Electric vehicles’ batteries, referred to as Battery Packs (BPs), are composed of interconnected battery cells and modules. The utilisation of different materials, configurations, and welding processes forms a plethora of different applications. This level of diversity along with the low maturity of welding designs and the lack of standardisation result in great variations in the mechanical and electrical quality of the joints. Moreover, the high-volume production requirements, meaning the high number of joints per module/BP, increase the absolute number of defects. The first part of this study focuses on associating the challenges of welding application in battery assembly with the key performance indicators of the joints. The second part reviews the existing methods for quality assurance which concerns the joining of battery cells and busbars. Additionally, the second part of this paper identifies the general trends and the research gaps for the most widely adopted welding methods in this domain, while it renders the future directions.

Welding Challenges and Quality Assurance in Electric Vehicle Battery Pack Manufacturing

The need for efficient manufacturing methods to produce battery packs is increasing with the growing demand for Electric Vehicles (EVs). A large number of individual battery cells are interconnected to meet the power and capacity requirements of EVs. As a result, several joining methods are under investigation to produce battery interconnects efficiently. Typically, ultrasonic metal welding is employed to produce pouch cell tab-to-tab interconnects. In addition, laser welding is also emerging as a fast and non-contact joining alternative. Detailed critical-to-quality investigations are needed to compare both joint types. This paper investigated the effect of multiple ultrasonic nuggets and laser seams on electrical resistance and thermal performance at the tab-to-tab interconnects. Multi-physics simulation models were developed to predict the joint resistance and temperature rise under different charge-discharge current values. Results show that electrical contact resistance was decreased by 54% when a 5 mm diameter circular laser weld-based tab-to-tab connection was replaced with six circular welds of the same diameter. Simulation-based comparative analysis showed that resistance and temperature rise obtained from the 3 or 6 circular laser welds were similar to 3 or 6 nuggets ultrasonic welds. As a result, both the ultrasonic and laser joints can be used as per need. 

Impact of multiple ultrasonic and laser welds on electro-thermal behaviours for connecting Li-ion battery cells

The present study involves the development of an electric cart, with future research aiming to enhance its efficiency by creating a hybrid solar-electric cart. To achieve this goal, a bibliometric analysis of electric vehicle (EV) batteries is required. This study aims to identify research gaps in EV batteries through Bibliometric Analysis, utilizing Scopus Analyze and VOSViewer to analyze 1,276 documents obtained from the Scopus database, including articles (49.7%), conference papers (43.3%) and various other publications such as reviews, book chapters, reports, short surveys, notes, books, erratum, and editorials. The analysis reveals a substantial surge in EV battery research and publications within the Scopus database since 2013, and this trend is projected to continue until the end of 2023. Based on researchers’ affiliations, Chinese institutions have ranked first in contributions, followed by institutions from the United States, India, the United Kingdom, and Canada. Surprisingly, the University of Warwick secured the top among research institutions, with the Beijing Institute of Technology claiming the second position. The VOSViewer analysis generated six keyword clusters relevant to EV battery research. Of particular interest is Cluster 5, which emphasizes the significance of battery management techniques, establishing efficient battery swapping stations, optimizing energy management strategies, and exploring the role of EV batteries in building intelligent grids. These gaps identified in Cluster 5 will become the focal point for future research, especially concerning efficiency enhancement through developing a hybrid battery system capable of a hybrid solar-electric cart. 

Hybrid solar-electric cart efficiency enhancement: A bibliometric analysis

Dual-mode laser beam welding of similar and dissimilar material tab-to-busbar for electric vehicle battery pack

Abstract The escalating necessity for more efficient and defect-free joining of ‘ultra-thin foil collectors-to-tabs’ in electric vehicle (EV) Li-ion pouch cells motivates this study. The prevalent ultrasonic welding (USW) method for these joint types, faces limitations such as design constraints and access requirements, laser welding (LW) emerges as a promising alternative offering flexibility, one-side access and faster speeds with efficient heat input. This study aims to investigate the feasibility of LW as a viable alternative to USW for joining current collectors-to-tab joints. It compares the mechanical, metallurgical, electrical and thermal analysis of the joints to evaluate both welding techniques for joint defects. The comparison of solid-state material mixing during USW and the intermixing of aluminium (Al) and copper (Cu) during fusion LW using EDX analysis presents interesting observations in the study. The USW generates a thin transition layer with intermetallic compounds (IMCs) attributed to the diffusion of Cu into the Al matrix during joining, which is comparatively lower as in the case of LW with higher material mixing with brittle IMCs like Al 2 Cu and Al 4 Cu 9 . However, the joint strength of LW is comparatively lower than the USW joint attributed to the reduced fusion zone area. Furthermore, from the electrical contact resistance and the joint temperature analysis, it was found that the resistance and temperature vary by as much as 13% and 6%, respectively, for the 50 A and 75 A passing currents when the USW is replaced with the LW process. 

Investigating laser and ultrasonic welding of pouch cell multi-foil current collectors for electric vehicle battery fabrication

In-depth evaluation of micro-resistance spot welding for connecting tab to 18,650 Li-ion cells for electric vehicle battery application

The micro-resistance spot welding is widely used for low-to-medium-volume applications due to its low cost, especially for cylindrical Lithium-ion cell-based modules. Using typical micro-resistance spot welding electrodes in a series configuration, two nuggets/welds are created in a single welding operation. As it is a contact joining process, productivity is limited. This paper developed a novel approach to enhance the productivity of micro-resistance spot welding, where four nuggets were produced instead of two nuggets in a single operation. The critical-to-quality criteria, including joint strength, microstructure, electrical resistance and temperature rise at joints, were demonstrated by comparing the existing and proposed approaches. A reduction in cycle time by up to 57% can be achieved by adopting the proposed approach while maintaining the weld quality. 

Utilising a novel multi-electrode approach for improving micro-resistance spot welding productivity for electric-mobility battery interconnects

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In-depth evaluation of micro-resistance spot welding for connecting tab to 18,650 Li-ion cells for electric vehicle battery application

Utilising a novel multi-electrode approach for improving micro-resistance spot welding productivity for electric-mobility battery interconnects