JP6668530B2 - Hydrogel for alkaline battery, gel electrolyte and battery using the same - Google Patents

Description

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

In recent years, with the increasing global interest in environmental issues, the use of renewable energy, the shift from gasoline vehicles to electric vehicles, and the use of smart grids are accelerating. With such a movement, the importance of a storage battery (secondary battery) exhibiting a high energy density is increasing.
A metal-air battery that uses 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 the negative electrode active material inside the battery. For this reason, metal-air batteries have attracted attention as next-generation secondary batteries having a 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, a hydrogen air battery, and the like are known.
However, in a metal-air battery, the positive electrode portion is isolated from the outside by a water-repellent film or the like, but the sealing performance is not sufficient, and the electrolyte evaporates from the positive electrode, so that the inside of the battery is easily dried, There is a problem that the strong basic electrolyte 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. Further, JP-A-2017-179328 (Patent Document 2) discloses a sheet-like hydrogel composed of a crosslinked body 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

In the hydrogels described in Patent Documents 1 and 2, in the presence of a high-concentration aqueous electrolyte solution as in Patent Document 3, ionization of a functional group bonded to a polymer constituting the hydrogel is weakened, and water retention is reduced. The resulting reduction in flexibility and hardening occurred. Therefore, there is a problem that this hydrogel cannot be used for an alkaline secondary battery using a high-concentration aqueous electrolyte.
In view of the above problems, the inventors of the present invention have introduced a high-concentration aqueous electrolyte solution by introducing a certain amount of a strongly ionized functional group (for example, a sulfone group) into the skeleton of a polymer matrix constituting a hydrogel. An attempt was made to suppress the curing of the hydrogel underneath. As a result, although some suppression was possible, the hydrophilicity of the skeleton was sometimes increased by the introduction of a strongly ionized functional group. Since the increase in hydrophilicity affects the degree of swelling when immersed in the electrolytic solution and the mechanical strength of the hydrogel, there is room for improvement.

As a result of extensive studies, the inventors have found that a polyacrylic acid-based polymer having a specific weight-average molecular weight is included in a hydrogel to prevent the copolymer from being precipitated and to be used even in an environment of a high-concentration aqueous electrolyte. The present inventors have found that a hydrogel that is possible and has excellent mechanical strength can be provided, and has led to the present invention.
Thus, according to the present invention, a hydrogel comprising water, a polyacrylic acid-based polymer, and a polymer matrix,
The polyacrylic acid-based polymer has a weight average molecular weight of 3,000 to 2,000,000,
The polymer matrix includes a monofunctional monomer having an ethylenically unsaturated group and a copolymer of a polyfunctional monomer having 2 to 6 ethylenically unsaturated groups,
The monofunctional monomer having an ethylenically unsaturated group includes a monofunctional monomer A having at least one group selected from a sulfone group and a phosphate group and one ethylenically unsaturated group,
A component derived from the monofunctional monomer A and the polyacrylic acid-based polymer are present in the hydrogel in a mass ratio of 100: 2.5 to 90,
The water, the polyacrylic acid-based polymer and the polymer matrix are contained in 21 to 89.5 parts by mass, 0.5 to 19 parts by mass, and 10 to 60 parts by mass, respectively, in 100 parts by mass of the hydrogel. A hydrogel for an alkaline battery is provided.

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,
(I) By introducing a sulfone group and / or a phosphate group into the skeleton of the polymer matrix constituting the hydrogel, it is possible to prevent the skeleton from being precipitated when a large amount of electrolyte is contained in the hydrogel, and to provide flexibility. (Ii) By including a polyacrylic acid-based polymer having a weight average molecular weight in a specific range, the hydrogel after immersion in the electrolyte can be provided with high mechanical strength.
Since the hydrogel of the present invention retains water retention and flexibility even in a state where the electrolyte is impregnated at a high concentration, the hydrogel exhibits good adhesion to electrodes and solid electrolytes, so An increase in interface resistance can be suppressed, and as a result, good battery characteristics can be realized. Furthermore, the hydrogel of the present invention is excellent in handling when used as a gel electrolyte for batteries because of its excellent mechanical strength.

Further, according to the present invention, when having the following constitution, it is possible to provide a hydrogel which is more excellent in handleability and battery characteristics.
(1) The monofunctional monomer having an ethylenically unsaturated group further includes a monofunctional monomer B having a carboxyl group and one ethylenically unsaturated group, and the content ratio of the monofunctional monomers A and B is The range is 30 mol% or more and 70 mol% or less.
(2) The polyacrylic acid-based polymer is a homopolymer of a carboxyl group-containing monomer or a copolymer of a carboxyl group-containing monomer and a sulfonic acid group-containing monomer.
(3) The polyacrylic acid polymer has an absorbance (absorbance _{[1650 ± 130 cm-1]} ) of the maximum peak in the range of 1650 ± 130 cm ⁻¹ and an absorbance of 1040 ± 20 cm ⁻¹ obtained in the FT-IR measurement. The absorbance ratio (absorbance _{[1040 ± 20 cm-1]} / absorbance _{[1650 ± 130 cm-1]} ) with the absorbance of the maximum peak (absorbance _{[1040 ± 20 cm-1]} ) is a value in the range of 0.001 to 5.0. It is a polymer which shows.
(4) 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 50 to 300%.
(5) 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 piercing strength of 0.35 N or more.
(6) When the hydrogel is immersed for one week in an aqueous solution containing 1.5 M LiOH and 10 M LiCl at a temperature of 25 ° C., the impedance at a frequency of 100 kHz shows a value of 20Ω or less.

(Hydrogel)
The hydrogel preferably shows a swelling degree of 50 to 300% 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 50%, the solid content of the hydrogel becomes large, which may cause a decrease in flexibility and, in some cases, a hardening. If it is more than 300%, the hydrogel after swelling has low mechanical strength, so that the hydrogel may be broken during handling. The degree of swelling is more preferably 50 to 280%.
The hydrogel preferably exhibits a puncture strength of 0.35 N or more 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 piercing strength here means the average value of the maximum stress until the tip of a jig having a diameter of 3 mm penetrates the hydrogel. When the puncture strength is less than 0.35 N, the mechanical strength is low, and the puncture strength may not be handled as a self-supporting film. The upper limit of the piercing strength is more preferably 300N.
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 impedance value is larger than 20Ω, the battery characteristics may be deteriorated due to an increase in the resistance of the electrolyte. The value of the impedance is more preferably 18Ω or less, further preferably 16Ω or less, and particularly preferably 14Ω or less. The lower limit of the impedance value is preferably 0.05Ω.

The hydrogel includes water, a polyacrylic acid-based polymer, and a polymer matrix.
(1) Polymer matrix The polymer matrix contains a copolymer of a monofunctional monomer having an 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 10 to 60 parts by mass in 100 parts by mass of the hydrogel. When the content is less than 10 parts by mass, the mechanical strength of the hydrogel becomes low, and the sheet shape may not be maintained. When the amount is more than 60 parts by mass, the movement of ions is hindered, so that the ion resistance may increase. The content is preferably from 10 to 55 parts by mass, more preferably from 10 to 50 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 includes a copolymer of a monofunctional monomer having an ethylenically unsaturated group and a polyfunctional monomer having 2 to 6 ethylenically unsaturated groups. The monofunctional monomer includes a monofunctional monomer A having at least one group selected from a sulfone group and a phosphate group and one ethylenically unsaturated group. The copolymer may further comprise, as an optional component, a monofunctional monomer B having a carboxyl group or a neutralized functional group thereof and one ethylenically unsaturated group.

(A-1) Monofunctional monomer A
The monofunctional monomer A 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 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 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, the ionization of the ionic functional groups when immersed in a high-concentration electrolytic solution is stabilized, and water retention and flexibility are maintained. it can. The ease of ionization can also be determined by the acid dissociation constant (pKa).

(A-2) Monofunctional monomer B
The monofunctional monomer B 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 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 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-3) Content ratio of component derived from monofunctional monomer A and component derived from monofunctional monomer B When the copolymer contains a component derived from monofunctional monomer B, the monofunctional monomer For a total of 100 mol% of the component derived from A and the component derived from the monofunctional monomer B, the component derived from the monofunctional monomer A is 30 mol% or more, and the component derived from the monofunctional monomer B is 70 mol% or less. It is preferred to include. By including both components in the copolymer within these ranges, it is possible to provide a hydrogel that can be used even in an environment of a high-concentration aqueous electrolyte solution.
The content of the component derived from the monofunctional monomer A can range from 30 mol% or more to less than 100 mol%, and specifically, 30 mol%, 40 mol%, 50 mol%, 60 mol%, 70 mol%, 80 mol%, 90 mol%. %, 99 mol%.

(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 divinylbenzene sulfonate, divinyl biphenyl, divinyl sulfone, diethylene glycol divinyl ether, pentaerythritol triallyl ether, pentaerythritol tetraallyl ether, dimethyldiallylammonium chloride, N, N'- Methylenebis (meth) acrylamide, N, N'-ethylenebis (meth) acrylamide, N, N '-{[(2-acrylamido-2-[(3-acrylamidopropoxy) methyl] propane-1,3-diyl) bis (Oxy)] bis (propane-1,3-diyl)｝ diacrylamide (CAS No. 139329-90-2), N, N ′, N ″ -triacryloyldiethylenetriamine (CAS No. 34330) 10-4), N, N ′, N ″, N ′ ″-tetraacryloyltriethylenetetramine (CAS No. 15849-66-7), N, N′-diacryloyl-2,7,10-trioxa -1,13-tridecaneamine (CAS No. 160432-07-5) and the like. 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 preferably 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 more preferably from 0.2 to 4.5 parts by mass, and even 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. Other polymers include cellulose derivatives and the like. The proportion of the other polymer in 100 parts by mass of the polymer matrix is preferably less than 50 parts by mass.

(2) Polyacrylic acid-based polymer The polyacrylic acid-based polymer is not particularly limited as long as it can be used as an additive to the hydrogel. Since the polyacrylic acid-based polymer has relatively high cohesive strength in an alkaline environment, it is considered that the polymer has an effect of increasing the entanglement of the polymer network constituting the hydrogel and strengthening the hydrogel.
Examples of the polyacrylic acid polymer include a homopolymer of a carboxyl group-containing monomer and a copolymer of a carboxyl group-containing monomer and a sulfonic acid group-containing monomer. Examples of the carboxyl group-containing monomer include (meth) acrylic acid, vinylbenzoic acid, maleic acid, fumaric acid, itaconic acid, and alkali metal salts thereof. Examples of the sulfonic acid monomer include vinyl sulfonic acid, methyl vinyl sulfonic acid, styrene sulfonic acid, (meth) acryl sulfonic acid, ethyl (meth) acrylate sulfonic acid, acrylamidohydroxypropane sulfonic acid, and (meth) acrylamidomethylpropane sulfonic acid. , Allyloxypropanesulfonic acid, allylsulfonic acid, and alkali metal salts thereof.
Specific examples of the polyacrylic acid-based polymer include poly (meth) acrylic acid, sodium poly (meth) acrylate, potassium poly (meth) acrylate, ammonium poly (meth) acrylate, and (meth) acrylic acid-maleic. Acid copolymers, (meth) acrylic acid-sulfonic acid monomer copolymers, and the like can be mentioned.

Polyacrylic acid-based polymer, in FT-IR measurement, preferably shows an absorption band in the range of 1650 ± 130 cm ^-1 range and 1040 ± 20 cm ^-1. The inventors believe that the absorption band in the range of 1650 ± 130 cm ⁻¹ is derived from a carboxylic acid or a salt thereof, and the absorber in the range of 1040 ± 20 cm ⁻¹ is derived from a sulfonic acid or a salt thereof.
Polyacrylic acid based polymer, the absorbance of the maximum peak of 1650 range of ± 130 cm ^-1 obtained in FT-IR measurements (absorbance _{[1650 ± 130cm-1])} and 1040 of the maximum peak in the range of ± 50 cm ^-1 The absorbance ratio (absorbance _{[1040 ± 20 cm-1]} / absorbance _{[1650 ± 130 cm-1]} ) with respect to the absorbance (absorbance _{[1040 ± 50 cm-1]} ) indicates a value in the range of 0.001 to 5.0. It is preferred that they are united. When the absorbance ratio is larger than 5.0, the ratio derived from the sulfonic acid group unit in the polymer increases, so that the cohesive force at the time of immersion in the high-concentration electrolyte solution becomes weak, and the strength reinforcing effect may not be obtained. If it is less than 0.001, the cohesive force becomes too strong, and the hydrogel is separated from the water and may be cured. The absorbance ratio is more preferably in the range of 0.001 to 4.5. The range of 0.005 to 4.0 is more preferable, the range of 0.01 to 3.5 is more preferable, the range of 0.025 to 3.0 is more preferable, and the range of 0.05 to 3.0 is more preferable. Preferably, the range is from 0.1 to 3.0, more preferably, from 0.2 to 2.0.
The polyacrylic acid-based polymer has a weight average molecular weight of 3,000 to 2,000,000. When the weight average molecular weight is less than 3,000, the cohesive force of the polyacrylic acid polymer in the presence of the high concentration electrolyte is weak, and the entanglement between the polymer network and the polyacrylic acid polymer is small. In some cases, an effect of improving mechanical strength may not be obtained. When it exceeds 2,000,000, the cohesive force of the polyacrylic acid-based polymer in the presence of the high-concentration electrolyte and the entanglement between the polymer network and the polyacrylic acid-based polymer become excessive, so that the hydrogel is not formed. It may shrink uniformly, resulting in a distorted shape. The average degree of polymerization is preferably from 3,000 to 1,800,000, and more preferably from 3,000 to 1,500,000.
The polyacrylic acid-based polymer is preferably contained in an amount of 0.5 to 19 parts by mass in 100 parts by mass of the hydrogel. If the content is less than 0.5 parts by mass, the effect of improving mechanical strength may not be obtained. If the amount is more than 19 parts by mass, the entanglement with the polymer network becomes too strong, and the water retention and flexibility of the hydrogel may decrease. The content is preferably from 0.5 to 15 parts by mass.
The component derived from the monofunctional monomer A and the polyacrylic acid-based polymer are present in the hydrogel at a mass ratio of 100: 2.5 to 90. When the mass ratio of the polyacrylic acid-based polymer is less than 2.5, the effect of improving mechanical strength may not be obtained. If it is more than 90, the entanglement with the polymer network becomes too strong, and the water retention and flexibility of the hydrogel may decrease. The mass ratio is preferably from 100: 5 to 90, more preferably from 100: 7.5 to 90, and even more preferably from 100: 10 to 90.

(3) Water 21 to 89.5 parts by mass of water is contained in 100 parts by mass of the hydrogel. When the content is less than 21 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 89.5 parts by mass, the mechanical strength of the hydrogel may decrease. The content is more preferably from 30 to 85 parts by mass, and still more preferably from 40 to 80 parts by mass.
(4) Electrolyte component An 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 70 parts by mass or less based on 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.

(5) 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. The protective film is preferably 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, gel strength improvers (eg, cellulose nano Fiber).

(Method for producing hydrogel)
Hydrogels, for example,
(I) a step of preparing a hydrogel precursor containing water, a monofunctional monomer A, a monofunctional monomer B as an optional component, a polyfunctional monomer, a polyacrylic acid-based polymer and a polymerization initiator; Process)
(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 to be used is preferably 0.05 to 5 parts by mass with respect to 100 parts by mass in 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, and the like. 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. The hydrogel precursor may contain other monomers and additives 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 a temperature of 4 to 80 ° C., room temperature (about 25 ° C.), and 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, a calcium-air battery, and a hydrogen-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 width of 5 mm × length of 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 soaking for 1 week at a temperature of 25 ° C., water draining was performed for 10 minutes, and the resultant was weighed to obtain a hydrogel-containing tea bag swelled in an aqueous solution containing 1.5 M LiOH and 10 M LiCl. 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. When the hydrogel used a nonwoven fabric or the like as the support material, 0.3 g of the hydrogel was scraped off from the support material, and the swelling degree was calculated in the same manner as described above.

(Bending test after immersion in electrolyte)
The hydrogel was cut into a width of 20 mm and a length of 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 ×.

(Puncture strength)
The obtained hydrogel was cut into a width of 30 mm × length of 30 mm × 2 mm. The cut hydrogel was immersed in 100 mL of 1.5 M LiOH and 10 M LiCl aqueous solution at 25 ° C. for 1 week, and the gel was immersed in an alkaline solution to obtain a hydrogel. The hydrogel immersed in the alkaline solution is pulled up from the electrolytic solution, drained for 10 minutes, and then subjected to texture analyzer TA. A piercing test was performed using XT Plus (manufactured by Eiko Seiki Co., Ltd.) according to the following procedure. The hydrogel after immersion in the alkaline solution was placed on a table having a hole having a diameter of 7 mm, and adjusted to a position where a jig of a stainless steel cylinder having a diameter of 3 mm passed through the center of the hole of the table. Thereafter, the piercing was performed at a speed of 1.0 mm / sec, and the maximum stress until the tip of the jig penetrated was measured. This measurement was performed on five test pieces, the maximum stress was calculated, and the average of these was defined as the piercing strength. When the thickness of the test piece was less than 2 mm, the sheets were laminated and adjusted so that the thickness of the laminated sheet became 2 mm.

(AC impedance measurement)
The hydrogel was cut into a width of 20 mm × length of 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 immersed 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. Using a FRA impedance analyzer (PGSTAT, manufactured by Autolab), the AC amplitude of the test piece was measured by a two-terminal method with an AC amplitude of 10 mV (rms) and a measurement frequency range of 100 kHz to 100 Hz. From the obtained measurement results, the real component of the impedance at a frequency of 100 kHz (Z ′ / Ω) was defined as the impedance at a frequency of 100 kHz, and the real component of the impedance at a frequency of 1 kHz (Z ′ / Ω) was defined as the impedance at a frequency of 1 kHz. When the thickness of the test piece was less than 2 mm, the sheets were laminated and adjusted so that the thickness of the laminated sheet became 2 mm.

(Weight average molecular weight)
The weight average molecular weight (Mw) was defined as pullulan-converted weight average molecular weight measured using gel permeation chromatography (GPC). Specifically, 50 mg of a sample was dissolved in 5 mL of a 0.2 M NaNO ₃ aqueous solution (permeation time: 24 ± 1 hr (complete dissolution)), and filtered through a 0.45 μm aqueous chromatodisk (13N) manufactured by GL. Was measured using a chromatograph under the following measurement conditions, and the weight average molecular weight of the sample was determined from a standard pullulan calibration curve prepared in advance.
Equipment used: Tosoh Corporation HLC-8020GPC EcoSEC (Built-in RI detector / UV detector)
Guard column: TSK GUARDCOLUMN PWXL-H (6.0 mm ID × 4.0 cm) × 1 by Tosoh Column: TSKgel G6000 PWXL (7.8 mm ID × 30 cm) × 1 by Tosoh + Tosoh TSKgel G3000 PWXL (7.8 mm ID × 30 cm) x 1 Column temperature: 40 ° C
Mobile phase: 0.2 M NaNO ₃ aqueous solution Mobile phase flow rate: Reference side pump = 0.6 mL / min
Sample side pump = 0.6mL / min
Detector: RI detector Sample concentration: 1.0 wt%
Injection volume: 100 μL
Measurement time: 65min
Sampling pitch: 500msec
The standard pullulan sample for the calibration curve was manufactured by Showa Denko KK and has a trade name of “shodex” having a weight average molecular weight of 2,560,000, 1,600,000, 380,000, 212,000, 100,000, 48,000. , 23,700, 12,200, 5,800.
The standard pullulan for the above calibration curve was A (1,600,000, 212,000, 48,000, 12,200) and B (2,560,000, 380,000, 100,000, 23,700, 5, 800), A was weighed in 1 to 2.5 mg and dissolved in 2 mL of distilled water, and B was weighed in 1 to 2.5 mg each and dissolved in 2 mL of distilled water. A standard pullulan calibration curve was obtained by injecting 100 μL of each of the prepared A and B lysates and creating a calibration curve (cubic equation) from the retention times obtained after measurement, and using the calibration curve, a weight average molecular weight was obtained. Was calculated.

(FT-IR measurement)
The absorbance of the polyacrylic acid-based polymer was measured by the following method to determine the absorbance _{[1040 ± 20 cm-1]} and the absorbance _{[1650 ± 130 cm-1]} , and the absorbance ratio = (absorbance _{[1040 ± 20 cm-1]} / absorbance) _{[1650 ± 130 cm-1]} ) was calculated.
Specifically, a sample dried at a temperature of 80 ° C. for 80 hours was taken out, and an infrared absorption spectrum was obtained by a single reflection ATR method (= micro surface analysis method).
-Measuring device: Fourier transform infrared spectrophotometer Nicolet iS10 (manufactured by Thermo SCIENTIFIC) and single reflection horizontal ATR Smart-iTR (manufactured by Thermo SCIENTIFIC)
・ ATR Crystal: Diamond with ZnSe Lens,
Angle 42 °
・ Measurement method: Single ATR method ・ Measurement wave number region: 4000 cm ^{-1 to} 650 cm ^-1
-Wave number dependence of measurement depth: uncorrected-Detector: deuterated triglycine sulfate (DTGS) detector and KBr beam splitter-Resolution: 4 cm ^-1
・ Number of integration: 16 times (same for background measurement)
・ Number of tests: n = 3
In the ATR method, since the intensity of the infrared absorption spectrum obtained by the measurement changes depending on the degree of adhesion between the sample and the high refractive index crystal, the degree of adhesion is almost uniform by applying the maximum load applied by the "Smart-iTR" of the ATR accessory. Was measured. The infrared absorption spectrum obtained under the above conditions was subjected to a peak treatment as follows to obtain an absorbance _{[1040 ± 20 cm-1]} and an absorbance _{[1650 ± 130 cm-1],} and an absorbance ratio = (absorbance _{[1040 ± 20 cm-1]) -1]} / absorbance _{[1650 ± 130 cm-1]} ). The obtained absorbance _{[1040 ± 20} cm ⁻¹ _] is calculated based on a straight line connecting a wave number of 1070 ± 10 cm ⁻¹ and 990 ± 20 cm ^{−1 at} a position of the lowest absorbance that does not intersect with the infrared absorption spectrum on the way. It means the maximum value of the difference in absorbance from the baseline in the infrared absorption spectrum of ± 20 cm ⁻¹ (measured absorbance−absorbance of the baseline). In the measurement of the absorbance, no peak separation was performed even when another absorption spectrum overlapped the maximum absorption spectrum.
The obtained absorbance _{[1650 ± 130} cm ⁻¹ _] is defined as a wave number based on a straight line connecting the wave number between 1770 ± 40 cm ⁻¹ and 1490 ± 20 cm ^{−1 at} the lowest absorbance position that does not intersect the infrared absorption spectrum on the way. It means the maximum value of the absorbance difference from the baseline in the infrared absorption spectrum at 1650 ± 130 cm ⁻¹ (measured absorbance−absorbance at the baseline). In the measurement of the absorbance, no peak separation was performed even when another absorption spectrum overlapped the maximum absorption spectrum.

<Example 1>
20 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (product name: TBAS, manufactured by MCC Unitech) and 0.3 parts by mass of sodium divinylbenzenesulfonate (product name: DVBS, manufactured by Tosoh Organic Chemicals), ion exchange 54.6 parts by mass of water was put in a container and stirred. Further, 25 parts by mass of a 20% by mass aqueous solution of Julimer AC-10LP (manufactured by Toagosei Co., Ltd., polyacrylic acid, weight average molecular weight: 20,000) 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 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 a swelling degree measurement, a bending test after immersion in an electrolytic solution, a piercing test, and an AC impedance measurement.
<Example 2>
20 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (product name: TBAS, manufactured by MCC Unitech) and 0.3 parts by mass of sodium divinylbenzenesulfonate (product name: DVBS, manufactured by Tosoh Organic Chemicals), ion exchange 67.1 parts by mass of water was put in a container and stirred. Further, 12.5 parts by mass of a 20% by mass aqueous solution of Julimer AC-10LP (manufactured by Toagosei Co., Ltd., polyacrylic acid, weight average molecular weight: 20,000) 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 this hydrogel precursor was used. The prepared hydrogel was subjected to a swelling degree measurement, a bending test after immersion in an electrolytic solution, a piercing test, and an AC impedance measurement.

<Example 3>
20 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (product name: TBAS, manufactured by MCC Unitech) and 0.3 parts by mass of sodium divinylbenzenesulfonate (product name: DVBS, manufactured by Tosoh Organic Chemicals), ion exchange 54.6 parts by mass of water was put in a container and stirred. Further, 25 parts by mass of a 20% by mass aqueous solution of polyacrylic acid (manufactured by Wako Pure Chemical Industries, polyacrylic acid, weight average molecular weight: 25,000) 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 this hydrogel precursor was used. The prepared hydrogel was subjected to a swelling degree measurement, a bending test after immersion in an electrolytic solution, a piercing test, and an AC impedance measurement.
<Example 4>
20 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (product name: TBAS, manufactured by MCC Unitech) and 0.3 parts by mass of sodium divinylbenzenesulfonate (product name: DVBS, manufactured by Tosoh Organic Chemicals), ion exchange 67.1 parts by mass of water was put in a container and stirred. Further, 12.5 parts by mass of a 20% by mass aqueous solution of polyacrylic acid (manufactured by Wako Pure Chemical Industries, polyacrylic acid, weight average molecular weight: 25,000) 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 this hydrogel precursor was used. The prepared hydrogel was subjected to a swelling degree measurement, a bending test after immersion in an electrolytic solution, a piercing test, and an AC impedance measurement.

<Example 5>
20 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (product name: TBAS, manufactured by MCC Unitech), 0.3 parts by mass of sodium divinylbenzenesulfonate (product name: DVBS, manufactured by Tosoh Organic Chemicals), polyacryl 80 parts by mass of a 5% by mass aqueous solution of an acid (manufactured by Wako Pure Chemical Industries, polyacrylic acid, weight average molecular weight: 1,000,000) 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 this hydrogel precursor was used. The prepared hydrogel was subjected to a swelling degree measurement, a bending test after immersion in an electrolytic solution, a piercing test, and an AC impedance measurement.

<Example 6>
20 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (product name: TBAS, manufactured by MCC Unitech) and 0.3 parts by mass of sodium divinylbenzenesulfonate (product name: DVBS, manufactured by Tosoh Organic Chemicals), ion exchange 39.6 parts by mass of water and 40 parts by mass of a 5% by mass aqueous solution of polyacrylic acid (manufactured by Wako Pure Chemical Industries, Ltd., polyacrylic acid, weight average molecular weight: 1,000,000) were 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 this hydrogel precursor was used. The prepared hydrogel was subjected to a swelling degree measurement, a bending test after immersion in an electrolytic solution, a piercing test, and an AC impedance measurement.
<Example 7>
15 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (product name: TBAS, manufactured by MCC Unitech) and 0.3 parts by mass of sodium divinylbenzenesulfonate (product name: DVBS, manufactured by Tosoh Organic Chemicals), ion exchange 54.6 parts by mass of water was put in a container and stirred. Further, 25 parts by mass of a 20% by mass aqueous solution of Julimer AC-10LP (manufactured by Toagosei Co., Ltd., polyacrylic acid, weight average molecular weight: 20,000) was added, and after stirring, 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 this hydrogel precursor was used. The prepared hydrogel was subjected to a swelling degree measurement, a bending test after immersion in an electrolytic solution, a piercing test, and an AC impedance measurement.

<Example 8>
20 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (product name: TBAS, manufactured by MCC Unitech) and 0.3 parts by mass of sodium divinylbenzenesulfonate (product name: DVBS, manufactured by Tosoh Organic Chemicals), ion exchange 29.6 parts by mass of water was put in a container and stirred. Further, 50 parts by mass of a 20% by mass aqueous solution of Julimer AC-10LP (manufactured by Toagosei Co., Ltd., polyacrylic acid, weight average molecular weight: 20,000) 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 this hydrogel precursor was used. The prepared hydrogel was subjected to a swelling degree measurement, a bending test after immersion in an electrolytic solution, a piercing test, and an AC impedance measurement.
<Example 9>
20 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (product name: TBAS, manufactured by MCC Unitech) and 0.3 parts by mass of sodium divinylbenzenesulfonate (product name: DVBS, manufactured by Tosoh Organic Chemicals), ion exchange 54.6 parts by mass of water was put in a container and stirred. Further, 25 parts by mass of a 20% by mass aqueous solution of Aqualic DL453 (manufactured by Nippon Shokubai Co., Ltd., sodium polyacrylate, weight average molecular weight: 50,000) 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 this hydrogel precursor was used. The prepared hydrogel was subjected to a swelling degree measurement, a bending test after immersion in an electrolytic solution, a piercing test, and an AC impedance measurement.

<Example 10>
20 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (product name: TBAS, manufactured by MCC Unitech) and 0.3 parts by mass of sodium divinylbenzenesulfonate (product name: DVBS, manufactured by Tosoh Organic Chemicals), ion exchange 68.7 parts by mass of water was put in a container and stirred. Further, 10.9 parts by mass of Aquaric GH001 (46% by mass aqueous solution of acrylic acid sulfonic acid-based monomer copolymer, weight average molecular weight: 11,000, 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 this hydrogel precursor was used. The prepared hydrogel was subjected to a swelling degree measurement, a bending test after immersion in an electrolytic solution, a piercing test, and an AC impedance measurement.
<Example 11>
20 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (product name: TBAS, manufactured by MCC Unitech) and 0.3 parts by mass of sodium divinylbenzenesulfonate (product name: DVBS, manufactured by Tosoh Organic Chemicals), ion exchange 54.6 parts by mass of water was put in a container and stirred. Further, 10.9 parts by mass of Aquaric GH003 (46 mass% aqueous solution of acrylic acid sulfonic acid-based monomer copolymer, weight average molecular weight: 11,000, 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 sheet-like hydrogel having a thickness of 2 mm was produced in the same manner as in Example 10 except that this hydrogel precursor was used. The prepared hydrogel was subjected to a swelling degree measurement, a bending test after immersion in an electrolytic solution, a piercing test, and an AC impedance measurement.

<Example 12>
20 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (product name: TBAS, manufactured by MCC Unitech) and 0.3 parts by mass of sodium divinylbenzenesulfonate (product name: DVBS, manufactured by Tosoh Organic Chemicals), ion exchange 54.6 parts by mass of water was put in a container and stirred. Further, 10.9 parts by mass of Aqualic GL234 (46% by mass aqueous solution of acrylic acid sulfonic acid-based monomer copolymer Na, manufactured by Nippon Shokubai Co., weight average molecular weight: 140,000) 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 sheet-like hydrogel having a thickness of 2 mm was produced in the same manner as in Example 10 except that this hydrogel precursor was used. The prepared hydrogel was subjected to a swelling degree measurement, a bending test after immersion in an electrolytic solution, a piercing test, and an AC impedance measurement.
<Example 13>
20 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (product name: TBAS, manufactured by MCC Unitech) and 0.3 parts by mass of sodium divinylbenzenesulfonate (product name: DVBS, manufactured by Tosoh Organic Chemicals), ion exchange 54.6 parts by mass of water was put in a container and stirred. Further, 10.9 parts by mass of Aqualic GL366 (manufactured by Nippon Shokubai Co., Ltd., 46 mass% aqueous solution of acrylic acid sulfonic acid-based monomer copolymer Na, weight average molecular weight: 6,000) 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 sheet-like hydrogel having a thickness of 2 mm was produced in the same manner as in Example 10 except that this hydrogel precursor was used. The prepared hydrogel was subjected to a swelling degree measurement, a bending test after immersion in an electrolytic solution, a piercing test, and an AC impedance measurement.

<Comparative Example 1>
20 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (product name: TBAS, manufactured by MCC Unitech), 0.3 parts by mass of sodium divinylbenzenesulfonate (product name: DVBS, manufactured by Tosoh Organic Chemicals), ion exchange 79.6 parts by mass of water was put in a container and stirred. To this solution was added 0.1 part 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 this hydrogel precursor was used. The prepared hydrogel was subjected to a swelling degree measurement, a bending test after immersion in an electrolytic solution, a piercing test, and an AC impedance measurement.
<Comparative Example 2>
20 parts by mass of acrylic acid (manufactured by Nippon Shokubai Co., Ltd.), 0.3 parts by mass of sodium divinylbenzenesulfonate (product name: DVBS, manufactured by Tosoh Organic Chemicals, Inc.), and 79.5 parts by mass of ion-exchanged water were put in a container and stirred. To this solution was added 0.20 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 this hydrogel precursor was used. The prepared hydrogel was subjected to a swelling degree measurement, a bending test after immersion in an electrolytic solution, a piercing test, and an AC impedance measurement.

<Comparative Example 3>
5 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (product name: TBAS, manufactured by MCC Unitech) and 0.3 parts by mass of sodium divinylbenzenesulfonate (product name: DVBS, manufactured by Tosoh Organic Chemicals), ion exchange 79.5 parts by mass of water 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. 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 this hydrogel precursor was used. The prepared hydrogel was subjected to a swelling degree measurement, a bending test after immersion in an electrolytic solution, a piercing test, and an AC impedance measurement.
<Comparative Example 4>
15 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (product name: TBAS, manufactured by MCC Unitech) and 0.3 parts by mass of sodium divinylbenzenesulfonate (product name: DVBS, manufactured by Tosoh Organic Chemicals), ion exchange 79.4 parts by mass of water was put in a container and stirred. Further, 5 parts by mass of acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) was added and stirred. To this solution was added 0.1 part 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 this hydrogel precursor was used. The prepared hydrogel was subjected to a swelling degree measurement, a bending test after immersion in an electrolytic solution, a piercing test, and an AC impedance measurement.

<Comparative Example 5>
10 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (product name: TBAS, manufactured by MCC Unitech) and 0.3 parts by mass of sodium divinylbenzenesulfonate (product name: DVBS, manufactured by Tosoh Organic Chemicals), ion exchange 54.6 parts by mass of water was put in a container and stirred. Further, 50 parts by mass of a 20% by mass aqueous solution of Julimer AC-10LP (manufactured by Toagosei Co., Ltd., polyacrylic acid, weight-average molecular weight: 20,000) was added, and the mixture was stirred, followed by 10 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 this hydrogel precursor was used. The prepared hydrogel was subjected to a swelling degree measurement, a bending test after immersion in an electrolytic solution, a piercing test, and an AC impedance measurement.
<Comparative Example 6>
20 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (product name: TBAS, manufactured by MCC Unitech), 0.3 parts by mass of sodium divinylbenzenesulfonate (product name: DVBS, manufactured by Tosoh Organic Chemicals), Julimer AC 80 parts by mass of a 25% by mass aqueous solution of -10 LP (manufactured by Toagosei Co., Ltd., polyacrylic acid, weight average molecular weight: 20,000) 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 this hydrogel precursor was used. The swelling degree of the produced hydrogel, a bending test after immersion in an electrolytic solution, a piercing test, and an AC impedance measurement were performed.
Tables 1 to 3 show the results of Examples and Comparative Examples.

From Tables 1 to 3, it can be seen that by including a polyacrylic acid-based polymer having a specific weight average molecular weight, a hydrogel having flexibility and high mechanical strength can be provided even in an environment of a high-concentration aqueous electrolyte solution.
Table 4 shows the absorbance and the absorbance ratio of the polyacrylic acid polymers used in Examples 1 to 13.

Claims (9)

A hydrogel comprising water, a polyacrylic acid polymer, and a polymer matrix,
The polyacrylic acid-based polymer has a weight average molecular weight of 3,000 to 2,000,000,
The polymer matrix includes a monofunctional monomer having an ethylenically unsaturated group and a copolymer of a polyfunctional monomer having 2 to 6 ethylenically unsaturated groups,
The monofunctional monomer having an ethylenically unsaturated group includes a monofunctional monomer A having at least one group selected from a sulfone group and a phosphate group and one ethylenically unsaturated group,
A component derived from the monofunctional monomer A and the polyacrylic acid-based polymer are present in the hydrogel in a mass ratio of 100: 2.5 to 90,
The water, the polyacrylic acid-based polymer and the polymer matrix are contained in 21 to 89.5 parts by mass, 0.5 to 19 parts by mass, and 10 to 60 parts by mass, respectively, in 100 parts by mass of the hydrogel. A hydrogel for an alkaline battery.   The monofunctional monomer having an ethylenically unsaturated group further includes a monofunctional monomer B having a carboxyl group and one ethylenically unsaturated group, and the content ratio of the monofunctional monomers A and B is 30 mol The hydrogel for an alkaline battery according to claim 1, which is in a range of not less than 70% and not more than 70 mol%.   The hydrogel for an alkaline battery according to claim 1 or 2, wherein the polyacrylic acid-based polymer is a homopolymer of a carboxyl group-containing monomer or a copolymer of a carboxyl group-containing monomer and a sulfonic acid group-containing monomer. The polyacrylic acid-based polymer, FT-IR maximum peak absorbance of 1650 range of ± 130 cm ^-1 obtained in the measurement (absorbance _{[1650 ± 130cm-1])} and 1040 the maximum peak in the range of ± 20 cm ^-1 The absorbance ratio (absorbance _{[1040 ± 20 cm-1]} / absorbance _{[1650 ± 130 cm-1]} ) with the absorbance (absorbance _{[1040 ± 20 cm-1]} ) of the sample shows a value in the range of 0.001 to 5.0. The hydrogel for an alkaline battery according to claim 3, which is a polymer.   The hydrogel according to any one of claims 1 to 4, 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 one week, the swelling degree is 50 to 300%. 4. A hydrogel for an alkaline battery according to any one of the above.   The hydrogel according to any one of claims 1 to 5, wherein the hydrogel exhibits a puncture strength of 0.35 N or more 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 alkaline batteries according to one of the above.   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 hydrogel exhibits a value of 20Ω or less as an impedance at a frequency of 100 kHz. The hydrogel for an alkaline battery according to any one of the above.   A gel electrolyte comprising the hydrogel according to any one of claims 1 to 7 and an electrolyte component contained in the hydrogel.   An alkaline battery using the hydrogel according to any one of claims 1 to 7 or the gel electrolyte according to claim 8.