[Filligree]

Gasoline manages 12kWh/kg, and I'm sure I've heard people talking about batteries at least approaching that density before, even if only on a theoretical basis.

Leaving aside how safe I'd feel with a supercap of that density under the hood, are you sure about the 800Wh/kg limit? I'd be very interested in seeing a reference.

[semi-extrinsic]

The 1eV per atom is really a rule of thumb, but easy to understand: At that value you are getting dangerously close to the ionization energy 13.6 eV for hydrogen, 5.4 eV for lithium), so you can no longer have a chemical battery. Note also that this is average eV for all atoms in the battery, so those actually providing electricity will be carrying atound 1.5 - 2 eV.

See e.g. here: http://www.ohio.edu/people/piccard/radnotes/radioactive.html

[jontro]

Found this article discussing some limits http://chargedevs.com/features/three-of-a-kind-polyplus-reac...