Advanced nanocrystalline Zr-based AB2 hydrogen storage electrode materials for NiMH EV batteries

Abstract

Abstract The metallurgical microstructure, crystal-structure and electrochemical properties of Laves phase Zr–V–Mn–Ni system alloys (modified with Ti, Co, Sn, etc.) were investigated systematically in the present paper. Conventional polycrystalline Zr-based alloys, which consist of cubic C15 Laves phase, hexagonal C14 Laves phase and non-Laves phase (such as Zr7Ni10, Zr9Ni11, Zr(NiMn)Sn0.35), 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 properties. Advanced nanocrystalline C15-Laves single-phase alloys were prepared by completely crystallizing the melt-spun amorphous Zr1−xTix[(NiVMnCo)1−ySny]2+α alloys. These alloys have a special microstructure composed of high-density interface phase and random-oriented grains varying from several nanometres to several dozens of nanometres. It was found that these materials had high discharge capacity (the maximum capacity is up to 379 mAh g−1) and long cycle life (the capacity only decreases 3% after 300 cycles). The maximum discharge capacities were found in the metallurgical microstructure and crystal-structure in Zr-based AB2 alloys. The maximum discharge capacity increases in regular nanocrystalline/C15-Laves single-phase>polycrystalline/multi-phase (Laves and non-Laves)>comorphous state/C15-Laves single-phase. It was shown that the complete crystallization method from amorphous solids is an effective way to greatly improve the electrochemical performance of Zr-based AB2 hydrogen storage electrode materials, which is not only significant for academic research but also valuable for practical applications in the NiMH battery system for pure electric vehicles (PEV) and hybrid electric vehicles (HEV).