Tailoring the shell thickness of yolk-shell structured carbon microspheres: applications in metal selenide and carbon composite microspheres for enhanced sodium ion storage properties

The yolk-shell structured material, characterized by its core@void@shell configuration, has garnered considerable attention as an anode material for sodium ion batteries due to its advantageous internal void space, large surface area, and short ion diffusion distance. While previous studies have mainly focused on controlling the thickness of the outer shell in a yolk@void@pure carbon shell configuration, tailoring the optimized thickness of the outer shell in metal compounds-carbon composites has not been reported until now. In this study, we propose a novel strategy for tailoring the thickness of the outer shell in yolk-shell structured carbon microspheres using spray pyrolysis. These carbon microspheres possess abundant pores and offer variable outer shell thickness, making them an ideal reservoir for nickel-cobalt selenide composites. Through optimization of the yolk-shell structured nickel-cobalt selenide-carbon composites for sodium ion batteries (SIBs), we achieved exceptional electrochemical performance, capitalizing on their structural advantages. The optimized nickel-cobalt selenide-carbon yolk-shell composite microspheres exhibited a remarkable cycling lifetime, retaining 344 mA h g⁻¹ over 200 cycles at 0.5