Recently, power batteries are hot popular ! The price of raw materials is "skyrocketing", the leading companies in the industry chain are stepping up production expansion, and the capital market has set off a wave of daily limit...

 

1 What is a power battery?

 

The basic agreement of the global electric vehicle industry: The batteries that provide driving power for electric vehicles are called power batteries, including traditional lead-acid batteries, nickel-hydrogen batteries and emerging lithium-ion power batteries, which are divided into power-type power batteries (hybrid vehicles) And energy-type power batteries (pure electric vehicles).

 

As we all know, power batteries are the "heart" of new energy vehicles. The power lithium battery is mainly ternary material battery and lithium iron phosphate battery, and the downstream is the installed application of new energy vehicles, which has higher discharge power than ordinary batteries.

 

As a supporting industry for new energy vehicles, driven by the new energy vehicle industry in recent years, the power battery industry has also ushered in explosive growth.



2 The relationship between power battery and laser welding

 

Power batteries account for 30%-40% of the cost of new energy vehicles, and are the largest part of the cost of new energy vehicles. They are very important for key indicators such as the range, vehicle life and safety of new energy vehicles. Therefore, improving the performance of power batteries is the key to improving the overall performance of new energy vehicles.

                        Schematic diagram of power lithium battery industry chain

Schematic diagram of power lithium battery industry chain

 

In the process of power battery production, from battery cell manufacturing to PACK assembly, welding is a very important manufacturing process. In particular, the power battery structure contains a variety of materials, such as steel, aluminum, copper, nickel, etc. These metals may be made into electrodes, wires or shells. Therefore, whether it is welding between one material or between multiple materials, higher requirements are placed on the welding process.

 

Laser welding uses the excellent directivity and high power density of the laser beam to work. The laser beam is focused in a small area through the optical system, so that the welded area forms a highly concentrated heat source in a very short time. Zone, so that the welded object melts and forms a firm solder joint and weld.

 

In the entire industry chain of power batteries, laser welding is mainly used in the midstream production of power lithium batteries. As a high-precision welding method, it is extremely flexible, precise and efficient, and can meet the performance requirements in the power battery production process. It is the first choice in the power battery manufacturing process. It has become the standard equipment of the power battery production line.


3 Common welding applications of power batteries

 

Power batteries are divided into prismatic, cylindrical and pouch batteries. At present, in the production of power batteries, the links using laser welding mainly include:

Middle process: welding of tabs (including pre-welding), spot welding of pole strips, pre-welding of battery cores into the shell, sealing welding of shell top cover, sealing welding of liquid injection port, etc.;

Back-end process: Including the welding of the connecting piece of the battery PACK module, and the welding of the explosion-proof valve on the cover plate behind the module.

 



1. Welding of battery explosion-proof valve

 

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 explosion-proof valve body is the first to vent and release the pressure to prevent the battery from bursting. The explosion-proof valve has an ingenious structure and uses laser welding to weld two aluminum metal sheets of a certain shape. When the internal pressure of the battery rises to a certain value, the aluminum sheet ruptures from the designed groove to prevent the battery from further expanding and causing an explosion. Therefore, this process has extremely strict requirements on the laser welding process. It requires the weld seam to be sealed, and the heat input is strictly controlled to ensure that the failure pressure value of the weld seam is stable within a certain range (usually 0.4~0.7MPa). It will be too large or too small. Greatly affect the safety of the battery.





Therefore, the explosion-proof valve generally adopts splicing welding. After a lot of practice, it has been proved that the use of UWLaser hybrid welding laser can achieve high-speed and high-quality welding, and welding stability, welding efficiency and yield can be guaranteed.


2. Pole welding

The poles on the battery cover are divided into battery internal and battery external connections. The internal connection of the battery is the welding of the battery pole ears and the cover pole; the external connection of the battery is the welding of the battery poles through the connecting piece to form a series and parallel circuit to form a battery module.

 

The poles of the battery are the positive and negative electrodes of the battery. Generally, aluminum is used for the positive electrode and copper is used for the negative electrode. The commonly used structure is the riveting structure, which is fully welded after the riveting is completed, and its size is generally a circle with a diameter of 8. When welding, in the case of meeting the design requirements of tensile and electrical properties, priority is given to fiber lasers or hybrid welding lasers with good beam quality and uniform energy distribution. The aluminum of the electrode column can be welded by using fiber lasers and hybrid welding lasers. Aluminum structure welding, copper-copper structure welding stability, reduce spatter, and improve welding yield.



3. Welding of the adapter piece

 

The adapter sheet and the flexible connection are the key components that connect the battery cover and the battery cell. It must also take into account the requirements of battery overcurrent, strength and low spatter, so during the welding process with the cover plate, there needs to be sufficient weld width, and it is necessary to ensure that no particles fall on the battery core to avoid battery short circuit. . As the negative electrode material, copper is a high-reflection material with low absorptivity. It requires higher energy density to weld during welding. United Win Laser’s latest blue composite laser can well solve traditional process problems such as high-reflection and spatter. .


4. Shell sealing welding

 

The shell materials of the power battery are aluminum alloy and stainless steel, of which aluminum alloy is the most used, and a few use pure aluminum. Stainless steel is the material with the best laser weldability, especially 304 stainless steel. Whether it is pulsed or continuous laser, welds with good appearance and performance can be obtained.

 

Using continuous laser to weld thin-shell lithium batteries, the efficiency can be increased by 5 to 10 times, and the appearance effect and sealing performance are better. Now in order to pursue faster welding speed and more uniform appearance, most companies have begun to use hybrid welding and circular spot to replace the previous low-speed single fiber welding. At present, the welding speed of most companies' mass production lines has reached 200mm/s. However, in order to ensure the stability of the welding bead, the low-speed wire of some manufacturers of optical fiber welding, the general mass production speed is 70mm/s.



5. Welding of sealing nail (electrolyte injection port)


There are also many forms of sealing nails (liquid hole caps), and their shape is usually 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 reaches 1.1MPa, and it is sealed and cannot have pinholes. , Cracks and explosion points.

 

As the last process of cell welding, the yield rate of sealing nail welding is particularly important. The presence of residual electrolyte during sealing nail welding leads to defects such as explosion points and pinholes. The key way to suppress these defects is to reduce the heat input. After long-term experiments and extensive market verification, the laser independently developed by UW Laser can greatly improve the stability and compatibility, thereby greatly improving the yield rate. At present, the yield rate of UW Laser sealing nail welding can reach 99.5%. .

 


6. Welding of power battery modules and PACK


The battery module can be understood as a combination of lithium-ion batteries in series and parallel, and a single battery monitoring and management device is added. The structural design of the battery module can often determine the performance and safety of a battery pack. Its structure must support, fix and protect the cell. At the same time, how to meet the overcurrent requirements, current uniformity, how to meet the control of cell temperature, and whether to cut off the power when there is a serious abnormality, to avoid chain reactions, etc., will all be the criteria for judging the quality of battery modules.

Since the use of laser welding between copper and aluminum is easy to form brittle compounds, which cannot meet the requirements of use, ultrasonic welding is usually used, and copper and copper, aluminum and aluminum are generally laser welded. At the same time, since copper and aluminum conduct heat very quickly, have a very high reflectivity to the laser, and the thickness of the connecting piece is relatively large, it is necessary to use a higher-power laser to achieve welding.

        



4 About UWLASER


UWLaser is recognized by the industry as the "power battery welding king". As the core supplier of new energy power battery laser welding system solutions, it has accumulated very rich practical experience in the field of power battery welding. It has a prismatic-shell power battery cell assembly line, a square-shell power battery module assembly line, a fuel cell bipolar plate welding line, a power battery module FPC automatic welding line, a cylindrical power battery module assembly line, a soft pack power battery module PACK assembly line, etc. Industry-leading semi-automatic and fully automatic laser welding solutions. After 16 years of concentrated research and development and technology accumulation, Win Laser can provide customers with tailor-made laser welding and automation solutions for their different needs.