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, iron(II) sulfide, carbon black, Kynar FLEX 2801(P(VdF-co-HFP)), lithium perchlorate ($LiClO_4$), and acetone. And the anode was made from lithium metal. As polymer electrolyte, we prepared polymer coated membrane (PCM) by coating Kynar 2801 on PE separator, and then immersed it in 1M $LiClO_4$ solution with tetra(ethylene glycol) dimethyl ether(TEGDME).
The cathode based on sulfur was prepared with different ratios of sulfur and iron(II) sulfide for the Li/S batteries. The cathode with the ratio of S:FeS = 8:2 showed the highest specific capacity and good battery performance at room temperature. To understand the effect of the iron on the electrochemical performance, the cells were characterized using FRA, CV, charging and discharging.
And we prepared composite polymer electrolytes consisting of PCM, TEGDME, $LiClO_4$ and studied on their electrochemical properties. A maximum ionic conductivity was found for the sample containing 50wt% salt to Kynar FLEX 2801 and they were $2.69×10^{-4}S/cm$ at room temperature. Increases of salt content in each polymer electrolytes seem to be main reasons for the initial increase of the ionic conductivities. The initial capacities of the cells were increased with the salt content. But they were decreased sharply at second discharging. As increase salt concentration, crystalline region of the polymer electrolyte was broken. To the contrast, at the high salt concentration viscosity increased and the relative fraction of the free ions in the polymer electrolyte reduced.
