|
Lithium Ion Battery
Current lithium battery use is primarily limited to small
electronic devices, like laptop computers and camcorders,
because of their high cost and safety concerns. Several
materials contribute to the high cost, but the most frequently
used cathode material -- lithium cobalt oxide -- is extremely
expensive.
Lithium battery research is currently underway at the US
Department of Energy's Sandia National Laboratories in New
Mexico to improve lithium ion battery materials and may
result in smaller, longer-lasting batteries for applications
as diverse as portable computers and electric vehicles.
“The research combines a new mixture of metals to
create the cathode portion of the lithium ion battery --
a high-tech, environmentally friendly electrical energy
storage device. For inorganic chemist Tim Boyle and chemical
engineer Jim Voigt, both in Sandia's Materials Processing
Department, building a better lithium ion battery is much
like baking a cake -- a matter of putting together the right
ingredients in the cathode. ‘We've tried various combinations
of lithium [a lightweight metal] with manganese, cobalt,
nickel, chromium, and aluminum and are making some breakthroughs,’
Boyle says. If the right combination of materials can be
found -- and the researchers think they are close -- lithium
ion rechargeable batteries may become economical enough
and have a long enough run time to be practical to power
electric cars or replace existing traditional lead-acid
batteries. A battery consists of three basic parts -- two
electrodes (a cathode and anode) separated by an electrolyte.
Lithium ion batteries use host materials for the electrodes
(for example, carbon as the anode and lithium cobalt oxide
as the cathode) to avoid using metallic lithium, thereby
improving safety. Electrochemical reactions at the electrodes
produce an electric current that powers an external circuit.
During charge and discharge of lithium ion rechargeable
batteries, lithium ions are shuttled between the cathode
and anode host materials in a ‘rocking horse’
fashion. Sandia has done extensive past work to improve
carbons for use as anodes. The cathode work builds on the
previous anode endeavors, says Dan Doughty, manager of Sandia's
Lithium Battery R&D Department. This is where Boyle
and Voigt's research could make a difference.
Two factors drive the quest for a better lithium ion
rechargeable battery, Boyle says. First, the batteries are
more ‘environmentally friendly.’ ‘Lithium
manganate is like sand. It has almost no environmental impact
-- unlike lead acid batteries that contain poisonous heavy
metal.’ Boyle says. ‘Also, the lithium battery
can be recharged -- meaning that it isn't thrown out, but
used over and over again.’
The second reason is that lithium batteries are lightweight
and provide more electricity than non-lithium batteries
of equal size and weight. As a result, they are ideal to
power portable electronics, a rapidly growing market. Also,
they might be used in electric cars, which require batteries
that are cheap, light, powerful, and long-lasting. The challenge,
then, is to find the right combination of cathode elements.
Boyle and Voigt are in a unique position to do this because
of a process they invented and patented three years ago
to combine elements.
Their system is a simple waterless process in which the
materials being combined are dissolved in methanol. The
solution is then dried in a vacuum, baked at 200 degrees
C in a box furnace for 24 hours, transferred to a tube furnace
where it is heated to 800 degrees C, and held for 24 hours
under a flowing oxygen atmosphere. The result is a homogenous
powder. Deciding which elements to combine is not a "hit
or miss" testing process, Boyle says. Before elements
are combined, computer models are developed showing the
structural integrity of the final material. After determining
via the computer modeling which combinations are best, the
solutions are mixed, powders processed and batteries tested.
The material's performance is tested by measuring the capacity
and useful life of the new cathode materials using electrochemical
methods. Also, X-ray diffraction is used to prove these
materials are phase pure. Boyle's experiments show that
cobalt, nickel, manganese, and other transition metals might
be the most effective combination of materials. The introduction
of the nickel to replace some of the cobalt would reduce
the cost of the final material while maintaining the high
capacity. The manganese allows for more flexibility in the
charge distribution and also would reduce costs because
it is replacing the expensive cobalt. Another advantage
of using manganese is that it is a benign material and therefore
environmentally less damaging than some of the other elements
used in lithium batteries. Sandia has long been a leader
in designing and building batteries for defense applications.
The lithium battery cathode development program is funded
by a Department of Energy Office of Basic Energy Science
initiative to develop novel, high performance battery materials.
‘They want us to find a higher capacity material for
the cathode that will give these batteries a longer life,’
Doughty says. ‘Boyle and Voigt's research fits right
into this goal.’
Work Cited
“Sandia Research May Bring Smaller, Longer Life Lithium
Batteries Into Our Lives”. Retrieved 20 June 2002
[online]
http://www.sandia.gov/media/lithium.htm
|
