Suppression of Co(II) ion deposition and hazards: Regulation of SEI film composition and structure

Despite the presence of LiF components in the solid electrolyte interphase (SEI) formed on the graphite anode surface by conventional electrolyte, these LiF components primarily exist in an amorphous state, rendering them incapable of effectively inhibiting the exchange reaction between lithium ions and transition metal ions in the electrolyte. Consequently, nearly all lithium ions within the SEI film are replaced by transition metal ions, resulting in an increase in interphacial impedance and a decrease in stability. Herein, we demonstrate that the SEI film, constructed by fluoroethylene carbonate (FEC) additive rich in crystalline LiF, effectively inhibits the undesired Li⁺/Co²⁺ ion exchange reaction, thereby suppressing the deposition of cobalt compounds and metallic cobalt. Furthermore, the deposited cobalt compounds exhibit enhanced structural stability and reduced catalytic activity with minimal impact on the interphacial stability of the graphite anode. Our findings reveal the crucial influence of SEI film composition and structure on the deposition and hazards associated with transition metal ions, providing valuable guidance for designing next-generation electrolytes.