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Lithium-ion batteries are widely used in various electronic devices (such as mobile phones, notebook computers, PDAs, digital cameras, digital video cameras, etc.) because of their high specific energy, long cycle life, low self-discharge, no memory effect, and no pollution. As well as transportation tools (patrol cars, electric bicycles, electric vehicles, etc.), it has become a high-tech industry supported by my country's energy sector.
Power battery refers to the battery used in electric vehicles. Compared with small-capacity batteries (such as mobile phone, laptop battery, etc.), it has larger capacity and output power and can be used in electric vehicle driving power and large mobile power applications. Secondary battery. There are many manufacturing 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, safety helmet spot welding, battery shell sealing welding, module and PACK welding. Take the laser welding machine as the process. The materials used for welding of power batteries are mainly pure copper (chemical formula Cu), aluminum (Al), aluminum alloy, and stainless steel.
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 valve body of the explosion-proof valve ruptures to prevent the battery from bursting. The safety valve (function: the control pressure does not exceed the specified value) has an ingenious structure. This process has extremely strict requirements on the laser welding process. Before continuous (Continuity) laser welding, the battery explosion-proof valve was welded using pulsed laser welding. Continuous sealing welding was achieved through the overlap and coverage of the welding point and the welding point, but the welding efficiency was low and the sealing performance was low. 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) (Al) material, and the negative electrode uses nickel (Ni) (Ni) material or copper-plated nickel (Ni-Cu) material. In the manufacturing process of power batteries, one of the steps is to weld the battery tabs and poles together. In the production of the secondary battery, it needs to be welded with another aluminum safety valve. Welding must not only ensure the reliable connection between the tab and the pole, but also requires a smooth and beautiful weld.
3, Battery pole strip spot welding
The materials used for the battery electrode belt include pure aluminum belt, nickel (Ni) belt, aluminum-nickel composite belt and a small amount of copper belt. The welding of battery electrode strips generally uses pulse welding machines. With the emergence of IPG's QCW quasi-continuous laser, it has also been widely used in battery electrode strip welding. At the same time, due to its good beam quality, the welding spot can be small , It has unique advantages in dealing with the welding of high-reflectivity aluminum strip, copper strip and narrow-band battery pole strip (the pole strip width is less than 1.5mm) (explanation: it can overwhelm the other party's favorable situation).
4, Power battery shell and cover plate sealing welding
Power battery shell materials include aluminum (Al) alloy and stainless steel (stainless acid-resistant steel). Among them, aluminum alloy is the most used, generally 3003 aluminum alloy, and a few use pure aluminum. Stainless steel is a laser weldable material, especially 304 stainless steel, whether it is pulsed or continuous laser can obtain welds with good appearance and performance.
The laser welding performance of aluminum and aluminum alloys (melting point 660°C) 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. Other series of aluminum alloys choose continuous laser welding to reduce crack sensitivity. At the same time, according to the thickness of the power battery shell, select a laser with appropriate power (referring to how much work the object does in a unit time). Generally, when the shell thickness is less than 1mm, single-mode lasers within 1000W can be considered, and the thickness is more than 1mm. Use single-mode or multi-mode lasers above 1000W.
Small-capacity lithium batteries often use relatively thin aluminum shells (about 0.25mm in thickness), and 18650 and the like use steel shells. Due to the thickness of the shell, a lower power laser is generally used for welding such batteries. Using Continuity laser to weld thin-shell lithium batteries, the efficiency can be increased by 5 to 10 times, and the appearance and sealing 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 and parallel connections between power batteries are generally completed by welding the connecting piece and the single battery. The materials of the positive and negative electrodes are different. Generally, there are two kinds of materials: copper and aluminum (Al). Because the copper and aluminum are brittle after laser welding The compound cannot meet the requirements of use. In addition to ultrasonic welding, copper and copper, aluminum and aluminum are generally welded by laser. At the same time, because copper and aluminum conduct heat very quickly, and the reflectivity of the laser is very high, the thickness of the connecting piece is relatively large, so a higher power (referring to how much work the object does in a unit time) laser is needed Can be welded.
6, Application cases are as follows:
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