A theoretical approach to evaluate and understand the electrical properties of the electrode materials of batteries

Abstract

A novel evaluation approach for evaluating the electrical properties of electrode materials for batteries (and the other similar electrochemical systems) is proposed, assuming the reacted–unreacted structure interface acts as a semiconductor junction. Density of state (DOS) diagrams, calculated by different methods of density functional theory (DFT), for practically important case studies are used to explain the approach. The approach allocates a value for each assessed electrode material, providing a semi-quantitative criterion of the rate-capability to allow comparisons between materials. Important cathode materials utilized in Li-ion batteries were considered as the case studies, namely LiCoO₂, LiFePO₄, LiFeSO₄F, and Li₂FeSiO₄. Our approach considers simultaneously the configuration of the intercalated–deintercalated structures with respect to each other and also the electric-field direction. The reacted and unreacted structures were electrically joined; therefore, to complete the electrical conduction process, electric-charge carriers move across these two structures. In the intercalation batteries, electrons always transfer from the deintercalated to the intercalated structure, and so electrons–holes also move from the intercalated to the deintercalated structure. The approach is inclusive while it simultaneously considers the band gaps, DOS bands’ configurations, semiconductor junction features, and configuration of the structures regarding the electric-field direction in the cell. It helps to understand the underlying mechanisms as well as aid the justification, prediction, and design of relevant electrochemical systems.