Locking-chain electrolyte additive enabling moisture-tolerant electrolytes for sodium-ion batteries

The unstable electrolyte-electrode interface and the trace H₂O in commercial organic electrolytes critically limit the cycling life of batteries. Herein, a locking-chain sodium 4,4'-(1,4-phenylenebis(oxy))-bis(butane-1-sulfonate)-15-crown-5 (15PBS) is designed for phase-to-interface electrolyte optimization. In the electrolyte phase, the strong hydrophilic sulfonate groups and 15-crown-5 in 15PBS effectively transform H₂O from a reactive aggregated state (strong H-bond) into an inactive state (weak H-bond) through adsorption, effectively suppressing H₂O-induced electrolyte decomposition. At the electrolyte-electrode interface, 15PBS preferentially adsorbed onto hard carbon, displacing solvents within the electric double layer to form insoluble phenyl-rich sulfide solid electrolyte interphase with fast Na⁺ transport. Simultaneously, 15PBS facilitates the formation of stable cathode-electrolyte interphase on Na_0.72Ni_0.32Mn_0.68O₂, improving Na⁺ migration kinetics and cycling reversibility. The hard carbon | |Na_0.72Ni_0.32Mn_0.68O₂ full cell with high specific energy of 191.7 Wh kg^-1 (based on the total active-material mass) delivers long lifespan of 2000 cycles at 500 mA g^-1. Moreover, 15PBS is compatible with ester-based electrolytes in lithium-ion batteries, enabling stable cycling of commercial graphite and Si/C negative electrodes. This work provides an effective approach for durable electrolytes towards safe and high-performance batteries.