Insight into the charge/discharge behaviour of intercalation cathode materials: Relation between delivered capacity and applied rate and analysis of multi-particle intercalation mechanisms

Exploration of the relationships and mechanisms underlying the charge/discharge behaviors of intercalation cathode materials for lithium batteries is mandatory to develop more efficient energy storage devices. Thus, herein, by combining theoretical concepts and experimental evidence, we establish/reestablish a relation/model to justify the charge-discharge behavior of many electrode materials for lithium and sodium ion batteries under a wide range of conditions. Our approach resembles a phase-field model and is correlated with the existence of diffusion regions inside the electrode particles. Regarding the determination of the relation between applied current rate and average obtained capacity (C), we propose that 1/C changes linearly versus the square root of the corresponding rate. This relation was established by previously proposed theoretical models and confirmed herein using experimental data from the literature. Accordingly, we propose an intercalation mechanism based on multi-particle (many-particle) systems, which corroborates previous experimental observations and the validity of the model. The proposed concepts can be used for better understanding the behavior of materials, predicting the C value versus current rate, predicting the fraction of (in)active particles, calculating the optimal cathode mass per collector area, and finally obtaining a criterion to evaluate the performance and rate-capability of cathodes, also allowing a functional comparison.