Lawrence Livermore graphene aerogels could improve performance of carbon-based superconductors by more than 100%
Researchers at Lawrence Livermore National Laboratory (LLNL) are developing modified graphene aerogels for application in supercapacitor electrodes. LLNL’s graphene aerogel material could potentially improve on the performance of commercial carbon-based supercapacitors by more than 100%, said LLNL’s Dr. Patrick Campbell, lead author of a paper on the technology published in the RSC journal Journal of Materials Chemistry A.
In the paper, the LLNL team reports a 2.9-fold increase in electrical energy storage capacity (up to 23 Wh kg−1) of their graphene materials by modifying them with anthraquinone. These hybrid electrodes demonstrate battery-like energy density, supercapacitor-like power performance, and superb long-term stability, the researchers said.
Binder-free, monolithic, high surface area graphene macro-assemblies (GMAs) are promising materials for supercapacitor electrodes, but, like all graphitic carbon based supercapacitor electrodes, still lack sufficient energy density for demanding practical applications. Here, we demonstrate that the energy storage capacity of GMAs can be increased nearly 3-fold (up to 23 Wh kg−1) by facile, non-covalent surface modification with anthraquinone (AQ). AQ provides battery-like redox charge storage (927 C g−1) without affecting the conductivity and capacitance of the GMA support.
The resulting AQ-GMA battery/supercapacitor hybrid electrodes demonstrate excellent power performance, show remarkable long-term cycling stability and, by virtue of their excellent mechanical properties, allow for further increases in volumetric energy density by mechanical compression of the treated electrode. Our measured capacity is very close to the theoretical maximum obtained using detailed density functional theory calculations, suggesting nearly all incorporated AQ is made available for charge storage.—Campbell et al.
Compared to traditional carbon-based supercapacitor electrodes fabricated from carbon black and binder materials, graphene aerogels offer many advantages such as control of density and pore size distribution, and increased conductivity due to carbon linkers between the active carbon sheets and the absence of binder materials.
Aerogels derived from carbon as well as inorganic materials were developed at LLNL and have found a number of applications—from capturing space dust to lining the inside of National Ignition Facility targets.
Graphene aerogels are a relatively new type of aerogel that are ideal for energy storage applications because of their extremely high surface area, excellent mechanical properties and very high electrical conductivity. We have been exploring various ways to enhance their energy storage properties such as increasing electrode density through mechanical compression. The non-covalent modification strategy is simply another route to increase the electrical energy storage capacity.—Patrick Campbell
Other Livermore researchers involved in the project include Brandon Wood, Marcus Worsley and Ted Baumann.
The research was funded by the Department of Energy Office of Energy Efficiency and Renewable Energy and the LLNL Laboratory Directed Research and Development Program.
P. G. Campbell, M. D. Merrill, B. C. Wood, E. Montalvo, M. A. Worsley, T. F. Baumann and J. Biener (2014) “Battery/supercapacitor hybrid via non-covalent functionalization of graphene macro-assemblies,” J. Mater. Chem. A 2, 17764-17770 doi: 10.1039/C4TA03605K