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Wall Street Journal, Tuesday, October 31, 1995


Compounds With Hydrogen Appear to Be Best Suited For Long-Term Results

by Amal Kumar Naj
Staff Reporter of The Wall Street Journal

Scientists said they found the carbon compounds that should fulfill a dream
of battery makers: longer-lasting, rechargeable-lithium batteries for laptop
computers, camcorders and other electronic products.

Nonrechargeable lithium batteries, which pack more energy in an ounce than most
other batteries, have been used in cameras and other electronic products for
years. Recently manufacturers have struggled to make them rechargeable. When
those lithium or metal batteries are exposed to repeated charges and
discharges, the highly reactive lithium in them tends to smoke and even catch
fire, explained Jeff R. Dahn, professor of physics at Simon Fraser University
in Burnaby, Canada.

Dr. Dahn said efforts to make a rechargeable, high-storage lithium battery have
been hampered by the lack of the ideal carbon to use in the battery as the
anode, the negative electrode, which on discharge gives off electrons. During
charging and discharging, the electrically-charged lithium atoms or ions move
back and forth between the carbon anode and a cathode made of an oxide of
cobalt or nickel.

"How good a lithium-ion battery is depends on how many lithium ions the carbon
material can store in it," Dr. Dahn said.

Commenting on Dr. Dahn's research, William Bowden, a principal scientist at
Duracell International Inc., said, "Betting against Jeff Dahn is a good way to
become poor." He said Duracell has scientists studying carbon materials for a
lithium-ion battery. "Jeff has done excellent work on carbon in the past," he
said. Duracell, which makes rechargeable nickel-hydride batteries, is "very
interested in lithium-ion batteries," he said, adding that existing
rechargeable batteries "only imperfectly" meet the ever increasing demands of
the computer industry for improved energy storage and light weight.

In a report in the weekly journal, Science, Dr. Dahn and his colleagues
described three classes of carbon materials that they said appear suitable
for use in advanced lithium batteries. Dr. Dahn said manufacturers are likely
to be confused over the best carbon to select from the hundreds of commercially
available carbon types, including natural and synthetic graphites, that can be
used in a lithium battery.

They researchers said they found that pure carbon derived from such raw
materials as petroleum products were least suitable for electrodes in a lithium
battery. That's because the carbon material stores the lithium ions in layers
and there is a limit on the number of lithium ions that can be stored in each

On the other hand, the researchers said, they found that carbon made from
starch or cellulose had a structure like a house of cards with large holes in
it to accommodate a lot more lithium ions.

The researchers found that carbon material that was composed of 80% carbon
atoms and 20% hydrogen atoms fared the best in storing the maximum number of
lithium ions. They synthesized the carbon materials by burning petroleum
products, sugar and wood at low temperatures to retain their hydrogen.

Dr. Dahn said the carbon with hydrogen as a component could prove to be the
ideal material because it doesn't lose its ability to store and give off
lithium ions during repeated charging and discharging.

"We haven't discovered any new carbon material," Dr. Dahn said. "What we have
done is identified carbon types that hold the most amount of lithium ions per
unit of mass, which is key to making longer-lasting, rechargeable lithium