A Phenoplast-based Structural Electrolyte with High Ionic Conductivity for Fire-Resistant Energy Storage Composites

Structural energy storage composites present a transformative solution for lightweight, multifunctional systems by simultaneously carrying mechanical loads and storing electrical energy, significantly benefiting battery-powered drones, aircraft, and mobile robots. However, conventional epoxy-based polymer electrolytes are highly flammable, limiting their practical applications. The present study addresses this critical challenge by introducing a fire-resistant polymer electrolyte consisting of phenolic resin (phenoplast), ionic liquid (EMIM TFSI), and lithium salt (LiTFSI). The innovation lies in the synergistic interaction between ionic liquid and lithium salt, which enables emulsion polymerization of the phenolic resin, yielding a 3D cocontinuous microstructure where lithium ions complex with hydroxyl groups to form highly efficient ionic conduction pathways. The electrolyte's ionic conductivity and mechanical properties are tunable by adjusting the weight ratios of ionic liquid and lithium salt, achieving a remarkable ionic conductivity of 2.87 mS/cm and mechanical strength of 19 MPa, with ionic conductivity nearing that of pure ionic liquid. Additionally, the inclusion of MXene nanofillers further enhances ionic conductivity without compromising mechanical strength. Remarkably, the phenoplast-based electrolyte achieves exceptional flame retardancy (V-0 rating), significantly exceeding those of conventional epoxy-based solidelectrolytes. Composite structural supercapacitors incorporating the new electrolyte demonstrate outstanding electrochemical, mechanical, and fire-resistance performance, indicating its significant potential to greatly advance safer and more efficient structural energy storage technologies.