Electrode characteristics of the Cr and La doped AB(2)-type hydrogen storage alloys

AB(2)-type alloy, a kind of hydrogen storage alloys used as an anode of Ni- MH batteries, has a large discharge capacity but still has several problems such as initial activation, cycle life and self-discharge. In this study, we have investigated the effects of Cr addition and fluorination after La a ddition on AB(2)-type alloy with Zr0.7Ti0.3V0.4Mn0.4Ni1,2 Composition. The EPMA and SEM surface analysis techniques were used and the crystal structur e was characterized by XRD analysis. Metal hydride negative was characteriz ed by galvanostatic cycling test, electrochemical impedance spectroscopy an d potentiodynamic polarization. Cr-addition is found to be effective to imp rove cycle life and self-discharge characteristics but ineffective to promo te initial activation due to the formation of stable oxide film on alloy su rface. Highly reactive particles have been formed by fluorination after La- addition to the alloys and those particles may remarkably improve the initi al activation of MH-negative electrodes. (C) 2001 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserve d.