High Performance Composite Lithium-Rich Nickel Manganese Oxide Cathodes for Lithium-Ion Batteries

Li 1.0 [Li 1/7 Mn 4/7 Ni 2/7 ]O 2 cathode material was prepared by a facile, one-pot synthesis method. The structure of the material was determined by Rietveld refinement of structural models using high-resolution synchrotron X-ray and neutron powder diffraction data and was found to consist of two distinct phases. The major phase, with composition Li 1.25(3) Ni 0.17(1) Mn 0.61(1) O 2 , close to the well-characterized Li 1.2 Ni 0.2 Mn 0.6 O 2 composition can be described as an intergrowth structure of Li 2 MnO 3 and LiMn 0.5 Ni 0.5 O 2 domains and the second phase is a lithium-deficient layered structure with refined composition Li 0.85(1) Ni 0.57(1) Mn 0.55(1) O 2 . The composite cathode has a high initial discharge capacity of 250 mAh/g which drops to 225 mAh/g on the 2 nd discharge cycle. This capacity is maintained on subsequent cycles. Time-resolved in-situ synchrotron XRD data was used to study the changes in the lattice parameters and phase evolution of the two phases during Li-insertion and extraction.