Abstract
High-value R2R processing is used to support a wide range of products in applications which span many industrial business sectors. The overall R2R process technology can be considered as “mature” as the process methodology and has been in use for decades. This continuous processing technique traditionally involves deposition of material(s) onto moving webs or carriers or other continuous R2R, belt-fed, or conveyor-based processes that enable successive steps to build a final version which serves to support the deposited materials. Current process technologies, which typify “roll to roll”, include tape casting, silk-screen printing, reel-to-reel vacuum deposition/coating and R2R lithography. Products supported by R2R manufacturing include micro-electronics, electro-chromic window films, PVs, fuel cells for energy conversion, battery electrodes for energy storage, and barrier materials. Due to innovation in materials and process equipment, high-quality yet very low-cost multi-layer technologies can be manufactured on a very cost-competitive basis. To move energy-related products from high-cost niche applications to the commercial sector, a means must be available to enable manufacture of these products in a cost-competitive manner that is affordable by the general consumer. Fortunately, products such as fuel cells, thin- and mid-film PVs, batteries, electrochromic and piezoelectric films, water separation membranes, and other energy saving technologies readily lend themselves to manufacture using R2R approaches.
Within the DOE EERE AMO, it was recognized that establishment of a program supported at the DOE National Laboratories, along with their immense design of materials and equipment modelling capabilities enabled with use of high-performance computing, could take advantage of available R2R infrastructure to manufacture new technologies. In FY 2016, a R2R Consortium was established and provided with initial “seed” funding to take an approach that was envisioned to be supportable by advanced manufacturing R2R processes. This collaborative approach was designed to foster identification and development of materials and processes related to R2R for clean-energy product development. Using computational and experimental capabilities by acknowledged subject matter experts within the supported National Laboratory system, this collaborative project would leverage the capabilities and expertise at each of four laboratories to further the development of an enabling high-volume cost-competitive platform technology.
The collaboration team that is comprised of ORNL, ANL, NREL and LBNL, coordinating with EPB and other selected industry partners, was formed in April 2016 to initially address enhancing battery electrode performance and R2R manufacturing challenges. The research efforts were to predict and measure changes and results in electrode morphology and performance based on process condition changes; to evaluate mixed, active, particle size deposition and drying for novel electrode materials; to model various process condition changes and the resulting morphology and electrode performance; and to develop and validate NDE techniques for in-line measurement of battery electrode material properties. These efforts carried through FY 2017 and completed at the end of FY 2018.
The approach was to look at compositions of materials with different particle sizes to make electrode samples using a R2R manufacturing process. The shape, size, and morphology of the materials, the chemistry of the formulation, the nature of slurries, their coating rate, the rate of drying all play a role in determining the final coating architecture, quality, and performance. A commercial cathode material was selected to make a series of cathodes and anodes by single pass, dual pass and slot die methods. Analysis of all the compiled results for this battery electrode development were that the best performing cathodes included: dual-pass electrode with large particles near the foil, mixed small and large particles, and small particles only. Whereas, the best performing anodes were with a mix of small and large graphite particles.
An additional core project was added in FY 2017 to conduct studies of fuel cell materials that can be produced using R2R processes. The goal of this project is to explore, understand and optimize material and process parameters to support increased throughput, increased quality, and reduced cost for high volume production of gas-diffusion electrodes (GDEs) for PEMFCs. Project work in FY 2018 were to use a R2R process to fabricate electrodes without ionomer overlayer that can produce the equivalent mass activity as spray-coated electrodes with an ionomer overlayer. Oxygen-limiting current measurements were utilized to optimize oxygen mass transport. Alcohol-rich solvents were investigated, and results were that the alcohol and water ratio can be tuned to control ionomer distribution. Water-rich solvents produce a more dispersed ink which results in better high-current density performance.
Two other projects for AMM Functional Materials and the R2R Water Project were added to the R2R portfolio in FY 2017 and completed in FY 2018. The AMM Functional Materials effort aims to enable advanced materials process research and development (R&D), scaleup and synthesis of next generation functional materials; develop several materials, processes, software tools and techniques that support and are potentially compatible with continuous manufacturing process technologies over a range of functional energy-related materials; prototype, characterize and develop a material properties database suitable to support related materials design; and provide uniform, baseline materials to industry for validation and to researchers for further development. Findings for functional materials were that the performance of LIB cathode materials depends significantly on the particle morphology, which is usually determined by the synthesis conditions. By combining experiments with computational models, a detailed framework has been developed that can minimize the cost associated with trials required for optimizing LIB cathode synthesis conditions. The objectives for the R2R Water Project were to remove the material manufacturing hurdle for water membrane materials, evaluate the manufacturing tools to improve material properties for energy and cost savings, and demonstrate the application of advanced manufacturing technology to improve water treatment efficiency and processing cost through development and installation of a semi-automated assembly system. Resin wafer technology is capable of providing greater than 35 % energy efficiency for water desalination compared to15 % for the current state-of-the-art technologies. Resin wafer electro-deionization (RW-EDI) technology was demonstrated for this project using a prototype continuous process line. Scaling up this process is expected to result in the potential to improve separation energy efficiency and material manufacturing costs (95% for labor and 90% production time) for multiple industrial sectors.
The FY 2018 collaborative effort successfully completed all tasks to develop an enhanced battery material using a R2R manufacturing process and to provide modeling, simulation, processing, and manufacturing techniques that demonstrate the feasibility and potential for scale-up. Technology transfer for these and other technologies applicable to R2R manufacturing was initiated collaboration with industry partners and through the initiation of three CRADA projects with industry. This DOE-industry partnership will result in low manufacturing costs, low energy processes, high volume production, high throughput due to improved materials, and compatibility with many material platforms.
Accomplishments
Collaboration and Outreach
The R2R AMM DOE Laboratory team participated in bi-monthly review meetings with DOE AMO and FCTO Program Managers to ensure information for each project was available on a continuous and regular basis. Team members also presented at the Association of International Metallizers, Coaters and Laminators, TechConnect World Innovation Conference, the 2018 DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Office Annual Merit Review and Peer Evaluation Meeting, the 2018 AMO Peer Review, the 2018 ASME Power and Energy Conference and Exhibition, the 19th International Coating Science and Technology Symposium, Beyond Lithium-Ion XI Symposium, and the Electro Chemical Society 2018 Spring Meeting. As a team, they initiated three CRADA projects that demonstrate all-solid-state batteries based on Li7La3Zr2O12 (LLZO) separators and cathode scaffolds that will allow scaling a freeze casting process to the pilot level, R2R production of an advanced separator for LIBs, and diffractive multiplexing for high-throughput R2R laser patterning of flexible organic PV modules. A fourth CRADA project to research R2R manufacturing of advanced (low loading, direct coated onto membrane) electrolysis electrodes for low-cost hydrogen production remained in the approval process at the end of FY 2018.
Structured Anode Study
Experiments and testing by ORNL and ANL achieved a significant improvement for rate capacity, power density, and energy density when structuring both the LIB anode and cathode. When a simple particle-size modification was made and combined with a thick bilayer approach, with an emphasis on materials processing and coating deposition methodology (dual slot-die and dual-pass), substantial improvements were realized in rated capacity at the higher discharge rates. The best long-term performer was a mixed particle cathode with a dual-pass, small-particle bottom layer. The worst performer was the all-large particle cathode paired with a single-pass, large-particle bottom layer. Findings for this technology will enable further development of simultaneous high energy and power density electrodes.
NREL and ORNL jointly developed and demonstrated a real-time in-line measurement for battery electrode porosity. This technique enables critical quality inspection for high performance battery electrode manufacturing. This joint effort also created and validated a transient heat transfer model of the electrode layer that linked porosity with thermal measurement. The model was used to validate measurements on cathodes coated on the ORNL R2R coating line.
Fuel Cell Study
The NREL-led study confirmed that R2R electrodes show the same trends and achieved equivalent mass activity as electrodes coated onto separate transfer liners and then hot-pressed onto the membrane or directly coated onto the membrane. R2R-fabricated electrodes without an ionomer overlayer produced equivalent mass activity to spray-coated electrodes with ionomer overlayer. Oxygen-limiting current measurements were utilized to further optimize oxygen mass transport. These efforts can be used to further optimize a continuous process for fabrication of multi-layer electrochemical media that has fuel cell application.
ANL x-ray scattering and tomography experiments provided support to NREL in developing catalyst-ionomer-solvent ink compositions and processing techniques for efficient R2R fabrication of GDEs. X-ray scattering was used to study the catalyst-ionomer ink agglomerate-aggregate structure as a function of ionomer content, ink solvent, and ink mixing procedure and time. X-ray tomography i.e., nano-computed tomography (CT) was used to visualize electrode structure and to quantify particle size and pore size distributions, thickness-dependent ionomer distribution, tortuosity, and effective transport properties. The optimum solvent and mixing procedures facilitate break-up of the catalyst support agglomerates into aggregates in the minimum amount of time and with the minimum input of energy while also not dislodging the catalyst nanoparticles from the carbon support. The optimum solvent and mixing procedures also result in an electrode microstructure forming an ionomer-rich layer at the electrode-air interface of the GDE while also having a uniform dispersion of catalyst/carbon, ionomer, and pores throughout the thickness of the electrode. The x-ray scattering results showed that inks with higher water content versus alcohol content lead to greater break-up of agglomerates and that 10 minutes of bath sonication is sufficient to reach the steady-state ink structure. The nano-CT studies showed that solvent has a strong influence on ionomer distribution, with less of an effect on porosity. The water-rich inks resulted in electrodes with a uniform distribution of ionomer through the thickness of the electrode, while the alcohol-rich inks resulted in high volume fractions of ionomer at the membrane and gas diffusion layer (GDL) interfaces. These studies also showed that drying temperature has a strong influence on porosity, but less influence on ionomer distribution. These results guided the NREL-led effort in GDE fabrication to achieve performance comparable to that of catalyst-coated membrane (CCM) electrodes.
Modeling, Simulation and Data Mining
The LBNL core project continued to focus on the modeling and simulation of electrode materials and data mining of material properties from the open literature for predictive synthesis of new materials. LBNL developed a physics model based on colloidal interactions and this model will be improved for predicting the rheological properties of slurries for electrode materials. Major interactions between particles, such as Van der Waals, electrostatic, and polymer steric interactions were included for calculating the viscosities. LBNL continued to investigate the properties of slurries, including particle size and zeta potential, particle and polymer mass ratio, and particle volume fractions. The current model well predicts the viscosities of anode slurries and will be modified for other materials including fuel cell materials.
A machine learning algorithm was implemented to identify potential targets and precursors of a synthesis route. The current accuracy estimated by calculation F1 score is: for materials F1 = 84%, for targets F1 = 83%, for precursors F1 = 84%. A Materials Entity Recognition algorithm was also developed and implemented to identify materials mentions in synthesis paragraphs and classify which materials are mentioned in context of starting compounds (precursors) and final products (targets) of the synthesis. The accuracy of the algorithm is ~90%. In significant number of paragraphs, target names are given in the form of an abbreviation, yet other significant fraction of target names contain off-stoichiometric variables. A third algorithm was implemented which obtains sequence of synthesis step from the synthesis paragraphs. The algorithm utilizes a feedforward neural network combined with a grammatical parser to traverse each sentence in the paragraph word by word and classifies them according to the following categories: not operation, start of synthesis, heating operation, mixing operation, drying operation, shaping operation and quenching operation.
Functional Materials
ANL researchers demonstrated the first-known studies for tracking, in situ, particle growth during synthesis and developed the first known model that links process conditions to growth morphology. Control of morphology during particle synthesis is rooted in empirical trial-and-error. This project demonstrated that a science-based approach can be developed to predict the morphology of the particle when changing process conditions. By developing in situ synchrotron-based methods to “watch” growth and combining them with growth models, this project brings science to empiricism and accelerates the time to develop new process conditions.
R2R Water Project
The ANL R2R Water Project completed the design and fabrication of a semi-automated assembly line (SAAL) to demonstrate a continuous process for the manufacture of a resin wafer to be used in industrial separations and desalination applications. The RW-EDI technology will provide a higher capacity and be more energy efficient than current processes and materials for water treatment. The assembly line is designed to increase the fabrication rate by 10x and incorporates industrial equipment which will significantly reduce the curing time by 60x for resin wafer fabrication. Application of this advanced manufacturing technology has the potential to improve separation energy efficiency and material manufacturing costs (95% for labor and 90% production time) for multiple industrial sectors. A new synthesis method of resin wafer has been developed that can reduce several unit operation steps using the SAL. A conceptual design of a full R2R manufacturing assembly line was completed based on the new synthesis method that can further reduce the manufacturing costs and production time.
CRADA Projects
Three CRADA projects were initiated mid-FY 2018. A project with Fisker, Inc. demonstrated the feasibility of a pilot-scale freeze-casting coating line at Montana State University and made initial recommendations to Fisker on how the freeze casting process could be industrially scaled. A project with Navitas Systems Inc. resulted in a down-selection of the separator material to be used in the CRADA project. Navitas also began some trial operations handling the separator in a R2R manner at their product site. A project with SolarWindow Technologies, Inc. selected a diffractive-optical-element-based multiplexing system for R2R laser scribing that will drastically reduce up-front capital and on-going operational costs compared to currently used laser/optics systems and will also increase process speeds over galvanometer step-and-scan systems.