Effect of Temperature and Atmosphere on Phase Stability and Morphology of LiMn2O4 Powder Synthesized by Citric Acid Gel Process.

Abstract

Defect spinel lithium manganese oxide and spinei LiMn2O4 compounds (which are of potential interest for lithium-ion battery cathode materials) with different 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-stoiciometric lithium-manganese-oxide spinel, Li1-δMn2-2δO4, had been synthesized at temperatures as low as 200°C. The structure of the crystalline compounds was found to be cubic spinel in which the lattice parameter and full width at half maximum (FWHM) were sensitive to calcination temperature. As the calcined temperature increased, the oxygen was lost and cation defects were removed from the structure with better crystallization. At temperatures >700°C, LiMn2O4 underwent phase transition from a cubic to a tetragonal phase by removing oxygen ion from the surface of powder in air. However, the samples calcined in O2 atmosphere did not show any phase transformation. These results highlight the importance of temperature and atmosphere control when synthesizing LiMn2O4 powder using a citric acid gel process. The specific surface area of the LiMn2O4-x powder prepared at 800°C for 24h was 11.6m2/g that is distinctly larger than that prepared by solid-state reaction. From the result of scanning electron microscope (SEM), the synthesized powders showed a spherical shape and a narrow particle size distribution.