Modeling Diffusion-Induced Mechanical Degradation in Dual-Graphite Battery Cathodes: Application to PF6− Intercalation

Abstract

In this work, we propose a finite element framework to analyze the diffusion-induced mechanical degradation in graphite active particles (APs) due to bulky anion intercalation in dual-graphite batteries (DGBs). Finite strain formulation is considered to account for the large volume expansion that typically occurs in graphite cathodes. The proposed model considers chemo-mechanical coupling, including the effect of the particle volume changes due to the penetration of ions and its eventual fracture, modeled using a phase-field fracture approach. To account for the stochastic nature of graphitic microstructures, the mechanical properties are described by means of a Weibull distribution function. Our model is able to reproduce realistic cracking patterns that take place during the charging and discharging processes in APs. Finally, we use the model to simulate different galvanostatic charging rates and particle sizes to provide insight into the mechanical degradation of graphite APs during PF 6 − intercalation. We use this information to provide design rules for improved graphite cathodes or better operation strategies in DGBs.