Roll-to-roll (R2R) comprises a series of manufacturing techniques for depositing functional materials, such as large circuits, onto moving rolls of plastic or metal foil. The process is continuous and generates rolls of finished materials that can be used in a wide range of applications, from battery electrodes to solar cells.

R2R manufacturing and processing can reduce production costs, increase precision, and enable in-line quality control and defect detection. Because of these benefits, it’s used in many areas of manufacturing today. However, its applications have the potential to grow even further, particularly in energy and transportation-related fields. Efforts to develop R2R technologies and expand their application can advance the production of clean energy technologies, such as fuel cells, batteries and solar cells.

Argonne National Laboratory joins four other national laboratories in advancing R2R manufacturing for energy systems. In a successful bid to DOE’s Advanced Manufacturing Office (AMO), Oak Ridge National Laboratory led a team of five labs including Argonne, the National Renewable Energy Laboratory, Lawrence Berkeley National Laboratory, and Sandia National Laboratories to receive a total of $9 million in funding over the next three fiscal years.

Argonne’s Role in the AMO R2R Collaboration: A Go-To Resource for Advanced Materials

Argonne researchers will contribute to the collaboration’s efforts by (1) synthesizing materials for device manufacture and testing, (2) performing advanced characterization of materials for the other labs, and (3) evaluating prototype devices, according to Greg Krumdick, interim division director of Argonne’s Applied Materials Division. These efforts can accelerate the development of new materials for R2R processing to drive innovation at all levels, from invention to commercialization.

Argonne leverages several facilities and programs to support these activities. Among them is the Materials Engineering Research Facility, home to resources that support analysis and scale-up of new materials. Another is the Advanced Photon Source, a DOE Office of Science User Facility that delivers powerful X-rays for materials imaging and characterization. Yet another one-of-a-kind resource is the Cell Analysis, Modeling, and Prototyping (CAMP) Facility, which enables the design, fabrication and characterization of battery materials.

There are many challenge in R2R, including material incompatibilities between additives, polymers, and curing processes that prevent multiple process steps from being performed in-line. Among these challenges, Argonne researchers will help address pressing needs for:

• Continuous processing on flexible substrates, including nontraditional substrates such as stretchable plastics and textiles particularly for multilayer devices.
• High-throughput and large-area printing/deposition techniques compatible with a wide range of materials, inks, and substrates.
• Novel aqueous ink and substrate materials compatible with R2R processing techniques for application-specific properties.
• Methods to detect and avoid defects in continuous R2R processes.
• Improved control of stoichiometry in continuous, high-speed coating systems to avoid non-uniformities.
• Databases populated with material properties and fabrication process parameters to enable effective modeling and simulation.

Consortium builds on past success

In its competitive bid and renewal of funding, the AMO R2R Consortium can point to notable successes in the last two fiscal years in applying R2R to the development of battery electrode and fuel cell materials.

Building on the science of its early-stage processing, the consortium doubled the battery electrode’s areal loading, which is a measure of its porosity and thickness. Doubling the electrode’s areal loading resulted in a 45% power boost and thus a possible means for increasing the overall energy density of lithium-ion batteries at the pack level. In this success, Argonne contributed by providing cathode materials and evaluated R2R-produced electrodes in coin cell electrochemical testing.

Again through the science of early-stage processing, researchers succeeded in replacing a multi-layer coating step with a single-layer R2R approach in the production of fuel cell materials. In doing so, they succeeded in matching the mass activity—a metric for evaluating the effectiveness of cathode catalysts in some fuel cells—between the products made from the multilayer and single-layer process. Doing so means that the cost and complexity for production of the fuel cell material can be reduced for production scaling purposes, Krumdick said.

Innovating transportation with electrospinning

In the development of electric vehicle batteries and fuel cell electrodes, electrospinning is another R2R technique that’s received much attention. The process produces nanofibers of a wide range of material kinds, compositions, and length-to-diameter aspect ratios — a capability that the other synthesis technologies lack.

By depositing fibers on a moving substrate, electrospinning can produce continuous sheets of nanofibrous advanced materials. (To view the electrospinning technique, go here or here.) These nanofibers have a high surface-to-volume ratio, making them ideal candidates for energy storage and transportation applications where high porosity and high surface areas are desirable, such as in battery or fuel cell electrodes.

At Argonne, researchers have built an integrated electrospinning system that can create useful quantities of advanced nanofiber-based materials for potential applications in transportation and elsewhere. The system will expand uses for the electrospinning products beyond polymer filtration membranes like water and gas filters. Argonne researchers are using this technique and others to pursue the next rounds of breakthroughs in R2R manufacturing.