The paper reports the investigations performed in the course of the ESA TRP activity (Contract No. 4000123997/18/NL/HK) on the use of solid polymer electrolytes for safe lithium ion batteries for clean space. The objective is to develop 1Ah prototype pouch cells without using any volatile liquid component. The exchange of conventional, highly flammable electrolytes with solid Li+-conducting polymers significantly improves the electrochemical and thermal stability range of the battery cells. Thereby fragmentation events, and thus propagation of space debris, caused by battery malfunction can be mitigated. In the presented work, filled polymer electrolytes were investigated for potential use in all-solid-state lithium-ion batteries. The polyethylene oxide-based polymer phase was either mixed with a lithium-ion conducting glass-ceramic (active) or BaTiO 3 (passive) filler resulting in self-sustaining solid electrolyte membranes. Furthermore, carbon anodes and NMC622 cathodes were optimized to enable the assembly of full cells with enhanced safety properties.