2D holey cobalt sulfide nanosheets derived from metal–organic frameworks for high-rate sodium ion batteries with superior cyclability

Abstract

Sodium ion batteries (SIBs) for large-scale grid applications are facing great challenges in terms of development of high-performance electrode materials and screening of suitable electrolytes. Herein, a versatile and scalable protocol for synthesizing two-dimensional (2D) holey cobalt sulfide (h-Co₄S₃) nanosheets is demonstrated for high-rate and long-life SIBs in an ether-based electrolyte of 1.0 M NaCF₃SO₃ in diglyme. The 2D h-Co₄S₃ nanosheets are prepared by sulfuration of leaf-like cobalt based metal–organic frameworks (CoMOFs), and subsequent annealing treatment. Benefiting from the nanosheet nature of in-plane nanopores (10–30 nm), ultra-thinness (<30 nm), crumpled morphology, and micron-scale lateral size that can provide more active sites and enhanced sodiation/desodiation kinetics, the resulting h-Co₄S₃ nanosheets achieve a high reversible capacity of 571 mA h g⁻¹ at 0.1 A g⁻¹, and long-life cycling stability with a retention of 80% after 400 cycles for SIBs. Furthermore, theoretical simulation reveals the enhanced structural stability of h-Co₄S₃ nanosheets with a lower binding energy (0.31 eV) of the Co–O bond in the ether-based electrolyte than that in the carbonate-based electrolyte. Notably, the h-Co₄S₃ anode offers an exceptional rate capacity of 257 mA h g⁻¹ at 12 A g⁻¹, outperforming most reported cobalt sulfide-based anodes. This strategy will pave a new way to rationally construct MOF-derived 2D nanostructures for various energy-related applications.