W.S. Sun

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

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)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 properties. Advanced nanocrystalline C15-Laves single-phase alloys were prepared by completely crystallizing the melt-spun amorphous Zr1-xTix[(NiVMnCo)(1-nu)Sn-nu](2+alpha) 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 AB(2) 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 AB(2) 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)

Modification of a rapidly solidified hydrogen storage electrode alloy by ball-milling with Co3Mo

Rapidly solidified hydrogen storage alloys were reported to have good cycle life, but they are very difficult to activate, especially for AB(2) type alloys. In this study, a Zr0.9Ti0.1 (Ni0.57V0.1Mn0.28Co0.05)(2.1) alloy was prepared by melt-spinning followed by ball-milling with Co3Mo additive in order to improve its kinetic characteristics. The experimental results showed that the alloy exhibited a much improved activation performance as well as electrochemical capacity after 2 hours milling. Cyclic voltammetry and electrochemical impedance experiments also showed that ball-milling of the alloy with Co3Mo could improve the surface activation property to a great extent. This can be attributed to the catalytic effect of Co3Mo, which had a much closer contact to the alloy powders after ball-milling, on the hydrogen oxidation. However, long time milling could decrease the capacity gradually due to the further amorphization of the ahoy

Electrochemical performance of Sn-substituted, LaNi5-based rapidly solidified alloys

Sn-substituted, LaNi5-based rapidly solidified alloys with low Co content, La(1-x)A(x)Ni(4.25)Co(0.5)Sn(0.25)(A=La, Nd, Ce,and x=0.2),were prepared by melt-spinning. The microstructure of the as-spun alloys was observed with SERI and the element distribution of the as-spun and annealed alloys was analyzed by EDX. It is found that the as-spun alloys had fine grains. However, there was Sn segregation in the grain boundaries of the as-spun alloys. XRD patterns show that for the as-spun alloys the lattice strain could be alleviated through vacuum annealing. The electrochemical performance of the as-spun and heat-treated alloys was investigated. It is found that the Ce-containing as-spun alloy had a cycle Life more than 300 cycles. After heat-treatment, the electrochemical performance of the Ce-free alloys could be further improved, which is attributed to the alleviation of the lattice strain and the change of Sn distribution

Thermodynamic prediction of the composition of Fe-based amorphous alloys

Abstract The liquidus univariant lines of the Fe-Nb-B ternary system have been thermodynamically calculated by means of CALPHAD method and Fe-based thermodynamic data. It is found that there are two eutectic reactions in the Fe-rich corner, that is, (1) L(Fe-3Nb-15B) → α + γ + M 2 B (1430 K), and (2) L(Fe-10Nb-27B) → FeB + Lc 14 + M 2 B (1575 K). Moreover, the eutectic points are very close to the compositions with high glass forming ability determined experimentally. This means that it is feasible to design the compositions of multicomponent bulk metallic glasses by looking for the eutectic points in the Fe-Nb-B system by means of thermodynamic calculation.