Novel synthetic strategy for a nanostructured metal hydroxysulfide-C and its initial electrochemical investigation as a new anode material for potassium-ion batteries

Efforts have been made to develop highly promising electrode materials for K-ion batteries (KIBs) by exploring new compositions, stable nanostructures, and combinations of various carbonaceous materials to overcome the slow reaction dynamics of K-ion. Recently, multiple anionic anode materials, such as metal hydroxychlorides, metal hydroxycarbonates, and metal hydroxysulfides, which contain metal−OH bonds, have caught attention as anode materials for Li- and Na-ions batteries owing to their ability to enhance the overall electrochemical kinetics by forming intrinsic electric fields at nanoscale heterointerfaces. Herein, a new synthetic strategy for metal hydroxysulfide@C yolk-shell nanosphere was introduced, and the electrochemical reaction mechanism between the metal hydroxysulfide and K-ion was initially investigated by rational structural and electrochemical analyses. This work synthesized yolk-shell nanospheres having a configuration of metal hydroxide@void@metal hydroxide-C by water-vapor-assisted heat treatment without requiring a strong alkali solution. Cobalt hydroxide@C nanospheres were finally transformed into cobalt hydroxysulfide@C yolk-shell nanospheres through a room-temperature sulfidation process. The metal hydroxysulfide transformed into a heterostructured nanocomposite consisted of metal hydroxide and metal sulfide following the initial cycle. The rationally nanostructured cobalt hydroxysulfide@C electrode exhibited high-rate capability (138.0 mA h g⁻¹ at 5.0 A g⁻¹) and long-term cycling stability (158.4 mA g⁻¹ at 1.0 A g⁻¹ following 300 cycles) in KIBs.