Lithium-sulfur batteries are considered a promising "beyond Li-ion" energy storage technology. Currently, the practical realization of Li-S batteries is plagued by rapid electrochemical failure of S cathodes due to aggravated polysulfide dissolution and shuttle in the conventional liquid ether-based electrolytes. A gel polymer electrolyte obtained by in situ polymerization of liquid electrolyte solvent at the cathode-electrolyte interface has been proven an effective strategy to prevent polysulfide shuttle. However, notably reduced polysulfide solubility in the gel electrolyte leads to enrichment of poorly conductive sulfide species, which hinders charge migration across the interface and therefore accounts for retarded polysulfide conversion and a low capacity/energy output of batteries. Here, we show that thioacetamide, as a cathode additive, inhibits interfacial polymerization of ether molecules while assisting dissolution of polysulfides and Li2S at the cathode/electrolyte interface. In this way, a layer of liquid, sulfide-soluble electrolyte is preserved between the highly gelled electrolyte and the S particle surface, avoiding interfacial sulfide accumulation and improving polysulfide conversion kinetics. A Li-S battery with the controllably solidified interface demonstrates, without adding other performance-boosting agents or catalysts, a high reversible capacity, a long cycle life, and a favorable rate performance, showing promises for the next-generation storage applications.
Keywords: cathode−electrolyte interface; gel polymer electrolyte; in situ polymerization; quasi-solid-state Li-S battery; thioacetamide.