Tailoring Metal-Insulator Interfaces to Boost Polysulfide Redox Kinetics in Binder-Free Separators for High-Stability Li-S Batteries

Lithium-sulfur (Li-S) batteries are promising next-generation energy storage devices due to their high theoretical capacity and energy density. 1 However, sluggish bidirectional reaction kinetics of lithium polysulfides (LiPSs) and the severe shuttle effect remain key obstacles to their commercialization. 2 While separator modification has emerged as an effective strategy to overcome these challenges, conventional surface modification techniques, such as blade coating or filtration, often require substantial quantities of binders and conductive additives. 3, 4 These materials not only add undesirable mass, thereby reducing the overall energy density, but also compromise the precise control of coating thickness and adhesion, which in turn can diminish catalytic efficiency. Metal compound-based heterostructures have recently emerged as promising anchoring materials for LiPSs in Li-S batteries, leveraging interfacial synergistic effects to enhance electronic structure built-in electric fields and catalytic activity. 5-7 Well-designed heterostructures can thus combine high adsorption capacity with strong catalytic performance for sulfur species. However, conventional synthesis methods, such as hydro/solvothermal techniques and chemical vapor deposition, often involve complex steps and long preparation times, limiting practical application. Herein, we report a novel bind-free separator medication by using precisely controlled magnetron sputtering. Specifically, the W 2 N-WO 3 metal-insulator interface is in situ formed to address these challenges systematically. By precisely controlling the coating process, W 2 N and WO 3 are co-deposited on a carbon-coated glass fiber (C/GF) substrate, producing a robust, uniform film. The unique heterojunction generates an internal electric field at the interface, driving spontaneous electron transfer and accelerating sulfur redox reactions. Our theoretical calculations further validate that the W 2 N-WO 3 heterostructure not only improves the redox kinetics of liquid-solid conversion but also effectively absorbs dissoluble long-chain LiPSs. As a result, Li-S cells using W 2 N-WO 3 /C/GF binder-free separators exhibit excellent rate capability and cycling stability. Notably, the Li-S pouch cell demonstrates high reversible capacity with outstanding mechanical properties, maintaining robust performance even under bending, highlighting its practical applicability. Overall, this work emphasizes the role of heterojunction engineering in synergistically regulating LiPSs adsorption and catalysis to provide a promising route for binder-free separator technologies in high-performance Li-S batteries. Reference T. Zhang, F. Hu, W. Shao, S. Liu, H. Peng, Z. Song, C. Song, N. Li, and X. Jian, ACS Nano , 15, 15027 (2021). J. Liu, H. Zhuo, X. Zhang, Y. Li, J. Yang, T. Wang, J. Cui, Y. Tian, J. Yan, Y. Yu, and Y. Wu, Adv Mater , e14402 (2025). X. Liu, X. R. Sun, R. Yan, J. Yang, M. Wu, R. Zhu, S. Li, and B. Yin, Advanced Functional Materials (2025). Y. Zhang, Y. Cao, L. Fan, G. Shi, T. Zheng, H. Liu, J. Song, and G. Gao, Chemical Engineering Journal , 482 (2024). H. Wang, N. Deng, Y. Lu, Y. Jin, G. Li, B. Cheng, and W. Kang, Applied Catalysis B: Environment and Energy , 357 (2024). H. Li, C. Chen, Y. Yan, T. Yan, C. Cheng, D. Sun, and L. Zhang, Adv Mater , 33, e2105067 (2021). M. Xu, P. Yang, K. Fan, Y. Gao, Z. Zhang, Y. Li, X. Li, J. Qi, K. Xi, H. Huang, and L. Fei, Nano Today , 57 (2024).