ATOMISTIC SIMULATION STUDIES OF LITHIUM AND PROTON INSERTION IN SPINEL LITHIUM MANGANATES

Atomistic simulation methods are used to investigate lithium and proto n insertion in spinel lithium manganates, The energetics of lithium ex traction and reinsertion by redox reactions in the LiMn2O4-lambda-MnO2 system are evaluated with respect to the formation of lithium vacanci es or interstitials and to overall changes in lattice energy. Lithium migration mechanisms are also investigated, considering the energies f or Li+ ions to migrate through different pathways in the interstitial space of the lattice. The local structures around Mn 16d vacancies in spinels of composition LiMn2O4+delta and Li1+xMn2-xO4 are modeled to d etermine the effects of the vacancies on Lithium and proton sites. Pos sible orientations of hydroxyl groups formed by inserted protons in th e structure are examined, and a strong energetic preference for the hy droxyl groups to coordinate the 16d vacancies is found. A model is pro posed for protonated spinel MnO2 in which four hydroxyl groups are sym metrically distributed in planar configuration around each 16d vacancy .