Study On The Positive Electrode Performance Of Single-Flow Zinc-nickel Battery

Nickel hydroxide is widely used in commercial batteries because of its excellent electrochemical performance.In recent years,the research hotspot is that,on the one hand,doping cheap elements to replace nickel can effectively reduce the price of nickel hydroxide,thereby reducing the cost of batteries,on the other hand,doping other metal ions into its lattice to replace nickel ions to form a hydroxideα-Ni（OH）₂,which can improve the overall specific capacity of nickel-based batteries.In this paper,cathode materials were synthesized by buffer solution method,phase analysis of electrode materials was carried out by X-ray diffraction（XRD）and scanning electron microscopy（SEM）,and electrochemical performance of batteries was tested by cyclic voltammetry and constant current charge-discharge technology.The conclusions of experiments are as follows.（1）Aluminum substituted Ni_1-xAl_x（OH）₂（x=0.10,0.14,0.18,0.22）were prepared and the effects of aluminum content on the properties of nickel hydroxide were studied.The samples of 0.1 is mixed phases of alpha and beta,and the others are pure alpha phases.Scanning electron microscopy measurements show that the Al doped samples are finer and more porous than commercialβ-Ni（OH）2.Cyclic voltammetry shows samples of 0.18 has a slightly higher peak current and a larger reduction peak area.The constant current charge-discharge test shows that the difference between the oxygen evolution potential and the normal charge potential of the sample of 0.18 is the greatest,and the discharge specific capacity is 303mAh/g compared with other samples 247 mAh/g（commercialβ-Ni（OH）₂）、250.9mAh/g（x=0.10）、280.2 mAh/g（x=0.14）、292.2 mAh/g（x=0.22）when the current density is100 mA/g.The material of 0.18 exhibits a highest capacity near 330 mAh/g at 300 mA/g.With the increase of current density to 800 mA/g,the sample of 0.18 exhibits good cyclic stability,and the specific discharge capacity decay rate is 9.1%after 150 cycles,the others are 27.1%（commercialβ-Ni（OH）₂）、15.8%（x=0.10）、7.1%（x=0.14）、26.0%（x=0.22）.Considering comprehensively,Ni_0.86Al_0.14（OH）₂ and Ni_0.82Al_0.18（OH）₂ are ideal materials for increasing the specific discharge capacity of cathode active materials.（2）Manganese doped Ni_1-xMn_x（OH）₂（x=0.1,0.2,0.3,0.4）were prepared by buffer solution method.X-ray diffraction measurements show that the samples are mainly composed ofβphase with little amount of Mn₃O₄ phase when the Mn content x is 0.1,0.2.Scanning electron microscopy measurements show that the Mn doped samples are finer and more porous than commercialβ-Ni（OH）₂ samples without Mn.Cyclic voltammetry results show that the integral area of reduction peak of Ni_0.8Mn_0.2（OH）₂ is the largest.The constant current charge-discharge tests show that the discharge capacity of Ni_0.8Mn_0.2（OH）₂ reaches 271.8mAh/g at the current density of 100 mA/g,which is higher than the other samples and commercialβ-Ni（OH）₂（253.6 mAh/g）.Moreover,the cycling stability of Ni_1-xMn_x（OH）₂ is superior to commercialβ-Ni（OH）₂.In addition,the electrode has excellent rate performance,when the Mn content x is 0.2,there is still the specific discharge capacity of 276 mAh/g after circulating 580 cycles at 800 mA/g,and its attenuation rate is 4.1%,the others are46.1%（commercialβ-Ni（OH）₂）、13.0%（x=0.1）、22.6%（x=0.3）、34.1%（x=0.4）.This indicates that Ni_0.8Mn_0.2（OH）₂ can improve the capacity and cycling stability of nickel electrodes at high current density,and greatly reduce the cost of nickel electrodes.（3）The cathode material Ni_0.955-xAl_xCo_0.015Zn_0.03（OH）₂（x=0.1、0.14、0.18、0.22）were prepared by buffer solution method.X-ray diffraction measurements show that sample of 0.1is the mixed phase ofαandβ,and the others are pureαphase.The constant current charge-discharge results show that the sample of 0.18 has maximum discharge specific capacity of350 mAh/g when the charge-discharge current density is 500 mA/g.With the increase of current density to 800 mA/g,the specific discharge capacity decay rate is 6.3%after 150cycles,which shows better charge-discharge performance and cyclic stability.Finally,Ni_0.775-yAl_0.18Mn_yCo_0.05Zn_0.03（OH）₂ is synthesized on the basis of Ni_0.775Al_0.18Co_0.015Zn_0.03（OH）₂（y=0.1、0.2、0.3）.Compared with commercialβnickel hydroxide,the sample of 0.1 is pureαphase.In the cyclic voltammetry curve,the reduction potential is 0.2 V higher than the 0.1V of commercialβnickel hydroxide.In a static single-flow zinc-nickel simulation battery,its discharge specific capacity is stable at about 250 mAh/g when the charge and discharge current density is 100 mA/g,which is equivalent to commercialβnickel hydroxide,but the latter has better cycle stability.When the current density is 800 mA/g,the discharge capacity is stable about 310 mAh/g,and there is no capacity decay after 150 cycles.Because the nickel content is reduced by 28%,the cost can be greatly reduced and the application prospect is promising.