Since pyrometallurgical approaches on lithium ion battery recycling are not yet capable of recovering lithium but only nickel, cobalt and manganese, the Chair of Thermal Processing Technology at the Montanuniversitaet Leoben started to investigate experimental reactor concepts on their suitability to overcome this major drawback. Therefor, the general behaviour of currently used cathode materials under reducing conditions and high temperatures is of great interest. This work expands previous performed heating microscope experiments by thermogravimetric analysis (TGA) to characterize the reactions that are responsible for certain changes in the cathode materials. By comparing the superficial changes of the samples in the heating microscope with the corresponding data from the TGA, it was possible to identify the temperature zones in which reduction reactions occured. For all investigated cathode materials, the reduction reactions started at technically feasible temperatures of approx. 1000 °C, which is favorable for the desired recycling process. On the other hand, this is some hundred degrees higher than the temperature at which first changes in the heating microscope could be observed and indicates that there are changes in the material before the reduction starts. Therefore, the results also emphasize the need for further analysis to clarify this offset and to complete the thermal characterisation of the cathode materials.