5 benefits of clad metals for Li-ion battery engineers - Engineering.com

Advanced Manufacturing

Mono-metal lose their shine in new Li-ion battery designs.

Engineered Materials Solutions has sponsored this post.

Lithium-ion (Li-ion) batteries are everywhere. Current consumer electronics, power tools, electric vehicles (EVs) and industrial power systems all use the technology. However, the performance demands on these batteries are increasing, presenting engineers with challenges that complicate the technology’s future ubiquity.

For many applications, traditional Li-ion battery designs can be limited by the material properties of their internal and external metallic parts. Different alloys can be selected to improve those properties, but there are only so many available options for mass production and there are often tradeoffs to consider when selecting alloys. For example, one alloy with greater electrical conductivity may be difficult to weld. Another might be easy to weld but have corrosion or conductivity issues. Engineers are therefore required to make choices from a limited number of materials, limiting the optimization of battery system performance.

“Battery systems have challenges related to increasing efficiency requirements, getting more power out of the cells, as well as controlling temperature in the application,” says Paul Galipeau, director of Thermal Controls at Engineered Materials Solutions. “High temperatures are very detrimental to Li-ion cells, so a material’s electrical and thermal conductivity is important. Joints need to be reliable but could be between dissimilar metals that are difficult to weld. There are challenges related to electrical conductivity, soldering and corrosion. In motive applications, everyone is trying to shave a pound off, so weight is also a consideration. Balancing all those needs can be a challenge for any designer.”

Galipeau suggests that clad metals — materials consisting of layers of different metals laminated and clad bonded together — can produce the bespoke properties engineers need to optimize their Li-ion applications. “You can tailor [them] to have unique properties that will enhance electrical/thermal conductivity or improve welding [when compared to] regular metals,” Galipeau says. “You can be creative and [utilize] unique properties that won’t be present in a mono-metal.” He presented five examples of how clad metals can benefit the design of Li-ion battery systems.

Galipeau explains that cylindrical cell connections were traditionally made using nickel, bronze, other copper alloys or nickel-plated steel. But these solutions all come with limitations. For instance, “nickel-plated steel was fine for low amps,” he says, “but as power needs increased the current carrying capacity wasn’t enough to handle it. It could overheat and cause a catastrophic failure or [even] a fire.”

He added that bronze and copper alloys improve conductivity but are hard to join to the nickel-plated steel of a cylindrical cell’s can. They can also introduce corrosion concerns, which is why they are typically nickel plated. Pure nickel, on the other hand, improves conductivity and corrosion resistance but can be expensive at the thickness needed for many applications.

Alternatively, engineers can use a clad metal consisting of layers of nickel, stainless steel, a copper center and two more layers of stainless steel and copper, respectively. Engineered Materials Solutions calls this material SIGMACLAD. It also offers a version without nickel, called SIGMACLAD Lite.

“The copper center imparts a high current carrying capacity,” says Galipeau, “while the steel layer increases its strength and results in strong welds. The nickel layer offers a corrosion resistant and solderable surface. So, it’s highly conductive electrically and thermally, easy to weld and solderable.”

In other words, the clad metal can offer all the benefits of each mono-metal in the mix with minimal downsides.

Continuing the topic of cylindrical cells, Galipeau talks about the historical challenges of their internal connections. For example, he references the connection between the jelly roll (the rolled-up layers of anodes, cathodes and separation materials) and the anode connector (where current leaves the cell). Traditionally, this connection is made of a nickel tab that is welded to the jelly roll and the bottom of the can.

“The conductivity of nickel is 20 percent of copper, leading to internal resistance and efficiency loss in the cell,” explains Galipeau. “The cell’s resistance is dissipated as heat which can harm the battery. By using nickel clad to copper, or [copper sandwiched by nickel], you have [more efficiency] and lower internal resistance due to the copper layer. This results in lower resistive losses and less energy lost to heat. While the exterior nickel layer provides a surface that is easily welded to the battery can.”

Galipeau moved on to discuss the design of pouch cell batteries. In this setup, instead of a jelly roll, plates of anodes, cathodes and separation materials are stacked inside a pouch. Cells are then packed into a housing traditionally made of aluminum.

Though aluminum is lighter than other options, its strength, ductility and puncture resistance can limit the volume of the cell and therefore its energy density. As an alternative to aluminum, the properties of a clad material can improve this application.

“An aluminum, steel and aluminum clad metal (called Feran) can have more ductility and be formed into a higher volume cell compared to pure aluminum. The higher volume cell can accommodate more plates and have higher energy density in the stack,” says Galipeau. He adds that “the steel center of a clad metal also has higher strength and is more rupture and puncture resistant.” As a result, engineers can use this material to design a housing that can hold more current collectors, increasing the energy density of the cell.

Galipeau next discussed the designs for connecting completed pouch and prismatic cells into modules. In either case, this process would entail connecting parts with dissimilar metals.

“Cells joined in series have one anode of copper and a cathode of aluminum. These are hard to join with a good conductivity path using a mono-metal,” says Galipeau. He adds that using clad metals consisting of copper and aluminum joined at an edge, overlay or inlay can address this challenge and ensure connections without welding dissimilar metals.

“We can be very creative in the solutions we come up with to join the materials, complete overlay, edge bonds and many more,” says Galipeau. “Depending on your need, we can facilitate the joining of two dissimilar metals and still maintain the copper-to-copper and aluminum-to-aluminum joint.”

Once all the cells are connected, Galipeau explains that large high current bus bars are used to connect modules in series to the system they are powering. “The bus bar is a thick material capable of carrying the larger current of the connected batteries,” he says. “It has to be thicker to handle the larger current and this is where weight becomes a concern.… Many opt to use copper, but it’s heavy and expensive. If you look at the savings of a copper-aluminum clad metal, you get equivalent carrying capacity at much lower weight and cost.”

The copper in this clad metal is used for its conductivity, while the aluminum helps to reduce the weight of the bus bars. The ratio of copper to aluminum, or other metals, can also be tailored to the specific current, weight and other considerations. For instance:

“There are lots of different varieties in the application of clad metals based on how you design the system,” concludes Galipeau. “There is a lot of variety in what can be in the clad and combined in different ways to suit the needs.”

In other words, Galipeau believes that the applications of clad-metals and the benefits they bring, compared to mono-metals, are limited only by the creativity of the engineering teams designing Li-ion battery designs. To help pique that creativity, he suggests learning more about Engineering Materials Solutions, a part of the Wickeder Group, which has over a hundred years of experience with clad metals and their applications.

To learn more please visit our web sites at Wickeder Group, Engineered Materials Solutions, LLC and Auerhammer Metallwerk.