A disordered rock-salt Li-excess cathode material with high capacity and substantial oxygen redox activity: Li1.25Nb0.25Mn0.5O2

A disordered rocksalt Li-excess cathode material, Li1.25Nb0.25Mn0.5O2, was synthesized and investigated. It shows a large initial discharge capacity of 287 mAh g− 1 in the first cycle, which is much higher than the theoretical capacity of 146 mAh g− 1 based on the Mn3+/Mn4+ redox reaction. In situ X-ray diffraction (XRD) demonstrates that the compound remains cation-disordered during the first cycle. Electron energy loss spectroscopy (EELS) suggests that Mn and O are likely to both be redox active, resulting in the large reversible capacity. Our results show that Li1.25Nb0.25Mn0.5O2 is a promising cathode material for high capacity Li-ion batteries and that reversible oxygen redox in the bulk may be a viable way forward to increase the energy density of lithium-ion batteries.