Unraveling hierarchical hollow NiCo2S4/MXene/N-doped carbon microspheres via dual templates for high-performance hybrid supercapacitors

Abstract

A multi-step strategy was rationally designed to fabricate hierarchical hollow core–shell microspheres of NiCo2S4MXene/N-doped carbon (NiCo2S4/MXene/NC) using dual templates of the polyethylene microspheres and metal–organic framework material of ZIF-67. The integration of MXene and N-doped carbon significantly enhances the electronic conductivity of electrode, while the construction of hollow spherical structures effectively alleviates the instability of NiCo2S4/NC during the charge–discharge cycles, leading to the excellent charge storage performance with a high specific capacitance (1786 F g−1 at 1 A g–1) and impressive cycling stability (over 100 % capacitance retention after 10,000 cycles). A corresponding hybrid supercapacitor displays a high specific capacitance (190 F g−1 at 1 A g–1) with a maximum energy density (67 Wh kg−1 at 796 W kg−1) and great cycling stability (over 80 % capacitance retention after 10,000 cycles). The charge storage mechanism of NiCo2S4/MXene/NC is elucidated, revealing a combination of pseudocapacitive and battery-like behavior. Density functional theory (DFT) calculations indicate that the participation of MXene significantly increases the state density of NiCo2S4/MXene near the Fermi level compared to NiCo2S4, affirming its superior metallic conductivity. This work provides a facile route only with room-temperature stirring and high-temperature calcination to prepare well-defined metal sulfide composite microstructures with high electrochemical performance.