Lithium needed for the battery revolution could be harvested from saltwater lakes thanks to a new membrane

Demand for lithium is rising due to its use in batteries for mobile devices, cars and clean energy storage. Securing access to natural deposits of the mineral is now a matter of strategic importance, but lithium can be found elsewhere in nature.

As an alternative to mining, Imperial researchers have created a technology that could be used to efficiently extract it from saltwater sources such as salt-lake brines or geothermal brine solutions.

Conventional lithium extraction from brines takes months and uses significant amounts of water and chemicals, generating greenhouse gas emissions in the process. The alternative developed by Dr. Qilei Song and his team in the Department of Chemical Engineering uses a membrane that separates lithium from salt water by filtering it through tiny pores.

The usual shortcoming with this approach is that the pores also let through magnesium and other contaminants, but the team have developed a class of special polymers that are highly selective for lithium. Details of the method, and how it can be scaled up for practical application, have just been published in the journal Nature Water.

Polymers of intrinsic microporosity

For more than a decade, Dr. Song has been working on a new generation of synthetic polymer membranes, based on materials known as polymers of intrinsic microporosity (PIMs). These polymers are shot through with tiny, hour-glass-shaped micropores that provide ordered channels through which small molecules and ions can travel.

In this new study, Dr. Song’s team fine-tuned the micropores to become highly selective for lithium. Used in an electrodialysis device, the lithium ions are effectively pulled through the membrane micropores by an electrical current, while larger magnesium ions are left behind.

Tested on simulated salt-lake brines, these PIM membranes were highly selective for lithium, and produced high-purity battery-grade lithium carbonate.

If these membranes are to be of practical use, however, they must be produced in large quantities. Fortunately, the polymers are soluble in common solvents and can be turned into membranes using established industrial techniques.

“The polymer synthesis routes are based on commercially available monomers and simple chemical modifications, which makes scaling up the membranes relatively easy,” said Dingchang Yang, a Ph.D. student in Dr. Song’s group who led the experimental work. They can also be incorporated easily into commercial membrane modules and combined with other separation processes, which will also speed their use.

Commercial prospects

Imperial has filed patent applications for these membranes and a range of different uses, including lithium extraction. Dr. Song is now working with Imperial Enterprise and ChemEng Enterprise, the technology transfer initiative of the Department of Chemical Engineering, to explore potential commercialization of the technology.

“We are in the process of establishing a climate tech company and are keen to build partnerships with companies to extract lithium at a large scale using real brine solutions,” he said.

Isolating lithium is just the beginning of the potential for these high-selectivity membranes. “This technology has tremendous potential in a variety of commercially important areas, from energy storage to water purification to recovery of critical materials in a circular economy,” said Professor Sandro Macchietto, Director of Enterprise in the Department of Chemical Engineering.

One line of investigation will apply the ion-exchange polymers and selective electrodialysis to the extraction of copper and other metal ions from mining process waters. “This links well with the sustainable extraction of critical materials, which is being pursued by the Rio Tinto Center for Future Materials at Imperial,” Dr. Song said.