Thermodynamics of Spinel-like Cation Partial Ordering in Ultrahigh Power and Energy Density Li-Ion Batteries for Fast-Charging Electric Vehicles

Abstract

Recently, a class of new materials exhibiting partial spinel-like cation order, but with excess Li and excess cation content was found to combine very high rate performance with high energy density [1]. Such spinels with a cation to anion ratio higher than 3 are unusual as it requires the face sharing of some tetrahedral and octahedral cations. In this presentation we will report on the ab-initio modeling of the metastable cation arrangements in these lithium manganese oxyfluorides that are responsible for the high-rate performance. The high dimensional configurational space of the materials is described by the cluster-expansion technique and parameterized with multiple hundreds of DFT calculations.Local, atomic-scale features, such as Li-Mn dumbbell formation, antisite defects, and interstitial defects giving rise to face-sharing cations which are challenging to resolve with state-of-the-art diffraction techniques are possible to directly evaluate in our computational approach. We present a computational analysis on how cation excess in spinel-like materials is accommodated and how local cation perturbations ultimately influence short-range order and bulk Li transport. Our understanding of how features in cation-excess spinel-like Li-Mn-O-F materials influence their high rate capabilities may motivate and accelerate design of other high-performance, fast-charging battery materials.[1] Ji, H., Wu, J., Cai, Z. et al. Ultrahigh power and energy density in partially ordered lithium-ion cathode materials. Nat Energy 5, 213–221 (2020).