Laser welding: high process barriers, new battery technologies such as large cylinders pulling welding volumes to the upside
Laser technology is used in the cutting, cleaning, welding and coding of lithium batteries because of its high efficiency, flexibility, reliability and stability, low loss of welding material, high automation and safety. Driven by the strong support of national policies and the accelerated promotion and application of new energy vehicles, the demand for automotive power batteries in China has grown significantly. In the three core components of new energy vehicles battery, motor, electric control, the core component power lithium battery in the cost of the vehicle accounted for a high proportion, but also directly determine the range of the vehicle. The production of lithium batteries is made up of a series of processes, which are divided into three main parts: the manufacture of electrodes, the production of cells and the assembly of batteries. The quality of the lithium battery directly determines the performance of the new energy vehicle and therefore requires the highest precision in its manufacturing process. Laser technology, as an advanced "light" manufacturing tool, is used in the cutting, cleaning, welding and coding processes of lithium battery components, due to its high efficiency and precision, flexibility, reliability and stability, low loss of welding material, automation and safety.
2. Laser welding: high process barriers, new battery technologies such as large cylinders pulling welding volumes to the upside
2.1 Principle: To guarantee the safety of the battery, the welding quality depends on the laser energy control and the process parameters.
Laser welding has many advantages such as deep melting, high speed and low distortion, which can significantly improve the safety of power batteries. As a modern welding technology, laser welding has the advantages of deep melting, high speed, low deformation, low requirements for the welding environment, high power density, not affected by magnetic fields, not limited to conductive materials, does not require vacuum working conditions and does not produce X-rays during the welding process, etc. It is widely used in the field of high-end precision manufacturing, especially in the new energy vehicle and power battery industries. Power battery welding parts are numerous, difficult and require high precision. Power battery manufacturers also have high requirements for the automation, safety, precision and processing efficiency of battery production equipment. The unique advantages of laser welding technology can significantly improve the safety, reliability and consistency of batteries, reduce costs and extend service life, making it the optimal choice for power battery manufacturers.
The main core elements that determine the quality of laser welding are the laser energy control and the welding process technology. Laser energy control: ①As the material to be welded has different absorption rates for different wavelengths of laser light (which can vary from 5% to 50%), the choice of laser source can make all the difference. In order to deliver a uniform and stable welding laser beam to the welded part, the laser output power needs to be consistent or precisely controlled. Too low power will lead to insufficient welding melt and affect welding quality, too high power or up and down fluctuations will lead to spatter, porosity and other undesirable effects. Therefore, the control of the laser source becomes one of the most critical technologies for laser welding.
②The laser welding effect is complex, related to dozens of factors such as laser wavelength, power density, welding time, welding head angle, focal distance, laser absorption rate and cleanliness of the weld, thickness and thermal conductivity of the weld, type and flow of shielding gas. Therefore, laser welding technology is also one of the key factors affecting the quality of welding, requiring laser welding process technicians to continuously explore the summary, only a long period of experimental accumulation can obtain good welding results.
According to the working principle welding can be divided into five types, depending on the requirements of the application different welding methods are selected to achieve the best results. Depending on the principle of operation, laser welding can be divided into five categories: heat conduction welding, deep fusion welding, composite welding, laser brazing and laser conduction welding. Depending on the customer and the processing application, the appropriate welding method is selected to achieve the best possible welding results.
2.2 Application status: core manufacturing, PACK welding worth about 10-30 million/GWh
Laser welding is used in the production of power cells in the cell manufacturing process and in the battery PACK process. In the production of power cells, the main segments that use laser welding include: ①Mid-process: welding of lugs (including pre-welding), spot welding of pole strips, pre-welding of cores into the shell, sealing welding of the top cover of the outer shell, sealing welding of the liquid injection port, etc. ②Post-process: including the welding of the connection piece in the battery PACK module and the welding of the explosion-proof valve on the cover behind the module, etc. The pre-welding value volume is about 10-30 million Yuan/GWh. Laser welding equipment in the power battery manufacturers to invest in about 5-15%, according to the power battery single GWh equipment investment of about 200 million yuan, the current power battery laser welding equipment single GWh investment in 10 million yuan to 30 million yuan.
2.3 Demand: Semiconductor factories expand capital expenditure amid global "core shortage", equipment boom continues upward
4680 Large cylinders have higher requirements for laser processes, and welding volumes are expected to rise compared to square cells and small cylinders. The 4680 cell requires a more demanding laser process and the uncontrolled shape of the lugs is a difficult process. The 4680 battery uses a full lug process, breaking the mould of the traditional battery with one positive and one negative lug, which is prone to short circuits, and is manufactured with two closed sections, which is a major obstacle to electrolyte penetration, and the multiple lugs are difficult to fold neatly and require a higher laser process. 4680 Laser welding of large cylindrical cells has increased in terms of welding process and required welding equipment compared to square cells and small cylindrical cells respectively. Compared to square cells, the laser welding process for the full lug of a large cylinder is increased from 5 to 7 passes. In terms of small cylindrical cells, the single GWh line has 5 additional welding machines compared to the 18650 and 21700 cell lines. Combined with the above, we believe that demand for laser welding of 4680 large cylinders is expected to grow compared to square cells and small cylinders.
Other welding link technology: to solve the problem of dissimilar metal welding, such as battery PACK in the busbar welding is expected to be replaced by laser welding, we judge that, as the laser welding process continues to move up, laser welding penetration is expected to move up. An example is the Al/Cu heterogeneous metal soldering of busbars in square cell back-end modules/PACKs. ①The low light absorption of Al and Cu and the tendency to produce highly brittle metal compounds are Al/Cu difficulties: laser welding of Al/Cu dissimilar metals has several challenging limitations due to the very different material physical properties of Al and Cu. One of the main challenges is the low absorption of Al at the laser wavelength of 1um and even lower absorption of Cu; another is the metallurgical properties of the Al-Cu alloy, i.e. the highly brittle metal compound may lead to crack formation. Intermetallic phases with a Cu content of 50-80% may be formed.
Busbar welding is still not a solution to the problem of brittle compounds, but laser welding is the probable direction. Due to the easy formation of brittle compounds between copper and aluminium after laser welding, which can not meet the requirements of use, usually using ultrasonic welding outside, copper and copper, aluminium and aluminium are generally used to laser welding. At the same time, the high heat transfer rate of both copper and aluminium, the high reflectivity of the laser and the relatively large thickness of the joining piece require a high power laser to achieve the weld. Through nine different parameters and methods of adjustment experiments, of which seven have different gains, we believe that, with the continuous progress of the laser process in the future, the problems of Al/Cu laser welding of busbars are expected to be solved, and laser welding is the most probable direction.
