Study: New nanotube membranes reveal unusually fast lithium-ion transport

Researchers have developed a novel class of nanotube membranes that enable ultrafast ion transport. The findings open new pathways for high-efficiency clean energy generation, lithium recovery and molecular separation.

The study, published in Nature Nanotechnology and co-authored by researchers at the University of Illinois Chicago, shows that tiny, tube-shaped channels called boron nitride nanotubes can transport certain ions much faster than expected. These tubes selectively move lithium ions over other types, acting like a highway express lane. The findings suggest a promising platform for applications ranging from “blue energy” generation, in which power is harvested from the convergence of salt and fresh water, to lithium extraction for batteries.

“This is a unique mechanism that transports lithium ions very quickly through nanotubes,” said Sangil Kim, associate professor of chemical engineering at UIC and an author of the paper. “The ion transport is much higher than the theoretical estimation, and also existing experimental systems.”

Ion transport is central to many industrial processes. When salts dissolve in water, they separate into positively and negatively charged ions that can move across nanochannels at different speeds. Controlling how these ions move through membranes is important for technologies such as batteries, desalination, critical mineral recovery and renewable energy systems. However, achieving both fast and selective ion transport remains a major scientific and engineering challenge.

In their new study, the researchers created membranes with millions of tiny tubes made of boron nitride nanotubes, which behave unusually and carry a charge on their surfaces. When the scientists placed the membranes between ionic solutions with different salinities, they found that ions moved through the pores much faster than predicted. Lithium ions, in particular, moved 31 times faster than the researchers expected. Also surprising was how ions moved in relation to each other: lithium ions sped through the channels much faster than other ions.

To further test the system, Kim and his colleagues showed that their small membranes could power everyday electronics using only salt solutions. “They can operate a watch and a calculator,” Kim said.

The idea of generating electricity from ion movement isn’t new. “This is how an electric eel generates electricity,” Kim said. In nature, eels produce bursts of electricity by controlling the flow of ions across specialized cells in their bodies called electrocytes. These cells use ion channels to convert chemical gradients into electricity. Scientists have long explored how to recreate similar processes in engineered devices, like in the membranes used in this study.

Moving ahead, Kim and his colleagues hope to test further applications of the membranes, particularly the tubes’ lithium-separation abilities.

“We could apply these findings to lithium recovery from waste batteries,” he said. They also plan to drill down on exactly how this abnormal ion transport occurs.

Kim began studying boron nitride nanotubules when he first came to UIC a decade ago. He credits the interdisciplinary collaboration and support from the College of Engineering, as well as the skill and dedication of student researchers at the university, with moving the project forward.

“My talented students, including former PhD students Aaditya Pendse and Kun Wang, should be acknowledged for their contributions to this study,” Kim said. “The quality of students here at UIC is very, very high.”

In addition to Kim, Pendse and Wang, the other UIC co-authors of the study are Pavel Rehak, Volodymyr Koverga, Selva Selvaraj, Naveen K. Dandu, Roya Jafari, Anh T. Ngo and Petr Kral.

Written by Tess Joosse