Phase structures and electrochemical behaviors of V2.1TiNi0.5Hf0.05Crx (x=0-0.152) hydrogen storage alloys

The phase structures and electrochemical behaviors of the V2.1TiNi0.5Hf0.05Crx (x=0, 0.074. 0.113 and 0.152) alloys have been investigated. It is found that the addition of Cr gives rise to a decrease in the amount of the V-based solid solution main phase and an increase in the amount of C14-type secondary phase without any change in the pattern of the three-dimensional network structure. On adding Cr, the unit cell of the main phase contracts, while that of the secondary phase significantly expands. Electrochemical measurements show that the maximum discharge capacity of the Cr-added alloys (x=0.074-0.152) is only 368-395 mAh/g, much less than that of the V2.1TiNi0.5Hf0.05 alloy (444 mAh/g), but their high-rate dischargeability and cycle stability are markedly improved. For the alloy with the Cr content of x=0.152, the best high-rate dischargeability and best cycle stability are obtained. (C) 2003 Elsevier B.V. All rights reserved.