Iron doping of NiSe2 nanosheets to accelerate reaction kinetics in sodium-ion half/full batteries

Transition metal selenides are important functional materials owing to their large sodium storage capacity. When used as the anode material of sodium-ion batteries (SIBs), the selenides undergo large volume changes during the (de)embedding process, resulting in electrode pulverization followed by rapid capacity decay. The poor conductivity of metal selenides further limits their rate capacity. In this work, Fe-doped NiSe2@C (Fe−NiSe2@C) nanosheets (NSs) with a porous structure were prepared through two-dimensional binary metal-organic framework templating and subsequent in situ selenization. The NSs exhibited an enhanced electronic transportation structure with a hierarchical porous architecture and fully exposed electrochemically active sites. Moreover, compared with NiSe2, the Fe−NiSe2@C NSs exhibited higher capacity (406 mA h g−1 at 1 A g−1 after 100 cycles), better cycle stability (99% capacity retention after 1000 cycles), and higher rate performance, attributed to the optimized stable porous structure and improved Na+ mobility. Furthermore, a high energy density of 107 W h kg−1 in sodium-ion full batteries was achieved. The storage mechanism of Na+ in Fe−NiSe2@C NSs was confirmed through theoretical calculations and a series of ex-situ characterizations. This study provides a reasonable design for improving metal selenides in SIBs.