Volta’s invention of the Volta pile in 1800 represents the beginning of the field of battery science and engineering. The pile consisted of alternating layers of zinc, electrolyte soaked into cardboard or leather, and silver. Following Volta’s report, many investigators constructed electrochemical cells for producing and storing electrical energy. For the first time, relatively large currents at high voltages were available for significant periods of time. Various versions of the pile were widely used. Unfortunately, there was a lack of understanding of how the cells functioned, but as we now know, the zinc was electrochemically oxidized and the native oxide layer on the silver was reduced. The cells were ‘‘recharged’’ by disassembling them and exposing the silver electrodes to air, which reoxidized them. Inevitably, many other electrochemical cells and batteries were developed.
John F. Daniell developed a two-fluid cell in 1836. The negative electrode was amalgamated zinc, and the positive electrode was copper. The arrangement of the cell is shown in Fig. 2. The copper electrodes were placed in (porous) porcelain jars, which were surrounded by cylindrical zinc electrodes and placed in a larger container. A copper sulfate solution was placed in the copper electrode’s compartment, and sulfuric acid was put in the zinc electrode compartment.
The electrode reactions were as follows:
Zn = Zn+2 + 2e~
Cu+2 + 2e~ = Cu.
FIGURE 2 A set of three Daniell cells connected in series.
Sir William R. Grove, a lawyer and inventor of the fuel cell, developed a two-electrolyte cell related to the Daniell cell in 1839. Grove used fuming nitric acid at a platinum electrode (the positive) and zinc in sulfuric acid (the negative). Variants on this formulation were popular for a number of years. Of course, all of these cells were primary cells in that they could be discharged only once and then had to be reconstructed with fresh materials.
Gaston Plante invented the first rechargeable battery in 1860. It was composed of lead sheet electrodes with a porous separator between them, spirally wound into a cylindrical configuration. The electrolyte was sulfuric acid. These cells displayed a voltage of 2.0 V, an attractive value. During the first charging cycles, the positive electrode became coated with a layer of PbO2. The charging operation was carried out using primary batteries—a laborious process. Because of the low cost and the ruggedness of these batteries, they remain in widespread use today, with various evolutionary design refinements.
The electrode reactions during discharge of the lead-acid cell are as follows:
Pb + H2SO4 = PbSO4 + 2H+ + 2e_
PbO2 + H2SO4 + 2H+ + 2e_ = PbSO4 + 2H2O.
Notice that sulfuric acid is consumed during discharge and that the electrolyte becomes more dilute (and less dense). This forms the basis for determining the state of charge of the battery by measuring the specific gravity of the electrolyte. The theoretical specific energy for this cell is 175 Wh/kg, a rather low value compared with those of other cells.
Waldemar Jungner spent much of his adult life experimenting with various electrode materials in alkaline electrolytes. He was particularly interested in alkaline electrolytes because there generally was no net consumption of the electrolyte in the cell reactions. This would allow for a minimum electrolyte content in the cell, minimizing its weight. Jungner experimented with many metals and metal oxides as electrode materials, including zinc, cadmium, iron, copper oxide, silver oxide, and manganese oxide.
In parallel with Jungner’s efforts in Sweden, Thomas Edison in the United States worked on similar ideas using alkaline electrolytes and many of the same electrode materials. Patents to these two inventors were issued at nearly the same time in 1901.
During the period since the beginning of the 20th century, a wide variety of cells have been investigated, with many of them being developed into commercial products for a wide range of applications. Representative cells are discussed in the next section.