Tensile and fatigue properties of aluminum and copper micro joints for Li-ion battery pack applications

Abstract

The current collectors of Li-ion batteries are generally composed of dissimilar materials, such as aluminum and copper that have a thickness of 500 μm. In battery pack welding, existing techniques such as ultrasonics and lasers are ineffective since the materials are micron-thickness, have the same crystal structure as the face-centred cubic, and are highly reflective materials. In the present study, friction stir spot welding (FSSW) is used to join micro sheets of AA1060 and pure copper in a lap configuration. Variations in FSSW process parameters affect friction heat generation. The combination of frictional heat and metal diffusion leads to the formation of intermetallic compounds (CuAl2, CuAl, and Al4Cu9) and a change in IMC thickness. A weld sample with optimal process parameters results in the formation of Al4Cu9, and the IMC thickness is 1.94 μm, yielding a maximum tensile load of ∼1150 N and fatigue strength of 101.24 MPa. The existing study indicates that the skewness of the hysteresis loop is a critical factor in fatigue failure.

Keywords

• Micro friction stir spot welding
• Dissimilar materials
• Li-ion battery tabs
• Fatigue
• Hysteresis loop