Effect of rapid quenching on electrochemical properties of AB5 and AB3.5-type hydrogen storage alloys

The energy infrastructure is facing ever more serious challenges due to limited supplies of oil, environmental concerns about CO₂ emissions and emissions from fossil fuels, and the ever-expanding energy demands of the growing economies in Asia. It is widely believed that hydrogen is a potential major alternative energy carrier. However, there remain problems with storage and transportation. An important aspect in the development of hydrogen as an energy carrier concerns the use of metal hydrides for hydrogen storage. Among the various types of hydrogen storage alloys, LaNi₅-type hydrogen storage alloy has been the most promising materials which has been used as metal hydride electrode material for Ni-MH batteries because of their high capacity, capable of performing a high-rate charge/discharge, high resistance to overcharging and over-discharging, a long cycle life, environmental friendliness and compatibility with Ni-Cd batteries, and the nickel metal hydride (Ni-MH) rechargeable batteries have been produced in large industry scale. In this paper, effect of rapid quenching on the electrochemical properties of AB₅ and AB_3.5-type hydrogen storage alloys was studied. The results indicated that the discharge capacities of the rapid quenching MmNi_3.55Co_0.75Mn_0.4Al_0.3 alloys decrease under 25 and -35°C with the increase of the quenching rate. Comparatively, the decrease extent of the quenching alloys at - 35°C is lower than that at 25°C. The result on the study of the cycle life indicated that the quenching process is favorable to improve the cycle stabilities of the MmNi_3.55Co_0.75 -Mn_0.4Al_0.3 alloys under 25 and -35°C. Whereas, the effect of the quenching process on the La_0.7Mg_0.3(Ni_0.85Co_0.15)_3.5 alloy is different at 25°C from at -35°C.- - Under 25°C, the cycle life of the alloy was obviously improved by the quenching process, however, the quenching process did not improve but decreased slightly the cycle life at -35°C.