LAUSR

Abstract An eco‐friendly and sustainable salt‐templating approach was proposed for the production of anode materials with a 3D sponge‐like structure for sodium‐ion capacitors using gluconic acid as carbon precursor and sodium carbonate as water‐removable template. The optimized carbon material combined porous thin walls that provided short diffusional paths, a highly disordered microstructure with dilated interlayer spacing, and a large oxygen content, all of which facilitated Na ion transport and provided plenty of active sites for Na adsorption. This material provided a capacity of 314 mAh g−1 at 0.1 A g−1 and 130 mAh g−1 at 10 A g−1. When combined with a 3D highly porous carbon cathode (S BET ≈2300 m2 g−1) synthesized from the same precursor, the Na‐ion capacitor showed high specific energy/power, that is 110 Wh kg−1 at low power and still 71 Wh kg−1 at approximately 26 kW kg−1, and a good capacity retention of 70 % over 10000 cycles.