Effects of Rapid Quenching on Electrochemical Properties of MlNi3.55Co0.75Mn0.4Al0.3/5wt% Mg2Ni Composite Hydrogen Storage Alloy

In order to improve the discharge capacity and the cycling stability of AB5-type hydrogen storage alloy, the effects of rapid quenching rate on the microstructures and electrochemical properties of MlNi3.55Co0.75Mn0.4Al0.3/5wt% Mg2Ni composite alloy were investigated by means of inductively coupled plasma (ICP), X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometry (EDS), transmission electron microscope (TEM) and electrochemical measurements. The results show that the as-cast composite alloy is composed of the LaNi5 phase and a small amount of the Mg2Ni phase. However, the quenched composite alloys consist of the (La,Mg)Ni3 new phase and the LaNi5 phase. When the rapid quenching rate is higher than 15 m/s, nanocrystalline structure are formed and partial amorphous structure appeares in the composite alloys. Electrochemical studies show that the maximum discharge capacity and the capacity retention of quenched composite alloys increase firstly and then decrease with increasing rapid quenching rate. The maximum discharge capacity and the capacity retention after 100 cycles of the quenched composite alloy at 20 m/s is up to 344 mAh/g and 93.9%, respectively.