Graphene-copper mix may improve efficiency of EV, industrial equipment motors

PNNL researcher Keerti Kappagantula holds highly conductive copper wire in bulk. (Image by Andrea Starr | Pacific Northwest National Laboratory).

Researchers at the Pacific Northwest National Laboratory discovered that by mixing the right amount of graphene with copper to make electrical wires it is possible to improve the efficiency of electricity distribution, as well as develop more efficient motors to power electric vehicles and industrial equipment. 

In a paper published in the journal Materials & Design, the scientists explain that when they added 18 parts per million of graphene to electrical-grade copper, the temperature coefficient of resistance decreased by 11% without reducing electrical conductivity at room temperature. 

The temperature coefficient of resistance is a property that explains why metal wires get hot when an electric current runs through them. In general, researchers want to reduce this resistance while enhancing a metal’s ability to conduct electricity. 

In the case of electric car engines, an 11% increase in the electrical conductivity of copper wire winding translates into a 1% gain in motor efficiency.

“This discovery runs counter to what’s generally known about the behaviour of metals as conductors,” materials scientist and senior author of the study, Keerti Kappagantula, said in a media statement. “Typically, introducing additives into a metal increases its temperature coefficient of resistance, meaning they heat up faster at the same current levels compared to pure metals. We are describing a new and exciting property of this metal composite where we observe enhanced conductivity in a manufactured copper wire.”

Previously, the research team performed detailed structural and physics-based computational studies to explain the phenomenon of enhancing the electrical conductivity of metals using graphene.

In this study, they showed that the solid-phase processing used to extrude the composite wire leads to a uniform, near pore-free microstructure punctuated with tiny flakes and clusters of graphene that may be responsible for decreasing the coefficient of resistance of the composite.

“We showed that flakes and clusters must both be present to make better conductors for high-temperature operations,” Kappagantula said.

According to the research team, when applied to any industrial application, the new copper-graphene composite wires will provide great design flexibility.

For example, coiled copper wire forms are used in the core of electric motors and generators. Motors today are designed to operate within a limited temperature range because when they get too hot, the electrical conductivity drops dramatically. With the new copper-graphene composite, motors could potentially be operated at higher temperatures without losing conductivity.

Likewise, the wiring that brings electricity from transmission lines into homes and businesses is typically made of copper. As the population density of cities increases, power demand follows suit. A composite wire that is more conductive could potentially help meet that demand with efficiency savings.

The research team continues its work to customize the copper-graphene material and measure other essential properties, such as strength, fatigue, corrosion, and wear resistance, which are crucial to qualify such materials for industrial applications.