Synthesis and characterization of Li1+xMn2-xO4 for Li-ion battery applications

Several series of Li1+2Mn2-xO4 samples prepared at different temperatures and in different oxygen environments were studied in order to further understand the dependence of the electrochemical performance on the sample heating temperature, on the amount of excess lithium rt, and on the oxygen stoichiometry. We show that a peak in the differential capacity of Li/Li11xMn2-xO4 electrochemical cells at 3.3 V on discharge always appears with the 4.5 V peak previously reported by Tarascon ct al. Powder x-ray diffraction and Rietveld refinement show that the mixing of Li and Mn cations in 8a sites is not the origin of these capacity peaks. Samples heated to 900 degrees C and samples that are more oxygen deficient exhibit larger 3.3 and 4.5 V peaks. Samples made at 750 degrees C in air or oxygen with x = 0.1 show almost no evidence for the 3.3 and 4.5 V peaks. Furthermore, these samples do not degrade even after cells are charged to 4.9 V, suggesting these samples should be excellent for Li-ion battery applications. A simple way of determining x with thermal gravimetric analysis is also demonstrated.