The formation energies of many kinds of defect in O-deficient material, including both O-vacancy types and metal-interstitial types, were determined by using first-principles plane-wave pseudopotential calculations. Two kinds of metal-excess defect exhibited the lowest formation energies. They were found to be more stable than the simple O vacancy that exhibited the lowest formation energy among O-vacancy type defects. In both metal-excess defects with the lowest formation energies, the excess Li occupied an empty 16c position in the spinel. Excess Mn was present either at the 8a position, where it replaced Li, or at empty 16c positions; where one neighboring Li was moved into the next 16c position. The results were consistent with experimental density and diffusion experiments and with decomposition reactions at high temperatures. A detailed examination of the electronic structures revealed that the formal charge on both interstitial and substituted Mn was +2.

First Principles Calculations of Formation Energies and Electronic Structures of Defects in Oxygen-Deficient LiMn2O4. Y.Koyama, I.Tanaka, H.Adachi, Y.Uchimoto, M.Wakihara: Journal of the Electrochemical Society, 2003, 150[1], A63-7