Energon: is it possible? I'm always quite curious about the "Energy cube" in Transformers, or namely Energon. 
Is it really possible to store energy, such as electricity, into such a compact form? safe to distribution, and seems nothing left after being consumed?
ps. Wikipedia has a page for Spark, which is more for transformer's soul. I'm not asking for that yet.
 A: It is possible to capture positrons (antiparticle of electron) in a magnetically confined plasma - the repulsive forces get very large unless you do something to equalize the charge. The energy density that could be achieved is stunning.
This was the principal plot line behind Dan Brown's "Angels and Demons" - this plasma (made at CERN, that den of mad scientists plotting to destroy the universe) was intended to be released (the power source containing it would become exhausted) underneath the Vatican, destroying the "center of the Evil Church" (the opinion of the perpetrators...). Of course the hero saves the day.
In principle a few grams of antimatter contains as much energy as the fuel tanks of the space shuttle...
A: Some energy densities for easily compactified substances:
Purely electric storage: 


*

*electric field in a capacitor, 0.000 36 MJ/kg

*electric field in a supercapacitor, up to 0.004 2 MJ/kg

*1 T magnetic field has energy density $\frac{1}{2\mu_0}B^2 = 0.4\,\mathrm{MJ/m^3} $, estimate mass for superconducting magnet enclosure to decide where to put this on the list (pretty low)


Chemical storage (atoms are allowed to trade electrons):


*

*lead-acid batteries, 0.15 MJ/kg

*nickel metal-hydride batteries, 0.30 MJ/kg

*alkaline batteries, 0.40 MJ/kg

*lithium-ion batteries, 0.46 MJ/kg

*theoretical maximum for Li/CuCl batteries [via], 4.2 MJ/kg

*carbohydrates or proteins, 17 MJ/kg

*coal, 24 MJ/kg

*fats, 38 MJ/kg

*combustion of pure lithium, 40 MJ/kg

*crude oil or gasoline, 45 MJ/kg

*methane, 55 MJ/kg (caveat: gaseous at standard temperature and pressure)

*hydrogen for combustion, 140 MJ/kg (also gaseous at STP)


Nuclear storage (atoms are allowed to trade nucleons):


*

*uranium, typical reactor, 500 000 MJ/kg

*thorium, uranium, (breeder reactors), 80 000 000 MJ/kg = 80 x 106 MJ/kg. This astounding number seems to assume that all of the fuel is consumed, which isn't how real reactors work.

*antimatter, Avogadro's number per gram * 1 GeV = 96 x 109 MJ/kg

