Unraveling the Mechanism of Chalcopyrite’s Superior Performance for Lithium Storage

Chalcopyrite (CuFeS2), a natural copper–iron bimetallic sulfide, has shown great promise as an active material for lithium-ion batteries because of its superior electrochemical performance, high abundance, and low cost. However, its reaction mechanisms are still indeterminate. Herein, we demonstrate that chalcopyrite CuFeS2 exhibits unique phase and structure transformations during electrochemical reactions, which are highly related to its superior electrochemical performance. In situ XRD and ex situ XPS characterizations reveal that CuFeS2 is converted into a nanoscale hybrid that contains Cu2S and FeSy after the initial discharge–charge cycle. The emerging heterostructure endows the electrode with structural integrity, suppressed polysulfide dissolution, and enhanced charge transfer and Li-ion diffusion during reactions. In consequence, CuFeS2 exhibits excellent lithium-storage performance with a high specific capacity of 990 mAh g–1 after 300 cycles under the current density of 1000 mA g–1. This work sheds light on the intrinsic electrochemical superiority of chalcopyrite CuFeS2 and provides guidelines to understand other bimetallic sulfides.