Choi and other researchers have also tried to use lithium-ion battery electrodes to pull lithium directly from seawater and brines without the need for first evaporating the water. Those electrodes consist of sandwichlike layered materials designed to trap and hold lithium ions as a battery charges. In seawater, a negative electrical voltage applied to a lithium-grabbing electrode pulls lithium ions into the electrode. But it also pulls in sodium, a chemically similar element that is about 100,000 times more abundant in seawater than lithium. If the two elements push their way into the electrode at the same rate, sodium almost completely crowds out the lithium.
Lithium is prized for rechargeables because it stores more energy by weight than other battery materials. Manufacturers use more than 160,000 tons of the material every year, a number expected to grow nearly 10-fold over the next decade. But lithium supplies are limited and concentrated in a handful of countries, where the metal is either mined or extracted from briny water.
Lithium’s scarcity has raised concerns that future shortages could cause battery prices to skyrocket and stymie the growth of electric vehicles and other lithium-dependent technologies such as Tesla Powerwalls, stationary batteries often used to store rooftop solar power.
Seawater could come to the rescue. The world’s oceans contain an estimated 180 billion tons of lithium. But it’s dilute, present at roughly 0.2 parts per million. Researchers have devised numerous filters and membranes to try to selectively extract lithium from seawater. But those efforts rely on evaporating away much of the water to concentrate the lithium, which requires extensive land use and time. To date such efforts have not proved economical.
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