Our renewable energy future will rely on cheap and scalable battery technologies. A promising option is an all-iron redox flow battery, which uses iron - an abundant, low-cost, and safe material. Battery performance depends on how iron ends on the on the negative electrode during battery use. Uniform iron deposits are best, but this doesn't always take place. Using neutron imaging, a team of TU/e researchers in collaboration with the Paul Scherrer Institute in Switzerland visualised the motion of metallic iron in all-iron redox flow battery and tracked how the solid, gas, and liquid phases of iron form in real time. Their results can help the design and performance of future batteries.
If you peer inside a redox flow battery, you'll see fluids on the move, otherwise known as electrolytes. In these electrolytes, there are ions, which in the case of an all-iron redox flow battery (AIRFB) are iron ions. Movement of these ions influences how well the battery charges and discharges. Of particular significance is how iron coats the negative electrode of the battery during use.
"This ultimately dictates battery performance," says PhD research Marina Tabuyo-Martinez , co-first author of the paper with Inmaculada Gimenez-Garcia and who both completed the work in the Electrochemical Materials and Systems group at the Department of Chemical Engineering at TU/e.
"A uniform deposit or plating of iron on the electrode is most desirable, but this doesn't always occur. Exploring the origins of non-uniform plating can help extend the lifetime of AIRFB designs," adds Tabuyo-Martinez.
Neutron visualisation
To investigate the cause of non-uniform deposits of iron, the researchers turned to neutron radiography to see inside an AIRFB. Neutrons pass through the casing parts of the battery while interacting with the iron ions in the electrolytes of the battery.
"Neutron imaging helps us to see things that traditional battery cycling methods just miss. The neutron radiographs show that iron is uniformly place on the negative electrode when the flow in the electrolyte is purely convective. In the case of an electrolyte flow where it's a mix between being convective and random," says Tabuyo-Martinez.
Disruptive for the future
"We've pinpointed the parameters that affect AIRFB performance," says Antoni Forner-Cuenca , full professor and lead of the Electrochemical Materials and Systems group at TU/e. "We envisage that our findings in this study will prove to be a positive disruption for future AIRFB designs."
