The positive electrode of new energy batteries is usually aluminum (Al), and the negative electrode is usually copper (Cu). When multiple battery cells are connected in series or parallel through busbars, the problem of “copper aluminum” dissimilar metal welding is encountered.
The challenge lies in:
1. There are significant differences in physical properties: copper and aluminum have different melting points (Cu: 1083 ° C, Al: 660 ° C), thermal conductivity, and electrical resistivity.
2. Easy to form brittle intermetallic compounds (IMC): such as Al ₂ Cu, AlCu, Al ₄ Cu ₉, etc. These compounds are brittle and hard, with poor conductivity, and are weak links in welded joints, which can easily lead to high resistance, heat generation, and even fracture.
3. Oxide layer: A dense thin film of aluminum oxide (Al ₂ O3) will rapidly form on the surface of aluminum, with a very high melting point (2050 ° C), which will hinder good fusion between metals.
Therefore, traditional fusion welding methods such as TIG/MIG welding are almost unable to be used for high-quality copper aluminum welding. At present, the mainstream industry adopts ultrasonic metal welding technology.
Mainstream technology: Ultrasonic metal welding machine
This is the absolute mainstream technology for welding battery poles (copper/aluminum) and connecting pieces (aluminum/copper) in the current new energy industry.
Working Principle:
Using the vibration energy of high-frequency ultrasound (usually 15kHz, 20kHz, or 40kHz), it is applied to overlapping metal parts under pressure through a horn. The friction and stress generated by vibration will:
1. Destroy the oxide film on the metal surface.
2. Make the metal atoms on the contact surface undergo plastic deformation and diffusion in the solid state (temperature far below the melting point).
3. Form a solid-state metallurgical bond instead of conventional melt welding.
Advantages:
·Solid phase welding: fundamentally avoids the generation of large amounts of brittle intermetallic compounds, resulting in low joint resistance and high strength.
·Energy saving and environmental protection: The energy only acts on the welding area, without the need for power consumption or heating, resulting in extremely low energy consumption.
·Efficient and stable: Welding time is usually completed within a few hundred milliseconds, making it easy to integrate into automated production lines.
·Beautiful and pollution-free: no sparks, no smoke, no need for solder, and the appearance of solder joints is clean.
Key components of the equipment:
1. Ultrasonic Generator: Convert power frequency electricity into high-frequency electrical signals.
2. Transformer/Piezoelectric Stack: Convert electrical signals into high-frequency mechanical vibrations.
3. Booster: Amplify the amplitude generated by the transducer.
4. Horn/Sonorod: Transfer the final vibration energy to the workpiece. Its design and material (usually titanium alloy or high-quality steel) are crucial.
5. Pneumatic pressurization system: Provides and precisely controls the pressure required during welding.
6. Rack and controller: High rigidity rack ensures stability; PLC or dedicated motion controller is used for precise control of welding parameters (energy, time, pressure, power, distance, etc.) and storage of welding formulas.
7. Human Machine Interface (HMI): Used by operators to set parameters, monitor production data, and diagnose faults.
Application scenarios
·Cell level: Welding of the tab and connector of a soft pack battery.
·Module level:
·Welding of the poles (copper or aluminum) and connecting plates (usually aluminum) of square/cylindrical batteries.
·Multiple battery cells are connected in series and parallel to form a battery module.
·PACK level: Connection between modules.
For the welding of positive and negative copper aluminum electrodes in new energy batteries, ultrasonic metal welding machines are currently the most mature, widely used, and comprehensive solution with the highest benefits. It effectively avoids the technical bottleneck of welding copper aluminum dissimilar materials while ensuring welding strength and high conductivity, and is an indispensable core equipment for modern intelligent battery production lines. When choosing, attention should be paid to its process stability, degree of automation, and data traceability capability.