Interconnection Technology for Battery Cells and Modules

Metallographic cross-section of a weld nugget after etching to make the grain structure layerable.
© Fraunhofer ISE
Metallographic cross-section of a weld nugget after etching to make the grain structure layerable.
X-ray image of a welded top cap (left). The analysis reveals the undesirable nickel accumulation next to the bosses. SAM image of a welded top cap (right). Analysis of the resulting contact surfaces after welding.
© Fraunhofer ISE
X-ray image of a welded top cap (left). The analysis reveals the undesirable nickel accumulation next to the bosses. SAM image of a welded top cap (right). Analysis of the resulting contact surfaces after welding.

Battery storage systems for the reliable and efficient intermediate storage of solar and wind power as well as for electromobility are composed of individual battery cells. The interconnection of single battery cells to form battery modules or battery packs is decisive for the reliability of a battery storage system. At Fraunhofer ISE, we are developing and analyzing suitable processes, such as resistance welding and laser bonding, to electrically contact battery cells via battery cell connectors.

Based on our experience in connection technology, we characterize the electrical and mechanical properties of joints as well as their reliability and long-term stability. The practical process development is supported by the modeling of the interconnection processes with the finite element method (FEM) and the dimensioning of the cell connectors. This also includes the simulation of heat generation during operation and the influence of contact resistances on the cell behavior in the interconnection as well as the aging processes.

Technical requirements for interconnection technology in electrical battery interconnection are:

  • Joints with contacts that are as identical as possible
  • Smallest possible electrical contact resistances
  • Lowest possible heat effect during the joining process
  • Flexible interconnection process for a wide range of surface conditions and materials
  • Long-term stability even under extreme operating conditions (temperature, humidity, vibrations, etc.)

Our R&D Services in this Topic include:

  • Process development for different cell types
    • Resistance welding
    • Laser bonding e.g. one-sided interconnection of round cells
  • Qualification of joining point
    • Analysis of materials and technologies with regard to quality assurance, economy, reliability, LCA
    • Metallographic analysis of the weld nuggets at the cross section e.g. by using etching techniques to visualize the grain structure
    • Analysis of metallographic cross sections by scanning electron microscopy and energy dispersive X-ray spectroscopy
    • Thermal ageing, temperature cycle test
    • Scanning Acoustic Microscopy (SAM),
    • Preparation of µ-CT images of X-ray analysis data
    • Peel tests with variable peel angle and tensile shear tests
  • Simulation and modeling
    • Modeling of the joining process by FEM simulations
    • Dimensioning of battery cell connectors
    • Simulation of the operating state of the battery pack
    • Electrical as well as thermal and mechanical simulation of the battery pack
The laser bonder uses laser microwelding to electrically connect electrically connect batteries to form a battery module and thus ensures reliable electrical connections with high current carrying capacity.
© Fraunhofer ISE
The laser bonder uses laser microwelding to electrically connect electrically connect batteries to form a battery module and thus ensures reliable electrical connections with high current carrying capacity.

More Information on the Topic 'Interconnection Technology for Battery Cells and Modules'

Research Project

Leopard

Laser Bonding as a Gentle Interconnection of Next-Generation Temperature-Sensitive Cells for the Energy Transition

Research Project

ElVis

Electric Battery Interconnection: Innovative, Flexible, Fast and Cost-Effective