Researchers in the United States have developed a new method to extract 99% pure lithium from a solution where the ratio of sodium to lithium was 1,000 to 1.
The team from the University of Chicago Pritzker School of Molecular Engineering found that electrochemical intercalation can be used to extract critical battery material lithium.
Common in the world of batteries and supercapacitors, it’s when researchers apply electricity to insert ions between the layers of a different material.
Using this technique to extract materials from water creates force-fed filters, using electrical currents to pull charged lithium ions through microscopic pathways. But the pathways that let lithium ions through will also admit other ions, including the vastly more common sodium.
The work reveals that the ion pathways that let lithium through layered material – in this particular research, cobalt oxide – are governed by the push and pull between two forces. This represents both an advance in pure science and a way forward for developing new, real-world extraction techniques, according to researchers.
Goal is to develop materials that can selectively separate lithium
“Our goal is to develop materials that can selectively separate lithium from other salts,” said the paper’s first author, former UChicago PME graduate student Grant Hill, PhD’24.
“For this class of materials, the main competitor is sodium, because they’re just so chemically similar in charge and size.”
Batteries are the workhorses of the global transition off fossil fuels, but the methods used to harvest the common battery material lithium are far from eco-friendly. They require huge quantities of acid to melt roasted spodumene ore or massive brine pits to pull millions of gallons of salt water from deep under the earth and let dry in the sun.
“We know there are two parallel reactions that will always occur at the same time,” said UChicago PME Assoc. Prof. Chong Liu, corresponding author of the new work. “One is driven by the charge, when put current in the material. The other one is that naturally, the materials will find equilibrium.”
Hill describes the ion pathways as a highway surrounded by parking lots.
“Every lithium ion when it’s starting has a lot of open sites next to it, and when the sodium is getting put in, it ends up squeezing all the lithium sites next to each other,” Hill said. “For the lithium-friendly areas of the material, that parking lot’s all full.”
Overcoming this challenge required both optimizing the particle size of the lithium ions and finding a balance between two competing reactions. The first of the two reactions is the intercalation itself, caused by the researchers using current to add ions between the layers. That’s the traffic down the highway. The second is the ion exchange as the competing sodium and lithium ions find equilibrium, the rate ions pull into the metaphoric parking lot, according to a press release.
Equilibrium occurs at its own rate, but the researchers can determine how quickly they pump ions in. This means they can set the “speed” of the first reaction to one of three options: faster, slower or the same as the speed of the second reaction, as per the release.
“We discovered that the three regimes behave very differently, and it’s only that when you allow enough time to let the ion exchange to catch up with the intercalation, then we can have this very reversible material response,” Liu said.
Researchers revealed that slowly inserting the ions and finding the ideal particle size allowed this reversibility.