A New Electrolyte Formulation for Securing High Temperature Cycling and Storage Performances of Na‐Ion Batteries

The Na-ion battery is recognized as a possible alternative to Li-ion battery for applications where power and cost override energy density performances. However, the increasing instability of their electrolyte with temperature is still problematic. Thus, a central question remains how to design Na-based electrolytes. Here, we report discovery of a Na-based electrolyte formulation which enlists four additives (vinylene carbonate (VC), succinonitrile (SN), 1, 3-propane sultone (PS) and sodium difluoro(oxalate)borate (NaODFB) in proper quantities that synergistically combined their positive attributes to lead a stable solid electrolyte interphase (SEI) at both negative and positive electrodes surface at 55 °C. Moreover, we rationalized the role of each additive that consists in producing specific NaF coatings, thin elastomers, sulfate-based deposits and so on via combined impedance (EIS) and X-ray photoelectron spectroscopy (XPS). We demonstrated that empirical electrolyte design rules previously established for Li-ion technology together with theoretical guidance is a vital strategy in the quest for better Na-based electrolytes that can be extended to other chemistries. Overall, this finding, which we implement to practical 18650 cells, widens the route to the rapid development of the Na-ion technology based on the Na 3 V 2 (PO 4) 2 F 3 /C chemistry.