Automotive battery packs for electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV) typically consist of a large number of battery cells. These cells must be assembled together with robust mechanical and electrical joints. Joining of battery cells presents several challenges such as welding of highly conductive and dissimilar materials, multiple sheets joining, and varying material thickness combinations. In addition, different cell types and pack configurations have implications for battery joining methods. This paper provides a comprehensive review of joining technologies and processes for automotive lithium-ion battery manufacturing. It details the advantages and disadvantages of the joining technologies as related to battery manufacturing, including resistance welding, laser welding, ultrasonic welding and mechanical joining, and discusses corresponding manufacturing issues. Joining processes for electrode-to-tab, tab-to-tab (tab-to-bus bar), and module-to-module assembly are discussed with respect to cell types and pack configuration.Copyright © 2010 by ASME and General Motors

Joining Technologies for Automotive Lithium-Ion Battery Manufacturing: A Review

This paper describes procedures for the joining of aluminum with copper via solid-state welding. Welding of dissimilar materials in order to reach a high strength and durable joints is a reasonable and outstanding challenge for industrial and especially for automotive applications. Nowadays, wiring and electrical systems, as for example batteries, turn out to be main drivers for new developments in the field of dissimilar joining technologies. Joining of aluminum to copper through a melting process leads to brittle intermetallic compounds, which cause failure of the joint already during cool down. Solid-state welding technologies allow the welding below melting temperature, so that phenomena at the interface, which lead to the formation of intermetallics under different conditions, are of interest to the resulting joint properties. Not only mechanical properties, but electrical resistivity and heat conduction are strongly dependent on those effects. Diffusion welding is performed as a model welding procedure, while friction stir welding and hybrid friction diffusion bonding are investigated as technological welding processes in this paper.

Solid-state welding of aluminum to copper—case studies

Micromanufacturing processes are expanding in their length and breadth as long as the related research and development (R&D) activities and applications are concerned. Products are getting miniatur...

Micromanufacturing: A review—part II

Dissimilar welding of aluminium (Al) and copper (Cu) has many applications in the electric power, electronic and piping industries. The weldments in these applications are highly valued for their corrosion resistance, heat and electricity conducting properties. The Al-Cu joints are lighter, cheaper and have conductivity equal to that of copper alloys. Much research has investigated dissimilar welding of Al-Cu by solid-state welding and fusion welding processes with the aim of optimising the properties and strength of such dissimilar joints. The main aim of the study is to critically review the factors influencing the properties of the Al-Cu joint. The study mainly discusses about the effects of intermetallic compounds (IMC) on the properties of Al-Cu joint and their effect while in service. The effects of joining aluminium alloy 1060 with pure copper by laser welding, friction stir welding and brazing have been reviewed and compared. The review shows that the various intermetallic compound formations in the joint have both beneficial and detrimental effects. The characteristics of these intermetallic compounds vary according to the location of the phase formed. Comparison of processes and parameters for welding of Al 1060 with pure Cu shows that the formation of the intermetallic compounds and their effects on the weld properties are mainly influenced by the welding speed, heat input, the thermal properties of the base metals and the filler metal as well as the dilution between the base metal and filler metal.

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Factors influencing Al-Cu weld properties by intermetallic compound formation

The electric vehicle (EV) battery systems are complex assemblies of dissimilar materials in which battery cells are connected using several thousand interconnect joints. Every single joint influences the functionality and efficiency of the whole battery system, making the joining process crucial. Laser welding is considered a desirable choice for EV battery manufacturing due to its non-contact nature, high energy density, precise control over the heat input, and ease of automation. However, incompatible thermos-physical properties of dissimilar materials used in battery tabs and interconnectors pose a significant challenge for achieving complete metallurgical bond. Furthermore, the formation of undesirable weld microstructures such as hard and brittle intermetallic compounds (IMCs) substantially undermines the structural, electrical, and thermal characteristics of battery joints. This paper reviews the fundamental difficulties and latest developments in dissimilar laser welding of steel-copper, steel-aluminum, aluminum-copper, and steel-nickel, some of the potential joint combinations in EV battery pack manufacturing. The weld microstructure and common metallurgical defects, as well as mechanical and electrical properties of joints are discussed. In addition, the effects of laser welding process parameters on the joint properties and the applicability of various interlayers and coatings in laser welding of battery materials are assessed.

A review on dissimilar laser welding of steel-copper, steel-aluminum, aluminum-copper, and steel-nickel for electric vehicle battery manufacturing

Aluminum combines comparably good thermal and electrical properties with a low price and a low material weight. These properties make aluminum a promising alternative to copper for a large number of electronic applications, especially when manufacturing high volume components. However, a main obstacle for a wide use of this material is the lack of a reliable joining process for the interconnection of copper and aluminum. The reasons for this are a large misalignment in the physical properties and even more a poor metallurgical affinity of both materials that cause high crack sensitivity and the formation of brittle intermetallic phases during fusion welding. This paper presents investigations on laser micro welding of copper and aluminum with the objective to eliminate brittle intermetallic phases in the welding structure. For these purposes a combination of spot welding, a proper beam offset and special filler material are applied. The effect of silver, nickel and tin filler materials in the form of thin foils and coatings in a thickness range 3-100 μm has been investigated. Use of silver and tin filler materials yields to a considerable improvement of the static and dynamic mechanical stability of welded joints. The analysis of the weld microstructure shows that an application even of small amounts of suitable filler materials helps to avoid critical, very brittle intermetallic phases on the interface between copper and solidified melt in the welded joints.

Laser micro welding of copper and aluminum

Ein
Verfahren zum Schweisen
artungleicher metallischer Fugepartner
weist folgende Verfahrensschritte auf: - Bereitstellen des einen
Fugepartners
(1, 8) aus einem ersten metallischen Werkstoff, - Bereitstellen
des anderen Fugepartners
(2, 9) aus einem zweiten metallischen Werkstoff, - Schichten
einer Lage eines Schweiszusatzwerkstoffes
(4, 11) aus einem dritten metallischen Werkstoff zwischen die beiden
Fugepartner
(1, 8; 2, 9) und - Verschweisen der beiden Fugepartner
(1, 8; 2, 9) unter Einbindung des Schweiszusatzwerkstoffes (4, 11)
mit Hilfe eines Energiestrahls, vorzugsweise Laserstrahls (7).

Verfahren zum Schweißen artungleicher metallischer Fügepartner, insbesondere von Aluminium-Kupfer-Verbindungsstellen

The most evident trend in electronics production is towards miniaturization. Regarding the materials involved, another trend can be observed: intelligent combinations of different materials. One example is the combination of copper and aluminium. Copper is the material of choice for electronic packaging applications due to its superior electrical and thermal conductivity. On the other hand, aluminium offers technical and economical advantages with respect to cost and component weight -- still providing thermal and electrical properties acceptable for numerous applications. Especially for high volume products, the best solution often seems to be a combination of both materials. This fact raises the question of joining copper and aluminium. With respect to miniaturization laser micro welding is a very promising joining technique. Unfortunately, the metallurgical incompatibility of copper and aluminium easily results in the formation of brittle intermetallic phases and segregations during laser welding, thus generating an unacceptable quality of the joints. This paper presents investigations on enhancing the quality during laser micro welding of copper and aluminium for applications in electronics production. In order to eliminate the formation of brittle intermetallic phases, the addition of a filter material in form of a foil has been investigated. It can be shown that the addition of pure metals such as nickel and especially silver significantly reduces the occurrence of brittle phases in the joining area and therefore leads to an increase in welding quality. The proper control of the volume fractions of copper, aluminium and filler material in the melting zone helps to avoid materials segregation and reduces residual stress, consequently leading to a reduction of crack affinity and a stabilization of the mechanical and electrical properties.

Laser micro welding of copper and aluminium using filler materials

Laser micro welding has become a standard manufacturing technique, particularly in industry sectors, such as automotive and aerospace electronics or medical devices, where the requirements for strength, miniaturization and temperature resistance are constantly rising. So far the use of laser micro welding is limited due to the fluctuation of the quality of the welded joints, because the welding results for material with high optical reflection and thermal conductivity, such as copper and copper alloys, depend very strongly on the condition of the material surface. This paper presents investigations on the use of a laser pre-pulse in spot welding of electronic materials with Nd:YAG laser. In order to achieve reproducible joining results two strategies are followed-up. The first one utilizes a reflection-based process control for measuring the reflection during the short pre-pulse. The intensity of the reflected light is used to calculate an appropriated welding pulse power, which corresponds to the measured relative absorption. Adjustment of laser parameters according to the condition of the surface is done in real time before laser main pulse. A second possibility for the stabilization of copper welding is the employment of a short and powerful laser pre-pulse before laser main pulse. This pre-pulse affects the workpiece surface and creates more reproducible absorption conditions for the main pulse, independent from the initial situation on material surface.

Use of pre-pulse in laser spot welding of materials with high optical reflection

The invention relates to a method for welding similar metal joining partners comprising the following steps: preparing one of the joining partners (1, 8) made from a first metal material, preparing the other joining partner (2, 9) made from a second metal material, layering a layer of a welding additional substance (4, 11), made of a third metal material, between both of the joining partners (1, 8; 2, 9), and welding both of the joining partners (1, 8; 2, 9), by integrating the welding additional material (4, 11), with the aid of an energy beam, preferably a laser beam (7).

Ihor Mys

Papers

Laser micro welding of copper and aluminum

Verfahren zum Schweißen artungleicher metallischer Fügepartner, insbesondere von Aluminium-Kupfer-Verbindungsstellen

Laser micro welding of copper and aluminium using filler materials

Use of pre-pulse in laser spot welding of materials with high optical reflection

Method for welding similar metal joining partners, in particular, aluminium-copper connecting points