If you want a safe, clean and cheap product, simply don't use hazardous, toxic or rare materials when you build it. At Allegro Energy ( https://allegro.energy ), we followed exactly this strategy when we were looking for a sustainable energy storage option that is also compatible with a circular economy. So not only have we developed a water-based super- or ultracapacitor with the highest reported voltage to date, but also one that costs a fraction of the price compared to current technology. More details can be found here:https://www.pv-magazine-australia.com/2021/07/28/aussie-sta
