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Graphene enables all-carbon lithium battery

24 Apr 2014

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Engineering researchers at Rensselaer Polytechnic Institute have developed a new type of rechargeable lithium battery with components made entirely of carbon. Unlike the lithium-ion batteries currently sold around the world to power smart phones, laptops, and countless other devices, this battery is made without the toxic metal cobalt.

The new technology, detailed in a research paper published this week in the journal Nature Communications, pairs an anode and cathode made from the nanomaterial graphene with metallic lithium to create an energy storage device. This research could lead to a new generation of batteries with significantly higher energy density, and that are nontoxic, easy to manufacture, and inexpensive to recycle.

"In this study, we show how to make a new type of battery using graphene, as well as an unlikely component—metallic lithium," said Nikhil Koratkar, the John A. Clark and Edward T. Crossan Professor of Engineering at Rensselaer, who led the study. "Metallic lithium is avoided in lithium-ion batteries due to its tendency to form dendrites which are considered unsafe, but we show that metallic lithium trapped within a porous graphene structure is safe and does not form dendrites. The result is an all-carbon lithium battery that offers up to three times higher energy density than conventional batteries. It is also more environmentally friendly, and with its simplified chemistry could be easier and less expensive to mass produce."

See the study, titled "Defect-induced plating of lithium metal within porous graphene networks," online at: http://go.nature.com/htWO9h

Lithium battery technology dates back to the 1970s, and some of the very first iterations used a metal lithium cathode. Energy is stored by moving lithium ions back and forth between the battery's cathode and an anode made of graphite. This results in a flow of electrons, which is harvested and put to use as electricity.

As the lithium gets cycled back and forth between the anode and cathode, it would settle and form dendrites—small, sharp towers on the cathode surface—that over time grow in size and eventually pierce the membrane separating the cathode and anode, causing the battery to fail. Even though lithium metal has an attractive energy density, this shortcoming led to serious safety concerns. As a consequence, the battery industry has avoided the use of metallic lithium and has resorted to storing elemental lithium in a matrix material such as cobalt-oxide or iron-phosphate. Atoms of cobalt or iron in the matrix bond with lithium and prevent lithium metal from forming, thereby solving the dendrite issue.

In most lithium-ion batteries sold today, the cathode is made from lithium cobalt oxide and the anode is made from graphite, comprised of many ultra-thin layers of graphene. When charging, lithium ions seek out the edges of the anode and work their way inside between the layers of graphene. This process, called intercalation, creates no bonds between the elemental lithium or between the lithium and graphene, which limits the energy density of the overall battery.

In place of graphite, Koratkar and his research team developed an anode made from thermally shocked graphene. This process is a way to intentionally create cracks, holes, voids, and other defects in the graphene. In previous studies, the researchers have shown that these defects enable lithium ions to more rapidly make their way into the anode, leading to shorter charge times.


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