Whether she is researching ways to improve the lithium-ion batteries that power our laptops, smartphones, and electric vehicles, or investigating corrosive damage caused by molten salt in nuclear salt reactors, Feifei Shi finds herself stuck at the surface.
Shi, an assistant professor of energy engineering in the John and Willie Leone Family Department of Energy and Mineral Engineering, is rethinking electrochemical models that describe what happens at the interface between two substances where an electrical field exists.
Her work could someday help improve how long our smartphone batteries last, or how far our electrical vehicles can travel, and how safe they are.
“This is a very established topic—a lot of great scientists have worked in the area, and it’s one of the first things our students learn about it in textbooks,” Shi said. “Something I’ve realized is the most common topic can be the most difficult. Because everyone is so familiar with it, introducing something new can be a big challenge.”
Solids and the surface
Interactions at the surfaces of materials are notoriously difficult to predict. Just ask Wolfgang Pauli, the Austrian theoretical physicist, pioneer of quantum physics and Nobel prize winner, who notably said, ‘God made solids, but surfaces were the work of the devil.’
“People may realize the bulk is easy to predict,” Shi said. “But at the surface, it’s much different and unpredictable. Unless you do the experiment, you never know how it will go.”
This is in part because of the electrical double layer (EDL), the physical phenomena that occurs at the interface between electrolyte and electrode causing a heterogeneous interfacial layer.
The EDL is the most important part of any electrochemical system because it is where the electron transfer and ion diffusion occur.
“Lithium-ion batteries, fuel cells, and electrochemical catalysis all have these solid-liquid interfaces,” Shi said. “Almost all electrochemical devices are greatly influenced by the double layer structures. It’s a core tenant or the holy grail for electrochemistry science.”
Lithium-ion batteries, for example, traditionally have solid positive and negative electrodes and then a gel or liquid electrolyte solution. The electrolytes contain ions that allow electrons to move back and forth between the ends of the battery, generating power.
Initial models of the EDL were created for dilute salt in aqueous solutions in the early 1900s and today are one of the first concepts students may learn when studying electrochemistry. But those classical models may not work when considering the organic electrolytes in lithium-ion ion batteries, Shi said.
A better understanding of these the ions and how to harness them may help produce higher power and more efficient batteries and other devices, something that’s particularly important as countries look to move away from fossil fuels and the carbon dioxide they emit into the atmosphere.
In battery applications, the EDL significantly impacts performance. However, the fundamental knowledge of EDL in batteries is still lacking.
“The key is, how well do we understand the double layer,” Shi said. “If we have a better understanding, we may be able to expend limited resources and reap a big reward.”
Better batteries
Improvements to lithium-ion batteries have helped revolutionize our daily lives—powering our technology and providing new solutions for energy storage that could help mitigate climate change.
“Today, electrochemical power sources like lithium-ion batteries, fuel cells, and supercapacitors are critical for developing alternatives to fossil fuels and mitigating the impacts of climate change,” Shi said.
Globally, marketing analysts expect the lithium-ion battery market to grow from $65.9 billion in 2021 to $273.8 billion by 2030. But even as it continues to grow, the industry is hitting obstacles to keep pace with the increasing demand due to the lack of improvements in fundamental battery technology.
Shi recently received a $594,788 Faculty Early Career Development Program (CAREER) Award from the National Science Foundation (NSF) to tackle the problem.
“This is a challenge but improving battery technology is a worthy goal,” Shi said. “We have developed our own experimental tools that marry interfacial energy variation with customized in-situ spectroscopy measurements. We would like to combine classical thermodynamic measurements with vibration spectroscopy measurements to have a comprehensive view of properties and structure.”
Shi’s team has developed new methods to help describe EDL properties by using mercury as an electrode. Mercury’s unique properties make it an affordable and easy way to observe and characterize the EDL.
“My ultimate goal is to push the boundary of surface science and electrochemistry,” she said.
Sustainability through electrochemistry
Chemistry —it seems—chose Shi and not the other way around. Her mother earned a doctorate in the field and Shi displayed a keen interest from a young age.
Pursing a bachelor’s degree in chemistry from Fudan University in China, Shi’s first project as a second-year student involved fuel-cell catalysis—a type of electrochemistry.
“I felt like it was magic,” Shi said. “In traditional chemistry we have to heat things up hundreds to a thousand degrees Celusis to make interesting things happen. But if you apply electricity and just give it several volts, it kicks off reactions. And you save a whole lot of energy.”
After graduating, Shi came to the United States to pursue her doctorate in mechanical engineering at the University of California, Berkeley. There she began working on lithium batteries for electric vehicles through the Department of Energy’s Vehicle Technologies Office and has continued working to improve batteries ever since.
Today, her work includes efforts with the Battery500 project, a team of scientists from national laboratories, academia, and industry working to develop more reliable, high performing, safe, and less expensive batteries for electric vehicles.
She also works with colleagues in the department to develop new ways to extract critical minerals like lithium needed for battery technology in economical and environmentally friendly ways.
“I’m interested in applying my knowledge of electrochemistry to mining and to help make a lot of processes like extraction more energy efficient and to reduce the environmental impacts,” Shi said. “My colleagues are the right partners to help achieve these goals.”