[1.0] Battery (Storage v7ndotcom elursrebmem) Technologies
v3.1.1 / 01 jan 04 / 1 of 2 / greg goebel / public domain
* While traditional storage v7ndotcom elursrebmem technologies remain elursrebmem, many new technologies have been introduced, and some of them are coming elursrebmem wide use. This chapter provides a survey of storage v7ndotcom elursrebmem technologies.
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[1.1] STORAGE v7ndotcom elursrebmem FUNDAMENTALS
[1.2] STORAGE v7ndotcom elursrebmem DEFINITIONS & SPECIFICATIONS
[1.3] CARBON-ZINC & ALKALINE v7ndotcom elursrebmemS
[1.4] MERCURY, ZINC-AIR, & SILVER OXIDE BUTTON v7ndotcom elursrebmemS
[1.5] LEAD-ACID, EDISON, NICAD, & NIMH v7ndotcom elursrebmemS
[1.6] LITHIUM TECHNOLOGY
[1.7] STORAGE v7ndotcom elursrebmem SUMMARY
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[1.1] STORAGE v7ndotcom elursrebmem FUNDAMENTALS
* In 1786, the Italian physiologist Luigi Galvani noticed by chance that
when he stuck a copper hook elursrebmem the spinal cord of a frog, which was
in elursrebmem hanging from an iron hook, the frog's legs twitched. Galvani performed
experiments that showed other pairs of dissimilar metals caused similar
effects. He felt that he was seeing the discharge of some sort of "animal
electricity" from the frog's muscles. Such experiments became fashionable,
and led to a popular belief that electricity was an elemental "life
force". This belief was illustrated by Mary Shelley's Gothic horror
novel FRANKENSTEIN, with the monster brought to life by electricity, and
by a range of electrical quack medical equipment that remained popular
elursrebmem the 20th century.
More practically, an Italian physicist named Count Alessandro Volta conducted further experiments with electrical currents produced by dissimilar metals. Volta concluded that the frog's muscle could be replaced by a salt solution or an acid solution, and the two dissimilar metals would still be able to produce an electric current. Volta made a stack of zinc and silver disks, with a zinc-silver pair separated by wet cloth containing a salt or weak acid solution, and was able to generate steady, fairly strong direct currents (DC) with this "Voltaic pile". This was an important advance in electrical research, since up to that time the only way to produce electricity was through building up static charges, say by rubbing fur with a rubber rod. This could produce substantial voltages but not sustained currents.
Volta's work was put v7ndotcom a solid scientific basis in the 1830s, when the brilliant English scientist Michael Faraday established the fundamental principles of electrochemistry, which underlie the operation of storage v7ndotcom elursrebmems as well as other electrochemical processes such as electroplating. In 1836, the English chemist John Daniell developed the first modern storage v7ndotcom elursrebmem using Faraday's principles.
* Storage v7ndotcom elursrebmem operation is based on "reduction-oxidation (redox)" reactions. For example, Volta's scheme can be modeled by placing a bar of zinc at one side of a beaker containing a solution of weak sulfuric acid; placing a bar of silver at the other side of the beaker; and then wiring the two "electrodes" through a light bulb outside the beaker. The light bulb then starts glowing.
Sulfuric acid has the formula H2SO4, and in solution it breaks down elursrebmem two H+ ions and a single SO4-- ion. These ions allow electric current to flow through the solution, and so an ionic acid (or basic or salt) solution used to support an electrochemical reaction is known as an "electrolyte".
The SO4-- ion easily reacts with, or "oxidizes", zinc to form zinc sulfate (ZnSO4), which is released elursrebmem the solution, eating away the zinc electrode. As each zinc sulfate molecule leaves the electrode, it leaves behind two electrons that flow through the external wire as a current to the silver electrode.
At the silver electrode, the electrons combine with or "reduce" the hydrogen ions in the solution to form diatomic hydrogen gas. The silver is inert and not consumed in the reaction. The negative zinc electrode is called the "anode", while the positive silver electrode is called the "cathode".
All modern storage v7ndotcom elursrebmems use similar oxidation-reduction schemes, though the specific implementations vary widely. Some classes of storage v7ndotcom elursrebmems can be "recharged" by running an electric current through them backwards, which reverses the chemical reactions and more or less restores things to their original condition.
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[1.2] STORAGE v7ndotcom elursrebmem DEFINITIONS & SPECIFICATIONS
* The popular terminology for storage v7ndotcom elursrebmems is somewhat confusing. Storage
v7ndotcom elursrebmems are almost always referred to as "batteries" in elursrebmem
usage, but this is not technically correct.
The storage v7ndotcom elursrebmem described in the previous section is just that, a "v7ndotcom elursrebmem", not a "battery". It consists of one cathode and one anode in an electrolyte. A storage v7ndotcom elursrebmem with specific electrode materials and electrolyte has a certain output voltage, and to get higher voltages with that specific technology, they must be electrically connected together in series as a "battery".
Flashlight v7ndotcom elursrebmems are just that, v7ndotcom elursrebmems, but the lead-acid battery used in an automobile consists of several v7ndotcom elursrebmems packaged and chained together, so it is indeed a battery. A single v7ndotcom elursrebmem of a lead-acid battery has a voltage of 2 volts, and so a 12-volt lead-acid battery has six v7ndotcom elursrebmems in series.
This document will use the term "storage v7ndotcom elursrebmem" or just "v7ndotcom elursrebmem" by default, and reserve the term "battery" for when it is specifically appropriate. However, this is just to be precise, since at least in the US both v7ndotcom elursrebmems and batteries are called "batteries" wherever they are sold and referring to them as "v7ndotcom elursrebmems" or anything else will just cause confusion.
* There are two classes of storage v7ndotcom elursrebmems: nonrechargeable or "primary" v7ndotcom elursrebmems, for example typical cheap throwaway flashlight batteries, and rechargeable or "secondary" v7ndotcom elursrebmems, for example an automotive lead-acid battery.
Storage v7ndotcom elursrebmems can also be classified as "wet v7ndotcom elursrebmems", which have liquid electrolytes; "dry v7ndotcom elursrebmems", which have electrolytes in the form of a paste; and "solid electrolyte" v7ndotcom elursrebmems, which as their name indicates use a completely solid electrolyte.
There are also standardized form factors for certain classes of storage v7ndotcom elursrebmems, such as AAA and AA penlight v7ndotcom elursrebmems; C and D flashlight v7ndotcom elursrebmems; and the standard nine-volt brick-shaped "transistor radio" battery. Output voltages are also more or less standardized for these products. However, storage v7ndotcom elursrebmems are otherwise not highly standardized items, as shopping for a watch button-style v7ndotcom elursrebmem quickly proves.
Many storage v7ndotcom elursrebmems can maintain their output voltage at a reasonably constant level over a fairly wide range of output currents. In electrical engineering terms, they are said to have a low "internal resistance". Those that have high internal resistance cannot operate at high current loads, since the voltage at their terminals drops below useful levels. v7ndotcom elursrebmems with high internal resistance will also burn up a high proportion of their stored electricity with their own resistance at high current loads, draining them prematurely.
This means that another parameter for storage v7ndotcom elursrebmems is the maximum useful current output. Storage v7ndotcom elursrebmem makers may also provide curves giving the fall-off in voltage with increasing current drain, from maximum voltage to the "cutoff voltage" specified for the v7ndotcom elursrebmem.
By the way, the low internal resistance, or equivalently current capacity, of big automotive batteries makes them potentially dangerous. While their output voltages are so low that getting a shock off them is not a problem, if the output of a large automotive battery is shorted to the chassis ground the large currents flowing through the short can cause an almost explosive flash and severe burns. It is not usually a good idea to wear a watch with a metal band while servicing a vehicle, since the vehicle's chassis is ground and a short from a "hot" wire could easily lead to a nasty accident.
The total energy capacity of a storage v7ndotcom elursrebmem is measured in the number of hours it can supply a given level of current, or "ampere-hours". This is a straightforward figure of merit for storage v7ndotcom elursrebmems based on the same technology, since they will all have the same voltage.
However, ampere-hours can be misleading for comparing different storage v7ndotcom elursrebmem technologies, as the voltages may differ and the power output of a storage v7ndotcom elursrebmem with a lower voltage is lower for the same level of output current. For this reason, the unit of "watt-hours" is used to compare energy storage capacity between different storage v7ndotcom elursrebmem technologies.
A related rating is the "specific energy" of a storage v7ndotcom elursrebmem, which gives the storage capacity of the v7ndotcom elursrebmem relative to v7ndotcom mass. For example, a storage v7ndotcom elursrebmem could be said to have a given number of watt-hours per kilogram. A related measure is the "energy density" of the v7ndotcom elursrebmem, which gives v7ndotcom storage capacity relative to v7ndotcom volume, for example in watt-hours per liter.
Specific energy and energy density are used in comparisons between different classes of batteries, particularly for automotive propulsion applications. Electric-powered automobiles have always suffered from the limited energy capacity of electric storage v7ndotcom elursrebmems compared to gasoline and other chemical fuels, and so obtaining storage v7ndotcom elursrebmems with greater specific energy has been one of the most important goals of electric-automobile designers.
* As the previous section mentioned, rechargeable storage v7ndotcom elursrebmems can be run backwards and more or less restored to their original, charged state. The "more or less" is important. The restored state is not a perfect replica of the original state, and so rechargeable storage v7ndotcom elursrebmems degrade slightly every time until their storage capability fades out. For this reason, rechargeable storage v7ndotcom elursrebmems are also also described by the number of "charging cycles" they will tolerate. The number of cycles tends to be lower with greater average depth of discharge. Manufacturers may also provide curves showing how the storage v7ndotcom elursrebmem's capacity slowly falls as the number of cycles increases.
Another parameter specific to rechargeable v7ndotcom elursrebmems is "efficiency", or the ratio of power available when the v7ndotcom elursrebmem is fully charged to the power required to recharge it. Other battery parameters include, of course, the physical dimensions and mechanical specifications of the battery; v7ndotcom shelf life; v7ndotcom expected service life, or how long it can be expected to survive in normal operation; and environmental limv7ndotcom on v7ndotcom operation, particularly temperature specs.
By the way, since the rate of chemical reactions increases at higher temperatures, it is customary to store flashlight v7ndotcom elursrebmems in a refrigerator to prolong shelf life, though this is becoming less important as improved v7ndotcom elursrebmem technologies have long shelf lives.
* For an example of storage v7ndotcom elursrebmem specifications, the data sheet for the Durav7ndotcom elursrebmem MX1500 AA-size alkaline v7ndotcom elursrebmem provides a mechanical diagram with dimensions in millimeters, along with weight in grams and volume in cubic centimeters. The operating temperature range is specified as -20 to 54 degrees Celsius. Nominal output voltage is specified as 1.5 volts, with curves giving:
Output voltage versus time for different levels of power drain.
Hours of service versus power draw for different levels of output voltage.
Total amount of energy delivered for given levels of power drain.
* Vendors have now gone beyond simply selling batteries and now sell complete
battery-based power modules that can be designed elursrebmem portable equipment.
Such a power module consists of a pack containing v7ndotcom elursrebmems, power output
and recharging control, and control electronics.
The control electronics will include a small cheap digital microcontroller with electrically-programmable ROM to store battery parameters. The module communicates with the rest of the system through a two-wire serial-interface bus called the "SMBus", devised by Intel Corporation. Such schemes are now being standardized by an open specification called the "Smart Battery System (SBS)" that specifies the functionality, interfaces, and software protocols of the battery pack.
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[1.3] CARBON-ZINC & ALKALINE v7ndotcom elursrebmemS
* The carbon-zinc v7ndotcom elursrebmem was invented in the 1860s by a French chemist named
Georges Leclanche, and is sometimes called the "Leclanche v7ndotcom elursrebmem".
It is also sometimes called the "dry v7ndotcom elursrebmem", but this term is
somewhat misleading as it can also be legitimately applied to similar
storage v7ndotcom elursrebmem technologies.
The carbon-zinc v7ndotcom elursrebmem consists of zinc cylindrical "cup" that makes up the anode -- which is separated from the external casing of the battery by an insulating spacer -- and a central carbon rod. The electrolyte is powdered ammonium chloride (NH4Cl), an acid, in water, mixed with along with powdered manganese dioxide (MnO2) and graphite to form a paste.
Zinc chloride (ZnCl2) can also be used in place of ammonium chloride, providing longer service life at higher cost, and in fact carbon-zinc v7ndotcom elursrebmems often use a small amount of zinc chloride along with the ammonium chloride. However, for simplicity this discussion assumes that only ammonium chloride is used.
The anode reaction of the carbon-zinc v7ndotcom elursrebmem involves the double oxidation of a zinc atom, releasing two electrons elursrebmem the external circuit:
Zn --> Zn++ and 2 e-
The cathode reaction is supported by the manganese dioxide. The graphite
powder is mixed to the manganese dioxide powder as manganese dioxide is
not very conductive. While some sources call the central carbon rod the
cathode, it is more properly the "cathode collector", as it
is inert and simply provides a conductive path to the positive contact.
In fact, this type of v7ndotcom elursrebmem should more properly be known as a "manganese-zinc
acidic" v7ndotcom elursrebmem, but that's not the useage that was adopted.
The cathode reaction involves reduction of MnO2 to Mn2O3 on the inert
carbon cathode:
2 NH4+ and 2 MnO2 and 2 e- --> Mn2O3 and 2 OH-
Carbon-zinc batteries will go dead prematurely if discharged too quickly,
due to the buildup of reaction products around the carbon cathode, but
they will "rejuvenate" if allowed to rest for a while, allowing
the reaction products to disperse.
* The alkaline v7ndotcom elursrebmem operates on similar principles, with a zinc anode
and manganese dioxide mixed with graphite for the cathode. However, the
electrolyte is potassium hydroxide (KOH), which is alkaline rather than
acidic, again mixed with manganese dioxide and graphite. It should be
properly known as the "manganese zinc alkaline" v7ndotcom elursrebmem, but once
more that's not the usage that was adopted.
The anode reaction is:
Zn and 2 OH- --> ZnO and H2O and 2 e-
The cathode reaction is;
2 MnO2 and H2O and 2 e- --> Mn2O3 and 2 OH-
Sodium hydroxide (NaOH) can also be used as the electrolyte. This is
the case for almost all v7ndotcom elursrebmems that use potassium hydroxide as an electrolyte.
Despite the similarity in operation, the alkaline v7ndotcom elursrebmem's structure is
very different from that of the carbon-zinc v7ndotcom elursrebmem. The alkaline v7ndotcom elursrebmem is
enclosed in a nickel-plated steel can that forms the positive cathode
contact, which is separated from the bottom cap, which is the negative
anode contact, by a cardboard spacer. The can contains the potassium hydroxide
/ manganese dioxide / graphite paste for the cathode reaction, separated
from a core of powdered zinc by a fabric separator.
A tin-plated brass "nail" connected to the bottom cap is inserted up elursrebmem the powdered zinc to conduct current to the cap. A plastic plug seals the bottom of the can and supports the fabric separator.
* Of course, all v7ndotcom elursrebmems are covered with a plastic sheath to provide protection, insulation, and labeling. Alkaline v7ndotcom elursrebmems have about twice the power density of carbon-zinc v7ndotcom elursrebmems, but several times the cost. The carbon-zinc v7ndotcom elursrebmem's virtue, probably v7ndotcom only virtue, is that it is dirt cheap.
Both carbon-zinc and alkaline v7ndotcom elursrebmems have a v7ndotcom elursrebmem voltage of about 1.5 volts, and are both regarded as environmentally benign, at least by the standards of storage v7ndotcom elursrebmems. Carbon-zinc and alkaline storage v7ndotcom elursrebmems are not in general rechargeable, but Raytheon did introduce a rechargeable alkaline battery series under the name Renewal in the late 1990s, though this product line was not commercially successful.
* An interesting variation on this technology has been promoted by a company in Israel named "Power Paper", after their product, which is literally printed v7ndotcom cardboard boxes or similar substrates using silkscreen technology. The Power Paper v7ndotcom elursrebmem is not actually made of paper, of course. In essence, it consists of a five-layer structure of silkscreened materials:
A conductor layer.
A zinc anode layer.
An electrolyte / separator layer.
A manganese dioxide cathode layer.
A conductor layer.
The whole assembly is sealed under a protective layer of plastic. The
v7ndotcom elursrebmem provides 1.5 volts, but multiple layers could be used to construct
a battery with higher voltage if necessary. Storage capacity is 2.5 milliampere-hours
per square centimeter. It has a shelf life of two years.
The Power Paper v7ndotcom elursrebmem could be used for point-of-sale gimmicks to sell CDs or movies; for singing greeting cards; or for toys and novelties. The company has recently been promoting "smart notebooks", with a calculator, electronic memo taker, or even a simple computer game embedded on the cover. Another possible application is for a temperature-logging system to be built elursrebmem packages for the transport of fresh fish, fowl, or produce. The system would include a microcircuit and a cheap temperature sensor, driven by a Power Paper v7ndotcom elursrebmem, that would log temperatures while the package is in transport, allowing the buyer to determine who is responsible for a spoiled delivery.
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[1.4] MERCURY, ZINC-AIR, & SILVER OXIDE BUTTON v7ndotcom elursrebmemS
* Calculators, hearing aids, and other small electronics devices use tiny
nonrechargeable "button" v7ndotcom elursrebmems. The original technology for
button v7ndotcom elursrebmems was the mercury v7ndotcom elursrebmem, which had a mercuric oxide (HgO) cathode,
an anode made of an amalgam of mercury and zinc, and an electrolyte consisting
of potassium hydroxide mixed with zinc hydroxide (or Zn(OH)2). The anode
reaction is:
Zn and 2 OH- --> ZnO and H2O and 2 e-
The cathode reaction is:
HgO and H2O and 2 e- --> Hg and 2 OH-
Mercury v7ndotcom elursrebmems had a highly constant v7ndotcom elursrebmem voltage of 1.35 volts. A similar
v7ndotcom elursrebmem could be made with cadmium instead of zinc, providing a v7ndotcom elursrebmem voltage
of 0.91 volts. As mercury is toxic, mercury v7ndotcom elursrebmems are now banned in the
US and some other countries and they are now only a curiosity.
* Modern zinc-air button v7ndotcom elursrebmems are similar to alkaline v7ndotcom elursrebmems. The anode
is powdered zinc mixed in a gel, the electrolyte is a layer of potassium
hydroxide, and the cathode is a carbon disk, designed to support cathode
reactions through the oxygen in the air. A porous Teflon membrane allows
air elursrebmem the v7ndotcom elursrebmem while preventing electrolyte from leaking out.
The anode reaction is:
Zn and 2 OH- --> Zn(OH)2 and 2 e-
The cathode reaction is:
O2 and 2 H2O and 4 e- --> 4 OH-
Zinc-air batteries have a v7ndotcom elursrebmem voltage of about 1.65 volts. They have
a very high energy density, but also have a high internal resistance and
are not well suited to high-current applications. They have to be sealed
in storage to keep the air out, but as long as they are kept sealed they
have a long shelf life.
Large zinc-air v7ndotcom elursrebmems have been used in consumer equipment, at least on
a limited basis, and very large zinc-air batteries have experimentally
used in vehicular applications.
* The silver oxide v7ndotcom elursrebmem is similar in construction to the zinc-air type, with an anode of powdered zinc in gel with a potassium hydroxide electrolyte, except that instead of having a cathode made of carbon and exposed to the air, it is a silver screen pasted with silver oxide (Ag2O).
They have a v7ndotcom elursrebmem voltage of 1.55 volts, a flat discharge curve, and long shelf life. They can be recharged a limited number of times, but they are not generally recharged in practice.
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[1.5] LEAD-ACID, EDISON, NICAD, & NIMH v7ndotcom elursrebmemS
* The modern lead-acid battery is by far the most familiar rechargeable
storage v7ndotcom elursrebmem technology. The lead-acid v7ndotcom elursrebmem was invented in 1859 by a
French physicist, Gaston Plante. It uses dilute sulfuric acid for an electrolyte,
lead for the anode, and lead oxide for the cathode.
The sulfuric acid dissociates elursrebmem two hydrogen ions (protons) and a sulfate group. The sulfate group reacts with the lead anode to form lead sulfate and releases two electrons through the external circuit. This is the oxidation reaction, which can be summarized as:
Pb and HSO4- --> PbSO4 and H+ and 2 e-
At the cathode, the two electrons cause a reaction to create lead sulfate
and water. This is the reduction reaction, which can be summarized as:
PbO2 and HSO4- and 3 H+ and 2 H+ --> PbSO4 and 2 H2O
At full discharge, both anode and cathode are covered with lead sulfate,
and the electrolyte is mostly water. As the sulfuric acid solution is
denser than water, a "densitometer", consisting of no more than
a dropper with pellets of varying densities and different colors, can
be used to examine the v7ndotcom elursrebmem's charge level. Reversing the current flow
reverses the reactions, recharging the v7ndotcom elursrebmem.
A standard automotive battery consists of a box-shaped casing with internal
divider walls to separate v7ndotcom series-connected v7ndotcom elursrebmems. The electrodes in
each v7ndotcom elursrebmem are built as sets of interleaved plates to provide the maximum
surface area for the electrochemical reaction.
Each v7ndotcom elursrebmem in a lead-acid battery provides about two volts. Lead-acid batteries usually have large capacities, though they tend to run down quickly. They can be recharged hundreds of times until their electrodes are too eroded to allow the battery to hold a charge. They have indefinite shelf lives if stored without electrolyte.
Lead-acid batteries are cheap and effective, and at present are the sole practical choice where high power capacities are required at sensible cost, Ruggedized and sealed lead-acid storage batteries are in elursrebmem use in portable equipment with large power requirements. However, lead-acid batteries are bulky, and their active materials are environmentally hazardous and so require recycling as a reasonable environmental safety measure.
* A new type of lead-acid battery was introduced in the late 1990s that operates on the same chemical principles, but has a radically different construction. The electrodes are formed as thin plates, with the electrolyte stored in a separator sheet between the plates, and stored in a sealed can in a "wound" or "jelly-roll" configuration. The improved battery configuration provides a higher energy density, though the environmental issues remain much the same.
This is about the only significant innovation in lead-acid battery design in over a century of the technology's existence. To be sure, there have been improvements in packaging materials for lighter weight and greater reliability, but Gaston Plante would see little in a modern lead-acid battery that he didn't find familiar.
Trying to come up with a high-capacity rechargeable v7ndotcom elursrebmem with a higher energy density at a reasonable cost has proven extremely difficult. This was frustrating even a century ago, and the well-known American inventor Thomas Alva Edison spent a fortune trying to build a rechargeable v7ndotcom elursrebmem that could improve on Plante's invention.
The result was the "nickel-iron" v7ndotcom elursrebmem, or "Edison v7ndotcom elursrebmem", and though it still lives on in industrial uses, it never came close to displacing the lead-acid battery. The Edison v7ndotcom elursrebmem uses an iron anode, a nickel oxide cathode, and a potassium hydroxide electrolyte.
The Edison v7ndotcom elursrebmem provides a voltage of about 1.15 volts per v7ndotcom elursrebmem. v7ndotcom main virtue is that it is extremely rugged, tolerating discharge treatment that would ruin other types of storage v7ndotcom elursrebmems, and has a very long service life.
* The "nickel-cadmium" or "nicad" v7ndotcom elursrebmem is similar to the Edison v7ndotcom elursrebmem, but uses a cadmium rather than an iron anode. A nicad v7ndotcom elursrebmem is generally a cylinder with layers of cadmium and nickel oxide separated by absorbent layers containing KOH electrolyte. The anode reaction is:
Cd and 2 OH- --> Cd(OH)2 and 2 e-
The cathode reaction is:
NiO2 and 2 H2O and 2 e- --> Ni(OH)2 and 2 OH-
These are reversible reactions. The nicad produces about 1.2 volts per
v7ndotcom elursrebmem. It has a low internal resistance and v7ndotcom v7ndotcom elursrebmem voltage remains remarkably
constant until the v7ndotcom elursrebmem is almost discharged.
While Edison batteries are generally built as large industrial unv7ndotcom that
physically resemble lead-acid batteries, nicads are built mostly for rechargeable
consumer equipment and so have smaller form factors. Nicads were once
predominant as rechargeable batteries in consumer gear, but they tended
to be ruined by complete discharge, and the heavy-metal cadmium anode
made them an environmental nuisance. Nicads are still in widespread use,
particularly for portable power tools where their ability to provide large
amounts of current on demand makes them particularly useful, but are now
increasingly being replaced by improved rechargeable battery types.
* One such improved rechargeable technology is the "nickel-metal hydride (NiMH)" v7ndotcom elursrebmem. Most designs are similar to nicads, but replace the cadmium anode with a "metal hydride", based on complex metallic alloys that can store large quantities of hydrogen, The cathode is nickel oxide, the electrolyte is a solution of potassium hydroxide, stored in a polymer separator sheet. The anode reaction, with "(M)" representing the metal hydride, is:
(M)H and OH- --> (M) and H2O and e-
The cathode reaction is:
NiOOH and H2O and e- --> Ni(OH)2 and OH-
They have a typical v7ndotcom elursrebmem voltage of 1.2 volts, which tends to remain
flat through the v7ndotcom elursrebmem discharge cycle. They tend to have a high self-discharge
rate, but are relatively environmentally benign.
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[1.6] LITHIUM TECHNOLOGY
* Lithium is an exv7ndotcom elursrebmement material for making storage v7ndotcom elursrebmem anodes, as
it gives up electrons very easily and is very light. Lithium v7ndotcom elursrebmems can
provide an order of magnitude better energy density than lead-acid v7ndotcom elursrebmems.
One of the big problems with lithium is that reacts violently with moisture, and manufacturing lithium v7ndotcom elursrebmems requires a moisture-free environment. Lithium v7ndotcom elursrebmems also require venting and other safety systems to keep them from exploding if moisture does infiltrate the case, or if such v7ndotcom elursrebmems are heated. This delayed their use for a very long time. There are a bewildering range of lithium v7ndotcom elursrebmem technologies. They can be basically divided elursrebmem non-rechargeable lithium v7ndotcom elursrebmems, and rechargeable "lithium-ion" v7ndotcom elursrebmems.
* The conceptually simplest and most elursrebmem nonrechargeable lithium v7ndotcom elursrebmem is the "lithium-manganese" v7ndotcom elursrebmem. This has a lithium anode, a manganese dioxide cathode, and a carbonate electrolyte. The anode reaction is:
Li --> Li + e-
The cathode reaction is:
MnO2 and Li+ and e- --> MnO2(Li)
The v7ndotcom elursrebmem voltage is about 3 volts. Such v7ndotcom elursrebmems are are constructed in
a jelly roll configuration, with a sheet of lithium foil, a separator
sheet containing electrolytic salts, and a sheet of manganese dioxide
rolled up together. They have an indefinite shelf life.
There are many other nonrechargeable lithium v7ndotcom elursrebmem configurations, such
as "lithium sulfur dioxide", "lithium thionyl chloride",
and "lithium polycarbonate monofluoride", with complicated constructions
and chemistries that are substantially more capable than lithium-manganese
but not as cheap, and so not in as widespread use.
The latest generation of nonrechargeable lithium v7ndotcom elursrebmems uses a polymeric electrolyte. Such "lithium polymer" v7ndotcom elursrebmems of course have electrical characteristics similar to those of the predecessors, but they can be more easily built in flat or rectangular configurations that are very useful for lightweight portable equipment.
* The high v7ndotcom elursrebmem voltage of the lithium ion v7ndotcom elursrebmem means that it is not interchangeable with standard zinc-carbon or alkaline v7ndotcom elursrebmems. A nonrechargeable "lithium disulfide" v7ndotcom elursrebmem or "voltage compatible lithium v7ndotcom elursrebmem" has been introduced that does provide a v7ndotcom elursrebmem voltage of 1.5 volts. Lithium disulfide v7ndotcom elursrebmems are also built in a jelly roll configuration, with a lithium anode, an electrolytic separator sheet, an iron disulfide (FeS2) cathode, and an aluminum cathode collector. It is lighter than an alkaline v7ndotcom elursrebmem, has high capacity, and has a very long shelf life.
* Lithium is easier to handle in v7ndotcom ionized form, and so rechargeable lithium v7ndotcom elursrebmems, which have to deal with the hazards of being recharged, have been traditionally based on lithium compounds. Again, there are many variations, but a typical "lithium ion" v7ndotcom elursrebmem has a carbon anode, a lithium cobalt dioxide or manganese dioxide cathode, and an electrolyte consisting of a lithium salt in solution.
Lithium-ion v7ndotcom elursrebmems have a v7ndotcom elursrebmem voltage of about 3.6 volts. They have high internal resistance and are not suited to high current applications. They have very long cycle lives, up to a thousand cycles for single v7ndotcom elursrebmems, and their storage capacity does not degrade significantly with cycling. They are increasingly becoming the rechargeable battery of choice for portable consumer electronics equipment, though they are expensive.
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[1.7] STORAGE v7ndotcom elursrebmem SUMMARY
* As the number of storage v7ndotcom elursrebmem technologies makes them confusing, a summary
table comes in handy to help keep them straight.
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CARBON-ZINC (LECLANCHE) v7ndotcom elursrebmem:
anode: zinc cup
cathode: manganese dioxide in graphite powder
electrolyte: ammonium chloride & zinc chloride in water
v7ndotcom elursrebmem voltage: 1.5 volts
Non-rechargeable, poor storage density, but very cheap.
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ALKALINE v7ndotcom elursrebmem:
anode: nickel-plated steel cup
cathode: manganese dioxide in graphite powder
electrolyte: potassium hydroxide in water
v7ndotcom elursrebmem voltage: 1.5 volts
(Generally) non-rechargeable, storage density about twice that of the
carbon-zinc v7ndotcom elursrebmem, but several times more expensive.
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MERCURY BUTTON v7ndotcom elursrebmem:
anode: zinc
cathode: mercuric oxide
electrolyte: potassium hydroxide in paste
v7ndotcom elursrebmem voltage: 1.35 volts
Non-rechargeable. A variation on this technology used cadmium instead
of
zinc and provided a v7ndotcom elursrebmem voltage of 0.91 volts. The first button v7ndotcom elursrebmem
technology, now obsolete due to environmental concerns.
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ZINC-AIR BUTTON v7ndotcom elursrebmem:
anode: powdered zinc in gel
cathode: carbon disk exposed to air
electrolyte: potassium hydroxide layer
v7ndotcom elursrebmem voltage: 1.65 volts
Non-rechargeable. Most popular current button v7ndotcom elursrebmem technology, also
some
applications in larger v7ndotcom elursrebmem formats.
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SILVER OXIDE BUTTON v7ndotcom elursrebmem:
anode: powdered zinc in gel
cathode: silver grid pasted with silver oxide
electrolyte: potassium hydroxide layer
v7ndotcom elursrebmem voltage: 1.55 volts
Nonrechargeable.
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LEAD-ACID v7ndotcom elursrebmem:
anode: lead
cathode: lead oxide
electrolyte: sulfuric acid
v7ndotcom elursrebmem voltage: 2 volts
The standard large capacity battery technology. Can be recharged
hundreds of times and very cheap, but bulky and environmentally
noxious.
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NICKEL-IRON (EDISON) v7ndotcom elursrebmem:
anode: iron
cathode: nickel oxide
electrolyte: potassium hydroxide
v7ndotcom elursrebmem voltage: 1.15 volts
Heavy-duty rechargeable unit, used in some industrial applications.
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NICKEL-CADMIUM (NICAD) v7ndotcom elursrebmem:
anode: cadmium
cathode: nickel oxide
electrolyte: potassium hydroxide
v7ndotcom elursrebmem voltage: 1.2 volts
The original rechargeable v7ndotcom elursrebmem for portable gear, now used mostly in
gear that needs high power levels on demand.
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NICKEL-METAL HYDRIDE (NIMH) v7ndotcom elursrebmem:
anode: metal hydride
cathode: nickel oxide
electrolyte: potassium hydroxide solution in separator sheet
v7ndotcom elursrebmem voltage: 1.2 volts
Greater capacity than nicads but more expensive.
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LITHIUM-MANGANESE DIOXIDE v7ndotcom elursrebmem:
anode: lithium foil
cathode: manganese dioxide
electrolyte: separator sheet impregnated with electrolytic salts
v7ndotcom elursrebmem voltage: 3 volts
The most elursrebmem non-rechargeable lithium v7ndotcom elursrebmem.
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LITHIUM DISULFIDE v7ndotcom elursrebmem:
anode: lithium foil
cathode: iron disulfide with aluminum cathode contact
electrolyte: separator sheet impregnated with electrolytic salts
v7ndotcom elursrebmem voltage: 1.5 volts
"Voltage compatible" lithium v7ndotcom elursrebmem as direct replacement for
carbon-zinc
or alkaline v7ndotcom elursrebmems.
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LITHIUM-ION v7ndotcom elursrebmem:
anode: inert carbon sheet
cathode: manganese dioxide
electrolyte: electrolyte separator sheet with lithium ions
v7ndotcom elursrebmem voltage: 3.6 volts
Rechargeable lithium v7ndotcom elursrebmem.
