New Insights on the Origin of Chemical Instabilities Between Poly(carbonate)-based Polymer and Li-containing Inorganic Materials

Composite electrolytes, owing to their ability to combine both polymeric and ceramic properties are promising candidates for Solid-State-Batteries (SSBs). In this paper, we assess the effect of ceramic fillers (Li_1+x Al_x Ti_2-x P₃ O₁₂ , Li_6.55 Ga_0.15 La₃ Zr₂ O₁₂ and Al₂ O₃ ) in a poly(ethylene oxide carbonate)-LiTFSI matrix. First, the role of the filler chemistry on thermal and electrochemical properties is evaluated: reduced polymer crystallinity leads to an increased ionic conductivity at low temperatures; and the ionic conductivity at low temperatures (<30 °C) is improved for LLZO filler particles. This behaviour is commonly attributed to new conduction pathways generated within the fillers. However, we also demonstrate that a polymer degradation is induced by the filler chemistry by modifying the polymer chemistry in poly(ethylene glycol), initiated by LiOH that can be found on the LLZO surface. The electrolyte containing LATP or Al₂ O₃ does not induce any degradation. Hence, special attention must be paid to surface impurities, as degradation may occur.