New approaches to consider electrical properties, band gaps and rate capability of same-structured cathode materials using density of states diagrams: Layered oxides as a case study

Abstract

Density functional theory (DFT) is a useful and important tool in chemistry and physics to predict and understand solid-state material properties. The important topics which have been massively studied by DFT are intercalation electrodes (namely Li-ion and Na-ion) in batteries. To evaluate electrical properties of the battery cathode materials and other analogous systems, we propose here a noble approach in DFT study, challenging previous methods for reporting of band-gap values and opening new evaluation land space. We introduce here new concepts in calculated band-gap by DFT, calling them extrinsic-like and intrinsic-like band gap. Also, we address a noble quantitative approach to compare rate-capability of cathode materials (at least with the same structure) using density of states (DOS) diagrams. The usage of lithiated-delithiated structure junction, aligning Fermi levels, and difference between valance band maximums (or conduction band minimums) is the basic of this comparison. In this study, layered oxide cathode materials for lithium-ion batteries were considered as important pioneer case studies. In this basis, a new justification for the well-known lower rate-capability of LiNiO2 and its derivations, in comparison with LiCoO2, is proposed.