Preparation And Research On Potassium Storage Performance With Mechansim Of Se-based Cathode Material

Fossil fuels based on traditional energy sources are facing depletion,environmental pollution,and global warming issues,which have caused great social concerns.The development of renewable and clean energy such as wind and solar energy is of great importance.Lithium ion batteries(LIBs)come into being under the background.However,LIBs cannot meet the increasing energy needs of people due to the low natural reserves and high cost of lithium resources.Recently,many efforts have been devoted to developing high performance K-ion battery(KIB)because of abundant potassium resources and lower redox potential,allowing KIBs to be potentially utilized in large-scale energy storage.Moreover,selenium has emerged as an attractive candidate for KIB cathode thanks to its superior electronic conductivity(10-3 S m-1)and great electrochemical compatibility with carbonate-based electrolyte together.with its intrinsically high specific gravimetric capacity(675 mAh g-1).Therefore,K-Se battery,in general,offers higher energy density compared to that based on conventional intercalation cathodes.However,its full potential has yet to be unlocked,which is due to the unsatisfactory electrochemical performance arising from low utilization of Se and large volume expansion during charge/discharge process.Moreover,the electrochemical reaction mechanisms involved in this new type of battery remain unclear.In view of the above problems,this paper aims to design the Se based electrodes with rational structure to optimize the electrochemical performance,and elucidate of their K-ion storage mechanism deeply.Chapter one,we describe the development overview of potassium ion batteries,and the research status of selenium-based cathode materials.We also introduce the principles and applications of electrospinning,and finally summarize the research background and content.Chapter two,we mainly sorted out the chemistry reagent,experimental apparatus,characterization methods,battery assembling and electrochemical performance test methods related to the paper.Chapter three,a high-performance flexible K-Se battery is achieved by employing the freestanding small molecule Se@peapod-like N-doped porous carbon nanofibers(Se@NPCFs)thin film cathode.Taking the advantages of shortened electron/ion diffusion path,sufficient conductivity,good structural stability and high chemical polarity,the Se@NPCFs cathode exhibits superior electrochemical performances,including high reversible capacity(635 mAh g-1 over 50 cycles at 50 mA g-1 with a high Se utilization of 94.1%)and ultralong cycling life(367 mAh g-1 after 1670 cycles at 0.5 A g-1).Meanwhile,we take advantage of in-situ Raman spectroscopy,ex-HRTEM,and first-principle calculation to elucidate the reaction mechanisms by identifying the existence of short-chain molecular Se encapsulated inside the microporous host,which transforms to K2Se via a two-step conversion reaction via an "all-solid-state"electrochemical process.Through the whole reaction,the generation of polyselenides(K2Sen,3?n?8)is effectively suppressed,which thus significantly alleviates the shuttle effect and improves electrochemical performance.Chapter four,we describe the innovation and shortcomings of this paper,and look forward to the future research plan.