Thermal stability and heat capacity of the LiMnO ₂ phase

Abstract The stability of the LiMnO 2 phase and its thermodynamic properties plays a critical role in the development of cathode materials for lithium‐ion batteries and Li recycling by smelting reduction, where Li 2 O dissolves in the oxide slag based on CaO, Al 2 O 3 , and SiO 2 . In this study, for the first time, the heat capacity of the orthorhombic LiMnO 2 phase was experimentally determined using differential scanning calorimetry under argon flow. The classical three‐step method was employed, and sapphire was used for calibration. Comparisons with predictions based on the Neumann–Kopp rule for oxides showed slight deviations over the temperature range investigated. Differential thermal analysis combined with gravimetry (thermogravimetric analysis) experiments were performed in air and argon atmospheres to support the analysis of microstructural changes. The results obtained in air showed that LiMnO 2 can be easily decomposed into cubic spinel and Li 2 MnO 3 on cooling. Investigation in Ar indicated that LiMnO 2 was stable up to 1330 K where it was possibly decomposed, but the reaction was reversible, and the same phases were found using x‐ray diffraction after cooling.