Lithium-Ion Transfer at an Electrolyte/Heat-Treated Nongraphitizable Carbon Electrode Interface

To elucidate the kinetics of lithium ions at a nongraphitizable carbon electrode, lithium-ion transfer at the interface between a heat-treated nongraphitizable carbon electrode and a liquid electrolyte was studied by ac impedance spectroscopy. In Nyquist plots at potentials below 0.9 V, a semicircle assigned to charge-transfer resistance due to lithium-ion transfer at the heat-treated nongraphitizable carbon electrode/electrolyte interface was observed in the intermediate frequency region. The value of the resistance was effectively decreased by heat-treatment of the nongraphitizable carbon. The temperature dependence of the resistance showed Arrhenius-type behavior, and the activation energy for lithium-ion transfer was evaluated. Although a high activation barrier of was noted at the untreated nongraphitizable carbon electrode/electrolyte interface for lithium-ion transfer regardless of the electrolyte used, heat-treated nongraphitizable carbon gave a lower activation barrier depending on the electrolyte used. Based on the present results and by considering the structural relaxation of nongraphitizable carbon upon heat-treatment, the rigid structure of nongraphitizable carbon may significantly affect lithium-ion transfer kinetics at a nongraphitizable carbon electrode/electrolyte interface.