Capacity fading of lithiated graphite electrodes studied by a combination of electroanalytical methods, Raman spectroscopy and SEM

We present herein Raman spectroscopy and SEM characterizations of composite graphite electrodes in conjunction with classical electroanalytical characterizations (SSCV and EIS) during prolonged cycling. During cycling, graphite particles crack into smaller pieces that are less oriented than the original platelets, with the possible filling of the cracks thus formed by the reduction products of the electrolyte solution. In addition, the average crystalline size (estimated by Raman spectroscopy) decreases as cycling progresses. The borders between the crystallites may possess dangling bonds and generally contain low-energy (or hollow) sites for irreversible interaction with Li-ions and solution species. The redistribution between the hollow and the shallow sites (i.e. the site for reversible Li-ion storage) occurring during electrode cycling is responsible for the moderate decrease of the reversible capacity of graphite electrodes observed during prolonged cycling.