NOVELTY - The redox flow energy storage device comprises a positive electrode current collector (110) or a first outer electrode current collector (120), a negative electrode current collector or a second inner electrode current collector, an ion-permeable membrane (130) or ion-permeable medium respectively separating the positive and negative current collectors or separating the first and second electrode current collectors, a positive electrode, a negative electrode, a storage tank, and a first electrode active material or a positive electrode active material.    USE - The redox flow energy storage device such as semi-solid and condensed ion-supporting liquid redox flow batteries, flow cells or reversible fuel cells is useful for applications in grid services or storage of intermittent renewable energy sources such as wind and solar power, and to power a plug-in hybrid or all-electric vehicle.    ADVANTAGE - The redox flow energy storage device can be economically manufactured with high energy and power density, improved device performance, enhanced charge and discharge characteristics, reduced power consumption, lightweight, reduced size and increased voltage characteristics.    DETAILED DESCRIPTION - The redox flow energy storage device comprises a positive electrode current collector (110) or a first outer electrode current collector (120), a negative electrode current collector or a second inner electrode current collector, an ion-permeable membrane (130) or ion-permeable medium respectively separating the positive and negative current collectors or separating the first and second electrode current collectors, a positive electrode, a negative electrode, a storage tank, a first electrode active material or a positive electrode active material, a second electrode active material or a negative electrode active material, an ion-permeable medium separating the first and second electrode active materials and separating the positive and negative active materials, a source of mixing fluid, and a movable surface present in contact with a flowable ion-storing redox composition. The positive and negative electrodes are disposed between the positive electrode current collector and the ion-permeable membrane and negative electrode current collector and the ion-permeable membrane respectively. The positive electrode current collector and the ion-permeable membrane and the negative electrode current collector and ion-permeable membrane are defined positive and negative electroactive zones accommodating the positive and negative electrodes respectively. The positive and negative electrodes comprises: electrode-active material comprising an insoluble flowable semi-solid, condensed liquid ion-storing redox composition or redox compound that is capable of taking up or releasing ions and remains insoluble during operation of the cell, where the remaining electrode is a conventional stationary electrode. The flowable semi-solid ion-storing redox composition comprises a solid comprising an ion storage compound. The second inner electrode current collector is disposed partially within the first electrode current collector. The storing tank is arranged for storing the flowable semi-solid or condensed liquid ion-storing redox composition, and is present in flow communication with the redox flow energy storage device. The first and second electrode active materials: are partially disposed between the first electrode current collector and the ion-permeable medium and the second electrode current collector and the ion-permeable medium respectively. The first and/or second electrode active materials comprise a fluid, and a flowable ion-storing redox composition that is capable of taking up or releasing the ions during operation of the device and cell. The first and/or second electrode current collectors are rotated about its longitudinal axis relative to the other electrode current collectors, and comprise protrusions extending toward an electrode from a surface proximate to the electrode. The source of mixing fluid is present in fluid communication with and/or located within a volume in which the flowable ion-storing redox composition is disposed. The mixing fluid is immiscible with the flowable ion-storing redox composition. The movable surface: is constructed and arranged to partially direct the flow of the flowable ion-storing redox composition through the redox flow energy storage device; comprises protrusions; and is partially disposed within an electroactive zone of the redox flow energy storage device. The flowable semi-solid or condensed liquid ion-storing redox composition is electronically conductive at a temperature at which the energy storage device is operated. INDEPENDENT CLAIMS are included for:    (1) a flowable ion-storing redox composition for a redox flow energy storage device;    (2) a source of acoustic energy for a redox flow energy storage device;    (3) an in-line sensor for a redox flow energy storage device; and    (4) a composition for a redox flow energy storage device.    DESCRIPTION OF DRAWING(S) - The figure shows a cross-sectional view of a redox flow energy storage device.    Positive electrode current collector (110)    Negative electrode current collector (120)    Ion permeable separator (130)    Positive flowable electrode active material (140)    Negative flowable electrode active material. (150)