Heavy Fluorination via Ion Exchange Achieves High-Performance Li-Mn-O-F Layered Cathode for Li-Ion Batteries

Lithium-excess manganese layered oxide Li2MnO3, attracts much attention as a cathode in Li-ion batteries, due to the low cost and the ultrahigh theoretical capacity (approximate to 460 mA h g(-1)). However, it delivers a low reversible practical capacity (<200 mA h g(-1)) due to the irreversible oxygen redox at high potentials (>4.5 V). Herein, heavy fluorination (9.5%) is successfully implemented in the layered anionic framework of a Li-Mn-O-F (LMOF) cathode through a unique ion-exchange route. F substitution with O stabilizes the layered anionic framework, completely inhibits the O-2 evolution during the first cycle, and greatly enhances the reversibility of oxygen redox, delivering an ultrahigh reversible capacity of 389 mA h g(-1), which is 85% of the theoretical capacity of Li2MnO3. Moreover, it also induces a thin spinel shell coherently forming on the particle surface, which greatly improves the surface structure stability, making LMOF exhibit a superior cycling stability (a capacity retention of 91.8% after 120 cycles at 50 mA g(-1)) and excellent rate capability. These findings stress the importance of stabilizing the anionic framework in developing high-performance low-cost cathodes for next-generation Li-ion batteries.