The Ball-milling Preparation And Electrochemical Properties Investigation Of Hydrogen Storage Alloys And Their Composites

The power density of a nickel metal hydride battery?Ni-MH?is determined by the high-rate dischargeability?HRD?of its anode material—hydrogen storage alloys.However,at the discharge current density of 3000mAg^-1,the capacity retention rate of the current commercial hydrogen storage alloys MmNi3.55Co0.75Mn0.4Al0.3?Mm represent cerium-rich mixed rare earth?is only 21.53%,can not meet the nickel-metal hydride batteries in the power tools,modern military equipments,new energy vehicles and other high-power applications.The HRD of the hydrogen storage alloys is mainly affected by two factors: the diffusion rate of hydrogen inside the alloys and the electrochemical reaction rate at the interface of the alloy/electrolyte.Therefore,in order to improve the HRD of the hydrogen storage alloys,?1?we can decrease the particles size of the hydrogen storage alloys to shorten the diffusion distance of hydrogen in its interior;and?2?reduce the contact resistance and charge transfer resistance to accelerate the rate of electrochemical reaction and electronic transmission at the interface.Ball milling as a simple and effective method,which could be used to reduce the particles size of hydrogen storage alloys.While the graphene nanoplatelets with excellent conductivity could significantly reduce the internal resistance of the electrode materials.So,in this paper,we combine these two strategies to enhance the HRD by ball milling a mixture of hydrogen storage alloys and graphene nanoplatelets.And the effects of milling time and addition of graphene nanoplatelets on the electrochemical properties of the alloys were studied in detail.The optimum milling time and the addition of graphene nanoplatelets were obtained,which greatly improved the HRD of the commercial hydrogen storage alloys.Firstly,we investigated the effect of different milling time?30,45,60,90 min?on the discharge capacity and HRD of commercial hydrogen storage alloys.When the ball milling time is 30 min,the capacity retention rate of the hydrogen storage alloys electrode is 53.0% at a discharge current density of 3000mAg^-1,which is almost 2.5 times higher than that of the original commercial hydrogen storage alloy electrode?21.5%?,and of course better than those of others milling time.In addition,we also studied the effect of the amount of graphene nanoplatelets?1 wt%,1.5 wt% and 2 wt%?on the electrochemical properties of commercial hydrogen storage alloys.When 1.5 wt% graphene nanoplatelets were added,the capacity retention rate was 68.3% at the discharge current density of 3000mAg^-1,almost 3.2 times that of original alloy electrode.This paper provides a new strategy to improve the HRD of hydrogen storage alloys,and is intended to be applied to other types of hydrogen storage alloys and their composites.