Laser beam welding of electrical contacts of lithium-ion batteries for electric- and hybrid-electric vehicles

Lithium-ion batteries are preferred in electric and hybrid-electric vehicles due to their high energy density. In the course of developing high performance battery systems, which consist of over a hundred single cells, the energy efficiency still needs to be increased. One promising measure concerning this purpose is to reduce the electrical losses of contacts between the lithium-ion cells using laser beam welding. This joining technology offers the opportunity to vary the contact area as well as its geometry or position in the joining zone. Nevertheless, aging effects of the cells result in a mechanical stress at the joints between the terminal and the busbar. Varying the geometrical shape of the contact area opens a high potential to reduce these mechanical stresses of the contacts within a high voltage battery. This work presents a method to optimize the addressed geometrical shape of the weld seam in order to minimize the mechanical stresses of electrical contacts. A solution is proposed to calculate the optimum weld seam shape by the use of a genetic algorithm (GA) linked with a solid mechanics FEM simulation. The GA compiles alternative weld seam shapes, while the FEM simulations evaluate their mechanical properties. The optimised result is further verified within an experimental study.