WO2020044246A1 - Hydrogel and uses therefor - Google Patents

Abstract

The present invention relates to a hydrogel and uses therefor. The present invention specifically relates to a hydrogel containing water and a macromolecular matrix and uses for said hydrogel, the hydrogel being characterized in that: the macromolecular matrix includes a copolymer of a monofunctional monomer having a hydrophilic group and one ethylenically unsaturated group and a polyfunctional monomer having an amide group and three to six ethylenically unsaturated groups but not having an ester bond; 40–95 parts by mass of water and 5–60 parts by mass of the macromolecular matrix are included per 100 parts by mass of the hydrogel; and when the hydrogel has been immersed in a 4M KOH aqueous solution at a temperature of 25°C for 14 days, the degree of swelling of the hydrogel is no more than 650%.

Description

Hydrogel and its use

The present invention relates to hydrogels and uses thereof. More specifically, the present invention relates to a hydrogel capable of suppressing the growth of dendrite, a hydrogel usable even in a high-concentration aqueous electrolyte environment, a gel electrolyte using the same, a separator, and an alkaline battery.

This application filed Japanese Patent Application No. 2018-163485 filed on Aug. 31, 2018, Japanese Patent Application No. 2018-168775 filed on Sep. 10, 2018, and filed on Mar. 4, 2019 Priority is claimed based on Japanese Patent Application No. 2019-038620, the contents of which are incorporated herein by reference.

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) having a high energy density is increasing.
A metal-air battery using oxygen in the air as a positive electrode active material does not need to be filled with a positive electrode active material in the battery, and can fill a large amount of the negative electrode active material in 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, and the like are known.
However, in a metal-air battery, although the positive electrode portion is isolated from the outside by a water-repellent film or the like, the sealing performance is not sufficient, and the electrolyte easily 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.
Furthermore, among metal-air batteries, an air battery using a negative electrode capable of generating dendrites such as zinc and lithium has attracted attention because of its high theoretical energy density. However, zinc-air batteries are known to have a problem in battery life because dendrites growing on the negative electrode cause internal short-circuits when repeatedly charged and discharged.
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 for an alkaline battery in which a polymer composition comprising polyvinyl alcohol and an anionic crosslinked copolymer contains an alkali hydroxide. A hydrogel electrolyte is described. Further, WO2017 / 51734 (Patent Document 2) and JP-A-2017-183204 (Patent Document 3) disclose a sheet-like hydrogel composed of a crosslinked product of a polyacrylic acid-based polymer. Is described.
Further, in a secondary battery using a negative electrode capable of generating dendrites, such as a zinc secondary battery, a method for suppressing internal short circuit due to dendrites is disclosed in, for example, Japanese Patent Application Laid-Open No. 2015-095286 (Patent Document 4) There is a method described. Patent Document 4 describes that an anion-conductive film using hydrotalcite or the like having a structure in which hydroxide ions are incorporated between crystal layers is used as a separator. It is said that this anion-conductive film has high mechanical strength while maintaining hydroxide ion conductivity, and can suppress the growth of dendrite.
Further, 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. 2012-033490 (Patent Document 5) proposes to use an aqueous electrolyte containing a high concentration of lithium halide.

JP 2005-322635 A WO 2017/51734 Japanese Patent Application Publication No. 2017-183204 JP-A-2005-095286 Japanese Patent Application Laid-Open No. 2012-033490

The hydrogel described in Patent Literature 1 is a hydrogel obtained by mixing an anionic crosslinked copolymer and polyvinyl alcohol and drying the mixture. Therefore, the polymers constituting the skeleton are independent of each other. However, such a hydrogel has a problem that it does not elongate and becomes brittle when moistened.
Moreover, since the hydrogels described in Patent Documents 2 and 3 are sheet-like hydrogels, they have excellent strength and elongation, and can be used as separators for zinc secondary batteries. However, these hydrogels have room for improvement in dendrite growth suppression.
In addition, the anion conductive membrane described in Patent Document 4 has selective ionic conductivity and excellent mechanical strength, and therefore has high performance of suppressing dendrite growth and can improve cycle characteristics of a zinc secondary battery. . However, since most of the anion conductive membrane is composed of a polymer or an inorganic substance, there is a problem that water retention and ionic conductivity are low.
Therefore, it has been desired to provide an ion-conductive film which is excellent in water retention and ion conductivity and can suppress the growth of dendrite. (Hereinafter, this will be referred to as "first problem.")

Further, in the conventional hydrogel, in the presence of a high-concentration aqueous electrolyte as described in Patent Document 5, ionization of a functional group bonded to a polymer constituting the hydrogel is weakened, resulting in a decrease in water retention and an accompanying increase in flexibility. Deterioration 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. (Hereinafter, referred to as "second problem")

The inventors of the present invention have conducted various studies on a monomer for forming a polymer matrix constituting a hydrogel in order to solve the first problem. As a result, a polyfunctional monomer having an amide group without an ester bond can improve densification of the network and physically inhibit dendrite growth in the positive electrode direction, thereby suppressing dendrite growth. It has been found that a hydrogel having a polymer matrix and excellent in water retention and ion conductivity can be provided. By the way, for example, in Japanese Patent Application Laid-Open No. 2017-068933, in the field of a separator for an alkaline secondary battery, when a polyamide-based nonwoven fabric is used as a separator, it is decomposed by being gradually decomposed in an alkaline electrolyte. It is described that a decomposition product is produced, and its decomposition product causes a decrease in battery characteristics. That is, in this publication, it was considered that it is common technical knowledge that it is not appropriate to use a substance having an amide bond as a component of the alkaline secondary battery. However, despite such general technical knowledge, in the present invention, a polymer matrix containing a component derived from a polyfunctional monomer having an amide group is excellent in water retention and ionic conductivity, and can suppress the growth of dendrites. It is extremely surprising that such an ion conductive membrane can be provided.

Thus, a first aspect of the present invention for solving the first problem is a hydrogel comprising water and a polymer matrix,
The polymer matrix includes a monofunctional monomer having a hydrophilic group and one ethylenically unsaturated group, and a polyfunctional monomer having no amide group and 3 to 6 ethylenically unsaturated groups without an ester bond. Including a copolymer with a functional monomer,
In 100 parts by mass of the hydrogel, the water contains 40 to 95 parts by mass, and the polymer matrix contains 5 to 60 parts by mass,
When the hydrogel is immersed in a 4 M aqueous KOH solution at a temperature of 25 ° C. for 14 days, the hydrogel exhibits a swelling degree of 650% or less.

Furthermore, the inventors of the present invention solve the second problem by introducing a certain amount of a strongly ionized functional group (for example, a sulfone group) into a skeleton of a polymer matrix constituting a hydrogel. We tried to suppress the hardening of the hydrogel in the environment of high concentration aqueous electrolyte. 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. Therefore, as a result of intensive studies, the precipitation of the copolymer was prevented by including a polyacrylic acid-based polymer with a specific weight-average molecular weight in the hydrogel, and it was possible to use it in an environment with a high-concentration aqueous electrolyte. The present inventors have found that a hydrogel having excellent strength can be provided, and have reached the present invention.

Thus, a second aspect of the present invention for solving the second problem is 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,
In 100 parts by mass of the hydrogel, 21 to 89.5 parts by mass of the water, 0.5 to 19 parts by mass of the polyacrylic acid-based polymer, and 10 to 60 parts by mass of the polymer matrix are contained. A hydrogel is provided.

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

According to the first aspect of the present invention, a polymer matrix capable of suppressing dendrite growth by improving denseness of a network and physically inhibiting dendrite growth in a positive electrode direction is provided. And a hydrogel having excellent ion conductivity can be provided.
Since the hydrogel according to the first aspect of the present invention can suppress the growth of dendrites, when used as a gel electrolyte and a separator, the number of charge / discharge repetitions of an alkaline battery can be increased.

Further, according to the first aspect of the present invention, when having the following constitution, it is possible to provide a hydrogel having a polymer matrix capable of suppressing the growth of dendrite and having excellent water retention and ion conductivity.
(1) 3 to 6 ethylenically unsaturated groups in the polyfunctional monomer are represented by the following formula (X)

Is included in the divalent group derived from vinylamide represented by
(2) The polyfunctional monomer is a monomer composed of a linear or branched hydrocarbon chain, wherein the carbon atom constituting the hydrocarbon chain is replaced with an oxygen atom and / or a nitrogen atom. Well,
The divalent group derived from the vinylamide,
(I) The following formula (XI)

(Wherein, R represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms)
And / or (ii) as a group represented by the formula (X) together with a nitrogen atom replacing a carbon atom of the hydrocarbon chain.
(3) The polyfunctional monomer is a water-soluble monomer having 10 to 40 carbon atoms and having a melting point of 70 to 150 ° C.
(4) The copolymer contains 100 parts by mass of a unit derived from a monofunctional monomer and 0.1 to 5 parts by mass of a unit derived from a polyfunctional monomer.
(5) After the hydrogel is immersed in a 4 M KOH aqueous solution saturated with zinc oxide, and placed between zinc electrodes at a distance of 200 μm, a direct current of 1 mA / cm ^{2 is applied} between the zinc electrodes. When subjected to a DC polarization test in which an electric current is applied, an energization time of 700 minutes or more is shown.
(6) After the hydrogel is immersed in a 4M aqueous KOH solution saturated with zinc oxide, and placed between zinc electrodes at a distance of 200 μm, a direct current of 1 mA / cm ^{2 is applied} between the zinc electrodes. When subjected to a DC polarization test in which a current is applied, a voltage of 2.0 to 15 mV per 1 cm ² of zinc electrode plate when 40 minutes have elapsed from the start of the current application.

Further, according to a second aspect of 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, high mechanical strength can be imparted to the hydrogel after immersion in the electrolytic solution.
Since the hydrogel according to the second aspect of the present invention retains water retention and flexibility even in a state where the electrolyte is impregnated at a high concentration, it shows good adhesion to electrodes and solid electrolytes. An increase in the interface resistance with these battery materials can be suppressed, and as a result, good battery characteristics can be realized. Furthermore, the hydrogel according to the second aspect 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 second aspect of the present invention, when the following configuration is provided, a hydrogel having more excellent handleability and battery characteristics can be provided.
(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 from 30 mol% to 70 mol%.
(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 a maximum peak absorbance (absorbance _{[1650 ± 130 cm-1]} ) 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 according to the first embodiment)
The hydrogel according to the first aspect of the present invention, after being immersed in a 4 M KOH aqueous solution saturated with zinc oxide, is placed between the zinc electrodes at a distance of 200 μm, and is placed between the zinc electrodes at 1 mA. When subjected to a DC polarization test in which a DC current of / cm ² is applied, it is preferable to show an energization time of 700 minutes or more. A long energization time means that, for example, dendrites growing from the zinc plate of the negative electrode hardly reach the positive electrode, in other words, excellent short-circuit suppression performance by the dendrites. If the energization time is less than 700 minutes, the short circuit due to dendrite may not be sufficiently suppressed. The energization time is more preferably 800 minutes or more, further preferably 900 minutes or more, and particularly preferably 1,000 minutes or more.

The hydrogel was immersed in a 4M aqueous solution of KOH saturated with zinc oxide, and then passed between the zinc plates at a distance of 200 μm, and a direct current of 1 mA / cm ² was applied between the zinc plates. When a DC polarization test is performed, a voltage of 2.5 to 15 mV per 1 cm ² of zinc electrode plate when 40 minutes have passed from the start of energization is shown. By exhibiting a voltage within this range, the resistance when used as a separator of an alkaline secondary battery can be reduced, so that battery characteristics can be improved. The voltage is more preferably from 2.5 to 12.5 mV, even more preferably from 2.5 to 10.0 mV.
When the hydrogel is immersed in a 4 M aqueous KOH solution at a temperature of 25 ° C. or 60 ° C. for 14 days, 21 days, and 35 days, it is preferable that the measured 6 types of swelling show 650% or less. . The low degree of swelling means that the network of the skeleton of the polymer matrix constituting the hydrogel is dense.The higher the density, that is, the lower the degree of swelling, the more the dendrite growth can be suppressed. The inventors are thinking. If the degree of swelling is larger than 650%, the strength of the hydrogel may decrease due to swelling. The degree of swelling is more preferably from 100 to 650%, further preferably from 100 to 600%, and particularly preferably from 100 to 550%.

When the hydrogel is immersed in a 4 M KOH aqueous solution at a temperature of 25 ° C. or 60 ° C. for 14 days, 21 days, and 35 days, the measured six types of piercing strengths show 0.25 N or more. preferable. 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. If the puncture strength is less than 0.25 N, the mechanical strength may be low, and the puncture strength may not be handled as a self-supporting film. The piercing strength is more preferably 0.25 to 20.0 N.
The hydrogel preferably has a thickness of 10 to 3,000 μm. When the thickness is less than 10 μm, when the battery is assembled, when the positive electrode, the hydrogel, and the negative electrode are laminated and then pressed, the convex portion on the positive electrode or the negative electrode may break through the hydrogel and cause a short circuit. If the thickness is more than 3,000 μm, the resistance between the electrodes may increase, and the battery characteristics when the hydrogel is used as a battery material may deteriorate. The thickness is preferably in the following descending order: 10 to 2,000 μm, 20 to 1,000 μm, 20 to 750 μm, 20 to 550 μm, 20 to 450 μm, 20 to 400 μm, 20 to 350 μm, 30 to 350 μm, and 30 to 300 μm .

The hydrogel according to the first aspect of the present invention includes water and a polymer matrix.

(1) Polymer matrix The polymer matrix contained in the hydrogel according to the first embodiment of the present invention is a polymer matrix having a monofunctional monomer having a hydrophilic group and one ethylenically unsaturated group, having no ester bond. And a copolymer with a polyfunctional monomer having an amide group and 3 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 5 to 60 parts by mass per 100 parts by mass of the hydrogel. When the content is less than 5 parts by mass, the strength of the hydrogel is reduced, and the sheet shape may not be maintained. If the amount is more than 60 parts by mass, the movement of ions is hindered, so that the resistance may increase. The content is preferably from 5 to 50 parts by mass, more preferably from 10 to 40 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) Monofunctional monomer The monofunctional monomer is not limited as long as it has a hydrophilic group and one ethylenically unsaturated group. Examples of the hydrophilic group include a carboxyl group and a sulfonic group. Here, the carboxyl group and the sulfonic acid group include those present in the monofunctional monomer in the form of a salt. Further, the monofunctional monomer may be a mixture of a monomer in a salt form and a monomer in a salt form. For example, monofunctional monomers include (meth) acrylic acid, sodium (meth) acrylate, potassium (meth) acrylate, lithium (meth) acrylate, vinyl benzoic acid, sodium vinyl benzoate, potassium vinyl benzoate, vinyl Lithium benzoate, vinyl acetic acid, sodium vinyl acetate, potassium potassium acetate, lithium vinyl acetate, vinyl sulfonic acid, sodium vinyl sulfonate, potassium vinyl sulfonate, lithium vinyl sulfonate, p-styrene sulfonic acid, sodium p-styrene sulfonate , Potassium p-styrenesulfonate, lithium p-styrenesulfonate, allylsulfonic acid, sodium allylsulfonate, potassium allylsulfonate, lithium allylsulfonate, 2-acrylamido-2-methylpropanesulfonic acid, - sodium acrylamido-2-methylpropanesulfonic acid, 2-acrylamido-2-potassium-methylpropanesulfonic acid, 2-acrylamido-2-methyl-lithium sulfonic acid and the like.

(B) Polyfunctional monomer The polyfunctional monomer has no ester bond and has an amide group and 3 to 6 ethylenically unsaturated groups. Since this polyfunctional monomer has a role of a cross-linking agent, the density of the network of the skeleton of the polymer matrix constituting the hydrogel can be improved. The inventors believe that as a result of this improvement, the internal short circuit due to dendrite generated on the negative electrode can be suppressed by physically inhibiting the growth of dendrite in the direction of the positive electrode. When the number of ethylenically unsaturated groups is two or less, the performance of suppressing the growth of dendrites may decrease due to the reduction in the density of the skeleton network. In the case of seven or more, a locally dense network is formed in the skeleton, and a high stress is locally applied to the hydrogel, so that the hydrogel may become brittle. The number of ethylenically unsaturated groups is preferably three or four.
3 to 6 ethylenically unsaturated groups in the polyfunctional monomer are represented by the following formula (X)

Is preferably contained in a divalent group derived from vinylamide represented by By using a polyfunctional monomer having a divalent group derived from vinylamide, the reactivity between the monofunctional monomer forming the main skeleton of the polymer matrix and the polyfunctional monomer can be improved. As a result, the denseness of the network forming the polymer matrix can be improved, so that a hydrogel with improved performance of suppressing internal short circuits due to dendrites can be obtained.
Further, the polyfunctional monomer is a monomer composed of a linear or branched hydrocarbon chain, and the hydrocarbon chain may have a carbon atom constituting the hydrocarbon chain replaced with an oxygen atom and / or a nitrogen atom. Good. And a divalent group derived from vinylamide is
(I) The following formula (XI)

(Wherein, R represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms)
And / or (ii) as a group represented by the formula (X) together with a nitrogen atom replacing a carbon atom of the hydrocarbon chain.
Further, the polyfunctional monomer is preferably a water-soluble monomer having 10 to 40 carbon atoms and having a melting point of 70 to 150 ° C.
Specific polyfunctional monomers include 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. 158749-66-7) and the like.
The polyfunctional monomer may be only one kind or a mixture of plural kinds.
The unit derived from the polyfunctional monomer is preferably contained in a proportion of 0.1 to 5 parts by mass based on 100 parts by mass of the unit derived from the monofunctional monomer. When the proportion of the unit 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 unit derived from the polyfunctional monomer may undergo phase separation, resulting in a hydrogel having a non-uniform crosslinked structure. The proportion is preferably from 0.2 to 4.5 parts by mass, more preferably from 0.4 to 4.0 parts by mass.
In addition, the copolymer includes units derived from a monofunctional monomer and a polyfunctional monomer, but the amount of each monomer used in the production of the copolymer, and the content of each unit in the copolymer, Almost the same. The content of the unit derived from the polyfunctional monomer in the copolymer can be measured by pyrolysis GC and / or IR.

(C) Other polymers Within a range that does not impair the effects of the present invention, polymers other than the above-mentioned copolymer of a monofunctional monomer and a polyfunctional monomer are not polymerized with the above-mentioned copolymer. It may be included in a matrix. Other polymers include polyvinyl sulfonic acid-based polymers, polyacrylic acid-based polymers, 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) Water The water contained in the hydrogel according to the first embodiment of the present invention is contained in an amount of 40 to 95 parts by mass per 100 parts by mass of the hydrogel. When the content is less than 40 parts by mass, the amount of the electrolyte component that can be contained is 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 95 parts by mass, the strength of the hydrogel may decrease. The content is more preferably from 50 to 90 parts by mass, and still more preferably from 60 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 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 dissolution amount is 4 to 70 parts by mass.

(4) Other Components (a) Supporting Material The hydrogel according to the first aspect of the present invention includes a supporting material such as a woven fabric, a nonwoven fabric, and a porous sheet (hereinafter, also referred to as an “intermediate base material”). Is also good. 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 material may be located on any of the front surface, the back surface, and the middle of the hydrogel.
When the thickness of the hydrogel is A and the thickness of the support is B, the support preferably satisfies the relationship of 0.45 ≦ B / A <1. When B / A is less than 0.45, when the hydrogel is immersed in the electrolytic solution to impregnate the electrolyte, winding and warping are caused by the swelling difference between the front and back of the sheet caused by uneven distribution of the support material in the hydrogel. May occur. In the case of 1 or more, since the support material is exposed from the surface of the hydrogel, the moisture retention of the electrolytic solution may decrease, and the adhesion to the electrode may decrease. The relationship of B / A is more preferably 0.45 ≦ B / A <1, and even more preferably 0.5 ≦ B / A <1.

(B) Protective film The hydrogel according to the first aspect of the present invention may have a protective film on its front surface and / or back surface. When a protective film is used as a separator, it is preferable that the protective film has been release-treated. 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 according to the first embodiment of the present invention may contain an additive, if necessary. Additives include electrolytes, preservatives, bactericides, fungicides, rust inhibitors, antioxidants, defoamers, stabilizers, fragrances, surfactants, coloring agents, gel strength improvers (eg, cellulose nano Fiber).

(Hydrogel according to the second embodiment)
The hydrogel according to the second aspect of the present invention exhibits 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. preferable. When the degree of swelling is less than 50%, 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 300%, the mechanical strength of the hydrogel after swelling is low, 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 reduced, 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 preferably shows a value of 20Ω or less as an impedance at a frequency of 100 kHz. When the impedance value is larger than 20Ω, the battery characteristics may be deteriorated due to the 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 according to the second aspect of the present invention includes water, a polyacrylic acid-based polymer, and a polymer matrix.

(1) Polymer matrix The polymer matrix contained in the hydrogel according to the second aspect of the present invention comprises a monofunctional monomer having an ethylenically unsaturated group and a polyfunctional monomer having 2 to 6 ethylenically unsaturated groups. Includes copolymers with functional monomers. 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 per 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. If the amount is more than 60 parts by mass, the movement of ions is hindered, and 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 include, 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 is a monomer having 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 may be vinyl sulfonic acid, sodium vinyl sulfonate, potassium vinyl sulfonate, lithium vinyl sulfonate, p-styrene sulfonic acid, sodium p-styrene sulfonate, potassium p-styrene sulfonate, p-styrene sulfonate. Lithium styrenesulfonate, allylsulfonic acid, sodium allylsulfonate, potassium allylsulfonate, lithium allylsulfonate, 2-acrylamido-2-methylpropanesulfonic acid, sodium 2-acrylamido-2-methylpropanesulfonate, 2-acrylamide Sulfonic acid group-containing monomers such as potassium 2-methylpropanesulfonate, lithium 2-acrylamido-2-methylpropanesulfonate, vinylphosphonic acid, sodium vinylphosphonate, potassium vinylphosphonate Beam, lithium vinyl phosphonic acid, diethyl vinylphosphonate, dimethyl vinylphosphonate, phenyl vinyl phosphonic acid, sodium phenyl vinyl phosphonic acid, potassium phenylvinyl phosphonic acid, phosphoric acid group-containing monomer of lithium phenyl vinyl phosphonic acid. 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 group when immersed in a high-concentration electrolyte 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 is a monomer having 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 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. 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% to less than 100 mol%, 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. 13933329-90-2), 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, the polyfunctional monomer preferably does not have an 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.
Incidentally, the copolymer is composed of components derived from monofunctional monomers and polyfunctional monomers, the amount of each monomer used in the production of the copolymer, the content of each component in the copolymer, 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 the monofunctional monomer and the polyfunctional monomer are highly polymerized in a form that does not polymerize with the copolymer. It may be contained in a molecular 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 polymer The polyacrylic acid polymer contained in the hydrogel according to the second aspect of the present invention 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 polyacrylic acid polymer has an effect of increasing the entanglement of the polymer network constituting the hydrogel and strengthening the hydrogel.
Examples of the polyacrylic acid-based 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 polyacrylic acid-based polymers include poly (meth) acrylic acid, sodium poly (meth) acrylate, potassium poly (meth) acrylate, ammonium poly (meth) acrylate, and maleic (meth) acrylate-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.
The polyacrylic acid-based polymer has an absorbance of the maximum peak in the range of 1650 ± 130 cm ⁻¹ (absorbance _{[1650 ± 130} cm ⁻¹ _] ) and an absorbance of the maximum peak in the range of 1040 ± 50 cm ⁻¹ obtained in the FT-IR measurement. Polymer having an absorbance ratio (absorbance _{[1040 ± 20 cm-1]} / absorbance _{[1650 ± 130 cm-1]} ) with respect to (absorbance _{[1040 ± 50 cm-1]} ) in the range of 0.001 to 5.0. It is preferable that When the absorbance ratio is larger than 5.0, the ratio derived from the sulfonic acid group unit in the polymer becomes high, 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 water and may be cured. The absorbance ratio is more preferably in the range of 0.001 to 4.5. The range is more preferably from 0.005 to 4.0, further preferably from 0.01 to 3.5, further preferably from 0.025 to 3.0, and further preferably from 0.5 to 3.0. Preferably, the range is 0.1 to 3.0, more preferably, 0.2 to 2.0.
The polyacrylic acid polymer has a weight average molecular weight of 3,000 to 2,000,000. If the weight average molecular weight is less than 3,000, the cohesion 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 per 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 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 in 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 be reduced. 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 The water contained in the hydrogel according to the second aspect of the present invention is contained in 21 to 89.5 parts by mass per 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. Note that the type and amount of the electrolyte component are the same as the electrolyte component in the above-described first embodiment, and a description thereof will be omitted.

(5) Other components The hydrogel according to the second aspect of the present invention may contain, as necessary, other components (a) a support material, (b) a protective film, and (c) an additive. Although it is good, it is the same as (a) the support material, (b) the protective film, and (c) the additive in the first embodiment described above, and thus the description is omitted.

(Method for producing hydrogel)
Hydrogels, for example,
(I) a hydrogel precursor according to the first aspect of the present invention, comprising water, a monofunctional monomer, a polyfunctional monomer, and a polymerization initiator, or water, a monofunctional monomer A, and Step of preparing a hydrogel precursor according to the second aspect of the present invention, including a monofunctional monomer B, a polyfunctional monomer, a polyacrylic acid-based polymer, 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) Preparation Step As the polymerization initiator in this step, either a thermal polymerization initiator or a photopolymerization initiator can be used. Of these, it is preferable to use a photopolymerization initiator which has little change in components before and after 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) BASF · 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 of all the monomers (monofunctional monomer, polyfunctional monomer and optionally other monomer) in total. 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 producing the hydrogel, the hydrogel precursor is formed into a sheet by, for example, (i) a method of injecting the hydrogel precursor into a mold, (ii) pouring the hydrogel precursor between protective films, And (iii) a method of 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 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 alkaline aqueous solution is dissolved in the water in the hydrogel by immersing the polymerized hydrogel in the aqueous electrolyte component solution. This immersion is performed under conditions for obtaining a hydrogel having a desired electrolyte component amount. For example, the immersion can be performed under cooling, normal temperature (about 25 ° C.) and heating at 4 to 80 ° C. 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)
The hydrogel can be used for an alkaline battery (eg, a gel electrolyte, a separator, etc.).
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, copper, or the like.

When the hydrogel is a separator, the hydrogel preferably includes a supporting material (intermediate base material).
In the charge / discharge cycle test described in Examples, the number of cycles at which the charge / discharge efficiency is 60% or less is preferably 65 cycles or more, more preferably 70 cycles or more, and even more preferably 75 cycles or more. And more preferably 80 cycles or more. A large number of cycles means that an internal short circuit due to dendrite generated on the negative electrode is suppressed.
Further, the charge / discharge efficiency after 40 times of charge / discharge is preferably 70% or more, more preferably 75% or more, and further preferably 80%.
Applications other than the alkaline battery include uses such as a material for a capacitor, a material for an electric double layer capacitor, and a material for a concrete anticorrosion method.

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)
(1) Degree of swelling in 4M KOH aqueous solution (Method a: Examples 1a to 5a and Comparative examples 1a to 7a)
The hydrogel before immersion in alkali was cut into 5 mm squares and weighed. Thereafter, the hydrogel was placed in a 250-mesh polyethylene tea bag, and the tea bag was immersed in 100 mL of a 4M KOH aqueous solution. Then, after immersing for 14 days, 21 days, and 35 days at a temperature of 25 ° C. and 60 ° C., the water was drained for 10 minutes, weighed, and a hydrogel-containing tea bag swollen with a 4 M aqueous KOH solution was obtained. . In addition, when the hydrogel became soft at the time of draining and passed through the mesh, it was described as "liquefied".
The degree of swelling is defined as a value obtained by subtracting the mass of a blank from the mass of a tea bag containing a hydrogel swelled in a 4M KOH aqueous solution, with the mass of a tea bag containing no hydrogel immersed in a 4M KOH aqueous solution as a blank. The swelling degree (%) was calculated by dividing by the mass of the hydrogel before swelling and multiplying by 100. The degree of swelling after immersion at 25 ° C. for 14 days, after immersion for 21 days, and after immersion for 35 days was B _{25 ° C. [14 days]} , B _{25 ° C. [21 days]} , and B _{25 ° C. [35 days].} The degree of swelling after dipping for 14 days, after dipping for 21 days, and after dipping for 35 days was B _{60 ° C [14 days]} , B _{60 ° C [21 days]} , and B _{60 ° C [35 days]} , respectively.
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 the above method using the sample as a measurement sample.

(2) Degree of swelling in an aqueous solution containing 1.5 M LiOH and 10 M LiCl (Method b: Examples 1b to 13b and Comparative Examples 1b to 6b)
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 immersing at 25 ° C. for one week, the water was drained for 10 minutes, weighed, and a hydrogel-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 draining and passed through the mesh, it was described as "liquefied".
The degree of swelling was determined by setting the mass of a tea bag not containing a hydrogel immersed in an aqueous solution containing 1.5 M LiOH and 10 M LiCl as a blank, and adding a hydrogel swelled to an aqueous solution containing 1.5 M LiOH and 10 M LiCl. The value obtained by subtracting the mass of the blank from the mass of the tea bag by the mass of the hydrogel before swelling was calculated as a swelling degree (%).
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.

(Puncture strength)
(1) Degree of swelling in 4M KOH aqueous solution (Method a: Examples 1a to 5a and Comparative examples 1a to 7a)
The hydrogel was cut into a width of 30 mm × length of 30 mm × 2 mm. The cut hydrogel was immersed in 100 mL of a 4M KOH aqueous solution at 25 ° C. and 60 ° C. for 14 days, 21 days, and 35 days, and then a hydrogel immersed in an alkaline solution. Various hydrogels pulled up after being immersed in an alkali solution for a predetermined time are placed in an environment of 23 ° C. and 50% humidity for 3 hours, and then subjected to a texture analyzer TA. A piercing test was performed using XT Plus (manufactured by Eiko Seiki Co., Ltd.). The hydrogel was placed on a table having a hole having a diameter of 7 mm, and adjusted to a position where a stainless steel jig 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 carried out for five test pieces, the maximum stress was calculated, and the average of these was defined as the piercing strength. At this time, the piercing strength after immersion at 25 ° C. for 14 days, after immersion for 21 days, and after immersion for 35 days was F _{25 ° C. [14 days]} , F _{25 ° C. [21 days]} , and F _{25 ° C. [35 days].} The piercing strength after immersion at 60 ° C. for 14 days, after immersion for 21 days, and after immersion for 35 days was F _{60 ° C. [14 days]} , F _{60 ° C. [21 days]} , and F _{60 ° C. [35 days]} . When the thickness of the sheet was less than 2 mm, the sheets were laminated so that the thickness was adjusted to 2 mm.

(2) Degree of swelling in an aqueous solution containing 1.5 M LiOH and 10 M LiCl (Method b: Examples 1b to 13b and Comparative Examples 1b to 6b)
The hydrogel was cut into a width of 30 mm × length of 30 mm × 2 mm. The cut hydrogel was immersed in 100 mL of an aqueous solution containing 1.5 M LiOH and 10 M LiCl at a temperature of 25 ° C. for one week, and the gel was used as a hydrogel after immersion in an alkaline solution. The hydrogel immersed in the alkali 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 carried out for 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 the thickness of the laminated sheet was adjusted to 2 mm and measured.

(Electrification time in DC polarization measurement)
A laminate of a zinc electrode plate and a hydrogel was produced by stacking two zinc electrode plates in a state where a hydrogel was interposed between opposed zinc electrode plates having a width of 15 mm, a length of 40 mm, and a thickness of 300 μm. . Further, the laminate was sandwiched and fixed between two 70 mm square acrylic plates to produce a cell for DC polarization measurement. Note that a sheet made of Teflon (registered trademark) having a width of 10 mm, a length of 30 mm, and a thickness of 800 μm is sandwiched between the acrylic plates at a position where the laminate of the zinc electrode plate and the hydrogel does not exist between the two acrylic plates. The distance between the electrode plates was adjusted to be 200 μm. This DC polarization measurement cell was immersed in a 4 M KOH aqueous solution in which zinc oxide was dissolved in saturation at 25 ° C. for 72 hours. The cell for DC polarization measurement after immersion is placed in an acrylic solution containing a 4M aqueous solution of KOH in which zinc oxide is dissolved in saturation, and the zinc in the cell for DC polarization measurement is measured using a measuring device HJ1010SD8 (manufactured by Hokuto Denko KK). A constant DC current of 1 mA / cm ² was passed between the electrode plates, and a change in voltage over time was measured. At this time, when the measured voltage was 0.014 V or more, the energized state was determined, and the time during which the energized state was maintained from the start of the measurement was defined as the energized time. When the measured voltage was less than 0.014 V, a short-circuit state was set.

(Voltage per 1 cm ² of zinc electrode after 40 minutes in DC polarization measurement)
In the DC polarization measurement, the value calculated by dividing the voltage at 40 minutes after the start of energization by the area of the zinc electrode plate is referred to as “voltage per 1 cm ² of zinc electrode plate after 40 minutes in DC polarization measurement”. And

(Charging / discharging test)
The hydrogel was immersed in a 4 M aqueous KOH solution (electrolyte component) in which zinc oxide was saturated and dissolved at 25 ° C. for 72 hours to obtain an electrolyte component-impregnated hydrogel.
After mixing 80 parts by mass of zinc oxide, 5 parts by mass of calcium carbonate, 5 parts by mass of acetylene black as a conductive aid, and 10 parts by mass of polyvinylidene fluoride (PVDF) as a binder, the solid content is appropriately adjusted to 40% by mass. An amount of NMP (n-methyl-2-pyrrolidone) was added. The obtained mixture was further mixed with a self-revolving mixer at 2,000 rpm for 20 minutes to prepare a negative electrode mixture. The obtained negative electrode mixture was fixed to Celmet (manufactured by Sumitomo Electric Industries, Ltd.), dried at 150 ° C. for 5 hours or more, roll-pressed, and cut into 20 mm × 30 mm to obtain a negative electrode. The thickness of the negative electrode was 700 μm on average, the negative electrode capacity per unit area was 25 mAh / cm ² , and the capacity of the manufactured negative electrode was 150 mAh.
91.5 parts by mass of nickel hydroxide, 3.15 parts by mass of cobalt hydroxide, 0.13 parts by mass of sodium carboxymethyl cellulose (manufactured by Daicel Corporation, 2260) as a thickener, and polyethylene glycol mono-p-isooctyl as a dispersant. After mixing 0.22 parts by mass of phenyl ether (manufactured by Nacalai Tesque, Triton X) and 5 parts by mass of polytetrafluoroethylene (PTFE) as a binder, an appropriate amount of ion exchange was performed so that the solid content became 50% by mass. Water was added. The obtained mixture was further mixed at 2,000 rpm for 20 minutes using a self-revolving mixer to prepare a positive electrode mixture. The obtained positive electrode mixture was fixed to Celmet (manufactured by Sumitomo Electric Industries, Ltd.), dried at 80 ° C. for 5 hours or more, roll-pressed, and cut into 20 mm square to obtain a positive electrode. The thickness of the positive electrode was 600 μm on average, the positive electrode capacity per unit area was 32 mAh / cm ² , and the capacity of the manufactured positive electrode was 128 mAh.
A nickel-zinc storage battery cell for a charge / discharge test is obtained by sandwiching both sides of the negative electrode with the electrolyte component-impregnated hydrogel of 40 mm × 30 mm, disposing the positive electrode on the outside thereof, and further fixing the whole with an acrylic plate. Was. This cell was a positive electrode capacity-regulated cell in which the positive electrode capacity was much larger than the negative electrode capacity. The nickel-zinc storage battery cell was charged at a rate of 1 / 4C with respect to the positive electrode capacity for 1 hour, discharged at a rate of 1 / 4C for 1 hour, charged at a rate of 1 / 4C for 2 hours, and discharged at a rate of 1 / 4C for 1 hour. did. The battery was subjected to a charge / discharge cycle test in which the battery was charged at a 1 / 2C rate for 1 hour and charged and discharged at a 1 / 2C rate for 1 hour. The number of times of charging and discharging was the number of times of charging and discharging at a 1 / 2C rate.
The charge / discharge cycle test was performed for 1 hour for charging and 1 hour for discharging, and the discharge cutoff voltage was 1.0 V. Here, the 1C rate is a current amount that can discharge or charge the entire capacity of the negative electrode in one hour. For example, when the capacity of the positive electrode is 128 mAh, the 1C rate is 128 mA, the 1 / 2C rate is 68 mA, and the 1 / 4C rate is 32 mA.

(Melting point)
The melting point of the polyfunctional monomer was calculated by differential scanning calorimetry (DSC measurement).

(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, when the hydrogel was not cracked, it was evaluated as ○, and when it was broken, it was evaluated as x.

(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 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. 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 the thickness of the laminated sheet was adjusted to 2 mm and measured.

(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 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, After being grouped into 800), A was weighed in 1 to 2.5 mg each 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. The 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 the measurement, and using the calibration curve, the weight average molecular weight was obtained. Was calculated.

(FT-IR measurement)
In the measurement of the absorbance of the polyacrylic acid-based polymer, the absorbance _{[1040 ± 20 cm-1]} and the absorbance _{[1650 ± 130 cm-1]} are obtained by the following method, and the absorbance ratio = (absorbance _{[1040 ± 20 cm-1]} / absorbance _{[ 1650 ± 130 cm-1]} ).
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).
-Measuring apparatus: Fourier transform infrared spectrophotometer Nicolet iS10 (manufactured by Thermo SCIENTIFIC) and single reflection type horizontal ATR Smart-iTR (manufactured by Thermo SCIENTIFIC)
・ ATR crystal: Diamond with ZnSe lenses, angle 42 °
・ Measurement method: Single ATR method ・ Measurement wave number region: 4,000 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]} ) was calculated. The obtained absorbance _{[1040 ± 20} cm ⁻¹ _] is calculated using the straight line connecting the wave numbers of 1070 ± 10 cm ⁻¹ and 990 ± 20 cm ⁻¹ at the lowest absorbance position that does not intersect with the infrared absorption spectrum in the middle as the baseline. It means the maximum value of the absorbance difference from the baseline in the infrared absorption spectrum at 1040 ± 20 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 with the maximum absorption spectrum.
The obtained absorbance _{[1650 ± 130} cm ⁻¹ _] is defined as 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 with 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 a wave number of 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 with the maximum absorption spectrum.

<Example 1a>
20 parts by mass of acrylic acid (manufactured by Toagosei Co., Ltd.) as a monofunctional monomer, and 0.34 parts by mass of N, N ′, N ″ -triacryloyldiethylenetriamine (manufactured by Fuji Film Co., FAM301, melting point 89 ° C.) as a polyfunctional monomer And 80 parts by mass of ion-exchanged water 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 using a magnetic stirrer (RS-6AR, manufactured by As One Corporation) to prepare a hydrogel precursor. did. 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. Then, using a small UV polymerization machine (manufactured by JATEC, J-cure 1500, metal halide lamp model name MJ-1500L), ultraviolet rays having an energy of 7,000 mJ / cm ² were applied under the conditions of a conveyor speed of 0.4 m / min and a work-to-work distance of 150 mm. By performing the irradiation step three times, a sheet-shaped hydrogel having a thickness of 2 mm was produced. A piercing test after immersion in the prepared hydrogel with an alkaline solution was performed.
The hydrogel used for the DC polarization measurement and the charge / discharge test was prepared by the following procedure. A polyolefin nonwoven fabric having a thickness of 103 μm and a basis weight of 45 g / m ² (OA-1887P, manufactured by Nippon Vilene Co., Ltd.) was placed as a support between the two releasable PET films, and after pouring the above-mentioned hydrogel precursor, After adjusting to a thickness of 200 μm with a roller, irradiation with UV light of irradiation conditions of 65 mW / cm ² and / 7,000 mJ / cm ² was performed using a UV lamp system (product name: Light Hammer 10, manufactured by Heraeus). Thus, a hydrogel having a thickness of 200 μm was produced. The swelling characteristics of the prepared hydrogel, a direct current polarization test, a charge / discharge test, and an appearance evaluation after immersion in an electrolyte were performed.

<Example 2a>
The polyfunctional monomer was N, N ′-{[(2-acrylamido-2-[(3-acrylamidopropoxy) methyl] propane-1,3-diyl) bis (oxy)] bis (propane-1,3-diyl A) Hydrogel was obtained in the same manner as in Example 1a, except that diacrylamide (FAM401, manufactured by Fuji Film Co., melting point 107 ° C.) was changed to 0.66 parts by mass. The swelling characteristics of the obtained hydrogel were evaluated, a piercing test after immersion in an alkaline solution, a DC polarization test, a charge / discharge test, and an appearance evaluation after immersion in an electrolyte were performed.

<Example 3a>
Except that the polyfunctional monomer was changed to 0.47 parts by mass of N, N ′, N ″, N ′ ″-tetraacryloyltriethylenetetramine (FAM402, FAM402, melting point 110 ° C.) A hydrogel was obtained in the same manner as in 1a. The swelling characteristics of the obtained hydrogel were evaluated, a piercing test after immersion in an alkaline solution, a DC polarization test, a charge / discharge test, and an appearance evaluation after immersion in an electrolyte were performed.

<Example 4a>
A hydrogel was obtained in the same manner as in Example 1a, except that the monofunctional monomer was changed to 2-acrylamido-2-methylpropanesulfonic acid (AMPS, manufactured by MCC Unitech). The swelling characteristics of the obtained hydrogel were evaluated, a piercing test after immersion in an alkaline solution, a DC polarization test, a charge / discharge test, and an appearance evaluation after immersion in an electrolyte were performed.

<Example 5a>
A hydrogel was obtained in the same manner as in Example 2a, except that the monofunctional monomer was changed to 2-acrylamido-2-methylpropanesulfonic acid. The swelling characteristics of the obtained hydrogel were evaluated, a piercing test after immersion in an alkaline solution, a DC polarization test, a charge / discharge test, and an appearance evaluation after immersion in an electrolyte were performed.

<Comparative Example 1a>
A hydrogel was obtained in the same manner as in Example 1a, except that the polyfunctional monomer was changed to 0.3 parts by mass of sodium divinylbenzenesulfonate (DVBS, manufactured by Tosoh Organic Chemicals, Inc.). The swelling characteristics of the obtained hydrogel were evaluated, a piercing test after immersion in an alkaline solution, a DC polarization test, and a charge / discharge test were performed.

<Comparative Example 2a>
A hydrogel was obtained in the same manner as in Example 1a, except that the polyfunctional monomer was changed to 0.6 parts by mass of sodium divinylbenzene sulfonate (manufactured by Tosoh Organic Chemicals, Inc.). The swelling characteristics of the obtained hydrogel were evaluated, a piercing test after immersion in an alkaline solution, a DC polarization test, and a charge / discharge test were performed.

<Comparative Example 3a>
Example 1a except that the polyfunctional monomer was changed to 0.3 parts by mass of A-200 (polyethylene glycol # 200 diacrylate manufactured by Shin-Nakamura Chemical Co., Ltd.) having two ethylenically unsaturated groups and an ester bond. A hydrogel was obtained in the same manner as described above. Since the obtained hydrogel was liquefied when immersed in an alkaline solution, various physical properties could not be measured.

<Comparative Example 4a>
Example 1a except that the polyfunctional monomer was changed to 0.4 parts by mass of A-400 (polyethylene glycol # 400 diacrylate manufactured by Shin-Nakamura Chemical Co., Ltd.) having two ethylenically unsaturated groups and an ester bond. A hydrogel was obtained in the same manner as described above. Since the obtained hydrogel was liquefied when immersed in an alkaline solution, various physical properties could not be measured.

<Comparative Example 5a>
Example 1a except that the polyfunctional monomer was changed to 0.45 parts by mass of A-GLY-9EA having three ethylenically unsaturated groups and an ester bond (Ethoxylated glycerine triacrylate manufactured by Shin-Nakamura Chemical Co., Ltd.). A hydrogel was obtained in the same manner. Since the obtained hydrogel was liquefied when immersed in an alkaline solution, various physical properties could not be measured.

<Comparative Example 6a>
Same as Example 1a except that the polyfunctional monomer was changed to 0.3 parts by mass of A-TMMT (pentaerythritol tetraacrylate manufactured by Shin-Nakamura Chemical Co., Ltd.) having four ethylenically unsaturated groups and an ester bond. To obtain a hydrogel. Since the obtained hydrogel was liquefied when immersed in an alkaline solution, various physical properties could not be measured.

<Comparative Example 7a>
According to the contents described in Japanese Patent Application Laid-Open No. 2015-95286, a polytetrafluoroethylene emulsion aqueous solution having a concentration of 60% by mass (Polyflon PTFE D made by Daikin Industries, Ltd.) is used for 2.5 g of hydrotalcite as a layered double hydroxide. -210C) 5 g, and 2.5 g of a 20% by mass aqueous solution of polyethyleneimine (EPOMIN SP200 manufactured by Nippon Shokubai Co., Ltd.) were kneaded and rolled to obtain a 200 μm sheet. The swelling characteristics of the obtained sheet were evaluated, a piercing test after immersion in an alkaline solution, a DC polarization test, and a charge / discharge test were performed.

Table 1 shows the raw material species of Examples 1a to 5a and Comparative examples 1a to 7a and their use ratios, and Table 2 shows the results of Examples 1a to 5a and Comparative examples 1a to 7a.

From Table 2, it can be seen that the use of a polyfunctional monomer having no amide group and 3 to 6 ethylenically unsaturated groups without an ester bond as a component of the copolymer results in a long energization time and a high charge-discharge cycle. It can be seen that a hydrogel having excellent properties, that is, a hydrogel having excellent performance of suppressing dendrite growth can be provided.

<Comparative Example 8a>
Example 1a Except that the polyfunctional monomer was changed to 0.6 parts by mass of sodium divinylbenzenesulfonate (manufactured by Tosoh Organic Chemicals) and the support was changed to a polypropylene-polyethylene nonwoven fabric (9515F manufactured by Shinwa) having a thickness of 80 μm. A hydrogel having a thickness of 200 μm was obtained in the same manner as described above. The appearance of the obtained hydrogel after immersion in the electrolytic solution was evaluated. Table 3 shows the results together with the results of Examples 1a to 5a. In addition, the appearance evaluation was the evaluation of the following warp winding.

(Evaluation of warp winding)
The obtained hydrogel was cut into a 30 mm square. The cut hydrogel was immersed in 100 mL of a 4 M aqueous KOH solution at a temperature of 25 ° C. for 3 days. The distance between adjacent vertices of the hydrogel after immersion was measured, and the distance D between vertices was determined. When the distance D between the vertices was divided by 30 mm and the value was less than 0.75, it means that the hydrogel after immersion in the electrolytic solution was warped or wound, and was evaluated as x. On the other hand, when the value was 0.75 or more, it means that the hydrogel sheet did not change in shape after immersion in the electrolytic solution, and was evaluated as ○.

From Table 3, it can be seen that the hydrogels of Examples 1a to 5a are sheets that do not warp or roll and have good handleability.

<Example 1b>
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 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. Then, using a small UV polymerization machine (manufactured by JATEC, J-cure 1500, metal halide lamp model name MJ-1500L), ultraviolet rays having an energy of 7,000 mJ / cm ² were applied under the conditions of a conveyor speed of 0.4 m / min and a work-to-work distance of 150 mm. By performing the irradiation step three times, a sheet-shaped hydrogel having a thickness of 2 mm was produced. The prepared hydrogel was subjected to swelling degree measurement, immersion in electrolyte solution, bending test, piercing test, and AC impedance measurement.

<Example 2b>
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 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 1b except that this hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, immersion in electrolyte solution, bending test, piercing test, and AC impedance measurement.

<Example 3b>
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 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 1b except that this hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, immersion in electrolyte solution, bending test, piercing test, and AC impedance measurement.

<Example 4b>
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 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, Ltd., 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 1b except that this hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, immersion in electrolyte solution, bending test, piercing test, and AC impedance measurement.

<Example 5b>
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 1b except that this hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, immersion in electrolyte solution, bending test, piercing test, and AC impedance measurement.

<Example 6b>
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 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, 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 1b except that this hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, immersion in electrolyte solution, bending test, piercing test, and AC impedance measurement.

<Example 7b>
15 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 54.6 parts by mass of water was put in a container and stirred. Furthermore, 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, and then, 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 1b except that this hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, immersion in electrolyte solution, bending test, piercing test, and AC impedance measurement.

<Example 8b>
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 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 1b except that this hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, immersion in electrolyte solution, bending test, piercing test, and AC impedance measurement.

<Example 9b>
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 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 1b except that this hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, immersion in electrolyte solution, bending test, piercing test, and AC impedance measurement.

<Example 10b>
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 68.7 parts by mass of water was put in a container and stirred. Further, 10.9 parts by mass of Aqualic GH001 (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 2 mm-thick sheet-like hydrogel was prepared in the same manner as in Example 1b except that this hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, immersion in electrolyte solution, bending test, piercing test, and AC impedance measurement.

<Example 11b>
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 54.6 parts by mass of water was put in a container and stirred. Further, 10.9 parts by mass of Aqualic GH003 (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 10b except that this hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, immersion in electrolyte solution, bending test, piercing test, and AC impedance measurement.

<Example 12b>
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 54.6 parts by mass of water was put in a container and stirred. Further, 10.9 parts by mass of Aqualic GL234 (46 mass% aqueous solution of acrylic acid sulfonic acid-based monomer copolymer Na, manufactured by Nippon Shokubai Co., Ltd., 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 2 mm-thick sheet-like hydrogel was prepared in the same manner as in Example 10b except that this hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, immersion in electrolyte solution, bending test, piercing test, and AC impedance measurement.

<Example 13b>
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 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 2 mm-thick sheet-like hydrogel was prepared in the same manner as in Example 10b except that this hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, immersion in electrolyte solution, bending test, piercing test, and AC impedance measurement.

<Comparative Example 1b>
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 1b except that this hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, immersion in electrolyte solution, bending test, piercing test, and AC impedance measurement.

<Comparative Example 2b>
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), 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 1b except that this hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, immersion in electrolyte solution, bending test, piercing test, and AC impedance measurement.

<Comparative Example 3b>
5 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 79.5 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 1b except that this hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, immersion in electrolyte solution, bending test, piercing test, and AC impedance measurement.

<Comparative Example 4b>
15 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 79.4 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 1b except that this hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, immersion in electrolyte solution, bending test, piercing test, and AC impedance measurement.

<Comparative Example 5b>
10 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 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 after stirring, 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 1b except that this hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, immersion in electrolyte solution, bending test, piercing test, and AC impedance measurement.

<Comparative Example 6b>
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, Inc.), Julimer AC 80 parts by mass of a 25% by mass aqueous solution of -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 1b except that this hydrogel precursor was used. The prepared hydrogel was subjected to swelling degree measurement, bending test after immersion in electrolyte, piercing test, and AC impedance measurement.

Tables 4 to 6 show the results of Examples 1b to 13b and Comparative Examples 1b to 6b.

From Tables 4 to 6, it can be seen that a hydrogel having flexibility and high mechanical strength can be provided even in a high-concentration aqueous electrolyte environment by containing a polyacrylic acid-based polymer having a specific weight average molecular weight.

Table 7 shows the absorbance and the absorbance ratio of the polyacrylic acid polymers used in Examples 1b to 13b.

Claims (18)

1. A hydrogel comprising water and a polymer matrix,
   The polymer matrix includes a monofunctional monomer having a hydrophilic group and one ethylenically unsaturated group, and a polyfunctional monomer having no amide group and 3 to 6 ethylenically unsaturated groups without an ester bond. Including a copolymer with a functional monomer,
   In 100 parts by mass of the hydrogel, the water contains 40 to 95 parts by mass, and the polymer matrix contains 5 to 60 parts by mass,
   A hydrogel, wherein the hydrogel exhibits a swelling degree of 650% or less when immersed in a 4M KOH aqueous solution at a temperature of 25 ° C. for 14 days.
2. 3 to 6 ethylenically unsaturated groups in the polyfunctional monomer are represented by the following formula (X)
   

   

   The hydrogel according to claim 1, which is contained in a divalent group derived from vinylamide represented by the following formula:
3. The polyfunctional monomer is a monomer composed of a linear or branched hydrocarbon chain, and the hydrocarbon chain may have a carbon atom constituting the hydrocarbon chain replaced with an oxygen atom and / or a nitrogen atom. Often,
   The divalent group derived from the vinylamide,
   (I) The following formula (XI)
   

   

   (Wherein, R represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms)
   And / or (ii) as a group represented by the formula (X) together with a nitrogen atom replacing a carbon atom of the hydrocarbon chain,
   The hydrogel according to claim 2.
4. 4. The hydrogel according to claim 1, wherein the polyfunctional monomer is a water-soluble monomer having 10 to 40 carbon atoms and having a melting point of 70 to 150 ° C.
5. 5. The copolymer according to claim 1, wherein the copolymer contains 100 parts by mass of a unit derived from the monofunctional monomer and 0.1 to 5 parts by mass of a unit derived from the polyfunctional monomer. 2. The hydrogel according to 1.
6. After the hydrogel was immersed in a 4 M KOH aqueous solution saturated with zinc oxide, and placed between zinc electrodes at a distance of 200 μm, a direct current of 1 mA / cm ² was applied between the zinc electrodes. The hydrogel according to any one of claims 1 to 5, wherein when subjected to a DC polarization test in which a current is applied, the hydrogel exhibits an energization time of 700 minutes or more.
7. After the hydrogel was immersed in a 4 M KOH aqueous solution saturated with zinc oxide, and placed between zinc electrodes at a distance of 200 μm, a direct current of 1 mA / cm ² was applied between the zinc electrodes. 7 shows a voltage of 2.0 to 15 mV per 1 cm ² of zinc electrode plate when 40 minutes have passed from the start of energization, when subjected to a DC polarization test in which energization is performed. gel.
8. 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,
   In 100 parts by mass of the hydrogel, 21 to 89.5 parts by mass of the water, 0.5 to 19 parts by mass of the polyacrylic acid-based polymer, and 10 to 60 parts by mass of the polymer matrix are contained. Hydrogel characterized by the following.
9. The monofunctional monomer having an ethylenically unsaturated group further includes a monofunctional monomer B having a carboxyl group and one ethylenically unsaturated group, the content ratio of the monofunctional monomers A and B, The hydrogel according to claim 8, which is in a range of 30 mol% or more and 70 mol% or less.
10. The hydrogel according to claim 8 or 9, 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.
11. 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 absorbance (absorbance _{[1040 ± 20cm-1])} and the ratio of absorbance (absorbance _{[1040 ± 20cm-1]} / absorbance _{[1650 ± 130cm-1])} indicates a value in the range of 0.001-5.0 The hydrogel according to any one of claims 8 to 10, which is a polymer.
12. 12. The hydrogel according to claim 8, wherein the hydrogel exhibits 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. The hydrogel according to claim 1.
13. 13. The hydrogel according to claim 8, 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. Or the hydrogel according to claim 1.
14. The hydrogel, when immersed in an aqueous solution containing 1.5 M LiOH and 10 M LiCl at a temperature of 25 ° C. for one week, exhibits a value of 20Ω or less as an impedance at a frequency of 100 kHz. 14. The hydrogel according to any one of 13).
15. 15. The hydrogel according to any one of claims 8 to 14, which is for an alkaline battery.
16. A gel electrolyte comprising the hydrogel according to any one of claims 1 to 15 and an electrolyte component contained in the hydrogel.
17. A separator using the hydrogel according to any one of claims 1 to 15 or the gel electrolyte according to claim 16.
18. An alkaline battery comprising the hydrogel according to any one of claims 1 to 15, the gel electrolyte according to claim 16, and the separator according to claim 17.