Electrochemical Fluoridation of Manganese Oxide by Perfluorinated‐Gas Conversion for Lithium‐Ion Cathodes

Fluoridation of Lithium‐ion (Li‐ion) cathodes is of growing interest for high‐capacity Li + storage materials, but well‐controlled fluoridation processes are elusive. We investigated an electrochemical methodology to grow lithium fluoride (LiF) by reduction of perfluorinated gas onto metal oxides (MO), which then forms M−O−F by splitting of LiF upon charge, using MnO as an example target phase. Unlike current methods where particle size <10 nm is necessary for high MnO utilization (subsequent discharge/lithiation capacity), owing to the nano‐crystallinity and intimate contact of electrochemically‐grown LiF, high MnO utilization (∼0.9 e − /MnO, 340 mAh g MnO −1 ) is achieved with large MnO particle size (∼400 nm), exceeding comparable MnO/LiF systems reported to date. Additionally, incorporation of perfluorinated‐gas additive benefits cycling, with capacity of ∼270 mAh g MnO −1 retained after 20 cycles. This work demonstrates the opportunity for electrochemically driven fluoridation to achieve high capacities with larger particle sizes needed to bring oxyfluorides closer to practical reality.