Thermodynamic properties of undoped and Fe-doped LiMn2O4 at high temperature

Thermodynamic properties of undoped and Fe-doped LiMn2O4 were studied at temperatures from room temperature to 1473 K and in oxygen partial pressures from 50 to 105 Pa by XRD, TG-DTA and drop calorimetric methods. For undoped LiMn2O4, three phase transitions (T1, T2, T3) in TG-DTA measurement were observed in various oxygen partial pressures, though in O2 any anomaly was not observed at T3. For doped LiMn2−xFexO4, the starting temperature of weight-loss of oxygen at T1 decreased with increasing doped content for x>0.1. Phase transition temperature at T2 decreased with increasing doped content, but any anomaly in TG-DTA curve was not observed at T3 for all Fe-doped LiMn2O4. Chemical potential diagram in the Li-Mn-O system was established on the basis of TG-DTA and high-temperature XRD results. The enthalpies of the disproponation reaction (ΔH=547±70 Jg−1 at x=0 and ΔH=573±120 Jg−1 at x=0.3) for LiMn2−xFexO4 at T2 calculated from chemical potential diagram were in good agreement with the values (ΔH=534±25 Jg−1 at x=0 and ΔH=537±26 Jg−1 at x=0.3) obtained from high-temperature drop calorimeter within the experimental error, respectively.