JP7797448B2 - 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, making them highly safe. Furthermore, due to the combination of zinc electrodes and nickel electrodes, they are known to have a high electromotive force for an aqueous battery. Furthermore, because nickel-zinc batteries have 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 considered.

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, zinc hydroxide (Zn(OH) ₂ ) is produced by the discharge reaction in zinc batteries. Zinc hydroxide is soluble in the electrolyte, and when zinc hydroxide dissolves in the electrolyte, tetrahydroxide zincate 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 conventional zinc batteries, when dendrites grow due to repeated charge and discharge, they may penetrate the separator, causing a short circuit. Therefore, various attempts have been made to prevent such short circuits caused by dendrites and improve battery life. For example, Patent Document 1 below discloses a technology for preventing short circuits caused by dendrites by inserting a nickel-plated nonwoven fabric between electrodes.

Japanese Unexamined Patent Publication No. 58-126665

When charging and discharging nickel-zinc batteries, side reactions such as decomposition of the electrolyte may occur. Since the occurrence of side reactions leads to a decrease in battery life performance, it is necessary to suppress these side reactions. Furthermore, in addition to improving battery life performance, zinc batteries are also required to improve their high-rate discharge performance.

The present invention therefore aims to provide a zinc battery that has excellent high-rate discharge performance and suppresses side reactions during charging and discharging.

One aspect of the present invention provides an electrolyte for zinc batteries that is an aqueous solution containing potassium hydroxide and at least one selected from the group consisting of sodium hydroxide and lithium hydroxide. This electrolyte can improve the high-rate discharge performance of zinc batteries and suppress the occurrence of side reactions during charging and discharging.

A zinc battery according to another aspect of the present invention comprises the above-described electrolyte. This zinc battery exhibits excellent high-rate discharge performance and is less susceptible to side reactions during charging and discharging.

The zinc battery preferably further comprises one or more separators having a total air permeability of 500 to 2500 sec/100 mL, and a positive electrode and a negative electrode adjacent to each other via the one or more separators. When the total air permeability of the separators disposed between adjacent positive and negative electrodes is within the above range, the occurrence of short circuits due to dendrites is more likely to be suppressed, making it easier to achieve better life performance (e.g., cycle life performance). Furthermore, in the present invention, because the amount of oxygen generated as a result of side reactions (decomposition reactions of the electrolyte) is reduced, even if the total air permeability of the separators is within the above range, the amount of oxygen released to the outside of the system without being absorbed by the negative electrode is small. In other words, electrolyte loss is less likely to occur.

It is preferable that at least one of the one or more separators has an air permeability of 0.1 to 150 sec/100 mL. In this case, better high-rate discharge performance and lifespan are likely to be achieved.

The present invention provides a zinc battery that has excellent high-rate discharge performance and suppresses side reactions during charging and discharging.

In this specification, numerical ranges indicated using "to" indicate ranges that include the numerical values before and after "to" as the minimum and maximum values, respectively. 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 that numerical range may be replaced with a value shown in an experimental example. "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 used refers to the total amount of those multiple substances present in the composition, unless otherwise specified. Furthermore, in this specification, the terms "film" and "layer" encompass structures that are formed over the entire surface as well as structures that are formed only partially when observed in a plan view. Furthermore, in this specification, the term "process" does not only refer to an independent process, but also includes processes 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.

<Electrolyte for zinc batteries>
[First embodiment]
The electrolytic solution of the first embodiment is an aqueous solution containing potassium hydroxide and sodium hydroxide as electrolytes. The potassium hydroxide and sodium hydroxide may be ionized in the aqueous solution or may exist as salts. For example, ion-exchanged water can be used as a solvent for the electrolytic solution.

The concentration (content) of potassium hydroxide in the electrolyte may be 3 mass% or more, 10 mass% or more, or 15 mass% or more, based on the total mass of the electrolyte, in order to further improve high-rate discharge performance. The concentration of potassium hydroxide in the electrolyte may be 35 mass% or less, 30 mass% or less, or 25 mass% or less, based on the total mass of the electrolyte, in order to further suppress side reactions.

The concentration (content) of sodium hydroxide in the electrolyte may be 1% by mass or more, 3% by mass or more, or 5% by mass or more, based on the total mass of the electrolyte, in order to further suppress side reactions. The concentration of sodium hydroxide in the electrolyte may be 25% by mass or less, 15% by mass or less, or 10% by mass or less, based on the total mass of the electrolyte, in order to further improve high-rate discharge performance.

From the viewpoint of achieving even better high-rate discharge performance and further suppressing side reactions, the total content of potassium hydroxide and sodium hydroxide in the electrolyte may be 12% by mass or more, 15% by mass or more, or 18% by mass or more, and may be 35% by mass or less, 30% by mass or less, or 28% by mass or less, based on the total mass of the electrolyte.

From the viewpoint of achieving even better high-rate discharge performance and further suppressing side reactions, the concentration (content) of the electrolyte in the electrolyte solution may be 12% by mass or more, 15% by mass or more, or 18% by mass or more, and may be 35% by mass or less, 30% by mass or less, or 28% by mass or less, based on the total mass of the electrolyte solution.

The electrolyte may further contain potassium phosphate, potassium fluoride, potassium carbonate, sodium phosphate, sodium fluoride, lithium hydroxide, zinc oxide, antimony oxide, titanium dioxide, a nonionic surfactant, an anionic surfactant, etc.

[Second embodiment]
The electrolytic solution of the second embodiment is an aqueous solution containing potassium hydroxide and lithium hydroxide as electrolytes. The potassium hydroxide and lithium hydroxide may be ionized in the aqueous solution or may exist as salts. As a solvent for the electrolytic solution, for example, ion-exchanged water can be used.

The concentration (content) of potassium hydroxide in the electrolyte may be 15% by mass or more, 18% by mass or more, or 20% by mass or more, based on the total mass of the electrolyte, in order to achieve even better high-rate discharge performance. The concentration of potassium hydroxide in the electrolyte may be 35% by mass or less, 30% by mass or less, or 25% by mass or less, based on the total mass of the electrolyte, in order to further suppress side reactions.

The concentration (content) of lithium hydroxide in the electrolyte may be 0.01% by mass or more, 0.1% by mass or more, or 0.2% by mass or more, based on the total mass of the electrolyte, in order to further suppress side reactions. The concentration of lithium hydroxide in the electrolyte may be 10% by mass or less, 5% by mass or less, or 3% by mass or less, based on the total mass of the electrolyte, in order to further improve high-rate discharge performance.

From the viewpoint of achieving even better high-rate discharge performance and further suppressing side reactions, the total content of potassium hydroxide and lithium hydroxide in the electrolyte may be 12% by mass or more, 15% by mass or more, or 18% by mass or more, and may be 35% by mass or less, 30% by mass or less, or 28% by mass or less, based on the total mass of the electrolyte.

From the viewpoint of achieving even better high-rate discharge performance and further suppressing side reactions, the concentration (content) of the electrolyte in the electrolyte solution may be 12% by mass or more, 15% by mass or more, or 18% by mass or more, and may be 35% by mass or less, 30% by mass or less, or 28% by mass or less, based on the total mass of the electrolyte solution.

The electrolyte may further contain potassium phosphate, potassium fluoride, potassium carbonate, sodium phosphate, sodium fluoride, sodium hydroxide, zinc oxide, antimony oxide, titanium dioxide, a nonionic surfactant, an anionic surfactant, etc.

[Third embodiment]
The electrolytic solution of the third embodiment is an aqueous solution containing potassium hydroxide, sodium hydroxide, and lithium hydroxide as electrolytes. The potassium hydroxide, sodium hydroxide, and lithium hydroxide may be ionized in the aqueous solution or may exist as salts. As a solvent for the electrolytic solution, for example, ion-exchanged water can be used.

The concentration (content) of potassium hydroxide in the electrolyte may be 3 mass% or more, 10 mass% or more, or 15 mass% or more, based on the total mass of the electrolyte, in order to further improve high-rate discharge performance. The concentration of potassium hydroxide in the electrolyte may be 35 mass% or less, 30 mass% or less, or 25 mass% or less, based on the total mass of the electrolyte, in order to further suppress side reactions.

The concentration (content) of sodium hydroxide in the electrolyte may be 1% by mass or more, 3% by mass or more, or 5% by mass or more, based on the total mass of the electrolyte, in order to further suppress side reactions. The concentration of sodium hydroxide in the electrolyte may be 25% by mass or less, 15% by mass or less, or 10% by mass or less, based on the total mass of the electrolyte, in order to further improve high-rate discharge performance.

The concentration (content) of lithium hydroxide in the electrolyte may be 0.01% by mass or more, 0.1% by mass or more, or 0.2% by mass or more, based on the total mass of the electrolyte, in order to further suppress side reactions. The concentration of lithium hydroxide in the electrolyte may be 10% by mass or less, 5% by mass or less, or 3% by mass or less, based on the total mass of the electrolyte, in order to further improve high-rate discharge performance.

From the viewpoint of achieving even better high-rate discharge performance and further suppressing side reactions, the total content of potassium hydroxide, sodium hydroxide, and lithium hydroxide in the electrolyte may be 12% by mass or more, 15% by mass or more, or 18% by mass or more, and may be 35% by mass or less, 30% by mass or less, or 25% by mass or less, based on the total mass of the electrolyte.

The concentration (content) of the electrolyte in the electrolyte solution may be 12% by mass or more, 15% by mass or more, or 18% by mass or more, based on the total mass of the electrolyte solution, from the viewpoints of achieving even better high-rate discharge performance and further suppressing side reactions, and may be 35% by mass or less, 30% by mass or less, or 25% by mass or less.

The electrolyte may further contain potassium phosphate, potassium fluoride, potassium carbonate, sodium phosphate, sodium fluoride, zinc oxide, antimony oxide, titanium dioxide, a nonionic surfactant, an anionic surfactant, etc.

The electrolyte solutions of the first to third embodiments described above are electrolyte solutions for zinc batteries that are incorporated into zinc batteries (e.g., zinc secondary batteries). Examples of zinc batteries include nickel-zinc batteries and zinc-air batteries. Zinc batteries can use zinc negative electrodes. Below, we will explain a nickel-zinc battery as an example of a zinc battery that can use the electrolyte solutions of the above embodiments.

<Nickel-zinc battery>
The nickel-zinc battery (e.g., nickel-zinc secondary battery) of this embodiment includes, for example, a battery case, an electrode group (e.g., an electrode plate group) and an electrolyte solution housed in the battery case. The zinc battery of this embodiment may be either 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. The positive electrode and negative electrode are adjacent to each other with one or more separators interposed between them. That is, one or more separators are provided between adjacent positive and negative electrodes. The electrode group may include multiple positive electrodes, negative electrodes, and separators. When the electrode group includes multiple positive electrodes and/or multiple negative electrodes, the positive electrodes and negative electrodes may be stacked alternately with separators interposed between them. The multiple positive electrodes and the multiple negative electrodes may be connected to each other with, for example, straps. In this embodiment, the positive electrode is a nickel (Ni) electrode, and the negative electrode is a zinc (Zn) electrode. That is, in the following description, "positive electrode" may be replaced with "nickel electrode," and "negative electrode" may be replaced with "zinc electrode." The same applies to terms such as "positive electrode material" and "negative electrode material."

The positive electrode includes, for example, a positive electrode current collector and a positive electrode material supported on the positive electrode current collector. The positive electrode may be either pre- or post-chemical formation.

The positive electrode current collector forms a conductive path for current from the positive electrode material. The positive electrode current collector may be, for example, flat or sheet-like. The positive electrode current collector may be a three-dimensional mesh-structured current collector composed of foamed metal, expanded metal, punched metal, or metal fiber felt. The positive electrode current collector is composed of a material that is conductive and alkali-resistant. Examples of such materials include materials that are stable even at the reaction potential of the positive electrode (e.g., materials with a redox potential higher than the reaction potential of the positive electrode, or materials that form a protective coating such as an oxide film on the substrate surface in an alkaline aqueous solution to stabilize the positive electrode). Furthermore, at the positive electrode, a side reaction occurs in which the electrolyte decomposes, generating oxygen gas. Materials with a high oxygen overvoltage are preferred because they can suppress the progression of such side reactions. Specific examples of materials that constitute the positive electrode current collector include platinum; nickel (e.g., foamed nickel); and metal materials (e.g., copper, brass, steel) plated with a metal such as nickel. Among these, a positive electrode current collector composed of foamed nickel is preferred. From the perspective of further improving high-rate discharge performance, it is preferable that at least the portion of the positive electrode current collector that supports the positive electrode material (positive electrode material support portion) be made of foamed nickel.

The positive electrode material may be, for example, layered. That is, the positive electrode may have a positive electrode material layer. The positive electrode material layer may be formed on a positive electrode current collector. If the positive electrode material support portion of the positive electrode current collector has a three-dimensional mesh structure, the positive electrode material may be filled between the meshes of the current collector to form the positive electrode material layer.

The positive electrode material contains a positive electrode active material (electrode active material) containing nickel. Examples of positive electrode active materials 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 further contain components other than the positive electrode active material as additives. Examples of additives include binders, conductive agents, and expansion inhibitors.

Examples of binders include hydrophilic or hydrophobic polymers. Specific examples include carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), hydroxypropyl methyl cellulose (HPMC), sodium polyacrylate (SPA), and fluorine-based polymers (such as polytetrafluoroethylene (PTFE)). The binder content is, for example, 0.01 to 5 parts by mass per 100 parts by mass of the positive electrode active material.

Conductive agents include cobalt compounds (metallic cobalt, cobalt oxide, cobalt hydroxide, etc.). The content of the conductive agent is, 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 is, for example, 0.01 to 5 parts by mass per 100 parts by mass of the positive electrode active material.

The negative electrode comprises a negative electrode current collector (current collector) and a negative electrode material (electrode material) supported on the negative electrode current collector. The negative electrode may be either pre- or post-chemical formation.

The negative electrode current collector forms a conductive path for current from the negative electrode material. The negative electrode current collector may be, for example, flat or sheet-like. The negative electrode current collector may also be a collector with a three-dimensional mesh structure composed of foam metal, expanded metal, punched metal, or metal fiber felt. The negative electrode current collector is made of a material that is conductive and alkali-resistant. Examples of such materials include materials that are stable even at the reaction potential of the negative electrode (e.g., materials with a redox potential higher than the reaction potential of the negative electrode, or materials that form a protective coating such as an oxide film on the substrate surface in an alkaline aqueous solution for stabilization). Furthermore, at the negative electrode, a side reaction occurs in which the electrolyte decomposes, generating hydrogen gas. Materials with a high hydrogen overvoltage are preferred because they can suppress the progression of such side reactions. Specific examples of materials that make up the negative electrode current collector include zinc, lead, tin, and metal materials plated with tin or other metals (e.g., copper, brass, steel, nickel, etc.).

The negative electrode material may be, for example, layered. That is, the negative electrode may have a negative electrode material layer. The negative electrode material layer may be formed on a negative electrode current collector. If the portion of the negative electrode current collector that supports the negative electrode material has a three-dimensional mesh structure, the negative electrode material may be filled between the meshes of the current collector to form the negative electrode material layer.

The negative electrode material contains a negative electrode active material (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 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 is, for example, in particulate form. That is, the negative electrode material may contain at least one particle selected from the group consisting of metallic zinc particles, zinc oxide particles, and zinc hydroxide particles. The content of the negative electrode active material is, for example, 50 to 95% by mass based on the total mass of the negative electrode material.

The negative electrode material may contain additives. Examples of additives include binders and conductive agents.

Examples of binders include polytetrafluoroethylene, hydroxyethyl 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 content of the conductive agent is, 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 flat plate or sheet shape. Examples of separators include polyolefin-based microporous membranes, nylon-based microporous membranes, oxidation-resistant ion-exchange resin membranes, cellophane-based recycled resin membranes, inorganic-organic separators, and polyolefin-based nonwoven fabrics.

From the viewpoint of even better high-rate discharge performance and excellent life performance (e.g., cycle life performance), the total air permeability of the separator is preferably 500 to 2500 sec/100 mL. From the viewpoint of even better cycle life performance, the total air permeability of the separator is more preferably 1000 sec/100 mL or more, even more preferably 1200 sec/100 mL or more, particularly preferably 1300 sec/100 mL or more, and extremely preferably 1350 sec/100 mL or more. From the viewpoint of even better high-rate discharge performance and even better cycle life performance, the total air permeability of the separator is more preferably 2000 sec/100 mL or less, even more preferably 1500 sec/100 mL or less, and particularly preferably 1400 sec/100 mL or less. Here, the total air permeability refers to the air permeability of one separator when there is one separator, and refers to the sum of the air permeabilities of the separators when there are multiple separators. The total air permeability also refers to the sum of the air permeabilities of the separators disposed between adjacent positive and negative electrodes. That is, even when an electrode group includes multiple separators, if there is only one separator disposed between adjacent positive and negative electrodes, the total air permeability refers to the air permeability of one separator. When an electrode group includes multiple positive electrodes and/or multiple negative electrodes, it is preferable that the total air permeability of the separators disposed in at least one space formed between adjacent positive and negative electrodes falls within the above range, and it is more preferable that the total air permeability of the separators disposed in all spaces falls within the above range.

The air permeability is a measure of the air permeability through a membrane, and can be expressed as the number of seconds it takes for a certain volume of air to pass through a membrane of a certain area under a certain pressure difference using a Gurley tester. The air permeability of a separator can be measured using a Gurley densometer (for example, manufactured by Yasuda Seiki Seisakusho Co., Ltd., product name: No. 323 GURLEY TYPE DENSOMETER, membrane area: 642 mm ² (diameter: 28.6 mm)).

When the total air permeability of the separators is 500 to 2500 sec/100 mL, it is preferable that at least one of the separators has an air permeability of 0.1 to 150 sec/100 mL. In this case, better high-rate discharge performance and lifespan performance are likely to be achieved. The air permeability of the separator is more preferably 5.0 sec/100 mL or more, even more preferably 40 sec/100 mL or more, and particularly preferably 80 sec/100 mL or more, in order to more easily achieve better high-rate discharge performance and lifespan performance. The air permeability of the separator is more preferably 140 sec/100 mL or less, even more preferably 130 sec/100 mL or less, and particularly preferably 100 sec/100 mL or less, in order to more easily achieve better high-rate discharge performance and lifespan performance.

The number of separators provided between adjacent positive and negative electrodes is not particularly limited, but three is preferred. Of the three separators, the separator located on the positive electrode side and the separator located on the negative electrode side are preferably microporous membranes, and the separator located in the middle is preferably a nonwoven fabric. It is more preferred that the separator located in the middle of the three separators has an air permeability of 0.1 to 150 sec/100 mL as described above. In this case, the air permeability of the separator located on the positive electrode side and the separator located on the negative electrode side may be, for example, 500 to 1000 sec/100 mL.

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, and zinc hydroxide), additives (e.g., the 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 other methods.

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 is poured into the battery case of the unformed zinc battery and left for a certain period of time. The battery is then 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 and negative electrode 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.

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 shape of the air electrode catalyst is not particularly limited, but it can be, for example, particulate. The amount of air electrode catalyst used in the air electrode can be 5 to 70% by volume, 5 to 60% by volume, or 5 to 50% by volume of the total amount of the air electrode.

The electron-conductive material may be electrically conductive and allow electron conduction between the air electrode catalyst and the separator. Examples of electron-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 electron-conductive materials such as polyphenylene derivatives; and mixtures of any of these. The electron-conductive material may be in particulate form or other shapes. It is preferable that the electron-conductive material be used in a form that provides a continuous phase through the thickness of the air electrode. For example, the electron-conductive material may be a porous material. The electron-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 electron-conductive material. The amount of electronically conductive material used 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 invention will be explained in more detail below using experimental examples, but the present invention is not limited to the following experimental examples.

[Preparation of nonwoven fabric]
The following nonwoven fabrics 1 to 6 were prepared.
Nonwoven fabric 1 (manufactured by Nippon Kodoshi Kogyo Co., Ltd., product name: VL-100, air permeability: 0.3 sec/100 mL)
Nonwoven fabric 2 (Oji F-Tex Co., Ltd., air permeability: 5.4 sec/100 mL)
Nonwoven fabric 3 (manufactured by Daio Paper Co., Ltd., product name: Ryuo moisture-resistant, air permeability: 46.6 sec/100 mL)
Nonwoven fabric 4 (manufactured by Daio Paper Co., Ltd., product name: foil base paper, air permeability: 84.3 sec/100 mL)
Nonwoven fabric 5 (manufactured by Daio Paper Co., Ltd., product name: Kinshachi, air permeability: 133.6 sec/100 mL)
Nonwoven fabric 6 (manufactured by Daio Paper Co., Ltd., product name: Ryuo Moisture-Resistant ST, air permeability: 146.2 sec/100 mL)

(Experimental Example 1)
[Preparation of Electrolyte Solution]
Potassium hydroxide (KOH) and sodium hydroxide (NaOH) were added as electrolytes to ion-exchanged water and mixed to prepare an electrolytic solution (potassium hydroxide concentration: 17.6 mass %, sodium hydroxide concentration: 6.0 mass %).

[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, PTFE, and ion-exchanged water were weighed and mixed, and the mixture was stirred to prepare a positive electrode material 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 material paste was adjusted to 27.5% by 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 portion of the positive electrode current collector and then dried at 80 ° C for 30 minutes. The mixture was then pressure-molded using a roll press to obtain an unformed positive electrode having a positive electrode material layer.

[Preparation of negative electrode]
A tin-plated punched steel sheet with a porosity of 60% was prepared as a negative electrode current collector. Next, predetermined amounts of zinc oxide, metallic zinc, HEC, and ion-exchanged water were weighed and mixed, and the resulting mixture was stirred to prepare a negative electrode material paste. The mass ratio of the solids was adjusted to "zinc oxide: metallic zinc: HEC = 85:11.5:3.5." AV-15F (trade 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 to the negative electrode current collector and then dried at 80°C for 30 minutes. This was then pressure-molded using a roll press to obtain an unformed negative electrode having a negative electrode material (negative electrode material layer).

<Preparing the separator>
For the separator, UP3355 (trade name, manufactured by Ube Industries, Ltd., air permeability: 638 sec/100 mL) was used as the microporous membrane, and Nonwoven Fabric 1 was used as the nonwoven fabric. Prior to battery assembly, the microporous membrane was hydrophilized with a surfactant, Triton-X100 (manufactured by The Dow Chemical Company). The hydrophilization was performed by immersing the microporous membrane in an aqueous solution containing 1% by mass of Triton-X100 for 24 hours, followed by drying at room temperature for 1 hour. The air permeability of the microporous membrane is the value after the hydrophilization treatment. Furthermore, the microporous membrane was cut to a predetermined size, folded in half, and heat-sealed at the sides to form a bag. One positive electrode (unformed positive electrode) and one negative electrode (unformed negative electrode) were housed in each of the microporous membranes processed into a bag shape. The nonwoven fabric was cut to a predetermined size before use.

<Preparation of nickel-zinc battery>
A positive electrode housed in a bag-shaped microporous membrane, a negative electrode housed in a bag-shaped microporous membrane, and a nonwoven fabric were stacked, and then the electrode plates of the same polarity were connected with a strap to prepare an electrode assembly (electrode plate assembly). The electrode assembly consisted of one positive electrode and two negative electrodes, with one nonwoven fabric placed between each of the positive and negative electrodes (between the microporous membrane on the positive electrode side and the microporous membrane on the negative electrode side). This electrode assembly was placed in a battery case, and a lid was attached to the top of the battery case to obtain an unformed nickel-zinc battery. Next, an electrolyte solution was poured into the battery case and left for 24 hours. The battery was then charged at 60 mA for 15 hours to produce a nickel-zinc battery with a nominal capacity of 600 mAh.

(Experimental Examples 2 to 5)
In preparing the electrolyte solution, the electrolyte solution was prepared in the same manner as in Experimental Example 1, except that the type and amount of electrolyte used were changed so that the composition of the electrolyte solution (type and concentration of electrolyte) would be the composition shown in Table 1. A nickel-zinc battery was fabricated in the same manner as in Experimental Example 1, except that the electrolyte solution thus obtained was used.

<Battery performance evaluation 1>
The nickel-zinc batteries of Experimental Examples 1 to 5 were evaluated for coulombic efficiency and discharge performance.

(Coulombic efficiency evaluation)
A nickel-zinc battery with an SOC of 0% was charged at 40°C and a constant voltage of 1.87 V for 24 hours, and the charge capacity (charged electricity amount) was measured. Next, the nickel-zinc battery was discharged to 1.1 V at a constant current of 120 mA (0.2 C) at 40°C, and the discharge capacity at 0.2 C was measured. The coulombic efficiency (discharge capacity/charge capacity x 100) was calculated from the obtained charge capacity and discharge capacity. It can be determined that the higher the coulombic efficiency, the more suppressed the side reaction.

The "C" represents the relative magnitude of the current when discharging the rated capacity from a fully charged state at a constant current. The "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."

(Discharge performance evaluation)
The nickel-zinc battery was charged at 25°C, 600 mA (1 C), and a constant voltage of 1.9 V until the current value decayed to 30 mA (0.05 C), and then discharged at constant currents of 30 mA (0.05 C) and 6000 mA (10 C) until the battery voltage reached 1.1 V, and the discharge capacity was measured. The ratio of the discharge capacity at 10 C to the discharge capacity at 0.05 C (discharge capacity ratio (%)) was calculated. The results are shown in Table 1.

(Experimental Example 6)
An electrolyte solution (potassium hydroxide concentration: 30.0 mass %, lithium hydroxide concentration: 1.0 mass %) was prepared by adding potassium hydroxide (KOH) and lithium hydroxide (LiOH) as electrolytes to ion-exchanged water and mixing them. A nickel-zinc battery was fabricated in the same manner as in Experimental Example 1, except that the obtained electrolyte solution was used.

(Experimental Examples 7 to 11)
Nickel-zinc batteries were fabricated in the same manner as in Experimental Example 6, except that nonwoven fabric 1 was replaced with nonwoven fabrics 2 to 6, respectively.

<Battery performance evaluation 2>
The cycle life performance and discharge performance were evaluated for the nickel-zinc batteries of Experimental Examples 6 to 11. The discharge performance was evaluated in the same manner as in Battery Performance Evaluation 1.

(Cycle life performance evaluation)
The nickel-zinc battery was charged at 25°C, 600 mA (1 C), and a constant voltage of 1.9 V until the current value decayed to 30 mA (0.05 C), and then discharged at a constant current of 300 mA (0.5 C) until the battery voltage reached 1.1 V. This test was completed as one cycle. The test was terminated when the discharge capacity fell below 50% 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. The number of cycles performed until the end of the test is shown in Table 2.

Claims (6)

a zinc battery electrolyte solution that is an aqueous solution containing potassium hydroxide and lithium hydroxide;
A plurality of separators having a total air permeability of 500 to 1400 sec/100 mL;
a positive electrode and a negative electrode adjacent to each other with the plurality of separators interposed therebetween ,
The concentration of the potassium hydroxide in the electrolytic solution is 20% by mass or more and 35% by mass or less,
A zinc battery , wherein the concentration of the lithium hydroxide in the electrolyte is 0.2% by mass or more and 3% by mass or less . The zinc battery of claim 1, wherein the current collector in the positive electrode is made of foamed nickel. the positive electrode material in the positive electrode contains a conductive agent,
3. The zinc battery according to claim 1, wherein the conductive agent comprises a cobalt compound. at least one of the plurality of separators is a hydrophilically treated microporous membrane;
The zinc battery according to any one of claims 1 to 3, wherein the hydrophilically treated microporous membrane is in contact with the negative electrode. A zinc battery according to any one of claims 1 to 4, wherein at least one of the plurality of separators has an air permeability of 0.1 to 150 sec/100 mL. the plurality of separators consists of three separators,
The zinc battery according to claim 5, wherein the separator located on the positive electrode side and the separator located on the negative electrode side have an air permeability of 500 to 1000 sec/100 mL.