batteries, coin batteries, and button batteries. For example, an all-solid-state secondary battery 10 shown in FIG. 1 , in which a positive electrode 1 and a negative electrode 2 are stacked with a solid electrolyte layer 3 interposed therebetween, can be housed in a prismatic container to form a prismatic battery.

[0112] <Configuration of Power Storage Device> The battery of this embodiment can be installed as a power storage unit (battery module) configured by assembling multiple batteries in automobile power sources such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), power sources for electronic devices such as personal computers and communication terminals, or power storage power sources. In this case, the technology of the present invention only needs to be applied to at least one battery included in the power storage unit. FIG. 2 shows an example of a power storage device 30 in which power storage units 20, each of which is an assembly of two or more electrically connected all-solid-state secondary batteries 10, are further assembled. The power storage device 30 may include a bus bar (not shown) that electrically connects the two or more all-solid-state secondary batteries 10, a bus bar (not shown) that electrically connects the two or more power storage units 20, or the like. The power storage unit 20 or the power storage device 30 may include a status monitoring device (not shown) that monitors the status of the one or more all-solid-state secondary batteries.

[0113] <Other Embodiments> The battery 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, or 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.

[0114] 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.

[0115] [Example 1] (Preparation of sulfide-based solid electrolyte) Li ２ S (0.478 g) and P ２ S ５(0.772 g) were mixed in an agate mortar. The mixture was placed in a sealed 80 mL zirconia pot containing 160 g of zirconia balls with a diameter of 4 mm. These steps were carried out in an argon atmosphere with a dew point of -50°C or less. Next, mechanical milling was carried out for 45 hours using a planetary ball mill (manufactured by FRITSCH, model number Premium line P-7) at an orbital rotation speed of 510 rpm to obtain 75Li, a sulfide-based solid electrolyte. ２ S・25P ２ S ５ (LPS) was obtained.

[0116] (Preparation of sulfur-porous carbon composite) Sulfur (manufactured by Aldrich) and activated carbon MH-00 (manufactured by Toyo Tanso), which is porous carbon, were mixed in a mass ratio of 65:35 to obtain mixture A. This mixture A was placed in a sealed electric furnace. The electric furnace was heated to 150°C at a heating rate of 5°C / min, held for 5 hours, and then allowed to cool to 80°C, at which point sulfur solidifies. Thereafter, the temperature was again raised to 300°C at a heating rate of 5°C / min and held for 2 hours, during which heat treatment was performed, and the mixture was allowed to cool to room temperature to produce a sulfur-porous carbon composite.

[0117] (Preparation of sulfur-porous carbon-solid electrolyte composite) The sulfur-porous carbon composite prepared above and the LPS prepared above were mixed in a mass ratio of 60:40 to obtain mixture B. This mixture B was placed in a sealed 80 mL zirconia pot containing 100 g of zirconia balls with a diameter of 4 mm. These steps were carried out in an argon atmosphere with a dew point of −50°C or lower. Next, the mixture was composited by mechanical milling using a planetary ball mill at an orbital rotation speed of 300 rpm for 15 minutes to obtain a sulfur-porous carbon-solid electrolyte composite.

[0118] (Preparation of Positive Electrode Slurry and Positive Electrode) 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, a fluorinated ether serving as a first solvent, and butyl butyrate, a carboxylic acid ester serving as a second solvent, were mixed in a mass ratio of 60:40 to prepare a 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether / butyl butyrate mixed solvent. 0.2 g of the binder fluororesin PVdF-HFP (soluble in butyl butyrate) and 3.8 g of the mixed solvent were placed in a glass container and stirred with a magnetic stirrer for 12 hours or more to dissolve the binder, thereby obtaining binder solution 1. 67.5 parts by mass of the sulfur-porous carbon-solid electrolyte composite prepared above (40.5 parts by mass of sulfur-porous carbon composite, 27 parts by mass of LPS) and acetylene black (conductive agent, BET specific surface area: 45 m) were added to the glass container. ２ 2.25 parts by mass of PVdF-HFP (Li / g) was mixed with 2.25 parts by mass of binder solution 1 so that the total weight of PVdF-HFP was 5.25 parts by mass (solid content equivalent), and the mixture was kneaded using a planetary centrifugal mixer. ６ P.S. ５ Cl, BET specific surface area: 14m ２ 25 parts by mass of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether / butyl butyrate mixed solvent prepared above was added thereto, and the mixture was further kneaded using a planetary centrifugal mixer to obtain a positive electrode slurry (solid content ratio: 35% by mass) according to Example 1. The obtained positive electrode slurry was applied to an Al foil serving as a positive electrode substrate, and dried under reduced pressure at 80°C to form a positive electrode active material layer, thereby obtaining a positive electrode according to Example 1.

[0119] [Example 2] 2H,3H-decafluoropentane, a fluorinated alkane serving as a first solvent, and butyl butyrate, a carboxylic acid ester serving as a second solvent, were mixed in a mass ratio of 60:40 to prepare a 2H,3H-decafluoropentane / butyl butyrate mixed solvent. Except for using this mixed solvent, a binder solution 2 and a positive electrode slurry according to Example 2 were obtained in the same manner as Example 1. Except for using the obtained positive electrode slurry, a positive electrode according to Example 2 was obtained in the same manner as Example 1.

[0120] Example 3 A fluorinated ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, was used as the first solvent, and a CF -terminated solvent was used as the second solvent. ３ A 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether / trifluoromethylbenzene mixed solvent was prepared by mixing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and trifluoromethylbenzene, a trifluoroalkylbenzene having a - group, in a mass ratio of 60:40. Except for using this mixed solvent, binder solution 3 and a positive electrode slurry according to Example 3 were obtained in the same manner as Example 1. Except for using the obtained positive electrode slurry, a positive electrode according to Example 3 was obtained in the same manner as Example 1.

[0121] Example 4: A fluorinated alkane, 1H,6H-dodecafluorohexane, was used as the first solvent, and a CF -terminated alkane was used as the second solvent. ３ A 1H,6H-dodecafluorohexane / trifluoromethylbenzene mixed solvent was prepared by mixing 1H,6H-dodecafluorohexane and trifluoromethylbenzene, a trifluoroalkylbenzene having a - group, in a mass ratio of 60:40. Except for using this mixed solvent, binder solution 4 and a positive electrode slurry according to Example 4 were obtained in the same manner as in Example 1. Except for using the obtained positive electrode slurry, a positive electrode according to Example 4 was obtained in the same manner as in Example 1.

[0122] [Comparative Example 1] A binder solution and a positive electrode slurry according to Comparative Example 1 were obtained in the same manner as in Example 1, except that only butyl butyrate was used as the solvent instead of the fluorinated ether / butyl butyrate mixed solvent. A positive electrode according to Comparative Example 1 was obtained in the same manner as in Example 1, except that the obtained positive electrode slurry was used.

[0123] [Comparative Example 2] A binder solution and a positive electrode slurry according to Comparative Example 2 were obtained in the same manner as in Example 3, except that only trifluoromethylbenzene was used as the solvent instead of the fluorinated ether / trifluoromethylbenzene mixed solvent. A positive electrode according to Comparative Example 2 was obtained in the same manner as in Example 1, except that the obtained positive electrode slurry was used.

[0124] Comparative Example 3 A binder solution and a positive electrode slurry according to Comparative Example 3 were obtained in the same manner as in Example 1, except that toluene was used as the solvent instead of the fluorinated ether / butyl butyrate mixed solvent.

[0125] Comparative Example 4 A binder solution and a positive electrode slurry according to Comparative Example 4 were obtained in the same manner as in Example 1, except that xylene was used as the solvent instead of the fluorinated ether / butyl butyrate mixed solvent.

[0126] The obtained positive electrodes of Examples 1 to 4 and Comparative Examples 1 and 2 were evaluated for coatability and binding ability, and charge-discharge tests were conducted. The results are shown in Table 1. The evaluation methods and charge-discharge test conditions are as follows. Note that in the binder solutions of Comparative Examples 3 and 4, which used toluene or xylene as the solvent, only a small amount of the binder dissolved in the solvent, so a coatable positive electrode slurry could not be obtained.

[0127] (Coatability Evaluation) The appearance of the positive electrode obtained by coating and drying the positive electrode slurry was observed to check for the presence or absence of smearing of the positive electrode active material layer, lumps, exposed Al foil, etc. The cases where there was almost no smearing of the positive electrode active material layer, lumps, or exposed Al foil were evaluated as ◯, and the cases where there was a significant smearing of the positive electrode active material layer, lumps, or exposed Al foil were evaluated as ×.

[0128] (Evaluation of adhesion) The positive electrode slurry was applied and dried to obtain a positive electrode, which was punched out to a diameter of 10 mm using an "electrode punch hand punch" (product name, manufactured by Nogami Giken Kogyo Co., Ltd.), and the degree of peeling (cracks, chips, powder falling, etc.) of the positive electrode active material layer from the Al foil was evaluated. After punching, positive electrodes in which the positive electrode active material layer was not peeled off at all from the Al foil were evaluated as ◯, and positive electrodes in which even a portion of the positive electrode active material layer was peeled off were evaluated as ×.

[0129] (Fabrication of Battery (All-Solid-State Secondary Battery)) The positive electrodes according to Examples 1 to 4 and Comparative Examples 1 and 2 were punched out to a diameter of 10 mm using an "electrode punch hand punch" (product name, manufactured by Nogami Giken Kogyo Co., Ltd.). An argyrodite-type solid electrolyte (Li ６ P.S. ５80 mg of HCl was inserted and pressure-molded using a uniaxial press at a pressure of 50 MPa for several seconds to form a solid electrolyte layer 3. After releasing the pressure, the above-mentioned positive electrode was laminated on one side of the solid electrolyte layer so that the positive electrode active material layer 5 faced the solid electrolyte layer, and then pressed using a uniaxial press at 400 MPa for 5 minutes. After releasing the pressure, In foil (manufactured by Nilaco, average thickness 100 μm, diameter 10 mm) and Li foil (manufactured by Honjo Metal, average thickness 100 μm, diameter 8 mm) were laminated on the side opposite the laminated surface of the above-mentioned positive electrode, and pressed using a uniaxial press at a pressure of 50 MPa for several seconds to form a negative electrode active material layer 6 made of a LiIn alloy. This was then removed from the ceramic powder molding machine to obtain a battery (all-solid-state secondary battery).

[0130] (Charge / Discharge Test) A charge / discharge test was carried out on each battery (all-solid-state secondary battery) using the positive electrodes according to Examples 1 to 4 and Comparative Examples 1 and 2. Charging was performed at a constant current of 0.1 C, with an upper limit voltage of 2.4 V. Discharging was performed at a constant current of 0.1 C, with a lower limit voltage of 0.7 V. A 10-minute rest period was provided after each charging and discharging. This charging / discharging cycle was carried out for two cycles, and the discharge capacity (mAh / g) of the second cycle was recorded. The results are shown in Table 1. Note that the discharge capacities shown in Table 1 are all discharge capacities per unit mass of sulfur.

[0131]

[0132] The positive electrode obtained using the positive electrode slurry of Comparative Example 1, which contained only butyl butyrate as the solvent, showed poor adhesion, with the positive electrode active material layer partially peeling off from the Al foil substrate at the edge of the positive electrode. The discharge capacity was also low. This is presumably due to the fact that the use of only butyl butyrate as the solvent for the positive electrode slurry failed to suppress dissolution of sulfur into the butyl butyrate. The positive electrode obtained using the positive electrode slurry of Comparative Example 2, which contained only trifluoromethylbenzene as the solvent, showed poor coatability, with the occurrence of lumps and exposure of the Al foil, the positive electrode substrate. This is presumably due to the low boiling point of trifluoromethylbenzene used as the solvent for the positive electrode slurry (101°C), which prevented the drying rate of the solvent contained in the positive electrode slurry from being suppressed, and the poor fluidity of the positive electrode slurry resulting from the failure to suppress dissolution of sulfur into trifluoromethylbenzene. In contrast to these, the first solvent is a fluorinated ether or a fluorinated alkane, and the second solvent is butyl butyrate (a carboxylic acid ester) or trifluoromethylbenzene (with CF at the end). ３ The positive electrodes obtained using the positive electrode slurries of Examples 1 to 4, which used a mixed solvent combining a fluorinated ether and a fluorinated alkane (a trifluoroalkylbenzene having a - group), exhibited good performance in all of coatability, binding ability, and discharge capacity. Although the first solvents, fluorinated ether and fluorinated alkane, have lower boiling points than the second solvent, trifluoromethylbenzene, the positive electrode slurries of Examples 3 and 4, which used a mixture of the two, had better coatability than the positive electrode slurry of Comparative Example 2, which used trifluoromethylbenzene alone. Therefore, it is presumed that by using a mixture of the first solvent and the second solvent, the solubility of sulfur in the mixed solvent was suppressed, and as a result, a positive electrode slurry with good fluidity was obtained.

[0133] (Relationship between the Hansen Solubility Parameter (HSP Value) of a Solvent and Binder Solubility) As described above, in the binder solutions of Comparative Examples 3 and 4, which used toluene or xylene as the solvent, the binder was only slightly soluble in the solvent, and therefore the effectiveness as a positive electrode slurry could not be confirmed. On the other hand, in the above Examples, the second solvent was a solvent in which the binder was highly soluble. Therefore, the relationship between the binder solubility and the HSP value and SP value of the solvent was investigated. Regarding binder solubility, 0.2 g of the binder fluororesin PVdF-HFP (soluble in butyl butyrate) and 3.8 g of each solvent were placed in a glass container and stirred with a magnetic stirrer for 12 hours or more. A score of ◯ was given to the binder solution in which no residual binder was observed, and a score of × was given to the binder solution in which residual binder was observed or the binder was barely dissolved. Based on the chemical structure of the target compound, the HSP value (dispersion term δ ｄ、 polarity term δ ｐ , and the hydrogen bond term δ ｈ ) and SP value σ ｔ The calculation was performed using the Y-MB method in the DYI program of Hansen Solubility Parameters in Practice (HSPiP) ver. 5.4.03. The SP value σ ｔ and HSP value (variance term δ ｄ、 polarity term δ ｐ , and the hydrogen bond term δ ｈ The relationship between σ and σ is expressed by the following equation (1): ｔ ２ = δ ｄ ２ +δ ｐ ２ +δ ｈ ２ ...(1) Table 2 shows the relationship between the Hansen solubility parameter (HSP value) of the solvent, the SP value and the binder solubility.

[0134]

[0135] From Table 2, the following can be seen: ｄ、 polarity term δ ｐ , and the hydrogen bond term δ ｈ and the value of δ is 14.8 or less.ｄ ≦17.5, 1.0≦δ ｐ ≦7.0, and 1.0≦δ ｈ The solvents 1,3-bis(trifluoromethyl)benzene, 1,4-bis(trifluoromethyl)benzene, (trifluoromethyl)benzene, butyl butyrate, and butyl acetate, which satisfy any of the ranges of 7.0 or less, have good binder solubility (○). In contrast, the fluorinated ethers 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether have a dispersion term δ ｄ is less than 14.8, and m-xylene, mesitylene, toluene, tetralin, anisole, and acetophenone have a dispersion term δ ｄ is greater than 17.5, and heptane and decane have a polar term δ ｐ and the hydrogen bond term δ ｈ is less than 1.0, which does not satisfy the above range, and therefore the binder solubility is not good (×). Furthermore, it can be seen that even solvents with similar SP values, such as decane and 1,3-bis(trifluoromethyl)benzene, have different binder solubility.

[0136] In this embodiment, the dispersion term δ in the Hansen solubility parameter (HSP value) of 1,3-bis(trifluoromethyl)benzene, 1,4-bis(trifluoromethyl)benzene, (trifluoromethyl)benzene, butyl butyrate, butyl acetate, etc., which have good binder solubility, is ｄ、 polarity term δ ｐ , and the hydrogen bond term δ ｈ and the value of δ is 14.8 or less. ｄ ≦17.5, 1.0≦δ ｐ ≦7.0, and 1.0≦δ ｈ It can be said that by combining a second solvent "which satisfies any of the ranges of 0.1 to 7.0" with a first solvent which is "one or more solvents selected from fluorinated ethers and fluorinated alkanes," a positive electrode slurry, a positive electrode, and a battery which are all excellent in coatability, binding property, and discharge capacity can be obtained.

[0137] (Sulfur Solubility Confirmation Test in Solvents) To evaluate the sulfur solubility of the solvents, sulfur was immersed in each solvent and the appearance was confirmed after 7 days. The volumes of the solvents and the masses of the sulfur were all approximately the same. Observing the appearance of the sulfur after 7 days of immersion in the solvents revealed that the number of sulfur particles decreased in the sample impregnated with butyl butyrate, indicating that butyl butyrate dissolves sulfur. Furthermore, the number of sulfur particles did not decrease in the sample impregnated with (trifluoromethyl)benzene, but aggregation between the particles was observed, indicating that sulfur dissolves, although not as well as butyl butyrate. On the other hand, when the sample was immersed in 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2H,3H-decafluoropentane, or 1H,6H-dodecafluorohexane, neither a decrease in the number of sulfur particles nor aggregation between the particles was observed, confirming that the sample had almost no sulfur solubility.

[0138] As described above, it is believed that the solubility of sulfur significantly affects the binding, coating properties, and discharge capacity of the positive electrode, and the boiling point of the solvent significantly affects the coating properties of the positive electrode. It has been found that bis(trifluoroalkyl)benzenes (1,3-bis(trifluoromethyl)benzene, 1,4-bis(trifluoromethyl)benzene) have sulfur solubility almost equivalent to that of (trifluoromethyl)benzene. Therefore, when 1,3-bis(trifluoromethyl)benzene (boiling point 116 ° C.) or 1,4-bis(trifluoromethyl)benzene (boiling point 117 ° C.), which have boiling points similar to those of (trifluoromethyl)benzene (boiling point 101 ° C.), are used as the second solvent, as in the case of (trifluoromethyl)benzene, by combining it with the first solvent, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether or 1H,6H-dodecafluorohexane, it is predicted that a positive electrode with good coating properties, binding properties, and discharge capacity can be obtained.

[0139] The positive electrode slurry according to one aspect of the present invention, the positive electrode using this positive electrode slurry, and the battery including this positive electrode are all excellent in coatability, binding property, and discharge capacity, and therefore this battery has high productivity and is useful as a battery for hybrid vehicles, plug-in hybrid vehicles, and electric vehicles.

[0140] REFERENCE SIGNS LIST 1 positive electrode 2 negative electrode 3 solid electrolyte layer 4 positive electrode substrate 5 positive electrode active material layer 6 negative electrode active material layer 7 negative electrode substrate 10 all-solid-state secondary battery 20 power storage unit 30 power storage device

Claims

1. A cathode active material containing sulfur, a sulfide-based solid electrolyte, a binder, a first solvent, and a second solvent, the first solvent being at least one selected from a fluorinated ether and a fluorinated alkane, and the second solvent being at least one selected from a dispersion term δ in the Hansen solubility parameter (HSP value). ｄ、 polarity term δ ｐ , and the hydrogen bond term δ ｈ and the value of 14.8≦δ ｄ ≦17.5, 1.0≦δ ｐ ≦7.0, and 1.0≦δ ｈ ≦7.0 2. The positive electrode slurry according to claim 1, wherein the binder is a fluororesin.

3. A cathode active material containing sulfur, a sulfide-based solid electrolyte, a binder, a first solvent, and a second solvent, the first solvent being at least one selected from a fluorinated ether and a fluorinated alkane, the second solvent being at least one selected from a carboxylate ester and a CF ３ The positive electrode slurry is at least one selected from trifluoroalkylbenzenes and bis(trifluoroalkyl)benzenes having a - group.

4. A positive electrode using the positive electrode slurry according to any one of claims 1 to 3.

5. A method for producing a positive electrode, comprising applying the positive electrode slurry according to any one of claims 1 to 3 to a substrate and drying the applied slurry.

6. A battery comprising the positive electrode according to claim 4.

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