Thermal stability and heat capacity of the LiMnO2 phase

The stability of the LiMnO₂ 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 Li₂O dissolves in the oxide slag based on CaO, Al₂O₃, and SiO₂. In this study, for the first time, the heat capacity of the orthorhombic LiMnO₂ 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 LiMnO₂ can be easily decomposed into cubic spinel and Li₂MnO₃ on cooling. Investigation in Ar indicated that LiMnO₂ 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.