Effect of Silica and Tin Oxide Nanoparticles on Properties of Nanofibrous Electrospun Separators

Recently the use of electrospun separators in lithium ion batteries has been studied due to the outstanding properties of the nanofibrous non-woven constructs [1]: high porosity, high pore interconnectivity and wide surface area that lead to a large electrolyte uptake with respect to a commercial microporous separator, e.g. Celgard. This behaviour makes electrospun mats suitable for high ionic conductivity applications in lithium cells. Further improvements in membrane properties can be achieved through dispersion of additives (such as oxides particles) inside nanofibers, aiming at increasing the mechanical, thermal and electrical properties of the polymeric separators, in order to satisfy lithium battery safety concerns and capacity requirements. The use of nanoadditive to improve the properties of electrospun membranes for polymer electrolyte batteries is a quite novel topic, not completely investigated in literature.

In this work Poly(vinylidene fluoride) (PVDF) solutions have been filled with fumed silica and tin oxide nanoparticles and electrospun to produce lithium battery separators. Membrane morphology characterization and energy dissipation spectroscopy have been carried out by means of a scanning electron microscope, in order to evaluate fiber quality, fiber diameter distribution and the presence of the additives inside the material. Thermogravimetric analysis, Differential Scanning Calorimetry, and tensile tests have been used to evaluate thermal stability, thermal and mechanical properties of the separators and to quantify the inorganic fraction. Electrical characteristics have been investigated through dielectric spectroscopy and conductivity measurements in order to ensure the very low electric conductivity of the membranes regarding electronic carriers. Nanoparticle dispersion inside the fibers has been evaluated by means of a transmission electron microscope. Finally, the electrospun separators have been soaked in electrolyte solution to estimate their uptake performance.

[1] F. Croce, M.L. Focarete, J. Hassoun, I. Meschini, B. Scrosati, A safe, high-rate and high-energy polymer lithium-ion battery based on gelled membrane prepared by electrospinning, Energy and Environmental Science, 2011, 4, 921–927.