Wired.co.uk – Battery redesign could make phones charge in 15 minutes, last for a week


Battery redesign could make phones charge in 15 minutes, last for a week

http://www.wired.co.uk/news/archive/2011-11/16/battery-redesign

16 November 11

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A team of engineers from Northwestern University haveredesigned the lithium-ion battery — the chunky energy cell found in the majority of modern gadgets — so that it can charge ten times faster than current batteries, and last ten times longer.

Chemical engineer and lead author of the research Harold Kung claims that his battery could charge your phone in just 15 minutes and go on to last for a week. “Even after 150 charges,” he says, “the battery is still five times more effective than lithium-ion batteries on the market today.”

Lithium-ion batteries are used in everything from your Android to your Nintendo 3DS and your iPad. They work by blasting lithium ions from one end of the battery to the other, passing through an electrolyte to transfer electrical charge.

When the device is being used, the ions in the battery whizz from the anode, through the electrolyte and into the cathode. When the battery is being recharged the ions travel in the reverse direction.

Batteries are hindered in capacity and charge speed for two reasons.

Capacity is limited because the anode — made of layers of carbon-basedgraphene sheets — can only hold one lithium atom for every six carbon atoms. Engineers experimented with silicon as a replacement, but it’s unstable because it dramatically expands and contracts while charging, causing fragmentation.

Charge speed takes a hit because the graphene sheets are very long — the lithium ions must travel all the way to the outer edges before entering and coming to rest. A sort of ionic traffic jam occurs around the edges of the material, resulting in hours-long periods to charge your iPhone.

Kung says that his team has fixed both issues in one fell swoop. Silicon is the answer after all — it can hold a whopping four lithium atoms for every silicon atom — but carefully sandwiching clusters of it between the graphene sheets avoids the disastrous fragmentation problem. And by poking tiny holes (10 to 20 nanometeres wide) in the graphene, the lithium ions have a “shortcut” to the anode.

The team, who described their research in the journal Advanced Energy Materials, reckons that the technology could be seen on the marketplace in the next two to five years. Although with power-hungry device requirements constantly going up — be it in 3D screens or quad-core tablet processors — it remains to be seen exactly how much of a difference it will make in the end.