Polypyrrol-based Functional Separator And CoSe₂ Composite Cathode:investigation Towards Electrochemical Performance Of Lithium-sulfur Battery

Lithium-sulfur(Li-S)batteries can provide high theoretical specific capacity(1675 mAh g^-1)and energy density(2600 Wh kg^-1),and is considered to be the most promising next-generation rechargeable battery.However,the infamous"shuttle effect"and slow redox kinetics limit the high-power output of Li-S batteries,results in apparent capacity degradation and hinder the commercialization of Li-S batteries.To achieve the high-capacity and long-cycling performance of Li-S batteries,this paper intends to develop functional separator by modifying the PP with polypyrrole/graphene composites and designing CoSe₂ composite cathode materials,respectively,which are detailed as follows:(1)A multi-functional composite interlayer(PPy/G)was developed by in-situ polymerizing pyrrole(PPy)on graphene nanosheet,which are characterization by FT-TR,XPS,SEM,BET,CV and UV-vis.Moreover,the electrochemical performance of the batteries under high sulfur load and low electrolyte were explored.At the same time,a lithium-lithium symmetric battery test was carried out to investigate the protective effect of the interlayer on the lithium anode.The results indicate that PPy/G inhibits the PSs shuttle effect and improves the protection of lithium anode,and the Li-S battery with PPy/G interlayer preserves a low attenuation rate of 0.04%after 1000 cycles at 1 C;Moreover,with the high sulfur load(the ratio of electrolyte to sulfur is 5 mL g^-1),the high reversible specific capacity of 664 mAh g^-1is also retained.(2)In addition,a nitrogen-doped carbon-coated core-shell structure composite(CoSe₂@NC)was prepared by sequential carbonization and selenization of ZIF-67@ZIF-8core-shell structure,the core-shell structure hold sulfur well and facilitate the contact between sulfur and CoSe₂ catalyst,realize the physical limitation of PSs and speed up the reaction kinetics of PSs,and physically protect the CoSe₂ catalyst.The Li-S battery with CoSe₂@NC cathode exhibited a high initial capacity of 1409 mAh g^-1 at 0.1 C.After 500 cycles at a current density of 1 C,a reversible specific capacity of 561 mAh g^-1 was released;Moreover,when the high sulfur load is 5 mg cm^-2,the initial area specific capacity reaches 5.2 mAh cm^-2.