SBIR-STTR Award

Carbon nanotube (CNT)-based copper hybrid-conductors, density ~5 g/cc, at copper level conductivity potentially have an ampacity of two orders of magnitude above bulk copper. In this proposal, we posit that by improving CNT wire conductivity and coupling with copper infiltration we will achieve these goals. This extraordinary ampacity and conductivity come from suppressing electromigration coupled with the extreme charge-carrier mobility through the CNT pathways. Achievement of these goals encompass two processes: (1) Removing the fundamental structural/physical obstructions to charge carrier transport in CNT conductors by doping to a higher density of charge carriers, addressing alignment factors, atomically cleaning the surfaces, reducing the effect of Schottky barriers and minimizing growth defects through processing. Our goal is > 20 x 10^6 S/m for CNT yarn alone, and then (2) Infiltrating this CNT fiber with copper to take advantage of the very high CNT charge carrier mobility and high charge carrier density in copper. The demonstrated suppression of electromigration by CNTs within copper is key to ampacity increases. We will have a plied composite Cu/CNT cable fabricated commercially. A new manufacturing process to produce Cu/CNT hybrid wire by infiltrating molten copper inside the CNT fiber is described.

We develop new classes of conducting materials consisting of metal-coated and metal-infiltrated carbon-nanotube wire, with a goal of achieving densities less than 2 g/cm3, specific conductivities exceeding copper and the ability to carry very high current. Quantum effects in CNT wire and consequent ballistic conduction coupled with the high electron density of copper enables a new kind of non-rule of mixtures wire that can exhibit extraordinary properties. Most Army cables need improved conductivity, reduced mass density, and flexibility. A few Army applications use copper at extreme current densities and temperatures where electromigration limits performance, rail guns cables for example. Both conductivity and high current density are addressed. We focus on four cable types: (1) We create a CNT wire made of predominantly metallic conducting nanotubes, (2) We fabricate a dual metal coated CNT wire with a linker element and copper, (3) We create copper- and/or aluminum-infiltrated CNT wire for applications requiring fully dense conductors (e.g. dictated by electromigration concerns), and (4) We create an aluminum coated CNT wire which, in Phase I, has demonstrated current carrying capacity higher than aluminum. We have partnered with Lockheed-Martin and Minnesota Wire for both commercialization scale-up as well as for cable fabrication.