High-power temperature resilient ionic liquid-driven graphene supercapacitor for an effective solar-powered energy backup system

The growing demand for high-power and energy-dense storage devices necessitates the development of advanced supercapacitor systems that can directly integrate with renewable energy sources. Here, we report an ionic liquid-driven supercapacitor (IL-SSC) device employing defect-engineered few-layer graphene (F-Gr) electrodes using tetraethylammonium tetrafluoroborate (TEABF4) in acetonitrile electrolyte. F-Gr, prepared via a double-step reduction and thermal activation strategy, exhibits ideal interlayer spacing, less oxygen groups, and restored sp2 networks, enabling rapid ion transport and superior conductivity. Structural and spectroscopic analyses confirm effective deoxygenation and defect tailoring, while density functional theory calculations reveal enhanced electronic delocalization of F-Gr compared to rGO. Electrochemically, the F-Gr device sustains an extended operating voltage of 3.0 V, delivering a high specific capacitance of 50 F g− 1 @ 10 mV s− 1, and an energy density of 50.7 Wh kg− 1 (@ 1.25 A g− 1), with a peak power density of 18,750 W kg− 1 (@ 12.5 A g− 1), with 85% capacitance retention after 5000 cycles. The F-Gr IL-SCC device maintains stable performance across a wide temperature window (-10 to 80 °C), highlighting robust ion dynamics in extreme sub-zero and high-temperature resilient conditions. Furthermore, direct integration with a photovoltaic panel demonstrates rapid solar charging to ~ 3 V within 20 s and successful powering of a portable electronic load. Establishing the F-Gr IL-SSC device as a versatile platform bridging the gap between batteries and capacitors, offering a promising route toward high-performance, renewable energy storage and off-grid applications.