Asymmetric Benzene Sulfonamide Sodium Salt Enabling Stable Cycling in Solid-State Sodium Metal Batteries

With renewable energy and electric vehicles driving demand, safer and cost-effective alternatives to lithium-ion batteries are being sought. This study explores the development of a novel sodium salt, sodium (benzenesulfonyl)(trifluoromethanesulfonyl) imide (NaBTFSI), for all-solid-state sodium metal batteries (ASSSMBs). NaBTFSI offers a promising electrolyte option by improving sodium-ion transference number ( $T_{\text{Na}}^{+}$ ), conductivity, and stability of sodium metal (Na°) anode cycling. When combined with poly(ethylene oxide), NaBTFSI forms safe solid polymer electrolytes with high mechanical strength, effectively mitigating dendrite growth and polarization issues common in sodium anodes. Characterization shows NaBTFSI enhances the electrochemical performance through π-π stacking interactions, which stabilize the polymer matrix and increase ionic conductivity (≈4.0 × 10^{- 4} S cm^-1) at elevated temperatures (70 °C). NaBTFSI-based electrolytes exhibit higher stability with sodium anodes than the conventional sodium bis(trifluoromethanesulfonyl)imide salt, supporting prolonged cycling in Na^o||Na^o symmetric cells and demonstrating potential for sustainable, high-performance ASSSMBs.