Thickness-control of ultrathin bimetallic Fe–Mo selenide@N-doped carbon core/shell “nano-crisps” for high-performance potassium-ion batteries

The abundance and low cost of potassium precursor materials make potassium-ion batteries (KIBs) a future energy storage system. However, the main challenge is the lack of suitable materials to offer enough space to stably store large-sized K ions. We herein investigate an ultrathin crisps-like bimetallic Fe–Mo selenide@N-doped carbon core/shell nanostructure (FMSC) as a superior anode for KIBs. The few-layered bimetallic selenide with high intrinsic conductivity and expanded interlayer spacing (ca. 0.74 nm) as a core can facilitate the transfer of both electrons and K ions. The ultrathin flexible N-doped carbon shell can further increase the electron mobility, simultaneously buffer the volume variation, confine the FeMoSe₄ from pulverization during cycling, and maintain the integrity of the electrode and the structural stability. By tuning the thickness of the FMSC “nano-crisps” excellent electrochemical performance has been achieved, for instance a high reversible capacity of 298 mAh g⁻¹ is achieved at 200 mA g⁻¹ over 100 cycles. When cycled at a very high current density of 1000 mA g⁻¹, the capacity can still achieve 178 mAh g⁻¹ over 400 cycles, which is among the best KIBs anodes ever reported. This work may open up an effective way to synthesize bimetallic chalcogenides as promising anodes for high-performance KIBs.