Basics for a beginner.

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CELLS & BATTERIES - Notes:
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.
Moderate energy primary cells: [1] 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

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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.
[2] 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.
Medium to high energy primary cells
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

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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.

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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
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.
Moderate energy storage cells: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.

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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.
High energy storage batteries
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

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Sodium/sulfur systems are high-temperature batteries that
operate well even at 177°F (80.6°C).
Books [1] Macaulay, David. The New Way Things Work. Boston:
Houghton Mifflin Company, 1998. [2]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.