A new possible mechanism of lithium insertion and extraction in low-temperature pyrolytic carbon electrode

Abstract

Lithium/carbon (Li/C) cells have been assembled with phenolic resin, pyrolyzed at 650°C for 2 h, as the working electrodes. By measuring the Raman spectra of the carbon electrodes discharged and charged to various equilibrium voltages and the discharge/charge curves of the Li/C cell, it is found that the intensity of the G-band of the discharged/charged pyrolytic carbon electrode in the Raman spectrum decreases to zero with decreasing discharge voltage and then gradually recovers with increasing charge voltage. However, the intensity of the D-band remains unchanged during the discharge/charge processes. This spectroscopic behavior is quite different from that of the other forms of carbonaceous electrodes. Based on the analysis of the characteristic Raman spectra and the discharge/charge curves of the pyrolytic carbon electrodes, a breaking-recovering model of the weak. C· · ·H bond within a graphene layer is suggested for the lithium insertion and extraction processes in the low-temperature pyrolytic carbon electrodes.