Within the context of energy shift towards a decrease in the contribution of fossil fuels, the development of new stationary energy storage systems is mandatory. Indeed, the intrinsic intermittent and variable nature of renewable energy sources, such as windmill and photovoltaic, require energy storage. Redox-flow batteries, allowing a decoupling of energy and power, are well adapted to such requirements. As a matter of fact, this technology presents advantages as compared to Li-ion systems presently under development for such applications, in particular for security and recyclability issues. However, the most advanced redox-flow batteries (Vanadium redox-flow batteries, studied since the 80’s) remain expensive with limitations in terms of stability and capacities. The present project aims at developing a full redox-flow battery, based on the flow of redox-mediators based aqueous solutions (pH around 7), using sodium insertion materials immobilized in the battery tanks. The use of these insertion materials will allow an increase in the energy density of these systems, and thus to potentially reduce their size. These materials will be free of toxic or expensive metallic element. To perform these research studies, we created a multidisciplinary team which will allow to break the technological locks related to the development of such innovative and performing systems. The project partners will pursue in particular the study and development of a pilot battery so as to demonstrate the potentialities of this approach for electrochemical energy storage at large scale (coupling with windmill and photovoltaic systems), with storage time of the order of a dozen hours.