Effect of a Size-Dependent Equilibrium Potential on Nano-LiFePO4 Particle Interactions

Abstract

Several electrode materials, such as LiFePO4, have a thermodynamic driving force toward phase separation. However, phase separation inside the electrode particles can be suppressed when the particles are nanosized. In this case, each individual particle remains monophasic, but phase separation can occur between particles via Li redistribution. Here, we investigate the dynamics of Li redistribution when the equilibrium potential is size dependent. We perform simulations of the charge-discharge cycle in a two-particle cell and in a 65-particle agglomerate. The difference in particle equilibrium potentials can lead to an asymmetry between lithiation and delithiation of an electrode, in which the order of transformation of the particles during lithiation and delithiation is reversed. This effect is more significant at low currents but almost negligible at high currents.