Wax, soap `clean up obstacles to better batteries`
A little wax and soap could help build electrodes for cheaper and better lithium ion batteries.
Washington: A little wax and soap
could help build electrodes for cheaper and better lithium ion
batteries, say scientists.
A team at the US Department of Energy has claimed the
one-step method will allow battery developers to explore lower
-priced alternatives to the lithium ion-metal oxide batteries
currently on the market, the `Nano Letters` journal reported.
"Paraffin provides a medium in which to grow
good electrode materials. This method will help researchers
investigate cathode materials based on cheaper transition
metals like manganese or iron," said team leader Daiwon Choi.
Consumers use long-lasting rechargeable lithium
ion batteries in everything from cell phones to the latest
portable gadget. Some carmakers want to use them in vehicles.
Most lithium ion batteries available today are designed with
an oxide of metal such as cobalt, nickel, or manganese.
For their research, Choi and colleagues at State
University of New York wanted to explore both cheaper metals
and the more stable phosphate in place of oxide.
Lithium iron phosphate batteries are commercially
available in some power tools and solar products but synthesis
of the electrode material is complicated. So, the scientists
wanted to develop a simple method to turn lithium metal
phosphate into a good electrode.
Lithium manganese phosphate can theoretically store
some of the highest amounts of energy of the rechargeable
batteries weighing in at 171 milliAmp hours per gram material.
Choi reasoned the 30 percent loss in capacity
could be due to lithium and electrons having to battle their
way through the metal oxide, a property called resistance.
The less distance lithium and electrons have to
travel out of the cathode, he thought, the less resistance and
the more electricity could be stored.
smaller particle would decrease that distance. But
growing smaller particles requires lower temperatures. However
lower temperatures means the metal oxide molecules fail to
line up well in the crystals.
Randomness is unsuitable for cathode materials, so
the scientists needed a framework in which the ingredients --
lithium, manganese and phosphate -- could arrange themselves
into neat crystals.
Paraffin wax is made up of long straight molecules
that don`t react with much, and the long molecules might help
line things up. Soap -- a surfactant called oleic acid --
might help the growing crystals disperse evenly.
So, Choi and colleagues mixed the electrode
ingredients with melted paraffin and oleic acid and let the
crystals grow as they slowly raised the temperature.
By 400 Celsius (four times the temperature of boiling
water), crystals had formed and the wax and soap had boiled
off. Materials scientists generally strengthen metals by
subjecting them to high heat, so the team raised the
temperature even more to meld the crystals into a plate.
"This method is a lot simpler than other ways of
making lithium manganese phosphate cathodes. Other groups have
a complicated, multi-step process. We mix all the components
and heat it up," said Choi.
To test LMP, the team shook the nanoplates free
from one another and added a conductive carbon backing, which
serves as the positive electrode. When they charged nanoplates
slowly over a day and then discharged them just as slowly, the
LMP mini battery held a little more than 150 milliAmp hours
per gram of material.
But when the battery was discharged fast -- say,
within an hour, that dropped to about 117, comparable to other