Preparation of electrodeposited copper foils with ultrahigh tensile strength and elongation: A functionalized ionic liquid as the unique additive

Improving the properties of electrodeposited copper foil, the negative current collector of lithium-ion batteries, is crucial to the ongoing development of high-energy–density batteries. Despite the broad usage of chemical additives to regulate the copper foil, there remains substantial room for advancement due to the complexity of the mixed additives and the lack of related mechanism research. In this study, a functionalized ionic liquid, 1-aminopropyl-3-methyl imidazole chloride ([C3NH2CIm][Cl]), was designed and used as a new and single additive for controlling the deposition growth of Cu2+ ions, allowing the preparation of copper foil with ultrahigh tensile strength and simultaneously high elongation. By using the optimal [C3NH2CIm][Cl] concentration of 30 mg/L, copper foil with a tensile strength of 455.6 MPa and an elongation as high as 17.1 % can be achieved. Subsequent structural characterizations and electrochemical analysis suggested that the addition of [C3NH2CIm][Cl] regulated the grain growth through cathode polarization and enhanced the copper foil properties by refining crystal grains and increasing the density of the Σ3 twin boundaries of the copper foil. A detailed understanding of the mechanism through which [C3NH2CIm][Cl] affects Cu2+ ions electrodeposition is crucial for the development of innovative additives for electrodeposited copper foils, particularly for the production of high-property copper foils.