Room-Temperature Hybrid Solid Polymer Electrolytes Incorporating Poly(vinylidene fluoride-co-hexafluoropropylene), Ionic Liquids, and Ceramic Particles for Solid-State Batteries

This work presents the development of solid polymer electrolytes (SPEs) for next-generation solid-state batteries. Solid polymer electrolytes were prepared based on a polymer matrix (poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP)) doped with 16 wt % ceramic particles (barium titanate oxide (BTO), barium strontium titanate (BST), and lead zirconate titanate (PZT)) and an ionic liquid (IL, [PMPyr][TFSI]) at 40 wt %. The ionic liquid allows improvement of the ionic conductivity of the system, whereas the ceramic particles are included to enhance the mechanical strength and thermal stability of the system. The physical, morphological, and electrochemical characteristics of the SPEs were studied. The addition of ceramic particles and ionic liquids does not affect the morphology, which remains a compact morphology. In the same way, the degree of crystallinity, polymer phase, and thermal properties of the SPE remain similar to the pristine polymer after filler addition. The inclusion of both ceramic particles and the ionic liquid allowed improvement of battery performance. Ionic conductivity in the order of 2.41 × 10^-5 S cm^-1 was achieved, accompanied by a battery capacity performance very close to theoretical values. Battery performance with PVDF-HFP/BST/IL (153 mAh g^-1) and PVDF-HFP/BTO/IL (148.2 mAh g^-1) composites proved to be successful in long-life cycling, bearing a higher capacity and stability compared to PVDF-HFP/IL (121.3 mAh g^-1). When varying C rates were applied, the PVDF-HFP/BST/IL sample presented superior results, revealing higher stability when compared to the other SPE samples. In conclusion, the fine-tuning of the ceramic particle type within SPE formulations offers an avenue for battery performance optimization. In particular, the inclusion of BST in the hybrid SPE composite allows improvement of battery cycling stability.