An Efficient, Scalable Route to Robust PVDF-co-HFP/SiO₂ Separator for Long-Cycle Lithium Ion Batteries

A highly uniform, heterogeneous-phase composite separator is synthesized by a direct post-solidation process from the mixture of nano-SiO₂/acetone monodisperse suspension and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP)/acetone gel, without any organic surfactants. This technique leads to the PVDF-co-HFP/SiO₂ composite separator outstanding microstructural uniformity. The incorporation of SiO₂ nanoparticles leads to reduced crystallinity (≈27%), enhanced wettability (≈14%), improved electrolyte uptake (≈420%), and enhanced mechanical strength (>14 MPa) of the composite separator. These enhanced properties of the separator translate into remarkable LiFePO₄/Li battery performance with reduced polarization, a high room-temperature capacity of 165 mAh g⁻¹ at 0.5 C, a high thermal dimensional stability (≈4.5% shrinkage after annealing at 160 °C for 1 h) and 5.2% capacity degradation after 1500 charge/discharge cycles at 2 C.