Our studies have shown that there is no single welding process that is ideal for all material combinations involved in the assembly of advanced batteries. Laser welding produces the strongest welds for like-to-like combinations. Welds made with lasers have shear strengths 10-100 times higher than those made with either resistance or ultrasonic welding techniques. Since laser welding is a non-contact process, it can be used in situations where access to the weld zone is limited by geometry or design. As a fusion process it does however have the potential to create bottle, high-resistance intermetallic compounds in the weld zone, particularly for aluminum-copper combinations. This technique also requires substantial fixturing to hold the substrates in contact for successful welding. This may limit the application of the technique in some cases. Resistance welding is the assembly method of choice for assembling battery packs for many industrial applications. In those applications, nickel tabs are often used because they are easy to weld and the applications do not require that the connection conduct high current flows. For transportation applications, however, low joint resistance is necessary so connections involving nickel are unattractive. Even though resistance welding does not product high mechanical strength welds, the small size of a resistance welding head may allow the technique to be sued in situations where the fixturing requirements of laser welding limits its use. Material combinations involving aluminum are, however, difficult to resistance weld. Other techniques are better suited to combinations involving aluminum. Ultrasonic metal welding is frequently used for assembly of aluminum and copper foils and sheets. It gives the highest strengths for dissimilar combinations of aluminum and copper and it gives good performance characteristics for most combinations involving nickel plated copper so long as the plating is applied with an electroless deposition process. This technique is also well adapted to make welds between multiple thin layers in a single welding step. The ultrasonic welding head is however larger than that required for resistance welding. This may limit the applications of this assembly technique for some battery module designs. Electrical and mechanical performance of battery tab-to-tab welds is not correlated. Strong welds and weak welds can show comparable resistance measurements in high current tests. The electrical properties depend more on the materials in the assembly than on the technique used to join them. This means that electrical continuity or resistance under load testing alone is not a good approach for monitoring the success of a joining process during battery module or pack assembly. Thermal imaging can be correlated to welds strength. If the weld area is large enough, an air-coupled ultrasonic transducer can lead to heat generation in the weld zone. The rate of temperature rise and the maximum temperature produced can both be used to monitor weld strength. Further investigation of this technique is underway.


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    Titel :

    Battery assembly: Welding of dissimilar materials


    Weitere Titelangaben:

    Batteriesatz: Schweißen unterschiedlicher Werkstoff


    Beteiligte:
    Speth, David (Autor:in)

    Erschienen in:

    Erscheinungsdatum :

    2012


    Format / Umfang :

    16 Seiten, 10 Bilder, 4 Tabellen, 10 Quellen



    Medientyp :

    Aufsatz (Konferenz)


    Format :

    Print


    Sprache :

    Englisch




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