Laser welding has always been an indispensable process in the lithium battery manufacturing process. From stainless steel shells to aluminum shells to polymers, laser welding is widely used. With the continuous development of the industry, higher requirements are put forward for the efficiency and quality of laser welding, and the use of optical fiber transmission laser welding is started. Due to the flexible connection between the welding machine host and the focusing head, this method is easier to match with the assembly line, Realize full automation. The appearance and performance of welding have also been significantly improved.
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Lithium-ion batteries are widely used in various electronic devices (such as mobile phones, notebook computers, PDAs, digital cameras, digital video cameras, etc.) because of their high specific energy, long cycle life, low self-discharge, no memory effect, and no pollution. As well as transportation tools (patrol cars, electric bicycles, electric vehicles, etc.), it has become a high-tech industry supported by my country's energy sector.
Power battery refers to the battery used in electric vehicles. Compared with small-capacity batteries (such as mobile phones, laptop batteries, etc.), it has larger capacity and output power and can be used in electric vehicle driving power and large mobile power applications.
Secondary battery. There are many manufacturing processes for lithium-ion batteries or battery packs, and there are many processes, such as explosion-proof valve sealing welding, tab welding, soft connection welding, safety helmet spot welding, battery shell sealing welding, module and PACK welding. Take the laser welding machine as the process. The materials used for welding of power batteries are mainly pure copper (chemical formula Cu), aluminum (Al), aluminum alloy, and stainless steel.
The laser welding machine has the characteristics of high positioning accuracy, simple operation, CNC programming or teaching mode, simple and easy to understand, high welding depth ratio, high speed, flat, beautiful, and small width of the weld, no need to handle after welding, and high weld quality. The whole machine has a split design, modular structure, and quick fixture replacement. The equipment has high utilization rate and can weld a variety of products. It is suitable for combined applications in various industries and can be used for assembly line operations to improve quality and efficiency. The three-dimensional workbench and fully customized fixture can be controlled by industrial computer or PLC, and can provide a variety of solutions for the needs of different industries.
The following is the process application of laser welding in the lithium battery industry summarized by Huiyao Laser for everyone:
1. Welding of battery explosion-proof valve
The explosion-proof valve of the battery 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 to prevent the battery from bursting. The safety valve (function: the control pressure does not exceed the specified value) has an ingenious structure. This process has extremely strict requirements on the laser welding process. Before the continuous (Continuity) laser welding, the battery explosion-proof valve was welded by pulse laser welding. The welding point and the welding point were overlapped and covered (Cover) to achieve continuous sealing welding, but the welding efficiency was low and the airtightness Relatively poor. Continuous laser welding can achieve high-speed and high-quality welding, and welding stability, welding efficiency and yield can be guaranteed.
2. Welding of battery tabs
The tabs are usually divided into three materials. The positive electrode of the battery uses aluminum (Al) material, and the negative electrode uses nickel (Ni) material or copper-plated nickel (Ni-Cu) material. In the manufacturing process of power batteries, one of the steps is to weld the battery tabs and poles together. In the production of the secondary battery, it needs to be welded with another aluminum safety valve. Welding must not only ensure the reliable connection between the tab and the pole, but also requires a smooth and beautiful weld.
3. Spot welding of battery poles
The materials used for the battery poles include pure aluminum tape, nickel (Ni) tape, aluminum-nickel composite tape, and a small amount of copper tape. The welding of battery electrode strips generally uses pulse welding machines. With the emergence of IPG's QCW quasi-continuous laser, it has also been widely used in battery electrode strip welding. At the same time, due to its good beam quality, the welding spot can be small, It has unique advantages in dealing with the welding of high-reflectivity aluminum strip, copper strip and narrow-band battery pole strip (the pole strip width is less than 1.5mm) (explanation: it can overwhelm the other side's advantageous situation).
4. The power battery shell and the cover plate are sealed and welded
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The shell materials of power batteries include aluminum (Al) alloy and stainless steel (stainless acid-resistant steel). Among them, aluminum alloy is mostly used, generally aluminum alloy, and a few use pure aluminum. Stainless steel is a laser weldable material, especially 304 stainless steel, whether it is pulsed or continuous laser can obtain welds with good appearance and performance.
The welding performance of laser welding of aluminum and aluminum alloys (melting point 660°C) varies slightly depending on the welding method used. Except for pure aluminum and 3 series aluminum alloys, there is no problem in pulse welding and continuous welding. Other series of aluminum alloys choose continuous laser welding to reduce crack sensitivity. At the same time, according to the thickness of the power battery shell, select a laser with appropriate power (referring to how much work the object does in a unit time). Generally, when the shell thickness is less than 1mm, single-mode lasers within W can be considered, and the thickness is more than 1mm. Use single-mode or multi-mode lasers above W.
Small-capacity lithium batteries often use relatively thin aluminum shells (thickness about 0.25mm), and and the like use steel shells. Due to the thickness of the shell, a lower power laser is generally used for welding such batteries. Using Continuity laser to weld thin-case lithium batteries, the efficiency can be increased by 5 to 10 times, and the appearance and sealing are better. Therefore, there is a trend to gradually replace pulsed lasers in this application field.
5. Power battery module and pack welding
The series and parallel connections between power batteries are generally completed by welding the connecting piece and the single battery. The materials of the positive and negative electrodes are different. Generally, there are two kinds of materials: copper and aluminum (Al). Because the copper and aluminum are brittle after laser welding The compound cannot meet the requirements of use. In addition to ultrasonic welding, copper and copper, aluminum and aluminum are generally welded by laser. At the same time, because copper and aluminum conduct heat very quickly, and have very high reflectivity to the laser, and the thickness of the connecting piece is relatively large, it is necessary to use a laser with higher power (referring to how much work the object does in a unit time). Can be welded.
New energy lithium battery industry application scenarios:
Using Lasers for Battery Tab Welding Applications
Battery Tabs Welding with laser
From a welding perspective, the most important aspects of tab welding are the thickness and material of both the tab and the terminal. Conductivity is the name of the game, so battery tabs are generally made of aluminum or copper, sometimes plated with nickel or tin. Terminals may be cold rolled steel, aluminum, or copper, depending upon the physical size of the finished battery.
The most common battery types are cylindrical lithium ion cells around the size (18 mm x 65 mm), large prismatic cells, and lithium polymer pouch cells. Each cell type has a different set of welding requirements.
The key to welding the cylindrical cell type lies in the negative terminal weld, where the battery tab is welded directly to the can as opposed to the separate platform on the positive side. The weld on the negative terminal must not penetrate the can thickness which is typically around 0.3mm. The thickness of the can dictates how thick the tab can be &#; a rule of thumb is that the tab should be 50-60 % that of the can. Cylindrical battery can material is usually nickel-plated steel, and the tab material nickel or tin-coated copper. Nickel plating is preferred over tin because it is more stable; tin&#;s very low boiling point can lead to weld porosity and excessive spatter.
These high capacity cells need thick tabs to ensure a sufficient current carrying cross-section to deliver the pack output. However, the tab connection needs only to deal with the capacity of a single cell. Therefore, thinning or &#;coining&#; of the thick tab material to enable a lap weld or creating a through hole for a fillet weld greatly reduces the size of the weld needed. This in turn reduces heat input to the can, which is always a concern when welding thicker tabs.
For a lap weld geometry, reducing the tab thickness to a 0.25-0.5 mm thickness enables sufficient weld area for strength and capacity while keeping the temperature during the weld low enough to avoid battery damage. Material selection is generally aluminum for both terminal and tab &#; recommended tab materials are and . Avoid aluminum alloy , which cracks when welded. If this material is already specified and cannot be changed, use a pre-form as a third material which will introduce a large amount of silicon into the weld, which prevents weld cracking.
These pouch type cells, which are thin with a rectangular footprint, are really gaining traction for consumer electronics. The terminals on these batteries are made up of thin layers of copper and aluminum foil which are laser welded to tab of copper and aluminum respectively. This weld is traditionally made using ultrasonic technology due to the need to weld through a stack of foil, however, fiber laser welders are now being used for increased weld quality and strength.
The key to success in welding polymer batteries with a fiber laser is making sure that the foils are in close contact and you&#;re using a pulsed laser or even better a wobbling laser to avoid overheating.
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