Insight Into Sulfur‐Containing Additive to Boost Anti‐Oxidation Ability of the Ether‐Based Electrolyte for Sodium‐Ion Full Batteries

Abstract Ether‐based electrolytes are considered as promising candidates for sodium‐ion batteries (SIBs) due to their high ionic conductivity and good compatibility with hard carbon (HC) anode. However, they suffer from poor anti‐oxidative ability with unstable cathode electrolyte interface, inducing successive electrolyte decomposition and rapid capacity fading. Herein, the sulfur‐containing additive (1,3‐propanediol cyclic sulfate, PCS) is introduced to boost the stability of the electrode‐electrolyte interface (EEI) in ether‐based electrolyte. PCS largely participates in the inner Na + sheath, causing more diglyme (G2) molecules and fewer PF 6 ‐ anions to occupy the inner Na + solvation sheath, avoiding the decomposition of G2 molecules at high operation voltage. Moreover, PCS is beneficial for simultaneously constructing thin and robust sulfur‐containing EEI on both Prussian blue (PB) cathode and HC anode, maintaining the structural stability of PB and alleviating the dissolution of transition metals. These enable PB||HC pouch cells to deliver a capacity retention of 60.3% after 400 cycles, significantly higher than the 32.1% in PCS‐free electrolytes. This work discloses the underlying mechanism of PCS to evoke the anti‐oxidation ability of ether‐based electrolyte and provides a promising method for realizing advanced sodium‐ion full cells.