by Lithium-ion batteries have changed everyday life – almost everyone has a smartphone, more electric vehicles are on the streets and they keep generators running in emergencies. As more portable electronic devices, electric vehicles and large grid deployments come online, the demand for safe and affordable batteries with higher energy densities continues to grow.
Now a University of Houston research team, in collaboration with researchers from the Pacific Northwest National Laboratory and the US Army Research Laboratory, has developed an operando-reflection interference microscope (RIM) that provides a better understanding of how batteries work, with significant implications for the next battery generation.
“We have achieved, for the first time, real-time visualization of solid electrolyte interphase (SEI) dynamics,” said Xiaonan Shan, assistant professor of electrical and computer engineering at UH’s Cullen College of Engineering and corresponding author of a study published in the journal nature nanotechnology. “This provides important insights into the rational design of interphases, a battery component that represents the least understood and greatest obstacle to the development of electrolytes for future batteries.”
The highly sensitive microscope allows researchers to examine the SEI layer, an extremely thin and fragile layer on the surface of the battery electrode that determines battery performance. Its chemical composition and morphology are constantly changing, making it challenging to study.
“A dynamic, non-invasive and highly sensitive operando imaging tool is required to understand the emergence and evolution of SEI. Such a technique capable of directly examining SEI has been rare and highly desirable,” said Yan Yao, Hugh Roy and Lillie Cranz Cullen, Distinguished Professor of Electrical and Computer Engineering and co-corresponding author, who published the last four years of working with Shan on this project.
“We have now shown that RIM is the first of its kind to provide critical insight into the working mechanism of the SEI layer and help in the design of better high-performance batteries,” said Yao, who is also the senior researcher at the Texas Center for Supraconductivity at the university of Houston.
How it works
In the project, the research team applied the principle of interference reflection microscopy, in which the light beam – centered at 600 nanometers with a spectral width of around 10 nanometers – was directed onto the electrodes and SEI layers and reflected. The collected optical intensity contains interference signals between different layers, which contain important information about the development process of SEI and allow researchers to observe the entire reaction process.
“The RIM is very sensitive to surface variations, which allows us to monitor the same location with high spatial and temporal resolution at large scale,” said UH PhD student Guangxia Feng, who performed much of the experimental work on the project.
The researchers note that most battery researchers currently use cryo-electron microscopes, which only take one picture at a time and cannot continuously track the changes in the same place.
“I wanted to approach energy research from a different angle by adapting and developing new characterization and imaging methods that provide new information to understand the reaction mechanism in energy conversion processes,” said Shan, who specializes in developing imaging techniques and spectrometry techniques to study electrochemistry has specialized reactions in energy storage and conversion. This new imaging technique could also be applied to other cutting-edge energy storage systems.
Feng, who has a Ph.D. in electrical engineering from UH in 2022, plans further research in the growing field of battery technology.
“To realize the next generation of batteries, it is important to understand the reaction mechanisms and novel materials,” she said, adding that the development of higher-energy batteries would also benefit the environment. “I always wanted to be a scientist because they can do great things for people and change the world for the better.”
Pacific Northwest National Lab’s Wu Xu, an expert in electrolyte designs, helped with the project design and provided critical insight into the electrolyte to be used. Kang Xu, an SEI research expert at the Army Research Lab, provided key insights to understand the observed phenomenon. Both are co-corresponding authors for the paper.
Feng and another UH engineering student, Yaping Shi, along with PNNL’s Hao Jia, are the lead authors of the study. Other contributors include Xu Yan, Yanliang Liang, Chaojie Yang and Ye Zhang from UH; Mark Engelhard at PNNL.
