Effects of Al-doping on the stabilization of monoclinic LiMnO2

Electronic structures of monoclinic LiMnO2 and LiMn0.9375Al0.0625O2 with ferromagnetic (FM) and antiferromagnetic (AF) ordering have been investigated by ab initio calculation within spin-polarized generalized gradient approximation method. An Al-doping induced complicated AF configuration has been calculated to be the ground state, which suggests a robust Al-doping effect on the magnetic and electronic structures of the monoclinic LiMnO2. The calculated Mulliken population analyses and partial density of states of Mn-3d and O-2p reveal that a single Al dopant stabilizes its six nearest-neighbor Mn ions in their respective octahedral sites, thereby hindering the migration of Mn ions into the interlayer Li sites during the Li intercalation–deintercalation and therefore improving both the structural stability and the electrochemical performance of the material. Additionally, it is found out that the Al-doping can decrease the JT effect and increase the intercalation voltage. The Al-doping-induced negative formation energy indicates that 6.25% Mn ions in monoclinic LiMnO2 can be substituted stably by Al ions, to which the equilibrium but not metastable phase of monoclinic LiMn0.9375Al0.0625O2 can be attributed.