Effect of Cu powder as an additive material on the inner pressure of a sealed-type Ni-MH rechargeable battery using a Zr-based alloy as an anode

Abstract

Extensive and systematic work on improving the surface catalytic activity of electrodes has been carried out to decrease the internal pressure of a sealed Ni-MH battery in which Zr0.9Ti0.1 (Mn0.7V0.5Ni1.2)(0.92) alloys are used in the anode. In order to improve the surface catalytic activity of a Zr-Ti-Mn-V-Ni alloy which are closely related to the inner pressure behavior in a sealed cell, the electrode was fabricated by mixing the alloy with Cu powder. By replacing 50% of carbon black with Cu powder the inner cell pressure rarely increased with cycles. This was due to the active gas recombination reaction. After measuring the surface area of the electrode and the surface catalytic activity, it was found that the surface catalytic activity for the oxygen recombination reaction was much more improved by the addition of Cu powder. This phenomenon is due to the thin Cu layer on the Zr-Ti-Mn-V-Ni alloy surface which is formed by alternate dissolution and precipitation reactions of mixed Cu powder during the charge-discharge cycle. This thin Cu layer has the role of preventing the alloy surface from oxidation and enhancing the possibility of the presence of metallic Ni, which is believed to have a high catalytic activity for the oxygen recombination reaction, on the MH surface. The inner pressure of the cell with the Zr-Ti-Mn-V-Ni alloy was lowered to a level equaling that of the commercial AB(5)-type alloys by the addition of Cu powder. (C) 1999 Elsevier Science S.A. All rights reserved.