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

摘要

Extensive and systematic work on improvingthe surface catalytic activity of electrodes has beencarried out to decrease the internal pressure of asealed Ni-MH battery in whichZr0.9Ti0.1(Mn0.7V0.5Ni1.2)0.92 alloys are used in theanode. In order to improve the surface catalyticactivity of a Zr-Ti-Mn-V-Ni alloy which are closelyrelated to the inner pressure behavior in a sealed cell,the electrode was fabricated by mixing the alloy withCu powder. By replacing 50% of carbon black with Cupowder the inner cell pressure rarely increased withcycles. This was due to the active gas recombinationreaction. After measuring the surface area of theelectrode and the surface catalytic activity, it wasfound that the surface catalytic activity for theoxygen recombination reaction was much more improvedby the addition of Cu powder. This phenomenon is dueto the thin Cu layer on the Zr-Ti-Mn-V-Ni alloy surfacewhich is formed by alternate dissolution andprecipitation reactions of mixed Cu powder during thecharge-discharge cycle. This thin Cu layer has therole of preventing the alloy surface from oxidationand enhancing the possibility of the presence ofmetallic Ni, which is believed to have a high catalyticactivity for the oxygen recombination reaction, on theMH surface. The inner pressure of the cell with theZr-Ti-Mn-V-Ni alloy was lowered to a level equalingthat of the commercial AB5-type alloys by the addition of Cu powder.