  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.
