Effect of Coagulation Bath Composition on Cellulose-Based Polymer Electrolyte Fabricated via Non-Solvent-Induced Phase Separation Method

Abstract

Cellulose acetate (CA) membrane was developed through a non-solvent-induced phase separation (NIPS) technique to replace the commercial petroleum-based Celgard separator membrane in Li-ion battery (LIB). The morphology of a membrane can have a substantial impact on both its mechanical and electrochemical properties, which are influenced by the solvent-nonsolvent interaction. Therefore, this study examined the effect of solvent fraction in an acetone-water system on the membrane morphology. CA dissolved in acetone was cast on a glass plate and immersed in the coagulation bath with varying acetone-water ratios. The resulting free-standing membrane was analyzed subsequently and showed increased porosity, hydrophilicity, and electrolyte uptake with higher acetone ratios in the coagulation bath. It was also found that a more porous membrane contributes to a lower tensile strength, including, 6.8 MPa, 5.5 MPa, 4.6 MPa, and 2.6 MPa for the coagulation baths containing 0%, 25%, 50%, and 75% acetone, respectively. These results showed that the mechanical properties of CA membranes are higher than those of commercial Celgard membranes (1.42 MPa). LIB separator performance was measured using electrochemical impedance spectroscopy (EIS). CA membrane fabricated with 50% acetone content in the coagulation bath possessed the highest ionic conductivity, 4.79×10-4 S/cm, which is higher than the ionic conductivity of the Celgard membrane (9.41×10-7 S/cm). Considering their superior mechanical properties and electrical performance, CA membranes could potentially substitute Celgard as a more sustainable alternative for LIB separators. 

Keywords

• cellulose acetate
• coagulation bath
• lib separator
• nips