Multiple Functional Bonds Integrated Interphases for Long Cycle Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have garnered significant interest as one of the most promising energy suppliers for power grid energy storage. However, the poor electrode/electrolyte interfacial stability leads to continual electrolyte decomposition and transition metal dissolution, resulting in rapid performance degradation of SIBs. In this work, we propose a strategy integrating multiple functional bonds to regulate electrode/electrolyte interphase by triple-coupling of succinonitrile (SN), sodium hexafluorophosphate (NaPF₆) and fluorinated ethylene carbonate (FEC). Theoretical calculation and experiment results show that the solvation structure of Na⁺ and ClO₄ ^- is effectively reconfigured by the solvated FEC, SN and PF₆ ^- in PC-based carbonate electrolyte. The newly developed electrolyte demonstrates increased Na⁺-FEC coordination, weakened interaction of Na⁺-PC and participation of SN and PF₆ ^- anions in solvation, resulting in the formation of a conformal interfacial layer comprising of sodium oxynitrides (NaN_xO_y), sodium fluoride (NaF) and phosphorus oxide compounds (NaP_xO_y). Consequently, a 3 Ah pouch full cell of hard carbon//NaNi_1/3Fe_1/3Mn_1/3O₂ exhibits an excellent capacity retention of 90.4 % after 1000 cycles. Detailed postmortem analysis of interface chemistry is further illustrated by multiple characterization methods. This study provides a new avenue for developing electrolyte formulations with multiple functional bonds integrated interphases to significantly improve the long-term cycling stability of SIBs.