The Rho Agenda sci-fi books rely on capacitors with absurdly high energy densities to power the tech. Is there any thing in the physics that would prevent a capacitor from having a higher energy density than a battery?
I remember some attempts to achieve that, do not have source anymore. The whole idea was to take two electrodes and grow thick forest of graphene tubes on them massively increasing surface of electrodes. But to get even close to batteries, electrolyte was necessary, however pouring electrolyte onto electrodes modified in such way caused graphene tubes to break off and create shorts. So ultimately went nowhere. Maybe if it would be possible to grow graphene in the electrolyte directly.
I would be very, very leery of storing large amounts of energy in supercapacitors. A li-ion battery pack can go into thermal runaway, but a supercapacitor inherently dumps it's energy if penetrated. Electricity moves at a respectable fraction of lightspeed, the energy dump will be *very* fast.
