Ultrahigh Loading MOF-Derived Co9S8 Nanoflowers: A Self-Supporting Multilevel Micronano Structured Electrode for Enhanced Energy Storage Performance in Supercapacitors

This research presents a method to construct multilevel micronano structures by exploiting the highly tunable composition and morphology of NiFe-layered double hydroxides (NiFe-LDHs) and metal-organic frameworks (MOFs) and introducing sulfide ions (S^2-) to improve composite conductivity. It effectively mitigates issues of poor cycle stability caused by the inherent volume expansion of transition metal sulfides (TMSs) and the agglomeration of electrode materials under high mass loading conditions, which significantly improves the electrochemical performance. Notably, at the current density of 1 mA cm^-2, the C-Co₉S₈/NiFe-S@NF electrode demonstrates an exceptionally high capacitance at approximately 17,338.6 mF cm^-2. As an asymmetric supercapacitor (ASC) electrode, C-Co₉S₈/NiFe-S@NF demonstrates energy and power densities of 1.05 mWh cm^-2 and 51.75 mW cm^-2, respectively. Moreover, the ASC device exhibits remarkable stability under cycling, with an 82.6% retention of its capacity and consistent Coulombic efficiency of 93.8% after 5000 cycles at a current density of 30 mA cm^-2. This study demonstrates that the multilevel micronano structured self-supporting electrode not only enhances the charge storage capacity but also strengthens the overall electrochemical stability of the electrode considerably. The findings offer a promising pathway for developing energy storage devices with superior performance, leveraging the synergistic effects of the integrated MOFs/NiFe-LDHs composite structures.