Fe-doped CoS2 nanospheres decorated by reduced graphene oxide nanosheets as ultrahigh-rate anodes for advanced sodium-ion capacitors

Abstract Sodium-ion capacitors (SICs) have gained greatly attention due to their high specific energy and power. Nevertheless, the anodes often suffer from low specific capacity, inferior rate capability, and poor cycling stability because of Na+ large ion radius and sluggish reaction kinetics. To improve the electrochemical performance of anodes, we design Fe-doped CoS2 nanospheres grown in situ on reduced graphene oxide nanosheets (Fe-CoS2/rGO) composite by a facile hydrothermal approach, which exhibits an outstanding reversible specific capacity of 590.7 mA h g-1 at specific current of 100 mA g-1 over 100 cycles. Galvanostatic intermittent titration technique (GITT) demonstrates that Fe-CoS2/rGO delivers high Na+ diffusion coefficient ranging from 1.137 × 10-7 to 3.64 × 10-7 cm2 s-1. Furthermore, the SICs composed of the optimized Fe-CoS2/rGO anodes and the pistachio shell-derived porous carbon cathodes display an admirable specific energy of 137.57 W h kg-1 (based on the total mass of anode and cathode) at the specific power of 937.5 W kg-1, with a voltage window of 2.5 V, which is benefit for the development of sodium-ion capacitors.