Necessity of Ultrasonic Metal Welding in Power Battery Production

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The role of ultrasonic metal welding in power battery production is not only reflected in its specific applications but also in its irreplaceable role in the lithium battery tab welding process compared with laser welding.

Applications of ultrasonic metal welding in power battery production

A power battery, often referred to as a rechargeable battery, is a type of energy storage device capable of converting chemical energy into electrical energy, commonly used in various applications ranging from portable electronics to electric vehicles.

Due to the complexity of the power battery production process, the particularity and diversity of materials, and the sensitivity and high standards of process parameters, the technological advancement of production and manufacturing equipment has become a key factor in power battery equipment.

The production process of lithium batteries involves cell manufacturing (including electrode fabrication, coating, drying, and electrolyte filling), cell assembly (stacking or winding electrodes, inserting into casings, and sealing), cell testing (quality checks and performance testing), and battery pack assembly (integrating cells into modules, connecting electrical components, and final pack assembly).

ultrasonic metal welding

1. Ultrasonic metal welding is predominantly used for welding the tabs of lithium-ion batteries. 

Tabs are conductive metal pieces that extend from the battery cell and are made from aluminum (positive) and copper (negative) foils. Ultrasonic welding technology joins these layered foils to connectors, ensuring excellent electrical conductivity and low internal resistance. This process is essential for both prismatic and pouch cells:

   – Prismatic Cells: Typically have aluminum positive connectors and copper negative connectors.

   – Pouch Cells: Use copper or nickel/copper-plated connectors.

2. Power batteries often involve welding multiple layers of thin metal sheets. 

Ultrasonic metal welding is ideal for this due to its ability to bond without melting, maintaining low heat input and avoiding damage to the battery’s internal structure. This application is particularly important for ensuring low internal resistance and high electrical conductivity in multi-layer structures.

3. The anode and cathode of lithium-ion batteries need to be connected to their respective tabs. 

Ultrasonic metal welding technology provides a reliable and efficient method for these connections, ensuring minimal heat impact and maintaining the integrity of the battery’s internal components.

4. Ultrasonic welding is also used for connecting busbars, terminals, and other components in battery modules and packs, where specialized battery pack welders ensure robust electrical connections.

This application is crucial for ensuring robust electrical connections that can handle high current loads without significant power loss or heating.

5. In the assembly of battery packs, ultrasonic welding, performed by battery pack welders, is used to join cells together and ensure the integrity of the pack.

This includes both series and parallel connections, where the quality of the welds directly impacts the overall performance and safety of the battery pack.

6. During the initial manufacturing stages of the battery, ultrasonic welding is used to join foil materials that make up the electrodes. 

This ensures that the electrodes have excellent conductivity and are free from contaminants that could affect battery performance.

ultrasonic metal welding

Why is Ultrasonic Welding Irreplaceable in the Welding of Lithium Battery Tabs?

Ultrasonic welding technology holds a unique and irreplaceable position in the welding of lithium battery tabs due to its technical advantages and suitability for the specific requirements of this application. The key reasons are detailed below:

1. Ultrasonic metal welding operates through solid-state bonding, which means that the materials being welded do not melt.

This near-cold welding process brings several benefits:

No Melting Defects: Since the materials do not melt, issues such as brittleness, porosity, and intermetallic compound formation, common in fusion welding methods, are avoided.

Low Internal Resistance: The absence of melting ensures the weld joint has very low electrical resistance, ensuring efficient current flow capability.

2. Post-welding, ultrasonic welds exhibit excellent electrical conductivity due to the high-quality bonds formed between the metal layers.

This is vital for the performance of the battery as it ensures that the current can flow with minimal resistance, reducing heat generation and improving battery efficiency.

3. Minimal Thermal Impact

The ultrasonic metal welding process generates much less heat compared to other welding methods. 

Low heat input prevents damage to the battery’s internal components, such as the electrolyte and separators, which could otherwise lead to leaks or short circuits.

In addition, it avoids problems associated with thermal expansion and contraction, such as warping or degradation of materials.

4. Ultrasonic welding is particularly effective for welding multiple layers of metal foils, which are common in battery tabs:

No Need for Surface Preparation: Ultrasonic metal welding can join oxidized or plated surfaces, reducing the need for extensive pre-welding preparation.

Flexibility in Layer Compression: Unlike laser welding, which requires precise control to avoid air gaps, ultrasonic metal welding can handle slight irregularities in layer compression, making it more adaptable and robust for multi-layer applications.

Comparison with Laser Welding

While laser welding is also used in battery production, it has certain limitations when compared to ultrasonic metal welding for tab welding:

Higher Internal Resistance: Laser welding can result in higher internal resistance due to the melting and solidification process, which can create defects and impurities at the weld joint.

Thermal Impact: The higher heat input of laser welding can cause damage to the battery cells and lead to thermal expansion issues.

Material Sensitivity: Laser welding is more sensitive to the surface conditions of the materials.

Laser welding has strict requirements for the air layers between the layers of the welding materials. When using laser welding for multi-layer tabs, complex fixtures are needed to compress and compact the tabs.

If there are gaps between the layers creating air layers, welding defects are likely to occur. In contrast, ultrasonic metal welding is not subject to these limitations and can proceed directly with welding.

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