Microemulsion Electrolytes with Micelle-Encapsulated AI-ISC Structures for High-Safety Sodium-Ion Batteries

Abstract Sodium-ion batteries are regarded as promising next-generation energy storage devices, yet conventional carbonate electrolytes pose major safety risks. Flame-retardant phosphate-based electrolytes are excellent alternatives; however, their poor reduction stability hinders widespread application. To address these challenges, a surfactant-mediated microemulsion electrolyte strategy is proposed in this work. By introducing tributyl phosphate (TBP) to mediate the miscibility between the NaFSI/TMP polar phase and PFPN (a high-performance yet poorly miscible solvent) nonpolar phase, a novel microemulsion electrolyte (MEE) is constructed. The micelles effectively protect the internal anion-induced ion–solvent-coordinated (AI-ISC) structure, while the microemulsion retains low viscosity and excellent wettability. The MEE exhibits good compatibility with various electrodes. Furthermore, Ah-level HC//NFPP pouch cells employing the MEE deliver an initial Coulombic efficiency of 89.2%, a capacity retention of 90.7% after 700 cycles, and pass rigorous safety tests, along with outstanding rate capability and low-temperature performance. This work provides a new paradigm for functional electrolyte design and offers fresh insights into the development of high-safety SIBs with superior electrochemical performance.