Laser beam microwelding of lithium-ion battery cells with copper connectors for electrical connections in energy storage devices

Overheating in the joining process to create Li-ion battery cells can lead to degradation of the cells an has to be avoided; moreover temperatures lower than 0°C can lower the energy output of the cells. To avoid these issues Fraunhofer has designed a battery concept for EV-applications with a storage of the cells in a phase change material (PCM) in smaller leakage-free sub-units to buffer heat. Cu current collectors are welded in overlap on the negative pole – the top of the battery can, which is made of nickel-plated DC04 steel. The cells are welded in charged and filled state, so the the cathode and anode material, the separator and the liquid electrolyte are already inside the cell. Another function of the Cu collector is the encapsulation of the PCM, therefore the weld must be liquid-tight. The laser microwelding process of the Cu connector and 18650 cells is analysed to describe the influence of process parameters (laser power, welding speed, spatial power modulation) on the resulting connection. The characterization of the joint is performed regarding tightness, electrical resistance, mechanical stability and possible damage to the cell