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

Abstract

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.