Nickel-zinc secondary battery

Abstract

The invention relates to a nickel-zinc secondary battery. The nickel-zinc secondary battery has a positive electrode, a negative electrode, and an alkaline electrolyte solution. The positive electrode contains a nickel composite hydroxide as a positive electrode active material, and the half-value width of the peak of the (101) plane appearing at 2 [theta] = 35 DEG to 45 DEG in X-ray diffraction measurement of the nickel composite hydroxide is less than 0.8 DEG.

Description

Technical Field

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

[0002] Nickel-zinc secondary batteries are known as batteries that replace the hydrogen storage alloy negative electrode of nickel-hydrogen secondary batteries with a negative electrode containing zinc or a zinc compound. Zinc is a material that is abundant in resources, cheap, and has a low environmental load. In addition, nickel-zinc secondary batteries have advantages such as an open circuit voltage of up to 1.8V, a high theoretical energy density, and high power.

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

[0004] Nickel composite hydroxide is also used as a positive electrode in nickel-hydrogen secondary batteries. In nickel-hydrogen secondary batteries, in order to improve the utilization rate of nickel hydroxide or the cycle characteristics, methods of solid-dissolving various elements such as Zn, Mg, and Co or coating the matrix particles containing the nickel composite hydroxide with a coating layer containing a cobalt compound are studied.

[0005] For example, Patent Document 2 discloses a nickel-metal hydride battery containing a nickel composite hydroxide powder containing 1.5 to 2.8% by mass of zinc dissolved therein as a positive electrode active material, wherein the half-value width of the peak of the (101) face of the nickel composite hydroxide in X-ray diffraction measurement is 0.85° to 1°. The document records that by setting the half-value width of the peak of the (101) face to 0.85° or more, the expansion of the positive electrode active material can be suppressed while maintaining the filling capacity density of the nickel composite hydroxide.

[0006] Patent document 3 discloses a nickel-hydrogen secondary battery containing nickel hydroxide as a positive electrode active material, wherein the half-value width of the peak of the (101) plane in X-ray diffraction measurement is 0.8° or more. The document records that, in particular, by setting the half-value width of the peak of the (101) plane to 0.95° or more, the deformation of the crystal is increased, thereby making the proton movement between the layers smooth, and the utilization rate of the positive electrode active material can be further improved.

[0007] Thus, in nickel-hydrogen secondary batteries, zinc is usually dissolved in nickel hydroxide. However, if the amount of zinc dissolved is too much, the capacity is reduced, and therefore, it is usually less than 5% by mass relative to nickel hydroxide. In addition, the half-value width of the peak of the (101) surface is usually set to be higher than 0.8°.

[0008] Problem that the invention aims to solve

[0009] However, the present inventors' research has revealed that when the above-mentioned nickel composite hydroxide is used in a nickel-zinc secondary battery, the capacity decreases significantly due to repeated charge and discharge, and the capacity retention rate after cycles is low.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent Application Publication No. 2023-144770

[0013] Patent Document 2: Japanese Patent Application Laid-Open No. 5-290841

[0014] Patent Document 3: Japanese Patent Application Laid-Open No. 10-177858 Summary of the invention

[0015] The object of the present invention is to provide a nickel-zinc secondary battery having a good capacity retention rate after cycling.

[0016] Solutions to the problem

[0017] [1] A nickel-zinc secondary battery comprising a positive electrode, a negative electrode and an alkaline electrolyte, wherein the positive electrode comprises particles containing a nickel composite hydroxide, and the half-value width of the peak of the (101) plane appearing at 2θ=35° to 45° in X-ray diffraction measurement of the particles containing the nickel composite hydroxide is less than 0.8°.

[0018] [2] The nickel-zinc secondary battery according to [1], wherein the particles contain at least nickel hydroxide in which zinc is solid-dissolved as the nickel composite hydroxide, and the amount of the zinc solid-dissolved in the particles is 5 to 10% by mass relative to the mass of the particles.

[0019] [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.

[0020] [4] The nickel-zinc secondary battery according to any one of [1] to [3], wherein the particle comprises: a base particle containing the nickel composite hydroxide; and a coating layer that covers the surface of the base particle and contains a cobalt compound doped with an alkali metal.

[0021] Effects of the Invention

[0022] According to the present invention, a nickel-zinc secondary battery having a good capacity retention rate after cycles can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1This is a partially cutaway perspective view of a nickel-zinc secondary battery according to an embodiment of the present invention.

[0024] Figure 2 This is a graph showing the results of X-ray diffraction measurement of positive electrode active material particles A to E.

[0025] Description of Reference Numerals

[0026] 10: Nickel-zinc secondary battery;

[0027] 12: External can:

[0028] 12A: Bottom wall:

[0029] 12C: Opening edge:

[0030] 14: Sealing body:

[0031] 16: Winding body (electrode group):

[0032] 18: Upper insulation part:

[0033] 20: Lower insulation part:

[0034] 22: Insulation pad:

[0035] 24: Cover:

[0036] 26: Valve body:

[0037] 28: Positive terminal:

[0038] 30: Positive electrode:

[0039] 32: Negative electrode:

[0040] 34: Diaphragm. DETAILED DESCRIPTION

[0041] The present inventors have studied the reasons why the capacity retention rate of nickel-zinc secondary batteries after cycles is low, focusing mainly on the positive electrode active material.

[0042] In a nickel-zinc secondary battery, for example, zinc oxide or zinc hydroxide contained in the negative electrode is dissolved, so a large amount of zinc ions are dissolved in an alkaline electrolyte. The inventors have thoroughly ascertained that the capacity of the nickel composite hydroxide as a positive electrode active material decreases by repeating charge and discharge cycles in such an electrolyte in which a large amount of zinc ions are dissolved; and that the capacity decrease occurs because the zinc ions in the electrolyte are inserted (invaded) into the interlayer of the nickel composite hydroxide as a layered compound.

[0043] The zinc ions that have penetrated into the interlayers of the nickel composite hydroxide not only cause expansion of the positive electrode active material but also inhibit the diffusion of protons that is a normal charge and discharge reaction, and thus it is estimated that the capacity retention rate after cycling is reduced.

[0044] In view of this, the present inventors have studied the relationship between the crystallinity of the nickel composite hydroxide, specifically, the degree of crystal deformation, and the ease with which zinc ions in the electrolyte penetrate into the interlayers of the nickel composite hydroxide.

[0045] Nickel composite hydroxide is a layered compound having a structure with layers stacked in the c-axis direction. The degree of deformation of the crystallization of nickel composite hydroxide is usually represented by the half-value width of the X-ray diffraction peak containing c-axis information, such as the half-value width of the peak using (001) face or (101) face. The peak equivalent to (001) face only contains c-axis information, so its half-value width represents periodic disorder (such as the distribution of interlayer spacing and crystallite size). On the other hand, the peak of (101) face contains information of both a-axis and c-axis, and its half-value width also includes the deformation of the crystalline structure caused by distortion in addition to periodic disorder. In other words, it is believed that (101) face more accurately represents the deformation of crystallization than (001) face.

[0046] Furthermore, the inventors have found that by reducing the half-value width of the peak of the (101) plane of the nickel composite hydroxide in the X-ray diffraction measurement to less than 0.8°, that is, reducing the degree of deformation of the crystal to increase the crystallinity, it is difficult for zinc ions to invade the interlayer of the nickel composite hydroxide, thereby suppressing the reduction in the capacity retention rate after cycling.

[0047] It is explained that as other methods for suppressing the deterioration of the nickel composite hydroxide caused by the zinc ions in the electrolyte invading the interlayer of the nickel composite hydroxide (also referred to as "zinc poisoning"), the concentration of the alkali metal hydroxide of the electrolyte can be reduced, or the method of reducing the zinc ion concentration in the electrolyte by adding an additive that forms a compound with the zinc ions, etc. can be cited. These methods are all prone to reduce the discharge capacity of the battery. In contrast, by using the particles containing nickel composite hydroxides whose half-value width of the peak of the (101) surface as described above is less than 0.8°, even if the zinc ion concentration in the electrolyte is high, the zinc poisoning of the nickel composite hydroxide can be suppressed. Therefore, the discharge capacity of the battery will not be reduced, and the capacity retention rate after the cycle caused by zinc poisoning can be suppressed.

[0048] Hereinafter, the nickel-zinc secondary battery according to the present embodiment will be described. In this specification, unless otherwise specified, the term "to" means a numerical range including the lower limit and the upper limit as endpoints.

[0049] 1. Nickel-zinc secondary battery

[0050] Figure 1 1 is a partially cutaway perspective view of a nickel-zinc secondary battery 10 according to an embodiment of the present invention. In this figure, a part of the winding body 16 is omitted from illustration.

[0051] like Figure 1 As shown, the nickel-zinc secondary battery 10 involved in this embodiment is, for example, a cylindrical battery of FA size, and has: an outer can 12, a sealing body 14, a winding body 16 (electrode group), an electrolyte (not shown), an upper insulating member 18 and a lower insulating member 20.

[0052] The outer can 12 is a container for accommodating the wound body 16, and in the present embodiment, is a container in the shape of a bottomed cylinder with an open top. The outer can 12 has conductivity, and its bottom wall 12A functions as a negative electrode terminal.

[0053] The material constituting the outer can 12 may be any material as long as it has conductivity and is resistant to corrosion by the electrolyte or electrochemical reactions within the battery, and generally includes a metal material such as iron or steel.

[0054] The sealing body 14 is fixed to the opening of the outer can 12 via the insulating gasket 22, and 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.

[0055] The cover plate 24 is a conductive disc-shaped member having a through hole 24A in the center. The insulating gasket 22 has a ring shape surrounding the cover plate 24 and is sandwiched between the outer can 12 and the sealing body 14. The insulating gasket 22 is fixed to the opening edge 12C of the outer can 12 by caulking the opening edge 12C of the outer can 12. Thus, the cover plate 24 and the insulating gasket 22 cooperate with each other to hermetically seal the opening of the outer can 12.

[0056] The valve body 26 is a rubber member, and is disposed on the outer surface of the cover plate 24 so as to close the through hole 24A.

[0057] The positive terminal 28 is a metal cylindrical member with a flange, and is electrically connected to the outer surface of the cover plate 24 so as to cover the valve body 26. The positive terminal 28 presses the valve body 26 toward the cover plate 24. The positive terminal 28 has an opening for a vent (not shown).

[0058] Furthermore, during normal operation, the through hole 24A is hermetically closed by the valve body 26. On the other hand, when gas is generated in the outer can 12 and the internal pressure thereof increases, the valve body 26 is compressed by the internal pressure and the through hole 24A is opened, and as a result, the gas is discharged from the outer can 12 to the outside through the through hole 24A and the exhaust hole (not shown) of the positive terminal 28. That is, the through hole 24A, the valve body 26 and the positive terminal 28 form a safety valve for the battery.

[0059] 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 in which the positive electrode 30 and the negative electrode 32 are wound in a stacked state with the separator 34 interposed therebetween. Specifically, the wound body 16 is a structure in which the separator 34, the positive electrode 30, the separator 34, and the negative electrode 32 are stacked and wound in a manner such that the negative electrode 32 is on the outside.

[0060] A 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 serving as a negative electrode terminal are electrically connected to each other.

[0061] 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. Thus, 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.

[0062] The upper insulating member 18 is disposed between the wound body 16 and the cover plate 24. Thus, the negative electrode 32 of the wound body 16 does not come into contact with the sealing body 14. The upper insulating member 18 has a slit 18A, and the positive electrode lead 36 is passed through the slit 18A.

[0063] The lower insulating member 20 is disposed between the wound body 16 and the bottom of the outer can 12 . Thus, the positive electrode 30 of the wound body 16 does not come into contact with the inner wall surface of the outer can 12 .

[0064] An alkaline electrolyte (not shown) is sealed in the outer can 12. The alkaline electrolyte is an aqueous solution containing an alkali metal hydroxide. Examples of alkali metal hydroxides 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 one kind or a combination of two or more kinds.

[0065] The concentration of the alkali metal hydroxide of the alkaline electrolyte is not particularly limited, but is preferably 25 to 45% by mass. The higher the concentration of the alkali metal hydroxide of the alkaline electrolyte, the higher the ionic conductivity, which is suitable for high power density applications, but zinc oxide is easily dissolved from the negative electrode, and as a result, it is easy to cause a decrease in capacity caused by zinc poisoning of the above-mentioned particles, and the capacity density is easy to become smaller. On the other hand, the lower the concentration of the alkali metal hydroxide of the alkaline electrolyte, the less zinc oxide is dissolved from the negative electrode, which is suitable for high capacity density applications, but the ionic conductivity is low and the power density is easy to become smaller. In addition, the more the solid solution amount of zinc in the particles containing nickel hydroxide solid-dissolved with zinc is increased, the more zinc poisoning can be suppressed, but since the proportion of nickel as an active material is reduced, the capacity density is reduced. Therefore, it is preferred to adjust the concentration of the alkali metal hydroxide of 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) surface or the solid solution amount of zinc, etc.) according to the use of the battery.

[0066] For example, in high capacity density applications, it is preferred to combine an alkaline electrolyte containing 25 to 35% by mass of an alkali metal hydroxide and nickel hydroxide containing 5 to 7% by mass of zinc dissolved therein as particles of a nickel composite hydroxide. On the other hand, in high power density applications, it is preferred to combine an alkaline electrolyte containing 35 to 45% by mass of an alkali metal hydroxide and nickel hydroxide containing 7 to 10% by mass of zinc dissolved therein as particles of a nickel composite hydroxide.

[0067] 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 dissolution of zinc or zinc oxide from the negative electrode to the electrolyte. For example, the alkaline electrolyte is preferably an electrolyte in which zinc oxide is dissolved to a saturated concentration. That is, the concentration of zinc ions in the alkaline electrolyte is preferably 4% by mass or more in terms of zinc oxide conversion. The concentration of zinc ions in the alkaline electrolyte can be measured by inductively coupled plasma emission spectrometry (ICP-OES).

[0068] In addition, in nickel-zinc secondary batteries, water is generated and consumed during the charge and discharge reactions. Therefore, by changing the concentration of the alkali metal hydroxide in the electrolyte, the solubility of zinc oxide increases or decreases, promoting the intrusion of zinc ions into the interlayer, which causes zinc oxide to precipitate toward the positive electrode. Therefore, the total water content of the alkaline electrolyte is preferably 1.5g to 2.5g per 1Ah battery capacity (nominal capacity). If the total water content of the alkaline electrolyte is more than 1.5g, the concentration of the alkali metal hydroxide in the electrolyte changes less (the amount of water generated is less than 0.34g under 1Ah charging), so it is possible to further suppress the precipitation of supersaturated zinc oxide toward the positive electrode. On the other hand, if the total water content of the alkaline electrolyte is less than 2.5g, the proportion of the electrolyte in the battery is not too high, so the reduction in the capacity density of the battery can be further reduced. 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.

[0069] It is noted that the reduction in capacity retention rate after cycling caused by zinc ions invading the interlayer of the nickel composite hydroxide is more likely to occur significantly when the capacity-liquid ratio is high. This is because the amount of electrolyte contacted by the nickel composite hydroxide is large. Even in this case, by using particles containing nickel composite hydroxides having a half-value width of the peak of the above-mentioned (101) surface less than 0.8°, the reduction in capacity retention rate after cycling can be suppressed.

[0070] That is, when the amount of electrolyte is set to M (ml) and the capacity is set to C (mAh), the capacity-liquid ratio M / C can be set to 1.5 to 2.5 ml / Ah, for example. Even if the capacity-liquid ratio M / C is relatively high, by using the above-mentioned nickel composite hydroxide-containing particles having a half-value width of the peak of the (101) plane of less than 0.8°, the reduction in the capacity retention rate after the cycle caused by zinc poisoning of the nickel composite hydroxide can be suppressed.

[0071] Next, each member constituting the wound body 16 will be described.

[0072] (1) Positive electrode

[0073] The positive electrode 30 includes a positive electrode current collector and a positive electrode mixture.

[0074] 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 metal punching plate or a steel plate mesh, etc. The material of the positive electrode current collector can be a metal material that is stable even at the reaction potential of the positive electrode, such as nickel, stainless steel, preferably nickel. That is, the positive electrode current collector can be a nickel foam, a nickel-made or nickel-plated mesh, a sponge or a fibrous metal body.

[0075] The positive electrode mixture is held on the positive electrode current collector and contains a positive electrode active material.

[0076] (Positive electrode active material)

[0077] The positive electrode active material includes particles containing nickel composite hydroxide. The nickel composite hydroxide may be nickel hydroxide or nickel hydroxide in which one or more different metal elements other than nickel such as zinc, cobalt, magnesium, manganese, cadmium, iron, aluminum, chromium, yttrium, etc. are solid-dissolved.

[0078] When the particles containing nickel composite hydroxide are measured by X-ray diffraction, the half-value width of the peak of the (101) surface appearing at 2θ=35°~45° is less than 0.8°. If the half-value width of the peak of the (101) surface is less than 0.8°, the nickel composite hydroxide has less crystal deformation and high crystallinity, so it is difficult for zinc ions in the electrolyte to invade the interlayer of the nickel composite hydroxide. Thus, the expansion of the positive electrode active material and the diffusion barrier of the proton (H+) can be suppressed, and the capacity retention rate after the cycle can be improved. The lower limit of the half-value width of the peak of the (101) surface of the nickel composite hydroxide is not particularly limited, but from the viewpoint of being less likely to damage the utilization rate of the positive electrode active material, it is, for example, 0.4° or more, preferably 0.6° or more.

[0079] In addition, when the particles containing nickel composite hydroxide are measured by X-ray diffraction, the half-value width of the peak of the (001) surface appearing at 2θ=15° to 30° is preferably, for example, less than 0.7°. If the half-value width of the peak of the (001) surface is less than 0.7°, the crystal deformation of the nickel composite hydroxide is less and the crystallinity is higher, so it is possible to make it more difficult for zinc ions in the electrolyte to invade the interlayer of the nickel composite hydroxide. The lower limit of the half-value width of the peak of the (001) surface of the nickel composite hydroxide can be, for example, set to more than 0.4°.

[0080] The X-ray diffraction measurement of the particles containing the nickel composite hydroxide can be performed under the following conditions.

[0081] As a measuring apparatus, an X-ray diffraction apparatus (for example, MiniFlex600 manufactured by Rigaku Corporation) can be used.

[0082] The measurement conditions are as follows.

[0083] X-ray: Cu-Kα ray, 40kV / 15mA

[0084] Scanning range: 5°~70°

[0085] Step width: 0.01°

[0086] Scanning speed: 5° / min.

[0087] The half-value width of the peak of the (101) plane or the (001) plane can be calculated using comprehensive powder X-ray analysis software PDXL2 (manufactured by Rigaku Corporation).

[0088] It should be noted that the above measurement can be performed on the particles containing nickel composite hydroxide as a raw material or on the particles containing nickel composite hydroxide obtained by washing the positive electrode obtained by disassembling a battery with ion exchange water, etc., and then drying and recovering it. It should be noted that the recovered composite particles are preferably screened to remove foamed nickel fragments.

[0089] The half-value width of the peak of the (101) face or (001) face of the particle containing nickel composite hydroxide can be adjusted by the composition of the raw material of the particle or the preparation conditions of the particle described later (pH or reaction temperature of the reaction solution during the precipitation reaction). For example, when preparing particles, the lower the pH of the reaction solution during the precipitation reaction of the nickel composite hydroxide, the more the half-value width of the peak of the (101) face can be reduced. In addition, the higher the temperature of the reaction solution, the more the half-value width of the peak of the (101) face can be reduced. In addition, the more the solid solution amount of zinc in the nickel composite hydroxide is, the more the half-value width of the peak of the (101) face can be reduced. It should be noted that the method for adjusting the half-value width of the above-mentioned peak is not limited to these. In addition, one or more of these methods can be performed.

[0090] Preferably, the particles contain at least nickel hydroxide in which zinc is solid-dissolved as a nickel composite hydroxide. In addition, the particles may contain nickel hydroxide in which cobalt (Co) is solid-dissolved in addition to zinc as a nickel composite hydroxide, or may contain nickel hydroxide in which cobalt (Co) is solid-dissolved instead of zinc as a nickel composite hydroxide. These zinc or cobalt are solid-dissolved in a manner that replaces a portion of the nickel atomic sites of the nickel hydroxide.

[0091] When zinc is dissolved in the nickel composite hydroxide, the amount of zinc dissolved in the particles is preferably 4% by mass or more, more preferably 5% by mass or more, and further preferably 5.1% by mass or more relative to the particles. If the amount of zinc dissolved in the particles is 4% by mass or more, it is difficult for zinc ions in the electrolyte to penetrate into the interlayer of the nickel composite hydroxide as a layered compound. Thus, the expansion of the positive electrode active material or the expansion of protons (H + ) diffusion barrier, can improve the capacity retention rate after the cycle. The upper limit of the solid solution amount of zinc is not particularly limited, but from the viewpoint of further reducing the discharge capacity density reduction associated with the filling capacity density reduction of the nickel composite hydroxide, it can be set to, for example, 10% by mass or less relative to the particle.

[0092] Furthermore, when the particles are composite particles described below, the amount of cobalt (Co) in the composite particles can be 2 to 5% by mass based on the composite particles.

[0093] The amount of zinc or cobalt in the above particles can be measured by inductively coupled plasma optical emission spectrometry (ICP-OES) according to the following procedure.

[0094] 1) A plurality of standard solutions of known concentrations of the element to be measured are prepared, and the emission intensity is measured using an inductively coupled plasma emission spectrometer (ICP spectrometer) to create a calibration curve.

[0095] 2) On the other hand, a solution prepared by dissolving a particle powder containing nickel composite hydroxide in nitric acid is used as a sample solution, and the emission intensity of the sample solution is measured using the above-mentioned apparatus.

[0096] 3) By comparing the measurement results of the sample solution with the calibration curve, the amounts of zinc and cobalt in the particles containing the nickel composite hydroxide can be determined. The measured amount of zinc corresponds to the solid solution amount of zinc.

[0097] Similar to the above-mentioned X-ray diffraction measurement, the above-mentioned measurement can be performed on the particles containing nickel composite hydroxide as a raw material or on the particles containing nickel composite hydroxide recovered by washing a positive electrode obtained by disassembling a battery with an alkaline solution or the like and then drying it.

[0098] Furthermore, the above-mentioned particles may be composite particles including a base particle containing a nickel composite hydroxide and a coating layer containing a cobalt compound doped with an alkali metal.

[0099] The coating layer is configured to coat at least a portion of the surface of the base particle. Preferably, the coating layer contains a cobalt compound doped with an alkali metal. Examples of alkali metals include sodium (Na), lithium (Li), etc. They can be one type or can contain two or more types. The cobalt compound is preferably a trivalent or higher valent cobalt compound such as cobalt oxycobalt hydroxide (CoOOH). In this way, the high-valent cobalt compound introduced with the alkali metal in the crystal has extremely high conductivity.

[0100] The thickness of the coating layer is not particularly limited, for example, it can be set to 0.05 μm to 0.5 μm. If the thickness of the coating layer is 0.05 μm or more, it can not only further improve the conductivity of the positive electrode active material, but also make it less likely for zinc ions to invade the interlayer of the nickel composite hydroxide through electrical action. Therefore, the utilization rate of the positive electrode active material or the capacity retention rate after cycling can be further improved. If the thickness of the coating layer is less than 0.5 μm, the reduction in filling capacity density can be further reduced.

[0101] 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 particle using a cross-sectional polisher and observing the cross section with a scanning electron microscope (SEM).

[0102] The average particle size of the particles containing nickel composite hydroxide is not particularly limited, and is preferably, for example, 10 μm to 20 μm. That is, if the average particle size of the particles is within the above range, the surface area of ​​the particles is further increased, thereby further improving the utilization rate of the positive electrode active material. It should be noted that the average particle size refers to the average particle size (median diameter) with a cumulative mass basis of 50%. The average particle size of the particles can be measured by a laser diffraction / scattering method using a particle size distribution measuring device.

[0103] (Method for producing positive electrode active material)

[0104] The above-mentioned particles containing nickel composite hydroxide can be prepared by any method, for example, by a reaction crystallization method. For example, the above-mentioned composite particles can be prepared by the following method.

[0105] 1) First, an aqueous solution containing nickel sulfate is prepared, and an alkaline aqueous solution such as an aqueous sodium hydroxide solution is slowly added to the aqueous solution to react while controlling the pH, ammonium ion concentration, reaction temperature, etc., thereby precipitating base particles containing nickel composite hydroxide.

[0106] It should be noted that, when zinc and / or cobalt are further dissolved in nickel hydroxide, an aqueous solution containing nickel sulfate and zinc sulfate and / or cobalt sulfate is used as the aqueous solution. In addition, the pH or reaction temperature during the precipitation reaction can be adjusted so that the half-value width of the peak of the (101) surface of the particles finally obtained in the X-ray diffraction measurement is within the above range.

[0107] 2) The obtained base particles are put into an ammonia aqueous solution, and a cobalt sulfate aqueous solution is added to the aqueous solution. Thus, cobalt hydroxide is precipitated on the surface of the base particles as cores, thereby obtaining intermediate particles having a cobalt hydroxide layer.

[0108] The obtained intermediate particles are convected in the air under a high temperature environment, and an aqueous solution containing an alkali metal hydroxide such as an aqueous sodium hydroxide solution or an aqueous lithium hydroxide solution is sprayed while being heat-treated (chemically oxidized) at a specified heating temperature and a specified heating time. Preferably, the heat treatment is maintained at 80°C to 100°C for 30 minutes to 2 hours. Through this treatment, the cobalt hydroxide on the surface of the intermediate particles is converted into a cobalt compound (cobalt hydroxide oxide, etc.) with high conductivity, and alkali metals such as sodium and lithium are introduced into the crystals. Thus, a coating layer containing a cobalt compound doped with an alkali metal is formed.

[0109] (Other ingredients)

[0110] The positive electrode mixture may further contain a positive electrode additive or a binder as needed.

[0111] Examples of positive electrode additives 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 or zinc hydroxide may be added for the purpose of suppressing positive electrode expansion. The content of the zinc compound may be set to 0.1 to 5% by mass relative to the total mass of the positive electrode active material.

[0112] The binder plays the following role: the positive electrode active material and the positive electrode additive are bonded to each other, and the positive electrode active material and the positive electrode additive are bonded to the positive electrode current collector. As the binder, for example, hydrophilic or hydrophobic polymers can be listed, for example, hydroxypropyl cellulose or carboxymethyl cellulose (CMC), sodium polyacrylate, fluorine polymers (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.) can be listed.

[0113] (2) Negative electrode

[0114] The negative electrode 32 includes a negative electrode current collector and a negative electrode mixture.

[0115] The negative electrode current collector may be a non-porous current collector or a porous current collector. The non-porous current collector may be a non-porous foil. The porous current collector may be a metal porous body, a metal perforated plate or a steel plate mesh in a mesh, sponge, fiber or felt shape. The material of the negative electrode current collector may be a metal material that is conductive and stable even at the reaction potential of the negative electrode, including copper and copper alloys (such as brass, etc.), iron, preferably copper. That is, the negative electrode current collector is preferably copper foil.

[0116] The negative electrode current collector may be plated on its surface. The metal constituting the plated film is a metal having a higher hydrogen overpotential than the metal constituting the negative electrode current collector body, preferably a metal having a higher hydrogen overpotential, more preferably a metal having a higher hydrogen overpotential than copper, such as tin.

[0117] The negative electrode mixture is retained on the negative electrode current collector and contains a negative electrode active material. As the negative electrode active material, at least one of zinc, zinc alloy and zinc-containing compound is contained. As metals constituting the zinc alloy, in addition to zinc, bismuth, aluminum, indium and the like can also be listed. As zinc-containing compounds, for example, zinc oxide (grade 1 / grade 2 / grade 3), zinc hydroxide, zinc sulfide, tetrahydroxy zinc ion salts, zinc halides, zinc acetate and zinc tartrate, zinc oxalate represented by carboxylic acid zinc compounds, magnesium zincate, calcium zincate, barium zincate, zinc borate, zinc silicate, zinc aluminate, zinc fluoride, zinc carbonate, zinc bicarbonate, zinc nitrate, zinc sulfate and the like can be listed. Among them, preferably, the negative electrode active material contains zinc oxide as the main component. Including as the main component means that the amount can be, for example, 50% by mass or more relative to the total mass of the negative electrode active material. In addition, preferably, the negative electrode active material further contains zinc (metallic zinc). Zinc can serve as both a discharge reserve and a conductive material.

[0118] The form of the negative electrode active material is, for example, powder. The particle size of the particles of the negative electrode active material is not particularly limited. When zinc or a zinc alloy is used, the average particle size is preferably 10 μm or more and 1000 μm or less. 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 above.

[0119] The negative electrode mixture may further include a negative electrode additive or a binder.

[0120] The negative electrode additive may be, for example, a component that reduces the dissolution 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 hydrates thereof. For example, if potassium oxalate and its hydrates are dissolved in the electrolyte, they dissociate into oxalate ions. Thus, the zinc ions dissolved into the electrolyte form a poorly soluble salt with the oxalate ions, covering the surface of the negative electrode active material, thereby reducing the contact between the metal zinc of the negative electrode active material and the electrolyte.

[0121] The binder plays the following role: the negative electrode active material and the negative electrode additive are bonded to each other, and the negative electrode active material and the negative electrode additive are bonded to the negative electrode current collector. Examples of the binder include hydroxypropyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylic acid, sodium polyacrylate, polyimide, polyamide-imide, polyamide, styrene butadiene rubber, polyethylene oxide, polytetrafluoroethylene, polyvinylidene fluoride, perfluoroalkoxy fluorine resin, tetrafluoroethylene-hexafluoropropylene copolymer, etc. Among them, styrene butadiene rubber is preferred from the viewpoints of high bonding effect and alkali resistance.

[0122] The content of the binder may be an amount sufficient to bind the negative electrode mixture to the negative electrode current collector, and may be, for example, 1% to 5% by mass, preferably 1% to 3% by mass, relative to the total amount of the negative electrode mixture.

[0123] (3) Diaphragm

[0124] As described above, the separator 34 is disposed between the positive electrode 30 and the negative electrode 32 (see Figure 1 ) The separator 34 may be a nonwoven fabric or a microporous membrane.

[0125] The material of the nonwoven fabric and the microporous membrane is 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, polyolefins are preferred, and polypropylene is more preferred, from the viewpoint of mechanical strength or shutdown characteristics.

[0126] The nonwoven fabric and the microporous membrane may be provided with a hydrophilic functional group by a hydrophilic treatment. For example, the nonwoven fabric and the microporous membrane may be provided with a sulfonic group by a sulfonation treatment such as immersion in an acid containing a sulfate group, such as sulfuric acid or fuming sulfuric acid. Thus, the alkaline electrolyte can more easily wet the nonwoven fabric or the microporous membrane.

[0127] The separator 34 may be used alone or in combination of two or more. For example, a laminate of a nonwoven fabric and a hydrophilized microporous membrane may be used as the separator 34 .

[0128] 2. Method for manufacturing nickel-zinc secondary battery

[0129] The nickel-zinc secondary battery can be manufactured by any method. For example, the nickel-zinc secondary battery can be manufactured by the following steps: 1) preparing a positive electrode, a negative electrode and a separator; 2) obtaining a nickel-zinc secondary battery using the prepared positive electrode, negative electrode and separator.

[0130] About the process of 1)

[0131] First, the positive electrode, negative electrode, and separator components are prepared.

[0132] The positive electrode 30 can be produced, for example, by the following steps.

[0133] First, the positive electrode active material, conductive aid, positive electrode additive, binder and water or solvent are mixed and kneaded to obtain positive electrode mixture slurry. Then, the obtained positive electrode mixture slurry is coated on the positive electrode current collector and dried, and then pressed and cut into a predetermined size to obtain the positive electrode. The negative electrode 32 can also be obtained in the same manner.

[0134] About the process of 2)

[0135] Next, a nickel-zinc secondary battery was fabricated using the prepared positive electrode, negative electrode, and separator components.

[0136] Specifically, the prepared positive electrode 30 and negative electrode 32 are wound in an overlapping state with a separator 34 (for example, a laminate of a nonwoven fabric and a microporous film) interposed therebetween to produce a wound body. A positive electrode lead 36 is welded to one end in the longitudinal direction of the positive electrode 30. Then, for example, after the separator 34, the positive electrode 30, the separator 34, and the negative electrode 32 are stacked in sequence, they are wound in the longitudinal direction in such a manner that the negative electrode 32 is on the outside, to obtain a wound body 16.

[0137] The obtained wound body 16 is housed in the outer can 12 , and after the electrolyte is injected, the opening of the outer can 12 is sealed with the sealing body 14 .

[0138] After being placed for a certain period of time, the battery is activated by charging under specified 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, the battery can be charged to a nominal capacity and then discharged to 1.3V at a constant current-constant voltage of 1.9V, and the cycle is performed 5 times. Thus, a nickel-zinc secondary battery 10 can be obtained.

[0139] 3. Modifications

[0140] In addition, in the above-mentioned embodiment, the example of the cylindrical nickel-zinc secondary battery is shown, but it is not limited to this, and a square type or a laminated type nickel-zinc secondary battery may be used.

[0141] Example

[0142] Hereinafter, the present invention will be described in further detail with reference to Examples, but the present invention is not limited thereto.

[0143] 1. Preparation of positive electrode active material particles

[0144] <Preparation of Positive Electrode Active Material Particles A>

[0145] The positive electrode active material particles A were prepared by a reaction crystallization method.

[0146] Specifically, nickel sulfate, zinc sulfate and cobalt sulfate are mixed to prepare an aqueous solution, and ammonium ions are added thereto to prepare an ammine complex. The pH, reaction temperature and ammonium ion concentration are adjusted to specified conditions, and a sodium hydroxide aqueous solution is added thereto to allow a continuous reaction, so that the crystals grow slowly. Thus, a matrix particle of nickel hydroxide in which zinc and cobalt are solid-dissolved is obtained.

[0147] The obtained substrate particles are placed in an aqueous ammonia solution, and an aqueous cobalt sulfate solution is added while adjusting the pH to precipitate cobalt hydroxide on the surface of the substrate particles. The precipitated cobalt hydroxide is converted into cobalt oxyhydroxide (conductive cobalt compound) by spraying an aqueous sodium hydroxide solution thereto in an oxygen-containing atmosphere and heating for chemical oxidation.

[0148] In this way, positive electrode active material particles A having a coating layer containing sodium-introduced cobalt oxyhydroxide on the surface of the base particles were obtained.

[0149] <Preparation of Positive Electrode Active Material Particles B to E>

[0150] Positive electrode active material particles B to E were prepared in the same manner as positive electrode active material particle A, except that the amounts of nickel sulfate, zinc sulfate and cobalt sulfate added in the preparation of the base particles were adjusted, and the pH and reaction temperature during the precipitation reaction when adding sodium hydroxide aqueous solution in the preparation of the base particles were adjusted so that the composition of the positive electrode active material particles finally obtained and the half-value width of the peak on the (101) plane became the values ​​shown in Table 1.

[0151] <Determination of physical properties>

[0152] (composition)

[0153] Composition analysis was performed by inductively coupled plasma optical emission spectrometry (ICP-OES) using a calibration curve method.

[0154] Specifically, a plurality of standard solutions with known concentrations of the elements to be measured are prepared, and the emission intensities are measured using an inductively coupled plasma emission spectrometer to create a calibration curve.

[0155] Then, a solution prepared by dissolving the positive electrode active material powder in nitric acid was used as a sample solution. The emission intensity of the sample solution was measured using the above-mentioned apparatus, and compared with the calibration curve to determine the solid solution amount of each element.

[0156] (Tapped bulk density)

[0157] The tapped bulk 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.

[0158] (Average particle size)

[0159] The average particle size (median diameter) at 50% accumulation on a mass basis is measured by a laser diffraction / scattering method using a particle size distribution measuring apparatus.

[0160] (Specific surface area)

[0161] The specific surface area is measured by the BET method.

[0162] (Half-value width)

[0163] The obtained positive electrode active material particles were subjected to X-ray diffraction measurement. MiniFlex600 manufactured by Rigaku Corporation was used as the measuring device for measurement, and the comprehensive powder X-ray analysis software PDXL2 (manufactured by Rigaku Corporation) was used to calculate the half-value width of the peak of the (101) surface appearing at 2θ=35° to 45° and the half-value width of the peak of the (001) surface appearing at 2θ=15° to 30°. The measurement conditions are as follows.

[0164] X-ray: Cu-Kα ray, 40kV / 15mA

[0165] Scanning range: 5°~70°

[0166] Step width: 0.01°

[0167] Scanning speed: 5° / min.

[0168] The compositions and physical properties of the positive electrode active material particles A to E prepared above are shown in Table 1. In addition, the X-ray diffraction measurement results are shown in the following diagrams: Figure 2 shown. Figure 2 In FIG. 1 , the horizontal axis represents 2θ (deg.) and the vertical axis represents intensity (au). Figure 2 , X-ray diffraction peaks of positive electrode active materials A, B, C, D, and E are shown in order from the bottom.

[0169] Table 1

[0170]

[0171] ※Total amount of Co dissolved in nickel hydroxide of the base particle and Co contained in the coating layer

[0172] (Cross-sectional observation of positive electrode active material particles)

[0173] The obtained positive electrode active material particles were subjected to cross-section polishing (CP) to prepare cross-section samples, and the cross-sections of the particles were observed using a scanning electron microscope (SEM). It was confirmed that the surfaces of the base particles of the obtained positive electrode active material particles were all coated with a coating layer. In addition, the thickness of the coating layer was about 0.1 μm.

[0174] 2. Battery production

[0175] [Example 1]

[0176] (Production of positive electrode)

[0177] 100 parts by mass of positive electrode active material powder consisting of the positive electrode active material particles A prepared above, 1 part by mass of zinc oxide powder, cobalt hydroxide powder, yttrium oxide powder, niobium oxide powder, thickener, PTFE and water were mixed in prescribed amounts to prepare positive electrode mixture slurry.

[0178] The obtained positive electrode mixture slurry was filled into nickel foam, dried, pressed, and cut into a specified size. Thus, a capacity per unit area of ​​13.4 mAh / cm was produced. 2 The positive electrode.

[0179] (Production of negative electrode)

[0180] 100 parts by mass of zinc oxide powder, 25 parts by mass of metal zinc powder, bismuth oxide powder, potassium oxalate monohydrate, a thickener, water, and styrene butadiene rubber were mixed in prescribed amounts to prepare a negative electrode mixture slurry.

[0181] The obtained negative electrode mixture slurry was coated on a copper non-porous foil with a tin-plated surface. After the plate was dried, it was pressed with a pressing roller and cut into a specified size. Thus, a capacity per unit area of ​​25 mAh / cm 2 of the negative electrode.

[0182] (Preparation of Electrolyte)

[0183] 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.

[0184] (Battery production)

[0185] The positive electrode and negative electrode prepared above are wound together with a separator group formed by integrating a non-woven fabric separator and a hydrophilized polypropylene microporous membrane to obtain an electrode group. Specifically, a material in which a separator group / positive electrode / separator group / negative electrode is stacked in sequence is wound to obtain an electrode group in which a negative electrode is arranged on the outermost peripheral surface. This is inserted into a tin-plated outer can.

[0186] Then, 4.550 g of the electrolyte solution prepared above was injected to prepare a cylindrical nickel-zinc secondary battery with a nominal capacity of 2000 mAh. Two nickel-zinc secondary batteries were prepared for analysis and evaluation of cycle characteristics.

[0187] (Activation treatment)

[0188] The obtained battery was activated by performing a cycle of charging to a nominal capacity and then discharging to 1.3 V under a constant current-constant voltage of 1.9 V for 5 times.

[0189] [Example 2, Comparative Example 1 and Comparative Example 2]

[0190] A positive electrode and a battery were prepared 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. The injection amount of the electrolyte solution in both Example 2 and Comparative Example 2 was 5.469 g.

[0191] 3. Evaluation

[0192] (1) Cycle test

[0193] The above-mentioned battery was subjected to a cycle test.

[0194] First, constant current constant voltage (CCCV) charging was performed for 24 hours at a rate of 0.5C and an upper voltage limit of 1.9 V. Then, after a 15-minute pause, constant current (CC) discharge was performed at 0.5C until the voltage reached 1.3 V, and the initial discharge capacity was determined.

[0195] Next, after a 15-minute pause, constant current (CC) charging was performed at a rate of 1.0C until 1.95V, and after a 3-minute pause, constant current constant voltage (CCCV) charging was performed at a rate of 1.0C, an upper limit voltage of 1.9V, and an end current of 0.2C. Then, after a 15-minute pause, constant current (CC) discharge was performed at 1.0C until the voltage reached 1.3V, which was considered as one cycle. 49 cycles of charge and discharge were performed under this condition.

[0196] Finally, constant current constant voltage (CCCV) charging was performed for 24 hours at a rate of 0.5C and an upper voltage limit of 1.9V. Then, after a 15-minute pause, constant current (CC) discharge was performed at 0.5C until the voltage reached 1.3V.

[0197] The charge and discharge of 50 cycles was defined as one set, and four sets (a total of 200 cycles) of charge and discharge were performed.

[0198] Then, the discharge capacity after 200 cycles (201st cycle) and the initial discharge capacity were applied to the following formula to calculate the capacity retention rate.

[0199] Capacity retention rate (%) = (discharge capacity after 200 cycles / initial discharge capacity) × 100

[0200] (2) Utilization rate of positive electrode active material

[0201] The utilization rate was calculated from the discharge capacity of the first cycle based on the following formula.

[0202] Utilization rate of positive electrode active material (%) = (initial discharge capacity / theoretical capacity) × 100

[0203] The evaluation results of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 2.

[0204] Table 2

[0205]

[0206] (Regarding the capacity retention rate after cycling)

[0207] As shown in Table 2, the batteries of Comparative Examples 1 and 2 using positive electrode active material particles having a half-value width of the peak of the (101) plane of 0.8° or more had a capacity retention rate of less than 90% after 200 cycles.

[0208] In contrast, it can be seen that the batteries of Example 1 and Example 2 using positive electrode active materials with a half-value width of the peak of the (101) plane of less than 0.8° have a capacity retention rate of more than 90% after 200 cycles, which is very high. In particular, although the composition of the positive electrode active material particles of Example 2 and Comparative Example 2 is basically the same, the crystallinity is very 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, it is possible to inhibit zinc ions from invading the interlayer of the nickel composite hydroxide.

[0209] This shows that reducing the half-value width of the peak of the (101) plane to less than 0.8° is effective in improving the capacity retention rate of the battery.

[0210] In addition, it is known that Example 2 and Comparative Example 2 with a large amount of injection are compared with Example 1 and Comparative Example 1 with a small amount of injection, and after 200 cycles, the reduction in capacity retention is greater. Generally, if the cycle is repeated, the electrolyte is consumed and the resistance increases. Therefore, it is believed that when the amount of electrolyte injection is large (the capacity-liquid ratio is high), the capacity retention rate after the cycle becomes high, but it is known that the above results are the opposite of the results. It is believed that this is because: the amount of electrolyte is large, the positive electrode is in contact with more electrolyte, and as a result, the amount of poisoning caused by the zinc ions in the electrolyte increases, and the capacity retention rate after the cycle decreases.

[0211] Industrial Applicability

[0212] According to the present invention, a nickel-zinc secondary battery having a good capacity retention rate after cycles can be provided.

Claims

1. A nickel-zinc secondary battery having a positive electrode, a negative electrode and an alkaline electrolyte, characterized in that: The positive electrode includes particles containing nickel composite hydroxide. The particles containing nickel composite hydroxide have a half-value width of a peak of a (101) plane appearing at 2θ=35° to 45° in an X-ray diffraction measurement of less than 0.8°.

2. The nickel-zinc secondary battery according to claim 1, wherein: The particles contain at least nickel hydroxide containing zinc in a solid solution as the nickel composite hydroxide. The amount of the zinc dissolved in the particles is 5 to 10% by mass based on the mass of the particles.

3. The nickel-zinc secondary battery according to claim 1, wherein: 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.

4. The nickel-zinc secondary battery according to claim 1, wherein: The particles have: Base particles containing the nickel composite hydroxide; and The coating layer covers the surface of the base particle and contains a cobalt compound doped with an alkali metal.

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