Conductive Metal–Organic Framework for High Energy Sodium-Ion Hybrid Capacitors

Sodium-ion hybrid capacitors (SICs) are attracting increasing attention due to their high energy/power superiority and potentially low cost. However, the sluggish sodium-ion diffusion in the bulk of a negative electrode is a knotty problem for their future applications. Here, we explore that a conductive metal–organic framework (MOF), Ni3(hexaaminobenzene)2 (named Ni-MOF), as a model material with a high-efficiency ion/electronic transport path, will facilitate the quick reversible function of sodium-ion storage. Ni-MOF exhibits a high capacity of about 300 mAh g–1, an extremely high rate competence of over 100 mAh g–1 even at a high current density of 10 A g–1. Notably, although Ni-MOF has a large pore structure, desolvation of sodium-ion is still necessary during discharge, which is confirmed by electrochemical quartz crystal microbalance (EQCM) technology. Given the exceptional electrochemical characteristic of Ni-MOF, a sodium-ion hybrid capacitor is successfully demonstrated using the Ni-MOF negative electrode. This SIC delivers a high energy density of 127 Wh kg–1, a high power density of 17,309 W kg–1, and a stable cycling of up to 5000 cycles, revealing the promising application in a high energy/power output and long calendar life field.