Spiderweb-Mimicking Anion-Exchanging Separators for Li-S Batteries

Abstract

Lithium-sulfur (Li-S) batteries have garnered considerable interest as a promising alternative to current state-of-the-art Li-ion batteries. However, the shuttle effect poses a formidable challenge to development of Li-S batteries. Considering that all ions in electrolytes move through separators between electrodes, significant attention should be paid to separators to prevent the shuttle effect. Here, a new class of spiderweb-mimicking, anion-exchanging separators based on polyionic liquids (spiderweb separators) is demonstrated to address the aforementioned issue. The spiderweb separator consists of sandwich-type functional nanomats (top/bottom layers = multi-walled carbon nanotube-wrapped polyetherimide nanomats, middle layer = poly(1-ethyl-3-methylimidazolium) bis(trifluoromethanesulfonyl)imide (PVIm[TFSI], polyionic liquid)/poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) nanomat) on polyethylene separator. The middle nanomat layer enables (discharge voltage-dependent) reversible trap/release of polysulfides via an anion exchange reaction between TFSI(-)anions (from PVIm[TFSI]) and polysulfides. The top/bottom nanomat layers respectively act as an upper current collector and a blocking layer to prevent crossover of polysulfides to Li anodes. Driven by its unique morphology and chemical functionalities, the spiderweb separator prevents the shuttle effect while ensuring facile ion transport, leading to exceptional improvement in the electrochemical performance (capacity = 819 mAh g(-1) and cycling retention = 72% (at 2.0 C/2.0 C) after 300 cycles) of Li-S batteries.