Interphase Optimization by Coupling FEC-Involved Solvation Structure with Mixed Salts for High-Performance Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have attracted extensive attention for large-scale energy storage applications. However, the inferior interfacial compatibility triggers severe electrolyte depletion and rapid performance deterioration of SIBs. In this work, we propose an inorganic phase modulation strategy that incorporates multicomponent functional inorganic species via rational electrolyte design to improve the interfacial stability between the electrode and electrolyte. Leveraging the triple-coupling synergy of succinonitrile (SN), sodium difluoro(oxalato)borate (NaDFOB), and sodium hexafluorophosphate (NaPF6), the optimized electrolyte reconstructs the Na+ solvation environment, with weakened Na+–solvent coordination and enhanced Na+–anion interactions in the solvation structure. Beyond the traditional fluoride- and carbonate-based inorganic components, a thin and uniform interphase film enriched with additional nitrides, borides, and phosphates is constructed on the electrode surface. Such a unique interphase configuration effectively mitigates continuous decomposition of solvent molecules, suppresses transition metal dissolution, and boosts Na+ transport kinetics. Consequently, the rationally designed electrolyte exhibits favorable interfacial compatibility toward sodium metal, hard carbon anodes, and cathode materials. More crucially, these enable enhanced capacity retention of the assembled hard carbon||NaNi1/3Fe1/3Mn1/3O2 full cells. This work provides a fundamental insight into interfacial stabilization strategies for developing long-cycle-life SIBs.