Modeling lithium plating onset on porous graphite elec- trodes under fast charging with hierarchical multiphase porous electrode theory

Lithium plating during fast charging of porous graphite electrodes in lithium-ion batteries accelerates degradation and raises safety concerns. Predicting lithium plating is challenging due to the close redox potentials of lithium reduction and intercalation, obscured by the nonlinear dynamics of electrochemically driven phase separation in hierarchical pore structures. To resolve dynamical resistance of realistic porous graphite electrodes, we introduce a model of porous secondary graphite particles to the multiphase porous electrode theory (MPET), based on electrochemical nonequilibrium thermodynamics and volume averaging. The resulting computational framework of "hierarchical MPET" is validated and tested against experimental data over a wide range of fast charging conditions and capacities. With all parameters estimated from independent sources, the model is able to quantitatively predict the measured cell voltages, and, more importantly, the experimentally determined capacity for lithium plating onset at fast 2C to 6C rates. Spatial and temporal heterogeneities in the lithiation of porous graphite electrodes are revealed and explained theoretically, including key features, such as idle graphite particles and non-uniform plating, which have been observed experimentally.