A bimetallic metal-organic framework derived MnS/CoS@C heterostructure with enhanced sodium-ion storage.

Manganese sulfide (MnS) has gained significant attention as a high capacity and durable anode material for sodium-ion batteries (SIBs) due to its high theoretical capacity and decent redox reversibility. However, sluggish Na diffusion and significant volume variation during charge/discharge cycles limited its rate capability and cycling stability. Here, a new MnS/CoS heterojunction embedded in S-doped carbon (MnS/CoS@C) is designed through sulfurization of a bimetallic metal-organic framework (MOF). The synergistic effect of heterojunction design and carbon framework encapsulation integrates several benefits, including facilitating ion/electron transport, alleviating volume variation, and preventing the agglomeration of metal sulfide nanoparticles. Therefore, the MnS/CoS@C composite manifests remarkable rate capability (526.1 mA h g at 0.1 A g and 273.7 mA h g at 10 A g) and stable long-term cycle life (214.8 mA h g after 1000 cycles at 5 A g). Meanwhile, the sodium storage mechanism is examined using electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Coupled with a carbon nanosheet cathode, a prototype sodium-ion capacitor (SIC) has been fabricated. The SIC can achieve a high energy density of 120.7 W h kg and a maximum power density of 12 250 W kg, demonstrating the high application potential of the composite for sodium-ion based energy storage systems.