Redefining the Conversion Mechanism of Chalcopyrite CuFeS ₂ Electrodes for Li‐Ion Battery via Multiscale Evolution Analysis

Natural chalcopyrite CuFeS 2 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, CuFeS 2 undergoes stepwise conversion: Li + intercalation first induces amorphization, Cu extrusion, and formation of amorphous Li 2 FeS 2 , followed by further decomposition into amorphous Fe and Li 2 S. 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 FeS 2 with S 2 2− dimers, whereas Cu remains irreversibly metallized. Subsequent cycles follow a lower‐energy Fe/FeS 2 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.