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Entire Zinc Air Bulletin
The zinc-air primary battery system
is different from most other batteries in that it “breathes”
oxygen from the air for use as the cathode reactant. The virtually
limitless supply of air enables the zinc air cell to offer many
performance advantages compared to other batteries.
The electrochemical system can be more formally defined
as zinc/potassium hydroxide/oxygen, but “zinc-air”
is the common name and is used throughout this text. Other zinc
anode battery systems are also referred to by their popular abbreviated
2. General Characteristics
2.1 System Description
zinc-air battery was discovered in the early nineteenth century,
but did not find its first commercial use until the 1930s when large
industrial-type cells were constructed for railway signaling. The
development of the thin and efficient air cathode used in today’s
zinc-air cells occurred in the early 1970s. This led to miniaturization
and ultimately to the commercialization of zinc-air button cells
in 1977. The world of zinc-air today includes button cells, batteries,
and a small number of customized battery packs. Zinc-air delivers
the highest energy density of any commercially available battery
system, and at a low operating cost. This advantage is derived from
its use of atmospheric oxygen as the cathode reactant. It allows
the zinc-air cell to be filled with more zinc "fuel",
which is the only material consumed during discharge. This increased
amount of anode material enables the cell to offer up to 5 times
more capacity than conventional zinc anode systems which must contain
their oxidant within the cell. For example, alkaline cells store
oxygen in the form of manganese dioxide, which comprises about 60%
of the cell weight. Most batteries contain roughly the same amount
of anode material as cathode material, so their service life is
limited by whichever is consumed first.
A schematic representation of a conventional zinc
anode cell and a DURACELL® zinc air cell is shown
in Figure 2.1.1. DURACELL® zinc-air
batteries are used in a number of consumer and industrial applications.
They are best suited for devices that are used frequently or continuously,
operate at low-to-medium drain rates, and require high energy density
and low operating cost. Hearing aids are an ideal application for
zinc-air because they are usually worn for up to 16 hours per day
and have a low-to-moderate requirement for electrical current (a
few milliamperes on average). Zinc-air batteries are often used
to power a number of medical devices, such as patient monitors and
recorders, nerve and muscle stimulators, and drug infusion pumps.
They are also well suited for use in telecommunication devices such
as pagers and wireless headsets.
DURACELL® zinc-air cells can be combined
in series and series-parallel connections to form a number of battery
pack configurations. Such packs have been designed for use in communications
equipment and emergency lighting products. To achieve optimum battery
performance in the application of interest, Duracell may be contacted
The advantages of using DURACELL®
zinc air cells are described below:
2.3 Comparison of Primary Battery
- High Energy Density – The
zinc-air cell has a gravimetric energy density of up to 442 Watt-hours/kilogram
(Wh/kg) (200 Watt-hours/pound) and a volumetric energy density
of up to 1673 Watt-hours/liter (Wh/l) (27.4 Watt-hours/cubic inch).
This is up to five times the energy of alkaline and mercury systems.
The highest energy is delivered under conditions of frequent or
continuous use, low-to-medium drain rates, and operating temperatures
between 0 ºC and 50 ºC (32 ºF and 122 ºF).
- Flat Discharge Profile –
Typically zinc-air cells maintain a constant output voltage between
1.1 and 1.25 volts throughout the discharge life of the cell.
- Excellent Sealed Shelf Life –
The sealed (unactivated) zinc-air cell has been demonstrated to
retain greater than 98% of its rated capacity after one year of
storage at 21 ºC (70 ºF). The unactivated storage life
is rated at 3 years.
- Intrinsically Safe – Zinc-air
cells offer a means of self-venting any internally generated gases
through air-access holes located on the cathode can, eliminating
the possibility of cell rupture or explosion. In addition, zinc-air
cells are generally considered environmentally safe, and under
most conditions do not require special handling or disposal procedures.
- Low Operating Cost –
Zinc-air cells and batteries offer a low operating cost on a per-milliampere-hour
basis when used in frequent or continuous use applications.
Primary batteries are most often described
by their energy as a function of cell weight and volume. A
per-unit-weight comparison of zinc-air with other primary
systems is shown in Figure 2.3.1. The gravimetric
energy density is greater than all other primary batteries
over an operating temperature range of 0 ºC to 50 ºC
(32 ºF to 122 ºF). The comparison on a volumetric
basis is provided in Figure 2.3.2. Zinc-air
to delivers its greatest energy per unit volume over a similar
temperature range. Under some conditions not shown in the
figure (50-100 mA/cm2), DURACELL® zinc-air cells can deliver
up to five times the energy of other zinc-anode systems.
shows the discharge characteristics of conventional zinc-anode
battery systems for cells of the same size over their discharge
life at 21 ºC (70 ºF). Unlike alkaline cells, DURACELL
zinc-air cells provide a constant output voltage during discharge.
During storage, zinc-air cells are sealed to
prevent oxygen, the cathode reactant, from entering the cell.
This characteristic gives the zinc-air cell excellent shelf
life as shown in Figure 2.3.4. At 21 ºC
(70 ºF) storage, a sealed zinc air cell retains 98% of
rated capacity over a one-year period. Zinc-air cells are
best if used within 3 years of manufacture.
3. Composition and Chemistry
3.1 Cell Chemistry
DURACELL® zinc-air cell consists of a zinc anode, an aqueous
alkaline electrolyte and an air cathode. Power is derived from the
reduction of oxygen at the cathode, and the oxidation of zinc at
the anode. The simplified net reaction is shown below:
Zn + ½O2 -> ZnO
anode in a zinc air cell is a powdered zinc amalgam. The zinc powder
contains a very low level of mercury (max. 25 mg per cell) to prevent
internal pressure buildup due to hydrogen evolution from the self-discharge
of the zinc in the electrolyte. A gelling agent is also mixed with
the zinc amalgam to maintain the uniformity of the zinc powder-electrolyte
mixture during discharge.
In the cell reaction, the zinc in the anode is oxidized
to form zinc hydroxide in the form of the soluble zincate [Zn(OH)42-]
ion. The half reaction for the anode is shown below:
Zn + 4OH- -> Zn(OH)42-
The zinc hydroxide accumulates around the zinc particle,
but does not impede either ionic or particle-to-particle conductance
until the zinc is fully oxidized. As the discharge proceeds, the
zincate ions eventually precipitate to form zinc oxide (ZnO).
Zn(OH)42- -> ZnO
+ H2O + 2OH-
Theoretical capacity of the anode is 0.82 ampere-hours
per gram of zinc (23 ampere-hours per ounce of zinc).
air cathode in a zinc-air cell is a mixture of carbon, Teflon, and
a small amount of manganese dioxide impressed onto a nickel-plated
screen. This material is then laminated with a Teflon layer on one
side and a separating membrane on the other. The Teflon layer allows
gases, most importantly oxygen, to diffuse into and out of the cell,
and also provides resistance to leakage. The separator acts as an
ion conductor between the electrodes and as an insulator to prevent
Atmospheric oxygen reacts with catalysts in the air
electrode and electrolyte to produce hydroxide ions.
The half reaction for the air cathode is shown below:
½O2 + H2O +
2e- -> 2OH-
Theoretical capacity of the air electrode is 820 mAh/g,
or 4.79 ampere-hours per liter (0.079 ampere-hours per cubic inch)
of molecular oxygen, which is roughly equivalent to one ampere-hour
per liter of air.
The alkaline electrolyte
employed in a zinc air cell is an aqueous solution of potassium
hydroxide with a small amount of zinc oxide to prevent self-discharge
of the anode. Potassium hydroxide provides good ionic conductance
between the anode and cathode to permit efficient discharge
of the cell.
4.1 Cell Construction
The button cell is a widely used battery
configuration for hearing aids, calculators, infusion pumps, and
pagers. The major components that make up a DURACELL®
zinc-air cell are illustrated in Figure 4.1.1.
The anode subassembly includes the anode can and the
insulator. The anode can, which holds the zinc anode, is a tri-clad
material comprised of a copper interior lining for good chemical
compatibility, a stainless steel layer in the middle for strength,
and nickel layer on the outside for good electrical contact. A nylon
insulator surrounds this can and insulates the negative terminal
from the positive terminal. A sealant coating is applied to the
insulator prior to its assembly with the anode can.
The cathode subassembly consists of the cathode can
and the air electrode. The cathode can is made of nickel-plated
steel, and contains multiple air holes punched into the bottom to
provide air access to the cathode. These air holes provide the pathway
for oxygen to enter the cell.
Placed directly over the holes is a porous membrane that helps ensure
uniform air distribution across the air electrode. On top of this
membrane is a loose layer of Teflon to help form the cathode seal,
and then the air electrode itself (i.e. cathode), which is oriented
with its Teflon side toward the air holes. There is an interference
between the ends of the nickel screen that protrude from the perimeter
of the cathode, and the cathode can to form a low resistance contact.
The zinc-anode mix and the electrolyte are dispensed into the anode
subassembly, over which the cathode subassembly is placed and sealed.
4.2 Tab Seal
Once constructed, the cells are sealed to provide
a consistently fresh product to the end user. The seal comprises
a special tab that is placed over the air holes and attached via
a mild adhesive. DURACELL® zinc-air button cells
are sealed with an EASYTAB, a tab that is longer than the tab on
ordinary hearing aid batteries — making it easier to remove
from the pack, handle and insert into the device.
4.3 Battery Construction
Battery cases are made of injection molded plastic
with special porous inserts to allow air circulation around the
cells. Some batteries may utilize a shrink-wrap plastic with air
access ports. Cells are packaged to allow adequate and equal air
access to each cell’s air access ports.
5. Performance Characteristics
5.1 Preparing Batteries
Zinc-air cells are stored with an adhesive
tab seal or, when in a battery, in a metallized plastic pouch that
inhibits gas and vapor transfer. The batteries are ready to be used
when the seal or pouch is removed, allowing oxygen from the air
to enter the batteries. In most cases, nominal voltage levels are
attained immediately after the seal is removed.
nominal open circuit voltage for a zinc air cell is 1.4 Volts. The
operating voltage during discharge is dependent on the discharge
load and the temperature. Typically, the operating voltage per cell
is between 1.25 and 1.0 Volts. Zinc-air cells are noted for a relatively
flat discharge profile, i.e. the voltage is relatively constant
during use. The typical end point or cutoff voltage, by which most
of the cell capacity has been expended, is 0.9 Volts.
5.3 Energy Density
batteries offer the highest gravimetric and volumetric energy density
of any primary battery system, due to their use of atmospheric oxygen
as the cathode reactant. The air electrode, the site at which the
cathode reaction occurs, occupies very little internal volume and
does not degrade throughout the discharge of the battery. The result
is an increase in the volume available for the zinc anode (fuel),
which translates into higher capacity.
To determine the energy density of a zinc air cell
under specific conditions of load and temperature, simply multiply
the capacity in ampere-hours that the cell delivers under those
conditions by the average discharge voltage, and divide by the cell
volume or weight. The equations for gravimetric and volumetric energy
densities are shown below.
Gravimetric Energy Density:
(Drain in Amperes x Service Hours) x Average
Discharge Voltage = Watt-Hours
of Cell in Pounds or Kilograms lb.
Volumetric Energy Density:
(Drain in Amperes x Service Hours) x Average
Discharge Voltage = Watt-Hours
of Cell in Cubic Inches or Liters
in3 or L
Table 1. Typical energy density of DURACELL®
zinc-air button cells
As a general rule, energy density decreases
as the cells get smaller since the percentage of inactive materials,
such as insulators, current collectors and cell containers, consume
proportionately more of the cell weight and volume. Table 1 lists
the approximate energy density of various DURACELL®
zinc air button cells.
Zinc-air capacity is usually
expressed in ampere-hours or milliampere-hours. The rated
capacity of a particular cell is what is derived under the
recommended specification for that cell. DURACELL® zinc-air
cells are offered in a wide range of sizes and capacities.
The capacity can be determined from the respective datasheet
for each cell. As with all battery systems, performance of
a zinc-air cell is dependent on the discharge current. As
an example, capacity is plotted as a function of discharge
current for various DURACELL® zinc-air cells in Figure
5.4.1. This graph provides an estimate of effective
capacities and is to be used as a general guideline. For anticipated
cell performance in a specific application, contact Duracell
Cell performance can also depend on temperature and ambient
relative humidity. Figure 5.4.2. shows how
the delivered capacity of a DURACELL® zinc air cell is
affected by the operating temperature.
5.5 Oxygen Starvation
Because of the unique design of the zinc-air battery
and its use of air as the cathode, the zinc-air cell's performance
is susceptible to the relative availability of air and must be considered
when evaluating the capabilities of the zinc-air system. Technically
speaking for all batteries, their performance begin to decline precipitously
due to the finite speed at which the reactants and products can
be delivered to and from the electrodes. In zinc-air, this is generally
due to oxygen starvation. That is, as the current demand increases,
the cell must provide air to the cathode at an increasing rate.
When the rate of oxygen reduction is about equal to the replacement
of air in the cell, the discharge current can be maintained without
air starvation. At higher drain rates, the voltage begins to steeply
decline. The reason that this parameter is so design dependent is
that it is most typically correlated with the size and number of
air holes. Zinc-air battery designers configure their cells to provide
the just the right amount of air access for the applications in
which the cells are used. Adding holes or making the holes larger
increases the cell's rate capability, but it also decreases the
activated life (see Section 5.9). DURACELL® zinc-air cells are
optimized for maximum performance and life in the applications listed
in this guide. Customers wishing to exploit the advantages of zinc-air
cells in other applications should consult with Duracell to assess
the product options.
5.6 Pulse Current Capability
The pulse current capability for a zinc-air
battery can be many times greater than the maximum current
that can be sustained under continuous discharge. Actual performance
will depend on the pulse width and duty cycle. This relationship
is illustrated in Figures 5.6.1. and 5.6.2.,
which show the pulse load performance of a typical zinc-air
button cell. In Figure 5.6.1, a pulse current
that is more than double the magnitude of the average current
is applied, but the width and frequency are sufficiently low
that that the cell does not become oxygen-starved before the
end of a single pulse. The voltage profile exhibits the ripple
effect of the pulse current, but the cell maintains a constant
average operating voltage. In contrast, the cell in Figure
5.6.1 is subjected to an average load that is high
relative to the pulse current. It suffers from oxygen starvation
and exhibits a progressively declining load voltage.
5.7 Internal Impedance
Cell impedance is a critical consideration in
some applications such as hearing aids where low impedance is required
for proper operation. The internal impedance of zinc-air batteries
is comparable to other zinc anode batteries of similar size. The
internal impedance specification for each DURACELL®
zinc-air battery (at 1000 Hz) is provided on the individual product
5.8 Shelf Life
Shelf life measures the ability of a sealed cell to
retain capacity under specified storage conditions. Zinc air cells
are essentially dormant until the cathode reactant, oxygen, is allowed
to enter. Oxygen is excluded during storage by means of a low-porosity
tab seal placed over the air holes. Removing this seal activates
the cell by allowing oxygen to enter. As was shown in Figure
2.3.4., a sealed zinc-air cell stored at 21ºC (70ºF)
will retain more than 98% of its rated capacity over a one-year
period. The rated storage life is three years.
5.9 Activated Life
Zinc-air activated life is a measure of the ability
of the cell to retain its performance after the tab is removed (and
not replaced). This differs from Service Life in that it refers
to the undischarged condition. It is what happens to the battery
when the tab is removed or the package is opened and it is placed
on a shelf or counter top. Since zinc-air cells obtain the cathode
reactant from the air, they are subject to the influence of the
environment. More specifically, they can dry-out under conditions
of low humidity, or become waterlogged at high humidity due to the
ingress of water vapor. They also absorb oxygen and carbon dioxide
from the air. The oxygen can dissolve in the electrolyte and react
with the zinc. The carbon dioxide reacts with the electrolyte. Although
the amount of carbon dioxide in the environment is small, its effects
on the battery are cumulative.
It is possible to prolong the life of the battery
by re-covering the air holes with the tab after each use, but the
benefits of this strategy vary considerably and are highly dependent
upon the environmental conditions. The best practice is to place
the cell in the device and use it until it is discharged.
5.10 Discharge Characteristics
In most applications, zinc-air cells provide a very
stable output voltage throughout the life of the cell. The discharge
characteristics of a typical zinc-air battery as a function of temperature
are illustrated in Figure 5.10.1. The discharge
rate is defined with respect to the cell capacity. For example,
a 300-hour rate for a DA13 cell (nominal capacity ~ 290 mAh) would
correspond to a discharge rate of approximately 0.95 mA (290 mAh/300
Effect of Temperature
Optimum performance for zinc air batteries is achieved at temperatures
between 0ºC and 50ºC (32ºF and 122ºF). At lower
temperatures, a continually sloping voltage profile will be exhibited,
with the degree of slope dependent upon on the temperature and the
discharge rate. Performance at temperatures above this range may
actually be improved in the short term, but long-term exposure to
elevated temperatures can accelerate moisture loss, which can reduce
Figures 5.10.2 and 5.10.3
show the effects of temperature at two additional rates of discharge.
The curves illustrate that temperature becomes more significant
parameter as the discharge rate increases.
Effect of Humidity
Relative humidity can affect the performance of a zinc air battery
over long periods of use. Moisture transfer through the battery’s
air access holes results from the difference in relative humidity
between the interior of the cell and the environment. The effect
of continued moisture loss or gain from the electrolyte would be
seen as shortened life or loss of power. Best results over long-term
discharge are achieved at relative humidity conditions between 35
and 80 percent.
Figure 5.10.4 shows an intermittent
discharge (4 hours per day) of a DURACELL® zinc air
battery at 30, 60 and 90 percent relative humidity conditions. Under
conditions of 40-60% R.H., the outside world most closely matches
the interior of the cell, at the maximum performance is obtained.
5.11 Cell Expansion
discharge of a zinc-air cell results in a small increase in the
overall cell volume as the zinc is oxidized. In the case of a DURACELL®
DA675 cell, cell height increases by about five thousandths of an
inch when fully discharged. If the battery is constrained so that
it cannot expand, it may not realize its full capacity. In a multi-cell
battery, the cells are packaged so that sufficient space is allowed
for growth during discharge. All DURACELL® zinc-air
cells are designed to fit within the IEC cell specifications during
6.1 Fundamentals of Battery
To optimize battery performance,
the battery selection process should begin in the early stages of
equipment design before the battery cavity is fixed. In this way
the most effective trade-off can be made between battery capabilities
and equipment features.
In the battery selection process, the following fundamental
requirements should be considered:
|Maximum permissible voltage, minimum operating
voltage, startup time.
||Shock; vibration, humidity, other
|Load or Current Drain:
| Average current, constant power; variable load,
||Capacity retention requirements,
storage time, temperature.
|Continuous or intermittent.
||Permissible variability, failure rates, potential
for gassing or leakage.
|Length of time operation.
||Type of usage (consumer, industrial, or military),
|Size, shape, and weight.
||Compatibility with cell terminals, corrosion
|Operating temperature range, storage temperature
||Operating or life cycle cost (i.e. cost per milliampere
hour) and initial per-unit cost.
When the important fundamental requirements are identified,
decisions can be made on the best battery system for the application.
With so many types of batteries available today, choosing the best
one can be a difficult task. There is no singular battery or battery
system than best fulfills the needs of all applications.
If the application requires a low-cost, longer-life
battery under a continuous or frequent use (many hearing aids used
only on weekends) and/or a small battery package with high energy
density, then DURACELL® zinc air batteries are an
6.2 Special Zinc-Air Design
The unique air-breathing property
of zinc-air cells is the key to their high energy density and high
capacity. This factor introduces application design considerations
that do not pertain to conventional primary battery systems:
- Air Access
Air access is a critical aspect of designing
equipment to use zinc air batteries. Air is admitted through the
holes in the positive cap of each cell, so the holes must not
be blocked. The oxidation of each atom of zinc requires a fixed
amount of oxygen and provides four electrons to the external circuit.
Based on this simple relationship, the amount of air required
per ampere-hour of capacity is about 1.2 liters at standard temperature
and pressure. It is difficult to provide hard and fast rules for
designing proper air access, such as the size and number of holes
or apertures, but simple calculations of gas transport via diffusion
of air provide a good starting point. DURACELL ® zinc-air cells are designed to provide the most efficient air access for optimum power. Figure 6.2.1 provides an example of sample hole patterns for DURACELL ® and competitor cells.
- Contact Methods
The recommended locations for making electrical
contact are the anode can top (-) and the cathode can side wall
(+). If contact to the bottom of the cathode can is required,
care should be taken to avoid the air holes and the "+" mark at the center of the can. An additional concern is the shape of the bottom of the battery which may either be flat or stepped, see Figure 6.2.2. The device manufacturer must correctly design their battery cavities to handle both battery shapes, since both bottom styles exist side-by-side in the marketplace. Improper design may result in poor fit of the cell within the device cavity. Table 2 provides some useful design criteria for use with DURACELL ® zinc-air cells.
- Device Voltage Cutoff
The nominal cutoff voltage for zinc-air cells
is 0.9 Volts. They can be discharged to lower values, but deep
discharge to 0.5 Volts or less can result in electrolyte leakage
from the air holes. The recommended practice is to design the
device with a voltage cutoff feature that shuts the equipment
off at a predetermined voltage setting.
6.3 Zinc-Air Application Design
The following design guidelines are provided to aid
in identifying the types of applications that zinc-air batteries
will best serve. They deliver their optimum service in devices that
- Highest capacity in a compact and lightweight form;
(40 - 600 mah in single button cells, depending on size, and up
to 1,500 mah in multicell batteries)
- Low to moderate drain rates (up to 20 mAh for the
DA675) at an operating voltage of 1.25 to 0.9 Volts or a multiple
- Continuous or frequent use that fully discharges
the battery within a two- to three-month period.
- Operation between 0°C and 50°C (32°F
- Long shelf life when in a sealed state awaiting
- Home Health Care Devices (e.g.. Crib Monitors)
- Hearing Aids (Behind-the-Ear and In-Canal Aids)
- Patient Monitors (Telemetry Transmitters)
- Portable Data Loggers
Figure 6.3.1 shows the discharge profile of a DURACELL ® zinc-air cell during a test typical of a conventional BTE hearing aid.
7. Handling and Disposal
The following care and handling procedures pertain
to the various zinc-air cells manufactured by Duracell.
zinc-air cells are safe to use because they offer a means of self-venting
any internally generated gases through the air access holes located
on the cathode can. This eliminates the probability of cell rupture
7.2 Packaging and Transportation
All DURACELL® zinc-air batteries are
supplied in the sealed state in one of the following packaging styles:
- Two or more individual button cells sealed on one
piece of adhesive tape
- Individual cells with their own tape seal (tab)
- Multicell batteries individually sealed in a metalized
The factory seal should not be removed or the pouch
opened until the battery is required for use. Generally DURACELL®
zinc air batteries do not require special handling or shipping precautions
for land, sea or air transportation.
with any electrochemical system, ambient storage temperatures of
21°C (70°F) or cooler are recommended for best capacity
retention. When storing zinc air batteries, do not stack more than
three cases high, as the additional weight may cause damage to the
internal cell packaging and potentially the cells.
cells should be used within the recommended operating conditions
specified for each cell size. Optimum performance is obtained via
operation on a frequent or continuous use basis within a temperature
range of 0°C to 50°C (32°F and 122°F) and a relative
humidity range of 25-80%. As is the case with all battery systems,
zinc-air batteries should be removed from equipment that will not
be used for prolonged periods of time.
When inserting zinc-air cells into equipment,
attention must be paid to the polarity. Reverse insertion can cause
charging and possible leakage. When a device requires more than
one battery, all batteries should be replaced at the same time.
Always use cells of the same chemical system to prevent voltage
incompatibilities and potential leakage.
DURACELL® zinc-air cells do not require
special disposal or reclamation after being discharged.