Entropymetry of Lithium Intercalation in Spinel Manganese Oxide: Effect of Lithium Stoichiometry

Cathodes based on cubic (spinel) structure LiMn_2O_4 were investigated by electrochemical entropymetry in an attempt to characterize their phase diagram according to the initial lithium composition. The stoichiometric material shows a very pronounced 2-phase region in the high 4V plateau and a solid- solution behavior in the lower 4V plateau. A third region is found in the non stoichiometric material characterized by a steep increase in entropy. This may relate to the onset of a stoichiometry induced anticipated cubic to tetragonal phase transition in the 4V area in this material. The later has been so far reported to occur only in the 3V area.