Optimization of ionic conductivity of electrospun polyacrylonitrile/poly (vinylidene fluoride) (PAN/PVdF) electrolyte using the response surface method (RSM)

Abstract

Polyacrylonitrile/poly (vinylidene fluoride) fibrous membranes were prepared by electrospinning of PAN and PVdF solution and were soaked in 1 M lithium perchlorate (LiClO4) in ethylene carbonate (EC)/diethyle carbonate (DEC) (1:1 wt.%) solution in order to prepare polymer electrolyte membranes. Response surface method (RSM) was used to obtain a quantitative relationship between selected electrospinning parameters, i.e., applied voltage, solution concentration, and PVdF content. The measured response is ionic conductivity of electrolyte membranes. The Box–Behnken method was applied to design of experiments. Importance of parameters in the model was determined by analysis of variance (ANOVA). The model was used to find the maximum ionic conductivity of electrolyte membranes as optimum result. The morphology of fibers was investigated by field emission scanning electron microscopy (FESEM). FESEM results show that the PAN/PVdF membrane has interconnected multifibrous layers with ultrafine porous structure that leads to a high ionic conductivity and efficient lithium ion transport. Produced fibrious membranes show uniform morphology. Average fiber diameter lies between 116 and 379 nm, and membranes have high porosity of 48–90 % and electrolyte uptake of 303–493 %. The polymer electrolyte membranes show good ionic conductivity in the order of 10−3 S cm−1 at ambient temperature. Ionic conductivity decreases with increase of solution concentration and increases with increase of PVdF composition. Voltage has no significant effect on ionic conductivity of the membranes. The model predicted the maximum ionic conductivity of 7.98 mS cm−1 when the voltage was set at 21.57 kV, the solution concentration set at 14.02 wt.%, and the PVdF composition set at 69.48 wt.%.