Construction Of High Performance Lithium-sulfur Battery Based On Photoelectrochemical Catalytic Regulation

Advanced electrode materials with high energy density have attracted much attenetion because the increasing demand for energy storage devices in electric vehicles.Li-sulfur batteries using sufur as the cathode are appealing candidates for next-generation energy storage devices because of their low cost,abundant resources and high energy density(2600 Wh kg-1),far superior to the lithium ion batteries.Unfortunately,the fast capacity degradation and low coulombic efficiency,caused by the insulating nature of sulfur and dissolution of polysulfides,are still bottlenecks,which limit the development of Li-sulfur batteries.In this dissertation,electrocatalists and photocatalyst were used to conquer these problems existing in the cathode of Li-S batteries.The results provide insight into the design and development of high performance Li-S batteries.The main results are summarized as follows:(1)We propose a Co and N doped carbon materials(CNC)to trigger the interface-mediated redox reaction of lithium polysulfide in lithium-sulfur batteries.The CNC is composed of N doped porous carbon encapsulated Co nanoparticle was coated on the commercial separator as the conductive membrane.We identified that Co and N coordination centres serve as a elctrocatalyst to facilitate the formation and reduction of sulfur.At the same time,the polysulfide is effectively blocked by the physical limitation method.Li2Sx(4≤x≤7)passes through the diaphragm,thereby overcoming the "shuttle effect" produced in lithium-sulfur batteries,resulting in significantly enhanced electrochemical performance.(2)A lithium-sulfur battery with electric energy saving was realized by introduce photocatalyst to cathode.During the photo-charging process,the S2-ions produced in the discharging process are oxidized to polysulfide ions(S22-and S42-)by photoexcited holes from the photocatalyst.According to the working mechanism,Co1-xS,g-C3N4 and SrTiO3/TiO2 were prepared and used as photocatalyst due to their suitable position of conduction band.The morphology and structure were studied.Various photoelectrodes will be utilized to study the effect of photoelectrode on the photo-assisted chargeable Li-S battery.This study will clarify the mechanism and general rules of effects of the conduction band,band gap and surface structure of photoelectrode on electrochemical performance of Li-S battery.Using SrTiO3/TiO2 as a photoelectrode can reduce the voltage by 0.3 V and save power by 12%.