Kinetics of electrochemically induced phase transitions in ion-insertion electrodes and the chemical diffusion coefficient

Abstract

In this paper, we report on the study, by numerical simulations, of the effect of slow external kinetics steps on the dynamics of electrochemically induced phase transitions in ion-insertion electrode materials. Two alternative kinetics steps such as slow interfacial ion transfer and slow small droplet formation were chosen to evaluate the errors in the calculation of the chemical diffusion coefficient, D, induced by incorrect application of non-equilibrium differential intercalation capacitances, C dif. Comparison between simulated and experimental curves shows that for a moderate limitation of phase transition by Butler–Volmer kinetics, the exact values D can be obtained up to the composition of the binodal point, and then errors increase towards the spinodal domain. Within the spinodal domain, the potential dependence of D obtained formally by application of the Cottrellian model, entirely relates to the potential dependence of C dif. The relevant description of phase transition dynamics in this region should include consideration of moving boundary between the coexisting phases formed via coalescing of growing nuclei.