JP6955995B2 - Separator for electrochemical elements - Google Patents

Description

The present invention relates to a separator for an electrochemical element. More specifically, the present invention relates to a separator used for an electrochemical element such as a battery, a capacitor, a capacitor, a sensor, a fuel cell, and an electrolyzer.

In recent years, the importance of electrochemical elements such as batteries has been rapidly increasing in many industries from small portable devices to large-scale applications such as automobiles, and they are mainly superior in terms of capacity, energy density and secondary batteries. Various new battery systems with properties have been developed and improved.

Various developments and improvements have also been made to separators used in electrochemical elements, for example, anions containing polymers and compounds containing at least one element selected from Groups 1 to 17 of the Periodic Table. A separator composed of a conductive material is disclosed (see, for example, Patent Document 1). Further, it is an anion conductive film containing a conjugated diene polymer and / or a (meth) acrylic polymer and the above compound, and the cross section thereof is the total area of the compound particles and anion conduction other than the compound. A separator composed of an anionic conductive film having a ratio of 70/30 to 30/70 to the total area of the sex film forming material components is disclosed (see, for example, Patent Document 2).

Further, as a separator for a non-aqueous secondary battery, one provided with a porous layer containing an inorganic filler is disclosed (see, for example, Patent Documents 3 and 4).

By the way, the relationship between the crystallite diameter of magnesium hydroxide and the X-ray diffraction peak intensity ratio and the flame retardancy is disclosed, and it is disclosed that such magnesium hydroxide is blended with a resin and used as a flame retardant. (See, for example, Patent Document 5.).

International Publication No. 2014/1196665 Japanese Unexamined Patent Publication No. 2017-27931 Japanese Unexamined Patent Publication No. 2012-134024 Japanese Unexamined Patent Publication No. 2011-108444 Japanese Unexamined Patent Publication No. 2009-114016

The separators described in Patent Documents 1 and 2 have excellent anionic conductivity and can suppress morphological changes of electrode active materials such as shape change and dendrite of electrode active materials. On the other hand, separators for electrochemical elements such as batteries, capacitors, capacitors, sensors, fuel cells, and electrolyzers (also simply referred to as electrolyzers in the present specification) are swelled by the internal liquid of the electrochemical elements. There is a problem that the electrochemical element cannot function as designed, and there is room for further ingenuity to solve this problem while making the conductivity of the ions involved in the reaction of the electrochemical element sufficiently excellent. was there.

The present invention has been made in view of the above-mentioned current situation, and suppresses the swelling of the separator due to the internal liquid of the electrochemical device while making the conductivity of the ions involved in the reaction of the electrochemical device sufficiently excellent. It is an object of the present invention to provide a method for making an electrochemical element function as designed.

The present inventors have studied various methods for suppressing the swelling of the separator due to the internal liquid of the electrochemical element to make the electrochemical element function as designed, and focused on using a specific magnesium hydroxide as the material of the separator. , Magnesium hydroxide having a crystallite diameter of 35 nm or more in the direction perpendicular to the (110) plane measured by X-ray diffraction, and a separator containing an organic polymer were prepared. The present inventors sufficiently permeate the ions involved in the reaction of the electrochemical element when this separator is used for an electrochemical element composed of an aqueous electrolyte solution, and the volume swelling rate due to the aqueous electrolyte solution. Is sufficiently low, and it has been found that the electrochemical element can function as designed. The reason is considered to be as follows. That is, the directional plane (corresponding to the (001) plane) perpendicular to the (110) plane measured by X-ray diffraction has hydroxyl groups arranged to form a highly hydrophilic crystal plane. By being composed of crystals having a large crystal plane with high hydrophilicity, the surface of magnesium hydroxide particles having high hydrophilicity and the highly hydrophilic surface is not covered with an organic polymer, and desired ions are formed. In addition to being able to fully exhibit conductivity, the aqueous electrolyte permeates the magnesium hydroxide particle side and suppresses the permeation into the organic polymer side where the volume can change, and as a result, the swelling of the film due to the aqueous electrolyte is sufficiently suppressed. can. The present inventors have come up with the idea that the above problems can be solved brilliantly in this way, and have arrived at the present invention.
Further, since this separator contains magnesium hydroxide particles having a highly hydrophilic surface, not only the surface of the separator but also the inside of the separator forms a state in which the affinity with the aqueous electrolytic solution is particularly good. In such a state, the permeation of the electrolytic solution into the separator becomes faster, and more stable electrochemical characteristics are obtained in the electrochemical element (particularly the battery) composed of the aqueous electrolytic solution having high thermal safety. Is considered to be obtained.

That is, the present invention is a separator used for an electrochemical element composed of an aqueous electrolyte, and the separator has a crystallite diameter of 35 nm in the direction perpendicular to the (110) plane measured by X-ray diffraction. The separator for an electrochemical element is characterized by containing magnesium hydroxide and an organic polymer as described above.

The separator for an electrochemical element of the present invention has sufficiently excellent conductivity of ions involved in the reaction of an electrochemical element composed of an aqueous electrolyte, while suppressing swelling due to the aqueous electrolyte. Is.

It is an image figure which shows the relationship between the (001) plane direction and the (110) plane direction of the crystallite which comprises magnesium hydroxide particles.

The present invention will be described in detail below.
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.

<Separator for electrochemical elements>
The separator for an electrochemical element of the present invention contains magnesium hydroxide having a crystallite diameter of 35 nm or more in the direction perpendicular to the (110) plane measured by X-ray diffraction, and an organic polymer. In the present specification, the separator for an electrochemical device of the present invention may be simply referred to as a separator. Also, the polymer may be a homopolymer or a copolymer, except as clearly limited.

(Magnesium hydroxide)
The magnesium hydroxide has a crystallite diameter of 35 nm or more in the direction perpendicular to the (110) plane measured by X-ray diffraction.
The crystallite diameter in the direction perpendicular to the (110) plane is preferably 40 nm or more, more preferably 50 nm or more, and more preferably 60 nm or more from the viewpoint of making the effect of the present invention more remarkable. It is more preferable, and it is particularly preferable that it is 65 nm or more.
The upper limit of the crystallite diameter in the direction perpendicular to the (110) plane is not particularly limited, but is usually 400 nm or less, for example.

The magnesium hydroxide preferably has a crystallite diameter of 15 nm or more in the direction perpendicular to the (001) plane measured by X-ray diffraction. Since the organic polymer easily collects on the surface perpendicular to the (001) plane (corresponding to the (110) plane direction), the hydrophilic surface is less covered with the organic polymer and the aqueous electrolytic solution collects, resulting in the collection. , The effect of the present invention becomes more remarkable.
The crystallite diameter in the direction perpendicular to the (001) plane is more preferably 18 nm or more, further preferably 21 nm or more, and particularly preferably 24 nm or more.
The upper limit of the crystallite diameter in the direction perpendicular to the (001) plane is not particularly limited, but is usually 300 nm or less, for example.
Each crystallite diameter described above can be measured according to the method described in Examples.

The method for obtaining magnesium hydroxide in the specific crystallite diameter range described above is, for example, as follows.
Using an aqueous solution of magnesium salt (magnesium chloride, magnesium nitrate, etc.) or an aqueous dispersion of magnesium oxide obtained by a conventionally known method as a raw material, alkaline substances (lithium hydroxide, sodium hydroxide, calcium hydroxide, aqueous ammonia) Etc.) to prepare magnesium hydroxide by carrying out a hydration reaction. At this time, the solubility of the produced magnesium hydroxide can be adjusted by adding an organic acid such as formic acid, acetic acid or propionic acid, a polybasic acid such as nitric acid or sulfuric acid, or a mixture thereof, or the temperature of the hydrothermal reaction. Particles having different crystallite diameters can be prepared by appropriately adjusting (for example, 150 ° C. to 270 ° C.) and time (for example, 30 minutes to 10 hours). The larger the amount of acid added, the more the crystal growth progresses and the larger the crystallite diameter. Further, the higher the temperature of the hydrothermal reaction and the longer the time, the more the crystal growth progresses and the larger the crystallite diameter.

The magnesium hydroxide is in the form of particles, and examples of the shape thereof include fine powder, powder, granules, granules, scales, polyhedrons, rods, and curved surfaces. Such magnesium hydroxide particles (primary particles) may be a single crystal composed of the above-mentioned crystallites or a polycrystal, and any of them exhibits the effect of the present invention. do.
The magnesium hydroxide preferably has a volume-based average particle size of 10 μm or less when measured by the following measuring method. The average particle size is more preferably 5 μm or less, still more preferably 4 μm or less. The average particle size is preferably 0.001 μm or more, more preferably 0.01 μm or more, further preferably 0.1 μm or more, and particularly preferably 0.2 μm or more. ..

<Measurement method of average particle size of magnesium hydroxide particles>
Laser diffraction / scattering type particle diameter of magnesium hydroxide particle dispersion liquid in which magnesium hydroxide particles (powder) and 0.2% by mass sodium hexametaphosphate aqueous solution are mixed and dispersed using an ultrasonic cleaner. Measurement is performed with a distribution measuring device (trade name: LA-950, manufactured by Horiba Seisakusho Co., Ltd.), and the obtained 50% frequency volume average particle size is defined as the average particle size of magnesium hydroxide particles.

For particles having an average particle size in the above range, for example, a method in which the particles are crushed by a ball mill or the like, the obtained coarse particles are dispersed in a dispersant to obtain a desired particle size, and then dried. In addition to a method of selecting the particle size by sieving the coarse particles, the production can be performed by a method of optimizing the preparation conditions at the stage of producing the particles and obtaining particles having a desired particle size.

The mass ratio of magnesium hydroxide is preferably 30% by mass or more in 100% by mass of the separator for an electrochemical element of the present invention from the viewpoint of improving the strength and ionic conductivity of the separator. The mass ratio is more preferably 40% by mass or more, still more preferably 45% by mass or more. The mass ratio is preferably 99% by mass or less. The mass ratio is more preferably 95% by mass or less, further preferably 90% by mass or less, and particularly preferably 85% by mass or less.

(Organic polymer)
As the organic polymer, various ones can be used and may be either thermoplastic or thermosetting. For example, a conjugated diene polymer, a (meth) acrylic polymer, a polyolefin polymer, or a polyvinyl alcohol can be used. Examples thereof include based polymers, fluoroethylene-based polymers, polysulfone-based polymers, aliphatic polyamides, aromatic polyamides, polyether ketones, styrene-based polymers, and polyesters. Among them, conjugated diene-based polymers, (meth) acrylic polymers, and polyolefins. At least one selected from the group consisting of based polymers, polyvinyl alcohol-based polymers, fluoroethylene-based polymers, polysulfone-based polymers, aromatic polyamides, and polyether ketones is preferable. In addition, these organic polymers (particularly polyolefin-based polymer, polyvinyl alcohol-based polymer) may be fibrous. Further, the organic polymer may be further crosslinked with a known cross-linking agent compound.

The conjugated diene polymer has a monomer unit derived from a conjugated diene monomer.
The conjugated diene-based monomer is preferably an aliphatic conjugated diene-based monomer. Examples of the aliphatic conjugated diene-based monomer include 1,3-butadiene, isoprene, 2-chloro-1,3-butadiene, chloroprene and the like, and 1,3-butadiene is preferable. The conjugated diene-based monomer may be used alone or in combination of two or more.

As the conjugated diene-based polymer, one or more monomer units derived from the conjugated diene-based monomer can be used, and the uniformity of the composition according to the present invention and the mechanical strength of the obtained separator can be determined. From the viewpoint of increasing the value and preferably adjusting the elongation and stress, it is preferable to further have, for example, a monomer unit derived from an aromatic vinyl monomer.

Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o-ethylstyrene, m-ethylstyrene, p-ethylstyrene, and o-methoxystyrene. , M-methoxystyrene, p-methoxystyrene, o-ethoxystyrene, m-ethoxystyrene, p-ethoxystyrene, o-fluorostyrene, m-fluorostyrene, p-fluorostyrene, o-chlorostyrene, m-chlorostyrene , P-chlorostyrene, o-bromostyrene, m-bromostyrene, p-bromostyrene, o-acetoxystyrene, m-acetoxystyrene, p-acetoxystyrene, o-tert-butoxystyrene, m-tert-butoxystyrene, Examples thereof include p-tert-butoxystyrene, o-tert-butylstyrene, m-tert-butylstyrene, p-tert-butylstyrene and vinyltoluene. Among these, styrene and α-methylstyrene are preferable in that the heat resistance and mechanical strength of the separator can be increased, and the elongation rate and stress can be preferably adjusted. These aromatic vinyl monomers may be used alone or in combination of two or more.

In the conjugated diene polymer, the mass ratio of the monomer unit derived from the aliphatic conjugated diene monomer and the monomer unit derived from the aromatic vinyl monomer is preferably 1/9 or more and 9/1 or less, for example, 2 It is more preferably 8/8 or more and 8/2 or less, and further preferably 3/7 or more and 7/3 or less.

The conjugated diene-based polymer has a carboxy-modified having a carboxy group and / or a carboxylate group which is a salt thereof, from the viewpoint of increasing the binding force between magnesium hydroxide and the organic polymer and improving the strength of the separator. It is preferably a conjugated diene-based polymer, and more preferably, for example, one further having a monomer unit derived from an unsaturated monomer having a carboxyl group and / or a carboxylate group which is a salt thereof. Examples of the unsaturated monomer having a carboxylate group which is a carboxy group and / or a salt thereof include an unsaturated monocarboxylic acid (salt) such as (meth) acrylic acid (salt); maleic acid (salt) and fumaric acid (salt). ), Unsaturated dicarboxylic acid (salt) such as itaconic acid (salt), etc., and these may be used alone or in combination of two or more.

The conjugated diene polymer has a mass ratio of 0.2% by mass of a monomer unit derived from an unsaturated monomer having a carboxy group and / or a carboxylate group which is a salt thereof from the viewpoint of improving the strength of the separator. The above is preferable, 0.3% by mass or more is more preferable, and 0.5% by mass or more is further preferable. Further, from the viewpoint of making the ionic conductivity of the separator more excellent, the mass ratio is preferably 10% by mass or less, more preferably 8% by mass or less, and more preferably 5% by mass or less. More preferred.

Examples of the conjugated diene polymer include styrene-butadiene polymer, carboxy-modified styrene-butadiene polymer, polybutadiene polymer, carboxy-modified polybutadiene polymer, polyisoprene polymer, carboxy-modified polyisoprene polymer, and acrylonitrile-butadiene polymer. One or more of carboxy-modified acrylonitrile-butadiene-based polymers and the like can be preferably used. Among these, a styrene-butadiene polymer and a carboxy-modified styrene-butadiene polymer are preferable, and a carboxy-modified styrene-butadiene polymer is particularly preferable.

The conjugated diene-based polymer is other than a monomer unit derived from an aliphatic conjugated diene-based monomer, a monomer unit derived from an aromatic vinyl monomer, and a monomer unit derived from an unsaturated monomer having a carboxy group and / or a carboxylate group which is a salt thereof. , Other unsaturated monomer-derived monomer units may be used.

Examples of other unsaturated monomers include sulfonic acid group-containing vinyl monomers such as acrylamide methylpropane sulfonic acid and styrene sulfonate; methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and the like. N-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, (meth) acrylic (Meta) acrylic acid ester monomers such as octyl acid, 2-ethylhexyl (meth) acrylic acid, nonyl (meth) acrylic acid, decyl (meth) acrylic acid; 2-hydroxyethyl (meth) acrylic acid, (meth) acrylic acid Hydroxyl group-containing vinyl monomer such as 4-hydroxybutyl; nitrile group-containing vinyl monomer such as (meth) acryliconitrile; (meth) acrylamide, N-methylol (meth) acrylamide, N-ethylol (meth) acrylamide, dimethyl (meth) acrylamide, (Meta) acrylamide-based monomers such as diethyl (meth) acrylamide; bifunctional vinyl monomers such as divinylbenzene, ethylene glycol dimethacrylate, isopropylene glycol diacrylate, tetramethylene glycol dimethacrylate; 3-methacryloxypropylmethyldimethoxysilane, 3 Examples thereof include alkossisilane group-containing vinyl monomers such as methacryloxypropyltrimethoxysilane and 3-methacryloxypropyltriethoxysilane.

The mass ratio of the monomer unit 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 0.1% by mass. The following is more preferable.

The (meth) acrylic polymer may have a monomer unit derived from a monomer having a (meth) acryloyl group, but a typical one mainly contains a monomer unit derived from a (meth) acrylic acid ester monomer. Examples thereof include (meth) acrylic acid ester-based polymers.

When the monomer unit derived from the (meth) acrylic acid ester monomer is mainly used, the content of the monomer unit derived from the (meth) acrylic acid ester monomer is 50% by mass or more in 100% by mass of the (meth) acrylic acid ester polymer. Say something. The content is preferably 70% by mass or more, more preferably 90% by mass or more, and further preferably 100% by mass.
The (meth) acrylic acid ester monomer is specifically as described above as one of the other unsaturated monomers in the carboxy-modified conjugated diene polymer.

The (meth) acrylic polymer is a monomer unit derived from an unsaturated monomer having a carboxy group and / or a carboxylate group which is a salt thereof, in addition to the monomer unit derived from the (meth) acrylic acid ester monomer, and other unsaturated monomers. It may have a monomer unit derived from a monomer. The (meth) acrylic polymer has a carboxy group and / or a carboxylate group which is a salt thereof, from the viewpoint of increasing the binding force between the magnesium hydroxide and the organic polymer and making the strength of the separator more excellent. It is preferably a (meth) acrylic polymer having a monomer unit derived from an unsaturated monomer.

As the other unsaturated monomer, the same as the above-mentioned unsaturated monomer in the carboxy-modified conjugated diene polymer can be mentioned (however, the (meth) acrylic acid ester monomer is excluded).

The polyolefin-based polymer may have a monomer unit derived from an unsaturated hydrocarbon.
The unsaturated hydrocarbons include, for example, ethylene, propylene, 1-butene, 1-hexene, 1-pentene, isoprene, diisobutylene, 1-heptene, 1-octene, 1-nonene, 1-undecene, 1-dodecene, 1 -Tridecene, 1-tetradecene, 1-pentadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene, propylene trimmers and tetramers, terminal olefins such as styrene, vinyltoluene, divinylbenzene; 2-butene, Examples thereof include intramolecular olefins such as 2-octene, 2-methyl-1-hexene, and 2,3-dimethyl-2-butene, and these may be used alone or in combination of two or more.

The polyolefin-based polymer is a carboxy-modified polyolefin having a carboxy group and / or a carboxylate group which is a salt thereof, from the viewpoint of increasing the binding force between magnesium hydroxide and the organic polymer and improving the strength of the separator. It is preferably a based polymer. Examples of the carboxy-modified polyolefin-based polymer include those having a monomer unit derived from an unsaturated monomer having a carboxy group and / or a carboxylate group which is a salt thereof, and a polyolefin which is graft-modified with an organic peroxide or the like. Therefore, a polymer containing a monomer unit derived from an unsaturated monomer having a carboxyl group and / or a carboxylate group which is a salt thereof is introduced into the side chain of the polyolefin. The preferred type and preferred mass ratio of the unsaturated monomer having a carboxylate group which is a carboxy group and / or a salt thereof are the same as those described above in the above-mentioned carboxy-modified conjugated diene-based polymer. The viewpoint that the carboxy-modified polyolefin-based polymer has an aggregate structure by allowing metal ions such as sodium ion and zinc ion to act (ionomer) to improve the flexibility of the separator. Therefore, it is preferable.

The polyolefin-based polymer has a monomer unit derived from an unsaturated hydrocarbon, a monomer unit derived from an unsaturated monomer having a carboxylate group which is a carboxy group and / or a salt thereof, and a monomer unit derived from another unsaturated monomer. You may be doing it.

Examples of other unsaturated monomers include those similar to those described above in the above-mentioned conjugated diene-based polymer.
The mass ratio of the monomer unit derived from other unsaturated monomers in 100% by mass of the polyolefin-based polymer is preferably 30% by mass or less, more preferably 5% by mass or less, still more preferably 0.1% by mass or less. ..

The polyvinyl alcohol-based polymer is a polymer obtained by saponifying polyvinyl acetate, and a polymer having a saponification degree of 100 mol% is represented by the general formula [CH ₂ CH (OH)] _n . The average degree of polymerization n of the polyvinyl alcohol-based polymer is not particularly limited, but is preferably 300 to 5000, for example.
The average degree of polymerization n can be calculated by the method described in JIS K6726.
The average saponification degree is preferably 50 to 100 mol%, more preferably 80 to 100 mol%, and further preferably 90 to 100 mol%.
The average saponification degree can be measured by the method described in JIS K6726.
The polyvinyl alcohol-based polymer is a carboxy-modified polyvinyl alcohol having a monomer unit derived from an unsaturated monomer having a carboxy group and / or a carboxylate group which is a salt thereof, and a polyethylene oxide-modified by adding polyethylene oxide to a hydroxyl group after saponification. It may be polyvinyl alcohol or vinylon that is further acetalized after saponification.

The fluorine-containing ethylene-based polymer has a structure in which a hydrogen atom of polyethylene is replaced with a fluorine atom, and examples thereof include polyvinylidene fluoride and polytetrafluoroethylene.
The polysulfone-based polymer refers to a polymer having a sulfonyl group as a repeating unit, and examples thereof include polysulfone (PSU), polyethersulfone (PESU), and polyphenylsulfone (PSSU).

The aromatic polyamide refers to a polymer composed of an aromatic dicarboxylic acid component and an aromatic diamine component, or an aromatic aminocarboxylic acid component, and examples thereof include polyphenylene terephthalamide and polyphenylene isophthalamide.
The polyetherketone is a polymer having an ether bond and a ketone bond, and examples thereof include polyetherketoneketone and polyetheretherketone.

By selecting the type of organic polymer contained in the separator for an electrochemical device of the present invention, the elongation rate and stress can be appropriately adjusted. For example, the separator for an electrochemical element of the present invention may contain at least one selected from the group consisting of a conjugated diene polymer, a polyolefin polymer, a polyvinyl alcohol polymer, a fluorine-containing ethylene polymer, and a polysulfone polymer. Especially preferable.

The organic polymer can be produced by copolymerizing a monomer component forming a structural unit contained in the polymer in the presence of a radical generator, and graft-modifying the monomer component if necessary.
The method for polymerizing the monomer component is not particularly limited, and examples thereof include an aqueous solution polymerization method, an emulsion polymerization method, a reverse phase suspension polymerization method, a suspension polymerization method, a solution polymerization method, and a bulk polymerization method.

The separator of the present invention preferably further has a porous substrate. As the porous substrate, the above-mentioned organic polymer can be used, and among them, polyolefin-based polymers such as polyethylene, polypropylene, ethylene-propylene copolymer, and cyclic polyolefin-based polymer; polyvinyl alcohol-based polymer such as vinylon; aliphatic polyamide. Aromatic polyamides; styrene-based polymers; non-woven fabrics, woven fabrics, microporous films and the like made of resin materials such as polyester-based polymers are preferable, and among them, polyolefin-based polymers and polyvinyl alcohol-based polymers are more suitable. preferable. The porous substrate may be hydrophilized by a conventionally known method. The porous base material is preferably, for example, a polyvinyl alcohol-based resin or a hydrophilized material. In these porous substrates, the introduction of hydroxyl groups and carboxy groups on the surface improves the bonding force with the composition according to the present invention, and the strength of the separator becomes more excellent.
When the separator of the present invention has a porous base material, it may be a laminate in which a film obtained from the above-mentioned composition according to the present invention and a porous base material are laminated, and the composition according to the present invention. The film obtained from the composition according to the present invention, which is obtained by impregnating the porous substrate with the above, and the porous substrate may be integrated. In the above laminated body, a part of the composition according to the present invention is impregnated with a part of the porous base material, and the film obtained from the composition according to the present invention and the porous base material are partially formed. The composition according to the present invention may fill some or all of the pores in the porous substrate.

The mass ratio of the organic polymer is preferably 1% by mass or more in 100% by mass of the separator for an electrochemical element of the present invention from the viewpoint of suitably adjusting the ionic conductivity of the separator and the elongation rate and stress of the separator. It is more preferably 5% by mass or more, further preferably 10% by mass or more, and particularly preferably 15% by mass or more. The mass ratio is preferably 70% by mass or less, and more preferably 60% by mass or less.

(Other ingredients)
The separator for an electrochemical element of the present invention may contain a water-soluble polymer used as a dispersant for magnesium hydroxide or the like.
Examples of the water-soluble polymer include celluloses such as carboxymethyl cellulose; poly (meth) acrylic acid (salt) such as sodium polyacrylate; and unsaturated carboxylic acids such as (meth) acrylic acid (salt) and maleic acid (salt). Examples thereof include polymers with unsaturated sulfonic acids (salts) such as acid (salt) and vinyl sulfonic acid (salt), and one or more of these can be used.

When the separator for an electrochemical element of the present invention contains a water-soluble polymer, the content ratio of the water-soluble polymer is for the electrochemical element of the present invention from the viewpoint of sufficiently dispersing magnesium hydroxide and exerting its action and effect. It is preferably 0.1% by mass or more in 100% by mass of the separator. Further, the content ratio is preferably 3% by mass or less from the viewpoint of further suppressing the water-soluble polymer from absorbing an electrolytic solution such as water to plasticize the separator.

The separator for an electrochemical element of the present invention may further contain other inorganic components such as conductive carbon and conductive ceramics.
The content ratio of other inorganic components in the separator for an electrochemical device of the present invention is preferably 30% by mass or less in 100% by mass of the separator from the viewpoint of the strength of the separator. It is more preferably 10% by mass or less, further preferably 1% by mass or less, and particularly preferably 0.1% by mass or less.

The separator for an electrochemical device of the present invention preferably has an average film thickness of 10 μm to 1 mm. If it is 10 μm or more, it is possible to sufficiently prevent the occurrence of damage during film formation. Further, if it is 1 mm or less, it is advantageous in terms of cost, and the ability of ion permeation is sufficiently excellent. The average film thickness is more preferably 15 μm or more, further preferably 20 μm or more, and particularly preferably 25 μm or more. The average film thickness is more preferably 800 μm or less, further 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 Examples.

The separator for an electrochemical device of the present invention preferably has an apparent density of 0.5 to 2.0 g / cm ^3. As a result, the separator for an electrochemical device of the present invention more sufficiently satisfies the basic performance required for the separator, and can be suitably used as a separator. The apparent density is ^{more preferably 0.55 g / cm 3} or more, and further preferably 0.6 g / cm ³ or more. Further,該見apparent density is more preferably 1.9 g / cm ³ or less, further preferably 1.8 g / cm ³ or less, particularly preferably 1.7 g / cm ³ or less.
The apparent density can be measured by a known method from the mass per unit area and the average film thickness.

The separator for an electrochemical element of the present invention is intended to be used as a separator used for an electrochemical element such as a battery, a capacitor, a capacitor, a sensor, a fuel cell, and an electrolytic device, which is composed of an aqueous electrolytic solution. ..

(Method for Manufacturing Separator for Electrochemical Device of the Present Invention)
The separator for an electrochemical element of the present invention is prepared by preparing a composition (also simply referred to as a composition according to the present invention in the present specification) used for forming a film to obtain a separator for an electrochemical element, and this composition. The product can be produced by forming a film by a method described later.
First, the raw materials of the composition according to the present invention (magnesium hydroxide having a specific crystallite diameter according to the present invention, an organic polymer, and other components) are mixed. For mixing, a mixer, blender, kneader, sand mill, bead mill, ready mill, roll mill, ball mill and the like can be used. At the time of mixing, water, an organic solvent such as methanol, ethanol, propanol, isopropanol, butanol, hexanol, tetrahydrofuran, N-methylpyrrolidone, or a mixed solvent of water and an organic solvent may be added as a medium.
After mixing, filtration, defoaming and the like can be performed as necessary to obtain the composition according to the present invention.
The magnesium hydroxide dispersion may be produced before mixing. For example, magnesium hydroxide and, if necessary, a dispersant of magnesium hydroxide and the like are mixed. By producing the magnesium hydroxide dispersion before mixing, it is possible to suppress the destabilization of the organic polymer during preparation. The above-mentioned equipment and medium can be used for mixing.

The method for producing a film from the composition according to the present invention is not particularly limited, and the composition according to the present invention is coated on a release base material such as a mirror-finished metal roll or a polyethylene terephthalate film, dried, and then dried. A method of peeling the obtained coating film to obtain a film (casting method), a method of rolling with a roll to form a film, a method of rolling with a flat plate press or the like to form a film, an injection molding method, extrusion. A method of molding into a film such as a molding method, or a method of coating and drying on an electrode sheet to form a film integrated with the electrode sheet can be used. These molding methods may be used alone or in combination of two or more methods.

The 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, if necessary. The heating temperature and heating time of the film may be appropriately set.

When the separator for an electrochemical element of the present invention further has a porous base material, for example, a film obtained from the composition according to the present invention and a porous base material may be laminated by a conventionally known method, or the present invention may be used. After coating the composition according to the present invention on a peeling base material, the porous base material is contacted and impregnated, the film is solidified, and then the peeling base material is peeled off to form a separator for an electrochemical element of the present invention. Can be manufactured.

<Electrochemical element>
The present invention is also an electrochemical element composed of the separator for an electrochemical element of the present invention and an aqueous electrolyte solution.
Examples of the electrochemical element of the present invention include a battery; a capacitor such as an electrolytic capacitor; a capacitor such as an electric double layer capacitor and a lithium ion capacitor; a sensor such as a humidity sensor and a gas sensor; a fuel cell such as an alkaline fuel cell; an alkaline type. Examples thereof include an electrolytic device such as a water electrolytic device.

The aqueous electrolyte is not particularly limited as long as it uses water as the main component of the electrolytic solution raw material, which is usually used as the aqueous electrolyte of the electrochemical element, and may contain an organic solvent together with water. Using water as the main component of the electrolytic solution raw material means that the mass ratio of water is 50% by mass or more in 100% by mass of the aqueous electrolytic solution. The mass ratio is preferably 80% by mass or more. Examples of the organic solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, dimethoxymethane, diethoxymethane, dimethoxyethane, tetrahydrofuran, methyl tetrahydrofuran, diethoxyethane, dimethylsulfoxide, sulfolane, acetonitrile, benzo. Examples thereof include nitriles, ionic liquids, fluorine-containing carbonates, fluorine-containing ethers, polyethylene glycols, fluorine-containing polyethylene glycols, and the like, and any one or more of these can be used.

Above all, the electrochemical element of the present invention is preferably an electrochemical element composed of an electrolytic solution using only water as an electrolytic solution raw material. An electrolytic solution using only water as an electrolytic solution raw material has higher thermal safety, and more stable electrochemical characteristics can be obtained by using the separator for an electrochemical element of the present invention.

The aqueous electrolytic solution is preferably, for example, an alkaline electrolytic solution. Examples of the alkaline electrolytic solution include potassium hydroxide aqueous solution, sodium hydroxide aqueous solution, lithium hydroxide aqueous solution, zinc sulfate aqueous solution, zinc nitrate aqueous solution, zinc phosphate aqueous solution, zinc acetate aqueous solution and the like, and these may be used alone. It can also be used as an aqueous solution in which two or more of these solutes are mixed.

(battery)
The case where the electrochemical element of the present invention is a battery will be described in detail below.
Batteries are usually configured to further include a positive electrode. As the active material of the positive electrode, a compound usually used as a positive electrode active material of a primary battery or a secondary battery can be used, and is not particularly limited. For example, oxygen (when oxygen is the positive electrode active material, the positive electrode is oxygen). Perovskite type compounds, cobalt-containing compounds, iron-containing compounds, copper-containing compounds, manganese-containing compounds, vanadium-containing compounds, nickel-containing compounds, iridium-containing compounds, platinum-containing compounds; palladium-containing compounds; gold Containing compound; Silver-containing compound; Air electrode composed of carbon-containing compound, etc.); Nickel-containing compound such as nickel oxyhydroxide, nickel hydroxide, cobalt-containing nickel hydroxide; Manganese-containing compound such as manganese dioxide; Oxidation Silver; lithium-containing compounds such as lithium cobaltate; iron-containing compounds; zinc species such as metallic zinc and zinc oxide.
Further, it is also one of the preferred embodiments of the present invention that the positive electrode active material is oxygen, such as an air battery.

The battery is usually configured to further include a negative electrode. As the negative electrode active material, those usually used as the negative electrode active material of the battery, such as carbon, lithium, sodium, magnesium, zinc, nickel, tin, cadmium, hydrogen storage alloy, and silicon-containing material, can be used. For example, the present invention can be suitably applied to a battery using an active material such as zinc, lithium, nickel, magnesium, cadmium, etc., which may generate dendrites due to an electrode reaction, as the negative electrode active material. .. Above all, it is preferable that the negative electrode active material contains a zinc compound.

Electrodes such as positive electrodes and negative electrodes constituting the battery can be manufactured by forming an active material layer on a current collector.
The current collectors that make up the electrodes include (electrolytic) copper foil, copper mesh (expanded metal), foamed copper, punching copper, copper alloys such as brass, brass foil, brass mesh (expanded metal), foamed brass, and punching brass. , Nickel foil, corrosion resistant nickel, nickel mesh (expanded metal), punching nickel, metallic zinc, corrosion resistant metallic zinc, zinc foil, zinc mesh (expanded metal), (punching) steel plate, conductive non-woven fabric; Ni, Zn, (Electrolytic) copper foil with Sn, Pb, Hg, Bi, In, Tl, brass, etc. added, copper mesh (expanded metal), foamed copper, punched copper, copper alloy such as brass, brass foil, brass mesh (expanded metal) ), Foamed brass, punching brass, nickel foil, corrosion resistant nickel, nickel mesh (expanded metal), punching nickel, metallic zinc, corrosion resistant metallic zinc, zinc foil, zinc mesh (expanded metal), (punching) steel plate, non-woven fabric; Ni, (Electrolytic) copper foil copper mesh (expanded metal) plated with Zn, Sn, Pb, Hg, Bi, In, Tl, brass, etc., foamed copper, punched copper, copper alloys such as brass, brass foil, brass mesh ( Expanded metal), foamed brass, punching brass, nickel foil, corrosion-resistant nickel, nickel mesh (expanded metal), punching nickel, metallic zinc, corrosion-resistant metal zinc, zinc foil, zinc mesh (expanded metal), (punching) steel plate, non-woven fabric; Silver: Examples of materials used as current collectors and containers for alkaline (storage) batteries and air zinc batteries.

The form of the battery is usually a secondary battery (storage battery) that can be charged and discharged. The battery of the present invention uses a mechanical discharge (mechanical replacement of a zinc negative electrode) in addition to a general secondary battery; a battery using a third pole (as a positive electrode, an electrode suitable for charging). It may be in any form such as (one in which electrodes suitable for discharge are used respectively).

(Fuel cell or electrolyzer)
The case where the electrochemical element of the present invention is a fuel cell or an electrolytic device will be described in detail below.
The separator for an electrochemical element of the present invention is suitably used as a member of an alkaline fuel cell and an alkaline water electrolyzer. Examples of the alkaline fuel cell and the alkaline water electrolyzer include an anode, a cathode, and a separator for an electrochemical element of the present invention arranged between the anode and the cathode. More specifically, the alkaline fuel cell and the alkaline water electrolyzer have an anode chamber in which the anode is present and a cathode chamber in which the cathode is present, which are separated by the separator for the electrochemical element of the present invention.
Examples of the anode and the cathode include known electrodes including a conductive substrate containing nickel, a nickel alloy, or the like.

[Fuel cell power generation method]
The method of power generation using the alkaline fuel cell including the separator for an electrochemical element of the present invention is not particularly limited, and a known method can be used. For example, an alkaline fuel cell containing the above-mentioned separator for an electrochemical element of the present invention is filled with an electrolytic solution, and an oxidizing agent (for example, oxygen) and a fuel (for example, hydrogen) are supplied to each of the anode and cathode in the electrolytic solution. By doing so, power can be generated.

[Electrolysis method of water electrolyzer]
The method of electrolyzing water using the alkaline water electrolyzer including the separator for an electrochemical element of the present invention is not particularly limited, and a known method can be used. For example, it can be carried out by filling the alkaline water electrolyzer including the above-mentioned separator for an electrochemical element of the present invention with an electrolytic solution and applying an electric current in the electrolytic solution.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. Unless otherwise specified, "part" means "part by weight" and "%" means "mass%".

<Average particle size of magnesium hydroxide particles>
The volume-based average particle size of the magnesium hydroxide particles was measured by the above-mentioned measuring method.

<Measurement of powder X-ray diffraction of magnesium hydroxide particles and calculation of crystallite diameter>
The magnesium hydroxide particles (powder) were measured under the following conditions using an X-ray diffractometer (trade name: SmartLab, manufactured by Rigaku Co., Ltd.).
(Measurement condition)
X-ray tube Cu
X-ray output 45kV, 200mA
Scan speed 5 ° / min
Scanning range 5 to 90 °
From the peak of each crystal plane of the obtained magnesium hydroxide, the crystal face diameter in the direction perpendicular to each crystal plane was calculated by the following method for calculating the crystal face.
(Calculation of crystallite diameter)
The crystallite diameter was calculated by Scherrer's formula (the following formula).
(Crystall diameter) = Kλ / (βcosθ)
K is a Scheller constant, which is 0.94.
λ is the wavelength of the X-ray tube used.
β is a value obtained from β = b−B, b is the full width at half maximum in a perfect and well-grown crystal, and B is the full width at half maximum obtained by actual measurement.
θ is the value of θ at the diffraction angle 2θ.

<Film thickness>
The thickness of the obtained separator was measured using a digital micrometer (manufactured by Mitutoyo Co., Ltd.). Arbitrary 10 points were measured, and the average value was taken as the film thickness.

<Ion conductivity>
When the cell formed with the following cell configuration is allowed to stand in a constant temperature bath at 25 ° C. for 30 minutes, then AC impedance is measured under the following measurement conditions, and the obtained section component (Ra) and the measurement sample are not added. Using the intercept component (Rb) and the film thickness obtained by the above film thickness measuring method, the ionic conductivity was calculated by the following formula.
[Ion conductivity (mS / cm)] = [Film thickness (cm)] ÷ [(Ra-Rb) × 1000 × 1.77]
(Measurement condition)
・ Number of charged cells: 5 cells (list the average value)
-Cell composition Working electrode: Ni plate counter electrode: Ni plate Electrolyte: 6.7 mol / L potassium hydroxide aqueous solution saturated with zinc oxide Sample pretreatment: Immerse in the above electrolyte overnight Measurement effective area: 1.77 cm ²
-AC impedance measurement conditions Applied voltage: 10 mV vs. Open circuit voltage frequency range: 100kHz to 100Hz

<Volume swelling rate>
The volume swelling rate was calculated by measuring the volume before immersion in the electrolytic solution and the volume after immersion in the electrolytic solution of a test piece cut out from the obtained separator in a size of 25 mm × 25 mm and using the following formula.
(Volume swelling rate) = [(Volume after immersion in electrolyte)-(Volume before immersion in electrolyte)] ÷ (Volume before immersion in electrolyte)
Here, the volume was calculated by measuring the length in the vertical direction and the length in the horizontal direction of the test piece using a caliper and measuring the film thickness based on the above-mentioned film thickness measuring method.
Table 1 shows the crystallite diameter in the direction perpendicular to the crystal plane shown in the table, which was calculated from the powder X-ray diffraction of the magnesium hydroxide particles.

[Example 1]
Weigh 100 parts by mass of magnesium hydroxide particles A (average particle size: 0.5 μm), 3 parts by mass of an aqueous polyacrylic acid solution (40% non-volatile content), and 42 parts by mass of ion-exchanged water having the crystallite diameter shown in Table 1. After being dispersed for 1 hour using a sand mill, filtration was performed to obtain an aqueous dispersion of magnesium hydroxide particles.
Weigh 50 parts by mass of the obtained magnesium hydroxide particle aqueous dispersion and 21 parts by mass of a carboxy-modified styrene-butadiene polymer aqueous dispersion (nonvolatile content: 48%), mix them, and then perform filtration and vacuum defoaming. A film-forming composition was obtained.
The obtained film-forming composition is coated on the silicone-treated surface of a polyethylene terephthalate (PET) film (release film) whose one side is silicone-treated with a comma coater, dried, and the obtained coating film is applied. It was peeled from the release film to obtain a separator.
The film thickness of the obtained separator was 85 μm, the ionic conductivity was 16 mS / cm, and the volume swelling rate was 0.0%.

[Example 2]
In Example 1, the separator was used in the same manner as in Example 1 except that the magnesium hydroxide particles A were changed to magnesium hydroxide particles B (average particle size: 3.3 μm) having the crystallite diameter shown in Table 1. Obtained.
The film thickness of the obtained separator was 94 μm, the ionic conductivity was 6.0 mS / cm, and the volume swelling rate was 1.0%.

[Example 3]
In Example 1, the separator was used in the same manner as in Example 1 except that the magnesium hydroxide particles A were changed to magnesium hydroxide particles C (average particle size: 3.1 μm) having the crystallite diameter shown in Table 1. Obtained.
The film thickness of the obtained separator was 93 μm, the ionic conductivity was 14 mS / cm, and the volume swelling rate was 5.0%.

[Comparative Example 1]
In Example 1, the separator was used in the same manner as in Example 1 except that the magnesium hydroxide particles A were changed to magnesium hydroxide particles D (average particle size: 3.5 μm) having the crystallite diameter shown in Table 1. Obtained.
The film thickness of the obtained separator was 87 μm, the ionic conductivity was 11 mS / cm, and the volume swelling rate was 5.6%.

From the comparison between Examples 1 to 3 and Comparative Example 1, in the separator using magnesium hydroxide particles having a crystallite diameter of 35 nm or more in the direction perpendicular to the (110) plane, while maintaining high ionic conductivity, Volume swelling when immersed in the electrolytic solution could be suppressed.

[Example 4]
100 parts by mass of magnesium hydroxide particles B (average particle size: 3.3 μm) having crystallite diameter shown in Table 1, 3 parts by mass of polyacrylate aqueous solution (nonvolatile content 40%), and 42 parts by mass of ion-exchanged water. After measuring and dispersing for 1 hour using a sand mill, filtration was performed to obtain an aqueous dispersion of magnesium hydroxide particles.
Weigh 50 parts by mass of the obtained magnesium hydroxide particle aqueous dispersion and 21 parts by mass of a carboxy-modified styrene-butadiene polymer aqueous dispersion (nonvolatile content: 48%), mix them, and then perform filtration and vacuum defoaming. A film-forming composition was obtained.
The resulting film-forming composition as weighed values membrane-forming composition components after drying of 8 mg / cm ^2, the nonwoven fabric of polyvinyl alcohol fiber (weighed value: 2.4mg / cm ^2, thickness S: 88 μm) was coated with a comma coater and dried to obtain a separator.
The film thickness of the obtained separator was 96 μm, the ionic conductivity was 7 mS / cm, and the volume swelling rate was 0.3%.

[Example 5]
In Example 4, a separator was obtained in the same manner as in Example 4 except that 21 parts by mass of the carboxy-modified styrene-butadiene polymer aqueous dispersion was changed to 5 parts by mass.
The film thickness of the obtained separator was 95 μm, the ionic conductivity was 13 mS / cm, and the volume swelling rate was 0.0%.

[Example 6]
In Example 4, the magnesium hydroxide particles B were added to the magnesium hydroxide particles A (average particle size: 0.5 μm) having the crystallite diameter shown in Table 1 in a carboxy-modified styrene-butadiene polymer aqueous dispersion (nonwoven fabric). : 48%) 21 parts by mass of polyolefin-based ionomer aqueous dispersion (nonvolatile content: 27%) and 5 parts by mass of non-woven fabric made of polyvinyl alcohol-based fibers (weighing value: 2.4 mg / cm ² , thickness: 88 μm) Separators were obtained in the same manner as in Example 4 except that they were changed to a non-woven fabric made of polyolefin fibers (weighing value: 4.0 mg / cm ^{2, thickness: 90 μm).}
The film thickness of the obtained separator was 101 μm, the ionic conductivity was 10 mS / cm, and the volume swelling rate was 0.0%.

[Example 7]
Magnesium hydroxide particles A (average particle size 0.5 μm) and N-methyl-2-pyrrolidone (manufactured by Wako Pure Chemical Industries, Ltd.) having crystallite diameters shown in Table 1 are mixed so as to have a mass ratio of 1: 1. , Magnesium hydroxide particle dispersion was obtained by carrying out dispersion treatment at room temperature for 6 hours in a pot mill containing zirconia media balls.
200 parts by mass of the obtained magnesium hydroxide particle dispersion, polysulfone resin (trade name: Ultrazone S3010, manufactured by BASF) at a concentration of 30% by mass at 80 to 100 ° C. N-methyl-2-pyrrolidone (Wako Pure Chemical Industries, Ltd.) Weigh 110 parts by mass of the polysulfone resin solution obtained by heat-dissolving it in (Yaku Kogyo Co., Ltd.), and use a rotation / revolution mixer (trade name: Awatori Rentaro ARE-500, manufactured by Shinky Co., Ltd.) at room temperature. After mixing for about 10 minutes at a rotation speed of 1000 ^{min -1} , filtration was performed to obtain a film-forming composition.
The film-forming composition is applied onto a polyethylene terephthalate (PET) film with an applicator so that the ^{measured value of the film-forming composition component after drying is 15 mg / cm 2, and the film is composed of polyolefin fibers.} By contacting the non-woven fabric (weighing value: 6 mg / cm ² , thickness: 160 μm), the non-woven fabric was completely impregnated with the film-forming composition. Then, the non-woven fabric impregnated with the film-forming composition is allowed to be bathed in water at room temperature for 10 minutes to solidify the coating film, and then the coating film is peeled off from the PET film together with the non-woven fabric in water to form magnesium hydroxide particles. , A water-containing film made of a polysulfone resin and a non-woven fabric was obtained. The obtained membrane was dried at 80 ° C. for 30 minutes in a dryer to obtain a separator.
The film thickness of the obtained separator was 240 μm, the ionic conductivity was 90 mS / cm, and the volume swelling rate was 0.0%.

As shown in Examples 4 and 5, even in combination with the non-woven fabric, high ionic conductivity is maintained by using magnesium hydroxide particles having a crystallite diameter of 35 nm or more in the direction perpendicular to the (110) plane. However, it was confirmed that the effect of suppressing volume swelling when immersed in the electrolytic solution is enhanced. Furthermore, in Examples 6 and 7, it was confirmed that these effects were retained even when different organic polymers were used.

Claims (4)

A separator used in an electrochemical device that contains an aqueous electrolyte solution.
The separator is a separator for an electrochemical element, which comprises magnesium hydroxide having a crystallite diameter of 35 nm or more in a direction perpendicular to the (110) plane measured by X-ray diffraction, and an organic polymer. The separator for an electrochemical element according to claim 1, wherein the magnesium hydroxide has a crystallite diameter of 15 nm or more in a direction perpendicular to the (001) plane measured by X-ray diffraction. The separator for an electrochemical device according to claim 1 or 2, wherein the separator further has a porous base material. An electrochemical device comprising the separator for an electrochemical device according to any one of claims 1 to 3 and an aqueous electrolytic solution.

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