Concentration-Dependent Chemical Expansion in Lithium-Ion Battery Cathode Particles

In this work, the effect of the concentration-dependent chemical-expansion coefficient, β, on the chemo-elastic field in lithium-ion cathode particles is examined. To accomplish this, an isotropic linear-elastic model is developed for a single idealistic particle subjected to potentiostatic-discharge and charge conditions. It is shown that β can be a key parameter in demarcating the chemo-stress–strain state of the cathode material undergoing nonlinear volumetric strains. As an example, such strains develop in the hexagonal-to-monoclinic-phase region of Li_xCoO₂ (0.37 ≤ x ≤ 0.55) and, subsequently, the corresponding β is a linear function of concentration. Previous studies have assumed a constant value for β. Findings suggest that the composition-generated chemo-elastic field that is based on a linear-β dramatically affects both the interdiffusion and the mechanical behavior of the Li_xCoO₂ cathode particle. Because the chemo-elastic phenomena emanate in a reciprocal fashion, the resulting linear β-based hydrostatic-stress gradients significantly aid the diffusion of lithium. Thus, diffusion is accelerated in either electrochemical process that the cathode material undergoes.