Memory Effects’ Mechanism in the Intercalation Batteries: The Particles’ Bipolarization

Abstract

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.

Evaluation of MXene Ti3C2 Charge–Discharge Behaviors as an Electrode Material for Intercalation Batteries

“…In turn, it causes breaking or shifting the curves upward. Accordingly, concave upward may mean deterioration of the active particles, i.e., decreasing APR, or changing undesired [8a] (bipolarizing [8d,11] ) phases [8a‐c] . In contrast, concave downward means increasing APR by cycling or enhancement of rate.…”

“…We have established that APR can be estimated by dividing C max to . On this basis, we had assumed that the amount of undesired [8a] (bipolarizing [8d,11] ) phases is neglectable [8a‐c] . The APR amount should be considered to be constant as far as behavior of the electrode follows almost a straight line in the diagrams [8b] …”

Origin of electrochemical voltage range and voltage profile of insertion electrodes

“…We have proposed that there should be main reaction phases and their concentration gradient region would be formed between the main phases or in the interface, originating voltage deviation from its ideal amount. Accordingly, a number of important phenomena and observations cannot be clarified without considering this concept, namely non-ideal voltage behavior 21 , bipolarization mechanism 11 , voltage hysteresis 11 , first cycle over voltage 11 , memory effect 22 , boundaries of charge/discharge curvatures 12 , voltage overshooting 23 , etc. Nevertheless, in the mentioned models, origin of the voltage-range and the corresponding main phases have not been discussed.…”

Normalization of charge/discharge time vs. current rate diagrams for rechargeable batteries

“…9 To find an effective and powerful mechanism for explaining the observed phenomena in the intercalation batteries, we have proposed a diffusion-based semi-empirical model. 10 The model is capable of explaining many observed charge/discharge behavior phenomena, including the memory effect, [11][12][13][14] etc.…”

“…Recently, we proposed another type of diagram 12 derived from the initial equations of the parent model. 21 This type of diagram uses charging/discharging time instead of the obtained capacity.…”