[tt] A Better Battery? The Lithium Ion Cell Gets Supercharged: Scientific American

[Brian Atkins]

http://www.sciam.com/article.cfm?id=better-battery-lithium-ion-cell-gets-supercharged&print=true

A new technique could pave the way for improving the workhorse lithium ion 
battery used in automobiles, cell phones and other devices so that it can 
recharge in seconds

By Adam Hadhazy

A new twist on the familiar lithium ion battery has yielded a type of 
power-storing material that charges and discharges at lightning speed. The 
finding could offer a boost for plug-in hybrid and electric vehicles and 
possibly allow cell phone batteries to regain a full charge in seconds rather 
than hours.

Scientists at the Massachusetts Institute of Technology (M.I.T.) report in 
Nature today that they devised a way for lithium ions in a battery to zip in and 
out about 100 times faster than previously demonstrated. "We took a basically 
great material called lithium iron phosphate [LiFePO4] and we tried to improve 
it further," says study author Byoungwoo Kang, a graduate student in M.I.T.'s 
Department of Materials Science and Engineering.

Rechargeable lithium ion batteries are small and light, yet can store copious 
amounts of energy, making them ideal for use in everyday electronic devices such 
as iPods and laptops. This valuable property, called energy density, can be 
scaled up for hybrid cars as well as for the all-electric Roadster built by 
Tesla Motors that relies on lithium ion batteries (6,831 individual cells) and 
the similarly powered Chevy Volt plug-in electric, about to hit the market.

One downside: lithium ion batteries do not dispense their charge—carried by 
lithium ions and electrons, hence the power source's name—very quickly compared 
with some other types of storage batteries. Like a huge auditorium that only has 
a few doors, getting a large volume of patrons (lithium ions) in and out is a 
drawn-out affair. This phenomenon explains why some electric vehicles (the 
rip-roaring $109,000 Tesla Roadster with its massive battery pack excluded) can 
reach high speeds, but they suffer from poor acceleration compared with the 
propulsive force unleashed by the rapid succession of mini explosions in an 
internal combustion engine. The slow exchange of ions also means lithium ion 
batteries recharge slowly—just think of how long you have to charge your tiny 
cell phone.

In an attempt to pick up the pace, the M.I.T. researchers coated the lithium 
iron phosphate material with an ion conductor, which in this case was a layer of 
glasslike lithium phosphate. Sure enough, the charge-carrying ions traveled much 
faster from their storage medium; a prototype battery the scientists built 
completely charged in about 10 to 20 seconds.

The results have impressed some battery experts. "I think this work is a really 
exciting breakthrough with clear commercial applications," says Yi Cui, an 
assistant professor of materials science and engineering at Stanford University.

Two companies have already licensed the technology, according to Kang. 
Researchers are not sure how much these batteries will cost when they hit the 
market, but Kang says they should be reasonably priced, given that it should be 
relatively cheap to produce them.

The study notes that residences cannot draw enough energy from the electrical 
grid to quickly charge a hybrid car's battery containing the new material, 
though smaller batteries for gadgets and perhaps power tools should not have 
that catch. But future roadside plug-in stations (service stations selling 
electricity instead of gasoline) with greater power pull could do the trick for 
vehicles, Kang says.

-- 
Brian Atkins
Singularity Institute for Artificial Intelligence
http://www.singinst.org/