Nickel zinc secondary battery

Abstract

To provide a nickel zinc secondary battery which can maintain a capacity as well after cycles.SOLUTION: The nickel zinc secondary battery includes a positive electrode, a negative electrode, and an alkaline electrolyte. The positive electrode includes nickel composite hydroxide as a positive electrode active material. In an X-ray diffraction measurement of the nickel composite hydroxide, the half bandwidth of the peak in the (101) surface which appears when 2θ=35 to 45° is satisfied is less than 0.8.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, as the positive electrode active material, nickel composite hydroxide such as nickel hydroxide is used. For example, Patent Document 1 discloses a nickel-zinc secondary battery using particles containing a nickel composite hydroxide as the positive electrode active material.

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

[0005] For example, Patent Document 2 discloses a nickel-metal hydride battery containing nickel composite hydroxide powder in which zinc is solid-solved at 1.5 to 2.8% by mass as the positive electrode active material, and the half-value width of the (101) plane peak in the X-ray diffraction measurement of the nickel composite hydroxide is 0.85 to 1°. In this document, it is described that by setting the half-value width of the (101) plane peak to 0.85° or more, swelling of the positive electrode active material can be suppressed while maintaining the packing volume density of the nickel composite hydroxide.

[0006] In Patent Document 3, a nickel-hydrogen secondary battery containing nickel hydroxide with a half-value width of the peak of the (101) plane in X-ray diffraction measurement of 0.8° or more is disclosed as a positive electrode active material. In this document, it is described that by making the half-value width of the peak of the (101) plane particularly 0.95° or more, the crystal distortion can be increased, thereby smoothing the proton transfer between layers and further increasing the utilization rate of the positive electrode active material.

[0007] Thus, in nickel-hydrogen secondary batteries, solid solution of zinc in nickel hydroxide and the like are generally carried out. However, if the solid solution amount of zinc becomes excessive, a decrease in capacity and the like will occur, so it is common to make it less than 5% by mass with respect to nickel hydroxide. Also, it is common to make the half-value width of the peak of the (101) plane higher than 0.8°.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0009] However, according to the study by the present inventors, in nickel-zinc secondary batteries, when using the above nickel composite hydroxide, it has been clarified that the capacity decrease 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 with 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 positive electrode contains particles containing a nickel composite hydroxide, and the particles containing the nickel composite hydroxide have a half-value width of a peak of a (101) plane appearing at 2θ = 35 to 45° in X-ray diffraction measurement of less than 0.8°. [2] The nickel-zinc secondary battery according to [1], wherein the particles contain nickel hydroxide in which at least zinc is solid-solved as the nickel composite hydroxide, and the solid-solution amount of zinc in the particles is 5 to 10% by mass based on the particles. [3] The nickel-zinc secondary battery according to [1] or [2], 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. [4] The nickel-zinc secondary battery according to any one of [1] to [3], wherein the particles have a base particle containing the nickel composite hydroxide and a coating layer covering the surface of the base particle and containing a cobalt compound doped with an alkali metal. [Advantages of the Invention]

[0012] According to the present invention, it is possible to provide a nickel-zinc secondary battery having a good capacity retention rate after cycling. [Brief Description of the Drawings]

[0013]

Figure 1

Figure 2

[0014] The inventors of the present invention mainly focused on the positive electrode active material and studied the cause of the low capacity retention rate after cycling of the nickel-zinc secondary battery. In a nickel-zinc secondary battery, for example, since zinc oxide or zinc hydroxide contained in the negative electrode elutes, a large amount of zinc ions are dissolved in the alkaline electrolyte. The inventors of the present invention have found that by repeating charge and discharge cycles in such an electrolyte in which a large amount of zinc ions are dissolved, the capacity of the nickel composite hydroxide, which is the positive electrode active material, decreases, and that this capacity decrease is caused by the intercalation (invasion) of zinc ions in the electrolyte between the layers of the nickel composite hydroxide, which is a layered compound. Zinc ions that have invaded between the layers of the nickel composite hydroxide are presumed to 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, thereby reducing the capacity retention rate after cycling.

[0015] In contrast, the inventors of the present invention examined the relationship between the crystallinity of the nickel composite hydroxide, specifically the degree of crystal distortion, and the ease of invasion of zinc ions in the electrolyte between the layers of the nickel composite hydroxide. The nickel composite hydroxide is a layered compound having a structure in which layers are stacked in the c-axis direction. The degree of crystal distortion of the nickel composite hydroxide is usually represented by the half-value width of the X-ray diffraction peak including c-axis information. For example, the half-value widths of the peaks of the (001) plane and the (101) plane are used. Since the peak corresponding to the (001) plane contains only c-axis information, its half-value width represents periodic disorder (e.g., distribution of interlayer spacing and crystallite size). On the other hand, the peak of the (101) plane contains information on both the a-axis and the c-axis, and its half-value width includes, in addition to periodic disorder, distortion of the crystal structure due to torsion. That is, it is considered that the (101) plane more accurately represents the crystal distortion than the (001) plane.

[0016] The inventors of the present invention have found that by making the half-value width of the peak of the (101) plane in the X-ray diffraction measurement of the nickel composite hydroxide less than 0.8°, that is, by reducing the degree of crystal distortion and increasing the crystallinity, it is possible to make it difficult for zinc ions to invade between the layers of the nickel composite hydroxide, and thereby suppress the decrease in the capacity retention rate after cycling.

[0017] In addition, as another method for suppressing the deterioration of the nickel composite hydroxide (also referred to as "zinc poisoning") due to the intrusion of zinc ions in the electrolytic solution between the layers of the nickel composite hydroxide, the concentration of the alkali metal hydroxide in the electrolytic solution can be lowered, or an additive that forms a compound with zinc ions can be added to lower the zinc ion concentration in the electrolytic solution. However, these methods are likely to lead to a decrease in the discharge capacity of the battery. On the other hand, by using particles containing a nickel composite hydroxide with a half-value width of the peak of the (101) plane of less than 0.8° as described above, even when the zinc ion concentration in the electrolytic solution is high, zinc poisoning of the nickel composite hydroxide can be suppressed. Therefore, it is possible to suppress a decrease in the capacity retention rate after cycling due to zinc poisoning without reducing the discharge capacity of the battery.

[0018] 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 that are endpoints, unless otherwise specified.

[0019] 1. Nickel-Zinc Secondary Battery FIG. 1 is a perspective view showing a partially broken nickel-zinc secondary battery 10 according to an embodiment of the present invention. In the figure, a part of the wound body 16 is not shown.

[0020] 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.

[0021] The outer can 12 is a container for housing the wound body 16. In the present 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.

[0022] The material constituting the outer can 12 may be any material that has conductivity and corrosion resistance against the electrolytic solution and the electrochemical reactions inside the battery, and usually includes metal materials such as iron and steel.

[0023] 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.

[0024] The cover plate 24 is a disk-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.

[0025] 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 block the through hole 24A.

[0026] 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.

[0027] And during normal operation, the through hole 24A is airtightly 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, opens the through hole 24A, and as a result, gas is released from inside 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.

[0028] 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 via the separator 34. Specifically, the wound body 16 is wound with the separator 34, the positive electrode 30, the separator 34, and the negative electrode 32 laminated so that the negative electrode 32 is on the outside.

[0029] On the outermost peripheral surface of the wound body 16, the negative electrode 32 is disposed, 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] An alkaline electrolytic solution (not shown) is enclosed in the outer 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, ammonium hydroxide, etc. Among them, potassium hydroxide and lithium hydroxide are preferred. The alkali metal hydroxide may be of one kind or a combination of two or more kinds.

[0034] The concentration of the alkali metal hydroxide in the alkaline electrolyte is not particularly limited, but is preferably 25 to 45% by mass. The higher the concentration of the alkali metal hydroxide in the alkaline electrolyte, the higher the ionic conductivity, which is suitable for high output density applications. However, elution of zinc oxide from the negative electrode is likely to occur, and as a result, capacity degradation due to zinc poisoning of the above particles is likely to occur. The capacity density is likely to be small. On the other hand, the lower the concentration of the alkali metal hydroxide in the alkaline electrolyte, the less elution of zinc oxide from the negative electrode, which is suitable 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, the more zinc poisoning can be suppressed. However, since the proportion of nickel as the active material decreases, the capacity density decreases. Therefore, according to the application of the battery, it is preferable to adjust the concentration of the alkali metal hydroxide in the alkaline electrolyte and the physical properties or composition of the particles containing the nickel composite hydroxide in the positive electrode (for example, the half-value width of the peak of the (101) plane, the amount of zinc dissolved, etc.).

[0035] For example, in applications with high capacity density, it is preferable to combine an alkaline electrolyte containing 25 to 35% by mass of an alkali metal hydroxide and particles containing nickel hydroxide in which 5 to 7% by mass of zinc is dissolved as the nickel composite hydroxide. On the other hand, in applications with high output density, it is preferable to combine an alkaline electrolyte containing 35 to 45% by mass of an alkali metal hydroxide and particles containing nickel hydroxide in which 7 to 10% by mass of zinc is dissolved as the nickel composite hydroxide.

[0036] Also, 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, the alkaline electrolyte is preferably one in which zinc oxide is dissolved 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).

[0037] In addition, in a nickel-zinc secondary battery, water is generated and consumed during charge and discharge reactions. 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. Thus, 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 by the change in mass when the battery is disassembled and heated or vacuum dried.

[0038] Note that the decrease in the capacity retention rate after cycling due to the intrusion of zinc ions into the interlayer of the nickel composite hydroxide is more likely to occur significantly when the volume-to-capacity ratio is high. This is because the amount of electrolyte in contact with the nickel composite hydroxide is large. Even in such a case, by using particles containing a nickel composite hydroxide with a half-value width of the peak of the (101) plane of less than 0.8°, the decrease in the capacity retention rate after cycling can be suppressed.

[0039] That is, when the electrolyte volume is M (ml) and the capacity is C (mAh), the volume-to-capacity ratio M / C can be, for example, 1.5 to 2.5 ml / Ah. Even when the volume-to-capacity ratio M / C is relatively high in this way, by using particles containing the above nickel composite hydroxide with a half-value width of the peak of the (101) plane of less than 0.8°, the decrease in the capacity retention rate after cycling due to zinc poisoning of the nickel composite hydroxide can be suppressed.

[0040] Next, each member constituting the wound body 16 will be described.

[0041] (1) Positive electrode The positive electrode 30 includes a positive electrode current collector and a positive electrode mixture.

[0042] 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, and preferably nickel. That is, the positive electrode current collector can be a foamed nickel or a metal body in the form of a mesh, sponge or fiber made of nickel or nickel-plated.

[0043] The positive electrode mixture is held by the positive electrode current collector and contains a positive electrode active material.

[0044] (Positive electrode active material) The positive electrode active material contains particles containing a nickel composite hydroxide. The nickel composite hydroxide may be nickel hydroxide, or may be nickel hydroxide in which one or more different metal elements other than nickel, such as zinc, cobalt, magnesium, manganese, cadmium, iron, aluminum, chromium, yttrium, are solid-solved.

[0045] When the particles containing the nickel composite hydroxide are subjected to X-ray diffraction measurement, the half-value width of the peak of the (101) plane appearing at 2θ = 35 to 45° is less than 0.8°. When the half-value width of the peak of the (101) plane is less than 0.8°, the crystal distortion of the nickel composite hydroxide is small and the crystallinity is high. Therefore, it is possible to make it difficult for zinc ions in the electrolytic solution to penetrate into the interlayer of the nickel composite hydroxide. Thereby, expansion of the positive electrode active material and inhibition of diffusion of protons (H + ) can be suppressed, and the capacity retention rate after cycling can be increased. The lower limit value of the half-value width of the peak of the (101) plane of the nickel composite hydroxide is not particularly limited, but from the viewpoint of making it less likely to impair the utilization rate of the positive electrode active material, for example, it is preferably 0.4° or more, and preferably 0.6° or more.

[0046] Also, when performing X-ray diffraction measurement on particles containing nickel composite hydroxide, the half-value width of the peak of the (001) plane that appears at 2θ = 15 to 30° is preferably, for example, 0.7° or less. When the half-value width of the peak of the (001) plane is 0.7° or less, the crystal distortion of the nickel composite hydroxide is less and the crystallinity is higher, so it is possible to make it difficult for zinc ions in the electrolyte to penetrate between the layers of the nickel composite hydroxide. The lower limit value of the half-value width of the peak of the (001) plane of the nickel composite hydroxide can be, for example, 0.4° or more.

[0047] The X-ray diffraction measurement of the particles containing nickel composite hydroxide can be performed under the following conditions. As the measuring device, it can be performed using an X-ray diffractometer (for example, MiniFlex600 manufactured by Rigaku Corporation). The measurement conditions are as follows. X-ray: Cu-Kα ray, 40 kV / 15 mA Scanning range: 5 to 70° Step width: 0.01° Scanning speed: 5° / min. The half-value width of the peak of the (101) plane or (001) plane can be calculated using integrated powder X-ray analysis software PDXL2 (manufactured by Rigaku Corporation).

[0048] In addition, the above measurement can be performed on particles containing nickel composite hydroxide as a raw material, or particles containing nickel composite hydroxide recovered by washing the positive electrode obtained by disassembling the battery with ion-exchanged water or the like and then drying. It is preferable to remove the foamed nickel fragments from the recovered composite particles by sieving or the like.

[0049] The half-value widths of the peaks of the (101) plane and (001) plane of the particles containing nickel composite hydroxide can be adjusted according to the composition of the raw materials of the particles and the preparation conditions of the particles described later (pH and reaction temperature of the reaction solution during the precipitation reaction). For example, during the preparation of the particles, the lower the pH of the reaction solution during the precipitation reaction of the nickel composite hydroxide, the smaller the half-value width of the peak of the (101) plane can be. Also, the higher the temperature of the reaction solution, the smaller the half-value width of the peak of the (101) plane can be. Further, the more the amount of zinc solid solution in the nickel composite hydroxide, the smaller the half-value width of the peak of the (101) plane can be. Note that the method for adjusting the half-value width of the above peak is not limited to these. Also, any one or more of these methods can be carried out.

[0050] It is preferable that the above particles contain nickel hydroxide in which at least zinc is solid-solved as the nickel composite hydroxide. Also, the above particles may contain nickel hydroxide in which cobalt (Co) is solid-solved in addition to or instead of zinc as the nickel composite hydroxide. These zinc and cobalt are solid-solved in a form that replaces a part of the nickel atom sites of nickel hydroxide.

[0051] When zinc is solid-solved in the nickel composite hydroxide, the solid-solution amount of zinc in the above particles is preferably 4% by mass or more, more preferably 5% by mass or more, and even more preferably 5.1% by mass or more with respect to the above particles. When the solid-solution amount of zinc is 4% by mass or more, it is possible to make it difficult for zinc ions in the electrolytic solution to penetrate into the interlayer of the nickel composite hydroxide which is a layered compound. Thereby, the expansion of the positive electrode active material and the diffusion inhibition of protons (H + ) can be suppressed, and the capacity retention rate after cycling can be increased. The upper limit value of the solid-solution amount of zinc is not particularly limited, but from the viewpoint of further reducing the decrease in the discharge capacity density due to the decrease in the packing capacity density of the nickel composite hydroxide, it can be, for example, 10% by mass or less with respect to the above particles.

[0052] Also, when the above particles are composite particles described later, the amount of cobalt (Co) in the composite particles can be 2 to 5% by mass with respect to the composite particles.

[0053] The amounts of zinc and cobalt in the above particles can be measured by high-frequency inductively coupled plasma optical emission spectrometry (ICP) according to the following procedure. 1) Prepare a plurality of standard solutions with known concentrations of the elements to be measured, measure the emission intensity using a high-frequency inductively coupled plasma optical emission spectrometer (ICP apparatus), and create a calibration curve. 2) On the other hand, a particle powder containing nickel composite hydroxide dissolved in nitric acid is used as a sample solution. The emission intensity of this sample solution is measured 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 composite hydroxide can be specified. The amount of zinc measured corresponds to the solid solution amount of zinc.

[0054] The above measurement can be performed on particles containing nickel composite hydroxide as a raw material, or particles containing nickel composite hydroxide recovered by washing the positive electrode obtained by disassembling the battery with an alkaline solution or the like and then drying, in the same manner as the above-described X-ray diffraction measurement.

[0055] Also, the above particles may be composite particles including base particles containing nickel composite hydroxide and a coating layer containing a cobalt compound doped with an alkali metal.

[0056] 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 one kind or two or more kinds. The cobalt compound is preferably a higher-order cobalt compound of trivalent or higher 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.

[0057] 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, not only can the conductivity of the positive electrode active material be further enhanced, but also the intrusion of zinc ions into the interlayer of the nickel composite hydroxide can be made less likely to occur due to the electrical action. Therefore, the utilization rate of the positive electrode active material and the capacity retention rate after cycling can be further increased. When the thickness of the coating layer is 0.5 μm or less, the decrease in the packing volume density can be made less.

[0058] 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 composite particles using a cross-section polisher and observing the cross-section with a scanning electron microscope (SEM).

[0059] The average particle size of the particles containing the nickel composite hydroxide is not particularly limited, but is preferably, for example, 10 to 20 μm. That is, when the average particle size of the particles is within the above range, the surface area of the particles increases more, so that the utilization rate of the positive electrode active material can be further increased. 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.

[0060] (Method for producing positive electrode active material) The particles containing the nickel composite hydroxide can be prepared by any method, and can be prepared, for example, by the reaction crystallization method. For example, the above-mentioned composite particles can be prepared by the following method. 1) First, prepare an aqueous solution containing nickel sulfate. While controlling the pH, ammonium ion concentration, reaction temperature, etc. in this aqueous solution, an alkaline aqueous solution such as an aqueous sodium hydroxide solution is gradually added and reacted to precipitate base particles containing a nickel composite hydroxide. In addition, when further dissolving zinc and / or cobalt in nickel hydroxide, an aqueous solution containing nickel sulfate, zinc sulfate and / or cobalt sulfate is used as the above aqueous solution. Further, the pH and reaction temperature during the precipitation reaction can be adjusted so that the half-value width of the peak of the (101) plane in the X-ray diffraction measurement of the finally obtained particles falls within the above range. 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 precipitated on the surfaces of the nuclei to obtain intermediate particles provided with a layer of cobalt hydroxide. The obtained intermediate particles are convected in air in a high-temperature environment, and heat-treated (chemically oxidized) at a predetermined heating temperature and for a predetermined heating time while spraying an aqueous solution containing an alkali metal hydroxide such as 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 an alkali metal such as sodium or lithium is incorporated into the crystal. Thereby, a coating layer containing a cobalt compound doped with an alkali metal is formed.

[0061] (Other components) The positive electrode active material may further contain a positive electrode additive and a binder as required.

[0062] 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 can 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.

[0063] 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 (such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF)).

[0064] (2) Negative electrode The negative electrode 32 includes a negative electrode current collector and a negative electrode mixture.

[0065] 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 net-like, sponge-like, fibrous or felt-like metal porous body, punched metal, expanded metal, etc. The material of the negative electrode current collector may be a metal material having conductivity and being stable even at the reaction potential of the negative electrode, and includes copper and copper alloys (such as brass), and iron, and preferably copper. That is, the negative electrode current collector is preferably a copper foil.

[0066] 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, such as tin.

[0067] The negative electrode mixture is held on 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, and 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, it is preferable that the negative electrode active material 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, it is preferable that the negative electrode active material further contains zinc (metallic zinc). Zinc can serve as both a discharge reserve and a conductive material.

[0068] 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 using zinc or zinc alloy, the average particle size is preferably 10 μm or more and 1000 μm or less, and when using zinc-containing compound, 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.

[0069] The negative electrode mixture may further contain a negative electrode additive and a binder.

[0070] The negative electrode additive may be, for example, a component that reduces the elution of the negative electrode active material into the electrolyte. 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 electrolyte, they dissociate into oxalate ions. Thereby, the zinc ions eluted into the electrolyte form a poorly 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 electrolyte can be reduced.

[0071] 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, 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 preferred from the viewpoints of high binding effect and alkali resistance.

[0072] The content of the binder may be such that the negative electrode mixture 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 mixture.

[0073] (3) Separator As described above, the separator 34 is disposed between the positive electrode 30 and the negative electrode 32 (see Fig. 1). The separator 34 may be a non - woven fabric or a microporous film.

[0074] The materials of the non - woven fabric and the microporous film are not particularly limited, and can be polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyphenylene sulfide, polyamide, etc. Among them, polyolefin is preferred from the viewpoints of mechanical strength and shutdown characteristics, and polypropylene is more preferred.

[0075] The non - woven fabric and the microporous film may each be provided with hydrophilic functional groups by a hydrophilization treatment. For example, the non - woven fabric or the microporous film may be sulfonated by immersion in an acid containing a sulfonic acid group such as sulfuric acid or fuming sulfuric acid, etc., so that a sulfone group is imparted. Thereby, the non - woven fabric and the microporous film can be made more wettable with the alkaline electrolyte.

[0076] The separator 34 may be used alone or in combination of two or more types. For example, as the separator 34, a laminate of a nonwoven fabric and a microporous film subjected to a hydrophilic treatment may be used.

[0077] 2. Method for manufacturing a nickel-zinc secondary battery The nickel-zinc secondary battery can be manufactured by any method. For example, the 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.

[0078] Regarding the step of 1) First, a positive electrode, a negative electrode, and a separator member are prepared.

[0079] 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, after applying and drying the obtained positive electrode mixture slurry on a positive electrode current collector, it is rolled and cut to a predetermined size to obtain a positive electrode. The negative electrode 32 can be obtained in the same manner.

[0080] Regarding the step of 2) Next, a nickel-zinc secondary battery is manufactured using the prepared positive electrode, negative electrode, and separator member.

[0081] Specifically, the prepared positive electrode 30 and negative electrode 32 are wound in a stacked state through a separator 34 (for example, a laminate of a nonwoven fabric and a microporous film) to produce a wound body. A positive electrode lead 36 is welded to one end in the length direction of the positive electrode 30. 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.

[0082] The obtained wound body 16 is stored in the exterior can 12. After injecting the electrolytic solution, the opening of the exterior can 12 is sealed with the sealing body 14.

[0083] After leaving it standing for a certain period of time, activation treatment is performed by charging under predetermined conditions. The activation conditions can be adjusted according to the properties of the electrode active material (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 1.9 V, a cycle of discharging to 1.3 V can be performed 5 times. Thereby, the nickel - zinc secondary battery 10 can be obtained.

[0084] 3. Modification 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 square - shaped or laminated nickel - zinc secondary battery may also be used.

Example

[0085] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

[0086] 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 the 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.

[0087] 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. Then, 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.

[0088] <Preparation of Positive Electrode Active Material Particles B to E> The blending amounts of nickel sulfate, zinc sulfate, and cobalt sulfate in the preparation of the base particles were adjusted, and the pH and reaction temperature when adding an aqueous sodium hydroxide solution for precipitation reaction in the preparation of the base particles were adjusted. Positive electrode active material particles B to E were prepared in the same manner as positive electrode active material particles A except that the composition of the finally obtained positive electrode active material particles and the half-value width of the peak of the (101) plane were adjusted to the values shown in Table 1.

[0089] <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, a sample solution was prepared by dissolving the positive electrode active material powder in nitric acid. 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.

[0090] (Tap Density) The tap density was measured as the apparent density when the positive electrode active material particles were filled in a container and tapped to fill the gaps between the particles.

[0091] (Average Particle Size) Using a particle size distribution measuring device, the average particle size (median diameter) corresponding to 50% by mass integration was measured by the laser diffraction / scattering method.

[0092] (Specific surface area) The specific surface area was measured by the BET method.

[0093] (Full width at half maximum) X-ray diffraction measurement was performed on the obtained positive electrode active material particles. As the measuring device, it was carried out using MiniFlex600 manufactured by Rigaku Corporation, and using integrated powder X-ray analysis software PDXL2 (manufactured by Rigaku Corporation), the full width at half maximum of the peak of the (101) plane appearing at 2θ = 35 to 45° and the full width at half maximum of the peak of the (001) plane appearing at 2θ = 15 to 30° were calculated respectively. The measurement conditions are as follows. X-ray: Cu-Kα ray, 40 kV / 15 mA Scanning range: 5 to 70° Step width: 0.01° Scanning speed: 5° / min.

[0094] The compositions and physical properties of the above-prepared positive electrode active material particles A to E are shown in Table 1. Also, a graph of the X-ray diffraction measurement results is shown in Figure 2. In Figure 2, the horizontal axis represents 2θ (deg.), and the vertical axis represents intensity (a.u.). In Figure 2, the X-ray diffraction peaks of positive electrode active materials A, B, C, D, and E are shown in order from the bottom.

[0095]

Table 1

[0096] (Observation of the cross-section of the positive electrode active material particles) For the obtained positive electrode active material particles, a cross-section sample was prepared using a cross-section polisher (CP), and the cross-section of the particles was observed with a scanning electron microscope (SEM). It was confirmed that the surface of the base particles of all the obtained positive electrode active material particles was covered with a coating layer. Also, the thickness of the coating layer was about 0.1 μm for all.

[0097] 2. Fabrication of the battery [Example 1] (Fabrication of the positive electrode) 100 parts by mass of a 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, a thickener, PTFE, and water were mixed in predetermined amounts to prepare a positive electrode mixture slurry.

[0098] The obtained positive electrode mixture slurry was filled into foamed nickel, dried, rolled, and cut to a predetermined size. Thereby, a positive electrode having a capacity of 13.4 mAh / cm per unit area was fabricated. 2 was fabricated.

[0099] (Fabrication of the negative electrode) 100 parts by mass of zinc oxide powder, 25 parts by mass of metallic zinc powder, bismuth oxide powder, potassium oxalate monohydrate, a thickener, water, and styrene-butadiene rubber were mixed in predetermined amounts to prepare a negative electrode mixture slurry.

[0100] 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 fabricated. 2 was fabricated.

[0101] (Fabrication of the electrolyte) An aqueous solution containing 6 mol / L of potassium hydroxide and 0.5 mol / L of lithium hydroxide was prepared by dissolving 4% by mass of zinc oxide therein to prepare an electrolyte.

[0102] (Fabrication of the battery) The fabricated positive electrode, the 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, a laminate 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, 4.550 g of the prepared electrolytic 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, one for analysis and the other for cycle performance evaluation.

[0103] (Activation treatment) The obtained battery was charged to the nominal capacity at a constant current-constant voltage of 1.9 V and then discharged to 1.3 V. This cycle was repeated 5 times to perform the activation treatment.

[0104] [Example 2, Comparative Example 1 and 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 the positive electrode active material particles shown in Table 2, and a battery was fabricated. The injection amount of the electrolytic solution was 5.469 g in both Example 2 and Comparative Example 2.

[0105] 3. Evaluation (1) Cycle test The above battery was subjected to a cycle test.

[0106] First, constant current-constant voltage (CCCV) charging was performed at a rate of 0.5 C and an upper limit voltage of 1.9 V over 24 hours. Then, after a 15-minute rest, constant current (CC) discharge at 0.5 C was performed until the voltage reached 1.3 V to obtain the initial discharge capacity.

[0107] Next, after a 15-minute rest, constant current (CC) charging was performed at a rate of 1.0 C up to 1.95 V. After a 3-minute rest, constant current-constant voltage (CCCV) charging was performed at a rate of 1.0 C with an upper limit voltage of 1.9 V and an end current of 0.2 C. Then, after a 15-minute rest, constant current (CC) discharge at 1.0 C was performed until the voltage reached 1.3 V, and this was defined as 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 0.5 C and an upper limit voltage of 1.9 V over 24 hours. Then, after a 15-minute rest, constant current (CC) discharge at 0.5 C was performed until the voltage reached 1.3 V. Taking this 50-cycle charge and discharge as one set, four sets (a total of 200 times) of charge and discharge were performed.

[0108] 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

[0109] (2) Utilization rate of the positive electrode active material Based on the discharge capacity of the first cycle, the utilization rate was calculated according to the following formula. Utilization rate of the positive electrode active material (%) = (Initial discharge capacity / Theoretical capacity) × 100

[0110] The evaluation results of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 2.

Table 2

[0111] (Regarding the capacity retention rate after cycling) As shown in Table 2, for the batteries of Comparative Examples 1 and 2 using positive electrode active material particles with a half-value width of the peak of the (101) plane of 0.8° or more, the capacity retention rate after 200 cycles was lower than 90% in both cases.

[0112] In contrast, for the batteries of Examples 1 and 2 using positive electrode active materials with a half-value width of the peak of the (101) plane smaller than 0.8°, the capacity retention rate after 200 cycles exceeded 90%, indicating that it is very high. In particular, comparing Example 2 and Comparative Example 2, although the composition of the positive electrode active material particles is almost the same, the crystallinity is significantly different. From these comparisons, it can be seen that by using positive electrode active material particles with a small half-value width of the peak of the (101) plane and high crystallinity, the intrusion of zinc ions into the interlayer of nickel composite hydroxide can be suppressed.

[0113] From these facts, it can be understood that to improve the capacity retention rate of the battery, it is effective to make the half-value width of the peak of the (101) plane less than 0.8°.

[0114] Also, it can be seen that the decrease in the capacity retention rate after 200 cycles is greater for Example 2 and Comparative Example 2 with a large amount of electrolyte injection than for Example 1 and Comparative Example 1 with a small amount of electrolyte injection. Generally, as the cycle is repeated, the electrolyte is consumed and the resistance increases. Therefore, it is said that the higher the amount of electrolyte injection (higher volume-to-liquid ratio), the higher the capacity retention rate after cycling. However, it can be seen that the above results are contrary to this. This is presumably because, as a result of a large amount of electrolyte and the positive electrode being in contact with a larger amount of electrolyte, the amount of poisoning by zinc ions in the electrolyte increases, leading to a decrease in the capacity retention rate after cycling.

Industrial Applicability

[0115] According to the present invention, it is possible to provide a nickel-zinc secondary battery having a good capacity retention rate after cycling.

Explanation of Signs

[0116] 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 positive electrode contains particles containing a nickel composite hydroxide, the particles containing the nickel composite hydroxide have a half-value width of a peak of the (101) plane appearing at 2θ = 35 to 45° in X-ray diffraction measurement of less than 0.8°, a nickel-zinc secondary battery.

2. the particles contain nickel hydroxide in which at least zinc is solid-solved as the nickel composite hydroxide, the amount of zinc solid-solved in the particles is 5 to 10% by mass based on the particles, the nickel-zinc secondary battery according to Claim 1.

3. the alkaline electrolyte 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.

4. the particles have base particles containing the nickel composite hydroxide, 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.

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