Thermoanalytical (TGA-DSC) and high temperature X-ray diffraction (HT-XRD) study of the thermal decomposition processes in Li 2CO 3–MnO mixtures

Abstract

The thermal decomposition processes taking place in solid state mixtures Li 2CO 3–MnO ( X Li=0.10–0.50, X Li=lithium cathionic fraction) have been studied (in air) by High Resolution Thermogravimetric Analysis (HRes-TGA), Heat Flux Differential Scanning Calorimetry (Heat Flux-DSC) and temperature variable X-ray Powder Diffractometry (HT-XRPD), in order to get a better understanding of the intermediate reaction stages and to assess the equilibrium compounds as well. As concerns the measurements performed on mixtures with X Li<0.333, LiMn 2O 4 and excess Mn 2O 3 are the obtained equilibrium products. By 0.33< X Li<0.50 a mixture of LiMn 2O 4 and Li 2MnO 3 is obtained whose proportions depend on the reaction path followed. A stoichiometric model, where both lithium manganese oxides form simultaneously, holds for X Li=0.45 and 0.50 mixtures. A two stage model, where Li 2MnO 3 forms first, followed by reaction with excess Mn 2O 3 to yield LiMn 2O 4, is the reaction path for the X Li=0.35 mixture.