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Thin-film lithium battery targets the world of microelectronics
Today's microprocessor and memory chips are smaller yet more powerful
than ever. Unfortunately, the batteries often supplying backup power to
this chips are usually much larger and must be added to the circuit as a
separate component. That may change in the not-too-distant future, thanks
to joint research by the Dept.of Energy's Oak Ridge National Laboratory
in Oak Ridge, TN, and Eveready Battery Company's facility in Westlake, OH.
Efforts are underway at both locations to produce rechargeable,
thin-film lithium batteries that can be incorporated directly into an IC
such as a computer memory chip. These batteries could also power miniature
sensors and micromotors, according to John Bates, principal investigator
for the cooperative research effort and leader of the Ceramic Thin-Film
Group in Oak Ridge National Laboratory's Solid State Division. The
batteries are produced using thin-film deposition techniques that are
similar to those used in the semiconductor industry. According to Bates,
the technology can be easily scaled to produce batteries of any size and
shape. Because the batteries can be fabricated on semiconductor processing
equipment, semiconductor manufacturers can economically produce them as a
value-added function to a semiconductor chip, notes Steve Jones, a staff
electrochemist for Eveready. Oak Ridge has developed a thin-film battery
is rated 3.7 V and typically measures about 1 cm square by 6 microns
thick. It uses a thin-film electrolyte, called lithium phosphorous
oxynitride. This electrolyte, designed to remain stable at high cell
voltages, resides between a noncrystalline vanadium oxide (forming the
cathode) and a top layer of lithium (forming the anode). Completing the
battery's construction is the substrate, which could be glass, silicon, or
other materials, and a proprietary protective coating. The figure shows a
cross-section of the battery. For its part, Eveready for over a year been
experimenting with a square 2.5 V battery whose structure resembles the
Oak Ridge battery. The main difference is that the electrolyte is made of
lithium pitanium disulfide instead of lithium phosphorous oxynitride.
Besides their small, thin profile, the thin-film lithium batteries promise
far longer life than the few existing rechargeable lithium batteries,
notes Eveready's Steve Jones. The thin-film lithium batteries has been
demonstrated to last for up to 10,000 recharging cycles. By contrast,
existing rechargeable lithiums last only several hundred cycles, says
Jones. Until recently, the major technical obstacle to producing
thin-film lithium batteries was developing a protective coating capable
of effectively sealing the battery against corrosion and leakage. Now that
Oak Ridge National Laboratories has successfully developed such a coating
(which will also be used by Eveready), for the battery, both groups are
optimistic that prototype production of thin-film lithium batteries could
begin soon, perhaps as early as next year. In fact, both John Bates of Oak
Ridge National Laboratories and Steve Jones of Eveready hope to organize a
workshop sometime in early 1993 to educate possible users about the
battery technology and explore potential applications. For more
information, contact John Bates at Oak Ridge National Laboratories, Oak
Ridge, TN, at 615-574-6280, or Steve Jones, Eveready Battery Company,
Westlake, OH, at 216-835-7734, or circle .
–Spencer Chin
Caption: Thin-film lithium batteries being developed by Oak Ridge
National Laboratories and Eveready use vapor deposition techniques,
similar to those used in the semiconductor industry, to produce thin, tiny
batteries that could be fabricated inside a chip or package. This 3.7 V,
6-micron thick version developed by Oak Ridge National Laboratories
comprises a lithium phosphorous oxynitride electrolyte, a noncrystalline
vanadium oxide cathode and a lithium anode.
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