Green Chemistry of Cellulose Acetate Membrane Plasticized by Citric Acid and Succinonitrile for Lithium-Ion Battery Application

Commercial lithium-ion batteries (LIBs) use polyolefins as separators. This has led to increased research on separators composed of renewable materials such as cellulose and its derivatives. In this study, the ionic conductivity of cellulose acetate (CA) polymer electrolyte membranes was enhanced via plasticization with citric acid and succinonitrile. The primary objective of this study was to evaluate the effectiveness of these plasticizers in improving cellulose-based separator membranes in LIBs. CA membranes were fabricated using solution casting technique and then plasticized with various concentrations of plasticizers. The structural, thermal, and electrochemical properties of the resulting membranes were characterized using Fourier Transform infrared (FTIR) spectroscopy, X-Ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and Electrochemical Impedance Spectroscopy (EIS). The FTIR and XRD results confirmed the successful incorporation of citric acid and succinonitrile into the polymer matrix, while the TGA analysis demonstrated the enhanced thermal stability of the plasticized membranes. The shift in the glass transition temperature was determined by DSC analysis. Most notably, the EIS results revealed a significant increase in ionic conductivity, achieving a maximum of 2.7 × 10⁻⁵ S/cm at room temperature. This improvement was attributed to the effect of plasticizers, which facilitated the dissociation of lithium salts and increase the mobility of the lithium ions. The ionic conductivities of plasticized CA membranes are better than those of unmodified CA membranes and commercially available Celgard separator membranes: 4.7 × 10⁻⁶ and 2.1 × 10⁻⁷ S/cm, respectively. These findings suggest that citric acid and succinonitrile are effective plasticizers for cellulose acetate membranes, making them promising substitutes for commercial polyolefin separators in LIB applications.