Sustainable [EMIM]OAc–Nanocellulose Ionogels for Flexible High-Performance Supercapacitors

Abstract

The increasing global demand for sustainable energy storage systems has intensified the investigation for advanced materials that combine high performance with environmental compatibility. In this context, ionogel electrolytes (IGEs) have emerged as promising candidates for all-solid-state energy storage devices owing to their outstanding thermal and chemical stability. Nevertheless, simultaneously achieving high ionic conductivity, mechanical flexibility, and thermal robustness remains a major challenge for conventional ionic liquid-based polymer ionogels. This work presents the fabrication of a supercapacitor based on an eco-friendly ionogel electrolyte composed of 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc) and a carboxymethyl cellulose nanofibrillar network (CMCNF) processed from carboxymethyl cellulose (CMC) using a combined physicochemical and mechanical fibrillation process. Flexible electrodes were prepared via a water-based slurry method using active carbon, acetylene black and polyvinylidene fluoride (PVDF). Material characterization revealed a homogeneous ionogel structure with strong intermolecular interactions and an amorphous nature, facilitating efficient ion transport. The supercapacitor achieved a specific capacitance of 144 F g–1 at 1 A g–1, while operating over an expanded voltage window about 2.0 V and exhibiting good thermal stability up to 250 °C, thereby overcoming the limitations of conventional aqueous electrolytes. Furthermore, the device exhibited remarkable mechanical flexibility and long-term durability, retaining about 80% of its initial capacitance after 10,000 charge–discharge cycles. These findings demonstrate that the proposed nanocellulose-based ionogel provides a sustainable and scalable strategy for high-performance flexible supercapacitors, effectively bridging the performance gap between high-power aqueous systems and high-energy organic electrolyte devices.