Preparation And Application Of Nano Additives For MH/Ni Battery

With the development of the electronic appliances, the demands for MH/Ni rechargeable battery with higher performances increase too. Due to the special physical and chemical characteristics, nano materials was begun to used in the batteries, especially the secondary batteries. In this paper, carbon nanotubes and nano Ni(OH)2 were selected to investigate the nano doping effects for MH/Ni battery.At first, the effect of carbon nanotubes additives on the electrochemical performances of hydrogen storage alloy electrode was investigated. The results showed that the hydrogen storage capacity of the carbon nanotubes was only 123.0mAh/g(CNT). The discharge capacity of the electrodes with carbon nanotube additive has no obvious improvement. But the comprehensive properties were improved remarkably. With the addition of carbon nanotubes, the polarization of charging process decreased, the plateau of discharge became flatter and the migration of potential of peaks value of cyclic voltemmograms reduced. For the other hand, the exchange current increased, ohm resistance and electrochemical reaction resistance of the electrodes decreased, the diffusion resistance of hydrogen and the resistance of adsorption decreased, too. In addition, carbon nanotubes can improve the activation performances of the hydrogen storage alloy electrodes.The aim of this paper was to optimize the preparation technology of nano Ni(OH)2. Nano-sized Ni(OH)2 was prepared using solid state reaction, the intermediate steps which affected the properties of nano Ni(OH)2 was investigated, i.e., the steps of preparing NiC2O4.2H2O and Ni(OH)2, respectively. The optimized technology for preparing NJC2O4-2H2O was as follows: adding 1.5mol/L H2C2O4 solution to 0.5 mol/L NiCb solution, reacting for 30mins with stirring, and aging for 5h at 60C. And the optimized technology for preparing Ni(OH)2 was as follows: the ratio of H2C2O4/NaOH was 1/2.5, grinding for 20min, aging in 9mol/L KOH solution for 2h at 40C, and dispersing with ultrasound in water media.The effects of cobalt and zinc additives on the electrochemical performances of the nano Ni(OH)2 electrodes were studied too. It was found that the defects were formed and the conductivity increased with the addition of Co, which improved the diffusion of proton and inhabited the formation of y-NiOOH. The electrochemical capacity of the electrode with cobalt additives changed slightly after 206 cycles. The electrode can exhibit excellent high-rate discharge performance, the capacity discharged at 6C (1800mA/g) can reach to 77.7% of which discharged at 1C condition. The coexistence of Co and CoO additive in the electrodes has the best effect on the electrochemical properties. However, in this paper, the zinc additive did not promote the properties of the electrode, the discharge capacities and the cyclic life of both electrodes using nano Ni(OH)2 and spherical Ni(OH)2.Using the as-prepared nano Ni(OH)2 as positives electrode materials, MH/Ni battery were prepared and its performances were investigated. The result showed that the performances of battery prepared by nano Ni(OH)2 were not good due to the low volume specific capacity of nano Ni(OH)2. When 8% of nano Ni(OH)2 was added into spherical Ni(OH)2, the capacity and high-rate performance of MH/Ni cell were not improved, however, the performances of self-discharge and cyclic life were improved obviously.