A rechargeable battery includes an iron electrode comprising carbonyl iron composition dispersed over a fibrous electrically conductive substrate. The carbonyl iron composition includes carbonyl iron and at least one additive. A counter-electrode is spaced from the iron electrode. An electrolyte is in contact with the iron electrode and the counter-electrode such that during discharge. Iron in the iron electrode is oxidized with reduction occurring at the counter-electrode such that an electric potential develops. During charging, iron oxides and hydroxides in the iron electrode are reduced with oxidation occurring at the counter-electrode (i.e., a nickel electrode or an air electrode).
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 The invention was made with Government support under Contract No. DE-AR0000136 awarded by the Advanced Research Projects Agency-Energy--U.S. Department of Energy. The Government has certain rights to the invention.