Lithium-ion transfer at an electrolyte/non-graphitizable carbon electrode interface Original Research Article

To elucidate the lithium-ion kinetics at a non-graphitizable carbon electrode, lithium-ion transfer at the interface between a non-graphitizable carbon electrode and a liquid electrolyte was studied by AC impedance spectroscopy. Non-graphitizable carbon prepared at 2273 K was used as a working electrode. After potential cycling between 3.0 and 0 V, Nyquist plots gave a semi-circle at 3.0 V vs. Li/Li+. At this potential, no lithium-ion insertion and extraction occurred, and therefore the semi-circle is due to surface film resistance. At potentials below 0.9 V, impedance spectra gave two semi-circles. The semi-circle in the middle to lower frequency region can be assigned to the charge transfer resistance due to lithium-ion transfer at the non-graphitizable carbon electrode/electrolyte interface. The temperature-dependence of the resistance showed Arrhenius-type behavior and gave an activation energy of about 70 kJ mol−1 regardless of the electrolyte used, indicating that a high activation barrier exists at the non-graphitizable carbon electrode/electrolyte interface for lithium-ion transfer. Non-graphitizable carbon treated by hot isostatic pressing (HIP) gives a smaller activation energy of about 60 kJ mol−1. Therefore, the structure of non-graphitizable carbon significantly affects lithium-ion transfer kinetics at a non-graphitizable carbon electrode/electrolyte interface.