Activity correction on electrochemical reaction and diffusion in lithium intercalation electrodes for discharge/charge simulation by single particle model

The activity correction for the electrochemical reaction and diffusion of lithium in the intercalation electrodes where structurally phase transition occurs during discharge and charge processes was examined. The equilibrium potentials for the lithium intercalation electrodes were represented successfully by the Nernst equation with the activity correction, which was expressed by the activity coefficient models for non-ideal behavior in LiCoO2 and mesocarbon-microbeads (MCMB) electrodes. Particularly for the LiCoO2 electrode, the NRTL model with the heterogeneous treatment was found to be suitable to describe accurately the concentration dependence of equilibrium potentials and phase transition in the electrode. Thereby, we formulated the particle-scale model by using the activity correction with the heterogeneous treatment for the diffusion of lithium in the intercalated electrodes and the electrochemical reaction on the surface of electrode particles in order to reproduce the discharge/charge voltage profile. In the heterogeneous treatment, we considered that the effective diffusivity and electrochemical reaction rate in coexisting region of two different phases for LiCoO2 electrode were able to be calculated by a linear function of lithium concentration. It was observed that the activity correction and heterogeneous treatment improved the prediction accuracy for the particle-scale diffusion model coupled with the electrochemical reaction model.