Seyedeh Nooshin Banitaba, Dariush Semnani, Elahe Heydari-Soureshjani, Behzad Rezaei,Ali Asghar Ensafi,

Summary Insertion of conductive fillers into solvent-free polymer electrolytes enhances electrochemical behavior of the electrolyte membranes leading to higher ionic conductivity, lower capacity fading, and so on. Although, the presence of the conductive fillers in the polymer matrixes increases the risk of electrical shorting, herein, polyethylene oxide (PEO)-based core-shell nanofibers were prepared via a simple electrospinning method. In the core-shell electrospun fibers, ethylene carbonate (EC) and lithium perchlorate (LiClO4) were used as a plasticizer and as a lithium salt, respectively. The core component was enwrapped by the PEO/EC/LiClO4 shell part incorporated with SiO2 nanoparticles. Various properties of the fabricated membranes were evaluated by changing the ratio of multiwall carbon nanotubes (MWCNTs) in the core part of the nanofibers. The morphology and core-shell structure of the electrospun fibers were studied by FESEM and TEM images. According to FTIR and XRD results, addition of the EC plasticizer and the fillers into the as-spun fibers increased the fraction of free ions and the amorphous regions. From electrochemical impedance spectroscopy studies, the ionic conductivity enhanced by insertion of the plasticizer molecules and the filler particles into the core-shell structures. The highest ionic conductivities of 0.09 and 0.21 mS.cm−1 were obtained for the free-filler and the fillerloaded nanofibrous membranes, respectively. The prepared mats obeyed the Arrhenius behavior (R2 ~1). Dielectric studies confirmed the obtained data from the ionic conductivities. Furthermore, the capacity residual was enhanced from 69% to 85% by incorporation of the MWCNTs filler into the core component of the electrospun nanofibers. The presented results may facilitate development of versatile nanofibrous membranes embedded with the conductive fillers as solvent-free electrolytes applicable in lithium-ion batteries.

KEYWORDS core-shell nanofibers, dielectric properties, electrospun polymer electrolyte, ion conductivity, multiwall carbon nanotube filler