Investigation on the characteristics of La 0.7Mg 0.3Ni 2.65Mn 0.1Co 0.75+ x ( x = 0.00–0.85) metal hydride electrode alloys for Ni/MH batteries Part II: Electrochemical performances

Abstract

In this paper, the electrochemical performances of the La 0.7Mg 0.3Ni 2.65Mn 0.1Co 0.75+ x ( x = 0.00–0.85) alloy electrodes were studied. The results show that, with increasing amount of Co addition, the maximum discharge capacities of the alloys decrease monotonously due to the relative change of the phase abundance of the (La, Mg)Ni 3 phase and the LaNi 5 phase coexisting in the alloys and the increase of the equilibrium pressure for hydrogen desorption. Moreover, the cycling stability of the alloy electrodes was noticeably improved with increasing Co addition because of the relatively lower value of V H and the formation of protective oxides (hydroxides). The high rate dischargeability of the alloy electrodes increases first and then decreases with increasing amount of Co addition, and the alloy electrode with x = 0.30 exhibits the best electrochemical kinetics. In addition, the electrochemical kinetic parameters study, including the charge-transfer resistance at the surface R ct, the polarization resistance R p, the exchange current density I 0, the limiting current density I L and the diffusion coefficient of hydrogen in the alloys D, also confirm this result.