Polymer Interface Enables Reversible Quasi‐Solid Sulfur Conversion in Sodium‐Sulfur Batteries

ABSTRACT Room‐temperature sodium–sulfur (Na─S) batteries are appealing candidates for large‐scale energy storage owing to their high theoretical capacity and the use of earth‐abundant, low‐cost active materials. The quasi‐solid conversion in Na─S batteries was proposed as a promising mechanism, lying between solid‐liquid‐solid and solid‐solid mechanisms, with suppressed polysulfide dissolution while retaining faster kinetics, enabling stable, high‐performance Na─S batteries. To realize the quasi‐solid conversions, the rational design of the cathode‐electrolyte interphase is the key; however, the study is at an early stage. Herein, a multifunctional cross‐linked polymer (MCP) is first introduced as an artificial interface for the quasi‐solid sulfur conversions in Na‐S batteries with enhanced stability, faster kinetics, mechanical robustness, and improved chemical confinement. The MCP interfaces demonstrate significantly improved electrochemical performances for various nanocarbon hosts with a one‐step quasi‐solid sulfur reversible conversion mechanism, even under high sulfur loading. Our study offers new insights and design guidelines for artificial interfaces enabling quasi‐solid conversion in Na─S batteries.