Regulation mechanism of tetrahydrothiazole thione additive in electroplated copper foil deposits: Synergistic optimization of mechanical properties and electrochemical behavior

Tetrahydrothiazole thione (H1) is a novel organic additive capable of optimizing the mechanical and interfacial electrochemical properties of electrolytic copper foils applied in lithium-ion batteries (LIBs). Nevertheless, how this compound regulates copper electrodeposition and microstructure evolution has not been fully elucidated. In this study, copper foils were electrodeposited in acidic plating solutions with varying H1 contents, while all other experimental conditions including electrolyte composition, applied current density and bath temperature were strictly fixed to ensure experimental validity. Experimental characterization results show that the copper foil achieves the best comprehensive performance at an H1 dosage of 1.0 mg/L, delivering a tensile strength of 556.5 MPa and an elongation at break of 6.64%. Meanwhile, the deposited foil presents an ultra-low root-mean-square roughness (Sq) of 0.306 μm. Contact angle testing reveals that the aqueous and organic contact angles of the modified copper surface drop to 30° and 37.7°, respectively, which clearly evidences the improved surface wettability after H1 modification. Microstructure analysis demonstrates that the incorporation of H1 effectively refines copper grains and promotes the preferential orientation of the (220) crystal plane. The grain refinement effect further strengthens the mechanical robustness of copper foils following the classic Hall-Petch strengthening principle. Electrochemical measurements illustrate that the presence of H1 restricts interfacial electron migration, enhances cathodic polarization behavior, and triggers instantaneous nucleation during electrodeposition, ultimately contributing to the formation of uniform, compact and fine-grained copper deposits. Density functional theory calculations confirm the excellent electron-donating characteristic of H1, with the HOMO energy level calculated as −5.809 eV. Collectively, this study systematically reveals the synergistic modification mechanism of H1 on electrodeposited copper foils. The findings provide a new feasible technical route for the design and preparation of high-quality copper current collectors applicable to high-performance LIBs.