Deterioration of Laves phase alloy electrode during cycling

A study is made of the deterioration mechanism of a Laves phase alloy elect rode without addition of Ni powder by means of electrochemical impedance sp ectra (EIS) X-ray diffraction (XRD), inductively coupled plasma (TCP) and X -ray photoelectron spectroscopy (XPS). The XRD analysis shows that after cy cling, the alloy bulk still has the capability to store hydrogen. The deter ioration mechanism is considered to be mainly a surface process. In particu lar, particle pulverization (increased specific surface area and reduced th e particle size) is the main reason for electrode deterioration. Dissolutio n of V and Mn increases gradually during cycling. On the other hand, partic le pulverization increases further the dissolution fates of V and Mn, which are proportional to the specific surface area due to the generation of a n ew, fresh surface. In addition, it is demonstrated by XPS that the depth of oxide layers of Zr and Mn increases with cycling and results in an increas e in the reaction impedance and a decrease in the surface electronic conduc tivity. Therefore, a change in the structure of the particle surface layer, due to particle pulverization and dissolution of V and Mn, contributes to the deterioration of the Laves phase electrode. (C) 1999 Elsevier Science S .A. All rights reserved.