> Are we at the theoretical limit of energy density in current batteries? Yes and no. Using air for the "ox" part of the redox reaction makes it possible to d

> Are we at the theoretical limit of energy density in current batteries? Yes and no. Using air for the "ox" part of the redox reaction makes it possible to dramatically increase energy density (gravimetric and volumetric both). The tricky part of that is making the battery rechargeable. Lots of research attention is focused on it. If you want your battery totally enclosed (e.g. for use in vacuum or corrosive environments), than we are closer to the limits. Probably within a factor of 5, maybe within a factor of 2. > Could it be that in 20 years we find drastically better materials for batteries? No, the periodic table is fixed.[1] Maybe, if you are prepared to consider using nuclear "batteries". 1. https://en.wikipedia.org/wiki/Reduction_potential https://en.wikipedia.org/wiki/Reduction_potential