The present invention is related to electrochemical energy generation devices including at least one electrode comprising an electrochemically active fluid that is enclosed within the cell, as well as related articles, systems, and methods. In some embodiments, the anode and/or cathode of the electrochemical energy generation devices described herein can be formed of an electrochemically active fluid, such as a semi-solid or a redox active ion-storing liquid. The electrochemical energy generation device can be configured such that the anode and/or cathode can be flowed into their respective electrode compartments, for example, during assembly. During operation, on the other hand, little or none of the electrochemically active fluid(s) are transported into or out of the energy generation device (e.g., out of the electrode compartments of the electrochemical energy generation device).
 This invention was made with government support under Grant No. DE-AR0000065 awarded by the Department of Energy and under Grant No. FA8650-09-D-5037 awarded by the Defense Advanced Research Projects Agency. The government has certain rights in this invention.