Design And Performance Investigation On Efficient Transition Metal Oxides Catalysts For Li-O₂ Batteries

There is a huge need today for advanced energy storage and conversion technics to drive electric vehicles with longer driving distance.Rechargeable lithium-oxygen(Li-O2)batteries,sometimes referred to as lithium-air batteries,have become one of the most promising alternatives because they can provide higher energy density than current advanced lithium-ion batteries.In 2009,IBM decided to launch the "Battery 500" project,with the goal of developing a Li-O2 battery that would allow cars to travel 500 miles.However,the practical application of Li-O2 battery is still limited by several key factors,such as severe polarization,high overpotential,poor cycle stability,low energy conversion efficiency,and easy corrosion of metal lithium anodes.The research on development and optimization of cathode catalyst materials for lithium-oxygen batteries helps to improve their electrochemical performance and promote the practicability of lithium-oxygen battery applications.Stable and efficient cathode catalyst materials can effectively accelerate the lagging redox reaction kinetics for lithium-oxygen batteries,reducing battery overpotential,and improve energy conversion efficiency.Transition metal oxides have been widely studied and used in the fields of energy catalysis and electromagnetic due to their excellent catalytic performance,diverse electronic structures,easy-controlled micromorphology,environment friendly,and abundant reserves.The micromorphology of the cathode catalyst material has a great impact on the performance of lithium-oxygen batteries.In addition,adjusting the composition and electronic structure of the cathode catalyst material could impose a huge impact on the formation and decomposition of Li2O2,a discharge product in lithium-oxygen batteries,which affects its morphology and e electrochemical performance.This paper mainly focuses on the electrode structure design of single metal Co and its oxide,and bimetal spinel NiFeO porous structure,and investigate the formation and decomposition mechanism of lithium peroxide when use Co/NiFeO as catalysts to optimize the material and acquire better performance.The main research contents of this thesis are as follows:(1)This wrok introduces a one-dimensional CoO/Co-N-C nanofiber for high-efficiency cathode materials used in lithium-oxygen batteries,and further studies its various electrochemical performances and corresponding reaction catalysis mechanisms.A one-dimensional carbon nanofiber composite material coated with Co and CoO particles was prepared by one-step heat treatment ultilizing classic electrostatic spinning method,and it was employed for the research of lithium-oxygen battery catalyst.After preliminary experiments and electrochemistry test,the one-dimensional CoO/Co-N-C structure synthesized by electrospinning has good catalytic performance in lithium-oxygen batteries,especially its mechanism for promoting the growth and decomposition of lithium peroxide,so adjusting the synthesis conditions is a way to obtain optimal material structure and electrochemical performance.As a result,optimized electrochemical performance with an outstanding capacity of 8798.6 mA h g-1 and an excellent reversibility of more than 140 cycles at a fixed capacity of 600 mA h g-1 are achieved by the as obtained materials.(2)This work provides a super-assembled anti-spinel structure NiFe3O4 cathode catalytic material,and further studyed its electrochemical performance and reaction mechanism.A super-assembly template sacrificial method was used,and the template was further removed by sintering to crystallize the structure and prepare a multistage porous spinel nickel ferrite.And intrinsic tetrahedron and octahedron contents of the material can be altered by adjusting the sintering temperature,the effect of the electronic structure of the transition metal oxide on the catalytic activity of the material are further explored,As a consequence,a large specific capacity of 23413 mAh g-1 and an excellent cyclability of 193 cycles at a high current of 1000 mA g-1,and 300 cycles at a current of 500 mA g-1,are achieved.The present work provides intrinsic insights into designing high-performance metal oxide electrocatalysts for Li-02 batteries with fine-tuned electronic and frame structure.