Capacitor Specification, doesnt exist yet maybe.. (theoretical)

I want to know how many farads i would need to hold about 20,000 amps of energy
How many joules would this be or should i use watts, and what would be the volt tolerance of the capacitor, how to increase volt tolerance
What would be the current, how to decrease charge time, what would the spacing between the plates need to be and how small can it be. smaller is better to increase capacitance.
How much surface area is needed for electrodes, and need a insulator with a dielectric strength that or higher than teflon which is 60x10^6, but its melting point is around 650 and would like to find a insulator that has a higher melting point. the idea is to use hafnium as an electrode.
this is all theoretical and i just need numbers to brainstorm with to assist with some research. many thanks and I appreciate any input that contributes to answering these questions. 

Capacitance = charge x voltage.Charge is measured in Coulombs - 1 coulomb is 1 amp for 1 second.So if you charge a 1F (one Farad) capacitor at one amp for one second it will raise its voltage by 1 volt.Your question does not really supply enough information:- what voltage do you need to work at?- You say 20 000 Amps of energy.  Amps are current, not energy.  How long do you need to supply 20 000 amps for? a millisecond, an hour...???- energy is measured in Watt-Hours - volts x amps x time.   So you see why I asked about voltage.A 20 000 Farad capacitor (which doesn't really exist yet) could deliver 20 000 amps for one second, theoretically.  It would lose one volt per second doing this until it was discharged.  You do get supercapacitors which can supply fairly large currents, but not this large.  We're talking about maybe 500F at 2.7 volts, or 36F at 16V (two examples I found on Google).  The smaller memory backup capacitors would be no use, they're intended for slow charge and discharge, but they do make car audio backup capacitors like the one above that can handle fairly high charge and discharge rates.So to supply 20 000 amps for even one second,  you'd be talking about many of these (20 000F worth) across some very large busbars (to carry the current).  A tall order.There's no way you'd be able to make a capacitor yourself that would have anything like the capacity of commercial units.  But depending on your requirements you may be able to get something approaching what you need.  We'd need information on what voltage you need, how much it can drop during discharge, and the amps for the time that you need.