WS2-Derived Na2S/W Composite Layer for Stable Sodium Metal Batteries

Abstract

Sodium metal is an attractive anode for next-generation secondary batteries due to its high theoretical capacity, low redox potential, and cost advantages. However, uncontrolled dendrite growth severely limits its practical implementation. Here, we introduce a scalable, straightforward blade-casting strategy to coat WS2 onto a polypropylene (PP) separator, effectively regulating Na deposition and extending safe battery operation. Upon contact with Na metal, WS2 spontaneously undergoes a conversion reaction to form Na2S and metallic W, generating a stable Na2S/W composite interlayer at the anode interface. This interlayer on a polymeric separator reduces the Na+ diffusion barrier, facilitates fast, uniform ion transport, and serves as a local electrolyte reservoir that homogenizes Na+ flux. Simultaneously, the metallic W phase induced by WS2 enhances the mechanical strength of the separator, providing physical resistance against dendrite penetration. Consequently, Na

Na symmetric cells using the WS2@PP separator deliver highly stable cycling for 1,000 h at 2 mA cm-2 with a low overpotential of ~20 mV. In Na

Na3V2(PO4)3 full cells, the separator enables stable cycling for 200 cycles at 2 C, with excellent capacity retention and no significant alteration. This separator-engineering strategy offers a practical and manufacturable route to stabilize sodium-metal anodes and advance long-life, high-energy sodium-metal batteries.