Abstract: Enhanced storage efficiency, reliability and durability of a redox flow battery system are achieved by employing distinct pluralities or groups of cells wherein all the cells of a first plurality have porous metallic electrodes in both compartments through which respective electrolyte solutions flow during a charging process of the battery system, and all cells of a second plurality may have porous carbon felt electrodes in both flow compartments through which the respective electrolyte solutions flow during a discharging process of the battery systems or solely in the compartment through which the negatively charged electrolyte solution flows and a porous metallic electrode in the other compartment where the positively charged electrolyte solution flows. All the cells of both groups of cells may be defined by repetitive sequences of stackable elements, according to a common bipolar or monopolar cell stack architecture.

Abstract: A frameless bipolar cell stack architecture with either internal manifolds of circulation of electrolyte solutions “in parallel” through all respective cell compartments or internal ducting adapted to provide for “serial” flow paths of the electrolyte solutions in succession through all respective cell compartments of the stack, does not employ any plastic frame and employs substantially planar bipolar electrical interconnects (I) of substantially homogeneous electrical conductivity with a perimeter that super-imposes to the perimeter of any other element of the stack. Whenever useful for the particular application, the planar interconnects may have a protruding “lug portion” that projects beyond the outer perimeter side of the other stacked elements, providing an externally contactable area sufficiently large for the power (current rating) of an electrical tap, at an intermediate voltage relative to the voltage difference between the end terminals of the stack, connectable to an external circuit.