Thermodynamic properties of undoped and Fe-doped LiMn 2O 4 at high temperature

Abstract

Thermodynamic properties of undoped and Fe-doped LiMn 2O 4 were studied at temperatures from room temperature to 1473 K and in oxygen partial pressures from 50 to 10 5 Pa by XRD, TG-DTA and drop calorimetric methods. For undoped LiMn 2O 4, three phase transitions ( T 1, T 2, T 3) in TG-DTA measurement were observed in various oxygen partial pressures, though in O 2 any anomaly was not observed at T 3. For doped LiMn 2− x Fe x O 4, the starting temperature of weight-loss of oxygen at T 1 decreased with increasing doped content for x>0.1. Phase transition temperature at T 2 decreased with increasing doped content, but any anomaly in TG-DTA curve was not observed at T 3 for all Fe-doped LiMn 2O 4. 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 (Δ H=547±70 Jg −1 at x=0 and Δ H=573±120 Jg −1 at x=0.3) for LiMn 2− x Fe x O 4 at T 2 calculated from chemical potential diagram were in good agreement with the values (Δ H=534±25 Jg −1 at x=0 and Δ H=537±26 Jg −1 at x=0.3) obtained from high-temperature drop calorimeter within the experimental error, respectively.