Stable Solid‐State Lithium‐Sulfur Batteries Enabled by Covalently Coupled Electrolyte–Electrode Interfaces

Solid‐state lithium–sulfur batteries (SSLSBs) are fundamentally limited by large interfacial resistance, interfacial instability, and polysulfide shuttling at solid–solid electrode/electrolyte contacts. Here, a covalent interfacial engineering strategy is proposed to chemically integrate sulfur/carbon cathodes with polymer electrolytes via surface functionalization and in situ interfacial polymerization. The resulting covalently bonded siloxane interphase establishes robust molecular‐level coupling across the solid‐state electrolyte‐cathode interface. This chemically integrated interface significantly reduces interfacial resistance, stabilizes impedance evolution during cycling, and introduces selective permeation that suppresses polysulfide migration while maintaining efficient Li + transport. Consequently, the SSLSBs exhibit enhanced cycling stability, reduced voltage polarization, and improved rate capability, delivering 819.1 mAh g − 1 at 0.5 C with 50.6% retention after 300 cycles and 506.4 mAh g − 1 at 2 C. This work highlights covalent interface coupling as an effective paradigm for addressing interfacial limitations in SSLSBs.