Three-layer membrane design extracts lithium from brines with greater speed, less waste

A team of researchers at Rice University has developed a new membrane that selectively filters out lithium from brines, offering a faster, cleaner way to produce the element at the heart of nearly every rechargeable battery.

According to a study published in Nature Communications, the new membrane achieved one of the highest selectivities for lithium among similar membranes while using considerably less energy.

The membrane design can be adapted to target the recovery of other valuable minerals, such as cobalt and nickel, and plugs into existing industrial setups. Tests of the material’s performance and durability indicate it is prime for large-scale synthesis.

Most of the world’s lithium is extracted from saltwater deposits, or brines, which involves sprawling evaporation ponds and extensive chemical treatments. The process is slow, inefficient and environmentally costly.

“The most widely used large-scale lithium extraction method today requires massive evaporation ponds and chemical precipitation,” said Qilin Li, the Karl F. Hasselman Professor of Civil and Environmental Engineering and co-director of Rice’s Nanotechnology Enabled Water Treatment (NEWT) Center.

“The process can take over a year to reach the target concentration and has fairly low lithium recovery rates. It also uses a lot of water, often in places that already experience water scarcity, and produces considerable amounts of chemical waste.”

The new membrane offers an alternative way of extracting the lithium via electrodialysis: When an electrical current is applied, lithium ions pass through the membrane, while far more abundant elements like sodium, calcium and magnesium remain behind.

“Typically, when you apply an electrical field, all the positively charged ions will transport across the cation exchange membrane,” Li said. “Lithium is actually a minor component in brine, but our membrane primarily allows lithium to transport across. Other ions stay behind.”

That selectivity makes the process both more efficient and less energy-intensive than standard industrial electrodialysis, which is typically used for desalination and wastewater treatment. The team achieved this by embedding nanoparticles of lithium titanium oxide (LTO) into the membrane, taking advantage of LTO’s crystal structure, which is just the right size for lithium ions to move through.

The challenge in utilizing LTO or other lithium ion sieves in membranes is the poor compatibility of the inorganic ion sieves with the polymeric membrane matrix, which often leads to defects in the membranes, undermining performance.

To overcome this limitation, the Rice team grafted the LTO with amine groups, which made it possible to mix them evenly into a plasticlike layer called polyamide, creating a strong, defect-free “skin” for the membrane.

“This project builds on our work through the NEWT Center, so it draws on 10 years of research on nanomaterials and nanotechnology,” said Li, who is one of the leaders of the Rice WaTER (Water Technologies Entrepreneurship and Research) Institute.

“We have learned how to incorporate nanomaterials into membranes and how to make nanocomposite membranes that fulfill a desired set of functions.”

Each of the membrane’s three layers can be independently optimized, making it a good platform for other applications such as the selective extraction of cobalt or nickel.

“Our goal was to develop a material that can extract lithium with minimum environmental impact,” Li said. “The smart design principles we used to develop the membrane architecture have ensured it can be adapted to help recover many other valuable resources from various waste streams.”

“One of the important features of our membranes is their potential to be produced at scale, which could pave the way for their use in industrial settings,” said Jun Lou, the Karl F. Hasselmann Professor of Materials Science and Nanoengineering.

The researchers tested the new membrane in an electrodialysis system and used computer simulations to zoom in and see how it works at the atomic level. The membrane proved strong and durable, maintaining its performance and withstanding degradation even after two weeks’ use.

Major contributors to the study included Rice alumni Yuren Feng and Xiaochuan Huang as well as Yifan Zhu, a postdoctoral researcher in the Lou lab.