Ab initio investigation of Jahn-Teller distortion tuned Li ion migration in λ-MnO2
Migration of Li ion in electrode materials is the main limiting factor to determine the rate capability of Li ion batteries. In this work, the influences of Jahn-Teller (JT) distortion on Li migration in full delithiated LiMn2O4 (λ-MnO2) are systematically studied by first-principles computational approach. Our results unravel the direction of JT distortion strongly affecting the activation barrier of Li ion migration in λ-MnO2. Particularly, Li ion migration has the lowest activation barrier when the two elongated Mn-O bonds of Mn3+ ion are quasi-collinear with the linked Li-O bonds at the transition state, as compared with the highest barrier when the elongated Mn-O bonds are approximately perpendicular to the linked Li-O bonds. In addition, lattice strain induced variation of Li migration barrier in λ-MnO2 exhibits either upward or downward trends, depending on the detailed coupling with the JT distortion. Further analysis shows that the difference of activation barriers can be explained by the different Li-O distances in terms of the Coulomb interaction energy, which is induced by the different position and direction of JT distortion. Finally, the Li migration in the whole λ-MnO2 system is also discussed by considering the influences of JT polaron.