Effect of Oxygen Hole in Li2MnO3 Revealed by Hard X-ray Photoemission Spectroscopy and Band Structure Calculations

We have studied the electronic structure of Li2MnO3 which has been attracting interest as a promising oxygen redox type cathode material for Li ion battery. Hard x-ray photoemission spectroscopy and subsequent cluster model analysis show that the Mn valence is 4+ and that the charge transfer energy Delta is close to 0 eV. Delta of Li2MnO3 is smaller than the typical Delta values of tetravalent Mn oxides. The small Delta value suggests that the delithiation process of Li2MnO3 is dominated by electron removal from the O 2p orbitals. In addition to the ground state properties of Li2MnO3, effect of Li or oxygen vacancy on the electronic structure is examined by means of band structure calculations. The Li vacancy drives the system metallic due to itinerant O 2p holes while the system with oxygen vacancy remains an insulator.