Weldability and shear strength feasibility study for automotive electric vehicle battery tab interconnects

Lithium-ion-based secondary battery packs are emerging as an alternative power source and are being increasingly used in electric vehicles, hybrid or plug-in hybrid electric vehicles. Typically, a standard automotive battery pack consists of hundreds, even thousands, of individual cells which are connected in series and/or parallel to deliver the required power and capacity. There is an increasing need for manufacturing of battery packs to meet the demand reflecting the uptake of these vehicles. This triggers the need for suitable joining methods which will provide mechanical strength on a par with electrical and thermal characteristics. This work focuses on characterisation of shear strength of battery tab-to-tab joints for both similar and dissimilar materials by using combinations of aluminium (Al) and nickel-coated copper (Cu[Ni]) tabs. The joining techniques with application for battery tab interconnects are ultrasonic metal welding, resistance spot welding and pulsed TIG spot welding. Lap shear and T-peel tests are performed to evaluate the joint strength. In general, lap shear strength is four to seven times higher than the T-peel strength obtained from all three joining methods. In addition, an indicator is developed in this paper based on lap shear-to-T-peel strength reduction ratio which provides additional information on joint strength characteristics, and subsequently, it can be used as a threshold by quality engineers for an indication on selection of joining methods having an acceptable strength reduction ratio