Capacitance Boosting via Equalization of Space and Ionic Charge Asymmetries

Abstract Carbon-based supercapacitors often suffer from limited capacitance, typically below 120 F g–1, even with structural modifications. This study achieves a significant capacitance boost, exceeding 200 F g–1, by ingeniously mitigating carrier asymmetry within both electrodes and electrolytes. Nitrogen- and boron-doped carbon, used as positive and negative electrodes, enhance the density of states and charge carrier mobility while compensating for quantum capacitance asymmetry. Concurrently, introducing isopropylammonium cations into the mixed electrolyte compresses the electric double layer, equalizing anionic and cationic charge disparities at the solid–liquid interface. This > 200 F g–1 value represents the highest gravimetric capacitance reported for carbon-based supercapacitors using organic electrolytes. Impressively, at a high current density of 100 A g–1, the device maintains 128 F g–1, outperforming commercial YP-50F at 1 A g–1. These results offer pivotal insights into overcoming supercapacitor capacitance limitations and understanding the fundamental enhancement mechanisms.