Cylindrical cells are commonly joined using several methods, each with distinct advantages and disadvantages depending on the application. Here are the most popular methods:
- Welded
- Spot weld
- Laser weld
- Ultrasonic bonding
- Resistance weld
- Micro tig welding
- Mechanical
- Bolted
- Micro-clinching
- Soldered
Spot Welding
Description: Spot welding uses a controlled electrical current to create localized heat, fusing a nickel strip to the positive and negative terminals of the cells.
World Electr. Veh. J. 2018, 9(2), 22; https://doi.org/10.3390/wevj9020022
Advantages:
- Widely Used: Spot welding is an established, reliable method in the battery industry.
- Strong and Durable Joints: Provides secure connections that can withstand mechanical stress.
- Cost-Effective: Spot welding equipment is relatively affordable compared to other welding technologies.
- Suitable for Automation: Often used in automated assembly lines, which increases production efficiency.
Disadvantages:
- Risk of Cell Damage: Excessive current or misalignment can cause overheating, damaging the cell or reducing its lifespan.
- Limited Precision: Spot welding can be less precise than laser welding, making it challenging for thinner materials or complex designs.
- Not Ideal for Dissimilar Metals: Struggles with joining highly conductive metals like copper and aluminium, which are increasingly used for cell tabs.
Laser Welding
Description: Laser welding uses a high-energy laser beam to locally melt and bond the metal surfaces of the cell’s terminals.
World Electr. Veh. J. 2018, 9(2), 22; https://doi.org/10.3390/wevj9020022
Advantages:
- High Precision: The laser’s focus allows for precise targeting, making it ideal for delicate or small joints.
- Minimal Heat-Affected Zone: Produces minimal heat spread, which reduces the risk of damaging sensitive cell components.
- Flexible with Materials: Effective for various metals, including steel, nickel, and aluminium.
- Automatable and Fast: Ideal for high-volume production environments, allowing for rapid and consistent welds.
Disadvantages:
- Expensive Equipment: Laser welding systems have a high initial cost and may require specialized maintenance.
- Complex Setup and Operation: Requires expertise in alignment and calibration, making it less accessible for smaller manufacturers.
- Safety Requirements: High-powered lasers need strict safety protocols, increasing the operational complexity.
Ultrasonic Welding
Description: Ultrasonic welding uses high-frequency vibrations to generate heat through friction, which joins the metal surfaces without applying direct heat.
World Electr. Veh. J. 2018, 9(2), 22; https://doi.org/10.3390/wevj9020022
Advantages:
- Low-Temperature Process: Generates heat only at the interface, reducing the risk of thermal damage to cells.
- Good for Dissimilar Metals: Works well with copper and aluminium, making it effective for certain modern battery designs.
- Quick and Clean Process: Ultrasonic welding is fast and produces no external heat, sparks, or fumes, which improves workplace safety and reduces cleaning needs.
Disadvantages:
- Equipment Costs and Complexity: Ultrasonic welders are costly and require skilled operators.
- Limited Thickness and Strength: Struggles with thicker materials and may not create as strong a bond as laser or spot welding.
- Alignment Sensitivity: Requires precise alignment for effective joining, which adds complexity to the setup.
Resistance Welding
Description: Resistance welding applies electrical current through the materials, generating heat at the interface due to resistance, resulting in a fused joint.
Choosing the right welding system for battery packs, Amada Weld Tech
Advantages:
- Effective for Multiple Cells: Can handle connecting multiple cells simultaneously, increasing production speed.
- Low Cost: More affordable than laser welding, with relatively simple equipment needs.
- Strong Connections: Provides durable joints, suitable for medium-power applications.
Disadvantages:
- Risk of Excessive Heat: Heat generation can damage cells if not well-controlled, and resistance welding can have a larger heat-affected zone.
- Precision Limitations: Less precise than laser or ultrasonic welding, making it less suitable for fine or delicate connections.
- Less Effective on Thin or Fragile Materials: Better suited to thick, robust materials and may struggle with thinner metal tabs.
Micro TIG Welding
Description: Micro TIG (Tungsten Inert Gas) welding uses an electrical arc between the tungsten tip and the cell tab to create a localised plasma which melts and fuses the materials together. It is a smaller scale version of a typical TIG welding process.
World Electr. Veh. J. 2018, 9(2), 22; https://doi.org/10.3390/wevj9020022
Advantages:
- High Precision: Micro TIG allows for precise control of the weld area, which is crucial for working with small components like battery terminals without causing excess heat or damage.
- Strong and Reliable Joints: The welds created by Micro TIG are very strong, making them suitable for high-stress applications where connections must handle significant currents and vibrations over time.
- Low Heat-Affected Zone (HAZ): Since the heat input is tightly controlled, the area affected by heat is small. This reduces the risk of damaging internal cell components or causing thermal runaway in lithium-ion cells.
- Flexible with Materials: Micro TIG can weld a variety of metals, including difficult materials like aluminium and copper, which are often used in battery tabs. This is a benefit over spot welding, which may struggle with these materials.
Disadvantages:
- High Equipment Cost: Micro TIG welding equipment is more expensive than spot welding or resistance welding setups.
- Requires Skilled Operators: Micro TIG welding demands precision and expertise, as the welder must carefully control arc length, power, and positioning.
- Slower Process: Compared to spot or laser welding, Micro TIG welding can be slower, especially if manual adjustments are required.
- Maintenance Needs: Tungsten electrodes wear down over time and require replacement or sharpening, which adds to maintenance demands.
- Limited for Thin or Fragile Tabs: While Micro TIG is precise, it may still produce too much heat for very thin or fragile materials, potentially causing warping or burn-through if not carefully controlled.
Source: https://amadaweldtech.com/blog/micro-tig-welding-what-is-it-and-how-can-i-use-it/
Mechanical Fastening
Description: Mechanical fastening involves physically clamping or screwing the cells’ terminals together, sometimes with conductive plates or adhesives.
Advantages:
- Non-Permanent: Allows for easy disassembly, making it ideal for applications needing replaceable or modular battery packs.
- No Heat Generation: Reduces risk of thermal damage to cells since no welding or high heat is involved.
- Low Setup Cost: Mechanical fastening requires minimal initial investment and is simpler to set up.
Disadvantages:
- Higher Resistance and Lower Conductivity: Mechanical connections may have higher electrical resistance than welded joints, impacting efficiency in high-current applications.
- Less Durable: May loosen over time with vibrations or shocks, making it unsuitable for applications requiring long-term reliability.
- Bulkier Connections: Fasteners may add weight and take up more space, making them less ideal for compact designs.
Micro Clinching
Description: Micro Clinching is a process of joining two pouch cell tabs by applying high pressure with a punch and die to deform the material forming a mechanical interlock between the tabs.
World Electr. Veh. J. 2018, 9(2), 22; https://doi.org/10.3390/wevj9020022
Advantages:
- Vertical tab connections: Allows for tabs to be attached vertically meaning cells spacing can be reduced.
- No Heat Generation: Reduces risk of thermal damage to cells since no welding or high heat is involved.
- Low Setup Cost: Mechanical fastening requires minimal initial investment and is simpler to set up.
Disadvantages:
- Higher Resistance and Lower Conductivity: Mechanical connections may have higher electrical resistance than welded joints, impacting efficiency in high-current applications.
- Less Durable: May loosen over time with vibrations or shocks, making it unsuitable for applications requiring long-term reliability.
Conductive Adhesives and Soldering
Description: Conductive adhesives or soldering use a conductive material to bond the cell terminals. Soldering uses heated metal (solder), while conductive adhesives use a paste that cures to create an electrical path.
Advantages:
- No High Pressure Needed: Ideal for delicate cells or thin materials where welding might cause damage.
- Good for Prototyping: Conductive adhesives are convenient for small-scale or prototype assemblies, allowing rework ability.
- Simple Equipment: Soldering requires relatively inexpensive equipment and is widely accessible.
Disadvantages:
- Risk of Heat Damage in Soldering: Soldering can overheat the cells if not carefully controlled, which can impact cell performance and safety.
- Lower Conductivity: Conductive adhesives generally have lower conductivity than metal welds, making them less suitable for high-current applications.
- Limited Durability: Adhesive bonds may degrade over time or under high temperatures, reducing their reliability in long-term applications.
Summary
The choice of method depends on factors like production scale, material compatibility, required durability, and cost constraints. Each method balances trade-offs between conductivity, strength, heat management, and cost-effectiveness.
| Joining Method | Advantages | Disadvantages |
|---|---|---|
| Spot Welding | Strong, reliable, cost-effective | Risk of cell damage, limited material versatility |
| Laser Welding | Precision, minimal heat, flexible with materials | Expensive, complex, safety requirements |
| Ultrasonic Welding | Low heat, clean process, good for dissimilar metals | High cost, limited thickness tolerance |
| Resistance Welding | Effective for multiple cells, strong connections | Risk of excessive heat, less precision |
| Micro TIG Welding | Precision, strong, flexible with materials | Expensive, slow, skilled operators needed |
| Mechanical Fastening | Non-permanent, no heat, low cost | Higher resistance, less durable, bulkier |
| Micro Clinching | No heat, no added mass | Sensitive to vibration, pouch cells only, limited tab thickness |
| Conductive Adhesives/Soldering | Simple, good for prototyping, reworkable | Heat damage risk in soldering, lower conductivity |
The Pugh matrix below provides a comparison of all the aforementioned methods.
World Electr. Veh. J. 2018, 9(2), 22; https://doi.org/10.3390/wevj9020022
Thank you for the test materials.
Additionally, it is believed that standards for joining methods and joining methods are needed when joining cylindrical cells.
For example, when joining the CID cathode during laser welding, the separator must not be damaged.
“Spot welding” is not exactly a correct term as it is a geometrical description of the weld. It should be specified as a resistance spot welding or laser spot or usw spot welding, etc. It is an welding industry slang.
good point, thanks, Nigel