Rensselaer Polytechnic researchers are experimenting with paper batteries. So far they’ve managed to create a prototype battery that yiels 2.3v. Not bad. That’s not going to drive your UMPC anytime soon, but this could be a promosing beginning.
How is the paper battery built? According to the article linked above:
“The battery contains carbon nanotubes, each about one millionth of a centimetre thick, which act as an electrode. The nanotubes are embedded in a sheet of paper soaked in ionic liquid electrolytes, which conduct the electricity.
The flexible battery can function even if it is rolled up, folded or cut.”