Molybdenum Substitution for Improving the Charge Compensation and Activity of Li2MnO3

Lithium-rich layer-structured oxides xLi(2)MnO(3)center dot(1-x)LiMO2 (0 < x < 1, M=Mn, Ni, Co, etc.) are interesting and potential cathode materials for high energy-density lithium ion batteries. However, the characteristic charge compensation contributed by O2- in Li2MnO3 leads to the evolution of oxygen during the initial Li+ ion extraction at high voltage and voltage fading in subsequent cycling, resulting in a safety hazard and poor cycling performance of the battery. Molybdenum substitution was performed in this work to provide another electron donor and to enhance the electrochemical activity of Li2MnO3-based cathode materials. X-ray diffraction and adsorption studies indicated that Mo5+ substitution expands the unit cell in the crystal lattice and weakens the Li-O and Mn-O bonds, as well as enhancing the activity of Li2MnO3 by lowering its delithiation potential and suppressing the release of oxygen. In addition, the chemical environment of O2- ions in molybdenum-substituted Li2MnO3 is more reversible than in the unsubstituted sample during cycling. Therefore molybdenum substitution is expected to improve the performances of the Li2MnO3-based lithium-rich cathode materials.