Understanding the Surface Film Formation on Si Electrodes in Lithium Secondary Batteries with Atomic Force Microscopy

The solid electrolyte interphase formation on the negative electrodes of lithium secondary batteries has been considered as one of the principal issues limiting the performance of batteries. Si is an attractive electrode material for improving energy density of lithium secondary batteries because of its high specific theoretical capacity (4200 mAh g^-1). However, solid electrolyte interphase formation on Si-based electrodes have not been clearly understood in spite of its significance. Herein, the solid electrolyte interphase formation on Si electrodes in electrolyte solutions containing ethylene carbonate or propylene carbonate was investigated by using in-situ atomic force microscopy. Large and irreversible capacity fade in SiO electrodes was confirmed in both electrolyte solutions through cyclic voltammetry and charge/discharge testing. The in-situ atomic force microscopy results indicated that the decomposition reaction occurred in the ethylene carbonate-based electrolyte solution at a potential of ~0.68 V, while the lithium alloying reaction occurred below 0.25 V during the first reduction process. The decomposition reaction was more vigorous and occurred at a higher potential in the propylene carbonate-based electrolyte solution, resulting in the formation of a thick solid electrolyte interphase film. These results suggest that the solid electrolyte interphase formation on Si electrodes is strongly influenced by the composition of the electrolyte solution.