Tethering Transition Metals of Li-Rich Manganese Oxides via Anion Coordination for High-Voltage Lithium-Metal Batteries

Transition metal (TM) ions dissolution from lithium-rich manganese oxides (LRMO) cathode is positioned to the central factor to widen the upper voltage and prolong cycle life. While a body of research documents elemental doping or surface coating to stabilize LRMO structure and inhibit TM-ion dissolution, a handful of literature considers the ion solvation chemistry to capture TM ions, namely, strong interactions between cation and anion promote salt deposition. Compared with monovalent Li with a radius of 0.68 Å, multivalent TM-ions with even smaller radius exhibit excessively high charge density, which preferentially interacts with high coordination anions to initially form cation–anion clusters and consequently facilitate cation–anion deposition. Based on these ion solvation principles, it is proposed to employ the high coordination anions to tether TM and suppress TM-dissolution-induced side reactions. This concept is verified by a strongly coordinating strength anion of difluoro(oxalato)borate (DFOB^–) that embraces bidentate oxygen sites with appreciable electron-donating ability. These structural features and chemical benefits cooperatively coordinate with TM ions and lead to twofold attributes: i) mitigate solvents decomposition through altering their lowest unoccupied molecular orbitals; and ii) facilitate TM-ion deposition by intensifying cation–anion interactions. These collective advantages endow the Li||LRMO cells with high mass loading, improved cycling, and rate performances. This work provides an approach based on solvation chemistry to regulate TM-ion deposition for high-energy-density LRMO batteries.