The effects of pulse charging on inner pressure and cycling characteristics of sealed Ni/MH batteries

The effects of pulse charging technique on inner pressure and cycling characteristics of sealed Ni/MH batteries were investigated by comparison with the conventional direct current (DC) charging. The electrochemical impedance spectroscopy of cycled Ni/MH batteries have been measured. The micrographs of individual electrodes in the batteries have also been examined by SEM. Experimental results show that pulse charging is an effective approach to lower the internal pressure of battery during charge and overcharge, moreover, the appropriate frequency is tp = 5 s and tn = 1 s in our experiments. The battery charged by pulse current exhibits slower capacity fade rate and smaller overpotential at the same charge–discharge rate. In addition, the anode charged by pulse current exhibits less serious pulverization than that charged by DC charging. The possible explanation is that the short relaxation periods interspersed during the charging process can effectively eliminate the concentration polarization and increase the power transfer rate, thus accelerating the charging process, reducing the gas evolution reaction, slowing down the pulverization rate of electroactive materials and keeping the water absorption capability of separator constant.