Ultrasound Tab Welding Microstructure and Joint Resistance Limits
Ultrasonic tab welding balances acoustic softening and static clamp force to break interfacial oxides, yielding sub-5-micro-ohm joints without foil cutting.
Copper Foil Stack
Meaning
Multiple layers of thin metallic collectors are grouped together to facilitate the transfer of electrical current from an electrochemical cell. This assembly consists of several sheets of copper foil, often ranging from six to ten micrometers in thickness, that have been pressed together before being welded to a terminal tab. The copper foil stack serves as the negative current collector, gathering electrons from the anode material and channeling them toward the external circuit.
Achieving a uniform bond across all layers in the stack is essential for minimizing internal resistance and preventing localized heating during high rate discharge. This configuration is a standard feature in both pouch and prismatic battery designs.
Layer Integration
Ultrasonic welding penetrates the entire depth of the group to create a monolithic metallic path. A poorly formed copper foil stack contains gaps that increase the ohmic resistance of the finished battery pack.
Thickness Constraint
Total height of the compressed layers must stay within the tolerances of the welding equipment and the cell housing. Because the copper foil stack is highly conductive, any misalignment during the assembly process can lead to short circuits or structural weaknesses at the tab interface.
Mechanical Strength
Tensile forces acting on the tabs during vibration testing can pull individual layers apart if the weld is insufficient. Ensuring the integrity of the copper foil stack involves monitoring the horn pressure and energy delivery to guarantee that the bottom layers receive the same bond quality as the top ones. Consistent bonding is essential for the long term reliability of automotive and grid scale energy storage systems.