Kinetics of Lithium-Ion Transfer at the Interface between Li0.35La0.55TiO₃ and Binary Electrolytes

The kinetics of lithium-ion transfer at a Li 0.35 La 0.55 TiO 3 (LLT)/liquid electrolyte interface were investigated by four-probe ac impedance spectroscopy. In Nyquist plots for a system consisting of Li/electrolyte/LLT/electrolyte/Li, two semicircles were observed at high- and midfrequency regions and were attributed to grain-boundary resistance in LLT and interfacial resistance between LLT and the liquid electrolyte. The activation energies of interfacial lithium-ion transfer were evaluated from the temperature-dependence of interfacial conductivities at the LLT/liquid electrolyte. When binary electrolytes consisting of LiClO 4 dissolved in mixtures of ethylene carbonate (EC) and dimethyl carbonate (DMC) of given volume ratios were used, the activation energies were around 50 kJ mol −1 . However, an electrolyte without EC (LiClO 4 /DMC) gave an activation energy of 32 kJ mol −1 . Since a theoretical calculation clarified that the solvation ability of EC is higher than that of DMC, the activation energies reflected energies for the desolvation of lithium-ion from solvent during interfacial lithium-ion transfer. Another important result is that the activation energies of interfacial lithium-ion transfer were almost the same (ca. 50 kJ mol −1 ) in EC:DMC (1:1 by vol) and EC:DMC (1:9 by vol). Furthermore, Raman spectra of EC:DMC binary electrolytes show that there is a dramatic difference in the solvation numbers of EC molecules per lithium-ion between EC:DMC (1:1 by vol) and EC:DMC (1:9 by vol). These results indicate that the desolvation of lithium-ion from the last solvent molecule is the rate-determining step in interfacial lithium-ion transfer.