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 (NaPF) and fluorinated ethylene carbonate (FEC). Theoretical calculation and experiment results show that the solvation structure of Na and ClO is effectively reconfigured by the solvated FEC, SN and PF in PC-based carbonate electrolyte. The newly developed electrolyte demonstrates increased Na-FEC coordination, weakened interaction of Na-PC and participation of SN and PF anions in solvation, resulting in the formation of a conformal interfacial layer comprising of sodium oxynitrides (NaNO), sodium fluoride (NaF) and phosphorus oxide compounds (NaPO). Consequently, a 3 Ah pouch full cell of hard carbon//NaNiFeMnO 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.