As industries across the country begin the transition to renewable energy, the demand for batteries, and therefore lithium, is projected to rise dramatically. But, with much of the global lithium supply located outside of the United States, researchers are looking for new techniques to extract it from local, if somewhat unconventional, sources such as petroleum wastewater and geothermal brines.
One of the most promising of these extraction techniques is electrochemical intercalation, a process in which electrodes draw lithium from otherwise unusable water. Until recently, the technology had not reached the desired level of Li selectivity for extremely dilute water resources.
Now, researchers at the University of Chicago’s Pritzker School of Molecular Engineering (PME) have shown that “seeding” electrodes with lithium ions can help increase the host’s lithium selectivity and repel unwanted elements. Their findings were published in Nature Communications.
“In lithium extraction, you have competing intercalations between lithium and sodium that severely limits our ability to draw out lithium effectively,” said Chong Liu, Neubauer Family Assistant Professor at Pritzker Molecular Engineering, who led the study. “We wanted to understand what was happening on the molecular level and how we could control that selectivity.”
A material distinction
In chemistry, intercalation is the process by which “guest” ions are drawn into and stored within a “host” material, the latter acting as a sort of molecular beehive. The process is also reversible, meaning those same ions can be extracted and the process repeated over and over. It is the key mechanism behind rechargeable batteries.
When used for lithium extraction, electrochemical intercalation relies on a host material—in this case, olivine iron phosphate (a type of crystal)—that is especially well suited to attract and store lithium ions. While widely studied and one of the best-suited materials for the job, olivine iron phosphate is far from perfect. Competing ions are often drawn into the host material along with lithium, elements such as sodium, which reduce the system’s effectiveness.
Liu and her team wanted to understand what drove those co-intercalations and what happened once the two ions were stored within the crystal.