Freestanding Carbon Nanotube-Pitch-Derived Porous Carbon Sponges for Enhanced Areal Capacities in Zinc-Ion Hybrid Capacitors

Zinc-ion hybrid capacitor (ZIHC) is a hybrid energy storage system containing battery-type and capacitor-type electrodes, which is expected to achieve high energy density at high power density. However, commonly used porous carbon ZIHC cathodes have relatively low specific capacity, limiting cell-level energy densities. Improving the areal capacity of the ZIHC cathode is an effective way. Herein, we fabricate carbon nanotube-pitch-derived porous carbon (CNT-PPC) sponges with various mass PPC loadings from 1.3[Formula: see text]mg/cm 2 to 12.8[Formula: see text]mg/cm 2 . The relationship between 3D CNT-PPC sponge network structures and the mass loading of PPC active materials is studied. CNT-PPC sponge can achieve a high specific capacity of 216.7[Formula: see text]mAh/g and a high rate capability as a ZIHC cathode. The influence of PPC mass loading on electrochemical properties and energy storage mechanisms is investigated by various electrochemical methods. CNT-PPC sponge with a PPC mass loading of 12.8[Formula: see text]mg/cm 2 (CNT-PPC sponge-12.8) has a high areal capacity of 1.56[Formula: see text]mAh/cm 2 . The assembled CNT-PPC sponge-12.8//Zn ZIHC can achieve a high areal energy density of 1.24[Formula: see text]mWh/cm 2 at 1.02[Formula: see text]mW/cm 2 . This work provides a freestanding electrode design with high mass loading for the ZIHC cathode.