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University of Houston microscopy sees details of lithium-ion battery structures

15 Feb 2023

Reflection interference technique could help improve next-generation power sources.

Laser-based technologies have played their part in the refinement of lithium-ion batteries and enhancement of battery performance, such as the use of lasers to cut the electrodes used in the rechargeable power sources.

Other examples include recent work by Trumpf applying the company's VCSEL sources to the drying of electrode foils, potentially extending the working life of a Li-ion battery and accelerating their manufacture.

A project at the University of Houston has now developed a microscopy technique intended to provide new views of the internal structures of Li-ion batteries, helping engineers to design more efficient power sources through a better understanding of the solid phase dynamics involved.

As published in Nature Nanotechnology, the UH method is an operando imaging tool, meaning that it collects optical data under reaction conditions from a working system and allows simultaneous evaluation of both the structure and the activity of the Li-ion battery.

In particular, the method allows researchers to study the solid electrolyte interphase (SEI), a passive layer known to form on the anode of Li-ion batteries and then reduce both the efficiency and life of the battery.

"We have achieved real-time visualization of SEI dynamics for the first time," said Xiaonan Shan, from UH's Cullen College of Engineering. "This provides key insight into the rational design of interphases, a battery component that has been the least understood and most challenging barrier to developing electrolytes for future batteries."

Powerful tool for battery design

The Houston technique uses reflection interference microscopy (RIM) in which a 600-nanometer light beam is directed towards the electrodes and SEI layers, and reflected back from them.

The returning optical intensity contains interference signals between different layers, according to the project, carrying information about the evolution of SEI and allowing the researchers to observe the entire reaction process.

"The RIM is very sensitive to surface variations, which enables us to monitor the same location with large-scale high spatial and temporal resolution," said UH's Guangxia Feng, who noted that this contrasts with the cryo-electron microscopy often used currently for the same task. Unlike RIM, an electron microscopy approach only takes a single picture at a particular time and cannot continuously track the changes at the same location.

Data from RIM observations indicated that the SEI's stratified structure was created through distinct individual steps, in a complex sequence involving both permanent and transient assembly of organic and inorganic species. Such real-time visualization of solid-electrolyte interphase dynamics provides a powerful tool for the rational design of battery interphases, said the team in its published paper.

"A technique capable of direct probing SEI has been rare and highly desirable," commented UH's Yan Yao. "We have now demonstrated that RIM is the first of its kind to provide critical insight into the working mechanism of the SEI layer, and help design better high-performance batteries."

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