Iron flow battery promises to take charge

A new battery which is safe, economical and water-based, has been designed to be used for large-scale energy storage.

It promises to be able to support intermittent green energy sources like wind and solar into energy grids.

In a proof-of-concept experiment, researchers at the US Department of Energy’s Pacific Northwest National Laboratory showed their iron-based battery has remarkable cycling stability. The newly designed battery maintained 98.7% of its maximum capacity even after more than 1,000 charging cycles.

Battery researcher in blue lab coat assembling test flow battery
Lead author and battery researcher Gabriel Nambafu assembles a test flow battery apparatus. Credit: Andrea Starr | Pacific Northwest National Laboratory.

The research is published in the journal Nature Communications.

Flow batteries consist of two chambers filled with different liquids. Unlike conventional batteries, flow battery chambers supply liquid constantly circulating through the battery to supply the electrolyte, or energy carrier.

Iron-based flow batteries have been around since the 1980s. The new battery is different because it stores energy in a unique chemical formula which combines charged iron with a neutral-pH liquid electrolyte. This nitrilotri-methylphosphonic acid (NTMPA) is commercially available in industrial quantities. It is often used to stop corrosion in water treatment facilities.

Phosphonates like NTMPA dissolve well in water and are non-toxic.

“We were looking for an electrolyte that could bind and store charged iron in a liquid complex at room temperature and mild operating conditions with neutral pH,” says senior author Guosheng Li, a senior scientist at PNNL who leads materials development for rechargeable energy storage devices. “We are motivated to develop battery materials that are Earth-abundant and can be sourced domestically.”

“Our system uses commercially available reagents that haven’t been previously investigated for use in flow batteries,” says co-author Aaron Hollas.

Despite the success, more work needs to be done to increase the energy density of the new battery. It stores 9 watt-hours per litre of liquid. In comparison, vanadium based systems are more than twice as energy dense at 25 Wh/L.

“Our next step is to improve battery performance by focusing on aspects such as voltage output and electrolyte concentration, which will help to increase the energy density,” says Li. “Our voltage output is lower than the typical vanadium flow battery output. We are working on ways to improve that.”

Large-scale storage of power using flow batteries and lithium-ion battery technology are going to be crucial in decarbonisation and the transition to renewable energies.

Buy cosmos print magazine

Please login to favourite this article.