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 μm 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°C in oxygen or air, but decompose to spinel LiMn₂O₄ and monoclinic Li₂MnO₃ at temperatures between 530 and 680°C, and to LiMnO₂ and Mn₃O₄ at temperatures above 680°C in nitrogen. No apparent structural change was detected with XRD and HT-XRD when Li₄Mn₅O₁₂ was heated in O₂ up to 700°C, but a reversible weight loss/gain due to the evolution/uptake of oxygen was observed by TGA between 400-700°C. The deficiency of oxygen in Li₄Mn₅O_12-δ is found to be in the region 0 < δ ≤ 0.5.