The global demand for lithium is continuously increasing. The energy-critical element is used to make rechargeable batteries, one of the core components of an electrified world. Electric vehicles (EVs) use them and power plants for storing energy from renewables when electricity demand is low. Lithium is the choice element for rechargeable batteries because it can store more energy by weight than other materials.
Unfortunately, it’s been predicted that there won’t be enough of it from land sources to meet the demand for decarbonizing the whole world. Lithium consumption went from 101,613 tons in 2009 to 212,719 in 2016 and is estimated to reach 498,000 tons in 2025. The rising demand is predominantly linked to the extensive use of Li-ion batteries in electronic devices, and now the high number of EV sales.
But seawater may hold the key. It contains almost 57,000 times more lithium than can be found on land. However, it’s highly diluted (present at approximately 0.2 parts per million) and challenging to extract because it coexists with other chemically similar ions, such as sodium. (When trying to filter lithium out, these other similar ions end up in the mix.) Luckily, researchers are persistent, and a team from Stanford University found a way to get around this problem.
The Stanford research team, led by materials scientist Yi Cui, used lithium-ion battery electrodes designed to be more selective. Common electrodes pulled lithium ions in, but also sodium. And since there’s 100,000 times more sodium in seawater than lithium, the lithium was wholly crowded out.
But the team’s purpose-built electrode is coated with a thin layer of titanium dioxide, which behaved as a barrier keeping most of the sodium out. Lithium is smaller than sodium, so it doesn’t have a problem going through the titanium dioxide. While this was effective, it wasn’t enough.
To shake off the excess sodium pulled in, they also have to change the voltage repeatedly. Every time the current reverses, the ions start to move away from the electrode. But the electrode material has a higher affinity for lithium, so those ions are the first to move into the electrodes and the last to leave. After ten cycles, the ratio of lithium to sodium is one-to-one. The whole process takes just a few minutes.
While this advance is a breakthrough, it’s still not as cheap as mining lithium on land. For now, the researchers are working on increasing selectivity further by testing other types of lithium-ion battery electrodes. Choi notes that the approach could potentially lead to recycling batteries by making it possible to recover lithium from spent cells.
