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

In this work, the effect of the concentration-dependent chemical-expansion coefficient, b, 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 b 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 LixCoO2 (0.37 x 0.55) and, subsequently, the corresponding b is a linear function of concentration. Previous studies have assumed a constant value for b. Findings suggest that the composition-generated chemo-elastic field that is based on a linear-b dramatically affects both the interdiffusion and the mechanical behavior of the LixCoO2 cathode particle. Because the chemo-elastic phenomena emanate in a reciprocal fashion, the resulting linear b-based hydrostatic-stress gradients significantly aid the diffusion of lithium. Thus, diffusion is accelerated in either electrochemical process that the cathode material undergoes. [DOI: 10.1115/1.4027833]