In Situ AFM Imaging of Surface Phenomena on Composite Graphite Electrodes during Lithium Insertion

Abstract

The behavior of composite graphite electrodes used as anodes in Li-ion batteries, in repeated lithium intercalation−deintercalation processes, largely depends on the solution's composition. Failure mechanisms of graphite electrodes were studied in selected solutions using in situ imaging by atomic force microscopy. Of special interest is the stable behavior of lithiated graphite electrodes in ethylene carbonate solutions, while in solutions of a very similar solvent, propylene carbonate (PC), lithiated graphite electrodes fail. The morphological studies reported herein seem to confirm that the major failure mechanism of graphite electrodes in PC solutions involves cracking of the particles and electrical isolation of most of the active mass by surface films, rather than a massive exfoliation of the graphite particles due to cointercalation of solvent molecules. Cracking of the graphite particles during cathodic polarization depends on the crevices that originally exist in some types of graphite particles, especially in synthetic materials, and is promoted by gas formation within the crevices, due to the reduction of solvent molecules.