Li-Mn-Co-O shelled LiMn2O4 spinel powder as a positive electrode material for lithium secondary batteries

A spray-drying process was used to coat a Li(Li0.033Mn1.967)O4 powder with a spinel-type Li-Mn-Co-O surface layer. After high-temperature (850 deg C) annealing, the coated powder was made into a positive electrode for rechargeable lithium cells. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectrometry (EDAX) were applied to analyze the structure of the annealed powders. It is found that a spinel-type Li[Mn1.56(1-sigma)Co0.44(1-sigma)Li2sigma]O4 layer was probably formed on the Li(Li0.033Mn1.967)O4 particles. The particle size distribution of the spray-treated powder becomes narrower than the original Li(Li0.033Mn1.967)O4 powder. As the active positive electrode material, the coated Li(Li0.033Mn1.967)O4 powder shows excellent electrochemical properties, especially in suppressing the capacity fading during elevated temperature cycling (with a fading rate of 0.045% per cycle). The rate capability of the cells is also improved as a result of this treatment.