Due to the advantages of high specific energy, long cycle life, small self-discharge, no memory effect and no pollution, lithium-ion batteries are widely used in various electronic equipment and vehicles, and have become a high-tech industry focused on the development of the energy field.
Power battery refers to the battery used in electric vehicles. Compared with small-capacity batteries, it has larger capacity and output power. It can be used for electric vehicle drive power and secondary batteries in large mobile power applications. There are many production processes for lithium-ion batteries or battery packs, and there are many processes, such as explosion-proof valve sealing welding, tab welding, soft connection welding, helmet spot welding, battery shell sealing welding, module and PACK welding. Laser welding is the best process. The materials used for welding of power batteries are mainly pure copper, aluminum and aluminum alloys, and stainless steel.
Application of laser welding in the field of lithium battery
1. Battery explosion-proof valve welding
The explosion-proof valve of the battery is a thin-walled valve body on the battery sealing plate. When the internal pressure of the battery exceeds the specified value, the explosion-proof valve body will rupture to prevent the battery from bursting. The safety valve has an ingenious structure, and this process has extremely strict requirements on the laser welding process. Before continuous laser welding was used, the welding of battery explosion-proof valves was carried out by pulsed laser welding, and continuous sealing welding was achieved by overlapping and covering the welding spot and the welding spot, but the welding efficiency was low and the sealing performance was relatively poor. Continuous laser welding can achieve high-speed and high-quality welding, and welding stability, welding efficiency and yield can be guaranteed.
2. Battery tab welding
The tabs are usually divided into three materials. The positive electrode of the battery uses aluminum (Al) material, and the negative electrode uses nickel (Ni) material or nickel-plated copper (Ni-Cu) material. In the manufacturing process of power batteries, one of the links is to weld the battery tabs and poles together. In the manufacture of the secondary battery, it needs to be welded with another aluminum safety valve. Welding not only needs to ensure the reliable connection between the tab and the pole, but also requires the welding seam to be smooth and beautiful.
3. Spot welding of battery poles
The materials used for battery pole strips include pure aluminum strips, nickel strips, aluminum-nickel composite strips, and a small amount of copper strips. The welding of battery pole strips generally uses a pulse welding machine. At the same time, due to its good beam quality and small welding spot, it is suitable for high-reflectivity aluminum strips, copper strips and narrow-band battery pole strips (pole strip width is 1.1. 5mm or less) welding has unique advantages.
4. Seal welding of power battery shell and cover plate
The shell materials of power batteries are aluminum alloy and stainless steel, among which aluminum alloy is the most used, generally 3003 aluminum alloy, and a few use pure aluminum. Stainless steel is the best material for laser weldability, especially 304 stainless steel, whether pulsed or continuous laser can obtain welds with good appearance and performance.
The laser welding performance of aluminum and aluminum alloys varies slightly depending on the welding method used. Except for pure aluminum and 3 series aluminum alloys, there is no problem with pulse welding and continuous welding. For other series of aluminum alloys, continuous laser welding is the best choice to reduce crack susceptibility. At the same time, choose a laser with appropriate power according to the thickness of the power battery casing. Generally, when the casing thickness is less than 1mm, a single-mode laser within 1000W can be considered, and a single-mode or multi-mode laser above 1000W should be used when the thickness is above 1mm.
Small-capacity lithium batteries often use relatively thin aluminum shells (about 0.25mm thick), and there are also 18650 and other steel shells. Due to the thickness of the shell, the welding of such batteries generally uses a lower power laser. Using continuous lasers to weld thin-shell lithium batteries, the efficiency can be increased by 5 to 10 times, and the appearance and sealing performance are better. Therefore, there is a trend to gradually replace pulsed lasers in this application field.
5. Power battery module and pack welding
The series-parallel connection between power batteries is generally completed by welding the connecting piece and the single battery. The positive and negative electrodes are made of different materials. Generally, there are two materials, copper and aluminum. Since copper and aluminum are laser welded to form brittle compounds, it is impossible to To meet the requirements of use, in addition to ultrasonic welding, copper and copper, aluminum and aluminum are generally laser welded. At the same time, due to the fast heat transfer of copper and aluminum, and the high reflectivity to the laser, the thickness of the connecting piece is relatively large, so it is necessary to use a higher power laser to achieve welding.
Features of Laser Welded Lithium Batteries
From the manufacture of lithium battery cells to battery pack grouping, welding is a very important manufacturing process. The conductivity, strength, air tightness, metal fatigue and corrosion resistance of lithium batteries are typical evaluation standards for battery welding quality. . The selection of welding method and welding process will directly affect the cost, quality, safety and consistency of the battery. Laser welding has become the first choice for many welding tasks due to its advantages of safe and reliable welding, precision technology, and environmental protection.