An energy storage device comprises a capacitor having a dielectric between opposite electrodes and a nonconductive coating between at least one electrode and the dielectric. The nonconductive coating allows for much higher voltages to be employed than in traditional EDLCs, which significantly increases energy stored in the capacitor. Viscosity of the dielectric material may be increased or decreased in a controlled manner, such as in response to an applied external stimulus, to control discharge and storage for extended periods of time.