The key application points of laser welding technology for lithium battery packs mainly include equipment and environmental management, material and process compatibility, parameter control, and operational safety, etc. The following is a specific analysis:

Equipment and environmental management

Equipment inspection: Before laser welding, a comprehensive inspection of the equipment is necessary to ensure that the laser generator, optical path system, cooling system, etc. are operating normally and that all parameters are stable, so as to guarantee the welding quality.

Environmental requirements: Keep the welding area clean to prevent dust, metal debris and other impurities from entering. Keep the environmental humidity within the range of 40% to 60% to prevent intensified oxidation of the electrode head, which could affect the welding effect. It can also avoid safety issues caused by the condensation of water vapor on the battery surface.

The materials are compatible with the process

Battery surface treatment: Ensure that the surface of the battery electrode sheets is clean, free of oil stains and oxide layers. It can be cleaned with a dedicated cleaning agent and then dried with dry nitrogen to ensure good contact between the electrode and the electrode sheet during welding and improve the welding quality.

TAB material matching: The material and thickness of the tabs should match the battery electrode sheets. Different materials and thicknesses of tabs and electrode sheets require different welding parameters when laser spot welding.

Welding material quality: The auxiliary materials used in the welding process, such as shielding gases, should be ensured to meet the quality requirements. The purity, flow rate and other parameters of the shielding gas will affect the atmosphere environment during welding, and thereby influence the welding quality.

Parameter control

Laser power: It is one of the key parameters affecting the quality of welding. If the power is too low, the metal material cannot be fully melted and the strength of the solder joint is insufficient. Excessive power may cause problems such as metal splashing and burning through the battery electrodes. For the common welding of lithium battery electrode sheets, the laser power can be adjusted within the range of 1000 to 3000 watts.

Welding time: It works in coordination with the laser power to jointly determine the input of welding energy. If the welding time is too short and the energy is insufficient, the weld points cannot form a good metallurgical bond. If the welding time is too long, the weld points will overheat, affecting the battery performance.

Pulse frequency: It affects the formation speed and quality of solder joints. If the frequency is too high, the solder joints may interfere with each other, affecting the stability of the solder joints. If the frequency is too low, the welding efficiency will decrease.

The inclination Angle of the welding head: Aluminum alloy has a high reflectivity to laser. To prevent the laser beam from being incident perpendicularly and causing vertical reflection, which could damage the laser focusing mirror, the welding head is usually deflected at a certain Angle during the welding process. The diameters of the solder joint and the effective bonding surface increase with the increase of the laser inclination Angle. When the laser inclination Angle is 40°, the largest solder joint and the effective bonding surface are obtained. The penetration depth of the weld point and the effective penetration depth decrease with the laser tilt Angle. When it is greater than 60°, the effective welding penetration depth drops to zero.

Operational safety

Personnel training: Operators must undergo professional training and be familiar with the operation methods, process flows and safety precautions of laser spot welding equipment. Operators should possess certain electrical knowledge and welding skills, be able to accurately judge the welding quality, and promptly handle problems that arise during the welding process.

Personal protection: When performing laser spot welding, operators must wear proper personal protective equipment, such as laser protective glasses, to prevent laser damage to the eyes. At the same time, protective clothing, gloves, etc. should be worn to avoid direct contact of the body with the laser beam and high-temperature objects to prevent scalding.