Batteries are used for the storage of electrical energy. They range in size from gigantic boxes as large as a house that are used by utility companies to paper-thin devices for the protection of memory in electronic devices. Storage batteries, and indeed all batteries, are simply electrochemical reactors. An oxidizer (an electron acceptor) and a reducer (an electron donor) react together by transferring electrons to form products and release chemical energy in the form of electricity. By arranging the components of a battery in a special way, it is possible to control the rate of the reaction and to release the electrical energy on demand.

The generation of electrical energy from chemical reactions in battery-like devices dates to the very early days of the investigation of electricity. At the end of the eighteenth century, Alessandro Volta (1745-1827) put together layers of substances in such a way that he...