The penetration of renewable energies into the electric grid increases the demand for energy storage to ensure reliable power supply, grid resiliency, and cost reductions. Long-duration and long-term energy storage (LDES and LTES) can bridge the intermittency of renewable sources and reduce the risks incurred by diminished fossil-fuel baseload generation. Electrochemical energy storage (EES), or Li-ion batteries (LIBs), are considered for short-duration energy storage (4-6 hours). When talking about seasonal storage, hydrogen storage is usually the preferable option. The goal of ReZilient is to fill the gap between short-term EES and long-term hydrogen storage by developing and demonstrating at lab-scale (0.5-1.5kW/6kWh) a completely new Zn-air flow battery technology. The estimated capital cost for large-scale deployment is approximately 80 €/kWh, with a levelized-cost-of-storage <0.5 €/kWh/cycle (based on 100 kW/1000 kWh system, 1 week discharge duration). A disruptive redox-mediated strategy for enhanced charge transfer processes is employed with the goal of confining the Zn/Zn2+ redox reaction in the negative reservoir (filled with a semi-solid zinc solution) and eliminating the electroplating process inside the cell (no dendrites) to improve battery lifetime. This will allow discharge times beyond days, contrary to conventional zinc-based batteries where long discharge is hampered by the formation of a cm-thick zinc anode. If successful, the technology has disruptive potential in terms of both extremely low levelized-cost-of-storage, extended storage time, recyclability, and use of non-critical-raw-materials. A pilot concept design of the cell will be conceived after demonstration of the technology. The output of this design will lead to an update of the business case of the distribution network operators and potential customers