Examination of Graphite Particle Cracking as a Failure Mode in Lithium-Ion Batteries: A Model-Experimental Study

Abstract

Capacity fade in lithium-ion batteries remains an area of active research, with failure of the graphite anode thought to be an important contributor. While the formation of the solid electrolyte interphase and the subsequent loss of cyclable lithium have been well studied, mechanical degradation remains an area where ambiguity remains. While there appears to be little experimental evidence that suggest that macroscopic particle cracking occurs, mathematical models have suggested that this phenomenon is likely. The goal of this paper is to clarify this ambiguity by combining experimental cycling, mathematical stress modeling, and post-mortem microscopy. We experimentally determine an average diffusion coefficient of lithium in graphite using a thin-layer electrode and use this information in a diffusion-induced stress model. Our results suggest that cracking is not likely during lithiation due to the proximity of equilibrium potential to the cutoff potential. On delithiation, at 25°C, even at 30 C rate cracking is unlikely while at −10°C, a rate of 10 C can lead to particle cracking. By extrapolating the results of the thin-layer electrode to a thick porous electrode, we found that graphite cracking is unlikely to occur during typical vehicle operations.