Thickness-dependent microstructure evolution and mechanical properties of electrodeposited copper foils

Electrolytic copper foil is a key material for electronic interconnection and energy-storage applications, and its performance is closely related to microstructural characteristics. However, the thickness-dependent relationship among microstructure evolution and mechanical behavior in electrodeposited copper foils remains insufficiently understood. In this study, electrolytic copper foils with thicknesses ranging from 7 to 35 μm were prepared by controlling the electrodeposition time, and their surface characteristics, microstructure, and tensile properties were systematically investigated. The results show that, with increasing thickness, the grains on the M side gradually coarsen, the preferred (220) Cu orientation becomes stronger, and the average cross-sectional grain size increases from 0.40 to 0.70 μm. The 14 μm-thick copper foil exhibits the highest twin boundary fraction of 45.5%, with a nanotwin lamellar thickness of approximately 10 nm. Correspondingly, it shows the highest tensile strength of 506.37 MPa, which is mainly attributed to the synergistic effect of grain-boundary strengthening and nanotwin strengthening. With increasing thickness, the glossiness of the M side decreases, while the surface roughness and elongation increase. Meanwhile, the fracture mode gradually changes from predominantly intergranular fracture to mainly transgranular fracture. These findings clarify the thickness-dependent structure–property relationship of electrolytic copper foils and provide guidance for thickness design and microstructure optimization of high-performance copper foils.