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

Abstract 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.