Enhancement of the electrochemical performance of CoB amorphous alloy through the addition of A2B7-type alloy

The CoB−xA2B7 composites (x = 0-30 wt.%) were prepared by ball milling the powdery mixture of both pristine alloys. As negative electrodes in nickel-metal hydride (Ni/MH) rechargeable batteries, the CoB−xA2B7 composites exhibit a superior electrochemical performance. It has a maximum discharge capacity (Cmax) of up to 730 mAh/g and its high-rate dischargeability (HRD) is significantly increased to 82.5% for x = 30 wt.% at a discharge density of 900 mA/g. The capacity retention rate (C100/Cmax) is increased firstly from 37.1% (x = 0 wt.%) to 45.6% (x = 5 wt.%), then decreased to 42.4% (x = 30 wt.%). The anodic polarization (AP) and potential-step measurements indicate that the diffusion ability of hydrogen atoms in the composite electrodes is distinctly improved by doping with A2B7-type alloy.