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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Niobium-based compounds with Wadsley–Roth crystallographic shear structures show promise as fast lithium storage materials in micrometer sizes without the need for nanostructure engineering. However, the lithium storage mechanism underlying their unique electrochemical properties has yet to be understood. Herein, we characterized the evolution of vibration bands in operando Raman spectra of the representative shear phase, H-Nb2O5, during lithiation in order to correlate the lithiation-induced structural variations of H-Nb2O5 with the electrochemical properties. Complemented by DFT calculations, the lithium storage mechanism was unraveled, including the preference for adsorption sites, the resultant electronic structure, and specific pathways for lithium transport. This work provides insight into the lithium storage mechanism in shear structure Nb2O5, which is believed to be useful for knowledge-based design of niobium-based compounds as high-rate lithium storage materials.