Phase transition observed in potential-composition profiles of LixMn2O4

Open circuit voltage (OCV) profiles of spinel type lithium manganese oxide LixMn2O4 (x less than or equal to 1) have been recorded at several temperatures (243 K less than or equal to T less than or equal to 323 K) using a single three-electrode glass cell. Deintercalation of Li ions from LixMn2O4 has been carried out at low temperature (243 K), and then OCV profile has been measured at both the processes of raising and descending temperatures on each state of lithium content (x). Quasi-equilibrium potential profiles above room temperature (298 K less than or equal to T), which are results of continuous measurements by first charge, overlap with OCV profiles in the process of raising temperature well. However, around x = 0.5, quasi-equilibrium potential profiles and OCV profiles do not overlap at low temperature (T less than or equal to 278 K). This result indicates that the low-temperature phase at x = 0.5 in LixMn2O4 is very sensitive to temperature change. Temperature dependence of OCV profiles in the process of descending temperature corresponds to a simulation based on assumption that distribution of Li ions is disordered in LixMn2O4 (0.5 less than or equal to x < 1). (C) 2003 Elsevier B.V. All rights reserved.