The secondary Li/S polymer batteries(LSPB) consist of sulfur composite cathode, polymer electrolyte, and lithium anode. In this study, the composite cathode was made from elemental sulfur, carbon black, Poly(ethylene oxide)PEO, lithium perchlorate($LiClO_4$), and acetonitrile. And the anode was made from lithium metal. We prepared the polymer coated membrane(PCM) by coating linear PEO on PE separator, and then immersed it in 1M ($LiClO_4$ solution with various plasticizers : ethylene glycol dimethyl ether(EGDME), tetra(ethylene glycol) dimethyl ether (TEGDME), TEGDME/poly(ethylene glycol)dimethyl ether500(PEGDME500), TEGDME/PEGDME1000, PEGDME500. Li/S battery using the polymer electrolyte with TEGDME showed the highest battery performance due to the good mobility of ions by short chain length of the TEGDME.
The plasticized polymer electrolyte based on PCM, TEGDME, LiClO4 were prepared with different salt concentration for the Li/S batteries. The polymer electrolyte made by 1.25M ($LiClO_4$ solution showed the maximum ionic conductivity, $7.81 × 10^{-5}S/cm$, at 25$^\circ$C. To understand the effect of the salt concentration on the electrochemical performance, the polymer electrolytes were characterized using FRA, FT-IR, viscometer, and DSC. As salt concentration increased, crystalline region of the polymer electrolyte was decreased. However, viscosity increased at the high salt concentration and the relative fraction of the free ions in the polymer electrolyte reduced. These conflicting effects optimized polymer electrolyte at 1.25M ($LiClO_4$ solution in TEGDME. Then, we also investigated the effect of salt concentration on the performance of sulfur composite cathode. The cell with EO:Li ratio of 8:1 showed the highest battery performance without fading capacity.
Finally, we prepared composite polymer electrolytes consisting of PCM, TEGDME, ($LiClO_4$, and silica particle. The polymer electrolyte containing 20wt% silica showed the maximum ionic conductivity, $8.95× 10^{-5}S/cm$, at 25℃. And we investigated performance and electrochemical properties of the cell containing silica and they showed good battery performance.
