Synthesis of MnSe@C yolk-shell nanospheres via a water vapor-assisted strategy for use as anode in sodium-ion batteries

This study introduces a simple and eco-friendly synthetic strategy for yolk-shell nanospheres that consist of manganese selenide yolks and carbon shells (MnSe@C) by reacting manganese salt impregnated in the porous hollow carbon nanospheres (HCNS) with H₂O vapor. First, manganese salt dissolved in ethanol was impregnated into the spacious pores of the HCNS by capillary force. Then, heat treatment of the powder in the presence of H₂O triggered the nucleation and crystal growth of manganese hydroxide, resulting in the formation of HCNS whose central voids are filled with multiple nanoparticles. Subsequent selenization yielded yolk-shell nanospheres with MnSe@void@carbon configuration. MnSe@C was applied as the anode for sodium-ion batteries (SIBs), and the following electrochemical reaction was confirmed from various analytical techniques: MnSe +2Na⁺ + 2e⁻ ↔ Mn + Na₂Se. MnSe@C nanospheres exhibited stable cycle performance up to 1000 cycles at 0.5 A g⁻¹, wherein a reversible capacity of 222 mA h g⁻¹ was delivered in the 1000th cycle. Furthermore, MnSe@C nanospheres exhibited a fair rate performance (209 mA h g⁻¹ at 2.0 A g⁻¹).