The development direction of lithium battery laser welding machine
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Based on the above trends. Lithium battery laser welding machines will develop in the direction of intelligence and efficiency, as well as precision and versatility. In terms of intelligence, the equipment will gradually realize intelligent control. Realize the whole production data monitoring and information management. In terms of efficiency: through robotic production and process innovation. The device will achieve high efficiency and low cost. In terms of precision, the equipment will continuously improve welding quality and precision. In terms of versatility, more functional modules will be added to the device. Realize multi-process integration.
Next, let's talk about the laser welding process of the power battery.
The explosive development of new energy vehicles in the past two years. It has attracted more and more attention from the outside world. Not only from the consumer side, but also from the industrial field. The technological trend led by new energy vehicles has grown into a powerful force that cannot be ignored. Today we are going to talk about the application of laser welding technology to the power core of new energy vehicles ' batteries.
With the increase in sales of new energy vehicles. The installed capacity of power batteries is also growing rapidly. The data shows that in , the sales volume of new energy vehicles in my country will be 3.521 million. A year-on-year increase of 157.5%. The installed capacity of power batteries reached 154.5GWh. A year-on-year increase of 142.8%. Battery manufacturers have expanded their production capacity. By , experts at the hundreds of people meeting on electric vehicles said. my country's power battery production capacity will reach kWh. in the manufacturing process of power batteries. Low cost, high quality, and high efficiency are the three goals pursued by manufacturing companies. therefore. The technological process and intelligent equipment that can achieve these three goals-lithium battery laser welding machine. It is favored by battery manufacturers.
The interior of the power battery is also a complex system. It has to go through various manufacturing processes from batteries, battery modules, and battery packs. Finally assembled into a complete power battery system. Among them, the connection between materials and modules and battery pack structures. They involve a very demanding welding process ' laser welding.
In the manufacturing process of power batteries. Reasonable selection of welding methods and processes. It will directly affect the cost and quality of batteries, as well as safety and consistency. Next, let's sort out the content of power battery welding.
Power batteries are divided into square, cylindrical, and pouch batteries. Common welding applications for power batteries:
The poles on the battery cover are divided into battery internal connections and external connections. The internal connection of the battery is the welding of the battery tab and the cover. The external connection of the battery is to weld the battery poles into a series or parallel circuit through connectors. A battery module is formed.
The main problem of laser welding of battery poles is also the defect of explosion holes. The reason is similar to that of explosion-proof valves. The weld of the rod is essentially the mating surface between the aluminum adapter block and the rod. The diameter of the hole in the aluminum block is only about 6mm. Impurities such as stamping oil and cleaning agent are easy to remain here. The high energy density laser causes the temperature of the welding part to rise sharply. As a result, the residual impurities at the poles are rapidly vaporized, and the bubbles overflow. And overcome the surface tension of the molten pool to leave the molten pool, resulting in hole defects. During this process, rapid changes in pulsed laser power further exacerbate the tendency for blast holes to form. Therefore, in addition to strengthening the cleaning before welding. Optimizing laser power variation can also reduce blast hole defects.
Power battery module and PACK welding
The structural design of the battery module often determines the performance and safety of the battery pack. Its structure must provide support for the battery as well as secure and protect it. at the same time. How to meet the following are the criteria for evaluating eligibility:
Overcurrent requirements,
Current uniformity,
How to control the core temperature,
Whether to cut off the power supply in case of serious abnormality,
Avoid chain reactions etc.
At the same time, due to the fast heat transfer rate of copper and aluminum. High laser reflectivity. The connection piece is thick. Therefore, high-power lasers are required to achieve welding.
At present, the main problems in laser welding of power batteries are welding defects such as pores, cracks, poor molding, and blast holes. These defects lead to a decrease in the strength of the battery pack as well as the sealing and conductivity. Eventually lead to a series of safety issues such as battery explosion, liquid leakage, and heat generation. To address these issues, a great deal of research has focused on process optimization. By adjusting laser welding power, pulse width, welding speed, defocus and other parameters, defects can be effectively reduced.
It is not difficult to see that the welding process of the power battery is a meticulous work. Any small problem may affect the performance and safety of the finished power battery.therefore. High-quality materials and high-quality laser welding equipment are the basis for a successful welding process. Laser welding path planning and weld seam identification. There are also intelligent technologies represented by defect identification and quality monitoring. The above is also one of the hot spots of future research.
Power batteries mainly include prismatic batteries, cylindrical batteries, and pouch batteries. Prismatic aluminum shell lifepo4 battery have become the primary focus of domestic lithium manufacturing and development due to their simple structure, good impact resistance, high energy density, large single capacity, and many other advantages.
In the manufacturing process of a single battery, key components that need laser welding include a pole, adapter, sealing port, electrolyte injection port, injection hole sealing nails, connecting piece, explosion-proof valve, flip-flop, top cover sealing, and more.
Flexible pack batteries mainly consist of positive and negative lugs connected in series, positive and negative lugs welded with copper converging pieces, and multi-layer negative aluminum and copper converging piece welding. The thickness of copper lugs is generally 0.2-0.5mm, and aluminum lugs are generally 0.2-0.6mm. Single-mode fiber laser lens welding is commonly used.
Advantages of Lithium Battery Welding:
Laser welding offers high energy density, minimal welding deformation, a small heat-affected zone, effective improvement of part precision, smooth and impurity-free weld seams, consistent density, and eliminates the need for additional grinding work. Laser welding allows for precise control, with a small focusing point of light, high-precision positioning, easy automation with robotic arms, improved welding efficiency, reduced man-hours, and cost savings. Laser welding of thin sheet metal or fine diameter wire is less susceptible to melting back compared to arc welding.
The advantage of the laser welding process is its ability to weld a wide range of materials and realize welding between different materials. In the power lithium-ion battery welding process, technicians select the appropriate laser and welding process parameters based on battery material, shape, thickness, tensile requirements, and more to establish reasonable welding process parameters. This ensures that the final welding effect meets the requirements of power lithium-ion battery manufacturers.
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Pole Welding:
For square batteries, each battery needs to be connected in series and parallel to a battery module unit through positive and negative electrode poles. Battery pole materials include copper and aluminum, which are high-resistance materials requiring good laser beam quality and high energy density.
Adapter Welding:
The adapter's role is to connect the top cover post of the square shell battery and the battery internal cell lugs, forming the current conduction. The current welding program selects a fiber laser with a wavelength of ~nm. The battery's negative pole adapter is made of copper, which has low absorption in this wavelength band and rapid heat dissipation. Therefore, high power density is needed for deep fusion welding.
In blue laser and fiber laser composite welding, the overall laser utilization rate is high. A lower total power can complete the adapter laser welding application, ensuring stability in the welding process. This reduces the likelihood of welding issues, eliminates spatter, and allows for adjustable weld width to significantly enhance the product performance of square shell batteries.
Spot welder for batteries:
Power battery shell materials mainly include aluminum alloy and stainless steel, with aluminum alloy being the most commonly used. Stainless steel, such as 304 stainless steel, exhibits better laser welding performance. Whether using a pulsed laser or continuous laser, it can achieve better weld appearance and mechanical properties. The square battery shell thickness is generally below 1mm, depending on capacity, with 0.6mm and 0.8mm being common. Laser welding square power battery shells can be categorized as side welding and top welding.
Sealing Nail (Electrolyte Injection Port) Welding:
The shape of the sealing nail (injection cap) is usually a round cap with a diameter of 8mm and a thickness of about 0.9mm. Traditional YAG pulsed lasers are commonly used for welding these sealing nails, producing well-shaped welds with good consistency and high yield. However, using fiber lasers for sealing nails through continuous light mode allows for significantly higher welding speeds'up to 80-120mm/s'compared to YAG laser welding. This represents a more than tenfold increase in welding speed.
Liquid Injection Hole Sealing Nails:
To inject electrolyte into the battery case, a liquid injection hole is present in the top cover piece. After completing the liquid injection, the liquid injection hole is sealed, typically using a rubber nail for initial sealing. The final sealing nail is then assembled and laser-welded.
Connecting Piece Welding:
The power battery module connecting piece adopts a multi-layer material composite, with one layer serving as the connecting layer of the connecting piece and pole to ensure welding performance. The multi-layer material superposition ensures the electrical conductivity of the connecting piece. Power battery module connectors are generally rectangular, trapezoidal, triangular, and stage-shaped, with a 0.1mm thick nickel-plated copper foil on the connecting surface.
Battery Explosion-Proof Valve Welding:
The primary function of the explosion-proof valve is to prevent the battery from exploding during thermal runaway, ensuring battery safety. The welding process for the explosion-proof valve is demanding. Explosion-proof valves can be welded with pulsed and continuous lasers. Continuous laser welding requires higher precision for product assembly but achieves higher-quality welding results, along with welding stability, efficiency, and yield rate guarantees. The explosion-proof valve is a pure aluminum (AL) round sheet with a thickness ranging between 0.08 and 0.1mm.
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