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^-1 at 0.1 A g^-1 and 273.7 mA h g^-1 at 10 A g^-1) and stable long-term cycle life (214.8 mA h g^-1 after 1000 cycles at 5 A g^-1). Meanwhile, the sodium storage mechanism is examined using in situ electrochemical impedance spectroscopy (EIS), ex situ X-ray diffraction (XRD) and ex situ 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^-1 and a maximum power density of 12 250 W kg^-1, demonstrating the high application potential of the composite for sodium-ion based energy storage systems.