The electrochemical performances of S₈ and polyanthra [1 ,9 ,8 -b,c,d,e][4 ,10 ,5 -b ,c ,d , e ]bis-[1,6,6a(6a-S^IV)trithia]pentalene (PABTH) in PEO-based polymer electrolyte are studied. It s found that there are phenomena of the solution of reduction products in the discharging process for Li/PEO-based polymer electrolyte/S₈ cell and Li/PEO-based polymer electrolyte/PABTH cell. It suggests that ether-based electrolytes even in the form of polymer (such as PEO-based Polymer Electrolytes) can t alleviate the loss of active material in sulfur electrode for the dissolution of its reduction products. For alleviating the solution of reduction production, designing electrolyte solvent with a special structure is necessary. Moreover, preliminary investigation on discharge capacity of the Li/PEO-based polymer electrolyte/S₈ cell and PABTH/ PEO₂₀LiTFSI/Li cell show that the utilization of the active material is lower than that in liquid electrolyte. It due to that sulfur and PABTH isn t ionic conductor, and the diffusivity values of Li^＋ in sulfur and PABTH are very low. PEO molecular with a large volume can t penetrate into particle of sulfur and PABTH carrying Li^＋, this is another main reason. From this point of view, electrolyte solvent with a small volume is favorable to the utilization of sulfur and PABTH.

Key words: rechargeable lithium sulfur battery, capacity fade, polymer electrolyte, PEO-based, molecular design of electrolyte solvent