Study Of Cathode Catalyst For Li-air Battery In Ambient Air

Lithium-air battery has drawn great focus due to it has the highest theoretical capacity among the commercialized energy storage devices.However,most of the present Li-air battery operates in pure O2 other than in ambient air which obviously prohibits its practical applications.Toward the ambient air used Li-air batteries,there are many challenges should be solved.1.Cathode: the discharge products will react with moisture,CO2 to produce Li OH and Li2CO3 which are more difficult to be decomposed,the energy utilization efficiency and battery cycle life will be reduced.2.Electrolyte: the electrolyte experiences more severe volatilization and decomposition problems.3.Anode: the air react with the Li metal anode and result in the anode corrosion,pulverization and so on,which seriously affect the life of lithium-air battery.Based on these problems,my research focus on designing and preparing high efficient cathode catalyst for reducing the charging voltage and improving the cycling performance.Firstly,we systematically investigated three kinds of commercially available carbon materials(acetylene black,ketjen black and carbon nanotubes)as Lithium-air battery cathode which operates in ambient air.All of the three kinds of materials display a stable cycle life.When performs the discharge/charge at the current density of 200 mA g-1 with a limited capacity of 500 mAh g-1,it can repeat more than 100 cycles.The ketjen black gives the most stable performance.The cycled electrodes were characterized by SEM and IR,which demonstrate the formation of Li2CO3 on the surface of the electrode.The Li metal anode also pulverizated to some extent.Both of the two aspects lead to the performance fading.Secondly,the MnO micro-sheets were designed and prepared to further improve the round-trip efficiency and cycling performance.It gives a stable cycle life more than 100 times when performed the discharge/charge test at a current density of 200 mA g-1 with a limited capacity of 500 mAh g-1.Even at the 100 th cycle,the discharging terminal voltage remains2.65 V,which is much higher than that of pure Kejten black electrode(2.36 V).The charging terminal voltage is only 4.0 V compared with that of 4.44 V for the pure Kejten black electrode.The introduction of MnO catalyst can efficiently reduce the charging polarization and improve the cycle stability.The generation process and depth distribution of discharge products have been investigated by SEM and XPS.Li2CO3 on the surface of the discharge product originates from CO2 in air,but the formation of Li2CO3 on the electrode surface may be caused by the reaction of CO2 and the corrosion of carbon.In this work,we investigated the low-cost carbon materials and MnO as catalyst for Lithium-air batteries in ambient air.This will benefit the practical applications and reduce the total cost of the Lithium-air battery.