Boosting Spatial Charge Storage in Ion-Compatible Pores of Carbon Superstructures for Advanced Zinc-Ion Capacitors.

Abstract

Capacitive carbon cathodes deliver great potential for zinc-ion hybrid capacitors (ZHCs) due to their resource abundance and structural versatility. However, the dimension mismatch between the micropores of carbons and hydrated Zn2+ ions often results in unsatisfactory charge storage capability. Here well-arranged heterodiatomic carbon superstructures are reported with compatible pore dimensions for activating Zn2+ ions, initiated by the supramolecular self-assembly of 1,3,5-triazine-2,4,6-triamine and cyanuric acid via in-plane hydrogen-bonds and out-of-plane π-π interactions. Flower-shaped carbon superstructures expose more surface-active motifs, continuous charge-transport routes, and more importantly, well-developed pores. The primary subnanopores of 0.82nm are size-exclusively accessible for solvated Zn2+ ions (0.86nm) to maximize spatial charge storage, while rich mesopores (1-3nm) allow for high-kinetics ion migration with a low activation energy. Such favorable superstructure cathodes contribute to all-round performance improvement for ZHCs, including high energy density (158Whkg-1), fast-charging ability (50Ag-1), and excellent cyclic lifespan (100000cycles). An anion-cation hybrid charge storage mechanism is elucidated for superstructure cathode, which entails alternate physical uptake of Zn2+/CF3SO3 - at electroactive pores and bipedal chemical binding of Zn2+ to electronegative carbonyl/pyridine motifs. This work expands the design landscape of carbon superstructures for advanced energy storage.