Laser technology has the characteristics of high efficiency, precision, flexibility, reliability, and stability, low welding material loss, and high automation and safety. It is thoroughly used in lithium battery cutting, cleaning, welding, coding, and other processes. According to the information on the official WeChat account of Laser Manufacturing Network, driven by the strong support of national policies and the acceleration of the promotion and application of new energy vehicles, the demand for automotive power batteries in China has grown significantly. Among the three core components of a new energy vehicle battery, motor, and electronic control, the core component power lithium battery accounts for a high proportion of the cost of the whole vehicle. It also directly determines the cruising range of the whole vehicle.
A series of processes connect the production and manufacture of lithium batteries. The process comprises pole-piece manufacturing, cell production, and battery assembly. The quality of lithium batteries directly determines the performance of new energy vehicles, so its manufacturing process has extremely high precision requirements.
As an advanced “light” manufacturing tool, laser technology is used for cutting, cleaning, welding, and coding of power lithium battery parts due to its high efficiency, precision, flexibility, reliability and stability, low welding material loss, high automation, and a high degree of safety. in process.
1. Laser welding: High process barriers and new battery technologies, such as large cylinders, drive welding volume up.
1.1 Principle:
Ensure battery safety; welding quality depends on laser energy control and process parameters.
Laser welding has many advantages, such as deep penetration, fast speed, and small deformation, which can significantly improve the safety of power batteries. According to the prospectus of Lian Ying Laser, laser welding, as a modern welding technology, has the advantages of deep penetration, fast speed, small deformation, low requirements for the welding environment, high power density, not being affected by magnetic fields, not limited to conductive materials, It does not require vacuum working conditions. It does not generate X-rays during the welding process. It is widely used in high-end precision manufacturing, especially in the new energy vehicle and power battery industries. Many welding parts of a power battery are complex and require high precision. Power battery manufacturers also have high requirements for battery production equipment’s automation, safety, precision, and processing efficiency. 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 best choice for power battery manufacturers. It has become the best choice for power battery manufacturers because of its stability, reliability, consistency, cost reduction, and long service life.
The central core elements determining the quality of laser welding are laser energy control and welding technology. ① Laser energy control: According to the prospectus of Lian Ying Laser, due to the different absorption rates of the materials to be welded to different wavelengths of laser light (which can vary from 5% to 50%), the laser selection is different, and the welding effect is entirely different. To output a uniform and stable welding laser beam to the weldment, the laser output power needs to have good consistency or be able to precisely control the laser output power. If the power is too low, it will lead to insufficient welding fusion and affect the welding quality. On the other hand, the power is too high or fluctuates up and down. It will cause adverse effects such as splashes and blowholes. Therefore, controlling laser energy has become one of the most critical technologies in laser welding.
Welding process technology: According to the laser prospectus, the process of laser and material action is complex; the laser welding effect with the laser wavelength, power density, welding time, welding head angle, focal distance, the weld on the laser absorption rate and cleanliness, the thickness of the weld and thermal conductivity, the type and flow of shielding gas and dozens of factors. Therefore, the laser welding process technology is also one of the key factors affecting the quality of welding, requiring laser welding process technicians to constantly explore the summary and a long period of experimental accumulation to obtain good welding results.
According to the working principle, welding can be divided into five types, according to the different application requirements, to choose different welding methods to achieve the best results. According to the laser prospectus, laser welding can be divided into five types: heat conduction welding, deep fusion welding, composite welding, laser brazing and laser conduction welding, according to the different working principles and different processing scenarios. According to the prospectus, there are five types of laser welding: heat conduction welding, deep fusion welding, composite welding, laser brazing, and laser conduction welding.
1.2 Application status:
The value of cell manufacturing and PACK welding is about 10-30 million/GWh
In the production of power batteries, laser welding is used in the cell manufacturing process and the battery PACK process. According to the information on the official website of Lianwin Laser, in the production of power batteries, the laser welding process mainly includes: (1) the middle process: welding of the lug (including pre-welding), spot welding of the pole belt, pre-welding of the cell into the shell, sealing welding of the top cover of the outer shell, sealing welding of the liquid injection port, etc.; (2) the back process: including the welding of the connection piece in the PACK module and the welding of the explosion-proof valve on the cover after the module.
According to the laser prospectus, laser welding equipment accounts for about 5-15% of the investment in power battery manufacturers; according to the information on the official website of Gaogong Lithium, the power battery single GWh equipment investment of about 30 million USD, the current power battery laser welding equipment single GWh investment in the range of 15 million USD to 45 million USD.
1.3 Demand:
Global “lack of chip” under the semiconductor factory to expand capital expenditure, equipment boom continued to rise.
The 4680 large cylinder has higher requirements for the laser process, and the welding volume is expected to rise compared to the square battery and small cylinder battery. 1) The 4680 battery has higher requirements for the laser process, and the uncontrolled shape of the pole lug is a process difficulty. According to the official website of the China Institute of Industrial Research, the 4680 battery adopts a complete lug process, breaking the traditional battery model of one positive and one negative lug; the process difficult is that the lug form is not controlled, prone to short circuit, the manufacturing of two closed sections, electrolyte infiltration obstruction, and multiple lugs is difficult to fold neatly, requiring higher requirements for laser technology. Cylindrical batteries are increased in the welding process, the required welding equipment. According to the information from the website of Huajing Industry Research Institute, 1) compared with square batteries, the laser welding process for the full lug of large cylindrical batteries has increased from 5 to 7 steps; 2) compared with 18650 and 21700 batteries, the single GWh production line has five additional welding equipment. Combined with the above, we believe that the demand for laser welding of 4680 large cylinders is expected to grow compared to square cells and small cylinders.
Another welding link technology: to solve the problem of heterogeneous metal welding, such as battery PACK in the busbar welding is expected to replace laser welding; we judge that with the laser welding process continuing to move up, laser welding penetration is expected to move up. The Al/Cu heterogeneous metal welding in the rear channel of the square battery module/PACK in the busbar welding as an example: ① Al, Cu low absorption rate of light, and easy to produce highly brittle metal compounds are Al/Cu difficulties: According to “New Advances in Al/Cu Heterogeneous Metal Laser Welding Technology for Automotive Battery Modules,” due to the very different material physical properties of Al and Cu, Al/Cu heterogeneous metal laser welding has several challenging limitations. The laser welding of Al/Cu dissimilar metals has several challenging limitations due to the very different material physical properties of Al and Cu. One is primarily the low absorption of Al at the laser wavelength of 1um and even lower absorption of Cu; another challenge comes from the metallurgical properties of the Al-Cu alloy, where the highly brittle metal compound can lead to crack formation. As a result, intermetallic phases with a Cu content of 50%-80% may be formed.
Busbar welding is stican still not the problem of brittle compounds, but laser welding is in the probable direction. According to the United Win Laser’s official website, the use of laser welding between copper and aluminum easy to form brittle compounds can not meet the requirements of use, usually using ultrasonic welding; copper and copper, aluminum, and aluminum are generally used in laser welding. At the same time, due to the rapid heat transfer between copper and aluminum and the high reflectivity of the laser, the thickness of the connection piece is relatively large, so it is necessary to use a higher-power laser to achieve welding. Through nine different parameters and methods of adjustment experiments, of which seven have different gains, we believe that, with the continuous progress of future laser technology, the convergence Al/Cu laser welding problems are expected to be solved, laser welding for the probable direction.
2. Laser cutting: Pole laser cutting replacement accelerates as high-rate cells drive lug/sheet cutting volume.
2.1 Advantages:
Higher accuracy and lower operating costs than die-cutting tools, helping to improve efficiency and reduce costs in battery production.
Laser cutting technology can be applied to the processes of lug cutting, slitting, and diaphragm slitting in the manufacturing process of lithium batteries. Compared with die-cutting, laser cutting has the advantages of higher accuracy and lower operating costs, which helps to improve efficiency and reduce costs in battery production. However, according to the official WeChat information on lithium batteries, traditional die-cutting will inevitably lead to wear, dust fall, and burr, which will cause various dangerous problems such as battery overheating, short circuits, and even explosions. Laser cutting is more suitable to avoid the dangers caused by the poor processing quality of lithium batteries. Compared with traditional mechanical cutting, laser cutting has the advantages of no physical wear, flexible cutting shape, edge quality control, higher accuracy, and lower operating costs, which help reduce manufacturing costs, increase productivity and significantly reduce the cycle time of new product die-cutting.
2.2 Polar ear cutting:
Laser cutting is the mainstream technology; unwinding speed and tension control are the main points of the competition.
Laser lug forming is the mainstream technology nowadays, and the process parameters, control system, and cutting station design determine the speed and quality of cutting. According to Liyuanheng’s official website, automatic die-cutting is traditionally used for lug forming. However, the mechanical die-cutting process has limitations such as fast die loss, long die change time, poor flexibility, and low production efficiency, which can no longer meet the development requirements of lithium battery manufacturing. Due to the advantages of laser cutting technology, with the maturity of high power, high beam quality nanosecond lasers, and single-mode continuous fiber technology, laser lug cutting is now becoming the mainstream lug forming technology. Stable unwinding speed, tension, and position control in the width direction of the pole piece, precise and stable unwinding speed, tension, and deflection control are the basis for high quality and high-speed pole lug forming. According to the speech by Miao Jianye, a software expert of HMS, at the 2nd International Conference on New Energy Vehicles and Power Batteries, as quoted on the official website of WK, HMS has an exclusive integrated tension technology, which is composed of drive and feedback system. The whole feedback system combines the overall trend of bringing it into real-time. The whole feedback system combines the overall belt into the real-time trend, using theoretical algorithms and actual feedback closed-loop development concept, the drive performance and mediation performance into one, tension fluctuations can be controlled within 2%, as well as a variety of cutting compatible technology, can realize the flight cutting one key to change row, to meet the customization of customer needs.
2.3 Pole chip cutting:
The quality of disc slitting and die-cutting products are unstable; laser energy and cutting movement speed are the two main process parameters. According to the information on the power battery network, there are three ways of cutting pole pieces: disc slitting, die cutting, and laser cutting. Both disc slitting and die cutting have the problem of tool wear, which will cause an unstable process and lead to poor cutting quality of pole pieces and degradation of battery performance. When the laser power is too low, or the moving speed is too fast, the poles cannot be cut completely, while when the power is too high, or the moving speed is too low, the laser area on the material becomes more extensive, and the cut size is bigger.
MOPA is a laser modulation technology that combines high peak power and high beam quality optimally, and Jeppe has been selected by Ningde Times. According to the official website of Gaogong Lithium, the current special customized pulsed fiber laser of Jepte can reach 120m/min, with a cutting burr of less than 7μm and a heat-affected zone less than 50μm, which is the only laser in the market with no burr and no heat impact. Quality problems. According to the “Announcement on Receipt of Supplier Notification” of JPT, on March 22, 2022, JPT announced that it had received a notification from Ningde Times for the supply of MOPA pulsed fiber laser for the electrode cutting process of power battery cell manufacturing. According to the prospectus of Innolux Laser, MOPA technology is to amplify the seed signal light and pump light with high beam quality by coupling them into the double-clad fiber in a certain way to achieve high power amplification of the seed light source; the MOPA structure of the laser is the optimal solution for ultrafast laser with both high peak power and high beam quality.
Picosecond is the best long-term choice, and MOPA is the most cost-effective choice. According to the “Analysis of Laser Cutting of Lithium-ion Power Battery Poles,” pulse width, repetition frequency, beam pattern, and laser wavelength also impact the cutting quality. Therefore, a picosecond laser with narrow pulse width and high repetition frequency is ideal for cutting aluminum and copper foil. However, because the picosecond technology is not fully mature, the price is still very high, and it isn’t easy to promote industrial use. The MOPA laser with a relatively “narrow” pulse width is the most cost-effective laser for cutting positive electrodes. Its application prospects will become more and more promising as its pulse width decreases and its frequency increases.
2.4 Diaphragm cutting:
Diaphragm laser cutting is still in the layout stage, and thermal impact control is the hard part.
Diaphragm cutting is currently dominated by knife cutting, and there are currently two patents for laser cutting technology. According to the Patent Star search system: ① Patent 1: According to the patent content of “a diaphragm laser cutting machine,” diaphragm cutting is usually done with steel diaphragm cutters. Using diaphragm cutter cutting, structural stability is poor; the cutter needs to be replaced regularly, the diaphragm cut at the effect is not suitable, easy to burr or curl, complex structure, inconvenient debugging, and maintenance. The above problems can be solved by laser cutting.
Thermal impact control is still a difficult point, and UV laser may replace traditional die-cutting. According to the official website of Cunningham Electric, the melting point of PP film and PE film for lithium-ion battery separators is different, with PE film at around 130°C and PP film at around 160°C. According to the prospectus of Innolux Laser, in the field of thin film processing of non-metallic materials, high-energy UV photons directly break the molecular bonds on the surface of non-metallic materials to make the molecules detach from the object, and this method does not produce high heat reaction, so it is usually called “cold processing.” We judge that in the diaphragm cutting process, which is still dominated by die-cutting, it is still difficult to control the thermal impact of laser cutting due to the low melting point of the diaphragm, and the UV laser has the advantage of “cold processing” to replace traditional die-cutting.
2.5 Stacking process technology:
Promising to bring increased demand for laser cutting
The demand for laser lug and pole cutting in the square stacking process is expected to increase. According to the official website of the Gopri battery, the square stacking method requires each pole lug to be installed and then welded together to form the final positive and negative poles because the positive and negative poles are isolated from each other. Still, the winding method only installs a pole lug every few layers to reduce the process, and the total number is usually only half of the former. Based on the above, we judge that the number of lugs is doubled in the stacking process compared to the winding process, and the demand for lug cutting is expected to increase in the stacking process.
3. Other applications: laser cleaning & laser marking
3.1 Laser Cleaning:
Avoid cleaning damage and other problems and improve battery manufacturing processes.
Laser cleaning before the coating of the electrode can effectively avoid the damage caused by the original wet ethanol cleaning; laser cleaning before the welding of the battery uses a pulse laser to make the substrate expand by heat vibration so that the pollutants overcome the surface adsorption force from the substrate to achieve the effect of decontamination; laser cleaning during the assembly of the battery can be laser cleaning of the insulation plate and end plate to clean the surface of the cell dirt, roughen the surface of the cell and improve the adhesion of the adhesive or coating. According to the information on the C114 communication network website: before the electrode coating: the positive and negative electrode of the lithium battery is coated with lithium battery positive and negative materials on a thin metal strip; the metal strip needs to be cleaned when coating the electrode materials, the thin metal strip is generally thin aluminum or copper thin, the original wet ethanol cleaning, easy to cause damage to other parts of the lithium battery. A laser dry cleaning machine can effectively solve the above problems.
Before battery welding: According to the official website of C114 Communication Network, the pulsed laser direct radiation decontamination is used to make the surface temperature rise and thermal expansion occurs. This method can effectively remove the dirt and dust from the end surface of the electrode column and prepare the battery for welding in advance to reduce defective welding products. In the process of battery assembly: According to the information on the website of C114 Communication Network, to prevent safety incidents of lithium batteries, it is generally necessary to apply adhesive treatment to the lithium battery cells to play the role of insulation, prevent short circuit and protect the lines from scratch. Laser cleaning of the insulation board and end plate can clean the core’s surface, roughen the core’s surface and improve the adhesion of the adhesive or glue coating. No harmful pollutants will be produced after cleaning.
3.2 Laser marking:
A more efficient and secure information tracking possibility for power batteries
The shortcomings of traditional marking technology are apparent. According to the official website of Bravo Laser Technology, there are several kinds of traditional marking technology, namely inkjet marking, steel needle engraving marking, sticker marking, etc. Still, these methods have corresponding process shortcomings, such as inkjet marking requires consumables after the ink is not dry for other processes will have the possibility of color loss, etc.; steel needle engraving speed is slow, processing efficiency is low, etc., so the new technology that has emerged is laser marking technology.
Safety has been improved to different degrees. For example, according to the information on the official website of Chutian Zhonggu Lianchu, to better control the quality of products, trace the complete production information of lithium batteries, including raw material information, production process, technology, product batches, manufacturers, and dates, etc., the critical information needs to be stored in the two-dimensional code and marked on the battery. However, traditional inkjet coding technology has problems such as easy friction and long-time missing information. In contrast, laser marking has the characteristics of solid permanence, high anti-counterfeiting, high precision, wear resistance, safety, reliability, etc., which can provide the best solution for product quality tracking.
