Principle and process analysis of Power battery cell laser welding

Laser welding technology is widely used in the manufacturing and assembly process of Lithium-ion batteries, with typical steps including welding of battery cell soft connections and cover plates, sealing welding of cover plates, and welding of sealing nails. The reason why laser welding has become the main welding method for square power batteries is due to its outstanding advantages such as high energy density, good power stability, high welding accuracy, and easy systematic integration. It plays an irreplaceable role in the production process of square aluminum shell lithium batteries.

From the perspective of market development, the market share of lithium battery aluminum shells is higher than that of steel shells, mainly due to the high hardness, lightweight, and excellent safety of aluminum shells. Lifepo4 power cells can be customized according to product size, and there are many models and specifications in the market, which also makes it difficult to standardize the process. The standardization of square batteries in the future will become an important trend, which has positive significance for group production and later maintenance.

The welding of the cover plate of the Power battery cell shell is mainly divided into two methods: top welding and side welding. In the top welding process, there is a rectangular cover plate on the top of the battery shell, which has a positive electrode lead out terminal. When assembling, insert the cover plate into the outer shell and make it flush with the upper opening. Then, use a laser to seal and weld along the rectangular gap between the cover plate and the outer shell in a repeated continuous laser process.

In actual production, top welding can fix the laser beam stationary, clamp the battery on the workbench, align the laser beam with the weld seam, and drive the battery along the X and Y coordinates to follow the same rectangular trajectory as the weld seam. It should be pointed out that when Lithium superpack batteries adopt a top welding sealing structure, there is no positioning step at the place where the cover plate is placed, and the length dimension tolerance requirements are strict, thus placing high demands on the welding assembly accuracy.

The laser welding of Lithium battery pack utilizes high-energy density laser pulses to locally heat small areas of the material. The energy radiated by the laser diffuses through the material through thermal conduction, causing the material to melt and form a specific molten pool. This technology is mainly suitable for welding thin-walled materials and fine parts, and can achieve various forms such as spot welding, butt welding, overlay welding, and sealing welding. It has the advantages of high aspect ratio, small weld width, small heat affected zone, small deformation, fast welding speed, smooth and beautiful weld, no or only simple treatment after welding, and high weld quality without pores. Meanwhile, laser welding can be precisely controlled, with a small focused spot and high positioning accuracy, making it easy to achieve automation.

Laser welding can be achieved using pulsed or continuous laser beams, and can be divided into two modes based on the principle: heat conduction welding and laser deep penetration welding. The working principle of thermal conduction welding in Lithium-ion battery cells is: laser radiation heats the surface to be processed, and the surface heat is guided to the interior for diffusion through thermal conduction. By controlling parameters such as the width, energy, peak power, and repetition frequency of the laser pulse, the workpiece is melted to form a specific molten pool.

In this mode, the laser power density is about 10 ⁵ W/cm ², the weld depth is generally less than 2.5mm, and the maximum weld depth to width ratio can reach 3:1. Deep penetration welding usually uses a continuous laser beam to complete material connection, and its energy conversion mechanism is achieved through a "small hole" structure. After laser irradiation, the material evaporates and forms small holes, which absorb all the energy of the incident beam. The local temperature can reach about 25000 ℃, causing the metal surrounding the hole cavity to melt, thus achieving deep welding of the Battery pack kit.

If you have further technical consultation or equipment selection requirements for the laser welding process of Power battery cells, please feel free to contact us. We will provide you with professional welding solutions and process support.