Fluorine-Rich Oxyfluoride Spinel Li1.25Ni0.625Mn1.125O3F Utilizing Redox-Active Ni and Mn for High Capacity and Improved Cyclability

Abstract

Extending the accessible capacity and cyclability is of central interest for cathode materials for Li-ion batteries. Here, we report the successful synthesis of a new spinel Li1.25Ni0.625Mn1.125O3F (Fd3 ̅m) with significant cation disorder characterised by combined refinement of X-ray and neutron diffraction data. Li1.25Ni0.625Mn1.125O3F utilizes redox reactions of both Ni and Mn, accessing capacities of 225 (i.e., 1.46 Li+ capacity) and 285 mAh g-1 (i.e., 1.85 Li+ capacity) at 25 °C and 40 °C, respectively, through intercalation of additional Li+ into the lattice. Moreover, compared to lithium transition metal disordered rocksalt or spinel-like oxyfluorides previously reported, Li1.25Ni0.625Mn1.125O3F shows significantly improved cycling stability. Ex situ compositional, structural and spectroscopic analysis of samples at different states of charge/discharge confirm a single-phase intercalation reaction and high structural integrity over cycling.