Accelerating Polysulfide Redox Kinetics via the Metal–Insulator Interface in a Binder-Free Separator for Long-Life Lithium–Sulfur Batteries

The sluggish bidirectional reaction kinetics of lithium polysulfides (LiPSs) and the severe shuttle effect continue to impede the commercialization of lithium–sulfur (Li–S) batteries. Herein, a binder-free separator featuring an in situ formed W₂N-WO₃ metal–insulator interface is developed to address these issues systematically. By precisely controlling the coating process, W₂N and WO₃ are codeposited on a carbon-coated glass fiber (C/GF) substrate to produce a robust and uniform film. The heterojunction generates an internal electric field at the interface, facilitating spontaneous electron transfer and accelerating sulfur redox reactions. Theoretical calculations further validate that the W₂N-WO₃ heterostructure improves the redox kinetics of liquid–solid conversion and enhances the absorption of long-chain LiPSs. Li–S cells employing W₂N-WO₃/C/GF binder-free separators exhibit an excellent rate capability and cycling stability. The Li–S pouch cell also maintains reversible capacity under bending conditions, demonstrating reliable mechanical integrity. These results illustrate the effectiveness of heterojunction engineering in regulating LiPS adsorption and catalysis for binder-free separators in high-performance Li–S batteries.