Design And Electrochemical Performance Study Of Sulfur Cathode And Interlayer Modification In Lithium Sulfur Battery

Sulfur affords a remarkably high theoretical capacity?1675 mAh/g?and energy density?2600 Wh/kg?,which nearly five-fold large than lithium ion batteries,when used as cathode in lithium sulfur batteries.In addition to its low cost and environmental friendliness,the lithium sulfur battery becomes a hotpot in the field of new energy storage batteries.However,there are some problems make the application of lithium sulfur batteries are still hindered,which can be conclude as follow:?1?The poor electrical conductivity of sulfur and discharge product?Li₂S?.?2?“Shuttle effect”caused by the high solubility of lithium polysulfides during the cycling.?3?The volume expansion between sulfur and Li₂S.These serious problems will lead to a serious capacity fading,low utilization rate of sulfur and overcharge phenomenon during the charge/discharge process.In this dissertation,different method including the microstructural design of the cathode and functional interlayer between sulfur cathode and separator have been adopted to suppress the dissolution and transformation of lithium polysulfides.1.The design of barrier interlayer on the surface of sulfur cathode.A metal-organic framework-derived porous nitrogen-carbon-cobalt interlayer is prepared to suppress polysulfides dissolution in electrolyte.Owing to the novel MOFs precursor,N-C-Co composite possesses hierarchical pores,pyridinic and pyrrolic nitrogen groups.This coating interlayer can act as a physical blocking layer and adsorption layer to suppress and confine free polysulfides.As a result,the improvement of electrochemical performance is achieved by the well-designed interlayer.The initial discharge capacity is 1216.9 mAh/g at 1 C and can retain 660.3 mAh/g after 250 cycles at sulfur loading of 1.5 mg/cm²,demonstrating an effective inhibition of the shuttle effect in lithium sulfur batteries.2.The modification of separator.?-MoC_1-x nanocrystalline enriched carbon nanosphere(?-MoC_1-x/CNS)was synthesized by self-assemble and applied as modifying material on the surface of normal polypropylene?PP?separator.The electrochemical performance of lithium sulfur batteries with modified separator is highly improved compared with the batteries with normal separator,which mainly because the pore on the surface of PP separator was cover by?-MoC_1-x/CNS and?-MoC_1-x/CNS have a special chemical adsorption for lithium polysulfides.The electrochemical performance exhibited the lithium sulfur batteries with?-MoC_1-x/CNS-PP have a better rate performance,cycling performance and Columbic efficiency.3.The composition and microstructural design of sulfur cathode.Sandwich-like N-C@rGO-S cathode and three-dimensional open nanosheets assembled nanoflower like MnO₂ was synthesized by in-situ growth and hydrothermal method,separately.The design concept of above sulfur cathode is aimed at increasing the adsorption sites for lithium polysulfide to suppress the“shuttle effect”.The results showed that the electrochemical performance is significantly improved by above both method for sulfur cathode.