Synthesis Conditions and Oxygen Stoichiometry Effects on Li Insertion into the Spinel LiMn₂O₄

Using a new electrolyte composition, which is stable against oxidation up to 5 V, the full electrochemical deintercalation of lithium from the spinel LiMn₂O₄ is studied. The origin of two new reversible oxidation-reduction peaks near 4.5 and 4.9 V are examined. The capacity associated with these peaks depends on both the nominal composition x in Li_xMn₂O₄ and the synthesis conditions (annealing temperatures and cooling rates), and thereby can be used as an indicator for electrochemically optimized LiMn₂O₄ powders. We present evidence that these peaks are related to local structural defects. Thermogravimetric measurements (TGA) on Li_xMn₂O₄ powders show a reversible loss of oxygen that can reach 5 % at 1000°C. We find that some of this weight loss is associated with the conversion of cubic LiMn₂O₄ to a new tetragonal spinel phase and then to the decomposition of this phase into the orthorhombic LiMnO₂ phase plus other products. This new tetragonal LiMn₂O₄ spinel is prepared as a single phase, and its electrochemical properties are reported.