Metal–Organic Framework Based Ultrafine-Fe1-xS-Nanoparticle-Confined Het-Erodimensional Anode and Hierarchical 3D Porous Carbon Cathode for Perfor-Mance Maximization of Sodium-Ion Hybrid Capacitors

While being the most popular, lithium-based energy storage devices have issues of geological distribution and rarity in the earth’s crust. Due to their abundance, sodium ion-based hybrid capacitors (SIHCs) are drawing significant attention as an alternative. However, the sluggish kinetics and low capacities of their anode and cathode need to be overcome. Here, we report a strategy to realize ultrahigh-performance SIHCs anode and cathode electrode materials derived from metal-organic frameworks (MOFs). Facile carbonization of MIL-100(Fe) precursor and subsequent sulfidation process generated ultrafine pyrrhotite nanoparticles in the carbon matrix. The embedded fine particles exhibited outstanding rate performance due to the reduced size effect. Moreover, heteroatom-rich cathode materials were synthesized via the pyrolysis of ZIF-8. The subsequent KOH activation maximized the surface area and constructed a porous structure to the cathode material. High capacity was achieved due to pseudocapacitance that was induced by abundant surface heteroatoms. As a result, the SIHC device that was composed of the as-synthesized anode and cathode materials exhibited ultrahigh energy density (>200 Wh/kg) and power density (>19,000 W/kg). This study suggests a novel design strategy for realizing high-performance SIHCs.