Stress development due to surface processes in graphite electrodes for Li-ion batteries: A first report

We report for the first time the development of irreversible compressive stresses in graphitic carbon electrodes during cycling in a Li-ion battery. The CVD grown c-axis oriented graphitic carbon thin film electrodes show that significant irreversible stresses develop in the first cycle, and then decrease with increasing number of cycles. The net irreversible compressive stress is roughly a factor of 4 higher than the actual Li-intercalation induced reversible compressive stress. A major fraction of the irreversible stress developed at potentials higher than the Li-intercalation potential, starting from ∼1.1 V and increasing in intensity from ∼0.75 V. Also, the variation of the irreversible stress with number of cycles follows very closely the variation of the irreversible capacity with cycle number. Measurements on carbon films with different thicknesses show that the irreversible stress is primarily a surface phenomenon. These stresses were also largely absent in films coated with a thin (0.5 nm) Al2O3 layer. Analysis of all of these observations indicates that SEI layer formation is a primary cause of the irreversible stress, along with some likely contribution from solvated Li-ion co-intercalation. The magnitude of these stresses is large enough to have a significant impact on the performance and cycle life of graphitic carbon electrodes.