The effect of polymer concentration on ion conductivity of the all-solid-state nanofibrous electrolytes applicable in lithium ion batteries

In recent decades, solid polymer electrolytes (SPEs) have appeared as a safe alternative for liquid electrolytes of lithium ion batteries (LIBs) which provides fabrication of all-solid-state and flexible LIBs. SPEs are basically consisted of a host polymer and a lithium salt which are commonly prepared through a film casting technique. Herein, fabrication of all-solid-state nanofibrous electrolytes by using an electrospinning process was reported. Polyethylene oxide (PEO) and Lithium perchlorate (LiClO4) were applied as polymer matrix and lithium salt, respectively. The effect of PEO concentration (7 %, 8/5 % and 10 % wt.) on morphology and ion conductivity of the electrospun electrolytes was evaluated. SEM images showed increase of average diameter of the nanofibers with the increment of polymer concentration. This can be assigned to the improvement of solution viscosity and so more entanglement between the polymer chains which lead to the formation of thicker electrospun fibers. FTIR spectra confirmed the complexation between the PEO and LiClO4. The Nyquist plot revealed decrease of impedance with the reduction of PEO concentration. The highest conductivity of 0/0167 mS.cm-1 was obtained for the electrospun electrolyte containing 7 % wt. PEO. This could be attributed to the difference between fiber diameters, leading to various porosities and pore sizes. With the reduction of nanofiber’s diameter, porosity increases while the 58 size of pores decreases. Thus, the lithium ions will go through tiny pores as well as PEO segment that gives rise to higher ionic conductivity. Notably, the as-spun electrolyte showed 10 times greater ion conductivity than the SPE synthesized by film casting method. The obtained results suggest that further optimization might lead to practical uses of nanofibrous electrolytes in lithium ion batteries.