[Oeva-list] battery recharge

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March 16, 2009 Researchers have developed a  new advanced Lithium Ion battery 
that will allow mobile phone and laptop  computers to be fully charged in 
seconds. Electric car batteries may be charged  in as little as five minutes, 
removing one of the main barriers to wider uptake  of EVs. Solar and wind power 
generation could also benefit as better batteries  could be used to store 
surplus energy. 
 
_MIT_ (http://www.gizmag.com/tag/mit)  researchers Byoungwoo Kang & Gerbrand 
Ceder have  discovered a way to make a lithium iron phosphate (LiFePO4) 
battery charge and  discharge about as fast as a supercapacitor. In a typical 
lithium ion cell when  a current is applied to charge the cell, lithium ions move 
away from the cathode  compound and are trapped at the anode storage medium. 
When the battery  discharges producing current, those ions travel back to the 
cathode medium and  in so doing produce current flow. 
Speed of charging in typical lithium-ion cells is slowed  by virtue of the 
fact that it takes time for the lithium ion to move off the  cathode material. 
Various techniques have been tried to increase that speed  including the 
nanoparticle doping strategy that A123 Systems uses.  
The scientists noted that lithium iron phosphate forms a  lattice that 
creates small tunnels through which the lithium ions flow, but that  although the 
cathode seemed ideal it still took some time for those ions to  travel. The 
novel solution they devised was to create a lithium phosphate glassy  surface to 
coat these tunnels. This glassy surface acts as a speedway that  rapidly 
transports the lithium ions on and off the cathode.  
Extremely high rates can be achieved, at a 200C rate  (corresponding to an 18 
second total discharge) more than 100mAh g can be  achieved, and a capacity 
of 60mAh g is obtained at a 400C rate (9 sec to full  discharge). Such 
discharge rates are two orders of magnitude larger than those  used in today’s lithium 
ion batteries. Typical power rates for lithium ion  battery materials are in 
the range of 0.5 to 2 kW/kg. The specific power  observed for the modified 
LiFePO4 (170kWkg at a 400C rate and 90kWkg at a 200C  rate) is two orders of 
magnitude higher. At this point the researchers have only  tested the cells to 50 
cycles but have noted no degradation. The a small  prototype cell can be fully 
charged in 10 to 20 seconds, compared with six  minutes for cells made in the 
standard way. 
This new ability to charge and discharge lithium-ion  batteries within 
seconds blurs the distinction between batteries and  ultracapacitors. Besides being 
able to charge one’s cellphone in seconds, this  will have a major impact on 
electric cars. If electric grid power was available,  an electric car with a 
15kWh battery could be charged in five minutes. This  would require the delivery 
of 180 kw of energy in that time frame.  
Two companies have already licensed the technology one of  which includes 
A123 Systems. Because it involves a new approach to manufacturing  lithium-ion 
battery materials, rather than a new material, it could be ready  within two to 
three years. 
Paul Evans 
off of gizmag    Wade 

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