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Project Outline

QCOALA will ensure further use of and increased confidence in employing the latest laser technologies for welding of thin-gauge aluminium and copper as used in electric car battery interconnections and in thin-film PV assemblies.

Electric car battery interconnections

The market for Electric Vehicles (EVs) and Hybrid Electric Vehicles (HEVs) is growing rapidly, and, with this, the need for batteries. There are two main types of batteries for these vehicles, i.e. lithium-ion batteries and super-capacitor batteries (Figure 1). The lithium-ion type of battery is currently the preferred choice for EVs and HEVs, which is due to their high energy densities, low weight and low discharge rates. However, in order for these batteries to achieve such excellent properties, they are extremely expensive, i.e. typically between €10k and €15k. The lithium-ion batteries require several stages of construction, with one particular stage requiring the joining of highly-conductive aluminium (or copper) Figure 1 Image of super-capacitor battery type (Image courtesy of Volkswagen).
Figure 1 Image of super-capacitor
battery type (Image courtesy of Volkswagen).
tabs to the electrode cell ends of the battery. Laser welding is being considered for replacing the current joining technique, which is considered too slow and produces too many weld imperfections.

The super-capacitor battery comprises a 'bank' or 'stack' of batteries, which are interconnected using aluminium (and sometimes copper) tabs. The cumulative aluminium weld area determines the electrical conductivity of the connection, and as such, the performance of the device. Laser welding offers the advantage of high-speed, low heat input and low-distortion compared with more the conventional resistance spot or TIG welding process.

Thin-film PV assemblies

The second application addressed in the QCOALA project represents a key technology in the future PV industry. Flexible organic and inorganic solar cells are increasingly becoming important as an alternative source of energy. Although photovoltaic or solar cells are a proven concept / product, many challenges remain in the production process of these flexible thin-film solar cells. For instance, an outstanding question is how to interconnect the individual cells? For this, the multilayer materials of the cell are patterned to form a "shingle" structure, which ensures its connectivity to adjacent cells (Figure 2). Subsequently, flexible metal tabs or foils, generally made of aluminium or copper, are welded to the cells to form modules. An accurate, low heat input process is required, since PV cells on <100µm thick foils are extremely fragile and sensitive to mechanical, chemical and thermal stress. Laser welding offers the advantage of a low chemical, thermal and mechanical impact (due to its temporally and spatially selective energy input) compared with ultrasonic welding and direct conductive adhesives.

Figure 2 Image of flexible solar cell (Image courtesy of Flisom).
Figure 2 Image of flexible solar cell (Image courtesy of Flisom).