What is Battery Tab Laser Welding?
Tab welding is a crucial process that directly impacts a battery's performance, lifespan, mechanical strength, and thermal efficiency. Any mistake in this step can lead to safety risks and reduced reliability.
Tab welding is a crucial process that directly impacts a battery's performance, lifespan, mechanical strength, and thermal efficiency. Any mistake in this step can lead to safety risks and reduced reliability.
The choice of welding method largely depends on the tab thickness and materials used. Among the various options, laser welding stands out for its precision, stability, and efficiency.
In this article, we’ll explore laser welding for battery tabs, examining its application across different battery types and the advantages it offers. Read on to discover more!
What is a Battery Tab?
A battery tab, also known as a terminal, is a critical component that connects the cells and enables the flow of electricity. It serves as the pathway for positive and negative currents, which are directed to designated terminals on the module’s busbar (or collector plate). This process allows multiple modules to be linked together, forming a complete battery pack.
Inside the cell casing, battery tabs are attached to current collectors or foils made of highly conductive materials such as copper and aluminum. These collectors efficiently transfer positive and negative currents from the electrodes.
Battery tabs come in various shapes and sizes, making them suitable for a wide range of battery types.
Using Lasers for Battery Tab Welding Applications
Different battery types require specific welding techniques to ensure strong, reliable connections. The most common battery types include cylindrical lithium-ion cells (such as the 18650 model, measuring 18 mm × 65 mm), large prismatic cells, and lithium polymer pouch cells. Each type has unique welding requirements, and laser welding provides a versatile and effective solution for all of them.
Cylindrical Batteries
Cylindrical battery cans are typically made of nickel-plated steel, while tabs are usually nickel or tin-coated copper. Nickel plating is preferred over tin because tin's low boiling point can cause weld defects, such as holes and excessive spatter.
For cylindrical cells, the most critical weld is at the negative terminal, where the battery tab is directly attached to the can. This weld must not penetrate the full thickness of the can, which is usually around 0.015 inches (0.3 mm).
The thickness of the battery tab should be 50–60% of the can’s thickness to maintain structural integrity and welding efficiency.
Large Prismatic Batteries
Prismatic battery cells require thicker tabs to handle high-capacity energy loads. Typically, both the terminals and tabs are made of aluminum, with alloys such as 1080 and 1100 being ideal choices due to their excellent conductivity and weldability.
To minimize heat input and reduce the risk of damage, manufacturers often create through-holes for fillet welds or thin out thick tab material for lap welds. The optimal tab thickness should be reduced to 0.01–0.02 inches to enhance weld strength and protect the battery from excessive heat exposure.
It’s important to avoid aluminum alloy 6061, as it tends to crack when welded. If using 6061 is unavoidable, a 4047 pre-form can be added as a filler material, introducing silicon into the weld to prevent cracking.
Lithium Polymer Batteries
Lithium polymer (LiPo) batteries are thin, rectangular, and commonly used in consumer electronics. These batteries require precise welding of thin sheets of copper and aluminum foil to form terminals.
Traditionally, ultrasonic welding is used for this application since it effectively bonds stacked foil layers. However, fiber laser welding is now being adopted for improved weld quality and strength.
For successful fiber laser welding in LiPo batteries, two key factors must be ensured:
1. The foils must be tightly stacked to ensure uniform welding.
2. A pulsed laser should be used to prevent excessive heat buildup, which can damage the thin foils.
By leveraging laser welding techniques tailored to each battery type, manufacturers can achieve stronger, more efficient connections while minimizing defects and safety risks.
Advantages of Laser Welding for Battery Tabs
Laser welding of battery tabs offers several key benefits during production:
- It improves process stability, resulting in higher system availability.
- The method significantly boosts battery production efficiency.
- No tool changes are required, offering greater flexibility in cell design.
- The process occupies less space compared to other welding techniques.
- It is virtually maintenance-free, reducing downtime and operational costs.
How to Choose the Right Welding Power for Battery Tabs
Proper welding requires the correct power to maintain a stable arc, generate enough heat to melt the joints, and ensure optimal metal transfer. To select the right welding power for battery tabs, follow these steps:
- The welding process is influenced by how materials absorb and conduct energy. Start by understanding how the tabs are assembled. Carefully assess the material to ensure the power setting is appropriate.
- Thicker tabs typically require more power. Use the varying thicknesses in your battery production to create a power gradient.
- The joint design also impacts the required welding power. Examine the joint geometry and adjust the power settings to accommodate design variations.
Conclusion
Laser welding is widely considered the optimal method for welding battery tabs, ensuring high-quality connections within batteries. However, different types of batteries may require different laser welding techniques.
Fiber laser machines are the top choice for battery tab welding. However, selecting the right equipment can be challenging, and failing to do so may result in subpar performance and reduced product quality.
