An Engineering\nPorous Spherical Carbon Cathode for\nHigh-Energy Sodium-Ion Capacitor

Sodium-ion hybrid capacitors (SICs) are emerging as promising\ndevices\nthat can balance energy and power output. However, the lack of a high-capacity\ncathode that can match the anode has limited its further application.\nIn this work, we develop an efficient method to prepare spherical\nporous carbons (SPCs) with great specific surface area and narrow\npore size distribution from coal-based humic acid via spray drying\nand a subsequent chemical activation process. Thanks to this unique\nporous structure, the SPC cathode has a superb capacity of 223 F g<sup>–1</sup> at 0.05 A g<sup>–1</sup>, as well as splendid\nrate performance and cycling stability. SICs constructed by an SPC\ncathode and hard carbon anode can exhibit a high energy density of\n179.8 Wh kg<sup>–1</sup> at 155 W kg<sup>–1</sup> and\nachieved 89.4% capacity retention after 10 000 cycles at 0.5\nA g<sup>–1</sup>. This outcome presents a viable approach to\nattaining high-capacity cathodes for constructing outstanding performance\nhybrid capacitors.