Study on morphology and N-doping effects of carbon cathodes for zinc-ion hybrid supercapacitors

Aqueous zinc-ion hybrid supercapacitors (ZHSCs) are spotlighted as next-generation energy storage devices; however, the carbon cathodes usually dictate their performance. Herein, we aim to optimize the electrochemical performance of the carbon cathodes through particle morphology control along with porosity and surface-active site control. N-doped spherical mesocelluler carbon foam (S-MCF-N) is synthesized using a mesoporous silica template, and spherical mesocelluler carbon foam (S-MCF) and irregularly shaped mesocellular carbon foam (MSUF-C) are synthesized as control samples. Consequently, S-MCF-N shows the best ion storage capability with its large surface area, with active sites that cause redox reactions and high electrical conductivity. In particular, the spherical morphology of S-MCF-N achieves a higher tap density and can reduce the electrode thickness, which decreases the diffusion length for electrolyte migration and electrode resistance. Therefore, S-MCF-N as the cathode materials deliver a specific capacitance of 208 F g-1 at 0.2 A g-1 and superb cycling stability of up to 7000 cycles at 5 A g-1 without capacity decay. Furthermore, benefiting from the reduced electrode thickness, S-MCF-N has a 112 % higher volumetric energy density than MSUF-C while showing a 42 % higher gravimetric energy density.