JP2020021572A - Hydrogel for alkaline battery, gelatinous electrolyte containing the same, and the alkaline battery - Google Patents

Abstract

To provide a hydrogel which can be used under an environment of a concentrated aqueous electrolyte.SOLUTION: A hydrogel contains a high polymer matrix and water, the high polymer matrix includes: a single functionality monomer A as an arbitrary component having a carboxyl group and one ethylenic unsaturated group; a single functionality monomer B having at least one base selected from a sulfone group and a phosphate group and one ethylenic unsaturated group; and a copolymer of a polyfunctional monomer having two to six ethylenic unsaturated groups. A mol ratio (Ma/Mb) of a mol number (Ma) of the carboxyl group in the copolymer and a mol number (Mb) of a total of the sulfone group and the phosphate group is 0 to 8.0. By the hydrogel for an alkaline battery, in which the hydrogel contains the high polymer matrix of 2 to 80 pts.mass in the 100 pts.mass, and contains the water of 20 to 98 pts.mass, the problem is solved.SELECTED DRAWING: None

Description

  The present invention relates to a hydrogel for an alkaline battery, a gel electrolyte containing the same, and an alkaline battery. More specifically, the present invention relates to a hydrogel that can be used even in a concentrated aqueous electrolyte environment, a gel electrolyte containing the same, and an alkaline battery.

Due to recent environmental problems, the use of renewable energy, the shift from gasoline vehicles to electric vehicles, and the use of smart grids are accelerating, and storage batteries that exhibit high energy densities (secondary Batteries) are becoming increasingly important.
A metal-air battery using oxygen in the air as a positive electrode active material does not need to fill the battery with a positive electrode active material, and can fill a large amount of a negative electrode active material. For this reason, metal-air batteries have attracted attention as next-generation secondary batteries having a very high energy density. As a metal air battery, a lithium air battery, a zinc air battery, an aluminum air battery, an iron air battery, a magnesium air battery, and the like are known.
However, in the metal-air battery, there are problems such as that the inside of the battery is easily dried because the electrolyte evaporates from the positive electrode, and that the strong alkaline solution used as the electrolyte leaks.
In the field of conventional alkaline secondary batteries, studies have been made to use a gelled electrolyte as a battery material in order to prevent drying and liquid leakage while maintaining ion conductivity. For example, Japanese Patent Application Laid-Open No. 2005-322635 (Patent Document 1) discloses a polymer hydrogel for an alkaline battery obtained by adding an alkali hydroxide to a polymer composition comprising polyvinyl alcohol and an anionic cross-linked copolymer. An electrolyte is described. JP-A-2017-179328 (Patent Document 2) discloses a sheet-like hydrogel composed of a crosslinked product of a polyacrylic acid-based polymer.
In addition, in a metal-air battery using lithium, since the lithium ion conductive solid electrolyte has low alkali resistance, it is desired to lower the pH of the electrolytic solution. Therefore, Japanese Patent Application Laid-Open No. 2012-33490 (Patent Document 3) proposes to use an aqueous electrolyte containing a high concentration of lithium halide.

JP 2005-322635 A JP 2017-179328 A JP 2012-33490A

  However, in the hydrogels described in Patent Documents 1 and 2, under the environment of a concentrated aqueous electrolyte as in Patent Document 3, the precipitation of the polymer is weakened due to weakening of the ionization of the functional group bonded to the polymer constituting the hydrogel. As a result, a decrease in water retention and a accompanying decrease in flexibility and curing occur, and thus there are problems in that it is difficult to assemble the battery and the battery characteristics are reduced due to an increase in the resistance of the electrolyte. Therefore, it has been desired to provide a hydrogel that can be used even in a concentrated aqueous electrolyte environment.

The inventors of the present invention have conducted intensive studies, and as a result, it has been found that a specific amount of a sulfone group and / or a phosphate group is introduced into a copolymer contained in a polymer matrix constituting a hydrogel, thereby precipitating the copolymer. The present invention has been found to be able to provide a hydrogel which can be used even in an environment of a concentrated aqueous electrolyte to prevent the occurrence of such a problem.
Thus, according to the present invention is a hydrogel comprising a polymer matrix and water,
The polymer matrix includes a monofunctional monomer A as an optional component having a carboxyl group and one ethylenically unsaturated group, at least one group selected from a sulfone group and a phosphate group, and one ethylene group. A monofunctional monomer B having an unsaturated group, and a copolymer of a polyfunctional monomer having 2 to 6 ethylenically unsaturated groups,
The molar ratio (Ma / Mb) of the number of moles of carboxyl groups (Ma) in the copolymer to the total number of moles of sulfone groups and phosphate groups (Mb) is 0 to 8.0,
The hydrogel for an alkaline battery is provided, wherein 100 parts by mass of the hydrogel contains 2 to 80 parts by mass of a polymer matrix and 20 to 98 parts by mass of water.

Further, according to the present invention, there is provided a gel electrolyte comprising the hydrogel and an electrolyte component contained in the hydrogel.
Further, according to the present invention, there is provided an alkaline battery including the hydrogel or the gel electrolyte.

  According to the present invention, a large amount of electrolyte is contained in a hydrogel by introducing a specific amount of a sulfone group and / or a phosphate group into a copolymer contained in a polymer matrix constituting a hydrogel. Even under an environment (in an environment of a concentrated aqueous electrolyte), it is possible to provide a hydrogel which retains flexibility by preventing precipitation of the copolymer. Since the hydrogel of the present invention retains flexibility even in the environment of a concentrated aqueous electrolyte, it exhibits good adhesion to electrodes and solid electrolytes of alkaline batteries, and can reduce interface resistance.

Further, according to the present invention, when having the following configuration, a hydrogel having higher flexibility can be provided even in an environment of a dense aqueous electrolyte.
(1) When the hydrogel is immersed in an aqueous solution containing 1.5 M LiOH and 10 M LiCl at a temperature of 25 ° C. for one week, it shows a swelling degree of 70 to 800%.
(2) When the hydrogel is immersed in an aqueous solution containing 1.5 M LiOH and 10 M LiCl at a temperature of 25 ° C. for one week, it shows a 30% compressive stress of 20 N / cm ² or less.
(3) When the hydrogel is immersed in an aqueous solution containing 1.5 M LiOH and 10 M LiCl at a temperature of 25 ° C. for one week, the impedance at a frequency of 100 kHz shows a value of 20Ω or less.
(4) The copolymer has a component derived from the monofunctional monomer A in an amount of 0 to 85 mol% and a total of 100 mol% of the component derived from the monofunctional monomer A and the component derived from the monofunctional monomer B. Contains 15 to 100 mol% of a component derived from the monofunctional monomer B.

(Hydrogel)
The hydrogel preferably exhibits a swelling degree of 70 to 800% when immersed in an aqueous solution containing 1.5 M LiOH and 10 M LiCl at a temperature of 25 ° C. for one week. When the degree of swelling is less than 70%, the solid content of the hydrogel becomes large, which may cause a decrease in flexibility or, in some cases, curing. If it is more than 800%, the strength of the hydrogel after swelling is low, so that the hydrogel may be broken during handling. The degree of swelling is more preferably from 70 to 600%, further preferably from 70 to 500%, and still more preferably from 70 to 450%.
When the hydrogel is immersed in an aqueous solution containing 1.5 M LiOH and 10 M LiCl at a temperature of 25 ° C. for one week, it preferably exhibits a 30% compressive stress of 20 N / cm ² or less. When the 30% compressive stress is larger than 20 N / cm ² , it means that the hydrogel is cured, and when the battery is assembled, the adhesion to the electrode is reduced and the resistance may be increased. The 30% compressive stress is more preferably 15 N / cm ² or less, and even more preferably 10 N / cm ² or less. The lower limit of the 30% compressive stress is preferably 0.05 N / cm ² .
When the hydrogel is immersed in an aqueous solution containing 1.5 M LiOH and 10 M LiCl at a temperature of 25 ° C. for one week, it is preferable that the impedance at a frequency of 100 kHz shows a value of 20Ω or less. When the value of the AC resistance is larger than 20Ω, the battery characteristics may be deteriorated due to an increase in the resistance of the electrolyte. The value of the AC resistance is more preferably 15 Ω or less, further preferably 10 Ω or less. The lower limit of the value of the AC resistance is preferably 0.05Ω.
When the hydrogel is immersed in an aqueous solution containing 1.5 M LiOH and 10 M LiCl at a temperature of 25 ° C. for one week, it is preferable that the impedance at a frequency of 1 kHz shows a value of 20Ω or less. When the value of the AC resistance is larger than 20Ω, the battery characteristics may be deteriorated due to an increase in the resistance of the electrolyte. The value of the AC resistance is more preferably 15 Ω or less, further preferably 10 Ω or less. The lower limit of the value of the AC resistance is preferably 0.05Ω. When the hydrogel is immersed in an aqueous solution containing 1.5 M LiOH and 10 M LiCl at a temperature of 25 ° C. for one week, it is preferable that the impedance at a frequency of 100 kHz shows a value of 20Ω or less. When the value of the AC resistance is larger than 20Ω, the battery characteristics may be deteriorated due to an increase in the resistance of the electrolyte. The value of the AC resistance is more preferably 15 Ω or less, further preferably 10 Ω or less. The lower limit of the value of the AC resistance is preferably 0.05Ω.

The hydrogel includes a polymer matrix and water.
(1) Polymer matrix The polymer matrix comprises at least one group selected from a monofunctional monomer A as an optional component having a carboxyl group and one ethylenically unsaturated group, and a sulfone group and a phosphate group. And a monofunctional monomer B having one ethylenically unsaturated group and a polyfunctional monomer having 2 to 6 ethylenically unsaturated groups. This copolymer can be formed by polymerizing and crosslinking various monomers.
The polymer matrix is contained in an amount of 2 to 80 parts by mass in 100 parts by mass of the hydrogel. When the content is less than 2 parts by mass, the strength of the hydrogel is reduced, and the sheet shape may not be maintained. If the amount is more than 80 parts by mass, the movement of ions is hindered, and the ion resistance may increase. The content is preferably from 5 to 70 parts by mass, more preferably from 10 to 60 parts by mass.
Further, the content of the copolymer in the polymer matrix is preferably at least 45 parts by mass, more preferably at least 55 parts by mass. The polymer matrix may be composed of only a copolymer.

(A) Copolymer The copolymer is a monofunctional monomer A as an optional component having a carboxyl group and one ethylenically unsaturated group, and at least one group selected from a sulfone group and a phosphate group. And a monofunctional monomer B having one ethylenically unsaturated group and a polyfunctional monomer having 2 to 6 ethylenically unsaturated groups. The molar ratio (Ma / Mb) of the mole number of the carboxyl group (Ma) in the copolymer to the total mole number of the sulfone group and the phosphoric acid group (Mb) is preferably 0 to 8.0. By introducing a predetermined amount of a sulfonate group and / or a phosphate group having a high ionization degree into the copolymer, the ionization of the ionic functional group when immersed in a high-concentration electrolytic solution is stabilized, and the water retention can be maintained. . When the molar ratio is larger than 8.0, when the concentrated electrolyte is impregnated, a polymer matrix constituting the hydrogel is precipitated, and the flexibility and the water retention of the hydrogel may be reduced. The molar ratio is preferably from 0 to 6.0, more preferably from 0 to 5.0, more preferably from 0 to 4.0, and still more preferably from 0 to 3.0. . Ma / Mb can take 0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0.
Although the monofunctional monomer A is an optional component, the copolymer preferably contains the monofunctional monomer A.
The copolymer is composed of components derived from a monofunctional monomer and a polyfunctional monomer.However, the amount of each monomer used in producing the copolymer and the content of each component in the copolymer are as follows. Almost the same. The number of moles of the functional group in the copolymer can be calculated from the blending amount of the monofunctional monomer and the polyfunctional monomer. Further, the content of the polymer derived from the polyfunctional monomer in the copolymer can be measured by pyrolysis GC and / or IR.

(A-1) Monofunctional monomer A
The monofunctional monomer A is not particularly limited as long as it has a carboxyl group and one ethylenically unsaturated group. Here, the carboxyl group includes the case where it is present in the monofunctional monomer A in the form of a salt. Further, the monofunctional monomer A may be a mixture of a monomer that is not in a salt form and a monomer in a salt form.
For example, the monofunctional monomer A includes (meth) acrylic acid, sodium (meth) acrylate, potassium (meth) acrylate, lithium (meth) acrylate, vinyl benzoic acid, sodium vinyl benzoate, potassium vinyl benzoate, Examples thereof include lithium vinyl benzoate, vinyl acetic acid, sodium vinyl acetate, potassium potassium acetate, and lithium vinyl acetate.

(A-2) Monofunctional monomer B
The monofunctional monomer B is not particularly limited as long as it has at least one group selected from a sulfone group and a phosphate group and one ethylenically unsaturated group. Here, the sulfone group and the phosphate group include those present in the monofunctional monomer B in the form of a salt. Further, the monofunctional monomer B may be a mixture of a monomer that is not in a salt form and a monomer in a salt form.
For example, the monofunctional monomer B is
Vinyl sulfonic acid, sodium vinyl sulfonate, potassium vinyl sulfonate, lithium vinyl sulfonate, p-styrene sulfonic acid, sodium p-styrene sulfonate, potassium p-styrene sulfonate, lithium p-styrene sulfonate, allyl sulfonic acid, Sodium allyl sulfonate, potassium allyl sulfonate, lithium allyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, sodium 2-acrylamido-2-methylpropanesulfonate, potassium 2-acrylamido-2-methylpropanesulfonate, A sulfone group-containing monomer such as lithium 2-acrylamide-2-methylpropanesulfonate;
Vinyl phosphonic acid, sodium vinyl phosphonate, potassium vinyl phosphonate, lithium vinyl phosphonate, diethyl vinyl phosphonate, dimethyl vinyl phosphonate, phenyl vinyl phosphonic acid, sodium phenyl vinyl phosphonate, potassium phenyl vinyl phosphonate, lithium phenyl vinyl phosphonate, etc. And a phosphoric acid group-containing monomer. By introducing a sulfonate group and / or a phosphate group having a high degree of ionization into the copolymer, ionization of the ionic functional group when immersed in a high-concentration electrolyte solution is stabilized, and water retention can be maintained. The ease of ionization can also be determined by the acid dissociation constant (pKa).

(A-3) Content ratio of component derived from monofunctional monomer A and component derived from monofunctional monomer B The copolymer is derived from component derived from monofunctional monomer A and monofunctional monomer B It is preferable to contain 0 to 85 mol% of the component derived from the monofunctional monomer A and 15 to 100 mol% of the component derived from the monofunctional monomer B based on 100 mol% of the total components. By including both components in the copolymer within these ranges, it is possible to provide a hydrogel that can be used even in a concentrated aqueous electrolyte environment.
The content of the component derived from the monofunctional monomer A is 0 mol%, 5 mol%, 10 mol%, 20 mol%, 30 mol%, 40 mol%, 50 mol%, 60 mol%, 70 mol%, 75 mol%, 80 mol%, 85 mol% I can take it.

(A-4) Polyfunctional monomer The polyfunctional monomer is not particularly limited as long as it has 2 to 6 ethylenically unsaturated groups. From the viewpoint of alkali resistance, it is preferable not to have an ester bond. For example, polyfunctional monomers include divinylbenzene, sodium divinylbenzenesulfonate, divinylbiphenyl, divinylsulfone, diethylene glycol divinyl ether, pentaerythritol triallyl ether, pentaerythritol tetraallyl ether, dimethyldiallylammonium chloride, N, N'- Methylene bis (meth) acrylamide, N, N'-ethylenelenebis (meth) acrylamide and the like can be mentioned. In order to provide better alkali resistance, it is preferable that the polyfunctional monomer has no amide bond. The polyfunctional monomer may be only one kind or a mixture of plural kinds.
The polymer derived from the polyfunctional monomer is contained at a ratio of 0.1 to 5 parts by mass with respect to 100 parts by mass of the copolymer. When the proportion of the polymer derived from the polyfunctional monomer is less than 0.1 part by mass, the crosslinking density may be low. If the amount is more than 5 parts by mass, the polymer derived from the polyfunctional monomer may undergo phase separation, resulting in a hydrogel having a non-uniform crosslinked structure. The ratio is preferably from 0.2 to 4.5 parts by mass, more preferably from 0.4 to 4.0 parts by mass.
The copolymer is composed of components derived from a monofunctional monomer and a polyfunctional monomer.However, the amount of each monomer used in producing the copolymer and the content of each component in the copolymer are as follows. Almost the same. Further, the content of the polymer derived from the polyfunctional monomer in the copolymer can be measured by pyrolysis GC and / or IR.

(B) Other polymers Within a range that does not impair the effects of the present invention, polymers other than the above-described copolymer of a monofunctional monomer and a polyfunctional monomer are not polymerized with the copolymer. It may be included in a matrix. Examples of other polymers include polyvinyl sulfonic acid polymers and cellulose derivatives. The proportion of the other polymer in 100 parts by mass of the polymer matrix is preferably less than 50 parts by mass.

(2) Water 20 to 98 parts by mass of water is contained in 100 parts by mass of the hydrogel. When the content is less than 20 parts by mass, the amount of the electrolyte component that can be contained becomes small, and when used as a gel electrolyte for a battery, the impedance is high and desired battery characteristics may not be obtained in some cases. If the amount is more than 98 parts by mass, the strength of the hydrogel may decrease. The content is more preferably from 30 to 95 parts by mass, and still more preferably from 40 to 90 parts by mass.
(3) Electrolyte component The electrolyte component may be dissolved in water. A hydrogel containing an electrolyte component can be used as a gel electrolyte. As the electrolyte components, sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca (OH) ₂ ), barium hydroxide (Ba (OH) ₂ ), lithium hydroxide (LiOH), and hydroxide Rubidium (RbOH), cesium hydroxide (CsOH), lithium fluoride (LiF), lithium chloride (LiCl), lithium bromide (LiBr), lithium iodide (LiI), sodium chloride (NaCl), sodium bromide (NaBr) ), Potassium chloride (KCl), potassium bromide (KBr), calcium chloride (CaCl ₂ ), and the like. The dissolved amount of the electrolyte component is preferably up to 70 parts by mass with respect to 100 parts by mass of water. When the amount of dissolution is more than 70 parts by mass, the impedance may be increased because the electrolyte concentration becomes too high. The preferred amount of dissolution is 4 to 70 parts by mass.

(4) Other Components (a) Supporting Material The hydrogel may include a supporting material such as a woven fabric, a nonwoven fabric, and a porous sheet. By including the support material, the shape of the hydrogel can be easily maintained. Examples of the material of the support include natural fibers such as cellulose, silk, and hemp, synthetic fibers such as polyester, nylon, rayon, polyethylene, polypropylene, and polyurethane, and blends thereof. When an electrolyte component is included, synthetic fibers such as rayon, polyethylene, and polypropylene having no component decomposed by the electrolyte component, and blends thereof are preferable. The support may be located on any of the front, back and middle of the hydrogel.

(B) Protective film The hydrogel may have a protective film on its front and / or back surface. When the protective film is used as a separator, it is preferable that the protective film has been subjected to a release treatment. When a protective film is provided on both the front surface and the back surface, the front and back surfaces may have different peel strengths. When a protective film is used as a support, there is no need for a release treatment.
Examples of the protective film include films made of polyester, polyolefin, polystyrene, polyurethane, paper, paper laminated with a resin film (eg, polyethylene film, polypropylene film), and the like. Examples of the release treatment include a baking type silicone coating which is crosslinked and cured by heat or ultraviolet rays.

(C) Additive The hydrogel may contain an additive as needed. Additives include electrolytes, preservatives, bactericides, fungicides, rust inhibitors, antioxidants, defoamers, stabilizers, fragrances, surfactants, coloring agents, medicinal ingredients (eg, anti-inflammatory agents, Vitamin preparations, whitening agents, etc.) and gel strength improvers (eg, polyvinyl alcohol polymers, cellulose nanofibers) and the like.

(Method for producing hydrogel)
Hydrogels, for example,
(I) water, a monofunctional monomer A as an optional component having a carboxyl group and one ethylenically unsaturated group, at least one group selected from a sulfone group and a phosphate group, and one ethylenic group Step of preparing a hydrogel precursor containing a monofunctional monomer B having an unsaturated group, a polyfunctional monomer having 2 to 6 ethylenically unsaturated groups, and a polymerization initiator (preparation step)
(Ii) Step of obtaining a hydrogel by polymerizing a monofunctional monomer and a polyfunctional monomer (polymerization step)
It can be manufactured by going through.

(1) Molding Step As the polymerization initiator in this step, any of a thermal polymerization initiator and a photopolymerization initiator can be used. Among them, it is preferable to use a photopolymerization initiator which has little change in components before and after the polymerization. Examples of the photopolymerization initiator include 2-hydroxy-2-methyl-1-phenyl-propan-1-one (product name: Omnirad 1173, manufactured by BASF Japan), 1-hydroxy-cyclohexyl-phenyl-ketone ( Product name: Omnirad 184, manufactured by BASF Japan Ltd.), 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-propan-1-one (product name: Omnirad 2959, BASF. Japan), 2-methyl-1-[(methylthio) phenyl] -2-morpholinopropan-1-one (product name: Omnirad 907, manufactured by BASF Japan), 2-benzyl-2-dimethylamino- 1- (4-morpholinophenyl) -butan-1-one (product name: Omnirad 369, ASF · Japan Co., Ltd.), and the like. The polymerization initiator may be only one kind or a mixture of plural kinds.

  The amount of the polymerization initiator used is preferably 0.05 to 5 parts by mass with respect to 100 parts by mass of the total of all the monomers (monofunctional monomer, polyfunctional monomer and optionally other monomer). When the amount is less than 0.05 parts by mass, the polymerization reaction does not sufficiently proceed, and unpolymerized monomers may remain in the obtained hydrogel. If the amount is more than 5 parts by mass, a residue of the polymerization initiator after the polymerization reaction may give an odor, or physical properties may be reduced due to the influence of the residue. The amount used is more preferably from 0.06 to 3 parts by mass, even more preferably from 0.07 to 1.5 parts by mass.

  When a sheet-shaped hydrogel is produced, the hydrogel precursor is formed into a sheet by, for example, (i) a method of injecting the hydrogel precursor into a mold, (ii) a hydrogel precursor between protective films. And a method of (iii) coating a hydrogel precursor on a protective film. Method (i) has the advantage that a hydrogel of any shape can be obtained. Methods (ii) and (iii) have the advantage that relatively thin hydrogels can be obtained. Suitably, the hydrogel containing the support is produced by method (i). The hydrogel precursor may contain other monomers, additives, and the like described above.

(2) Polymerization Step A network structure can be obtained by polymerizing the monofunctional monomer and the polyfunctional monomer in the hydrogel precursor by applying heat or irradiating light. The conditions of heat application and light irradiation are not particularly limited as long as a network structure can be obtained, and general conditions can be adopted.
(3) Other Steps Other steps include an electrolyte component-containing step. In the electrolyte component-containing step, the electrolyte component in the aqueous alkaline solution is dissolved in the water in the hydrogel by immersing the hydrogel after polymerization in the aqueous electrolyte component solution. This immersion is performed under conditions for obtaining a hydrogel having a desired electrolyte component amount. For example, as the immersion temperature, cooling can be performed at 4 to 80 ° C., at room temperature (about 25 ° C.), and under heating. The immersion time can be 6 to 336 hours at normal temperature.
After immersion, the water content may be adjusted by drying the hydrogel. As the adjustment, for example, the mass of the hydrogel before and after immersion is made substantially the same.

(Use of hydrogel)
Hydrogels can be used in alkaline batteries.
The alkaline battery here is a secondary battery that can use a hydrogel as an electrolyte layer and / or a separator between a positive electrode and a negative electrode. Examples of such a secondary battery include a nickel-hydrogen secondary battery, a nickel-zinc secondary battery, a zinc-air battery, a lithium-air battery, an aluminum-air battery, a magnesium-air battery, and a calcium-air battery. Since these secondary batteries use an alkaline aqueous solution as an electrolytic solution, liquid leakage from the secondary batteries can be prevented by the hydrogel.
The configuration of the alkaline battery is not particularly limited, and any general configuration can be used. For example, nickel or a nickel alloy is used as a positive electrode of a nickel-hydrogen secondary battery, a hydrogen storage alloy is used as a negative electrode, nickel or a nickel alloy is used as a positive electrode of a nickel-zinc secondary battery, and zinc or zinc oxide is used as a negative electrode. Can be used. The positive electrode and the negative electrode may be formed on a current collector made of nickel, aluminum, or the like.
When the hydrogel is a separator, the hydrogel preferably includes a support.

Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto. First, methods for measuring various physical properties measured in Examples will be described.
(Swelling degree)
The hydrogel was cut into a thickness of 5 mm × 5 mm × 2 mm and weighed. Thereafter, the hydrogel was placed in a 250-mesh polyethylene tea bag, and the tea bag was immersed in 100 mL of an aqueous solution containing 1.5 M LiOH and 10 M LiCl. Then, after one week at a temperature of 25 ° C., after draining for 10 minutes, a water-containing tea bag swelled in an aqueous solution containing 1.5 M LiOH and 10 M LiCl was obtained. In addition, when the hydrogel became soft at the time of drainage and passed through the mesh, it was described as "liquefied". The degree of swelling (%) was determined by using the mass of a tea bag containing no hydrogel immersed in an aqueous solution containing 1.5 M LiOH and 10 M LiCl as a blank and swelling the aqueous solution containing 1.5 M LiOH and 10 M LiCl. The value obtained by subtracting the blank mass from the mass of the hydrogel-containing tea bag was divided by the mass of the hydrogel before swelling and multiplied by 100.

(Bending test after immersion in electrolyte)
The hydrogel was cut into 10 mm × 30 mm, and immersed in 100 mL of an aqueous solution containing 1.5 M LiOH and 10 M LiCl for one week. The hydrogel after immersion was bent until both ends on the long side were in contact. At this time, the case where the hydrogel did not crack was evaluated as ○, and the case where the hydrogel cracked was evaluated as ×.

(AC impedance)
The hydrogel was cut to a thickness of 20 mm × 20 mm × 2 mm and immersed in 100 mL of an aqueous solution containing 1.5 M LiOH and 10 M LiCl for one week to obtain a hydrogel after immersion in a high-concentration electrolyte. The hydrogel after immersion in the high-concentration electrolyte was sandwiched between two Ni plates (width 20 mm, length 40 mm, thickness 1.0 mm) to obtain a test piece. At a temperature of 25 ° C., using a FRA impedance analyzer (PGSTAT manufactured by Autolab), the AC amplitude was set to 10 mV (rms), and the measurement frequency range was set to 100 kHz to 100 Hz. The AC impedance was measured. From the obtained measurement results, the real component of the impedance at a frequency of 100 kHz (Z '/ Ohm) was taken as the impedance at a frequency of 100 kHz, and the real component of the impedance at a frequency of 1 kHz (Z' / Ohm) was taken as the impedance at a frequency of 1 kHz.

(30% compression stress test after immersion in high concentration electrolyte)
The hydrogel was cut into a thickness of 30 mm × 30 mm × 2 mm and immersed in 100 mL of an aqueous solution containing 1.5 M LiOH and 10 M LiCl for one week to obtain a hydrogel immersed in a high-concentration electrolyte. The thickness of the hydrogel after immersion in the high-concentration electrolyte was measured at five points using a dial thickness gauge (DS-3010S manufactured by Niigata Seiki Co., Ltd.), and the average value was taken as the thickness after immersion in the high-concentration electrolyte. A texture analyzer (TA.XT Plus, manufactured by Eiko Seiki Co., Ltd.) was used as a measuring device for the compression test.
At a temperature of 25 ° C., a stainless-steel cylindrical measuring jig having a diameter of 10 mm was compressed at a rate of 0.1 mm / sec so that the deformation ratio was 30% with respect to the thickness after immersion in the high-concentration electrolyte. This measurement was performed on five test pieces, the maximum stress was calculated, and the average of these was defined as the average stress.
The 30% compressive strength after immersion in the high-concentration electrolyte was determined as follows.
30% compressive strength after immersion in high-concentration electrolyte σ _c = P _c / A ₀ (N / cm ² )
P _c : Load of average stress (N)
A _p: cross-sectional area of the cylindrical test fixture (= 0.5cm × 0.5cm × 3.14 = 0.785cm 2)

<Example 1>
20 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (manufactured by MCC Unitech), 0.3 parts by mass of sodium divinylbenzenesulfonate (manufactured by Tosoh Organic Chemicals), and 79.6 parts by mass of ion-exchanged water are put in a container. Stirred. 0.10 parts by mass of Omnirad 1173 (manufactured by BASF Japan) as a polymerization initiator was added to this solution, and the mixture was stirred to prepare a hydrogel precursor. A silicon frame having a thickness of 2 mm was placed on the peelable PET film, and the hydrogel precursor was poured into the frame. Then, the peelable PET film was placed on the hydrogel precursor. Thereafter, ultraviolet light having an energy of 7000 mJ / cm ² is irradiated by a small UV polymerization machine (manufactured by JATEC, J-cure 1500, metal halide lamp type name MJ-1500L) under the conditions of a conveyor speed of 0.4 m / min and a distance between works of 150 mm. By performing the process three times, a sheet-shaped hydrogel having a thickness of 2 mm was produced. The prepared hydrogel was subjected to swelling degree measurement, bending test after immersion in electrolyte, 30% compression stress test after immersion in high concentration electrolyte, and AC impedance measurement.

<Example 2>
17.5 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (manufactured by MCC Unitech), 0.3 part by mass of sodium divinylbenzenesulfonate (manufactured by Tosoh Organic Chemicals), and 79.6 parts by mass of ion-exchanged water And stirred. Further, 2.5 parts by mass of acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) was added and stirred. 0.10 parts by mass of Omnirad 1173 (manufactured by BASF Japan) as a polymerization initiator was added to this solution, and the mixture was stirred to prepare a hydrogel precursor.
A 2 mm-thick sheet-like hydrogel was prepared in the same manner as in Example 1 except that the above-mentioned hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, bending test after immersion in electrolyte, 30% compression stress test after immersion in high concentration electrolyte, and AC impedance measurement.

<Example 3>
2 mm thick sheet in the same manner as in Example 2, except that 15 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (manufactured by MCC Unitech) and 5 parts by mass of acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) were used. A hydrogel was prepared. The prepared hydrogel was subjected to swelling degree measurement, bending test after immersion in electrolyte, 30% compression stress test after immersion in high concentration electrolyte, and AC impedance measurement.

<Example 4>
Same as Example 2 except that 12.5 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (manufactured by MCC Unitech) and 7.5 parts by mass of acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) were changed. A sheet-shaped hydrogel having a thickness of 2 mm was prepared. The prepared hydrogel was subjected to swelling degree measurement, bending test after immersion in electrolyte, 30% compression stress test after immersion in high concentration electrolyte, and AC impedance measurement.

<Example 5>
10 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (manufactured by MCC Unitech), 10 parts by mass of acrylic acid (manufactured by Nippon Shokubai Co., Ltd.), 0.13 parts by mass of a polymerization initiator, and 79. Except having changed to 57 mass parts, it carried out similarly to Example 2, and produced the sheet-shaped hydrogel of 2 mm thickness. The prepared hydrogel was subjected to swelling degree measurement, bending test after immersion in electrolyte, 30% compression stress test after immersion in high concentration electrolyte, and AC impedance measurement.

<Example 6>
17.5 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (manufactured by MCC Unitech), 0.3 part by mass of sodium divinylbenzenesulfonate (manufactured by Tosoh Organic Chemicals), and 79.6 parts by mass of ion-exchanged water And stirred. Further, 2.5 parts by mass of vinylbenzoic acid (4VBA, manufactured by Tosoh Organic Chemicals, Inc.) was added and stirred. 0.10 parts by mass of Omnirad 1173 (manufactured by BASF Japan) as a polymerization initiator was added to this solution, and the mixture was stirred to prepare a hydrogel precursor.
A 2 mm-thick sheet-like hydrogel was prepared in the same manner as in Example 1 except that the above-mentioned hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, bending test after immersion in electrolyte, 30% compression stress test after immersion in high concentration electrolyte, and AC impedance measurement.

<Example 7>
Example 6 except that 15 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (manufactured by MCC Unitech) and 5 parts by mass of vinylbenzoic acid (product name: 4VBA, manufactured by Tosoh Organic Chemicals) were used. Similarly, a sheet-like hydrogel having a thickness of 2 mm was prepared. The prepared hydrogel was subjected to swelling degree measurement, bending test after immersion in electrolyte, 30% compression stress test after immersion in high concentration electrolyte, and AC impedance measurement.

<Example 8>
15 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (manufactured by MCC Unitech), 0.3 parts by mass of sodium divinylbenzenesulfonate (manufactured by Tosoh Organic Chemicals), and 49.6 parts by mass of ion-exchanged water are put in a container. Stirred. Separately, an aqueous solution was prepared by adding 3.03 parts by mass of lithium hydroxide monohydrate (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) to 30 parts by mass of ion-exchanged water. This aqueous solution was added to the previously prepared mixed solution of 2-acrylamido-2-methylpropanesulfonic acid, sodium divinylbenzenesulfonate and ion-exchanged water while cooling. Further, 5 parts by mass of acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) was added to this solution, followed by stirring. 0.10 parts by mass of Omnirad 1173 (manufactured by BASF Japan) as a polymerization initiator was added to this solution, and the mixture was stirred to prepare a hydrogel precursor.
A 2 mm-thick sheet-like hydrogel was prepared in the same manner as in Example 1 except that the above-mentioned hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, bending test after immersion in electrolyte, 30% compression stress test after immersion in high concentration electrolyte, and AC impedance measurement.

<Example 9>
A 2 mm-thick sheet-like hydrogel was prepared in the same manner as in Example 3 except that the acrylic acid was changed to potassium acrylate (manufactured by Nippon Shokubai Co., Ltd.). The prepared hydrogel was subjected to swelling degree measurement, bending test after immersion in electrolyte, 30% compression stress test after immersion in high concentration electrolyte, and AC impedance measurement.

<Comparative Example 1>
20 parts by mass of acrylic acid (manufactured by Nippon Shokubai Co., Ltd.), 0.3 parts by mass of sodium divinylbenzenesulfonate (manufactured by Tosoh Organic Chemicals), and 79.5 parts by mass of ion-exchanged water were put in a container and stirred. To this solution was added 0.2 parts by mass of Omnirad 1173 (manufactured by BASF Japan) as a polymerization initiator, and the mixture was stirred to prepare a hydrogel precursor.
A 2 mm-thick sheet-like hydrogel was prepared in the same manner as in Example 1 except that the above-mentioned hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, bending test after immersion in electrolyte, 30% compression stress test after immersion in high concentration electrolyte, and AC impedance measurement.

<Comparative Example 2>
5 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (manufactured by MCC Unitech), 0.3 parts by mass of sodium divinylbenzenesulfonate (manufactured by Tosoh Organic Chemicals), and 79.53 parts by mass of ion-exchanged water are put in a container. Stirred. Further, 15 parts by mass of acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) was added and stirred. 0.17 parts by mass of Omnirad 1173 (manufactured by BASF Japan) as a polymerization initiator was added to this solution, and the mixture was stirred to prepare a hydrogel precursor.
A 2 mm-thick sheet-like hydrogel was prepared in the same manner as in Example 1 except that the above-mentioned hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, bending test after immersion in electrolyte, 30% compression stress test after immersion in high concentration electrolyte, and AC impedance measurement.

<Comparative Example 3>
5 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (manufactured by MCC Unitech), 0.3 parts by mass of sodium divinylbenzenesulfonate (manufactured by Tosoh Organic Chemicals), 39.57 parts by mass of ion-exchanged water, and as a plasticizer 40 parts by mass of glycerin of polyhydric alcohol was put in a container and stirred. Further, 15 parts by mass of acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) was added and stirred. 0.17 parts by mass of Omnirad 1173 (manufactured by BASF Japan) as a polymerization initiator was added to this solution, and the mixture was stirred to prepare a hydrogel precursor.
A 2 mm-thick sheet-like hydrogel was prepared in the same manner as in Example 1 except that the above-mentioned hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, bending test after immersion in electrolyte, 30% compression stress test after immersion in high concentration electrolyte, and AC impedance measurement.

<Comparative Example 4>
5 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (manufactured by MCC Unitech), 15 parts by mass of acrylic acid (manufactured by Nippon Shokubai Co., Ltd.), 0.3 parts by mass of sodium divinylbenzenesulfonate (manufactured by Tosoh Organic Chemicals) 39.5 parts by mass of ion-exchanged water and 40 parts by mass of polyethylene glycol 300 (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) of a polyhydric alcohol as a plasticizer were placed in a container and stirred. 0.17 parts by mass of Omnirad 1173 (manufactured by BASF Japan) as a polymerization initiator was added to this solution, and the mixture was stirred to prepare a hydrogel precursor.
A 2 mm-thick sheet-like hydrogel was prepared in the same manner as in Example 1 except that the above-mentioned hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, bending test after immersion in electrolyte, 30% compression stress test after immersion in high concentration electrolyte, and AC impedance measurement.
Table 1 shows the results of Examples and Comparative Examples.

  From Table 1, if the molar ratio (Ma / Mb) of the functional group mole number (Ma) of the carboxyl group in the copolymer and the functional group mole number (Mb) of the sulfone group is 0 to 8.0. It can be seen that a hydrogel that can be used even in a concentrated aqueous electrolyte environment can be provided.

Claims (7)

A hydrogel containing a polymer matrix and water,
The polymer matrix includes a monofunctional monomer A as an optional component having a carboxyl group and one ethylenically unsaturated group, at least one group selected from a sulfone group and a phosphate group, and one ethylene group. A monofunctional monomer B having an unsaturated group, and a copolymer of a polyfunctional monomer having 2 to 6 ethylenically unsaturated groups,
The molar ratio (Ma / Mb) of the number of moles of carboxyl groups (Ma) in the copolymer to the total number of moles of sulfone groups and phosphate groups (Mb) is 0 to 8.0,
The hydrogel for an alkaline battery, wherein the hydrogel contains 2-80 parts by mass of a polymer matrix and 20-98 parts by mass of water in 100 parts by mass.   2. The alkaline battery according to claim 1, wherein the hydrogel exhibits a swelling degree of 70 to 800% when immersed in an aqueous solution containing 1.5 M LiOH and 10 M LiCl at a temperature of 25 ° C. for one week. Hydrogel. 3. The hydrogel according to claim 1, wherein the hydrogel exhibits a 30% compressive stress of 20 N / cm ² or less when immersed in an aqueous solution containing 1.5 M LiOH and 10 M LiCl at a temperature of 25 ° C. for one week. The hydrogel for an alkaline battery according to the above.   The hydrogel according to claim 1, wherein when the hydrogel is immersed in an aqueous solution containing 1.5 M LiOH and 10 M LiCl at a temperature of 25 ° C. for 1 week, the impedance at a frequency of 100 kHz is 20 Ω or less. The hydrogel for an alkaline battery according to any one of the above.   The copolymer has 0 to 85 mol% of a component derived from the monofunctional monomer A with respect to 100 mol% in total of a component derived from the monofunctional monomer A and a component derived from the monofunctional monomer B. The hydrogel for an alkaline battery according to any one of claims 1 to 4, comprising 15 to 100 mol% of a component derived from the monofunctional monomer B.   A gel electrolyte comprising the hydrogel according to any one of claims 1 to 5, and an electrolyte component contained in the hydrogel.   An alkaline battery comprising the hydrogel according to any one of claims 1 to 5 or the gel electrolyte according to claim 6.