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

Abstract

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.

Modelling and characterisation of ultrasonic joints for Li-ion batteries to evaluate the impact on electrical resistance and temperature raise

“…For example, comprehensive research has been undertaken focusing on Li-ion battery chemistry, power capacity improvements, material development, modelling and simulation, performance enhancements or battery testing and characterisation, and safety [9][10][11]. However, the joining aspects of the Li-ion cells are mainly limited to metallurgical and mechanical characterisation of joining process [12][13][14]. There are a few literature available focusing on the comprehensive performance, characterisation and modelling of electrical resistance and thermal behaviours of the tab to bus-bar joints.…”

Comparison of Tab-To-Busbar Ultrasonic Joints for Electric Vehicle Li-Ion Battery Applications

“…Furthermore, Li-ion batteries are progressively being used for large-scale energy storage systems for grid applications [5]. As a consequence, there is substantial demand for battery manufacturing which involves a large number of individual cells to be connected either in series or parallel to deliver the required power and driving range [6]. For example, the widely used pouch cell format uses a tab-to-busbar connection as the electrical interconnect.…”

“…One of the widely accepted joining methods to connect the pouch cell tab to the busbar is ultrasonic metal welding (UMW) due to several advantages, including joining of dissimilar materials of varying thickness, joining of highly reflective and conductive material, multiple stack-ups and low thermal input during the welding [6,13]. Li-ion battery packs for General Motors' (GM) Chevy Volt and the Nissan LEAF are currently being manufactured using UMW where the pouch cell tabs are connected with busbars [6,14].…”

“…One of the widely accepted joining methods to connect the pouch cell tab to the busbar is ultrasonic metal welding (UMW) due to several advantages, including joining of dissimilar materials of varying thickness, joining of highly reflective and conductive material, multiple stack-ups and low thermal input during the welding [6,13]. Li-ion battery packs for General Motors' (GM) Chevy Volt and the Nissan LEAF are currently being manufactured using UMW where the pouch cell tabs are connected with busbars [6,14]. Research has been conducted on understanding the ultrasonic metal welding joining mechanism [15][16][17][18], microstructure and material properties [19][20][21], thin to thick material joining (i.e., varying stack-ups) [22], process robustness and optimisation [13,23,24], and mechanical and vibrational behaviours of the welded joints [25,26], which are reported in the literature.…”

Electro-Thermo-Mechanical Behaviours of Laser Joints for Electric Vehicle Battery Interconnects

“…For example, Das, et al [2] have identified the suitable joining methods for cylindrical cell based battery pack building of which laser welding, micro-TIG welding and ultrasonic wedge bonding are the preferred joining methods. As dissimilar thin material joining is one of the key requirements for battery joining applications, several joining techniques are adopted to make satisfactory dissimilar interconnects, including ultrasonic metal welding [4], [5], ultrasonic wedge bonding [6], resistance spot welding [7], [8], soldering [9], micro-TIG welding [7], [10], micro-clinching [11] or laser welding [12]. Among these joining methods, laser welding provides several advantages over other joining methods including easy automation, contactless one-sided joining, high throughput, less heat input etc.…”