Lithiation heterogeneities of graphite according to C-rate and mass-loading: A model study

Abstract

Performance and durability of lithium-ion batteries highly rely on local conditions inside electrodes during operation. In this paper, local physical conditions inside a standard graphite electrode are explored at various C-rate and mass-loading with a physic-based model, validated with electrochemical experiments.The typical equilibrium potential curve of graphite controls strongly the intercalation heterogeneity along thickness and this heterogeneity is maximal for state of charge corresponding to regions of flat equilibrium potential. Indeed, a flat equilibrium potential promotes lithiation disparities along thickness, whereas a variable equilibrium potential enhances a quick return to a homogeneous lithiated electrode. Current and mass loading affect proportionally these heterogeneities, which are linked with a decrease in cell performance. A correlation between heterogeneities and equivalent resistances interpolated from galvanostatic discharge is found. Pathway resistances calculated from simulation outputs indicate preferential locations of intercalation under operation, depending on the difference between the local and global equilibrium potential of the graphite electrode.