| Carbon Zinc Batteries
Zn/MnO2
Carbon zinc batteries are of two basic
categories, Classic and Super Heavy Duty. The Classic category, usually the least
expensive battery line, is recomended for light to moderate periodic power needs. The
Super Heavy Duty category, premium carbon zinc, performs better than the Classic
category on moderate to heavy drains or continuous drains. Two electrochemical systems are
used in carbon zinc batteries, LeClanche and Zinc Chloride. Classic product is often
constructed using the LeClanche system. Super Heavy Duty product is usually constructed
using the Zinc Chloride system. For several years, battery companies has aggressively
pursued the reduction of heavy metals in all carbon zinc batteries. The batteries
described here have no added mercury or cadmium.
System Description
Carbon Zinc -- A generic term for
primary dry batteries of the LeClanche or Zinc Chloride system. These batteries have an
anode of zinc, a cathode of manganese dioxide, and a slightly acidic electrolyte.
LeClanche -- carbon zinc battery with a
slightly acidic electrolyte consisting of ammonium chloride and zinc chloride in
water.
Zinc Chloride -- A carbon zinc battery with
a slightly acidic electrolyte consisting mainly of zinc chloride in water.
Carbon zinc batteries provide an economical
power source for devices requiring light to moderate drain because of the use of
inexpensive materials and their time proven constructions. The service capacity of a carbon zinc battery is not a fixed
number of ampere hours because the battery functions at different efficiencies depending
upon the conditions imposed upon it. The service varies with current drain, operating
schedule, and cutoff voltage. The battery is also affected by the operating temperature
and storage conditions.
Characteristics
Zinc Chloride
The general characteristics of an Zinc
Chloride battery is that they are less expensive than alkaline. Economical in terms of
cost per hour on moderate current drains or use frequency. Output capacity decreases as
the battery is discharged, performance reduced at low temperatures, sensitive to changes
in the discharge rate and/or use frequency. Economical in terms of cost per hour on
moderate current drains or use frequency. Less output capacity decrease than LeClanche as
the drain rate increases. Less sensitive than LeClanche to changes in the discharge
rate and/or duty cycle. Lower internal resistance than LeClanche. Better low temperature
performance than LeClanche.Energy density of approximately 2 to 2.5 watt hours per cubic
inch. Average service maintenance exceeds 90% after one year storage at 21°C on typical
tests.Higher open circuit and initial closed circuit voltage than LeClanche or alkaline.
Lower unit weight than alkaline. Available in voltages ranging from 1.5 volts to 12 volts
and in a variety of shapes and sizes.
LeClance
Economical in terms of cost per hour of use
on light current drains. The widest variety of shapes, sizes, and capacities within the
primary battery system. Available in voltages ranging from 1.5 volts to 510 volts. Energy
density of approximately 1-2 watt hours per cubic inch. Average service maintenance
exceeds 90% after one year storage at 21°C on typical tests. Lower unit weight less
than akaline less expensive than alkaline or Zinc Chloride.
Construction
The carbon zinc battery uses a zinc anode,
a manganese dioxide cathode, and an electrolyte of ammonium chloride and/or zinc chloride
dissolved in water. Powdered carbon is used in the cathode mix, usually in the form of
carbon black to improve conductivity of the mix and for moisture retention. Carbon zinc
batteries are produced in two general configurations: Cylindrical - -available as unit
cells or in assembled multi-cell batteries Within the carbon zinc cylindrical battery
category are two constructions: LeClanche and Zinc Chloride. The Zinc Chloride battery
contains proportionately more zinc chloride in the electrolyte than the LeClanche battery
and therefore requires different battery design. Cathodes are a mixture of manganese
dioxide, carbon conductor and electrolyte. Anodes are zinc alloy can. The can also
confines the active materials in the battery. Separators are flour/starch paste or
coated paper selected to prevent migration of solid particles in the battery. Carbon
electrode serves as the cathode current collector. Top and bottom covers provide contact
surfaces of plated steel. The outside of the battery is covered with plastic film, Kraft
paper and a printed plastic label. Asphalt or plastic closure acts as the battery seal.
Venting mechanisms are incorporated in the battery either through the carbon electrode or
plastic seal. Flat cells -- used in the construction of 9 volt batteries are of the
LeClanche system. The flat cell contains no voids or carbon rod as does the cylindrical
battery. The flat cell, because of its rectangular form, reduces wasted space in assembled
batteries. The energy to volume ratio of a multi-cell battery utilizing cylindrical cells
is decreased by the voids occurring between the cells. These two factors account for
substantially higher energy volume ratio for flat cell batteries when compared to
batteries consisting of cylindrical cells. The cutaway of a typical flat cell battery is
shown here: Typical Flat Cell LeClanche Components Cathodes are a mixture of manganese
dioxide, carbon conductor and electrolyte. Anodes are zinc alloy sheets. Separators are
specially selected to prevent migration of solid particles in the cell. Plastic envelope
confines active cell materials. Carbon conductive coating on the zinc anode serves as the
cathode collector for the adjacent cell. Wax coating provides the battery seal. Connector
strips connect the flat cell stack to the battery terminals. XXXXXXXXX ally insulated from
battery components. Specialized terminals provide positive and negative external contact
surfaces.
Electro-Chemistry
LeClanche
The performance of a LeClanche battery is
the result of an electrochemical reaction between: A cathode composed of carbon and
refined manganese dioxide which may contain some naturally occurring manganese dioxide.
The more pure the cathode material, the better the performance. (The carbon component of
the cathode is usually carbon black and provides increased conductivity and moisture
retention.) An anode of high purity zinc alloy. A highly conductive, slightly acidic,
electrolyte solution of ammonium chloride and zinc chloride in water.
Zinc Chloride
The performance of a Zinc Chloride battery
is the result of an electrochemical reaction between: A cathode composed of carbon and
refined manganese dioxide which may contain some naturally occurring manganese dioxide.
The carbon component of the cathode is usually carbon black and provides increased
conductivity and moisture retention. Typically, Zinc Chloride batteries have a
higher proportion of carbon to manganese dioxide than LeClanche. A highly conductive,
slightly acidic, electrolyte solution of zinc chloride in water which may contain a small
amount of ammonium chloride. A Zinc Chloride battery contains a greater volume of
electrolyte than the same size LeClanche battery.The electrolyte is slightly more acidic
than a LeClanche electrolyte. The open circuit voltage of a fresh LeClanche Battery is
typically over 1.55 volts. A Zinc Chloride battery is typically over 1.60 volts. The
closed circuit voltage declines gradually as a function of the depth of discharge. The
energy output of Zinc Chloride batteries is less sensitive to variations in the discharge
current and duty cycle than comparable size LeClanche batteries. Typical D size
performance to a 0.75 volt cutoff is shown in the following diagrams: The efficiency of a
carbon zinc or alkaline battery improves as the current drain decreases. This is
more dramatically seen in the LeClanche and Zinc Chloride systems. As a result, an
important application guideline should be considered: For increased efficiency, use as
large a battery as possible, consistent with the physical limitations of the device. This
has the same effect as lowering the current. As an example, doubling the size of a carbon
zinc battery will more than double the service life at a given drain. The electrochemical
inputs of cylindrical D size batteries typically are in a ratio of 2:3:5 for LeClanche,
Zinc Chloride and Alkaline respectively. The differences in efficiency and rate
sensitivity between the three systems cause variations in actual output. Carbon Zinc
batteries are more efficient when used in low rate applications. Typical carbon zinc light
drain is defined as a current that would discharge the battery after 50 or more hours of
use at room temperature. As the drain is increased, the service difference between
Alkaline, Zinc Chloride and LeClanche systems increases. Typical carbon zinc moderate
drain is defined as a current that would discharge the cell within 10-50 hours of use at
room temperature. Changes in temperature will affect the reactivity of battery chemical
components. The storage of carbon zinc batteries at temperatures below 21°C will increase
their service maintenance. While freezer storage (-20°C) of a carbon zinc battery is not
harmful, storage at 5 to 10°C is effective.
Batteries to be stored at low temperature
storage should be allowed to reach room temperature in their packing so as to avoid
condensations of moisture which may cause electrical leakage and/or destruction of the
jackets. Storage at high temperatures exceeding 21°C for sustained periods of time will
significantly reduce service maintenance.
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