AbstractThe Li-Mn-O system is a crucial constituent of cathode materials used in lithium-ion batteries (LIBs). Numerous research teams have focused on enhancing its electrochemical properties and thermal stability at lower temperatures to develop high-performance cathode materials. However, in the recycling of LIBs in pyrometallurgical processing, the high temperature phase behavior of the Li-Mn-O system is important. Today, there is still a lack of systematic understanding regarding the high-temperature phase behavior of the Li-Mn-O system under well-defined atmospheric conditions, which is highly sought after in the pyrometallurgical process route to increase the recycling efficiency of lithium from spent LIBs. In this study, we investigate the high temperature phase behavior of the pseudo binary system Li2O-MnO under inert atmosphere. Thermal and caloric properties are measured as well as the contact angle at high temperatures to identify the solid-liquid transition. Based on the obtained phase behavior, thermodynamic database of Li2O-MnO within the Calphad framework is developed, where the liquid phase is modelled by the Modified Quasichemical Model (MQM).