Lithium-manganese-rich　transition　metal　oxides　have　attracted　substantial　R&D　attention　due　to　their　potential　for　high　energy-density　lithium-ion　batteries.　In　this　work,　in　situ　high-energy　X-ray　diffraction　was　deployed　to　investigate　the　phase　evolution　during　the　solid-state　synthesis　of　Li[Li0.2Mn0.54Ni0.13Co0.13]O-2.　A　step-wise　consumption　of　the　starting　materials　was　observed　during　the　one-step　heating　process　primarily　due　to　the　heterogeneous　nature　of　the　precursor.　According　to　observations　from　in　situ　high-energy　X-ray　diffraction,　a　two-step　process　was　adopted　to　minimize　the　elemental　heterogeneity　of　the　final　product.　The　electrochemical　characterization　results　showed　a　substantial　improvement　on　the　reversible　specific　capacity　for　the　material　synthesized　through　the　two-step　process.