Fluorine and Nitrogen Codoped Carbon Nanosheets In Situ Loaded CoFe₂O₄ Particles as High-Performance Anode Materials for Sodium Ion Hybrid Capacitors

Sodium ion hybrid capacitors (SIHCs) are acknowledged to be one of the promising electrochemical energy storage devices because of their high energy/power density and ultralong cycle life. Nevertheless, the imbalance between the slow Faraday reaction of the anode and the rapid capacitive reaction of the cathode leads to a kinetic imbalance of the electrochemical reaction between two electrodes, thus restricting the overall energy density and power density improvement of SIHCs. Herein, CoFe2O4 nanoparticles were grown in situ on the surface of nitrogen–fluorine atoms codoped ultrathin porous carbon nanosheets (NF-CNs) as anode electrode materials of SIHCs by simple high-temperature pyrolysis and a subsequent one-step hydrothermal method. The excellent electrical conductivity and abundant mesopores of the carbon matrix not only accelerate the electron transport rate but also realize the ultrafast Na+ migration kinetics at the same time, thus contributing significantly to expediting the reaction kinetics of the anode in SIHCs. Systematic experiments demonstrate that CoFe2O4@NF-CNs provide SIHCs with excellent energy/power density (maximum 96 W h kg–1/4 kW kg–1) while maintaining outstanding cyclic stability (capacity retention ≈60.7% after 3000 cycles).