Technology Profile: The Promise of Lithium
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A very sage purveyor of technology once offered this observation: "The best
technology is that technology that is the farthest in the future, because it
always holds the most promise!" In the battery technology arena this is the
current mantra concerning lithium- based batteries ð they are the solution
to almost all the battery problems of today. While lithium-based battery
products are becoming more available in smaller applications, there is a
significant amount of development work required to make lithium the material
of choice for the majority of battery applications.
About Lithium
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Lithium is the lightest of all metals; it has the greatest electrochemical
potential of all the elements. In the parameters of batteries, lithium
provides the most energy content per unit weight and volume. Lithium has
medicinal value in some formulations. In its pure form, lithium is a very
volatile material ð it is normally stored in a pure inert gas (argon)
environment or immersed in oil. The challenge with pure lithium is that it
is very reactive, an exposure to a little moisture is catastrophic. Even
though it is a difficult material to work with ð the upside of high energy
density and a lightweight makes it attractive for batteries.
Lithium Metal Batteries
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Research on lithium based batteries was recorded as early as 1912. It was
not until the 1970?s that the first primary (non-rechargeable) lithium
batteries appeared in the marketplace. The first batteries were small,
button cells for hearing aids, watches and other low power devices. Several
attempts were made in the 1970?s and early 1980?s to develop rechargeable
batteries using lithium metal, but most failed due to safety concerns. In
the late 1980?s Nippon Telephone & Telegraph (NTT) imported a large quantity
of lithium rechargeable batteries based on lithium metal. After one of the
batteries exploded in a cell phone, causing serious burns, the batteries
(1.5 million) were recalled.
The problem with using metallic lithium was the tendency of the material to
form dendrites (thread-like extensions), that would cause internal shorting
when they grew from plate to plate. Once a lithium dendrite connected with
another plate, a short would form and would result in thermal runaway. Once
the cell temperature reached the melting point of lithium, the reaction
became explosive. The term ?lithium rocket? was used to describe some of
the resultant failures.
Non-Metallic Compounds
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To deal with the instability of metallic lithium, battery developers shifted
research to a non-metallic lithium battery using lithium ions from a variety
of compounds. Although lithium-ion batteries have a lower energy density
than metallic lithium, the increased safety was considered worth the change.
Sony Corporation (SNE) was the first to commercialize lithium-ion in 1991,
and is currently the largest supplier of lithium-ion batteries.
Sony developed a version of the lithium-ion battery technology termed the
"coke" version, while a number of competing manufacturers built a slightly
different approach termed the "graphite" version. The primary difference in
the two technologies is in their discharge characteristics: the graphite
version has a flatter discharge curve and only needs to be discharged to 3.0
volts to obtain maximum capacity, whereas the coke version requires
discharge to 2.5 volts for maximum utilization. Both technologies have a
fully charged voltage of 4.0 volts.
Despite the fact that lithium-ion batteries are safer than metallic lithium,
they still require special controls to insure safe operations. Smart
chargers are used with lithium-ion batteries to insure that the maximum
voltage is not exceeded, and where multiple cells are used, a thermister is
used to monitor the temperature profile to prevent thermal runaway. There
is still considerable development work being done on lithium-ion battery
technology as developers attempt to lower the cost. A number of developers
are using new carbon compounds in the negative electrode and are looking for
substitutes for the expensive cobalt content of the batteries.
Although safety of the commercially available batteries has improved in the
1990?s, the manufacturing process still presents challenges. In the past
three years, two major Japanese lithium-ion facilities have burned to the
ground as the result of lithium based fires. Engineers and electro-chemists
that work with lithium have a wealth of stories of explosions and fires that
have resulted from working with lithium. As the number of lithium-ion
batteries increases in the marketplace, the potential hazards are increased
as they get included in waste that may be incinerated.
The Japanese battery manufacturers invested very heavily in lithium-ion
battery technology development. Sony and Panasonic are major players with a
number of other companies entering the market. In the US, there was
considerable investment made by Bellcore, the research element that was spun
out of the breakup of ATT. A number of companies have licensed Bellcore
lithium-ion technology for production batteries.
One of the key technical challenges with all lithium-based battery
technologies is the issue of scale. Lithium battery developers have had the
greatest success with the smaller sized batteries. Button cells for use in
watches, hearing aids and other electronic devices have served the industry
well. As the developers increase the size and capacity of the batteries,
they become more difficult to control and operate safely.
Lithium Polymer
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The "Mount Olympus" for lithium battery developers is lithium polymer.
Borrowing from a body of work created by developers of thin-film
technologies, lithium polymer battery developers envision a battery built by
layering several materials together in a thin sheet. The positive and
negative electrodes would be solid polymers and would use a solid
electrolyte. These materials could be fabricated in rolls and integrated
into thin-film batteries that could be as thin as one millimeter (0.039").
These ?sheets? of batteries could be rolled, shaped or formed to conform to
the requirements of the system. There are some developers that envision use
of the lithium polymer batteries as structures or covering for a product
(imagine a laptop where the case is the battery).
Because of the manufacturing techniques, it is assumed that lithium polymer
batteries can be made very inexpensively. The known limitations for lithium
polymer at this time are specific power performance and recharge time.
Lithium polymer has excellent energy density characteristics, but is not
able to deliver the same level of peak power as other battery technologies.
The solid electrolyte has some limitations on conductivity so developers are
seeking ways to introduce some liquid electrolyte into the manufacturing
process. Early lithium polymer batteries have recharge profiles similar to
lead-acid, requiring up to 16 hours to recharge.
There are a number of players in the lithium polymer development arena. One
of the most prominent is 3M Corporation (MMM). 3M is involved with a major
Canadian utility company (Hydro Quebec) to develop a lithium polymer battery
for electric vehicle applications. They have received significant funding
from the US Advanced Battery Consortium (USABC) and hope to have a
demonstrable product after the turn of the century. A check of the
exchanges on the Internet will reveal several small companies in various
stages of developing lithium polymer. If successful, the rewards would be
tremendous ð the question is who has the right approach?
A Battery Tale
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Having joined the battery business somewhat late in my career, I was
surprised by the state of the technology. Coming from electronic
manufacturing (where processes were predictable and yields were 99+
percent), I was amazed how much art there is in battery development. It
borders on alchemy in some cases. Process development is often by guess,
and if it works ð adopt it! My assumptions about the application of
well-founded scientific principles being exercised by professional engineers
were in error. If you find a battery company where the chief technologist
likes to dress like Merlin the Magician, it might be a good investment.
On visits to several customers of new battery technology I have been greeted
with two signs (often on display over the desk of the battery buyer): one
reads, "There are liars, damn liars, and battery suppliers!" the other reads
"In God We Trust, all others bring data!" The signs are symptomatic of the
broken promises of a number of battery companies in the recent past. Before
jumping into an investment in what appears to be a promising lithium battery
technology, one should ask the following questions:
- How many batteries have you actually made?
- How large a battery can you safely make?
- When was your last fire?
In the early 1990?s an emerging company with lithium polymer battery
technology, Valence Technology, Inc. (VLNC) made a significant splash on the
market. The CEO was reported to have given presentations on Wall Street
where he would measure the voltage potential of a sheet of lithium polymer
battery developed by his company and display the results to the audience.
He would then take out a pair of scissors and cut the sheet in half and
measure the voltage potential again. The audience was so amazed that the
potential was the same, that they never questioned the CEO about the ability
to manufacture this technology. It is a fact of physics, that any cell will
produce a certain voltage independent of its size. The issue is whether or
not the technology is commercially viable at the right price-performance
point.
This company was then reported to have followed up with the release of what
we call an "if, then" letter from a major manufacturer of cell phones
(Motorola - MOT). The letter stated that if Valence could indeed produce a
battery with the specifications required by the manufacturer, at the cost
quoted, then Motorola would commit to the purchase of $100M worth of
batteries. Wall Street was enamoured, the IPO was hugely successful, and
then the company subsequently announced that they could not manufacture the
product and the stock dropped rapidly in mid 1994. Lawsuits followed (won
by Valence) and the battery industry was tainted in Wall Street's eyes.
Valence is still researching and developing advanced, rechargeable, lithium
polymer battery technology, but have no revenues and have not yet been
successful in commercializing the technology.
If you track battery stocks today, you will find it hard to find a strong
performer. However, all is not bleak. The good news is that if one of the
emerging companies is successful, the market is huge! Lead-acid and Nickel
Cadmium batteries have served us well, but they cannot keep pace with the
demands of the system developers. Lithium-based products offer some
significant performance enhancements, but not without a price. |
