A comparative study on the electrochemical performance of rapidly solidified and conventionally cast hydride electrode alloy Zr(NiMnM)(2.1)

The crystalline structure, phase abundance, microstructure and electrochemi cal properties of hydrogen storage electrode alloy Zr(NiMnM)(2.1) (M=V, Cr) prepared by rapid solidification (melt-spinning) and conventional cast met hods have been investigated and compared. Results indicate that conventiona l cast (CC) alloy is composed of Laves phase, non-laves phases and a little ZrO2, while rapid solidification (RS) alloy are completely composed of Lav es phase only. The microscopic structure of RS alloy is completely differen t from that of the CC alloy. The microstructure of RS alloys is fine grain, while the microscopic structure of CC alloy is coarse dendrite. Obvious di fferences in electrochemical properties exist in electrodes made of these t wo differently prepared alloys due to the difference of their phase abundan ce, composition distribution and microstructure. The discharge capacity of RS alloy is 56 mAh g(-1) higher than that CC alloy, it reaches 356 mAh g(-1 ) and its cycle life is much longer than that CC alloy too. But RS alloy ar e fully only activated after 14 cycles, more difficulty than that CC alloy, which is activated around 9 cycles. As a whole RS (melt-spinning) process improves greatly the comprehensive electrochemical properties of the alloy. (C) 1999 Elsevier Science S.A. All rights reserved.