Ionic liquid-based molecular design for transparent, flexible, and fire-retardant triboelectric nanogenerator (TENG) for wearable energy solutions

Transparent and flexible triboelectric nanogenerator (TENG) represent an efficient and invisible energy solution for generating eco-friendly electricity from mechanical human motion for wearable electronic devices and systems. In addition to boosting the output performance of TENG, the molecular design relying on non-flammable materials and anti-ignition invulnerability should be considered when designing TENG devices, to ensure the safety of personnel working under extreme temperature conditions. However, the requirement for non-flammability of conventional transparent triboelectric materials in wearable applications remains either unmet or almost unexamined to date. Here, we propose bi-continuous and flame-retarding epoxy-based ion-gel films that retain mechanical flexibility, optical transparency, and fast ionic polarization for high-performance and deformable TENG. It is found that our transparent and flexible TENG devices produce an output voltage and current as high as approximately 150 V and 45 μA, respectively, from an external mechanical stimulus while also retaining their fire retardancy and low flammability. This TENG is not flammable even after 20 s of trying, whereas conventional triboelectric materials were completely burned by the fire under the same conditions. Therefore, we propose that our synergistic design of triboelectric ion-gel films, including fire-retardant epoxy-based dual cation-incorporated ionic liquid, represents a significant step toward a high-performance, durable, and transparent wearable energy solution.