ZINC ELECTRODE SHAPE CHANGE .1. INSITU MONITORING

Zinc electrode shape change, the redistribution of zinc material over the electrode during repeated cycling, has been identified as one of the main life-limiting factors for alkaline nickel oxide/zinc secondary batteries. To investigate this phenomenon in situ, a radiotracer, Zn-65, is incorporated in the battery and its movement monitored during repeated cycling of the battery. The changes in the distribution of Zn-65 over the electrode during battery operation are attributed to the displacement of radioactive zincate ions via the battery electrolyte. It is shown that the spatial distribution of Zn-65 offers a reliable indication for the zinc material distribution over the electrode, provided an electrode with uniformly specific radioactivity is used in the measurements. Radiotracer experiments using zinc electrodes containing 2 weight percent HgO as an additive and uniformly labeled with Hg-203, have revealed that during battery cycling no substantial net transport of mercury species occurs. It is concluded that it is highly unlikely that the mercury additive detaches from or moves over the zinc electrode surface during the cycling process. Also, these experiments show that zinc material transport as a result of detachment of electode mass did not occur.