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Voltage
The nominal voltage of Li/M nO2 cells is 3.0 volts,
twice that of conventional cells due to the high electrode potential
of elemental lithium. Consequently a single Li/MnO2 cell
can replace two conventional cells connected in series, as shown
in the table below. Actual open circuit voltage is typically 3.1
to 3.3 volts.
| BATTERY
SYSTEM |
NOMINAL
VOLTAGE |
TYPICAL
OPERATING VOLTAGE |
|
Nickel Cadmium |
1.20 |
1.15
- 1.25 |
|
Mercuric Oxide |
1.35 |
1.15
- 1.30 |
|
Alkaline Manganese Dioxide |
1.50 |
1.10
- 1.30 |
|
Silver Oxide |
1.50 |
1.20
- 1.50 |
|
Lithium Manganese Dioxide |
3.00 |
2.50
- 3.00 |
The operating voltage of a battery during discharge
is dependent on the discharge load and temperature. Typical discharge
curves for Li/MnO2 coin and spiral-wound cylindrical cells
at 20°C (68°F) are shown in the following figures. The end
or cutoff voltage by which most of the cell’s capacity has been
expended is usually 2.0 volts.
Figure 5.1.1
Typical constant resistance discharge profile for all Li/MnO2
coin cells at 21°C
Figure 5.1.2
Typical constant current discharge profiles of Li/MnO2
spiral-wound DL2/3A cells at 20°C
As evident, the voltage profile of DURACELL Li/MnO2 cells
is flat throughout most of the discharge with a gradual slope near
the end of life. The moderately sloping profile towards the end of
life can be an advantage in certain applications, such as utility
meters and security devices. The gradual drop-off in voltage can serve
as a state-of-charge indicator to show when the battery is approaching
the end of its useful life. Incorporating a low voltage indicator
into equipment circuitry provides a way of alerting users to replace
the battery before it drops below the minimum voltage required to
operate the device.
Capacity
The output capability of a cell over a period of time is referred
to as cell capacity. Cell capacity is the amount of current withdrawn
from the cell multiplied by the number of hours that the cell delivers
current to a specific end-point voltage.
Rated capacity is the capacity a cell typically delivers under specific
conditions of load and temperature. A cell will usually deliver
less than rated capacity when discharged at loads heavier than the
rated load, and/or temperatures lower than the rated temperature.
Conversely, capacity greater than the rated value is usually obtained
at lighter loads and higher temperatures.
Figure 5.2.1:
Capacity of a DURACELL® spiral-wound DL123A cell
as a function of continuous discharge rate and temperature to a
2.0 volt cutoff.
DURACELL Li/MnO2 cells are offered in a variety of cell
sizes and capacities. Coin cells range from 75 to 550 mAh; spiral-wound
cells are available in 160 and 1,300 mAh capacities; and bobbin
cells range from 650 to 1,900 mAh. Capacity ratings for DURACELL
Li/MnO2 products are listed in the DURACELL Product
Specification Summary and individual product data sheets available
from Duracell upon request.
Effect of Temperature
Li/MnO2 cells are capable of performing over a wide temperature
range. The temperature range recommended for each cell type is a
function of cell construction and seal design. Although -20°C
to 60°C is the range in temperature recommended for optimum
efficiency, Li/MnO2 cells are being used in applications
ranging from -40°C to 71°C
Operation at low temperatures is limited to very low rates of discharge
when using coin cells and laser-sealed bobbin cells. Figure 5.3.1.
shows the effect on the discharge characteristics of a DURACELL
MicrolithiumTM coin cell under low microampere drain.
FIGURE 5.3.1
Effect of temperature on Li/MnO2 coin cell performance;
800 hour rate.
Figure 5.3.2. illustrates the effect of temperature on the
discharge characteristics of a bobbin cell under a microampere drain.
The Li/MnO2 cell provides reliable, continuous operation
even under extreme temperature conditions.FIGURE
5.3.2
Effect of temperature on performance of a DURACELL®
MicrolithiumTM Li/MnO2 bobbin cell (DL1/2AAL).
Spiral-wound Li/MnO2 cells are designed to operate effectively
during high rates of discharge at very low temperatures. In Figure
5.3.3. and 5.3.4., the performance of the spiral-wound
DURACELL® DL123A size cell is shown at various temperatures
to -20°C (-4°F). Good voltage regulation is evident over
the wide temperature range. DURACELL® Li/MnO2
cells are able to perform at temperature extremes where most consumer
replaceable battery types no longer operate.
FIGURE 5.3.3
Discharge characteristics of DURACELL® DL123A at
-20°C (-4°F) under various loads.
FIGURE 5.3.4
Effect of temperature on DURACELL® DL123A at 30 mA
continuous current.
Actual testing of commercially available spiral-wound Li/(CF)n 2/3A-size
cells and DURACELL® Li/MnO2 spiral-wound
2/3A-size cells at low temperatures indicates that the DURACELL®
Li/MnO2 product delivers much more service at moderate
to high rates of discharge than the spiral-wound poly-carbonmonofluoride
2/3A-size cell currently available. (Figure 5.3.5.).
FIGURE 5.3.5
DURACELL® DL2/3A Li/MnO2 cell versus Li/(CF)n
2/3A cell at 8 ohms continuous discharge.
Energy Density
Energy density is the ratio of the energy available from a cell
to its volume or weight. A comparison of the performance of various
battery systems is normally made on practical, delivered energy
density per-unit-weight or volume using production-based cells and
performance as opposed to theoretical energy density.
To determine the practical energy density of a cell under specific
conditions of load and temperature, multiply the capacity in ampere-hours
that the cell delivers under those conditions by the average discharge
voltage, and divide by cell volume or weight.
| Gravimetric Energy Density: |
(Drain in Amperes x Service
Hours)
x Average Discharge Voltage |
= |
Watt-Hours |
| --------------------------------------------------- |
-------------------------- |
| Weight of Cell in Pounds or
Kilograms |
Pound or Kilogram |
| Volumetric Energy Density: |
(Drain in Amperes x Service
Hours)
x Average Discharge Voltage |
= |
Watt-Hours |
| --------------------------------------------------- |
-------------------------- |
| Volume of cell in Cubic Inches
or Liters |
Cubic Inch or Liter |
Designers of battery-powered devices should place
minimal emphasis on the theoretical energy density of electrochemical
systems. Theoretical energy density comparisons have limited practical
significance: they are calculated from the weight or volume of active
anode and cathode materials with no consideration given to the weight
or volume of inactive materials required for cell construction.
Additionally, losses due to cell polarization on discharge are not
factored into theoretical values. Consequently, comparative testing
may show that the battery system with the higher theoretical value
does not deliver higher actual energy output.
Comparing energy densities, one must consider the influence of cell
size, internal design (bobbin or spiral-wound configuration), discharge
rate, and temperature conditions, as these parameters strongly impact
performance characteristics.
Spiral-Wound Lithium Cells versus Conventional Cells
A comparison of the performance of DURACELL Li/MnO2
spiral-wound cylindrical cells and similar-size conventional cells,
under favorable conditions on a weight (gravimetric) basis, is
shown on Figure 5.4.1. The energy delivered by the Li/MnO2
cell is two to four times greater than the practical energy delivered
by many similar-size conventional cells. This advantage becomes
more significant at low temperatures.
FIGURE 5.4.1
Gravimetric energy density comparison of primary cylindrical
cells.
In Figure 5.4.2., a comparison of the performance of
spiral-wound DURACELL Li/MnO2 cells with similar-size
conventional cells on a volumetric basis is shown. Under favorable
conditions of load and temperature, Li/MnO2 cells
deliver considerably more energy on a volumetric basis than
the conventional zinc systems shown.
FIGURE 5.4.2
Volummetric energy density comparison of primary cylindrical
cells.
Coin Cells
Energy-per-unit-volume is usually of more interest than energy-per-unit-weight
in applications requiring coin (button) cells. Figure 5.4.3. compares
the average volumetric energy density of Li/MnO2 coin
cells with conventional button cells under favorable load conditions.
DURACELL MicroLithiumTM coin cells deliver more energy
on a volumetric basis than Alkaline Manganese Dioxide and mercuric
oxide button cells, and compare favorably with silver oxide button
cells when cost is a factor.
FIGURE 5.4.3
Volummetric energy density comparison of primary button cells.
As a general rule, energy density decreases with decreasing cell size
since the percentage of inactive materials, such as grommets and cell
containers, take up proportionately more of the total cell weight
and volume. The following table compares the energy density of various
Li/MnO2 coin cells under conditions of rated load and temperature.
DURACELL®
MicrolithiumTM
Coin Cells |
ENERGY DENSITY |
| Volumetric |
Gravimetric |
| Wh/in.3 |
Wh/L |
Wh/lb. |
Wh/kg |
DL2016 |
7.1 |
433 |
59 |
129 |
DL2032 |
9.1 |
555 |
90 |
198 |
DL2325 |
9.1 |
555 |
86 |
190 |
DL2430 |
9.8 |
598 |
95 |
210 |
DL2450 |
11.5 |
699 |
122 |
270 |
Bobbin Cells
Due to the use of thick electrodes, bobbin-type Li/MnO2
cylindrical cells have slightly greater energy density (up to
1.2 times as much) than spiral wound Li/MnO2 cells
of similar size. The following table shows how energy density
increases with increasing cell size.
DURACELL®
MicrolithiumTM
Bobbin Cells |
ENERGY DENSITY |
| Volumetric |
Gravimetric |
| Wh/in.3 |
Wh/L |
Wh/lb. |
Wh/kg |
DL1/2AAL |
7.5 |
456 |
95 |
209 |
DL2/3AL |
9.4 |
574 |
132 |
291 |
DLAAL |
10.9 |
668 |
149 |
329 |
Internal Impedance
The conductivity of organic electrolytes used in lithium cells
is about 100 to 300 times less than aqueous electrolytes used
in zinc anode cells. Consequently, lithium batteries are generally
higher in internal impedance than batteries using aqueous electrolytes.
The impedance of Li/MnO2 cells varies with cell structure
and size. Typically, impedance decreases with increasing cell
size and electrode surface area.
DURACELL Li/MnO2 spiral-wound cells utilize high
surface area electrodes in a “ jelly roll ”
configuration to achieve low impedance and high current carrying
capability.
Figure 5.5.1 shows the relationship between impedance
and depth of discharge for a spiral-wound DURACELL DL123A cell.
Internal impedance is plotted using a one kilohertz AC signal
versus the discharge voltage under a continuous drain. As illustrated,
the internal impedance remains essentially constant throughout
the discharge of the Li/MnO2 cell.
FIGURE 5.5.1:
Internal impedance of a DURACELL DL123A at 1kHz versus discharge
voltage at 1 ampere continuous current.
The following table compares the impedance of various Li/MnO2
cells at 1 kHz. The range in values shown is typical of fresh
cells.
| Li/MnO2 CELL TYPE |
MODEL NO. |
IMPEDANCE AT 1 kHz (OHMS) |
| Coin Cells |
DL2016 |
12-18 |
|
DL2025 |
12-18 |
|
DL2032 |
12-18 |
|
DL2325 |
8-15 |
|
DL2430 |
8-15 |
|
DL2450 |
8-15 |
| Bobbin Cells |
DL1/2AAL |
9-13 |
|
DL2/3AL |
5-8 |
|
DLAAL |
4-6 |
| Spiral-Wound |
DL1 /3N |
3-5 |
| Cells |
DL2/3A |
.2-.6 |
Shelf Life and Performance After Storage
In order to withstand extreme fluctuations in temperature
and humidity conditions and perform after long periods of storage,
a battery must have a precise balance of cell chemistry and
internal and external hardware. DURACELL Li/MnO2
batteries are designed to store exceptionally well under a range
of environmental conditions.
FIGURE 5.6.1:
Capacity retention characteristics at various storage temperatures.
DURACELL Li/MnO2 batteries have superior capacity
retention characteristics, with capacity determined to be over
97 percent after five years at room temperature. In addition
to having excellent capacity retention characteristics, DURACELL
Li/MnO2 spiral-wound batteries possess excellent
rate retention capabilities. When discharged under a continuous
or intermittent drain after very long storage periods, DURACELL
Li/MnO2 batteries maintain their ability to perform
on demand. Figure 5.6.2. demonstrates the ability of
the spiral-wound DURACELL DL123A cell to operate at high rates
of continuous discharge, even after years of ambient storage
or after long periods at high temperatures. As shown, 3.3 years
of ambient storage is equated to 60 days of storage at 60 °C
or (140°F)
FIGURE 5.6.2:
Continuous discharge of fresh versus stored DURACELL DL123A
cells at 8 ohms at 0°C (32°F).
Figure 5.6.3. and Figure 5.6.4. show the ability
of the DURACELL DL123A to perform at high current pulse drains
after lengthy storage periods. Unlike liquid cathode lithium
systems, such as lithium-thionyl chloride, voltage delays do
not pose a problem when using DURACELL Li/MnO2 batteries.
The absence of a voltage delay ensures immediate start-up of
battery-powered devices even at very low temperatures.
FIGURE 5.6.3:
Pulse Discharge of fresh versus stored DURACELL DL123A cells
at 20°C (68°F), 3 seconds on, 7 seconds off at 1.2A.
FIGURE 5.6.4:
Pulse Discharge of fresh versus stored DURACELL DL123A cells
at -20°C (-4°F), 3 seconds on, 7 seconds off at 1.2A.
Many battery operated electronic devices such as cameras, are
allowed to sit idle for a long period of time between uses.
Having a battery which can tolerate this intermittent use pattern
is therefore very important. While many battery systems are
not tolerant to this type of intermittent usage cycle, DURACELL
Li/MnO2 batteries deliver equivalent energy even
after long periods of storage. As demonstrated in Figure
5.6.5., the DURACELL DL123A, stored for the equivalent of
3.3 years in a 60 percent discharged state, performed as well
as a 60 percent discharged DL123A that had not been stored at
all.
FIGURE 5.6.5:
Performance of 60 percent discharged DURACELL DL123A after storage,
3 seconds on, 7 seconds off at 1.2A at 20°C (68°F).
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