High Capacitance Based on Vacancy Defective Porous Carbon in Ionic Liquid

Abstract Porous carbons have been extensively studied in electrochemical capacitors (ECs). However, low capacitance remains a limitation due to the electrical double layer (EDL) storage mechanism when porous carbons are used in ionic liquids (ILs) based ECs. Herein, the nitrogen‐derived vacancy defects in porous carbon nanospheres are found which can boost capacitive charge storage and present reversible high capacitance of 427 F g⁻¹ in pure IL electrolyte, equal to a normalized area capacitance (C_A) of 16 µF cm⁻²_, surpassing the theoretical EDL C_A (≈11 µF cm⁻²). When used as capacitive cathode, the assembled Lithium hybrid capacitor express high energy density of 635 Wh kg⁻¹ based on active material under much high‐power density of 14.5 kW kg⁻¹. A combination of control experiments and density functional theory investigation indicate that the EC's performance improvement mostly stems from strong interactions at vacancy defects, triggering extraordinary faradaic capacitance. The results shed light on defect engineering for realizing extra faradaic capacitance of carbon materials, and open up new opportunities for improving EC's energy density.