SHINHOP laser

The development of power batteries is rapid, especially in the past year or two, with strong basic development forces driving the entire industry chain to accelerate the expansion of production scale, and the industrial support becoming more complete. Various battery technology innovations have sparked a wave of enthusiasm, and the competition in industry technology has become intense......
1. What is a power battery?
The global electric vehicle industry generally agrees that the battery providing driving power for electric vehicles is called a power battery, which includes traditional lead-acid batteries, nickel-hydrogen batteries, and emerging lithium-ion power batteries, divided into power-type power batteries (hybrid electric vehicles) and energy-type power batteries (pure electric vehicles).
As we all know, power batteries are the "heart" of new energy vehicles. Power lithium batteries mainly consist of ternary material batteries and lithium iron phosphate batteries, with downstream applications in new energy vehicle installations, having a higher discharge power compared to ordinary batteries.
As a supporting industry for new energy vehicles, the power battery industry has also experienced explosive growth in recent years driven by the new energy vehicle industry.

2. The relationship between power batteries and laser welding
Power batteries account for 30%-40% of the total cost of new energy vehicles, making it the largest part of the cost of new energy vehicles. They have a very important impact on key indicators such as the range, lifespan, and safety of new energy vehicles. Therefore, improving the performance of power batteries is key to enhancing the overall performance of new energy vehicles.

In the production process of power batteries, welding is a very important manufacturing process from cell manufacturing to PACK assembly. Especially since the structure of power batteries includes various materials, such as steel, aluminum, copper, nickel, etc., these metals may be made into electrodes, wires, or shells. Therefore, whether it is welding between a single material or multiple materials, it places higher demands on the welding process.
Laser welding works by utilizing the excellent directionality and high power density of laser beams. Through an optical system, the laser beam is focused on a very small area, creating a highly concentrated heat source in a very short time, causing the welded area to melt and form a strong weld point and seam.
In the entire power battery industry chain, laser welding is mainly applied in the midstream production of power lithium batteries. As a high-precision welding method, it is extremely flexible, precise, and efficient, meeting the performance requirements in the production process of power batteries, making it the preferred choice in the manufacturing process of power batteries. It has now become standard equipment on power battery production lines.
3. Common welding applications for power batteries
Power batteries are divided into square, cylindrical, and soft-pack batteries. Currently, in the production of power batteries, the stages using laser welding mainly include:
Mid-process: welding of tabs (including pre-welding), spot welding of strips, pre-welding of cell into shell, sealing welding of the shell top cover, sealing welding of the liquid injection port, etc.;
Post-process: including the welding of connecting pieces during battery PACK module assembly, as well as the welding of explosion-proof valves on the cover plate after module assembly.

1. Welding of explosion-proof valves
The explosion-proof valve is a thin-walled valve body on the battery sealing plate. When the internal pressure of the battery exceeds the specified value, the valve body of the explosion-proof valve ruptures first to release pressure, preventing the battery from exploding. The structure of the explosion-proof valve is clever, often using laser welding to securely attach two aluminum metal sheets of a certain shape. When the internal pressure of the battery rises to a certain value, the aluminum sheet ruptures at the designed groove position, preventing further expansion of the battery that could cause an explosion. Therefore, this process has very strict requirements for the laser welding process, requiring the weld seam to be sealed, strictly controlling the heat input, and ensuring that the rupture pressure value of the weld seam remains stable within a certain range (generally between 0.4~0.7MPa). Both too high and too low can greatly affect the safety of the battery.

Therefore, explosion-proof valves generally use butt welding. Extensive practice has proven that using a laser hybrid welding laser can achieve high-speed, high-quality welding, and ensure the stability, efficiency, and yield of the welding.

2. Welding of terminals
The terminals on the battery cover plate are divided into internal and external connections. The internal connection is the welding of the cell tabs to the cover plate terminals; the external connection is the welding of the battery terminals through connecting pieces, forming series and parallel circuits to make up the battery module.

The battery terminals are the positive and negative terminals of the battery, with the positive terminal generally made of aluminum and the negative terminal made of copper. The commonly used structure is a riveted structure, which is fully welded after riveting, with a typical size of a diameter 8 circle. During welding, while meeting the design requirements for tensile strength and conductivity, it is preferable to choose fiber lasers or hybrid welding lasers with good beam quality and uniform energy distribution. Using fiber lasers and hybrid welding lasers can achieve stable welding of aluminum-aluminum and copper-copper structures for terminal columns, reduce spatter, and improve welding yield.
3. Welding of connecting pieces
The connecting piece and soft connection are key components connecting the battery cover plate and the cell. It must consider the battery's overcurrent, strength, and low spatter requirements simultaneously. Therefore, during the welding process with the cover plate, sufficient weld seam width is required, and it must be ensured that no particles fall onto the cell to avoid battery short circuits. As the negative electrode material, copper is a high-reflectivity material with low absorption rate, requiring higher energy density for welding. The blue light hybrid laser can effectively solve traditional process challenges such as high reflectivity and spatter.

4. Shell sealing welding
The shell materials of power batteries include aluminum alloy and stainless steel, with aluminum alloy being the most commonly used, and a few using pure aluminum. Stainless steel is the best material for laser welding, especially 304 stainless steel, which can achieve good appearance and performance welds with both pulsed and continuous lasers.
Using continuous lasers to weld thin-shell lithium batteries can increase efficiency by 5 to 10 times, and the appearance and sealing performance are better. Now, in pursuit of faster welding speeds and more uniform appearances, most companies have begun to adopt hybrid welding and annular spot lasers to replace the previously low-speed single fiber welding. Currently, the welding speed of mass production lines in most companies has reached 200mm/s, while some manufacturers' low-speed fiber welding lines generally have a mass production speed of 70mm/s to ensure stable weld paths.

5. Sealing nail (electrolyte injection port) welding
The sealing nail (liquid injection hole cap) comes in various forms, typically shaped as a circular cap with a diameter of 8mm and a thickness of about 0.9mm. The basic requirement for welding is that the pressure resistance value must reach 1.1MPa, and it must be sealed without the presence of pinholes, cracks, or explosion points.
As the final process of cell welding, the yield of sealing nail welding is particularly important. During sealing nail welding, the presence of residual electrolyte can lead to defects such as explosion points and pinholes, and the key method to suppress these defects is to reduce the heat input.

6. Power battery module and PACK welding
The battery module can be understood as a combination of lithium-ion cells in series and parallel, equipped with monitoring and management devices for individual batteries. The structural design of the battery module often determines the performance and safety of a battery pack. Its structure must support, fix, and protect the cells. Additionally, how to meet overcurrent requirements, current uniformity, control the temperature of the cells, and whether it can cut off power in case of severe abnormalities to avoid chain reactions, etc., will all be standards for evaluating the quality of the battery module.

Due to the formation of brittle compounds after laser welding between copper and aluminum, which cannot meet usage requirements, ultrasonic welding is usually employed. For copper to copper and aluminum to aluminum, laser welding is generally used. At the same time, since both copper and aluminum have high thermal conductivity and very high reflectivity to lasers, and the thickness of the connecting piece is relatively large, a higher power laser is required to achieve welding.