Iron-air batteries promise a higher energy density than present-day lithium-ion batteries. Their main constituent, iron, is an abundant and cheap material. Scientists from Forschungszentrum Jülich are pursuing research into this concept, first reported in the 1970s. Together with Oak Ridge National Laboratory (ORNL) in the U.S., they have observed at the nanometre level how deposits form at the iron electrode during operation. A deeper understanding of the charging and discharging reactions is viewed as the key for further development of this type of rechargeable battery to market maturity. The results were published in Nano Energy.