Solid electrolyte composition, solid electrolyte membrane, laminate, battery, and method for producing solid electrolyte composition

Abstract

To provide a solid electrolyte composition that can be prepared by a simple process and enables formation of a homogeneous film, a solid electrolyte membrane formed using the solid electrolyte composition, a laminate including the solid electrolyte membrane, a battery including the laminate, and a method for producing the solid electrolyte composition.SOLUTION: A solid electrolyte composition comprises an acid-modified cellulose nanofiber, a solvent, and an ion-conducting aid.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a solid electrolyte composition, a solid electrolyte membrane, a laminate, a battery, and a method for producing a solid electrolyte composition. [Background technology]

[0002] A lithium-ion secondary battery has a negative electrode, a positive electrode, and an electrolyte sandwiched between the negative and positive electrodes. A lithium-ion secondary battery is a storage battery that can be charged and discharged by moving lithium ions back and forth between the negative and positive electrodes. Conventionally, lithium-ion secondary batteries have used organic electrolyte solutions as the electrolyte. However, lithium-ion secondary batteries using organic electrolyte solutions are prone to leakage and can cause short circuits and fires within the battery due to overcharging or overdischarging. Therefore, further improvements in the safety and reliability of lithium-ion secondary batteries are required. Under these circumstances, all-solid-state secondary batteries using solid electrolytes instead of organic electrolyte solutions have attracted attention. All-solid-state secondary batteries, which have a negative electrode, electrolyte, and positive electrode all made of solids, are thought to significantly improve the safety and reliability issues faced by batteries using organic electrolyte solutions, while also enabling longer battery life.

[0003] Solid electrolytes are broadly classified into three types: sulfide-based solid electrolytes, oxide-based solid electrolytes, and polymer-based solid electrolytes. Each of these solid electrolytes has its own advantages and disadvantages.

[0004] Sulfide-based solid electrolytes can be used to fabricate electrolyte membranes with low grain boundary resistance by pressure forming at room temperature. Therefore, sulfide-based solid electrolytes can be used as electrolytes for bulk-type all-solid-state secondary batteries. In addition, sulfide-based solid electrolytes have -3 Scm -1 However, sulfide-based solid electrolytes generate hydrogen sulfide through hydrolysis with traces of water, so they must be manufactured, processed, and stored in an extremely dry environment.

[0005] Unlike sulfide-based solid electrolytes, oxide-based solid electrolytes do not pose the risk of emitting toxic gases, making them safer batteries. However, oxide-based solid electrolytes are hard and brittle, making it difficult to form electrolyte membranes. Furthermore, electrolyte membranes formed from oxide-based solid electrolytes lack flexibility, resulting in poor contact with electrodes and making it difficult to achieve high battery performance.

[0006] Polymer-based solid electrolytes are flexible, which allows for easy interfacial bonding with electrodes and reduces grain boundary resistance. However, polymer-based solid electrolytes have inferior ionic conductivity compared to sulfide-based and oxide-based solid electrolytes.

[0007] Conventionally, composite sheets of acid-modified cellulose nanofibers (hereinafter sometimes referred to as "acid-modified CNF") and inorganic solid electrolytes have been known, with the aim of suppressing a drop in battery voltage, the occurrence of short circuits, and the deterioration of inorganic solid electrolytes (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 6714172 Summary of the Invention [Problem to be solved by the invention]

[0009] The acid-modified CNF used in Patent Document 1 is modified with carboxyl or phosphate groups. A composite sheet using this acid-modified CNF is formed by drying a coating film made of a solid electrolyte composition containing an inorganic solid electrolyte and acid-modified CNF. Therefore, the composite sheet shrinks significantly during formation. This makes it difficult to form a flat, uniform composite sheet. Furthermore, to reduce the water content of the solid electrolyte composition to 50 ppm or less, the water contained in the solid electrolyte composition must be replaced with an organic solvent. Replacing the water contained in the solid electrolyte composition with an organic solvent places a heavy burden on the environment and is a complicated process.

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a solid electrolyte composition that can be prepared by a simple process and that is capable of forming a homogeneous film, a solid electrolyte membrane formed using the solid electrolyte composition, a laminate including the solid electrolyte membrane, a battery including the laminate, and a method for producing the solid electrolyte composition. [Means for solving the problem]

[0011] The present invention has the following aspects. [1] A solid electrolyte composition comprising acid-modified cellulose nanofibers, a solvent, and an ion-conducting assistant. [2] The solid electrolyte composition according to [1], wherein the acid-modified cellulose nanofibers are sulfated cellulose nanofibers. [3] The solid electrolyte composition according to [1], wherein the acid-modified cellulose nanofibers have a degree of substitution of 1.3 mmol / g or more and 3.5 mmol / g or less. [4] The solid electrolyte composition according to any one of [1] to [3], wherein the ion-conducting assistant contains at least one of inorganic particles, polyether, and lithium salt. [5] The solid electrolyte composition according to [4], wherein the inorganic particles are oxide-based solid electrolyte particles or inert inorganic particles. [6] The solid electrolyte composition according to any one of [1] to [5], wherein the solvent is water, and the content of the water is 90.0% by mass or more and 99.0% by mass or less. [7] The solid electrolyte composition according to [4], wherein the content of the inorganic particles is 0.01% by mass or more and 2.0% by mass or less. [8] The solid electrolyte composition according to [4], wherein the content of the polyether is 0.5% by mass or more and 5.0% by mass or less. [9] The solid electrolyte composition according to [4], wherein the content of the lithium salt is 0.01% by mass or more and 3.0% by mass or less.

[10] The solid electrolyte composition according to [5], wherein the content of the oxide-based solid electrolyte is 0.01% by mass or more and 2.0% by mass or less.

[11] The solid electrolyte composition according to [5], wherein the content of the inert inorganic particles is 0.01% by mass or more and 2.0% by mass or less.

[12] A solid electrolyte membrane comprising acid-modified cellulose nanofibers and an ion-conducting additive.

[13] The solid electrolyte membrane according to

[12] , wherein the acid-modified cellulose nanofibers are sulfated cellulose nanofibers.

[14] A laminate comprising an electrode and the solid electrolyte membrane according to

[12] or

[13] disposed on the electrode.

[15] A battery comprising the solid electrolyte membrane according to

[12] or

[13] or the laminate according to

[14] .

[16] A step of mixing acid-modified cellulose nanofibers, a solvent, and an ion-conducting assistant to obtain a mixed solution; and removing air bubbles contained in the mixed liquid. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a solid electrolyte composition that can be prepared by a simple process and that is capable of forming a homogeneous film, a solid electrolyte membrane formed using the solid electrolyte composition, a laminate including the solid electrolyte membrane, a battery including the laminate, and a method for producing the solid electrolyte composition. DETAILED DESCRIPTION OF THE INVENTION

[0013] Embodiments of the solid electrolyte composition, solid electrolyte membrane, laminate, and battery, as well as the method for producing the solid electrolyte composition, of the present invention will be described below. It should be noted that the present embodiment is specifically described to allow a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[0014] [Solid electrolyte composition] A solid electrolyte composition according to one embodiment of the present invention includes acid-modified cellulose nanofibers, a solvent, and an ion-conducting assistant.

[0015] The substituents (acid groups) introduced into the acid-modified cellulose nanofibers are not particularly limited, but examples include sulfate ester groups, carboxyl groups, phosphate ester groups, carboxymethyl ester groups, phosphite ester groups, and groups in which at least one element of the organic residue of these substituents has been substituted with a metal. Examples of acid-modified cellulose nanofibers include, but are not limited to, sulfated cellulose nanofibers, carboxylated cellulose nanofibers, phosphated cellulose nanofibers, carboxymethyl esterified cellulose nanofibers, phosphite esterified cellulose nanofibers, etc. Among these, sulfated cellulose nanofibers are preferred from the viewpoint of the homogeneity of the solid electrolyte membrane obtained by coating.

[0016] The acid-modified cellulose nanofibers preferably have a degree of substitution of 1.3 mmol / g to 3.5 mmol / g, more preferably 1.4 mmol / g to 2.7 mmol / g, and even more preferably 1.5 mmol / g to 2.7 mmol / g. When the degree of substitution is within this preferred range, the acid-modified cellulose nanofibers have high dispersibility, making it easier to form a homogeneous solid electrolyte membrane.

[0017] The degree of substitution of acid-modified cellulose nanofibers refers to the amount of hydroxyl groups in the cellulose nanofibers that have been substituted with sulfate ester groups, carboxyl groups, phosphate ester groups, carboxymethyl ester groups, phosphite ester groups, etc. The degree of substitution of the acid-modified cellulose nanofibers can be determined, for example, by combustion-ion chromatography.

[0018] The content of the acid-modified cellulose nanofibers relative to the total mass of the solid electrolyte composition is preferably 0.001% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 5.0% by mass or less, and even more preferably 0.5% by mass or more and 2.0% by mass or less. When the content of the acid-modified cellulose nanofibers is within this preferred range, the viscosity of the solid electrolyte composition can be controlled to an appropriate level for coating due to the thickening effect of the acid-modified cellulose nanofibers.

[0019] Examples of the solvent include water, methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2-propyl alcohol, ethylene glycol, propylene glycol, dimethyl sulfoxide, N-methyl-2-pyrrolidone, formamide, N,N-dimethylformamide, acetone, methyl ethyl ketone, methyl isobutyl ketone, acetonitrile, propylonitrile, ethyl acetate, and butyl acetate.

[0020] The content of the solvent relative to the total mass of the solid electrolyte composition is preferably 50.0 mass % or more and 99.9 mass % or less, more preferably 70.0 mass % or more and 99.5 mass % or less, and even more preferably 90.0 mass % or more and 99.0 mass % or less. When the content of the solvent is within the above-mentioned preferred range, an appropriate dry film thickness can be obtained in coating the solid electrolyte composition.

[0021] When the solvent is water, the content of water relative to the total mass of the solid electrolyte composition is preferably 90.0 mass % or more and 99.0 mass % or less. When the water content is within this preferred range, an appropriate dry film thickness can be obtained when coating the solid electrolyte composition.

[0022] The solid electrolyte composition of this embodiment contains at least one of inorganic particles, polyether, and lithium salt as an ion conduction aid. By containing at least one of inorganic particles, polyether, and lithium salt in a predetermined content described below, the solid electrolyte composition of this embodiment can form a homogeneous film (solid electrolyte film) when coated, and when the obtained solid electrolyte layer is used in a battery, it can exhibit a short-circuit suppression effect.

[0023] The inorganic particles include oxide-based solid electrolytes and inert inorganic particles. Examples of oxide-based solid electrolytes include solid electrolytes containing Li, Y (Y is at least one of Nb, B, Al, Si, P, Ti, Zr, Mo, W, and S), and O. Specific examples of oxide-based solid electrolytes include Li7La3Zr2O 12 , Li 7-x La3(Zr 2-x Nb x )O 12 (0≦x≦2), Li5La3Nb2O 12 perovskite-type solid electrolytes such as (Li,La)TiO3, (Li,La)NbO3, (Li,Sr)(Ta,Zr)O3; Nasicon-type solid electrolytes such as Li(Al,Ti)(PO4)3 and Li(Al,Ga)(PO4)3; Li-PO-based solid electrolytes such as Li3PO4 and LIPON (a compound in which some of the O in Li3PO4 is substituted with N); and Li-BO-based solid electrolytes such as Li3BO3 and a compound in which some of the O in Li3BO3 is substituted with C. Examples of inert inorganic particles include silica, alumina, zirconia, zinc oxide, antimony oxide, indium oxide, tin oxide, titanium oxide, iron oxide, magnesium oxide, aluminum hydroxide, magnesium hydroxide, boehmite, talc, kaolin, clay, calcium silicate, calcium carbonate, potassium titanate, barium titanate, mica, montmorillonite, zeolite, metal organic frameworks (MOFs), and glass fibers.

[0024] The content of the inorganic particles relative to the total mass of the solid electrolyte composition is preferably 0.01% by mass or more and 2.0% by mass or less, more preferably 0.05% by mass or more and 2.0% by mass or less, and even more preferably 0.1% by mass or more and 2.0% by mass or less. When the content of the inorganic particles is within this preferred range, a homogeneous film (solid electrolyte film) can be formed in the coating of the solid electrolyte composition, and when the obtained solid electrolyte layer is used in a battery, a short-circuit suppression effect can be exhibited.

[0025] When the inorganic particles are oxide-based solid electrolytes, the content of the oxide-based solid electrolyte relative to the total mass of the solid electrolyte composition is preferably 0.01% by mass or more and 2.0% by mass or less, more preferably 0.05% by mass or more and 2.0% by mass or less, and even more preferably 0.1% by mass or more and 2.0% by mass or less. When the content of the oxide-based solid electrolyte is within the above-mentioned preferred range, a homogeneous film (solid electrolyte film) can be formed in the coating of the solid electrolyte composition, and when the obtained solid electrolyte layer is used in a battery, a short-circuit suppression effect can be exhibited.

[0026] When the inorganic particles are inert inorganic particles, the content of the inert inorganic particles relative to the total mass of the solid electrolyte composition is preferably 0.01% by mass or more and 2.0% by mass or less, more preferably 0.05% by mass or more and 2.0% by mass or less, and even more preferably 0.1% by mass or more and 2.0% by mass or less. When the content of the inert inorganic particles is within the above-mentioned preferred range, a homogeneous film (solid electrolyte film) can be formed in the coating of the solid electrolyte composition, and when the obtained solid electrolyte layer is used in a battery, a short-circuit suppression effect can be exhibited.

[0027] As the polyether, for example, glyme shown in the following formula (1) can be used. Glyme has a basic structure of ethylene glycol dimethyl ether, and depending on the number of repetitions of the basic structure, there are monoglyme, diglyme, triglyme, tetraglyme, pentaglyme, hexaglyme, etc. Polyethylene oxide can also be used.

[0028] [ka]

[0029] The content of the polyether relative to the total mass of the solid electrolyte composition is preferably 0.5% by mass or more and 5.0% by mass or less, more preferably 1.0% by mass or more and 3.0% by mass or less, and even more preferably 1.2% by mass or more and 2.0% by mass or less. When the content of the polyether is within the above-mentioned preferred range, a homogeneous film (solid electrolyte film) can be formed by coating the solid electrolyte composition, and when the obtained solid electrolyte layer is used in a battery, a short-circuit suppression effect can be exhibited. Furthermore, the obtained solid electrolyte layer can have good ionic conductivity.

[0030] Examples of lithium salts include LiClO4, LiBF4, LiI, LiF, LiCl, LiBr, LiPF6, LiPO4, LiCF3SO3, LiCF3COO, LiCH3COO, LiNO3, LiNO2, Li2SO4, LiAsF6, LiSbF6, LiAlCl4, LiB(C2H5)4, LiC4BO8, LiCH3SO3, LiC4F9SO3, Li(CF3SO2)2N, Li(C2F5SO2)N, Li(FSO2)2N, and phosphate salts.

[0031] The content of the lithium salt relative to the total mass of the solid electrolyte composition is preferably 0.01% by mass or more and 3.0% by mass or less, more preferably 0.05% by mass or more and 2.0% by mass or less, and even more preferably 0.1% by mass or more and 1.0% by mass or less. When the content of the lithium salt is within the above-mentioned preferred range, a homogeneous film (solid electrolyte film) can be formed by coating the solid electrolyte composition, and when the obtained solid electrolyte layer is used in a battery, a short-circuit suppression effect can be exhibited. Furthermore, the obtained solid electrolyte layer can have good ionic conductivity.

[0032] The solid electrolyte composition of the present embodiment may contain components (other components) other than the acid-modified cellulose nanofibers, the solvent, and the ion-conducting assistant, as needed. Other components include, for example, cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose; synthetic water-soluble polymers such as polyacrylic acid, polymethacrylic acid, polyethylene glycol, polyvinyl alcohol, and polyvinylpyrrolidone; latexes such as styrene butadiene resin (SBR); polyvinylidene fluoride; and polytetrafluoroethylene.

[0033] The solid electrolyte composition of the present embodiment can be applied to the surface of an object such as an electrode to form a coating film, and then the coating film can be dried and cured to form a solid electrolyte membrane made of a cured product of the solid electrolyte composition.

[0034] The solid electrolyte composition of this embodiment contains acid-modified cellulose nanofibers, making it possible to form a homogeneous solid electrolyte membrane. Furthermore, the resulting solid electrolyte membrane has mechanical properties and flexibility suitable for roll-to-roll processing. The solid electrolyte composition of the present embodiment contains acid-modified cellulose nanofibers and an oxide-based solid electrolyte or inert inorganic fine particles as an ion conduction aid, and therefore can prevent short circuits between electrodes when used as a solid electrolyte membrane of a battery. The solid electrolyte composition of the present embodiment contains at least one of polyether and lithium salt as the ion-conducting assistant, and thus can form a solid electrolyte membrane having high ion conductivity.

[0035] [Method of manufacturing solid electrolyte composition] A method for producing a solid electrolyte composition according to one embodiment of the present invention includes a step of mixing acid-modified cellulose nanofibers, a solvent, and an ion-conducting assistant to obtain a mixed solution (hereinafter referred to as the "first step"), and a step of removing air bubbles contained in the mixed solution (hereinafter referred to as the "second step").

[0036] "First step" In the first step, the acid-modified cellulose nanofibers, solvent, and ion-conducting assistant in the solid electrolyte composition of the above-described embodiment are used, and the acid-modified cellulose nanofibers, solvent, and ion-conducting assistant are mixed so that the content of each of these components falls within the above-described ranges to obtain a mixed solution.

[0037] The method for mixing the acid-modified cellulose nanofibers, the solvent, and the ion-conducting aid is not particularly limited, but for example, a method of mixing by stirring using a mixing device such as a planetary ball mill, a bead mill, a wet jet mill, a three-roll mill, a homogenizer, or a paint shaker can be used.

[0038] "Second step" In the second step, the mixture obtained in the first step is stirred using a planetary centrifugal mixer to remove air bubbles contained in the mixture (degassing).

[0039] When the mixture is stirred using a planetary centrifugal mixer, the stirring speed (number of rotations) is adjusted appropriately depending on the type and content of each component contained in the mixture, but for example, it is preferably 500 rpm or more and 2200 rpm or less, and more preferably 1500 rpm or more and 2000 rpm or less.

[0040] The time for which the mixture is stirred using a planetary centrifugal mixer (stirring time) is adjusted appropriately depending on the type and content of each component contained in the mixture, but is preferably, for example, from 30 seconds to 10 minutes, and more preferably from 1 minute to 5 minutes.

[0041] In the method for producing the solid electrolyte composition of the present embodiment, components other than the acid-modified cellulose nanofibers, the solvent, and the ion-conducting assistant (other components) may be mixed, if necessary.

[0042] The method for producing the solid electrolyte composition of this embodiment does not require a step of replacing with an organic solvent, so the solid electrolyte composition can be prepared by a simple process. Furthermore, the solid electrolyte composition of this embodiment can reduce volatile organic compounds (VOCs) during production, so the environmental impact can be reduced.

[0043] [Solid electrolyte membrane] A solid electrolyte membrane according to one embodiment of the present invention includes acid-modified cellulose nanofibers and an ion-conducting additive. In other words, the solid electrolyte membrane according to this embodiment is made of a cured product of the solid electrolyte composition according to the above-described embodiment. That is, the solid electrolyte membrane according to this embodiment does not include a solvent.

[0044] The solid electrolyte membrane of this embodiment contains at least acid-modified cellulose nanofibers. The acid-modified cellulose nanofibers are the same as the acid-modified cellulose nanofibers in the solid electrolyte composition of the above-described embodiment. The solid electrolyte membrane of this embodiment is formed, for example, by applying the solid electrolyte composition of the above-described embodiment to an object to form a coating film, and then heating and drying the coating film. However, the degree of substitution of the acid-modified cellulose nanofibers contained in the solid electrolyte membrane does not change due to drying.

[0045] The content of the acid-modified cellulose nanofibers relative to the total mass of the solid electrolyte membrane is preferably 5% by mass or more and 99% by mass or less, more preferably 10% by mass or more and 95% by mass or less, and even more preferably 15% by mass or more and 90% by mass or less. When the content of the acid-modified cellulose nanofibers is within this preferred range, the resulting solid electrolyte membrane has mechanical properties and flexibility suitable for roll-to-roll processing.

[0046] The solid electrolyte membrane of this embodiment preferably contains at least one of inorganic particles, polyether, and lithium salt as an ion conduction aid. In other words, the solid electrolyte membrane of this embodiment may contain only one of inorganic particles, polyether, and lithium salt, or may contain two or more of inorganic particles, polyether, and lithium salt. The inorganic particles, polyether, and lithium salt are the same as the inorganic particles, polyether, and lithium salt in the solid electrolyte composition of the above-mentioned embodiment.

[0047] The content of the inorganic particles relative to the total mass of the solid electrolyte membrane is preferably 1% by mass to 90% by mass, more preferably 5% by mass to 80% by mass, and even more preferably 10% by mass to 70% by mass. When the content of the inorganic particles is within this preferred range, the solid electrolyte membrane has a short-circuit suppression effect when used in a battery.

[0048] When the inorganic particles are oxide-based solid electrolytes, the content of the oxide-based solid electrolyte relative to the total mass of the solid electrolyte membrane is preferably 1% by mass to 90% by mass, more preferably 5% by mass to 80% by mass, and even more preferably 10% by mass to 70% by mass. When the content of the oxide-based solid electrolyte is within the above-mentioned preferred range, the solid electrolyte membrane has a short-circuit suppression effect when used in a battery.

[0049] When the inorganic particles are inert inorganic particles, the content of the inert inorganic particles relative to the total mass of the solid electrolyte membrane is preferably 1% by mass to 90% by mass, more preferably 5% by mass to 80% by mass, and even more preferably 10% by mass to 70% by mass. When the content of the inert inorganic particles is within the above-mentioned preferred range, the solid electrolyte membrane has a short-circuit suppression effect when used in a battery.

[0050] The content of the polyether relative to the total mass of the solid electrolyte membrane is preferably 15% by mass to 65% by mass, more preferably 20% by mass to 60% by mass, and even more preferably 25% by mass to 55% by mass. When the polyether content is within the above preferred range, the solid electrolyte membrane has a short-circuit suppressing effect when used in a battery, and also has good ionic conductivity.

[0051] The content of the lithium salt relative to the total mass of the solid electrolyte membrane is preferably 1% by mass to 30% by mass, more preferably 3% by mass to 25% by mass, and even more preferably 5% by mass to 20% by mass. When the content of the lithium salt is within the above preferred range, the solid electrolyte membrane has a short-circuit suppressing effect when used in a battery, and further has good ionic conductivity.

[0052] The solid electrolyte membrane of this embodiment is a homogeneous membrane because it contains acid-modified cellulose nanofibers. In addition, the solid electrolyte membrane of this embodiment has mechanical properties and flexibility that make it suitable for roll-to-roll processing. The solid electrolyte membrane of this embodiment contains an oxide-based solid electrolyte or inorganic fine particles, and therefore can prevent short circuits between electrodes when used as a solid electrolyte membrane of a battery. The solid electrolyte membrane of this embodiment has high ionic conductivity by containing at least one of polyether and lithium salt.

[0053] [Method of manufacturing solid electrolyte membrane] The solid electrolyte membrane of this embodiment can be produced, for example, by the following method. The solid electrolyte composition is applied to a substrate such as a resin film to a predetermined thickness using an applicator set to a predetermined clearance, to form a coating film made of the solid electrolyte composition. Thereafter, the coating film is dried at room temperature (25° C.), and then heated and dried under vacuum to form a solid electrolyte film on the substrate.

[0054] [Laminate] A stack according to one embodiment of the present invention includes an electrode and the solid electrolyte membrane according to the above embodiment disposed on the electrode.

[0055] The electrode may be a negative electrode or a positive electrode. The negative electrode has a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector. Examples of the negative electrode current collector include copper, aluminum, nickel, stainless steel (SUS), and nickel-plated steel. The negative electrode active material layer is composed of graphite, hard carbon, soft carbon, acetylene black, ketjen black, carbon black, carbon nanotubes, graphene, VGCF (vapor grown carbon fiber), silicon, SiO, Li2TiO3, TiO2, Mg2Si, Mg2Ge, Sn, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, and SbSn. The thickness of the negative electrode is not particularly limited, but is preferably, for example, 10 μm to 300 μm, more preferably 50 μm to 200 μm, and even more preferably 80 μm to 120 μm.

[0056] The positive electrode has a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. Examples of the positive electrode current collector include aluminum, nickel, stainless steel (SUS), copper, etc. "Aluminum" includes pure aluminum and aluminum alloys. The positive electrode active material layer is made of lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO4), and NMC (LiNi x Mn y Co z O2) and NCA (LiNi x Co y Al zIt is composed of lithium transition metal composite oxides such as O2. The thickness of the positive electrode is not particularly limited, but is preferably, for example, 10 μm or more and 300 μm or less, more preferably 70 μm or more and 250 μm or less, and even more preferably 100 μm or more and 200 μm or less.

[0057] The thickness of the solid electrolyte membrane is not particularly limited, but is preferably, for example, 3 μm to 100 μm, more preferably 5 μm to 50 μm, and even more preferably 10 μm to 30 μm.

[0058] The laminate of this embodiment includes the solid electrolyte membrane of the above-described embodiment, and therefore has mechanical properties and flexibility that make it applicable to roll-to-roll manufacturing. The laminate of this embodiment has high ionic conductivity because it includes the solid electrolyte membrane of the above embodiment.

[0059] [battery] A battery according to one embodiment of the present invention includes the solid electrolyte membrane of the above embodiment or the laminate of the above embodiment.

[0060] The battery of this embodiment has a negative electrode, a positive electrode, and an electrolyte sandwiched between the negative electrode and the positive electrode. In the battery of this embodiment, the electrolyte may be the solid electrolyte membrane of the above-described embodiment. Also, in the battery of this embodiment, the laminate including the negative electrode and the solid electrolyte membrane disposed on the negative electrode may be the laminate of the above-described embodiment. Also, in the battery of this embodiment, the laminate including the positive electrode and the solid electrolyte membrane disposed on the positive electrode may be the laminate of the above-described embodiment.

[0061] The battery of this embodiment includes the solid electrolyte membrane of the above-described embodiment or the laminate of the above-described embodiment, and therefore has mechanical properties and flexibility that make it applicable to roll-to-roll manufacturing. The battery of this embodiment includes the solid electrolyte membrane of the above-described embodiment or the laminate of the above-described embodiment, and therefore has excellent charge / discharge characteristics due to good ionic conductivity and short circuit suppression effect. [Example]

[0062] The present invention will be explained in more detail below by way of experimental examples, but the present invention is not limited to the following experimental examples.

[0063] [Experimental Example] "Preparation of acid-modified (sulfate esterified) CNF aqueous dispersion" 180 g of dimethyl sulfoxide (DMSO), 20 g of acetic anhydride, and 5.6 g of sulfuric acid were placed in a 300 ml sample bottle and stirred for approximately 30 seconds using a magnetic stirrer at room temperature of 25°C to prepare a defibration solution. Next, 6.0 g of softwood kraft pulp NBKP (manufactured by Nippon Paper Industries Co., Ltd.) was added to the defibrating solution and stirred for an additional 2 hours at room temperature of 25°C to carry out a sulfate esterification reaction. After stirring, 250 ml of distilled water was added to the cellulose-containing defibrating solution to stop the reaction, and then a 5% by mass aqueous solution of sodium hydroxide was added until the pH reached 7 to neutralize the reaction solution. The supernatant was then removed by centrifugation. Further, 1350 ml of distilled water was added and stirred until uniformly dispersed, and then the supernatant was removed by centrifugation. The same procedure was repeated for a total of three washings. Water was added to the obtained sulfated cellulose nanofibers to bring the total weight to 600 g, and the mixture was stirred for 3 minutes using a mixer (product name: G5200, manufactured by Biolomix) to obtain a uniform aqueous dispersion of sulfated CNF with a concentration of 1% by mass.

[0064] "Preparation of acid-modified (TEMPO-oxidized) CNF aqueous dispersion" 0.13 mmol of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) and 10 mmol of sodium bromide were dissolved in water to obtain a 250 mL aqueous solution. 5 g of absolute dry softwood kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) was added to this solution and stirred until the pulp was uniformly dispersed. After the mixture was cooled to 20°C, 32 mmol of aqueous sodium hypochlorite solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to initiate the oxidation reaction. During the reaction, the temperature of the reaction system was maintained at 20°C, and a 3N aqueous solution of sodium hydroxide was gradually added to maintain the pH at 10. After the reaction for 3 hours, the resultant was filtered through a glass filter, and the filter cake was thoroughly washed with water. Water was added to the resulting TEMPO-oxidized cellulose nanofibers to bring the total weight to 500 g, and the mixture was stirred for 3 minutes using a mixer (G5200, manufactured by Biolomix) to obtain a uniform aqueous dispersion of TEMPO-oxidized CNF with a concentration of 1% by mass.

[0065] "Preparation of solid electrolyte composition" The above 1% by mass acid-modified CNF aqueous dispersion and the above inorganic particles in the amounts shown in Tables 1 to 4 were placed in a 50 mL PP container and mixed at 2000 rpm for 1 minute using a planetary centrifugal mixer (product name: ARE-310, manufactured by THINKY). Thereafter, LiTFSI as a lithium salt and tetraglyme (TG) as a polyether were added in the amounts shown in Tables 1 and 2, and the mixture was degassed by mixing at 2000 rpm for 1 minute using the planetary centrifugal mixer to obtain a solid electrolyte composition. The solid electrolyte composition was used in the next step without replacing the water contained therein with a nonaqueous organic solvent. In Tables 1 and 2, acid-modified S indicates that sulfated CNF was used, and acid-modified T indicates that TEMPO-oxidized CNF was used.

[0066] "Fabrication of solid electrolyte-containing sheets" The solid electrolyte composition was applied onto a PET film (product name: Lumirror, thickness 100 μm, manufactured by Toray Industries, Inc.) using an applicator with a clearance set to 1000 μm, to form a coating film made of the solid electrolyte composition. Thereafter, the coating film was dried at 25° C. for 24 hours, and then dried under vacuum at 60° C. for 1 hour to form a solid electrolyte membrane on the PET film. Thereafter, the solid electrolyte membrane was peeled off from the PET film to obtain a solid electrolyte composite sheet having a thickness of 10 μm.

[0067] "Evaluation of film formation properties of solid electrolyte-containing sheets" The solid electrolyte composite sheets obtained were marked with a "good" if they maintained homogeneity after drying, and marked with an "x" if they were deformed due to shrinkage. The results are shown in Tables 3 and 4.

[0068] "Evaluation of short circuit prevention properties of solid electrolyte-containing sheets" A Li|Li symmetric cell was fabricated using the obtained solid electrolyte membrane, and constant current charge / discharge measurements were performed using a charge / discharge evaluation device (HJ1001SD8, product name) manufactured by Hokuto Denko Corporation to evaluate the lithium dendrite generation suppression effect. The applied current was 0.5 mA / cm. 2 The sign was then reversed, and those for which no voltage drop was observed after 200 cycles were marked with "Good," and those for which a voltage drop was observed were marked with "Poor." The results are shown in Tables 3 and 4.

[0069] "Measurement of lithium ion conductivity" The obtained solid electrolyte composite sheet was cut into a circle with a diameter of 10 mm, and the solid electrolyte composite sheet was sandwiched between two stainless steel plates as electrodes, and the impedance between the stainless steel plates was measured. To measure the impedance, an AC voltage (applied voltage of 50 mV) was applied between the electrodes, and the resistance component was measured using the AC impedance method. The ionic conductivity was calculated from the real impedance intercept of the obtained Nyquist plot. A potentiostat / galvanostat (product name: SP-150, manufactured by Biologic) was used for the measurement. The ionic conductivity (σ) was calculated using the following formula (2). σ=L / (R×S) (2) In equation (1), σ is the ionic conductivity (unit: S cm -1 ), R is the resistance (unit: Ω), S is the cross-sectional area of ​​the solid electrolyte membrane at the time of measurement (unit: cm 2 ), and L indicates the distance between the electrodes (unit: cm). The measurement temperature was set to 25° C. The ionic conductivity (σ) was calculated from the complex impedance measurement results. The results are shown in Tables 1 and 2.

[0070] In Tables 1 and 2, LICGC indicates oxide solid electrolyte particles manufactured by Ohara Corporation, acid-modified S indicates sulfated cellulose nanofiber, and acid-modified T indicates TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-catalyzed oxidized cellulose nanofiber.

[0071] [Table 1]

[0072] [Table 2]

[0073] [Table 3]

[0074] [Table 4]

[0075] The results of Experimental Examples 1 to 6 shown in Table 3 indicate that when the degree of substitution of the acid-modified cellulose nanofibers contained in the solid electrolyte composition is 1.3 mmol / g or more and 3.5 mmol / g or less, the film-forming properties and short-circuit prevention properties of the solid electrolyte-containing sheet are excellent. That is, in Experimental Example 1, the degree of substitution of the sulfated cellulose nanofibers was 1.2 mmol / g, and therefore the film-forming properties and short-circuit prevention properties of the solid electrolyte-containing sheet were poor. The results of Experimental Examples 7 to 10 shown in Table 3 indicate that when the content of LiTFSI in the solid electrolyte composition is 0.00 to 0.79 mass%, the solid electrolyte-containing sheet has excellent film-forming properties and short-circuit prevention properties. Although Experimental Example 7 does not contain LiTFSI, it contains inorganic particles and polyether, and therefore the solid electrolyte-containing sheet has excellent film-forming properties and short-circuit prevention properties. The results of Experimental Examples 11 to 14 shown in Tables 3 and 4 indicate that when the content of sulfated cellulose nanofibers in the solid electrolyte-containing sheet (dry film) is 50 to 90 mass %, the film-forming properties and short-circuit prevention properties of the solid electrolyte-containing sheet are excellent. That is, in Experimental Example 11, the solid electrolyte-containing sheet does not contain sulfated cellulose nanofibers, and therefore the film-forming properties and short-circuit prevention properties of the solid electrolyte-containing sheet are poor. In addition, in Experimental Example 12, the content of sulfated cellulose nanofibers in the solid electrolyte-containing sheet is 10 mass %, and therefore the film-forming properties and short-circuit prevention properties of the solid electrolyte-containing sheet are poor. The results of Experimental Example 15 shown in Table 4 demonstrate that even when the counter cation of the sulfate group of the sulfated cellulose nanofiber is Li, the solid electrolyte-containing sheet has excellent film-forming properties and short-circuit prevention properties. The results of Experimental Examples 16 to 19 shown in Table 4 demonstrate that even when the inorganic particles are silicon dioxide, the solid electrolyte-containing sheet has excellent film-forming properties and short-circuit prevention properties. The results of Experimental Example 20 shown in Table 4 reveal that even when no inorganic particles are contained but polyether and lithium salt are contained, the solid electrolyte-containing sheet has excellent film-forming properties and short-circuit prevention properties. The results of Experimental Examples 21 to 24 shown in Table 4 reveal that when TEMPO-catalyzed oxidized cellulose nanofibers were used as acid-modified cellulose nanofibers, the film-forming properties and short-circuit prevention properties of the solid electrolyte-containing sheet were poor. It should be noted that Experimental Examples 2 to 10 and Experimental Examples 13 to 20 are examples of the present invention, and Experimental Examples 1, 11, 12, and Experimental Examples 21 to 24 are comparative examples of the present invention.

[0076] The upper and / or lower limits of the numerical ranges described herein can be arbitrarily combined to define a preferred range. For example, the upper and lower limits of the numerical ranges can be arbitrarily combined to define a preferred range, the upper limits of the numerical ranges can be arbitrarily combined to define a preferred range, and the lower limits of the numerical ranges can be arbitrarily combined to define a preferred range. Furthermore, in this specification, numerical ranges expressed using the symbol "to" include the numerical values ​​written before and after the symbol "to" as the upper and lower limits, respectively.

[0077] Although the present embodiment has been described in detail above, the specific configuration is not limited to this embodiment, and even if there are design changes within the scope that do not deviate from the gist of this disclosure, they are included in this disclosure.

Claims

1. A solid electrolyte composition comprising an acid-modified cellulose nanofiber, a solvent, and an ion-conducting assistant.

2. The solid electrolyte composition according to claim 1 , wherein the acid-modified cellulose nanofibers are sulfated cellulose nanofibers.

3. The solid electrolyte composition according to claim 1, wherein the acid-modified cellulose nanofibers have a degree of substitution of 1.3 mmol / g or more and 3.5 mmol / g or less.

4. The solid electrolyte composition according to claim 1 , wherein the ion-conducting aid comprises at least one of inorganic particles, polyether, and lithium salt.

5. The solid electrolyte composition according to claim 4 , wherein the inorganic particles are oxide-based solid electrolyte particles or inert inorganic particles.

6. The solid electrolyte composition according to claim 1 , wherein the solvent is water, and the content of the water is 90.0 mass % or more and 99.0 mass % or less.

7. The solid electrolyte composition according to claim 4 , wherein the content of the inorganic particles is 0.01% by mass or more and 2.0% by mass or less.

8. The solid electrolyte composition according to claim 4 , wherein the content of the polyether is 0.5% by mass or more and 5.0% by mass or less.

9. The solid electrolyte composition according to claim 4 , wherein the content of the lithium salt is 0.01% by mass or more and 3.0% by mass or less.

10. The solid electrolyte composition according to claim 5 , wherein the content of the oxide-based solid electrolyte is 0.01% by mass or more and 2.0% by mass or less.

11. The solid electrolyte composition according to claim 5 , wherein the content of the inert inorganic particles is 0.01% by mass or more and 2.0% by mass or less.

12. A solid electrolyte membrane comprising acid-modified cellulose nanofibers and an ion-conducting assistant.

13. The solid electrolyte membrane according to claim 12 , wherein the acid-modified cellulose nanofibers are sulfated cellulose nanofibers.

14. A laminate comprising an electrode and the solid electrolyte membrane according to claim 12 disposed on the electrode.

15. A battery comprising the solid electrolyte membrane according to claim 12 or the laminate according to claim 14.

16. A step of mixing acid-modified cellulose nanofibers, a solvent, and an ion-conducting assistant to obtain a mixed solution; and removing air bubbles contained in the mixed liquid.

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