Construction And Performance Of Li-Se Battery Based On Carbon Nano-materials

As a congener of S,Selenium(Se)is proven to be a promising cathode material of Li-Se battery with great application prospect.Se has a comparable theoretical volumetric capacity(3253 mAh cm-3)to that of S(3467 mAh cm-3)and much higher electronic conductivity than S.However,Se materials still face some challenges.In the discharge/charge process of Li-Se batteries,some electrolyte soluble polyselenides formed,leading to shuttle effect which causes loss of Se.In consequence,a fair amount of Se is lost during cycling.Besides,the volume of Se cathode changes remarkably in the charge-discharge process.All these problems limit the application of lithium-selenium battery(Li-Se battery).The key lies in the inhibition of shuttle effect in the charge/discharge process to overcome the limitations above.This paper designs and builds Se composite cathode and carries on work of decorating of cell separators to weaken shuttle effect and achieve a better electrochemical performance of Li-Se battery.It provides good reference for the improvement of Li-Se battery.The main results are as follows:Using graphite oxide and multiwalled carbon nanotubes as raw material,a three-dimensional porous carbon materials,or graphene-carbon nanotubes(G-CNTs)is obtained by hydrothermal reduction method and post processed by freeze drying methods.Then Se and G-CNTs are compounded through melt-infusion process to produce the Se/graphene-carbon nanotubes composite(Se/G-CNTs).When used as cathode of lithium batteries,Se/G-CNTs exhibits better rate capability and cycling stability than pure Se or Se/graphene cathode.The improvement ascribes the confining effect of unique porous structure of the G-CNTs for the Se cathode.The effect of the content of carbon nanotubes in the G-CNTs on the performance of lithium-selenium battery is explored.The results show that when the mass ratio of carbon nanotubes and graphene is 1:5.7,the composite electrode material(Se/G-18CNTs)exhibits the best electrochemical characteristics.The Se/G-18 CNTs delivers an initial specific capacity of 575 mAh g-1 and retains 410 mAh g-1 after 100 cycles under a current density of 0.5 A g-1.Moreover,Se/G-18 CNTs has outstanding rate ability with a specific capacity of 479 mAh g-1 when the current density increases to 2 A g-1.The result demonstrates that Se/G-18 CNTs is a promising cathode material.In order to further improve the performance of Li-Se batteries,a carbon nanotube-decorated separator is prepared and applied in the cells.The porous three-dimensional CNT-decorated separator further hinders the dissolution of polyselenides to the electrolyte and the migration to the lithium anode.Hence,the Li-Se battery with CNT-decorated separator show better electrochemical performance than cell with pristine separator with a specific capacity of 538 mAh g-1 after 80 cycles under a current density of 0.5 A g-1.The capacity retention rises to 87% from 74%.