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 (TEABF 4 ) in acetonitrile electrolyte. F-Gr, prepared via a double-step reduction and thermal activation strategy, exhibits ideal interlayer spacing, less oxygen groups, and restored sp 2 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.