A solid state energy storage device has two electrodes, a membrane separator and a solid electrolyte having a substantially solid solvent, a salt and a mediator. The energy storage device stores electric charge by both Faradaic and non-Faradaic systems. The energy storage device may include activated carbon mixed with the electrolyte and sonicated to provide connection between the activated carbon and the mediator. The energy storage device is hot pressed to increase conductivity. The two electrodes may be asymmetric in amount of reduced and oxidized species of mediator.