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The Race for Batteries

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Graphene and Nanotubes Triple Lithium Metal Battery Density

May 22nd 2017

Graphene carbon mesh

Researchers at Rice University in the US have used a combination of graphene and carbon nanotubes to build a rechargeable lithium metal battery with three times the capacity of commercial lithium-ion batteries.

The Rice battery uses an anode built of a hybrid of graphene and carbon nanotubes. The 3D surface provides more area for lithium to inhabit and approaches the theoretical maximum for storage of lithium metal while resisting the formation of damaging dendrites.

These dendrites are lithium deposits that grow into the battery's electrolyte and if they bridge the anode and cathode and create a short circuit, the battery may fail, catch fire or even explode.

Led by chemist James Tour, the researchers found that when the new batteries are charged, lithium metal evenly coats the highly conductive carbon hybrid in which nanotubes are covalently bonded to the graphene surface.

"Lithium-ion batteries have changed the world, no doubt," said Tour, "but they're about as good as they're going to get.” The low density anode has plenty of space for lithium particles to slip in and out as the battery charges and discharges and the lithium is evenly distributed, spreading out the current carried by ions in the electrolyte and suppressing the growth of dendrites.

Though the prototype battery's capacity is limited by the cathode, the anode material achieves a lithium storage capacity of 3,351 milliamp hours per gram, close to the theoretical maximum and 10 times that of lithium-ion batteries, said Tour.

To test the anode, the Rice lab built full batteries with sulfur-based cathodes that retained 80 percent capacity after more than 500 charge-discharge cycles. Electron microscope images of the anodes after testing showed no sign of dendrites or the moss-like structures that have been observed on flat anodes.

"Many people doing battery research only make the anode, because to do the whole package is much harder," said Tour. "We had to develop a commensurate cathode technology based upon sulfur to accommodate these ultrahigh-capacity lithium anodes in first-generation systems. We're producing these full batteries, cathode plus anode, on a pilot scale, and they're being tested."


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