Redefining the Conversion Mechanism of Chalcopyrite CuFeS₂ Electrodes for Li-Ion Battery via Multiscale Evolution...

Natural chalcopyrite CuFeS₂ is a promising sulfide electrode for lithium-ion batteries, yet its multiscale structural and chemical evolution during cycling remains insufficiently understood. Here, synchrotron X-ray absorption spectroscopy, Raman spectroscopy, operando synchrotron computed tomography (CT), molecular dynamics (MD), and density functional theory are combined to clarify its lithiation mechanism and stability origin. During the first discharge, CuFeS₂ undergoes stepwise conversion: Li⁺ intercalation first induces amorphization, Cu extrusion, and formation of amorphous Li₂FeS₂, followed by further decomposition into amorphous Fe and Li₂S. Thermodynamic calculations show that the amorphous pathway is more favorable than the crystalline route, confirming reaction-induced amorphization. Upon charging, amorphous Fe is re-sulfurized to form amorphous FeS₂ with S₂ ^2- dimers, whereas Cu remains irreversibly metallized. Subsequent cycles follow a lower-energy Fe/FeS₂ redox pathway, which prevents chalcopyrite reconstruction. Operando CT and impedance analysis reveal that, despite severe particle fragmentation, the retained metallic Cu network maintains electronic transport, while the absence of soluble polysulfides suppresses parasitic reactions. These findings explain the cycling stability of natural chalcopyrite electrodes and guide the design of durable sulfide-based materials.