Poly(vinylidene fluoride)/SiO₂ composite membranes prepared by electrospinning and their excellent properties for nonwoven separators for lithium-ion batteries

PVdF/SiO₂ composite nonwoven membranes exhibiting high safety (thermal stability), high ionic conductivity and excellent electrochemical performances are firstly prepared by electrospinning poly(vinylidene fluoride) (PVdF) homopolymer and silicon dioxide (SiO₂) sol synchronously for the separators of lithium-ion batteries (LIBs). Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and hot oven tests show that the PVdF/SiO₂ composite nonwoven membranes are thermally stable at a high temperature of 400 C while the commercial Celgard 2400 PP membrane exhibits great shrinkage at 130 C, indicating a superior thermal stability of PVdF/SiO₂ composite nonwoven membranes than that of Celgard membrane. Moreover, the composite membrane exhibits fairly high ionic conductivity (7.47 × 10^-3 S cm^-1) that significantly improves the performance of LIBs. The PVdF/SiO₂ composite membranes are also evaluated to have higher level of porosity (75-85%) and electrolyte uptake (571-646 wt%), lower interfacial resistance compared to the Celgard separator. The lithium-ion cell (using LiFePO₄ cathode) assembled with the composite membrane exhibits more stable cycle performance, higher discharge capacity (159 mAh g^-1) and excellent capacity retention which proves that they are promising candidates for separators of high performance rechargeable LIBs.