Short-Range Order and Li$_x$TM$_{4-x}$ Probability Maps for Disordered Rocksalt Cathodes

TL;DR

This paper investigates short-range order in disordered rocksalt cathodes, revealing how local ordering influences Li4 cluster probabilities and proposing strategies to surpass the random limit, thereby enhancing understanding of FCC system thermodynamics.

Contribution

It provides a systematic analysis of pair SRO parameters and Li_xTM_{4-x} probabilities, introducing strategies to exceed the random Li4 probability limit in disordered rocksalt cathodes.

Findings

Li4 probability is governed by nearest neighbor SRO.

Strategies can surpass the random Li4 probability limit.

Fundamental thermodynamic insights into FCC ordering behaviors.

Abstract

Short-range order (SRO) in the cation-disordered state is a controlling factor influencing the probability of finding Li$_{4}$ tetrahedron clusters in disordered rocksalt (DRX) cathode materials. However, the prevalent Li$_4$ probability below the random limit across reported DRX compositions has not been systematically investigated, active strategies to surpass the random limit of Li$_4$ probability are lacking, and the fundamental ordering behavior on the face-centered cubic (FCC) lattice remains insufficiently explored. This research quantitatively examines pair SRO parameters and Li$_x$TM$_{4-x}$ probabilities via exhaustive Monte Carlo mapping across a simplified subset of the parameter space. The results indicate that, in the disordered state, the Li$_4$ probability is governed by the nearest neighbor (NN) pair-wise SRO parameter, and that these quantities do not necessarily represent a simple attenuation of their corresponding low-temperature long-range order, particularly for the important cases of Layered and Spinel-like orderings. Strategies are proposed to mitigate or even reverse the lithium and transition metals mixing tendency of NN pair SRO to achieve Li$_4$ probabilities that exceed the random limit. This study advances the fundamental thermodynamic understanding of ordering behaviors, which can be generalized to any FCC system.