Preparation And Research Of Nickel Hydroxide Coated By Cobalt

Pasted nickel hydroxide electrodes are widely used in the nickel-based alkaline secondary batteries such as nickel-cadmium (Ni-Cd), nickel-metal-hydride (Ni-MH) batteries. It is known that the active material-nickel hydroxide is a low conductivity p-type semiconductor, there is a relatively large resistance between the nickel hydroxide particles and the current collector, thus resulting in poor electrode performance and a relatively low active material utilization. To reduce the resistance between the active material and current collector, and to maximize electrode performance, many researchers add increased quantities of cobalt to their electrodes, or coat different amounts of cobalt oxy-hydroxide on the surface of nanometer Ni(OH)2particles.1. The influnces of CoOOH content, pH value, temperature and NH3.H2O addition on Ni(OH)2’s electrochemical performance are studied by orthogonal test, and the optimal preparation condition are obtained comparing with different Ni(OH)2by CV curves:wCoOOh=2.5%, pH=11, T=60℃, c(NH3.H2O)=2.5mol.L"1. The results show that a well distributed conductive network on the surface of nickel hydroxide particles was formed under the best conditions, the utilization of active material and the conductivity of Ni(OH)2was greatly improved.2. Under the optimum conditions, nanometer nickel hydroxide particles coated by different amounts of cobalt oxy-hydroxide are prepared through chemical precipitation method. The morphology and crystal structure of coated Ni(OH)2particles is characterized by using X-ray diffraction, scanning electron microscopy. The results show that a structure of P-Ni(OH)2is preserved,2.5wt%CoOOH can form a well distributed conductive network on the surface of nickel hydroxide particles during charge to provide a good electrical connection between the active material and the substrate, thus improving utilization of active material.3. Constant current charge/discharge test,cyclic voltammetry and electrochemical impedance spectroscopy test are focused on the effects of different amounts of cobalt oxy-hydroxide on structure and electrochemical characteristics of nickel hydroxide. The results show that the specific capacity and cycling stability of the electrodes with2.5wt%coated CoOOH can be greatly improved and it’s specific capacity after300cycles only decreases by15%, the electrodes also has better reversibility of the Ni(OH)2/NiOOH redox couple, and higher oxygen evolution potential, thereby enhancing the combination properties of Ni(OH)2particles, so it is suitable for the positive material of the Ni-MH high power battery.