Effect Of Layered Porous Ni Structure On The Low-temperature Performance Of Hydrogen Storage Alloys

The new energy vehicles,mainly focus on pure electric vehicles,hybrid electric vehicles and fuel-cell electric vehicles,play a key role in reducing the emission of greenhouse gas and responding to the global energy crisis.A series of advanced energy storage and conversion devices have made great strides for applications in new energy vehicles,nickel-metal hydride?Ni-MH?batteries,lithium-ion batteries,fuel cells and supercapacitors.The Ni-MH batteries are widely used in new energy equipments due to their safety,consistency,recyclability and wide temperature adaptability.It has been demonstrated that the low-temperature performance of Ni-MH batteries is dominated by the electrochemical kinetics of their negative electrode materials-hydrogen storage alloys.However,the poor low-temperature performance of commercial hydrogen storage alloys(MmNi_3.55Co_0.75Mn_0.4Al_0.3)limites the application of Ni-MH battery in cold regions and polar exploration.Therefore,it is necessary to improve the low-temperature performance of the hydrogen storage alloy in order to realize the application of the Ni-MH battery in an extremely cold region.The factors which affect the low-temperature dischargeabilities of hydrogen storage alloys are mainly the following two aspects:?1?the diffusion rate of hydrogen atoms in the alloy and?2?the electrochemical reaction rate at the interface of the electrode and electrolyte.Therefore,the low-temperature dischargeability of the hydrogen storage alloy could be improved by increasing the concentration of OH^-at the interface between the electrode and electrolyte.Mentioned that,a porous structure contributes to regulate the concentration of OH^-,While the layered Ni formed on alloy surface could be used to reduce the charge transfer resistance during the electrochemical reaction and improve the catalytic activity.In this thesis,we prepared hydrogen storage alloys with a layered porous Ni structure via hydrochloric acid etching and heat treatment.The effects of layered porous Ni structure on the electrochemical properties of the hydrogen storage alloys were studied in detail,and the mechanism for improving the low-temperature performance of hydrogen storage alloy was explained.The prepared alloys show enhanced low-temperature dischargeabilities with a discharge capacity of 102.63 mAh g^-1 at 233 K,which is 10 times that of the commercial hydrogen storage alloy.At a temperature of 273 K and a current density of 1500 mAh g^-1,the capacity retention of the prepared alloy is 36.05%,which is superior to the original alloy electrode.This paper provides a simple and effective method for improving the low-temperature dischargeability of the hydrogen storage alloys and is intented to be applied to other types of hydrogen storage alloys.