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

Abstract

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 gMnO−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 gMnO−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.