Capture Lithium in αMnO2: Insights from First Principles

Here we report the study of Li and Li oxides insertion in alpha MnO2 with first-principles density functional theory calculations. For Li insertion, the redox reaction is characterized with a particular order of the reduction of Mn ions. It induces asymmetric changes of lattice parameters through Jahn-Teller distortion of MnO6 units. At composition of LiMn2O4, the ratio between lattice parameter a and b extends to the highest value, 1.19. The severe structural deformation is concluded to be the major cause of the irreversible capacity when alpha MnO2 is used as Li-ion battery cathodes. On the other hand, the structure of alpha MnO2 is stable to reversibly insert and remove Li oxides. Li oxides inserted alpha MnO2 is half metallic instead of insulating. On the basis of our results, a mechanism is proposed to explain the role of alpha MnO2 in the catalyzed decomposition of Li2O2. The key step in this mechanism is the insertion of Li oxides in alpha MnO2. The insertion transfers electrons from Li oxides to MnO2 and partially oxidized Li oxides, making the subsequent release of O-2 easier.