JP7613845B2 - Zinc battery negative electrode and zinc battery - Google Patents

Description

The present invention relates to a negative electrode for a zinc battery and a zinc battery.

Nickel-zinc batteries (e.g., nickel-zinc secondary batteries) are aqueous batteries that use an aqueous electrolyte such as an aqueous potassium hydroxide solution, and are therefore highly safe. In addition, due to the combination of zinc 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 nickel-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 nickel-zinc batteries, when dendrites grow due to repeated charging and discharging, the dendrites penetrate the separator and cause a short circuit, and the generation of the dendrites leads to a decrease in life performance. In response to this, for example, Patent Document 1 discloses a technology for preventing internal short circuits between positive and negative electrodes caused by zinc dendrites by interposing a nickel-plated nonwoven fabric between the positive and negative electrodes.

Japanese Unexamined Patent Publication No. 58-126665

There is a demand for further improvements in the lifespan performance of zinc batteries, such as nickel-zinc batteries, and there is a need to develop new technologies to improve lifespan performance.

One aspect of the present invention aims to provide a zinc battery anode that can provide excellent life performance in a zinc battery. Another aspect of the present invention aims to provide a zinc battery that includes the zinc battery anode.

One aspect of the present invention relates to a negative electrode for a zinc battery, which has a negative electrode current collector and a negative electrode material supported on the negative electrode current collector, and the negative electrode material contains a negative electrode active material containing zinc and a metal boride.

Another aspect of the present invention relates to a zinc battery comprising the above-mentioned zinc battery negative electrode and a positive electrode.

These zinc battery negative electrodes and zinc batteries can provide excellent life performance in zinc batteries.

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

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 the value shown in the examples. "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 in detail the embodiments of the present invention. However, the present invention is not limited to the following embodiments, and can be modified in various ways within the scope of the gist of the invention.

Examples of the zinc battery (e.g., zinc secondary battery) according to this embodiment include a nickel-zinc battery, an air-zinc battery, and a silver-zinc battery. The basic configuration of the zinc battery according to this embodiment can be the same as that of a conventional zinc battery. The zinc battery according to this embodiment may be either before or after chemical formation.

The zinc battery according to this embodiment includes a negative electrode (negative electrode for zinc batteries, e.g., a negative electrode plate) and a positive electrode (positive electrode for zinc batteries, e.g., a positive electrode plate). The zinc battery according to this embodiment may have an electrode group consisting of multiple negative electrodes and multiple positive electrodes. The negative electrodes and positive electrodes are alternately stacked, for example, with the main surface of the negative electrode facing the main surface of the positive electrode, with a separator interposed between them. The electrode group may include a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode. The negative electrode and the positive electrode face each other with the separator interposed between them. The multiple negative electrodes and the multiple positive electrodes may be connected to each other, for example, with a strap.

The negative electrode (negative electrode for zinc batteries) has a negative electrode current collector and a negative electrode material supported on the negative electrode current collector. The negative electrode material contains a negative electrode active material containing zinc and a metal boride. The positive electrode has a positive electrode current collector and a positive electrode material supported on the positive electrode current collector. Each of the negative electrode and positive electrode may be either before or after chemical formation.

According to this embodiment, the negative electrode material contains a metal boride, so that a zinc battery can obtain excellent life performance. The reason for obtaining such an effect is not clear, but according to the knowledge of the inventor, it is speculated as follows. However, the cause is not limited to the following. That is, in the negative electrode of a zinc battery, the reaction is likely to proceed in the highly electrically conductive part of the negative electrode material, and various problems (generation of dendrites, morphological changes, etc.) occur starting from this part. Therefore, it is required to make the electrical conductivity uniform throughout the negative electrode material. In contrast, in this embodiment, the metal boride tends to have high hardness while having high electrical conductivity. Since the metal boride has high hardness, even if various external forces (shear force, etc.) are applied to the metal boride during the preparation of the negative electrode material, charging and discharging, etc., the crystal structure of the metal boride is not easily broken, so that high electrical conductivity can be stably maintained. As a result, the electrical conductivity can be made uniform throughout the negative electrode material, so that excellent life performance can be obtained.

Below, we will explain a nickel-zinc battery as an example of a zinc battery according to this embodiment.

The zinc battery according to this embodiment includes, for example, a battery case, an electrode group (e.g., a plate group), and an electrolyte. The electrode group and the electrolyte are contained in the battery case. The electrode group includes a negative electrode, a positive electrode, and a separator.

The negative electrode current collector of the negative electrode 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 material of 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 it, 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 progress 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 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 meshes of the negative electrode current collector to form the negative electrode material layer.

The negative electrode material contains a negative electrode active material containing zinc. Examples of the negative electrode active material include metallic zinc, zinc oxide, and zinc hydroxide. For example, the negative electrode material contains metallic zinc in a fully charged state, and contains zinc oxide and zinc hydroxide in an end-of-discharge state. The negative electrode active material may be, for example, in particulate form, and may contain metallic zinc particles, zinc oxide particles, zinc hydroxide particles, and the like.

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 obtaining excellent life performance, the content of the negative electrode active material is preferably 50 mass% or more, more preferably 70 mass% or more, even more preferably 75 mass% or more, particularly preferably 80 mass% or more, extremely preferably 85 mass% or more, and very preferably 90 mass% or more. From the viewpoint of easily obtaining excellent life performance, the content of the negative electrode active material is preferably 99 mass% or less, more preferably 95 mass% or less, and even more preferably 92 mass% or less. From these viewpoints, the content of the negative electrode active material is preferably 50 to 99 mass%.

The negative electrode material contains a metal boride. Examples of the metal boride include titanium boride such as _TiB2 , zirconium boride such as _ZrB2 , niobium boride such as _NbB2 , hafnium boride such as _HfB2 , vanadium boride such as _VB2 , tantalum boride such as _TaB2 , chromium boride such as CrB, _CrB2 , _molybdenum boride such as MoB, _MoB2 , _Mo2B5 , lanthanum boride such as _LaB6 , praseodymium boride such as _PrB6 , neodymium boride such as _NdB6 , cerium boride such as _CeB6 , yttrium boride such as _YB6 , and tungsten _boride such as _W2B5 .

From the viewpoint of easily obtaining excellent life performance, the y/x (molar ratio) of the chemical formula M _x B _y (M: metal element, B: boron) in the metal boride is preferably in the following range. y/x is preferably greater than 1, and more preferably 2 or more. y/x is preferably 6 or less, more preferably 5 or less, even more preferably 3 or less, particularly preferably 2.5 or less, and extremely preferably 2 or less. From these viewpoints, y/x is preferably greater than 1 and less than 6, more preferably greater than 1 and less than 2.5, and even more preferably 2.

From the viewpoint of easily obtaining excellent life performance, the metal boride preferably contains at least one selected from the group consisting of titanium boride, zirconium boride, niobium boride, hafnium boride, vanadium boride, tantalum boride, chromium boride, and molybdenum boride, more preferably contains at least one selected from the group consisting of titanium boride, zirconium boride, niobium boride, and hafnium boride, and even more preferably contains at least one selected from the group consisting of titanium boride, zirconium boride, and niobium boride. The metal boride may not contain zinc. The negative electrode may have a negative electrode material (e.g., a negative electrode material layer) that contains a metal boride and is in contact with the negative electrode current collector.

From the viewpoint of easily obtaining excellent life performance, the content of the metal boride is preferably in the following range per 100 parts by mass of the negative electrode active material. The content of the metal boride is more than 0 parts by mass, preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, particularly preferably 2 parts by mass or more, extremely preferably 3 parts by mass or more, very preferably 4 parts by mass or more, and even more preferably 5 parts by mass or more. The content of the metal boride is preferably 100 parts by mass or less, more preferably less than 100 parts by mass, even more preferably 50 parts by mass or less, especially preferably 30 parts by mass or less, extremely preferably 10 parts by mass or less, very preferably 8 parts by mass or less, and even more preferably 6 parts by mass or less. From these viewpoints, the content of the metal boride is preferably 0.1 to 100 parts by mass, more preferably 0.1 parts by mass or more and less than 100 parts by mass, and even more preferably 0.5 to 10 parts by mass.

From the viewpoint of easily obtaining excellent life performance, the content of the metal boride is preferably in the following range based on the total mass (solid content) of the negative electrode material. The content of the metal boride is more than 0 mass%, preferably 0.1 mass% or more, more preferably 0.5 mass% or more, even more preferably 1 mass% or more, particularly preferably 2 mass% or more, extremely preferably 3 mass% or more, very preferably 4 mass% or more, and even more preferably 5 mass% or more. The content of the metal boride is preferably 50 mass% or less, more preferably less than 50 mass%, more preferably 30 mass% or less, even more preferably 10 mass% or less, extremely preferably 8 mass% or less, very preferably 6 mass% or less, and even more preferably 5 mass% or less. From these viewpoints, the content of the metal boride is preferably 0.1 to 50 mass%, more preferably 0.1 to 30 mass%, and even more preferably 0.5 to 10 mass%.

The negative electrode material may contain additives other than the negative electrode active material and the metal boride. Examples of additives include a binder and a conductive agent. Examples of binders include polytetrafluoroethylene, hydroxyethyl cellulose (HEC), carboxymethyl 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 positive electrode current collector of the positive electrode 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 constituted by foam metal, expanded metal, punching metal, felt-like metal fiber, or the like. The positive 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 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 it, 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 current 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 current collector made of foamed nickel is preferable.

The positive electrode material may be in a layered form (positive electrode material layer). For example, the positive electrode material layer may be formed on the 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 meshes of the positive electrode current collector to form the positive electrode material layer.

The positive electrode material contains a positive electrode active material. The positive electrode active material may contain 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 99 mass% based on the total mass of the positive electrode material.

The positive electrode material may contain additives other than the positive electrode active material. Examples of additives include a binder, a conductive agent, an expansion inhibitor, and a rare earth metal compound (e.g., yttrium oxide). Examples of binders include hydrophilic or hydrophobic polymers, such as hydroxyethyl cellulose (HEC), hydroxypropyl methyl cellulose (HPMC), carboxymethyl cellulose (CMC), sodium polyacrylate (SPA), and fluorine-based polymers (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.

Materials for the separator include organic materials (resin materials, etc.) and inorganic materials. Resin materials include polyamide-based polymers (e.g., polyamide), olefin-based polymers (polyolefins), nylon-based polymers (e.g., nylon), etc. Inorganic materials include oxides such as alumina, titania, and silicon dioxide; nitrides such as aluminum nitride and silicon nitride; and sulfates such as barium sulfate and calcium sulfate. The separator may be an ion-exchange resin membrane, a cellophane-based recycled resin membrane, an inorganic-organic separator, a polyolefin-based nonwoven fabric, etc. Methods for manufacturing the separator include a wet method (phase separation method), a dry method (stretching and perforating method), melt-blowing, electrospinning, etc.

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

The electrolyte contains, for example, a solvent and an electrolyte. Examples of the solvent include water (e.g., ion-exchanged water). Examples of the electrolyte include basic compounds, such as alkali metal hydroxides such as potassium hydroxide (KOH), sodium hydroxide (NaOH), and lithium hydroxide (LiOH). The zinc battery according to this embodiment can be used as an alkaline zinc battery using an alkaline electrolyte. The electrolyte may contain components other than the solvent and electrolyte, such as potassium phosphate, potassium fluoride, potassium carbonate, sodium phosphate, sodium fluoride, sodium hydroxide, lithium hydroxide, zinc oxide, antimony oxide, titanium dioxide, nonionic surfactants, anionic surfactants, etc.

The manufacturing method of the zinc battery (nickel-zinc battery) according to this embodiment includes, for example, an electrode manufacturing process for obtaining electrodes (positive and negative electrodes) and an assembly process for assembling components including the electrodes to obtain a zinc battery (nickel-zinc battery).

In the electrode manufacturing process, electrodes (positive and negative electrodes) are manufactured. For example, a solvent (e.g., water) is added to the raw materials of the electrode materials (positive and negative electrode materials) and kneaded to obtain an electrode material paste (a paste-like electrode material), and then the electrode material paste is used to form an electrode material layer.

Positive electrode raw materials include positive electrode active material raw materials (e.g., nickel hydroxide), additives (e.g., binders), etc. Negative electrode raw materials include negative electrode active material raw materials (e.g., zinc metal, zinc oxide, and zinc hydroxide), additives (e.g., binders), 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 electrode manufacturing process are first stacked alternately with separators between them, and the positive electrodes and negative electrodes are connected with straps to form 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).

Next, the electrolyte is poured into the battery case of the unformed zinc battery and left for a certain period of time. Next, 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).

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments. For example, in the above-mentioned embodiments, an example of a nickel-zinc battery (e.g., a nickel-zinc secondary battery) in which the positive electrode is a nickel electrode has been described, but the zinc battery may 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 content of the air electrode catalyst in the air electrode may be 5 to 70 volume % relative to 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 content of the electronically conductive material in the air electrode may be 10 to 80% by volume, 15 to 80% by volume, or 20 to 80% by volume, 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 negative electrode>
Example 1
As a negative electrode current collector, a tin-plated punched copper metal plate (porosity: 55% by volume) was prepared.
Next, zinc oxide (ZnO), zinc metal (Zn), titanium diboride (TiB ₂ ), and hydroxyethyl cellulose (HEC, product name: AV-15F, manufactured by Sumitomo Seika Chemicals Co., Ltd.) were weighed in predetermined amounts. These components were mixed with ion-exchanged water, and the resulting mixture was stirred to prepare a negative electrode material paste. The mass ratio (solid content) of each component was adjusted to "zinc oxide:zinc metal:titanium diboride:HEC=80:11.5:5:3.5". 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 material support portion, and then dried for 30 minutes at 80° C. Thereafter, pressure molding was performed using a roll press to obtain an unformed negative electrode having a negative electrode material (negative electrode material layer).

Example 2
A negative electrode was obtained in the same manner as in Example 1, except that titanium diboride was changed to zirconium diboride (ZrB ₂ ).

Example 3
A negative electrode was obtained in the same manner as in Example 1, except that titanium diboride was changed to niobium diboride (NbB ₂ ).

(Comparative Example 1)
A negative electrode was obtained in the same manner as in Example 1, except that titanium diboride was changed to bismuth trioxide (Bi ₂ O ₃ ).

(Comparative Example 2)
A negative electrode was obtained in the same manner as in Example 1, except that titanium diboride was changed to indium trioxide (In ₂ O ₃ ).

<Preparation of Positive Electrode>
A grid made of foamed nickel (porosity: 95% by volume) was 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, carboxymethylcellulose (CMC), polytetrafluoroethylene (PTFE), and ion-exchanged water were weighed. The mixture obtained by mixing these components was stirred to prepare a positive electrode paste. The mass ratio (solid content) of each component was adjusted to "nickel hydroxide: metallic cobalt: yttrium oxide: cobalt hydroxide: CMC: PTFE = 88: 10.3: 1: 0.3: 0.3: 0.1". The moisture content of the positive electrode paste was adjusted to 27.5 mass% based on the total mass of the positive electrode 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 for 30 minutes at 80° C. Thereafter, pressure molding was performed using a roll press to obtain an unformed positive electrode having a positive electrode material (positive electrode material layer).

<Preparation of Electrolyte Solution>
An electrolyte solution (potassium hydroxide concentration: 30 mass %, lithium hydroxide concentration: 1 mass %) was prepared by mixing potassium hydroxide (KOH) and lithium hydroxide (LiOH) with ion-exchanged water.

<Preparing the separator>
As the separator, a microporous membrane, Celgard 2500 (manufactured by POLYPORE International, Inc.), and a nonwoven fabric, VL100 (manufactured by Nippon Kodoshi Kogyo Co., Ltd.), were prepared. 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 25°C for 1 hour. Furthermore, the microporous membrane was cut to a predetermined size, folded in half, and processed into a bag shape by heat welding the sides. One positive electrode (unformed positive electrode) was stored in the bag-shaped microporous membrane, and similarly, one negative electrode (unformed negative electrode) was stored in the bag-shaped microporous membrane. The nonwoven fabric was cut to a predetermined size.

<Preparation of nickel-zinc battery>
Two of the above-mentioned positive electrodes, each housed in a bag-shaped microporous membrane, and three of the above-mentioned negative electrodes, each housed in a bag-shaped microporous membrane, were alternately stacked, the above-mentioned nonwoven fabric was sandwiched between the positive and negative electrodes, and the plates of the same polarity were connected with a strap to prepare an electrode group (electrode plate group). 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, an electrolyte was poured into the battery case of the unformed nickel-zinc battery, and the battery was left for 24 hours. After that, charging was performed under the conditions of 25 mA and 15 hours to prepare a nickel-zinc battery with a nominal capacity of 320 mAh.

<Evaluation of life performance>
The nickel-zinc battery was charged at 25°C, 320mA (1C), and a constant voltage of 1.9V until the current value attenuated to 16mA (0.05C), and then discharged at a constant current of 1280mA (4C) until the battery voltage reached 1.1V, forming one cycle. The test was terminated when the discharge capacity fell below 80% 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 was 112 in Example 1, 104 in Example 2, 95 in Example 3, 78 in Comparative Example 1, and 82 in Comparative Example 2.

Claims (6)

A negative electrode current collector and a negative electrode material supported on the negative electrode current collector,
The negative electrode material contains a negative electrode active material containing zinc and a metal boride,
The content of the metal boride is 0.1 to 50 mass% based on the total mass of the negative electrode material,
The negative electrode for a zinc secondary battery, wherein the metal boride comprises at least one selected from the group consisting of titanium boride, zirconium boride, niobium boride, hafnium boride, tantalum boride, chromium boride and molybdenum boride. The negative electrode for zinc secondary batteries according to claim 1, wherein the content of the metal boride is 0.5 to 10 parts by mass per 100 parts by mass of the negative electrode active material. A negative electrode current collector and a negative electrode material supported on the negative electrode current collector,
The negative electrode material contains a negative electrode active material containing zinc and a metal boride,
The content of the metal boride is 0.1 to 50 mass% based on the total mass of the negative electrode material,
The content of the metal boride is 0.5 to 10 parts by mass per 100 parts by mass of the negative electrode active material. 4. The negative electrode for zinc secondary batteries according to claim 1, wherein y/x in the chemical formula M _x B _y (M: metal element, B: boron) in the metal boride is 2. A zinc secondary battery comprising the negative electrode for zinc secondary batteries according to any one of claims 1 to 4 and a positive electrode. The zinc secondary battery according to claim 5 which is a nickel-zinc secondary battery.