Battery Welding

Battery applications often join metals that can be challenging to weld. Copper, aluminum, and nickel are commonly used in battery construction, and while welding a material to itself is easy, welding dissimilar combinations, such as copper to nickel, can be problematic.

Copper

A wonderful electrical conductor, copper is often at the center of many battery designs, used in terminals and/or bus bars. Copper’s high thermal conductivity and low melting point make it very weldable, but if the joint is to a metal with very different conductive and thermal properties, such as nickel, getting quality welds requires careful design of the joint. A joint design might require heat sinking, or beam access to the weld area from an unorthodox angle, or even a specialized weld head to keep the copper component of the weld from “blowing out.” There are also copper materials that are cladded or alloyed that might be cost effective in an application and, in many cases, easier to weld.

Aluminum

Aluminum is another material of choice for use in batteries, due to its low cost, light weight, and good conductivity. However, not all aluminum types have the same weldability. Some aluminum series and alloys have a propensity for hot cracking and are very difficult to join. The process used, electron beam or laser, can become critical, and certain series of aluminum, such as the 5000s, tend to always yield marginal results. When utilized in battery production, the aluminum grade must be carefully selected and rigorously tested, and the welding should be done by a qualified vendor with appropriate experience.

Nickel

A strong material with excellent corrosion resistance and good electrical properties, nickel is used in battery terminals and interconnects. Nickel is stronger than copper and aluminum, and welds more readily as well. The issue is generally joining nickel to copper or aluminum, which have much lower melting points. These types of joins have to be carefully designed and executed, with testing to ensure quality. As mentioned above, there are cladded materials, as well as specialty alloys, that can make executing some of these difficult weld combinations feasible and cost effective.

An issue with all the materials noted above is reflectivity, especially when laser welded. When a laser beam hits a material, a percentage of the energy is absorbed, and a percentage is reflected. Copper, nickel and aluminum are highly reflective, and require higher power densities to create the necessary seal between components. The type of welding process also comes into play here, as well as the type and color of the laser.

At EB Industries, we have decades of experience welding the metals used in battery construction. We’ve worked with pure metal, alloys, and cladded materials, and have successfully joined some of the most difficult to weld combinations of metals by using proprietary processes and technology to minimize the heat input required to produce an acceptable weld.

Fusion welding — using electron beams or lasers — is the best way to weld battery components. Both electron beam and laser welding have high power densities, pinpoint accuracy, and lend themselves to automated welding processes and small, miniature weld applications. Both processes make welds that are mechanically strong and have high current carrying capacity.

The specifics of the process used depends on requirements and standards, the configuration of the welds involved, the materials to be joined, etc. Both laser welding and electron beam welding can be cost effective, depending on the parameters of the project.

Typically, bus bars are flat strips, solid metal bars, or in some cases, hollow tubes. However, battery array configurations are becoming more compact, and designs are continually evolving. Installations in electric vehicles, drones and increasingly smaller devices have led engineers to develop battery systems with complex form factors. To accommodate design requirements, bus bars need to be bent, cut, and welded across three dimensions. To meet these requirements, designers are looking for welding providers that can meet form needs, deliver a solution that scales, and provide testing to ensure safety and reliability.

Modern bus bar designs also require the welding of differing materials, often with diametrically opposed properties thermal and electrical properties. This necessitates the balancing of heat transfer, thermal and electrical conductivity, mechanical strength and melting points in the weld development, and then designing a complete process to quality welds at high production rates in a cost-effective manner.

Burst disks, also known as pressure safety discs, rupture discs, or burst diaphragm, are major safety features on many batteries.

Basically, a burst disk is a component of the battery shell that is designed to mechanically fail if the pressure in an individual battery cell reaches an unsafe level. The “burst” and subsequent release of pressure prevents a runaway failure of the entire battery or array, which could prove catastrophic.

Burst disks are increasingly used on miniaturized batteries, and this makes joining burst disks to the rest of a cell’s casing a process that requires high accuracy with repeatable precision. Fusion welding processes, such as electron beam and laser beam, are well suited for these types of application. In both processes, the beam can provide excellent power density at any size or geometry. Further, fully automated welding systems allow for the needed precision while maintaining high production rates.

Providing a rugged, sealed and secure container for batteries has led to the use of technology from other fields. Laser Hermetic sealing, used for decades in aerospace and defense applications, provides the secure packaging these components need, reliably and relatively easily. As geometries become smaller and more complex, Laser Hermetic Sealing has proven flexibility and toughness, as well as weight savings, making it efficient for compact designs.

Ultra-capacitor arrays are similar to batteries, the main difference being the mechanism of power storage. Batteries store energy via chemical reactions, while ultra-capacitors use electric fields — capacitance. Ultra-capacitors have some advantages over batteries: quicker discharge and recharge cycles, longer life, and consistent power handling across that lifetime. Welding of ultra-capacitor arrays can require specific grounding schemes to ensure quality welds and operator safety.