Application of laser technology in lithium battery processing

Application of laser technology in lithium battery processing

1. Laser welding: high process barriers, new battery technologies such as large cylinders drive the welding volume up

Laser technology has the characteristics of high efficiency, precision, flexibility, reliability and stability, low welding material loss, high automation and safety. It is fully used in lithium battery cutting, cleaning, welding, coding and other processes. According to the official WeChat account of Laser Manufacturing.com, 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 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, and also directly determines the cruising range of the whole vehicle. The production and manufacture of lithium batteries are connected by one process, and the production process is mainly divided into three parts: pole piece manufacturing, cell manufacturing and battery assembly. The quality of lithium batteries directly determines the performance of new energy vehicles, so there are extremely high precision requirements for their manufacturing processes. As an advanced "light" manufacturing tool, laser technology is used in the 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 high degree of safety. in process.

2. Laser welding: high process barriers, new battery technologies such as large cylinders drive the welding volume up

2.1 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 greatly 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 welding environment, high power density, not affected by magnetic fields, not limited to conductive materials, It does not require vacuum working conditions and does not generate X-rays during the welding process. It is widely used in high-end precision manufacturing fields, especially in the new energy vehicle and power battery industries. There are many welding parts of power battery, which is difficult and requires 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 greatly improve the safety, reliability and consistency of batteries, reduce costs and prolong 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 main core elements that determine 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 completely different. In order 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 melting and affect the welding quality. The power is too high or fluctuates up and down. It will cause adverse effects such as splashes and blowholes. Therefore, the control of laser energy has become one of the most critical technologies in laser welding.

②Welding process technology: According to the prospectus of Lianying Laser, the interaction process between laser and material is relatively complex. The effect of laser welding is related to laser wavelength, power density, welding time, welding head angle, focal distance, and the absorption rate of laser light by welding parts. It is related to dozens of factors such as the degree of cleanliness, the thickness and thermal conductivity of the weldment, the type and flow of the shielding gas. Therefore, the laser welding process technology is also one of the key factors affecting the welding quality. It is necessary for the laser welding process technicians to continuously explore and summarize, and to accumulate a long time of experiments to obtain a good welding effect.

Welding can be divided into five types according to the working principle, and different welding methods are selected according to different application requirements to achieve the best effect. According to the prospectus of Lian Ying Laser, according to different working principles, it is suitable for different processing scenarios. Laser welding can be divided into five types: heat conduction welding, deep penetration welding, compound welding, laser brazing and laser conduction welding. According to different customers and different processing application scenarios, select the appropriate welding method to achieve the best welding effect.

2.2 Application status: The value of cell manufacturing and PACK welding is about 10-30 million/GWh

The use of laser welding in the production of power batteries is 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 use of laser welding mainly includes: (1) Middle process: welding of pole ears (including pre-welding), spot welding of pole strips, and pre-welding of battery cells into the shell , Shell top cover sealing welding, liquid injection port sealing welding, etc.; ② Post-process: including the connection piece welding when the battery pack module, and the explosion-proof valve welding on the cover plate after the module, etc.

The value of the former laser welding is about 10-30 million yuan/GWh. According to the prospectus of Lianying Laser, laser welding equipment accounts for about 5-15% of the investment of power battery manufacturers. According to the information on the official website of Gaogong Lithium Battery, according to the calculation of the investment amount of power battery single GWh equipment is about 200 million yuan, the current power battery laser The single GWh investment in welding equipment ranges from RMB 10 million to RMB 30 million.

2.3 Demand: Semiconductor factories expand capital expenditure under the global "core shortage", and equipment prosperity continues to rise

The 4680 large cylinder has higher requirements on the laser process, and the welding volume is expected to increase compared with the square battery and the small cylindrical battery. 1) The 4680 battery has higher requirements for the laser process, and the uncontrolled shape of the tab is a process difficulty. According to the official website of the Huajing Industry Research Institute, the 4680 battery adopts the all-pole process, which breaks the traditional battery model of one positive and one negative two poles. The segment is closed, the electrolyte infiltration is hindered, and the multi-pole tabs are difficult to fold neatly, which requires higher laser technology. 2) Compared with the square battery and the small cylindrical battery, the laser welding of the 4680 large cylindrical battery has an increase in the welding process and the required welding equipment. According to the official website of Huajing Industrial Research Institute, 1) Compared with the square battery, the laser welding process required for the large cylindrical lug is increased from 5 to 7; 2) From the perspective of the small cylindrical battery, the single GWh phase Compared with the 18650 and 21700 battery production lines, 5 welding equipments are added. Combined with the above situation, we believe that the laser welding demand for 4680 large cylinders is expected to increase compared to square batteries and small cylindrical batteries.

Other welding technologies: Solve the problem of dissimilar metal welding. For example, the busbar welding in the battery pack is expected to be replaced by laser welding. We judge that with the continuous improvement of the laser welding process, the penetration rate of laser welding is expected to increase. Take the Al/Cu dissimilar metal welding in the back-end module/PACK of the prismatic battery as an example: ①Al and Cu have low light absorption rates and are prone to produce highly brittle metal compounds. New Advances in Laser Welding Technology of Al/Cu Dissimilar Metals for Battery Module Assemblies, Al/Cu dissimilar metal laser welding has several challenging limitations due to the very different physical properties of Al and Cu materials. One is mainly due to the low absorptivity of Al and lower absorption of Cu at the laser wavelength of 1um; another challenge comes from the metallurgical properties of Al-Cu alloys, that is, highly brittle metal compounds may lead to crack formation. An intermetallic phase with a Cu content of 50%-80% may be formed.

Busbar welding At present, laser welding cannot solve the problem of brittle compounds, but laser welding is a high probability direction. According to the company's official website, laser welding is generally used for copper and copper, and aluminum and aluminum, since brittle compounds are easily formed after laser welding between copper and aluminum, which cannot meet the requirements for use. At the same time, due to the fast heat transfer of copper and aluminum, high reflectivity to the laser, and relatively large thickness of the connecting piece, it is necessary to use a higher power laser to achieve welding. Through adjustment experiments of nine different parameters and methods, seven of which have different gains, we believe that with the continuous progress of laser technology in the future, the problems of Al/Cu laser welding of busbars are expected to be solved, and laser welding is a high probability direction.

3. Laser cutting: The pole piece laser cutting replaces the acceleration, and the high-rate battery promotes the cutting volume of the pole lug/pole piece

3.1 Advantages: Compared with die cutting tools, it has the advantages of higher accuracy and lower operating costs, which helps battery production to improve efficiency and reduce costs

Laser cutting technology can be used in the process of tab cutting and forming, pole piece cutting and diaphragm cutting in the lithium battery manufacturing process. Compared with die cutting, laser cutting has the advantages of higher accuracy and lower operating costs, which helps Improve efficiency and reduce costs in battery production. According to the official WeChat account of Veken Lithium Battery, traditional die-cutting will inevitably wear out, dust will fall and burrs will be generated, which will lead to various dangerous problems such as battery overheating, short circuit, and even explosion. In order to avoid the danger caused by the poor processing quality of lithium batteries, it is more suitable to use laser cutting. 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 is conducive to reducing manufacturing costs, improving production efficiency, and greatly shortening new product molds. cut cycle.

3.2 Tab cutting: laser cutting is the mainstream technology, and unwinding speed and tension control are the main points of competition

Laser tab forming is the current mainstream technology. Process parameters, control system, and cutting station design determine the cutting speed and quality. According to Lyric Robot's official website, traditionally, the tab forming process mainly uses a mechanical die-cutting process. The mechanical die-cutting process has limitations such as rapid die loss, long die change time, poor flexibility and low production efficiency, and has been increasingly unable to meet the development requirements of lithium battery manufacturing. Due to the many advantages of laser cutting technology, with the maturity of high-power, high-beam quality nanosecond lasers and single-mode continuous fiber technology, laser tab cutting has gradually become the mainstream of tab forming technology. Stable unwinding speed, tension and pole piece width direction position control, precise and stable unwinding speed, tension and rectification control are the basis for realizing high-quality and high-speed pole lug forming. Taking Hymustar as an example, according to the speech content of Miao Jianye, a software expert of Haimuxing in the 2nd International Exchange Conference on New Energy Vehicles and Power Batteries quoted on the official website of Veken, Hymuxing has an exclusive integrated tension technology, which is driven by It is composed of a feedback system, the entire feedback system combines the overall trend into real-time, adopts the development concept of combining theoretical algorithms and practical feedback closed-loop, integrates the driving performance and the adjustment performance, and the tension fluctuation can be controlled within 2%, and Various cutting compatible technologies can realize one-key line feed for on-the-fly cutting, which meets the customized needs of customers.

3.3 Pole piece cutting: traditional die cutting efficiency has become the bottleneck of production line efficiency improvement, MOPA technology has both cost and performance advantages

The quality of disc slitting and die-cutting products is unstable; laser energy and cutting movement speed are the two main process parameters. According to the information of the power battery network, there are three methods of pole piece cutting: disc cutting, die cutting, and laser cutting. Both disc cutting and die cutting have the problem of tool wear, which is easy to cause process instability and lead to the quality of pole piece cutting. poor, causing the battery performance to decline; laser energy and cutting speed are the two main process parameters, which have a huge impact on the cutting quality. When the laser power is too low or the moving speed is too fast, the pole piece cannot be completely cut, and when the power is too high or the moving speed is too low, the laser action area on the material becomes larger and the slit size is larger.

MOPA is a laser modulation technology that combines high peak power and high beam quality. According to the official website of Gaogong Lithium Battery, JPT’s special customized pole piece cutting pulse fiber laser has a production line cutting efficiency of up to 120m/min, cutting burr less than 7μm, and heat affected zone less than 50μm. For lasers with no burr and no thermal influence, the response time of frequency conversion and power conversion is less than 10μs, which can effectively reduce the quality problems caused by parameter changes at the corner joints. According to JPT's "Announcement on Receiving Designated Notice from Suppliers", on March 22, 2022, JPT announced that it received a designated notice from CATL to provide MOPA pulsed fiber lasers for use in pole pieces for the manufacture of power battery cells cutting process. According to the prospectus of Inno Laser, the MOPA technology is to couple the seed signal light and pump light with high beam quality into the double-clad fiber for amplification in a certain way, so as to achieve high-power amplification of the seed light source; MOPA of the laser The structure is the optimal way to solve the combination of high peak power and high beam quality of ultrafast lasers.

Picosecond is the best long-term choice, and MOPA is currently the most cost-effective choice. According to "Analysis of Laser Cutting of Lithium-ion Power Battery Pole Pieces", in addition to pulse width, repetition frequency, beam mode, and laser wavelength also affect the cutting quality. Therefore, picosecond lasers with narrow pulse width and high repetition rate are the most ideal lasers for cutting aluminum and copper foils. However, because the picosecond technology is not fully mature and the price is still high, it is difficult to promote industrially. The MOPA laser with a relatively "narrow" pulse width is inexpensive, and the cut positive plates also fully meet the industrial requirements. It is the most cost-effective laser for cutting positive plates. With the reduction of its pulse width and the increase of its frequency, its application prospects will become more and more. the better.

3.4 Diaphragm cutting: Diaphragm laser cutting is still in the layout stage, and heat impact control is difficult

Diaphragm cutting is currently dominated by knife cutting, and there are currently two laser cutting technology patents. According to the patent star retrieval system information: ①Patent 1: According to the patent content of "A Diaphragm Laser Cutting Machine", the cutting of the diaphragm is usually carried out with a steel diaphragm cutter. The diaphragm cutter is used for cutting, which has poor structural stability. The cutter needs to be replaced regularly. The effect of the diaphragm incision is not good, and it is easy to burr or curl. The above problems can be solved by laser cutting; ②Patent 2: According to the patent content of "Laser Cutting Equipment for the Production of Lithium Battery Diaphragm", the laser cutting component cuts the diaphragm wound by the turning roller alternately switching the two diaphragm curling components, which realizes automatic uniformity The function of cutting diaphragm avoids the phenomenon of powder removal, wire picking, film breaking and continuous cutting during the cutting process, which is convenient for practical use in mass production lines.

Heat impact control is still difficult, and UV lasers may replace traditional die cutting. According to the information on the official website of Suneng Electric, the melting point of the PP film and the PE film of the lithium-ion battery separator is different, the PE separator is about 130°C, and the PP separator is about 160°C. According to the prospectus of Inno Laser, in the fields of thin-film non-metallic material processing, high-energy ultraviolet photons directly destroy the molecular bonds on the surface of non-metallic materials, so that the molecules are separated from the object. This method does not produce high-heat reaction, so it is usually called For "cold processing", UV laser machines have irreplaceable advantages in the field of micro-processing. We judge that, in the current segment of diaphragm cutting, which is still mainly die-cutting, it is still difficult to control the thermal impact of laser cutting due to the lower melting point of the diaphragm. Ultraviolet laser may replace traditional die-cutting with the advantage of "cold processing".

3.5 Lamination process technology: expected to increase the demand for laser cutting

The demand for laser tab and pole piece cutting in the square lamination process is expected to increase. According to the information on the official website of Gepuri battery, the square lamination method is because the positive and negative plates are isolated from each other, so each pole piece must be installed with a tab, and then welded together to form the final positive and negative electrodes, but the roll In order to reduce the process of winding method, only one tab is installed in several layers, and the total number is usually only half of the former. Based on the above situation, we judge that the number of tabs in the lamination process is doubled compared with the winding process, and the demand for tab cutting under the lamination process is expected to increase. Composite technology process), the demand for pole piece cutting will also increase.

4. Other applications: laser cleaning, laser marking

4.1 Laser cleaning: avoid cleaning damage and other problems, and improve the level of battery manufacturing technology

Laser cleaning before electrode coating can effectively avoid the damage caused by the original wet ethanol cleaning; laser cleaning before battery welding uses pulsed laser to make the substrate heat and vibrate to expand, so that the pollutants can overcome the surface adsorption force and separate from the substrate to achieve decontamination; during the battery assembly process Laser cleaning can perform laser cleaning on insulating plates and end plates, clean the surface of the cell, roughen the surface of the cell, and improve the adhesion of glue or glue. According to the official website information of C114 communication website: Before electrode coating: The positive and negative plates of lithium batteries are made by coating the positive and negative electrodes of lithium batteries on metal strips. When the metal strips are coated with electrode materials, it is necessary to The thin strip is cleaned. The metal thin strip is generally thin aluminum or copper. The original wet ethanol cleaning is easy to cause damage to other parts of the lithium battery. Laser dry cleaning machine can effectively solve the above problems.

Before battery welding: According to the information on the official website of C114 communication website, use pulsed laser to directly radiate decontamination, so that the surface temperature rises and thermal expansion occurs. The purpose of removing stains on the surface of objects. This method can effectively remove the dirt, dust, etc. on the end face of the cell pole, prepare for the battery welding in advance, and reduce the defective products of welding. During battery assembly: According to the information on the official website of C114 communication website, in order to prevent safety accidents of lithium batteries, it is generally necessary to apply glue to the lithium battery cells to play an insulating role, prevent short circuits, and protect circuits and prevent scratches. hurt. Laser cleaning the insulating plate and end plate, cleaning the surface of the cell, roughening the surface of the cell, and improving the adhesion of the glue or glue, and no harmful pollutants will be generated after cleaning. It is an environmentally friendly green cleaning method. This has become more and more important in a situation where the world is highly concerned about environmental protection.

4.2 Laser marking: providing more efficient and safe information tracking possibilities for power batteries

The shortcomings of traditional marking technology are obvious. According to the official website of Qiming Laser Technology, there are several traditional marking technologies, namely inkjet marking, steel needle engraving marking, sticker marking, etc., but these methods have corresponding process defects. For example, inkjet marking requires Consumables, other processes may fade if the ink is not dry after spraying, etc.; the steel needle engraving speed is slow and the processing efficiency is low. The new technology that emerged from this is the laser marking technology.

Security has been improved to varying degrees. According to the information on the official website of Chutian Zhonggu Lianchuang, in order to better control product quality and trace the entire production information of lithium batteries, including raw material information, production process and process, product batch, manufacturer and date, etc., it is necessary to store key information. Inside the QR code and marked on the battery. The traditional ink jet coding technology has problems such as easy friction and easy loss of information for a long time, while laser marking has the characteristics of strong permanence, high anti-counterfeiting, high precision, strong wear resistance, safety and reliability, and can track product quality. Provide the best solution.