Effects of the addition of ZnO and Y 2O 3 on the electrochemical characteristics of a Ni(OH) 2 electrode in nickel–metal hydride secondary batteries

Abstract

This study examined the effects of the addition of ZnO and Y 2O 3 on the electrochemical characteristics of a Ni(OH) 2 electrode in nickel–metal hydride (Ni–MH) secondary batteries. The discharge capacity of the electrode was less affected by the addition of ZnO and Y 2O 3 at a 0.2 C-rate and 25 °C. However, the addition of Y 2O 3 deteriorated the discharge capacity and the cycle life of the electrode by increasing the charge transfer resistance of the electrode at an increased C-rate of 1 C and 25 °C. Under severer conditions at 1 C-rate and 60 °C, the electrode materials were separated from the current collector and, accordingly, the discharge capacity was abruptly degraded with cycling for the electrodes comprising only 4 wt% ZnO or 4 wt% Y 2O 3. In contrast, the electrodes containing both 2 wt% ZnO and 2 wt% Y 2O 3 exhibited stable discharge capacity with cycling and excellent cycle life due to the high overvoltage for oxygen evolution. The present results indicate that the addition of ZnO and Y 2O 3 with an optimum composition suppresses oxygen evolution in the interfaces between active materials and the current collector and improves the cycle life of the electrode.