A new composite from Oak Ridge National Laboratory (ORNL) increases the electrical current capacity of copper wires, providing a new material that can be scaled to improve energy-efficiency in electric vehicles.

With an improved performance, manufacturers have the ability to reduce volume and increase the power density in advanced motor systems.

The material can be deployed in any component that uses copper, including bus bars and smaller connectors for electric vehicle traction inverters, as well as for applications such as wireless and wired charging systems.

To produce a lighter weight and great conductive properties, the ORNL team created lengths of composite copper-carbon nanotube materials. The researchers deposited and aligned carbon nanotubes on flat copper substrates, resulting in a metal-matrix composite material with better current handling capacity and mechanical properties than copper alone.

"You get a better conductor with less power loss, which in turn increases the efficiency and performance of the device," said Tolga Aytug, lead investigator on the project .

Aytug and his colleagues deposited single-wall carbon nanotubes (CNTs) using a controlled process called electrospinning, which creates fibers as a jet of liquid speeds through an electric field. The process allowed scientists to successfully orient the fibers in one general direction to facilitate enhanced flow of electricity.

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The team then used magnetron sputtering, a vacuum coating technique, to add thin layers of copper film on top of the CNT-coated copper tapes. The coated samples were then annealed in a vacuum furnace to produce a highly conductive Cu-CNT network. A dense, uniform copper layer allowed diffusion of copper into the CNT matrix.

Using this method, ORNL scientists created a copper-carbon nanotube composite measuring 10 centimeters long and 4 centimeters wide. The microstructural properties of the material were analyzed using instruments at the Center for Nanophase Materials Sciences at ORNL, a U.S. Department of Energy Office of Science user facility.

Researchers found the composite reached 14% greater current capacity, with up to 20% improved mechanical properties compared with pure copper, as detailed in ACS Applied Nano Materials .

In a short Q&A below, lead investigator Tolga Aytug tells Tech Briefs if the improved power will boost adoption of electric vehicles.

Tech Briefs: What are the barriers to electric-vehicle adoption that your composite material is designed to address and overcome?

Tolga Aytug: Issues related to component size, weight/volume, and performance/reliability are several key barriers to achieving electric traction drive system technical R&D targets and increased EDV market adoption.

The effort to reduce motor volume reduction and improve efficiency, however, is limited in part by the electrical conductivity limitations of copper windings.

To meet DOE’s Vehicle Technologies Office ’s 2025 electric vehicle targets and goals, we need to increase power density of the electric drive and reduce the volume of motors by 8 times, and that means improving material properties. In addition, copper is used in all electric conduction on and off board the vehicle: in battery interconnects, electric motor windings, wiring, bus bars, and charging infrastructure.

Thus all these electric-vehicle components will significantly benefit from such advanced composite conductors.

Tech Briefs: What inspired your carbon-nanotube design?

Tolga Aytug: Previous research on ultra-conductive metal composites (UCC) materials mostly involved mixing liquid copper with CNTs and extrusion to wire-forms, which mostly resulted in lack of controlled alignment of CNTs along the direction of the current flow; inhomogeneous distribution of CNTs on and into the metal matrix; and a poor fundamental understanding of Cu-CNT interactions affecting bulk electrical transport properties.

In our R&D activities, we were inspired by our previous research on the development of high temperature superconducting (HTS) wires where we have used tape geometries to produce these wires in wide width webs which were then slitted into smaller widths to assemble them into HTS wires. We have mainly used thin-film approaches on a thin metal substrate/foil to create these HTS materials.

Here we have followed similar approaches where we have deposited CNTs using commercially scalable, solution-based techniques on thin copper foils flowed by deposition of additional Cu thin films to produce a highly conductive sandwiched multilayer tape architecture. We have used CNTs because of their excellent electrical, thermal, and mechanical properties.

Tech Briefs: How complex and challenging is the process to create the created a copper-carbon nanotube? And will that complexity potentially limit adoption?

Tolga Aytug: The basic approach to fabrication begins with formulating stable CNT dispersions for the deposition of uniform CNT coatings. Following CNT deposition in a manner that intentionally aligns the CNTs, samples were heat treated to remove all organic chemicals from the CNT matrix. Subsequent deposition of thin copper overlayers by industry-standard physical vapor deposition and annealing processes enables high percolation conductivity throughout the entire CNT/metal matrix ensemble. The production of these material utilizes scalable and commercially viable processing methods, but the process is not as simple as melting copper and mixing CNTs together.

Tech Briefs: What does this kind of composite provide for electric vehicles, and how do you envision this kind of material supporting a future of electric vehicles?

Tolga Aytug: Such conductors can improve energy utilization through reduced ohmic losses, transport power with smaller size and/or lightweight wires/cables, and enable better thermal management across system components. Hence, the conductors potentially can result in immense technological and economic value in all energy sectors, ranging from on- and off-board components in electric vehicles (EV), interconnects to electronic devices, and motors.

This question can also be tied to the barriers for accelerated EV market adaption, where significant advances substantially affect the efficiency and performance of electrification in applications where mass and size are a key metric. These kinds of advanced materials and conductors can help to meet the U.S. Department of Energy (DOE) Vehicle Technology Office (VTO) 2025 performance targets by significantly improving the efficiency of all on- and off-board electrical conduction applications for electric vehicles (i.e., converters, batteries, wiring, interconnects, busbars, charging systems, etc.), while enabling much needed reduced weight/volume, higher power density, and improved reliability and thermal characteristics for all electrified powertrain components.

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