Memory Effects' Mechanism in the Intercalation Batteries: The Particles' Bipolarization.

To develop energy-storage devices, understanding their charge-discharge behaviors and their underlying mechanisms is mandatory. Memory effect (ME) is among the most important behaviors that should be understood, influencing the batteries' applications. In this paper, the intercalation batteries' ME and their features are justified and explained by employing the particles' bipolarization mechanism. Diffuse regions, located in both sides of the reactant/product phases, turn the particles into dipoles (bipolarized particles) during/after the processes. This bipolarization and subsequent neutralization can explain many charge-discharge behaviors, including the ME. Here, the mechanism explains and justifies all the known features and some aspects of the phenomena which have not been considered so far. According to the proposed mechanism, the aged-neutralized particles react later and in a higher voltage than the fresh-neutralized particles, causing a bump in the curve called the ME. It is the same mechanism that causes the increase in the charge voltage by increasing the open-circuit voltage rest time. Our experiments sufficiently verified the mechanism. In the paper, impacts of the average particle size, relaxation/rest time, discharge cutoff voltage of the memory-writing cycle (MWC), Li-mobility kinetics, current rate, state of charge, depth of discharge of the MWC, boundaries of the charge-discharge curve, and so forth are considered, and their influences on the ME are explained. This mechanism sheds light on the relevant characteristics of the batteries and helps design, tune, control, and engineer the behaviors.