Development of Mg-containing MmNi5-based alloys for low-cost and high-power Ni–MH battery

Mg-added MmNi5-based alloy with low Co content was developed for nickel/metal hydride (Ni–MH) battery, satisfying low-cost, high-power, and long-term endurance, simultaneously. High rate capability and cycle life of the alloy was improved by controlling alloy composition and alloy preparation-conditions. Alloy with overstoichiometric composition (B/A = 5.2) showed higher rate capability than stoichiometric alloy (B/A = 5.0), in spite of its lower theoretical capacity.AAA-sized sealed battery using the developed alloy (Mm0.96Mg0.04Ni4.2Co0.3Mn0.4Al0.3) showed comparable high rate capability and cycle life to that using the conventional alloy (MmNi4.0Co0.65Mn0.3Al0.28). Hybrid electric vehicle (HEV) mode cycle test was then carried out at 45 °C using short-D-sized sealed cell (diameter: 32 mm, height: 44 mm). Both capacity and power output of the cell remained more than 80% of the initial values even after 25,000 cycles (corresponding to 100,000 km). It is concluded that the developed alloy with low cost would be used for HEV application, satisfying both high-power output and long cycle life.