Negative electrode material and preparation method and application thereof

Abstract

The invention relates to a negative electrode material which is of a core-shell structure and comprises a core layer and a surface shell layer coating the surface of the core layer, the core layer comprises zinc and / or zinc oxide, and the surface shell layer comprises a magnesium-containing compound. The thickness of the surface shell layer is 1-5 [mu] m. The chemical formula of the magnesium-containing compound is MgxMy, M is at least one of OH <->, CO3 < 2->, F <->, SO3 < 2->, S2 <-> and C2O4 < 2->, the solubility product constant of the magnesium-containing compound in water at 25 DEG C is not less than 1E-11, and based on the total mass of the negative electrode material, the content of magnesium is 0.02-1.0 wt%. The average particle size D50 of the negative electrode material is 50 [mu] m to 100 [mu] m, and the conductivity of the negative electrode material ranges from 1E0 S / cm to 1E + 04 S / cm. The invention also relates to a preparation method of the negative electrode material, and the negative electrode material can also be applied to a zinc-based battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chemical batteries, in particular to a negative electrode material, a preparation method of the negative electrode material and application of the negative electrode material. BACKGROUND

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

[0003] The existing zinc-based battery includes a positive electrode, a negative electrode, a separator and an electrolyte, wherein the negative electrode of the zinc-based battery mainly uses zinc and / or zinc oxide as the active material. The zinc-based battery mainly includes: traditional disposable batteries such as zinc-manganese dry batteries, carbon-zinc batteries, zinc-silver button batteries, etc., and also includes new generation rechargeable batteries such as: zinc-air batteries, nickel-zinc batteries, zinc-ion batteries, etc. Specifically, the zinc-air battery using oxygen in the air as the positive electrode active material, the nickel-zinc battery using a nickel-containing compound as the positive electrode active material, the manganese-zinc battery using a manganese-containing compound as the positive electrode active material, the silver-zinc battery using a silver-containing compound as the positive electrode active material, the zinc-ion battery using vanadium pentoxide as the positive electrode active material, etc. The common feature of zinc-based batteries is derived from their core element: metallic zinc. In addition, zinc-based batteries mainly use aqueous electrolyte, for example, carbon-zinc batteries use weakly acidic electrolyte, nickel-zinc batteries, zinc-air batteries, silver-zinc batteries and zinc-manganese dry batteries mainly use alkaline electrolyte, and zinc-ion batteries use nearly neutral electrolyte. Therefore, zinc-based batteries have the advantages of high safety, environmental friendliness, low cost, etc.

[0004] Among them, the nickel-zinc battery is a kind of secondary chemical power source which takes spherical nickel hydroxide and metal nickel as the positive electrode active material, metal zinc and zinc oxide as the negative electrode active material, and aqueous solution of potassium hydroxide, sodium hydroxide, lithium hydroxide, etc. as the electrolyte, and its electrochemical reaction equation is as follows: Positive electrode reaction: Negative electrode reaction: Total reaction: Based on the electrochemical redox reaction, the nickel hydroxide (Ni(OH)2) of the positive electrode is converted into the charged state of nickel oxyhydroxide (NiOOH) during the charging process, while the zinc oxide (ZnO) of the negative electrode is reduced into the charged state of metallic zinc (Zn) during the discharging process. Due to the standard electrode potential E°≈ +0.49 V (relative to the standard hydrogen electrode) of the positive electrode (NiOOH / Ni(OH)2) and the standard electrode potential E°≈ -1.25 V (relative to the standard hydrogen electrode) of the negative electrode (Zn / ZnO), the theoretical voltage of the nickel-zinc battery is about 1.74 V. It should be noted that the metallic zinc in the negative electrode not only plays an important role as a conductive agent, but also is one of the key negative active materials. In addition, the zinc-containing compounds in the negative electrode can generate zincate ions Zn(OH)4 2- .

[0005] Currently, the rated voltage of the nickel-zinc battery is 1.65 V, and the platform voltage is about 1.6-1.7 V, which is significantly higher than that of the nickel-hydrogen battery (1.2 V). The mass energy density of the nickel-zinc battery can reach 80-120 Wh / kg. In actual use, the open circuit voltage (OCV) of the fully charged nickel-zinc battery is about 1.85 V, but it will quickly stabilize at about 1.6-1.7 V during discharging, and the voltage will drop to about 1.0-1.2 V at the end of discharging. Due to the use of aqueous electrolyte, the nickel-zinc battery has no risk of flammability and explosion, and does not contain toxic heavy metals such as lead and cadmium, which is environmentally friendly. The nickel-zinc battery has low internal resistance, supports high-rate charging and discharging, and has outstanding pulse discharge capability. Especially at a 20C rate, the discharge capacity can achieve ≥90% of the rated capacity, and it is expected to be widely used in large-scale grid energy storage, uninterruptible power supplies (UPS) in data centers, low-speed electric vehicle power supplies, electric tools, and other fields.

[0006] The existing nickel-zinc battery has the following technical problems: when the nickel-zinc battery is subjected to long-term charging and discharging cycles, the negative electrode with zinc and / or zinc oxide as the negative active material will produce metal zinc dissolution and gas evolution side reactions in the local part of the electrode. For the charged nickel-zinc battery, since zinc oxide is a typical amphoteric oxide, the active material of the negative electrode is easily dissolved into the alkaline electrolyte, not only causing the loss of active material, but also causing the generation of a large amount of zincate ions Zn(OH)4 2- . In addition, the dissolution process of metallic zinc easily causes gas evolution side reactions, not only consuming water molecules in the alkaline electrolyte, but also causing the internal pressure of the battery to rise sharply, resulting in the problem of battery leakage.

[0007] Through the research on the existing zinc negative electrode, the following knowledge is obtained: The high solubility of the negative active material of nickel-zinc batteries and its discharge product, zinc oxide (ZnO), in the strong alkaline electrolyte (usually potassium hydroxide, sodium hydroxide, lithium hydroxide) can lead to the production of zincate ions. This dissolution behavior is a thermodynamically spontaneous process, the essence of which is the complexation reaction of zinc oxide as an amphoteric oxide with hydroxide ions. The main dissolution reaction equation is as follows: The reaction shows that the concentration of OH⁻ ions in the alkaline electrolyte directly drives the dissolution reaction to the right, causing the negative active material ZnO to continuously dissolve to form soluble Zn(OH)4²⁻.

[0008] During the charging process of nickel-zinc batteries, these freely migratable Zn(OH)4²⁻ will preferentially undergo electrochemical reduction at the original active sites on the zinc negative electrode surface or at the current distribution uneven places, depositing as metallic zinc. This electrochemical deposition process is difficult to control, leading to uneven deposition of zinc and formation of mossy dendritic structures. The growth of zinc dendrites can pierce the separator, causing internal micro-short circuits in the battery, leading to a sharp capacity decay and eventual failure, seriously threatening the cycle life and safety of nickel-zinc batteries. In addition, the dissolved Zn(OH)4²⁻ can migrate through the porous separator to the positive electrode of the nickel-zinc battery. In the high potential oxidation environment of the positive electrode, Zn(OH)4²⁻ will decompose and deposit as poorly conductive zinc oxide, "poisoning" the active materials such as nickel hydroxide and / or nickel oxyhydroxide on the surface of the positive electrode, not only increasing the polarization impedance of the positive electrode, but also reducing the capacity contribution and coulombic efficiency of the positive electrode, further exacerbating the performance degradation of the entire nickel-zinc battery system. Therefore, the generation and migration of Zn(OH)4²⁻ are the root causes of key technical problems such as zinc negative electrode dendrite growth, shape change, and positive electrode poisoning, which seriously restrict the cycle life of nickel-zinc batteries.

[0009] In addition, metallic zinc is also prone to cause gas evolution side reactions at the negative electrode, mainly because of the instability of metallic zinc in alkaline environments, rooted in its amphoteric nature and thermodynamic spontaneous reaction tendency. Studies have shown that metallic zinc in alkaline environments is simultaneously subjected to chemical corrosion and electrochemical corrosion, making it unable to exist stably. From the perspective of chemical corrosion, even without external current, metallic zinc is easily chemically reacted with water: The generated Zn(OH)2 further chemically reacts with OH⁻ ions in the electrolyte to generate freely migratable zincate ions Zn(OH)4²⁻. This chemical reaction not only consumes the metallic zinc active material of the negative electrode, causing severe self-discharge of the nickel-zinc battery, but also produces a gas evolution side reaction, producing hydrogen gas that can cause the internal pressure of the nickel-zinc battery to rise and the electrolyte to dry out.

[0010] From the perspective of electrochemical corrosion, the surface of zinc negative electrode is not uniform at the micro level. The presence of any impurities will form small anode and cathode areas, forming a primary cell.

[0011] Anode area (oxidation reaction): Cathode area (reduction reaction): These two electrochemical reactions are coupled together and can continuously and spontaneously corrode and dissolve metal zinc in an alkaline environment and produce hydrogen gas. The hydrogen evolution side reaction is the main reason for the low coulombic efficiency of the zinc negative electrode and the decline of the discharge capacity. In addition, the dissolved oxygen in the alkaline electrolyte also aggravates the corrosion of metal zinc. While oxygen is consumed in the electrochemical process, a large amount of OH - ions are generated, which can further corrode metal zinc. The electrochemical corrosion reactions involved are as follows: Anode area: Cathode area: As can be seen, metal zinc and zinc oxide in the negative electrode of the nickel-zinc battery are prone to chemical and electrochemical reactions in an alkaline environment, generating a large amount of zincate ions Zn(OH)4²⁻ and hydrogen gas. In order to inhibit the dissolution of zinc oxide and metal zinc in the negative electrode in the alkaline electrolyte, a saturated zinc oxide dissolved alkaline electrolyte is usually used. Even if the electrolyte contains saturated zinc oxide, the products generated during the charging and discharging process of the nickel-zinc battery, especially the freely movable Zn(OH)4²⁻, can easily diffuse and move randomly in the alkaline electrolyte. When the local concentration of Zn(OH)4²⁻ exceeds the saturation solubility, or the local OH - concentration of the electrolyte is low, Zn(OH)4²⁻ can be converted to solid zinc oxide and precipitated through the following chemical reaction: In addition, the charging reaction of the zinc negative electrode generates metal zinc by electrochemically reducing the discharge product of zinc (ZnO or Zn(OH)4 2- ). Metal zinc is prone to crystallization, thus zinc dendrites are easily formed on the surface or certain points of the zinc negative electrode. The electrochemical reactions involved are as follows: Charging reaction 1: Charging reaction 2: In summary, metal zinc and zinc oxide, as the most important negative active material, their chemical stability is directly related to the overall performance of the nickel-zinc battery. By further improving the stability of the negative electrode material in the alkaline environment, the growth of zinc dendrites and the gas evolution side reaction are inhibited, thereby improving the overall performance of the nickel-zinc battery. SUMMARY

[0012] In view of the technical problems existing in the prior art, the present application aims to provide a negative electrode material and a preparation method, which can effectively prevent corrosion in a strong alkaline electrolyte and inhibit the occurrence of a gas evolution side reaction. A nickel-zinc battery using the negative electrode material has greatly improved electrochemical performance. It should be noted that the negative electrode material provided by the present application can be applied not only to nickel-zinc batteries but also to other zinc-based batteries, including zinc-manganese batteries, silver-zinc batteries, zinc-air batteries, carbon-zinc batteries, zinc-iron batteries, zinc-ion batteries, zinc-bromine batteries, etc. Using the negative electrode material provided by the present application as the negative electrode active material of a nickel-zinc battery can simultaneously achieve: (a) inhibition of deformation of the zinc negative electrode and growth of zinc dendrites; (b) inhibition of corrosion of the negative electrode active material due to dissolution in a strong alkaline environment; and (c) significant improvement in the cycle performance, rate performance, coulombic efficiency, and self-discharge of the nickel-zinc battery.

[0013] In a first aspect, the present application provides a negative electrode material, which is of a core-shell structure and comprises a core layer and a surface shell layer coated on the surface of the core layer. The core layer comprises zinc and / or zinc oxide, and the surface shell layer comprises a magnesium-containing compound. The thickness of the surface shell layer is about 1 μm to about 5 μm. The average particle size D50 of the negative electrode material is about 50 μm to about 100 μm. The electrical conductivity of the negative electrode material is in the range of about 1E0 S / cm to about 1E+04 S / cm.

[0014] The negative electrode material can simultaneously achieve: (a) inhibition of self-discharge during storage in a charged state; (b) inhibition of severe morphological changes of the core layer during charging and discharging; (c) inhibition of dissolution of zinc oxide and metallic zinc in a strong alkaline electrolyte; (d) improvement in the affinity of the negative electrode active material to water; (e) improvement in the conductivity of hydroxyl ions during charging and discharging; and (f) enhancement of the electronic transport property in an electrochemical process.

[0015] The chemical formula of the magnesium-containing compound is Mg x M y , wherein M is at least one of OH - , CO3 2- , F - , SO3 2- , S 2- , and C2O4 2- . The content of Mg is about 0.02 wt% to about 1.0 wt% based on the total mass of the negative electrode material.

[0016] In one or more embodiments, the core layer is doped with one or more oxides, sulfides, inorganic salts, organic salts, or hydroxides of a material selected from the group consisting of calcium, magnesium, barium, aluminum, lanthanum, strontium, tin, gallium, bismuth, antimony, titanium, chromium, yttrium, lead, and indium.

[0017] The negative electrode prepared by using the negative electrode material provided by the application can be called "zinc negative electrode", which can be used in a nickel-zinc battery. The nickel-zinc battery can not only improve the stability of the negative active material (zinc and / or zinc oxide) in a strong alkaline environment, but also effectively avoid the generation of a large amount of Zn(OH)4 2- which can move freely, and reduce or eliminate the gas evolution side reaction of the zinc negative electrode in the strong alkaline environment. By effectively preventing the uneven deposition of metallic zinc, the growth of zinc dendrites in the nickel-zinc battery during charging and discharging is prevented, thereby effectively improving the coulombic efficiency and cycle life of charging and discharging.

[0018] Without affecting the technical effects described in the application, the core layer can also include other zinc compounds, which can be, for example, zinc hydroxide, basic zinc carbonate, zinc carbonate, zinc sulfide, tetrahydroxy zinc ion salt, zinc halide, zinc carboxylate compound (such as zinc acetate, zinc tartrate, etc.), magnesium zincate, calcium zincate, barium zincate, zinc borate, zinc silicate, zinc aluminate, zinc fluoride, zinc alloy, etc. Among them, the zinc alloy can contain 0.01wt.%-0.08wt.% indium (In), 0.005wt.%-0.05wt.% bismuth (Bi), 0.005wt.%-0.05wt.% aluminum (Al), 0.005wt.%-0.05wt.% calcium (Ca), 0.005wt.%-0.05wt.% titanium (Ti), 0.005wt.%-0.05wt.% tin (Sn), 0.005wt.%-0.05wt.% lead (Pb), etc. trace elements. The above-mentioned zinc-containing compounds can be one or more than two.

[0019] In a second aspect, the application provides a preparation method of the negative electrode material, comprising the following steps: a step of dissolving a precipitant in deionized water to prepare a first solution; a step of mixing zinc and / or zinc oxide particles into the first solution to obtain a first mixture; a step of dissolving a water-soluble metal salt containing magnesium in deionized water to prepare a second solution; a step of adding the second solution into the mixture to react and obtain a second mixture; a step of filtering the second mixture and collecting the precipitate; a step of drying the precipitate.

[0020] Preferably, the cation of the precipitant is potassium, sodium and / or ammonium, and the anion of the precipitant is OH - , CO3 2- , F - , SO3 2- , S 2- , C2O4 2- .

[0021] Preferably, the water-soluble metal salt is a water-soluble magnesium salt, such as magnesium chloride, magnesium acetate, magnesium sulfate, magnesium nitrate, magnesium lactate, magnesium gluconate, magnesium aspartate, magnesium citrate, magnesium glycinate, etc.

[0022] By adding the second solution containing magnesium ions into the first mixture containing zinc and / or zinc oxide particles, the magnesium ions and the precipitant react to precipitate on the surface of the zinc and / or zinc oxide particles to coat the surface of the particles. It is unexpectedly found that if the value of the solubility product constant (Ksp, 25°C) of the product of the reaction between magnesium ions and the precipitant is less than 1E-11, the product cannot completely wrap the zinc and / or zinc oxide particles, which will cause the surface of the zinc and / or zinc oxide particles to be partially exposed. During the precipitation reaction, most of the precipitated product exists mainly in the free state, which cannot effectively achieve the coating effect.

[0023] The average particle size D50 of the negative electrode material prepared by the above preparation method can be controlled by controlling the average particle size D50 of the zinc and / or zinc oxide particles, the amount of the second solution added, the reaction temperature, and the reaction time. It is unexpectedly found that when the negative electrode material simultaneously satisfies the conditions of "the average particle size D50 being about 50 μm to about 100 μm" and "the thickness of the surface shell layer being about 1 μm to about 5 μm", the negative electrode material has good electrical conductivity and can withstand large-rate charging and discharging, and at the same time, the wrapping effect can effectively improve the stability of the active material in an alkaline environment and improve the self-discharge during charging and storage under the charged state. Therefore, the nickel-zinc battery can exhibit good electrochemical performance. The reasons are speculated to include: (1) The surface shell layer in the thickness range can significantly improve the stability of the core layer in an alkaline environment, thereby effectively inhibiting the morphological change of the core layer during charging and discharging. If the thickness of the surface shell layer is less than the range, the core layer is exposed due to incomplete wrapping, which cannot improve the stability of the active material; if the thickness of the surface shell layer is greater than the range, although the alkali resistance of the negative electrode material can be greatly improved, the electrical conductivity of the negative electrode material and the electron transport during charging and discharging are greatly affected, which seriously affects the specific capacity of the negative electrode material and the rate performance of the battery; (2) Since in the process of charge and discharge, zinc and / or zinc oxide particles can directly contact with water or strong alkaline electrolyte, leading to active material dissolution and gas evolution side reaction. The use of the surface shell layer which can completely and uniformly wrap the core layer can avoid the core layer being completely exposed to the electrolyte, effectively inhibit the free migration of zincate ions and the gas evolution side reaction of nickel-zinc battery in the process of charge and discharge, not only can improve the charge-discharge coulomb efficiency and cycle performance of nickel-zinc battery, but also can reduce the internal pressure of the battery and improve the battery leakage problem, etc. (3) When the average particle size D50 of the negative electrode material is about 50 μm to about 100 μm, the following can be simultaneously improved: (a) the effective contact between the particles of the negative electrode material, ensuring efficient electron and ion transmission in the electrochemical process; (b) the effective contact between the particles of the negative electrode material and the functional auxiliary materials such as the conductive additives, corrosion inhibitors, binders and surfactants in the zinc negative electrode, realizing the high compaction density and high surface capacity density of the zinc negative electrode; (c) the effective contact between the particles of the negative electrode material and the metal current collector, avoiding the particle shedding due to the thickness change of the electrode sheet in the process of charge and discharge. When the average particle size D50 of the negative electrode material is lower than or higher than the above range, the smaller particle size is easy to make the negative electrode material have higher activity, which not only aggravates the gas evolution side reaction of the zinc negative electrode in the strong alkaline environment, but also easily causes the serious self-discharge problem of the zinc negative electrode. Since the metal zinc active material has a higher density, the larger particle size distribution is easy to cause the sedimentation problem of the negative electrode slurry, resulting in the uneven distribution of the negative electrode active material in the zinc negative electrode.

[0024] Compared with the existing zinc negative electrode, the zinc negative electrode formed by using the negative electrode material provided by the application can effectively improve the stability of the negative electrode active material in the strong alkaline environment, and effectively inhibit the generation of hydrogen evolution side reaction, which can not only improve the cycle performance, rate performance and coulomb efficiency of the nickel-zinc battery, but also improve the internal pressure of the nickel-zinc battery and avoid the leakage problem of the battery. Further, it is found that the negative electrode material provided by the application can also effectively inhibit the deformation, passivation and self-discharge problem of the zinc-containing negative electrode active material in the charged state and during storage in the charged state. The zinc negative electrode with such characteristics is more suitable for use as the negative electrode of the nickel-zinc battery. In addition, since the nickel-zinc battery using such zinc negative electrode can particularly use aqueous electrolyte, the nickel-zinc battery has the intrinsic safety feature.

[0025] The following will be described in conjunction with specific examples. BRIEF DESCRIPTION OF DRAWINGS

[0026] The accompanying drawings further illustrate the present application, but are not intended to limit the application in any way.

[0027] Figure 1Microstructure of the negative electrode material provided in Example 1 under field emission scanning electron microscope (FE-SEM). Wherein, Figure 1 (a) corresponding magnification: 200 times; Figure 1 (b) corresponding magnification: 1000 times; Figure 1 (c) corresponding magnification: 5000 times; Figure 1 (d) corresponding magnification: 10000 times.

[0028] Figure 2 Elemental distribution map of the negative electrode material provided in Example 1 measured by energy dispersive X-ray spectroscopy (EDS). Wherein, Figure 2 (a) is the superimposed map of Zn, O, Mg element distribution; Figure 2 (b) is the distribution map of Zn element; Figure 2 (c) is the distribution map of O element; Figure 2 (d) is the distribution map of Mg element.

[0029] Figure 3 Thickness test map of the coating layer of the negative electrode material provided in Example 1 measured by FESEM. Wherein, Figure 3 (a) corresponding magnification: 8000 times; Figure 3 (b) corresponding magnification: 5000 times.

[0030] Figure 4 Microstructure of the zinc powder used in the embodiment of the present application under field emission scanning electron microscope (FE-SEM). Wherein, Figure 4 (a) corresponding magnification: 200 times; Figure 4 (b) corresponding magnification: 1000 times; Figure 4 (c) corresponding magnification: 5000 times; Figure 4 (d) corresponding magnification: 10000 times.

[0031] Figure 5 Elemental distribution map of the zinc powder used in the embodiment of the present application measured by energy dispersive X-ray spectroscopy (EDS). Wherein, Figure 5 (a) is the FE-SEM map; Figure 5 (b) is the distribution map of Zn element; Figure 5 (c) is the distribution map of O element.

[0032] Figure 6 Microstructure of the negative electrode material provided in Example 2 under field emission scanning electron microscope (FE-SEM). Wherein, Figure 6 (a) corresponding magnification: 200 times; Figure 6 (b) corresponding magnification: 1000 times;Figure 6 (c) Corresponding magnification: 5000x; Figure 6 (d) Corresponding magnification: 10000x.

[0033] Figure 7 Elemental mapping of the negative electrode material provided in Example 2 measured by Energy Dispersive X-ray Spectroscopy (EDS). Wherein, Figure 7 (a) is the superimposed map of Zn, O, Mg element distribution; Figure 7 (b) is the distribution of Zn element (c) is the distribution of O element; Figure 7 (d) is the distribution of Mg element.

[0034] Figure 8 Microstructure of the negative electrode material provided in Example 3 under Field Emission Scanning Electron Microscope (FE-SEM). Wherein, Figure 8 (a) Corresponding magnification: 200x; Figure 8 (b) Corresponding magnification: 1000x; Figure 8 (c) Corresponding magnification: 5000x; Figure 8 (d) Corresponding magnification: 10000x.

[0035] Figure 9 Elemental mapping of the negative electrode material provided in Example 3 measured by Energy Dispersive X-ray Spectroscopy (EDS). Wherein, Figure 9 (a) is the superimposed map of Zn, O, Mg element distribution; Figure 9 (b) is the distribution of Zn element; Figure 9 (c) is the distribution of O element; Figure 9 (d) is the distribution of Mg element.

[0036] Figure 10 Thickness test of the coating layer of the negative electrode material provided in Example 3 measured by FESEM. Wherein, Figure 10 (a) Corresponding magnification: 8000x; Figure 10 (b) Corresponding magnification: 8000x.

[0037] Figure 11 Microstructure of the negative electrode material provided in Example 4 under Field Emission Scanning Electron Microscope (FE-SEM). Wherein, Figure 11 (a) Corresponding magnification: 200x; Figure 11 (b) Corresponding magnification: 1000x; Figure 11 (c) Corresponding magnification: 5000x; Figure 11 (d) Corresponding magnification: 10000x.

[0038] Figure 12 Elemental mapping of the negative electrode material provided in Example 4 by energy dispersive X-ray spectroscopy (EDS) measurement. Among them, Figure 12 (a) is the superimposed map of Zn, O, Mg element distribution; Figure 12 (b) is the distribution of Zn element; Figure 12 (c) is the distribution of O element; Figure 12 (d) is the distribution of Mg element.

[0039] Figure 13 Microstructure diagram of the negative electrode material provided in Comparative Example 1 under field emission electron microscope (FE-SEM). Among them, Figure 13 (a) corresponding magnification: 200 times; Figure 13 (b) corresponding magnification: 500 times; Figure 13 (c) corresponding magnification: 1000 times; Figure 13 (d) corresponding magnification: 2000 times.

[0040] Figure 14 Microstructure diagram of the negative electrode material provided in Comparative Example 3 under field emission electron microscope (FE-SEM). Among them, Figure 14 (a) corresponding magnification: 200 times; Figure 14 (b) corresponding magnification: 1000 times; Figure 14 (c) corresponding magnification: 5000 times; Figure 14 (d) corresponding magnification: 10000 times. DETAILED DESCRIPTION

[0041] It should be understood that the specific examples described herein are merely illustrative of the present application and are not intended to limit the present application in any way.

[0042] It should be understood that the embodiments provided by the disclosure can take a wide variety of alternative variations and sequence of steps, unless otherwise explicitly stated. Additionally, except in the examples, or where otherwise explicitly indicated, all numerical specifications in this description, such as amounts of ingredients, are to be interpreted as approximations, unless otherwise indicated. Consequently, unless otherwise indicated, the numerical parameters set forth in the following specification and attached claims are approximations that can vary depending upon the desired properties to be obtained by employing the principles of the present application. At the very least, therefore, and not as an attempt to limit the application's scope, each numerical parameter should at least be construed in light of the number of significant figures and by applying ordinary rounding techniques.

[0043] It should be appreciated that, while the numerical ranges and parameters setting forth the broad scope of the application are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0044] It should be appreciated that, in the present application, any numerical range recited is intended to include all sub-ranges subsumed therein. For example, a range of "1 to 10" is intended to include all sub-ranges, for example, from and including the minimum "1" to and including the maximum "10", i.e. having the same minimum and maximum values as the range recited; and, every subrange between (and including) the minimum "1" and the maximum "10". In the present application, "about" means a range of plus or minus five percent of the value of the number.

[0045] It should be appreciated that, in the present application, recited 1E0 to 1E4 means a numerical value whose exponent ranges from 0 to 4 in scientific notation, and recited 1E+04 means a numerical value whose exponent is +4 in scientific notation. It should be appreciated that, in the present application, the numerical value of the solubility product constant (Ksp) is obtained based on the solubility product constant table of the compound.

[0046] It should be appreciated that, in the present application, the average particle diameter recited can be measured using a field emission electron microscope (FE-SEM), a laser particle size analyzer (PSD), or the like.

[0047] It should be appreciated that, in the present application, recited "state at the time of charging and state at the time of storage in the charged state" means a state in which part or all of the zinc-containing compound as an active material is metallic zinc when the zinc negative electrode is used as the negative electrode of the full cell (the reaction in which zinc oxide is reduced to metallic zinc is the charging process, and the reaction in which metallic zinc is oxidized to zinc oxide is the discharging process), at the time of charging and discharging of the battery, and at the time of storage of the battery. Note that, as long as part or all of the zinc-containing compound as an active material is in a state of metallic zinc, it means that the full cell is in a charged state.

[0048] It should be appreciated that, in the present application, recited "discharge product of zinc" specifically means a product obtained by the discharging reaction of the zinc negative electrode, and includes compounds of divalent zinc, such as: ZnO, Zn(OH)2, and Zn(OH)4 2- It should be appreciated that, in the present application, recited "zinc dendrite" means Zn(OH)4 2- As the concentration polarization becomes larger, it becomes easier to form a dendritic zinc deposit at the protruding part of the zinc negative electrode to which the zinc is more easily diffused.

[0049] It should be understood that in the present application, the "cycle life" as recited refers to when the cycle to a certain cycle, the discharge capacity is less than 60% of the discharge capacity of the first cycle, the cycle test is terminated, and the cycle number at this time is the cycle life of the battery; It should be noted that the components used in the embodiments of the present application are all commercially available goods unless otherwise specified.

[0050] It should be noted that the zinc and zinc oxide used in the embodiments of the present application are both in the form of particles, and the average particle size D50 of the zinc is about 50 μm to about 62 μm, and the average particle size D50 of the zinc oxide is about 100 nm to 500 nm. The average particle size of the zinc particles and the zinc oxide particles can be controlled by the following methods, for example, a method of mechanically crushing the particles with a ball mill, dispersing the obtained particles in a dispersing agent, and drying after obtaining the desired particle size range; a method of sieving the coarse particles; and a method of optimizing the preparation conditions at the stage of manufacturing the particles to obtain the desired particle size range.

[0051] It should be noted that the current collector used in the embodiments of the present application can use all current collectors known in the art that can be used for zinc negative electrodes, and the present application does not have a particular limitation, for example, it can be a foamed copper current collector, a pure copper mesh current collector, a copper alloy mesh current collector, a punched copper belt current collector, a stainless steel mesh current collector, a pure copper belt current collector, a pure titanium belt current collector, a pure zinc belt current collector, a copper alloy belt current collector, a zinc alloy belt current collector, or a punched stainless steel belt current collector. Preferably, the surface of the current collector has a protective plating layer such as bismuth plating, tin plating, indium plating, zinc plating, chromium plating, and titanium plating.

[0052] It should be noted that the binder used in the embodiments of the present application can use all binders known in the art that can be used for zinc negative electrodes, and the present application does not have a particular limitation, and a hydrophobic binder or a hydrophilic binder can be used, for example, but not limited to, polytetrafluoroethylene, butadiene rubber, hydroxypropyl methylcellulose, sodium hydroxymethyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol, sodium alginate, polyimide, polyethylene oxide, polyvinylpyrrolidone, polyacrylonitrile, polyacrylic acid and its derivatives, etc., and it can also be a mixture thereof.

[0053] Note that the electrically conductive aid used in the present embodiment can use an electrically conductive carbon, and the electrically conductive carbon can include graphite, natural graphite, artificial graphite, glassy carbon, amorphous carbon, graphene, fullerene, carbon black, graphitized carbon black, ketjen black, vapor-grown carbon fiber, pitch-based carbon fiber, mesocarbon microbeads, metal-coated carbon, carbon-coated metal, fibrous carbon, boron-containing carbon, nitrogen-containing carbon, multi-walled / single-walled carbon nanotube, carbon nanotube, acetylene black, carbon material subjected to hydrophilic treatment by introducing an oxygen-containing functional group, and the like. An electrically conductive metal can also be used, and the electrically conductive metal can include cobalt, nickel, titanium, tungsten, zinc, chromium, manganese, aluminum, bismuth, indium, tin, silver, oxides, sulfides, carbides, and nitrides thereof, and one or more of the above electrically conductive aids can be used.

[0054] Note that the method for manufacturing the zinc negative electrode in the present embodiment includes the following steps: Step 1: uniformly mixing the negative electrode material, the electrically conductive aid, the binder, and the solvent to obtain a negative electrode slurry; Step 2: uniformly filling and / or coating the negative electrode slurry on the current collector, and then performing rolling and cutting to obtain the zinc negative electrode, wherein the method and conditions for coating and / or filling the negative electrode slurry on the current collector and the method for rolling are known to those skilled in the art.

[0055] It should be noted that the nickel-zinc battery in the embodiment of the present application comprises a pole group, an electrolyte and a shell, the pole group comprises a positive electrode, a negative electrode and a separator of the battery, the pole group is placed in the shell in a laminated or rolled column shape, the alkaline electrolyte is injected, and then the nickel-zinc battery can be obtained after sealing. The negative electrode of the battery is a zinc negative electrode prepared by using the negative electrode material provided in the embodiment of the present application. The positive electrode of the battery can be an electrode prepared by a conventional method in the art, as an example, the above positive electrode can be prepared by the following method: a cobalt-coated spherical nickel hydroxide is matched with necessary additives (at least one metal, metal oxide or hydroxide selected from the group consisting of calcium, magnesium, barium, aluminum, lanthanum, strontium, tin, ytterbium, gallium, bismuth, antimony, titanium, chromium, yttrium, lead and indium), a conductive additive, a water-soluble binder (such as polytetrafluoroethylene, sodium carboxymethyl cellulose, butadiene rubber) and water to prepare a uniform positive electrode slurry, then the positive electrode slurry is uniformly filled in a foamed nickel current collector, and the nickel hydroxide positive electrode is prepared through processes such as drying, rolling, cutting and welding. The separator is arranged between the positive electrode and the negative electrode, has hydrophilicity, electrical insulation, alkali resistance, mechanical strength and liquid absorption capacity, can effectively block the penetration of zinc dendrites through the separator, and can accommodate the pole group and the alkaline electrolyte in the battery shell. Preferably, the separator is a microporous membrane that can block the penetration of zinc dendrites, and can be a polypropylene microporous membrane, a nylon microporous membrane, a polytetrafluoroethylene microporous membrane, a polyvinylidene fluoride microporous membrane and the like, as long as it can hinder the penetration of zinc dendrites through the microporous membrane. The electrolyte comprises an alkaline electrolyte, and the alkaline electrolyte is selected from an aqueous solution of alkali metal and / or alkaline earth metal hydroxide with a concentration of 30-60%, and can be sodium hydroxide, lithium hydroxide and potassium hydroxide. The shell can be various shells of various types of batteries, and can be AAA, AA, SubC, D and F type cylindrical batteries, and a person skilled in the art can determine a suitable battery shell according to the specific shape of the pole group.

[0056] [Examples 1-4] Example 1 The present embodiment provides a negative electrode material, and a preparation method thereof is as follows: 10g of zinc powder is slowly added to a 0.1 M Na2C2O4 solution, the solid-liquid ratio (S / L) of the zinc powder and the solution is 100g / L, then 0.02M MgSO4 solution is slowly added dropwise under stirring, the volume of the MgSO4 solution is 90 mL, the precipitation reaction is maintained for 60 min, finally the precipitate is collected after filtration treatment, and the precipitate is washed with deionized water and then dried to obtain the negative electrode material. The stirring rate is 500r / min, and the precipitation reaction is carried out at room temperature.

[0057] The surface shell layer of the negative electrode material is MgC2O4, and the Ksp (25℃) of MgC2O4 is 8.5×10 –5 .

[0058] Example 2 The negative electrode material is prepared by slowly adding 10 g of zinc powder to a 0.1 M NaOH solution, the solid-liquid ratio (S / L) of the zinc powder and the solution is 100 g / L, then slowly adding a 0.02 M MgSO4 solution under stirring, the volume of the added MgSO4 solution is 90 mL, the precipitation reaction is maintained for 60 min, finally, the precipitate is collected after filtration and washing with deionized water, and the negative electrode material is obtained after drying treatment. The stirring rate is 500 r / min, and the precipitation reaction temperature (using water bath heating) is 80°C.

[0059] The surface shell layer of the negative electrode material is Mg(OH)2, and the Ksp of Mg(OH)2 (at 25°C) is 1.8 x 10 –11 .

[0060] Example 3 The negative electrode material is prepared by slowly adding 10 g of zinc powder to a 0.1 M Na2CO3 solution, the solid-liquid ratio (S / L) of the zinc powder and the solution is 100 g / L, then slowly adding a 0.02 M MgSO4 solution under stirring, the volume of the added MgSO4 solution is 90 mL, the precipitation reaction is maintained for 60 min, finally, the precipitate is collected after filtration and washing with deionized water, and the negative electrode material is obtained after drying treatment. The stirring rate is 500 r / min, and the precipitation reaction temperature (using water bath heating) is 50°C.

[0061] The surface shell layer of the negative electrode material is MgCO3, and the Ksp of MgCO3 (at 25°C) is 3.5 x 10 –8 .

[0062] Example 4 The negative electrode material is prepared by slowly adding 10 g of zinc powder to a mixed solution containing 0.1 M Na2CO3 and 0.1 M NaOH, the solid-liquid ratio (S / L) of the zinc powder and the solution is 100 g / L, then slowly adding a 0.04 M MgSO4 solution under stirring, the volume of the added MgSO4 solution is 50 mL, the precipitation reaction is maintained for 60 min, finally, the precipitate is collected after filtration and washing with deionized water, and the negative electrode material is obtained after drying treatment. The stirring rate is 500 r / min, and the precipitation reaction temperature (using water bath heating) is 50°C.

[0063] The physical parameters of the negative electrode materials provided in Examples 1-4 are shown in Table 1, and the thickness of the surface shell layer of the negative electrode materials provided in Examples 1-4 is in the range of about 1 μm to about 5 μm.

[0064] Table 1 [Comparative Examples 1-4] Comparative Example 1 This comparative example provides a negative electrode material, and the preparation method thereof is as follows: 10 g of zinc powder is slowly added into deionized water, the solid-liquid ratio (S / L) of the zinc powder and the deionized water is 100 g / L, then 0.02 M MgSO4 solution is slowly added dropwise under stirring, the volume of the added MgSO4 solution is 50 mL, the precipitation reaction is maintained for 60 min, finally, the precipitate is collected after filtration treatment, and the precipitate is washed with deionized water and then dried to obtain the negative electrode material. The stirring rate is 500 r / min, and the precipitation reaction temperature (using water bath heating) is 50°C.

[0065] Comparative Example 2 This comparative example provides a negative electrode material, and the preparation method thereof is as follows: 12.5 g of zinc oxide and 0.25 g of magnesium oxide are mixed with sodium hexametaphosphate as a dispersant, then the mixture is ground in a superfine stirring mill at a speed of 900 r / min for 6 h to obtain a slurry; after the slurry is suction filtered, it is quickly dried in a blast drying oven at 120°C, and then mechanically pulverized to obtain a magnesium hydroxide-coated zinc oxide composite powder. The magnesium oxide is ground by mechanical force to generate magnesium hydroxide, and in the blending system with the zinc oxide, the newly generated magnesium hydroxide grows a shell layer of magnesium hydroxide on the surface of the zinc oxide core layer.

[0066] Comparative Example 3 This comparative example provides a negative electrode material, and the preparation method thereof is as follows: 10 g of zinc powder is slowly added into 0.1 M Na3PO4 solution, the solid-liquid ratio (S / L) of the zinc powder and the solution is 100 g / L, then 0.02 M MgSO4 solution is slowly added dropwise under stirring, the volume of the added MgSO4 solution is 90 mL, the precipitation reaction is maintained for 60 min, finally, the precipitate is collected after filtration treatment, and the precipitate is washed with deionized water and then dried to obtain the negative electrode material. The stirring rate is 500 r / min, and the precipitation reaction temperature (using water bath heating) is 50°C.

[0067] The shell layer of the negative electrode material is Mg3(PO4)2, and the Ksp of Mg3(PO4)2 at 25°C is 1.0 x 10 –25 .

[0068] Comparative Example 4 This comparative example provides a negative electrode material prepared by dissolving zinc sulfate (ZnSO4) and magnesium sulfate (MgSO4) in deionized water, then adding 1M NaOH solution dropwise under stirring (stirring rate 500 r / min) for two hours. The precipitate is separated by centrifugation, washed twice with deionized water, then washed with isopropanol, and finally dried at 80℃ for 24 hours to obtain the negative electrode material. During the drying process, Zn(OH)2 is converted to ZnO. By controlling the mass ratio of zinc sulfate to magnesium sulfate, the magnesium content in the negative electrode material is approximately 0.5 wt%.

[0069] [Microstructure and elemental distribution] Microstructure images obtained through field emission electron microscopy (FE-SEM) were obtained from... Figure 1 , Figure 6 , Figure 8 and Figure 11 As can be seen, the anode materials prepared by the preparation method provided by this invention (Examples 1, 2, 3, and 4) mainly exhibit a spherical structure, with a distinct coating layer on the surface of the particles, and the outer shell layer has a distinct, complete, and uniform coating layer. Therefore, the prepared anode materials are micron-sized particles with a core-shell structure.

[0070] according to Figure 2 , Figure 7 , Figure 9 and Figure 12 The elemental distribution diagrams of energy-dispersive X-ray spectroscopy (EDS) show that the anode materials prepared using the method provided in this invention (Examples 1, 2, 3, and 4) have a uniform distribution of Zn, O, and Mg elements. The Mg and O elements mainly originate from the surface coating core layer. For example, the anode material provided in Example 1 can form a MgC₂O₄ coating layer, the anode material provided in Example 2 can form a Mg(OH)₂ coating layer, the anode material provided in Example 3 can form a MgCO₃ coating layer, and the anode material provided in Example 4 can form a Mg₂(OH)₂CO₃ coating layer. It should be noted that the uniform Mg distribution indicates a relatively uniform thickness of the coating layer of the anode material.

[0071] according to Figure 3 and Figure 10The thickness of the coating layer can be measured by FESEM. It can be seen that the thickness of the surface shell layer of the negative electrode material provided by the inventive example 1 and the inventive example 3 is 4.25-5 μm and 2-2.25 μm, respectively. It is found that by changing the reaction conditions, such as the concentration of the reactants, the reaction temperature, the reaction time, the solid-liquid ratio (S / L) of the zinc powder and the solution, the thickness of the surface shell layer of the negative electrode material can be controlled in the range of about 1 μm to about 5 μm.

[0072] The morphology of the spherical structure mainly depends on the metal zinc powder raw material. Figure 4 It can be seen from the metal zinc powder that the overall performance is spherical particles, the morphology is regular, the sphericity is good, the surface is relatively clean, there is no obvious coating layer, and the whole belongs to micron-level particles. Figure 5 According to the energy dispersive X-ray spectroscopy (EDS), it can be seen that the elements Zn and O are uniformly distributed, and the element O may be related to the oxidation of the surface of the metal zinc powder in the air.

[0073] Figure 13 and Figure 14 The microstructure of the negative electrode material provided by the comparative example 1 and the comparative example 3 under the field emission electron microscope (FE-SEM) can be seen from the figure. It can be seen that the surface of the negative electrode material is partially exposed and smooth, and the morphology is basically similar to the metal zinc powder raw material ( Figure 4 ), which indicates that the surface shell layer cannot form a complete coating core layer.

[0074] It needs to be further explained that regarding the particle size distribution of the negative electrode material, according to the test results of the laser particle size analyzer (PSD), the D50 of the metal zinc powder raw material is about 54.1 μm, and the negative electrode material prepared by the preparation method provided by the application, such as: example 1, example 2, example 3 and example 4, is 62.1 μm, 61.7 μm, 66.4 μm and 60.8 μm, respectively. After the coating treatment provided by the application, it can be found that the particle size distribution D50 value of the negative electrode material increases significantly.

[0075] It needs to be further explained that the element mass percentage of the negative electrode material is measured by energy dispersive X-ray spectroscopy. The mass percentage of Zn and O elements of the metal zinc powder raw material is 95.1% and 4.9%, respectively. The mass percentage of Zn, O and Mg elements of the negative electrode material provided in Example 1 is 73.4%, 22.1% and 4.5%, respectively; the mass percentage of Zn, O and Mg elements of the negative electrode material provided in Example 2 is 73.7%, 17.2% and 9.1%, respectively; the mass percentage of Zn, O and Mg elements of the negative electrode material provided in Example 3 is 76.4%, 15.1% and 8.5%, respectively; the mass percentage of Zn, O and Mg elements of the negative electrode material provided in Example 4 is 83.4%, 14.1% and 2.5%, respectively. According to the test results of energy dispersive X-ray spectroscopy, the mass percentage of element Mg in the negative electrode material is 2.5%-9.1%. In addition, the mass percentage of Zn, O and Mg elements of the negative electrode material provided in Comparative Example 1 is 91%, 8.2% and 0.8%, respectively; the mass percentage of Zn, O and Mg elements of the negative electrode material provided in Comparative Example 3 is 92%, 7.5% and 0.5%, respectively. It can be seen that when the mass percentage of element Mg in the negative electrode material is less than 1%, the core-shell structure of the negative electrode material is not obvious, which is not conducive to improving the stability in the alkaline environment.

[0076] When the mass percentage of Mg element in the negative electrode material is measured by inductively coupled plasma spectrometer (ICP), the negative electrode material prepared by the preparation method provided in the application contains 0.06%, 0.14%, 0.11% and 0.10% respectively, which is much higher than the content (0.01-0.02%) of Comparative Examples 1 and 3. It needs to be explained that energy dispersive X-ray spectroscopy can generally only test the element content of the surface or subsurface of the material, and ICP can accurately measure the percentage of Mg element in the total mass of the negative electrode material.

[0077] It needs to be further explained that the coating layer can effectively improve the stability of the negative electrode material in the alkaline environment. For the metal zinc powder, chemical and electrochemical corrosion occurs in the alkaline environment, and then hydrogen evolution side reaction occurs. This has a great side effect on the cycle life and internal pressure of the alkaline nickel-zinc battery. This may be because the coating layer can effectively physically block the corrosion of the strong alkaline electrolyte to the metal zinc, and the coating layer can effectively inhibit the volume change of the metal zinc during charging and discharging.

[0078] In order to further verify the good alkali resistance of the negative electrode material prepared by the preparation method provided by the present application, a certain amount of negative electrode material is placed in a KOH solution with pH = 13, wherein the concentration of zinc powder is 10 g / L, and after being sealed, it is placed in a 50°C oven for 24 hours. Through high-temperature gas evolution quantitative experiment, it is found that: the gas evolution amount of the metal zinc powder raw material without a coating layer is about 2.9 mL; the negative electrode materials prepared by the preparation method provided by the present application, such as: Example 1, Example 2, Example 3 and Example 4, are 0.45 mL, 1.0 mL, 1.4 mL and 0.8 mL respectively. However, the gas evolution amounts of the negative electrode materials provided by Comparative Example 1 and Comparative Example 3 are 2.1 mL and 2.6 mL respectively. Taking the gas evolution amount (2.9 mL) of the metal zinc powder raw material as a benchmark (i.e. 100%), the gas evolution amounts of the negative electrode materials provided by Example 1, Example 2, Example 3 and Example 4 are only 15.5%, 34.5%, 48.3% and 27.6% of the uncoated metal zinc powder respectively. The gas evolution amounts of the negative electrode materials provided by Comparative Example 1 and Comparative Example 3 are 72.4% and 90% of the uncoated metal zinc powder respectively. As can be seen, the negative electrode material with a magnesium compound shell layer can exhibit excellent corrosion resistance and stability in an alkaline environment.

[0079] [zinc negative electrode] The negative electrode materials provided by Examples 1-4 and the negative electrode materials provided by Comparative Examples 1-4 are used to prepare zinc negative electrodes, and the method for preparing the zinc negative electrode mainly includes the following steps: The method for preparing the zinc negative electrode is realized by a wet slurry process. The active material composition of the zinc negative electrode is: 20%-50% of nano-zinc oxide, 10%-60% of metal zinc powder, 1%-5% of bismuth oxide, 1%-5% of indium oxide, 1%-3% of carboxymethyl cellulose (CMC) and 1%-3% of butadiene styrene rubber (SBR). The preferred ratio is 35% of nano-zinc oxide, 45% of metal zinc powder, 10% of bismuth oxide, 5% of indium oxide, 3% of CMC and 2% of SBR. All the active materials need to be pre-treated by 100 o C drying treatment to remove the moisture on the surface of the active material, so as to avoid affecting the stability and uniformity of the negative electrode slurry. Generally, a mechanical stirrer is used for preliminary mixing at a low speed for 15-30 minutes to ensure uniform mixing between the dry powder particles. Subsequently, deionized water is slowly added as a solvent, and a planetary mechanical stirrer is used for slurry mixing at room temperature for 60-120 minutes until a uniform and non-agglomerated negative electrode slurry is formed.

[0080] The particle size of the nano-zinc oxide is controlled in the range of 100-500 nm to ensure high specific surface area and electrochemical reactivity; both CMC and SBR are of industrial grade purity to improve the adhesion and flexibility of the negative active layer and ensure the integrity of the zinc negative electrode during the charge-discharge cycle, effectively avoiding the detachment of the active layer from the surface of the current collector. The solid content of the negative electrode slurry is controlled in the range of 50%-85%, and the preferred proportion of the solid content of the slurry is 70-75%. The obtained negative electrode slurry is coated on the surface of a porous tin-plated copper foil or tin-plated inclined cable net current collector, and is subjected to sufficient air drying at 100-120°C, and then is rolled to a thickness of 350-500 μm, and finally is cut by a slitting device to obtain zinc negative electrodes of appropriate size.

[0081] [Performance test of zinc negative electrode] Zinc negative electrodes with an apparent area of about 0.5 cm 2 are prepared by a punching machine, which are used as working electrodes, zinc plates are used as counter electrodes, zinc wires are used as reference electrodes, 4M KOH aqueous solution saturated with zinc oxide is used as electrolyte, a three-electrode system is used to perform charge-discharge cycle test at a current value of 0.85 mA, the charge-discharge time is 1 hour, the charge cut-off voltage is 0.4V, and the discharge cut-off voltage is -0.2V. The charge capacity A1 of the 10th charge is recorded, then discharge operation is performed, after the zinc oxide in the zinc negative electrode is completely converted into metallic zinc, the zinc negative electrode is placed for 24 hours, then charge operation is performed under the same conditions, and the discharge capacity A2 at this time is recorded. The surface of the zinc negative electrode after charge-discharge test is observed by field emission scanning electron microscopy (FE-SEM). The test results are as follows: 1. The zinc negative electrodes corresponding to Examples 1-4: the discharge capacity A1 and the discharge capacity A2 are equal, indicating that no self-discharge occurs, and the surface of the zinc negative electrode after charge-discharge test is observed by SEM, and it is found that the shape of the zinc negative electrode active material has not changed significantly; 2. The zinc negative electrode corresponding to Comparative Example 1: the discharge capacity A2 is close to 0 mAh, indicating that self-discharge occurs, and the surface of the zinc negative electrode after charge-discharge test is observed by FE-SEM, and it is found that the shape of the zinc negative electrode active material has changed; 3. The zinc negative electrodes corresponding to Comparative Examples 2-4: the discharge capacity A2 is about 90% to 95% of the discharge capacity A1, indicating that almost no self-discharge occurs, and the surface of the zinc negative electrode after charge-discharge test is observed by FE-SEM, and it is found that the shape of the zinc negative electrode active material has changed.

[0082] The negative electrode material provided by the application can be used as a negative electrode of a secondary battery, and can inhibit the concentration of current and the decomposition of water in the negative electrode, thereby inhibiting the deterioration of the negative active material caused by the change in the morphology, dissolution, corrosion and passivation of the negative active material, and the generation of hydrogen and oxygen during charging and discharging, and most importantly, the self-discharge problem during charging and storage can be improved.

[0083] [Assembly of cylindrical AA nickel-zinc battery] The prepared zinc negative electrode, commercial nickel hydroxide positive electrode and commercial separator are assembled into an AA cylindrical battery by an automatic winding device. The positive electrode is mainly prepared by uniformly coating spherical nickel hydroxide, metal nickel powder, yttrium oxide, polytetrafluoroethylene (PTFE) and the like on a foamed nickel, the negative electrode is a zinc negative electrode prepared by using the negative electrode material provided by the application, and the commercial separator is a composite separator mainly including a non-woven fabric separator with high liquid absorption capacity and a microporous separator for preventing zinc dendrites, and the total thickness of the composite separator is in the range of 0.10-0.20 mm. During winding, the positive and negative electrode sheets are kept in precise alignment with the separator, and the tabs are respectively welded to the corresponding current collectors. The wound battery is loaded into a cylindrical AA nickel-plated stainless steel battery shell (size: Φ14.1x50.5mm). An insulating gasket needs to be placed at the bottom of the battery shell, and the battery is fixed by a hydraulic device after being loaded. The alkaline electrolyte is injected by a vacuum injection method. The electrolyte is a 6-8M potassium hydroxide solution, and 2-5% lithium hydroxide can also be added as an electrolyte additive. The inside of the battery is vacuumed before injection, and then a certain amount of alkaline electrolyte is injected. After the processes of tamping, sealing, cleaning, drying and packaging, the cylindrical AA nickel-zinc battery is prepared, which is used for the test of the cycle performance of the nickel-zinc battery, aiming to compare the capacity attenuation of the battery during repeated charging and discharging.

[0084] [Cycle performance test] The prepared cylindrical AA nickel-zinc battery is fully activated at room temperature to ensure the uniform distribution of the alkaline electrolyte in the battery. The test conditions of the cycle performance of the cylindrical AA nickel-zinc battery are as follows: The cycle performance test of the nickel-zinc battery is carried out in a constant temperature environment by using the constant current-constant voltage charging method, and the environmental temperature is controlled at 25℃±2℃. First, the battery is charged at a constant current rate of 0.5C. The charging continues until the voltage reaches 1.9V, and then the constant voltage charging stage is immediately carried out. The voltage of the charging is maintained at 1.9V, and the charging continues until the cutoff current is 0.02-0.03C, and the charging program of the nickel-zinc battery is terminated.

[0085] After the end of the charging phase, the battery is left for a while (for example: 5 minutes), and then immediately discharged at a constant current rate of 0.5C. The discharge continues until the battery voltage drops to the specified 1.2-1.3V, and the actual capacity of this discharge is recorded. After the end of the discharge, the next charging and discharging cycle can be entered.

[0086] When the actual discharge capacity of the battery decreases to 60% compared to its initial rated capacity, the cycle test of the cylindrical AA nickel-zinc battery is automatically stopped.

[0087] The test results are shown in Table 2. As can be seen from Table 2, the nickel-zinc batteries corresponding to Examples 1-4 have significant improvements in discharge capacity and cycle life compared to the nickel-zinc batteries corresponding to Comparative Examples 1-4, and the cycle stability and reliability of the nickel-zinc batteries are also improved. The deposition difference and deformation problem of the zinc negative electrode of the nickel-zinc battery are relatively small between different technical solutions in each charging and discharging process, and are not easy to characterize, but these small differences can be continuously added and amplified to be significant enough through cycle life test. When the zinc negative electrode is formed using the negative electrode material provided by the present application, compared with the existing zinc negative electrode, the cycle characteristics, rate characteristics and coulomb efficiency of the nickel-zinc battery can be improved while the self-discharge is inhibited, and the battery becomes high safety in the case of using aqueous electrolyte.

[0088] Table 2 The technical features of the above-described embodiments can be combined in any manner. In order to make the description concise, not all possible combinations of the technical features in the above-described embodiments are described, but as long as the combinations of the technical features do not contradict, they should be considered within the scope of the present disclosure.

[0089] 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 noted 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 scope of protection of the present application should be subject to the appended claims.

Claims

1. A negative electrode material, characterized in that, the negative electrode material is a core-shell structure comprising a core layer and a surface shell layer coated on the surface of the core layer, the core layer comprises zinc and / or zinc oxide, and the surface shell layer comprises a magnesium-containing compound, the solubility product constant of the magnesium-containing compound in water at 25℃ is not less than 1E-11; the content of magnesium is 0.02wt% to 1wt% based on the total mass of the negative electrode material; the electrical conductivity of the negative electrode material ranges from 1E0 S / cm to 1E+04 S / cm; the thickness of the surface shell layer is 1 μm to 5 μm, and the average particle size D50 of the negative electrode material is 50 μm to 100 μm.

2. The negative electrode material according to claim 1, characterized in that, The chemical formula of the magnesium-containing compound is Mg x M y , wherein the M is at least one of OH - , CO3 2- , F - , SO3 2- , S 2- , and C2O4 2- .

3. The method for producing the negative electrode material according to claim 2, characterized by, the preparation method comprises the following steps: a step of dissolving a precipitant in deionized water to prepare a first solution; a step of mixing zinc and / or zinc oxide particles into the first solution to obtain a first mixture; a step of dissolving a water-soluble magnesium salt containing magnesium in deionized water to prepare a second solution; a step of mixing the second solution into the first mixture to obtain a second mixture; a step of filtering the second mixture and collecting the precipitate; a step of drying the precipitate.

4. The production method according to claim 3, characterized by, The cation of the precipitant is potassium and / or sodium and / or ammonium, the anion of the precipitant is OH - , CO3 2- , F - , SO3 2- , S 2- , C2O4 2- , at least one of these.

5. The production method according to claim 4, characterized by, the water-soluble magnesium salt is at least one of magnesium chloride, magnesium acetate, magnesium sulfate, magnesium nitrate, magnesium lactate, magnesium gluconate, magnesium aspartate, magnesium citrate, and magnesium glycinate.

6. The production method according to claim 5, characterized by, the precipitant is Na2C2O4, the water-soluble magnesium salt is magnesium sulfate, and the reaction temperature is room temperature.

7. The production method according to claim 6, wherein the precipitant is NaOH and / or Na2CO3, the water-soluble magnesium salt is magnesium sulfate, and the reaction temperature is 50-80℃.

8. The production method according to claim 6, characterized by, 9.The negative electrode material of claim 1 or 2 is applied in a zinc-based battery. the zinc-based battery is a nickel-zinc battery.

10. Use according to claim 9, characterized in that, ​

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