Engineer receives NSF CAREER award to improve lithium

Oct 26, 2023

Credit: Adobe Stock. All Rights Reserved.

May 31, 2023

UNIVERSITY PARK, Pa. — Lithium-ion batteries power most electronics, from smartphones to electric vehicles, and are even used to store energy to power entire homes. Globally, marketing analysts expect the lithium-ion battery market to grow from $65.9 billion in 2021 to $273.8 billion by 2030. Although lithium-ion battery use continues to expand at a rapid rate, not much is known about the forces that govern key processes that impact performance.

Feifei Shi, assistant professor in the John and Willie Leone Family Department of Energy and Mineral Engineering, received a $594,788 Faculty Early Career Development Program (CAREER) Award from the National Science Foundation (NSF) to rethink foundational electrochemical models, and potentially transform how lithium-ion batteries are designed. The impact could be seen in all electrochemical applications that use liquid electrolytes, such as flow batteries, fuel cells and supercapacitors whose usage spans from consumer products to grid-scale energy storage.

According to Shi, the lack of a more in-depth understanding stems, in part, from the discovery of the electronic double layer (EDL), the electrical phenomena that occur when a liquid and surface interact causing an electrically charged surface layer. The initial models created in the early 1900s have been a mainstay in electrochemistry, but not many researchers have taken a further look at them until now.

"Learning about electrical double layer is one of the first few models you're exposed to in a classical electrochemistry class, if not the very first," said Shi. "The model imagines perfectly spherical, ideal ions, but in reality, that simplicity does not exist. We cannot ignore the size, the shape or the space that ions occupy anymore."

Shi frequently deals with EDL in her research exploring interfacial properties, and finding ions like those depicted in the model has not been her experience. She explained that ions branch out and have visible ripples in battery electrolytes. Also, in organic salt solvents the microsystems are bigger, more dynamic, and have a wider range of expectant properties than in simple solvents like water. Shi believes a more accurate physical picture of those differences will enable battery researchers and developers to better understand the interfacial kinetics in battery performance, she said.

"Everything is designed based on the EDL," said Shi. "So, if your starting point is not 100% understood, how can you even know where to start? Understanding such a crucial component is essential to better, more rational battery design."

Many processes that occur in the EDL directly impact battery performance, said Shi, pointing to her cell phone and noting how everyone has experienced the results of an aging battery, and how over time batteries don't hold a charge as long or require more frequent charging. This decay in power is the result of corrosion or build-up on the passivation layer within the interface, she explained. Eventually, power is eaten and the liquid electrolytes inside the battery dry up. The rate a battery charges is determined by the kinetic behaviors in the EDL that affect how fast and freely electrons transfer, and how ions migrate between the interface. For electric vehicles (EVs), that means the top priorities of most potential electric-car shoppers such as driving range and charging speed can be improved with a better understanding of EDL.

As Shi sees it, there is an urgency to the work, she said. She is motivated by how advances in applied science and engineering outpace developments in fundamental science. She often sees new products released before knowledge can accumulate through experimentation and fundamental understanding. On the backdrop of the 2050 net zero deadline in the Paris Agreement, the need to focus on fundamentals is more important, said Shi.

"We need a new canon of understanding," said Shi. "Now is the time for fundamental research to catch up and push the frontier of our knowledge, and hopefully inspire a new picture or a new hypothesis that can help us meet the energy needs of our societies in an as sustainable way as possible."

Inspired by an electrocapillarity study from the 1950s, Shi's team developed new methods to explore the EDL using mercury as an electrode. Shi described mercury as a "miracle element" for its unique properties that make it affordable, easy to observe and measure. The allows for repeated studies to confirm results.

"When we began to look through the literature my graduate student came back and said most of the work is from the 1950s-1970s," said Shi. "It is intriguing to stand on the shoulders of giants and bring together with our advanced computers and more accurate ways to collect data to build on their groundbreaking work."

Shi said she is excited that her research may inspire the next generation of STEM scientists, engineers and researchers to come together to break down barriers in thermodynamics, interfacial chemistry and electrochemistry. Shi's research interests lie broadly at the intersection of surface chemistry, material science and mechanical engineering, with emphasis on integrated energy systems, such as catalysis, battery and nuclear energy systems.

Shi received a WiSTEM2D Scholar Award from Johnson & Johnson in 2022, which is designed for mid-career women working in science, technology, engineering, mathematics, manufacturing and design. In 2021, she was awarded a George H. Deike Jr. Research Grant and in 2019 the Virginia S. and Philip L. Walker Faculty Fellowship from the College of Earth and Mineral Sciences. She is the author of 55 articles and one book chapter, and has served as a guest editor for the journals Frontiers in Energy Research and Energy & Environmental Materials. She currently serves on the editorial board for the journal Energy Materials.

Shi earned her bachelor of science degree in chemistry from Fudan University, China, in 2010, and doctoral degree in mechanical engineering from the University of California, Berkeley, in 2015. Before joining Penn State in 2019, Shi was a postdoctoral researcher in the Materials Science and Engineering Department at Stanford University from 2016 to 2019.

Feifei Shi, assistant professor in the John and Willie Leone Family Department of Energy and Mineral Engineering. Credit: Penn State. Creative Commons

Patricia Craig

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