"Having a massive database at hand allowed us to find the products of very complex, previously unexplored chemical reactions that determine the coating's effectiveness."Muratahan Aykol, Lawrence Berkeley National Laboratory
It's always exciting to bring home a new smartphone that seems to do everything, but it can be all downhill from there. With every charge and discharge cycle, the device's battery capacity lowers a little bit more – eventually rendering the device completely useless.
"Why does this degradation occur? In some cases, we know; in other cases, we don't," said Christopher Wolverton, professor of materials science and engineering at Northwestern University's McCormick School of Engineering. "But, in many cases, something probably happened to the cathode."
Wolverton has now developed a new computational design strategy that can pinpoint optimal materials for coating the cathode in lithium-ion batteries, in order to protect it from degradation and ultimately extend the life of both the battery and the device.
The cathode, which holds the battery's lithium ions when it is discharged, typically comprises a compound containing lithium, a transition metal and oxygen. Batteries also contain an electrolyte through which the lithium ions move as they travel between the cathode and the anode, which holds the lithium when the battery is charged.
As the electrolyte decomposes over time, it can release hydrofluoric acid, a highly reactive substance that can attack the cathode. Researchers hypothesize this could be one reason why the battery loses capacity over time.
"A coating could serve multiple functions: it could provide a barrier around the cathode, preventing attack from hydrofluoric acid," Wolverton said. "Or a coating could preferentially react with the hydrofluoric acid, so there's none left to react with the cathode."
Partially supported by The Dow Chemical Company and the US Department of Energy, Wolverton's design strategy and results are described in a paper in Nature Communications. Muratahan Aykol, a former graduate student in Wolverton's laboratory, was the paper's first author.
Wolverton previously developed the ever-growing Open Quantum Materials Database (OQMD), which proved essential for his group's quest to find cathode-coating materials. Containing information on more than 470,000 compounds, the OQMD is one of the world's largest materials databases, is open to the public, and can be downloaded online. Wolverton's group designed a way to screen the materials in the database to discover those that could make effective barriers to or scavengers of hydrofluoric acid. The group ultimately identified and ranked 30 top candidates, one of which the Dow Chemical Company experimentally tested to discover that the coating could successfully prevent battery degradation.
"Having a massive database at hand allowed us to find the products of very complex, previously unexplored chemical reactions that determine the coating's effectiveness," said Aykol, who is now a postdoctoral fellow at Lawrence Berkeley National Laboratory. "Not only can we unveil a list of promising functional coatings, but we are helping our experimental colleagues target their resources to the best candidates."
While the search for cathode coatings is not a new venture, up to now researchers have explored potential coating materials largely through trial-and-error, which can be a slow and limited process. Exploring every material and combination of materials can result in millions, or even billions, of possibilities – far too many to test experimentally.
"There has never really been a design strategy for these coating materials," Wolverton said. "Computationally, we can quickly screen the vast landscape of possible material combinations to pinpoint 25 compounds that are potentially very promising. Now, 25 is a more manageable number that you could test experimentally."
Wolverton said that this design strategy extends beyond developing better batteries. It also aims to fulfill the vision of the Materials Genome Initiative, established by President Barack Obama in 2011 to help accelerate the discovery, development and deployment of new materials.
"These kinds of databases and computational approaches, in principle, are not limited to batteries," Wolverton said. "We are using computation to help design many types of materials."
This story is adapted from material from Northwestern University's McCormick School of Engineering, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.