Batteries free ions that behaves as an electrical conductor. An ion is an atom or molecule that has lost or gained one or more electrons, giving it a positive or negative electrical charge. As stated earlier, there are two kinds of batteries. In a primary battery, the chemical action eats away one of the electrodes (usually the negative), and the cell must be discarded or the electrode replaced; in a secondary battery, the chemical process is reversible, and the active materials can be restored to their original condition by recharging the cell. A battery can consist of only one cell, such as the primary battery that powers your flashlight, or several cells in a common encasement, such as the secondary battery that powers your automobile starter.
Active Materials Active materials are defined as electrochemical couples. This means that one of the active materials, the positive pole, or anode, is electron-deficient; the other active material, the negative pole, or cathode, is electron-rich. The active materials usually are solid (lead-acid) but can be liquid (sodium-sulfur) or gaseous (zinc-air, aluminum-air). Table 7-2 lists comparisons of a few of these elements. Table 7-2  Electrodes: Common Chemicals
Anode Materials (Negative Terminals) Best + Most Positive
Cathode Materials (Positive Terminals) Best – Most Negative
Lithium
Ferrate
Magnesium
Iron Oxide
Aluminum
Cuprous Oxide
Zinc
Iodate
Chromium
Cupric Oxide
Iron
Mercuric Oxide
Nickel
Cobaltic Oxide
Tin
Manganese Dioxide
Lead
Lead Dioxide
Hydrogen
Silver Oxide
Copper
Oxygen
Silver
Nickel Oxyhydroxide
Palladium
Nickel Dioxide
Mercury
Silver Peroxide
Platinum
Permanganate
Gold
Bromate
Worst Least Negative
Worst Least Positive
137