Lithium-ion batteries are widely used in various electronic devices (such as mobile phones, notebook computers, PDAs, digital cameras and digital camcorders, etc.) due to their high specific energy, long cycle life, small self-discharge, no memory effect and no pollution. As well as transportation (patrol cars, electric bicycles, electric vehicles, etc.), it has become a high-tech industry supported by my country's energy field.

Power batteries refer to batteries used in electric vehicles. Compared with small-capacity batteries (such as mobile phone, laptop computer batteries, etc.), they have larger capacity and output power and can be used in electric vehicle driving power supplies and large mobile power supply applications. Of secondary batteries. There are many manufacturing processes for lithium-ion batteries or battery packs, among which there are many processes, such as explosion-proof valve sealing welding, tab welding, soft connection welding, safety helmet spot welding, battery case sealing welding, module and PACK welding. Laser welding is the best process.  The materials used for welding of power batteries mainly include pure copper, aluminum, aluminum alloys, stainless steel, etc.

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 ruptures to prevent the battery from bursting. The safety valve has an ingenious structure, and this process requires extremely strict laser welding processes. Before continuous laser welding was used, pulse laser welding was used to weld battery explosion-proof valves. Continuous sealing welding was achieved through the overlap and coverage of solder joints. However, 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 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 secondary batteries, it needs to be welded with another aluminum safety valve. Welding must not only ensure a reliable connection between the tab and the pole, but also requires the weld to be smooth and beautiful.

3. Battery poles with spot welding

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 pulse welding machines. With the emergence of IPG's QCW quasi-continuous laser, it has also been widely used in battery pole strip welding. At the same time, due to its good beam quality, the welding spot can be very small. , which has unique advantages in dealing with the welding of high-reflectivity aluminum strips, copper strips and narrow-band battery pole strips (pole strip width below 1.5mm).

4. Sealing and welding of power battery shell and cover plate

The shell materials of power batteries include aluminum alloy and stainless steel. Among them, aluminum alloy is used the most, usually 3003 aluminum alloy, and a few use pure aluminum. Stainless steel is the material with the best laser weld ability, especially 304 stainless steel. Whether using pulse or continuous laser welds with good appearance and performance can be obtained.

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, both pulse welding and continuous welding have no problem. 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 case. Generally, when the case thickness is less than 1mm, you can consider using a single-mode laser within 1000W. If the thickness is more than 1mm, you need to use a single-mode or multi-mode laser with more than 1000W.

Small-capacity lithium batteries often use relatively thin aluminum shells (thickness is about 0.25mm), and some such as 18650 use steel shells. Due to the thickness of the casing, lower power lasers are generally used for welding this type of battery. Using continuous laser to weld thin-shell lithium batteries can increase the efficiency by 5 to 10 times, and the appearance and sealing properties are better. Therefore, there is a trend to gradually replace pulsed lasers in this application field.