JP7720699B2 - Zinc battery electrolyte and zinc battery - Google Patents

Description

This disclosure relates to electrolytes for zinc batteries, zinc batteries, etc.

Nickel-zinc batteries are aqueous batteries that use an aqueous electrolyte such as an aqueous potassium hydroxide solution, making them highly safe. Furthermore, the combination of zinc and nickel electrodes gives them a high electromotive force for an aqueous battery. Furthermore, because nickel-zinc batteries offer excellent input/output performance and low cost, their potential for industrial use (e.g., as backup power sources) and automotive use (e.g., in hybrid vehicles) is being explored.

The charge and discharge reactions of a nickel-zinc battery proceed, for example, according to the following formula (discharge reaction: rightward, charge reaction: leftward).
(Positive electrode) 2NiOOH+2H ₂ O+2e ^- → 2Ni(OH) ₂ +2OH ^-
(Negative electrode) Zn+2OH ^- → Zn(OH) ₂ +2e ^-

As shown in the above formula, in nickel-zinc batteries, zinc hydroxide (Zn(OH) ₂ ) is produced by the discharge reaction. Zinc hydroxide is soluble in the electrolyte, and when zinc hydroxide dissolves in the electrolyte, zinc tetrahydroxide ions ([Zn(OH) ₄ ] ²⁻ ) diffuse into the electrolyte. As a result, the morphology (deformation) of the negative electrode progresses and the distribution of the charging current becomes uneven, causing zinc to precipitate locally on the negative electrode, resulting in the formation of dendrites (branched crystals). In nickel-zinc batteries, if dendrites grow due to repeated charge and discharge, they can penetrate the separator, causing a short circuit, and the formation of such dendrites leads to a decrease in battery life. In response to this, for example, Patent Document 1 discloses a technology for preventing internal short circuits between positive and negative electrodes caused by zinc dendrites by interposing a nickel-plated nonwoven fabric between the positive and negative electrodes.

Japanese Unexamined Patent Publication No. 58-126665

Zinc batteries, such as nickel-zinc batteries, are required to have further improved lifespan performance.

One aspect of the present disclosure aims to provide a zinc battery electrolyte that can achieve excellent life performance in zinc batteries. Another aspect of the present disclosure aims to provide a zinc battery that includes the zinc battery electrolyte.

One aspect of the present disclosure provides an electrolyte solution for zinc batteries containing an alkali metal hydroxide and an organic compound having at least one group selected from the group consisting of a carboxyl group, a carboxylate salt group, an ether group, and a hydroxy group (excluding polyoxyethylene octylphenyl ether and polyoxyethylene alkyl ether phosphate ester).

Another aspect of the present disclosure provides a zinc battery comprising a positive electrode, a negative electrode, and the above-described zinc battery electrolyte.

The above-mentioned zinc battery electrolyte and zinc battery can provide excellent life performance.

According to one aspect of the present disclosure, it is possible to provide a zinc battery electrolyte that can achieve excellent life performance in a zinc battery. According to another aspect of the present disclosure, it is possible to provide a zinc battery that includes the zinc battery electrolyte.

A numerical range of "A or greater" refers to a range exceeding A and A. A numerical range of "A or less" refers to a range exceeding A and A. In the numerical ranges described in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. In the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in the examples. "A or B" may include either A or B, or both. Unless otherwise specified, the materials exemplified in this specification can be used alone or in combination of two or more. In this specification, when multiple substances corresponding to each component are present in the composition, the amount of each component refers to the total amount of those multiple substances present in the composition, unless otherwise specified. In this specification, the terms "film" and "layer" encompass structures that are formed over the entire surface as viewed from a plan view, as well as structures that are formed only partially. In this specification, the term "process" refers not only to an independent process, but also to processes that cannot be clearly distinguished from other processes as long as the intended effect of the process is achieved. The unit "C" represents the relative magnitude of the current when discharging the rated capacity at a constant current from a fully charged state. The unit "C" means "discharge current value (A) / battery capacity (Ah)". For example, a current that can discharge the rated capacity in 1 hour is expressed as "1C", and a current that can discharge the rated capacity in 2 hours is expressed as "0.5C".

Embodiments of the present disclosure are described in detail below. However, the present disclosure is not limited to the following embodiments and can be implemented in various modifications within the scope of its essence.

The zinc battery electrolyte according to this embodiment (hereinafter sometimes simply referred to as "electrolyte") is used as the electrolyte for a zinc battery (e.g., a zinc secondary battery). The zinc battery according to this embodiment includes a positive electrode, a negative electrode, and the electrolyte according to this embodiment. The zinc battery may include a zinc electrode as the negative electrode. Examples of zinc batteries include nickel-zinc batteries (e.g., nickel-zinc secondary batteries) in which the positive electrode is a nickel electrode; air-zinc batteries (e.g., air-zinc secondary batteries) in which the positive electrode is an air electrode; and silver-zinc batteries (e.g., silver-zinc secondary batteries) in which the positive electrode is a silver oxide electrode.

The electrolyte solution according to this embodiment contains an alkali metal hydroxide and an organic compound having at least one group selected from the group consisting of a carboxyl group, a carboxylate salt group, an ether group, and a hydroxyl group (excluding polyoxyethylene octylphenyl ether and polyoxyethylene alkyl ether phosphate ester; hereinafter, this organic compound will also be referred to as "organic compound A").

The electrolyte solution according to this embodiment can achieve excellent battery life. Factors that contribute to this effect include, but are not limited to, the following: The electrolyte solution contains an alkali metal hydroxide and organic compound A, which coordinates with zinc. This inhibits zinc elution and diffusion, thereby preventing deterioration of battery performance.

Examples of alkali metal hydroxides include potassium hydroxide (KOH), sodium hydroxide (NaOH), and lithium hydroxide (LiOH). The alkali metal hydroxide may be ionized (dissociated) in aqueous solution or may exist as a salt. From the viewpoint of easily achieving excellent life performance, the alkali metal hydroxide may include at least one selected from the group consisting of potassium hydroxide and lithium hydroxide, and may also include potassium hydroxide.

From the viewpoint of easily achieving excellent life performance, the content of alkali metal hydroxide in the electrolyte (total amount of alkali metal hydroxide) may be within the following ranges based on the total mass of the electrolyte. The content of alkali metal hydroxide may be 10 mass% or more, 15 mass% or more, 20 mass% or more, 25 mass% or more, or 30 mass% or more. The content of alkali metal hydroxide may be 50 mass% or less, 45 mass% or less, 40 mass% or less, or 35 mass% or less. From these viewpoints, the content of alkali metal hydroxide may be 10 to 50 mass%.

From the viewpoint of easily achieving excellent life performance, the potassium hydroxide content in the electrolyte may be within the following ranges based on the total mass of the electrolyte. The potassium hydroxide content may be 10 mass% or more, 15 mass% or more, 20 mass% or more, 25 mass% or more, or 30 mass% or more. The potassium hydroxide content may be 50 mass% or less, 45 mass% or less, 40 mass% or less, or 35 mass% or less. From these viewpoints, the potassium hydroxide content may be 10 to 50 mass%.

From the viewpoint of easily achieving excellent life performance, the lithium hydroxide content in the electrolyte may be within the following ranges based on the total mass of the electrolyte. The lithium hydroxide content may be 0.1 mass% or more, 0.3 mass% or more, 0.5 mass% or more, 0.8 mass% or more, or 1 mass% or more. The lithium hydroxide content may be 3 mass% or less, 2 mass% or less, 1.5 mass% or less, or 1.2 mass% or less. From these viewpoints, the lithium hydroxide content may be 0.1 to 3 mass%.

The electrolyte solution according to this embodiment contains an organic compound A having at least one group selected from the group consisting of a carboxyl group, a carboxylate salt group, an ether group, and a hydroxyl group. Examples of salts of the carboxylate salt group include sodium salts and potassium salts.

Organic compound A, excluding polyoxyethylene octylphenyl ether and polyoxyethylene alkyl ether phosphate ester, may include an organic compound having at least one selected from the group consisting of a carboxyl group and a carboxylate salt group (hereinafter also referred to as a "carboxyl group-containing compound"), an organic compound having an ether group (excluding carboxyl group-containing compounds; hereinafter also referred to as an "ether group-containing compound"), or an organic compound having a hydroxy group (excluding carboxyl group-containing compounds and ether group-containing compounds; hereinafter also referred to as a "hydroxy group-containing compound").

Organic compound A may be an aliphatic compound or a saturated aliphatic compound. The electrolyte solution according to this embodiment may contain an organic compound other than organic compound A, or may contain organic compound A and polyoxyethylene octylphenyl ether and/or polyoxyethylene alkyl ether phosphate ester. The electrolyte solution according to this embodiment does not need to contain a compound having a polyoxyethylene structure (a structure represented by the general formula ^R1 ( _CH2CH2O ) _nR2 ^, where _n is a natural number and ^R1 and ^R2 each independently represent a hydrogen atom, a metal atom, or an organic group).

Carboxyl group-containing compounds may have functional groups other than carboxyl groups. Examples of such functional groups include ether groups, hydroxy groups (excluding the OH structure encompassed by carboxyl groups), alkyl groups, aryl groups, vinyl groups, ester groups, ketone groups, aldehyde groups, and amino groups. Carboxy group-containing compounds may include compounds that do not have ether groups, compounds that do not have hydroxy groups, and compounds that do not have ether groups or hydroxy groups.

The total number of carboxyl groups and carboxylate salt groups in the carboxyl group-containing compound may be within the following ranges, from the viewpoint of easily achieving excellent life performance. The total number of carboxyl groups and carboxylate salt groups may be 10 or less, 7 or less, 5 or less, 3 or less, 2 or less, or 1 or less. The total number of carboxyl groups and carboxylate salt groups may be 1 or more, or 2 or more. From these viewpoints, the total number of carboxyl groups and carboxylate salt groups may be 1 to 10.

The number of ether groups possessed by the carboxyl group-containing compound may be within the following ranges, from the viewpoint of easily achieving excellent life performance. The number of ether groups may be 10 or less, 5 or less, 3 or less, 2 or less, or 1 or less. The number of ether groups may be 0 or more, or 1 or more. From these viewpoints, the number of ether groups may be 0 to 10.

The number of hydroxy groups in the carboxyl group-containing compound may be within the following ranges, from the viewpoint of easily achieving excellent life performance. The number of hydroxy groups may be 10 or less, 5 or less, 3 or less, 2 or less, or 1 or less. The number of hydroxy groups may be 0 or more, 1 or more, or 2 or more. From these viewpoints, the number of hydroxy groups may be 0 to 10.

Carboxylate-containing compounds include carboxylic acid compounds without ether groups or hydroxy groups, such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, and benzoic acid, and their salts; ether-containing carboxylic acid compounds (carboxylic acid compounds with ether groups) such as methoxyacetic acid, ethoxyacetic acid, and 4-(β-D-glucopyranosyloxy)-2-methylenebutanoic acid, and their salts; and hydroxy-containing carboxylic acid compounds (carboxylic acid compounds with hydroxy groups, excluding ether-containing carboxylic acid compounds) and their salts, such as glycolic acid, lactic acid, tartronic acid, glyceric acid, malic acid, tartaric acid, and citric acid. From the viewpoint of easily achieving excellent life performance, organic compound A may include at least one selected from the group consisting of carboxylic acid compounds having no ether groups or hydroxy groups, ether group-containing carboxylic acid compounds, hydroxy group-containing carboxylic acid compounds, and salts thereof; may include at least one selected from the group consisting of oxalic acid, lactic acid, methoxyacetic acid, glyceric acid, and salts thereof; or may include at least one selected from the group consisting of lactic acid and salts thereof.

From the viewpoint of easily achieving excellent life performance, the content of the carboxyl group-containing compound may be 50% by mass or more, 70% by mass or more, 90% by mass or more, 95% by mass or more, 98% by mass or more, 99% by mass or more, or substantially 100% by mass (an embodiment in which organic compound A in the electrolyte solution consists of a carboxyl group-containing compound) based on the total mass of organic compound A in the electrolyte solution.

The ether group-containing compound may have a functional group other than a carboxyl group, a carboxylate salt group, and an ether group. Examples of such functional groups include a hydroxyl group (excluding the OH structure included in a carboxyl group), an alkyl group, an aryl group, a vinyl group, an ester group, a ketone group, an aldehyde group, and an amino group. The ether group-containing compound may also include a compound that does not have a hydroxyl group.

The number of ether groups in the ether group-containing compound may be within the following ranges, from the viewpoint of easily achieving excellent life performance. The number of ether groups may be 10 or less, 7 or less, 5 or less, 3 or less, 2 or less, or 1. The number of ether groups may be 1 or more. From these viewpoints, the number of ether groups may be 1 to 10.

The number of hydroxy groups in the ether group-containing compound may be within the following ranges, from the viewpoint of easily achieving excellent life performance. The number of hydroxy groups may be 10 or less, 5 or less, 3 or less, or 2 or less. The number of hydroxy groups may be 0 or more, 1 or more, or 2 or more. From these viewpoints, the number of hydroxy groups may be 0 to 10.

Examples of ether group-containing compounds include polyoxyethylene structure-containing compounds such as diethylene glycol, polyethylene glycol, polyoxyethylene alkyl ethers, and polyoxyethylene alkylphenyl ethers (ether compounds having a polyoxyethylene structure (a structure represented by the general formula R ¹ (CH ₂ CH ₂ O) _n R ² , where n is a natural number, and R ¹ and R ² each independently represent a hydrogen atom, a metal atom, or an organic group)); ether compounds without a hydroxy group (excluding polyoxyethylene structure-containing compounds) such as dimethyl ether, ethyl methyl ether, and diethyl ether; and hydroxy group-containing ether compounds (ether compounds having a hydroxy group, excluding polyoxyethylene structure-containing compounds) such as 2-methoxyethanol, 2-ethoxyethanol, 3-methoxy-1,2-propanediol, glucose, and glucosylglycerol. From the viewpoint of easily obtaining excellent life performance, the organic compound A may contain a hydroxy group-containing ether compound or 3-methoxy-1,2-propanediol. The ether group-containing compound may include a compound that does not have a polyoxyethylene structure.

From the viewpoint of easily achieving excellent life performance, the content of the ether group-containing compound may be 50% by mass or more, 70% by mass or more, 90% by mass or more, 95% by mass or more, 98% by mass or more, 99% by mass or more, or substantially 100% by mass (an embodiment in which organic compound A in the electrolyte solution consists of an ether group-containing compound) based on the total mass of organic compound A in the electrolyte solution.

The hydroxyl group-containing compound may have a functional group other than a carboxyl group, a carboxylate salt group, an ether group, or a hydroxyl group. Examples of such functional groups include alkyl groups, aryl groups, vinyl groups, ester groups, ketone groups, aldehyde groups, and amino groups.

The number of hydroxy groups in the hydroxy group-containing compound may be within the following ranges, from the viewpoint of easily achieving excellent life performance. The number of hydroxy groups may be 10 or less, 7 or less, 6 or less, 5 or less, 4 or less, 3 or less, 2 or less, or 1. The number of hydroxy groups may be 1 or more, 2 or more, or 3 or more. From these viewpoints, the number of hydroxy groups may be 1 to 10.

The number of ester groups in the hydroxyl group-containing compound may be within the following ranges, from the viewpoint of easily achieving excellent life performance. The number of ester groups may be 10 or less, 5 or less, 3 or less, 2 or less, or 1 or less. The number of ester groups may be 0 or more, or 1 or more. From these viewpoints, the number of ester groups may be 0 to 10.

Hydroxy group-containing compounds include monohydric alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, methyl glycolate, and ethyl glycolate; dihydric alcohols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, and dihydroxyacetone; trihydric alcohols such as 1,2,3-propanetriol, 1,2,3-butanetriol, 1,2,4-butanetriol, and 1,2,5-pentanetriol; and polyhydric alcohols such as polyvinyl alcohol. From the perspective of easily achieving excellent life performance, organic compound A may contain at least one alcohol selected from the group consisting of monohydric alcohols and trihydric alcohols, and may contain at least one alcohol selected from the group consisting of methyl glycolate, 1,2,3-butanetriol, and 1,2,4-butanetriol. The hydroxy group-containing compound may include a compound different from ethylene glycol, 1,2-propanediol, 1,3-propanediol, and 1,2,3-propanetriol. The electrolyte solution according to this embodiment does not need to contain ethylene glycol, 1,2-propanediol, 1,3-propanediol, or 1,2,3-propanetriol.

From the viewpoint of easily achieving excellent life performance, the content of the hydroxy group-containing compound may be 50% by mass or more, 70% by mass or more, 90% by mass or more, 95% by mass or more, 98% by mass or more, 99% by mass or more, or substantially 100% by mass (an embodiment in which organic compound A in the electrolyte solution consists of a hydroxy group-containing compound) based on the total mass of organic compound A in the electrolyte solution.

From the viewpoint of easily achieving excellent life performance, the total number of carboxyl groups, carboxylate salt groups, ether groups, and hydroxy groups contained in organic compound A may be within the following ranges. The total number of carboxyl groups, carboxylate salt groups, ether groups, and hydroxy groups may be 15 or less, 10 or less, 8 or less, 6 or less, 5 or less, 4 or less, 3 or less, 2 or less, or 1. The total number of carboxyl groups, carboxylate salt groups, ether groups, and hydroxy groups may be 1 or more, 2 or more, or 3 or more. From these viewpoints, the total number of carboxyl groups, carboxylate salt groups, ether groups, and hydroxy groups may be 1 to 15.

From the viewpoint of easily achieving excellent life performance, the number of carbon atoms in organic compound A may be within the following ranges. The number of carbon atoms may be 20 or less, 15 or less, 10 or less, 8 or less, 6 or less, 4 or less, 3 or less, or 2 or less. The number of carbon atoms may be 1 or more, 2 or more, or 3 or more. From these viewpoints, the number of carbon atoms may be 1 to 20.

From the viewpoint of easily achieving excellent life performance, the molecular weight of organic compound A may be within the following ranges. The molecular weight may be 300 or less, 260 or less, 220 or less, 180 or less, 150 or less, 130 or less, 110 or less, or 100 or less. The molecular weight may be 30 or more, 50 or more, 70 or more, 80 or more, 90 or more, or 100 or more. From these viewpoints, the molecular weight may be 30 to 300.

The content of organic compound A in the electrolyte solution (total amount of organic compound A contained in the electrolyte solution) may be within the following ranges based on the total mass of the electrolyte solution. From the viewpoint of easily achieving excellent life performance, the content of organic compound A may be 0.01 mass% or more, 0.1 mass% or more, 0.5 mass% or more, 1 mass% or more, 2 mass% or more, 3 mass% or more, 4 mass% or more, or 5 mass% or more. From the viewpoint of easily achieving excellent discharge performance, the content of organic compound A may be 20 mass% or less, 10 mass% or less, 8 mass% or less, 6 mass% or less, 5 mass% or less, 4 mass% or less, 3 mass% or less, 2 mass% or less, or 1 mass% or less. From these viewpoints, the content of organic compound A may be 0.01 to 20 mass%, 0.1 to 10 mass%, 0.5 to 8 mass%, or 1 to 5 mass%.

The content of organic compound A in the electrolyte solution (total amount of organic compound A contained in the electrolyte solution) may be within the following ranges per 100 parts by mass of alkali metal hydroxide. From the viewpoint of easily achieving excellent life performance, the content of organic compound A may be 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, 7 parts by mass or more, 9 parts by mass or more, 12 parts by mass or more, or 15 parts by mass or more. From the viewpoint of easily achieving excellent discharge performance, the content of organic compound A may be 30 parts by mass or less, 20 parts by mass or less, 15 parts by mass or less, 12 parts by mass or less, 10 parts by mass or less, 7 parts by mass or less, 5 parts by mass or less, or 4 parts by mass or less. From these viewpoints, the content of organic compound A may be 1 to 30 parts by mass.

The content of organic compound A in the electrolyte solution (total amount of organic compound A contained in the electrolyte solution) may be within the following ranges per mole of alkali metal hydroxide. From the viewpoint of easily achieving excellent life performance, the content of organic compound A may be 0.0010 moles or more, 0.0050 moles or more, 0.010 moles or more, 0.015 moles or more, 0.018 moles or more, 0.030 moles or more, 0.055 moles or more, 0.075 moles or more, or 0.090 moles or more. From the viewpoint of easily achieving excellent discharge performance, the content of organic compound A may be 1.0 moles or less, 0.50 moles or less, 0.25 moles or less, 0.12 moles or less, 0.10 moles or less, less than 0.10 moles, 0.080 moles or less, 0.060 moles or less, 0.040 moles or less, or 0.020 moles or less. From these viewpoints, the content of organic compound A may be 0.0010 to 1.0 mole.

The electrolyte solution according to this embodiment may further contain a surfactant (excluding organic compound A) in order to facilitate excellent life performance. The reason why the inclusion of a surfactant in the electrolyte solution facilitates excellent life performance is presumed to be, but not limited to, the following: In other words, the inclusion of a surfactant in the electrolyte solution forms a coating on the surface of the zinc in the electrode material, thereby preventing oxidation of the zinc in the electrode material. It is presumed that the prevention of zinc oxidation makes it difficult for a passive state (zinc oxide) to form on the surface of the electrode material, thereby preventing a decrease in battery performance.

Examples of surfactants include nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants. From the viewpoint of easily achieving excellent lifespan performance, the surfactant may include at least one selected from the group consisting of nonionic surfactants and anionic surfactants, or may include both nonionic surfactants and anionic surfactants.

Nonionic surfactants have a nonionic hydrophilic group and a hydrophobic group. Examples of nonionic surfactants include polyoxyethylene octylphenyl ether and polyacrylamide. The nonionic surfactant may contain polyoxyethylene octylphenyl ether, which facilitates achieving excellent long-lasting performance.

Anionic surfactants have anionic hydrophilic groups and hydrophobic groups. Examples of anionic surfactants include polyoxyethylene alkyl ether phosphate esters, sodium alkylbenzenesulfonate, sodium alkylnaphthalenesulfonate, ammonium lauryl sulfate, and sodium lauryl sulfate. The anionic surfactant may contain polyoxyethylene alkyl ether phosphate esters, which facilitates achieving excellent long-lasting performance.

Cationic surfactants have a cationic hydrophilic group and a hydrophobic group. Examples of cationic surfactants include aliphatic amines or their salts, alkylamidoamine salts, monoalkyltrimethylammonium salts, dialkyldimethylammonium salts, alkylbenzyldimethylammonium salts, alkylpyridinium salts, and quaternary ammonium salt-type cationic surfactants such as benzethonium chloride salts. From the viewpoint of easily achieving excellent life performance, the cationic surfactant may include at least one selected from the group consisting of monoalkyltrimethylammonium salts and dialkyldimethylammonium salts, and may also include monoalkyltrimethylammonium salts.

Examples of monoalkyltrimethylammonium salts include dodecyltrimethylammonium bromide, dodecyltrimethylammonium chloride, tridecyltrimethylammonium bromide, tridecyltrimethylammonium chloride, tetradecyltrimethylammonium bromide, tetradecyltrimethylammonium chloride, pentadecyltrimethylammonium bromide, pentadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, heptadecyltrimethylammonium bromide, heptadecyltrimethylammonium chloride, octadecyltrimethylammonium bromide, and octadecyltrimethylammonium chloride.

Examples of dialkyldimethylammonium salts include didodecyldimethylammonium bromide, didodecyldimethylammonium chloride, ditridecyldimethylammonium bromide, ditridecyldimethylammonium chloride, ditetradecyldimethylammonium bromide, ditetradecyldimethylammonium chloride, dipentadecyldimethylammonium bromide, dipentadecyldimethylammonium chloride, dihexadecyldimethylammonium bromide, dihexadecyldimethylammonium chloride, diheptadecyldimethylammonium bromide, diheptadecyldimethylammonium chloride, dioctadecyldimethylammonium bromide, and dioctadecyldimethylammonium chloride.

When the surfactant contains a nonionic surfactant or an anionic surfactant, the content of the nonionic surfactant or anionic surfactant in the surfactant may be 50% by mass or more, 70% by mass or more, 90% by mass or more, 95% by mass or more, 97% by mass or more, or 99% by mass or more based on the surfactant content (total amount of surfactants), from the viewpoint of easily achieving excellent life performance. The surfactant may be substantially composed of a nonionic surfactant or an anionic surfactant (an embodiment in which substantially 100% by mass of the surfactant is a nonionic surfactant or an anionic surfactant).

When the surfactant contains a nonionic surfactant and an anionic surfactant, the mass ratio of the anionic surfactant content to the nonionic surfactant content (anionic surfactant content/nonionic surfactant content) may be within the following ranges, from the viewpoint of easily achieving excellent lifespan performance. The mass ratio may be 0.1 or more, 0.3 or more, 0.5 or more, 0.7 or more, or 1 or more. The mass ratio may be 3 or less, 2.5 or less, 2 or less, 1.5 or less, 1.2 or less, or 1 or less. From these viewpoints, the mass ratio may be 0.1 to 3.

From the viewpoint of easily achieving excellent life performance, the surfactant content in the electrolyte solution (total amount of surfactants) may be within the following ranges based on the total mass of the electrolyte solution. The surfactant content may be 0.001 mass% or more, 0.003 mass% or more, 0.005 mass% or more, or 0.01 mass% or more. The surfactant content may be 0.1 mass% or less, 0.08 mass% or less, 0.05 mass% or less, or 0.01 mass% or less. From these viewpoints, the surfactant content may be 0.001 to 0.1 mass%.

The electrolyte solution according to this embodiment may contain a liquid medium such as water (e.g., ion-exchanged water).

Below, we will explain a nickel-zinc battery as an example of a zinc battery that uses the electrolyte according to the above embodiment.

The zinc battery according to this embodiment includes, for example, a battery case, an electrode group (e.g., a plate group) housed in the battery case, and an electrolyte. The zinc battery according to this embodiment may be either chemically formed or unformed.

The electrode group includes, for example, a positive electrode (e.g., a positive electrode plate), a negative electrode (e.g., a negative electrode plate), and a separator disposed between the positive and negative electrodes. The positive and negative electrodes are alternately stacked with the separator interposed between them, with the main surface of the positive electrode and the main surface of the negative electrode facing each other. The electrode group may be composed of multiple positive electrodes and multiple negative electrodes. The multiple positive electrodes and multiple negative electrodes may be connected to each other, for example, by straps.

The positive electrode has a positive electrode current collector (current collector) and a positive electrode material (electrode material) supported on the positive electrode current collector. The positive electrode material may be disposed on at least one main surface of the positive electrode current collector, or may be disposed on both main surfaces of the positive electrode current collector. The negative electrode has a negative electrode current collector and a negative electrode material supported on the current collector. The negative electrode material may be disposed on at least one main surface of the negative electrode current collector, or may be disposed on both main surfaces of the negative electrode current collector. The positive electrode and negative electrode may each be either before or after chemical formation.

The current collector (positive electrode current collector or negative electrode current collector) forms a conductive path for current from the electrode material (positive electrode material or negative electrode material). The current collector has a shape such as a flat plate or sheet. The current collector may be a collector with a three-dimensional mesh structure made of foamed metal, expanded metal, punched metal, or metal fiber felt.

Specific examples of materials that can be used to make up the current collector include platinum; nickel (foamed nickel, etc.); and metal materials (copper, brass, steel, etc.) plated with metals such as tin and nickel.

The electrode material (positive electrode material or negative electrode material) may be a layered electrode material layer (positive electrode material layer or negative electrode material layer). For example, the electrode material layer may be formed on a current collector, and if the current collector has a three-dimensional mesh structure, the electrode material may be filled between the meshes of the current collector to form the electrode material layer.

The thickness of the current collector may be 0.01 mm or more, 0.05 mm or more, 0.08 mm or more, or 0.10 mm or more. The thickness of the current collector may be 1.0 mm or less, 0.80 mm or less, 0.50 mm or less, 0.30 mm or less, 0.20 mm or less, or 0.10 mm or less. From these perspectives, the thickness of the current collector may be 0.01 to 1.0 mm.

The positive electrode material contains a positive electrode active material (electrode active material) containing nickel. When the zinc battery is a nickel-zinc battery, the positive electrode active material can contain nickel. Examples of positive electrode active materials include nickel oxyhydroxide (NiOOH) and nickel hydroxide. For example, the positive electrode material contains nickel oxyhydroxide in a fully charged state and nickel hydroxide in an end-of-discharge state. The content of the positive electrode active material may be, for example, 50 to 99 mass% based on the total mass of the positive electrode material.

The positive electrode material may contain additives other than the positive electrode active material. Examples of additives include binders, conductive agents, expansion inhibitors, and rare earth metal compounds (e.g., yttrium oxide). Examples of binders include hydrophilic or hydrophobic polymers, such as hydroxyethyl cellulose (HEC), hydroxypropyl methyl cellulose (HPMC), carboxymethyl cellulose (CMC), sodium polyacrylate (SPA), and fluorine-based polymers (e.g., polytetrafluoroethylene (PTFE)). The binder content may be, for example, 0.01 to 5 parts by mass per 100 parts by mass of the positive electrode active material. Examples of conductive agents include cobalt compounds (e.g., metallic cobalt, cobalt oxide, cobalt hydroxide). The conductive agent content may be, for example, 1 to 20 parts by mass per 100 parts by mass of the positive electrode active material. Examples of expansion inhibitors include zinc oxide. The content of the expansion inhibitor may be, for example, 0.01 to 5 parts by mass per 100 parts by mass of the positive electrode active material.

The negative electrode material contains a negative electrode active material containing zinc. Examples of negative electrode active materials include metallic zinc, zinc oxide, and zinc hydroxide. The negative electrode active material may contain one of these components alone, or may contain multiple types. For example, the negative electrode material contains metallic zinc in a fully charged state, and zinc oxide and zinc hydroxide in an end-of-discharge state. The negative electrode active material may be in particulate form, and may contain metallic zinc particles, zinc oxide particles, zinc hydroxide particles, etc. The content of the negative electrode active material is, for example, 50 to 99% by mass based on the total mass of the negative electrode material.

The negative electrode material may contain additives other than the negative electrode active material. Examples of additives include binders, surfactants, and conductive agents. Examples of binders include polytetrafluoroethylene, hydroxyethyl cellulose (HEC), carboxymethyl cellulose, polyethylene oxide, polyethylene, and polypropylene. The binder content may be, for example, 0.5 to 10 parts by mass per 100 parts by mass of the negative electrode active material. Examples of conductive agents include indium compounds (such as indium oxide). The conductive agent content may be, for example, 1 to 20 parts by mass per 100 parts by mass of the negative electrode active material.

The separator may be bag-shaped with an opening so that it can accommodate a positive electrode and/or a negative electrode. In a zinc battery, for example, the opening opens vertically upward. The side of the separator perpendicular to the opening direction of the opening (for example, the side that is positioned horizontally when the positive electrode and/or a negative electrode are accommodated in the zinc battery) may be shielded or open. The shielding portion can be formed, for example, by heat welding the separator. The separator may be a single-layer porous membrane or a laminate of multiple porous membranes.

Separator materials include organic materials (such as resin materials) and inorganic materials. Resin materials include polyamide-based polymers (e.g., polyamide), olefin-based polymers (e.g., polyolefins such as polyethylene and polypropylene), and nylon-based polymers (e.g., nylon). Inorganic materials include oxides such as alumina, titania, and silicon dioxide; nitrides such as aluminum nitride and silicon nitride; and sulfates such as barium sulfate and calcium sulfate. The separator may be an ion-exchange resin membrane, a cellophane-based recycled resin membrane, an inorganic-organic separator, a polyolefin-based nonwoven fabric, etc.

To make the separator hydrophilic, it may contain anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, etc., and may be surface-treated by surfactant treatment, sulfonation treatment, fluorine gas treatment, acrylic acid graft polymerization treatment, corona discharge treatment, plasma treatment, etc. Making the separator hydrophilic makes it more compatible with the electrolyte, making it easier to obtain a sufficient current density.

The manufacturing method for the nickel-zinc battery described above includes, for example, a component manufacturing process for obtaining components for the zinc battery, and an assembly process for assembling the components to obtain the zinc battery. In the component manufacturing process, at least electrodes (positive and negative electrodes) are obtained.

Electrodes can be obtained, for example, by adding a solvent (e.g., water) to the raw materials for the electrode materials (positive and negative electrode materials) and kneading them to obtain an electrode material paste (a paste-like electrode material), and then using the electrode material paste to form an electrode material layer.

Cathode raw materials include cathode active material raw materials (e.g., nickel hydroxide), additives (e.g., the binder), etc. Anode raw materials include anode active material raw materials (e.g., zinc metal, zinc oxide, zinc hydroxide), additives (e.g., binder), etc.

One method for forming the electrode material layer is to apply or fill an electrode material paste onto a current collector and then dry it to obtain the electrode material layer. If necessary, the electrode material layer may be densified by pressing or the like.

In the assembly process, for example, the positive and negative electrodes obtained in the component manufacturing process are stacked alternately with separators in between, and then the positive electrodes and negative electrodes are connected to each other with straps to create an electrode group. Next, this electrode group is placed in a battery case, and a lid is attached to the top of the case to obtain an unformed zinc battery (nickel-zinc battery).

Next, the electrolyte solution according to this embodiment is poured into the battery case of the unformed zinc battery and left for a certain period of time. Then, the battery is formed by charging under specified conditions to obtain a zinc battery (nickel-zinc battery). The formation conditions can be adjusted depending on the properties of the electrode active materials (positive electrode active material and negative electrode active material).

The above describes an example of a nickel-zinc battery (e.g., a nickel-zinc secondary battery) in which the positive electrode is a nickel electrode, but the zinc battery may also be an air-zinc battery (e.g., an air-zinc secondary battery) in which the positive electrode is an air electrode, or a silver-zinc battery (e.g., a silver-zinc secondary battery) in which the positive electrode is a silver oxide electrode.

A known air electrode used in air-zinc batteries can be used as the air electrode of an air-zinc battery. The air electrode includes, for example, an air electrode catalyst, an electron-conductive material, etc. The air electrode catalyst can be an air electrode catalyst that also functions as an electron-conductive material.

The air electrode catalyst can function as the positive electrode in an air-zinc battery, and various air electrode catalysts that can use oxygen as the positive electrode active material can be used. Examples of air electrode catalysts include carbon-based materials (such as graphite) with redox catalytic properties, metal materials (such as platinum and nickel) with redox catalytic properties, and inorganic oxide materials (such as perovskite-type oxides, manganese dioxide, nickel oxide, cobalt oxide, and spinel oxide) with redox catalytic properties. The air electrode catalyst may be, for example, particulate. The content of the air electrode catalyst in the air electrode may be 5 to 70% by volume, 5 to 60% by volume, or 5 to 50% by volume relative to the total volume of the air electrode.

The electronically conductive material may be electrically conductive and allow electron conduction between the air electrode catalyst and the separator. Examples of electronically conductive materials include carbon blacks such as ketjen black, acetylene black, channel black, furnace black, lamp black, and thermal black; graphites such as natural graphite (e.g., flake graphite), artificial graphite, and expanded graphite; conductive fibers such as carbon fiber and metal fiber; metal powders such as copper, silver, nickel, and aluminum; organic electronically conductive materials such as polyphenylene derivatives; and mixtures of any of these. The electronically conductive material may be in particulate form or other shapes. The electronically conductive material may be used in a form that provides a continuous phase in the thickness direction of the air electrode. For example, the electronically conductive material may be a porous material. The electronically conductive material may also be in the form of a mixture or composite with the air electrode catalyst, or, as described above, may be an air electrode catalyst that also functions as an electronically conductive material. The content of the electronically conductive material in the air electrode may be 10 to 80% by volume, 15 to 80% by volume, or 20 to 80% by volume relative to the total volume of the air electrode.

The silver oxide electrode of a silver-zinc battery can be a known silver oxide electrode used in silver-zinc batteries. Examples of silver oxide electrodes include silver(I) oxide.

The present disclosure will be explained in more detail below using examples. However, the present disclosure is not limited to the following examples.

<Preparation of Electrolyte>
(Examples 1 to 14)
Ion-exchanged water, potassium hydroxide (KOH), lithium hydroxide (LiOH), the organic compounds shown in Table 1, a nonionic surfactant (polyoxyethylene octylphenyl ether, Triton X-100, manufactured by Sigma-Aldrich), and an anionic surfactant (polyoxyethylene alkyl ether phosphate ester, a mixture of monoesters and diesters, manufactured by Rhodafac, trade name: RA-600) were mixed to prepare an electrolyte solution (potassium hydroxide concentration: 30% by mass, lithium hydroxide concentration: 1% by mass, organic compound content: the content shown in Table 1, nonionic surfactant: 0.005% by mass, anionic surfactant: 0.005% by mass). The contents of the above components are based on the total mass of the electrolyte solution.

(Comparative Example 1)
An electrolytic solution (potassium hydroxide concentration: 30 mass%, lithium hydroxide concentration: 1 mass%, nonionic surfactant: 0.005 mass%, anionic surfactant: 0.005 mass%) was prepared in the same manner as in Examples 1 to 14, except that no organic compound was used.

<Preparation of positive electrode>
A grid made of foamed nickel with a porosity of 95% was prepared and pressure-molded to obtain a positive electrode current collector. Next, a predetermined amount of cobalt-coated nickel hydroxide powder, metallic cobalt, cobalt hydroxide, yttrium oxide, CMC (carboxymethyl cellulose), PTFE (polytetrafluoroethylene), and ion-exchanged water were weighed and mixed to obtain a mixture. The resulting mixture was stirred to prepare a positive electrode paste. The mass ratio of the solids was adjusted to "nickel hydroxide: metallic cobalt: yttrium oxide: cobalt hydroxide: CMC: PTFE = 88: 10.3: 1: 0.3: 0.3: 0.1." The moisture content of the positive electrode paste was adjusted to 27.5% by mass based on the total mass of the positive electrode paste. The positive electrode paste was then applied to a positive electrode current collector and dried at 80 ° C for 30 minutes. The resulting mixture was then pressure-molded using a roll press to obtain an unformed positive electrode having a positive electrode material (positive electrode material layer) on both sides.

<Preparation of negative electrode>
As a negative electrode current collector, a tin-plated copper punching metal (pore size: 50%, thickness: 0.10 mm) was prepared. Next, a predetermined amount of zinc oxide, metallic zinc, HEC (hydroxyethyl cellulose, manufactured by Sumitomo Seika Chemicals Co., Ltd., trade name: AV-15F), surfactant (manufactured by BASF, trade name: Dispex AA 4140), and ion-exchanged water were weighed and mixed to obtain a mixed solution, which was then stirred to prepare a negative electrode material paste. At this time, the mass ratio of the solids was adjusted to "zinc oxide: metallic zinc: HEC: surfactant = 84.5: 11.5: 3.5: 0.5". The water content of the negative electrode material paste was adjusted to 32.5 mass% based on the total mass of the negative electrode material paste. Next, the negative electrode material paste was applied to the negative electrode current collector and then dried at 80 ° C. for 30 minutes. Thereafter, the mixture was pressure-molded using a roll press to obtain an unformed negative electrode having a negative electrode material (negative electrode material layer) on both sides.

<Preparation of nickel-zinc battery>
Before battery assembly, a porous membrane (manufactured by Ube Industries, Ltd., trade name: UP3355, air permeability: 440 sec / 100 mL) was hydrophilized with a surfactant (manufactured by Sigma-Aldrich Japan LLC, trade name: Triton (registered trademark) -X100). The hydrophilization treatment was performed by immersing the porous membrane in an aqueous solution containing 1% by mass of Triton-X100 for 24 hours and then drying at room temperature for 1 hour. The air permeability of the porous membrane indicates the value after hydrophilization treatment. The porous membrane was cut to 3.0 cm x 10.0 cm and then folded in half to obtain a porous membrane A (3.0 cm x 5.0 cm). A pair of both side surfaces (long sides) of this porous membrane A were heat-sealed to obtain a bag-shaped porous member, and then one unformed positive electrode was placed in this bag-shaped porous member to obtain a positive electrode body. In addition, a pair of both side surfaces (long sides) of the porous membrane A was heat-sealed to obtain a bag-shaped porous member, and then one unformed negative electrode was placed in this bag-shaped porous member to obtain a negative electrode body.

Nippon Kodoshi Industries' VL100 (material: cellulose, thickness: 100 μm, air permeability: 0.3 sec/100 mL) was cut to a size of 3.0 cm x 10.0 cm and then folded in half to obtain a nonwoven fabric (3.0 cm x 5.0 cm). This nonwoven fabric was sandwiched between the positive and negative electrodes, and two positive and three negative electrodes were alternately stacked. Plates of the same polarity were then connected with straps to produce an electrode assembly (plate assembly). This electrode assembly was placed in a battery case, and a lid was attached to the top of the case to obtain an unformed nickel-zinc battery. Next, electrolyte was poured into the unformed nickel-zinc battery case and allowed to stand for 24 hours. The battery was then charged at 32 mA for 15 hours to produce a formed nickel-zinc battery (nominal capacity: 320 mAh).

<Characteristics evaluation>
The life performance (cycle life performance) and high-rate discharge performance of the nickel-zinc batteries were evaluated using the nickel-zinc batteries of Examples 1 to 14 and Comparative Example 1. The specific evaluation methods are shown below, and the results are shown in Table 1.

(Evaluation of life performance)
The test was conducted by charging the nickel-zinc battery at 40°C at a constant voltage of 1.88 V at 105.7 mA (0.33 C) until the current value decayed to 16 mA (0.05 C), and then discharging the nickel-zinc battery at a constant current of 105.7 mA (0.33 C) until the battery voltage reached 1.1 V, which constituted one cycle. The test was terminated when the discharge capacity fell below 60% of the discharge capacity at the first cycle, and the life performance was evaluated based on the number of cycles performed until the end of the test.

(Evaluation of high rate discharge performance)
At 25°C, the nickel-zinc battery was charged at a constant voltage of 1.88 V at 320 mA (1 C) until the current value decayed to 16 mA (0.05 C), and then discharged at a constant current of 3200 mA (10.0 C) until the battery voltage reached 1.1 V, and the discharge capacity was measured. The high-rate discharge performance was evaluated based on the measured discharge capacity.

Claims (7)

an alkali metal hydroxide;
an organic compound having at least one selected from the group consisting of a carboxyl group, a carboxylate group, an ether group, and a hydroxy group (excluding polyoxyethylene octylphenyl ether and polyoxyethylene alkyl ether phosphate ester) ;
the organic compound contains at least one selected from the group consisting of oxalic acid and salts thereof,
The content of the organic compound is 0.1 to 10 mass % based on the total mass of the electrolyte solution. The zinc battery electrolyte according to claim 1, wherein the alkali metal hydroxide comprises potassium hydroxide. 3. The zinc battery electrolyte according to claim 1, wherein the organic compound has a molecular weight of 300 or less. 4. The zinc battery electrolyte solution according to claim 1 , wherein the content of the organic compound is less than 0.10 mol per 1 mol of the alkali metal hydroxide. The zinc battery electrolyte solution according to any one of claims 1 to 4 , further comprising a surfactant. 6. The zinc battery electrolyte according to claim 5 , wherein the surfactant comprises at least one selected from the group consisting of a nonionic surfactant and an anionic surfactant. A zinc battery comprising a positive electrode, a negative electrode, and the zinc battery electrolyte solution according to any one of claims 1 to 6 .