A dual-functional electrolyte additive for stabilizing the solid electrolyte interphase and solvation structure to enable pouch sodium ion batteries with high performance at a wide temperature range from-30 ° C to 60 ° C

An electrolyte containing a sodium difluorophosphate (NaDFP) dual-functional additive is developed to enhance the temperature performance of NaNi 0.33 Fe 0.33 Mn 0.33 O 2 (NFM)/hard carbon (HC) sodium -ion batteries (SIBs). The addition of NaDFP in the electrolyte not only induces solid electrolyte interphases (SEIs) and cathode electrolyte interphases with excellent properties on the anode and cathode surfaces but also optimizes of the solvation structure of sodium ions, resulting in a better cycle stability of NFM/HC SIBs over a wide temperature range from -30 degrees C to 60 degrees C. In addition, high capacity retentions of 85 % after 700 cycles at 25 degrees C, 90 % after 150 cycles at -10 degrees C and 90 % after 150 cycles at 45 degrees C are achieved, respectively. And those common problems such as gas generation and sodium evolution of pouch NFM/HC SIBs are also effectively relieved, indicating the promising application prospect of NaDFP additive in the functional electrolyte of NFM/HC SIBs.