Application Of Laser Welding in Lithium Battery Field

Application of Laser Welding in Lithium Battery Field

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 weldability, 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, there is no problem with pulse welding or continuous welding. For other series of aluminum alloys, continuous laser welding is the best choice to reduce crack sensitivity. 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 a power of 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, 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 connection between power batteries is generally completed by welding the connecting piece to the single battery. The materials of the positive and negative electrodes are different, generally copper and aluminum. Since copper and aluminum form a brittle compound after laser welding, they cannot To meet the usage requirements, in addition to ultrasonic welding, copper and copper, aluminum and aluminum are generally laser welded. At the same time, because both copper and aluminum conduct heat very quickly and have very high laser reflectivity, and the thickness of the connecting piece is relatively large, a higher-power laser is required to achieve welding.

 

 

Characteristics of laser welding lithium batteries
From the manufacture of lithium battery cells to the assembly of battery packs, welding is a very important manufacturing process. The conductivity, strength, air tightness, metal fatigue and corrosion resistance of lithium batteries are typical battery welding quality evaluation standards. . The selection of welding methods and welding processes will directly affect the cost, quality, safety and consistency of the battery. Laser welding has become the preferred solution for many welding tasks due to its advantages such as safe and reliable welding, precision technology, and environmental protection.

 

Laser Welding Advantages
1.	Laser welding is an integrated manufacturing process that breaks raw materials such as positive and negative electrode materials, separators, and electrolytes into whole parts. All raw materials are welded into battery cells or PACK modules, which can be directly used in the automotive field.
2.	Ordinary battery raw materials account for an increasing proportion of the cost and are purchased in large quantities in tons. Laser welding equipment basically saves costs by purchasing raw materials in one go.
3.	Laser welding can greatly improve the safety, reliability and service life of automobile power batteries, with high welding quality and automation: Laser welding has high energy density, small welding deformation and small heat-affected zone, which can effectively improve the accuracy of parts. The welds are smooth, impurity-free, uniform and dense, and do not require additional grinding work. Laser welding can be precisely controlled, with a small focused light spot and high Accurate positioning, easy to realize automation with robotic arms, stable equipment performance and easy operation, improve welding efficiency, reduce working hours, and reduce costs. When laser welding thin plates or thin-diameter wires, it will not be as susceptible to meltback as arc welding.