Application of laser welding in lithium battery
2021-08-12
A power battery is a battery that should be used in an electric car. Compared with small capacity battery (such as mobile phone, laptop battery, etc.) , it has large capacity and output power, which can be used in electric vehicle driving power and large mobile power applications. There are many manufacturing processes for lithium-ion battery, and laser welding is the best, such as explosion-proof Valve Sealing Welding, welding rod welding, soft connection welding, helmet spot welding, battery Shell Sealing Welding, module and packaging welding, etc. . The main materials used for welding power battery are pure copper, aluminum, aluminum alloy, stainless steel and so on. 1. The battery explosion-proof Valve is welded, and the battery explosion-proof Valve is a thin-walled valve body on the battery sealing plate. When the battery internal pressure exceeds the specified value, explosion-proof valve body failure to prevent the battery burst. The safety valve structure is exquisite, to the laser welding craft request is very strict. Before continuous laser welding, the welding of battery explosion-proof valve is pulse laser welding. The continuous sealing welding is realized by overlapping the welding spot and the welding spot, but the welding efficiency is low and the sealing performance is relatively poor. Continuous laser welding can achieve high-speed and high-quality welding, welding stability, welding efficiency and good quality rate can be guaranteed. 2. The electrode lug is usually divided into three kinds of materials: aluminum (Al) for the positive electrode, nickel (Ni) or copper-plated nickel (Ni-cu) for the negative electrode. In the production process of power battery, welding the battery sheet and the battery electrode is one of the links. Secondary battery production requires welding to another aluminum safety valve. The welding not only guarantees the reliable connection between the pole lug and pole, but also requires the smooth and beautiful welding seam. 3. Battery electrode spot welding, battery electrode tape using materials including pure aluminum tape, nickel tape, aluminum-nickel composite tape and a small amount of copper tape. Pulse Welder is usually used to weld the electrode strip of battery. With the appearance of QCW QUASI-CW LASER OF IPG company, it has been widely used in the welding of battery strip. At the same time, because of its good beam quality and small spot, it has a unique advantage in welding high reflectivity aluminum strip, copper strip and narrow band electrode strip (the width of electrode strip is less than 1.5 mm) . 4. Power Battery Shell and cover plate sealed welding, power battery Shell materials have aluminum and stainless steel, aluminum alloy is the most 3003 aluminum alloy, a few pure aluminum. Stainless steel is the best material for laser welding, especially 304 stainless steel. Both pulse welding and continuous laser welding can obtain good appearance and performance. The laser welding performance of aluminum and aluminum alloy is slightly different due to different welding methods. In addition to the pulse welding and continuous welding of pure aluminum and 3 series aluminum alloys, continuous laser welding is the best choice to reduce the crack sensitivity of other aluminum alloys. At the same time, according to the thickness of the power battery Shell to choose the appropriate power laser. When the thickness of the Shell is less than 1mm, the single mode laser with thickness less than 1000W can be used. If the thickness is greater than 1mm, a single-mode laser or a multi-mode laser with a thickness greater than 1000W can be used. The thin aluminum shell (thickness about 0.25 mm) and the steel shell around 18650 are often used in small capacity lithium battery. Because of the thickness of the case, such cells are usually welded using a low-power laser. The efficiency of continuous laser welding thin-shell lithium battery can be increased by 5-10 times, and the appearance and sealing performance are better. Therefore, there is a trend to replace pulse laser in this field. 5. Power Battery Modules and group welding, power batteries between the series-parallel connection is generally through the welding connection plate and a single battery to complete. The positive and negative electrodes are made of different materials. Generally there are two kinds of copper and aluminum materials. Because of copper-aluminum laser welding, Brittle compound is formed, which can not meet the application requirements. Ultrasonic welding, copper and copper, aluminum and aluminum are usually laser welded. At the same time, it is necessary to use high-power laser to realize welding because of the fast heat transfer of cu-al and the high reflectivity of laser.
