Li0.33MnO2 cathode material was synthesized by solid state reaction which showed a monoclinic structure.In situ synchrotron diffraction showed a reversible structural transition of Li0.33MnO2 during Li+ insertion/extraction.However,it is difficult to determine the crystal structure of lithiated Li0.33+xMnO2 based on their poorly resolved diffraction patterns.This difficulty was successfully resolved by X-ray absorption spectroscopy(XAS) and Raman scattering which are sensitive to the short-range ordering of material lattice.Extended X-ray absorption fine structure shows the co-existence of corner- and edge-shared[MnO6]in Li0.33MnO2,whereas only edge-shared[MnO6]in lithiated Li0.96MnO2.Significantly,the differences between the Raman spectra of Li0.33MnO2 and Li0.96MnO2 indicate the phase transition of the material with Li+ intercalation.This work shows that Li0.33MnO2 transforms to monoclinic LiMnO2 with Li+ intercalation.This phase transformation was suggested to evolve from the migration of Mn ions.