Chemical/Electrochemical Dual‐Driven Transition Behavior of Copper Element from Current Collector to Chalcogenide Anode in Sodium‐Ion Batteries

Abstract The transition phenomenon involving copper replacing the transition metal elements within transition metal chalcogenides (TMCs) is a recent and unique observation in the context of sodium ion batteries (SIBs) where TMCs serve as anodes. Fundamental understanding of the driving forces and kinetics governing this transition is crucial for elucidating the sodium storage mechanism in TMCs anodes. Herein, cobalt disulfide (CoS₂) has been chosen as a representative anode. It is revealed that the transition behavior of copper replacing cobalt during the cycling originates from chemical/electrochemical dual‐driving forces. The chemical driving force emanates from the interaction between Cu+ dissolved in the electrolyte and the resulting sodium polysulfide products. The reaction extent is intricately linked to the surface roughness of the copper collector. The electrochemistrical driving force is effectively elucidated through the application of the Hard‐Soft‐Acid‐Base theory. Multiple charaterization techniques, such as Solid‐state nuclear magnetic resonance (ssNMR) have been employed to confirm that cobalt exists as cation instead of metal after transition. This research offers a novel perspective understanding the transition behavior exhibited by CoS₂, with potential wider implications for understanding analogous behaviors in other metal sulfide anodes.