Nonaqueous redox flow batteries (RFBs) can utilize a metal and a cation of the metal (M.sup.n+) as an active redox couple for a first electrode and electrolyte, respectively, in a first half-cell. The RFBs can also utilize a second electrolyte having I-based species. The I-based species can be selected from the group consisting of I.sup.- anions, I.sub.2, anions of I.sub.x (x.gtoreq.3), or combinations thereof. Two different ones of the I-based species compose a second redox active couple in the second half cell.
STATEMENT REGARDING FDERALLY SONSORED RESEARCH OR DEVELOPMENT
 This invention was made with Government support under Contract DE-AC0576RL01830 awarded by the U.S. Department of Energy. The Government has certain rights in the invention.