Studies On Synthesis And Electrochemical Performance Of Metal-substituted α-Ni(OH)₂

At the present time, Ni-MH battery as a rechargeable and high capacity battery has been drawn close attention because of his wide application prospect. Nickel hydroxide is the positive electrode active material of Ni-MH battery. In this paper, the process of preparing metal-substituted a -Ni(OH)2 by chemical deposit and the effects of preparing condition have been investigated. The discharge capacity, average discharge potential and utilization of active material were determined under different conditions. The effects of various doped elements on electrochemical properties of doped a -Ni(OH)2 were investigated. The electrochemical reaction mechanisms in the course of electrode reaction were studied in detail. The charge-discharge abilities of nickel hydroxide electrodes doped with Cu2+, Mn2+, Zn2+, Fe2+, Co2+, Fe3+, Mn3+, A13+ and Co3+ were studied. The results showed that different doped metals have different effects on the performance of the products and trivalent cations doped products are better than divalent cations doped products. Here we selected A13+ as a doped element and studied the performance of A13+ doped a -Ni(OH)2 completely.The results of preparing metal-substituted a -Ni(OH)2 showed that the pH is the most important fact of preparing nickel hydroxide. A low apparent density could be obtained when pH was low, we found that the product has a good electrochemical characteristic at pH=12. The content of metal is also a important fact of preparing nickel hydroxide, it can effect on the crystal form, we can get pure metal-substituted a -Ni(OH)2 when the content of doped Al element is more than 20%. Besides the temperature of reaction, the temperature of aging, etc, have little effects on discharge capacity.The cycle voltammetric studies of powder microelectrodes of metal-substituted a -Ni(OH)2 showed that there is a higher anode peakpotential and a lower cathode peak potential when scanning rate increased from Imv/s to 10mv/s. The anode peak current (ip) and the square root of scan rate (V1/2) have a good linear relationship. The proton difiusion coefficient (D°=2.35 × 10-10) was as much as 3 -spherical nickel hydroxide (D°=3.80× 10-10).We also studied the effect of state of charge on impedance spectra of Ni-MH battery, the Nyquist spectra showed that they all appear electrochemistry impedance at high frequency and Warburg impedance at low frequency.We also analyzed the data with software EQU.