Effect of temperature and atmosphere on phase stability and morphology of LiMn2O4 powder synthesized by citric acid gel process

Defect spinel lithium manganese oxide and spinel LiMn2O4 compounds (which a re of potential interest for lithium-ion battery cathode materials) with di fferent crystallization degrees have been synthesized by a citric acid gel process using lithium acetate and manganese acetate as sources for lithium and manganese at various temperatures and in different atmospheres. Non-sto ichiometric lithium-manganese-oxide spinel, Li1-6Mn2-2 deltaO4, had been sy nthesized at temperatures as low as 200 degrees C. The structure of the cry stalline compounds was found to be cubic spinel in which the lattice parame ter and full width at half maximum (FWHM) were sensitive to calcination tem perature. As the calcined temperature increased, the oxygen was lost and ca tion defects were removed from the structure with better crystallization, A t temperatures > 700 degrees C, LiMn2O4 underwent phase transition fr-om a cubic to a tetragonal phase by removing oxygen ion from the surface of powd er in air. However, the samples calcined in O-2 atmosphere did not show any phase transformation. These results highlight the importance of temperatur e and atmosphere control when synthesizing LiMn2O4 powder using a citric ac id gel process. The specific surface area of the LiMn2O4-x. powder prepared at 800 degrees C for 24 h was 11.6 m(2)/g that is distinctly larger than t hat prepared by solid-state reaction. From the result of scanning electron microscope (SEM), the synthesized powders showed a spherical shape and a na rrow particle size distribution.