Surface treatment for hydrogen storage alloy of nickel/metal hydride battery

Abstract

The electrochemical performance of AB 2-type (Ti 0.35Zr 0.65Ni 1.2V 0.6Mn 0.2Cr 0.2) and AB 5-type (MmB 4.3(Al 0.3Mn 0.4) 0.5) hydrogen storage alloys modified by hot KOH etching and electroless nickel coating has been investigated. It is found that the alloy modified with hot KOH solution shows quick activation but at the expense of cycle-life stability. The alloy coated with nickel was effectively improved in both cycle-life stability and discharge capacity. Both the exchange and limiting current densities were increased by modifying the alloys by hot KOH solution dipping or electroless nickel coating as compared with untreated alloy electrode. The electrode with higher exchange current density and limiting current density leads to increased high-rate dischargeability. A duplex surface modified alloy (i.e., alloy first treated with hot KOH solution and then coated with nickel) has been developed, which performs satisfactorily with respect to both quick activation and long cycle life. In addition, the high-rate dischargeability for the electrode with duplex surface modification is superior to that of electrode solely treated with KOH etching or Ni plating.