Exceptional cyclability of thermally stable PVdF-co-HFP/SiO₂ nanocomposite polymer electrolytes for sodium ion batteries

Thermally stable composite polymer electrolyte (CPE) devising PVdF–co–HFP polymer with in–situ generated silica (SiO₂) as filler is synthesised via non–solvent– induced phase inversion technique. The filler loading of in–situ synthesised silica in PVdF–co–HFP is varied from 0 to 9 wt% and its morphological, thermal and electrochemical characterization is carried out. Among the different composite electrolytes, the PVdF–co–HFP containing 6 wt% SiO₂ shows the uniform microporous structure with a highest porosity (84 %), surface area (784.14 m² g⁻¹), electrolyte uptake (262 %) and electrolyte retention value (0.48). The incorporation of in–situ SiO₂ on CPE shows not only the enhancement in thermal stability but also reduced thermal shrinkage with an increase in the filler content. The electrochemical studies of PVdF–co–HFP containing 6 wt% SiO₂ shows a higher ionic conductivity (0.71 mS cm⁻¹) and potential stability >4.5 V verses Na/Na⁺. The Na–ion half–cells assembled with PVdF–co–HFP/SiO₂ composite electrolyte show a specific capacity of ∼120 mAh g⁻¹ at 0.3C rate in room temperature and a stable cycle performance with a Coulombic efficiency of around 100 % for 200 cycles.