The rational design of nickel-cobalt selenides@selenium nanostructures by adjusting the synthesis environment for high-performance sodium-ion batteries

The exploitation of metal selenides in sodium-ion batteries has attracted significant interest. However, obtaining an effective balance between energy density, rate performance, and cycling performance has been difficult, as complexity and consistency during metal selenide nanostructure design and fabrication are hard to achieve. Herein, we propose a facile selenization strategy to prepare a nickel-cobalt selenides@selenium (NiCoSe2@Se) nanocomposite in a liquid phase environment. The Se melt can infiltrate and diffuse along the surface of the nickel-cobalt layered double hydroxide (NiCo-LDH) precursor. Controlling the Se melting and diffusion processes can allow the homogenous deposition of the Se coating layer. Meanwhile, the melt-diffusion approach can also induce the formation of numerous NiCoSe2 nanosheets, playing the role of regulating the nanostructure. The obtained unique NiCoSe2@Se nanocomposite exhibits small-sized NiCoSe2 nanosheets, and the surface is uniformly coated with numerous Se nanoparticles, endowing the composite with robust structural stability and exposing a maximum number of surface active sites. A battery with a NiCoSe2@Se anode exhibits a reversible capacity of 394.7 mA h g(-1) at 25 A g(-1), together with excellent cycling stability over 1600 cycles at 20 A g(-1). These results clarify a new approach for constructing high-performance metal selenides for use in sodium-ion batteries.