Structure and electrochemical characterization of Li_1+xMn_2-xO₄ spinels for rechargeable lithium batteries

Neutron and X-ray powder diffraction and Rietveld refinements have been carried out for the well-crystallized samples with a homogeneous composition Li_1+xMn_2-xO₄ (0 ≤ x ≤ 0.125). The lattice parameter of these spinels changes with both the composition and the synthesis temperature. SEM and TEM micrographs show that the crystallites appear as single crystals with a size of 0.1-2 μm. The phase transition from cubic Fd3m to orthorhombic Fddd around 280 K of samples Ei_1+xMn_2-xO₄ (x ≤ 0.04) was observed using low temperature XRD and DSC. The orthorhombic phase further converts to a single tetragonal phase I4₁/amd around 65 K. The charge/discharge capacity, and cyclability of these samples were examined in both the 3 V and the 4 V regions. We found that the discharge capacity as well as the cyclability of the cell Li/Li_1+xMn_2-xO₄ change largely with not only the value of x but also the crystal structure which depends on the synthesis conditions.