New layered chalcogenides (Na0.5OH)Fe0.5Cu0.5X (X = Se, S): Synthesis, structure, magnetic and electrochemical properties

Abstract

Two new layered chalcogenides (Na0.5OH)Fe0.5Cu0.5X (X = Se, S) have been successfully synthesized via a combination of solid-state reaction and hydrothermal ion-exchange method. They crystallize in a tetragonal space group P4/nmm and represent the very rare examples isostructural to the iron-based superconductor (Li1−xFexOH)FeSe, with (Na0.5OH) layers intercalated between adjacent Fe0.5Cu0.5X layers. Magnetization and electrical measurements suggest that the title compounds exhibit spin-glass and semiconducting properties rather than superconductivity. This is mainly attributed to the random distribution of Fe and Cu in the tetrahedral sites. Preliminary electrochemical test indicates that (Na0.5OH)Fe0.5Cu0.5S can be a good electrode material for lithium-ion batteries, especially when carbon nanotubes are incorporated (discharge capacity of 745 mAh g−1 at 0.2 A g−1, capacity retention of 49.1% after 50 cycles and rate capacity of 120 mAh g−1 at 5 A g−1). These results not only provide an efficient strategy to synthesize new intercalated chalcogenides but also demonstrate their potential applications in lithium-ion batteries.