Study On Synthesis And Performances Of Nickel Hydroxide Electrode Material Based On Ni/MH

There are lots of problem on application of nickel hydroxide electrode materials suchas low discharge capacity, short cycle life, poor performance of high-current charge-discharge and using in the long temperature range. The main reason is that the study on therelationships between structure and electrochemical performance, structural characteristicsand electrochemical properties is not deep enough. Therefore, The micro-structures ofnickel hydroxidewas studied, and the preparation, the structure, and the relationshipsbetween them were carefully and systematically discussed in this paper.In this paper, different structural characteristics of nickel hydroxide can be preparedby the hydrothermal treatment and crystal growth controlled crystallization method. Theresults were as follows: the content of adsorbed water decreases and the crystallization ofnickel hydroxide getting better as the hydrothermal treatment temperature and the molarratio of Ni/NH3increase.0.2C and1C discharege capacity of nickel hydroxide at25℃growing high with increasing hydrothermal treatment temperature.In order to prepare more ordered nickel hydroxide, we studied more depth by changedother reaction conditions of hydrothermal treatment. Nickel hydroxides were prepared atdifferent hydrothermal treatment time in170℃. X-ray diffraction analysis showed that thestructure of nickel hydroxide changed little and ruleless. By changing the molar ratio ofNi/NH3, we found that the structure of nickel hydroxide with molar ratio of Ni/NH3increased getting better and better. As ammonia content increases, the electrochemicalperformance of the products are enhanced.The micro-structural defects of spherical nickel hydroxide was quantitativecalculation. As the exitence of stacking faults and small crystallite size, the nickelhydroxide X-ray diffraction pattern become broadening. The amount of stacking faults inspherical nickel hydroxide was calculated by Langford method. The electrochemicalperformance of the products getting better with increasing amount of stacking faults. It is easy to jude electrochemical performance of nickel hydroxide electrode materials by thestacking fault probability.Micro-structure defects of nickel hydroxide crystal mainly caused by growth faults,deformation faults and layer displacement faults. Growth faults and deformation faultsdetermined by synthetic methods and synthesis conditions. Stacking faults are closelyrelated to the elements substitute Ni and the matter insert layer of crystal. A new stylenickel hydroxide materials were prepared by chemically precipitating cobalt, zinc, calcium,magnesium, copper, manganese and nickel elements at a special stoichiometric based onthe synergic effect of many elements, and they were dopped. It indicated that the positivematerial showed excellent electrochemical performances at25℃and65℃. At25℃, thehighest discharge capacity was294mAh/g at0.2C rate; At65℃, the highest dischargecapacity was303.9mAh/g at1C rate. Though30charge-discharge cycles, the dischargecapacity were still more than280mAh/g and the charging efficiency were kept as85%. Thestacking faults in nickel hydroxide can increase proton diffusion rate, thus improving theelectrochemical activity of materials.