Positive electrode active material, nickel electrode, and alkaline storage battery

Abstract

The present invention relates to a positive electrode active material comprising: a core comprising a material having the general formula Ni 1‑x (Al, Mg) x (OH)2; a first coating layer coated on the surface of the core, the first coating layer comprising a material having the general formula Ni 1‑x1‑y1 Al x1 Mg y1 (OH)2; a second coating layer coated on the surface of the first coating layer, the second coating layer comprising a material having the general formula Ni 1‑x2‑y2 Al x2 Mg y2 (OH)2. The present invention also relates to a nickel electrode obtained by filling a porous substrate with the above-mentioned positive electrode active material. The present invention also relates to an alkaline storage battery using the above-mentioned nickel electrode.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chemical batteries, and in particular to a positive electrode active material that can be applied to alkaline storage batteries, a nickel electrode prepared using the positive electrode active material, and an alkaline storage battery having the nickel electrode. BACKGROUND

[0002] This section provides background information which is not necessarily prior art.

[0003] Active materials containing nickel hydroxide have long been used in the positive electrodes of rechargeable or secondary batteries, particularly alkaline rechargeable batteries. Typical batteries using such active materials include nickel-metal hydride batteries, nickel-cadmium batteries, nickel-hydrogen batteries, nickel-iron batteries, and nickel-zinc batteries. Nickel hydroxide active materials have two phases in their molecular structure, alpha and beta phases, and the beta phase material is generally oxidized and reduced between +2 and +3 oxidation states, and the alpha phase nickel hydroxide can be prepared by oxidizing the nickel valence to +4 oxidation state. The alpha phase nickel hydroxide can exchange up to 1.67 electrons per nickel atom, which can increase the electrode storage capacity by 85% compared to electrodes using beta phase nickel hydroxide. However, the alpha phase nickel hydroxide material is unstable when repeatedly charged and discharged (the alpha phase material slowly generates an undesirable secondary beta phase material when repeatedly charged and discharged).

[0004] Studies have shown that partial substitution of nickel cations with more than 20 wt% of cations such as aluminum, cobalt, iron, or magnesium can stabilize the alpha phase structure of the nickel hydroxide material. Although the addition of these cations can increase the discharge voltage of the nickel hydroxide material and suppress self-discharge of the nickel hydroxide material, the addition of these cations also acts as impurities that are detrimental to the performance of the nickel hydroxide material, for example, the addition of magnesium and aluminum can cause the electrochemical capacity of the nickel hydroxide material to decrease, and the addition of magnesium and aluminum can cause the crystal structure of the nickel hydroxide material to change, which can cause significant expansion during charge and discharge cycles. SUMMARY

[0005] The purpose of the present application is to provide a positive electrode active material and a method for manufacturing the same, a nickel electrode including the positive electrode active material, and an alkaline storage battery including the nickel electrode. The positive electrode active material exhibits excellent performance in terms of discharge recovery after overdischarge, discharge recovery after long-term storage at high temperature, and high-temperature characteristics. The alkaline storage battery has high capacity, high discharge voltage, high open-circuit voltage, and excellent charge-discharge cycle stability characteristics.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solution: a positive electrode active material, the positive electrode active material comprising:

[0007] a core, the core being mainly composed of nickel hydroxide or a solid solution of nickel hydroxide in which two or more other elements are solid-solved;

[0008] a first coating layer coated on the surface of the core, the first coating layer mainly comprising nickel hydroxide or nickel hydroxide solid solution solid-solutioned with one or more other elements;

[0009] a second coating layer coated on the surface of the first coating layer, the second coating layer mainly comprising nickel hydroxide solid solution solid-solutioned with two or more other elements.

[0010] the core comprises a material with a general formula of Ni 1-x (Al, Mg) x (OH)2; the first coating layer comprises a material with a general formula of Ni 1-x1- y1 Al x1 Mg y1 (OH)2; the second coating layer comprises a material with a general formula of Ni 1-x2-y2 Al x2 Mg y2 (OH)2. And the positive electrode active material satisfies:

[0011] 0.15 ≥ x ≥ 0;

[0012] x2 > x1 ≥ 0, x2 is 0.01-0.1;

[0013] y2 > y1 ≥ 0, y2 is 0.01-0.1.

[0014] The content of Al element and Mg element decreases in the direction from the second coating layer to the first coating layer. Wherein, the “decreases” can be specifically “gradually decreases”. The core material of the positive electrode active material can play a synergistic effect with the first coating layer material and the second coating layer, and in cooperation with the higher mass ratio of the core material, the positive electrode active material can have high tap density, high coulomb efficiency, high specific capacity, good rate performance and the like. Further, the positive electrode active material provided by the present application can not introduce any Co-containing material, which can help to reduce the preparation cost of the positive electrode active material.

[0015] When y1 and y2 are within the above-mentioned range, it was found that when (x1 + x2) is 0.03 or more, the discharge characteristics curve of the battery prepared using the positive electrode active material changes in the slope at the end of discharge, and the effect is such that the SOC can be accurately detected from the battery voltage, and thus the remaining capacity of the battery can be detected, but when (x1 + x2) is less than 0.01, it is difficult to sufficiently obtain this effect. Preferably, (x1 + x2) is not less than 0.05; more preferably, (x1 + x2) is not less than 0.06. On the other hand, when (x1 + x2) is 0.2 or more, the content of nickel in the positive electrode active material decreases accordingly, resulting in a decrease in capacity, and the advantage of the voltage characteristics of the positive electrode active material becomes less apparent (the difference between the equilibrium potential and the oxygen generation potential becomes smaller), and the cycle life characteristics of the positive electrode active material decrease. Preferably, x2 is not more than 0.1; more preferably, x2 is not more than 0.07.

[0016] When x1 and x2 are within the above-mentioned range, it was found that when (y1 + y2) is 0.03 or more, the discharge characteristics curve of the battery prepared using the positive electrode active material changes in the slope at the end of discharge, and the effect is such that the SOC can be accurately detected from the battery voltage, and thus the remaining capacity of the battery can be detected, but when (y1 + y2) is less than 0.01, it is difficult to sufficiently obtain this effect. Preferably, (y1 + y2) is not less than 0.05; more preferably, (y1 + y2) is not less than 0.06. On the other hand, when (y1 + y2) is 0.2 or more, the content of nickel in the positive electrode active material decreases accordingly, resulting in a decrease in capacity, and the advantage of the voltage characteristics of the positive electrode active material becomes less apparent (the difference between the equilibrium potential and the oxygen generation potential becomes smaller), and the cycle life characteristics of the positive electrode active material decrease. Preferably, y2 is not more than 0.1; more preferably, y2 is not more than 0.07.

[0017] The second coating layer contains magnesium, and the first coating layer does not necessarily contain magnesium, but when the first coating layer contains magnesium, the amount of magnesium contained in the first coating layer should be less than the amount of magnesium contained in the second coating layer. The positive electrode active material provided by the present application includes a case where the second coating layer contains magnesium and the first coating layer does not contain magnesium at all. The equilibrium potential of nickel hydroxide increases due to the solid solution of magnesium in nickel hydroxide. Since the content of magnesium and the equilibrium potential are related, different amounts of magnesium result in changes in the discharge curve.

[0018] The second coating layer contains aluminum, and the first coating layer does not necessarily contain aluminum, but when the first coating layer contains aluminum, the amount of aluminum contained in the first coating layer should be less than the amount of aluminum contained in the second coating layer. The positive electrode active material according to the present application includes a case where the second coating layer contains aluminum and the first coating layer does not contain aluminum at all. The equilibrium potential of nickel hydroxide increases due to the solid solution of aluminum in nickel hydroxide. In addition, the solid solution of aluminum in nickel hydroxide promotes the formation of α-phase nickel hydroxide, thereby improving the charge-discharge utilization rate of the positive electrode active material.

[0019] It is unexpectedly found that by stacking the first coating layer and the second coating layer having different aluminum solid solutions and different magnesium solid solutions, the volume expansion of the positive electrode active material during charge and discharge can be reduced, and the decrease in the capacity per unit volume due to the volume expansion can be suppressed, which is presumably the result of a synergistic effect of the aluminum solid solution and the magnesium solid solution.

[0020] In one or more embodiments, for the positive electrode active material, at least one element selected from zinc and cobalt is solid-solubilized in the nickel hydroxide of the core and / or the nickel hydroxide of the first coating layer and / or the nickel hydroxide of the second coating layer in addition to magnesium and aluminum.

[0021] In one or more embodiments, the positive electrode active material further includes a third coating layer. Preferably, the third coating layer includes cobalt oxyhydroxide (CoOOH) and / or cobalt oxide (CoO).

[0022] The proportion of the core in the positive electrode active material is preferably 85 to 97% by weight, and when it is within this range, the conductivity and the electrode capacity of the positive electrode active material will become better. When the proportion is less than 80% by weight, this can lead to a decrease in the capacity of the positive electrode active material; when the proportion exceeds 97% by weight, it can be impossible to sufficiently improve the conductivity and the charge-discharge cycle stability of the positive electrode active material. The nickel hydroxide in the core is preferably α-phase nickel hydroxide because it can improve the conductivity of the positive electrode active material.

[0023] The proportion of the nickel hydroxide in the first coating layer is preferably not less than 50% by weight based on the total mass of the first coating layer; the proportion of the nickel hydroxide in the second coating layer is preferably not less than 50% by weight based on the total mass of the second coating layer.

[0024] In one or more embodiments, the powder resistance of the positive electrode active material is less than 200 Ω·cm, and such a low powder resistance provides high conductivity. Therefore, in an electrode using the positive electrode active material, a higher active material utilization coefficient is obtained. For the purpose of further reducing the powder resistance of the positive electrode active material, yttrium oxide, tungsten oxide, titanium oxide, zinc oxide, or a combination thereof is included in the core and / or the first coating layer and / or the second coating layer, and the above additives can improve the conductivity of the positive electrode active material and can inhibit the expansion of the positive electrode active material during charging and discharging.

[0025] In one or more embodiments, the specific surface area S of the positive electrode active material is less than or equal to 30 m 2 / g. The specific surface area S can be measured by the nitrogen adsorption method (BET method). The specific surface area of the positive electrode active material should not be too high to significantly reduce the tap density. Moreover, the present application controls the total mass ratio of the first coating layer and the second coating layer to be small, so that the tap density of the positive electrode active material is higher. The specific surface area of the positive electrode active material is preferably 1-30 m 2 / g, and more preferably 5-25 m 2 / g, at which the specific surface area of the positive electrode active material is more appropriate, and the high tap density and high rate output capability can be better balanced.

[0026] In one or more embodiments, the coverage of the first coating layer and the second coating layer on the surface of the core is greater than or equal to 90%, for example, ≥ 92%, ≥ 95%, or ≥ 98%, etc. This parameter can reflect that the coating layer has a high degree of coating on the surface of the core, and its distribution is more uniform, greatly avoiding the problem of uneven coating caused by conventional secondary deposition technology, and the coating layer has a good effect on inhibiting the oxygen evolution of the core. The coating layer has a pore structure, and the average pore size of the pore is 1 nm-50 nm, which is much lower than the pore size in the loose coating layer prepared by the conventional coprecipitation method. The smaller average pore size can also reflect the close packing of the above-mentioned coating layer on the surface of the core, which is beneficial to the positive active material to have high tap density and high coulomb efficiency; at the same time, it is also beneficial to improve the porosity of the coating layer, and thus improve the porosity of the overall positive active material, which can better relieve the stress change of the positive active material in the charging and discharging cycle process, thereby reducing the particle pulverization phenomenon of the positive active material, and improving the cycle life of the battery. Therefore, it can be understood that the coating layer of the present application is closely packed / coated and has pores, wherein the close coating of the coating layer can inhibit the particle pulverization phenomenon of the core in the cycle process and improve the cycle stability, and the presence of the porous structure in the coating layer can further facilitate the stress release of the core in the charging and discharging process, so that the positive active material can have high tap density, high coulomb efficiency, high specific capacity, good rate performance, long cycle life, etc. The average pore size of the pore can be obtained by cross-sectional electron microscope characterization of the positive active material, or by nitrogen adsorption method.

[0027] In one or more embodiments, the porosity of the positive active material can be 5-40%. The porosity can be obtained by cross-sectional electron microscope characterization of the positive active material, or by nitrogen adsorption method. The porosity at different positions of the positive active material can be different, and the porosity at a position closer to the core can be lower. The overall pore volume of the positive active material is less than or equal to 0.2 cm 3 / g (measured by nitrogen adsorption method), which is beneficial to make the tap density of the positive active material higher and the electrochemical performance better.

[0028] In one or more embodiments, the particle diameter of the positive active material is D0, the thickness of the first coating layer is D1, and the thickness of the second coating is D2, which satisfies: 0 < D1 ≤ D2 ≤ 0.08D0. Wherein, D0, D1 and D2 can be obtained by electron microscope photograph of the positive active material. The thickness of the coating layer composed of the first coating layer and the second coating layer is thin, which is beneficial to ensure a closer coating. Wherein, D0 can be in the range of 2 μm-25 μm, and D1 and D2 can be in the range of 10 nm-800 nm.

[0029] In one or more embodiments, the average secondary particle size of the positive electrode active material is 5 μm-15 μm, which is the average particle size of the particles of the positive electrode active material in its dispersion liquid measured by a dynamic light scattering method (DLS method), and a suitable average secondary particle size can adjust the transport channels of electrons, ions, etc. during the electrochemical reaction of the positive electrode active material, ensure its high electrochemical activity, and achieve its high specific capacity and high rate performance.

[0030] The preparation process of the positive electrode active material of the present application comprises the following steps (a) to (c).

[0031] Step (a): preparing core particles.

[0032] Step (b): forming a first coating layer on the surface of the core.

[0033] Step (c): forming a second coating layer on the surface of the first coating layer.

[0034] The positive electrode active material provided by the present application can be prepared by a coprecipitation method or by an ion permeation self-exchange reaction.

[0035] In one or more embodiments, step (a) comprises the following steps: configuring an aqueous solution containing a given amount of a soluble salt containing nickel, a soluble salt containing Al, and a soluble salt containing Mg, configuring an aqueous solution containing a given amount of ammonium sulfate and sodium hydroxide, mixing the two aqueous solutions, stirring and performing water bath heating, and maintaining the pH value of the reaction system at 8-12 (using an alkaline aqueous solution to adjust the pH value of the reaction system) and the reaction temperature at 50°C-90°C (for example, 50°C, 60°C, 70°C, 80°C, 85°C, 90°C, etc.) throughout the operation process, and the reaction time is 1-10 hours (for example, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 8 h, 10 h, etc.), thereby obtaining core particles including nickel hydroxide particles, which contain aluminum hydroxide and magnesium hydroxide solid-solved in the form of ammonia complex ions. Adjusting the pH value of the reaction system to 8-10 obtains α-phase Ni(OH)2, and adjusting the pH value thereof to 10-12 obtains β-phase Ni(OH)2. When the soluble salt containing Al and the soluble salt containing Mg are omitted in step (a), core particles composed of nickel hydroxide particles are obtained.

[0036] In one or more embodiments, step (b) comprises the following steps: mixing the core particles with a first reaction solution containing a given amount of a soluble salt containing nickel, the first reaction solution also containing a given amount of a soluble salt containing Al and a soluble salt containing Mg, after mixing the core particles with the first reaction solution, stirring and water bath heating are performed, and then a basic aqueous solution is added to adjust the pH value of the reaction system to 10-13, thereby generating a first coating layer on the surface of the core particles, the temperature of the reaction in this process is 50-90°C, and the reaction time is 1-24 hours. Preferably, the mass ratio of the core particles to the first reaction solution is 1:5-100, and a suitable solid-liquid ratio can ensure that the coating thickness and compactness of the first coating layer are suitable, and the preparation efficiency of the first coating layer is improved. The concentration of the soluble salt containing Al and the soluble salt containing Mg in the first reaction solution is not more than 3.0 mol / L, which is conducive to ensuring that the first coating layer has a suitable generation speed and can control the content of Al and Mg in the first coating layer. When the soluble salt containing Mg is omitted in step (b), a first coating layer without magnesium solid solution can be obtained; when the soluble salt containing Al is omitted in step (b), a first coating layer without aluminum solid solution can be obtained; when the soluble salt containing Al and the soluble salt containing Mg are omitted in step (b), a first coating layer composed of nickel hydroxide particles can be obtained.

[0037] In one or more embodiments, step (c) comprises the following steps: mixing the particles with the first coating layer with a second reaction solution containing a given amount of a soluble salt containing nickel, the first reaction solution also containing a given amount of a soluble salt containing Al and a soluble salt containing Mg, after mixing, stirring and water bath heating are performed, and then a basic aqueous solution is added to adjust the pH value of the reaction system to 10-13, thereby generating a second coating layer on the surface of the first coating layer, the temperature of the reaction in this process is 50-90°C, and the reaction time is 1-24 hours.

[0038] In one or more embodiments, the preparation process of the positive electrode active material further includes step (d), which includes the following steps: mixing the particles with the second coating layer, a cobalt sulfate aqueous solution and a sodium hydroxide aqueous solution, stirring and water bath heating, and adjusting the pH value of the reaction system to 11 to 13 using the alkaline aqueous solution, thereby forming a third coating layer containing cobalt hydroxide on the surface of the second coating layer. The particles with the third coating layer are oxidized in water or in an alkaline aqueous solution with a concentration of 20% by weight or less than 20% by weight at a temperature of 60°C or less than 60°C (i.e., an oxidation treatment process), and then the particles are heated in an alkaline aqueous solution with a concentration of 30% by weight or more than 30% by weight at a temperature of 80°C or more than 80°C (i.e., a heating treatment process). Through the oxidation treatment process, cobalt and part of nickel in the positive electrode active material are oxidized, and the self-discharge of the positive electrode active material is inhibited, so that the battery using the positive electrode active material will have excellent internal pressure characteristics and charge / discharge cycle characteristics. The positive electrode active material obtained through the oxidation treatment process has a relatively high powder resistance. However, since the alkaline aqueous solution with a concentration of 30% by weight or more than 30% by weight is added, and the material is subjected to the heating treatment at a temperature of 80°C or more than 80°C, the positive electrode active material will have a sufficiently low powder resistance after the heating treatment. If the heating treatment is performed using an alkaline aqueous solution with a concentration of less than 30% by weight or at a temperature of less than 80°C, a sufficiently low powder resistance will not be obtained.

[0039] It should be noted that the alkaline aqueous solution described in the present application is preferably a sodium hydroxide aqueous solution, but the alkaline aqueous solution is not limited to this. The alkaline aqueous solution can be an aqueous solution of one or more of lithium hydroxide, sodium hydroxide and potassium hydroxide.

[0040] It should be noted that the "soluble salt" described in the present application specifically refers to a salt that is soluble in water. For example, the soluble salt of Al can specifically include one or more of the sulfate, nitrate or chloride of Al, and the soluble salt of Mg can specifically include one or more of the sulfate, nitrate or chloride of Mg. Preferably, the soluble salt containing nickel is nickel sulfate, the soluble salt of Al is aluminum sulfate, and the soluble salt of Mg is magnesium sulfate.

[0041] The nickel electrode of the present application is characterized in that the nickel electrode is obtained by filling a porous substrate with the positive electrode active material described above. The porous substrate can be a nickel-plated mesh, sponge or fibrous metal body or a nickel foam. The nickel electrode containing the positive electrode active material significantly increases the potential difference between the oxygen evolution potential and the oxidation potential in the nickel electrode, and thus the charge efficiency can be further improved.

[0042] In one or more embodiments, the preparation process of the nickel electrode is as follows: a positive electrode active material is mixed with a conductive material, an additive, water, and an aqueous binder (for example, carboxymethyl cellulose, methyl cellulose, polytetrafluoroethylene dispersion, hydroxypropyl cellulose, etc.) to prepare a slurry; the obtained slurry is filled into a foamed nickel and dried, and then roll-pressed and cut to obtain the nickel electrode. The additive is preferably a compound containing one or more rare earth elements, and the oxygen evolution potential of the nickel electrode during charging is positively shifted due to the rare earth compound, thereby inhibiting the oxygen evolution reaction and enhancing the oxidation reaction of nickel. Therefore, the charging efficiency is further improved.

[0043] The alkaline storage battery of the present application is an alkaline storage battery using a nickel electrode, characterized in that the positive electrode of the alkaline storage battery comprises the nickel electrode. The alkaline storage battery refers to a battery system relying on the positive electrode active material, the alkaline aqueous electrolyte, and the different negative electrode provided by the present application. According to the different negative electrodes, the alkaline storage battery can be divided into different types, for example, the alkaline storage battery can be specifically a nickel-metal hydride battery, a nickel-zinc battery, a nickel-iron battery, or a nickel-cadmium battery, etc. Correspondingly, the negative electrode of the alkaline storage battery is a metal hydride negative electrode, a zinc negative electrode, an iron negative electrode, or a cadmium negative electrode, respectively. Taking the zinc negative electrode as an example, it specifically refers to a negative electrode comprising a negative electrode active material containing Zn element, such as ZnO, etc. Among them, the electrolyte of the alkaline storage battery can contain an alkaline electrolyte and water, and the alkaline electrolyte can comprise one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide. Preferably, the concentration of the alkaline electrolyte in the electrolyte can be 0.5-10 mol / L.

[0044] The positive electrode active material provided by the present application has good electrochemical performance. The nickel electrode provided by the present application can balance high capacity and good charge-discharge cycle stability. The alkaline storage battery provided by the present application has high volumetric energy density, high coulombic efficiency and specific capacity, and good cycle performance.

[0045] The following will be described in conjunction with specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0046] The accompanying drawings further illustrate the present application, but the embodiments in the drawings do not constitute any limitation on the present application.

[0047] Figure 1 The structure schematic diagram of the positive electrode active material provided for the embodiment 1 of the present application.

[0048] Among them, the reference signs are: core 10, first coating layer 11, second coating layer 12, third coating layer 13. DETAILED DESCRIPTION

[0049] It is to be understood that the specific embodiments described herein are merely illustrative of the present application and do not limit the scope of the application.

[0050] [Example 1]

[0051] The present embodiment provides a positive electrode active material, Figure 1 is a structural schematic diagram of the positive electrode active material. The positive electrode active material provided by the present embodiment is a shell structure, and the packing degree of the shell material is higher. The positive electrode active material comprises a core 10, a first coating layer 11 coated on the surface of the core 10, a second coating layer 12 coated on the surface of the first coating layer 11, and a third coating layer 13 coated on the surface of the second coating layer 12.

[0052] The core 10 of the positive electrode active material is a spherical or spherical-like particle. After coating, the core 10 still maintains its spherical or near-spherical morphology, which is beneficial to ensure that the positive electrode active material has a high tap density (the tap density of the positive electrode active material is greater than or equal to 1.8 g / cm 3 ) and specific area, which is beneficial to improve the ion transmission and the wettability of the electrolyte, improve the kinetic characteristics, and improve the rate output capability.

[0053] The core 10 is an α-phase nickel hydroxide material, which can be obtained by in-situ phase transition reaction of a β-phase nickel hydroxide raw material. The first coating layer 11 is a β-phase nickel hydroxide. The second coating layer 12 is a β-phase nickel hydroxide material in which Al and Mg are solid-solved, and the chemical formula of the material of the second coating layer 12 is Ni 0.9 Al 0.05 Mg 0.05 (OH)2. The third coating layer is a cobalt oxyhydroxide. Compared with a pure α-phase nickel hydroxide material, the positive electrode active material of the present application is beneficial to ensure the good structural stability of the α-phase nickel hydroxide material, inhibit its conversion back to the β-phase during the charge and discharge cycle, and improve the cycle stability of the positive electrode active material by coating three coating layers. At the same time, the β-phase nickel hydroxide of the first coating layer 11 can generate α-phase nickel hydroxide by in-situ reaction, and realize in-situ coating of the α-phase nickel hydroxide material of the core 10, and as mentioned above, the Al element and the Mg element in the second coating layer 12 enter the β-phase nickel hydroxide material body phase, which can further inhibit the oxygen evolution side reaction of the positive electrode active material. When the Al element and the Mg element exist in the β-phase nickel hydroxide material at the same time, it is helpful to improve the oxygen evolution overpotential, and thus improve the coulombic efficiency of the positive electrode active material, and improve the comprehensive electrochemical performance of the positive electrode active material. The third coating layer is more beneficial to improve the structural stability and ion conductivity of the positive electrode active material.

[0054] The embodiment also provides a nickel electrode for an alkaline storage battery, the nickel electrode comprising the positive electrode active material provided by the embodiment, the nickel electrode comprising a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer comprising the positive electrode active material provided by the embodiment, and the positive electrode active material layer being disposed on one side surface or opposite side surfaces of the positive electrode current collector. The positive electrode current collector can be a conventional selection in the battery field, for example, can be a foamed nickel, a porous nickel foil, a nickel-plated perforated steel strip, a perforated steel strip, or the like. The positive electrode active material layer can further comprise a binder, a conductive agent, other positive electrode active components, or the like.

[0055] The embodiment also provides an alkaline storage battery, the alkaline storage battery comprising the nickel electrode provided by the embodiment. The alkaline storage battery provided by the embodiment comprises a nickel electrode, a negative electrode, an electrolyte, and a separator, and corresponding communication accessories and circuits. The separator is located between the nickel electrode and the negative electrode, and the nickel electrode, the negative electrode, and the separator are soaked in the electrolyte.

[0056] [Embodiment 2-8]

[0057] Embodiments 2-8 each provide a positive electrode active material, a preparation method of the positive electrode active material comprising the following steps:

[0058] Step one, 6g of nickel sulfate is dissolved in 50mL of deionized water, and then aluminum sulfate and magnesium sulfate are added and stirred to dissolve to obtain solution A, 2g of sodium hydroxide and 0.03g of ammonium sulfate are dissolved in 50mL of deionized water to obtain solution B;

[0059] Step two, under the action of magnetic stirring, solution A and solution B are mixed and reacted in a reaction container, 1mol / L of sodium hydroxide solution is used to control the pH value of the reaction system to be 11-11.5, and the reaction is carried out at 80℃ for 10h, the obtained reaction material is filtered, and then the solid is washed and dried to obtain a core material;

[0060] Step three, 0.28g of nickel sulfate is dissolved in 100mL of deionized water, and then aluminum sulfate and magnesium sulfate are added and stirred to dissolve to obtain a first reaction liquid required for coating reaction, under the action of magnetic stirring, the core material prepared in step two is mixed and reacted with the first reaction liquid in a reaction container, 1mol / L of sodium hydroxide solution is used to control the pH value of the reaction system to be 11-11.5, and the reaction is carried out at 50℃ for 3h, the obtained reaction material is filtered, and then the solid is washed and dried to obtain a material with a first coating layer;

[0061] Step four, step three, 0.56 g of nickel sulfate is dissolved in 100 mL of deionized water, and then aluminum sulfate and magnesium sulfate are added and stirred to dissolve to obtain the second reaction solution required for the coating reaction. The material prepared in step three is mixed with the second reaction solution in a reaction vessel under the action of magnetic stirring, and 1 mol / L sodium hydroxide solution is used to control the pH value of the reaction system to be 11-11.5, and the reaction is carried out at 90°C for 5 h. The obtained reaction material is filtered, and the solid is washed and then placed in a 120°C oven for 2 h, then taken out, and naturally cooled to room temperature to obtain the positive electrode active material;

[0062] The concentration of aluminum sulfate in the first reaction solution and the second reaction solution is not more than 3.0 mol / L, and the concentration of magnesium sulfate is not more than 3.0 mol / L. By adjusting the concentration of aluminum sulfate and magnesium sulfate in solution A, the content of aluminum and magnesium elements in the core material is adjusted. By adjusting the concentration of aluminum sulfate and magnesium sulfate in the first reaction solution, the content of aluminum and magnesium elements in the first coating layer material is adjusted. By adjusting the concentration of aluminum sulfate and magnesium sulfate in the second reaction solution, the content of aluminum and magnesium elements in the second coating layer material is adjusted.

[0063] The particle diameter distribution range of the positive electrode active material provided in examples 1-8 is 8-22 μm, and the average secondary particle diameter of the positive electrode active material is 10-11 μm. The thickness of the first coating layer is in the range of about 400-500 nm, and the thickness of the second coating layer is in the range of about 500 nm-600 nm. The thickness of the third coating layer of the positive electrode active material provided in example 1 is in the range of about 100 nm.

[0064] [Comparative example 1]

[0065] The uncoated β-phase cobalt-free Ni(OH)2 is directly used as the positive electrode active material. 0.9 Al 0.05 Mg 0.05 (OH)2 is directly used as the positive electrode active material.

[0066] [Comparative examples 2-7]

[0067] Comparative examples 2-7 all use the same preparation method as example 2 to obtain the positive electrode active material, and the only difference is that the concentration of aluminum sulfate and magnesium sulfate in solution A is different, or the concentration of aluminum sulfate and magnesium sulfate in the first reaction solution is different, or the concentration of aluminum sulfate and magnesium sulfate in the second reaction solution is different.

[0068] [Comparative example 8]

[0069] The uncoated β-phase cobalt-free Ni(OH)2 is directly used as the positive electrode active material.

[0070] Table 1 shows the chemical formula of the core and coating layer of the positive electrode active material provided in examples 1-8 and the positive electrode active material provided in comparative examples 1-8.

[0071] Table 1

[0072] Core First cladding layer Second cladding layer Example 1 [Ni(OH)2] [Ni(OH)2] Ni 0.9 Al 0.05 Mg 0.05 (OH)2]]> Example 2 Ni 0.9 Al 0.05 Mg 0.05 (OH)2]]> Ni 0.96 Al 0.02 Mg 0.02 (OH)2]]> Ni 0.88 Al 0.06 Mg 0.06 (OH)2]]> Example 3 Ni 0.7 Al 0.15 Mg 0.15 (OH)5]]> Ni 0.96 Al 0.02 Mg 0.02 (OH)2]]> Ni 0.88 Al 0.06 Mg 0.06 (OH)2]]> Example 4 [Ni(OH)2] Ni 0.96 Al 0.02 Mg 0.02 (OH)2]]> Ni 0.88 Al 0.06 Mg 0.06 (OH)2]]> Example 5 Ni 0.9 Al 0.05 Mg 0.05 (OH)2]]> [Ni(OH)2] Ni 0.88 Al 0.06 Mg 0.06 (OH)2]]> Example 6 Ni 0.9 Al 0.05 Mg 0.05 (OH)2]]> Ni 0.96 Mg 0.02 (OH)2]]> Ni 0.89 Al 0.1 Mg 0.01 (OH)2]]> Example 7 Ni 0.9 Al 0.05 Mg 0.05 (OH)2]]> Ni 0.96 Al 0.02 (OH)2]]> Ni 0.89 Al 0.01 Mg 0.1 (OH)2]]> Example 8 [Ni(OH)2] [Ni(OH)2] Ni 0.8 Al 0.1 Mg 0.1 (OH)2]]> Comparative Example 1 Ni 0.9 Al 0.05 Mg 0.05 (OH)1]]> / / Comparative Example 2 Ni 0.9 Al 0.05 Mg 0.05 (OH)2]]> / Ni 0.88 Al 0.06 Mg 0.06 (OH)2]]> Comparative Example 3 Ni 0.9 Al 0.05 Mg 0.05 (OH)2]]> Ni 0.96 Al 0.02 Mg 0.02 (OH)2]]> / Comparative Example 4 Ni 0.9 Al 0.05 Mg 0.05 (OH)2]]> Ni 0.88 Al 0.06 Mg 0.06 (OH)2]]> Ni 0.96 Al 0.02 Mg 0.02 (OH)2]]> Comparative Example 5 Ni 0.9 Al 0.05 Mg 0.05 (OH)2]]> Ni 0.96 Al 0.02 Mg 0.02 (OH)2]]> [Ni(OH)2] Comparative Example 6 Ni 0.9 Al 0.05 Mg 0.05 (OH)2]]> Ni 0.6 Al 0.2 Mg 0.2 (OH)2]]> Ni 0.88 Al 0.06 Mg 0.06 (OH)2]]> Comparative Example 7 Ni 0.9 Al 0.05 Mg 0.05 (OH)2]]> Ni 0.96 Al 0.02 Mg 0.02 (OH)2]]> Ni 0.6 Al 0.2 Mg 0.2 (OH)2]]> Comparative Example 8 [Ni(OH)2] / /

[0073] [Preparation of nickel electrode]

[0074] A nickel electrode was prepared using the positive electrode active material provided in Examples 1-8 and the positive electrode active material provided in Comparative Examples 1-8, respectively, as follows:

[0075] Step 1. A composite slurry was prepared by mixing 100 parts by mass of the positive electrode active material, 0.3 parts by mass of yttrium oxide, 0.6 parts by mass of tungsten oxide, 0.2 parts by mass of HPC (hydroxypropyl cellulose), 0.2 parts by mass of a polytetrafluoroethylene dispersion, and 30 parts by mass of water;

[0076] Step 2. The composite slurry was filled into a foamed nickel sheet as a positive electrode substrate, and then sequentially subjected to drying, rolling, and cutting to obtain a nickel electrode having a size of AA.

[0077] [Preparation of alkaline storage battery]

[0078] An alkaline storage battery was prepared using the nickel electrode described above, respectively, as follows:

[0079] Step 1. A compound including a rare earth element, magnesium, nickel, aluminum, and cobalt were mixed in a molar ratio of 1.00:0.02:3.24:0.15:0.07, and then uniformly mixed and placed in a furnace to be melted. The liquid obtained by melting was poured into a mold and cooled to room temperature to prepare a hydrogen storage alloy ingot. A sample extracted from the ingot was analyzed for composition by inductively coupled plasma (ICP), and the composition of the hydrogen storage alloy was (La 0.32 Sm 0.55 ) 1.00 Mg 0.14 Ni 3.24 Al 0.15 Co 0.07 ;

[0080] Step 2. The hydrogen storage alloy ingot was heat-treated at a temperature of 1050°C for 8 hours under an argon atmosphere, and after heat treatment, the hydrogen storage alloy ingot cooled to room temperature was mechanically pulverized in an argon atmosphere to obtain a hydrogen storage alloy powder. The particle size of the obtained hydrogen storage alloy powder was measured using a laser diffraction and scattering particle size distribution instrument, and the volume average particle size (MV) of the hydrogen storage alloy particles was 40 μm;

[0081] Step 3. 100 parts by mass of the hydrogen storage alloy powder, 0.4 parts by mass of sodium polyacrylate, 0.1 parts by mass of carboxymethyl cellulose, 1.0 parts by mass of a styrene-butadiene rubber (SBR) dispersion, 1.0 parts by mass of carbon black, and 30 parts by mass of water were mixed to prepare a paste;

[0082] Step four, the paste is coated on both sides of the steel perforated plate as the negative electrode substrate and the coating thickness is uniform, the thickness of the steel perforated plate is 60 μm and the surface of the steel perforated plate is plated with nickel, after the coating is completed, drying, rolling and cutting are carried out in sequence to obtain the negative electrode with the size of AA;

[0083] Step five, the negative electrode, the separator (the separator is made of sulfonated polypropylene fiber non-woven fabric, the thickness is 0.11 mm and the density is 48 g / m2) and the nickel electrode are stacked in sequence and then wound to obtain the electric core, the electric core is put into a bottomed cylindrical shell, a predetermined amount of prepared alkaline electrolyte (an aqueous solution containing potassium hydroxide, sodium hydroxide and lithium hydroxide is used as the alkaline electrolyte, the mass ratio of potassium hydroxide, sodium hydroxide and lithium hydroxide in the alkaline electrolyte is 1.3:6.4:0.85, and the concentration of hydroxide in the alkaline electrolyte is 5 mol / L) is injected into the alkaline electrolyte, then the opening of the cylindrical shell is sealed with a cap, and an AA size alkaline storage battery (i.e. a nickel-hydrogen rechargeable battery) with a nominal capacity (the nominal capacity refers to the discharge capacity of the battery at 0.2 C when the battery voltage reaches 1.0 V after being charged at 0.1 C for 16 hours at a temperature of 20°C) of 1450 mAh is assembled;

[0084] Step six, the alkaline storage battery is charged at 0.1 C for 16 hours and then discharged at 0.2 C, and the charging and discharging operation is repeated five times until the voltage of the alkaline storage battery reaches 1.0 volt, and the initial activation treatment of the battery is completed.

[0085] The alkaline storage battery after the initial activation treatment is tested as follows:

[0086] (1) Determination of the ratio of the actual discharge capacity to the theoretical capacity: at an ambient temperature of 20°C, the battery is charged at a charging current of 0.1 C (calculated according to the theoretical capacity) for 12 hours, then allowed to stand for 1 hour, and then discharged at a current of 0.2 C (calculated according to the theoretical capacity). When the battery voltage reaches 1.0 V, the discharge is terminated. The actual discharge capacity during this period is measured.

[0087] The ratio of the actual discharge capacity to the theoretical capacity (%) = measured discharge capacity ÷ 1450 x 100.

[0088] (2) Determination of the ratio of the high-rate discharge capacity to the theoretical capacity: at an ambient temperature of 20°C, the battery is charged at a charging current of 0.1 C (calculated according to the theoretical capacity) for 12 hours, then allowed to stand for 1 hour, and then discharged at a current of 3 C (calculated according to the theoretical capacity). When the battery voltage reaches 1.0 V, the discharge is terminated. The actual discharge capacity during this period is measured.

[0089] Determination of the ratio of high-rate discharge capacity to theoretical capacity (%) = measured discharge capacity ÷ 1450 x 100.

[0090] (3) Cycle performance test: 2 hours of constant current charging at 0.5 C, followed by constant current discharging at 0.5 C until 1.0 V, was repeated to perform charging and discharging for a maximum of 500 cycles at an ambient temperature of 20°C. The capacity retention rate (%) was calculated using the discharge capacity at the 1st charging and discharging cycle and the discharge capacity at a predetermined cycle number.

[0091] Capacity retention rate (%) = discharge capacity at the 500th charging and discharging cycle ÷ discharge capacity at the 1st charging and discharging cycle x 100.

[0092] The test results described above are shown in Table 2.

[0093] Table 2

[0094]

[0095] As shown from the results of Table 2, the rate discharge capacity and the stability of the cycle charging and discharging of the alkaline storage battery prepared using the positive active material provided in Examples 1-8 were improved compared to those of the alkaline storage battery prepared using the positive active material provided in Comparative Examples 1-8, and the alkaline storage battery prepared using the positive active material provided in Examples 1-8 can improve the active material utilization rate.

[0096] Each of the technical features of the above-described embodiments can be combined arbitrarily, and for the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combinations of the technical features do not contradict each other, they should be considered to be within the scope of the present specification.

[0097] 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 application. 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 positive electrode active material, characterized by comprising: the positive electrode active material satisfies: a core comprising a material having the general formula Ni 1-x (Al, Mg) x (OH)2. a first cladding layer cladded on a surface of the core, the first cladding layer comprising a material having a general formula of Ni 1-x1-y1 Al x1 Mg y1 (OH)2. a second cladding layer cladded on a surface of the first cladding layer, the second cladding layer comprising a material having a general formula Ni 1-x2- y2 Al x2 Mg y2 (OH)2. x2 > xi > 0, (xi + x2) > 0.03, x2 is 0.01-0.07; 0.15≥x≥0 ； y2 > yi > 0, (yi + y2) > 0.03, y2 is 0.01-0.07; the proportion of the inner core in the positive electrode active material is 85-97% by weight; the first coating layer is precipitated on the surface of the inner core, and the proportion of nickel hydroxide in the first coating layer is not less than 50% by weight based on the total mass of the first coating layer; the second coating layer is precipitated on the surface of the first coating layer, and the proportion of nickel hydroxide in the second coating layer is not less than 50% by weight based on the total mass of the second coating layer. the positive electrode active material further comprises a third coating layer, and the third coating layer comprises cobalt oxyhydroxide and / or cobalt oxide.

2. The positive electrode active material according to claim 1, characterized by the nickel electrode comprises the positive electrode active material according to claim 1 or 2.

3. A nickel electrode characterized in that, the alkaline storage battery comprises a positive electrode, a negative electrode, and an electrolyte and a separator located between the positive electrode and the negative electrode, and the positive electrode comprises the nickel electrode according to claim 3.

4. An alkaline storage battery characterized by comprising: the negative electrode of the alkaline storage battery comprises a metal hydride negative electrode, a zinc negative electrode, an iron negative electrode, or a cadmium negative electrode.

5. An alkaline storage battery according to claim 4, characterised in that ​

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