Design And Preparation Of Sulfur Cathode And Study Of Modified Separator For Lithium-sulfur Battery

Lithium-sulfur(Li-S)batteries which possess high theoretical specific capacity(1675 mAh g-1)and high specific energy(2800 Wh L-1),together with the low-cost,abundance and non-toxicity of sulfur,promise great potential to be the next-generation high-energy system.However,the commercialization of Li-S batteries still have a long way to go because of the low utilization of the active material and the poor cycling performance due to the poor conductivity of the active material of the cathode and the dissolution and shuttling of polysulfide.In this thesis,the cathode and separator are designed and modified to improve the electrochemical performance of Li-S batteries by the efficient use of reactive species and the encapsulation of the dissolved and diffused polysulfides through the cathode,and the interception and activation of "shuttling" polysulfide through the separator.The main content in this research is shown as following:(1)Gelatin was used as a dispersant,and sodium thiosulfate and hydrochloric acid were used to chemically synthesize gelatin-coated sulfur(gelatin@sulfur)composite which was then used for the preparation of the cathode of Li-S batteries.Cyclic voltammetry(CV),electrochemical impedance spectroscopy(EIS),and electron microscopy were used to characterize that the design of the gelatin@sulfur composite(G@S)cathode could realize the sufficient contact between the small particle reactive material and the conductive additive,and enable the gelatin@sulfur composite to be electrochemically reacted in a limited area through the coating of gelatin,thereby improving the utilization ratio of the active material,the electrochemical stability and the rate performance of the Li-S batteries.The initial discharge specific capacity of the battery with G@S cathode reached 1217.7 mAh g-1 at 0.2 C.After 100 cycles,the capacity could still maintain 1007.3 mAh g-1,and the capacity retention was 82.7%.(2)The modified separators with different content of magnesium oxide(MgO)was prepared and used in Li-S batteries.The results showed that the20%MgO-coated separator exhibited the best electrochemical performance.The initial discharge specific capacity reached 1238.1 mAh g-1 at 0.2C,and the capacity retention was 70.67%after 100 cycles.CV,EIS,UV analysis,and electron microscopy characterization indicated that the proper addition of MgO in modified separator could enhance the bonding of polysulfide,and then inhibit their shuttling,at the same time,with the fully mixture of conductive agent acetylene black(AB),the precipitated "dead sulfur" could be activated and reused.