Improving Ultracapacitors with a Nanoscopic Hairbrush

FastCAP states that its ultracapacitors improve upon commercial competitors by a factor of ten and work even in extreme heat and cold. (Image courtesy of FastCAP Systems).

Ultracapacitors, the jacked up big brothers of standard capacitors, are an appealing form of energy storage. And for good reason: they recharge in seconds, have near 100 percent efficiency with high longevity and are both lighter and less volatile than conventional batteries.

But of course, they’re not without their drawbacks. They have low energy-storage capacity, and even then some of their stored energy is unavailable for use. That’s why you’ll find ultracapacitors in the decidedly less-than-ultra position of backup power for things like electric cars and consumer devices.

Enter FastCAP Systems, an MIT spinoff working to develop improved ultracapacitors and ultracapacitor-based systems. The company has reported a number of recent advancements in ultracapacitor technology, including greater energy density and temperature operation range, opening the door to applications across a wide range of industries.

A Nanoscopic Hairbrush

Ultracapacitors are made up of two polarized electrodes, one positive and the other negative, that are usually coated with a porous material called activated carbon. In between is an electrolyte with positive and negative ions. The ions are attracted to the electrodes and form electric layers (called Helmholtz double layers) that effectively act as two capacitors in series.

(Image courtesy of FastCAP Systems.)

The energy storage capacity of an ultracapacitor is limited by the surface area of its electrodes. FastCAP’s breakthrough was in finding a way to increase this surface area using a tightly packed array of carbon nanotubes protruding vertically from the electrode. This also proved to be much more uniform than the porous structure of activated carbon, providing ions more efficient access to the electrode surface.

“A way to look at it is the industry standard looks like a nanoscopic sponge, and the vertically aligned nanotube array looks like a nanoscopic hairbrush,” explained John Cooley, president and CTO of FastCAP.

Ultracapacitor Applications

According to Cooley, FastCAP’s hairbrush-style ultracapacitors can store up to 10 times as much energy and achieve 10 times the power density of sponge-style ultracapacitors. What’s more, they can withstand extreme temperatures ranging from -110°C to 300°C.

These properties have put FastCAP on the radars of big players across several industries. The company has received grants from the U.S. Department of Energy and NASA, funding from the Ford-MIT Alliance and equity firm Energy Ventures and a deal with electric vehicle manufacturer Mullen Technologies.

The ultracapacitors have potential in several markets including:

Oil & Gas (for their use in harsh environments with the added benefit that they pose no risk of explosion if damaged)
Aerospace and Defense (for deep space missions, planetary balloons and miniature satellites called CubeSats)
Electric and hybrid vehicles (high power capabilities for stop-start and engine starting, torque assist and augmented battery life).

While FastCAP has already made inroads into some of these markets (specifically, oil and gas), the company is still in the process of making its mark on the rest. “In our long-term product market, we hope that we can make an impact on transportation, for increased energy efficiency,” said Cooley.

In light of this initial success, it looks like the company may do just that.

For more advancements in battery technology, read about improving the life and performance of fuel cell electrodes.