An EIS study on the capacity fades in metal-hydride electrodes

Capacity fade, generally observed in metal-hydride electrodes of nickel metal-hydride batteries with prolonged cycling, is a problem of concern. To investigate the capacity fade, electrochemical impedance spectroscopy (EIS) measurements were performed in lanthanum rich mischmetal alloy ( MmNi 3.6 Al 0.4 Mn 0.3 Co 0.7 ) electrodes. The impedance measurements were conducted during charging at different stages of cycle life. A novel approach was made to get reaction resistances and limiting currents from impedance data based on an equivalent circuit for finite spherical hydrogen diffusion. The main cause of the capacity fade occurring in metal-hydride electrodes with number of cycles was due to particle pulverization and consequent poor hydrogen desorption kinetics, thereby making it more difficult for hydrogenation to occur because of passivation and resistance of electron conduction between the alloy particles.