Capacitor dielectric material made from sol-gel and fatty acid, offers very high energy storage


While MIT’s tiny nanowire-based supercapacitor might be tailored to smartwatches, researchers from School of Chemistry and Biochemistry (at the Georgia Institute of Technology) have devised their own version of an advanced capacitor dielectric material. Created from silica sol-gel and self-assembled layers of a common fatty acid, this new material is touted to have an impressive energy storage capacity that equals some varieties battery system. In essence, the material has the rare advantages of both high energy density and high power density – and thus can be developed as a potential alternative to conventional electrolytic capacitors.

In terms of composition, the capacitor consists of a thin film of sol-gel (with polarized silicon atoms) and self-assembled monolayer (in nanoscale) of octylphosphonic acid. This bi-layer formation shields the sol-gel material from intrusion of electrons, thus accounting for low leakage of current while maintaining the efficiency in high energy extraction. Interestingly, the hybrid sol-gel capacitor material in itself has quite a high energy density, but was also found have the tendency to leak current. This predicament was solved by depositing a nanoscale self-assembled monolayer of n-octylphosphonic acid – which credibly acted as the insulating layer. As Joseph Perry, a professor from School of Chemistry and Biochemistry, made it clear –

Our silica sol-gel is a hybrid material because it has polar organic groups attached to the silica framework that gives the sol-gel a high dielectric constant, and in our bilayer dielectric, the n-octylphosphonic acid groups are inserted between the sol-gel layer and the top aluminum layer to block charge injection into the sol-gel. It’s really a bilayer hybrid material that takes the best of both reorientation polarization and approaches for reducing injection and improving energy extraction.

Now, when translated to pure figures, the new capacitor dielectric material accounts for maximum energy densities of up to 40 joules per cubic cm; an energy extraction efficiency of 72 percent (at 830 volts per micron); and a power density of 520 watts per cubic cm. It should be noted that while these numbers do not exceed that of lithium ion batteries used in electric vehicles and gizmos, they surely cross the threshold of common electrolytic capacitors (and even thin-film Li-ion batteries). In other words, they can potentially complement the existing battery systems – with their advantage of quick ‘bursts’ of energy provision, when needed.

Lastly, in terms of practicality, the scientists are looking forward to scale up the materials for their application on larger devices. And quite intriguingly, if this crucial phase is successful, the capacitor can even be commercially mass-produced through a startup company or SBIR project.


The study was originally published in the Advanced Energy Materials.

Source: GATech / Featured Image Credit: John Toon, Georgia Tech

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