Inorganic Fillers as Stabilizing Agents for PVdF-HFP QSSEs: Inhibition of HF Degradation Pathways

The urgent demand for efficient energy storage systems, driven by the global green transition, has catalysed the development of innovative solutions to enhance the safety, capacity, durability, and recyclability of lithium-ion batteries. In this context, PVdF-HFP-based quasi-solid-state electrolytes (QSSEs) represent a promising pathway toward safer and more robust battery technologies. However, these electrolytes typically employ fluorine-based lithium salts (e.g., LiPF6, LiFSI, and LiTFSI), which are susceptible to hydrolysis in the presence of moisture—whether introduced during manufacturing or through accidental cell compromise. This process leads to the formation of hydrofluoric acid (HF) , a highly corrosive species that attacks the cathode material, resulting in severe capacity fade and reduced operational life. To mitigate these degradation pathways, the incorporation of specific inorganic fillers into the polymeric matrix has been proposed to inhibit HF-related reactions and ensure long-term stability under humid conditions. In the present study, various lithium salts were initially screened, with LiFSI selected as the optimal candidate due to its superior ionic conductivity. Subsequently, cerium oxide nanoparticles, functionalized to enhance compatibility with the polymer matrix, were integrated into the electrolyte. The resulting QSSEs underwent comprehensive thermal, mechanical, and electrochemical characterization. Furthermore, deliberate water contamination tests were performed to validate the material's efficacy in preventing HF formation. The optimized QSSEs were successfully integrated into full cells, demonstrating remarkable capacity retention and coulombic efficiency even in the presence of significant moisture levels.