Thermal stability and structural changes of Li4Mn5O12 under oxygen and nitrogen atmosphere

The thermal stability and structural changes of well-crystallized Li4Mn5O12 powder with a grain size of 0.1-0.3 mu m have been investigated with thermogravimetric analysis (TGA), X-ray diffraction (XRD), and high-temperature X-ray diffraction measurements (HT-XRD). Li4Mn5O12 crystallites are stable at temperatures up to 600 degrees C in oxygen or air, but decompose to spinel LiMn2O4 and monoclinic Li2MnO3 at temperatures between 530 and 680 degrees C, and to LiMnO2 and Mn3O4 at temperatures above 680 degrees C in nitrogen. No apparent structural change was detected with XRD and HT-XRD when Li4Mn5O12 was heated in O-2 up to 700 degrees C, but a reversible weight loss/gain due to the evolution/uptake of oxygen was observed by TGA between 400-700 degrees C. The deficiency of oxygen in Li4Mn5O12-delta is found to be in the region 0 < delta less than or equal to 0.5. (C) 1996 Academic Press, Inc.