Stable sodium metal anode enhanced by advanced electrolytes with SbF3 additive

Abstract

The practical application of sodium metal batteries (SMBs) is hampered due to the inferior interfacial stability between Na metal and conventional electrolytes. Therefore, a high-concentration electrolyte is proposed to solve this issue. However, high viscosity, low ionic conductivity, and unsatisfactory wettability toward the separator need to be overcome. In this study, a localized high-concentration electrolyte (LHCE) is formulated with 1 wt% SbF3 as an interface-stabilized additive to protect the Na metal anode. This reformulated LHCE retains the special coordination structure in HCE with improved wettability and high ionic conductivity. Moreover, the introduction of the SbF3 additive into the LHCE resulted in a bilayer-structured solid electrolyte interface (SEI) including a Na–Sb alloy inner layer and a NaF-rich outer layer on the Na metal. As expected, the Na||Na cells using LHCE + 1 wt% SbF3 show a long cycle lifespan of over 1200 h at 0.5 mA·cm−2 with negligible polarization, and Na||Na3V2(PO4)3 cells exhibit a high capacity exceeding 97 mAh·g−1 at 40C.