NOVELTY - A redox flow energy storage device comprises a positive electrode current collector (110), a negative electrode current collector (120), an ion-permeable membrane (130) separating positive and negative current collectors, a positive electrode and a negative electrode. The positive electrode is disposed between the positive electrode current collector and ion-permeable membrane. The positive electrode current collector and ion-permeable membrane defines a positive electroactive zone accommodating positive electrode.    USE - Redox flow energy storage device is used for electric vehicle, and application of grid services and storage of intermittent renewable energy source such as wind and solar power.    ADVANTAGE - The redox flow energy storage device provides high energy density and high power operation.    DETAILED DESCRIPTION - A redox flow energy storage device comprises a positive electrode current collector, a negative electrode current collector, an ion-permeable membrane separating positive and negative current collectors, a positive electrode and a negative electrode. The positive electrode is disposed between the positive electrode current collector and ion-permeable membrane. The positive electrode current collector and ion-permeable membrane defines a positive electroactive zone accommodating positive electrode. The negative electrode is disposed between negative electrode current collector and ion-permeable membrane. The negative electrode current collector and ion-permeable membrane defines a negative electroactive zone accommodating the negative electrode. The positive electrode and/or negative electrode comprises flowable semi-solid or condensed liquid ion-storing redox composition which is capable of taking up or releasing the ions during operation of cell. An INDEPENDENT CLAIM is included for operation method of redox flow energy storage device.    DESCRIPTION OF DRAWING(S) - The drawing shows the cross-sectional view of redox flow battery.    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)