Hard carbon-based electrode boosts the performance of a solid-state symmetric supercapacitor

Hard carbon materials have gained extensive utilization in energy storage systems because of their stable chemical properties, unique lamellar arrangement, and significant interlayer spacing. In this study, we present a novel porous carbon electrode based on hard carbon to enhance the performance of a solid-state symmetric supercapacitor. This electrode was fabricated through an efficient and straightforward synthetic approach using natural asphalt as the precursor. The resulting carbon electrode exhibits remarkable features including a large surface area (2334.48 m² g⁻¹), a well-distributed pore size (mesopore ratio of 16.04 %), an appropriate oxygen content (18.11 %), and a lamellar structure. As a result, the as-prepared carbon electrode demonstrates a high specific capacitance of 325.82 F g⁻¹ at 0.5 A g⁻¹, along with excellent rate capability, with coulombic efficiency ranging from 99.89 % at 0.5 A g⁻¹ to 98.92 % at 10 A g⁻¹. Moreover, the assembled symmetrical all-solid-state supercapacitor utilizing this electrode achieves an energy density of 18.91 Wh Kg⁻¹, an equivalent series resistance of 0.820 Ω, a relaxation time of 9.0 s, and self-discharge performance lasting up to 72 h. Notably, owing to its large layer spacing (0.391 nm), the electric double layer capacitor contributes as much as 94 %, indicating favorable electrical double layer characteristics. Our work not only showcases a high-performance electrode material but also contributes to the expanded application of hard carbon.