Synergistic Ternary Coating Enables Degradable and Flame-Retardant Air-Laid Paper Separators for Supercapacitors

Abstract Green and safe separators are regarded as key materials for the construction of renewable and environmentally friendly energy storage devices. Air-laid paper (AP) exhibits promising application prospects owing to its excellent flexibility, high porosity, and acceptable degradability, yet its inherent high flammability severely restricts its use in high-safety energy storage devices. Accordingly, a starch/ammonium polyphosphate/montmorillonite (ST/APP/MMT) ternary composite flame-retardant separator is fabricated on an AP substrate via a facile coating method. Benefiting from the synergistic effects of catalytic charring, intumescent charring, physical barrier, and gas dilution, an organic–inorganic hybrid three-dimensional carbonization network is formed on the fiber surface, which effectively improves the flame retardancy of the separator while maintaining its porous structure and ion transport properties. The resultant separator achieves a high limiting oxygen index (LOI) of 46.25%, and the char residue at 800 °C is increased by 28.09% compared with pure AP, demonstrating outstanding flame-retardant performance. Besides, the flame-retardant separator exhibits an ionic conductivity of 2.78 mS cm–1, showing no significant reduction relative to the pure AP separator. The supercapacitor assembled with the separator still exhibits a capacitance retention rate of 91.74% after 5000 charge–discharge cycles, demonstrating superior electrochemical performance that outperforms most reported flame-retardant separators. This work achieves synergistic optimization of flame retardancy, ionic conductivity, and comprehensive electrochemical properties for paper-based separators, paving a feasible route toward the application of paper-based materials in advanced energy storage systems.