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‘More conductive’ copper will lead to more efficient motors

20 October, 2020

US researchers have developed a process that, they say, can boost the conductivity of copper wire by about 5%, thus either improving the efficiencies of electric equipment such as motors, or reducing their weight while operating with the same efficiency.

The researchers, from the US Governement's Pacific Northwest National Laboratory (PNNL), have teamed up with General Motors to test the improved copper wire in components for vehicle motors. As part of a cost-shared research project, they validated the increase in conductivity and also found that the copper is also more ductile – it can stretch further before it breaks.

In other respects, the material behaves like conventional copper, so it can be welded and subjected to mechanical stresses with no loss of performance. No specialised manufacturing methods are needed to use the enhanced copper in motors.

The new material can be used in any application that uses copper to transport electrical energy, such as cables, power transmission systems, generators, batteries and wireless chargers.

The improved performance is achieved by adding graphene – a highly conductive, extremely thin sheet of carbon atoms – to copper and using this to produce wire with a higher conductivity than pure copper. A first-of-its-kind machine – that includes patented and patent-pending technologies – combines and extrudes the metal and composite materials.

The process, called Shape (Shear-Assisted Processing and Extrusion), applies an oppositional, or shear, force by rotating a metal or composite as it is pushed through a die to create a new shape. Deforming the metal causes internal heating which softens it and allows it to be formed into wires, tubes or bars.

“Shape is the first process that has achieved improved conductivity in copper at the bulk scale, meaning it can produce materials in a size and format that industry currently uses, like wires and bars,” says Glenn Grant, principal investigator at PNNL. “The benefit of adding graphene to copper has been investigated before, but these efforts have focused primarily on thin films or layered structures that are extremely costly and time-consuming to make. The Shape process is the first demonstration of a considerable conductivity improvement in a copper-graphene composites made by a truly scalable process.”

PNNL materials scientist Keerti Kappagantula holds an ultra-high conductivity copper wire with graphene additives produced using the PNNL-developed process that could help to boost motor efficiencies
Photo: Andrea Starr / PNNL

Previous attempts to add graphene to copper have run into problems because the additives did not blend uniformly, creating clumps and pore spaces within the structure. The new process eliminates pores while also distributing the additives uniformly within the metal, which may explain the improved electrical conductivity.

“Shape’s uniform dispersion of the graphene is the reason why only really tiny amounts of additive are needed – about six parts per million of graphene flakes – to get a substantial improvement of 5% in conductivity,” explains PNNL material scientist, Keerti Kappagantula. “Other methods require large quantities of graphene, which is very expensive to make, and still have not approached the high conductivity that we've demonstrated at a bulk scale.

R&d engineers at GM have verified that the high-conductivity copper wire can be welded, brazed, and formed in the same way as conventional copper wire, suggesting seamless integration into existing motor manufacturing techniques.

“To further light-weight motors, advances in materials are the new paradigm,” says Darrell Herling of PNNL's Energy Processes and Materials Division. “Higher conductivity copper could be a disruptive approach to light-weighting and/or increasing efficiencies for any electric motor or wireless vehicle charging system.”

According to a report on electric vehicles produced by the US Department of Energy in 2018, motor efficiencies need to be improved to boost EV power densities. Additionally, components need to fit within increasingly smaller spaces available in vehicles. Reducing motor volumes has, until now, been limited by material properties and by the electrical conductivity limitations of conventional copper windings.

Pacific Northwest National Laboratory is managed and operated by Battelle for the US Department of Energy.

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