Thermogravimetry and X-ray diffraction study of the thermal decomposition processes in Li2CO3-MnCO3 mixtures

The thermal decomposition processes taking place in solid state mixtures Li2CO3–MnCO3 (xLi=0.10–0.50, xLi=lithium cathionic fraction) have been studied (both in air and nitrogen flow) by thermogravimetric analysis (TGA), in order to get a better understanding of the different possible by-products, and by X-ray powder diffractometry (XRD) to assess the equilibrium compounds. As concerns the measurements performed in air, LiMn2O4 and excess Mn2O3 are the equilibrium products obtained for xLi up to 0.33. By 0.33xLi0.50 a mixture of LiMn2O4 and Li2MnO3 is obtained. In this case the TGA data show that an excess lithiated spinel phase (Li1+xMn2O4) is obtained as an intermediate phase. The measurements performed in nitrogen (xLi up to 0.33) show, when examined by TGA, the formation reaction of LiMn2O4 and Mn3O4 which is completed within about 720°C. At higher temperatures a rather complex reaction takes place between LiMn2O4 and the excess Li2O present at 720°C, leading to the formation of the compounds Li2Mn2O4 and LiMnO2 again with excess of Mn3O4. At higher mixture lithium content (0.33xLi0.50) LiMn2O4, Li2MnO3 and Mn3O4 form up to about 720°C. At higher temperatures LiMnO2 is by far the majority phase present which is formed by solid state reactions occurring between LiMn2O4 and Li2MnO3 and between Li2MnO3 and Mn3O4.