Electrospun PVDF/PU Nanofiber Web As Lithium Ion Polymer Separator

Electrospinning is one of the most important methods to produce nanofibers or ultrafine fibers. In this work isocyanate reactive polyurethane(PUR) was added into Poly(vinylidene fluoride)(PVDF) in term of immersing and electrospinning. PUR is prone to form a chemically semi-interpenetrating network based on PVDF electrospun fibrous membrane through cross-linking, and plays a role of shutter by melting on PVDF nanofibers.Influential factors of PVDF nanofiber membrane in electrospinning were firstly studied. The fiber morphology was investigated by scanning electron microscopy (SEM). The optimum condition of electrospinning is given as follows:12wt% solutions of PVDF in a mixed solvent (acetone/DMF=4/6 by weight), the distance of 15cm between the capillary tip and the collector, applied voltage of 15kv, and flow rate of 0.3ml/h.By introducing PUR, PVDF was also electrospun at the optimum condition of PVDF. The morphology and average diameter of electrospun fibers was possibly affected by the addition and PUR's polyreaction. SEM observation indicates that the most ultrafine fibers was obtained from the compound which consist of 5wt% PUR, and the addition amounts of PUR have no more difference on the morphology and average diameter before polymerization. As PUR increasing the diameter of nanofibers becomes large.The electrospun PVDF nanofiber network was immersed in polyurethane adhesives' liquor, then the hybrid membrane was obtained after be treated. Observation of SEM indicates the optimum fibers were obtained when the PVDF nanofiber membrane was immersed in the 5wt% PUR's liquid. After cross-linking reaction, the non-woven fibers were bonded each other, leading to the increase of the dimensional size of nanofiberMembrane natures of the prepared PVDF and PVDF/PU nanofiber membranes including the mechanical property, electrolyte uptake, porosity and thermal stability were measured and compared. The results show that the tensile strength of electrospun PVDF/PU nanofiber membranes was 7.5Mpa and immersed PVDF/PU membranes was 11.2Mpa, was remarkably enhanced in comparison with pristine PVDF membrane (4.5Mpa). Electrolyte uptake and porosity of the immersed membranes were 65±2% and 230±10%, respectively, showing slight decrease after cross-linking reaction. While the electrospun membranes is 80%,342%, respectively.The ion conductivty of immersed and electrospun membranes were 0.88 x 10-3,1.18 x10-3. In addition, the immersed membranes kept rather stable compared to the electrospun membranes which shrinked 3% within 200℃.