Unlocking Zn-Ion Diffusion in Disordered Rocksalt Cathodes for Nonaqueous Zn-Ion Batteries

Multivalent batteries, particularly zinc-ion batteries (ZIBs), are promising candidates for high-energy-density energy storage. However, their development is hindered by a scarcity of suitable cathode materials capable of the reversible (de)intercalation of Zn²⁺. To address this challenge, we propose cation-disordered rocksalt (DRX) cathodes, which have demonstrated excellent performance in Li-ion batteries, as a versatile host framework for nonaqueous ZIBs. Specifically, a vacancy-containing Mn_0.4Ti_0.4O₂ DRX cathode demonstrates a reversible capacity of 170 mAh g^-1 in nonaqueous ZIBs. Our investigation reveals that the Zn²⁺ ionic diffusion mechanism within the DRX framework is intrinsically sluggish compared to monovalent ions like Li⁺ due to strong electrostatic repulsion. Therefore, to successfully unlock Zn²⁺ migration, we show that it is necessary to introduce cation vacancies into the host, which significantly reduces the ion migration barrier. Additionally, we suggest that anion engineering may further enhance diffusion kinetics. This work expands the cathode material landscape for ZIBs and provides general insights into the design of disordered hosts for multivalent ion storage.