A review on the development of AB2-type Zr-based Laves phase hydrogen storage alloys for Ni–MH rechargeable batteries in the Korea Advanced Institute of Science and Technology

Abstract

Our second endeavor was concentrated on improving the shortcomings of Zr-based alloys for commercialization, i.e., poor activation property and low rate capability. To improve the activation property of AB2-type Zr0.7Ti0.3Cr0.3Mn0.3V0.4Ni1.0 alloy electrode, a new activation process called hot-charging treatment has been developed. In this new process, alloy electrodes were immersed in KOH solution and charged simultaneously at various solution temperatures and charging current densities for various treatment times. It was found that the activation property of this alloy electrode are greatly improved after the hot-charging treatment, and furthermore the electrode treated at 80°C and 50 mA g−1 for 8 h was fully activated after the first cycle. Extensive work has been carried out on the development of the Zr-based Laves phase alloy with high capacity and especially with high rate capability for electrochemical application. After careful alloy design of ZrMn2-based Laves phase alloys through varying their stoichiometry by substituting or adding some alloying elements, Zr0.9Ti0.1(Mn0.7V0.5Ni1.4)0.92 alloy with high capacity and high rate capability was developed consequently. This alloy has the design capacity of 394 mAh g−1, i.e., 35% higher capacity than that of commercialized AB5-type alloys, at the discharge rate of 0.25C and shows a very high rate capability. It is therefore believed that the commercialization of Zr-based alloy for Ni–MH rechargeable batteries is coming soon.