PNNL Develops Iron-Based Flow Battery for Safe, Grid-Scale Energy Storage

A team at the Department of Energy’s Pacific Northwest National Laboratory (PNNL) has created a new battery design using an ordinary chemical used in water treatment facilities. The aqueous iron redox flow battery they designed shows the potential for grid-scale deployment with enhanced safety features.

The chemical – nitrogenous triphosphate, nitrilotri-methylphosphonic acid (NTMPA) – is commercially available due to its use in water treatment plants to inhibit corrosion. NTMPA has the ability to charge iron with a neutral-pH phosphate-based liquid electrolyte.  

“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. We are motivated to develop battery materials that are Earth-abundant and can be sourced domestically, ” said senior author of the study, Guosheng Li.

Using this, the team designed a lab-scale, iron-based flow battery with unparalleled cycling stability. According to the study paper, the battery “exhibited remarkable cycling stability over one thousand consecutive charging cycles, while maintaining 98.7% of its maximum capacity.” 

Flow batteries were chosen for the study due to their potential for deployment at any scale and their versatility for energy storage.

“A BESS facility using the chemistry similar to what we have developed here would have the advantage of operating in water at neutral pH,” Aaron Hollas, a study author  stated. “In addition, our system uses commercially available reagents that we have not previously investigated for use in flow batteries.”

Though the new battery design from PNNL only has an energy density of 9 watt-hours per liter (Wh/L), lower than commercialized vanadium-based systems, the team believes it holds promise for future improvements. They have plans to enhance the battery performance, focusing on aspects such as voltage output and electrolyte concentration to increase energy density. Further plans include scaling up the technology at the Grid Storage Launchpad, PNNL’s national grid energy storage research and development facility.