High-performance Conductors Research Articles

Carbon Nanomaterial Enabled Ultra High Conductivity Cu Composites for Advanced Conductors

Growing demand for electrical energy and increasing need for high power grid systems necessitates development of new conductors for enhanced electrical and thermal conductivity. The power losses associated with the electrical resistance of Cu adversely impact the efficiency and performance of all electric devices. Ballistic electrical transport in carbon nanotubes (CNTs) is expected to improve the conductivity of the Cu matrix with additional CNT-enabled benefits that can enable low-weight, flexibility, and better thermal management. By using scalable, cost-effective, and commercially viable processing methods, we demonstrate a novel technological platform to produce high-performance conductors that incorporates CNTs into the Cu matrix ― ultra-conductive metal composites (UCC), which promise significant technological and economic impact in all energy sectors, ranging from electrical vehicles to power grid. Our approach, which combines materials synthesis, characterization, and first-principles modeling, enables an efficient and systematic exploration of the multidimensional complex materials parameter space of Cu-CNT composites with dopants and identifies the key individual structural and interfacial components that govern the electronic transport properties of the UCC composites. Our experimental technology platform is concentrated on Cu tapes and involves processes from production of stable CNT dispersions, electrospinning techniques to deposit shear induced aligned CNT coatings along the direction of the current flow, post thermal treatment procedures, and homogeneous deposition of metal overlayers onto CNT coated tapes. Here, we demonstrate that the prototype UCC composites exhibit improved electrical conductivity (by > 5%), higher current carrying capacity (> 10%), and higher mechanical strength (> 10%) than the reference pure Cu counterparts.

22.56% total area efficiency of n-TOPCon solar cell with screen-printed Al paste

Screen-printing Ag paste on the rear side of the Tunnel Oxide Passivated Contact solar cells (TOPCon) is still the mainstream method to form electrodes. However, the high price of precious metals increases the cost of TOPCon cells. Al is a cheap and high-performance conductor, and its work function is compatible with the rear side of TOPCon cells. In this study, we used a UV pulse laser (355 nm, 10 ps) to ablate the rear side SiNx passivation layer of TOPCon cells and then printed Al paste with different weight percentages of silicon (Si-wt.%) on the phosphorus-doped polycrystalline silicon (n+-poly-Si) layer to reduce the cost. We investigated the damage mechanism of laser on SiOx/n+-poly-Si/SiNx passivation structure and the contact mechanism between Al paste and n+-poly-Si layer. The results show that the Voc of SiOx/n+-poly-Si/SiNx passivation structure reduced about 6–7 mV when the laser energy density was 0.431 J/cm2. We got the best electrical performance of TOPCon cells printed with Al paste (25 wt%-29 wt% silicon). The open-circuit voltage (Voc) and the conversion efficiency (Eff), have reached 663.60 mV and 22.56 % respectively. Although the efficiency was 9.40 % relative lower than that of TOPCon cells printed with Ag paste, but the cost of Al paste only accounted for 10 % of Ag paste. In the future, the highest Eff of TOPCon solar cells printed with Al paste on the rear side are expected to reach the commercial TOPCon based on Ag paste, which applies laser doping selective emitter technology (SE) and bifacial poly-Si passivation structure.

Continuous intercalation compound fibers of bromine wires and aligned CNTs for high-performance conductors

This work presents macroscopic fibers of aligned double-walled carbon nanotubes (DWCNTs) intercalated with long-range ordered bromine, with a stoichiometry close to C17Br. Tribromide ions lie inside interstitial sites between hexagonally-packed DWCNTs and extend parallel to their axis as ordered supramolecular “wires”. First-principles simulations confirm this structure and a transfer of 0.13 electrons per Br atom. The structure of nested bundles of CNTs with a homogeneous distribution of bromine species in the interstitial sites of the superlattice is directly imaged by cross-sectional HRTEM, showing full intercalation of highly dense and aligned fibers. The presence of Br2 and Br3– is confirmed by Raman spectroscopy, and their supramolecular organization is resolved by 2D wide-angle X-ray scattering. Intercalation increases room-temperature longitudinal electrical conductivity by a factor of 8.4. Through low-temperature transport measurements in the longitudinal and transverse directions, we show that the intercalate reduces the tunneling-dominated resistance associated with transport between adjacent CNTs, rather than exclusively acting as a dopant that increases conductance of individual CNTs. By preserving the separation between CNTs, the exceptional mechanical properties of the CNT fiber host are retained. The combined tensile strength above 2.46 GPa and conductivity of 10.68 MS/m makes intercalated CNT fibers attractive lightweight conductors with combined properties superior to metals and graphite intercalation compounds.

High-throughput discovery of fluoride-ion conductors via a decoupled, dynamic, and iterative (DDI) framework

AbstractFluoride–ion batteries are a promising alternative to lithium–ion batteries with higher theoretical capacities and working voltages, but they have experienced limited success due to the poor ionic conductivities of known electrolytes and electrodes. Here, we report a high-throughput computational screening of 9747 fluoride-containing materials in search of fluoride-ion conductors. Via a combination of empirical, lightweight DFT, and nudged elastic band (NEB) calculations, we identified >10 crystal systems with high fluoride mobility. We applied a search strategy where calculations are performed in any order (decoupled), computational resources are reassigned based on need (dynamic), and predictive models are repeatedly updated (iterative). Unlike hierarchical searches, our decoupled, dynamic, and iterative framework (DDI) began by calculating high-quality barrier heights for fluoride-ion mobility in a large and diverse group of materials. This high-quality dataset provided a benchmark against which a rapid calculation method could be refined. This accurate method was then used to measure the barrier heights for 6797 fluoride–ion pathways. The final dataset has allowed us to discover many fascinating, high-performance conductors and to derive the design rules that govern their performance. These materials will accelerate experimental research into fluoride–ion batteries, while the design rules will provide an improved foundation for understanding ionic conduction.

Continuous Intercalation Compound Fibers of Bromine Wires and Aligned Cnts for High-Performance Conductors

Continuous Intercalation Compound Fibers of Bromine Wires and Aligned Cnts for High-Performance Conductors

Superconducting Accelerator Magnets Based on High-Temperature Superconducting Bi-2212 Round Wires

Superconducting magnets are an invaluable tool for scientific discovery, energy research, and medical diagnosis. To date, virtually all superconducting magnets have been made from two Nb-based low-temperature superconductors (Nb-Ti with a superconducting transition temperature Tc of 9.2 K and Nb3Sn with a Tc of 18.3 K). The 8.33 T Nb-Ti accelerator dipole magnets of the large hadron collider (LHC) at CERN enabled the discovery of the Higgs Boson and the ongoing search for physics beyond the standard model of high energy physics. The 12 T class Nb3Sn magnets are key to the International Thermonuclear Experimental Reactor (ITER) Tokamak and to the high-luminosity upgrade of the LHC that aims to increase the luminosity by a factor of 5–10. In this paper, we discuss opportunities with a high-temperature superconducting material Bi-2212 with a Tc of 80–92 K for building more powerful magnets for high energy circular colliders. The development of a superconducting accelerator magnet could not succeed without a parallel development of a high performance conductor. We will review triumphs of developing Bi-2212 round wires into a magnet grade conductor and technologies that enable them. Then, we will discuss the challenges associated with constructing a high-field accelerator magnet using Bi-2212 wires, especially those dipoles of 15–20 T class with a significant value for future physics colliders, potential technology paths forward, and progress made so far with subscale magnet development based on racetrack coils and a canted-cosine-theta magnet design that uniquely addresses the mechanical weaknesses of Bi-2212 cables. Additionally, a roadmap being implemented by the US Magnet Development Program for demonstrating high-field Bi-2212 accelerator dipole technologies is presented.

Direct writing of silver microfiber with precise control on patterning for robust and flexible ultrahigh-performance transparent conductor

Ultrafine silver fiber is an alternative to commercial indium tin oxide (ITO) as a new-generation flexible transparent conductor that can be used in flexible electronics. However, its primary limitation is the unrepeatable optoelectronic properties due to the disordered distribution of silver fibers. In this work, we report the in-situ direct writing of the silver microfiber pattern with high conductivity and transparency to attain a flexible transparent conductor. The silver network is composed of silver microfibers, which can be artificially designed and regularly patterned under the precise control of the fiber position and shape; this is crucial for regulating its optoelectronic properties. Herein, a high-performance conductor is achieved in the silver network with high stability. This novel conductor has a sheet resistance of 2 Ω sq−1 at 90% transparency, which corresponds to a high Figure of merit σdc/σopt = 1742. The in-situ direct writing technique developed here is distinct from other fabrication methods because it requires no transfer steps, templates or heating. Further, this silver network is integrated into a light-printable rewritable device, and can be used as a wearable heater; this heater when driven by a 1.5 V battery attains a temperature of up to 55.6 ℃. Therefore, in-situ direct writing is expected to offer a new platform for facile, scalable, and ultralow-cost production of high-performance metal networks for flexible transparent conductors.

Identifying superionic conductors by materials informatics and high-throughput synthesis

Combinatorial chemistry has been proven effective in the search for novel functional materials, especially in the field of organic chemistry, and is being used to identify functional inorganic compounds. However, there is a growing need for approaches that predict and experimentally realize new materials, beyond composition optimization of known systems. Application of combinatorial chemistry to materials discovery is typically hindered by a limited ability to search a wide chemical composition space, and by our ability to experimentally screen promising compounds. Here, a combinatorial scheme is proposed that combines a materials informatics technique to define a chemical search space with high-throughput synthesis and evaluation. We identify high-performance superionic conductors in the Ca-(Nb,Ta)-Bi-O system, demonstrating the effectiveness of this approach for accelerated materials discovery.

Interfacial reaction induced efficient load transfer in few-layer graphene reinforced Al matrix composites for high-performance conductor

Fabricating high-strength Al matrix composites without sacrificing their electrical conductivity is a critical issue in the design of Al-based conductors. Here, we demonstrate for the first time, an example of improving the interfacial load transfer and strength of few-layer graphene (FLG)/Al composites by an appropriate interfacial reaction. Monocrystalline Al4C3 nanorods that tightly conjoined the FLG platelets with the Al matrix were produced by manipulating the sintering temperature. As revealed by transmission electron microscopy and by a shear lag model that provides a quantitative estimate of the strengthening, the Al4C3 nanorods ensured an efficient load transfer at the FLG-Al interface, thereby giving rise to a considerable enhancement of strength in the composite. Moreover, the electrical conductivity is almost as high as that of pure Al, which could be a significant step toward the preparation of high-performance Al-based conductors.

Progressing in cable-in-conduit for fusion magnets: from ITER to low cost, high performance DEMO

The performance of ITER toroidal field (TF) conductors still have a significant margin for improvement because the effective strain between −0.62% and −0.95% limits the strands’ critical current between 15% and 45% of the maximum achievable. Prototype Nb3Sn cable-in-conduit conductors have been designed, manufactured and tested in the frame of the EUROfusion DEMO activities. In these conductors the effective strain has shown a clear improvement with respect to the ITER conductors, reaching values between −0.55% and −0.28%, resulting in a strand critical current which is two to three times higher than in ITER conductors. In terms of the amount of Nb3Sn strand required for the construction of the DEMO TF magnet system, such improvement may lead to a reduction of at least a factor of two with respect to a similar magnet built with ITER type conductors; a further saving of Nb3Sn is possible if graded conductors/windings are employed. In the best case the DEMO TF magnet could require fewer Nb3Sn strands than the ITER one, despite the larger size of DEMO. Moreover high performance conductors could be operated at higher fields than ITER TF conductors, enabling the construction of low cost, compact, high field tokamaks.

P3D Micro Dispensing & Photonic Curing of Silver Nanoparticle Inks on Low Thermal Stability Molded Plastic Parts

In this paper, we describe an additive processing technique that would enable fast and reliable processing of conductive circuits upon a wide range of thermally molded plastics. Precise patterns of silver nanoparticle based pastes are printed on to 3D injection molded plastic parts and other 3D surfaces using a nScrypt micro dispensing tool and then processed in seconds using a NovaCentrix PulseForge flash lamp photonic curing system. The additive digital printing technique enables rapid manufacturing of intricate designs with quick turnaround time from design to production. The non-equilibrium heating technology enables sintering the nanoparticle based inks into high performance conductor circuits directly on 3D and 2D low thermal sensitive polymer materials. It will be demonstrated that the nanoparticle based pastes have a superior performance to the conventional polymer thick film pastes and that they are also more cost effective. Specific examples will be shown demonstrating how the combination of the two tools and processes could result in a versatile and cost effective additive manufacturing process. As of right now, there is no tool or combination of tools that could provide such a versatile design and production environment. The new process is faster, more cost effective, and more environmentally friendly compared to conventional processing techniques.

Inkjet printing of multifilamentary YBCO for low AC loss coated conductors

Considerable progress has been made with the development of REBCO coated conductors in recent years, and high performance conductors are available commercially. For many applications, however, the cost remains prohibitive, and AC losses discourage their selection for higher frequency applications. Chemical solution deposition (CSD) methods are attractive for low-cost, scalable preparation of buffer and superconductor layers, and in many respects inkjet printing is the method of choice, permitting non-contact deposition with minimal materials wastage and excellent control of coating thickness. Highly textured coatings of YBCO and Gd-doped CeO2 have previously been reported on buffered metal substrates. Inkjet printing also introduces the possibility of patterning - directly depositing two and three dimensional structures without subtractive processing - offering a low-cost route to coated conductors with reduced AC losses. In this contribution, the inkjet deposition of superconducting YBCO tracks is reported on industrially relevant buffered metal substrates both by direct printing and an inverse patterning approach. In the latter approach, ceria tracks were printed reported, which are a candidate both for resistive filament spacers and buffer layers. TFA-based precursor solutions have been printed on SS/ABAD-YSZ/CeO2 and Ni-W/LZO/CeO2 RABiTS substrates, and the resulting multifilamentary samples characterised by microscopy and scanning Hall probe measurements. The prospects for future inkjet-printed low AC loss coated conductors are discussed, including control of interfilamentary resistivity and bridging, transposed filamentary structures and stabilisation material.

The SMC (Short Model Coil) ${\rm Nb}_{3}{\rm Sn}$ Program: FE Analysis With 3D Modeling

The SMC (Short Model Coil) project aims at testing superconducting coils in racetrack configuration, wound with cable. The degradation of the magnetic properties of the cable is studied by applying different levels of pre-stress. It is an essential step in the validation of procedures for the construction of superconducting magnets with high performance conductor. Two SMC assemblies have been completed and cold tested in the frame of a European collaboration between CEA (FR), CERN and STFC (UK), with the technical support from LBNL (US). The second assembly showed remarkable good quench results, reaching a peak field of 12.5 T. This paper details the new 3D modeling method of the SMC, implemented using the ANSYS Workbench environment. Advanced computer-aided-design (CAD) tools are combined with multi-physics Finite Element Analyses (FEA), in the same integrated graphic interface, forming a fully parametric model that enables simulation driven development of the SMC project. The magnetic and structural model is described and the results are compared with the experimental data from the strain gauges, which monitor the mechanical strain of the structure.

Rapid fabrication of patterned high-performance conductor poly (vinylidene fluoride) surfaces using a 248nm excimer laser

This work describes a method for rapidly and conveniently fabricating high-performance conductive patterns on poly (vinylidene fluoride) substrates using a 248 nm excimer laser. It shows that the artificial active centre, created by laser direct etching technique, could facilely control the formation of modified layer, avoiding the laser threshold in processing. Using the etching lines to structure the nonconductive paths, the controllable patterns can be formed in selective areas through the designed photo-mask when 248nm laser irradiation. The modified layer exhibits a high-grade electrical conductivity of 2.80 Ω(-1)cm(-1) increased by 13 orders of magnitude, and the considerable improvement in conductivity could be attributed to the carbon enrichment, especially the structural formation of C-C.

High-Tc superconducting materials for electric power applications

Large-scale superconducting electric devices for power industry depend critically on wires with high critical current densities at temperatures where cryogenic losses are tolerable. This restricts choice to two high-temperature cuprate superconductors, (Bi,Pb)2Sr2Ca2Cu3Ox and YBa2Cu3Ox, and possibly to MgB2, recently discovered to superconduct at 39 K. Crystal structure and material anisotropy place fundamental restrictions on their properties, especially in polycrystalline form. So far, power applications have followed a largely empirical, twin-track approach of conductor development and construction of prototype devices. The feasibility of superconducting power cables, magnetic energy-storage devices, transformers, fault current limiters and motors, largely using (Bi,Pb)2Sr2Ca2Cu3Ox conductor, is proven. Widespread applications now depend significantly on cost-effective resolution of fundamental materials and fabrication issues, which control the production of low-cost, high-performance conductors of these remarkable compounds.

A high current density low cost niobium/sub 3/tin conductor scalable to modern niobium titanium production economics

Several configurations of an internal tin type conductor were fabricated designed to explore a concept to produce low cost high performance conductors suitable for future High Energy Physics magnet applications. Conductors with integral barriers were evaluated as well as a separated stabilizer concept. Critical current measurements are presented and utilized to project potential current densities expected to be achieved in more optimized designs. The separated stabilizer concept proved impractical for high current densities. Cost estimates for conductors of both types are presented for production scales such as the VLHC.

Pre-industrial PIT conductor and coil development at Alcatel

In 1995 the PIT conductor development was strengthened at Alcatel and important progress has been achieved since. During 1997 the patented rectangular Alcatel route was upscaled and pre-industrial conductors have been fabricated in a wire drawing mill. After the successful transfer the first high performance conductors have been realized in kilometer lengths. The conductors are realized in cooperation with Aventis Research and Technologies using precursor powders optimized for the Alcatel conductor route. The simpler Bi-2212/AgPd matrix conductor is used as a working horse where engineering current densities of J/sub e/=65 kA/cm/sup 2/ have been reached at 4 K, 0 T. Significant progress has also been achieved on Bi-2223 conductors where critical current densities of J/sub c/=30 kA/cm/sup 2/ at 77 K, 0 T are reached. First solenoids generating a field up to 2.3 Tesla have been realized using Bi-2212 conductors. In a background field of 3 Tesla this magnet still generates a field of 2 Tesla. The results on test coils are consistent with J/sub c/(H) measurements on short samples showing that an important step towards high homogeneity conductors has been achieved.

A new step in AC superconducting conductors

High current AC superconducting cables are made of numerous co-assembled wires. The assembly mode may be a source of performance degradation, due to different causes, such as wire deformation, mechanical instabilities, heating, anomalous current distribution among the different wires, longitudinal self magnetic field, inadequate junctions. These possible causes have been systematically investigated. Significant results are presented for possible applications of high-performance multi-kA conductors. >

A solder bond requirement for large, built-up, high-performance conductors

Some of the large built-up conductors being fabriccated for large superconducting magnets are designed to operate above the maximum recovery current. Because the stability of these conductors is sensitive to the quality of the solder bond joining the composite superconductor to the high-conductivity substrate, a minimum bond requirement is necessary for an acceptable design. The present analysis finds that the superconductor is unstable and becomes abruptly resistive when there are temperature excursions into the current sharing region of a poorly bonded conductor. This abrupt transition, in turn, produces eddy current heating in the vicinity of the superconducting filaments and causes a sharp reduction in the minimum propagating zone (MPZ) energy. This sensitivity of the MPZ energy to the solder bond contact area is used to specify a minimum bond requirement. For the superconducting MHD magnet being built by General Electric for the Component Development Integration Facility (CDIF), the minimum bonded surface area is .68 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /cm which is 44% of the composite perimeter.