Lithium is needed for smartphone, electric vehicle and power grid batteries. But extracting it is slow and energy-intensive. Researchers from the University of Texas at Austin have proposed a new way to separate lithium from other elements. The work is published in the Journal of the American Chemical Society.
The technology is based on nanoscale artificial channels. These are tiny pores built into a membrane. Their prototype was the natural "doors" in living cells through which ions and molecules enter. The new channels let lithium through but hold back competing ions that usually accompany it in nature.
In laboratory tests, these channels proved two to five times more selective for lithium than other recently created lithium transporters. According to the authors, their channels are among the most selective ever created.
"Lithium is in our phones, cars and power grids, but extracting it from the ground cleanly is still difficult," says Manish Kumar, a professor in the Department of Civil, Architectural and Environmental Engineering and the Department of Chemical Engineering, and one of the leaders of the research. "Our goal is a process that is faster, cleaner and easier to launch."
Lithium is found in underground salt waters - brines, in hard rock and in recycled batteries. There it is mixed with other dissolved substances: sodium, potassium, magnesium and calcium. Separating lithium from these "lookalikes" is difficult. Existing methods require a lot of time and energy, and sometimes leave hazardous waste.
The new work continues a technology previously created to separate other rare-earth elements - they are used in wind turbine magnets, electric vehicle batteries and screens. Now the approach has been extended to lithium. The scientists showed that the interaction of ions with chemical groups at the channel entrance, together with its narrow structure, ensures highly selective lithium transport.
"Now we have a toolkit rather than a single result," says Harekrushna Behera, a research fellow in Kumar's laboratory. "By understanding how ions interact with chemical groups at the channel entrance, we can design more selective channels for lithium and possibly other critical minerals."
The team is now working on packaging the channels into larger membranes. For this they use a recently developed material made of linked cell-like layers that can be made from lipids or plastic-like polymers. The goal is a continuous lithium separation process without harsh solvents.
However, the approach still has to be tested on real brines, where many salts are present at once, and at industrial scale. Only such tests will show how the technology works outside the laboratory. The researchers also see potential beyond extraction: recycling lithium from used batteries and, in the future, creating better separators inside the batteries themselves.