Different welding processes are used depending on the design and requirements of each battery pack or module. Joints are also made to join the internal anode and cathode foils of battery cells, with ultrasonic welding (UW) being the preferred method for pouch cells.
“We see a lot of laser welding and ultrasonic wedge bonding for the larger packs,” says Boyle at Amada Weld Tech. “If the packs or the overall volume are smaller, then resistance welding is often used. Micro-TIG comes up for specialised battery packs with low-volume production.
When comparing joining technologies for battery welding, it is realised that the applicability of a technology depends not only on the connection resistance and its scatter but also on the specific joining task, i.e. the battery cell type. Ultrasonic welding appears to be suitable particularly for joining pouch cells.
Other joining methods such as micro-tungsten-inert-gas welding (micro-TIG), micro-clinching, soldering, and magnetic-pulse welding exist and have been proposed for battery assembly applications, but they are not well established, and therefore their feasibility is still being evaluated, or they are not widely used in the industry.
Welding is a vitally important family of joining techniques for EV battery systems. A large battery might need thousands of individual connections, joining the positive and negative terminals of cells together in combinations of parallel and series blocks to form modules and packs of the required voltage and capacity.
There are only so many ways to join materials together, and for battery applications – particularly where high currents and voltages and tough operating environments are encountered – welding beats alternatives such as soldering, conductive adhesives and mechanical fasteners.