Research and Application of Airtightness Control of Aluminum Alloy Battery Enclosures

 

Aluminum alloy tailor-welded battery enclosures are a crucial component of power battery cells for new energy vehicles. Their airtightness directly impacts the safety and stability of the entire system. Especially in lithium-ion battery packs that utilize liquid cooling systems, airtightness control is a key technology. By analyzing the liquid cooling structure, assembly process, and welding parameters, this paper proposes improvement measures from the perspectives of material extrudability and welding process optimization, effectively enhancing the airtightness and consistency of aluminum alloy enclosures in lithium-ion battery manufacturing.

 

 

 

With the rapid development of new energy vehicles and energy storage systems, demand for lithium-ion batteries, Lifepo4 power cells, and solar energy storage systems (Lithium Battery Packs) continues to grow in the power and energy storage sectors. To achieve vehicle lightweighting and improved range, aluminum alloy battery enclosures (Battery Enclosures) are widely used in the manufacture of lithium battery packs and battery pack kits due to their excellent strength-to-weight ratio and corrosion resistance.

 

Compared to cast aluminum structures, welded aluminum housings offer advantages such as low mold development costs, high structural flexibility, and superior heat dissipation. However, during the multi-component assembly and welding process, poor airtightness can easily occur, allowing coolant or moisture to penetrate, thereby impacting the performance and lifespan of the lithium-ion battery cell. Poor airtightness control can not only cause system failures such as short circuits and corrosion, but also affect the safe operation of the battery for lithium-ion energy storage systems. Therefore, controlling the airtightness of aluminum alloy housings has become a critical issue in the manufacturing of lithium-ion batteries for new energy vehicles and solar home systems.

 

 

Power battery packs primarily use air cooling and liquid cooling for heat dissipation. While liquid cooling is structurally complex, it offers excellent thermal conductivity and temperature control, making it the mainstream option. Liquid-cooled aluminum alloy housings are typically welded together from multiple aluminum plates and consist of an upper cover, a lower shell, and cooling channels.

 

In products like Lithium SuperPack Batteries and Lithium-ion Batteries for Solar Products, the airtightness requirements of the liquid cooling channel are much higher than those of the housing. Testing requires a dedicated airtightness test fixture, where compressed air is injected under standard temperature and pressure conditions, and the sealing performance is assessed using the pressure drop method. Poor airtightness often leads to leaks, corrosion, and short circuits in the liquid cooling system, posing a threat to the reliability of the entire Lithium Solar Battery system.

 

The primary manufacturing processes for the aluminum sheet welded housing include: aluminum ingot casting, sheet extrusion, sawing, machining, arc welding and friction stir welding, airtightness testing, and assembly. The processing quality of the liquid cooling baseplate directly determines the safety and durability of the entire Lithium-ion Battery Pack.

 

 

Analysis of failed battery tray samples revealed that airtightness defects were primarily concentrated in the welds and baseplate cavity. Approximately 83% of air leaks are caused by poor welds, including problems such as arc-ending center porosity and burn-through; approximately 16% are caused by cracking and delamination in the plate cavity.

 

The main causes of these defects include:

Improper plate extrusion, resulting in poor weld quality;

Improper matching of welding current and speed, resulting in incomplete fusion;

Insufficient clamping of the base plate, resulting in deformation caused by welding shrinkage;

Insufficient strength of the plate flow channel sidewalls, resulting in cracks caused by welding stress.

 

These issues not only affect the structural integrity of the box but can also lead to coolant leakage, threatening the long-term operational stability of the Lithium Ion Battery for Solar Energy System.

 

 

(1) Optimization of Materials and Extrusion Process

To improve the quality of sheet metal welding, we should start with the extrusion die structure and process parameters:

 

Appropriately thicken the upper die and reduce the diameter of the diversion hole to increase the welding chamber volume and improve the hydrostatic pressure.

Adjust the extrusion temperature and speed (e.g., from 475°C to 440°C, and from 3 m/s to 2.4 m/s);

Select a higher tonnage extruder (e.g., from 2800T to 4000T) to increase the extrusion force and material density.

 

These measures effectively improve the weldability of the material and provide a more stable base material quality for subsequent welding.

 

(2) Welding process and deformation control

To solve the welding deformation and air leakage problems, the following measures are taken:

 

Set different currents, voltages, and welding speeds according to the plate thickness and weld requirements;

Add clamping fixtures to prevent the bottom plate from warping and displacement.

Precisely control the heat input to ensure that the weld is fully fused and the surface is smooth.

Perform 100% airtightness testing on the welded Lithium Battery Pack box to ensure no leakage.

 

After the improvement, the airtightness qualification rate of the finished box increased from the original 55% to more than 90%, meeting the application standards of high-performance Lithium-ion Battery Pack and Solar Energy Storage Systems Lithium Batteries Pack.

 

 

 

The airtightness of the aluminum alloy battery box is directly related to the safety, life, and environmental adaptability of the Lithium batteries and Power Battery Cell systems. Through the systematic optimization of the plate extrusion process, die design, and welding parameters, the airtightness problem of the liquid cooling box can be effectively solved, and the product consistency and reliability can be improved.

 

This research result is of great reference value to manufacturers of batteries for lithium-ion energy storage systems, solar home system lithium-ion batteries, and lithium-ion battery packs. In the future, as the application scope of lithium solar batteries and Lifepo4 power cells continues to expand, the high-airtightness and high-reliability manufacturing technology of aluminum alloy battery boxes will become a key quality control link in the new energy industry chain.