Abstract: Mechanical properties of current collection foils, particularly the elastic moduli, and yield and fracture strengths, are critical for the design and fabrication of electrodes of Li-ion batteries. Characterization of these mechanical properties provides useful guidance for the design and subsequent manufacture of the current collectors. This paper reports our recent work on the mechanical properties of rolled copper foils and electrolytic copper foils for Li-ion batteries. Microtensile experiments were carried out and the mechanical properties are compared for two manufacturing processes and six different thicknesses. It was found that the elastic moduli were about 70 GPa and 50 GPa for electrolytic copper foils and rolled copper foils, respectively. The yield strength of the copper foils increased with decreasing thickness, showing a trend of smaller being stronger. To investigate fracture mechanisms of the copper foils, selected cross-sections of the copper foils were observed using a scanning electron microscope (SEM). The results suggested the electrolytic copper foils failed in the brittle fracture mode, whereas the failure of the rolled copper foils was through ductile fracture.

Key words: current collector, copper foil, Li-ion batteries, fracture