High-rate cathode materials for Li-ion batteries require fast Li-transport kinetics, which typically relies on topotactic Li intercalation/de-intercalation because it minimally disrupts Li-transport pathways. In contrast to this conventional view, herein, we demonstrate that the rate capability in a Li-rich cation-disordered rocksalt (DRX) cathode can be significantly improved when the topotactic reaction is replaced by a non-topotactic reaction. The fast non-topotactic lithiation reaction is enabled by facile and reversible transition-metal (TM) octahedral-to-tetrahedral migration, which improves rather than impedes Li transport. Using this concept, we show that high-rate performance can be achieved in Mn-and Ni-based DRX materials when some of the TM content can reversibly switch between octahedral and tetrahedral sites. This study provides a new perspective on the design of high-performance cathode materials by demonstrating how the interplay between Li and TM migration in materials can be conducive to fast non-topotactic Li intercalation/de-intercalations.

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Using both computations and experiments we demonstrate that the performance of Li-excess cation-disordered rocksalt cathodes can be improved by Mg substitution.Mg reduces the amount of Li in the compound that is strongly bound to F and thereby increase the capacity. This enables the use of fluorination as a tool to improve stability of the compounds without significant loss of capacity. Mg emerged as the most optimal substitution element from a systematic computational study aimed at identifying inactive doping elements with a strong enough bonding strength to fluorine to displace Li from the F environments. Our results also show that capacity can be traded for 1 cycle life depending on whether Mg is substituted for Li or for the redox metal. This design strategy should be considered in fluorinated cathodes, which will facilitate the design of optimized disordered-rocksalt oxyfluoride cathodes.