This article appears in the Spring 2013 issue of Energy Futures, the magazine of the MIT Energy Initiative. Subscribe today.
MIT Professor Yang Shao-Horn admits that as a girl she wasn’t a very good student — at least according to traditional standards. Born and raised in Beijing, where standardized exams were the common measure of academic success, Shao-Horn excelled at exploring open-ended questions. She dreamed of becoming a dancer.
Now, as the Gail E. Kendall associate professor of mechanical engineering and associate professor of materials science and engineering at MIT, Shao-Horn works at the cutting edge of basic energy science research, endeavoring to uncover the secret forces at work inside batteries and fuel cells—research that holds promise for a wide range of energy-related applications, from electric cars to solar power.
Already, she has made several key discoveries. In 2008, she was part of a team that took the first atomic-scale compositional images of fuel-cell nanoparticles. In 2011, she established a design principle that governs oxygen electrocatalysis on oxides and identified a new catalyst capable of speeding up water oxidation — the reaction central to advanced energy-storage systems — by a factor of 10. And in 2012, Shao-Horn’s lab used X-ray photoelectron spectroscopy to reveal new details of the complex reactions taking place within advanced lithium-air batteries.
Shao-Horn has won numerous honors for her work in electrochemical and photoelectrochemical energy storage and conversion, including the Charles W. Tobias Young Investigator Award (2008), the Tajima Prize of the International Society of Electrochemistry (2008), and the International Battery Association Research Award (2013). But energy research was not what Shao-Horn set out to do when she first headed off to Beijing University of Technology. Her goal was to become a metallurgist like her father.
It was at graduate school at Michigan Technological University that she made the surprising decision to study lithium-ion battery materials, which were just then hitting the market. This research topic was not known in materials science and engineering at that time. “I chose a topic I knew nothing about,” she says. “I wanted to go into a completely new area and be adventurous.” Using transmission electron microscopy, she explored how the material structure functions and influences battery capacity during charge and discharge.
Ever since, Shao-Horn has continued to venture across disciplinary boundaries. In 2002, she joined MIT’s faculty in mechanical engineering—even though her degrees are in metallurgical and materials engineering. She credits her husband, Dr. Quinn Horn, with getting her to apply for the position. “I said, look, first of all I don’t have a mechanical engineering degree. Second, I know nothing about fuel cells,” which was the specialty requested in the posting, she recalls. But he could see that her skills were a good match and encouraged her to apply anyway. She got the job.
Initially, she admits, she found the prospect of joining the Institute “daunting.” But now, she says, “I just find that MIT is really a fascinating place with many stimulating, exciting, admirable faculty.”
Shao-Horn quickly became involved in multidisciplinary energy projects on campus. In particular, she served on the MIT Energy Research Council, which launched the MIT Energy Initiative in 2006. She also helped found MIT’s Electric Vehicle Team in 2007, donating a 1976 Porsche for students to convert to battery power. “It was a fantastic project with students from multiple disciplines and departments involved,” she says, adding that the project helped her understand how to utilize the lithium-ion batteries she was researching in a practical application.
Today, as director of MIT’s Electrochemical Energy Laboratory, she oversees the work of more than 20 graduate students and postdoctoral associates. “I find that it is the most rewarding, to work with students and see them transform from when they arrive and some don’t know what they want to do in life...into confident, brilliant, and professional individuals,” she says. Her PhD students have gone on to industry and to faculty positions at Cornell University, Georgia Institute of Technology, and various universities in Asia.
To ensure that MIT students are equipped with a fundamental understanding of the concepts, tools, and applications central to electrochemical science and engineering, Shao-Horn introduced a new subject in 2006, 2.625J/10.625J Electrochemical Energy Conversion and Storage. This graduate-level class has drawn students from mechanical engineering, chemical engineering, and materials science at MIT and from Harvard, Northeastern, and Tufts. “We combine the traditional concepts of electrochemistry or electrochemical techniques with chemical physics or surface chemistry, looking at how molecules react at surfaces. These traditionally separate concepts are combined in one course,” she says.
“Energy storage is becoming a very popular topic,” she says, explaining that it is central to the practical use of such renewable but intermittent power sources as wind and solar energy. “We store solar energy or wind energy by splitting water into hydrogen and oxygen, and then in batteries or fuels cells we combine them and power our needs.” The difficulty is that current storage solutions lose energy due to the inefficiency of the electrochemical reactions.
To make these technologies practical, Shao-Horn investigates the fundamental nature of the chemical reaction that drives battery technology—the movement of electrons from a positively charged electrode (anode) to a negatively charged electrode (cathode) through an electrolyte. The oxidation reaction at the heart of this process strips ions from the electrolyte and binds them to the anode, freeing electrons to travel from the anode to the cathode, powering a load along the way.
Most recently, Shao-Horn has been exploring ways to improve the performance and lifespan of lithium-air batteries in an effort to develop a viable alternative to the lithium-ion batteries now used in electric vehicles. While lithium-ion batteries remain the state of the art, lithium-air batteries are lighter and more powerful, providing two to three times as much energy by weight. However, to date they have proved much less efficient. Typical lithium-air batteries return just 60 percent of the energy used to charge them, while lithium-ion batteries are 90 percent to 95 percent efficient.
Together with her team and collaborators, Shao-Horn has already managed to develop an experimental lithium-air battery that demonstrates a round-trip efficiency of 75%—among the highest efficiencies reported. To move further forward, she continually asks fundamental questions about the process, such as: What is the physics behind the reactions that control the functionality of materials? What is the mechanism by which a material or series of materials exhibits high stability or low stability?
The goal of creating better energy-storage technology is ever present. “Not only do we push the boundaries of knowledge, but we’re also passionate about applying our new findings in practice to create new catalysts, new battery electrodes, and new energy-storage systems,” she says. “We’re interested in understanding how the surface, for example, reacts with lithium, reacts with oxygen, how the surface reacts with water—that could have huge fundamental implications in terms of understanding...catalytic activity for solar fuel applications or for lithium-air batteries.”
Succeeding in this work requires multidisciplinary collaboration, and Shao-Horn continually reaches out to a “bigger pool of people with multiple talents to work with,” she says. “We work with chemists and chemical engineers, physicists and mechanical engineers, and materials scientists.”
She is also involved with the Singapore-MIT Alliance for Research and Technology’s interdisciplinary research group on low-energy electronic systems as well as with the Center for Clean Water and Clean Energy at MIT and the King Fahd University of Petroleum and Minerals in Saudi Arabia. Projects for these groups include trying to change the architecture of electronics so that devices consume less energy, and helping Saudi Arabia diversify from an oil-dependent economy.
Clearly, Shao-Horn enjoys tackling new challenges. “I enjoy adventure and like to sense the unknown,” she says. “That’s why I like to work on open-ended problems.”