Tailored ordering enables high-capacity cathode materials

TL;DR

This paper introduces a computational framework for designing high-capacity, cobalt-free Li-ion battery cathodes by tailoring cation orderings, validated through synthesis and characterization of new materials with promising electrochemical performance.

Contribution

The study develops a novel ordering design framework combining computational descriptors, heuristics, and elemental statistics to guide the creation of stable, Li-diffusive cathode materials.

Findings

Successful synthesis of LiCr₀.₇₅Fe₀.₂₅O₂ with 234 mAhg⁻¹ capacity

Li₁.₂Cr₀.₆Fe₀.₂O₂ achieves 320 mAhg⁻¹ capacity in Li-excess form

Presented elemental ordering statistics for 32 elements based on extensive first-principles studies

Abstract

Newly designed Li-ion battery cathode materials with high capacity and greater flexibility in chemical composition will be critical for the growing electric vehicles market. Cathode structures with cation disorder were once considered suboptimal, but recent demonstrations have highlighted their potential in Li$_{1+x}$M$_{1-x}$O$_{2}$ chemistries with a wide range of metal combinations M. By relaxing the strict requirements of maintaining ordered Li diffusion pathways, countless multi-metal compositions in LiMO$_2$ may become viable, aiding the quest for high-capacity cobalt-free cathodes. A challenge presented by this freedom in composition space is designing compositions which possess specific, tailored types of both long- and short-range orderings, which can ensure both phase stability and Li diffusion. However, the combinatorial complexity associated with local cation environments impedes the development of general design guidelines for favorable orderings. Here we propose ordering design frameworks from 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, validated through multiple successful synthesis and characterization experiments, we not only demonstrate the design of LiCr$_{0.75}$Fe$_{0.25}$O$_2$, showcasing initial charge capacity of 234 mAhg$^{-1}$ and 320 mAhg$^{-1}$ in its 20% Li-excess variant Li$_{1.2}$Cr$_{0.6}$Fe$_{0.2}$O$_2$, but also present the elemental ordering statistics for 32 elements, informed by one of the most extensive first-principles studies of ordering tendencies known to us.