Composition valence diagram and stoichiometry in the Li-Mn-O spinel system

The synthesis of Li-Mn-O spinels with manganese valence > 3.5 has been investigated using thermogravimetry and X-ray analysis. The results are discussed as a function of starting reagents and processing temperature. Acetates and gamma-MnO2 were found to react well at low temperature, especially for high Li/Mn ratios. beta-MnO2 could not be totally reacted, but yielded well-crystallized spinels. Shifts in composition due to the presence of secondary phases are discussed with the help of composition-valence diagrams. The variation of the spinel cell parameter along the LixMn3-xO4 (1 less than or equal to x less than or equal to 4/3) solid solution is given by a = 8.4243 - 0.3753 .(Li/Mn). We confirm that the composition of the end member Li4Mn5O12 cannot be reached in single phase form.