A reduction/oxidation ("redox") flow battery system includes a series of electrochemical cells arranged in a cascade, whereby liquid electrolyte reacts in a first electrochemical cell (or group of cells) before being directed into a second cell (or group of cells) where it reacts before being directed to subsequent cells. The cascade includes 2 to n stages, each stage having one or more electrochemical cells. During a charge reaction, electrolyte entering a first stage will have a lower state-of-charge than electrolyte entering the nth stage. In some embodiments, cell components and/or characteristics may be configured based on a state-of-charge of electrolytes expected at each cascade stage. Such engineered cascades provide redox flow battery systems with higher energy efficiency over a broader range of current density than prior art arrangements.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Inventions conceived after the filing of the priority application (U.S. patent application Ser. No. 12/498,103, filed on Jul. 6, 2009) that are included in this continuation-in-part patent application were made with Government support under DE-OE0000225 "Recovery Act--Flow Battery Solution For Smart Grid Renewable Energy Applications" awarded by the US Department of Energy (DOE). The Government has certain rights in such inventions. However, the Government does not have rights in U.S. Pat. No. 7,820,321 which was conceived and filed without Government support, nor in the direct continuation and divisional applications thereof.