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Boffins build bionic battery

Ten times' Li-ion capacity, charges in a tenth of the time

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Researchers have devised an electrode material that allows lithium-ion batteries to hold ten times the charge they do today - and recharge ten times as quickly.

The trick, uncovered by scientists at Northwestern University in Evanston, Illinois led by Professor Harold Kung, is to build the battery's positive electrode, the anode, out of graphene, a form of carbon comprised of atom-thick sheets.

The anode is formed from a "flexible, self-supporting three-dimensional conducting graphenic scaffold" with clusters of silicon nanoparticles held between each sheet of graphene.

Silicon has been proposed before as a material for lithium-ion battery anodes as it can hold more lithium ions than carbon can: four lithium ions for every silicon atom, compared to one lithium ion for every six carbon atoms.

Replacing carbon with silicon is hard, however, because silicon expands and contracts during the charging process, causing the material to break up and the anode to lose its charge capacity rapidly.

By placing the silicon between the graphene sheets, Kung and his team, found that even if the clusters break up as a result of the expansion and contraction, the silicon is not lost, so the capacity reduction over time is much reduced.

Kung and co also used an oxidation process to create defects in the atomic lattices that make up each graphene sheet, essentially drilling holes in the lattice to enable the lithium ions to reach and react with the silicon more quickly.

The upshot, they said, is a li-ion battery that recharges in a tenth of the time and a tenfold increase in capacity too.

And - yes! - ten times the longevity too. "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 claimed.

All good stuff, but Kung's anode doesn't deliver the speed that University of Illinois scientists Huigang Zhang, Xindi Yu and Paul Braun managed with their "self-assembled three-dimensional bicontinuous nanoarchitecture consisting of an electrolytically active material sandwiched between rapid ion and electron transport pathways" cathode back in March.

That structure allowed a lithium-ion battery to charge up to 75 per cent of capacity in just 2.7 seconds. Reaching 90 per cent capacity took 20 seconds.

Someone should get these teams together. Put the new anode and new cathode in the same battery and we might at last put an end to regular day or every other day charging. ®

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