Batteries and electrochemical capacitors

The invention of the battery can be attributed to Alessandro Volta (1745-1827) of Como, Italy, who in 1800 described an assembly consisting of plates of two different metals, such as Zn and Cu, placed alternately in a stack-like fashion separated by paper soaked in an aqueous solution, such as brine or vinegar. As discovered by Volta, this contraption was capable of producing an electrical shock when its ends were touched. In a broad sense, batteries can be defined as devices that convert chemical into electrical energy using electrodes, immersed in media (liquids, gels, and even solids) that support the transport of ions, or electrolyte. This mode of operation is fundamentally different from that associated with conventional solid-state capacitors, invented about half a century earlier in Leyden, The Netherlands, in which charge is physically stored in nonreactive electrodes separated by a dielectric, or insulating material. However, the latter shares important commonalities with yet another class of devices developed much later known as electrochemical capacitors, which, as described later in this article, rely on charge separation at electrode|electrolyte interfaces to store energy.