Molybdenum substitution for improving the charge compensation and activity of Li2MnO3

Abstract

Lithium-rich layer-structured oxides xLi2 MnO3 ⋅ (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 O(2-) in Li2 MnO3 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 Li2 MnO3 -based cathode materials. X-ray diffraction and adsorption studies indicated that Mo(5+) 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 Li2 MnO3 by lowering its delithiation potential and suppressing the release of oxygen. In addition, the chemical environment of O(2-) ions in molybdenum-substituted Li2 MnO3 is more reversible than in the unsubstituted sample during cycling. Therefore molybdenum substitution is expected to improve the performances of the Li2 MnO3 -based lithium-rich cathode materials.

Keywords: charge transfer; doping; layered compounds; lithium; molybdenum.