Sustainable approach for Li-ion battery separators: Interfacial interactions in modified cellulose acetate/chitin nanofiber membranes

The rapid escalation of electronic waste has driven interest in developing sustainable materials for lithium-ion batteries. Conventional polyolefin separators are difficult to recycle and can persist after disposal, which motivates the development of bio-based alternatives. Herein, a nature-based composite membrane based on cellulose acetate (CA) and chitin nanofibers (CN) is developed to balance ionic transport, thermal stability, and structural integrity. The membranes were fabricated by non-solvent-induced phase inversion and chemically modified to improve electrolyte stability. CN incorporation can increased porosity and improved electrolyte wettability. CN also reduced wrinkling and dimensional shrinkage during drying, and the modified membranes maintained low thermal shrinkage at elevated temperature. With an optimized CN content, the CA/CN membrane achieved an ionic conductivity of 0.57 mS cm⁻¹ while retaining low shrinkage. These improvements are attributed to the rigid CN framework and a strengthened hydrogen-bond network in the modified CA matrix. Density functional theory (DFT) calculations suggest that chitin incorporation modifies the local coordination environment and slightly weakens Li⁺-polymer binding, supporting more reversible ion coordination and enhanced ionic mobility. Overall, this work shows how interfacial interactions in modified CA/CN membranes control electrolyte affinity and Li⁺ transport, providing a design guide for sustainable lithium-ion battery separators.