In a world that is actively trying to reach a more sustainable future, energy storage represents the challenge of the present. As renewable sources are not continuous (in the sense that their availability is affected by factors such as weather and time of day), and energy harvesting devices become more and more efficient, the need for a reliable storage system is critical. In this work, the focus is directed towards the long-term viability of energy storage units, which should encompass environmental impact of manufacturing processes, cyclability and end-of-life disposal. A strong effort is put in designing an hybrid device combining strong power capabilities with high energy density.