Boosting polysulfide capture and redox conversion by functional separator combined with porous hosts for advanced Li-S batteries

Large-scale applications of lithium-sulfur (Li-S) batteries are hampered by the notorious ‘shuttle effect’ of lithium polysulfides (LiPS) and their sluggish redox kinetics. Herein, advanced sulfur host materials and multi-functional separator are proposed to collaboratively address these conundrums. The phosphorus-doped porous carbon (PPC) with a specific surface of 2131.5 m²/g was prepared as a sulfur host material in combination with a multi-step heat treatment. The PPC with high concentration of phosphorus doping, large surface area and reasonable pore sizes can improve the chemical adsorption of soluble polysulfides. The three-dimensional TiN/polyimide (PI) composite separator (TiN/PI) was prepared via electrospinning and stepwise imidization. The high affinity of the polar imide group in PI greatly improves the wettability of electrolytes, while the highly porous interconnected fibrous structure facilitates the fast transportation of Li⁺. Besides, the TiN nanoparticles can effectively inhibit the LiPS shuttle and stimulate the LiPS conversion. Consequently, the Li-S battery combining a PPC/S cathode and a TiN/PI separator offers a satisfactory performance of 630 mAh/g at 1.0C after 140cycles. This work provides a low-cost, facile and controllable method to design functional components for Li-S batteries.