When Yong L. Joo, Chemical and Biomolecular Engineering, finished his PhD, he didn’t follow the traditional academic path—he couldn’t. As a South Korean citizen, he was required to return to Korea to fulfill his military obligation.
The government gave him a choice: three years serving in the military or five years doing research in the private sector. He chose the latter, taking a job producing fibers and bulletproof composite materials for soldiers’ helmets and gear. When he returned to the states and to academia, he wanted to design projects that combined his applied knowledge from industry and the fundamental training from his PhD. “I wanted to more fundamentally understand these processes used in industry,” Joo says, “and it also gave me a strong motivation, that I might be able to contribute something to the field.” Joo joined Cornell’s faculty in 2001 and began his work.
In 2010, when entrepreneur Eric Donsky came to Cornell in search of the next promising technology to commercialize, Joo was ready. He had refined a process to produce nanofibers without the use of expensive, toxic solvents. His cleaner process and materials had applications in filtration but also more promisingly in the competitive race to make materials for the next generation lithium-ion battery. Donsky and Joo teamed up to cofound a company, Axium Nanofibers.
That’s not the end of the story—it would take another six years of development to find a process and materials that fit the needs of manufacturers.
Advanced Electrospinning, an Evolving Technology
Electrospinning, a conventional fiber-making process, applies an electric field and a whipping motion to draw a fiber out of a polymer solution or melted polymer. Early on, Joo removed the solvents and began experimenting with water-based electrospinning. This allowed him to add metals and ceramics to the nanofibers, creating new materials with promising properties.
In the next evolution, Joo added more power. “Typically, we just use the electric field as the driving force, but we added high-speed, controlled air. So there are two driving forces—that’s what makes it so effective and synergistic,” Joo explains.
Dubbed “gas-assisted electrospinning,” this new process achieved what many had been chasing in the field: scalability. “Before, nanofiber from this conventional electrospinning process was limited because the production rate is low and the operating cost is high,” Joo says. “We are eliminating the use of solvent and are basically refining and augmenting this process to improve speed of production and control over the products.”
From Electrospinning Fibers to Electrospraying Droplets
With the refined process, Joo was able to make materials to improve all the major components of the lithium-ion battery: the anode, cathode, and the separator between them. In 2014, Axium opened a lab in Austin, Texas. When they went to manufacturers, however, they faced a major hurdle.
“Since the fiber dimension is so small, the material’s bulk density is relatively low, meaning that with the given space, you can’t put in large amounts of the material,” Joo says. “Initially, we were very naïve. We thought that if we made good materials, battery manufacturers would use them. But the industry wants materials that are ready to be used in their systems without modification. So we took it back to the drawing board.”
Since then, Joo’s process has evolved again—instead of fibers, he’s now able to use the same combination of forced air and electric field but this time to create small droplets that form a film. In other words, his group has moved from electrospinning fibers to electrospraying droplets. “The deposition of the sub-micron scale droplets makes a very dense coating or film that can resolve a lot of issues we had with the fiber-based system,” Joo says.
“We thought that if we made good materials, battery manufacturers would use them. But the industry wants materials that are ready to be used in their systems without modification. So we took it back to the drawing board.”
“It’s been a learning process,” Joo says, “working on the process and secondly, how to meet the manufacturer’s requirements. But as this process has evolved, it has given us ways to use the technology in many different areas other than batteries. This new electrospray process could be used in nanocoatings, sensor-making, and many other applications.”
Still Advancing—Adding Silicon for Lithium Ions Storage, and Graphene
The battery materials Joo has created with this technique surmount another challenge that the industry has faced—how to effectively incorporate silicon to store lithium ions. In current batteries, lithium ions flow between an anode and a cathode, generating electricity. “This anode and cathode material needs to accommodate large amounts of lithium because that’s your energy and storage capacity,” says Joo.
Most anodes in current batteries are made of graphite, a carbon material, which is not very efficient. “To accommodate one lithium ion, you need six carbon molecules,” says Joo. “One silicon molecule, on the other hand, can accommodate four lithium ions, that’s 24 times more effective.
“But nothing’s free,” Joo adds. When silicon stores the large amount of lithium ions, it swells, creating a structural challenge. “The electrode will eventually disintegrate with this expansion and contraction taking place over the charge and discharge,” Joo explains.
With the electrospray process, Joo’s team is making particles of silicon that form very dense layers of film. Then a two-dimensional sheet of conductive graphene is placed over the particles. “The concept is like a fishnet covering the live fish,” Joo says. “When the silicon tries to expand, these layers of graphene keep them in the right structure.”
The idea is not entirely new, Joo continues. “A lot of academics have worked on similar ideas but from a bottom-up approach, starting at the level of the atom and building up,” he explains. “But that approach is expensive and can only make micrograms to milligrams per day. Our process can lead to the formation of nanostructures at nanoscale, but we’re doing so with a top-down, scalable approach, using larger structures, but still achieving control at the nanoscale.”
He adds, “Our contribution is to use unique new science in nanotechnology and realize it in a scalable manner.”
Frustration, Patience, Rewards
Joo says the number one thing needed through the process of commercialization is patience. “We’re now about to have really good products, but it took us almost six years, and we had a lot of frustrations,” Joo says. “You also have to be able to convince nonexperts about your technology, so they have confidence in your approaches and the impact.”
Joo says the wait and work have been worth it, however, because the process has given him a new perspective. “My whole experience, going through this startup, gave me a broader perspective on how to run the research program here,” he explains. “After all, we are in engineering, so whatever you do eventually has to be linked to the benefits of mankind. We have a strong footing in fundamentals, but having some exposure to the real-world application provides new angles for tackling problems. That has been very valuable.”
These new considerations have benefited students, giving them more diverse exposure to fundamental as well as applied research and entrepreneurship. “It can be a new way of thinking and linking to a career path,” Joo says. “As opposed to working for a large company or becoming an academic, this is another option. It basically diversifies the possibilities, and there may be a lot of students who really fit this kind of path.”
Alumni working in industry, in turn, can help more students—and professors—bridge the gap between the university and industry. “If you do collaborate with industry, being a professor at Cornell gives a lot of benefits because of our extensive network of alumni. In many cases, you can find an alum working in the industry, and they value Cornell quite a lot.”
Joo adds, “As a part of the Cornell community, I want to share this experience because it’s opened up doors to different paths for the students and for our research—and that seems very important.”