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17/11/2011
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A mobile phone battery that stays charged for more than a week and can be recharged in just 15 minutes could soon be on the way thanks to researchers in the US.
 The Northwestern University team has developed a novel electrode for lithium ion batteries which it claims charges 10x faster and holds its charge up to 10x longer than existing technologies.
In addition to better batteries for mobile phones and mp3 players, the researchers believe the technology could pave the way for more efficient, smaller batteries for electric cars.
"We have found a way to extend a new lithium ion battery's charge life by 10 times," explained project lead Harold Kung. "Even after 150 charges, which would be one year or more of operation, the battery is still five times more effective than lithium ion batteries on the market today."
Kung and his fellow engineers combined two chemical engineering approaches techniques to address two major battery limitations - energy capacity and charge rate.
First, they stabilised the silicon found in the anode, which is made of layer upon layer of carbon based graphene sheets. In order to maintain maximum charge capacity, they sandwiched clusters of silicon between the graphene sheets.
This allowed for a greater number of lithium atoms in the electrode while utilising the flexibility of graphene sheets to accommodate the volume changes of silicon during use.
"Now we almost have the best of both worlds," Kung said. "We have much higher energy density because of the silicon, and the sandwiching reduces the capacity loss caused by the silicon expanding and contracting. Even if the silicon clusters break up, the silicon won't be lost."
Kung's team also used a chemical oxidation process to create miniscule holes 10 to 20nm wide in the graphene sheets so that the lithium ions would have a 'shortcut' into the anode and be stored there by reaction with silicon. This reduced the time it took the battery to recharge by up to 10x.
Kung believes the technology could be seen in the marketplace in the next three to five years. In the meantime, he and his team are looking into developing an electrolyte system that will allow the battery to automatically and reversibly shut off at high temperatures - a safety mechanism that could prove vital in electric car applications.
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Author
Laura Hopperton
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