Nonwoven fabric and solid electrolyte supporting sheet

Abstract

The present invention addresses the problem of providing: a solid electrolyte loaded sheet which is loaded with solid electrolyte particles in the spaces between fibers, and which is capable of achieving a good balance among reduction in the thickness, fall-off of the solid electrolyte particles and electrical conductivity; and a nonwoven fabric which is suitable for the formation of this solid electrolyte loaded sheet. A nonwoven fabric according to the present invention is characterized by satisfying 0.25 ≤ (L2 / V) ≤ 10, where L (μm) is the average fiber diameter of all fibers and V is the volume (cm3) per 1 m2; and it is preferable that this nonwoven fabric contains fibers having a fiber diameter of 1.0 μm or less and fibers having a fiber diameter of more than 1.0 μm.

Description

[Technical Field]

[0001] The present invention relates to a solid electrolyte supporting sheet in which solid electrolyte particles are supported between fibers, and a nonwoven fabric suitable for forming the sheet. [Background technology]

[0002] Even after all-solid-state lithium-ion batteries have been put into practical use, research into them continues to be actively pursued. In such all-solid-state lithium-ion batteries, a solid electrolyte-containing sheet, which mainly contains a solid electrolyte containing a sulfide or the like, is used as a material for forming the solid electrolyte layer. Since solid electrolytes are generally in the form of particles and it is difficult to form a sheet using the solid electrolyte alone, attempts have been made to form a sheet by mixing the solid electrolyte with a thermoplastic resin, or to combine solid electrolyte particles (particle diameter usually 1 to several tens of μm) with a sheet-like reinforcing material (support) having voids.

[0003] For example, Patent Document 1 discloses a solid electrolyte sheet including a glass solid electrolyte containing at least lithium (Li) and sulfur (S) and a support made of electronically insulating inorganic fibers, and proposes a solid electrolyte sheet using glass paper, primarily composed of chopped strand glass fibers, as the support. In the case of glass nonwoven fabric, chopped strands of long glass fibers (6 to 11 μm diameter, several to several tens of mm long) are made into paper and impregnated with a wet organic binder resin to impart strength. The amount of organic binder resin is around 10%.

[0004] Furthermore, Patent Document 2 discloses a solid electrolyte sheet in which a solid electrolyte is filled into openings in a support made of woven glass fiber fabric. Furthermore, Patent Document 3 discloses a solid electrolyte sheet including a sheet-like porous substrate and an inorganic solid electrolyte material filled in the pores of the porous substrate, and the porous substrate is made of a PET nonwoven fabric or a natural fiber / PET / acrylic resin-coated nonwoven fabric.

[0005] Here, the higher the uniformity of the solid electrolyte in the solid electrolyte-containing sheet used to manufacture the solid electrolyte layer of the all-solid-state lithium ion battery, the more preferable. In order to manufacture a solid electrolyte-containing sheet in which the solid electrolyte is more uniformly contained using a sheet-like reinforcing material (support) and solid electrolyte particles, either a dry method or a wet method can be applied, but the wet method is preferred. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-96311 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-127982 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-153460 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the case of the technology described in Patent Document 1, even if solid electrolyte particles are arranged by a wet method using a nonwoven fabric made of thick glass fibers (6 to 11 μm diameter) as a reinforcing material, there is a problem that the particles easily fall off during subsequent handling. While it is conceivable to use an adhesive in combination to improve the powder falling off, there is a problem that the electrical conductivity decreases because the adhesive component does not have ionic conductivity. Furthermore, although the use of thin fibers improves powder shedding, it is difficult to arrange the solid electrolyte particles uniformly throughout the nonwoven fabric, including the interior thereof, and the desired conductivity cannot be obtained.

[0008] An object of the present invention is to provide a solid electrolyte-supporting sheet in which solid electrolyte particles are supported between fibers, which can be made thin and which can achieve both good dusting resistance of the solid electrolyte particles and good electrical conductivity, and a nonwoven fabric suitable for forming the sheet. [Means for solving the problem]

[0009] The present invention is illustrated below. 1. The average fiber diameter of all fibers is L (μm), 1 m 2 Volume per (cm 3 ) is V, 0.25≦(L 2 / V)≦10. Below is the calculation formula L 2 / V is called the "mesh opening index." 2. The nonwoven fabric according to item 1, comprising fibers (F1) having a fiber diameter of 1.0 μm or less and fibers (F2) having a fiber diameter of more than 1.0 μm. 3. The nonwoven fabric according to item 1 or 2, wherein the average fiber diameter is 0.85 μm or more. 4. The nonwoven fabric according to item 2 or 3, wherein the fibers (F1) contain inorganic fibers. 5. The nonwoven fabric according to any one of items 2 to 4, wherein the fibers (F2) contain resin fibers. 6. The nonwoven fabric according to item 5, wherein the fibers (F2) further contain inorganic fibers. 7. The nonwoven fabric according to item 5 or 6, wherein at least a portion of the resin fibers bond the fibers constituting the nonwoven fabric together. 8. The nonwoven fabric according to any one of items 1 to 7, which is used to support solid electrolyte particles. 9. A solid electrolyte-supporting sheet, characterized in that solid electrolyte particles are supported between the fibers constituting the nonwoven fabric according to any one of items 1 to 8 above. 10. The amount of the solid electrolyte particles supported is 10 to 200 g / m 2 10. A solid electrolyte-supporting sheet according to item 9, wherein [Effects of the Invention]

[0010] The nonwoven fabric of the present invention has an opening index within a specific range, which makes it easy to fill the voids in the nonwoven fabric with solid electrolyte particles, suppresses the powder shedding of the solid electrolyte particles, and makes the nonwoven fabric suitable as a material for forming a solid electrolyte-supported sheet having the desired electrical conductivity. The solid electrolyte-supporting sheet of the present invention can be made thin, and has good electrical conductivity and good dusting properties of the solid electrolyte particles, and is therefore suitable as a component for manufacturing all-solid-state lithium-ion batteries. DETAILED DESCRIPTION OF THE INVENTION

[0011] The nonwoven fabric of the present invention is obtained, for example, by piling raw material fibers in a certain direction or randomly and binding them with an adhesive, by mechanically entangling them as in papermaking, by entangling them with a pressurized water stream, or by binding them with heat-fusible fibers, and is a fiber assembly that satisfies the following formula (1): 0.25≦(L 2 / V)≦10 (1) In the above formula (1), L is the average fiber diameter (μm) of all fibers constituting the nonwoven fabric, and V is the average fiber diameter (μm) of 1 m of the nonwoven fabric. 2 Volume per (cm 3 / m 2 (hereinafter referred to as "occupied volume").

[0012] In the present invention, the diameter of a fiber (fiber diameter) means the long diameter when the fiber is viewed in cross section. In addition, in the above formula (1), the average fiber diameter L is calculated based on the BET specific surface area (m 2 / g) and average density (g / cm 3 ) is calculated from the following formula (2), and the occupied volume V is calculated based on the basis weight (g / m 2 ) and the density and content of each fiber contained in the nonwoven fabric, and, if necessary, the adhesive and its density. Average density = Σ [density of individual fibers × content (mass%) / 100] Average fiber diameter L = 4 / [BET specific surface area (m 2 / g) x average density (g / cm 3 ) (2)

[0013] In the above formula (1), from the viewpoint of the conductivity of the solid electrolyte support sheet obtained using the nonwoven fabric of the present invention, the index of opening (L 2 / V) has a lower limit of 0.25, preferably 0.5, and more preferably 1.0. In order to suppress the powder shedding of solid electrolyte particles from the produced solid electrolyte-supporting sheet, the upper limit is 10, preferably 8.0, more preferably 6.0, even more preferably 5.5, and particularly preferably 3.0. The higher the aperture index value, the larger the aperture (the gap between fibers).

[0014] The fibers constituting the nonwoven fabric of the present invention are not particularly limited and may be any of inorganic fibers, organic fibers, organic-inorganic composite fibers, and natural fibers, or may be a combination of two or three of these fibers.

[0015] The constituent material of the inorganic fiber is not particularly limited, but is preferably an inorganic compound such as an oxide, nitride, carbonate, or titanate. Specific examples of inorganic fibers include glass fiber, silica fiber, alumina fiber, silica-alumina fiber, silica-alumina-magnesia fiber, silica-alumina-zirconia fiber, silica-magnesia-calcia fiber, rock wool, slag wool, potassium titanate whisker, calcium carbonate whisker, basalt fiber, mineral fibers such as sepilite and apalalgite, and carbon-based fibers such as cellulose nanofiber. Of these, glass fiber is preferred. The glass constituting the glass fibers is not particularly limited, but in a solid electrolyte-supporting sheet obtained using the nonwoven fabric of the present invention, the fibers are in contact with a solid electrolyte (described later). When such a solid electrolyte-supporting sheet is used in an all-solid-state lithium-ion battery, C-glass, B-glass, E-glass, etc. are preferred because the glass fibers and solid electrolyte particles are stable and durable.

[0016] Resin fibers are preferred as organic fibers. Examples of materials constituting resin fibers include polyester resins (such as polyethylene terephthalate), aliphatic polyamide resins, aramid resins, polyolefin resins, cyclic olefin resins, acrylic resins, polyacrylonitrile resins, polyvinyl alcohol resins, polyacetal resins, polyvinyl chloride resins, polyvinylidene chloride resins, ethylene-vinyl acetate copolymers, fluororesins, polyethersulfone resins, polyphenylene sulfide resins, and cellulose. Resin fibers can be single-phase fibers containing one or more types of resin, or multi-phase fibers having a low-melting-point resin portion and a high-melting-point resin portion (hereinafter referred to as "composite resin fibers"). Composite resin fibers can be, for example, sheath-core fibers or side-by-side fibers. Examples of resin combinations for composite resin fibers include PET / low-melting-point copolymer polyester, PET / PE, PP (polypropylene) / PE (polyethylene), and PP / low-melting-point copolymer PP. Here, examples of low-melting point copolyesters include modified resins having a basic skeleton such as PET, PPT (polypropylene terephthalate), or PBT (polybutylene terephthalate), i.e., modified copolymers of these polyesters with aromatic dicarboxylic acids such as isophthalic acid, 5-sodium sulfoisophthalic acid, and naphthalenedicarboxylic acid, and / or aliphatic dicarboxylic acids such as adipic acid and sebacic acid, and aliphatic polyhydric alcohols such as diethylene glycol, propylene glycol, and 1,4-butanediol. As the organic fiber (resin fiber), polyester fiber (resin fiber) is particularly preferable.

[0017] The organic-inorganic composite fibers include fibers having a film or granular portion containing an inorganic material on at least a part of the surface of the resin fiber. Examples of the natural fibers include plant fibers and animal fibers.

[0018] The nonwoven fabric of the present invention preferably contains inorganic fibers. When solid electrolyte particles are supported on a nonwoven fabric containing inorganic fibers and then pressure-molded into a thin solid electrolyte-supporting sheet, the inorganic fibers act as a reinforcing material, resulting in excellent mechanical strength. Furthermore, the solid electrolyte-supporting sheet can be provided with heat resistance. When the nonwoven fabric of the present invention contains inorganic fibers, the content of the inorganic fibers constituting the nonwoven fabric is preferably 40 mass % or more based on the total amount of fibers.

[0019] From the viewpoint of the ability to support solid electrolyte particles and mechanical strength, it is particularly preferable that the nonwoven fabric of the present invention contains both inorganic fibers and organic fibers (including those derived from composite resin fibers). The contents of the inorganic fibers and organic fibers, when the total is taken as 100% by mass, are preferably 40 to 70% by mass and 30 to 60% by mass, more preferably 50 to 70% by mass and 30 to 50% by mass, respectively. When the nonwoven fabric of the present invention contains organic fibers derived from composite resin fibers having a low melting point resin portion and a high melting point resin portion, the fibers may be included as fibers that do not have the low melting point resin portion of the composite resin fibers.

[0020] The fiber diameter of the fibers constituting the nonwoven fabric of the present invention is not particularly limited, but is preferably in the range of 0.1 to 20 μm, more preferably 0.2 to 10 μm, from the viewpoint of the mechanical strength of the nonwoven fabric. Furthermore, the fiber length is not particularly limited, but is preferably in the range of 0.1 to 10 mm, more preferably 0.5 to 6 mm, from the viewpoint of the mechanical strength of the nonwoven fabric. The nonwoven fabric is composed of a plurality of fibers, and in the present invention, the size (diameter or length) of each fiber may be either uniform or nonuniform among fibers containing the same material. Furthermore, when the nonwoven fabric contains a plurality of different types of fibers, the diameter or length between fibers made of one material and fibers made of another material may be either uniform or nonuniform.

[0021] The nonwoven fabric of the present invention preferably contains two or more fibers having different fiber diameters. In this case, the lower limit of the average fiber diameter of the fibers contained in the nonwoven fabric is preferably 0.85 μm, more preferably 0.90 μm, and even more preferably 0.95 μm, and the upper limit is preferably 6 μm, more preferably 5 μm, and particularly preferably 3.5 μm, so that the voids in the nonwoven fabric are easily filled with solid electrolyte particles and the powder shedding of the solid electrolyte particles is suppressed.

[0022] A nonwoven fabric that fully exhibits the effects of the present invention is one that is made by combining fibers having a fiber diameter of 1.0 μm or less (hereinafter referred to as "fibers (F1)") and fibers having a fiber diameter of more than 1.0 μm (hereinafter referred to as "fibers (F2)"). The contents of fibers (F1) and fibers (F2) are preferably 2 to 70% by mass and 30 to 98% by mass, and more preferably 5 to 65% by mass and 35 to 95% by mass, respectively, when the total of these is taken as 100% by mass.

[0023] In a preferred embodiment of the present invention, the fibers (F1) contain fibers having a fiber diameter of 0.1 to 1.0 μm (hereinafter referred to as "fibers (F1-1)") in an amount of preferably 40 to 100 mass%, more preferably 60 to 100 mass%, based on the total mass of the fibers. Therefore, the fibers (F1) may be a combination of fibers (F1-1) and fibers having a fiber diameter of less than 0.1 μm.

[0024] The constituent material of the fibers (F1) is not particularly limited, but the fibers (F1) preferably contain inorganic fibers. In a preferred embodiment of the present invention, the fibers (F1) contain inorganic fibers in an amount of preferably 40 to 100% by mass, more preferably 50 to 100% by mass, and particularly preferably 70 to 100% by mass, based on the total mass of the fibers. Therefore, the fibers (F1) may be a combination of inorganic fibers and other fibers (organic fibers, organic-inorganic composite fibers, natural fibers, etc.). The other fibers are preferably organic fibers.

[0025] In a preferred embodiment of the present invention, the fibers (F2) contain fibers having a fiber diameter of more than 1.0 μm and not more than 20 μm (hereinafter referred to as "fibers (F2-1)") in an amount of preferably 30 to 100 mass%, more preferably 50 to 100 mass%, based on the total mass of the fibers. Therefore, the fibers (F2) may be a combination of fibers (F2-1) and fibers having a fiber diameter of more than 20 μm.

[0026] The constituent material of the fibers (F2) is not particularly limited, but the fibers (F2) preferably contain organic fibers (resin fibers). In a preferred embodiment of the present invention, the fibers (F2) contain resin fibers in an amount of preferably 30 to 100% by mass, more preferably 50 to 100% by mass, based on the total mass of the fibers. Therefore, the fibers (F2) may be a combination of resin fibers and other fibers (inorganic fibers, organic-inorganic composite fibers, natural fibers, etc.). The other fibers are preferably inorganic fibers.

[0027] The nonwoven fabric of the present invention is a fiber assembly, and may be either one in which the fibers are simply entangled with each other, or one in which the fibers are entangled and also bonded with each other. In the present invention, the latter type of nonwoven fabric is preferred, and it is preferable that the fibers are bonded with an adhesive at their contact points. The adhesive used to bond the fibers together is not particularly limited, and can be a thermoplastic resin adhesive (including polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinyl acetate, acrylic resin, polyester resin, polyamide-imide resin, acrylonitrile-butadiene copolymer, styrene-butadiene copolymer, acrylonitrile-styrene-butadiene copolymer, etc.), a curable resin adhesive (including urethane resin, melamine resin, urea resin, thermosetting acrylic resin, phenolic resin, epoxy resin, thermosetting polyester, etc.), a water-based resin adhesive (including acrylic resin emulsion, etc.), an inorganic adhesive (colloidal silica, water glass, calcium silicate, silica sol, alumina sol, etc.), etc. When these adhesives are used, the bonded portion is usually made of a thermoplastic resin, a curable resin, etc. The adhesive may also be derived from composite resin fibers such as core-sheath fibers and side-by-side fibers.

[0028] When the nonwoven fabric of the present invention contains an adhesive, the content of the adhesive relative to the nonwoven fabric is preferably 10% by mass or less, more preferably 6% by mass or less, so that the conductivity of the solid electrolyte support sheet formed from the nonwoven fabric is not too low compared to the conductivity of the solid electrolyte particles themselves.

[0029] In the present invention, the basis weight of the nonwoven fabric is preferably 1 to 9 g / m from the viewpoint of the ability to support the solid electrolyte particles. 2 , more preferably 2 to 6 g / m 2 The thickness of the nonwoven fabric is usually 10 μm or more, but when used as a material for forming a solid electrolyte-supporting sheet having the desired conductivity, it is preferably 12 to 60 μm, more preferably 15 to 50 μm. The porosity of the nonwoven fabric is preferably 70 to 95%, more preferably 80 to 95%.

[0030] The method for producing the nonwoven fabric of the present invention is not particularly limited, and can be any conventional method, such as a method of making a paper from a slurry containing raw fibers and an adhesive, or a method of preparing a fiber assembly using raw fibers containing composite resin fibers and then heat-treating the fiber assembly. When inorganic fibers are used as the raw fibers, the fiber diameter is preferably 0.1 to 6.0 μm, more preferably 0.2 to 4.0 μm. When using multiple inorganic fibers with different fiber diameters, including inorganic fibers with a fiber diameter of 1.0 μm or less, a nonwoven fabric having the above-mentioned preferred basis weight and excellent mechanical strength can be obtained. Furthermore, when producing a nonwoven fabric by papermaking, wet paper strength can be maintained. When organic fibers are used, the fiber diameter is preferably 1 to 20 μm, more preferably 1 to 10 μm. When composite resin fibers are used as the organic fibers, the fiber diameter is preferably 2 to 20 μm, more preferably 2 to 10 μm.

[0031] The nonwoven fabric of the present invention is an article suitable for forming a solid electrolyte-supporting sheet in which solid electrolyte particles are supported between fibers, but it can also be used in other fields, for example, as a reinforcing material for resin products, a substrate for impregnation or immersion, etc.

[0032] The solid electrolyte-supporting sheet of the present invention is one in which particles made of a solid electrolyte are supported between the fibers (voids) constituting a nonwoven fabric. When manufacturing an all-solid-state lithium-ion battery, a thin, pressure-molded solid electrolyte-supporting sheet (hereinafter referred to as a "thin sheet") is usually used, but the present invention includes not only the solid electrolyte-supporting sheet before pressure molding, but also the pressure-molded thin sheet. This thin sheet is preferably a plate-like sheet that is not breathable from one side to the other, and forms a continuous phase made of solid electrolyte particles in the areas where the solid electrolyte particles contact each other.

[0033] The thickness of the solid electrolyte-supporting sheet before pressure molding is usually equal to or greater than the thickness of the nonwoven fabric of the present invention. The thickness of the thin sheet is preferably 1 to 200 μm, and more preferably 10 to 50 μm.

[0034] The solid electrolyte is not particularly limited as long as it is suitable for use in all-solid-state lithium-ion batteries. Preferred solid electrolytes include sulfide-based solid electrolytes and oxide-based solid electrolytes, and may be amorphous, glassy, ​​or crystalline (crystallized glass). Specific examples include Li2S-P2S5 materials, Li2S-SiS2 materials, Li2S-GeS2 materials, Li2S-Al2S3 materials, Li2S-SiS2-Li3PO4 materials, Li2S-P2S5-GeS2 materials, Li2S-Li2O-P2S5-SiS2 materials, Li2S-GeS2-P2S5-SiS2 materials, Li2S-SnS2-P2S5-SiS2 materials, and the like.

[0035] The solid electrolyte particles contained in the solid electrolyte support sheet of the present invention may be of only one type, or may be of two or more types.

[0036] The particle diameter of the solid electrolyte particles is preferably 1 to 20 μm, more preferably 1 to 10 μm. The particle diameter can be measured by image analysis using an electron microscope.

[0037] The content (carrying amount) of solid electrolyte particles in the solid electrolyte supporting sheet of the present invention is preferably 10 to 200 g / m 2 , more preferably 20 to 100 g / m 2 is.

[0038] The method for producing the solid electrolyte-supporting sheet of the present invention is not particularly limited, but a preferred method is to apply a dispersion obtained by dispersing solid electrolyte particles in a dispersion medium to a nonwoven fabric and dry the nonwoven fabric under normal pressure or reduced pressure. During drying, heating may be performed while taking into consideration whether or not the crystallinity of the solid electrolyte may change. The concentration of the solid electrolyte particles in the dispersion is not particularly limited. The dispersion medium is not particularly limited as long as it does not dissolve or alter the fibers of the nonwoven fabric. The dispersion may also contain an adhesive. Examples of methods for applying the dispersion include roll coating, gravure coating, knife coating, kiss coating, die coating, screen coating, doctor blade coating, bar coating, curtain coating, spin coating, dipping, casting, spraying, and extrusion coating.

[0039] Thereafter, when a thin sheet is produced, a method using a press machine, a roll press method in which the sheet is passed between two rolls, etc. The pressure when pressing is preferably 10 to 100 MPa.

[0040] The thin sheet of the present invention can also be produced by applying the above-mentioned dispersion to a nonwoven fabric containing composite resin fibers having a high-melting-point resin portion and a low-melting-point resin portion, drying the nonwoven fabric without melting the low-melting-point resin to volatilize the dispersion medium, and then producing a solid electrolyte particle-adhered nonwoven fabric (contained in the solid electrolyte-supported sheet of the present invention), and then pressing the nonwoven fabric at a temperature at which the high-melting-point resin does not melt but the low-melting-point resin melts.

[0041] By using the thin sheet of the present invention together with a cathode material, an anode material, etc. and subjecting it to a conventionally known manufacturing method, an all-solid-state lithium ion battery with excellent structural stability can be manufactured. In the obtained all-solid-state lithium ion battery, the thin sheet acts as a solid electrolyte layer. This solid electrolyte layer may be even thinner than the thin sheet. [Example]

[0042] Hereinafter, the embodiments of the present invention will be described more specifically with reference to examples and comparative examples.

[0043] The solid electrolyte used in the examples and comparative examples was obtained in Synthesis Example 1 below. Synthesis Example 1 In a glove box under an argon atmosphere, 1.379 g of commercially available high-purity lithium sulfide (LiS) and 2.222 g of high-purity diphosphorus pentasulfide (PS) were placed in a zirconia pot for a FRITCH planetary ball mill "P-7" (model number) so that the molar ratio was 3:1. Next, 100 g of zirconia balls with a diameter of 5 mm were placed in the pot. Then, 8 g (11.7 ml) of normal heptane was placed in the pot, and the pot was completely sealed. Next, mechanical milling was performed for a total of 25 hours in the planetary ball mill under the conditions of "mill rotation speed 500 rpm for 60 minutes, followed by a 15-minute rest period," with 20 cycles. After that, with the ball mill lid open, normal heptane was evaporated in a glove box, and a pale yellow, glassy solid electrolyte powder was obtained.

[0044] Next, experimental examples relating to nonwoven fabrics and solid electrolyte supporting sheets will be described.

[0045] Example 1 Inorganic fiber with a fiber diameter of 0.3 μm and a density of 2.5 g / cm 365% by mass of B glass short fiber (Jones Manville "#100") and organic fiber with a fineness of 0.1 dtex, a fiber diameter of 3 μm, a fiber length of 3 mm, and a density of 1.37 g / cm 3 The material consisted of 15% by mass of regular PET (polyethylene terephthalate) fiber (Teijin's "Tepirus TA04PN") and a 160°C heat-bondable fiber with a fineness of 1.1 dtex, fiber length of 5 mm, fiber diameter of 10 μm, and density of 1.37 g / cm. 3 The mixture was dispersed and mixed in water with 20% by mass of sheath-core PET-PET fiber ("Casven 7080" manufactured by Unitika Ltd.). Next, this mixture was wet-formed in a test paper machine and heated in a dryer at 200°C to obtain a nonwoven fabric. This nonwoven fabric was made by melting the sheath of the sheath-core PET-PET fiber through the heating, and the molten resin bonded the fibers together. The nonwoven fabric had a basis weight of 2.8 g / m. 2 The nonwoven fabric has a thickness of 24 μm. The basis weight is measured on a digital balance in accordance with JIS P 8124. 2 Measure the mass of the nonwoven fabric of the area, multiply it by 20 to get the basis weight (g / m 2 ) The thickness was measured in accordance with JIS P 8118 using a "Dial Thickness Gauge" manufactured by Ozaki Seisakusho Co., Ltd., under a pressure of 19.6 MPa (size of the smaller surface of the parallel circular plate: φ22.5 mm). The "regular PET" in "regular PET fiber" refers to unmodified pure polyethylene terephthalate, whose melting point is 260°C.

[0046] The average fiber diameter L was calculated from the BET specific surface area of ​​this nonwoven fabric and the average density calculated from the individual densities and blending ratios (volume %) of the raw fiber materials, and was found to be 1.8 μm. The basis weight of 2.8 g / m was calculated from the density of these raw fiber materials using the following formula: 2 The volume occupied by the fiber, V, was calculated to be 1.44 (cm 3 / m 2 ) was calculated using these values. 2 / V) is 2.24. Occupied volume V (cm 3 / m 2 ) = basis weight of nonwoven fabric (g / m 2) × [{Inorganic fiber blending ratio (mass%) ÷ Density of inorganic fiber (g / cm 3 )} + {Composition ratio of organic fiber (mass%) ÷ Density of organic fiber (g / cm 3 )} + {Adhesive blending ratio (mass%) ÷ Adhesive density (g / cm 3 )}÷100

[0047] Next, a solid electrolyte supporting sheet was produced by the following method, and various evaluations were carried out.

[0048] 1.5 g of the solid electrolyte powder obtained in Synthesis Example 1 and 3.75 g of normal heptane as a dispersion medium were placed in an agate mortar, and the solid electrolyte powder was mixed while being ground. The resulting mixture (hereinafter referred to as the "mixed solution") was placed in a sample vial and temporarily stored. The particle diameter of the solid electrolyte particles in the mixed solution was approximately 10 μm. Next, a PE sheet was prepared as a base, and a nonwoven fabric cut to 30 mm x 90 mm was placed on top of it. 1 ml of the mixed solution was dropped around the center of the nonwoven fabric and applied using a commercially available film applicator (gap 9 mil). The coated nonwoven fabric was dried in a glove box for 2 hours to remove the normal heptane. Next, the nonwoven fabric with the solid electrolyte particles attached was adjusted to a size of 30 mm x 30 mm, and this nonwoven fabric was sandwiched between 40 mm x 40 mm aluminum foils from above and below, and then sandwiched between two SUS plates and pressed at 26 MPa (hereinafter referred to as "low press") using a hydraulic press to fix the solid electrolyte particles throughout the nonwoven fabric, including the voids. Thereafter, the SUS plates and aluminum foils were removed to obtain a solid electrolyte-supported sheet (thin sheet).

[0049] (1) Evaluation of powder shedding The solid electrolyte-supporting sheet was punched into a circular shape (φ10 mm) using a punch, which was used as “test piece A.” Then, using this test piece A, the powder shedding property was evaluated. First, the weight (mg) of test piece A was measured, and it was placed in a cylindrical screw cap vial (Maruem Co., Ltd., No. 5, internal volume 20 ml). This screw cap vial was shaken 200 times in the minor axis direction (left and right) at an amplitude of 150 mm. Test piece A was then removed and its weight (mg) was measured, and the weight loss was calculated (see Table 1). Powder shedding was evaluated from this weight loss.

[0050] (2) Conductivity evaluation A cell (diameter 10 mm) for measuring resistance (conductivity) was prepared in the following manner. The above test piece A (φ10 mm) was packed into a cylindrical body (inner diameter 10 mm) made of polyether ether ketone (PEEK), and then stainless steel pins with a diameter of 10 mm and flat surfaces at the tip were inserted from both sides of the cylindrical body to clamp the test piece A, and the test piece B was obtained by pressing at 300 MPa (hereinafter referred to as "high pressing") using a hydraulic press. The resistance value (Ω) of test piece B placed inside the cylindrical body was measured using an impedance measuring device. The cell length (mm) before and after the insertion of test piece A and the cell length (mm) after the application of 300 MPa pressure were measured using a micrometer, and the thickness (μm) of test piece B was calculated from the difference between the measured values. The conductivity (S / cm) was calculated from the resistance value and the diameter and thickness of test piece B (see Table 1). Furthermore, after measuring the resistance value, test piece B was removed from the cell and visually observed. It was found that the solid electrolyte was sufficiently adhered to the fibers of the nonwoven fabric, just as when it was produced by high pressing, and there was no cracking or chipping. An attempt was made to evaluate the conductivity using the above method using only the same amount of solid electrolyte powder (5 mg) as the solid electrolyte contained in the above test piece A, but the solid electrolyte powder could not be uniformly distributed in the cell, resulting in a short circuit and making it impossible to measure. In addition, the test piece broke when being removed, making it impossible to remove.

[0051] Example 2 Inorganic fiber with a fiber diameter of 3 μm and a density of 2.5 g / cm 350% by mass of C-glass short fiber ("#210X" manufactured by Jones Manville) and 5% by mass of the above-mentioned B-glass short fiber ("#100" manufactured by Jones Manville) with a fiber diameter of 0.3 μm, and organic fiber with a fineness of 0.06 dtex, a fiber diameter of 2 μm, a fiber length of 3 mm, and a density of 1.37 g / cm 3 15% by mass of the regular PET fiber (Teijin Limited, "Tepirus TA04PN") and 30% by mass of the above-mentioned core-sheath PET-PET fiber (Unitika Limited, "Casven 7080") were dispersed and mixed in water. This mixture was then wet-formed using a test papermaking machine and heated in a dryer at 200°C to obtain a nonwoven fabric. The basis weight of this nonwoven fabric was 5.5 g / m 2 The thickness was 42 μm, the average fiber diameter was 4.2 μm, and the aperture index was 5.85. Thereafter, a solid electrolyte supporting sheet was produced using this nonwoven fabric in the same manner as in Example 1, and various evaluations were carried out (see Table 1).

[0052] Example 3 Inorganic fiber with a fiber diameter of 0.26 μm and a density of 2.5 g / cm 3 65% by mass of B glass short fiber (B-X9-F manufactured by Lauscher) and organic fiber with a fineness of 0.06 dtex, a fiber diameter of 2 μm, a fiber length of 3 mm, and a density of 1.37 g / cm 3 25% by mass of the regular PET fiber (Teijin Limited, "Tepirus TA04PN") and 10% by mass of the above core-sheath PET-PET fiber (Unitika Limited, "Casven 7080") were dispersed and mixed in water, wet-formed using a test paper machine, and heated in a dryer at 200°C to obtain a nonwoven fabric. The basis weight of this nonwoven fabric was 2.6 g / m 2 The thickness was 19 μm, the average fiber diameter was 1.2 μm, and the aperture index was 1.07. Thereafter, a solid electrolyte supporting sheet was produced using this nonwoven fabric in the same manner as in Example 1, and various evaluations were carried out (see Table 1).

[0053] Example 4 The inorganic fiber was 45% by mass of the above-mentioned B glass short fiber ("B-X9-F" manufactured by Lauscher), and the organic fiber was 0.06 dtex, 2 μm in diameter, 3 mm in length, and 1.37 g / cm in density.3 This was dispersed and mixed with 55% by mass of regular PET fiber (Teijin Limited's "Tepyrus TA04PN") in water, wet-formed using a test paper machine, and heated in a dryer at 160°C to obtain a nonwoven fabric. The basis weight of this nonwoven fabric was 2.3 g / m 2 The thickness was 19 μm, the average fiber diameter was 1.0 μm, and the aperture index was 0.75.

[0054] Example 5 As inorganic fibers, 25% by mass of the above-mentioned B glass short fiber ("B-X9-F" manufactured by Lauscher) and a fiber diameter of 0.53 μm and a density of 2.5 g / cm 3 25% by mass of C glass short fiber ("C-04-F" manufactured by Lauscher) and organic fiber with a fineness of 0.06 dtex, a fiber diameter of 2 μm, a fiber length of 3 mm, and a density of 1.37 g / cm 3 This was dispersed and mixed with 50% by mass of regular PET fiber (Teijin Limited's "Tepirus TA04PN") in water, wet-formed using a test paper machine, and heated in a dryer at 200°C to obtain a nonwoven fabric. The basis weight of this nonwoven fabric was 5.0 g / m 2 It was. Next, this nonwoven fabric was coated with a styrene-butadiene resin (SBR) adhesive (density 1.0 g / cm 3 ) was applied to the nonwoven fabric using a dip coater and dried to obtain a nonwoven fabric in which the fibers were bonded with an adhesive. The basis weight of this nonwoven fabric was 5.6 g / m 2 The thickness was 30 μm, the average fiber diameter was 1.0 μm, and the aperture index was 0.29. The amount of SBR attached was 10% by mass. Thereafter, a solid electrolyte supporting sheet was produced using this nonwoven fabric in the same manner as in Example 1, and various evaluations were carried out (see Table 1).

[0055] Comparative Example 1 A 0.2% by mass concentration of polyethylene oxide (PEO-3 manufactured by Sumitomo Seika Chemicals) was used as a thickener in an aqueous solution. Inorganic fibers with a fiber diameter of 7 μm, a fiber length of 6 mm, and a density of 2.5 g / cm were added. 3The resulting wet paper was sandwiched between upper and lower meshes and coated with an acrylic resin emulsion (Boncoat SFC manufactured by Dai Nippon Ink Co., Ltd., density 1.2 g / cm) as an adhesive. 3 The nonwoven fabric was dehydrated by immersing it in a dryer and then heated at 160°C to obtain a nonwoven fabric in which the fibers were bonded with an adhesive. This nonwoven fabric contained the glass chopped strands and acrylic resin in proportions of 92% by mass and 8% by mass, respectively, and had a basis weight of 9.5 g / m 2 The thickness was 75 μm, the average fiber diameter was 7.0 μm, and the aperture index was 11.87. Thereafter, a solid electrolyte supporting sheet was produced using this nonwoven fabric in the same manner as in Example 1, and various evaluations were carried out (see Table 1).

[0056] Comparative Example 2 The inorganic fibers were 30% by mass of the above-mentioned B short glass fiber ("#100" manufactured by Jones Manville) and 30% by mass of the above-mentioned C short glass fiber ("C-04-F" manufactured by Lauscher), and the organic fibers were 0.06 dtex, 2 μm in diameter, 3 mm in length, and 1.37 g / cm in density. 3 This was dispersed and mixed with 40% by mass of regular PET fiber (Teijin Limited's "Tepyrus TA04PN") in water, wet-formed using a test paper machine, and heated in a dryer at 200°C to obtain a nonwoven fabric. The basis weight of this nonwoven fabric was 10.0 g / m 2 The thickness was 60 μm, the average fiber diameter was 0.8 μm, and the aperture index was 0.13. Thereafter, a solid electrolyte supporting sheet was produced using this nonwoven fabric in the same manner as in Example 1, and various evaluations were carried out (see Table 1).

[0057] Comparative Example 3 The nonwoven fabric prepared in Comparative Example 2 was coated with the above acrylic resin emulsion (density 1.2 g / cm 3 ) was applied to the nonwoven fabric using a dip coater and dried to obtain a nonwoven fabric in which the fibers were bonded with an adhesive. The basis weight of this nonwoven fabric was 11.1 g / m 2The thickness was 60 μm, the average fiber diameter was 0.8 μm, and the aperture index was 0.11. The amount of acrylic resin attached was 10% by mass. Thereafter, a solid electrolyte supporting sheet was produced using this nonwoven fabric in the same manner as in Example 1, and various evaluations were carried out (see Table 1).

[0058] Comparative Example 4 The inorganic fiber was 70% by mass of the above-mentioned glass chopped strand (manufactured by Unitika Ltd.), and the organic fiber was 0.1 dtex, 3 μm in diameter, 3 mm in length, and 1.37 g / cm in density. 3 20% by mass of regular PET fiber (Teijin "Tepirus TA04PN") and 160°C heat-bondable fiber with a fineness of 1.1 dtex, fiber length of 5 mm, fiber diameter of 10 μm, and density of 1.37 g / cm 3 The resulting nonwoven fabric was dispersed and mixed with 10% by mass of sheath-core PET-PET fiber ("Casven 7080" manufactured by Unitika Ltd.) in water, wet-formed using a test paper machine, and heated at 200°C in a dryer to obtain a nonwoven fabric. The basis weight of the nonwoven fabric was 8.0 g / m 2 The thickness was 55 μm, the average fiber diameter was 6.7 μm, and the aperture index was 11.25. Thereafter, a solid electrolyte supporting sheet was produced using this nonwoven fabric in the same manner as in Example 1, and various evaluations were carried out (see Table 1).

[0059] [Table 1]

[0060] From Table 1, it can be seen that Examples 1 to 5 are examples in which the aperture index is within the range of the present invention, the amount of powder falling off from the solid electrolyte support sheet (thin sheet) before high pressing is 10 mass % or less, and the conductivity of the solid electrolyte support sheet after high pressing is also sufficiently high, so that these performances are compatible. [Industrial Applicability]

[0061] By using the nonwoven fabric of the present invention, the voids can be easily filled with solid electrolyte particles, and a solid electrolyte-supporting sheet can be easily formed. In the obtained solid electrolyte-supporting sheet, the powdering of the solid electrolyte particles is suppressed, and therefore the solid electrolyte-supporting sheet has the desired conductivity and is suitable as a component for manufacturing all-solid-state lithium-ion batteries.

Claims

1. The average fiber diameter of all fibers is L (μm), 1 m ２ Volume per (cm ３ ) is V, 0.25≦(L ２ / V)≦10, the nonwoven fabric comprising fibers (F1) having a fiber diameter of 1.0 μm or less and fibers (F2) having a fiber diameter of more than 1.0 μm, wherein the fibers (F1) comprise inorganic fibers.

2. 2. The nonwoven fabric according to claim 1, wherein the average fiber diameter is 0.85 μm or more.

3. The nonwoven fabric according to claim 1 or 2, wherein the fibers (F2) contain resin fibers.

4. The nonwoven fabric according to claim 3, wherein the fibers (F2) further comprise inorganic fibers.

5. 5. The nonwoven fabric according to claim 3, wherein at least a portion of the resin fibers bond the fibers constituting the nonwoven fabric together.

6. The nonwoven fabric according to claim 1 , which is used to support solid electrolyte particles.

7. 7. A solid electrolyte-supporting sheet, comprising the nonwoven fabric according to claim 1, and solid electrolyte particles supported between the fibers.

8. The amount of the solid electrolyte particles supported is 10 to 200 g / m ２ 8. The solid electrolyte supporting sheet according to claim 7, wherein

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