WITHDRAWN: A semi-quantitative approach to evaluate electrical rate-capability and conductivity of polyanion cathode materials of intercalation batteries using DOS diagrams

Abstract

Abstract Understanding relevant mechanisms and properties of the electrochemical energy-storage systems are prerequisites for their development. Here, we propose new approaches to evaluate rate-capability, band-gaps and electrical properties of cathode materials of intercalation batteries. As case studies and to perform comparisons, three important Fe-based polyanion cathodes (i.e., LiFePO4, Li2FeSiO4 and LiFeSO4F) are assessed here. To evaluate the density of state (DOS) diagrams, spin-up and down should be considered separately, because the spin is an inherent property of electrons. Establishing rate-capability criterion, Fermi levels of intercalated-deintercalated pair should be aligned, then the difference between their maximum/minimum intrinsic valence/conduction bands (ΔVB/ΔCB) presents the criterion for the rate-capability evaluation (considering spin up and down separately). Consequently, the lowest obtained ΔVB/ΔCB up/down is the governing value, using for the comparison. Regarding the band-gap (BG) evaluations, intrinsic/extrinsic-like ban gaps (ILBG/ELBG) are assessed. For an individual structure, the lower value among calculated spin-up and spin-down BGs should be taken. For BG of joint pairs (intercalated-deintercalated), the higher BG among intercalated and deintercalated structures and also the lower BG among the spins determine the governing BG. According to experimental observations in literature, consideration of the proposed rate-capability criterion leads to the more realistic and unisonous conclusion than consideration of BG of either individual structures or even pair joints.