Effects of Electrolyte Concentration on Surface Film Formation on Graphite in Ethylene Carbonate-Based Solutions

The physicochemical properties of a surface film generated on a graphite surface were greatly dependent on the concentration of the electrolyte solution. Cyclic voltammetry results obtained using four ethylene carbonate- based solutions of different electrolyte (i.e., LiN(SO2C2F5)(2)) concentrations showed that the amount of irreversible current used to generate the surface film between 0.8 and 0.1 V decreased upon increasing the electrolyte concentration. Transmission electron microscopy results revealed that the thickness and morphology of the surface film were greatly affected by the concentration of the electrolyte solution. In addition, electrochemical impedance spectroscopy revealed that the resistance of the surface film was also affected by the electrolyte concentration. These results therefore indicated that both the chemical and physical properties of the surface film were affected by the concentration of the electrolyte solution.