| Jul 15, 2013 |
New graphene technique can significantly increase the storage capacity of lithium ion
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(Nanowerk News) A few months back, the Air Force Office of Scientific Research (AFOSR) was proud to publish an article regarding a research accomplishment by Dr. Jim Tour and his research team at Rice University. AFOSR, along with other funding agencies, supported Dr. Tour's research effort to make graphene suitable for a variety of organic chemistry applications -- especially the promise of advanced chemical sensors, nanoscale electronic circuits and metamaterials.
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Four years ago, Tour's research team demonstrated that they could chemically unzip cylindrical shaped carbon nanotubes into soluble graphene nanoribbons (GNR) without compromising the electronic properties of the graphitic structure. A recent paper by the Tour team, published in IEEE Spectrum and partially funded by AFOSR, showed that GNR can significantly increase the storage capacity of lithium ion (Li-ion) by combining graphene nanoribbons with tin oxide.
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By producing GNR in bulk, a necessary requirement for making this a viable process, the Tour team mixes GNR and 10 nanometer wide particles of tin oxide to create a slurry. By adding a cellulose gum binding agent and water, the mixture is then applied to a capacitor, which is then fitted to a button-style lithium-ion battery.
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In the Tour lab tests, the prototype battery had an initial charge capacity of more than 1,520 milliamp hours per gram (mAh/g). After repeated charge-discharge cycles that number began to plateau at about 825 mAh/g, but after 50 discharge cycles, the batteries retained far more capacity -- more than double -- that of Li-ion batteries that employ standard graphite anodes.
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The critical key that makes the increase in battery capacity possible is the significant improvement in flexibility that graphene nanoribbons lend to the anode. By comparison, conventional Li-ion batteries with graphite anodes break down and lose efficiency because of their inability to flex, as they expand and contract, with repeated charge and discharge cycles; over time the graphite cracks and the battery cannot charge. Conversely, anodes with a graphene nanoribbon platform allow the tin oxide particles to maintain a consistent size, rather than expanding and contracting, and thus eliminating the brittleness and cracking associated with a graphite-based anode.
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This breakthrough may very well lead to the next generation of the lithium-ion battery -- a promising new platform for creating more durable, lightweight and efficient lithium-ion power.
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