Abstract
Structural instability due to intercalation-induced stresses in electrode materials is one of the key degradation mechanisms of Li-ion batteries. Fragmentation of material degrades structural integrity and electrical resistance, and also accelerates harmful side reactions. In situ experiments are the appropriate approach to investigate the actual time dependent nature of behavior changes of an electrode material while it is charged and discharged. In the current work, a unique in situ electrochemical atomic force microscopy (ECAFM) measurement is made on samples of cylindrical shape, which are micro-machined by focused ion beam (FIB) microscopy. This pre-defined geometry allows the exclusion of secondary, non-active materials from the electrochemically active material as well as the removal of any vagueness coming from the irregular geometry of particles. Also, the experimental results are used to validate a proposed coupled electrochemical and mechanical model for determination of the stress-strain state of active electrode material during electrochemical cycling. The results produced using the model correlate the experimental data rather well. The combined results reveal the key effects of the geometry, kinetics, and mechanics of electrode materials on the stress-strain state, which is a barometer of structural stability of a material.
