Zinc electrode for alkaline nickel-zinc batteries and method for the production of the zinc electrode

Abstract

The present application relates to a preparation method of a zinc electrode, comprising the following steps: dissolving a water-soluble organic acid calcium salt in deionized water to obtain a first mixed solution; mixing the first mixed solution, an aqueous binder, a thickening agent and an active material comprising zinc oxide to prepare a negative electrode slurry; coating the slurry on the surface of a current collector and high-temperature baking to prepare the zinc electrode. The present application also relates to the zinc electrode prepared by the above preparation method and the application of the zinc electrode in an alkaline nickel-zinc battery. The zinc electrode prepared by the present application can not only effectively improve the deformation of the zinc electrode and solve the problem of zinc dendrite growth, but also help to improve the utilization rate of the active material of the zinc electrode and improve the cycle performance of the alkaline nickel-zinc battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chemical batteries, in particular to a zinc electrode for alkaline nickel-zinc batteries and a preparation method of the zinc electrode. BACKGROUND

[0002] This section provides background information relating to the application and is not necessarily prior art.

[0003] Alkaline nickel-zinc batteries are electrochemical energy storage devices containing zinc electrodes, and the electrolyte used in alkaline nickel-zinc batteries is an alkaline electrolyte with deionized water as the main solvent. Among them, the zinc electrode as the negative part of the nickel-zinc battery mainly undergoes reversible electrochemical conversion reactions of zinc oxide and metal zinc. Generally, the zinc electrode is composed of zinc oxide, metal zinc powder, binder, metal element, metal oxide or metal hydroxide additives with certain functionality, especially additives to alleviate the hydrogen evolution side reaction, control the deformation of the negative electrode and inhibit the growth of zinc dendrites. The alkaline electrolyte is mainly composed of an aqueous solution of alkaline electrolytes such as sodium hydroxide, potassium hydroxide, lithium hydroxide, etc., which mainly provides hydroxyl ions to participate in the electrochemical reaction of the positive and negative electrodes. Therefore, alkaline nickel-zinc batteries have the intrinsic safety feature, and have broad application prospects in the fields of large-scale electrochemical energy storage, power batteries, data center emergency power supply, backup power supply, electric tools, electric two-wheeled bicycles, etc.

[0004] Because the active material zinc oxide in the zinc electrode has a large solubility in the alkaline electrolyte, it can generate zincate ions Zn(OH)4 2- , such as: at room temperature, the solubility of zinc oxide in 30wt.% potassium hydroxide solution is about 54g / L, and the solubility in 45wt.% potassium hydroxide solution can be as high as 80g / L. Generally, with the increase of the ambient temperature, the solubility of zinc oxide in potassium hydroxide solution will also increase significantly. The chemical reaction that occurs during dissolution is shown below:

[0005] ZnO + H2O + 2OH - → Zn(OH)4 2-

[0006] In addition, the zinc negative electrode of the nickel-zinc battery can also generate zincate ions during the charging and discharging process, which can easily cause the deformation of the zinc negative electrode during electrochemical deposition, and even cause short circuit of the battery due to zinc dendrites, so that the zinc electrode shows a relatively short charging / discharging cycle life. In view of this technical problem, the existing technical solutions include adding various organic and / or inorganic additives to the zinc electrode and / or the alkaline electrolyte to inhibit the dissolution of the zinc electrode discharge product in the alkaline electrolyte, so as to prolong the cycle life of the alkaline nickel-zinc battery.

[0007] The commonly used additive in the prior art is an insoluble inorganic calcium salt (including calcium hydroxide, calcium titanate, calcium oxide, etc.). For example, a zinc electrode uses nano-zinc oxide and metal zinc powder as the main negative active material, and insoluble calcium hydroxide (Ca(OH)2) is added to the zinc electrode as an additive during the manufacturing process of the zinc electrode. During the charging and discharging process of the alkaline nickel-zinc battery, the calcium hydroxide additive can combine with zinc oxide and intermediate products of charging and discharging to form an insoluble phase called calcium zincate, and is identified by x-ray diffraction (XRD) to have the structural formula Ca[Zn(OH)3]2·2H2O. This relatively insoluble phase Ca[Zn(OH)3]2·2H2O can be quickly formed on the surface or inside of the zinc electrode, avoiding the loss of negative active material. On the one hand, by effectively inhibiting the solubility of the zinc oxide active material of the zinc electrode in the alkaline electrolyte, the zincate ion Zn(OH)4 2- is controlled to diffuse randomly in the alkaline electrolyte, and the electrochemical deposition reaction of zinc is limited to a specific area. On the other hand, by anchoring the intermediate products generated during the charging and discharging process of the zinc negative electrode, especially the zincate ion Zn(OH)4 2- , the discharge products of the zinc electrode are limited to a specific area of the zinc electrode, which can effectively inhibit the deformation of the negative electrode and the growth of zinc dendrites to some extent, thereby achieving the purpose of prolonging the cycle life of the zinc electrode.

[0008] However, the commonly used additive in the prior art cannot achieve the desired effect and cannot meet the requirements of the existing production manufacturing process. On the one hand, the micron or sub-micron insoluble inorganic calcium salt (including calcium hydroxide, calcium titanate, calcium oxide, etc.) and the negative active material (nano-zinc oxide and micron metal zinc powder) are in the form of particulate matter in the negative electrode slurry. Due to the large difference in density and particle size of the particulate matter, the uniformity of the negative electrode slurry mixture is still poor, which makes the soluble intermediate product Zn(OH)4 2- generated during the electrochemical process of the zinc electrode become unevenly converted to calcium zincate. As can be seen, the added insoluble inorganic calcium salt has poor anchoring effect on Zn(OH)4 2- , and the calcium element inside cannot be combined with Zn(OH)4 2-The interaction occurs, and the utilization rate of calcium element is low. It should be pointed out that the calcium oxide and other additives will generate a large amount of heat in the production process of the negative electrode slurry, which not only consumes the water in the slurry, but also easily destroys the molecular structure and viscosity of the organic binder in the slurry, seriously affects the slurry drawing or coating effect of the zinc negative electrode, and increases the difficulty of quality control of the zinc electrode. On the other hand, calcium hydroxide and calcium oxide with strong alkalinity can easily react with carbon dioxide in the air to generate calcium carbonate (CaCO3) particles in the actual preparation process of the negative electrode slurry. This will cause the negative electrode slurry to easily deteriorate, and even cause the softness of the zinc electrode to deteriorate. The hardening of the zinc electrode greatly increases the difficulty of the actual cell winding, and the zinc negative electrode is prone to "fragmentation" problems. In addition, the insoluble inorganic calcium salt (such as calcium hydroxide and calcium oxide) with strong alkalinity not only easily causes corrosion to the iron production equipment, but also introduces trace impurity elements such as iron, nickel and manganese in the production equipment into the zinc negative electrode, aggravates the hydrogen evolution side reaction of the zinc negative electrode during charging, and is not conducive to the performance of the alkaline nickel-zinc battery. SUMMARY

[0009] The purpose of the present application is to provide a zinc electrode for an alkaline nickel-zinc battery, and the electrochemical performance of the alkaline nickel-zinc battery using the zinc electrode is significantly improved.

[0010] The zinc electrode mainly includes active material, aqueous binder, functional material and current collector. The active material can be uniformly coated on the surface or pores of the current collector with the assistance of the aqueous binder and thickening agent to form the zinc electrode. The active material mainly includes nano-zinc oxide and metal zinc powder, and can also include carbon-coated zinc oxide nanoparticles. The functional material can include binder, thickening agent, metal oxide, metal hydroxide additive and conductive agent, etc. By introducing water-soluble organic acid calcium salt into the zinc electrode, under the action of alkaline electrolyte (potassium hydroxide, sodium hydroxide, lithium hydroxide), the surface of the active material such as nano-zinc oxide or metal zinc powder of the zinc negative electrode can be in-situ coated to generate uniform calcium hydroxide, calcium zincate and their combinations. During the discharge process of the alkaline nickel-zinc battery, when the zinc oxide or metal zinc is converted into soluble intermediate product zincate ion, it can immediately interact with the uniformly distributed calcium element in the zinc electrode, rapidly generate electrochemically reversible and relatively insoluble calcium zincate phase (Ca(OH)2·2Zn(OH)2·xH2O, x=2 or 3) on the surface and specific area of the zinc electrode by in-situ coating, reduce the solubility of zinc oxide in the alkaline electrolyte and solve the problem of random diffusion of zincate ion, realize the effect of anchoring the soluble intermediate product in a specific area, and effectively reduce the deformation of the zinc electrode and inhibit the growth of zinc dendrites. During the charging and discharging process, the calcium zincate in the zinc electrode can undergo reversible charging and discharging reaction according to the following reaction formula:

[0011]

[0012] During the charging process, the calcium zincate can be electrochemically reduced into a mixture of metallic zinc and calcium hydroxide, which is uniformly present in the zinc electrode, wherein the calcium hydroxide can uniformly coat the surface of active materials such as nano zinc oxide and metallic zinc, not only effectively solving the problem of dissolution of nano zinc oxide in alkaline electrolyte, but also effectively protecting the metallic zinc from corrosion in the alkaline electrolyte environment; during the discharging process, the discharge product zincate ion formed after the oxidation of the metallic zinc can react with the calcium hydroxide at the original position to generate insoluble calcium zincate. Therefore, through the in-situ anchoring of the freely movable zincate ion by chemical interaction, not only the solubility of zinc oxide in the alkaline electrolyte is effectively inhibited, but also the problem of random diffusion of the discharging intermediate product (including zincate ion) of the zinc electrode is completely solved, thereby inhibiting the dendrite growth and negative deformation of the zinc electrode, and the purposes of improving the discharge capacity of the alkaline nickel-zinc battery and prolonging the cycle life of the zinc electrode can be achieved.

[0013] It should be noted that, since the uniformly distributed calcium element in the zinc negative electrode can chemically react with the hydroxyl ion in the alkaline electrolyte, the soluble organic calcium salt helps the penetration or infiltration of the hydroxyl ion in the alkaline electrolyte to the zinc electrode, which is conducive to improving the utilization rate of the negative active material and improving the discharge performance of the alkaline nickel-zinc battery.

[0014] The preparation method of the zinc electrode comprises the following steps:

[0015] a step of dissolving the water-soluble organic acid calcium salt in deionized water to obtain a first mixed solution;

[0016] a step of mixing the first mixed solution, a water-soluble binder, a thickening agent, and an active material including zinc oxide to prepare a slurry;

[0017] a step of uniformly coating the slurry on the surface of the current collector and high-temperature baking to prepare the zinc electrode.

[0018] In the slurry, preferably, the content of the active material is 80-97wt.%, based on the total weight of the water-soluble organic acid calcium salt, the water-soluble binder, the thickening agent, and the active material. Preferably, the total content of the water-soluble binder and the thickening agent is 1-5wt.%, based on the total weight of the water-soluble organic acid calcium salt, the water-soluble binder, the thickening agent, and the active material.

[0019] Among them, the water-soluble organic acid calcium salt used in the present application can be listed as calcium lactate, calcium acetate, calcium L-threonic acid, calcium gluconate, calcium benzoate, calcium glycerophosphate, calcium formate, calcium fumarate, calcium aspartate, calcium malate, calcium maleate, calcium propionate, calcium methylsulfonate, calcium triflate, calcium mellitate, calcium p-toluenesulfonate, and other water-soluble organic acid calcium compounds.

[0020] In one or more embodiments, the water-soluble organic calcium salt can be prepared using an insoluble inorganic calcium salt (e.g., calcium oxide, calcium hydroxide, calcium titanate, calcium carbonate, calcium bicarbonate, etc.) and an organic acid, wherein the organic acid is a water-soluble polyvalent carboxylic acid, such as citric acid, acetic acid, ethylenediaminetetraacetic acid, N-hydroxyethylenediaminetriacetic acid, nitrilotriacetic acid, 1,3-propanediaminetetraacetic acid, succinic acid, fumaric acid, maleic acid, 1,2,3,4-cyclopentanetetraacetic acid, tartaric acid, glutamic acid, methylsulfonic acid, trifluoromethanesulfonic acid, benzenehexacarboxylic acid, p-toluenesulfonic acid, etc.

[0021] In one or more embodiments, the water-soluble organic calcium salt in the first mixed solution has a concentration of 0.005-2 mol / L, preferably 0.01-1.0 mol / L, and more preferably 0.05-0.5 mol / L.

[0022] In one or more embodiments, the pH value of the first mixed solution is 6-8, preferably 6.5-7.5, and more preferably 6.8-7.2. When the pH value of the first mixed solution is greater than 8, calcium hydroxide or calcium carbonate is likely to be formed in the negative electrode slurry prepared subsequently, which in turn causes the zinc electrode to harden and is not conducive to the winding process of the battery cell. In one or more embodiments, the pH value of the first mixed solution can be adjusted using the organic acid corresponding to the water-soluble organic calcium salt contained therein. When the pH value of the first mixed solution is less than 6, the dissolution of the active material zinc oxide and the corrosion of the metal zinc are likely to occur. In one or more embodiments, the pH value of the first mixed solution can also be adjusted using an alkaline solution.

[0023] In one or more embodiments, when the zinc electrode is used as the negative electrode of the alkaline nickel-zinc battery, the following electrochemical reactions mainly occur during the charging and discharging processes: during the charging process, the active material zinc oxide of the zinc electrode is reduced to metal zinc by obtaining electrons; and during the discharging process, the metal zinc is oxidized to zinc oxide by losing electrons. It should be noted that during the electrochemical conversion reaction between zinc oxide and metal zinc, the soluble intermediate product zincate ion Zn(OH)4 2- is likely to be generated. In addition, zinc oxide and metal zinc can also interact with alkaline substances such as potassium hydroxide, sodium hydroxide, and lithium hydroxide in the alkaline electrolyte to generate soluble zincate ions. As can be seen, the zinc negative electrode mainly undergoes the electrochemical mutual conversion reaction between metal zinc and zinc oxide, which is actually the electrochemical deposition of zinc and the dissolution of zinc.

[0024] Charging process: ZnO + H2O + 2e - → Zn + 2OH -

[0025] Discharging process: Zn + 2OH - → ZnO + H2O + 2e-

[0026] Therefore, the active material of the zinc electrode can include any one of metal zinc, zinc compounds and zinc alloys in addition to the nano-zinc oxide. It should be noted that the composite material with carbon coated on the surface of zinc oxide or zinc compounds can be used as the active material of the zinc electrode. The mercury-free zinc alloy, as a kind of zinc alloy, contains trace elements such as 0.01-0.06wt.% indium (In), 0.005-0.02wt.% bismuth (Bi), 0.0035-0.015wt.% aluminum (Al), etc., and has a good effect on inhibiting hydrogen evolution, so it is preferably used. In particular, the indium (In) and bismuth (Bi) elements have a significant effect on improving the charge and discharge performance of the alkaline nickel-zinc battery. Using the mercury-free zinc alloy as the active material of the zinc electrode can effectively slow down the corrosion rate of the zinc electrode in the alkaline electrolyte, and can also effectively inhibit the hydrogen evolution side reaction, avoid the dryness of the electrolyte or the "alkali climbing" phenomenon of the alkaline nickel-zinc battery, and prolong the cycle service life of the nickel-zinc battery.

[0027] In one or more embodiments, the average particle size of the zinc oxide in the active material is 100-400 nm.

[0028] In one or more embodiments, the average particle size of the metal zinc powder in the active material is 10-200 μm.

[0029] In one or more embodiments, the average particle size of the mercury-free zinc alloy is 10-200 μm.

[0030] The water-soluble binder is used to improve the binding properties of the active material particles to each other and the binding properties of the active material to the current collector. The water-soluble binder can be a rubber-based binder or a polymer resin binder. The rubber-based binder can be selected from styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymer resin binder can be selected from polytetrafluoroethylene, ethylene propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof. The thickening agent can be sodium carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, sodium alginate, beta-cyclodextrin, sodium starch phosphate, hydroxypropyl starch, gelatin, and xanthan gum, and combinations thereof.

[0031] The alkaline solution comprises any one or several of lithium hydroxide solution, sodium hydroxide solution and potassium hydroxide solution. The mass ratio of potassium hydroxide, sodium hydroxide and lithium hydroxide is 10-30:1-10:1. The concentration of hydroxyl ions is preferably 6-18 mol / L, more preferably 8-16 mol / L, and even more preferably 10-15 mol / L.

[0032] As examples of the current collector, there are, for example, a porous metal, an expanded alloy, a screen, a cable-stayed net, a foam, a three-dimensional punched foil, a three-dimensional burr net, a punched foil, and a porous metal. As a material constituting the current collector, a metal having high conductivity and high corrosion resistance is preferable, and a pure copper and a copper alloy (for example, brass, phosphor copper, and the like) are more preferable, and a pure copper is most preferable. In addition, the surface of the current collector has good conductivity. Therefore, it can be a structure in which the surface is made of copper, tin, a copper alloy, or a tin alloy, and the inside is made of other materials such as zinc (Zn), aluminum (Al), antimony (Sb), bismuth (Bi), indium (In), titanium (Ti), and the like, and the material in the inside is not limited to a metal. The surface of the current collector can be plated with a metal such as zinc (Zn), tin (Sn), indium (In), bismuth (Bi), aluminum (Al), silver (Ag), mercury (Hg), lead (Pb), and the like, and plating with tin is preferable. According to such plating, it is possible to effectively suppress the occurrence of a hydrogen evolution side reaction on the surface of the zinc electrode and to improve the corrosion resistance of the current collector in an alkaline environment.

[0033] It should be noted that the addition of the alkaline electrolyte containing potassium hydroxide, sodium hydroxide and lithium hydroxide into the cell composed of a zinc negative electrode sheet and a Ni(OH)2positive electrode sheet mainly causes the following chemical reactions in the negative electrode sheet:

[0034]

[0035] From the thermodynamic aspect, the reaction can occur spontaneously inside the alkaline nickel-zinc battery. The active material (zinc oxide and zinc powder particles) on the surface of the zinc electrode is coated with calcium hydroxide, calcium zincate and their combinations in situ. In addition, the soluble zincate ions formed during the charging and discharging process can be effectively anchored in a specific area of the zinc electrode by the uniformly distributed calcium element, avoiding the deformation of the zinc electrode and inhibiting the growth of zinc dendrites during the charging and discharging process.

[0036] In one or more embodiments, the active material for preparing the slurry can also be carbon-coated zinc oxide nanoparticles, carbon-coated zinc carbonate, carbon-coated calcium zincate, carbon-coated metallic zinc, and combinations thereof.

[0037] In one or more embodiments, functional materials such as rare earth oxides, metal oxide additives, metal hydroxide additives, binders, tackifiers, conductive agents, etc. are also added when preparing the slurry. As the rare earth oxides, cerium dioxide, yttrium oxide, erbium oxide, dysprosium oxide, samarium oxide, gadolinium oxide, lanthanum oxide, etc. can be mentioned. As the oxide additives, magnesium oxide, mercury oxide, lead oxide, barium oxide, aluminum oxide, bismuth oxide, indium oxide, boron oxide, and silicon dioxide, etc. can be mentioned. As the hydroxide additives, bismuth hydroxide, indium hydroxide, barium hydroxide, magnesium hydroxide, and aluminum hydroxide, etc. can be mentioned. As examples of the binders, polytetrafluoroethylene emulsion, butadiene-styrene rubber emulsion, polyvinyl alcohol, and acrylonitrile multi-copolymer aqueous binder, etc. can be mentioned. As examples of the tackifiers, sodium carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, sodium alginate, beta-cyclodextrin, sodium starch phosphate, hydroxypropyl starch, gelatin, and xanthan gum, etc. can be mentioned. As examples of the conductive agents, metal tin powder, mercury-free zinc alloy powder, metal copper powder, metal indium powder, metal bismuth powder, metal titanium powder, metal antimony powder, metal tungsten powder, natural graphite, artificial graphite, carbon fiber, graphene, graphene oxide, carbon nanotube, conductive carbon black, and organic polymer compound calcined body, etc. can be mentioned.

[0038] In one or more embodiments, a roll pressing process is performed on the zinc electrode after high-temperature baking to prevent active material shedding and improve the compaction density of the zinc electrode.

[0039] In one or more embodiments, an edge grinding process is performed on the zinc electrode to remove metal burrs generated during the hardware mold or laser slitting process, further avoiding the possibility of short circuiting between the zinc electrode and the positive electrode.

[0040] In one or more embodiments, a kneading softening process is performed on the zinc electrode to improve the softness of the zinc electrode, further improving the penetration and infiltration of the alkaline electrolyte into the zinc electrode.

[0041] In one or more embodiments, tab welding is required for the zinc electrode, and the tab can use a metal sheet with good electrical conductivity, high alkaline resistance, and high hydrogen overpotential, such as a copper sheet, a zinc sheet, a tin-plated copper sheet, a zinc-copper alloy, etc., to improve electron transport during charging and discharging.

[0042] It should be noted that the zinc electrode provided by the present application can not only be applied to alkaline zinc-nickel batteries, but also to alkaline silver-zinc secondary batteries and alkaline zinc-manganese secondary batteries, etc.

[0043] Compared with the prior art, the present application has the following advantages:

[0044] 1. The zinc electrode prepared by the preparation method provided by the present application can significantly improve the performance of alkaline nickel-zinc batteries, especially the utilization rate of zinc oxide active material and the capacity retention rate during the cycle process.

[0045] 2. The preparation method provided by the application can effectively improve the infiltration of the zinc electrode to the alkaline electrolyte, which is mainly due to the interaction between the soluble calcium ions in the zinc electrode and the hydroxyl ions in the alkaline electrolyte, which is beneficial to promote the rapid penetration and infiltration of the hydroxyl ions to the zinc electrode in the charging and discharging process.

[0046] 3. The water-soluble organic acid calcium salt provided by the application has high solubility, which is helpful to the uniform distribution of calcium elements in the zinc electrode, effectively improves the utilization rate of calcium atoms, and further strengthens the anchoring effect between the calcium elements and the zinc oxide nanoparticles and the charging and discharging intermediates. By the zinc electrodeposition and dissolution reaction in a specific area, the deformation of the zinc electrode can be maximally reduced, and even the growth of zinc dendrites can be reduced, thereby prolonging the cycle life of the alkaline nickel-zinc battery.

[0047] 4. The preparation method provided by the application can be realized on the existing electrode piece preparation equipment. Since the negative electrode slurry has mild properties without strong alkalinity and corrosion, the "hardening" of the zinc electrode caused by calcium hydroxide or calcium carbonate generated in the preparation process can be avoided, and the impurity elements such as iron, nickel and manganese in the equipment can be effectively avoided to be introduced into the zinc electrode, thereby affecting the performance of the alkaline nickel-zinc battery.

[0048] The application will be described in detail below with reference to specific examples. BRIEF DESCRIPTION OF DRAWINGS

[0049] The accompanying drawings further illustrate the application, but the examples in the drawings do not constitute any limitation on the application.

[0050] Figure 1 The surface FE-SEM microstructure and EDS element distribution test results of the zinc electrode provided for the application example 1 are shown in the following table. Figure 1 a is the FE-SEM microstructure; Figure 1 b is the Zn element distribution; Figure 1 c is the O element distribution; Figure 1 d is the C element distribution; Figure 1 e is the Ca element distribution.

[0051] Figure 2 The surface FE-SEM microstructure and EDS element distribution test results of the zinc electrode provided for the application example 2 are shown in the following table. Figure 2 a is the FE-SEM microstructure; Figure 2 b is the Zn element distribution; Figure 2 c is the O element distribution; Figure 2 d is the C element distribution; Figure 2 e is the Ca element distribution.

[0052] Figure 3The surface FE-SEM microstructure and EDS element distribution test results of the zinc electrode provided in Example 3 of the present application are shown in the following figures: Figure 3 a is the FE-SEM microstructure; Figure 3 b is the Zn element distribution; Figure 3 c is the O element distribution; Figure 3 d is the C element distribution; Figure 3 e is the Ca element distribution.

[0053] Figure 4 The contact angle test results of the zinc electrode are shown in the following figures: Figure 4 a is the zinc electrode provided in Example 3 of the present application; Figure 4 b is the zinc electrode provided in Comparative Example 1 of the present application.

[0054] Figure 5 The performance test results of the CR2032 button cell prepared by using the zinc electrode provided in Example 1 of the present application are shown in the following figures: Figure 5 a is the cycle performance data; Figure 5 b is the data of discharge platform, Figure 5 c is the first 5 cycles of charge-discharge curves.

[0055] Figure 6 The performance test results of the CR2032 button cell prepared by using the zinc electrode provided in Example 2 of the present application are shown in the following figures: Figure 6 a is the cycle performance data; Figure 6 b is the data of discharge platform, Figure 6 c is the first 5 cycles of charge-discharge curves.

[0056] Figure 7 The performance test results of the CR2032 button cell prepared by using the zinc electrode provided in Example 3 of the present application are shown in the following figures: Figure 7 a is the cycle performance data; Figure 7 b is the data of discharge platform; Figure 7 c is the first 5 cycles of charge-discharge curves.

[0057] Figure 8 The performance test results of the CR2032 button cell prepared by using the zinc electrode provided in Comparative Example 1 of the present application are shown in the following figures: Figure 8 a is the cycle performance data; Figure 8 b is the data of discharge platform; Figure 8 c is the first 5 cycles of charge-discharge curves. DETAILED DESCRIPTION

[0058] It should be understood that the specific embodiments described herein merely exemplify the application and do not limit the application.

[0059] The zinc electrode provided in the embodiments of the present application can be applied to alkaline nickel-zinc batteries as the negative electrode of the alkaline nickel-zinc batteries.

[0060] [Alkaline nickel-zinc battery]

[0061] The alkaline nickel-zinc battery includes a sealed container, and a positive electrode, an electrolyte, a negative electrode, and a separator are provided in the sealed container.

[0062] [Positive electrode]

[0063] The positive electrode includes a positive electrode active material and a positive electrode current collector, and the positive electrode active material contains nickel hydroxide and / or nickel oxyhydroxide. The nickel hydroxide is usually in the form of spherical particles, and can have a doping element other than nickel solid-solved in the crystal lattice thereof, which helps to improve the cycle performance and higher coulomb efficiency at high temperatures of the alkaline nickel-zinc battery. As examples of the doping element, elements such as zinc (Zn), cobalt (Co), aluminum (Al), magnesium (Mg), tungsten (W), titanium (Ti), barium (Ba), zirconium (Zr), and the like can be listed. A cobalt-based compound can be directly added to the nickel hydroxide active material for use, and as examples of such a cobalt-based compound, cobalt metal powder, cobalt monoxide, cobalt sesquioxide, cobalt trioxide, and any combination thereof can be listed. In addition, the nickel hydroxide spherical particles, particularly the positive electrode material having the doping element solid-solved therein, can be subjected to surface coating treatment with a cobalt-based compound. As examples of such a cobalt-based compound, cobalt monoxide, α-type cobalt hydroxide, β-type cobalt hydroxide, a compound of a higher valence cobalt than 2, and any combination thereof can be listed.

[0064] The positive electrode active material can further contain an additional element in addition to the nickel hydroxide-based compound and the doping element that can be solid-solved in the nickel hydroxide-based compound. As examples of such an additional element, elements such as scandium (Sc), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), lutetium (Lu), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), and any combination thereof can be listed. The form of the additional element is not particularly limited, and can be in the form of a metal element or a metal compound (e.g., an oxide, a hydroxide, a nitride, a sulfide, a carbide, a halide, and a carbonate). The amount of the metal element or the metal compound of the additional element to be added is preferably 0.5 to 20 parts by weight, and more preferably 1 to 5 parts by weight, with respect to 100 parts by weight of the nickel hydroxide-based compound.

[0065] The positive electrode may also contain a conductive material, a binder, and a thickener as needed. Examples of conductive materials include graphite, graphene, graphene oxide, carbon black, nickel powder, tungsten powder, and cobalt powder. Examples of binders and thickeners include polyvinylidene fluoride, polyvinyl alcohol, hydroxypropyl methylcellulose, sodium carboxymethylcellulose, sodium polyacrylate, polystyrene butadiene copolymer, and polytetrafluoroethylene.

[0066] The positive electrode can also be prepared using a dry process or a wet process as needed. During the preparation process, the positive electrode active material, conductive agent, binder, etc. can be fully premixed.

[0067] As a preferred example of the positive electrode current collector, a nickel porous substrate such as a foamed nickel plate can be cited. In this case, for example, it is preferred to uniformly apply a positive electrode slurry containing an active material such as nickel hydroxide on a nickel porous substrate and dry it to produce a positive electrode formed by a positive electrode active material and a positive electrode current collector. At this time, it is also preferred to perform a roller pressing process on the dried positive electrode to prevent the positive electrode active material from falling off and to increase the compaction density of the electrode. It is also preferred to perform an edge grinding process on the dried positive electrode to reduce the risk of battery short circuit by removing possible metal burrs. It is also preferred to perform a sheet kneading process on the dried positive electrode to improve the softness of the positive electrode sheet, thereby not only avoiding the breakage of the electrode sheet during the winding process of the battery cell, but also helping the alkaline electrolyte to quickly penetrate into the positive electrode sheet.

[0068] [Electrolyte]

[0069] The electrolyte contains an alkali metal hydroxide. An aqueous solution containing an alkali metal hydroxide is used as the electrolyte for alkaline nickel-zinc batteries. Examples of alkali metal hydroxides include potassium hydroxide, sodium hydroxide, and lithium hydroxide. The mass ratio of potassium hydroxide, sodium hydroxide, and lithium hydroxide is 10-30:1 to 10:1. To inhibit zinc corrosion in an alkaline environment, compounds such as zinc oxide, zinc hydroxide, fumed silica, and aluminum hydroxide may be added to the alkaline electrolyte. To inhibit gas evolution during charge and discharge, trace amounts of compounds such as indium (In), bismuth (Bi), tin (Sn), lead (Pb), magnesium (Mg), barium (Ba), calcium (Ca), aluminum (Al), mercury (Hg), and lead (Pb) may be added to the alkaline electrolyte. Examples include hydroxides, sulfides, halides, nitrates, nitrites, sulfates, phosphates, pyrophosphates, polyphosphates, and any combination thereof. To inhibit deformation of the zinc negative electrode, soluble organic calcium salts, zinc oxide, and calcium hydroxide may be added to the alkaline electrolyte. Examples of the soluble organic calcium salt include at least one of calcium lactate, calcium acetate, calcium L-threonate, calcium gluconate, calcium benzoate, calcium glycerophosphate, calcium formate, calcium fumarate, calcium aspartate, calcium malate, calcium maleate, calcium propionate, calcium methanesulfonate, calcium trifluoromethanesulfonate, calcium mellitic acid, and calcium p-toluenesulfonate.

[0070] The preferred concentration of the alkali hydroxide in the electrolyte is 6-18 mol / L, more preferably 8-16 mol / L, and even more preferably 10-15 mol / L. A higher concentration of hydroxyl ions in the alkaline electrolyte can not only improve the ion conductivity of the electrolyte, reduce the internal resistance of the alkaline nickel-zinc battery, and improve the rate performance of the alkaline nickel-zinc battery, but also promote the participation of soluble organic calcium salt in the in-situ coating reaction on the surface of the active material, effectively inhibit the deformation of the zinc electrode, and prolong the cycle life of the alkaline nickel-zinc battery.

[0071] [Separator]

[0072] The separator is a component that is interposed between the nickel hydroxide positive electrode and the zinc negative electrode, maintains insulation between the positive electrode and the negative electrode, and can conduct hydroxyl ions. As the separator, for example, a resin-made porous membrane, a resin-made non-woven fabric, or the like can be used. As examples of the resin, polyolefin, fluorine-based polymer, cellulose-based polymer, polyimide, nylon, and the like can be given. The separator can be a single-layer structure or a laminated structure of two or more layers. For example, a three-layer composite structure in which a polyethylene (PE) plastic layer is laminated on both sides of a polypropylene (PP) plastic layer, and the composite can be made by water-soluble glue or hot-pressing technology. The separator of the alkaline nickel-zinc battery has a strong electrolyte absorption capacity and can solve the short circuit problem caused by zinc dendrites. In order to further improve the hydrophilicity and liquid absorption performance of the separator, the surface of the non-woven fabric separator can be subjected to grafting or sulfonation treatment. In order to avoid short circuit caused by zinc dendrites, the pore size range of the separator needs to be controlled to 10-80 nm. In addition, in order to improve the thermal stability of the separator, the separator can use a separator coated with oxides such as zinc oxide, silicon dioxide, aluminum oxide, titanium dioxide, magnesium oxide, and / or nitrides such as aluminum nitride, silicon nitride, and boron nitride on a porous substrate.

[0073] [Example 1]

[0074] The present embodiment provides a zinc electrode, and a preparation method thereof, which comprises the following steps:

[0075] Step one, dissolving calcium lactate in deionized water to obtain a first mixed solution, the content of calcium ions in the first mixed solution is 0.1 mol / L;

[0076] Step two, mixing the first mixed solution, carbon-coated zinc oxide particles (average particle size: 100-400 nm), zinc powder particles, and styrene-butadiene rubber, sodium carboxymethyl cellulose in a general mixer and stirring sufficiently to obtain a uniformly dispersed negative electrode slurry, the mass ratio of calcium lactate, carbon-coated zinc oxide particles, zinc powder particles, styrene-butadiene rubber, and sodium carboxymethyl cellulose in the negative electrode slurry is 1:90:7:1:1;

[0077] Step three, tin-coated copper foil with a thickness of 25 μm was used as the current collector. The negative electrode slurry was uniformly coated on the surface of the current collector according to a conventional method with a coating amount of 8 mg / cm 2 , and then vacuum high-temperature baking was performed at 150°C for 1 hour.

[0078] Step four, the dried electrode sheet was subjected to roll pressing treatment with a roll pressing tonnage of 35T to obtain a zinc electrode.

[0079] [Example 2]

[0080] The example provides a zinc electrode, and a preparation method of the zinc electrode comprises the following steps:

[0081] Step one, calcium L-threonate was dissolved in deionized water to obtain a first mixed solution, and the content of calcium L-threonate in the first mixed solution was 0.05 mol / L;

[0082] Step two, the first mixed solution, carbon-coated zinc oxide particles (average particle size: 100-400 nm), zinc powder particles, and styrene-butadiene rubber and sodium carboxymethyl cellulose were mixed and fully stirred in a general mixer to obtain a uniformly dispersed negative electrode slurry, and the mass ratio of calcium L-threonate, carbon-coated zinc oxide particles, zinc powder particles, styrene-butadiene rubber and sodium carboxymethyl cellulose in the negative electrode slurry was 1:90:7:1:1;

[0083] Step three, tin-coated copper foil with a thickness of 25 μm was used as the current collector. The negative electrode slurry was uniformly coated on the surface of the current collector according to a conventional method with a coating amount of 8 mg / cm 2 , and then vacuum high-temperature baking was performed at 150°C for 1 hour.

[0084] Step four, the dried electrode sheet was subjected to roll pressing treatment with a roll pressing tonnage of 35T to obtain a zinc electrode.

[0085] [Example 3]

[0086] The example provides a zinc electrode, and a preparation method of the zinc electrode comprises the following steps:

[0087] Step one, calcium acetate was dissolved in deionized water to obtain a first mixed solution, and the content of calcium acetate in the first mixed solution was 0.1 mol / L;

[0088] Step two, the first mixed solution, carbon-coated zinc oxide particles (average particle size: 100-400 nm), zinc powder particles and styrene-butadiene rubber, sodium carboxymethyl cellulose are mixed and fully stirred in a general mixer to obtain a uniformly dispersed negative electrode slurry, and the mass ratio of calcium acetate, carbon-coated zinc oxide particles, zinc powder particles, styrene-butadiene rubber and sodium carboxymethyl cellulose in the negative electrode slurry is 1:87:10:1:1;

[0089] Step three, using a tin-plated copper foil with a thickness of 20 μm as the current collector. According to a conventional method, the negative electrode slurry is uniformly coated on the surface of the current collector with a coating amount of 12 mg / cm 2 , and then vacuum high-temperature baking is performed at 180°C for 30 minutes.

[0090] Step four, the dried electrode piece is subjected to roll pressing treatment with a roll pressing tonnage of 35T to obtain a zinc electrode.

[0091] [Comparative Example 1]

[0092] The difference between this comparative example and Example 1 is only that calcium lactate is not used in the preparation of the zinc electrode.

[0093] Step one, carbon-coated zinc oxide particles (average particle size: 100-400 nm), zinc powder particles, styrene-butadiene rubber and sodium carboxymethyl cellulose are mixed in a mass ratio of 90:8:1:1 and fully stirred in a general mixer to obtain a uniformly dispersed negative electrode slurry;

[0094] Step two, using a tin-plated copper foil with a thickness of 25 μm as the current collector. According to a conventional method, the negative electrode slurry is uniformly coated on the surface of the current collector with a coating amount of 10 mg / cm 2 , and then vacuum high-temperature baking is performed at 160°C for 30 minutes.

[0095] Step three, the dried electrode piece is subjected to roll pressing treatment with a roll pressing tonnage of 35T to obtain a zinc electrode.

[0096] [Comparative Example 2]

[0097] This comparative example provides a zinc electrode, and the preparation method of the zinc electrode comprises the following steps:

[0098] Step one, calcium hydroxide and deionized water are mixed to obtain a first suspension liquid, and 7.41 g of calcium hydroxide corresponds to 1 L of deionized water;

[0099] Step two, the first mixed solution, carbon-coated zinc oxide particles (average particle size: 100-400 nm), zinc powder particles, styrene-butadiene rubber and sodium carboxymethyl cellulose are mixed and fully stirred in a general mixer to obtain a uniformly dispersed negative electrode slurry, and the mass ratio of calcium hydroxide, carbon-coated zinc oxide particles, zinc powder particles, styrene-butadiene rubber and sodium carboxymethyl cellulose in the negative electrode slurry is 1:90:7:1:1;

[0100] Step three, using a tin-plated copper foil with a thickness of 25 μm as the current collector. According to the conventional method, the negative electrode slurry is uniformly coated on the surface of the current collector with a coating amount of 10 mg / cm 2 , and then vacuum high-temperature baking is carried out at 150°C for 1 hour.

[0101] Step four, the dried electrode piece is subjected to roll pressing treatment, and the roll pressing tonnage is 35T to obtain a zinc electrode.

[0102] [Comparative Example 3]

[0103] The present comparative example provides a zinc electrode, and the preparation method of the zinc electrode comprises the following steps:

[0104] Step one, acetic acid is dissolved in deionized water to obtain a first mixed solution, and the content of acetic acid in the first mixed solution is 0.1 mol / L;

[0105] Step two, the first mixed solution, carbon-coated zinc oxide particles (average particle size: 100-400 nm), zinc powder particles, styrene-butadiene rubber and sodium carboxymethyl cellulose are mixed, and the mass ratio of acetic acid, carbon-coated zinc oxide particles, zinc powder particles, styrene-butadiene rubber and sodium carboxymethyl cellulose is 1:87:10:1:1, and fully stirred in a general mixer to obtain a uniformly dispersed negative electrode slurry;

[0106] Step three, the pH of the negative electrode slurry is adjusted to 7.2 using a 0.5 mol / L sodium hydroxide solution, and a tin-plated copper foil with a thickness of 10 μm is used as the current collector. According to the conventional method, the negative electrode slurry is coated on the surface of the copper foil with a coating amount of 22 mg / cm 2 , and then vacuum high-temperature baking is carried out at 140°C for 10 hours;

[0107] Step four, the dried electrode piece is subjected to roll pressing treatment, and the roll pressing tonnage is 35T to obtain a zinc electrode. Current collector.

[0108] [Comparative Example 4]

[0109] The present comparative example provides a zinc electrode, and the preparation method of the zinc electrode comprises the following steps:

[0110] Step one, put calcium hydroxide particles and zinc oxide particles with average particle size of 100-400nm into the ball mill pot of the planetary ball mill;

[0111] Step two, according to the mass ratio of ball to material of 4:1, add stainless steel balls into the ball mill pot, then add deionized water, and carry out ball milling under the protection of argon gas at a rotating speed of 300r / min. After ball milling for 15 hours, take out the product and bake at 50℃ for 12 hours to obtain a first mixture;

[0112] Step three, fully stir deionized water, the first mixture, zinc powder particles, and styrene-butadiene rubber and sodium carboxymethyl cellulose in a general mixer until a uniform negative electrode slurry is obtained. In the negative electrode slurry, the mass ratio of calcium hydroxide, zinc oxide particles, zinc powder particles, styrene-butadiene rubber and sodium carboxymethyl cellulose is 1:90:7:1:1. Adjust the pH of the slurry to 7.2 using 0.5mol / L sodium hydroxide solution;

[0113] Step four, use a tin-plated copper foil with a thickness of 10μm as the current collector. According to the conventional method, coat the slurry on the surface of the copper foil with a coating amount of 22mg / cm 2 , and then carry out vacuum high-temperature baking at 140℃ for 10 hours to obtain a zinc electrode.

[0114] [Comparative test]

[0115] The zinc electrodes prepared in Examples 1-3 were observed by field emission scanning electron microscopy (FE-SEM), and the observed areas were tested for element distribution using an x-ray energy dispersive spectrometer (EDS) device. The results are shown in Figures 1-3 . The calcium element distribution of the zinc electrodes prepared by the preparation methods of Examples 1-3 is uniform and good. On the one hand, the uniform distribution of calcium elements is conducive to reducing the solubility of zinc oxide in the alkaline electrolyte and inhibiting the diffusion of zincate ions in the electrolyte, improving the deformation of the zinc electrode and inhibiting the growth of zinc dendrites. On the other hand, the uniform distribution of calcium elements helps to effectively anchor the zincate ions formed during the charging and discharging process of the alkaline nickel-zinc battery, forming a relatively insoluble calcium zincate phase on the surface or in a specific area of the zinc electrode, thereby improving the cycle performance of the alkaline nickel-zinc battery.

[0116] It should be noted that, as shown in Figure 1 a, Figure 2 a and Figure 2 c, the surface FE-SEM microtest results of the zinc electrode show that the zinc negative electrode is mainly composed of 100-400nm carbon-coated nanometer zinc oxide particles. In addition, the EDS element distribution test can clearly see the uniform distribution of Zn, O, C and Ca elements. Among them, as shown in Figure 1 b, Figure 2 b andFigure 3 b, Zn element is uniformly distributed, mainly from active material zinc oxide or zinc metal; as shown in Figure 1 c, Figure 2 cand Figure 3 c, O element is uniformly distributed, mainly from active material zinc oxide; as shown in Figure 1 d, Figure 2 dand Figure 3 d, C element is uniformly distributed, mainly from carbon coating layer, water-based binder and thickening agent; as shown in Figure 1 e, Figure 2 eand Figure 3 e, Ca element is uniformly distributed, mainly from soluble organic calcium salt. If insoluble inorganic calcium salt is used, Ca element is relatively concentrated, mainly affected by its particle size and solubility. Ca element in zinc electrodes prepared in Examples 1-3 is uniformly distributed, mainly related to the fact that calcium ions exist in the negative electrode slurry.

[0117] The zinc electrodes prepared in Examples 1-3 and the zinc electrodes prepared in Comparative Examples 1-4 were subjected to contact angle test with alkaline electrolyte. The contact angle test was carried out in an environment with temperature of 20-25°C and humidity of ≤50% RH. 1 μL of alkaline electrolyte was dropped onto the surface of the zinc electrode through a plastic dropper. The smaller the angle between the liquid surface and the zinc electrode, the more sufficient the wetting of the alkaline electrolyte. The better the wetting of the zinc electrode with the alkaline electrolyte, the more conducive to the performance improvement of the alkaline nickel-zinc battery. The contact angle test results are shown in Table 1.

[0118] It should be noted that the soluble organic calcium salt can greatly improve the wetting of the zinc electrode with the alkaline electrolyte. As shown in Figure 4 , by comparing Example 3 Figure 4 (a) and Comparative Example 1 Figure 4 (b), when the soluble organic calcium salt (calcium acetate) is added, the contact angle of the zinc electrode with the alkaline electrolyte is 73.2°, which is significantly lower than that of the zinc electrode without the addition of the organic calcium salt (83.6°). This is mainly related to the uniform distribution of the soluble organic calcium salt in the zinc electrode. The calcium ions in the soluble organic calcium salt can chemically react with the hydroxide ions in the alkaline electrolyte, and calcium hydroxide or calcium zincate can be generated in situ on the surface of the active material zinc oxide and zinc powder in the alkaline nickel-zinc battery. This not only promotes the penetration of the alkaline electrolyte into the interior of the zinc negative electrode, but also reduces the solubility of zinc oxide in the alkaline electrolyte and solves the problem of random diffusion of zincate ions in the alkaline electrolyte during the charging and discharging process.

[0119] [Manufacturing method of alkaline nickel-zinc battery]

[0120] The zinc electrodes prepared in Examples 1-3 and the zinc electrodes prepared in Comparative Examples 1-4 were applied to the preparation of alkaline nickel-zinc batteries, in accordance with the following procedure.

[0121] Step 1. The positive and negative steel can of a standard CR2032 button cell were prepared by drawing a metal sheet, using a nickel and tin plated iron substrate, respectively.

[0122] Step 2. The positive electrode was prepared by using foamed nickel as the positive current collector, and filling the foamed nickel with a positive active material, a conductive agent, and a binder. The positive electrode mainly comprised: nickel hydroxide, metallic nickel, yttrium oxide, polytetrafluoroethylene, and carboxymethyl cellulose. The mass ratio of nickel hydroxide, metallic nickel, yttrium oxide, polytetrafluoroethylene, and carboxymethyl cellulose was 92:2:2:2:2. In addition, the coating amount of the positive electrode was about 200 mg / cm 2 , the thickness of the positive electrode was about 300 μm, and the diameter of the positive electrode was 15 mm.

[0123] Step 3. The zinc electrodes prepared in Examples 1-3 and Comparative Examples 1-4 were cut into zinc electrode pieces having a diameter of 14 mm.

[0124] Step 4. A composite water-based separator having a thickness of about 120 μm and a diameter of about 16 mm was used. The composite water-based separator comprised a non-woven fabric having a strong liquid absorption capacity having a thickness of about 100 μm, and a microporous separator having a thickness of about 20 μm. The composite water-based separator was interposed between the positive electrode and the zinc electrode piece by sequentially stacking the positive electrode, the separator, and the zinc electrode piece, and then was subjected to liquid injection and sealing, and was housed in a standard CR2032 button cell container. The concentration of the hydroxyl ions of the alkaline electrolyte was about 12 mol / L.

[0125] The alkaline nickel-zinc button cell prepared was subjected to the following performance tests.

[0126] [Charge-discharge cycle test]

[0127] The alkaline nickel-zinc button cell was subjected to the following charge-discharge cycle test using a new battery testing system.

[0128] As the first charge-discharge cycle, the alkaline nickel-zinc button cell prepared was subjected to constant current charging at a current value of 1 / 10 C until 1.9 V, and then was subjected to constant voltage charging at 1.9 V until the current cutoff of 0.1 C. Finally, the cell was subjected to constant current discharging at a current value of 1 / 2 C until 1.2 V.

[0129] Next, as the second charge-discharge cycle, the nickel-zinc button cell prepared was subjected to constant current charging at a current value of 1 / 5 C until 1.9 V, and then was subjected to constant voltage charging at 1.9 V until the current cutoff of 0.1 C. Finally, the cell was subjected to constant current discharging at a current value of 1 / 2 C until 1.2 V.

[0130] After that, as the 3rd charge-discharge cycle, the nickel-zinc battery prepared above was charged at a current value of 1 / 2 C to 1.9 V, and then charged at 1.9 V to a current cutoff of 0.1 C. Finally, the battery was discharged at a current value of 1 / 2 C until 1.2 V.

[0131] After that, the 3rd charge-discharge cycle was repeated, and the battery was charged and discharged for a maximum of 100 cycles.

[0132] The capacity retention rate (%) was calculated using the discharge gram capacity at the 1st charge-discharge cycle and the discharge gram capacity at the predetermined cycle number. In addition, according to the theoretical discharge gram capacity of zinc oxide of 658 mAh / g, the utilization rate of the zinc oxide active material in the alkaline nickel-zinc battery can be calculated by dividing the actual discharge gram capacity of the zinc oxide by the theoretical gram capacity of the zinc oxide of 658 mAh / g. The results are shown in Table 1.

[0133] According to the results shown in Table 1, the zinc electrodes provided in Examples 1-3 of the present application have better initial discharge gram capacity, zinc oxide utilization rate, and capacity retention rate than the comparative examples provided in the present application. By adding the soluble organic calcium salt to the zinc electrode, not only is the problem of dissolution of the zinc oxide active material in the alkaline electrolyte overcome, but the random diffusion of the intermediate product zincate ion formed during the charge-discharge process is also effectively inhibited. By improving the deformation of the zinc electrode and inhibiting the growth of zinc dendrites, the cycle stability of the alkaline nickel-zinc battery and the utilization rate of the active material are significantly improved.

[0134] In addition, the soluble organic calcium salt helps the penetration and infiltration of the alkaline electrolyte, and the electrolyte wetting angle of the zinc electrode provided in Examples 1-3 of the present application is significantly smaller than that of the comparative examples provided in the present application. Excellent electrolyte wettability helps to improve the utilization rate of the active material zinc oxide. In general, zinc oxide is an important active material for the negative electrode of the alkaline nickel-zinc battery, and its theoretical gram capacity is 658 mAh / g. The utilization rate of the active material in the existing alkaline nickel-zinc battery technology is only 20-30%. Therefore, during the design of the alkaline nickel-zinc battery, the amount of negative electrode active material needs to be much higher than the theoretical design value, and the theoretical capacity of the negative electrode can even be more than twice the capacity of the positive electrode. The comparative example 1 of the present application uses carbon-coated zinc oxide, and the utilization rate of the active material can be increased to 64%. By adding the soluble organic calcium salt to the zinc electrode, the zinc electrode provided in Examples 1-3 of the present application can exhibit an active material utilization rate of 73%-88% during the charge-discharge process, which helps to further improve the mass energy density of the battery.

[0135] It should be noted that the capacity retention rate of the zinc electrode provided by the embodiments 1-3 of the present application after 100 cycles of charge and discharge is obviously superior to that of the zinc electrode provided by the comparative example of the present application. In particular, the discharge gram capacity of the zinc electrode of the embodiment 3 of the present application is basically maintained stable after 100 cycles. By limiting the activity of the soluble zincate ions in a specific area, the diffusion of the zincate ions to the alkaline electrolyte, the separator and even the surface of the positive electrode is avoided. The zinc electrode provided by the embodiments 1-3 of the present application can achieve a higher capacity retention rate by alleviating the loss of zinc oxide active material in the zinc electrode.

[0136] Table 1

[0137]

[0138] In order to further illustrate the effect of the soluble organic calcium salt, the prepared alkaline nickel-zinc button cell CR2032 is subjected to cycle test by using a new battery detection system.

[0139] As to the discharge gram capacity of the active material zinc oxide, as shown in Figure 5 a, Figure 6 a, Figure 7 a and Figure 8 a, the zinc electrode provided by the embodiments 1-3 and the comparative example 1 of the present application is subjected to 100 cycles of charge and discharge in the nickel-zinc button cell CR2032. The first cycle discharge gram capacity of the zinc electrode provided by the embodiment 1 of the present application is 481 mAh / g, and after 100 cycles of charge and discharge, the discharge gram capacity is 454 mAh / g, and the capacity retention rate is 94%; the first cycle discharge gram capacity of the zinc electrode provided by the embodiment 2 of the present application is 513 mAh / g, and after 100 cycles of charge and discharge, the discharge gram capacity is 423 mAh / g, and the capacity retention rate is 82%; the first cycle discharge gram capacity of the zinc electrode provided by the embodiment 3 of the present application is 582 mAh / g, and after 100 cycles of charge and discharge, the discharge gram capacity is 591 mAh / g, and the discharge gram capacity does not obviously decline. However, the first cycle discharge gram capacity of the zinc electrode provided by the comparative example 1 of the present application is 422 mAh / g, and after 100 cycles of charge and discharge, the discharge gram capacity is 338 mAh / g, and the capacity retention rate is 80%.

[0140] As to the discharge platform, as shown in Figure 5 b, Figure 6 b, Figure 7 b and Figure 8As shown in b, the zinc electrodes provided by the embodiments 1-3 and the comparative example 1 of the present application have a discharge platform of about 1.7 V after 100 cycles of charge-discharge in the nickel-zinc button cell CR2032. Generally, the zinc electrodes prepared from pure zinc oxide can have a discharge platform of 1.60-1.65 V, and the zinc electrodes provided by the embodiments 1-3 and the comparative example 1 of the present application can have a higher discharge platform due to the use of the carbon-coated zinc oxide active material, which is helpful to improve the mass energy density of the alkaline nickel-zinc battery. It can be seen that the soluble organic calcium salt has no effect on the discharge platform of the alkaline nickel-zinc battery.

[0141] For the charge-discharge curves, as shown in a, b, c, d, e and f, the charge-discharge curves of the first 5 cycles of the zinc electrodes provided by the embodiments 1-3 and the comparative example 1 of the present application are basically overlapped, which indicates good electrochemical reversibility and charge-discharge stability. It should be pointed out that the initial discharge capacity is slightly improved, which is mainly related to the further activation of the alkaline nickel-zinc button cell in the initial charge-discharge process. Figure 5 c, Figure 6 c, Figure 7 c and Figure 8 c, the charge-discharge curves of the first 5 cycles of the zinc electrodes provided by the embodiments 1-3 and the comparative example 1 of the present application are basically overlapped, which indicates good electrochemical reversibility and charge-discharge stability. It should be pointed out that the initial discharge capacity is slightly improved, which is mainly related to the further activation of the alkaline nickel-zinc button cell in the initial charge-discharge process.

[0142] It should be pointed out that for different soluble organic calcium salts, the cation is calcium ion, and the anion can be an organic group with different molecular weights. By further optimizing the addition amount of the soluble organic calcium salt provided by the present application in the zinc electrode, the comprehensive performance of the alkaline nickel-zinc battery can be further optimized and improved.

[0143] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, all possible combinations of the technical features in the above-described embodiments are not described, but as long as the combinations of the technical features do not contradict, they should be considered as within the scope of the present disclosure.

[0144] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the patent. It should be pointed out that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the protection scope of the present application patent should be subject to the appended claims.

Claims

1. A method for preparing a zinc electrode for alkaline nickel-zinc batteries, characterized in that: The process includes the following steps: dissolving a water-soluble organic acid calcium salt in deionized water to obtain a first mixed solution; The process of preparing a slurry by mixing a first mixed liquid, an aqueous binder, a thickener and an active material including zinc oxide; The process of coating the slurry on the surface of the current collector and baking it at high temperature to prepare the zinc electrode; The content of the water-soluble organic acid calcium salt in the first mixed solution is 0.005-2 mol / L, and the water-soluble organic acid calcium salt is at least one of calcium lactate, calcium acetate, calcium L-threonate, calcium gluconate, calcium benzoate, calcium glycerophosphate, calcium formate, calcium fumarate, calcium caseinate, calcium aspartate, calcium maleate, calcium propionate, calcium methanesulfonate, calcium trifluoromethanesulfonate, calcium mellitic acid, and calcium p-toluenesulfonate.

2. The preparation method according to claim 1, characterized in that The pH value of the first mixed solution is 6-8.

3. The preparation method according to claim 1, characterized in that Based on the total weight of the water-soluble organic acid calcium salt, the aqueous binder, the thickener and the active material, the active material content is 80 wt.% to 97 wt.%; The total content of the water-soluble organic acid calcium salt, the aqueous binder, the thickener and the active material is 1 wt.% to 5 wt.%.

4. The preparation method according to claim 3, characterized in that The water-soluble adhesive is a rubber adhesive or a polymer resin adhesive.

5. The preparation method according to claim 4, characterized in that The rubber adhesive is at least one of styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, and fluororubber; The polymer resin binder is at least one of polytetrafluoroethylene, ethylene propylene copolymer, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, and polyvinyl alcohol; The thickener is at least one of sodium carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, sodium alginate, β-cyclodextrin, sodium starch phosphate, hydroxypropyl starch, gelatin, and xanthan gum.

6. The preparation method according to claim 1, characterized in that The temperature of the high-temperature baking is 100-180° C., and the time of the high-temperature baking is 5 minutes to 5 hours.

7. A zinc electrode prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the zinc electrode according to claim 7 in alkaline nickel-zinc batteries.

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