Batteries and supercapacitors serve complementary roles in energy storage. Batteries have much a larger energy density, while supercapacitors have a longer lifespan and a quicker charge time. Many engineers use them together in applications like electric vehicles, where the batteries provide the distance and supercapacitors accept the rapid charge from regenerative braking and contribute a boost for quick acceleration. If supercaps could store more energy, they might replace batteries altogether. But a supercap big enough to hold a significant amount of energy would add too much material and weight to a product … unless the structure of the product was the supercap.
A Structural Supercapacitor
That’s what researchers at Vanderbilt University have envisioned with their newest invention: a structural supercapacitor. Professor Cary Pint and graduate student Andrew Westover have developed a supercapacitor made with silicon electrodes that have nanoscale pores, creating a large surface area on both sides of the supercap. A polymer between the electrodes serves as the electrolyte and also produces a strong mechanical bond between the sides. The nanoscale pores not only increase the plate size, which increases the capacitance, but they also allow the polymer to seep into the crevices and make a connection that’s stronger than super glue. Although silicon is costly to produce, the researchers believe that the same principles can be applied to other materials such as carbon nanotubes and aluminum.
Strength and Efficiency
When tested, the structural supercaps were strong enough to withstand 300 kPa of stress and over 80 g of acceleration while retaining their electrical capabilities. Here’s one supporting the weight of a laptop computer:
The supercaps have an energy density of about 10 Wh/kg, about one-tenth the energy density of a Li-ion battery and on par with many other supercaps. Lab testing showed a round-trip energy storage efficiency of 98%.
Applications
This device has obvious potential (no pun intended) in low voltage applications such as personal electronics. The researchers also envision PV panels, electric vehicles, and even building materials made of structural supercaps. I like the idea of integrating storage into PV panels, but I’m a little cautious about EV door panels and building materials holding large quantities of electrical energy. Something tells me that it wouldn’t get past the fire codes. Firefighters already have issues with PV panels on rooftops - imagine if the entire structure was one giant charged capacitor! With that said, I think that’s a problem that can be overcome with innovative safety procedures and devices.
So a question to the power engineers out there: how would you ensure electrical and fire safety in a building that’s literally made of a supercapacitor?
Images courtesy of Vanderbilt University