Co-Vacancy, Co1-xS@C flower-like nanosheets derived from MOFs for high current density cycle performance and stable sodium-ion storage

Transition metal sulfides (TMSs), especially cobalt-based sulfides have great potential use in battery anode materials. However, low coulombic efficiency and poor cycle stability limit their application in battery fabrication. In this work, a two-dimensional MOF material ZIF-9 was treated by a two-step calcination method that obtained a flower-shaped carbon skeleton coated with Co-vacancy, Co1-xS nanoparticles. The skeleton effectively restrains the volume expansion that happens on electrodes, which improved the electrical conductivity of the compound. The cobalt vacancy changes the local electronic structure and atomic populations; the DFT calculation also proves that this structure is beneficial to the migration of sodium ions and provides good cycling performance under high current density. According to our electronic experiments, Co1-xS@C exhibited good electrochemical performance, which maintains a capacity of about 300 mA h g(-1) at a high current density of 5 A g(-1) after 250 cycles. All results indicate the outstanding electrochemical performance of our composite material, especially under a high current density. This work may provide a method in MOFs-derived TMSs compounds to stimulate the potential of transition metal sulfide materials in energy storage.

Automated summary

In this study, a two-dimensional MOF material ZIF-9 was treated to obtain a flower-shaped carbon skeleton coated with Co-vacancy, Co1-xS nanoparticles, which effectively improved the electrical conductivity and cycling performance of the compound. The cobalt vacancy altered the local electronic structure and atomic populations, promoting sodium ion migration and showing good cycling performance under high current density. The obtained Co1-xS@C exhibited excellent electrochemical performance, maintaining a capacity of about 300 mA h g(-1) at a high current density of 5 A g(-1) after 250 cycles, indicating the potential of transition metal sulfide materials in energy storage applications.