Linden D., Reddy T.B. (eds.) Handbook of batteries
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13.6 CHAPTER THIRTEEN
FIGURE 13.4 In zinc /air button cell, water vapor
transfer is the dominant form of gas transfer degra-
dation. (Courtesy of Duracell, Inc.)
FIGURE 13.5 In zinc / air button cell, gas transfer
regulation determines limiting current and useful ser-
vice life. (Courtesy of Duracell, Inc.)
It should be noted that under conditions of continuous discharge, the limiting current
would not be sustained indefinitely. It will gradually begin to decline as the voltage falls
and internal impedance increases. The limiting current will thus vary depending on the state
of charge of the battery. The limiting currents shown in Table 13.2 represents the maximum
current that is achievable within the first 3 minutes of fresh cell discharge, and hence is
representative of only the early stage of cell discharge.
13.4 PERFORMANCE CHARACTERISTICS
13.4.1 Cell Sizes
Zinc/ air button and coin batteries are available in a variety of sizes. Capacities range from
about 40 to 1100 mAh. Table 13.2 lists the physical and electrical characteristics of some
available batteries. The smaller sizes are commonly used as hearing-aid batteries, the medium
to larger ones for continuous-drain applications such as pager or telemetry devices.
Zinc/ air batteries for hearing aid applications continue to be improved to meet the more
stringent needs of new devices and user requirements. High rate zinc/air batteries have been
developed for example, the Rayovac Proline High Power batteries, designed for better air
access thus improving power output, the potential trade-off being shorter operating life on
low rate drain due to higher water vapor loss or gain from the cell. (See Section 13.4.10.)
Batteries have also been designed for greater service life by maximizing the amount of
zinc in the cell. The zinc content in these batteries is maximized by creating the largest
allowable internal cell volume while not exceeding standard external cell dimensions.
14
Table
13.2b lists some characteristics of these batteries. The zinc content is maximized without
compromising the internal free volume needed for anode expansion as zinc metal becomes
converted to zinc oxide, as this would lead to premature end of life. Designers of zinc/air
button cells will experience challenges in the future as digital hearing aids emerge which
will require greater power and energy to operate compared to existing models.
ZINC / AIR BATTERIES—BUTTON CONFIGURATION 13.7
TABLE 13.2 Characteristics of Zinc/ Air Button and Coin Batteries
a. Standard Single-Cell Batteries, 1.4 Volts
Generic
type IEC No.
ANSI
no.
Nominal
diameter
(mm)
Nominal
height,
(mm)
Average
weight
(g)
Rated
capacity,
(mAh)
Standard
drain
(mA)
Limiting
current
(mA)
Typical
useful
service life
(months)
5*
10*
312*
13*
675*
2330**
630**
PR63
PR70
PR41
PR48
PR44
PR2330
PR1662
7005ZD
7002ZD
7000ZD
7003ZD
5.7
5.7
7.7
7.7
11.4
23.2
16.0
2.0
3.5
3.9
5.2
5.2
3.0
6.2
—
0.3
0.6
0.9
1.8
—
3.5
42
70
134
260
600
960
1100
0.4
0.4
0.8
0.8
2
4
4
—
2
7
12
22
—
—
1–2
1–2
1–2
1–2
2–3
1–2
2–3
(*) Source: Duracell, a Gillette Company).
(**) Source: Panasonic Matsushita) Product literature (coin batteries).
b. High Capacity Zinc /Air Single-cell Batteries, 1.4 Volts
Generic
type ANSI no.
Max. ANSI
diameter
(mm)
Max. ANSI
height
(mm)
Rated capacity
(mAh)
10
312
13
675
7005ZD
7002ZD
7000ZD
7003ZD
5.8
7.9
7.9
11.6
3.6
3.6
5.4
5.4
90
160
290
630
Source: Rayovac Corporation, Ultra Hearing Aid Batteries.
TABLE 13.3 Zinc / Air Multicell Batteries
Generic type
ANSI
no.
Battery
voltage
(V)
Maximum dimensions,
(mm)
Average
weight
(g )
Rated
capacity,
(mAh)
Standard
drain
(mA)
Typical
useful
service
life
(months)
DA164
DA146
—
7004Z
5.6
8.4
16.8 (Dia) ⫻ 44.5 (H)
26.5 (L), 17.5 (W) 48.5 (H)
20
36
950
1500
3
6
1–2
1–2
Source: Duracell, Inc.
The first commercially successful zinc /air coin cell was introduced in 1989. The 2330
coin cell has become the predominant power source for credit-card-style pagers.
15
The 675
zinc/ air battery is the most common BTE hearing aid power source, and also serves as
battery for the Timex wristwatch Beep pager. Portable Holter telemetry heart monitors the
‘‘9-volt’’ zinc/air batteries to transmit patient data via portable radio transmitters to base
station monitors.
Data on two zinc /air multicell batteries are listed in Table 13.3.
13.8 CHAPTER THIRTEEN
13.4.2 Voltage
The nominal open-circuit voltage for a zinc /air battery is 1.4 V. The initial closed-circuit
voltage at 20
⬚C ranges from 1.15 to 1.35 V, depending on the discharge load. The discharge
is relatively flat, with 0.9 V the typical end voltage.
13.4.3 Energy Density
The zinc/air button batteries have a high volumetric energy density compared with other
primary battery systems. They range from approximately 442 Wh /L for a PR63 (size 5
hearing aid battery) to 970 Wh /L for a PR1662 battery.
13.4.4 Discharge Characteristics
Discharge profiles for the DA13 and DA675-size zinc/air button batteries are presented in
Fig. 13.6. As the air cathode in the cell is not chemically altered during discharge, the voltage
remains quite stable. Data for the zinc/mercuric oxide and zinc/silver oxide batteries are
provided for comparison. On continuous discharge at the loads shown, the zinc /air battery
will deliver twice the service of the other batteries of the same size. The DA13 battery, which
has less than half the volume of the other batteries, outperforms the larger metal oxide
batteries.
0 50 100 150 200 250 300 350
DA675
(Zn/air)
Hours of Discharge
DA 13 (Zn/air)
Alkaline (LR-44)
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1
0.9
0.8
Voltage
Ag O (SR-44)
2
FIGURE 13.6 Discharge profiles of primary button batteries discharged
at 620 ohm and 20⬚C. LR-44, SR-44 and DA-675 (11.6 mm ⫻ 5.4 mm)
and DA-13 (7.9 mm ⫻ 5.4 mm) (Courtesy of Duracell, Inc. Company)
ZINC / AIR BATTERIES—BUTTON CONFIGURATION 13.9
620 ohm
2 mA
150 ohm
8 mA
51 ohm
20 mA
Capacity, Ah
Voltage, V
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
1.6
1.5
1.4
1.3
1.2
1.1
1
0.9
FIGURE 13.7 Discharge curves for a 675 size zinc / air battery discharged at three
loads at 20⬚C. The average discharge current is also shown (Courtesy of Duracell, Inc.)
A set of discharge curves, typical of the performance of zinc/ air button batteries at 20⬚C,
is presented in Fig. 13.7. The typical discharge curves are relatively flat. The cell delivers
about the same capacity over the current range shown when operating below the limiting
current. The operating voltage is lower at the higher discharge currents, as is typical with
all battery systems. Discharge drains near the limiting current show increasing polarization
of the battery voltage and deliver less than the rated capacity.
13.4.5 Voltage-Current Performance
The degree of oxygen access to the cathode and the catalytic activity of the cathode material
generally define the voltage-current profile of a zinc /air battery. Oxygen access is defined
by the degree of air access to the battery. The higher the access of air to the battery, the
greater is the power output. This generally means that increasing the number of air access
holes in the battery case will increase the power capability. The consequences of high air
access is the increased opportunity for greater water vapor loss due to evaporation from the
cell. A higher rate of water vapor loss results in faster dry-out leading to increased electrolyte
concentration and higher internal impedance. Thus, more air access shortens the useful op-
erating service life of the battery, once the battery is opened to the air. Zinc/air batteries
can be designed for maximum power output and shorter operating life by maximizing air
access. A longer operating life can be achieved by minimizing air access, but at the expense
of cell power output.
The impact of air access on the limiting current of a zinc/air battery is demonstrated in
Fig. 13.8. Limiting current is the maximum current output for a given set of conditions, i.e.
temperature, relative humidity and cell design parameters. The limiting current is typically
determined by potentiostatically polarizing the battery to a voltage of 1.1 V and measuring
the height of the maximum output current within 1 to 5 minutes after the start of the test.
In Fig. 13.8, the effect on increasing the number of air access holes in a 675 size zinc /air
battery on the limiting current is shown.
13.10 CHAPTER THIRTEEN
FIGURE 13.8 Limiting current measured as a function of the number of air
holes in a 675-size zinc / air cell. Limiting current increases with increased air
access. (Courtesy of Rayovac, Inc.)
The ability of the cathode to catalyze the oxygen reaching the reactive sites on the active
surface of the cathode also determines the degree of maximum power output from a battery.
The use of catalytic additives to the carbon mix making up the air cathode is a common
practice. The use of catalytic agents such as MnO
x
compounds is typical. Figure 13.9 illus-
trates the discharge characteristics of a carbon cathode in a 675 size cell with and without
a manganese oxide catalyst. The manganese-containing cathode produces a cell with a higher
average operating voltage.
The voltage-current profiles for various sized button batteries are shown in Fig. 13.10.
As can be seen, the voltage falls rapidly when continuous currents above the limiting current
are applied. This occurs because the cell has become oxygen-starved. It is consuming oxygen
at a faster rate than the rate at which oxygen is entering the cell. Voltage will fall until the
load current is reduced to an equilibrium condition.
ZINC / AIR BATTERIES—BUTTON CONFIGURATION 13.11
FIGURE 13.9 Voltage as a function of discharge current density. The Mn(II) cathode
delivers higher performance due to greater catalytic activity. (Courtesy Rayovac, Inc.)
FIGURE 13.10 Voltage-current profiles for various zinc /air button bat-
teries at 20⬚C(Courtesy of Duracell, Inc.)
13.12 CHAPTER THIRTEEN
FIGURE 13.11 Internal impedance profiles vs. discharge level.
(a) 675-size battery. (b) 13-size battery. Signal frequency: a ⫽ 50
Hz; b ⫽ 100 Hz; c ⫽ 250 Hz; d ⫽ 500 Hz; e ⫽ 1000 Hz; f ⫽
3000 Hz. (Courtesy of Duracell, Inc.)
13.4.6 Cell Internal Impedance
The effects of discharge level and signal frequency on the internal impedance characteristics
of the DA13 and DA675 button batteries are presented in Fig. 13.11.
ZINC / AIR BATTERIES—BUTTON CONFIGURATION 13.13
FIGURE 13.12 Pulse load performance of zinc/ air
button batteries (a) I ⬍ I
L
, short pulse duration, (b)
av
I ⬎ I
L
, short pulse duration; (c) I ⬍ I
L
, long pulse
av av
duration. (Courtesy of Duracell, Inc.)
13.4.7 Pulse Load Performance
Zinc/ air cells can handle pulse currents much higher than the limiting current (I
L
), the current
level depending on the nature of the pulse. This capability results from a reservoir of oxygen
that builds up within the cell when the load is below the limiting current.
Figure 13.12 illustrates general voltage profiles for various pulse waveforms. In Fig.
13.12a a pulse current double the magnitude of I
L
is applied. However, the pulses are spaced
so that the average current is less than I
L
. Therefore the average rate of oxygen ingress is
sufficient to sustain the average load current. Furthermore, the pulses are of short duration
so that the battery does not become oxygen-starved before the end of a single pulse. The
voltage profile shows the ripple effect of the pulse current, but the battery maintains a
continuous useful average operating voltage. If the peak pulse current is increased so that
the average load current is greater than I
L
, the battery will eventually become oxygen-starved
and voltage will decline, as shown in Fig. 13.12b.
13.14 CHAPTER THIRTEEN
In choosing a battery for a particular application, the designer must ensure that the average
current for the duration of the pulse load is less than I
L
. The designer must also check for
the possibility of the battery becoming oxygen-starved during the application of a single
pulse. This condition is illustrated in Fig. 13.12c. In this figure the average current is less
than I
L
, but the battery becomes oxygen-starved and the voltage declines sharply during the
time that a pulse is applied because of the long pulse duration. The voltage recovers between
pulses, maintaining an average close to the average of Fig. 13.12a. A method for improving
pulse performance by incorporating an air reservoir into the zinc/ air battery has been pro-
posed. Figure 13.13 illustrates the performance of a DA675 battery subjected to sustained
current drains above and below the limiting current.
FIGURE 13.13 Voltage-time response of 675-size zinc / air batteries sub-
jected to continuous loads above and below limiting current. (Courtesy of
Duracell, Inc.)
13.4.8 Effect of Temperature
The effect of temperature on discharge performance at various discharge rates is illustrated
in Fig. 13.14. This degradation of performance is caused primarily by a reduction in ionic
diffusion capability through the electrolyte. Rather high concentrations of potassium or so-
dium hydroxide (25 to 40% by weight) are used to obtain good electrical conductivity. This
high concentration is subject to changes in viscosity and a general lowering of ionic mobility
as the temperature drops.
The operating voltage also varies with temperature. At lower temperatures and a fixed
current, the voltage is lower than when the battery is discharged at room temperature or
warmer. Although the optimum discharge temperature is between 10 and 40
⬚C, the battery
can still function at temperatures below 10
⬚C, but at lower voltages and energy densities.
The operating voltage of the zinc/ air battery at various discharge loads and temperatures is
shown in Fig. 13.15.
It should be noted that at low discharge rates and moderate temperatures, the effect of
temperature is minimal. In selecting a zinc/air system that must perform at low temperatures
it is important to consider the required current density in order to preclude failure due to
diffusion limitations.
ZINC / AIR BATTERIES—BUTTON CONFIGURATION 13.15
FIGURE 13.14 Comparison of performance of zinc/ air batteries
at various temperatures. (a) Discharged at 300-h rate. (b) Dis-
charged at 75-h rate. (c) Discharged at 50-h rate. (Courtesy of
Duracell, Inc.)