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Battery - Background, Primary Cells - Moderate energy primary cells, Medium to high energy primary cells, Secondary cells, Moderate energy storage cells

zinc manganese dioxide power

If two metals are immersed in an aqueous solution that can conduct electricity (electrolyte), they will have different tendencies to dissolve in the solution. A difference in voltage arises because one of the metals appears positive or negative relative to the other.

The combination of two metals (electrodes) in an aqueous solution for the purpose of producing electrical energy from chemical energy is referred to as a galvanic cell. A battery is a set of two or more galvanic cells connected in a series or parallel. (Though not strictly correct usage, a single galvanic cell is also frequently referred to as a battery.) Each cell contains two types of electrodes, an anode (positive electrode) and a cathode (negative electrode), that together provide and absorb electrons with sufficient voltage (electromotive force) to operate useful machines or devices. The electromotive force for every cell reaction that is well understood can be calculated, and the voltage of an actual cell will not exceed this value.

Metals and other conductors can be arranged in an electrochemical, or electromotive, series in which each conductor's tendency to lose electrons relative to another conductor is ranked. The higher the electric potential, the more likely the metal is to appear electrically positive. In terms of electric potential, carbon has a higher potential than gold, gold a higher potential than silver; this sequence is followed in order by copper, tin, lead, iron, and zinc.

Zinc/manganese dioxide systems

The cell developed by Georges LeClanche in 1866 used inexpensive, readily available ingredients. It therefore quickly became a commercial success. The anode is a zinc alloy sheet or cup (the alloy contains small amounts of lead, cadmium, and mercury). The electrolyte is an aqueous solution of zinc chloride with solid ammonium chloride present. The cathode is manganese dioxide blended with either graphite or acetylene black to conduct electrons to the oxide. The system is relatively tolerant of many impurities. These cells are used in barricade flashers, flashlights, garage door openers, lanterns, pen lights, radios, small lighted toys and novelties, and in others.

The zinc chloride cell without ammonium chloride was patented in 1899, but the technology from commercially producing such cells did not prove practical until about 70 years later. Currently zinc chloride cells deliver more than seven times the energy density of the original LeClanche cell. This cell is used in same applications as the LeClanche cell.


Zinc/manganese dioxide alkaline cells

The zinc/manganese dioxide alkaline cell's anode consists of finely divided zinc. The cathode is a highly compacted mixture of very pure manganese dioxide and graphite. The cells operate with higher efficiency than the zinc chloride or LeClanche cells at temperatures below 32°F (0°C). Manganese/manganese dioxide cells have much higher energy densities than zinc chloride systems. Cylindrical batteries are used in radios, shavers, electronic flash, movie cameras, tape recorders, television sets, cassette players, clocks, and camera motor drives. Miniature batteries are used in calculators, toys, clocks, watches, and cameras.

Mercuric oxide/zinc cells

Mercuric oxide/zinc cells use alkaline electrolytes and are frequently used in small button cells. The cell has about five to eight times the energy density available in the LeClanche cell and four times that in an alkaline manganese dioxide/zinc cell. The cell provides a very reliable voltage, and is used as a standard reference cell. These cells are used for walkie-talkies, hearing aids, watches, calculators, microphones, and cameras.


Silver oxide/zinc cells

Silver oxide/zinc cells use cellophane separators to keep the silver from dissolving and the cells from self discharging. The system is very popular with makers of hearing aids and watches because the high conductivity of the silver cathode reaction product gives the cell a very constant voltage to the end of its life. These cells are also used for reference voltage sources, cameras, instruments, watches, and calculators.


Lithium (nonaqueous electrolyte) cells

Lithium/iron sulfide cells take advantage of the high electrochemical potential of lithium and low cost of iron sulfide. The high reactivity of lithium with water requires that the cells use a nonaqueous electrolyte from which water is removed to levels of 50 ppm.

Lithium/manganese dioxide cells are slowly increasing in commercial importance. The voltage provides a high energy density, and the materials are readily available and relatively inexpensive.

Lithium/copper monofluoride cells are used extensively in cameras and smaller devices. They provide high voltage, high power density, long shelf life, and good low temperature performance.

Lithium/thionyl chloride cells have very high energy densities and power densities. The cells also function better at lower temperatures than do other common cells.

Lithium/sulphur cells are used for cold weather use and in emergency power units.


Air-depolarized cells

Zinc/air cells are high energy can be obtained in a galvanic cell by using the oxygen of air as a "liquid" cathode material with an anode such as zinc. If the oxygen is reduced in the part of the cell designed for that purpose and prevented from reaching the anode, the cell can hold much more anode and electrolyte volume.

Aluminum/air cells have difficulty protecting the aluminum from the electrolyte during storage. Despite much research on this type of cell, aluminum/air cells are not in much current use.


Secondary cells are designed so that the power withdrawn can be replaced by connecting the cell to an outside source of direct current power. The chemical reactions are reversed by suitably applying voltage and current in the direction opposite to the original discharge.


Lead secondary cells

The lead/acid rechargeable battery system has been in use since the mid-1950s. It is the most widely used rechargeable portable power source. Reasons for the success of this system have included: great flexibility in delivery currents; good cycle life with high reliability over hundreds of cycles; low cost; relatively good shelf life; high cell voltages; ease of casting, welding, and recovery of lead.

The chief disadvantage of this battery is its high weight.


Nickel electrode cells with alkaline electrolytes

Nickel/cadmium cells provide portable rechargeable power sources for garden, household tools, and appliance use. The system carries exceptionally high currents at relatively constant voltage. The cells are, however, relatively expensive. These cells are used for portable hand tools and appliances, shavers, toothbrushes, photoflash equipment, tape recorders, radios, television sets, cassette players and recorders, calculators, personal pagers, and laptop computers.


Alkaline zinc/manganese dioxide cells

Alkaline zinc/manganese dioxide systems been developed and used as special batteries for television sets and certain portable tools or radios.


Silver/zinc cells

Silver/zinc cells are expensive. They are chiefly used when high power density, good cycling efficiency, and low weight and volume are critical, and where poorer cycle life and cost can be tolerated. They are used in primarily four areas: under water, on the ground, in the atmosphere, and in space.

Lithium secondary cells

Lithium secondary cells are attractive because of their high energy densities.


Sodium/sulfur systems

Sodium/sulfur systems are high-temperature batteries that operate well even at 177°F (80.6°C).

Resources

Books

Macaulay, David. The New Way Things Work. Boston: Houghton Mifflin Company, 1998.

Meyers, Robert A., Encyclopedia of Physics Science and Technology. New York, NY: Academic Press, Inc., 1992.

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Anode

—A positively charged electrode.

Battery

—A battery is a container, or group of containers, holding electrodes and an electrolyte for producing electric current by chemical reaction and storing energy. The individual containers are called "cells". Batteries produce direct current (DC).

Cathode

—A negatively charged electrode.

Direct current (DC)

—Electrical current that always flows in the same direction.

Electrode

—The conductor by which electricity enters or leaves a galvanic cell.

Electrolyte

—The medium of ion transfer between anode and cathode within the cell. Usually liquid or paste that is either acidic or basic.

Galvanic cell

—Combination of electrodes separated by electrolyte capable of producing electric energy by electrochemical action.

Primary cell

—A galvanic cell designed to deliver its rated capacity once and then be discarded.

Secondary cell

—A galvanic cell designed for reconstitution of power by accepting electrical power from an outside source.

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