Tailored Ordering Enables High-Capacity Cathode Materials

Abstract

Novel Li-ion battery cathode materials with high capacity and greater compositional flexibility are essential for the growing electric vehicle market. Cathode structures with cation disorder were once considered suboptimal, but recent demonstrations have highlighted their potential in Li_{1 + x}M_{1 − x}O₂ chemistries with a wide range of metal combinations M. By relaxing requirements of maintaining ordered Li diffusion pathways, countless multi-metal compositions in LiMO₂ may become viable, aiding the quest for high-capacity cobalt-free cathodes. A challenge presented by this freedom in composition space is designing compositions that possess specific, tailored types of both long- and short-range orderings, which can ensure both phase stability and Li diffusion. Ordering design frameworks are proposed based on computational ordering descriptors, which in tandem with low-cost heuristics and elemental statistics can be used to simultaneously achieve compositions that possess favorable phase stability as well as configurations amenable to Li diffusion. Utilizing this computational framework, accompanied by illustrative synthesis and characterization experiments, we not only demonstrate the design of LiCr_0.75Fe_0.25O₂, showcasing initial charge capacity of 234 and 320 mAhg⁻¹ in its 20% Li-excess variant Li_1.2Cr_0.6Fe_0.2O₂, but also present the elemental ordering statistics for 32 elements, informed by one of the most extensive first-principles studies of ordering tendencies.