Microstructure and electrochemical properties of cobalt-substituted A2B7-type La-Y-Ni-based hydrogen storage alloys

La-Y-Ni-based superlattice hydrogen storage alloys exhibit key technological advantages as negative electrode materials for Nickel-metal hydride (Ni-MH) batteries; however, the function of Co has not been studied systematically. A series of LaY2Ni10-xMn0.5Cox (x = 0, 0.3, 0.5, and 0.9) alloys with only A2B7-type phases were prepared in this study, and the effects of Co on the microstructure and electrochemical properties were studied. Co has a minor effect on phase composition; however, it increased cell parameters because of its larger atomic size compared to that of Ni. Co-substituted alloys exhibited excellent activation performance and achieved the maximum discharge capacity in the first cycle. Moreover, Co promoted the discharge capacities of the alloys, but aggravated cycling degradation attributed to the accelerated pulverisation of the alloy particles that leads to serious oxidation/corrosion. Furthermore, an appropriate amount of Co enhances the electrochemical kinetics performance by promoting the charge transfer rates on the alloy surface and the hydrogen diffusion rates in the alloy bulk.