Regulating SEI Components of Sodium Anode via Capturing Organic-Molecule Intermediates in Ester-Based Electrolyte.

Abstract

Highly reversible sodium metal anodes are still regarded as a stubborn hurdle in ester-based electrolytes due to the issue of uncontrollable dendrites and incredibly unstable interphase. Evidently, a strong protective film on sodium is decisive, while the quality of the protective film is mainly determined by its components. However, it is challenging to actively adjust the expected components. This work can regulate the solid electrolyte interphase (SEI) components by introducing a functional electrolyte additive (2-chloro-1,3-dimethylimidazoline hexafluorophosphate (CDIH, namely CDI+ +PF6 - )) into FEC/PC ester-based electrolyte. Specifically, the chloride element in the CDI+ can easily react to form a NaF/NaCl-rich SEI together with the decomposition products of FEC; then the CDI+ without chlorine as a gripper to capture the organic-molecule intermediates generated during FEC decomposition to greatly reduce the content of unstable organic components in SEI, which can be confirmed by molecular dynamic simulation and experiment. Eventually, a highly reversible Na deposition behavior can be delivered. As expected, under the action of CDIH additives, the Na||Na symmetrical cell performs an excellent long-term cycling (>800h, 0.5mA cm-2 -0.5 mAh cm-2 ) and rate performance (0.5-4mA cm-2 ). Furthermore, the Na||PB full cell exhibits the outstanding electrochemical performance with small polarization.