The Stability of Polymers in Liquid Li-S Battery

Polymers have been widely employed as the binders, separators, separator modifiers and gel polymer electrolytes in lithium-sulfur batteries. Considering the special electrolyte system and discharge/charge mechanism, to verify whether the common polymer is applicable for Li-S battery is extremely necessary but often overlooked. In this paper the stability of some frequently-used polymersin the ether electrolyte(1 M LiTFSI + 0.2 MLiNO3/dioxolane (DOL) and 1,2-dimethoxyethane(DME) (1:1, v/v)) on the cycling and storage performances of Li-S batteryis examined by testing the solubility of the PEO, PVDF and PVDF-HFP particles/membranes in ether electrolyte and detecting the structure and composition changes of PVDF and PVDF-HFP membranes after cycling and storage as the separators of Li-S batteries. The results show that PEO particle and membrane both can dissolve in DOL and DME(1:1). PVDF and PVDF-HFP particles also dissolve in DOL and DME(1:1) but the membranes remain relatively stable, whereas PVDF-HFP react with Li2Sx in liquid Li-S cellto form sulfone, which induce the crystalline phase transformation (from α-phase to γ-phase) and cystallinity decrease. PVDF can also react with Li2Sxin liquid Li-S cell, but the action is less intensive than PVDF-HFP.