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

Abstract

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, Co_1−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, Co_1−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.