Concentration Dependent Chemical Expansion in Lithium Ion Battery Cathode Particles

Abstract

In this work, the effect of the concentrationdependent chemicalexpansion coefficient, خ², on the chemoelastic field in lithiumion cathode particles is examined. To accomplish this, an isotropic linearelastic model is developed for a single idealistic particle subjected to potentiostaticdischarge and charge conditions. It is shown that خ² can be a key parameter in demarcating the chemostress–strain state of the cathode material undergoing nonlinear volumetric strains. As an example, such strains develop in the hexagonaltomonoclinicphase region of LixCoO2 (0.37 ≤ x ≤ 0.55) and, subsequently, the corresponding خ² is a linear function of concentration. Previous studies have assumed a constant value for خ². Findings suggest that the compositiongenerated chemoelastic field that is based on a linearخ² dramatically affects both the interdiffusion and the mechanical behavior of the LixCoO2 cathode particle. Because the chemoelastic phenomena emanate in a reciprocal fashion, the resulting linear خ²based hydrostaticstress gradients significantly aid the diffusion of lithium. Thus, diffusion is accelerated in either electrochemical process that the cathode material undergoes.