Nickel zinc secondary battery

Abstract

To provide a nickel zinc secondary battery which can maintain a capacity as well after cycles.SOLUTION: A nickel zinc secondary battery includes a positive electrode, a negative electrode, and an alkaline electrolyte. The positive electrode includes a positive electrode, a negative electrode, and an alkaline electrolyte. The alkaline electrolyte contains 25 to 45% by mass of an alkali metal hydroxide, and the positive electrode includes particles containing nickel hydroxide in which zinc is dissolved, and the amount of zinc dissolved is 5 to 10% by mass relative to the particles containing nickel hydroxide with zinc in solid solution.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a nickel-zinc secondary battery.

Background Art

[0002] A nickel-zinc secondary battery is known as a battery in which the hydrogen storage alloy negative electrode of a nickel-metal hydride secondary battery is replaced with a negative electrode containing zinc or a zinc compound. Zinc is a material that is rich in resources, inexpensive, and has a low environmental impact. In addition, the nickel-zinc secondary battery has advantages such as a high open-circuit voltage of 1.8 V, a high theoretical energy density, and a high output.

[0003] On the other hand, nickel hydroxide is used as the positive electrode active material. For example, Patent Document 1 discloses a nickel-zinc secondary battery using particles containing nickel hydroxide as the positive electrode active material.

[0004] Nickel hydroxide is also used as the positive electrode in nickel-metal hydride secondary batteries. In nickel-metal hydride secondary batteries, methods such as solid-solubilizing various elements such as Zn, Mg, and Co, or coating with a coating layer containing a cobalt compound have been studied for the purpose of improving the utilization rate and cycle characteristics of nickel hydroxide.

[0005] For example, Patent Document 2 discloses a nickel-metal hydride battery containing nickel hydroxide powder in which 1.5 to 2.8% by mass of zinc is solid-solubilized as the positive electrode active material. In this document, it is said that by setting the solid-solution amount of zinc to 1.5 to 2.8% by mass, swelling of the positive electrode active material can be suppressed while maintaining the packing volume density of nickel hydroxide.

[0006] In addition, adding zinc oxide to the positive electrode binder (see Patent Document 3) or impregnating the positive electrode with a zinc oxide dispersion (see Patent Document 4) has been studied to improve cycle characteristics and charging characteristics at high temperatures.

[0007] Thus, in nickel-metal hydride secondary batteries, solid solution of zinc in nickel hydroxide and the like are generally performed. However, if the amount of solid solution of zinc becomes excessive, a decrease in capacity or the like occurs, so it is common to make it less than 5% by mass with respect to nickel hydroxide.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0009] However, according to the studies of the present inventors, in nickel-zinc secondary batteries, when using nickel hydroxide as described above, it has become clear that the decrease in capacity due to repeated charge and discharge is remarkable and the capacity retention rate after cycling is low.

[0010] An object of the present invention is to provide a nickel-zinc secondary battery having a good capacity retention rate after cycling.

Means for Solving the Problems

[0011] [1] A nickel-zinc secondary battery having a positive electrode, a negative electrode, and an alkaline electrolyte, wherein the alkaline electrolyte contains 25 to 45% by mass of an alkali metal hydroxide, the positive electrode contains particles containing nickel hydroxide in which zinc is solid-solved, and the amount of solid solution of zinc is 5 to 10% by mass with respect to the particles. [2] A nickel-zinc secondary battery having a positive electrode, a negative electrode, and an alkaline electrolyte, wherein the alkaline electrolyte contains 25 to 45% by mass of an alkali metal hydroxide, and the positive electrode contains particles containing nickel hydroxide in which zinc is solid-dissolved, and in the X-ray absorption fine structure (XAFS) spectrum of the K absorption edge of zinc measured by the transmission method of the particles after activation, the intensity of the first peak at 9640 to 9690 eV is 1.9 to 2.3. Nickel-zinc secondary battery. [3] The nickel-zinc secondary battery according to [1] or [2], wherein the total amount of zinc contained in the particles after activation is 10 to 15% by mass based on the total amount of nickel and zinc contained in the particles. [4] The nickel-zinc secondary battery according to any one of [1] to [3], wherein the particles have a base particle containing nickel hydroxide in which zinc is solid-dissolved and a coating layer covering the surface of the base particle and containing a cobalt compound doped with an alkali metal. [5] The nickel-zinc secondary battery according to any one of [1] to [4], wherein the alkaline electrolyte contains zinc ions, and the concentration of the zinc ions in the alkaline electrolyte is 4% by mass or more in terms of zinc oxide. [6] The nickel-zinc secondary battery according to any one of [1] to [5], wherein the total water content contained in the alkaline electrolyte is 1.5 to 2.5 g per 1 Ah of the battery capacity. [Effect of the Invention]

[0012] According to the present invention, a nickel-zinc secondary battery having a good capacity retention rate after cycling can be provided. [Brief Description of the Drawings]

[0013]

Figure 1

Figure 2

Figure 3

BEST MODE FOR CARRYING OUT THE INVENTION

[0014] The inventors mainly focused on the positive electrode active material and studied the reason for the low capacity retention rate after cycling of the nickel-zinc secondary battery. In a nickel-zinc secondary battery, for example, when the concentration of the alkali metal hydroxide in the alkaline electrolyte is 25 to 45% by mass, not only 3 to 8% by mass of the zinc oxide contained in the negative electrode elutes, but zinc hydroxide dissolves more. By repeating charge and discharge cycles in such an electrolyte in which a large amount of zinc ions are dissolved, a decrease in the capacity of nickel hydroxide, which is the positive electrode active material, occurs. It was found that the capacity decrease is caused by the intercalation (invasion) of zinc ions in the electrolyte into the layers of nickel hydroxide, which is a layered compound (also referred to as "zinc poisoning"). The zinc ions that have invaded into the layers of nickel hydroxide not only cause swelling of the positive electrode active material but also inhibit the diffusion of protons, which is a normal charge and discharge reaction, and thus are presumed to reduce the capacity retention rate after cycling.

[0015] On the other hand, in the present invention, by using nickel hydroxide in which 5 to 10% by mass of zinc is solid-dissolved, it has been found that zinc ions are less likely to invade into the layers of the nickel hydroxide, and thereby the decrease in the capacity retention rate after cycling can be suppressed. Although the reason why zinc ions are less likely to invade into the layers of the nickel hydroxide by increasing the solid solution amount of zinc is not clear, it is presumed that the hydrogen bond between the Ni atoms and O atoms in the layers of the nickel hydroxide is strengthened by the solid-dissolved zinc, resulting in a narrower layer spacing.

[0016] Thus, in a nickel-zinc secondary battery using nickel hydroxide in which zinc is solid-soluted in a predetermined amount or more, there is little change in the crystal structure of nickel hydroxide before and after activation. This can be confirmed by the fact that in the X-ray Absorption Fine Structure (XAFS) spectrum of the K absorption edge of zinc in nickel hydroxide in which zinc is solid-soluted, there is little change in the predetermined peak intensity before and after activation. That is, in a conventional battery using nickel hydroxide in which less than 5% by mass of zinc is solid-soluted, the intensity of the first peak at 9640 to 9690 eV in the XAFS spectrum of the K absorption edge of zinc in the nickel hydroxide after activation is likely to significantly decrease compared to before activation and becomes lower than 1.9 (Fig. 3A to be described later). On the other hand, in a battery using nickel hydroxide in which 5 to 10% by mass of zinc is solid-soluted, the intensity of the first peak after activation is as high as 1.9 to 2.3, and there is little decrease in intensity compared to before activation (Fig. 2 to be described later). This suggests that the intrusion of zinc ions in the electrolytic solution into the interlayer of nickel hydroxide is suppressed.

[0017] Hereinafter, the nickel-zinc secondary battery according to the present embodiment will be described. In this specification, the description of "~" means a numerical range including the lower limit and the upper limit which are endpoints unless otherwise specified.

[0018] 1. Nickel-Zinc Secondary Battery Fig. 1 is a perspective view showing a nickel-zinc secondary battery 10 according to an embodiment of the present invention, partially broken. In the figure, a part of the wound body 16 is not shown.

[0019] As shown in Fig. 1, the nickel-zinc secondary battery 10 according to the present embodiment is, for example, a cylindrical battery of FA size, and includes an outer can 12, a sealing body 14, a wound body 16 (electrode group), an electrolytic solution (not shown), an upper insulating member 18, and a lower insulating member 20.

[0020] The outer can 12 is a container for storing the wound body 16, and in this embodiment, it is a bottomed cylindrical container with an open upper end. The outer can 12 has conductivity, and its bottom wall 12A functions as a negative electrode terminal.

[0021] The material constituting the outer can 12 may be any material that has conductivity and corrosion resistance against the electrolytic solution and the electrochemical reaction inside the battery, and usually includes metal materials such as iron and steel.

[0022] The sealing body 14 is fixed to the opening of the outer can 12 via an insulating packing 22, seals the outer can 12, and provides a positive electrode terminal. The sealing body 14 includes a cover plate 24, a valve body 26, and a positive electrode terminal 28.

[0023] The cover plate 24 is a disc-shaped member having conductivity and has a through-hole 24A at the center. The insulating packing 22 has a ring shape surrounding the cover plate 24 and is interposed between the outer can 12 and the sealing body 14. The insulating packing 22 is fixed to the opening edge 12C of the outer can 12 by caulking the opening edge 12C of the outer can 12. Thereby, the cover plate 24 and the insulating packing 22 cooperate with each other to airtightly close the opening of the outer can 12.

[0024] The valve body 26 is a member made of rubber and is disposed on the outer surface of the cover plate 24 so as to close the through-hole 24A.

[0025] The positive electrode terminal 28 is a member having a cylindrical shape with a flange made of metal, and is electrically connected to the outer surface of the cover plate 24 so as to cover the valve body 26. The positive electrode terminal 28 presses the valve body 26 toward the cover plate 24. The positive electrode terminal 28 has a gas vent hole (not shown) opened.

[0026] During normal operation, the through-hole 24A is hermetically closed by the valve body 26. On the other hand, when gas is generated inside the outer can 12 and its internal pressure increases, the valve body 26 is compressed by the internal pressure, opening the through-hole 24A. As a result, gas is released from the inside of the outer can 12 to the outside through the through-hole 24A and the gas vent hole (not shown) of the positive electrode terminal 28. That is, the through-hole 24A, the valve body 26, and the positive electrode terminal 28 form a safety valve for the battery.

[0027] The wound body 16 includes a positive electrode 30, a negative electrode 32, and a separator 34. That is, the wound body 16 is an electrode group wound in a state where the positive electrode 30 and the negative electrode 32 are laminated with the separator 34 in between. Specifically, the wound body 16 is wound by laminating the separator 34, the positive electrode 30, the separator 34, and the negative electrode 32 so that the negative electrode 32 is on the outside.

[0028] The negative electrode 32 is disposed on the outermost peripheral surface of the wound body 16, and the negative electrode 32 is in contact with the inner wall surface of the outer can 12. That is, the negative electrode 32 and the outer can 12, which is the negative electrode terminal, are electrically connected to each other.

[0029] On the other hand, a positive electrode lead 36 is connected to the positive electrode 30 of the wound body 16. One end of the positive electrode lead 36 is connected to the positive electrode 30, and the other end is connected to the cover plate 24. Thereby, the positive electrode 30 and the positive electrode terminal 28 are electrically connected to each other via the positive electrode lead 36 and the cover plate 24.

[0030] The upper insulating member 18 is disposed between the wound body 16 and the cover plate 24. Thereby, the negative electrode 32 of the wound body 16 is prevented from contacting the sealing body 14. Further, the upper insulating member 18 has a slit 18A, and the positive electrode lead 36 passes through the slit 18A.

[0031] The lower insulating member 20 is disposed between the wound body 16 and the bottom of the outer can 12. Thereby, the positive electrode 30 of the wound body 16 is prevented from contacting the inner wall surface of the outer can 12.

[0032] An alkaline electrolytic solution (not shown) is enclosed within the exterior can 12. The alkaline electrolytic solution is an aqueous solution containing an alkali metal hydroxide. Examples of the alkali metal hydroxide include potassium hydroxide, sodium hydroxide, lithium hydroxide, etc. Among these, potassium hydroxide and lithium hydroxide are preferred. The alkali metal hydroxide may be of one type or a combination of two or more types.

[0033] The concentration of the alkali metal hydroxide in the alkaline electrolytic solution is not particularly limited, but is preferably 25 to 45 mass%. The higher the concentration of the alkali metal hydroxide in the alkaline electrolytic solution, the higher the ionic conductivity and the more suitable it is for high output density applications. However, elution of zinc oxide from the negative electrode is likely to occur, and as a result, a decrease in capacity due to zinc poisoning of the above particles is likely to occur. On the other hand, the lower the concentration of the alkali metal hydroxide in the alkaline electrolytic solution, the less elution of zinc oxide from the negative electrode and the more suitable it is for high capacity density applications. However, the ionic conductivity is low and the output density is likely to be small. Also, the more the amount of zinc dissolved in the particles containing nickel hydroxide in which zinc is dissolved increases, the more zinc poisoning can be suppressed. However, since the proportion of nickel as the active material decreases, the capacity density decreases. Therefore, it is preferable to adjust the concentration of the alkali metal hydroxide in the alkaline electrolytic solution and the amount of zinc dissolved in the particles containing nickel hydroxide in which zinc is dissolved according to the application of the battery.

[0034] For example, in applications with high capacity density, it is preferable to combine an alkaline electrolytic solution containing 25 to 35 mass% of an alkali metal hydroxide and particles containing nickel hydroxide in which 5 to 7 mass% of zinc is dissolved. On the other hand, in applications with high output density, it is preferable to combine an alkaline electrolytic solution containing 35 to 45 mass% of an alkali metal hydroxide and particles containing nickel hydroxide in which 7 to 10 mass% of zinc is dissolved.

[0035] In addition, zinc compounds such as zinc oxide and zinc hydroxide may be further dissolved in the alkaline electrolyte. This is to further suppress the elution of zinc and zinc oxide from the negative electrode into the electrolyte. For example, it is preferable that the alkaline electrolyte dissolves zinc oxide up to the saturation concentration. That is, the concentration of zinc ions in the alkaline electrolyte is preferably 4% by mass or more in terms of zinc oxide. The concentration of zinc ions in the alkaline electrolyte can be measured by high-frequency inductively coupled plasma optical emission spectrometry (ICP).

[0036] In addition, in the nickel-zinc battery, the generation and consumption of water occur during the charge-discharge reaction. Therefore, when the concentration of the alkali metal hydroxide in the electrolyte changes, the solubility of zinc oxide increases or decreases, leading to the precipitation of zinc oxide on the positive electrode and promoting the intrusion of zinc ions into the interlayer. Therefore, the total water content of the alkaline electrolyte is preferably 1.5 to 2.5 g per 1 Ah of the battery capacity (nominal capacity). When the total water content of the alkaline electrolyte is 1.5 g or more, the change in the concentration of the alkali metal hydroxide in the electrolyte is less (the amount of water generated during charging of 1 Ah is 0.34 g or less), so that the precipitation of supersaturated zinc oxide on the positive electrode can be more effectively suppressed. On the other hand, when the total water content of the alkaline electrolyte is 2.5 g or less, the proportion of the electrolyte in the battery is not too high, so that the decrease in the capacity density of the battery can be reduced more. The total water content in the alkaline electrolyte can be calculated from the mass change when the battery is disassembled and heated or vacuum dried.

[0037] Next, each member constituting the wound body 16 will be described.

[0038] (1) Positive electrode The positive electrode 30 includes a positive electrode current collector and a positive electrode mixture.

[0039] The positive electrode current collector can be, for example, a metal foil, a mesh, a sponge, a fibrous or felt-like metal porous body, or a punched metal or expanded metal. The material of the positive electrode current collector may be a metal material that is stable even at the reaction potential of the positive electrode. For example, it is nickel or stainless steel, preferably nickel. That is, the positive electrode current collector can be a foamed nickel or a net-like, sponge-like or fibrous metal body made of nickel or nickel-plated.

[0040] The positive electrode mixture is held by the positive electrode current collector and contains a positive electrode active material.

[0041] (Positive electrode active material) The positive electrode active material contains particles containing nickel hydroxide in which zinc (Zn) is solid-dissolved. The solid-dissolved zinc is the zinc added during the preparation of nickel hydroxide and is solid-dissolved in a form substituting for a part of nickel atom sites.

[0042] The solid-dissolved amount of zinc in the particles containing nickel hydroxide in which zinc is solid-dissolved is 5 to 10% by mass with respect to the particles containing nickel hydroxide in which zinc is solid-dissolved. When the solid-dissolved amount of zinc is 5% by mass or more, it is possible to make it difficult for zinc ions in the electrolytic solution to penetrate between the layers of nickel hydroxide which is a layered compound. Thereby, the expansion of the positive electrode mixture layer and the inhibition of the diffusion of protons (H + ) can be suppressed, and the capacity retention rate after cycling can be increased. When the solid-dissolved amount of zinc is 10% by mass or less, since the filling capacity density of nickel hydroxide does not decrease too much, a decrease in the discharge capacity density can be suppressed. The solid-dissolved amount of zinc in the particles containing nickel hydroxide in which zinc is solid-dissolved is preferably 5.1 to 10% by mass with respect to the particles.

[0043] In addition, one or more foreign metal elements other than nickel such as cobalt, magnesium, manganese, cadmium, iron, aluminum, chromium, and yttrium may be further solid-dissolved in the nickel hydroxide in which zinc is solid-dissolved.

[0044] Further, the particles containing nickel hydroxide with zinc solid solution may be composite particles including base particles containing nickel hydroxide with zinc solid solution and a coating layer containing a cobalt compound doped with an alkali metal.

[0045] The coating layer is disposed so as to cover at least a part of the surface of the base particles. The coating layer preferably contains a cobalt compound doped with an alkali metal. Examples of the alkali metal include sodium (Na), lithium (Li), etc. These may be of one kind or two or more kinds may be included. The cobalt compound is preferably a higher-order cobalt compound of trivalent or more such as cobalt oxyhydroxide (CoOOH). Thus, the higher-order cobalt compound in which an alkali metal is incorporated into the crystal has extremely high conductivity.

[0046] The thickness of the coating layer is not particularly limited, but can be, for example, 0.05 to 0.5 μm. When the thickness of the coating layer is 0.05 μm or more, the conductivity of the positive electrode active material can be further increased. Therefore, the utilization rate of the positive electrode active material and the capacity retention rate after cycling can be further increased. On the other hand, when the thickness of the coating layer is 0.5 μm or less, the decrease in the capacity density can be made less.

[0047] The presence or absence of the coating layer and the thickness of the coating layer can be confirmed by preparing a cross-sectional sample of the particles containing nickel hydroxide with zinc solid solution using a cross-section polisher and observing the cross-section with a scanning electron microscope (SEM).

[0048] The amount of cobalt (Co) in the composite particles can be 2 to 5% by mass with respect to the composite particles.

[0049] The amounts of zinc, cobalt, etc. in the particles containing nickel hydroxide with zinc solid solution can be measured by the following procedure using high-frequency inductively coupled plasma optical emission spectrometry (ICP). 1) Prepare a plurality of standard solutions with known concentrations of the measurement elements, measure the emission intensity using a high-frequency inductively coupled plasma optical emission spectrometer (ICP apparatus), and create a calibration curve. 2) First, dissolve the powder of particles containing nickel hydroxide with zinc dissolved therein in nitric acid to obtain a sample solution. Measure the emission intensity of this sample solution using the above apparatus. 3) By comparing the measurement results of the sample solution with the calibration curve, the amounts of zinc and cobalt in the particles containing nickel hydroxide with zinc dissolved therein can be specified. Note that the amount of zinc measured can usually correspond to the amount of zinc dissolved.

[0050] The above measurement can be performed on particles containing nickel hydroxide with zinc dissolved therein as a raw material, or on particles containing nickel hydroxide with zinc dissolved therein that are obtained by washing the positive electrode obtained by disassembling the battery with ion-exchanged water or the like, drying it to remove the alkaline electrolyte, and then peeling and recovering it from the positive electrode by ultrasonic treatment.

[0051] The average particle size of the above particles is not particularly limited, but is preferably, for example, 10 to 20 μm. That is, when the average particle size of the above particles is within the above range, the surface area of the particles increases more, so the utilization rate of the positive electrode active material can be further increased. Note that the average particle size means the average particle size (median diameter) at which the integration based on the mass standard is 50%. The average particle size of the above particles can be measured by the laser diffraction / scattering method using a particle size distribution measuring device.

[0052] (Method for manufacturing positive electrode active material) The particles containing nickel hydroxide with zinc dissolved therein can be prepared by any method, and can be prepared, for example, by the reaction crystallization method. The above composite particles can be obtained, for example, by the following method. 1) First, prepare an aqueous solution containing nickel sulfate and zinc sulfate. While controlling the pH, ammonium ion concentration, reaction temperature, etc. in this aqueous solution, gradually add an alkaline aqueous solution such as an aqueous sodium hydroxide solution and react to precipitate base particles containing nickel hydroxide with zinc dissolved therein. When further dissolving cobalt in nickel hydroxide, use an aqueous solution containing nickel sulfate, zinc sulfate and cobalt sulfate as the above aqueous solution. (2) The obtained base particles are put into an aqueous ammonia solution, and an aqueous cobalt sulfate solution is added to this aqueous solution. Thereby, using the base particles as nuclei, cobalt hydroxide is deposited on the surfaces of these nuclei to obtain intermediate particles provided with a layer of cobalt hydroxide. The obtained intermediate particles are convected in air under a high-temperature environment and heat-treated (chemically oxidized) at a predetermined heating temperature and for a predetermined heating time while spraying an aqueous sodium hydroxide solution or an aqueous lithium hydroxide solution. The heat treatment is preferably carried out, for example, at 80 to 100 °C for 30 minutes to 2 hours. By this treatment, the cobalt hydroxide on the surface of the intermediate particles is converted into a highly conductive cobalt compound (such as cobalt oxyhydroxide), and sodium or lithium is incorporated into the crystal. Thereby, a coating layer containing a cobalt compound containing one or more selected from the group consisting of sodium and lithium is formed.

[0053] (Other components) The positive electrode active material may further contain a positive electrode additive and a binder as required.

[0054] Examples of the positive electrode additive include yttrium oxide; cobalt compounds such as cobalt oxide, metallic cobalt, and cobalt hydroxide; zinc compounds such as metallic zinc, zinc oxide, and zinc hydroxide; rare earth compounds such as erbium oxide; and niobium oxide. For example, zinc compounds such as zinc oxide and zinc hydroxide may be added for the purpose of suppressing positive electrode swelling. The content of the zinc compound can be 0.1 to 5% by mass based on the total mass of the positive electrode active material.

[0055] The binder functions to bind the positive electrode active material and the positive electrode additive to each other and to bind the positive electrode active material and the positive electrode additive to the positive electrode current collector. Examples of the binder include hydrophilic or hydrophobic polymers, such as hydroxypropyl cellulose, carboxymethyl cellulose (CMC), sodium polyacrylate, and fluorine-based polymers (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), etc.).

[0056] (2) Negative electrode The negative electrode 32 includes a negative electrode current collector and a negative electrode mixture.

[0057] The negative electrode current collector may be a non-porous current collector or a porous current collector. The non-porous current collector can be a non-porous foil. The porous current collector can be a metal porous body such as a net shape, sponge shape, fiber shape or felt shape, punched metal or expanded metal, etc. The material of the negative electrode current collector only needs to be a metal material having conductivity and stable at the reaction potential of the negative electrode, and includes copper and copper alloys (such as brass, etc.), iron, and preferably copper. That is, the negative electrode current collector is preferably a copper foil.

[0058] The surface of the negative electrode current collector may be plated. The metal constituting the plating film is a metal having a higher hydrogen overvoltage than the metal constituting the main body of the negative electrode current collector, preferably a metal having a higher hydrogen overvoltage, more preferably a metal having a higher hydrogen overvoltage than copper, for example, tin.

[0059] The negative electrode mixture is held by the negative electrode current collector and contains a negative electrode active material. The negative electrode active material includes at least one of zinc, zinc alloy and zinc-containing compound. Examples of the metal constituting the zinc alloy include bismuth, aluminum, indium, etc. in addition to zinc. Examples of the zinc-containing compound include zinc oxide (one kind / two kinds / three kinds), zinc hydroxide, zinc sulfide, tetrahydroxy zinc ion salt, zinc halide, zinc carboxylate compounds such as zinc acetate, zinc tartrate, zinc oxalate, magnesium zincate, calcium zincate, barium zincate, zinc borate, zinc silicate, zinc aluminate, zinc fluoride, zinc carbonate, zinc hydrogen carbonate, zinc nitrate, zinc sulfate, etc. Among them, the negative electrode active material preferably contains zinc oxide as a main component. Containing as a main component means that it can be, for example, in an amount of 50% by mass or more based on the total mass of the negative electrode active material. Also, the negative electrode active material preferably further contains zinc (metallic zinc). Zinc can serve as both a discharge reserve and a conductive material.

[0060] The form of the negative electrode active material is, for example, powdery. The particle size of the particles of the negative electrode active material is not particularly limited, but when zinc or a zinc alloy is used, the average particle size is preferably 10 μm or more and 1000 μm or less, and when a zinc-containing compound is used, it is preferably 0.1 μm or more and 100 μm or less. The average particle size can be measured by the same method as described above.

[0061] The negative electrode binder may further contain a negative electrode additive and a binder.

[0062] The negative electrode additive may be, for example, a component that reduces the elution of the negative electrode active material into the electrolytic solution. Examples of such negative electrode additives include bismuth oxide, bismuth hydroxide, indium oxide, indium hydroxide, potassium oxalate, and their hydrates. For example, when potassium oxalate and their hydrates elute into the electrolytic solution, they dissociate into oxalate ions. Thereby, the zinc ions eluted into the electrolytic solution form a sparingly soluble salt with the oxalate ions and cover the surface of the negative electrode active material, so that the contact between the metallic zinc of the negative electrode active material and the electrolytic solution can be reduced.

[0063] The binder functions to bind the negative electrode active material and the negative electrode additive to each other, and at the same time, to bind the negative electrode active material and the negative electrode additive, etc. to the negative electrode current collector. Examples of the binder include hydroxypropyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylic acid, sodium polyacrylate, polyimide, polyamideimide, polyamide, styrene-butadiene rubber, polyethylene oxide, polytetrafluoroethylene, polyvinylidene fluoride, perfluoroalkoxy fluororesin, ethylene tetrafluoride-hexafluoropropylene copolymer, etc. Among them, styrene-butadiene rubber is preferable from the viewpoints of high binding effect and alkali resistance.

[0064] The content of the binder may be such that the negative electrode binder can be sufficiently bound to the negative electrode current collector. For example, it can be 1% by mass or more and 5% by mass or less, preferably 1% by mass or more and 3% by mass or less, based on the total amount of the negative electrode binder.

[0065] (3) Separator The separator 34 is disposed between the positive electrode 30 and the negative electrode 32 as described above (see Fig. 1). The separator 34 may be a nonwoven fabric or a microporous film.

[0066] The materials of the nonwoven fabric and the microporous film are not particularly limited, and may be polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyphenylene sulfide, polyamide, etc. Among them, from the viewpoints of mechanical strength and shutdown characteristics, polyolefin is preferable, and polypropylene is more preferable.

[0067] The nonwoven fabric and the microporous film may each be provided with hydrophilic functional groups by a hydrophilization treatment. For example, the nonwoven fabric or the microporous film may be one provided with sulfone groups by a sulfonation treatment such as immersion in an acid containing a sulfate group such as sulfuric acid or fuming sulfuric acid. Thereby, the alkaline electrolyte can be made more likely to wet the nonwoven fabric and the microporous film.

[0068] Only one type of separator 34 may be used, or two or more types may be used in combination. For example, as the separator 34, a laminate of a nonwoven fabric and a hydrophilized microporous film may be used.

[0069] (4) Physical properties after activation The above battery is activated by charge and discharge such as an activation treatment. After activation refers to a state in which an activation treatment process of performing charge and discharge a plurality of times is performed on a battery assembled by injecting and sealing an electrolyte. For example, it refers to a state in which charge and discharge are performed about 3 to 5 cycles, also serving as a quality inspection of the battery. Therefore, in the nickel hydroxide in which the above zinc is dissolved after activation, in addition to the dissolved zinc, free zinc such as zinc ions that have penetrated into the layers from the electrolyte may be slightly contained.

[0070] The total amount of zinc contained in the particles containing nickel hydroxide with the above zinc dissolved therein after activation can be, for example, 10 to 15% by mass with respect to the total amount of nickel and zinc contained in the particles. The total amount of zinc means the total amount of zinc including the dissolved zinc and the free zinc. Thus, even when the total amount of zinc after activation is large, by using nickel hydroxide in which the amount of dissolved zinc is equal to or more than a predetermined amount, a decrease in the capacity retention rate after cycling due to zinc poisoning can be suppressed.

[0071] The total amount of zinc contained in the particles containing nickel hydroxide with the above zinc dissolved therein after activation can be measured by compositional analysis using SEM / EDX. Specifically, from the battery after activation, particles containing nickel hydroxide with zinc dissolved therein are recovered, and SEM / EDX measurements are performed at 25 or more points by point analysis and averaged to obtain the ratio of the amount of zinc to the total amount of the amount of nickel and the amount of zinc (Ni / (Ni + Zn)).

[0072] (X-ray absorption spectrum) As described above, by using the particles containing nickel hydroxide with the above zinc dissolved therein as the positive electrode active material, the intrusion of zinc ions into the electrolyte can be suppressed. This can be confirmed by the XAFS spectrum of the particles containing nickel hydroxide with zinc dissolved therein, which are recovered from the positive electrode after disassembling the battery after complete discharge after activation.

[0073] The X-ray absorption fine structure (XAFS) spectrum of the zinc K absorption edge of the particles containing nickel hydroxide with the above-mentioned zinc dissolved therein after activation is represented by a graph with the X-ray energy (eV) on the horizontal axis and the normalized absorbance on the vertical axis (see FIG. 2 described later). And in the above spectrum, the intensity of the first peak at 9640 to 9690 eV is 1.9 to 2.3. The intensity of the first peak is 1.9 or more, and the decrease amount is small compared to the intensity of the first peak of 2.3 of the nickel hydroxide with the above-mentioned zinc dissolved therein before activation. This means that the intrusion of zinc ions into the nickel hydroxide with zinc dissolved therein is suppressed. The first peak at 9640 to 9690 eV refers to the first peak observed from the low energy side in the range of 9640 to 9690 eV.

[0074] The X-ray absorption spectrum after activation can be measured by the transmission method using the synchrotron radiation X-ray of the large synchrotron radiation facility SPring-8. Specifically, the positive electrode is taken out from the battery in the discharged state after activation, and the nickel hydroxide powder with zinc dissolved therein is recovered and used as a sample. Then, the sample is pressed on the tape to be thinly and smoothly formed, and then irradiated with X-rays to obtain the intensity I before incidence 0 and the absorbance I / I is measured from the ratio of the intensity I after transmission. 0 I / I 0 The spectrum of I / I is normalized by the jump amount from the pre-edge line and the post-edge line by fitting.

[0075] The intensity of the above-mentioned first peak in the XAFS spectrum can be adjusted by the amount of zinc dissolved in the particles containing nickel hydroxide with zinc dissolved therein. The more the amount of zinc dissolved in the particles containing nickel hydroxide with zinc dissolved therein, the more the intrusion of zinc ions in the electrolytic solution is suppressed. Therefore, the intensity of the first peak tends to be close to the intensity of the first peak (near 2.3) of the particles containing nickel hydroxide with the above-mentioned zinc dissolved therein before activation.

[0076] 2. Manufacturing method of nickel-zinc secondary battery The above nickel-zinc secondary battery can be manufactured by any method. For example, the above nickel-zinc secondary battery can be manufactured through 1) a step of preparing a positive electrode, a negative electrode, and a separator member, and 2) a step of obtaining a nickel-zinc secondary battery using the prepared positive electrode, negative electrode, and separator member.

[0077] Regarding the step of 1) First, a positive electrode, a negative electrode, and a separator member are prepared.

[0078] The positive electrode 30 can be manufactured, for example, by the following procedure. First, a positive electrode active material, a conductive assistant, a positive electrode additive, a binder, and water or a solvent are mixed and kneaded to obtain a positive electrode mixture slurry. Next, the obtained positive electrode mixture slurry is applied and dried on a positive electrode current collector, and then rolled and cut to a predetermined size to obtain a positive electrode. The negative electrode 32 can also be obtained in the same manner.

[0079] Regarding the step of 2) Next, a nickel-zinc secondary battery is manufactured using the prepared positive electrode, negative electrode, and separator member.

[0080] Specifically, the prepared positive electrode 30 and negative electrode 32 are wound in a stacked state with a separator 34 (for example, a laminate of a nonwoven fabric and a microporous film) in between to form a wound body. A positive electrode lead 36 is welded to one end of the positive electrode 30 in the length direction. Then, for example, after laminating the separator 34, the positive electrode 30, the separator 34, and the negative electrode 32 in this order, they are wound along the length direction so that the negative electrode 32 is on the outside to obtain a wound body 16.

[0081] The obtained wound body 16 is housed in an outer can 12, an electrolytic solution is injected, and then the opening of the outer can 12 is sealed with a sealing body 14.

[0082] After leaving it for a certain period of time, an activation treatment is performed by charging under predetermined conditions. The activation conditions can be adjusted according to the properties of the electrode active materials (positive electrode active material and negative electrode active material). In this embodiment, for example, after charging to the nominal capacity at a constant current - constant voltage of 1.9V, a cycle of discharging to 1.3V can be performed 5 times. Thereby, the nickel - zinc secondary battery 10 can be obtained.

[0083] 3. Modified Example In the above - mentioned embodiment, an example of a cylindrical nickel - zinc secondary battery was shown, but the present invention is not limited thereto, and a rectangular or laminated nickel - zinc secondary battery may also be used.

Examples

[0084] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

[0085] 1. Preparation of Positive Electrode Active Material Particles <Preparation of Positive Electrode Active Material Particles A> The positive electrode active material particles A were prepared by a reaction crystallization method. Specifically, nickel sulfate, zinc sulfate, and cobalt sulfate were mixed to prepare an aqueous solution, and ammonia ions were added thereto to prepare an ammine complex. The pH, reaction temperature, and ammonium ion concentration were adjusted to predetermined conditions, and an aqueous sodium hydroxide solution was added and continuously reacted to gradually grow crystals. Thereby, base particles of nickel hydroxide in which zinc and cobalt were solid - dissolved were obtained.

[0086] The obtained base particles were put into an aqueous ammonia solution, and an aqueous cobalt sulfate solution was added while adjusting the pH to precipitate cobalt hydroxide on the surface of the base particles. An aqueous sodium hydroxide solution was sprayed in an atmosphere containing oxygen and heat - treated for chemical oxidation to convert the precipitated cobalt hydroxide into cobalt oxyhydroxide (a conductive cobalt compound). Thereby, positive electrode active material particles A having a coating layer containing cobalt oxyhydroxide into which sodium was introduced on the surface of the base particles were obtained.

[0087] <Preparation of Cathode Active Material Particles B> In the preparation of the base particles, cathode active material particles B were prepared in the same manner as the cathode active material particles A, except that the compounding amounts of nickel sulfate, zinc sulfate, and cobalt sulfate were changed to the ratios of nickel, zinc, and cobalt in Table 1.

[0088] <Measurement of Physical Properties> (Composition) Composition analysis was performed by the calibration curve method using high-frequency inductively coupled plasma optical emission spectrometry (ICP). Specifically, a plurality of standard solutions with known concentrations of the measured elements were prepared, the emission intensity was measured using a high-frequency inductively coupled plasma optical emission spectrometer, and a calibration curve was created. Then, the cathode active material powder was dissolved in nitric acid to obtain a sample solution. The emission intensity of the obtained sample solution was measured using the above apparatus and compared with the calibration curve to measure the solid solution amount of each element.

[0089] (Tap Density) The tap density was measured as the apparent density when the cathode active material particles were filled in a container and tapped to fill the gaps between the particles.

[0090] (Average Particle Diameter) Using a particle size distribution measuring device, the average particle diameter (median diameter) corresponding to 50% of the mass-based integration was measured by the laser diffraction / scattering method.

[0091] (Specific Surface Area) The specific surface area was measured by the BET method.

[0092] (Half-Width) The crystallinity of the obtained active material was measured by X-ray diffraction measurement. As the measuring device, it was carried out using MiniFlex600 manufactured by Rigaku Corporation, and using the integrated powder X-ray analysis software PDXL2 (manufactured by Rigaku Corporation), the half-width of the peak of the (101) plane appearing at 2θ = 35 to 45° was calculated. The measurement conditions are as follows. X-ray: Cu-Kα ray, 40 kV / 15 mA Scanning range: 5 - 70° Step width: 0.01° Scanning speed: 5° / min.

[0093] The compositions and physical properties of the prepared positive electrode active material particles A and B are shown in Table 1.

Table 1

[0094] (Cross-sectional observation of positive electrode active material particles) For the obtained positive electrode active material particles, cross-section samples were prepared using a cross-section polisher (CP), and the cross-sections of the particles were observed with a scanning electron microscope (SEM). As a result, it was confirmed that the surface of the base particles was covered with a coating layer. Also, the thickness of the coating layer was about 0.1 μm for all.

[0095] 2. Fabrication of battery [Example 1] (Fabrication of positive electrode) 100 parts by mass of positive electrode active material powder composed of the prepared positive electrode active material particles A, 1 part by mass of zinc oxide powder, cobalt hydroxide powder, yttrium oxide powder, niobium oxide powder, thickener, PTFE, and water were mixed in predetermined amounts to prepare a positive electrode mixture slurry.

[0096] The obtained positive electrode mixture slurry was filled into foamed nickel, dried, rolled, and cut to a predetermined size. Thereby, a positive electrode with a capacity of 13.4 mAh / cm 2 per unit area was fabricated.

[0097] (Fabrication of negative electrode) 100 parts by mass of zinc oxide powder, 25 parts by mass of metallic zinc powder, bismuth oxide powder, potassium oxalate monohydrate, thickener, water, and styrene-butadiene rubber were mixed in predetermined amounts to prepare a negative electrode mixture slurry.

[0098] The obtained negative electrode mixture slurry was applied to a copper non-porous foil with a tin plating on its surface. After drying this electrode plate, it was rolled with a rolling roll and cut to a predetermined size. Thereby, a negative electrode having a capacity of 25 mAh / cm per unit area was produced. 2

[0099] (Preparation of electrolyte solution) An electrolyte solution was prepared by dissolving 4 mass% of zinc oxide in an aqueous solution containing 6 mol / L of potassium hydroxide and 0.5 mol / L of lithium hydroxide.

[0100] (Preparation of battery) The above-prepared positive electrode, negative electrode, and a separator group in which a non-woven fabric separator and a polypropylene microporous membrane subjected to a hydrophilic treatment were integrated were wound together to obtain an electrode group. Specifically, the one laminated in the order of separator group / positive electrode / separator group / negative electrode was wound to obtain an electrode group with the negative electrode disposed on the outermost peripheral surface. This was inserted into an exterior can with a tin plating. Then, a predetermined amount of the above-prepared electrolyte solution was injected to fabricate a cylindrical nickel-zinc secondary battery with a nominal capacity of 2000 mAh. Two nickel-zinc secondary batteries were fabricated for analysis and cycle characteristic evaluation.

[0101] (Activation treatment) The obtained battery was charged to the nominal capacity at a constant current-constant voltage of 1.9 V, and then a cycle of discharging to 1.3 V was performed 5 times to conduct an activation treatment.

[0102] [Comparative Example 1] A positive electrode was fabricated in the same manner as in Example 1 except that the positive electrode active material particles A were changed to positive electrode active material particles B, and a battery was fabricated.

[0103] [Comparative Example 2] A positive electrode was fabricated in the same manner as in Example 1 except that the positive electrode active material particles A were changed to positive electrode active material particles B, and the amount of zinc oxide was increased to 4.3 parts by mass so that the total amount of zinc in the positive electrode was the same as that in Example 1, and a battery was fabricated.

[0104] 3. Evaluation ​(1) Evaluation of the positive electrode active material powder (Sampling of the positive electrode active material powder) The positive electrode active material particles were sampled from the battery after activation by the following procedure. That is, the battery after activation was disassembled in the discharged state to recover the positive electrode, washed with water to wash away the electrolyte, and then dried at 60 °C. The active material was detached from the obtained positive electrode, the coarse particles were removed by a sieve, and then the metallic nickel derived from the foamed nickel was removed using a magnet. Then, for each of the positive electrode active material particles before making into an electrode (positive electrode active material particles before activation) and the positive electrode active material particles recovered from the battery after activation (positive electrode active material particles after activation), composition analysis by SEM / EDS and X-ray absorption spectrum measurement were performed.

[0105] (Composition analysis by SEM / EDS) Spherical positive electrode active material particles were selected, and more than 25 points of SEM / EDS measurement were performed by point analysis and averaged to obtain the ratio Zn / (Ni + Zn) of the amount of zinc to the total amount of nickel and zinc. The obtained results were corrected with the values measured using samples with known amounts of Ni and Zn. Specifically, nickel hydroxide active material with an accurate known value by ICP can be used for correction.

[0106] (Measurement of X-ray absorption spectrum) The X-ray absorption fine structure (XAFS) spectrum at the K absorption edge of zinc was measured by the transmission method using the synchrotron radiation X-ray of the large synchrotron radiation facility SPring-8. The sample was pressed on a tape to be thinly and smoothly formed, and then irradiated with X-rays to measure the ratio of the intensity I 0 before incidence to the intensity I after transmission, and the absorbance I / I 0 was measured. The spectrum of I / I 0 was normalized by the jump amount from the fitting of the pre edge line and the post edge line to obtain the XAFS spectrum as shown in the figure. In each figure, the horizontal axis indicates the energy (eV) of the X-ray, and the vertical axis indicates the normalized absorbance (a.u.).

[0107] (2) Cycle test The above cell was subjected to a cycle test. First, constant current constant voltage (CCCV) charging was performed at a rate of 0.5C and an upper limit voltage of 1.9V over 24 hours. Then, after providing a 15-minute pause, constant current (CC) discharge at 0.5C was performed until the voltage reached 1.3V to obtain the initial discharge capacity.

[0108] Next, after a 15-minute pause, constant current (CC) charging was performed at a rate of 1.0C up to 1.95V. After a 3-minute pause, constant current constant voltage (CCCV) charging was performed at a rate of 1.0C with an upper limit voltage of 1.9V and an end current of 0.2C. Then, after providing a 15-minute pause, constant current (CC) discharge at 1.0C was performed until the voltage reached 1.3V, and this was considered one cycle. Charge and discharge were performed 49 cycles under these conditions. Finally, constant current constant voltage (CCCV) charging was performed at a rate of 0.5C and an upper limit voltage of 1.9V over 24 hours. Then, after providing a 15-minute pause, constant current (CC) discharge at 0.5C was performed until the voltage reached 1.3V. Taking one set of these 50 cycles of charge and discharge, charge and discharge were performed 4 sets (a total of 200 times).

[0109] Then, the discharge capacity after 200 cycles (the 201st cycle) and the initial discharge capacity were applied to the following formula to calculate the capacity retention rate. Capacity retention rate (%) = (Discharge capacity after 200 cycles / Initial discharge capacity) × 100

[0110] The evaluation results of Example 1, Comparative Examples 1 and 2 are shown in Table 2. Also, the XAFS spectrum of Example 1 is shown in Figure 2, the XAFS spectrum of Comparative Example 1 is shown in Figure 3A, and the XAFS spectrum of Comparative Example 2 is shown in Figure 3B.

[0111]

Table 2

[0112] (Regarding the cycle test) As shown in Table 2, it can be seen that the battery of Example 1 using cathode active material particles with a high solid solution amount of zinc has a high capacity retention rate of 97.7%.

[0113] In comparison, it can be seen that the battery of Comparative Example 1 using cathode active material particles with a low solid solution amount of zinc has a low capacity retention rate of 89.4%. Also, it can be seen that the battery of Comparative Example 2, in which the addition amount of zinc oxide to the cathode was increased to make the total zinc amount in the cathode the same as that in Example 1, also has a low capacity retention rate of 88.4%.

[0114] From these results, it can be understood that it is important to set the solid solution amount of zinc to a certain level or more in order to improve the capacity retention rate of the battery.

[0115] (Regarding the results of SEM / EDS) As shown in Table 2, in all batteries, the amount of zinc in the cathode active material particles after activation increased compared to the raw cathode active material particles. This is considered to be because zinc ions dissolved in the electrolyte migrated to the cathode. The zinc that migrated to the cathode penetrated into the surface and inside of the cathode active material particles. It is considered that the zinc that penetrated into the inside of the cathode active material particles precipitated as zinc oxide inside the mesopores or intercalated between the layers of the crystal structure. Among them, it can be seen that Example 1 had the least increase in the amount of zinc. This suggests that there is less zinc intercalating between the layers of the crystal structure of the cathode active material particles.

[0116] (Regarding the X-ray absorption spectrum) As shown in FIGS. 2, 3A, and 3B, in the state before activation, the XAFS spectra completely matched among Example 1, Comparative Example 1, and Comparative Example 2. Also, when the same measurements were made for those with the zinc amount reduced to 2.5% or increased to 10%, it was confirmed that in the state before activation, all the XAFS spectra matched. Since the XAFS spectrum changes according to the valence and chemical state of the atom (here, zinc atom) and the electron distribution in its vicinity, these results indicate that even when the solid solution amount of zinc is changed, all of them enter equivalent sites and there is no change in valence, chemical state, etc., that is, they replace the nickel sites of nickel hydroxide.

[0117] On the other hand, in the activated state, a large difference was observed in the XAFS spectra among Example 1, Comparative Example 1, and Comparative Example 2. That is, in the activated state, in all of Example 1, Comparative Example 1, and Comparative Example 2, the intensity of the first peak after the jump in the XAFS spectrum decreased compared to before activation. Such a phenomenon is not observed in nickel-metal hydride batteries that also use nickel hydroxide for the positive electrode, and it is a deterioration peculiar to nickel-zinc batteries. Among them, the amount of decrease in the intensity of the first peak was the smallest in the battery of Example 1, where the difference between the activated state and the raw material was small and the proportion of the solid solution zinc amount was high. That is, it can be seen that in the battery of Example 1, the deterioration due to zinc poisoning of the positive electrode active material is suppressed more than in the batteries of Comparative Example 1 and 2. From this, it can be seen that for improving the cycle characteristics of the battery, it is effective to dissolve zinc in the positive electrode active material rather than adding zinc oxide to the positive electrode binder.

[0118] That is, if the positive electrode active material is composed only of nickel hydroxide in which zinc is solid-solved and zinc oxide, almost no change occurs in the peak intensity before and after activation. This is because both nickel hydroxide in which zinc is solid-solved and zinc oxide have a six-coordinate structure and the general shapes of their XAFS spectra are similar. That is, the change in the intensity of the first peak before and after activation as described above is due to components other than the above-mentioned nickel hydroxide and zinc oxide, that is, OH in the electrolyte - and zinc complex ions in which water molecules are four-coordinated (for example, Zn(OH) 4 2- or Zn(H 2 O) 4 2+) It is suggested that similar zinc atoms exist in particles containing nickel hydroxide. Considering the XRD crystal structure results, it is thought that zinc ions penetrate into the Ni - O layer of nickel hydroxide in a solvated state.

Industrial Applicability

[0119] According to the present invention, a nickel - zinc secondary battery with good capacity retention rate after cycling can be provided.

Explanation of Symbols

[0120] 10 Nickel - zinc secondary battery 12 Outer can 12A Bottom wall 12C Opening edge 14 Sealing body 16 Wound body (electrode group) 18 Upper insulating member 20 Lower insulating member 22 Insulating packing 24 Cover plate 26 Valve body 28 Positive electrode terminal 30 Positive electrode 32 Negative electrode 34 Separator

Claims

1. A nickel-zinc secondary battery having a positive electrode, a negative electrode, and an alkaline electrolyte, wherein the alkaline electrolyte contains 25 to 45% by mass of an alkali metal hydroxide, the positive electrode contains particles including nickel hydroxide in which zinc is solid-dissolved, the amount of solid-dissolved zinc is 5 to 10% by mass with respect to the particles, a nickel-zinc secondary battery.

2. A nickel-zinc secondary battery having a positive electrode, a negative electrode, and an alkaline electrolyte, wherein the alkaline electrolyte contains 25 to 45% by mass of an alkali metal hydroxide, the positive electrode contains particles including nickel hydroxide in which zinc is solid-dissolved, in the X-ray absorption fine structure (XAFS) spectrum of the K absorption edge of zinc measured by the transmission method of the particles after activation, the intensity of the first peak at 9640 to 9690 eV is 1.9 to 2.3, a nickel-zinc secondary battery.

3. The total amount of zinc contained in the particles after activation is 10 to 15% by mass with respect to the total amount of nickel and zinc contained in the particles, The nickel-zinc secondary battery according to claim 1 or 2.

4. The particles are base particles including nickel hydroxide in which zinc is solid-dissolved, and a coating layer covering the surface of the base particles and containing a cobalt compound doped with an alkali metal, and have The nickel-zinc secondary battery according to claim 1 or 2.

5. the alkaline electrolyte further contains zinc ions, the concentration of the zinc ions in the alkaline electrolyte is 4% by mass or more in terms of zinc oxide, The nickel-zinc secondary battery according to claim 1 or 2.

6. the total amount of water contained in the alkaline electrolyte is 1.5 to 2.5 g per 1 Ah of the battery capacity, The nickel-zinc secondary battery according to claim 1 or 2.

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