Improvement in the electrochemical properties of gas atomized AB2 metal hydride alloys by hydrogen annealing

The effects of high temperature hydrogen annealing were studied on powders made by gas atomization of both conventional vanadium-containing AB2 metal hydride alloys and new vanadium-free AB2 alloys designed for high power and low self-discharge applications. In both alloy systems, annealing in 950 °C hydrogen for 30 min was proven to be effective in improving the capacity, formation, high power, and low temperature performance in the nickel metal hydride battery compared to previous gas atomization trials where each property was reduced. The advantage in improving the cycle life by gas atomization was further extended by the hydrogen annealing process. Reduction in the surface oxide was confirmed by the use of Auger electron spectroscopy depth profiling and magnetic susceptibility. Metallic elements were reduced from the oxide state by hydrogen to react with the metallic nickel particulates originally embedded in the surface oxide in a high temperature environment and created a new surface free of oxygen.

Research highlights
► Annealing condition of gas atomized powder was optimized.
► Annealing in hydrogen was demonstrated to improve NiMH battery performance.
► Mechanism of surface restoration was introduced.