<i>In situ</i> polymerized quasi-solid polymer electrolytes enabling void-free interfaces for room-temperature sodium–sulfur batteries

Rechargeable room-temperature Na–S (RT Na–S) batteries are promising for large-scale energy storage because of their high energy density and low cost. However, their practical viability is limited by polysulfide shuttling and Na dendrite formation. Here, a quasi-solid polymer electrolyte with dual sodium salts (DS-QSPE) was created through in situ polymerization, demonstrating high ionic conductivity (4.8×10⁻⁴ S cm⁻¹ at 25 °C), a high sodium-ion transference number (0.73), and effective confinement of polysulfides. Theoretical calculations confirm enhanced Na-ion transport, attributed to the strengthened coordination of anions with the poly-dioxolane chain and the increased dissociation of sodium salts, consistent with the experiment results. More importantly, the DS-QSPE forms an interconnected network structure within the sulfurized polyacrylonitrile (SPAN) cathode, providing abundant and seamless electrochemical reaction interfaces that promote efficient and uniform ion transport pathways. Consequently, the Na||SPAN battery with DS-QSPE maintains a high capacity of approximately 327.4 mAh g⁻¹ (based on the mass of SPAN) after 200 cycles at 0.2 A g⁻¹, achieving 81.4% capacity retention, which is much superior to that in liquid electrolyte counterpart. This study presents a facile approach to resolving the interfacial issue of solid-state Na–S batteries.