Solid state batteries (SSBs) are a promising alternative to currently available Lithium ion batteries (LIBs). Instead of organic liquids in LIBs, the electrolyte is replaced with an ion conducting solid in SSBs. One important advantage of SSBs is their improved safety due to the lack of flammable liquids within the battery cell. However, while safety is an often-quoted property, investigations on thermal stability are still scarce.

In the past decades, numerous solid state electrolytes have been fabricated and their material properties are well characterized. Polymer electrolytes are especially attractive due to their facile processing options. In addition, composite cathodes containing both electrode active material and electrolyte are easily prepared with polymer electrolytes. A homogeneous composite cathode is crucial for SSB operation, but examinations about their thermal stability are rare.

Thus, we decided to investigate the influence of a cathode material with different states of charge towards the thermal stability of some polymer electrolytes to determine possible reactivity changes due to charging or discharging. Using NMC 622 and PEO based electrolytes with different lithium salts we fabricated composite electrodes for maximizing the electrode/electrolyte interface contact. Examining the thermal stability of these materials was carried out by TGA/DSC. We identified both exothermal or endothermal processes and the temperature range in which decomposition took place. Volatile decomposition products were analyzed during the measurement using FTIR and mass spectroscopy to collect information about the kinds of chemical reaction during decomposition.