Lithium-ion batteries used to power electric vehicles are the key to a clean energy economy. But their electrodes are often made using a wet slurry containing toxic solvents, an expensive manufacturing method that poses health and environmental risks.
Early experiments at the Department of Energy’s Oak Ridge National Laboratory revealed significant benefits to the dry battery manufacturing process. It eliminates the solvent while showing the promise of delivering a battery that is durable, less burdened by inactive elements and able to maintain a high energy storage capacity after use. Such improvements could drive greater EV adoption, help reduce carbon emissions and meet US climate goals.
The research was published in Journal of Chemical Engineering.
Dry processing is a new alternative that saves factory floor space as well as time, energy, waste disposal and start-up costs. However, until now, researchers had a limited understanding of how and why it works.
ORNL and industry partner Navitas Systems are investigating how the dry process affects the structure of battery materials and their electrochemical properties. Batteries generate energy as lithium ions travel between electrodes called the cathode and anode. The team focused on an electrode dry processing strategy, which involves mixing dry powders with a binder, then compacting the material to improve contact between particles. This strategy can be applied to the anode and cathode by focusing on any materials or mixing methods.
After Navitas developed the electrodes, the ORNL researchers, led by Jianlin Li and Runming Tao, measured their electrochemical performance under different conditions over different timeframes. The ORNL team was able to achieve a new understanding of how dry-processed electrodes degrade.
Batteries produced using the dry process show an “excellent” ability to maintain their capacity after long-term use, according to the study results. Dry process batteries are “highly chemically desirable” because their structure allows lithium ions to take a more direct path between the anode and cathode, the researchers found. The electrodes are thicker to allow a higher energy charge while reducing the inactive components that increase the size and weight.
“There are more active electrode materials,” Tao said. “And even after cycling, it has some cracks.” These two advantages show a high energy density and good long-term cyclability. The electrode can bend and flex well, showing excellent mechanical strength and the winding capability required for mass production of batteries.
The dry process can offer a variety of benefits to manufacturers and the US supply chain: It is highly compatible with today’s state-of-the-art electrode manufacturing equipment, while its reduced environmental impact makes the battery plants suitable for many areas.
“When you’re looking at gigascale factories, you’re looking at billions of dollars to scale up batteries,” said Bryan Steinhoff, technical lead and lead researcher on the project for Navitas. “Dry processing eliminates the coating and solvent equipment currently required for mass battery production. If you can use a dry process instead, you can reduce your footprint by up to 40 or 50%, save hundreds of millions of dollars and begin to be able to create an infrastructure that will replace the one that relies on Asia at the moment.”
The next step in the research is to strengthen the material that attaches the anode components to a thin metal current collector. “A main goal of this project is to develop or identify a better binder for the dry process, because the current binder is not very stable for the anode environment,” said Li. The team also worked on reducing the amount of carbon black, a material that maintains the battery’s conductivity but degrades its energy density.
ORNL and Navitas researchers continue to refine the process to improve electrochemical performance. The goal is to balance the benefits and disadvantages of a thicker electrode: It has the potential for a higher energy charge and is easy to roll, but it gives less power, because the ions there is more travel.
Running Tao et al, High-throughput and high-performance lithium-ion batteries by dry processing, Journal of Chemical Engineering (2023). DOI: 10.1016/j.cej.2023.144300
Provided by Oak Ridge National Laboratory
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