Using aluminum and copper for battery tab to cell welding improves electrical efficiency and battery module/battery pack performance

As the world becomes more mobile and components become smaller, the demand for longer lasting batteries has been increasing. Increasing battery life requires lower electrical resistance to reduce loss. New laser sources, including single mode fiber lasers and lasers with nanosecond pulses, provide an important opportunity to reduce resistance by enabling the joining of aluminum and copper battery tab material – reducing resistance and improving performance. Tests have shown the technology works well with metal thickness of less than 0.25 millimeters (mm), providing good pull and peel strengths in these dissimilar joints.

A brief history of battery pack manufacturing

This article concentrates on commonly used cylindrical cell batteries to explain the concept of dissimilar metal joining with lasers. The same technology can also be used for some other battery types, including pouch cells, which typically feature one aluminum and one copper tab that requires an electrical connection to the busbars.

Most cylindrical battery cans are made of cold rolled steel (CRS) that has been nickel-plated for corrosion resistance. Figure 1 shows one of the most common cells – lithium ion 18650. To connect multiple cells together, or connect one cell to outside equipment, a strap or tab must be connected to the battery.

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Historically, tabs were made of nickel, stainless steel, nickel plated steel, or Hilumin® (an electro nickel-plated diffusion annealed steel strip) due to their similar properties and the ease with which they can create a fusion bond. These materials join well in a variety of welding techniques, including resistance spot welding, pulsed arc welding, and laser welding.

As the demand for battery and battery pack performance increases, new materials are being considered to improve current delivery. When we assume a certain type of battery is being used, the material of the two terminals of the battery is a given and can’t be changed by the battery module manufacturer. So a further optimizing of the electrical performance of the battery module requires consideration of dissimilar metal bonding to allow the usage of highly electrical conductive battery tabs to the battery terminals.

The benefits of dissimilar joining for battery applications

Designers of battery packs for hybrid and electric automobiles, motorcycles, buses, heavy industrial vehicles, and hand-held power tools are looking for more energy to support the vehicle or device and increase its life. To do this, they must change the batteries’ electrode, isolator, and electrolyte, and lower its internal resistance to reduce energy losses on a battery cell level. The lower the loss, the more efficiently energy is stored in the battery. These improved batteries store more energy and can also charge and discharge faster, as measured by the battery’s “C” rate– the ratio between the charge/discharge acceptance and its capacity.

2018 07 27 090455The higher voltages and currents generated by improved batteries means the battery interconnection (battery tab) must improve its electrical conductivity. The higher electrical conductivity results in lower electrical losses when charging and discharging, so more electrical energy is available for the vehicle or device powered by the pack. By improving the electrical conductivity, the pack also stays cooler during operation, which provides additional performance and battery lifetime benefits. Last, but not least, improving battery performance lowers costs, because fewer batteries are required for a particular performance level.

The three options for improving battery interconnect performance are using thicker tabs to carry more current, using different tab materials (for example, copper or aluminum) with higher conductivity, or creating a larger tab to battery pole contacting area.

In the past, steel and nickel-based materials were commonly welded to the CRS terminals. However, more recently, as batteries have move towards higher capacity and higher “C” values, designers began looking at using aluminum or copper materials for tabs to reduce electrical losses. See Figure 2.

Challenges of using traditional Nd:YAG lasers for welding dissimilar metals

This rise in the use of dissimilar material welding comes with a variety of challenges for traditional welding options like pulsed Nd:YAG (neodymium-doped yttrium aluminum garnet) lasers, which typically make spots that are 0.5 mm in diameter with one pulse. Each weld pulse takes between 1 and 10 milliseconds; depending on its power level, the laser can generate about 10 of these pulses every second. To create a joint with sufficient electrical and mechanical properties, between 2 and 50 welding spots must be placed on each battery pole. See Figure 3.

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This method worked well for the traditional battery tab materials because of their weldability. However, welding of dissimilar materials is significantly more challenging because of:

  • Different melting temperatures (see Table 1)
  • Different thermal expansion coefficients
  • Different absorption coefficient of laser light
  • Incompatible chemistry and atomic structures

Joining aluminum to stainless steel has always been an impossible welding combination. The mixing of these two metals creates a brittle intermetallic zone leading to weld cracks.

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Innovative laser welding technologies

New laser technologies are rewriting the textbooks on which materials can be joined together. Single mode fiber lasers and lasers with nanosecond pulses are joining new combinations of metal that were previously not considered compatible.

The single mode laser can be focused to spot diameters of 20-50 microns – smaller than the diameter of a human hair! This makes a very small welding line of 20-50 microns wide, which can be pulsed like “a hot knife through butter” to make a weld. The linear speed of this laser beam movement is typically in the 100 to 1000 mm/sec (4-inch-40-inch/second) range. See Figure 4.

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To create sufficient joint area, the length of this joint needs to be 10 to 100 mm per battery pole. To fit this onto the 3 to 6 mm diameter available on a battery pole, the line must be in a spiral shape or concentric circles, rather than spots. Using a galvo scanning weld head, the total weld can be very fast; it takes about 50 milliseconds of weld time.

Another method of welding dissimilar metals is to concentrate the laser energy in time by using nanosecond pulsed fiber welding instead of the traditional millisecond pulse. The weld pulses are typically 100,000 times shorter, providing energy in a much shorter period. This increases the laser peak power level by the same amount. The spot size is also very small, about 30 to 40 microns. The high peak power on a small area results in such a high peak power density that all metals are molten. This process can be best described as “pushing a hot needle in the material and pulling it out again.” The spots are very small, so a great many spots are needed, typically 10,000 or more. As the timeframe for creating one spot is very small, the laser can be fired at high repetition rates, typically 30 kilohertz (kHz) and above.

2018 07 27 090628The best method of getting enough weld spots with the nanosecond laser on a small area like a battery pole is to make a line coiled into a spiral. This spiral is typically welded from the inside to the outside, so the laser beam always “sees” a fresh and cold piece of metal in front of it. If the laser went from the outside to the inside, there would be heat build-up and increased penetration depth towards the center, as the part heats up during the welding.

Figure 5 shows an example of a spiral weld made on aluminum tab material. Testing showed single layer shear strengths of around 44 N (10 pounds) and double layer shear strength at around 88 N (20 lbs.).

Figure 6 is an application photo showing an aluminum battery tab welded to a nickel-plated cold rolled steel can using the spiral weld technique. A closer look at the cross sections reveals that the spot welds do not show the characteristic form of conventional pulsed spot welds – they more closely resemble multi‐staking. The intermetallic zone was less than 10 microns. Pull strength was good and peel strength was adequate. There was barbed solidification of aluminum into steel.

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One example of the new technology is AMADA MIYACHI’s 70-Watt LMF70-HP OEM fiber laser, which can be integrated into the LMWS pulsed fiber laser welding system. The new technology is an advanced processing system for welding battery cans with wall thicknesses of 300-350 microns. It features shorter pulses, resulting in less mixing of materials, and hence less of an intermetallic zone and less brittleness with aluminum tab materials. This laser solution is good for contract manufacturing settings, where operators may be producing one product one day and something different the next. The XY galvo program quickly positions welds; a new program can be loaded in as little as five minutes, and operators can be ready to start the next product.

New battery tab welding technologies widen the design portfolio by providing good solutions for dissimilar material joining

The new nanosecond pulsed fiber laser and the single mode fiber laser provide opportunities for dissimilar metal joining and show great potential as a solution for welding battery tabs to cells. Allowing for aluminum and copper tab material, which reduce electrical resistance and improve battery performance, the new technology shows great promise for a wide range of industries.

Published inProduction

AMADA MIYACHI EUROPE announces the availability of the LMWS Pulsed Fiber Laser Welding System. Paired with the ML-7370D 70W pulsed fiber laser, the LMWS offers an advanced processing system ideal for welding dissimilar metals, including copper (Cu) to aluminum, aluminum to stainless steel (SS) and steel, and copper to stainless steel. The LMWS enables the joining of aluminum and copper battery tab material – reducing resistance and improving performance. It is also a good choice for Cu-SS thin sheet welding and plastic welding.

2018 07 27 084134With the ML-7370D 70W pulsed fiber laser, more electrical energy is available for the newest generation of smaller, lighter, more cost-effective, and reliable battery packs used in hybrid and electric automobiles, motorcycles, buses, and heavy industrial vehicles, as well as hand-held power tools. By improving the electrical conductivity, the pack stays cooler during operation. This provides additional benefits to both pack performance and battery lifetime. Improving battery performance also lowers battery pack costs, because fewer batteries are required for a particular performance level. Weight and size of the pack is similarly positively influenced.

Tests have shown that the new high-speed fiber laser welding system works well for welding thin metals up to 250 microns thick. This is an ideal tab thickness for battery cans with wall thicknesses of 300-350 microns. The new technology features shorter pulses with a higher peak power than traditional laser options. The shorter pulse results in less mixing of materials, and hence less of an intermetallic zone and less brittleness with copper and aluminum tab materials.

The highly configurable, compact LMWS unit is designed for lean manufacturing. By simply changing the settings, this laser can also mark, engrave, cut, drill, and ablate thin materials. The versatile high-power, high-speed laser LMWS is available with a variety of integration options to match process needs. It comes standard with an XY galvanometric scanner. A rotary stage option is also available. 

The LMWS unit can be used for several weld types, including single point object arrays, basic shapes (rectangle, circle, spiral), wobble function and vector graphics including CAD and line-drawings, and logos.

The LMWS complies with IEC13849 – 1, category 3 PLd safety circuitry requirements for ease of usage and integration into any quality system.

Published inEquipment

Perfect benchtop operation and designed for lean manufacturing

2018 05 14 102544Amada Miyachi Europe announces its new LMWS low-cost Laser Marking Workstation, specifically designed for benchtop operation. A major facelift to Miyachi’s LMW2020 and LMW2030 marker workstations, the LMWS features a fresh design, available as an operator-safe Class 1 or open Class 4, with improved functionality. Designed for lean manufacturing, LMWS offers the widest range of marking capability in its class.

The versatile and easily configurable LMWS is ideal for marking metals, ceramics, and many plastics, and also has cutting, drilling, and welding capabilities. Requiring only minimal workspace, the updated unit is perfect for low volume production and research and development environments in the automotive, medical, aerospace, electronic components, and battery industries. Although the design has been modernized and several features added, the new LMWS is available at a reduced price point.

Standard LMWS models are powered by Miyachi’s popular 10-50W ML fiber laser markers and use the same graphic user interface for easy transfer from prototype to production phase. Although separable from the base LMF, the two machines are designed to function as one unit.

The fast and precise motorized Z axis and rotary stage make for easy adjustment of part and focus. The spring loaded manual door opens for easy 270 degree access to parts and tooling, and the large viewing window allows for easy mark monitoring. The LMWS is equipped with F-Theta 100mm, 160mm and 254mm lens options for marking various parts and sizes. The LMWS features an optional compact motorized rotary for marking cylindrical parts, as well as an optional programmable Z-axis.

Published inMachinery

Perfect benchtop operation and designed for lean manufacturing

2018 04 20 072535Amada Miyachi Europe announces its new LMWS low-cost Laser Marking Workstation, specifically designed for benchtop operation. A major facelift to Miyachi’s LMW2020 and LMW2030 marker workstations, the LMWS features a fresh design, available as an operator-safe Class 1 or open Class 4, with improved functionality. Designed for lean manufacturing, LMWS offers the widest range of marking capability in its class.

The versatile and easily configurable LMWS is ideal for marking metals, ceramics, and many plastics, and also has cutting, drilling, and welding capabilities. Requiring only minimal workspace, the updated unit is perfect for low volume production and research and development environments in the automotive, medical, aerospace, electronic components, and battery industries. Although the design has been modernized and several features added, the new LMWS is available at a reduced price point.

Standard LMWS models are powered by Miyachi’s popular 10-50W ML fiber laser markers and use the same graphic user interface for easy transfer from prototype to production phase. Although separable from the base LMF, the two machines are designed to function as one unit.

The fast and precise motorized Z axis and rotary stage make for easy adjustment of part and focus. The spring loaded manual door opens for easy 270 degree access to parts and tooling, and the large viewing window allows for easy mark monitoring. The LMWS is equipped with F-Theta 100mm, 160mm and 254mm lens options for marking various parts and sizes. The LMWS features an optional compact motorized rotary for marking cylindrical parts, as well as an optional programmable Z-axis.

About Amada Miyachi Europe

Amada Miyachi Europe is a leading manufacturer of equipment and systems for Laser Welding, Laser Marking, Laser Cutting, Resistance Welding, Hermetic Sealing and Hot Bar Reflow Soldering & Bonding.  We customize our products around specific micro-joining applications for all our customers around the globe. Amada Miyachi Europe product markets include medical devices, battery, automotive, solar industry, electronic components and aerospace.  We are an ISO9001 certified company. Contact Amada Miyachi Europe at This email address is being protected from spambots. You need JavaScript enabled to view it.. Find out more about the company’s products and services at www.amadamiyachi.eu

Laser Welding Workstations for precision laser spot and seam welding

AMADA MIYACHI EUROPE announces the availability of its MIYACHI EAPRO NOVA3 Laser Welding Workstations, ideal for precision spot- or seam welding of metal parts, including medical, automotive, electronic, and aerospace components.

2017-01-10 092352The NOVA3 is an excellent choice for seam sealing of medical devices and high frequency aerospace radar components, spot welding of small mechanical parts and battery housings, as well as hermetic seam welding of sensors, batteries and battery packages. The MIYACHI laser welders can join a wide range of stainless steels, nickel alloys, titanium, aluminium, and copper.

The modular, flexible, lean-manufacturing-ready NOVA3 Series Laser Welding Workstations feature CE-approved, Class 1 eye-safe enclosures. The stable and ergonomic platform facilitates continuous production and stress-free, concentrated, and effective operators. An integrated touchscreen enables easy programming.

Comprised of high performance ruggedized industrial laser equipment, the NOVA3 is customizable to specific production requirements. It can be equipped with pulsed Nd-YAG lasers up to 600W, continuous wave fibre lasers up to 5000W and quasi-continuous wave (pulsed) fibre lasers up to 600W average power. Manual, pneumatic, and motorized door configurations are available, with horizontal or vertical opening direction. The NOVA3 offers servo motor driven axis (XYZ) CNC motion.

More information on AMADA MIYACHI EUROPE’S NOVA3 Series Laser Welding Workstations can be found at http://www.amadamiyachieurope.com/products/laser-welding/nova3-laser-welding-workstations/.

About Amada Miyachi Europe
AMADA MIYACHI EUROPE is a leading manufacturer of equipment and systems for Laser Welding, Laser Marking, Laser Cutting, Resistance Welding, Hermetic Sealing and Hot Bar Reflow Soldering & Bonding.  We customize our products around specific micro-joining applications for all our customers around the globe. AMADA MIYACHI EUROPE product markets include medical devices, battery, automotive, solar industry, electronic components and aerospace.  We are an ISO9001 certified company. Contact AMADA MIYACHI EUROPE at This email address is being protected from spambots. You need JavaScript enabled to view it..">This email address is being protected from spambots. You need JavaScript enabled to view it.. Find out more about the company’s products and services at www.amadamiyachi.eu.

Published inMachinery

Acquisition expands resistance welding product offerings, service expertise

AMYE LogoAmada Miyachi Europe announces that it has acquired Macgregor Welding Systems of Suffolk, England, a leader in the design and manufacture of precision micro joining equipment. MacGregor Welding Systems products include DC micro resistance welding equipment, micro pulsed arc and percussive arc and other welding technologies. With this acquisition, Amada Miyachi Europe is able to expand its range of products and services to meet the complete joining needs of its global customer base.

“Acquiring MacGregor creates an excellent opportunity to grow the business through the effective collaboration of the Amada Miyachi Europe and MacGregor teams and  to further develop new resistance welding and other welding products that meet the demands of modern industrial customers worldwide,” said David Fawcett, Group CEO and President Amada Miyachi America and Amada Miyachi Europe.

MacGregor Welding Systems produces resistance welding equipment. Additionally, the company designs and produces automatic and semi-automatic integrated resistance welding and related process systems, ranging in size and complexity from single work cells to fully-integrated, multi-station production line systems. The company’s in-house expertise in mechanical engineering, electronics design, software, and power system control engineering enables it to build customized equipment to meet each customer's specific requirements.

“We believe that the MacGregor Welding Systems has developed superior engineering capabilities, excellent customer relationships and a differentiated line of products which complement our line of business,” Fawcett added.

About Amada Miyachi Europe
Amada Miyachi Europe is a leading manufacturer of equipment and systems for Laser Welding, Laser Marking, Laser Cutting, Resistance Welding, Hermetic Sealing and Hot Bar Reflow Soldering & Bonding.  We customize our products around specific micro-joining applications for all our customers around the globe. Amada Miyachi Europe product markets include medical devices, battery, automotive, solar industry, electronic components and aerospace.  We are an ISO9001 certified company. Contact Amada Miyachi Europe at This email address is being protected from spambots. You need JavaScript enabled to view it..">This email address is being protected from spambots. You need JavaScript enabled to view it.. Find out more about the company’s products and services at www.amadamiyachi.eu

Published inProduction