Cation-disordered rock salts (DRXs), a new class of cathode
materials
for Li-ion batteries, have attracted a great amount of attention in
recent years due to their fascinatingly simple cubic structure, highly
diverse composition, and great electrochemical performance. As cations
in DRXs are randomly distributed in a long range, how the cations
are spatially arranged is an intriguing question for the community
of solid-state materials chemistry. In this work, we report the vibrational
structure of a series of Mn- and Fe-based DRXs with well-controlled
compositions and reveal significant layered-like cation ordering in
the DRXs. A scheme is proposed to describe how the layered-like anisotropy
could exist in rock salt structures with an overall cubic diffraction
pattern. Furthermore, we raise a model of Li-ion transport based on
the proposed scheme, which complements the theory of Li percolation
in DRXs. The electrochemical behavior of the DRX cathodes used in
the study supports the scheme and clearly demonstrates the role of
layered anisotropy in the battery performance of DRXs.
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