| From portable electronics to electric vehicles and grid-scale storage,as an efficient energy storage system,battery is participating in energy ecological evolution through its expanded applications.Facing the practical requirements of high specific energy secondary battery,lithium sulfur battery has become post-lithium-ion battery technology with great application potential by its advantages of high theoretical specific capacity and high energy density.However,the commercialization of lithium sulfur battery is restricted by the polysulfide shuttle effect based on the solution-deposition reaction of sulfur species and the slow redox reaction kinetics.Therefore,starting from the design of functional membrane,this study carried out systematic research,with a view to controllable construction of electrochemical reaction interface with high catalytic conversion activity,and construction of high specific energy lithium sulfur battery through organic/inorganic composite technology.The main research works are as follows:（1）Aiming at the shuttle effect of polysulfide,an efficient and stable pre-oxidation polyacrylonitrile nanofiber separator（OPAN）with polysulfide ion immobilization function was constructed by electrospinning technology,combining with the regulation of pre-oxidation reaction.The scientific problems related to the adsorption mechanism of polysulfide by nanofiber separator were explored.The regulation rules of reaction temperature on pore structure and surface state of nanofiber separator was revealed.The structure-activity relationship between reaction temperature and separator structure-property-function was explored.The OPAN separator prepared at280℃showed a suitable three-dimensional pore structure,the oxygen-containing functional groups and nitrogen-containing structures in the fiber can provide polysulfide adsorption sites,which can co-inhibit the shuttling of polysulfide through physical limiting domain and chemical absorption,and improve the Li+transport rate and the utilization of active substances at the physical limit and chemical absorption.At the same time,SEI stability can be improved to a certain extent to achieve uniform deposition of Li+.The capacity retention rate of the 280-OPAN separator battery was86.97%after 200 charge/discharge cycles at 0.5 C,and the average capacity fading rate of each cycle was only 0.065%.This strategy provides a new way for the development of advanced lithium sulfur battery functional separator.（2）In order to improve the redox reaction kinetics of lithium sulfur battery,based on the regulation of pre-oxidation reaction and pyrolytic carbonization reaction of PAN,a carbon nanofiber interlayer with high catalytic activity and uniform doping of titanium nitride（Ti N@CNFs）was designed to explore the catalytic conversion process of polysulfide on the interlayer conductive network.The effect of carbonization temperature on the immobilization of polysulfide ions,charge transport and catalytic activity of the interlayer was revealed.The 800-Ti N@CNFs carbon nanofibers exhibited good electrical conductivity and provided electron transport path for the electrochemical reaction of the system,which can effectively regulate the redox reaction kinetics and accelerate the transformation of polysulfide.The carbon nanofiber structure with uniform loading of titanium nitride can regulate the deposition morphology of lithium sulfide,reduce the internal resistance of the electrochemical reaction system,and significantly improve the electrochemical performance of lithium sulfur battery.The lithium sulfur battery equipped with 800-Ti N@CNFs interlayer still maintained the reversible discharge specific capacity of 833.9 m Ah g-1after 200 cycles at 1 C,and the coulombic efficiency is close to 100%,and it also exhibited excellent performance with high sulfur loading(3.5 mg cm-2)and high current density（4 C）.This study provides an original idea for regulating polysulfide conversion and promotes the practical application of high specific energy lithium sulfur battery. |
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