Study On Preparation And Electrochemical Performance Of Positive Active Material In Ni/MH Battery

The preparation and electrochemical performance of nickel hydroxide as a positive active material for the high capacity MH/Ni alkaline rechargeable batteries were studied. The research result in this paper has some significance for the further development of nickel electrode with good properties.Based on the theory of crystal growth, we realized effective control on the crystallizing process of nickel hydroxide by coordinate precipitation method. The effects of main process factors such as feeding mode, reaction pH values, and ratio of ammonia and nickel ion, reaction time, agitation, reaction temperature and aging et al on the crystallization course and physical properties of nickel hydroxide were studied in detail. At last, we acquired the optimal preparation parameters, the spherical nickel hydroxide with high tap density and crystalloid degree, perfect flow ability were prepared. We also studied the influence of doping Co, Zn elements by chemical co-precipitation method on the character of nickel hydroxide. The physical properties of nickel hydroxide samples such as tap density, particle surface shape, particle size and distribution and flow ability were investigated to confirm above conclusion.The crystal and chemical structure characteristics of various nickel hydroxide samples were investigated by analysis methods such as SEM, XRD, TG, EDS. The results showed that the nickel hydroxide samples prepared in our experiment belong to p-Ni(OH)2, with well-ordered crystal structure. The crystal structure of doped nickel hydroxide became disordered.The effects of various additives elements and doping methods on foam nickel electrode's performance were studied using constant current charge-discharge test. We compared two doping methods: mechanical mixing doping and chemical co-precipitation doping. Experiments results showed that the doping of Co can improve the electrochemical properties of nickel hydroxide and foam nickel electrode, such as discharge specific capacity, utilization of active material, cyclic performance. With the increase of Go's doping amount, the discharge specific capacity improved obviously, e.g. when mechanical doping 5% Co, the discharge specific capacity is 225mAh/g, the ratio of active material utilization is 78%.The addition of Zn can prevent the swelling of nickel electrode and prolong the cyclic life, decrease the existence of y-NiOOH when over-charged.