JP7566452B2 - 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 are 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.

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

As shown in the above formula, in zinc batteries, zinc hydroxide (Zn(OH) ₂ ) is generated by a discharge reaction. Zinc hydroxide is soluble in an electrolyte, and when zinc hydroxide dissolves in the electrolyte, tetrahydroxide zincate 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, and dendrites (dendritic crystals) are generated. In conventional zinc batteries, when dendrites grow due to repeated charging and discharging, the dendrites may penetrate the separator and cause a short circuit. Therefore, various attempts have been made to prevent such short circuits caused by dendrites and improve the life performance. For example, the following Patent Document 1 discloses a technology for preventing short circuits caused by dendrites by interposing a nickel-plated nonwoven fabric between electrodes.

Japanese Unexamined Patent Publication No. 58-126665

When nickel-zinc batteries are charged and discharged, side reactions such as electrolyte decomposition reactions may occur. The occurrence of side reactions leads to a decrease in life performance, so it is necessary to suppress the occurrence of side reactions. In addition to improving life performance, zinc batteries are also required to improve high-rate discharge performance.

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

The zinc battery electrolyte of one aspect of the present invention 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 the zinc battery and suppress the occurrence of side reactions during charging and discharging.

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

It is preferable that the zinc battery 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 through the one or more separators. When the total air permeability of the separators arranged between the adjacent positive and negative electrodes is within the above range, the occurrence of short circuits due to dendrites is easily suppressed, and better life performance (e.g., cycle life performance) is easily obtained. In addition, in the present invention, since the amount of oxygen generated as a result of side reactions (decomposition reaction of the electrolyte) is reduced, even if the total air permeability of the separators is within the above range, the amount of oxygen that is not absorbed by the negative electrode and is discharged to the outside of the system is small. In other words, the electrolyte is less likely to be reduced.

At least one of the one or more separators preferably has an air permeability of 0.1 to 150 sec/100 mL. In this case, it is easier to obtain better high-rate discharge performance and life performance.

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, 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 addition, in this specification, the term "film" or "layer" includes a structure having a shape formed on the entire surface when observed as a plan view, as well as a structure having a shape formed on a part of the surface. In addition, 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.

<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. 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, from the viewpoint of further improving the 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, from the viewpoint of further suppressing side reactions.

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

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, based on the total mass of the electrolyte, from the viewpoint of further improving the high-rate discharge performance and further suppressing side reactions, and may be 35% by mass or less, 30% by mass or less, or 28% by mass or less.

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

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. Potassium hydroxide and lithium hydroxide may be ionized in the aqueous solution or may exist as salts. As the solvent of the electrolytic solution, for example, ion-exchanged water can be used.

The concentration (content) of potassium hydroxide in the electrolyte may be 15 mass% or more, 18 mass% or more, or 20 mass% or more, based on the total mass of the electrolyte, from the viewpoint of further improving the 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, from the viewpoint of further suppressing side reactions.

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

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 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 mass% or more, 15 mass% or more, or 18 mass% or more, and 35 mass% or less, 30 mass% or less, or 28 mass% or less, based on the total mass of the electrolyte solution, from the viewpoint of further improving the high-rate discharge performance and further suppressing side reactions.

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. Potassium hydroxide, sodium hydroxide, and lithium hydroxide may be ionized in the aqueous solution or may exist as salts. As the solvent of 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, from the viewpoint of further improving the 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, from the viewpoint of further suppressing side reactions.

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

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

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 35% by mass or less, 30% by mass or less, or 25% 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, based on the total mass of the electrolyte solution, from the viewpoint of further improving the 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 electrolytes of the first to third embodiments are electrolytes for zinc batteries that are incorporated into zinc batteries (e.g., zinc secondary batteries). Examples of zinc batteries include nickel-zinc batteries and air-zinc batteries. In zinc batteries, a zinc negative electrode can be used. Below, a nickel-zinc battery will be described as an example of a zinc battery in which the electrolytes of the above embodiments can be used.

<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 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, negative electrodes, and separators. When the electrode group includes multiple positive electrodes and/or multiple negative electrodes, the positive electrodes and the negative electrodes may be alternately stacked via separators. The multiple positive electrodes and the multiple negative electrodes may be connected to each other, for example, by 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, the "positive electrode" may be replaced with a "nickel electrode", and the "negative electrode" may be replaced with a "zinc electrode". The same applies to descriptions 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 before or after chemical formation.

The positive electrode collector constitutes a conductive path for the current from the positive electrode material. The positive electrode collector has a shape such as a flat plate or a sheet. The positive electrode collector may be a collector having a three-dimensional mesh structure composed of foam metal, expanded metal, punching metal, felt-like metal fiber, or the like. The positive electrode collector is made 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 as such a material. 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 progress of such a side reaction. Specific examples of materials that constitute the positive electrode collector include platinum; nickel (foamed nickel, etc.); and metal materials (copper, brass, steel, etc.) plated with a metal such as nickel. Among these, a positive electrode collector made of foamed nickel is preferably used. From the viewpoint of further improving the 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) is made of foamed nickel.

The positive electrode material is, 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. When the positive electrode material support part 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 a positive electrode material layer.

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

Examples of binders include hydrophilic or hydrophobic polymers. Specifically, for example, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), hydroxypropyl methyl cellulose (HPMC), sodium polyacrylate (SPA), fluorine-based polymers (polytetrafluoroethylene (PTFE), etc.), etc. can be used as binders. The content of the binder is, 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 is, for example, 1 to 20 parts by mass per 100 parts by mass of the positive electrode active material.

Examples of the expansion inhibitor 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 before or after chemical formation.

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 collector with a three-dimensional mesh structure constituted by foam metal, expanded metal, punching metal, felt-like metal fiber, or the like. The negative electrode current collector is constituted by a material having electrical conductivity and alkali resistance. For example, a material that is stable even at the reaction potential of the negative electrode (a material having an oxidation-reduction potential more noble than the reaction potential of the negative 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 material, etc.) can be used. In addition, in the negative electrode, a decomposition reaction of the electrolyte proceeds as a side reaction, generating hydrogen gas, and a material with a high hydrogen overvoltage is preferable in that it can suppress the progression of such a side reaction. 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 is, 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. When the part 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 the negative electrode active material include metallic zinc, zinc oxide, and zinc hydroxide. The negative electrode active material may contain one of these components alone, or may contain multiple types. 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 a particulate form. That is, the negative electrode material may contain at least one 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 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 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 the conductive agent 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 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.

From the viewpoint of even better high-rate discharge performance and even better 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 means the air permeability of one separator when there is one separator, and means the total air permeability of each separator when there are multiple separators. The total air permeability is the total air permeability of the separators provided between adjacent positive and negative electrodes. That is, even if the electrode group includes multiple separators, if there is only one separator provided between adjacent positive and negative electrodes, the total air permeability means the air permeability of one separator. When the electrode group includes multiple positive electrodes and/or multiple negative electrodes, it is preferable that the total air permeability of the separators provided in at least one space formed between adjacent positive and negative electrodes is within the above range, and it is more preferable that the total air permeability of the separators provided in the space is within the above range in all spaces.

Air permeability is a measure of the permeability of a membrane to air, 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 the Gurley tester method. 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 life performance are easily obtained. 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 that better high-rate discharge performance and life performance are easily obtained. 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 that better high-rate discharge performance and life performance are easily obtained.

The number of separators provided between adjacent positive and negative electrodes is not particularly limited, but is preferably three. 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. Of the three separators, it is more preferable that the separator located in the middle 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 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 binder), etc.

One method for forming the electrode material layer is, for example, to apply or fill an electrode material paste onto a 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 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 described 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 Kodo Paper 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 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, PTFE, 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, a predetermined amount of zinc oxide, metal zinc, HEC and ion-exchanged water were weighed and mixed, 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).

<Preparing the separator>
For the separator, UP3355 (manufactured by Ube Industries, product name, air permeability: 638 sec/100 mL) was used as the microporous membrane, and nonwoven fabric 1 was used as the nonwoven fabric. The microporous membrane was hydrophilized with a surfactant Triton-X100 (manufactured by Dow Chemical Co., Ltd.) 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. Furthermore, the microporous membrane was cut to a predetermined size, folded in half, and heat-sealed on the sides to form a bag. One positive electrode (unformed positive electrode) and one negative electrode (unformed negative electrode) were stored in the microporous membrane 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 laminated, and the plates of the same polarity were connected with a strap to prepare an electrode group (electrode plate group). The electrode group was configured to have one positive electrode and two 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 to obtain an unformed nickel-zinc battery. Next, the electrolyte was poured into the battery case of the unformed nickel-zinc battery, and the battery was left for 24 hours. Then, charging was performed under conditions of 60 mA and 15 hours, and a nickel-zinc battery with a nominal capacity of 600 mAh was prepared.

(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) was the composition shown in Table 1. A nickel-zinc battery was produced 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 rating)
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. From the obtained charge capacity and discharge capacity, the coulombic efficiency (discharge capacity/charge capacity×100) was calculated. It can be determined that the higher the coulombic efficiency, the more the side reaction is suppressed.

The "C" refers to 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 one hour is expressed as "1C", and a current that can discharge the rated capacity in two hours is expressed as "0.5C".

(Discharge performance evaluation)
The nickel-zinc battery was charged at 25°C, 600 mA (1C), and a constant voltage of 1.9 V until the current value attenuated 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)
Potassium hydroxide (KOH) and lithium hydroxide (LiOH) were added as electrolytes to ion-exchanged water and mixed to prepare an electrolytic solution (potassium hydroxide concentration: 30.0 mass%, lithium hydroxide concentration: 1.0 mass%). A nickel-zinc battery was fabricated in the same manner as in Experimental Example 1, except that the obtained electrolytic 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 (1C), and a constant voltage of 1.9 V until the current value attenuated 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. The test was terminated when the discharge capacity fell below 50% of the discharge capacity of 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 (2)

An electrolyte for zinc batteries, which is an aqueous solution containing potassium hydroxide and at least one selected from the group consisting of sodium hydroxide and lithium hydroxide;
A plurality of separators having a total air permeability of 1200 to 1400 sec/100 mL;
A positive electrode and a negative electrode adjacent to each other with the plurality of separators interposed therebetween ,
A zinc battery in which at least one of the plurality of separators has an air permeability of 40 to 100 sec/100 mL (however, this does not include zinc batteries having a separator with an air permeability of 1000 sec/100 mL or more). the plurality of separators comprises three separators,
The zinc battery according to claim 1 , 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 .