Cornell researchers have developed a porous crystal capable of absorbing lithium-ion electrolytes and transporting them through one-dimensional nanochannels. This was achieved by combining two contorted molecular structures, as detailed in a study published in the Journal of the American Chemical Society. The design has the potential to improve the safety of solid-state lithium-ion batteries.
The lead author of the study is Yuzhe Wang ’24, with the project led by Yu Zhong, an assistant professor of materials science and engineering at Cornell Engineering. Zhong’s lab focuses on developing soft and nanoscale materials to enhance sustainability and energy storage technologies. Wang, a junior transfer student, approached Zhong about conducting a research project, and they embarked on developing safer lithium-ion batteries.
In conventional lithium-ion batteries, liquid electrolytes can cause the formation of dendrites—spiky structures that may short out the battery or even lead to explosions. Solid-state batteries are safer but face challenges due to higher resistance, slowing down ion movement through solids.
Zhong aimed to address these issues by creating a crystal with nanochannels large enough for smooth ion transport. Wang developed a technique combining two complementary molecular structures—molecular cages and macrocycles—to create this porous crystal.
Macrocycles are molecules with rings of 12 or more atoms; molecular cages are compounds with multiple rings. Their combination offers a pathway that reduces interactions between lithium ions and the crystal, providing smooth transport for the ions and high ion concentration.
Wang’s work was supported by the college’s Engineering Learning Initiatives.
Both macrocycles and molecular cages have intrinsic pores where ions can sit and pass through. By using them as the building blocks for porous crystals, the crystal would have large spaces to store ions and interconnected channels for ions to transport.
Yuzhe Wang, PhD Student, Massachusetts Institute of Technology
Wang designed the structure by attaching three macrocycles radially, resembling wings or arms, to a molecular cage at the center. These components then fused together, forming larger, more complex, three-dimensional crystals. According to Zhong, these crystals are nanoporous, creating one-dimensional channels that provide “the ideal pathway for ion transport.”
The macrocycle-cage molecules self-assemble, using hydrogen bonds and their interlocking shapes to achieve impressive ionic conductivity, reaching up to 8.3 × 10-4 Siemens per centimeter.
That conductivity is the record high for these molecule-based, solid-state lithium-ion-conducting electrolytes.
Yu Zhong, Study Senior Author and Assistant Professor, Materials Science and Engineering, Cornell University
To better understand the composition of their crystal, the researchers worked with Judy Cha, Ph.D. ’09, a professor of materials science and engineering, who examined its structure using scanning transmission electron microscopy, and Jingjie Yeo, an assistant professor of mechanical and aerospace engineering, whose simulations made clear how the molecules interacted with the lithium ions.
Zhong added, “So with all the pieces together, we eventually established a good understanding of why this structure is really good for ion transport, and why we get such a high conductivity with this material.”
The material can be used to create mixed ion-electron-conducting structures for bioelectronic circuits and sensors, as well as to separate ions and molecules in water purification and create safer lithium-ion batteries.
“This macrocycle-cage molecule is definitely something new in this community. The molecular cage and macrocycle have been known for a while, but how you can really leverage the unique geometry of these two molecules to guide the self-assembly of new, more complicated structures is kind of an unexplored area. Now, in our group, we are working on the synthesis of different molecules and how we can assemble them and make a molecule with a different geometry so we can expand all the possibilities to make new nanoporous materials. Maybe it is for lithium-ion conductivity or maybe for even many other different applications,” Zhong stated.
Doctoral student Kaiyang Wang, M.S. ’19; master’s student Ashutosh Garudapalli; postdoctoral researchers Stephen Funni and Qiyi Fang; and researchers from Rice University, University of Chicago, and Columbia University are the other study authors.
Cornell Engineering’s Engineering Learning Initiatives supported the study.
The researchers used the Cornell Center for Materials Research and the Columbia University Materials Research Science and Engineering Center, both of which are supported by the National Science Foundation’s Materials Research Science and Engineering Center program.
Journal Reference:
Wang, Y. et al. (2024) Supramolecular Assembly of Fused Macrocycle-Cage Molecules for Fast Lithium-Ion Transport. Journal of the American Chemical Society. doi.org/10.1021/jacs.4c08558
