A reversible storage system for electric energy, including charging or discharging surfaces as a positive collector terminal and a charging or discharging area as a negative collector terminal and a flow electrode with a pumpable dispersion with particles storing electric energy and at least one supply line and at least one drain line for the pumpable dispersion. The pumpable dispersion includes particles storing electric energy in a capacitive and/or chemical fashion, having an average grain size distribution: 1 nM to 500 μm. For chemically storing particles, the negative and the positive collector terminals have a planar shape with a single exterior closed border and with their planar sides each contacting an ion-selective diaphragm or spacers, and the pumpable dispersion is arranged on a side facing away from the planar side of the respective collector, contacting the ion-selective diaphragm or spacers, and the dispersion at least partially penetrates the respective collector.