Survey of the Polyvinylidene Fluoride (PVDF) ratio and evaluation of electrochemical properties of Gel-Polymer PEO/PVDF/SiO2/LiTFSI membranes used for Li||LiFePO4 batteries

This paper presented the preparattion of a gel polymer electrolyte (GPE) based on poly(ethylene oxide) (PEO) as the host polymer, by blending with the additives polyvinylidene fluoride, PVDF, and a combination of nano silica (SiO2) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. The GPE membranes were prepared by dissolving the compounds in N,N-dimethylformamide (DMF) solvent and drying at 60 oC. The results showed that the addition of PVDF improved the thermal stability and enhanced the mechanical properties of the GPE membrane structure. Futhermore, the incorporation of SiO2 promoted the dissociation of the Li+ ion from the LiTFSI salt. The electrochemical properties of the GPE membranes were investigated within the range of PVDF mass concentrations at 0%, 5%, 10%, 15% and 20%, with a fixed 5 wt% SiO2 and 15 wt% LiTFSI relative to the total PEO mass. The Linear Sweep Voltammetry (LSV) measure showed that the sample with the composition of PEO – 5 wt% PVDF – 5 wt% SiO2 – 15 wt% LiTFSI being the best oxidation onset potential (3.9 V vs. Li+/Li). The Electrochemical Impedance Spectroscopy (EIS) results showed that the Li+ ion conductivity of this GPE membranes reached 2.32 × 10-4 S/cm at 60 oC, and the discharge capacity was 104 mAh/g at C/10 rate. The obtained results showed that the GPEs would be for applications in Li−ion batteries.