Suppressing Surface Lattice Oxygen Evolution by Fluorinated Graphene-Scaffolded Lithium-Rich Manganese-Based Cathode for Enhanced Stability

Li-rich manganese-based layered oxides (LRMLO) have aroused widespread concern because of their much higher theoretical specific capacity than conventional cathode materials. However, unsuppressed lattice oxygen evolution brings about critical issues such as layer-to-spinel phase transition and oxygen release, extremely restricting their practical implementation. Herein, a fluorinated graphene-scaffolded LRMLO (LRMLO@FG) is prepared to effectively promote the oxygen redox stabilization and suppress lattice oxygen evolution. The investigations on oxygen redox couple (O2-/On–, n < 2) and manganese electronic structure illustrated that LRMLO@FG electrode preserved more lattice oxygen (O2-) and Mn4+ accounted for a higher proportion of total manganese after cycling, which were ascribed to the increase of the formation energy of oxygen vacancy and the reinforcement of Mn-O bond as suggested by DFT calculations. Furthermore, in situ XRD characterization demonstrated the lattice spacing of LRMLO@FG electrode was well restored to the original value, indicating that FG promoted the reversibility of crystal structure transition and the oxygen redox stabilization during the lithiation-delithiation process. The LRMLO@FG||Li cell exhibits greatly improved cycling stability with capacity retention of 88 % after 100 cycles and more stable Coulombic efficiency. This work offers an effective method to overcome the intrinsic challenges of LRMLO towards practical and high-energy lithium-ion batteries.