"Super-iron" is a moniker for a special kind of ferrate salt (iron(VI)), this is, potassium ferrate (K2FeO4) or barium ferrate (BaFeO4), used in this new class of batteries.
As of 2004 chemist Stuart Licht of the University of Massachusetts in Boston was leading research into a Super-iron battery.
"…the new cathode employs salts of an unusual ionic form of iron — hexavalent or superoxidized iron — that readily accept three electrons per ion, Licht explains. The more electrons the cathode can accept, the more electricity the battery can supply." —Peter Weiss