Effect of Cu powder as compacting material on the discharge characteristics of negative electrodes in Ni-MH batteries

Abstract

In order to investigate the effect of Cu powder as a compacting material on the electrode performance, negative electrodes were prepared by mixing Ti-Zr-Cr-Mn-V-Ni alloy powder with copper powder of various sizes and contents, and were analyzed with electrochemical techniques and scanning electron microscopy (SEM) after cycling. The electrode performances such as the rate capability and the low-temperature dischargeability of the Cu-compacted electrode are improved as the size of Cu powder decreased or its content increased. These performances are better than those of the Ni-compacted electrode. The Cu-compacted electrode shows a high exchange current density for the hydrogen evolution reaction and a low contact and reaction resistance. From SEM analysis of the cycled electrode compacted with copper powder, it is also found that the surface of the MH (metal hydride) particles of the cycled Cu-compacted electrode is covered with copper grains (2 similar to 3 mu m) and whiskers. Therefore, it is suggested that the improved electrode characteristics are attributed to the copper layer deposited on the MH particles by the dissolution and precipitation (DP) process. (C) 1998 Elsevier Science S.A.