Properties of Nickel Metal Hydride Battery Using Molybdenum-added Superlattice Metal Hydride Alloy

Abstract

The performance of sealed cells comprising of a series of superlattice metal hydride (MH) alloys with compositions of Mm 0.83Mg0.17Ni2.94‒xAl0.17Co0.20Mox (Mm is a mixture of La, Pr, and Nd, x = 0.00, 0.05, 0.10, 0.15, and 0.20) was evaluated and compared against other substitutional elements, such as Fe, Mn, and Co. The capacities of cells with Mo-containing alloys are higher than the ones using Mo-free alloy due to the former’s higher active material utilization in positive electrodes. Cells with alloy of x = 0.10 showed the highest capacity and high-rate dischargeability, the best low-temperature (−10 and −20 °C), and the longest cycle performance (C-rates charge and discharge). This level of Mo (x = 0.10) is effective in protecting the alloy surface from oxidation. The main failure mechanism of the sudden capacity drop for cells in this study is the venting of gas/ electrolyte mixture from the build-up of internal pressure; this is caused by a dense surface oxide layer formed on the MH alloy blocking the path for gas-recombination during overcharge.