Dynamic lithium battery welding method and process introduction

　　Author ：Iflowpower – Portable Power Station Supplier

Dynamic lithium battery manufacturing process welding method and reasonable selection of processes will directly affect the cost, quality, security, and battery consistency of batteries. Next, organize the content of the power lithium battery welding. 1 Laser welding principle Laser welding is to operate by characteristics of the laser beam excellent direction and high power density, and the laser beam is focused in a small area by the optical system, and the weld is formed in a very short period of time.

Highly concentrated heat source area, which is melted and forms a strong solder joint and weld. 2 Laser welding type thermally conductive welding and deep gadding laser power density is 105 to 106 w / cm2 to form laser heat transfer welding, laser power density is 105 ~ 106W / cm2 to form laser deep split welding, welding, welding, welding, connecting piece No punching, relatively simple processing. Laser welding machine with large penetrating welding power.

The penetrating melted depth is lower than the sling of the soldering, and the reliability is relatively alteration. Sewer is soldered, only less power laser welder. The melting of seam welding is high than the penetrating melt deep, and the reliability is relatively good.

But the connecting piece needs to be punched, and the processing is relatively difficult. Pulse Welding and Continuous Welding 1) Pulse mode Welding laser welding should be selected for suitable welding waveforms, common pulse waveforms, spikes, bispanoids, etc., the reflectance of the aluminum alloy is too high, when high intensity laser The beam is shot to the surface of the material, and the metal surface will have 60% -98% laser energy loss due to reflection, and the reflectance varies with surface temperature.

Generally welding aluminum alloy, the pointed wave and bisproof wave are optimally selected. The welding waveform is long and the sediment is long, and the occurrence of air holes and cracks can be effectively reduced. Pulsed laser welding samples Due to the high reflectivity of the laser, in order to prevent vertical reflection of the laser beam, the laser beam is damaged, and the welding head is generally deflected in a certain angle during the welding process.

The diameter of the solder joint diameter and the effective binding surface increases with the laser inclination angle, when the laser tilt angle is 40, the maximum solder joint and effective combination surface are obtained. The solder joint melt deep and the effective melt deep with the laser inclination angle, when it is greater than 60, its effective soldering melt deep is reduced to zero. Therefore, the tilt welding to a certain angle, can add weld melt deep and melt.

In addition, in the weld, the weld is boundary, and the laser weld bias cover is required, 35% of the housing can be welded, which can effectively reduce the fire caused by the problem. 2) Duration of the welding continuous laser welding due to its heat-inspiration process is not as hot as pulse machine, the crack tendency is not very obvious, in order to improve the quality of the weld, the continuous laser is welded, the weld surface is smooth, no splash, no Defect, no cracks were found inside the weld. In terms of the welding of aluminum alloys, the advantages of continuous lasers are obvious.

Compared with traditional welding methods, production efficiency is high, without filling; it can solve their defects in welding compared to pulsed laser solders, such as cracks, Pore, splash, etc., to ensure that the aluminum alloy has good mechanical properties after the welding; the welding is not depressed, the amount of polishing after welding is reduced, and the production cost is saved, but because the spot of the continuous laser is small, the assembly accuracy of the workpiece is High demand. Continuous laser welding samples are in power lithium battery welding, and the welding process technicians will select suitable lasers and welding process parameters according to customer battery materials, shape, thickness, tension requirements, etc.

, including welding speed, waveform, peak, welding head tilt angle. Wait to set reasonable welding process parameters to ensure that the final welding effect meets the requirements of the power lithium battery manufacturer. 3 The energy concentration of laser welding advantages, high welding efficiency, high processing accuracy, welding is wide than large.

The laser beam is easily focused, aligned and guided by the optical instrument, and can be placed at the appropriate distance of the unwaffement, and can be further guided between the fixture or obstacle around the workpiece, and other welding methods cannot be played by the above-mentioned space limit. Small thermal input, small thermal influence area, workpiece residual stress and deformation; welding energy can be accurately controlled, welding effect is stable, welding appearance; non-contact welding, optical fiber transmission, good accessibility, high degree of automation. When welding thin materials or fine trails, it is not easy to have a stiffness like arc welding.

Because the battery of the power lithium battery is usually used in light aluminum materials, it is often done, and the general case, the cover, the bottom is required to reach 1.0mm or less, and the mainstream manufacturer is currently basic. The thickness is around 0.

8mm. It can supply high-strength welding for various material portfolios, especially when the copper material is welded between the copper material and the welding between the aluminum material is more effective. This is also the only technique that can be soldered to copper materials in a copper material.

4 Laser welding technology is difficult to point, the battery case of aluminum alloy materials accounts for more than 90% of the entire powertrain battery. The difficulty of its welding is that the aluminum alloy is extremely high in the reflectance of the laser, and some problem defects are sensitive during the welding process, and some problems can occur when welding will prevent it. The most important is that the pores, thermal cracks and fires.

During the laser welding process of aluminum alloy, there is an important type of air holes. It is important to have two categories: hydrogen holes and bubbles. Since the cooling speed of the laser welding is too fast, the hydrogen hole problem is more severe, and there is also a hole in laser welding, a hole in which the collapse of the small hole occurs.

Hot cracking problem. Aluminum metal metal is prone to thermal cracks when welding, including weld crystallization cracks and HAZ liquefied cracks, due to the segregation of the weld zone, and the grain boundary, in the stress use Liquefied cracks are formed at the grain boundary, reducing the performance of the welded joint. Fried fire (also known as splash).

There are many factors that cause the fire, such as the cleanliness of the material, the purity of the material itself, the material itself, etc., and the decisive use is the stability of the laser. Housing surface projection, air hole, internal bubble.

The reason is that it is important that the fiber core diameter is too small or the laser energy is set too high. Not some laser equipment suppliers, the better the beam quality, the better the welding effect, and the quality of the beam is suitable for a deep-larger superimposed welding. Finding the right process parameters is the winning way to solve the problem.

Other difficulties soft bag gel welding, the requirements for welding tools, must press the extreme ear to ensure welding gap. High-speed welding of complex trajectories such as S-shaped, spiral, and increased welding strength while increasing weld joints. Welding of the cylindrical cell is important for welding of the positive electrode, because the negative electrode housing is thin, it is easy to weld.

For example, some of the negative electrode employed by the manufacturer, the positive electrode is used for laser welding. When the square battery is welded, the pole column or the connecting piece is contaminated. When welding the film, the pollutant is decomposed, which is easy to form a welding point, causing a hole; the pole column is thin, the lower plastic or ceramic structural components, easy to weld Put on.

When the pillar is small, it is also easy to weld to plastic burning, forming an explosion point. Do not use multi-layer connectors, there is a pore between the layers, not easy to weld. The most important process of the welding process of the square battery is the package of the shell cover, and the welding of the top cover and the bottom cover according to the location of the position.

Some battery manufacturers use the production of the battery shell due to the production of the battery, and only the top cover welding is required. Square power lithium battery side welding sample square battery welding method is important to side welding and top welding, where the important benefits of lateral welding is smaller, and the spatter does not easily enter the inside of the shell cover. Since the welding may result in a projection, this will have some microveliven impact on the assembly of subsequent processes, so the side welding process is extremely high for the stability of the laser.

The top welding process is relatively low for welding equipment integration due to welding, and there are two unfavorable places. High processing requirements will result in cost problems. 5 Welding quality influencing factors Laser welding is an important method of high-end battery welding.

Laser welding is a high energy bundle laser irradiation workpiece, so that the working temperature rises sharply, the workpiece is melted and reconnected to form a permanent connection. The shear strength and tear strength of laser welding are better. Battery welding is good or bad of conductivity, strength, airtightness, metal fatigue, and corrosion resistance is a typical welding quality evaluation criteria.

Many factors affecting laser welding quality. Some of these very easy fluctuations have considerable instability. How to properly set and control these parameters, allowing it to control in a suitable range during high-speed laser welding to ensure welding quality.

The reliability and stability of weld formation is an important issue that is related to laser welding techniques and industrialization. Important factors affecting laser welding quality are divided into welding equipment, workpiece status and process parameters. 1) Welding equipment is most important to the quality requirements of the laser is the beam mode and output power and its stability.

The beam mode is an important indicator of the beam quality. The lower the beam mode step, the better the light beam focus performance, the smaller the spot, the higher the power density at the same laser power, the larger the weld is wide. Generally requiring the base mode (TEM00) or low order, otherwise it is difficult to meet the requirements of high quality laser welding.

At present, domestic lasers are used for laser welding in terms of beam quality and power output stability. From a foreign situation, the beam quality and output power stability of the laser are quite high, which will not become a problem with laser welding. The factors affecting the quality of the welding quality are focusing on the focusing mirror, and the focal length used is generally between 127 mm (5in) to 200 mm (7.

9). The focal length is small to reduce the wicher diameter of the focus beam, but too small is easy to weld. Pollution and splash damage during the process.

The shorter the wavelength, the higher the absorption rate; the general conductive material is high, the reflectance is high, and the reflectivity of the YAG laser is 96%, aluminum is 92%, copper 90%, iron 60%. The higher the temperature, the higher the absorption rate, the linear relationship; generally surface phosphite, carbon black, graphite, etc. can improve the absorption rate.

2) Workpiece status laser welding requires processing of the edge of the workpiece, is equipped with high precision, the spot and weld are strictly pair, and the original assembly accuracy of the workpiece and the spot is in the welding process cannot be varied during welding. This is because the laser spot is small, the weld is narrow, and generally does not fill the metal. If the assembly is not strict, the beam can pass through the gap, or the bias is caused by obvious bite, depression, such as a variety of spots.

Slightly, it is possible to cause unfucks or unmatched. Therefore, the general sheet metal is not greater than 0.1mm, and the shampoo should not be greater than 0.

2mm. In actual production, there is sometimes due to these requirements, laser welding technology cannot be used. To obtain a good welding effect, the docking allows the gap and the lap gap to be controlled within 10% of the thin plate thickness.

Successful laser welding requires close contact between solder substrates. This should be carefully fastened to achieve the best results. This is difficult to do on the slim eurus substrate, because it is easy to be bent, especially in the case of extracting large battery modules or components in the extract.

3) Welding parameters (1) The most important in the welding parameters of the welding parameters (1) in the welding parameters are the power density of laser spot, which affects the welding mode and weld forming stability as follows: with laser spot power density Based on small changes in stabilizing thermal soldering, mode unstable welding and stable deep welding welding. When the power density of the laser spot, when the beam mode and the focus mirror are focused, it is important to determine the position of the laser power and beam focus position. Laser power density is proportional to laser power.

There is an optimal value in the influence of the focus position; when the beam focus is in a certain position under the surface of the workpiece (within 1 to 2 mm, it is different from the thickness and parameters), it can get the most ideal weld. Offset from this optimal focus position, the surface of the workpiece becomes large, causing the power density to be small, to a certain range, will cause a variation in the form of welding process. The welding speed on the form of welding process and the stabilizer is not as significant as the laser power and the focus position, only when the welding speed is too large, due to the high heat input too small, there is no maintenance of the stable deep gwatering process.

When actually welding, the stabilizing deep welding or stabilizing thermal soldering should be selected according to the welding of the welding, and the mode is not stable. (2) In the deep cellar welding range, the impact of welding parameters on the deep depth: In the stable deep gauge range, the higher the laser power, the larger the depth, about 0.7 times; and the welding speed changes Dae shallow.

In the optimum position of the focus at a certain laser power and welding speed, the molten is depressed, deviates from this position, the melting depth, or even becomes a mode unstable welding or stabilizing the thermal soldering. (3) The impact of protecting gas, the important use of protective gas is to protect the workpiece from being oxidized during the welding process; protect the focus lens from sputtering of metal steam contamination and liquid fuse; plasma dispersing high power laser welding; cooling Workpiece, reduce thermal impact area. Protective gas is usually used with argon or helium, and nitrogen can be used without high quality requirements.

They have a significant difference in plasma: helium is high due to its high ionized electrophotome, and the tendency to be plasma than argon is small, and thus a larger melting deep is smaller than argon. Within a certain range, as the flow of gas flows increases, the tendency of plasma is increased, and thus the melt is new, but it increases to a certain range. (4) Monitorability analysis of each parameter: In four welding parameters, the welding speed and protective gas flow belong to the parameters that are easy to monitor and maintain stable, and the laser power and focus position is the possibility of fluctuating during welding and difficult to monitor.

Parameter. Although the laser power stability output from the laser is high and easy to monitor, due to the loss of the light guiding and focusing system, the laser power reaching the workpiece will change, and this loss and optical workpiece are contaminated. The situation is related, so it is not easy to monitor, become an uncertainty of welding quality.

The beam focus position is a factor in the impact of welding quality and the most difficult monitoring and control in the welding parameters. At present, the method of manual adjustment and repeated process trial is required to determine the right focus position to obtain the ideal melted deep. However, during the welding process, due to the modification of the workpiece, the thermal lens effect or the multi-dimensional welding of the spatial curve, the focus position can be changed and the permissible range may be exceeded.

With regard to the above two cases, on the one hand, high quality, high stability optical components, and often maintained, prevent pollution, keep cleaning; on the other hand, the real-time monitoring and control method of laser welding process is required to optimize parameters, surveillance arrival Changes in the laser power and focus position of the workpiece, enhance the reliability and stability of laser welding quality. Finally, pay attention to laser welding is a melting process. This means that the two substrates melt in the laser welding process.

This process is very fast, so the entire hot input is lower. But because this is a melting process, it may form a fragile high-resistance metal compound when welding different materials. Aluminum-copper combination is particularly easy to form a metallic compound.

These compounds have shown that there is a negative impact on short-term electrical properties and long-term mechanical properties of the microelectronic equipment. The effects of these intermetallic compounds about the long-term performance of lithium ion batteries are still uncertain. .