Analysis of LiFePO4 battery cell laser welding process

Power battery cells occupy a high market share in the lithium battery market, thanks to the high toughness, lightweight, and excellent safety performance of aluminum shell materials. In the manufacturing process of square batteries, the welding of the shell and cover plate is one of the key processes, which directly affects the cost, quality, consistency, and safety of the battery. The top of the battery case is equipped with a rectangular cover plate, which includes a positive electrode lead out terminal. During assembly, embed the cover plate into the shell and align it with the upper opening.

Then, use laser welding to continuously weld along the rectangular gap between the cover plate and the shell to achieve sealing.

This process is called 'top welding'. In actual welding, the laser light source can be fixed, and the Lithium ion batteries can be clamped on the workbench. After the laser beam is aligned with the weld seam, the workbench drives the battery to move along the X and Y coordinates in a rectangular trajectory to complete the welding. For square batteries with top welded sealing structures, there is no precise positioning step for the cover plate, and strict length tolerance requirements are imposed, thus requiring high welding assembly accuracy.

To ensure the quality of high-speed laser welding of the top cover of LiFePO4 battery cells, the following technical conditions must be met:

Firstly, the weld seam needs to have sufficient width and a reasonable aspect ratio, which requires the laser heat source to have an appropriate range of action and the welding line energy to be controlled within a reasonable range.

Secondly, the surface of the weld seam should be smooth, and sufficient thermal cycling time is required during the welding process to maintain good fluidity of the molten pool, which solidifies into a smooth metal weld seam under the action of protective gas.

Thirdly, the weld seam should have good consistency, with few porosity and hole defects. This requires stable laser action on the workpiece during the welding process, continuous generation of high-energy plasma and action on the interior of the molten pool, forming a stable and sufficiently sized 'keyhole'. The stability of the keyhole of Lithium superpack batteries can prevent the violent spraying of metal vapor and plasma, which can bring out molten droplets and cause splashing, while avoiding the collapse of the molten pool around the keyhole or the entrapment of gas.

The shell materials mainly include aluminum alloy and stainless steel, among which aluminum alloy is the most widely used, commonly 1 series and 3 series aluminum alloys. In actual production, it is necessary to select the appropriate laser type and set welding process parameters based on the specific material type, shell thickness, shape structure, and tensile performance requirements of the Lithium battery pack, including welding speed, laser waveform, peak power, and welding head tilt angle. Only through systematic parameter optimization can the final welding effect meet the technical specifications of battery manufacturers.

Laser welding technology has demonstrated multiple advantages for the top welding and internal component welding of Battery pack kits:

Firstly, laser energy is mainly concentrated inside the dynamic keyhole, with less scattered energy to the outside. Therefore, effective welding can be achieved with lower laser power, reducing heat input by about 30% compared to composite welding methods, and lowering equipment energy consumption and losses.

Secondly, using swing welding can improve the adaptability to assembly errors of workpieces and effectively reduce welding defects caused by assembly steps and other issues.

Thirdly, swing welding has a strong repairing effect on the holes in the weld seam, and has a good application effect in repairing the holes in the battery cell weld seam.

Fourthly, laser welding can achieve precise control, with a small focused spot and high positioning accuracy, making it easy to integrate with automated equipment such as robotic arms, improving the production efficiency of Lithium solar batteries, reducing labor hours and costs, and having a simple system structure for easy debugging and maintenance.

If you have further requirements or technical inquiries regarding the laser welding process of LiFePO4 battery cells, please feel free to contact us. We will provide you with professional welding solutions and process support.