Sulfonate betaine modified PVDF/SiO2 composite electrolyte for solid state lithium ion battery

High thermal stability, mechanical property and electrochemical stability of polyvinylidene fluorid (PVDF) make it a promising solid electrolyte polymer matrix. However, it also faces some challenges such as low ionic conductivity, high crystallinity degree and the absence of reactive groups. Herein, PVDF powder was modified by chemical grafting amphiprotic sulfonate betaine (SB) for solid electrolyte (SB-PVDF) with high ionic conductivity and chemical stability. Furthermore, to improve the mechanical property and reduce the crystallinity degree of SB-PVDF, 3%, 6% and 9% SiO 2 nanospheres were also incorporated into SB-PVDF, and the resultant composite polymer solid electrolytes were marked as 3% SiO 2 /SB-PVDF, 6% SiO 2 /SB-PVDF, 9% SiO 2 /SB-PVDF. The results showed that 6% SiO 2 /SB-PVDF membrane exhibited the best overall performances, possibly due to the synergistic effect of amphiprotic SB modification and uniform dispersion of SiO 2 filler in PVDF matrix. For example, the solid-state battery Li//6%SiO 2 /SB-PVDF//LiFePO 4 delivered the initial discharge capacity of 153.0 mAh/g at 0.2 C and the reversible discharge capacity of 124.4 mAh/g at 1.0 C with the capacity retention rate of 93.8%, indicating high feasibility for solid-state lithium ion battery.