Why Has Laser Welding Become an Indispensable Option in Power Battery Manufacturing?

In today's rapidly evolving new energy vehicle industry, the safety, range, and consistency of power batteries directly determine the core competitiveness of the entire vehicle. Laser welding technology, with its unique advantages of micron-level precision control, high-efficiency processing capabilities, and low heat impact, has become an indispensable "golden process" in power battery manufacturing – from shell sealing to electrode connection, from module integration to safety component welding, it runs through the entire battery production process, silently safeguarding the stability and reliability of every power battery.

Laser welding is not simply "high-temperature fusion," but an advanced process that achieves rapid melting and strong connection of materials through the precise focusing of a high-energy-density laser beam. Its prominence in power battery manufacturing stems from three core advantages:

1. Precise adaptation to ultra-thin material requirements

Power battery casings and covers mostly use 0.6-0.8mm aluminum alloy sheets (accounting for over 90%), and traditional arc welding easily leads to deformation, penetration, or residual stress. Laser spots can be compressed to the micron level, with concentrated and controllable energy, enabling sealed welding of ultra-thin materials without damaging the internal structure. The weld seam has a high depth-to-width ratio and excellent consistency.

2. Overcoming the challenges of welding highly reflective materials

Battery electrodes and connecting plates often involve highly reflective materials such as copper and aluminum (copper has a laser reflectivity of over 90%, and aluminum reaches 92%), making effective fusion difficult with ordinary welding techniques. Laser welding, through waveform optimization and angle adjustment, can achieve reliable connection of dissimilar metals such as copper-aluminum and aluminum-nickel, and can even weld electroplated nickel to copper, perfectly matching the material requirements of the battery current path.

3. Automation and non-contact advantages

The non-contact welding mode can flexibly handle the complex three-dimensional structure of battery modules, enabling complex trajectory welding such as S-shaped and spiral shapes. The automation yield is improved by more than 30% compared to traditional processes. Simultaneously, the welding process involves no physical contact, avoiding mechanical damage to precision components and meeting the demands of large-scale mass production.

The core principle of laser welding is to adapt to different welding requirements by controlling parameters such as laser energy, focus position, and welding speed. Based on process characteristics, it is mainly divided into the following categories:

1. By energy transfer method: Heat conduction welding vs. Deep penetration welding

• Heat conduction welding: Laser energy acts only on the material surface, causing the surface layer to melt and solidify through heat conduction. It is suitable for welding thin materials (usually <1mm), with a weld width greater than the depth, resulting in less deformation but limited penetration depth.

• Deep penetration welding: High-power laser focusing instantly forms a "keyhole," allowing heat to penetrate rapidly into the material. It offers fast welding speed and a small heat-affected zone, enabling simultaneous welding of multiple layers of material. It is the mainstream choice for applications such as power battery casing sealing and module connection. The core difference between the two lies in the laser power density – when the power density reaches a critical value, the welding mode changes from heat conduction welding to deep penetration welding. The specific critical value needs to be adjusted according to the material type.

2. By welding form: Penetration welding vs. Seam welding

• Penetration welding: The connecting piece does not require punching, making processing simple, but it requires a high-power laser, resulting in lower penetration depth and relatively weaker reliability.

• Seam welding: The connecting piece requires a pre-reserved gap. Laser energy achieves fusion through the gap, requiring only low-power equipment, resulting in higher penetration depth and stronger reliability, but the processing technology is more complex.

3. By laser output mode: Pulsed welding vs. Continuous welding

• Pulsed welding: The laser outputs energy in pulses, concentrating energy instantaneously, making it suitable for welding materials prone to porosity and cracking, such as aluminum alloys. By selecting waveforms such as peak waves and double-peak waves, defects can be reduced – for example, the gradual decline part of the double-peak wave can extend the cooling time of the molten pool, effectively suppressing the generation of pores;

• Continuous welding: The laser continuously outputs energy, resulting in a stable heating process, a smooth weld surface without spatter, and no cracks or depressions. It is especially suitable for aluminum alloy welding. However, it requires extremely high precision in workpiece assembly (small spot size, deviation needs to be <0.1mm) to avoid incomplete fusion problems.

The welding requirements for different components of power batteries vary greatly, and laser welding processes need to be customized according to the specific application scenarios:

1. Explosion-Proof Valve Welding

The explosion-proof valve is the pressure relief channel when the battery overheats. It requires a sealed weld on an 8mm diameter aluminum sheet to withstand a burst pressure of 0.4-0.7 MPa. Using continuous laser welding instead of pulsed welding improves weld seal integrity by 50%, completely eliminating the risk of electrolyte leakage and providing the first line of defense for battery safety.

2. Housing and Cover Plate Sealing

As the "outer shell protection" of the battery, the welding of the housing and cover plate directly affects airtightness. There are two main processes:
• Side welding: Welding spatter is less likely to enter the inside of the battery cell, but it requires extremely high material cleanliness and laser stability;
• Top welding: High mass production efficiency and simple equipment integration, but requires strict control of spatter contamination.

3. Terminal Welding

The positive (aluminum) and negative (copper) terminals need to withstand a tensile strength of ≥500 MPa and must not have "blowhole" defects. Because the terminal mating surface (approximately 6mm in diameter) is prone to residual oil and impurities, actual production requires "pre-weld plasma cleaning + power gradient control" to ensure defect-free welds and stable current conduction.

4. Connector Welding

Connectors are responsible for connecting battery cells in series/parallel and often involve welding dissimilar materials such as copper and aluminum, which can easily generate brittle intermetallic compounds, leading to reduced conductivity. Through a laser-ultrasonic composite process, the formation of these compounds can be suppressed, improving the mechanical strength and conductivity of the welded joint.

5. 4680 Large Cylindrical Battery Full Tab Welding

The full tab structure of the 4680 large cylindrical battery increases the welding area by 5 times, but tab folding can easily lead to misalignment and short circuits. By employing beam shaping technology (such as annular beam spots), multi-tab simultaneous welding can be achieved, reducing heat input by 40%, ensuring connection reliability while avoiding damage to the internal structure of the battery.

6. PACK Module Welding

When the thickness of copper/aluminum connecting tabs reaches 2mm, high-power fiber lasers of 6kW or more are required for penetration welding. The investment in welding equipment for a single GWh production capacity is approximately 10-30 million RMB, which is one of the core equipment investments in the module integration stage, directly affecting the connection stability and heat dissipation efficiency of the module.

The ACEY-LWM galvanometer-based gantry fiber laser welding machine integrates a high-performance fiber laser source with our proprietary design, delivering exceptional rigidity and operational stability. Its precision-guided rail mechanism, powered by responsive servo motors, ensures accurate high-speed performance. This equipment is specifically engineered for prismatic and soft-pack lithium battery module assembly applications.

As power batteries develop towards higher energy density and longer cycle life, laser welding technology is also continuously iterating:

1. Intelligent Monitoring and Closed-Loop Control

In the future, "real-time visualization of the welding process" systems will become widespread. Through high-speed cameras, spectral analysis, and other technologies, defects such as pores, incomplete fusion, and cracks will be detected online, and welding parameters will be automatically adjusted to achieve a complete closed-loop process of "detection - feedback - optimization," further improving yield and consistency.

2. Adaptation to Solid-State Battery Welding

The electrolyte of sulfide solid-state batteries is heat-sensitive, and the thermal effects of traditional laser welding may lead to performance degradation. Ultrashort pulse picosecond lasers (heat-affected zone < 10μm) have become a research focus, enabling precise connections while maximizing the protection of electrolyte stability.

3. Multi-Process Integration and Innovation

Composite welding processes such as laser-ultrasonic and laser-arc welding will be further promoted. These processes leverage the precision advantages of laser welding while using other processes to compensate for the shortcomings of a single technology, adapting to the welding needs of more dissimilar materials and complex structures.

Laser welding of power batteries may seem like a "local process," but it actually affects the overall battery safety, range, and cost – a precise weld can reduce the risk of electrolyte leakage; efficient welding can improve mass production efficiency; and an innovative solution can adapt to higher energy density battery structures. In today's increasingly competitive new energy vehicle industry, differences in process details often determine a product's core competitiveness. The continuous iteration of laser welding technology not only represents an improvement in power battery manufacturing levels but also reflects the new energy industry's pursuit of high-quality development.

In the future, with continuous breakthroughs in intelligent, localized, and composite technologies, laser welding will continue to empower the power battery industry, providing stronger technological support for the safe and long-range driving experience of new energy vehicles.