Novel synthesis process and structure refinements of Li_4Mn_5O_12 for rechargeable lithium batteries

摘要

Well-crystallized Li_4Mn_5O_(12) powder with grain size of 0.1-0.4 μm was prepared by heating a eutectic mixture of lithium acetate (LiOAc), and manganese nitrate (Mn(NO_3)_2), in an oxygen atmosphere. The structure of Li_4Mn_5O_(12) crystallites was found to be a cubic spinel using Rietveld refinement of both neutron and X-ray powder diffraction data. We confirmed that lithium ions occupy both the tetrahedral 8a sites, and part of the octahedral 16d sites, but not the 16c sites in the space group Fd3-bar m, while all the manganese ions occupy the 16d sites. The lattice parameter was found to be sensitive to the synthesis temperature as a result of the variation in manganese valence. Samples prepared at 500℃ showed better electrode performance. A rechargeable capacity of about 135 mAh/g for the cell Li/Li_4Mn_5O_(12) was obtained in the 2.5-3.6 V range of cell voltages.