Kinetics of Lithium Ion Transfer at the Interface between Graphite and Liquid Electrolytes: Effects of Solvent and Surface Film

The kinetics of lithium ion transfer at an interface between graphite and liquid electrolyte was studied by ac impedance spectroscopy. Using highly oriented pyrolytic graphite (HOPG) as a model electrode, we evaluated the activation energies of the interfacial lithium ion transfer from the temperature dependences of the interfacial conductivities. When a binary electrolyte consisting of LiClO4 dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) (1:1 by volume) was used, the activation energy of the interfacial lithium ion transfer was 58 kJ mol−1, while an electrolyte consisting of LiClO4 dissolved in DMC gave an activation energy of 40 kJ mol−1. A calculation with the density functional theory clarified that the solvation ability of EC is higher than that of DMC. Therefore, we concluded that the activation energies of the interfacial lithium ion transfer at graphite reflected the energies for the desolvation of lithium ion from the solvent molecule. Furthermore, the activation energies of the interfacial lithium ion transfer varied in the presence of different surface films (solid electrolyte interphase, SEI). These results suggest that the kinetics of the interfacial lithium ion transfer at graphite is influenced by the compositions of SEI films as well as the desolvation of lithium ion from solvent molecules.