Lithium, the lightest metal on the periodic table, plays a pivotal role in modern life. Its low weight and high energy density make it ideal for electric vehicles, cellphones, laptops and military technologies where every ounce counts. As demand for lithium skyrockets, concerns about supply and reliability are growing.
To help meet surging demand and possible supply chain problems, scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory have developed an innovative membrane technology that efficiently extracts lithium from water. Several team members also hold joint appointments with the University of Chicago Pritzker School of Molecular Engineering (UChicago PME).
“The new membrane we have developed offers a potential low-cost and abundant alternative for lithium extraction here at home,” said Seth Darling, chief science and technology officer for Argonne’s Advanced Energy Technologies directorate. He is also director of the Advanced Materials for Energy-Water Systems (AMEWS) Energy Frontier Research Center at Argonne and a UChicago PME senior scientist.
Right now, most of the world’s lithium comes from hard-rock mining and salt lakes in just a few countries, leaving supply chains vulnerable to disruption. Yet most of the Earth’s lithium is actually dissolved in seawater and underground salt water reserves. The problem? Extracting it from these unconventional sources has been prohibitively expensive, energy-hungry and inefficient. Traditional methods struggle to separate lithium from other, more abundant elements like sodium and magnesium.
In salt water, lithium and other elements exist as cations. These are atoms that have lost one or more electrons, giving them a positive electric charge. The key to efficient lithium extraction lies in filtering out the other cations based on both size and degree of charge.
The new membrane offers a promising low-cost solution. It’s made from vermiculite, a naturally abundant clay that costs only about $350 per ton. The team developed a process to peel apart the clay into ultrathin layers — just a billionth of a meter thick — and then restack them to form a kind of filter. These layers are so thin they’re considered 2D.
But there was a hitch: Untreated, the clay layers fall apart in water within half an hour due to their strong affinity to it.
To solve this problem, researchers inserted microscopic aluminum oxide pillars between the layers, giving the structure the look of a high-rise parking lot under construction — with many solid pillars holding each “floor” in place. This architecture prevents collapse while neutralizing the membrane’s negative surface charge, a crucial step for subsequent modifications.
Next, sodium cations were introduced into the membrane, where they settled around the aluminum oxide pillars. This changed the membrane’s surface charge from neutral to positive. In water, both magnesium and lithium ions carry a positive charge, but magnesium ions carry a higher charge (+2) compared with lithium’s (+1). The membrane’s positively charged surface repels the higher charged magnesium ions more forcefully than it does the lithium ions. This difference allows the membrane to capture lithium ions more easily while keeping magnesium ions out.
To further refine performance, the team added even more sodium ions. This decreased the membrane’s pore size. The result is that the membrane allows the smaller ions like sodium and potassium to pass through while catching the larger lithium ions.
“Filtering by both ion size and charge, our membrane can pull lithium out of water with much greater efficiency,” said first author Yining Liu, a Ph.D. candidate at UChicago and a member of the AMEWS team. “Such a membrane could reduce our dependence on foreign suppliers and open the door to new lithium reserves in places we never considered.”
The researchers believe this breakthrough could have broader applications, from recovering other key materials like nickel, cobalt and rare earth elements, to removing harmful contaminants from water supplies.
“There are many types of this clay material,” said Liu. “We’re exploring how it might help collect critical elements from seawater and salt lake brines or even help clean up our drinking water.”
In a world increasingly shaped by access to clean water and secure supplies of critical materials, innovations like this may help power not just our devices, but our future.
This research was funded by AMEWS, an Energy Frontier Research Center funded by the DOE Office of Basic Energy Sciences.
The findings first appeared in the journal Advanced Materials. In addition to Darling and Liu, Argonne authors include Yuqin Wang, Bratin Sengupta, Omar Kazi, Alex B. F. Martinson and Jeffrey W. Elam. Liu, Wang, Kazi, Elam and Darling also hold joint appointments with UChicago PME.