Large hysteresis during lithium insertion into and extraction from high-capacity disordered carbons

Perylene-based disordered carbon (PBDC) heat-treated at 550 degrees C for anodes in Li-ion cells showed large hysteresis and a high reversible capacity of 800 mAh/g. The hysteresis was analyzed by polarization and impedance measurements. The overpotential during lithium extraction increased markedly in the range of open-circuit potential, 0.5-1 V vs Li/Li+. The impedance spectra of PBDC during lithium insertion were significantly different from those during extraction. The charge-transfer resistance for lithiated PBDC during extraction above 0.5 V was much larger than that for the PBDC during insertion. The chemical diffusion coefficient of lithium, D-Li of PBDC during lithium insertion decreased almost linearly from 5 x 10(-10) to 3 x 10(-12) cm(2) s(-1) with increasing lithium storage capacity. The values of D-Li during lithium extraction above 0.5 V were much smaller than those during insertion. The large hysteresis was due to the large charge-transfer resistance and the slow diffusion of lithium during lithium extraction from the fully lithiated PBDC. The large charge-transfer resistance during lithium extraction has been interpreted as the rectification of lithiated PBDC, which is similar to that of n-type semiconductors under anodic polarization.