Pulverization and corrosion studies of bare and cobalt-encapsulated metal hydride electrodes

Electrochemical impedance spectroscopy was used as an in situ technique to determine the average particle size of metal hydride electrodes. Using this, the pulverization of bare and cobalt-encapsulated LaNi4.27Sn0.24 alloy was studied as a function of charge-discharge cycles. In the case of bare alloy, pulverization causes an exponential decay in particle size with cycling. Cobalt-encapsulated alloys do not undergo much pulverization with cycling. Bode responses obtained for bare alloy electrodes indicate the increase in particle to particle resistance with cycling. Alloy oxidation, which is responsible for the increase in particle to particle resistance is absent in the case of cobalt encapsulated alloy. Surface analysis indicates the presence of alloy segregation for bare LaNi4.27Sn0.24. Decrease in particle size and increase in bare alloy resistance is accompanied with severe decay in electrode discharge capacity.