Preparation And Modification Of PES-based Polymer Separator For Lithium-Oxygen Batteries

In recent years,with the increasing demand for energy storage systems with high energy density,lithium-oxygen batteries with high energy density have become the research focus of major researchers.As an important part of lithium-oxygen battery,the physicochemical properties of separators are closely related to the electrochemical performance of battery.Therefore,polyethersulfone（PES）-based polymer separators were prepared by non-solvent induced phase separation（NIPS）method and applied in lithium-oxygen batteries for the first time in this paper.Meanwhile,some modified methods of PES-based separator were proposed to study the internal relationship between the physicochemical properties of separators and electrochemical performance of lithium-oxygen batteries.Some innovative results were obtained,and the specific research contents are as follows:（1）The PES separator with asymmetric finger-hole structure was prepared by NIPS method,and the lithium-oxygen battery assembled with PES separator can stably cycle for 63 times under the limited capacity of 1000 mAh g^-1.At the same time,the PES separator was modified by blending with polyacrylonitrile（PAN）.The results show that PES/PAN separator has better ion transport capability.However,the strength of the PES/PAN separator is poor,which makes the battery own safety risk.（2）In view of the fact that PES separator with poor ion transport capacity and PES/PAN separator with weak strength were prepared in the previous chapter.The PES separator was modified by doping with alumina（Al₂O₃）and polyvinylpyrrolidone（PVP）.The results show that PES/Al₂O₃/PVP composite separator has excellent mechanical strength and ionic conductivity(0.56 mS cm^-1).The lithium-oxygen battery based on the PES/Al₂O₃/PVP composite separator can stably cycle for 100 times under the limited capacity of 1000 mAh g^-1.（3）The PES/Al₂O₃/PVP separator was used as the research object.The surface of the separator was functionalized coated with perfluorinated sulfonic acid（Nafion）,which is rich in sulfonic acid groups,and the Nafion/PES/Al₂O₃/PVP composite separator with ion selective permeability is obtained.The prepared Nafion/PES/Al₂O₃/PVP separator has an extremely high number of lithium ion migration（0.80）and longer cycling stability（120 cycles）.At the same time,the Nafion/PES/Al₂O₃/PVP separator can effectively solve the shuttle effect of redox mediators,therefore the lithium-oxygen battery with lithium iodide（LiI）redox mediators can stably cycle for 180 times.