Solvation Reprogramming With Dual Cations Enables Catalytic Polysulfide Conversion and Stable Sodium Metal for...

The practical development of room-temperature sodium-sulfur batteries faces significant challenges, primarily stemming from the polysulfide shuttle effect and the instability of the sodium anode. In this study, we propose a dual-cation electrolyte engineering strategy that simultaneously addresses both bottlenecks by introducing K⁺ into the conventional NaPF₆/1-ethoxy-2-(2-methoxyethoxy)ethane electrolyte. The larger ionic radius and lower Lewis acidity of K⁺ competitively modified the Na⁺ solvation structure, weakening Na-Solvent interactions and reorganizing the solvation shell into contact ion pairs (CIPs), thus promoting the formation of inorganic-rich solid electrolyte interphase. Theoretical calculations reveal that dominant NaKS_x intermediates adsorbed via Na sites weaken S─S and Na─S bonds with dual-cation induced charge delocalization, establishing catalytic cycle that lowers the kinetic barrier and relieves polysulfide shuttling. Meanwhile, the dendrite growth and parasitic side reactions are further suppressed within electrostatic shielding evoked by introduced K⁺. Consequently, a symmetric full cell architecture, with concave hollow mesoporous carbon nanospheres as both sulfur cathode matrix and sodiophilic anode coating, achieves a record lifespan of 10,000 cycles and a high-capacity retention of 95.3% at 10 A g^-1 and high energy density of 223 Wh kg^-1 for pouch cell. This work offers a comprehensive design strategy, advancing practical metal-sulfur batteries through electrolyte solvation and electrode interface engineering.