Advanced nanocrystalline Zr-based AB(2) hydrogen storage electrode materials for NiMH EV batteries

The metallurgical microstructure, crystal-structure and electrochemical pro perties of Laves phase Zr-V-Mn-Ni system alloys (modified with Ti, Co, Sn, etc.) were investigated systematically in the present paper. Conventional p olycrystalline Zr-based alloys, which consist of cubic C15 Laves phase, hex agonal C14 Laves phase and non-laves phase (such as Zr7Ni10, Zr9Ni11, Zr(Ni Mn)Sn-0.35), show the highest discharge capacity of 342 mAh g(-1) (at 60 mA g(-1) charge-discharge current), which decreases by 7.8% after 300 cycles. Amorphous phase alloys in melt-spun alloys exhibit poor electrochemical pr operties. Advanced nanocrystalline C15-Laves single-phase alloys were prepa red by completely crystallizing the melt-spun amorphous Zr1-xTix[(NiVMnCo)( 1-nu)Sn-nu](2+alpha) alloys. These alloys have a special microstructure com posed of high-density interface phase and random-oriented grains varying fr om several nanometres to several dozens of nanometres. It was found that th ese materials had high discharge capacity (the maximum capacity is up to 37 9 mAh g(-1)) and long cycle life (the capacity only decreases 3% after 300 cycles). The maximum discharge capacities were found in the metallurgical m icrostructure and crystal-structure in Zr-based AB(2) alloys. The maximum d ischarge capacity increases in regular nanocrystalline/C15-Laves single-pha se>polycrystalline/multi-phase (Laves and non-laves)>comorphous state/C15-L aves single-phase. It was shown that the complete crystallization method fr om amorphous solids is an effective way to greatly improve the electrochemi cal performance of Zr-based AB(2) hydrogen storage electrode materials, whi ch is not only significant for academic research but also valuable for prac tical applications in the NiMH battery system for pure electric vehicles (P EV) and hybrid electric vehicles (HEV). (C) 1999 Elsevier Science S.A. All rights reserved.