Morphology Control,pre-lithiation And Electrochemical Performance Of Vanadium Oxide Cathode Materials

At present,rechargeable lithium-ion batteries are used in most convenient electronic devices due to their high energy density and good stability.Among most cathode materials,vanadium oxide has attracted the attention of researchers due to its high specific capacity and high energy density.However,in the actual charge-discharge cycle process,the lithium ion intercalation amount often cannot reach the theoretical capacity and the actual cycle performance is poor.The research shows that the electrochemical performance of lithium ions can be effectively improved by preparing nano-scale cathode materials,and the structure of the materials can be stabilized by means of pre-lithiation.（1）The VO_xnanosheets were prepared by the hydrothermal method as the precursor,by calcining the precursor at different temperatures.The V₆O₁₃nanosheets ofs uniform morphology were obtained,but the calcination at different temperatures play a greater effect on the phase of vanadium oxide.A purer V₆O₁₃phase was obtained at 400°C.When used as a cathode material for lithium-ion batteries,it still has a capacity retention rate of 98%at a super-high current density（2000 m A/g）for300 cycles.The excellent cycling performance is mainly due to the ultrathin 2D nanosheet structure,which greatly shortens the diffusion and migration distance of lithium ions.（2）Sea urchin-like V₆O₁₃was prepared by a simple hydrothermal method combined with heat treatment.Sea urchins are 8-10μm in diameter.And by changing the ratio of NH₄VO₃and oxalic acid in the reaction solution,ion regulation was carried out,and three different morphologies,nanobelts,microflowers and sea urchins,were obtained respectively.Although the obtained phases were all V₆O₁₃,the morphology was completely different.The sea urchin-like V₆O₁₃has a higher specific capacity（375.7 m Ah/g at 100 m A/g）,even after 100 cycles at high current densities（1 A/g and 2 A/g）,the capacity retention is 85%and 81%.The sea urchin-like morphology with large specific surface area and regular morphology is the main reason for the excellent electrochemical performance.（3）To improve the lithium storage properties of V₆O₁₃and VO₂（B）,prelithiated V₆O₁₃nanosheets and prelithiated VO₂（B）nanobelts were synthesized by a secondary hydrothermal method.Compared with the V₆O₁₃nanosheets,the prelithiated V₆O₁₃nanosheets have higher specific capacity and better rate cycling performance.Meanwhile,compared with pure VO₂（B）nanobelts,the pre-lithiated VO₂（B）nanobelts exhibited a uniformly dispersed morphology with larger specific surface area.The prelithiated VO₂（B）nanobelts exhibit better electrochemical performance in terms of cycling stability and high rate capability.Due to the enlargement of the lattice after prelithiation,the diffusion coefficient of lithium ions in prelithiated VO₂（B）increases.The prelithiated VO₂（B）nanobelts cathode exhibits a high specific capacity of 264 m Ah/g with a capacity retention of 81.6%even after 100 cycles.The prelithiated VO₂（B）electrode exhibited excellent long-cycle cycling stability（87.2%capacity retention after 800 cycles at 1000 m A/g）.