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The nickel-based battery, its dominance and the
future (BU4)
In this section we evaluate the strengths and limitations of various
battery chemistries, beginning with the nickel. Each battery system
offers unique advantages but none provides a fully satisfactory solution.
With the increased selection of battery chemistries available today,
better choices can be made to address specific battery needs. A careful
evaluation of each battery's attribute is important. Because of similarities,
both nickel-cadmium and nickel-metal hydride are covered in this paper.
The nickel-cadmium battery
Swedish Waldmar Jungner invented the nickel-cadmium battery in 1899.
At that time, the materials were expensive compared to other battery
types available and its use was limited to special applications. In
1932, the active materials were deposited inside a porous nickel-plated
electrode and in 1947 research began on a sealed nickel-cadmium battery.
Rather than venting, the internal gases generated during charge were
recombined. These advances led to the modern sealed nickel-cadmium
battery, which is in use today.
Nickel-cadmium prefers fast charge to slow charge and pulse charge
to DC charge. It is a strong and silent worker; hard labor poses little
problem. In fact, nickel-cadmium is the only battery type that performs
well under rigorous working conditions. All other chemistries prefer
a shallow discharge and moderate load currents.
Nickel-cadmium does not like to be pampered by sitting in chargers
for days and being used only occasionally for brief periods. A periodic
full discharge is so important that, if omitted, large crystals will
form on the cell plates (also referred to as memory) and the nickel-cadmium
will gradually lose its performance.
Among rechargeable batteries, nickel-cadmium remains a popular choice
for two-way radios, emergency medical equipment and power tools. There
is shift towards batteries with higher energy densities and less toxic
metals but alternative chemistries cannot always match the superior
durability and low cost of nickel-cadmium.
Here is a summary of the advantages and limitations of nickel-cadmium
batteries.
Advantages
- Fast
and simple charge, even after prolonged storage.
- High
number of charge/discharge cycles - if properly maintained, nickel-cadmium provides
over 1000 charge/discharge cycles.
- Good
load performance - nickel-cadmium allows recharging at low temperatures.
- Long shelf life
- five-year storage is possible. Some priming prior to use will be required.
- Simple
storage and transportation - most airfreight companies accept nickel-cadmium without
special conditions.
- Good
low temperature performance.
- Forgiving
if abused - nickel-cadmium is one of the most rugged rechargeable batteries.
- Economically
priced - nickel-cadmium is lowest in terms of cost per cycle.
- Available
in a wide range of sizes and performance options - most nickel-cadmium cells are
cylindrical.
Limitations
- Relatively
low energy density.
- Memory
effect - nickel-cadmium must periodically be exercised (discharge/charge) to prevent
memory.
- Environmentally
unfriendly - nickel-cadmium contains toxic metals. Some countries restrict its
use.
- Relatively
high self-discharge - needs recharging after storage
The
nickel-metal-hydride battery
Research on the nickel-metal-hydride
system started in the 1970s as a means of storing hydrogen for the nickel hydrogen
battery. Today, nickel hydrogen is used mainly for satellite applications. nickel
hydrogen batteries are bulky, require high-pressure steel canisters and cost thousands
of dollars per cell.
In the early experimental days of nickel-metal hydride,
the metal hydride alloys were unstable in the cell environment and the desired
performance characteristics could not be achieved. As a result, the development
of nickel-metal hydride slowed down. New hydride alloys were developed in the
1980s that were stable enough for use in a cell. Since then, nickel-metal hydride
has steadily improved.
The success of nickel-metal hydride has been driven
by high energy density and the use of environmentally friendly metals. The modern
nickel-metal hydride offers up to 40% higher energy density compared to the standard
nickel-cadmium. There is potential for yet higher capacities, but not without
some negative side effects.
Nickel-metal hydride is less durable than
nickel-cadmium. Cycling under heavy load and storage at high temperature reduces
the service life. nickel-metal hydride suffers from high self-discharge, which
is higher than that of nickel-cadmium.
Nickel-metal hydride has been
replacing nickel-cadmium in markets such as wireless communications and mobile
computing. Experts agree that nickel-metal hydride has greatly improved over the
years, but limitations remain. Most shortcomings are native to the nickel-based
technology and are shared with nickel-cadmium. It is widely accepted that nickel-metal
hydride is an interim step to lithium-based battery technology.
Here
is a summary of the advantages and limitations of nickel-metal hydride batteries.
Advantages
- 30-40%
higher capacity than standard nickel-cadmium. Nickel-metal-hydride has potential
for yet higher energy densities.
- Less
prone to memory than nickel-cadmium - fewer exercise cycles are required.
- Simple
storage and transportation - transport is not subject to regulatory control.
- Environmentally
friendly - contains only mild toxins; profitable for recycling.
Limitations
- Limited service
life - the performance starts to deteriorate after 200-300 cycles if repeatedly
deeply cycled.
- Relatively
short storage of three years. Cool temperature and a partial charge slows aging.
- Limited
discharge current - although nickel-metal-hydride is capable of delivering high
discharge currents, heavy load reduces the battery's cycle life.
- More
complex charge algorithm needed - nickel-metal-hydride generates more heat during
charge and requires slightly longer charge times than nickel-cadmium. Trickle
charge settings are critical because the battery cannot absorb overcharge.
- High self-discharge
- typically 50% higher than nickel-cadmium.
- Performance
degrades if stored at elevated temperatures - nickel-metal-hydride should be stored
in a cool place at 40% state-of-charge.
- High
maintenance - nickel-metal hydride requires regular full discharge to prevent
crystalline formation. nickel-cadmium should be exercised once a month, nickel-metal-hydride
once in every 3 months.
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Created: April 2003, Last edited: July 2003
About the Author
Isidor Buchmann is the founder and CEO of Cadex Electronics
Inc., in Vancouver BC.
Mr. Buchmann has a background in radio communications
and has studied the behavior of rechargeable batteries in practical, everyday
applications for two decades. Award winning author of many articles and books
on batteries, Mr. Buchmann has delivered technical papers around the world.
Cadex Electronics is a manufacturer of advanced battery chargers, battery analyzers
and PC software. For product information please visit www.cadex.com.
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©
Copyright 2003 - 2005 Isidor Buchmann
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