Preparation Of Vanadium-based Materials And Their Applications In Lithium And Sodium Batteries

Vanadium-based materials have attracted widespread attention in the field of energy storage due to their advantages such as no pollution,low cost,high energy density,and fast charge/discharge.At the same time,the rich valence state of vanadium element helps to achieve the multi-electron electrochemical reaction,thereby providing higher theoretical specific capacity.However,in the long-term repeated insertion/deinsertion process of lithium and sodium ions in vanadium-based materials,severe volume expansion and structural collapse will occur,and an unstable solid electrolyte interface film will be formed,leading to the severely damaged structure and the significantly attenuated capacity.In response to these problems,a large number of studies have certified that nano-materials,forming hollow structures,and compounding materials with carbon materials can effectively alleviate the problem of volume expansion during charging and discharging,thereby obtaining stable long-cycle performance.This thesis focuses on the research of vanadium-based anode materials.Through simple and reasonable design,we have synthesized vanadium trioxide nanoparticles confined in conductive multi-channel carbon nanofibers?V₂O₃@MCNFs?and vanadium nitride quantum dots confined in a hollow nitrogen-doped spherical carbon shell?VNQD@NC HSs?.Thanks to their unique structural characteristics,the above materials all show good rate performance and excellent cycle performance.The main research contents of this paper are as follows:?1?We report a favorable pseudocapacitive sodium-ion storage nanohybrid with V₂O₃nanoparticles confined in multichannel carbon nanofibers network?V₂O₃@MCNFs?.The multi-channel carbon nanofibers increase the conductivity of the material,limit the volume expansion of the vanadium trioxide particles,and enhance the structural stability of the V₂O₃@MCNFs material.Moreover,the cross-linked three-dimensional carbon nanofiber network provides a channel for electron transmission and ensures fast reaction kinetics.As anode materials of sodium batteries,V₂O₃@MCNFs shows high capacity of 321.6 mAh g^-1 at a current density of 0.1 A g^-1 after 200 cycles.At a high current density of 1 A g^-1,it still maintains232 mAh g^-1 after 4,000 cycles,corresponding a capacity retention of 80%.The capacity retention is 82%even at a current density of 5 A g^-1 after 10,000 cycles.?2?The conductivity of V₂O₃@MCNFs is still limited.Although the vanadium oxide nanoparticles are controlled at the nanometer level,they still face problems such as volume expansion and limited ions/electron transfer kinetics.We have also designed a structure in which vanadium nitride quantum dots are confined in nitrogen-containing hollow carbon spheres?VNQD@NC HSs?.Vanadium nitride quantum dots can shorten the transmission distance of electron ions,improve the transmission kinetics of lithium/sodium ions,and improve the rate performance of the material.The nitrogen-doped hollow carbon shell can not only improve the conductivity of the material,but also increase its stability.At the same time,it provides sufficient buffer space for volume expansion and improves the cycle stability performance.In the application of lithium and sodium batteries,VNQD@NC HSs electrode materials show good electrochemical lithium storage and sodium storage performance.VNQD@NC HSs can achieve 832 mAh g^-1 after 200 cycles at a current density of 0.1 A g^-1,showing excellent lithium storage performance.At the same time,for sodium batteries,VNQD@NC HSs deliver a capacity of 360 mAh g^-1 after 200 cycles at 0.1 A g^-1 and show a capacity of 306mAh g^-1 after 1400 cycles at 1 A g^-1.