In this work we report the investigation of the structural and the electrical properties of orthorhombic LiMnO2 in a wide temperature range in air and in high purity argon (N5). Also we present a correlation between the electrical and the electrochemical properties of the material upon lithium deintercalation. Moreover, its chemical stability against LiPF6 based liquid electrolyte at elevated temperatures was measured and compared with other cathode materials. High temperature investigations revealed occurrence of phase transitions. During heating in oxidizing and in inert atmosphere orthorhombic phase decomposes into LiMn2O4 and LiMn2O3. The conducted experiments also pointed to the instability of orthorhombic LiMnO2 during electrochemical lithium deintercalation. Both electrical conductivity and thermoelectric power of deintercalated samples altered substantially. DSC measurements proved high thermal stability of LiMnO2 based cathode material in contact with commercial liquid electrolyte.