Batteries provide fresh jolt to desalination technology

Engineers at the University of Illinois are developing a desalination device that uses materials in batteries to remove salt from water.

Illinois mechanical science and engineering professor Kyle Smith and graduate student Rylan Dmello published their work in the Journal of the Electrochemical Society.

Smith said: “By publishing this paper, we’re introducing a new type of device to the battery community and to the desalination community.”

The most-used method, reverse osmosis, pushes water through a membrane that keeps out the salt, a costly and energy-intensive process. By contrast, the battery method uses electricity to draw charged salt ions out of the water.

The researchers were reportedly inspired by sodium ion batteries, which contain salt water. Batteries have two chambers, a positive electrode and a negative electrode, with a separator in between that the ions can flow across. When the battery discharges, the sodium and chloride ions – the two elements of salt – are drawn to one chamber, leaving desalinated water in the other.

In a normal battery, the ions diffuse back when the current flows the other direction. The Illinois researchers had to find a way to keep the salt out of the now-pure water.

“In a conventional battery, the separator allows salt to diffuse from the positive electrode into the negative electrode,” Smith said in a statement. “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.”

The battery approach is said to hold several advantages over reverse osmosis. The battery device can be small or large, adapting to different applications, while reverse osmosis plants must be very large to be efficient and cost effective, Smith said. The pressure required to pump the water through is much less, since it’s flowing the water over the electrodes instead of forcing it through a membrane. This translates to much smaller energy needs, close to the very minimum required by nature, which in turn translates to lower costs. In addition, the rate of water flowing through it can be adjusted more easily than other types of desalination technologies that require more complex plumbing.

Smith and Dmello conducted a modelling study to see how their device might perform with salt concentrations as high as seawater, and found that it could recover an estimated 80% of desalinated water. Their simulations don’t account for other contaminants in the water, however, so they are working toward running experiments with real seawater.

“We believe there’s a lot of promise,” Smith said. “There’s a lot of work that’s gone on in developing new materials for sodium ion batteries. We hope our work could spur researchers in that area to investigate new materials for desalination. We’re excited to see what kind of doors this might open.”