Tue, 30 September, 2025
A new research paper co-written by TWI’s Chris Allen alongside Rita Bola and Rafael Afonso from the European Federation for Welding in Portugal has been presented at the International Institute of Welding’s (IIW) 78th Annual Assembly and International Conference in Genoa, Italy.
The paper, ‘Laser Welding of Busbar-to-Cell Terminal Connections for Battery Modules,’ details the development and application of laser welding for creating connections between busbars and cell terminals in a new design of cylindrical cell Li ion battery module.
A scanning infrared (IR) single-mode laser system was used, due to its benefits of speed and versatility, with initial trials on coupons defining the baseline parameters and suitable scanning patterns, before carrying out different weld quality and property characterisations.
Challenges successfully addressed during the work included the dealing with the intolerance of the laser welding process to any joint gaps > 10 µm, and satisfying the needs of very precise beam focus and penetration controls to guarantee joining, whilst avoiding cell damage.
Welding trials progressed through coupons on to empty cells, then to discharged (sub-sized) ‘mini-modules’, and then to full-sized discharged and, finally, live modules. The optimised process yielded joints with acceptably low heat inputs (bulk cell temperatures < 80⁰C), an electrical resistance of < 400 µΩ, and with sufficient mechanical strength, as seen by the busbar failing before the weld in mechanical tests.
Transitioning to full modules highlighted further joint fit-up issues related to module design, but these were satisfactorily solved through iterative design changes and appropriate welding process sequencing. Procedures for weld repair and safety protocols for welding live cells were also established.
In total, nearly 10,000 welds were made when welding these prototype live modules, with an overall welding success rate approaching 99.95%, and a product yield approaching 94% once all of the challenges referred to were resolved.
This research builds on our existing expertise and technical excellence in laser applications and battery welding – to find out more, please email contactus@twi.co.uk.