Nitrogen-Doped Hard Carbon as Symmetric Electrodes for Sodium-Ion Capacitor

Sodium-ion capacitors (SICs) as new sodium storage devices combining the advantages of batteries and capacitors have been widely researched in recent years. Nevertheless, exploring kinetic matching of anode and cathode electrodes is a great challenge. In this work, the sodium-ion capacitor (SIC) was integrated with nitrogen-doped hard carbons (N-HCs) as the symmetric electrode, which possesses the virtues of a battery and supercapacitor. The SIC delivers not only a reversible capacity of 88 mA h g–1 at 1000 mA g–1 after 5000 cycles but also a high energy density of 197 Wh kg–1 at 219 W kg–1.