Zinc selenide/cobalt selenide in nitrogen-doped carbon frameworks as anode materials for high-performance sodium-ion hybrid capacitors

Transition metal selenides are considered reliable anode materials for sodium-ion batteries (SIBs) on account of their commendable sodium storage capability. Yet they still face problems such as substantial volume amplification and unsatisfied conductivity which are detrimental to the circulation performance of the battery. In view of this, nitrogen-doped carbon (NC) packaged ZnSe/CoSe heterostructures (ZnSe/CoSe@NC) octahedron are rationally designed in this work. The NC capsulated heterostructures octahedron could substantially mitigate the issues of volume expansion and low conductivity for transition metal selenides. Additionally, the rich phase boundary derived from ZnSe/CoSe heterostructured interfaces yields numerous active sites for sodium ions and the formed electric field inside ZnSe/CoSe heterostructure can largely boost charge transfer. Most importantly, the unique heterostructure endows ZnSe/CoSe@NC with relatively stronger sodium adsorption, leading to long cycling stability with a reversible capacity of 289 mAh g⁻¹ underneath 900 cycles at 1 A g⁻¹. Given the pseudocapacitance effect of ZnSe/CoSe@NC in SIBs, a sodium ion capacitor (SIC) on the basis of ZnSe/CoSe@NC capacitor-type anode and Na₂FePO₄F (NFPF) battery-type cathode is rationally conceived and features high energy densities of 209.4 and 80.4 Wh kg⁻¹ at 240 and 4000 W kg⁻¹. The findings offer a promising pathway toward developing advanced energy storage devices with enhanced cycling stability and high energy density.