Achieving Ultrahigh Volumetric Energy Storage by Compressing Nitrogen and Sulfur Dual‐Doped Carbon Nanocages via Capillarity

High volumetric performance is a challenging issue for carbon-based electrical double-layer capacitors (EDLCs). Herein, collapsed N,S dual-doped carbon nanocages (cNS-CNC) are constructed by simple capillary compression, which eliminates the surplus meso- and macropores, leading to a much increased density only at the slight expense of specific surface area. The N,S dual-doping induces strong polarity of the carbon surface, and thus much improves the wettability and charge transfer. The synergism of the high density, large ion-accessible surface area, and fast charge transfer leads to state-of-the-art volumetric performance under the premise of high rate capability. At a current density of 50 A g^-1 , the optimized cNS-CNC delivers a high volumetric capacitance of 243 and 199 F cm^-3 in KOH and EMIMBF₄ electrolyte, with high energy density of 7.9 and 93.4 Wh L^-1 , respectively. A top-level stack volumetric energy density of 75.3 Wh L^-1 (at power density of 0.7 kW L^-1 ) and a maximal stack volumetric power density of 112 kW L^-1 (at energy density of 18.8 Wh L^-1 ) are achieved in EMIMBF₄ , comparable to the lead-acid battery in energy density but better in power density with 2-3 orders. This study demonstrates an efficient strategy to design carbon-based materials for high-volumetric-performance EDLCs with wide practical applications.