A first-principles study on phase transition induced by charge ordering of Mn3+/Mn4+ in spinel LiMn2O4

A first-order transition at 290 K in LiMn2O4 with a cubic spinel-type structure is known to degrade the electrochemical performance of the positive electrode of rechargeable lithium-ion batteries. Using first-principles density functional theory (DFT), we confirm that the phase transition is induced by charge-ordering of Mn3+/Mn4+ accompanied by orbital-ordering due to Jahn-Teller distortion, which is in agreement with the previous experimental results of Rodriguez-Carvajal et al. [J. Rodriguez-Carvajal, G. Rousse, C. Masquelier, M. Hervieu, Phys. Rev. Lett. 81 (1998) 4660]. The optimized structure of the low-temperature (LT) phase has orthorhombic symmetry with five distinct crystallographic sites for Mn. The spin integration at each Mn site shows that Mn3+ resides at three Mn sites and the remaining two sites are occupied by Mn4+ ions. Total energy calculations indicate that the LT phase is about 0.23 eV/LiMn2O4 more stable than cubic LiMn2O4 (high-temperature phase). The electrochemical Li extraction reaction from the LT phase is also investigated using DFT calculations. The results indicate that the reaction is initially divided into two voltage regions. Electrostatic interactions in the LT phase are calculated using a point charge model, accounting for the features of the electronic configurations and electrochemical reactions. (C) 2010 Elsevier Ltd. All rights reserved.