Anomaly in the potential–composition profile of a LiMn2O4 spinel at low temperature

The potential–composition (φ–x) curve of a stoichiometric LiMn2O4 spinel shows an anomaly that a new voltage step appears at x≒0.7 (in LixMn2O4) at low temperature (T≤278 K). To investigate the relation between this anomaly and structural transition due to the Jahn–Teller distortion, we recorded the φ–x profiles at 298 and 273 K with several nonstoichiometric specimens, Li-excess Li1+yMn2−yO4 as well as Li-deficient compounds apparently expressed by Li1−y′Mn2O4, because it is sensitive to stoichiometry whether the compound undergoes the transition or not. It was found that Li-deficient compounds (y′=0.03–0.05) showed a similar anomalous step, though no first-order transition was observed in the relevant temperature range by the DSC technique. The same thing was also found for a Li-excess sample with y=0.01. These facts indicate that the origin of the anomaly is not directly related to the Jahn–Teller distortion.