Preparation of PVdF nanofiber membranes by electrospinning and their use as secondary battery separators

This paper reports the development and characterization of polyvinylidene fluoride (PVdF) nanofiber separators for high rate discharge secondary batteries. The preparation of PVdF nanofiber separators was performed by an electrospinning method. The pore properties of PVdF nanofiber separators were optimized by variation of spinning conditions, after post treatment and sheet forming. The optimized PVdF nanofiber separators were characterized by scanning electron microscopy (SEM), pore properties, mechanical/thermal characteristics, water/electrolyte uptakes and electric properties. The high porosity (48%) led to a high electrolyte uptake level (142 wt%) which is necessary for thin batteries. The PVdF nanofiber separators reached higher tensile strength of 14.8 MPa/cm2 and elongation of 117% and compared to commercial PE separator, they also exhibit higher thermal stability, up to 135 °C under air. Also, PVdF nanofiber separators showed excellent performance in tests of cyclic fading rates and high rates of discharge.