Investigation on the dissolution of Mn ions from LiMn_2O _4 cathode in the application of lithium ion batteries: First principle molecular orbital method

摘要

The dissolution phenomenon of Mn ions in LiMn_2O_4 (LMO) cathode material for lithium ion batteries (LIBs) was investigated by a first principle calculation using the discrete variational Xα molecular orbital method. It was found that the oxidation number of Mn ions easily increases at high temperatures due to the empty levels of Mn 3d orbitals located in the vicinity of the Fermi energy level of LMO crystal. The changes of density of states (DOS) and Mn-O bonding properties with doping were examined. Analysis of DOS showed that the substitution of elements with a smaller oxidation number than Mn was found effective in keeping Mn ions at higher oxidation states. From the calculation of bonding properties, the dissolution of Mn was found to be strongly correlated with the covalent nature of Mn-O bond. Based on the results, we concluded that increasing the covalent character of Mn-O bond is effective to minimize the dissolution of Mn ions, along with suppressing the formation of Jahn-Teller-active Mn~(3+) by inducing Mn ions at high oxidation state with proper selection of doping elements.