Disordered Rocksalts as High-Energy and Earth-Abundant Li-Ion Cathodes

Abstract

To address the growing demand for energy and support the shift toward transportation electrification and intermittent renewable energy, there is an urgent need for low-cost, energy-dense electrical storage. Research on Li-ion electrode materials has predominantly focused on ordered materials with well-defined lithium diffusion channels, limiting cathode design to resource-constrained Ni- and Co-based oxides and lower-energy polyanion compounds. Recently, disordered rocksalts with lithium excess (DRX) have demonstrated high capacity and energy density when lithium excess and/or local ordering allow statistical percolation of lithium sites through the structure. This cation disorder can be induced by high temperature synthesis or mechanochemical synthesis methods for a broad range of compositions. DRX oxides and oxyfluorides containing Earth-abundant transition metals have been prepared using various synthesis routes, including solid-state, molten-salt, and sol-gel reactions. This review outlines DRX design principles and explains the effect of synthesis conditions on cation disorder and short-range cation ordering (SRO), which determines the cycling stability and rate capability. In addition, strategies to enhance Li transport and capacity retention with Mn-rich DRX possessing partial spinel-like ordering are discussed. Finally, the review considers the optimization of carbon and electrolyte in DRX materials and addresses key challenges and opportunities for commercializing DRX cathodes.