Configurational entropy of lithium manganese oxide and related materials, LiCryMn2-yO4 (y=0, 0.3)

The change in entropy of LixCryMn2-yO4 (y = 0, 0.3), Delta S, was determined by potentiometric and calorimetric approaches. The Delta S obtained by the two different methods showed similar trends. The peak in Delta S was explained by the partial Li-ion ordering of the Li(1)(0, 0, 0) and Li(2)(0.25, 0.25, 0.25) sites in the sublattice of the 8a site at x = 0.6. The following complete ordering at x = 0.5 was accompanied with the rearrangement of the partial ordering between Li(1) and Li(2). Although the Delta S peak was diminished by partial Cr-ion substitution because of the incomplete ordering due to the random dispersion of Cr ions, the peak position (x) of Delta S remained unchanged. This suggested that the voltage step between 0.6 > x > 0.5 in LixCryMn2-yO4 was not due to the structural change in the host spinel structure but mainly caused by the Li-ion partial ordering at x = 0.6, the rearrangement of the two domains (0.6 > x > 0.5), and the following perfect ordering (x = 0.5). (c) 2007 The Electrochemical Society.