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, CoFe 2 O 4 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 CoFe 2 O 4 @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).