Study On Cathode Materials For High Performance Lithium Oxygen Battery

With social development and economic progress,people put forward higher requirements for energy storage devices with high energy density in production and life.Lithium-oxygen batteries have broad application prospects due to their high theoretical energy density of 5200 Wh/kg(vs.Li&O).However,there are still many problems to be solved in the practical application of lithium-oxygen batteries,such as slow ORR/OER dynamic process of oxygen electrode reaction,poor conductivity of discharge product Li2O2,instability of electrolyte and cathode materials under high charging voltage,which seriously restrict the application of lithium-oxygen batteries.In order to improve these problems,researchers have done extensive research on cathode catalysts,electrolytes and negative protection of lithium-oxygen batteries,but they have not solved the two fundamental problems of low discharge capacity and poor reversibility of oxygen electrodes.Aiming at these problems,the structure-activity relationship between pore structure and catalytic performance of cathode materials was studied in this paper,aiming at improving discharge capacity and reversibility of electrochemical reactions.A macroporous carbon material(MPC)with abundant pore structure was developed using glucose as carbon source.On the basis of optimizing the preparation process,a new method of electrochemical treatment and post-treatment was proposed,which improved the pore structure and inner surface electrochemical activity of the material,and increased the discharge capacity significantly.The results showed that the macroporous carbon(MPCSD,MPCFD)obtained by spray drying and flash drying compared with the traditional evaporation drying(MPCED)had more uniform thin-walled pore structure and larger specific surface area,and the discharge capacity of the first cycle increased by 11.6%and 14.4%respectively in the lithium oxygen battery,reaching 5265 mAh g-1 MPC and 5397 mAh g-1 MPC.Macroporous carbon(MPCFSH2O,MPCFDCD2)treated by hydrogen peroxide and carbon dioxide oxidation after electrochemical lithium intercalation effectively improved the inner surface activity of macroporous carbon.The first cycle discharge specific capacity was further increased by 8.2%and 29.8%,reaching 5837 mAh g-1 mpc and 7005 mAh g-1 mpc,respectively.Doped nitrogen atoms and Co-supported(N-MPC,Co@N-MPC)also increase the specific discharge capacity of macroporous carbon,and effectively improve the catalytic activity of macroporous carbon materials,reduce charging overpotential and prolong cycle life.Further,the N-MPCSD prepared by spray drying increased the discharge platform to 2.725 V in the lithium oxygen battery,and the discharge capacity of the first cycle was as high as 10470 mAh g-1 MPC-After Co loading(using Co@N-MPCSD),the discharge platform was further improved(2.77 V),and the charging medium voltage(3.89 V)was kept low.The discharge capacity of the first cycle reached 11584 mAh g-1 MPC.On this basis,CO@N-MPCFD prepared by liquid nitrogen flash freezing was electrochemically intercalated into lithium and then treated by chemical oxidation.The results show that the specific surface area of Co@N-MPCFDCO2 and Co@N-MPCFDH2O materials obtained by oxidation of CO2 and H2O after lithium intercalation is further increased,and the discharge capacity is increased by 26.2%and 8.3%respectively,reaching 15168 mAh g-1 MPC and 13016 mAh g-1 MPC.Among them,Co@N-MPCFDCO2 has a cycle life of 100 cycles due to its excellent catalytic performance and pore structure.