Investigation of the potassium-ion storage mechanism of nickel selenide materials and rational design of nickel selenide-C yolk-shell structure for enhancing electrochemical properties

Metal selenide is contemplated as expeditious anode material for potassium-ion batteries (KIBs). Here, nickel selenide (NiSe₂-Ni_0.85Se) was investigated as an anode material for KIBs. The NiSe_x transformed into K₂Se and K₂Se₃ (K₂Se_x) and reversibly returned to NiSe_x after the discharge and charge processes (17NiSe₂ + 3Ni_0.85Se + 38 K⁺ + 38e⁻ ↔ 19.55Ni + 10K₂Se + 9K₂Se₃). Furthermore, to enhance the electrochemical properties of nickel selenide, yolk-shell-structured nickel selenide and hollow carbon nanosphere composites, in which nickel selenides intensively existed in the core and were partially formed into nanocrystals in the shell, were produced by simple salt-infiltration and a post-treatment. NiSe_x@C exhibited improved cycle and rate properties compared to bare NiSe_x because of its structural merits that led to stable cycle performance and high electrochemical kinetics. NiSe_x@C exhibited 373 mA h g⁻¹ for the 100th cycle at 0.05 A g⁻¹ and 234 mA h g⁻¹ at 1.0 A g⁻¹.