Author: Conner Allen
Figures A through E illustrate ion behavior within battery structure tunnels. Image from Nature Materials.

A Johns Hopkins materials scientist was part of a team that has discovered how to make the lithium-ion batteries used in smartphones and electric vehicles charge faster and hold a charge longer. 

“We wanted to improve the energy storage of these batteries that power everything from laptops and tablets to cars, power tools, and even backup energy systems. We figured out a way to pack the battery with more lithium ions to allow them to store more energy,” said team member Yuting Luo, an assistant professor of materials science and engineering at the Whiting School of Engineering, who worked with collaborators at Texas A&M University on the project. Their results appear in Nature Materials. 

The key is a technique called pre-intercalation, during which the researchers first insert metal ions into the battery material, opening tunnels and creating more space for ions to move around and store more energy. In addition, for this study, the team chose to work with vanadium oxide, a metal material that is not only stable but also readily available. 

“We are searching for a cobalt substitute for battery manufacturing since cobalt is toxic to the environment and heavily relied on globally,” says Luo. “Vanadium oxide has a high capacity for energy storage, is very thermodynamically stable, and abundant around the world. Using it can help reduce dependence on cobalt for batteries.”  

She says that V2O5 was used in this work as the active material to create a cathode, which is a positively and negatively charged electrode that allows electricity into a battery. 

To start, the team introduced sodium and potassium into the V2O5 tunnels, forming two pre-intercalated compounds: sodium ions (NaxV2O5) and potassium ions (KxV2O5). These materials exhibit different electrochemical behaviors, including variations in their energy storage capabilities and the pathways along which the ions can move through the crystal structure. Luo and the researchers observed these distinctions by applying two experimental techniques: they examined the electrochemical reactions using a synchrotron (a powerful x-ray source), then analyzed individual crystals using specialized diffraction methods. 

“When lithium ions passed through the structure, we were surprised to discover that the pre-intercalated sodium ions rearranged themselves within the tunnels whereas potassium-ions retained their original positions,” says Luo. “Our findings show that diffusion pathways have a significant impact on electrochemical performances, offering a new approach to the design of battery materials and a new understanding of ion diffusion.”  

Luo presented her findings at the APS and Center for Nanoscale Materials Users Meeting on May 6.