text: You need to plates and a dielectric.  The dielectric can be air, and a lot of variable capacitors use air and change the capacitance by moving the plates and thus changing the amount of area overlapped by the plates.\n\nIf you want to be able to store a lot of energy, you need to use different dielctrics and materials for the plates.  To increase the capacitance, you have to either increase the surface area of the plates or use a dielectric material with a high dielectric constant.  \n\nIn aluminum capacitors, the plates are made of aluminum and the surface area is increased by using solutions that cause tunnels to form inside aluminum foil. This can increase the surface area over 100 times.  The dielectric is formed by growing an oxide layer on top of the aluminum which is very thin (microns).  \n\nIn tantalum capacitor, one of the plates called the anode is formed from tantalum by taking tantalum powder, pressing it into a pellet, and sintering (or partially fusing) the tantalum particles together in a furnace.  This makes a solid pellet with a lot of pores, and so it has a very high suface area. A tantalum wire is either pressed with the pellet or welded later to form one of the terminations in the finished capacitor. Tantalum oxide can then be grown on to of the tantalum to form the dielectric.  The other plate, called the cathode, is formed by dipping this pellet into manganese dioxide solutions.  The manganese dioxide is able to penetrate the pores and cover much of the surface area on top of the dielectric.  It is then dipped into a carbon paint solution and cured, and the carbon layer efficiently contacts the manganese dioxide layer and protects the sensitive dielectic layer from the next layer, the silver layer which is also normally applied by dipping the pellet into a paint and curing.  The robustness of the silver layer and its excellent conductivity is needed beacause a second termination is attached to it.  This assembly is covered with epoxy to protect it from mechanical stresses, but the terminations remain partially exposed to allow for attaching to a circuit board.