Preparation And Performance Control Of Fe-Mo-C Composite Metal Carbide As Lithium Oxygen Hattery Positive Catalyst

Lithium oxygen battery is considered as one of the most promising new energy materials because of its higher theoretical energy density than lithium ion battery.However,the commercial application of lithium oxygen battery need to solve a series of difficult problems,like high overpotential,volatile electrolyte and decomposition,serious polarization,poor cycle stability,low energy conversion efficiency,poor rate performance and so on.It is favourable for lithium oxygen batteries to obtain excellent performance by develop positive catalytic materials.The study shows that the morphology,specific surface area,pore size distribution,conductivity and other factors have great influence on the performance of the battery.Therefore,researchers have done a lot of work on the regulation of cathode materials by adjusting the interaction between the cathode surface and the reaction intermediates to improve the electrochemical performance of the cathode.We put forward a reasonable strategy to prepare carbide particles evenly loaded carbon fibers composite material with mesoporous structure.Carbide particles anchored in carbon fibers can not only effectively avoid the agglomeration and growth of particles,but also prevent the catalytic particles from falling off in the catalytic reaction.Furthermore,this technology effectively prevents carbon material from being exposed to electrolyte and discharge products,thus preventing the corrosion of carbon material.In this thesis,the Fe₃C and Mo₂C composite metal carbide and single-phase Fe₃C metal carbide are studied,respectively.The single-phase Fe₃C fiber and Fe₃C/Mo₂C composite fiber were prepared respectively.Electrochemical test results show that the catalyst has good catalytic activity,especially excellent capacity and cyclic stability.The research contents of this thesis are as follows:（1）The Fe₃C/Mo₂C composite electrode materials was prepared by electrospinning and high temperature calcination.The materials were characterized by SEM,XRD,TEM,XPS and other means,their electrochemical properties were systematically tested and studied.The results show that the Fe₃C/Mo₂C exhibit the best electrochemical performance as the ratio of Fe to Mo is 2 to 1 and the carbonization temperature is 800℃.Finally,the Fe₃C/Mo₂C-CF cathode delivered an outstanding specific capacity of 21120.1 mAh g^-1 at current density of100 mA g^-1,and an excellent reversibility of 147 cycles at a fixed capacity of 600 mAh g^-1.（2）Fe₃C metal carbide was prepared by electrostatic spinning and high temperature calcination.The effect of carbonization temperature on the synthesis and electrochemical properties of Fe₃C metal carbide was studied.The results show that the Fe₃C fiber obtain the best catalytic performance with polyvinylpyrrolidone as carbon source at a carbonization temperature is 700℃ and a holding time of 2 h.As a consequence,the well-designed electrode catalyst obtained a large specific capacity of 17653.1 mAh g^-1,and an excellent cyclability of 263 cycles at a current of 200 mA g^-1.