Preparation And Electrochemical Properties Of Nafion-based SEI Membranes

Lithium-sulfur batteries(Li-S)have become the most promising next-generation energy battery due to its environment friendliness,low cost and high energy density(2600 Wh kg^-1).However,the greater safety hazards and rapid capacity decay caused by instability of Li anode in Li-S batteries seriously restrict its commercialization.In response to the above problems,based on Li-Nafion(LN)materials,we successfully prepared artificial solid electrolyte interface(SEI)film of Li-Nafion@TiO₂(or Li₂CO₃)and studied its electrochemical properties.The rate performance,cycle life and stability of Li-S batteries with anode protected by artificial SEI film shows significant improvement.The specific processes are as follow:(1)In order to improve the stability of anode,we designed and prepared the composite film of Li-Nafion@Li₂CO₃(LNL).In the composite film,the addition of Li₂CO₃salt can improve the lithium-ionic conductivity of composite film for realizing the uniform deposition of lithium ions on surface of Li anode.Under the action of the SEI film,Li anode exhibits a much longer cycle life.The Li anode can be cycled stably up to 400 cycles at 1 m A cm^-2.Moreover,it also achieves higher capacity retention rate of 62.6%at 0.1 C in Li-S batteries.(2)On the basis of the above experiments,in order to further suppress side reactions,we successfully prepared the artificial SEI film of Li-Nafion@TiO₂(LNT)and studied its effect on electeochemical properties of Li-S batteries.The negative potential of LN material can repel the polysulfide(Li PSs)in electrolyte by electrostatic action for reducing the side reaction in Li-S batteries.More importantly,TiO₂salt further reduces the potential of LNT film,so that the side reaction is well suppressed.Moreover,the addition of appropriate amount of TiO₂inorganic salt could increase lithium-ionic conductivity and mechanical strength of composite film,thereby promoting the uniform deposition of lithium ions on Li anode surface.Therefore,compared to the pure Li-S batteries,the batteries with artificial film exhibits longer battery cycle life and higher capacity retention.The Li-S batteries with artificial film achieves a higher capacity retention of 74.9%at 0.1 C,and a much longer cycle life of380 cycles at 1 m A cm^-2.This work provides a new idea for development of practical high-energy-density lithium-sulfur batteries from the aspects of material preparation and structure design.