Hidden structural order controls Li-ion transport in cation-disordered oxides for rechargeable lithium batteries

TL;DR

This study reveals that hidden cation short-range order in disordered Li-excess cathodes significantly influences Li-ion transport, challenging the assumption of complete randomness and offering new design insights.

Contribution

It uncovers the presence of hidden cation short-range order in disordered cathodes and demonstrates its impact on Li-ion diffusion, providing novel guidelines for material design.

Findings

Hidden cation short-range order exists in disordered cathodes.

Cation order controls local environments affecting Li-ion transport.

New design principles for cathode materials are proposed.

Abstract

Crystal structures play a vital role in determining materials properties. In Li-ion cathodes, the crystal structure defines the dimensionality and connectivity of interstitial sites, thus determining Li-ion diffusion kinetics. While a perfect crystal has infinite structural coherence, a class of recently discovered high-capacity cathodes, Li-excess cation-disordered rocksalts, falls on the other end of the spectrum: Their cation sublattices are assumed to be randomly populated by Li and transition metal ions with zero configurational coherence based on conventional X-ray diffraction, such that the Li transport is purely determined by statistical effects. In contrast to this prevailing view, we reveal that cation short-range order, hidden in diffraction, is ubiquitous in these long-range disordered materials and controls the local and macroscopic environments for Li-ion transport. Our work not only discovers a crucial property that has previously been overlooked, but also provides new guidelines for designing and engineering disordered rocksalts cathode materials.