Gradient‐Engineered Separator for Room Temperature Sodium‐Sulfur Batteries: Enabling Effective Polysulfides Conversion and Uniform Sodium Deposition

Abstract

Room temperature sodium‐sulfur (RT Na‐S) batteries are promising for energy storage, yet suffer from polysulfide shuttling and sodium dendrite issues. Herein, we report a gradient‐engineered separator asymmetrically coated with ZIF‐67 and ZnF2 on a polypropylene membrane to address both interfacial issues. On the cathode side, the ZIF‐67 layer acts as a “catalytic trap”, providing physical confinement of polysulfides through its microporous structure and chemical adsorption via Co‐S bonding, while its Co sites catalytically accelerate polysulfide redox conversion at the cathode interface. On the anode side, the ZnF2 layer functions as an “ion regulator”, homogenizing Na+ flux across the anode interface through its polar surface and inducing the formation of a mechanically robust, NaF‐rich solid‐electrolyte interphase (SEI) that effectively suppresses dendrite penetration. This integrated gradient design enables exceptional electrochemical performance, achieving stable sodium plating/stripping for over 2000 h at 1.0 mA cm−2 and a high reversible capacity of 1476 mA h g−1 at 0.1C in Na‐S full cells with 76% capacity retention after 400 cycles at 0.5C. This work demonstrates that a gradient‐engineered separator, via simultaneously optimizing the cathode and anode interfaces, provides a powerful strategy for developing safe, high‐performance RT Na‐S batteries.