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

Abstract

Cathodes based on cubic (spinel) structure LiMn2O4 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.