Two paths, many benefits

Credit: ORNL, U.S. Dept. of Energy

Project lead Edgar Lara-Curzio said the effort provides three key benefits: Enabling wider adoption of electric vehicles to slow climate change impacts; protecting national security by reducing dependence on foreign materials; and bringing economic development to former coal mining communities.

Bishnu Thapaliya, an electrochemist on the research team, said the potential impact is inspiring. "We can pivot from using coal to generate electricity to using coal to enable clean energy technologies, while helping people get back jobs and diversifying the supply chain for industry," he said.

The University of Kentucky Center for Applied Energy Research partnered with ORNL to prepare and supply pitches, coal and waste coal materials for use in the project.

Industry partner Ramaco Carbon, a subsidiary of Ramaco Resources, Inc. which owns coal mines in Wyoming and Appalachia, supplies coal for the project and is poised to commercialize the technology. "We are encouraged by the progress and breakthroughs we've made working with ORNL and are actively reviewing plans to design and build a pilot production facility that we can ramp into larger-scale production," said Ramaco chairman and CEO Randy Atkins.

The project has rapidly produced a series of significant scientific and engineering advances. First, ORNL researchers optimized a process to heat the coal without oxygen, which prevents burning and transforms it into two major products: gases that can be condensed into coal liquids, and coal char. One branch of the research team invented a method to treat the liquid byproduct before using an existing pressure-spray technique to make fine particles. Meanwhile, colleagues developed a recipe for converting either the particles or the char into graphite inside an electrochemical reactor.

"Lithium and cobalt are two critical minerals in batteries that grab all the headlines, but the biggest material by weight in the EV battery is graphite," said Eric Wolfe, an engineer leading ORNL's effort to scale up the electrochemical reactor. "The better the quality of graphite, the better battery you're going to have. We can't mine it here in the U.S., but now we can make it."

The performance and cost are competitive. A preliminary techno-economic analysis concluded the new process could be less expensive than conventional methods of making graphite. Test batteries made using ORNL graphite maintain their capacity after hundreds of cycles almost as effectively as their commercial counterparts.

The ORNL method can even make graphite with waste from coal processing and old mines, creating value while performing environmental restoration. "We are very excited because we have found a way to utilize as much coal waste as possible," Lara-Curzio said.

Laying the groundwork

ORNL's electrochemical approach begins with preparing the feedstock by heating coal granules in a process called pyrolysis to produce coal char and coal liquids, while simultaneously analyzing their organic components. A set of researchers led by Thapaliya developed a benchtop electrochemical process for converting these coal byproducts to graphite.

The conventional synthetic graphite approach, named for inventor Edward Goodrich Acheson in the 1890s, relies mostly on extreme heat. In an iron crucible, batches of silica or quartz sand are combined with a powdered carbon material called coke at over 4,000 degrees Fahrenheit.

ORNL's electrochemical approach creates the graphite from coal byproducts at just 1500 degrees Fahrenheit. The conversion occurs when 2.7 volts are applied into an electrochemical reactor, causing ions to travel through molten salts between electrodes. The method creates no emissions or waste products.

Thapaliya's team made the graphite into negatively charged electrodes called anodes, which they incorporated into experimental lithium-ion batteries and tested. Experiments with various combinations of voltage, time and salts created the ideal surface area and porosity for ion movement. The researchers found that even coal mining waste, which is full of silica and inorganic materials, can be made into a carbon/graphite composite that works as a battery anode.

To understand the materials at a molecular level, researchers used a comprehensive collection of techniques such as X-ray diffraction, computed tomography or CT scanning, mass spectrometry, nuclear magnetic resonance, small-angled neutron scattering, and examination with high-resolution electron microscopes.

Two pathways

Wolfe brings 30 years of experience in the coal char industry to his job of scaling up Thapaliya's benchtop graphite process to a larger reactor. Wolfe grinds char into small, round particles, mixes it with a binder and presses the material into cylindrical pellets 36 millimeters across. Pellets are loaded into an electrically conductive cylindrical holder, which is inserted into a chest-high reactor in Wolfe's lab.

Unlike char, coal liquids require further treatment before entering Wolfe's reactor. First, they are filtered and then heat-treated to produce pitch, which is dissolved in a solvent. Researchers led by ORNL's Frederic Vautard adapted an industrial process to spray this mixture through a nozzle. Pressurized air causes the solvent to evaporate while the pitch solidifies into spherical particles which fall into a glass jar.

ORNL computational scientist Stephan Irle and his team developed software to automatically generate 3D molecular models of different types of coals and pitches, and performed large-scale simulations which helped with the selection of the best solvent and with predicting how changes to the process would affect the final product.

Spray-drying eliminates the energy-intensive grinding step for creating uniform, round particles. This shape flows more easily in a liquid slurry during battery manufacturing, and later allows ions to move more easily between electrodes during battery operation. Wolfe said shaping round particles from graphite results in wasting part of the resource.

"The spray-drying method allows us to dictate the particle size without losing valuable material," Lara-Curzio said. "That is an important innovation because for making lithium-ion batteries, companies want tiny particles of about 20 microns."

Wolfe continues improving not only graphite quality, but production quantity and speed. He has already scaled up from generating 5 grams of graphite to 500 grams at a time, although the reactor can produce kilograms in each batch. Process improvements are increasing the quantity converted during the reaction.

Wolfe also is working to accelerate production time, which clocks in at 4.5 hours. "Any time we reduce the cycle time, you bring down costs, and that's the key to bringing this to commercialization," he said.

Conversion might be happening more quickly already. To find out, the team is awaiting access to an immensely powerful particle accelerator, which generates a light beam that will allow researchers to peer inside the molten salt reaction while it occurs in a test tube. "That's the key to understanding the mechanism of reorienting the carbon atoms to form graphite and how fast it happens," Lara-Curzio said.

From research to rollout

While many ORNL experts work to improve graphite production, others are already pivoting to commercialization.

The recent preliminary economic analysis led by ORNL researcher Prashant Nagapurkar confirmed that the electrochemical approach could be scaled up profitably. Based on a factory manufacturing 10,000 tons a year, the new process would cost about 13% less than the cost of the conventional Acheson process, which ranges from $7 to $20 per kilogram.

The study considered the cost of raw materials, labor, energy, equipment, depreciation and more. The ORNL method produces more graphite than the Acheson method for the same amount of wear on equipment because it takes only hours instead of 3 to 6 days.

"In the ORNL process, if the electricity is green, the whole process is green," Nagapurkar said. "Especially because coal historically has this reputation as 'dirty,' a particularly important next step is to track emissions from the entire supply chain through the manufacturing process. This could demonstrate that it is indeed a greener option to manufacture graphite from coal."

Ramaco's cooperative research and development agreement with ORNL covers ways to use coal to make a variety of valuable products. The company, founded in 2011, began with the purchase of an older Wyoming mine for coal supplying power plants but also opened new mines in Virginia and West Virginia that produce coke for making steel.

"Our approach has been guided by our mantra that 'coal is too valuable to burn,'" Atkins said. "We are actively pursuing new technologies that use coal as a feedstock to make advanced carbon products and materials. We view partners like ORNL as critical to providing the research and guideposts for how we can best approach the commercialization process."

Atkins said Ramaco is already experimenting with making graphite from char in its Wyoming lab and exploring the possibility of manufacturing graphite near its Appalachian mines, an endeavor that would take several years as the company develops procedures to confirm the quality of the product.

Lara-Curzio said ORNL will eventually hold workshops to share the study results with other battery and equipment manufacturers. "We are pursuing translational research that enables scaling up these technologies. Then companies can license them and set up shop in Appalachia or communities that have a very strong connection to coal - not just to make the graphite, but hopefully to make the batteries as well," he added.

The project was funded by the DOE Fossil Energy and Carbon Management Program. Additional researchers who contributed to the research include Ercan Cakmak, Harry Meyer, Albina Borisevich, Gs Jung, Huimin Luo, Sheng Dai, Vlad Lobodin and Matthew Ryder and former ORNL researcher Pilsun Yoo.

UT-Battelle manages ORNL for the Department of Energy's Office of Science, the single largest supporter of basic research in the physical sciences in the United States. The Office of Science is working to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science.