Separator for electrochemical elements

Abstract

The present invention provides a method for obtaining a separator for electrochemical elements, the separator being stable even in the presence of an acid, an alkali, or a carbonate anion. The present invention provides a separator for electrochemical elements, the separator being characterized by containing titanium dioxide particles that have a rutile crystal structure, and a binder.

Description

Separators for electrochemical elements

[0001] The present invention relates to a separator for an electrochemical element, and more particularly to a separator used in electrochemical elements such as batteries, condensers, sensors, fuel cells, and electrolysis (electrolysis) devices.

[0002] In recent years, the importance of electrochemical devices, including batteries, has rapidly increased in many industries, from small portable devices to large applications such as automobiles, and various new battery systems have been developed and improved, with advantages mainly in terms of capacity, energy density, and rechargeability.

[0003] Various developments and improvements have also been made to separators used in electrochemical elements. For example, the applicant has proposed a separator comprising an anion conductive membrane containing a polymer and inorganic compound particles (see, for example, Patent Documents 1 to 3).

[0004] The applicant has also proposed a separator for an electrochemical element using magnesium hydroxide particles as inorganic compound particles (see, for example, Patent Documents 4 to 6).

[0005] Furthermore, zinc battery separators containing titanium oxide have been disclosed (see, for example, Patent Documents 7 and 8).

[0006] International Publication No. 2014 / 119665 International Publication No. 2016 / 194872 International Publication No. 2020 / 111027 JP 2018-142444 A JP 2019-110099 A JP 2019-110270 A JP 2019-216057 A JP 2022-97953 A

[0007] Although magnesium hydroxide is stable in alkalis, it can dissolve in acids or form salts with carbonate anions, and separators containing magnesium hydroxide are at risk of deterioration in the presence of acids or carbonate anions. It has also been desired to make separators containing other inorganic compounds, such as titanium oxide, more stable.

[0008] The present invention has been made in view of the above-mentioned current situation, and an object of the present invention is to provide a method for obtaining a separator for an electrochemical element that is stable even in the presence of an acid, an alkali, or a carbonate anion.

[0009] The present inventors have conducted extensive research into methods for obtaining separators for electrochemical elements that are stable even in the presence of acids, alkalis, or carbonate anions, and have focused on titanium dioxide particles as a separator material, examining various titanium dioxide particles, and have produced separators for electrochemical elements that contain titanium dioxide particles having a rutile crystal structure and a binder. The present inventors have found that this separator is extremely stable even in the presence of acids, alkalis, or carbonate anions and can be suitably applied to various electrochemical elements. They have conceived the idea of ​​successfully solving the above-mentioned problems and have arrived at the present invention.

[0010] That is, the present invention (1) is a separator for an electrochemical element, characterized by comprising titanium dioxide particles having a rutile crystal structure and a binder.

[0011] The present invention (2) is the separator for an electrochemical element according to the present invention (1), characterized in that the titanium dioxide particles have a ratio (Ia101 / Ir110) of the integrated intensity of the (101) diffraction line (Ia101) in an anatase crystal structure to the integrated intensity of the (110) diffraction line (Ir110) in a rutile crystal structure, as measured by X-ray diffraction, of 1.3 or less.

[0012] The present invention (3) is the separator for an electrochemical element according to the present invention (1) or (2), in which the binder is a polymer.

[0013] The present invention (4) is an electrochemical element characterized by comprising the separator for an electrochemical element according to any one of the present inventions (1) to (3) and an electrolyte solution.

[0014] The separator for electrochemical elements of the present invention is stable even in the presence of an acid, an alkali, or a carbonate anion, and can be suitably applied to various electrochemical elements.

[0015] 1 is a graph showing XRD patterns of titanium dioxide particles used in Examples and Comparative Examples.

[0016] The present invention will be described in detail below. Note that a combination of two or more of the individual preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

[0017] <Separator for Electrochemical Device> The separator for an electrochemical device of the present invention comprises titanium dioxide particles having a rutile crystal structure and a binder. In this specification, the separator for an electrochemical device of the present invention may also be simply referred to as a separator.

[0018] (Titanium dioxide particles having a rutile crystal structure) The titanium dioxide particles have a rutile crystal structure. The rutile crystal structure can be confirmed by X-ray diffraction measurement based on the presence of a peak attributable to the rutile crystal structure (for example, a (110) diffraction line in a rutile crystal structure at a diffraction angle 2θ of approximately 27.5°). Whether or not titanium dioxide particles have a rutile crystal structure, i.e., whether or not a peak attributable to the rutile crystal structure is present, can be determined by the method described in the Examples. Among titanium dioxide particles, those having a rutile crystal structure have low photocatalytic activity specific to titanium dioxide. As a result, it is believed that gas generation and particle slippage can be sufficiently prevented when immersed in an electrolyte, thereby stabilizing a separator for an electrochemical element. In this specification, a stable separator means that gas generation and particle slippage can be sufficiently prevented when the separator is immersed in an electrolyte.

[0019] Titanium dioxide particles having a rutile crystal structure have, as measured by X-ray diffraction, when the peak intensity (Ia101) of the (101) diffraction line in the anatase crystal structure is 100,000 cps, the peak intensity (Ir110) of the (110) diffraction line in the rutile crystal structure is 50 cps or more, preferably 100 cps or more, more preferably 1,000 cps or more, even more preferably 10,000 cps or more, and particularly preferably 100,000 cps or more. The upper limit of the peak intensity (Ir110) of the (110) diffraction line in the rutile crystal structure is not particularly limited, but is usually 5,000,000 cps or less. Here, when the peak intensity (Ia101) of the (101) diffraction line in the anatase crystal structure is 100,000 cps, whether or not the peak intensity (Ir110) of the (110) diffraction line in the rutile crystal structure is within the above range, as measured by X-ray diffraction, can be determined by a method similar to that described in the Examples.

[0020] The titanium dioxide particles preferably have a ratio (Ia101 / Ir110) of the integrated intensity of the (101) diffraction line (Ia101) in the anatase crystal structure to the integrated intensity of the (110) diffraction line (Ir110) in the rutile crystal structure, as measured by X-ray diffraction, of 1.3 or less. Typically, the (110) diffraction line in the rutile crystal structure is a peak at a diffraction angle 2θ of approximately 27.5°, and the (101) diffraction line in the anatase crystal structure is a peak at a diffraction angle 2θ of approximately 25.4°. Note that the lattice spacing may fluctuate depending on the impurities and the size of the titanium dioxide particles, resulting in a deviation in the value of the diffraction angle 2θ. It is believed that a small proportion of the anatase crystal structure, which has high photocatalytic activity, can further stabilize the separator for electrochemical elements.

[0021] The ratio (Ia101 / Ir110) is more preferably 1.0 or less, even more preferably 0.9 or less, even more preferably 0.8 or less, still more preferably 0.7 or less, and particularly preferably 0.6 or less. The lower limit of the ratio (Ia101 / Ir110) is not particularly limited, and may be 0.

[0022] The titanium dioxide particles have a crystallite diameter in the direction perpendicular to the (110) plane of the rutile crystal structure, as measured by X-ray diffraction, of preferably 1 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more, and the crystallite diameter in the direction perpendicular to the (110) plane is preferably 200 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less.

[0023] When the titanium dioxide particles have an anatase crystal structure, the crystallite diameter in the direction perpendicular to the (101) plane of the anatase crystal structure, as measured by X-ray diffraction, is preferably 1 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more, and the crystallite diameter in the direction perpendicular to the (101) plane is preferably 200 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less.

[0024] In the titanium dioxide particles, the crystallite diameter in the direction perpendicular to the (110) plane in the rutile crystal structure, as measured by X-ray diffraction, is preferably larger than the crystallite diameter in the direction perpendicular to the (101) plane in the anatase crystal structure. In particular, the crystallite diameter in the direction perpendicular to the (110) plane in the rutile crystal structure is more preferably 1 nm or more larger, even more preferably 3 nm or more larger, and particularly preferably 5 nm or more larger than the crystallite diameter in the direction perpendicular to the (101) plane in the anatase crystal structure. The difference in the crystallite diameters is usually 100 nm or less. The integrated intensity and crystallite diameters described above are measured and calculated according to the methods described in the Examples.

[0025] The titanium dioxide particles having the above-mentioned rutile crystal structure can be obtained by appropriately adjusting the preparation conditions using a conventionally known method such as a sulfuric acid method or a chlorine method. For example, titanium dioxide particles having a high proportion of the rutile crystal structure can be obtained by adding a rutile transition promoter during the production process or by heat-treating at 700°C or higher (the heat-treatment temperature is described in, for example, "anatase TiO ２(See "3.1 Phase transition temperature of titanium oxide raw material powder" in "Preparation of sintered body and its photocatalytic effect," Asano Makoto et al., and one other person, Nara Prefectural Industrial Technology Center, Research Report No. 26, 2000).

[0026] The titanium dioxide particles having a rutile crystal structure are preferably those whose surfaces are composed of titanium dioxide having a rutile crystal structure. For example, the titanium dioxide particles having a rutile crystal structure described above may be surface-treated with aluminum oxide or the like, but are preferably not surface-treated.

[0027] Titanium dioxide particles having a rutile crystal structure preferably have a titanium atom content of 85% by mass or more relative to 100% by mass of the total of elements other than oxygen atoms and hydrogen atoms contained in the particles. It is more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 97% by mass or more. The titanium atom content can be confirmed by X-ray fluorescence analysis, atomic absorption analysis, ICP emission analysis, etc. Among these, confirmation by X-ray fluorescence analysis is preferred.

[0028] The shape of the titanium dioxide particles may be fine powder, powder, granules, granules, scales, polyhedrons, rods, or shapes containing curved surfaces. Such titanium dioxide particles may be single crystals or polycrystalline as long as they have a rutile crystal structure, and either type will achieve the effects of the present invention. The titanium dioxide particles preferably have an average particle size of 10 μm or less as measured by the measurement method described in the Examples. The average particle size is more preferably 5 μm or less, even more preferably 1 μm or less, and particularly preferably 500 nm or less. The average particle size is preferably 1 nm or more, more preferably 10 nm or more, even more preferably 50 nm or more, and particularly preferably 100 nm or more.

[0029] Particles having an average particle size in the above range can be produced, for example, by a method of pulverizing particles using a ball mill or the like, dispersing the resulting coarse particles in a dispersant to a desired particle size, and then drying and solidifying the particles, or by a method of screening the coarse particles through a sieve or the like to select the particle size, or by a method of optimizing preparation conditions in the particle production stage to obtain particles of a desired particle size.

[0030] The mass proportion of the titanium dioxide particles is preferably 30% by mass or more, based on 100% by mass of the separator for electrochemical elements. This mass proportion is more preferably 40% by mass or more, even more preferably 45% by mass or more, and particularly preferably 50% by mass or more. Furthermore, this mass proportion is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less.

[0031] (Binder) The binder is not particularly limited as long as it can bind and fix titanium dioxide particles having a rutile crystal structure in the separator for electrochemical elements, but is preferably a polymer. Examples of the polymer include organic polymers; inorganic polymers such as hydrolyzates and condensates of metal alkoxides such as silicon alkoxides and titanium alkoxides; and organic-inorganic composite polymers, among which organic polymers are preferred. The organic polymer may be a homopolymer or a copolymer, unless otherwise clearly limited.

[0032] The organic polymer may be either thermoplastic or thermosetting, but is preferably a component having a glass transition temperature of less than 60°C. The organic polymer binds particles together, thereby contributing to the structural stability of the separator. The organic polymer preferably has a glass transition temperature of 50°C or lower. In this specification, the glass transition temperature is measured using a differential scanning calorimeter (apparatus name: thermal analyzer DSC3100S, BRVKER) at a heating rate of 10°C / min for a dried product obtained by applying a material such as a polymer to a glass plate and drying it at 120°C for 1 hour.

[0033] The organic polymer is also preferably an amorphous organic polymer. Being amorphous facilitates bonding with surrounding components and functions favorably as a binder component. Examples of the organic polymer include hydrocarbon moiety-containing polymers such as polyethylene and polypropylene; aromatic group-containing polymers such as polystyrene; ether group-containing polymers such as alkylene glycol; halogen atom-containing polymers such as polytetrafluoroethylene; epoxy resins; quaternary ammonium salt- or quaternary phosphonium salt-containing polymers; ion-exchange polymers used in cation / anion exchange membranes; conjugated diene-based polymers; (meth)acrylic polymers; amino group-containing polymers such as polyethyleneimine; carbamate group-containing polymers; carbamide group-containing polymers; epoxy group-containing polymers; heterocyclic and / or ionized heterocyclic moiety-containing polymers; polymer alloys; and heteroatom-containing polymers. One or more of these may be used. Among these, halogen atom-containing polymers and conjugated diene-based polymers are preferred. Furthermore, from the viewpoint of further improving the life of the secondary battery by partially maintaining the particle shape and filling the voids in the separator to densify the separator, it is more preferable that the organic polymer be a halogen atom-containing polymer such as polytetrafluoroethylene. These polymers act as binders for titanium dioxide particles having a rutile crystal structure contained in the separator for electrochemical devices, and can prevent the occurrence of cracks.

[0034] Preferred examples of the halogen atom-containing polymer include polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, and polypentafluoroethylene, and among these, polytetrafluoroethylene, polyvinylidene fluoride, and polypentafluoroethylene are more preferred.

[0035] The conjugated diene polymer has a monomer unit derived from a conjugated diene monomer. As the conjugated diene polymer, one or more of styrene-butadiene polymers (SBR), carboxy-modified styrene-butadiene polymers, polybutadiene polymers, carboxy-modified polybutadiene polymers, polyisoprene polymers, carboxy-modified polyisoprene polymers, acrylonitrile-butadiene polymers, and carboxy-modified acrylonitrile-butadiene polymers can be suitably used. Among these, styrene-butadiene polymers and carboxy-modified styrene-butadiene polymers are preferred.

[0036] The conjugated diene polymer may contain monomer units derived from other unsaturated monomers other than monomer units derived from aliphatic conjugated diene monomers, monomer units derived from aromatic vinyl monomers, and monomer units derived from unsaturated monomers having a carboxy group and / or a carboxylate group (a salt thereof). The mass proportion of the monomer units derived from other unsaturated monomers in 100% by mass of the conjugated diene polymer is preferably 30% by mass or less, more preferably 5% by mass or less, and even more preferably 0.1% by mass or less.

[0037] The (meth)acrylic polymer has a monomer unit derived from a monomer having a (meth)acryloyl group other than a (meth)acrylic acid monomer, and a representative example thereof is one mainly composed of a monomer unit derived from a (meth)acrylic acid ester monomer.

[0038] "Containing mainly monomer units derived from (meth)acrylic acid ester monomers" means that the content of monomer units derived from (meth)acrylic acid ester monomers is 50% by mass or more relative to 100% by mass of the (meth)acrylic polymer. Specific examples of the (meth)acrylic acid ester monomer include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, and decyl (meth)acrylate.

[0039] The (meth)acrylic polymer may contain, in addition to the monomer units derived from the (meth)acrylic acid ester monomer, monomer units derived from unsaturated monomers having a carboxy group and / or a carboxylate group (a salt thereof), or monomer units derived from other unsaturated monomers. The mass proportion of the monomer units derived from other unsaturated monomers in 100% by mass of the (meth)acrylic polymer is preferably 30% by mass or less, more preferably 5% by mass or less, and even more preferably 0.1% by mass or less.

[0040] The organic polymer can suitably adjust the strength, anion conductivity, etc. of the separator by applying heat, pressure, etc.

[0041] From the viewpoint of suitably adjusting the ionic conductivity and elongation and stress of the separator, the mass proportion of the binder (preferably an organic polymer) is preferably 3 mass% or more relative to 100 mass% of the separator for electrochemical elements. This mass proportion is more preferably 5 mass% or more, and even more preferably 7 mass% or more. Furthermore, this mass proportion is preferably 70 mass% or less. This mass proportion is more preferably 60 mass% or less, even more preferably 50 mass% or less, even more preferably 45 mass% or less, and particularly preferably 40 mass% or less.

[0042] (Porous Substrate) The separator for electrochemical elements of the present invention preferably further comprises a porous support (porous substrate). The separator for electrochemical elements of the present invention may be a resin-impregnated layer in which a porous substrate is impregnated with a mixture of titanium dioxide particles having a rutile crystal structure, a binder, and, if necessary, other components, or may have a laminate structure obtained by contacting the mixture with the porous substrate and drying the mixture if necessary.

[0043] The porous substrate is not particularly limited, but examples thereof include nonwoven fabrics, woven fabrics, and microporous films made of resin materials such as polyolefin polymers (e.g., polyethylene (PE), polypropylene (PP), ethylene-propylene copolymers, polybutene, polymethylpentene, and cyclic polyolefin polymers); polyvinyl alcohol polymers (e.g., vinylon); aliphatic polyamides; aromatic polyamides; styrene polymers; polyester polymers; and polyphenylene sulfide polymers. Among these, polyolefin polymers, polyvinyl alcohol polymers, and polyphenylene sulfide polymers are more preferred. The separator for electrochemical elements of the present invention is preferably a porous substrate at least partially integrated with a resin-impregnated layer obtained by impregnating the porous substrate with the mixture. In the separator, the solid content of the mixture fills at least a portion of the pores in the porous substrate.

[0044] The mass proportion of the porous substrate is preferably 1 mass% or more, more preferably 3 mass% or more, and even more preferably 5 mass% or more, relative to 100 mass% of the separator for electrochemical elements of the present invention, and is preferably 50 mass% or less, more preferably 30 mass% or less, even more preferably 20 mass% or less, even more preferably 15 mass% or less, and particularly preferably 10 mass% or less.

[0045] (Other Components) The separator for electrochemical elements of the present invention may contain other components in addition to the titanium dioxide particles having a rutile crystal structure, the binder, and the porous substrate. For example, the separator for electrochemical elements of the present invention may contain a water-soluble polymer as a dispersant for the titanium dioxide particles having a rutile crystal structure. Examples of water-soluble polymers include celluloses such as carboxymethyl cellulose; poly(meth)acrylic acid (salts) such as sodium polyacrylate; and copolymers of (meth)acrylic acid (salts) with unsaturated carboxylic acids (salts) such as maleic acid (salts) or unsaturated sulfonic acids (salts) such as vinyl sulfonic acid (salts). One or more of these may be used.

[0046] When the separator for electrochemical elements of the present invention contains a water-soluble polymer, the content of the water-soluble polymer is preferably 0.1 mass% or more relative to 100 mass% of the separator for electrochemical elements of the present invention from the viewpoint of sufficiently dispersing the titanium dioxide particles having a rutile crystal structure and thereby exerting their effects, and the content is preferably 3 mass% or less from the viewpoint of further suppressing the water-soluble polymer from absorbing the electrolyte solution such as water and plasticizing the separator.

[0047] The separator for electrochemical elements of the present invention may further contain other inorganic components other than the titanium dioxide having a rutile crystal structure described above, such as oxides, hydroxides, layered double hydroxides, phosphate compounds, conductive carbon, conductive ceramics, etc. The content of other inorganic components in the separator for electrochemical elements of the present invention is preferably 30% by mass or less, more preferably 10% by mass or less, even more preferably 1% by mass or less, and particularly preferably 0.1% by mass or less, based on 100% by mass of the separator.

[0048] The separator for electrochemical elements of the present invention preferably has an average film thickness of 10 μm to 1 mm. A thickness of 10 μm or more can adequately prevent breakage during film formation. A thickness of 1 mm or less is advantageous from a cost perspective and also provides sufficiently excellent ion permeability. The average film thickness is more preferably 20 μm or more, even more preferably 50 μm or more, and particularly preferably 100 μm or more. The average film thickness is more preferably 800 μm or less, even more preferably 500 μm or less, and particularly preferably 200 μm or less. The average film thickness can be measured according to the method described in the Examples.

[0049] The separator for electrochemical elements of the present invention is used in electrochemical elements such as batteries, condensers, capacitors, sensors, fuel cells, and electrolysis devices, and is generally used in electrochemical elements configured to contain an electrolytic solution. In one preferred embodiment of the present invention, the electrolytic solution is an acidic electrolytic solution and / or a carbonate-containing electrolytic solution. The electrolytic solution may be, for example, an aqueous electrolytic solution or an organic solvent-based electrolytic solution.

[0050] (Method for Manufacturing a Separator for Electrochemical Elements of the Present Invention) The separator for electrochemical elements of the present invention can be manufactured by preparing a composition (hereinafter, simply referred to as the composition of the present invention) to be used for forming a film to obtain a separator for electrochemical elements, and then forming this composition into a film by the method described below. First, the raw materials for the composition of the present invention (titanium dioxide particles having a rutile crystal structure of the present invention, a binder, and, if necessary, other components such as a dispersant for the titanium dioxide particles) are mixed. For mixing, a mixer, blender, kneader, sand mill, bead mill, ready mill, roll mill, ball mill, or the like can be used. During mixing, water, an organic solvent such as methanol, ethanol, propanol, isopropanol, butanol, hexanol, tetrahydrofuran, or N-methylpyrrolidone, or a mixed solvent of water and an organic solvent may be added as a medium. After mixing, filtration, degassing, or the like may be performed as necessary to obtain the composition of the present invention. Note that a dispersion of titanium dioxide particles having a rutile crystal structure may be prepared before mixing. For example, titanium dioxide particles having a rutile crystal structure and a dispersant for the titanium dioxide particles are mixed together. By producing a dispersion of titanium dioxide particles having a rutile crystal structure before mixing, it is possible to prevent the binder, such as an organic polymer, from becoming unstable during preparation. The above-mentioned equipment and medium can be used for mixing. When producing the titanium dioxide particle dispersion, the preparation method is not particularly limited, but for example, the dispersant can be added to a medium such as water and stirred, and then the titanium dioxide particles can be further added and dispersed.

[0051] The method for producing a film from the composition according to the present invention is not particularly limited, and examples that can be used include a method in which the composition according to the present invention is coated on a release substrate such as a mirror-finished metal roll or a polyethylene terephthalate (PET) film, dried, and the resulting coating film is peeled off to obtain a film (casting method), a method in which the composition is rolled with a roll to form a film, a method in which the composition is rolled with a flat press or the like to form a film, a method in which the composition is formed into a film by injection molding, extrusion molding, or the like, or a method in which the composition is coated on an electrode sheet, dried, and formed into a film integrated with the electrode sheet. These forming methods may be used alone, or two or more of them may be used in combination.

[0052] The above-mentioned production method preferably includes a step of drying the film during and / or after the step of forming the composition according to the present invention into a film. The drying step after the film formation may be performed by heating the film as necessary. The heating temperature and heating time of the film may be appropriately set.

[0053] When the separator for electrochemical elements of the present invention further comprises a porous substrate, the separator for electrochemical elements of the present invention can be produced, for example, by laminating a film obtained from the composition of the present invention and the porous substrate by a conventionally known method, by applying the composition of the present invention to a release substrate, bringing the composition into contact with and impregnating the porous substrate, solidifying the film, and then peeling it off from the release substrate, or by applying the composition of the present invention to a porous substrate and then drying it.

[0054] <Electrochemical element> The present invention also relates to an electrochemical element comprising the separator for an electrochemical element of the present invention and an electrolytic solution. Examples of the electrochemical element of the present invention include batteries; capacitors such as electrolytic capacitors; capacitors such as electric double layer capacitors and lithium ion capacitors; sensors such as humidity sensors and gas sensors; and electrolysis devices such as water electrolysis devices and carbon dioxide electrolysis devices.

[0055] The electrochemical element of the present invention is configured to contain an electrolyte. For example, one preferred embodiment of the present invention is that the electrochemical element of the present invention is configured to contain an acidic electrolyte and / or a carbonate-containing electrolyte. Examples of acidic electrolytes include inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid, or aqueous solutions thereof; organic acids such as (meth)acrylic acid, maleic acid, and fumaric acid, or aqueous solutions thereof; and aqueous solutions of halides such as zinc chloride and zinc iodide. Examples of carbonate-containing electrolytes include aqueous solutions of carbonates such as sodium carbonate and potassium carbonate.

[0056] The electrochemical element of the present invention may be configured to contain an aqueous electrolyte solution. The aqueous electrolyte solution is not particularly limited as long as it is one that uses water as the main component of the electrolyte solution raw material, which is commonly used as an aqueous electrolyte solution for electrochemical elements. It may also contain an organic solvent in addition to water. "Using water as the main component of the electrolyte solution raw material" means that the mass ratio of water is 50% by mass or more in 100% by mass of the aqueous electrolyte solution. This mass ratio is preferably 80% by mass or more. Examples of organic solvents include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, dimethoxymethane, diethoxymethane, dimethoxyethane, tetrahydrofuran, methyltetrahydrofuran, diethoxyethane, dimethyl sulfoxide, sulfolane, acetonitrile, benzonitrile, ionic liquids, fluorine-containing carbonates, fluorine-containing ethers, polyethylene glycols, and fluorine-containing polyethylene glycols. These may be used alone or in combination of two or more.

[0057] In particular, the electrochemical element of the present invention is preferably an electrochemical element comprising an electrolyte solution using only water as an electrolyte raw material. Electrolytes using only water as an electrolyte raw material have higher thermal stability, and by using the separator for an electrochemical element of the present invention, more stable electrochemical properties can be obtained.

[0058] In another preferred embodiment of the present invention, the aqueous electrolyte solution is an alkaline electrolyte solution. Examples of the alkaline electrolyte solution include aqueous solutions of hydroxides such as potassium hydroxide, sodium hydroxide, and lithium hydroxide. These may be used alone, or aqueous solutions of two or more of these solutes may be used in combination.

[0059] (Battery) The case where the electrochemical element of the present invention is a battery will be described in detail below. A battery usually further comprises a positive electrode. The active material of the positive electrode can be any material commonly used as a positive electrode active material for primary or secondary batteries, and is not particularly limited. Examples include oxygen (when oxygen is the positive electrode active material, the positive electrode becomes an air electrode composed of a perovskite-type compound capable of reducing oxygen or oxidizing water, a cobalt-containing compound, an iron-containing compound, a copper-containing compound, a manganese-containing compound, a vanadium-containing compound, a nickel-containing compound, an iridium-containing compound, a platinum-containing compound, a palladium-containing compound, a gold-containing compound, a silver-containing compound, a carbon-containing compound, or the like); nickel-containing compounds such as nickel oxyhydroxide, nickel hydroxide, and cobalt-containing nickel hydroxide; manganese-containing compounds such as manganese dioxide; silver oxide; lithium-containing compounds such as lithium cobalt oxide; and iron-containing compounds.

[0060] The battery typically further includes a negative electrode. The active material of the negative electrode may be any material typically used as a negative electrode active material for batteries, such as carbon, sodium, zinc, lithium, nickel, magnesium, cadmium, tin, a hydrogen storage alloy, or a silicon-containing material. For example, the present invention can be suitably applied to batteries that use, as the negative electrode active material, active materials that may generate dendrites during electrode reactions, such as zinc, lithium, nickel, magnesium, or cadmium.

[0061] Electrodes such as positive and negative electrodes constituting the battery can be produced by forming an active material layer on a current collector. Examples of the current collector constituting the electrode include (electrolytic) copper foil, copper mesh (expanded metal), foamed copper, punched copper, copper alloys such as brass, brass foil, brass mesh (expanded metal), foamed brass, punched brass, nickel foil, corrosion-resistant nickel, nickel mesh (expanded metal), punched nickel, metallic zinc, corrosion-resistant metallic zinc, zinc foil, zinc mesh (expanded metal), (punched) steel plate, and conductive nonwoven fabric; (electrolytic) copper foil, copper mesh (expanded metal), foamed copper, punched copper, copper alloys such as brass, brass foil, brass mesh (expanded metal), foamed brass, punched brass, nickel foil, corrosion-resistant nickel, nickel metal, zinc foil, zinc mesh (expanded metal), (punched) steel plate, and conductive nonwoven fabric; and (electrolytic) copper foil, copper mesh (expanded metal), foamed copper, punched copper, brass alloys such as brass foil, brass mesh (expanded metal), foamed brass, punched brass, nickel foil, corrosion-resistant nickel, and nickel metal. Examples of materials include (electrolytic) copper foil plated with Ni, Zn, Sn, Pb, Hg, Bi, In, Tl, brass, etc., copper alloys such as copper mesh (expanded metal), foamed copper, punched copper, and brass, brass foil, brass mesh (expanded metal), foamed brass, punched brass, nickel foil, corrosion-resistant nickel, nickel mesh (expanded metal), punched nickel, metal zinc, corrosion-resistant metal zinc, zinc foil, zinc mesh (expanded metal), (punched) steel plate, and nonwoven fabric; silver; and materials used as current collectors or containers in alkaline (storage) batteries and air-zinc batteries.

[0062] The battery may be, for example, a secondary battery (storage battery) that can be charged and discharged. The secondary battery may be any type, such as a general secondary battery, a battery that uses mechanical charging (mechanical replacement of a zinc negative electrode), or a battery that uses a third electrode (a battery that uses an electrode suitable for charging and an electrode suitable for discharging as positive electrodes).

[0063] (Fuel Cell or Electrolysis Device) The case where the electrochemical element of the present invention is a fuel cell or an electrolysis device will be described in detail below. The separator for an electrochemical element of the present invention is suitably used as a component of a fuel cell or a water electrolysis device. Examples of the fuel cell or water electrolysis device include those comprising an anode, a cathode, and the separator for an electrochemical element of the present invention disposed between the anode and the cathode. More specifically, the fuel cell or water electrolysis device has an anode chamber in which the anode is present and a cathode chamber in which the cathode is present, separated by the separator for an electrochemical element of the present invention. Examples of the anode and the cathode include known electrodes comprising a conductive substrate containing nickel, a nickel alloy, or the like.

[0064] [Method for generating electricity from fuel cells] The method for generating electricity using a fuel cell comprising the separator for electrochemical elements of the present invention is not particularly limited, and can be performed by a known method. For example, electricity can be generated by filling an electrolyte solution into a fuel cell comprising the separator for electrochemical elements of the present invention described above, and supplying an oxidant (e.g., oxygen) and a fuel (e.g., hydrogen) to the anode and the cathode, respectively, in the electrolyte solution.

[0065] [Electrolysis Method for Water Electrolysis Apparatus] The method for electrolyzing water using a water electrolysis apparatus including the separator for an electrochemical element of the present invention is not particularly limited, and can be performed by a known method. For example, water electrolysis can be performed by filling an electrolytic solution into the water electrolysis apparatus including the separator for an electrochemical element of the present invention described above and applying a current in the electrolytic solution.

[0066] (Method of Using a Film Comprising Titanium Dioxide Particles Having a Rutile Crystal Structure and a Binder) The present invention also relates to a method of using a film comprising titanium dioxide particles having a rutile crystal structure and a binder, which comprises a step of constructing an electrochemical element using the film comprising titanium dioxide particles having a rutile crystal structure and a binder as a separator, which is a component of the electrochemical element. The step of constructing the electrochemical element preferably comprises, for example, a step of disposing the film as a separator between electrodes (e.g., between a positive electrode and a negative electrode). In the disposing step, the order of disposing the film and various electrodes is not particularly limited, as long as the film is disposed between the electrodes as a separator. In other words, the present invention also relates to a method of using a film comprising titanium dioxide particles having a rutile crystal structure and a binder as a separator for an electrochemical element. The present invention also relates to the use of a film comprising titanium dioxide particles having a rutile crystal structure and a binder as a separator for an electrochemical element. The above-mentioned film (or separator) may further comprise a porous support (porous substrate) and other components.

[0067] Specific examples and preferred embodiments of the titanium dioxide particles having a rutile crystal structure, the binder, the porous support (porous substrate), and other components constituting the membrane (or separator) are the same as those described above for the separator for electrochemical elements of the present invention, and the same explanations apply mutatis mutandis. Furthermore, specific embodiments (contexts) and preferred embodiments (contexts) of the separator configuration (the form of the separator membrane (e.g., a porous substrate impregnated with a mixture of titanium dioxide particles having a rutile crystal structure, a binder, etc.) and the separator membrane thickness), the separator manufacturing method, and the electrochemical element comprising the separator are the same as those described above for the separator for electrochemical elements of the present invention and the electrochemical element of the present invention, and the same explanations apply mutatis mutandis.

[0068] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" means "parts by weight" and "%" means "% by mass."

[0069] <XRD Measurement> Titanium oxide (powder) was measured using an X-ray diffractometer (product name: SmartLab, manufactured by Rigaku Corporation) under the following conditions: (Measurement Conditions) X-ray tube: Cu X-ray output: 45 kV, 200 mA Scan speed: 5° / min Scan range: 5 to 90°

[0070] From the diffraction lines obtained for the sample (titanium oxide), the presence or absence of a (101) diffraction line in the anatase crystal structure and the presence or absence of a (110) diffraction line in the rutile crystal structure were confirmed to determine whether the sample had a rutile crystal structure. Specifically, when the peak intensity (Ia101) of the (101) diffraction line in the anatase crystal structure was 100,000 cps, and the peak intensity (Ir110) of the (110) diffraction line in the rutile crystal structure was 50 cps or more, the sample was determined to have a rutile crystal structure, and when the peak intensity (Ir110) was less than 50 cps, the sample was determined to not have a rutile crystal structure. Here, even if the peak intensity (Ia101) of the (101) diffraction line in the anatase crystal structure is 100,000 cps or less, if the peak intensity (Ir110) of the (110) diffraction line in the rutile crystal structure is 50 cps or more, the sample was determined to have a rutile crystal structure. Also, even if the peak intensity (Ia101) of the (101) diffraction line in the anatase crystal structure is 100,000 cps or more, if the presence of the (110) diffraction line in the rutile crystal structure cannot be confirmed, specifically, if the peak intensity (Ir110) is less than 50 cps, the sample was determined not to have a rutile crystal structure.

[0071] From the obtained diffraction lines, the peak intensity, integrated intensity and full width at half maximum of the (101) diffraction line of the anatase crystal structure, and the peak intensity, integrated intensity and full width at half maximum of the (110) diffraction line of the rutile crystal structure were determined.

[0072] (Integrated Intensity Ratio R) The ratio R of the integrated intensity (Ia101) of the (101) diffraction line in the anatase crystal structure to the integrated intensity (Ir110) of the (110) diffraction line in the obtained rutile crystal structure was calculated using the following formula: R=Ia101 / Ir110

[0073] (Crystallite diameter) For the obtained diffraction lines, the crystallite diameter in the direction perpendicular to the (101) plane of the anatase crystal structure was calculated using the following Scherrer formula. Similarly, the crystallite diameter in the direction perpendicular to the (110) plane of the rutile crystal structure was calculated. Scherrer formula (crystallite diameter) = Kλ / (β cos θ) K: Scherrer constant, set to 0.94. λ [Å]: wavelength of X-ray tube β [rad]: β = b - B b [rad]: full width at half maximum of standard silicon B [rad]: full width at half maximum obtained by actual measurement θ [rad]: value of θ at diffraction angle 2θ

[0074] <Separator coating amount> Separator is cut into 5cm x 10cm pieces and the weight m １ (g) was measured, and the coating amount M (g / m) of the separator was calculated using the following formula: ２ ) was calculated. Here, m ２ is the basis weight of the substrate (g / m ２ ) M = m １ / (0.05 × 0.10)-m ２

[0075] <Separator Film Thickness> The separator film thickness was measured with a Digimatic Micrometer (manufactured by Mitutoyo Corporation) and calculated as the average of the thicknesses at 10 arbitrary measurement points.

[0076] <Particle diameter of titanium dioxide particles> The average particle diameter is the average particle diameter in a volume-based particle size distribution, and is measured by diluting titanium dioxide particles with a dispersion medium (ion-exchanged water containing 0.2% sodium hexametaphosphate), collecting about 10 mL of the obtained diluted solution in a glass cell, and using a particle size distribution measuring device (manufactured by Particle Sizing Systems, Inc., trade name: NICOMP Model 380) based on the dynamic light scattering method.

[0077] <Immersion evaluation> Sheet sample: 40 mm x 40 mm Aqueous solution: 10 g Temperature: 23°C Time: 1 night Evaluation method: Visually observe the aqueous solution and sheet sample

[0078] (Evaluation criteria) ○: No swelling of the sheet sample or clouding of the aqueous solution. Swelling △: There were a few areas where the sheet sample swelled locally, but there was no major swelling or clouding of the aqueous solution, and gas generation and particle slippage were sufficiently prevented. Swelling ×: There were many areas where the sheet sample swelled locally, and the swelling was significant. Swelling and cloudiness ×: There were many areas where the sheet sample swelled locally, and the swelling was significant. In addition, many titanium dioxide particles slid down, and the aqueous solution became clearly cloudy.

[0079] Example 1 Titanium dioxide (1) was synthesized as inorganic particles by a sulfuric acid method. The obtained titanium dioxide (1) had an average particle diameter of 180 nm, and an integrated intensity ratio R obtained by XRD measurement was 0.091 (9.1%). This titanium dioxide (1), a sodium polyacrylate aqueous dispersion (molecular weight 3500, solid content concentration 44%) as a dispersant, and ion-exchanged water were mixed in a mass ratio of 100:1.8:75 to form a slurry, thereby preparing a titanium dioxide dispersion (1). The titanium dioxide dispersion was mixed with a styrene butadiene rubber dispersion and a polytetrafluoroethylene dispersion as binders in a solid content mass ratio of 66:3:31 to obtain a separator preparation coating material (1). The obtained separator preparation coating material (1) was applied to a PP / PE nonwoven fabric (basis weight 19 g / m). ２ The separator (1) was obtained by applying the paste to a substrate (70 mm x 200 mm, film thickness 90 μm) using an applicator and then drying at 90° C. The coating amount of the obtained separator (1) was 228 g / m ２ The PP / PE nonwoven fabric is a nonwoven fabric containing composite fibers of PP and PE.

[0080] [Example 2] Titanium dioxide (2) was synthesized as inorganic particles by the chlorine method. The obtained titanium dioxide (2) had an average particle diameter of 130 nm, and the integrated intensity ratio R obtained by XRD measurement was 0.519 (51.9%). A separator (2) was produced in the same manner as in Example 1, except that this titanium dioxide (2) was used instead of the titanium dioxide (1) in Example 1. The coating amount of the obtained separator (2) was 240 g / m ２ The film thickness was 142 μm.

[0081] [Example 3] Titanium dioxide (3) was synthesized as inorganic particles by the chlorine method. The obtained titanium dioxide (3) had an average particle diameter of 70 nm, and the integrated intensity ratio R obtained by XRD measurement was 1.257 (125.7%). A separator (3) was produced in the same manner as in Example 1, except that this titanium dioxide (3) was used instead of the titanium dioxide (1) in Example 1. The coating amount of the obtained separator (3) was 237 g / m ２ The film thickness was 140 μm.

[0082] [Example 4] Instead of coating the separator-making coating material (1) on a PP / PE nonwoven fabric, a polyphenylene sulfide nonwoven fabric (basis weight 18 g / m) was used. ２ A separator (4) was produced in the same manner as in Example 1, except that the coating was carried out to a thickness of 84 μm. The coating amount of the obtained separator (4) was 212 g / m ２ The film thickness was 127 μm. The polyphenylene sulfide nonwoven fabric is a nonwoven fabric containing polyphenylene sulfide fibers. The titanium dioxides (1) to (3) used in Examples 1 to 4 were confirmed to have a rutile crystal structure by XRD measurement.

[0083] [Comparative Example 1] Titanium dioxide (4) was synthesized as inorganic particles by a sulfuric acid method. The obtained titanium dioxide (4) had an average particle diameter of 150 nm, and XRD measurement confirmed that the particles were formed with an anatase crystal structure and did not contain a rutile crystal structure. A separator (c1) was produced in the same manner as in Example 1, except that this titanium dioxide (4) was used instead of the titanium dioxide (1) in Example 1. The coating amount of the obtained separator (c1) was 234 g / m ２ The film thickness was 139 μm.

[0084] The following Table 1 shows the evaluation results of the titanium oxides and separators used in Examples 1 to 4 and Comparative Example 1. In Table 1, the "crystallite size" refers to the crystallite size in the direction perpendicular to the (101) plane in the anatase crystal structure or the (110) plane in the rutile crystal structure.

[0085]

[0086] The results shown in Table 1 above demonstrate that separators (1) to (4) containing titanium dioxide particles having a rutile crystal structure and a binder are stable and can adequately prevent gas generation and particle slippage even in the presence of acid, alkali, or carbonate anions, and are therefore suitable for use as separators for electrochemical elements.

Claims

1. The present invention comprises titanium dioxide particles having a rutile crystal structure and a binder, A separator for an electrochemical element, characterized by being used in an electrochemical element comprising an acidic electrolyte.

2. 2. The separator for an electrochemical element according to claim 1, wherein the titanium dioxide particles have a ratio (Ia101 / Ir110) of the integrated intensity of the (101) diffraction line (Ia101) in an anatase crystal structure to the integrated intensity of the (110) diffraction line (Ir110) in a rutile crystal structure, as measured by X-ray diffraction, of 1.3 or less.

3. 3. The separator for an electrochemical element according to claim 1, wherein the binder is a polymer.

4. 3. An electrochemical element comprising the separator for an electrochemical element according to claim 1 or 2 and an acidic electrolyte.