Application of laser welding in power battery and super capacitor industry

In order to alleviate the increasingly serious energy crisis and atmospheric pollution problems, my country, like the developed countries such as the United States, Japan and Germany, is focusing on promoting the development of the new energy vehicle industry chain and making it a national strategic priority industry. The national “New Energy Vehicle Technology Development “Twelfth Five-Year” Special Plan” has made electric vehicles one of the main directions for the future development of China’s automobiles; China plans to have 1 million new energy vehicles in 2015, and a power battery production capacity of approximately 100 Billion watt-hours; by 2020, the annual sales of new energy vehicles will reach 2 million units.

The battery reliability, high cost, and lack of production capacity of new energy vehicles is a worldwide problem. The reliability and stability of existing battery technology is insufficient, and the cycle life of products is not long and other factors have long affected new energy vehicles. development of. In recent years, major automobile manufacturers have invested huge research and development expenses in new energy vehicles and have also made great progress. It is foreseeable that the next ten years will be a decade of explosive growth of new energy vehicles.

Shenzhen Lianying Laser Co., Ltd. has made great progress in cooperating closely with various battery manufacturers to jointly develop laser welding technology for automotive power batteries. So far, we have designed and manufactured fully automatic or semi-automatic laser welding production lines for hundreds of domestic power battery manufacturers, and have obtained very rich practical experience.

One, the main parts of power battery laser welding

Power battery cells can be divided into three types according to their appearance, namely square, cylindrical and soft-packed cells (see Figure 1). The shell materials are mainly aluminum and stainless steel, but aluminum is the main material, of which the 1000 series and 3000 series are more.

Figure 1 Common power battery shape

At present, these three types of batteries are used in domestically produced electric vehicles: For example, BYD E6 and K9 electric vehicles use square batteries; Hangzhou Wanxiang is a battery cell supplier and some electric vehicle manufacturers use its soft pack batteries. ; Certain electric vehicle models of SAIC Motor use round batteries made by the American company A123. The automated laser welding systems and processes of these three types of batteries are also different; on the whole, prismatic batteries are the majority.

There are four main laser welding parts for various batteries: the packaging of the shell, according to the position 口) welding, the welding of the battery’s tabs and the top cover. In addition, the welding of the super capacitor is mainly based on the welding of the connecting piece and the negative electrode seal. The welding positions of various power batteries and super capacitors are shown in Figure 2.

Figure 2 Laser welding of various batteries

2. Difficulties in welding process of power battery

Generally, the shell thickness is required to be 1.0 mm or less, and mainstream manufacturers currently have two main shell material thicknesses: 0.6mm and 0.8mm according to the battery capacity. Welding methods are mainly divided into side welding and top welding. The main advantage of side welding is that it has a small impact on the inside of the cell, and spatter will not easily enter the inside of the cover. Since the welding may cause bumps, which will have a slight impact on the subsequent process assembly, the side welding process has higher requirements on the stability of the laser, the cleanliness of the material, and the matching gap between the top cover and the shell. The top welding process can use a more efficient galvanometer scanning welding method because it is welded on one surface, but it has high requirements for the previous process to enter the shell and positioning, and has high requirements for equipment automation.

At present, aluminum shell batteries account for more than 90% of the entire power battery. The laser welding of aluminum is very difficult, and it will face the problem of surface protrusion of the weld mark, the problem of pores, the problem of fire, and the problem of internal air bubbles. Surface protrusions, pores, and internal bubbles are fatal injuries of laser welding. Many applications have to be stopped or avoided due to these reasons. Many battery manufacturers will be troubled by this in the early stage of research and development. The main reason is that the fiber core diameter is too small or the laser energy is set too high. There are also many factors that cause explosions (also known as Splash), such as the cleanliness of the material, the purity of the material itself, and the characteristics of the material itself. The decisive role is the stability of the laser. In power battery welding, the welding process technicians will select the appropriate laser and welding process parameters according to the customer’s battery material, shape, thickness, and tensile requirements, including welding speed, waveform, peak value, welding head inclination angle, etc. to set reasonable Welding process parameters to ensure that the final welding effect meets the requirements of power battery manufacturers.

Due to factors such as the matching accuracy of the incoming materials, the square battery is most likely to have problems at the corners during welding. It is necessary to continue to explore according to the actual situation and adjust the welding speed to solve these problems. The circular battery does not have this problem, but the subsequent integration into a battery module is more difficult.

3. Brief introduction of laser automatic welding system for power battery

Figure 3 is a square power battery automatic laser welding line, including two production lines with welding, leakage detection, short circuit detection and coding marking as the main functions. The production capacity is ≧16PPM, and the welding strength is above 6kgf/c㎡ without leakage.

This system can complete the laser welding, air tightness test, short circuit test, battery marking, automatic rejection of unqualified products and other related processes in sequence.

The laser welding part is composed of laser, laser welding head, XYZ three-axis motion control axis, rotating mechanism, battery fixture (compression and correction fixture), loading and unloading manipulator, etc. Its main function is to clamp the battery from the assembly line Go to the soldering workbench for soldering operations, and put it on the reflow line after soldering.

The air tightness and short circuit test part is composed of air tightness test components, short circuit test components, internal assembly line conveying system, inspection feeding manipulator, inspection and unloading manipulator, etc. Its main function is: the battery clamp after welding on the assembly line Hold it to the internal assembly line conveying system, and perform positioning, air tightness, and short-circuit related tests in sequence. After the test is completed, the good products are returned to the mainstream water line, and the defective products are captured in the waste box. The leak detection part adopts the tripartite test function of pole and cover plate.

The marking part is composed of a laser marking machine, a grasping and positioning mechanism, etc. Its main function is to mark the product after welding. Metal products (including aluminum) can be tested with positive pressure, short-circuit test has a 12-digit number plus letter code (three-digit letter code). , 9-digit digital code), plus 8*8 two-dimensional code.

The assembly line part is composed of the assembly line double-speed chain, fixture tray, positioning cylinder, blocking and distributing cylinder, etc. Its main function is to drive the battery to the corresponding position, which is convenient for welding and inspection, and has a certain storage function.

Figure 3 Fully automatic laser welding line for square power battery

Figure 4 is a semi-automatic production line for the top cover of a square battery. The welding workbench is controlled by industrial PLC. The welding battery range is H: 130-300mm, W: 110-250mm, T: 20-50mm, and the welding pattern trace is Flat rectangle, automatic welding process.

The system can be used with the circular conveyor line for automatic laser sealing welding of the battery top cover and the shell, where the top cover and the shell are made of stainless steel or aluminum alloy. Welding parameters can be set through the operation interface. After welding, ensure that there is no leakage in the weld. After welding, it meets the withstand voltage test requirements. It will not damage or damage the surrounding parts of the battery. It has both automatic and manual functions.

Figure 4 Automatic laser welding line for the top cover of the square power battery

Four, summary

High-efficiency and precise laser welding can greatly improve the safety, reliability and service life of automotive power batteries, which will surely bring revolutionary advancements in automotive power technology in the future. There are many laser welding parts for power batteries, and there are requirements for pressure resistance and leakage testing. Most of the materials are aluminum, so welding is difficult and requires higher welding technology. In the future, most manufacturers need fully automatic production lines, which will further increase the difficulty of integration of the welding system. High-quality power batteries require close collaboration between the manufacturer’s designers and laser welding technicians to optimize the design in terms of material, shape, thickness, process, and real-time inspection to achieve the desired welding effect.