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 the Li-ion battery for applications where power and cost override energy density performance. However, the increasing instability of their electrolyte with temperature is still problematic. Thus, a central question remains how to design Na-based electrolytes. Here, the discovery of a Na-based electrolyte formulation is reported which enlists four additives (vinylene carbonate, succinonitrile, 1,3-propane sultone, and sodium difluoro(oxalate)borate) in proper quantities that synergistically combine their positive attributes to enable a stable solid electrolyte interphase at both negative and positive electrodes surface at 55 °C. Moreover, the role of each additive that consists in producing specific NaF coatings, thin elastomers, sulfate-based deposits, and so on via combined impedance and X-ray photoelectron spectroscopy is rationalized. It is demonstrated that empirical electrolyte design rules previously established for Li-ion technology together with theoretical guidance is vital in the quest for better Na-based electrolytes that can be extended to other chemistries. Overall, this finding, which is implemented to 18 650 cells, widens the route to the rapid development of the Na-ion technology based on Na3V2(PO4)2F3/C chemistry