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Battery Technology Could Transform Seawater To Freshwater

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The technology that charges batteries could turn salty seawater into fresh water, new research from University of Illinois has shown.

The team of mechanical science and engineering professor Kyle Smith and graduate student Rylan Dmello found that electricity that runs through a battery filled with salt water draws salt ions out of the water – and they are developing a device that will do this using the smallest energy amount possible.

Lithium-ion batteries are the main feature of electronic devices such as laptops and smartphones, but lithium’s relative scarcity has led researchers to seek a fitting alternative, one of which is sodium, which composes over 2.6 percent of Earth’s crust.

Sodium-ion battery technology, while still in its early phases, emerges as a potential key in cost-effective energy solutions.

The researchers developed a sodium battery that, much like lithium-ion ones, has ions flowing from one electrode to another. The batteries contain salt water, and when they discharge the two elements of salt – namely sodium and chloride ions – are drawn to one of its two chambers, leaving desalinated water in the other.

The team had to devise a way to keep the salt from getting to the purified water.

Normal battery separators allow salt to diffuse from the positive electrode into the negative one, said Smith. "That limits how much salt depletion can occur. We put a membrane that blocks sodium between the two electrodes, so we could keep it out of the side that's desalinated.”

Reverse osmosis is the prevailing method in water desalination, pushing water through a membrane that keeps the salt out but in an expensive, inefficient fashion. In contrast, this novel battery method uses electricity for drawing charged salt ions out of the water.

Smith highlighted several advantages of their battery approach over reverse osmosis, including its ability to be small or large depending on the intended application. There is also much less pressure needed for pumping water, which translates to lower energy needs and costs, added Smith.

Based on their test runs so far, the researchers found that the device could retrieve about 80 percent of desalinated water from settings as highly concentrated as seawater. The experiment will turn to real seawater next.

The findings were published in the Journal of the Electrochemical Society.

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