Study of the effect of silica and tin oxide nanoparticles on electrospun separator properties

In this work we develop nanostructured electrospun separators for lithium batteries made of Poly(vinylidene fluoride) (PVDF) loaded with either fumed silica or tin oxide nanoparticles. The use of high porosity and wide surface area material allows a massive electrolyte uptake; oxide nanoparticles are added to the polymer to increase mechanical, thermal and electrical properties of the separator with the aim to fulfil capacity and safety requirements of lithium batteries. Fiber morphology was observed by SEM and the presence of the additives inside the material was revealed by energy dissipation spectroscopy (EDS). Tensile tests, thermogravimetric measurements and differential scanning calorimetry are carried out to study mechanical properties of the separators, to quantify the inorganic fraction and to evaluate thermal properties. TEM was used to evaluate the quality of nanoparticle dispersion inside the fibers. Conductivity measurements and dielectric spectroscopy on membrane are carried out to ensure low values of electron carriers conductivity. Finally, the electrospun separators are soaked in electrolyte solution to estimate their uptake. The most remarkable effect of nanoparticles addition is a significant improvement of separator mechanical properties, namely the increase of stress at break and elongation at break.