Closed-Loop Fabrication of Regenerated Cellulose Battery Separator via Solvent-Guided Structural Regulation

The development of battery separators derived from renewable feedstocks that can simultaneously achieve high porosity, robust mechanical strength, excellent thermal stability, reliable electrochemical performance, and satisfactory environmental sustainability remains a core challenge in the field of sustainable energy storage material. Herein, we report a regenerated cellulose membrane prepared through a dissolution/regeneration process using lithium bromide Molecular dynamics simulation results show that water is the effective antisolvent for driving the formation of cellulose–cellulose H-bonds, yielding cellulose with a better crystalline structure. Subsequently, tert-butanol was utilized to replace water in the cellulose membrane precursor prior to drying, preventing capillary-induced pore collapse. This membrane exhibits high porosity of 70.1%, excellent electrolyte uptake capacity of 243.7%, ionic conductivity of 0.77 mS/cm, excellent thermal stability (no shrinkage at 150 °C), and roust mechanical strength. The Na/HC half-cells assembled with this membrane displays high cycle capacity retention rate of 87.1% at 0.1 C after 500 cycles, which is comparable to commercial separators. This membrane fabrication process enables closed-loop solvent recycling, and the membrane fully degraded after 4 months of soil burial, and life cycle assessment indicated lower impacts than commercial battery separators. These results establish a practical closed-loop strategy for sustainable, high-performance battery separators.