Electrochemical impedance spectroscopy of AB3 active electrode in nickel metal hydride accumulators: The effect of temperatures and immersion times

Abstract

The electrochemical impedance spectroscopy (EIS) method was employed systematically to investigate the kinetic properties of the LaY2Ni9 electrode, which serves as negative electrode in Ni-MH accumulators. Through this analysis, a comprehensive understanding of the electrode’s behaviour was achieved.EIS measurements were performed on the LaY2Ni9 electrode at different temperatures (ranging from 15 °C to 75 °C) and at different immersion times using a potentiostat and frequency response analyser.The EIS spectra were fitted using an equivalent circuit model to extract the electrode impedance parameters, such as the charge transfer resistance, Rtc, the absorption/double layer capacities, Cad and Cdl, the specific current density, I0,EIS, and the hydrogen penetration depth, δ. The results show that temperatures have significant effects on the EIS impedance of the LaY2Ni9 electrode. The Rtc and the Cdl parameters increase with temperature, indicating a decrease in electrode kinetics due to the higher activation energy and an increase in electrode area due to thermal expansion. The penetration depth, δ, is directly proportional to the temperature increase.According to the EIS results, it is generally considered advantageous to maintain an operating temperature of around 30 °C for the LaY2Ni9 electrode. Moreover, a correlation can be observed between the variations in the kinetic parameter (DH) and the corresponding changes in other electrochemical parameters.Inconsistencies arise when comparing the exchange current density values obtained through cyclic voltammetry (I0,CV) and impedance spectroscopy (I0,EIS), highlighting contradictory findings. These disparities can be ascribed to multiple factors, including temperature variations, electrode geometry, and concentration gradients near the electrode interface. Overall, this study provides valuable information on the performance and degradation mechanisms of the LaY2Ni9 electrode under temperature and immersion time conditions and highlights the importance of EIS impedance measurements for battery research and development.