Application of cellulose/poly(vinylidene fluoride) blend films as polymer electrolytes in lithium ion batteries

Polymer electrolytes are the most promising replacement for liquid electrolytes in lithium ion batteries (LIBs) due to their unique properties. Beside this, polymer blends are usually used as polymer electrolytes to achieve expectable properties including properties of each component. In this study, cellulose/poly(vinylidene fluoride) (PVDF) blend films are prepared <i>via</i> solution casting at different weight ratios. To investigate phase behavior of binary system, the thermodynamic interaction parameter of Flory-Huggings is evaluated. The X-ray diffraction spectroscopy (XRD) analysis is conducted to investigate the structural properties of samples. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) analyses were performed to study thermal behaviors. Mechanical properties are investigated by tensile test and electrochemical properties such as electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), and chronoamperometry are studied. The results and morphology of these blends showed phase separation of two polymers. This phase separation led to the creation of free volume, which is a path for ion transfer; therefore, the ion conductivity was obtained in the range of 10^-4 S cm^-1. In addition, high transfer number (0.41 < t⁺ < 0.97), wide electrochemical stability window (>5 V), acceptable charge capacity (>200 mAh/g at 0.2C), and long cycle stability was achieved.