New developments in designing high-energy lithium batteries could accelerate and increase their performance, scientists have claimed.
Researchers at the Massachusetts Institute of Technology (MIT) claim to have uncovered a new approach to analysing and designing new ion conductors, a key component of rechargeable batteries. It relies on understanding the way vibrations move through the crystal lattice of lithium ion conductors and correlating that with the way they inhibit ion migration.
"This provides a way to discover new materials with enhanced ion mobility, allowing rapid charging and discharging. At the same time, the method can be used to reduce the material's reactivity with the battery's electrodes, which can shorten its useful life," said the research team, which was led by Keck Professor of Energy Yang Shao-Horn, graduate student Sokseiha Muy, recent graduate John Bachman, and Research Scientist Livia Giordano.
The findings, which were reported in the journal Energy and Environmental Science, have been about five years in the making, said Shao-Horn. It started when she and her group were looking at how to control catalysts for water splitting, and applying it to ion conduction.
"We realised that there are a lot of materials that could be discovered, but no understanding or common principle that allows us to rationalise the discovery process," said Muy, the paper's lead author. "We came up with an idea that could encapsulate our understanding and predict which materials would be among the best."
The key was to look at the lattice properties of the solid materials' crystalline structures. This governed how vibrations, such as waves of heat and sound - known as phonons - passed through materials.
"This new way of looking at the structures turned out to allow accurate predictions of the materials' actual properties," said the team. "And once you know [the vibrational frequency of a given material], you can use it to predict new chemistry or to explain experimental results."
The researchers were then able to observe a good correlation between the lattice properties determined using the model and the lithium ion conductor material's conductivity. "We did some experiments to support this idea experimentally" and found the results matched well," Shao-Horn added.
The team found, in particular, that the vibrational frequency of lithium itself could be fine-tuned by tweaking its lattice structure, using chemical substitution or dopants to subtly change the structural arrangement of atoms.
"The new concept can now provide a powerful tool for developing new, better-performing materials that could lead to dramatic improvements in the amount of power that could be stored in a battery of a given size or weight, as well as improved safety," the researchers said.
The techniques could also be adapted to analyse materials for other electrochemical processes such as solid-oxide fuel cells, membrane based desalination systems, or oxygen-generating reactions.
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