Duracell Ni-MH User Manual
able of Contents
T
1 Introduction
2 General Characteristics
3 Composition and Chemistry
3.1 Active Components: Positive and Negative Electrodes
3.2 Electrolyte
3.3 Cell Reactions
4 Battery Construction
4
.1 Basic Cell Construction
4.2 Cylindrical Cell Construction
4.3 Prismatic Cell Construction
5 Performance Characteristics
5.1 General Characteristics
5.2 Discharge Characteristics: Effect of Discharge Rate
and Temperature
5.3 Capacity: Effect of Discharge Rate
and Temperature
5.4 Energy Density
Ni-MH Rechargeable Batteries
5.5 Constant Power Discharge Characteristics
5.6 Polarity Reversal During Overdischarge
5.7 Internal Impedance
5.8 Self-Discharge and Charge Retention
5.9 Voltage Depression (“Memory Effect”)
6 Charging Sealed Nickel-Metal Hydride Batteries
6.1 General Principles
6.2 Techniques for Charge Control
6.2.1 Timed Charge
6.2.2 Voltage Drop (-∆V)
6.2.3 Voltage Plateau (zero ∆V)
6.2.4 Temperature Cutoff
6.2.5 Delta Temperature Cutoff (∆TCO)
6.2.6 Rate of Temperature Increase (dT/dt)
7 Cycle and Battery Life
7.1 Cycle Life
7.2 Battery Life
8 Safety Considerations
9 Proper Use and Handling
9.1
Care and Handling
9.2 Transportation
9.3 Waste Management: Recycling and Disposal
6.3 Charging Methods
6.3.1 Duracell’s Recommendation:
Three-Step Charge Procedure
6.3.2 Low-Rate Charge
6.3.3 Quick Charge
6.3.4 Fast Charge
6.3.5 Trickle Charge
6.4 Thermal Devices
Ni-MH Rechargeable Batteries
Introduction
1
Rapid advancements in electronic technology have expanded the number of battery-powered portable
devices in recent years, stimulating consumer demand for higher-energy rechargeable batteries capable of
delivering longer service between recharges or battery replacement.
The trend towards smaller, lighter more portable battery-powered devices is expected to continue well
into the future, with the so-called “3C” applications — cellular phones, portable computers and consumer
electronics — expanding rapidly beyond the traditional business user and into the consumer marketplace.
As with other battery-powered consumer devices, battery performance and convenience will influence
the rate of consumer acceptance for 3C devices. Yet conventional rechargeable batteries often fail to meet the
needs of consumers, as well as equipment designers, in terms of their size and weight, operating time, easeof-use, availability and environmental acceptability. New battery systems are needed to meet their growing list
of demands.
The sealed nickel-metal hydride (Ni-MH) battery is one rechargeable battery system that is responding
to these demands by offering significant improvements over conventional rechargeable batteries in terms of
performance and environmental friendliness. First introduced to the commercial market in 1988, nickel-metal
hydride battery technology is at a very early stage of maturity and manufacturers such as Duracell have
identified many opportunities to improve battery performance. These improvements will make DURACELL
nickel-metal hydride batteries an attractive power source for 3C devices for many years to come.
General Characteristics
2
Many of the operating characteristics of the sealed nickel-metal hydride rechargeable battery are similar to those of the sealed nickel-cadmium rechargeable battery. The nickel-metal hydride battery, however, has
the advantage of higher energy density (or capacity) which translates into longer service life. In addition, the
nickel-metal hydride battery is environmentally friendlier than nickel-cadmium and other battery systems
because it contains no added cadmium, mercury or lead.
Features of the sealed nickel-metal hydride battery include:
Higher capacity — Up to 40 percent longer service
•
life than ordinary nickel-cadmium batteries of
equivalent size.
High rate discharge — Efficient discharge at rates
•
as high as 2C.
Fast charge — Can be charged in approximately
•
one hour.
Safe — Designed to safely withstand abusive
•
conditions in consumer devices.
Long cycle life — Up to 500 charge/discharge cycles.
•
Performs at extreme temperatures — Capable of
•
operation on discharge from -20°C to 50°C (-4°Fto
122°F) and charge from 0°C to 45°C (32°F to
113°F).
Environmentally friendlier than nickel-cadmium
•
batteries — Zero percent cadmium.
Similar operating voltage to nickel-cadmium
•
batteries — Allows user to upgrade easily to longer
lasting nickel-metal hydride batteries.
1
Ni-MH Rechargeable Batteries
Composition and Chemistry
3
A rechargeable battery is based on the principle that the charge/discharge process is reversible, that is, the
energy delivered by the battery during discharge can be replaced or restored by recharging.
3.1 Active Components: Positive and Negative Electrodes
Nickel oxyhydroxide (NiOOH) is the active material in the positive electrode of the nickel-metal hydride
battery in the charged state, the same as in the nickelcadmium battery.
The negative active material, in the charged state,
is hydrogen in the form of a metal hydride. This metal
alloy is capable of undergoing a reversible hydrogen
absorbing/desorbing reaction as the battery is charged
and discharged, respectively.
The unique attribute of the hydrogen storage
alloy is its ability to store hundreds of times its own
volume of hydrogen gas at a pressure less than atmospheric pressure. Many different intermetallic compounds have been evaluated as electrode materials for
nickel-metal hydride batteries. Typically, these fall into
two classes: AB
alloys, of which LaNi5is an example,
5
3.2 Electrolyte
An aqueous solution of potassium hydroxide is
the major component of the electrolyte of a nickelmetal hydride battery. A minimum amount of electrolyte is used in this sealed cell design, with most of
and AB
ogy is based on the use of AB
AB
tics, resulting in longer cycle life and better rechargeability following storage. The composition of the metal
alloy is formulated for optimal stability over a large
number of charge/discharge cycles. Other important
properties of the alloy include:
this liquid being absorbed by the separator and the
electrodes. This “starved electrolyte” design facilitates
the diffusion of oxygen to the negative electrode at the
end-of-charge for the “oxygen recombination” reaction.
alloys, of which TiMn2or ZrMn2are examples.
2
DURACELL nickel-metal hydride battery technol-
instead of AB2alloys.
5
alloys offer better corrosion resistance characteris-
5
Large hydrogen storage capability for high energy
•
density and battery capacity.
Favorable kinetic properties for high rate capability
•
during charge and discharge.
Low hydrogen pressure alloy and high purity mate-
•
rials to minimize self-discharge.
3.3 Cell Reactions
During discharge, the nickel oxyhydroxide is
reduced to nickel hydroxide
NiOOH + H
and the metal hydride (MH) is oxidized to the metal
alloy (M).
MH + OH-——> M + H
O + e-——> Ni(OH)2+ OH
2
O + e
2
-
-
The overall reaction on discharge is:
MH + NiOOH ——> M + Ni(OH)
The process is reversed during charge.
2
2
Composition and Chemistry (cont.)
Ni-MH Rechargeable Batteries
The sealed nickel-metal hydride cell uses the
“oxygen-recombination” mechanism to prevent a buildup of pressure that may result from the generation of
oxygen towards the end of charge and overcharge.
This mechanism requires the use of a negative electrode
(the metal hydride/metal electrode) which has a higher
effective capacity than the positive (nickel oxyhydroxide/nickel hydroxide electrode) electrode. A schematic
drawing of the electrodes is shown in Figure 3.3.1.
During charge, the positive electrode reaches
full charge before the negative electrode which causes
the evolution of oxygen to begin:
2OH
- _____
> H
O +
2
1
O2+ 2e
2
-
The oxygen gas diffuses through the separator
to the negative electrode, a process which is facilitated
by the “starved-electrolyte” design and the selection of
an appropriate separator system.
At the negative electrode, the oxygen reacts
with the metal hydride and oxidizes or discharges the
metal hydride to produce water:
FIGURE 3.3.1
Positive Electrode
NiOOH/Ni(OH)
Useful Capacity
MH/Alloy
Charge
Reserve
Schematic representation of the electrodes, divided
into useful capacity, charge reserve and discharge
reserve.
Negative Electrode
2
Discharge
Reserve
2MH +
O
2
2
> 2M + H
O
2
1
_____
Thus, the negative electrode does not become fully
charged and pressure does not build up.
The charge current, however, must be controlled at the end of charge and during overcharge to
limit the generation of oxygen to below the rate of
recombination. Thus, charge control is required to prevent the build-up of gases and pressure. Duracell recommends that continuous overcharge not exceed C/300
for optimal performance.
As shown in Figure 3.3.1, the nickel-metal
hydride cell is designed with a discharge and charge
reserve in the negative electrode. The discharge
reserve minimizes gassing and degradation of the cell in
the event of overdischarge. The charge reserve ensures
that the cell maintains low internal pressure on overcharge.
The negative electrode has excess capacity
compared to the positive electrode and is used to
handle both overcharge and overdischarge. Thus,
the useful capacity of the battery is determined by
the positive electrode.
3
Ni-MH Rechargeable Batteries
Battery Construction
4
DURACELL standard-sized nickel-metal hydride batteries are constructed with cylindrical and prismatic nickelmetal hydride cells. DURACELL nickel-metal hydride batteries are a sealed construction designed for optimal performance and maximum safety. The batteries are manufactured to strict quality control standards to ensure reliability
and consumer satisfaction and offer such features as:
High energy density — Minimizes battery volume
•
and weight
Wide voltage range — Meets operating voltage
•
requirements of 3C devices
Thin profiles — Innovative wall-less design
•
Advanced interconnect — Self securing, voltage-
•
keyed interconnect provides a highly reliable batteryto-device contact
4.1 Basic Cell Construction
The electrodes in both cylindrical and prismatic
cell configurations are designed with highly porous
structures which have large surface areas to provide low
internal resistance which results in superior high rate
performance. The positive electrode in the cylindrical
4.2 Cylindrical Cell Construction
The assembly of a cylindrical cell is shown in
Figure 4.2.1. The electrodes are separated by the separator which is a synthetic, non-woven material that
serves as an insulator between the two electrodes and as
a medium for absorbing the electrolyte. The electrodes
are spirally-wound and inserted into a cylindrical nickelplated steel can. The electrolyte is added and contained
within the pores of the electrodes and separator.
The positive electrode is connected to the metal
lid with a tab. The cell is then sealed by crimping the
Durability — Manufactured with LEXAN®and
•
LUSTRAN
retardant polymers
UL listing — Independent approval of battery use
•
in devices
nickel-metal hydride cell is a highly porous nickel-felt
substrate into whichthe nickel compounds are pasted.
Similarly, the negative electrode is a perforated nickelplated steel foil onto which the plastic-bonded, active
hydrogen storage alloy is coated.
top assembly to the can. The top assembly incorporates
a resealable safety vent, a metal lid and a plastic gasket.
A heat-shrink tube is placed over the metal can. The
bottom of the metal can serves as the negative terminal
and the metal lid as the positive terminal. The insulator
and gasket insulate the terminals from each other. The
vent provides additional safety by releasing any excess
pressure that may build up if the battery is subjected to
abusive conditions.
®
polycarbonate high impact and flame
LEXAN®is a registered trademark of the General Electric Company.
LUSTRAN®is a registered trademark of the Monsanto Company.
FIGURE 4.2.1
Safety Vent
(+) Positive Terminal
Metal Can
Separator
Negative Electrode
Heat Shrink Tube
Positive Electrode
(-) Negative Terminal
Insulator
Positive Tab
Metal Lid
Cosmetic Disk
Gasket
4
Battery Construction (cont.)
Ni-MH Rechargeable Batteries
4.3 Prismatic Cell Construction
The basic differences between the prismatic
c
ell and the cylindrical cell are the
the electrodes and the shape of the
cells are designed to meet the needs
equipment where space for the battery is
The rectangular shape of the prismatic cell
more efficient battery assembly by eliminating
voids that occur in a battery constructed with
cylindrical cells. Thus, the volumetric energy density
of a battery can be increased by constructing it with
prismatic instead of cylindrical cells.
Figure 4.3.1 shows the structure of the pris-
matic nickel-metal hydride cell. The electrodes are
manufactured in a manner similar to those of the
cylindrical cell, except that the finished electrodes are
flat and rectangular in shape. The positive and
negative electrodes are interspaced by separator
sheets. The assembly is then placed in a nickel-plated
steel can and the electrolyte is added. The positive
electrodes are connected to the metal lid with a tab.
The cell is then sealed by crimping the top assembly to
the can. The top assembly incorporates a resealable
safety vent, a metal lid and a plastic gasket that is
similar to the one used in the cylindrical cell. A heatshrink tube is placed over the metal can. The bottom
of the metal can serves as the negative terminal and
the top metal lid as the positive terminal. The insulator and gasket insulate the terminals from each
other. The vent provides additional safety by releasing any excess pressure that may build up if the
battery is subjected to abusive conditions.
construction of
can. Prismatic
of compact
limited.
permits
the
FIGURE 4.3.1
Cosmetic
Disk
Gasket
Insulator
Positive Tab
Positive Electrode
Separator
Negative Electrode
Metal Lid
(+) Positive Terminal
Safety Vent
Heat Shrink Tube
(-) Negative Terminal
5
5
Ni-MH Rechargeable Batteries
Performance Characteristics
5.1 General Characteristics
The discharge characteristics of the nickel-metal
hydride cell are very similar to those of the nickelcadmium cell. The charged open circuit voltage of both
systems ranges from 1.25 to 1.35 volts per cell. On
discharge, the nominal voltage is 1.2 volts per cell and
the typical end voltage is 1.0 volt per cell.
Figure 5.1.1 illustrates the discharge characteristics of nickel-metal hydride and nickel-cadmium
rechargeable cells of the same size. As shown, the voltage profile of both types of cells is flat throughout most
of the discharge. The midpoint voltage can range from
1.25 to 1.1 volts per cell, depending on the discharge
load. Figure 5.1.1 can also be used to compare the
capacity of the two rechargeable types. Note that the
capacity of the nickel-metal hydride cell is typically up to
40 percent higher than that of a nickel-cadmium cell of
equivalent size.
FIGURE 5.1.1
1.5
1.4
1.3
1.2
1.1
Voltage (V)
1.0
.9
0 20 40 60 80 100 120 140 160
Ampere-Hour Capacity (%)
Comparison of discharge voltage and capacity of
same-size Ni-MH and Ni-Cd cells.
[Conditions: Charge: C/3 for 5 hours, Temperature: 21°C (70°F)]
C/5
Ni-Cd
C/5
Ni-MH
5.2 Discharge Characteristics: Effect of
Discharge Rate and Temperature
Typical discharge curves for DURACELL nickel-
metal hydride batteries under constant current loads at
various temperatures are shown in Figures 5.2.1 to
5.2.3. Discharge voltage is dependent on discharge
current and discharge temperature.
FIGURE 5.2.1
8.5
8.0
7.5
7.0
Voltage (V)
6.5
6.0
5.5
0 0.5 1.0 1.5 2.0 2.5
FIGURE 5.2.2
8.5
8.0
7.5
7.0
Voltage (V)
6.5
6.0
5.5
0 0.5 1.0 1.5 2.0 2.5
Discharge Capacity (Ah)
Discharge Capacity (Ah)
Temperature: 45°C (113°F)
C (2.4A)
Temperature: 21°C (70°F)
C (2.4A)
FIGURE 5.2.3
8.5
8.0
7.5
7.0
Voltage (V)
6.5
6.0
5.5
0 0.5 1.0 1.5 2.0 2.5
Voltage and capacity of DURACELL DR30 Ni-MH
batteries at various discharge temperatures
and rates.
[Conditions: Charge: 1C to -∆V = 60mV @ 21°C (70°F)]
C/5 (0.48A)
C (2.4A)
C (2.4A)
Temperature: -20°C (-4°F)
Temperature: 0°C (32°F)
C/5 (0.48A)
C (2.4A)
Discharge Capacity (Ah)
C/5 (0.48A)
C/5 (0.48A)
6
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