Lithium is a vital element in many electronic devices and chip technology. Lithium-based batteries are also a highly promising way of storing energy efficiently. The quantity of lithium available worldwide is, however, limited. One of the most important sources of lithium is seawater, in which lithium occurs in ionic form (as charged particles). Unfortunately, lithium is only present in seawater at very low concentrations, whereas other ions like sodium and chloride are present in high concentrations.
Membranes that selectively bind to positively charged ions (such as lithium) but not to negatively charged ions (such as chloride) exist and are used to separate positive and negative ions from each other. Membranes that selectively separate different positively charged ions (for example, lithium and sodium) do not exist. However, this type of technology is vital to meet the demand for lithium.
Separating positive ions
Researchers from the programme 'Spectroscopic analysis of particles in water' are therefore working on the development of polymer membranes that can selectively separate lithium from other positive ions. These membranes can be made selective by incorporating so-called crown ethers into the polymer. Crown ethers are molecules in which organic ether compounds form a closed circle.
It is very difficult to make a direct chemical bond between such crown ethers and the polymer chain. Nevertheless, this year the researchers managed to chemically place a specific crown ether in a polymer membrane. The first experiments have shown that the materials developed in this manner do indeed selectively bind to certain positive ions.
During the follow-up study the physicists want to place other crown ethers in the polymer membranes as well. They also want to achieve a higher crown ether density so that the permeability and selectivity of the membranes can be further increased. Then in the future it will be possible to obtain lithium from seawater.