Constructing metal-free and cost-effective multifunctional separator for high-performance lithium-sulfur batteries

Highlights: • A metal-free and cost-effective multifunctional separator was developed based on red phosphorus (RP). • RP was revealed with strong chemisorption to polysulfide via Lewis acid-base interaction and sulfur-chain catenation. • An important by-product Li₃PO₄ was discovered upon the interactions which favored Li⁺ transfer within the coating layer. • Li-S batteries with RP-based separator achieved a high capacity retention of 82% over 500 cycles. -- Abstract: As numerous efforts have been devoted to the construction of nano-structured sulfur electrodes, the rational design of multi-functional separator is attracting an increasing research enthusiasm recently as another promising approach towards high-performance lithium-sulfur (Li-S) batteries. Herein, red phosphorus nanoparticles are employed, for the first time, to establish a metal-free and cost-effective multifunctional separator, which not only efficiently immobilizes the lithium polysulfides but also facilitates the ion conduction for fast and durable sulfur redox reactions. The computational and experimental results reveal that red phosphorus is capable of chemically confining the polysulfides through a combination of the Lewis acid-base interaction and sulfur-chain catenation, while the highly conductive Li₃PO₄ is generated during the cell operation and facilitates ion transportation. Attributed to these unique features, the cells based on the as-developed separator exhibit a high sulfur utilization of 1287 mAh g⁻¹ at 0.1 C, superb rate capability of 809 mAh g⁻¹ at up to 2 C, and excellent cycling performance with 82% capacity retention after 500 cycles at 1 C. This facile and low-cost strategy not only offers an effective pathway towards enhancement in battery performance, but could also inspire new thinking on developing metal-free functional agents for improved sulfur electrochemistry.