Bifunctional Fluorinated Separator Enabling Polysulfide Trapping and Li Deposition for Lithium-Sulfur Batteries.

Abstract

Lithium-sulfur batteries (LSBs) are deemed as one of the most promising next generation energy storage system substitutes for conventional lithium ion batteries due to their high energy density, low cost, and environmental friendliness. The practical application of LSBs has long been blocked by the serious lithium polysulfide (LiPS) shuttle effect and notorious Li dendrite growth, inducing fast capacity decay and limited cycling lifespan. Herein, fluorinated carbon prepared via a safe and scalable strategy has rationally been coated on a separator affording bifunctional fluorinated Celgard (F-Celgard) for LSB construction. The F-Celgard shows superior Li+ flux modulation and LiPS trapping capability, which has been verified by the density function theory calculations. The Li symmetric cells demonstrate long and stable Li plating/stripping with much smaller polarization voltage and dendrite-free Li deposition. In addition, LSBs show superior rate performances with higher discharge capacities and long-time stable cycling over 1000 cycles at 1 C with a low decay rate of ∼0.038% per cycle. With a high sulfur loading (∼5.2 mg cm-2), a high initial areal capacity of ∼4.2 mAh cm-2 can be obtained with a superior capacity retention of ∼91.8% at 0.2 C. This work demonstrates a facile, cost-effective, and scalable strategy toward highly stable LSBs for practical usage.