Effect of Milling Time on the Electrochemical Properties of AB_5/10 wt.% CNTs Composite Hydrogen Storage Alloys

Mm(NiCoMnAl)5/10wt.% CNT composite hydrogen storage alloys are prepared by ball milling Mm(NiCoMnAl)5 with a small amount of CNTs as addition under an atmosphere of high purity argon.Structures and electrochemical properties of the composite alloys are investigated systematically by X-ray diffraction,scanning electron microscope and electrochemical experiments.The results indicate that the composite alloys possess a structure of CaCu5 on whose surface a plenty of CNTs are bonded.The content of CNTs in composite alloys decreases with increasing milling time.The electrochemical studies show that maximum discharge capacity,the capacity retention after 60 cycles and high rate discharge-ability of the composite alloys increase firstly and then decrease with increasing milling time.The alloy milled for 5 h exhibits the best maximum discharge capacity(291.9 mAh/g).And the alloy milled for 3 h is the best capacity retention after 60 charge-discharge cycles(91.2%) and high rate dischargeability.