Laser Welding & Laminated Busbars for Prismatic Cell Lithium Batteries

A Complete Technical Guide for EV & Energy Storage Manufacturers

With the increasing popularity of EVs, BESS, and industrial lithium-based batteries, there is pressure on manufacturers to continue improving all components within the battery pack. Discussions on battery chemistry (e.g., Li-ion, LiFePO₄, and NMC) typically dominate the conversation; however, there are two critical/overlooked elements that play a direct role in determining performance, safety, and efficiency levels (throughout their lifecycle):

Laser welding/laminated busbars are used to facilitate connecting busbars to prismatic lithium cells.

The design of the busbars within high-energy packs of prismatic lithium cells greatly impacts thermal management, electrical efficiency, vibration durability, short-circuit protection, and long-term reliability directly.

This comprehensive guide explains everything you need to know about laser welding type aluminum busbars for prismatic cells, including:

• Why do prismatic packs need advanced busbar systems?

• What is laser welding vs. other traditional joining processes?

• Benefits of laminated busbar construction and manufacturing processes

• How do I design engineers for optimal performance?

• Manufacturing procedures/operations.

• Applications in EV and energy storage.

• What is the future of hydrogen battery interconnects?

1. What are lithium prismatic battery cells?

Lithium prismatic battery cells are rectangular-shaped aluminum-cased cells that can be used in the following applications:

• Electric vehicles

• E Buses & Commercial EVs

• Energy storage systems

• Industrial battery packs

Compared to cylindrical and pouch cells, they provide:

• Better space utilization

• More structural rigidity

• A simpler, more efficient module design

• Higher energy density per pack

However, prismatic cells also require a precise electrical connection system due to their:

• Flat terminal design

• High current flow

• High packing density

• Thermal sensitivity

Because of this, laser welding and laminated busbars become crucial components of the product.

2. What is a laser-welding busbar?

Laser-welding type aluminum busbars are highly conductive metal connectors (preferably aluminum) that are attached to the terminals of a cell using laser welding technology.

Why Use Laser Welding?

Traditional joining methods include:

• Ultrasonic welding

• TIG welding

• Resistance welding

• Bolted connections

These methods have limitations when used to join components in high-energy-density battery packs. Laser welding has numerous advantages over traditional methods, including:

• Very small heat-affected zone (HAZ)

• High accuracy

• Exceptional metallurgical bond

• Low electrical resistance

• Repeatable automated mass production

Precision is critical in prismatic lithium battery packs. A poorly executed laser weld could result in:

• Increased internal resistance

• Localized heating

• Voltage drop

• Cell imbalance

• Thermal runaway

Overall, using laser-welding busbar technology greatly reduces each of these concerns.

3. What Are Laminated Busbars?

A laminated busbar is an electrical assembly containing multiple layers, which include metal (copper, aluminum) conductors, insulating material layers (PET, Mylar, Nomex, epoxy), and a compact stack. Instead of having multiple individual conductors, they are combined into a single component that has been engineered by an electrical/electronic engineer.

Composition of a laminated busbar’s core structure varies but includes:

• Positive Conductor Layer

• Insulation Layer

• Negative Conductor Layer

• Optional Signal/Monitoring Layers as Required

Laminated busbars provide an efficient design when compared to traditional methods (multiple conductors), especially in terms of both thermal and electrical performance.

4. Why Prismatic Cell Packs Need Laminated Busbars

Prismatic cell packs need laminated busbars in order to provide thermal and electrical performance that is equal to or greater than the performance of traditional wiring methods. The primary reason these cells require laminated busbars is that they are closely packed in modules, creating:

The prismatic cell packs create:

• Elevated Current Density

• Minimal Air Gap

• Thermal Accumulation

• EMI Issues

Laminated busbars provide solutions to the above difficulties.

Key benefits 

1. Reduced Inductance

Due to the close spacing between positive and negative conductors, the overall loop area is reduced (which results in lower inductance). 

Lower loop area = Lower inductance

This is especially important in systems with rapid charge/discharge times (e.g., EVs with heavy batteries, etc.).

2. Improved Heat Distribution

Because of the flat layered design, the heat generated by current flows (positive and negative conductors) is evenly distributed across the total surface area of the busbars. This will also help to decrease the number of hot spots.

3. Space Optimization

Compared to conventional cable harnesses, the use of laminated busbars is beneficial because they will:

• Decrease Overall Module Volume

• Increase the Energy Density of Module Components

• Make Assembly Simple.

4. Improved Safety

Due to the laminated busbar’s insulated layered structure, the risk of short circuits is greatly reduced.

5. Laser Welding vs Bolted Busbars in Prismatic Cells

Let’s compare:

 

When are busbars to be used in laser welding? Examples include laser welding busbars to be used in:

• Automotive electric vehicle battery packs

• High-voltage battery modules

• High-vibration environments

• Long-lifetime applications

Examples of when busbars can be bolted as opposed to laser welding include:

• Industry packs that require servicing

• Development Stages of a Prototype

6. Considerations for Engineering Design

Engineering design considerations for laminated busbar construction using laser welding on prismatic lithium batteries require precision engineering.

1. Current-Carrying Capacity—Based upon:

• Peak current

• Continued current

• Ambient temperature

• Cooling system

Copper has a high conductivity, while aluminum has a weight advantage.

2. Skin Effect at a High Frequency

High ripple currents in fast charging systems create increased losses. Therefore, laminated busbars minimize this effect by having:

• Very thin wall conductor layers

• Very small current paths.

3. Thermal Expansion Matching

Because of the thermal expansion characteristics of prismatic batteries (typically made of aluminum), during charge and discharge cycles, the busbar materials and welds need to take ADA into consideration:

• Coefficient of Thermal Expansion (CTE)

• State of mechanical stress (distribution)

4. Weld Nugget Geometry

The parameters for the laser weld process require optimization based upon:

• Penetration Depth

• Weld Width

• Mechanical Strength

• Contact Resistance

7. Manufacturing Process of Laser Welding & Laminated Busbars

1. Material Selection

• Alloy C11000 copper

• 1050 or 1060 (aluminum)

• Tin Plated copper Busbar to protect against corrosion

2. Material Preparation

• CNC machining for cutting

• Laser cutting

• Stamping

3. Preparation for Laminating

• Tinning

• Nickeling

• Silver plating

Surface pretreatment enhances the following:

• Resistance to corrosion,

• Contact performance and

• Solderability

4. Laminating Insulation

• Heat laminated,

• Bonded with an adhesive,

• Vacuum laminated.

5. Laser Weld Cells to Terminals

• Fiber laser welding

• Fully automated real-time quality control inspection

• Automated robotic systems

6. Inspection and Testing

• Resistance test,

• Pull test,

• Thermal cycle test,

• Vibration test, and

• Insulation voltage test.

Uses of Laser-Welding Aluminum Busbars in Electric Vehicle and Battery Energy Storage Systems

8. Applications in EV & Energy Storage

Laser-welding laminated busbars can be used for many applications, such as

Electric Vehicle Applications:

• Battery packs in two- and three-wheeled electric vehicles

• Electric passenger vehicles

• Electric commercial vehicles

• E-buses

Battery Energy Storage Systems

• Grid energy storage

• PV hybrid systems

• Industrial backups

Fast Charge Systems

• High-speed DC applications

• High-speed switching

9. Safety Features of Lithium Battery Packs

When designing lithium batteries, the most important factor is always safety.

Laser-welding aluminum busbars improve the safety of lithium batteries by:

• Minimizing the contact resistance between conductors

• Reducing the potential for overheating

• Reducing electromagnetic interference (EMI)

• Preventing the loosening of mechanical fasteners

• Providing improved insulation integrity

In prismatic cell packs, even minor differences in resistance may affect how well the packs are balanced. The laser welding process provides consistent electrical connections between each cell in a cell pack.

10. Common Problems and Their Respective Solutions

Problem 1: Aluminum-Copper Welding

Directly welding these two metals can lead to brittle intermetallics forming as a result of the thermal cycles associated with the welding.

Solution:

• Bi-metal transition plates

• Optimize laser parameters for each application.

Problem 2: Pack Expansion

During cycling, cell packs will expand from their original size.

Solution:

• Design busbars with flexibility built into them.

• Use slots for stress relief in busbars.

Problem 3: High Voltage Insulation

High-voltage electric vehicle (EV) packs (in excess of 400V/800V) require an extremely high level of insulation.

Solution:

• Multiple layers of insulation

• Perform partial discharge testing on all busbars used in EV applications.

11. Future Developments in Busbar Technologies

EV manufacturers are migrating toward:

• 800V battery systems

• Ultra-fast charging capabilities

• Higher density modules

• Cell-to-Pack (CTP) architectures

• Cell-to-chassis integration

These developments will require:

• Thinner laminated busbars

• Advanced laser welding automation

• Integrated sensing layers

• Smart busbars with temperature-sensing capabilities.

Numerous battery failures are caused by the following factors:

• Poor welding quality.

• Inequitable current distribution.

• Improper insulation.

• Mechanical fatigue.

An ingenious laser-welding aluminum busbar design will provide you with:

• Lower internal resistance.

• Increased pack efficiency.

• Longer battery life span.

• Higher degree of safety.

• Lower level of warranty claims.

When it comes to EV production & battery integration, investing in quality busbars will ultimately enhance brand reliability.

Conclusion

As prismatic cell lithium batteries become the norm in both the EV market & the energy storage industry, advancement of interconnect systems will continue to be paramount.

Using laminated busbars & laser welding will result in:

• Better electrical performance.

• Lower inductance.

• Better heat management.

• More durability.

• Improved safety.

In modern high-voltage battery packs, busbars are becoming more than just an electrical conductor, they have now become components specifically designed to perform.

Manufacturers that use advanced laser-welding & laminated busbars to optimize their design will have a distinct advantage over their competitors in:

• EV efficiency.

• Timesaving on charging.

• Durability.

• reliability.

If you are designing or manufacturing prismatic lithium battery packs, upgrading to laser-welding laminated busbars should be regarded as not merely an option it should be a requisite for next-generation energy systems.