Session: 20-17-01: Rising Stars of Mechanical Engineering

Paper Number: 172164

Axially Bi-Continuous Graphene-Copper Composites With Ultrahigh Electrical Conductivity 

Graphene has excellent electrical properties far exceeding those of pure metal conductors such as copper. As a result, small graphene flakes are often dispersed into a copper matrix to fabricate graphene-copper composite conductors. However, these conductors suffer from low electrical performance due to the discontinuous interfaces between the dispersed graphene flakes and the copper matrix. This poster presents an innovative graphene-copper composite conductor, called axially bi-continuous graphene copper (ACGC) wire, that achieves excellent thermoelectrical properties and chemical inertness at high temperatures.

Our ACGC approach addresses two intrinsic challenges in use of graphene–copper composites for thermoelectrical applications: 1) removal of discontinuous graphene–graphene and graphene–copper interfaces in the direction of electrical current, and 2) retention of the pristine graphene–copper interface by directly growing graphene onto small-scale copper wires instead of the commonly used mechanical mixing methods. Due the axially bi-continuous graphene-copper structure, the tube-shaped continuous graphene layers on a Cu wire reduce the inelastic surface scattering at the graphene–copper interface and protect the wire from being oxidized during joule heating, giving rise to the significantly enhanced thermoelectrical properties of the ACGC wires.

This study demonstrates that the ACGC wire achieves a significant increase (≈4.5 times) in current density breakdown limit with superb thermal stability. The carefully designed experiments and theoretical analysis presented in this study reveal the underlying mechanisms of the enhanced thermoelectrical properties including 224% higher surface heat dissipation, 41% higher electrical conductivity, and 41.2% lower resistivity after thermal cycles up to 450 °C, compared to conventional pure copper wires. In addition, our theoretical analysis indicates that the higher surface heat dissipation of the ACGC offers a reasonable explanation for the unique failure behavior of the ACGC wires, captured by high-speed cameras, near the current density limit. Our ACGC wire consisting of high-quality, multilayer continuous graphene tubes on the surface of a fine Cu wire, increases the current density, electrical conductivity, the long-term oxidation resistance at high temperatures, and its thermal stability compared to the previous reported work.

These promising results and fundamental understanding of the underlying mechanisms may bring a technical paradigm shift in designing high-performance, axially bi-continuous graphene–copper composites for high-power transmission applications. The ACGC wire, with excellent thermoelectrical properties combined with its chemical inertness at high temperatures, will offer new engineering solutions to the challenges of modern electric power systems requiring high-power transmission, including aerospace industries, transportation systems, and advanced electronic and communication devices. Also, the advantages of the ACGC wire could be utilized to address one of the technical issues in miniaturized electric devices, i.e., failure of electrical connectors by electromigration driven by large current density.

Presenting Author: Wonmo Kang Arizona State University

Presenting Author Biography: Wonmo Kang is an associate professor in the School for Engineering of Matter, Transport and Energy at Arizona State University (ASU). He received his Ph.D. in 2012 from the University of Illinois at Urbana-Champaign. Before joining ASU, he was a research scientist at the US Naval Research Laboratory. His current research includes graphene-metal composites for multifunctional applications, in situ material characterization, nano/bio-mechanics, and NEMS/MEMS/bioMEMS. Dr. Kang has published his work in leading scientific journals including Advanced Materials, Advanced Functional Materials, Small, and Acta Biomaterialia. Dr. Kang is the recipient of several awards/fellowships including the National Science Foundation (NSF) CAREER Award, the U.S. Air Force Research Laboratory (AFRL) Summer Faculty Fellowship, the Defense University Research Instrumentation Program (DURIP) Award, the postdoctoral fellowship from the American Society for Engineering Education (ASEE), the Leidos technical publication awards, and the Outstanding Mechanical Engineering PhD Award.

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