JP7613844B2 - Electrolyte for zinc battery and zinc battery - Google Patents

Description

The present invention relates to an electrolyte for zinc batteries and zinc batteries.

Known zinc batteries include nickel-zinc batteries, air-zinc batteries, and silver-zinc batteries. For example, nickel-zinc batteries are aqueous batteries that use an aqueous electrolyte such as an aqueous potassium hydroxide solution, and therefore are highly safe. In addition, due to the combination of zinc electrodes and nickel electrodes, they are known to have a high electromotive force for an aqueous battery. Furthermore, nickel-zinc batteries have excellent input/output performance and low cost, so their applicability to industrial applications (e.g., backup power sources, etc.) and automotive applications (e.g., hybrid vehicles, etc.) is being considered.

In zinc batteries, zinc hydroxide (Zn(OH) ₂ ) is generated 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 morphological change (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 conventional zinc batteries, when dendrites grow due to repeated charging and discharging, they may penetrate the separator, causing a short circuit.

Japanese Unexamined Patent Publication No. 58-126665

In zinc batteries such as those described above, there is a demand for improving life performance (e.g., cycle life performance).

Therefore, the present invention aims to provide a zinc battery with excellent cycle life performance.

One aspect of the present invention relates to an electrolyte for zinc batteries that contains an alkali metal hydroxide and chloride ions.

The electrolyte described above allows for the production of a zinc battery with excellent cycle life performance.

The alkali metal hydroxide preferably includes potassium hydroxide.

It is preferable that the electrolyte further contains ammonium ions.

The electrolyte is preferably for use in nickel-zinc batteries.

Another aspect of the present invention relates to a zinc battery comprising the above-mentioned electrolyte.

The present invention provides a zinc battery with excellent cycle life performance.

In this specification, the numerical range indicated by "~" indicates a range including the numerical values described before and after "~" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this specification, the upper limit or lower limit of a certain stage of the numerical range can be arbitrarily combined with the upper limit or lower limit of the numerical range of another stage. In the numerical ranges described in this specification, the upper limit or lower limit of the numerical range may be replaced with a value shown in an experimental example. "A or B" may include either A or B, or may include both. Unless otherwise specified, the materials exemplified in this specification may be used alone or in combination of two or more types. In this specification, the amount of each component used in the composition means the total amount of the multiple substances present in the composition when multiple substances corresponding to each component are present in the composition, unless otherwise specified. In this specification, the term "film" or "layer" includes a structure having a shape formed over the entire surface when observed in a plan view, as well as a structure having a shape formed only in a part of the surface. In this specification, the term "process" refers not only to an independent process, but also to a process that cannot be clearly distinguished from other processes, as long as the intended effect of the process is achieved.

The following describes preferred embodiments of the present invention. However, the present invention is not limited to the following embodiments.

The electrolyte of one embodiment is an electrolyte for a zinc battery, for example, a basic (alkaline) electrolyte (also called an alkaline electrolyte). Here, a zinc battery is a battery that uses a zinc electrode (for example, an alkaline zinc battery). Examples of zinc batteries include nickel-zinc batteries (for example, nickel-zinc secondary batteries) in which the positive electrode is a nickel electrode; air-zinc batteries (for example, air-zinc secondary batteries) in which the positive electrode is an air electrode; and silver-zinc batteries (for example, silver-zinc secondary batteries) in which the positive electrode is a silver oxide electrode.

The electrolytic solution contains an alkali metal hydroxide and chloride ions (Cl ⁻ ). The alkali metal hydroxide is dissolved in, for example, a liquid medium (for example, an aqueous liquid medium containing water such as ion-exchanged water) that is a solvent for the electrolytic solution. Therefore, it can also be said that the electrolytic solution contains alkali metal ions and chloride ions (Cl ⁻ ). Furthermore, the chloride ions (Cl ⁻ ) are, for example, ions derived from an electrolyte that generates chloride ions by ionization (dissociation). Therefore, it can also be said that the electrolytic solution contains an alkali metal hydroxide and an electrolyte that generates chloride ions by ionization.

The above electrolyte solution provides a zinc battery with excellent cycle life performance. The reason why such an effect is obtained is not clear, but the inventors speculate as follows. First, in a zinc battery, as the battery reaction progresses, a zinc passive film is formed on the surface of the zinc electrode. It is believed that this passive film is one of the factors that reduces the cycle life performance, but when the above electrolyte solution is used, the above passive film is corroded by the chloride ions in the electrolyte solution, so it is believed that the thickening of the passive film is suppressed. As a result, it is speculated that in a zinc battery using the electrolyte solution of the above embodiment, the deterioration of cycle life performance caused by the passive film is suppressed, and excellent cycle life performance is obtained. In addition, the discharge characteristics are not deteriorated due to the presence of chloride ions, so the above electrolyte solution makes it possible to achieve both excellent cycle life performance and sufficient discharge performance.

Examples of the alkali metal hydroxide include potassium hydroxide (KOH), sodium hydroxide (NaOH), and lithium hydroxide (LiOH). That is, examples of the alkali metal ions contained in the electrolyte include potassium ions (K ⁺ ), sodium ions (Na ⁺ ), and lithium ions (Li ⁺ ). From the viewpoint of excellent discharge performance, the alkali metal hydroxide preferably contains at least one selected from the group consisting of potassium hydroxide and lithium hydroxide, and more preferably contains potassium hydroxide. From the viewpoint of excellent discharge performance, the alkali metal ions preferably contain at least one selected from the group consisting of potassium ions and lithium ions, and more preferably contains potassium ions.

The content of alkali metal hydroxide in the electrolyte (total amount of alkali metal hydroxide) is preferably 10% by mass or more, and may be 15% by mass or more, 20% by mass or more, 25% by mass or more, or 30% by mass or more, based on the total mass of the electrolyte, from the viewpoint of excellent discharge performance. The content of alkali metal hydroxide in the electrolyte is preferably 50% by mass or less, and may be 45% by mass or less, 40% by mass or less, or 35% by mass or less, based on the total mass of the electrolyte, from the viewpoint of easily achieving both excellent life performance and excellent discharge performance.

From the viewpoint of excellent discharge performance, the content of potassium hydroxide in the electrolyte is preferably 10 mass% or more based on the total mass of the electrolyte, and may be 15 mass% or more, 20 mass% or more, 25 mass% or more, or 30 mass% or more. From the viewpoint of easily achieving both excellent life performance and excellent discharge performance, the content of potassium hydroxide in the electrolyte is preferably 50 mass% or less, and may be 45 mass% or less, 40 mass% or less, or 35 mass% or less.

From the viewpoint of excellent discharge performance, the content of lithium hydroxide in the electrolyte is preferably 0.1 mass% or more, and may be 0.3 mass% or more, 0.5 mass% or more, 0.8 mass% or more, or 1 mass% or more, based on the total mass of the electrolyte. From the viewpoint of easily achieving both excellent life performance and excellent discharge performance, the content of lithium hydroxide in the electrolyte is preferably 3 mass% or less, and may be 2 mass% or less, 1.5 mass% or less, or 1.2 mass% or less.

From the viewpoint of excellent discharge performance, the content (concentration) of alkali metal ions in the electrolyte is preferably 5.0 mol/L or more, more preferably 6.0 mol/L or more, and even more preferably 7.0 mol/L or more, based on the total amount of the electrolyte. From the viewpoint of easily achieving both excellent life performance and excellent discharge performance, the content (concentration) of alkali metal ions in the electrolyte is preferably 10.0 mol/L or less, more preferably 9.0 mol/L or less, and even more preferably 8.0 mol/L or less, based on the total amount of the electrolyte.

From the viewpoint of excellent discharge performance, the content (concentration) of potassium ions in the electrolyte is preferably 5.0 mol/L or more, more preferably 6.0 mol/L or more, and even more preferably 7.0 mol/L or more, based on the total amount of the electrolyte. From the viewpoint of easily achieving both excellent life performance and excellent discharge performance, the content (concentration) of potassium ions in the electrolyte is preferably 10.0 mol/L or less, more preferably 9.0 mol/L or less, and even more preferably 8.0 mol/L or less, based on the total amount of the electrolyte.

From the viewpoint of excellent discharge performance, the content (concentration) of lithium ions in the electrolyte is preferably 0.3 mol/L or more, more preferably 0.4 mol/L or more, and even more preferably 0.5 mol/L or more, based on the total amount of the electrolyte. From the viewpoint of easily achieving both excellent life performance and excellent discharge performance, the content (concentration) of lithium ions in the electrolyte is preferably 0.8 mol/L or less, more preferably 0.7 mol/L or less, and even more preferably 0.6 mol/L or less, based on the total amount of the electrolyte.

The alkali metal ions may be, for example, ions derived from an electrolyte other than an alkali metal hydroxide that produces alkali metal ions upon ionization (dissociation). That is, in this embodiment, the electrolyte may further contain an electrolyte other than an alkali metal hydroxide that produces alkali metal ions upon ionization.

Examples of electrolytes that generate alkali metal ions through ionization include potassium phosphate ( _K3PO4 ) _, potassium fluoride (KF), potassium carbonate ( _K2CO3 ), sodium _phosphate ( _Na3PO4 ), sodium fluoride ( _NaF ), etc. In other words, the electrolyte may further contain phosphate ions, carbonate ions, fluoride ions, etc.

The electrolyte that generates alkali metal ions upon ionization may be an electrolyte that generates alkali metal ions and chloride ions upon ionization. Examples of electrolytes that generate alkali metal ions and chloride ions upon ionization include potassium chloride (KCl), sodium chloride (NaCl), and lithium chloride (LiCl).

The chloride ion ( ^Cl- ) may be an ion derived from an electrolyte that generates chloride ions upon ionization other than an electrolyte that generates alkali metal ions and chloride ions upon ionization. Examples of such electrolytes include ammonium chloride ( _NH4Cl ), calcium chloride ( _CaCl2 ), magnesium chloride (MgCl2), phosphorus trichloride ( _PCl3 ), phosphorus pentachloride ( _PCl5 ), lead dichloride ( _PbCl2 ), _zinc chloride ( _ZnCl2 ), aluminum chloride ( _AlCl3 ), indium chloride ( _InCl3 ), and tin chloride ( _SnCl2 ).

As the electrolyte that generates chloride ions through ionization, from the viewpoint of further improving cycle life performance, it is preferable to use at least one selected from the group consisting of ammonium chloride, potassium chloride, and lead dichloride, and it is more preferable to use ammonium chloride.

From the viewpoint of obtaining a better life performance, the content (concentration) of chloride ions in the electrolyte is preferably 0.01 mol/L or more, more preferably 0.05 mol/L or more, and even more preferably 0.1 mol/L or more, based on the total amount of the electrolyte. From the viewpoint of easily achieving both excellent life performance and excellent discharge performance, the content (concentration) of chloride ions in the electrolyte is preferably 0.5 mol/L or less, more preferably 0.4 mol/L or less, and even more preferably 0.3 mol/L or less, based on the total amount of the electrolyte.

From the viewpoint of obtaining a more excellent life performance, it is preferable that the electrolyte further contains ammonium ions (NH ₄ ⁺ ). The ammonium ions are, for example, ions derived from an electrolyte that generates ammonium ions by ionization (dissociation). Examples of electrolytes that generate ammonium ions by ionization include the above-mentioned ammonium chloride (an electrolyte that generates chloride ions and ammonium ions by ionization), as well as ammonium carbonate, ammonium nitrate, and the like.

The content (concentration) of ammonium ions in the electrolyte is preferably 0.01 mol/L or more, more preferably 0.05 mol/L or more, and even more preferably 0.1 mol/L or more, based on the total amount of the electrolyte, from the viewpoint of obtaining better life performance. The content (concentration) of ammonium ions in the electrolyte is preferably 0.5 mol/L or less, more preferably 0.4 mol/L or less, and even more preferably 0.3 mol/L or less, based on the total amount of the electrolyte, from the viewpoint of easily achieving both excellent life performance and excellent discharge performance. The content (concentration) of ammonium ions in the electrolyte may be 0.8 to 1.2 times the concentration of chloride ions in the electrolyte.

The electrolyte may further contain an organic compound containing oxygen atoms (hereinafter, sometimes referred to as "oxygen-containing compound"). When the electrolyte contains an oxygen-containing compound, the decrease in discharge capacity of the zinc battery due to repeated charging and discharging tends to be suppressed, and there is a tendency for such advantages to be obtained that the decrease in discharge capacity during storage of the zinc battery can be suppressed and excellent high-rate discharge performance can be easily obtained. These effects tend to be more pronounced when an alkali metal hydroxide is used as the electrolyte.

The oxygen-containing compound may have a functional group containing an oxygen atom. Examples of the functional group containing an oxygen atom include a carboxyl group, a carboxylate group, a hydroxyl group (excluding the OH structure included in the carboxyl group), an epoxy group, an ether group, an alkoxide group, an ester group, a ketone group, and an aldehyde group. From the viewpoint of easily suppressing the decrease in discharge capacity during storage of the zinc battery and from the viewpoint of easily obtaining excellent high-rate discharge performance, it is preferable that the oxygen-containing compound has at least one selected from the group consisting of a carboxyl group, a carboxylate group, a hydroxyl group, an epoxy group, and an ether group.

When the oxygen-containing compound has an OH structure, the ratio of the number of OH structures to the number of carbon atoms in the oxygen-containing compound (number of OH structures/number of carbon atoms) is preferably in the following range from the viewpoint of easily suppressing the decrease in discharge capacity when the zinc battery is stored and from the viewpoint of easily obtaining excellent high-rate discharge performance. The ratio is preferably 0.01 or more, 0.03 or more, 0.05 or more, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 5/6 or more. The ratio is preferably 2 or less, 1.5 or less, 1.2 or less, 1 or less, 0.9 or less, or 5/6 or less. The oxygen-containing compound does not have to have an OH structure.

From the viewpoint of easily suppressing the decrease in discharge capacity during storage of the zinc battery and easily obtaining excellent high-rate discharge performance, the oxygen-containing compound preferably contains at least one selected from the group consisting of sugars, carboxylic acids (excluding compounds corresponding to sugars), carboxylates (excluding compounds corresponding to sugars), epoxy compounds (compounds having an epoxy group; excluding compounds corresponding to sugars, carboxylic acids, or carboxylates), and ether compounds (compounds having an ether group; excluding compounds corresponding to sugars, carboxylic acids, carboxylates, or epoxy compounds).

As the sugar, monosaccharides, disaccharides, trisaccharides, polysaccharides (excluding sugars corresponding to disaccharides or trisaccharides), etc. can be used. Examples of monosaccharides include glucose, fructose, galactose, arabinose, ribose, mannose, xylose, sorbose, rhamnose, fucose, ribodesose, etc. Examples of disaccharides include maltose, trehalose, sucrose, cellobiose, gentiobiose, lactose, melibiose, etc. Examples of trisaccharides include raffinose, gentianose, melezitose, etc. Examples of polysaccharides include cyclodextrin (e.g., γ-cyclodextrin), stachyose, etc. It is preferable that the oxygen-containing compound contains at least one selected from the group consisting of glucose, maltose, and raffinose, from the viewpoint of easily suppressing the decrease in discharge capacity during storage of the zinc battery and easily obtaining excellent high-rate discharge performance.

Examples of carboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, benzoic acid, salicylic acid, 3,4,5-trihydroxybenzoic acid, benzenehexacarboxylic acid, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, aconitic acid, pyruvic acid, oxaloacetic acid, glycidyl formate, glycidyl acetate, and glycidyl benzoate. Examples of carboxylates include salts of these carboxylic acids. Examples of carboxylates include alkali metal salts such as sodium salts (e.g., disodium terephthalate) and potassium salts. The carboxylate preferably contains an alkali metal salt, and more preferably contains a sodium salt, from the viewpoint of easily suppressing the decrease in discharge capacity when the zinc battery is stored and from the viewpoint of easily obtaining excellent high-rate discharge performance. From the viewpoint of easily suppressing the decrease in discharge capacity during storage of the zinc battery and easily obtaining excellent high-rate discharge performance, the oxygen-containing compound preferably contains at least one selected from the group consisting of carboxylic acids having aromatic rings and carboxylates having aromatic rings, more preferably contains at least one selected from the group consisting of terephthalic acid and terephthalic acid salts, and even more preferably contains at least one selected from the group consisting of terephthalic acid and sodium salts of terephthalic acid.

The number of carboxyl groups in the carboxylic acid or the number of carboxylate salts in the carboxylate is 1 or more, and the following ranges are preferred from the viewpoint of easily suppressing the decrease in discharge capacity during storage of the zinc battery and from the viewpoint of easily obtaining excellent high-rate discharge performance. The number of carboxyl groups or carboxylate salts is preferably 2 or more. The number of carboxyl groups or carboxylate salts is preferably 4 or less, 3 or less, or 2 or less.

Epoxy compounds include monofunctional epoxy compounds, polyfunctional epoxy compounds, etc. Examples of monofunctional epoxy compounds include 1,2-epoxyethane, 1,2-epoxypropane, 1,2-epoxybutane, 1,2-epoxy-2-methylpropane, 1-phenyl-1,2-epoxyethane, epichlorohydrin, epibromohydrin, glycidyl methyl ether, allyl glycidyl ether, polyethylene oxide glycidyl ether, glycidyl amide, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, stearyl glycidyl ether, lauryl glycidyl ether, butoxy polyethylene glycol glycidyl ether, phenol polyethylene glycol glycidyl ether, allyl glycidyl ether, phenyl glycidyl ether, p-methylphenyl glycidyl ether, p-ethylphenyl glycidyl ether, p-sec-butylphenyl glycidyl ether, p-tert-butylphenyl glycidyl, glycidyl acrylate, glycidyl methacrylate, etc. Examples of polyfunctional epoxy compounds include bisphenol A type epoxy compounds, bisphenol F type epoxy compounds, phenol novolac type epoxy compounds, cresol novolac type epoxy compounds, polyphenol type epoxy compounds, cyclic aliphatic epoxy compounds, aliphatic glycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds, glycidyl diamine type epoxy compounds, heterocyclic epoxy compounds, cyclic aliphatic epoxy compounds, etc. The oxygen-containing compound preferably contains a monofunctional epoxy compound, more preferably 1,2-epoxy-2-methylpropane, from the viewpoint of easily suppressing the decrease in discharge capacity during storage of the zinc battery and easily obtaining excellent high-rate discharge performance.

The ether compounds include crown ether compounds such as 18-crown-6, 15-crown-5, 12-crown-4, dibenzo-18-crown-6, dicyclohexano-18-crown-6, and dibenzo-24-crown-8; polyalkylene glycols such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; and glycerin. The ether compounds may be polyether compounds. From the viewpoint of easily suppressing the decrease in discharge capacity during storage of the zinc battery and easily obtaining excellent high-rate discharge performance, the oxygen-containing compound preferably contains an ether compound having a heterocycle containing an ether group, and more preferably contains 18-crown-6.

The number of ether groups in the ether compound is 1 or more, and the following ranges are preferred from the viewpoint of easily suppressing the decrease in discharge capacity during storage of the zinc battery and from the viewpoint of easily obtaining excellent high-rate discharge performance. The number of ether groups is preferably 2 or more, 3 or more, 4 or more, 5 or more, or 6 or more. The number of ether groups is preferably 10 or less, 9 or less, 8 or less, 7 or less, or 6 or less.

The molecular weight of the oxygen-containing compound is preferably 50 or more, 70 or more, 80 or more, 100 or more, 120 or more, 150 or more, 160 or more, 170 or more, or 180 or more, from the viewpoint of easily suppressing the decrease in discharge capacity when the zinc battery is stored and from the viewpoint of easily obtaining excellent high-rate discharge performance. The molecular weight of the oxygen-containing compound is preferably 2000 or less, 1500 or less, 1300 or less, 1200 or less, 1000 or less, 800 or less, or 600 or less, from the viewpoint of easily suppressing the decrease in discharge capacity when the zinc battery is stored and from the viewpoint of easily obtaining excellent high-rate discharge performance. From these viewpoints, the molecular weight of the oxygen-containing compound is preferably 50 to 2000. The molecular weight of the oxygen-containing compound may be 190 or more, 200 or more, 210 or more, 220 or more, 240 or more, 260 or more, 300 or more, 340 or more, 350 or more, 400 or more, 450 or more, or 500 or more. The molecular weight of the oxygen-containing compound may be 500 or less, 400 or less, 350 or less, 340 or less, 320 or less, 300 or less, 280 or less, 270 or less, 260 or less, 250 or less, 230 or less, 220 or less, 210 or less, 200 or less, 190 or less, or 185 or less.

As the oxygen-containing compound, it is preferable to use a compound that is highly soluble in the electrolyte. Even if the compound is not highly soluble, it can be used by removing the residue by filtration, etc. The electrolyte according to this embodiment does not need to contain alcohol.

The content of the oxygen-containing compound in the electrolyte is preferably in the following range based on the total amount of the electrolyte. The content of the oxygen-containing compound is preferably 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 from the viewpoint of easily suppressing the decrease in discharge capacity when the zinc battery is stored and from the viewpoint of easily obtaining excellent high-rate discharge performance. The content of the oxygen-containing compound is preferably 5 mass% or less, 4.5 mass% or less, 4 mass% or less, 3.5 mass% or less, or 3 mass% or less from the viewpoint of easily suppressing the decrease in discharge capacity when the zinc battery is stored and from the viewpoint of easily obtaining excellent high-rate discharge performance. From these viewpoints, the content of the oxygen-containing compound is preferably 0.1 to 5 mass%. The content of the oxygen-containing compound is preferably 1.2 mass% or more, 1.5 mass% or more, 1.8 mass% or more, 2 mass% or more, 2.2 mass% or more, 2.5 mass% or more, 2.7 mass% or more, or 3 mass% or more from the viewpoint of further easily suppressing the decrease in discharge capacity when the zinc battery is stored. The content of the oxygen-containing compound may be 3.5% by mass or more, 4% by mass or more, 4.5% by mass or more, or 5% by mass or more. From the viewpoint of easily obtaining even better high-rate discharge performance, the content of the oxygen-containing compound is preferably 2.7% by mass or less, 2.5% by mass or less, 2.2% by mass or less, 2% by mass or less, 1.7% by mass or less, 1.5% by mass or less, 1.2% by mass or less, or 1% by mass or less. The content of the oxygen-containing compound may be less than 0.5 mol/L based on the total amount of the electrolyte.

The content of the oxygen-containing compound is preferably in the following ranges relative to 100 parts by mass of the alkali metal hydroxide. The content of the oxygen-containing compound is preferably 1 part by mass or more, 1.5 parts by mass or more, 2 parts by mass or more, 2.5 parts by mass or more, or 3 parts by mass or more from the viewpoint of easily suppressing the decrease in discharge capacity when the zinc battery is stored and from the viewpoint of easily obtaining excellent high-rate discharge performance. The content of the oxygen-containing compound is preferably 30 parts by mass or less, 25 parts by mass or less, 20 parts by mass or less, 16 parts by mass or less, 15 parts by mass or less, 13 parts by mass or less, 12 parts by mass or less, or 10 parts by mass or less from the viewpoint of easily suppressing the decrease in discharge capacity when the zinc battery is stored and from the viewpoint of easily obtaining excellent high-rate discharge performance. From these viewpoints, the content of the oxygen-containing compound is preferably 1 to 30 parts by mass. The content of the oxygen-containing compound is preferably 4 parts by mass or more, 5 parts by mass or more, 6 parts by mass or more, 7 parts by mass or more, 8 parts by mass or more, or 9 parts by mass or more from the viewpoint of easily suppressing the decrease in discharge capacity when the zinc battery is stored. The content of the oxygen-containing compound may be 10 parts by mass or more, 12 parts by mass or more, 13 parts by mass or more, 15 parts by mass or more, or 16 parts by mass or more. From the viewpoint of easily obtaining even better high-rate discharge performance, the content of the oxygen-containing compound is preferably 9 parts by mass or less, 8 parts by mass or less, 7 parts by mass or less, 6 parts by mass or less, 5 parts by mass or less, or 4 parts by mass or less.

The electrolyte may contain an indium compound (a compound containing indium). By containing an indium compound in the electrolyte, it is possible to further suppress the decrease in discharge capacity during storage of the zinc battery, and for example, it is possible to further reduce the amount of change in discharge capacity before and after storage when the zinc battery is stored at 40°C for 7 days and then charged and discharged.

Examples of indium compounds include indium sulfate, indium oxide, indium fluoride, indium chloride, indium bromide, indium iodide, indium nitrate, and indium carbonate. It is preferable that the indium compound contains indium sulfate, from the viewpoint of further suppressing the decrease in discharge capacity during storage of the zinc battery.

From the viewpoint of further suppressing the decrease in discharge capacity during storage of the zinc battery, the content of the indium compound in the electrolyte is preferably in the following range based on the total amount of the electrolyte. The content of the indium compound is preferably 0.01 mass% or more, 0.03 mass% or more, 0.05 mass% or more, 0.08 mass% or more, or 0.1 mass% or more. The content of the indium compound is preferably 2 mass% or less, 1.5 mass% or less, 1 mass% or less, 0.7 mass% or less, 0.5 mass% or less, 0.3 mass% or less, 0.2 mass% or less, or 0.1 mass% or less. From these viewpoints, the content of the indium compound is preferably 0.01 to 2 mass%.

The content of the indium compound is preferably in the following range per 100 parts by mass of the alkali metal hydroxide, from the viewpoint of further suppressing the decrease in discharge capacity during storage of the zinc battery. The content of the indium compound is preferably 0.01 parts by mass or more, 0.03 parts by mass or more, 0.05 parts by mass or more, 0.1 parts by mass or more, 0.15 parts by mass or more, 0.2 parts by mass or more, 0.25 parts by mass or more, or 0.3 parts by mass or more. The content of the indium compound is preferably 10 parts by mass or less, 5 parts by mass or less, 3 parts by mass or less, 1 part by mass or less, 0.8 parts by mass or less, 0.5 parts by mass or less, 0.45 parts by mass or less, 0.4 parts by mass or less, or 0.35 parts by mass or less. From these viewpoints, the content of the indium compound is preferably 1 to 10 parts by mass.

From the viewpoint of further suppressing the decrease in discharge capacity during storage of the zinc battery, the content of the indium compound is preferably in the following range per 100 parts by mass of the oxygen-containing compound. The content of the indium compound is preferably 0.1 parts by mass or more, 0.3 parts by mass or more, 0.5 parts by mass or more, 1 part by mass or more, 2 parts by mass or more, 3 parts by mass or more, 4 parts by mass or more, or 5 parts by mass or more. The content of the indium compound is preferably 20 parts by mass or less, 15 parts by mass or less, 10 parts by mass or less, 9 parts by mass or less, 8 parts by mass or less, 7 parts by mass or less, 6 parts by mass or less, or 5 parts by mass or less. From these viewpoints, the content of the indium compound is preferably 0.1 to 20 parts by mass.

The electrolyte may further contain other components such as zinc oxide, antimony oxide, titanium dioxide, and surfactants.

Examples of surfactants include nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants. From the viewpoint of easily suppressing the decrease in discharge capacity when the zinc battery is stored and from the viewpoint of easily obtaining excellent high-rate discharge performance, it is preferable that the surfactant contains at least one selected from the group consisting of nonionic surfactants, anionic surfactants, and cationic surfactants. The surfactant is preferably an embodiment that contains a nonionic surfactant, preferably an embodiment that contains an anionic surfactant, and preferably an embodiment that contains a cationic surfactant.

The electrolyte solution of the above embodiment can be obtained by, for example, blending and mixing an alkali metal hydroxide, an electrolyte that generates chloride ions upon ionization, and, optionally, the optional components described above (electrolytes other than alkali metal hydroxides that generate alkali metal ions upon ionization, electrolytes that generate ammonium ions upon ionization, oxygen-containing compounds, indium compounds, surfactants, etc.) in a liquid medium that is a solvent.

In the above embodiment, an electrolyte that generates alkali metal ions and chloride ions upon ionization may be used as the electrolyte that generates chloride ions upon ionization. Also, an electrolyte that generates chloride ions and ammonium ions upon ionization may be used as the electrolyte that generates chloride ions upon ionization.

Below, we will explain a nickel-zinc battery as an example of a zinc battery in which the electrolyte of the above embodiment can be used.

The zinc battery of one embodiment includes a battery case, an electrode group (e.g., a plate group) and an electrolyte contained in the battery case. The zinc battery of one embodiment may be either chemically formed or unchemically formed.

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. The positive electrode and the negative electrode are adjacent to each other via one or more separators. That is, one or more separators are provided between adjacent positive electrodes and negative electrodes. The electrode group may include multiple positive electrodes, multiple negative electrodes, and multiple separators. When the electrode group includes multiple positive electrodes and/or multiple negative electrodes, the positive electrodes and the negative electrodes may be stacked alternately via separators. The multiple positive electrodes and the multiple negative electrodes may be connected to each other, for example, by straps.

The positive electrode has, for example, a positive electrode current collector and a positive electrode material supported on the positive electrode current collector.

The positive electrode current collector constitutes a conductive path for the current from the positive electrode material. The positive electrode current collector has a shape such as a flat plate or a sheet. The positive electrode current collector may be a collector with a three-dimensional mesh structure composed of foam metal, expanded metal, punching metal, felt-like metal fiber, or the like. The positive electrode current collector is composed of a material having electrical conductivity and alkali resistance. For example, a material that is stable even at the reaction potential of the positive electrode (a material having an oxidation-reduction potential more noble than the reaction potential of the positive electrode, a material that forms a protective film such as an oxide film on the substrate surface in an alkaline aqueous solution to stabilize the substrate, etc.) can be used. In addition, in the positive electrode, a decomposition reaction of the electrolyte proceeds as a side reaction, generating oxygen gas, and a material with a high oxygen overvoltage is preferable in that it can suppress the progression of such a side reaction. Specific examples of materials that constitute the positive electrode current collector include platinum; nickel; and metal materials (copper, brass, steel, etc.) plated with metals such as nickel.

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

The positive electrode material contains a positive electrode active material. Examples of the positive electrode active material include nickel oxyhydroxide (NiOOH) and nickel hydroxide. The positive electrode material contains, for example, 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 95 mass% based on the total mass of the positive electrode material.

The positive electrode material may contain additives. Examples of additives include binders, conductive agents, and expansion inhibitors. Examples of binders include hydrophilic or hydrophobic polymers, such as hydroxypropylmethylcellulose (HPMC), carboxymethylcellulose (CMC), sodium polyacrylate (SPA), and fluorine-based polymers (polytetrafluoroethylene (PTFE)). The content of the binder 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 (metallic cobalt, cobalt oxide, cobalt hydroxide, etc.). The content of the conductive agent 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 has, for example, a negative electrode current collector and a negative electrode material supported on the negative electrode current collector.

The negative electrode current collector constitutes a conductive path for the current from the negative electrode material. The negative electrode current collector has a shape such as a flat plate or a sheet. The negative electrode current collector may be a three-dimensional mesh-structured current collector made of foam metal, expanded metal, punching metal, felt-like metal fiber, or the like. The negative electrode current collector is made of a material having electrical conductivity and alkali resistance. Examples of such materials include materials that are stable even at the reaction potential of the negative electrode (materials having an oxidation-reduction potential more noble than the reaction potential of the negative electrode, materials that form a protective film such as an oxide film on the substrate surface in an alkaline aqueous solution to stabilize the substrate, etc.). In addition, in the negative electrode, a decomposition reaction of the electrolyte proceeds as a side reaction, generating hydrogen gas, and materials with a high hydrogen overvoltage are preferable in that they can suppress the progression of such side reactions. Specific examples of materials that constitute the negative electrode current collector include zinc, lead, tin, and metal materials plated with metals such as tin (copper, brass, steel, nickel, etc.).

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

The negative electrode material contains a negative electrode active material that contains zinc. Examples of negative electrode active materials that contain zinc include metallic zinc, zinc oxide, and zinc hydroxide. 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 content of the negative electrode active material is preferably in the following range based on the total mass of the negative electrode material. From the viewpoint of easily achieving both excellent life performance and discharge performance, the content of the negative electrode active material is preferably 50 mass% or more, more preferably 70 mass% or more, and even more preferably 75 mass% or more. From the viewpoint of easily achieving both excellent life performance and discharge performance, the content of the negative electrode active material is preferably 95 mass% or less, more preferably 90 mass% or less, and even more preferably 85 mass% or less. From these viewpoints, the content of the negative electrode active material is preferably 50 to 95 mass%.

The negative electrode material may contain additives other than the negative electrode active material. Examples of additives include binders and conductive agents. Examples of binders include polytetrafluoroethylene, hydroxyethyl cellulose, polyethylene oxide, polyethylene, and polypropylene. The content of the binder 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 content of the conductive agent 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, for example, a separator having a shape such as a flat plate or a sheet. Examples of the separator include a polyolefin-based microporous membrane, a nylon-based microporous membrane, an oxidation-resistant ion-exchange resin membrane, a cellophane-based recycled resin membrane, an inorganic-organic separator, and a polyolefin-based nonwoven fabric. The separator may be processed into a bag shape so that it can accommodate the positive electrode and/or the negative electrode. In this case, the positive electrode and/or the negative electrode may be accommodated in the separator. The separator may be used alone or in combination of two or more types.

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

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

The raw materials for the positive electrode material include raw materials for the positive electrode active material (e.g., nickel hydroxide), additives (e.g., the binder), etc. The raw materials for the negative electrode material include raw materials for the negative electrode active material (e.g., zinc metal, zinc oxide, and zinc hydroxide), additives (e.g., the indium compound and the binder), etc.

One method for forming the electrode material layer is, for example, to apply or fill an electrode material paste onto a current collector and then dry it to obtain an electrode material layer. If necessary, the density of the electrode material layer may be increased 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 between them, and then the positive and negative electrodes are connected 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 battery case to obtain an unformed zinc battery (nickel-zinc battery).

Then, the electrolyte 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 according to the properties of the electrode active materials (positive and negative active materials).

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.

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

As the air electrode catalyst, one that functions as the positive electrode in an air-zinc battery can be used, and various air electrode catalysts that can use oxygen as a positive electrode active material can be used. Examples of the air electrode catalyst include carbon-based materials (graphite, etc.) that have an oxidation-reduction catalytic function, metal materials (platinum, nickel, etc.) that have an oxidation-reduction catalytic function, and inorganic oxide materials (perovskite-type oxides, manganese dioxide, nickel oxide, cobalt oxide, spinel oxide, etc.) that have an oxidation-reduction catalytic function. The shape of the air electrode catalyst is not particularly limited, but may be, for example, particulate. The amount of the air electrode catalyst used in the air electrode may be 5 to 70 volume % of the total volume of the air electrode, 5 to 60 volume %, or 5 to 50 volume %.

As the electronically conductive material, a material that has electrical conductivity and enables electronic conduction between the air electrode catalyst and the separator can be used. Examples of the electronically conductive material include carbon blacks such as ketjen black, acetylene black, channel black, furnace black, lamp black, and thermal black; graphites such as natural graphite such as flake graphite, artificial graphite, and expanded graphite; conductive fibers such as carbon fibers and metal fibers; metal powders such as copper, silver, nickel, and aluminum; organic electronically conductive materials such as polyphenylene derivatives; and any mixtures thereof. The shape of the electronically conductive material may be particulate or may be other shapes. It is preferable that the electronically conductive material is used in a form that provides a continuous phase in the thickness direction in 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 complex with the air electrode catalyst, and may be an air electrode catalyst that also functions as an electronically conductive material as described above. The amount of electronically conductive material used in the air electrode may be 10-80% by volume, 15-80% by volume, or 20-80% by volume, based on the total volume of the air electrode.

A known silver oxide electrode used in silver-zinc batteries can be used as the silver oxide electrode of the silver-zinc battery. The silver oxide electrode includes, for example, silver(I) oxide.

The present invention will be specifically explained below with reference to examples. However, the present invention is not limited to the following examples.

<Preparation of Electrolyte Solution>
Electrolyte solutions 1 to 6 were prepared by mixing ion-exchanged water, potassium hydroxide (KOH), lithium hydroxide (LiOH), and additives shown in Table 1 below in the amounts shown in Table 1. The amounts shown in Table 1 are amounts (unit: mass%) based on the total mass of the electrolyte solution. Triron X-100 manufactured by Sigma-Aldrich and RA-600 manufactured by Rhodafac were used as surfactants.

Example 1
[Preparation of Positive Electrode]
A lattice body made of foamed nickel with a porosity of 95% was prepared, and the lattice body was pressure-molded to obtain a positive electrode current collector. Next, a predetermined amount of cobalt-coated nickel hydroxide powder, metal cobalt, cobalt hydroxide, yttrium oxide, CMC (carboxymethylcellulose), PTFE (polytetrafluoroethylene), and ion-exchanged water were weighed and mixed, and the mixed liquid was stirred to prepare a positive electrode material paste. At this time, the mass ratio of the solid content was adjusted to "nickel hydroxide: metal cobalt: yttrium oxide: cobalt hydroxide: CMC: PTFE = 88: 10.3: 1: 0.3: 0.3: 0.1". The moisture content of the positive electrode material paste was adjusted to 27.5 mass% based on the total mass of the positive electrode material paste. Next, the positive electrode material paste was applied to the positive electrode material support part of the positive electrode current collector, and then dried at 80 ° C. for 30 minutes. Then, pressure molding was performed with a roll press to obtain an unformed positive electrode having a positive electrode material layer.

[Preparation of negative electrode]
A tin-plated steel plate punching metal with an aperture ratio of 60% was prepared as a negative electrode current collector. Next, zinc oxide, metal zinc, HEC (hydroxyethyl cellulose) and ion-exchanged water were weighed and mixed in a predetermined amount, and the resulting mixture was stirred to prepare a negative electrode material paste. At this time, the mass ratio of the solid content was adjusted to "zinc oxide: metal zinc: HEC = 85: 11.5: 3.5". AV-15F (product name) manufactured by Sumitomo Seika Chemicals Co., Ltd. was used as the HEC. The moisture 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 onto the negative electrode current collector and then dried at 80 ° C. for 30 minutes. Thereafter, pressure molding was performed with a roll press to obtain an unformed negative electrode having a negative electrode material (negative electrode material layer).

[Preparation of separator]
For the separator, UP3355 (manufactured by Ube Industries, Ltd., product name, air permeability: 440 sec/100 mL) was used as the microporous membrane, and nonwoven fabric (manufactured by Nippon Kodoshi Kogyo Co., Ltd., product name: VL-100, air permeability: 0.3 sec/100 mL) was used as the nonwoven fabric. The microporous membrane was hydrophilized with a surfactant Triton-X100 (manufactured by Sigma-Aldrich Japan LLC) before the battery was assembled. The hydrophilization was performed by immersing the microporous 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 microporous membrane indicates the value after the hydrophilization treatment. Furthermore, the microporous membrane was cut to a predetermined size, folded in half, and processed into a bag shape by heat welding the sides. The nonwoven fabric was cut to a predetermined size.

[Preparation of nickel-zinc battery]
A positive electrode (unformed positive electrode) and a negative electrode (unformed negative electrode) were housed in a microporous membrane processed into a bag shape. After laminating the positive electrode housed in the bag-shaped microporous membrane, the negative electrode housed in the bag-shaped microporous membrane, and the nonwoven fabric, the electrodes of the same polarity were connected with a strap to prepare an electrode group (electrode plate group). The electrode group was configured with two positive electrodes and three negative electrodes, with one nonwoven fabric placed between the positive electrode and the negative electrode (between the microporous membrane on the positive electrode side and the microporous membrane on the negative electrode side). After placing this electrode group in a battery case, a lid was attached to the top surface of the battery case, and the electrolyte 1 was poured into the battery case to obtain an unformed nickel-zinc battery. Thereafter, charging was performed under conditions of 32 mA and 15 hours to prepare a nickel-zinc battery with a nominal capacity of 320 mAh.

<Examples 2 to 3 and Comparative Examples 1 to 3>
Nickel-zinc batteries were fabricated in the same manner as in Example 1, except that electrolyte solutions 2 to 6 were used instead of electrolyte solution 1, respectively.

<Characteristics evaluation>
The cycle life performance and high rate discharge performance of the nickel-zinc batteries were evaluated using the nickel-zinc batteries of Examples 1 to 3 and Comparative Examples 1 to 3. The specific evaluation methods are shown below, and the results are shown in Table 2.

[Cycle life performance evaluation]
The test was conducted by charging the nickel-zinc battery at 25° C., 320 mA (1 C), and a constant voltage of 1.9 V until the current value attenuated to 16 mA (0.05 C), and then discharging the nickel-zinc battery at a constant current of 1280 mA (4 C) until the battery voltage reached 1.1 V, which constituted one cycle. The test was terminated when the discharge capacity fell below 80% of the discharge capacity at the first cycle, and the cycle life performance was evaluated based on the number of cycles performed until the end of the test.

Claims (5)

An electrolyte for a zinc battery, comprising an alkali metal hydroxide and chloride ions,
The alkali metal ions include potassium ions and lithium ions,
The content of the potassium ions is 7.0 mol/L or more and 10.0 mol/L or less based on the total amount of the electrolyte,
The electrolyte for a zinc battery has a lithium ion content of 0.3 mol/L or more and 0.8 mol/L or less, based on the total amount of the electrolyte. The electrolyte of claim 1, wherein the alkali metal hydroxide comprises potassium hydroxide. The electrolyte solution according to claim 1 or 2, further comprising an ammonium ion represented by NH ₄ ⁺ . The electrolyte solution according to any one of claims 1 to 3, which is for use in a nickel-zinc battery. A zinc battery comprising the electrolyte solution according to any one of claims 1 to 4.