Lithium Battery Laser Welding

The emergence of lithium batteries has solved many of our daily problems, such as the ability to quickly charge, but also in the case of the battery is not fully charged first, and then continue to charge, will not cause any impact on the life of the battery, so whether in the digital industry, or in the power tool industry has become a very important part. The lithium battery in the manufacturing process, each step needs to go through strict quality testing, the final quality of the lithium battery directly determines the performance of the entire device. And lithium batteries in the production, welding link is essential, such as some battery sealing welding, point welding of the battery pole ear, many manufacturers have begun to use laser welding.

Understanding the importance of lithium batteries, it can be seen that laser welding plays a pivotal role in the manufacturing process of lithium batteries. The lithium battery laser welding machine can be controlled by a microcomputer to control the temperature and heat-affected zone, the energy density of high and low are controlled to an acceptable range to ensure the accuracy of the entire welding, including the uniformity of the welded joints, without any impurities, while a one-time completion of the entire welding process, without repeated welding, so as to ensure that our welded joints can be smooth and very flat. The final production of lithium batteries, from its electrical conductivity, and air tightness, and finally corrosion resistance, are an important quality standard to determine whether our welding process is up to standard.

Lithium battery laser welding samples



The lithium battery sealing performance is good to ensure the service life of the battery, has been in the process of use will not appear dangerous situation. And the application of lithium batteries are among the more sophisticated equipment and instruments, so when laser welding, not only to ensure the entire welding plane, smooth appearance and no defects, but also to ensure the quality of the welded joints, which can ensure the safety of lithium batteries when working, but also a responsible for our personal safety.

Lithium battery pole lug welding and pole piece cutting laser process analysis!

1. Preface

In the past two decades, laser processing technology has become one of the fastest growing high-tech, providing sufficient support for the transformation of traditional manufacturing industries. Compared with the traditional pole lug welding and pole piece cutting mode, laser welding and laser cutting mode can realize automatic operation and solve a series of problems such as burr, white dew and powder drop, which provide the basis for the improvement of lithium battery performance. Therefore, starting from the application of laser processing technology, to explore the pole lug welding and pole piece cutting process has a very prominent practical significance.

2. Laser welding and laser cutting principle

2.1 Laser welding

Laser welding is mainly a high energy density laser beam as a heat source, in the power density of less than 104 ~ 105W/cm2, the heat conduction heating the surface of the workpiece, slow welding, welding melt depth shallow; or in the power density of more than 105 ~ 107W/cm2, through the control of laser pulse peak power, width, repetition frequency, energy to promote the melting of the workpiece and the formation of a specific melt pool, for Fast welding, welding depth of fusion is larger.

2.2 Laser cutting

Laser cutting mainly refers to the use of laser cutting materials, which requires the use of optical devices to guide the output of high power laser beam. At the same time, according to the motion control system in the laser to track the trajectory of the workpiece to be cut, the laser beam is focused on the material, prompting the material to melt, evaporate, burn, blow away and other reactions to obtain a high surface finish edge.

3. Laser welding in the pole ear welding application

3.1 Welding device selection

According to the pole lug welding requirements, welding processors can choose semi-automatic welding device or fully automatic welding device. The former is mainly handheld laser welding machine, which is mainly a disc structure, every interval of 90 ° for the opening of the V-slot, V-slot can be placed in the battery cylinder parts, pressed parts after focusing the laser beam to the welding site, each welding a part for 90 ° rotation, the second welding point is rotated 0.50 mm; the latter is through the straight funnel way of feeding, each after a "round pit", V-slot are automatically put into the battery cover, the battery body to be welded, for automatic welding. Commonly used laser welding equipment for SOUPACT compact laser assembly welding equipment, Tide laser welding system, etc.

3.2 Welding parameters settings

Considering the current soft pack lithium-ion batteries for a variety of negative aluminum and copper convergence welding mode, copper lug thickness in the 0.2-0.5mm, aluminum lug welding thickness in the 0.2 to 0.6mm or so. Therefore, laser welding lug, you need to set the laser wavelength of 1064nm, laser power of 110W ~ 200W, spot 28μm, laser scanning speed and pulse frequency of 500mm / s, 200kHz, repeat frequency of 0.4 ~ 20MHz, pulse width of 50-120ns. and control lug welding gap The width of the lug welding gap is within 1.2-2.4mm and the depth of the welding gap is within 1.2-1.8mm. Also ensure the accuracy of the lug width and lug spacing accuracy, lug height accuracy are less than or equal to ± 0.15mm.

3.3 Welding process control

Currently, in the process of lug laser welding, semi-automatic welding method is used less, to fully automatic welding is more common.

In the fully automatic welding process, the welding process is as follows: first of all, you need to start the device to carry out the detection of the position of the parts to be welded, only the battery cover, the main body of the battery to be welded are in the correct position, before starting the welding, turning flat, under the material, shifting and other processes.
Secondly, after determining the correct position of the welded parts, it is necessary to complete the automatic flattening operation of the pole lug. Because the battery body is automatically put in, it is impossible to ensure that the pole lug is in a horizontal position. At this time, it is necessary to use photoelectric detection method to stop automatically after the pole lug is turned into a horizontal position to ensure that the subsequent pressing and welding operations are carried out normally. At the same time, because the pole lug has high requirements for welding straightness, it is necessary to use electromagnetic removal device to automatically remove the battery parts that are not in line with the standard, such as bending and twisting, to prevent and control the phenomenon of "welding waste".

Again, in the pressing process, mainly rely on automatic pressing device, mostly microcomputer-controlled four-linked electromagnetic automatic mechanism, can be pressed before welding lug, safety valve, to provide good conditions for laser penetration welding. Because each lithium battery welding point position is 2 (the distance is around 0.50mm), therefore, to ensure the reliability and safety of electrode contact, it is necessary to repeatedly start the pressing mechanism 2 times and carry out 2 times welding of the laser.

Finally, after welding is completed, the cell is transferred to the next process for automatic discharging. Generally, the automatic discharging mechanism is permanent magnetic roller scraper chute type, which can make the battery body enter the bending and descending slide chute by the scraper by magnet adsorption of the battery roller under the proper angle and position, and enter the next process by the chute.

4. Application of laser cutting in pole cutting

4.1 Cutting equipment selection

According to the lithium battery pole material, you can choose different lithium battery pole cutting system. For example, for the negative copper foil of lithium battery, 1064nm MOPA fiber laser can be selected, with a peak power density of 2.4×106W/mm2, which can achieve "narrow pulse width" cutting of a few nanometers to tens of nanometers within the megahertz operating frequency by modulating the electricity of the seed source. For example, for lithium battery positive aluminum foil, picosecond lasers with picosecond pulses can be selected, which can be mode-locked by the seed source to obtain ultra-narrow pulse signals. The output is then amplified to achieve "ultra-narrow pulse width" cutting of a few nanometers within a few tens of megahertz operating frequency. At the same time, the picosecond laser can use triple frequency technology to convert 1064 nm near infrared laser to 355 nm ultraviolet light and 532 nm green light to meet the needs of a variety of material processing, and to achieve "cold processing" when the laser pulse width is less than the material electro-acoustic relaxation time.

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