A novel strategy for encapsulating metal sulfide nanoparticles inside hollow carbon nanosphere-aggregated microspheres for efficient potassium ion storage

Tremendous efforts are being made to develop advanced electrode materials for potassium-ion batteries (PIBs), which have the potential to replace the currently dominant power source, lithium-ion batteries. Herein, an innovative strategy for the synthesis of microspherical superstructures comprising nanosized yolk-shell-structured particles via a facile spray drying process is introduced. Iron sulfide (Fe_1−xS) nanoparticles were successfully encapsulated within the central void space of each hollow carbon nanosphere, forming a yolk-shell configuration. The design of such a unique carbon-composited 3D structure consisting of agglomerated yolk-shell nanospheres led to high specific capacity, easy electrolyte penetration, accelerated ion/electron transport, and high structural robustness. The electrochemical reaction mechanism of the anode with potassium ions was elucidated through systematic in situ and ex situ characterization studies. When applied as the anode for PIBs, the uniquely structured microspheres delivered a high reversible capacity of 401 mA h g⁻¹ after 200 cycles at 0.1 A g⁻¹. When tested at a high current density of 7.0