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High Energy Density Ultracapacitors

FastCAP Systems
ARPA-E Award: 
Boston, MA
Project Term: 
04/01/2010 to 12/31/2013
Project Status: 
Technical Categories: 
Graphic of FastCAP's technology
Critical Need: 

Battery-related challenges are preventing the widespread use of hybrid electric vehicles (HEVs) and electric vehicles (EVs). HEVs and EVs are propelled by an electric motor that is powered by rechargeable battery packs. These battery packs have energy-storage problems that prevent HEVs and EVs from being able to travel as far as gasoline-powered vehicles, and they also take a long time to recharge. There is a critical need to find more effective ways to power HEVs and EVs. Improvements in capacitors--electronic devices that help store electricity and move it from the battery pack to the electric motor--have the potential to significantly improve the performance of these vehicles.

Project Innovation + Advantages: 

FastCAP Systems is improving the performance of an ultracapacitor--a battery-like electronic device that can complement, and possibly even replace, an HEV or EV battery pack. Ultracapacitors have many advantages over conventional batteries, including long lifespans (over 1 million cycles, as compared to 10,000 for conventional batteries) and better durability. Ultracapacitors also charge more quickly than conventional batteries, and they release energy more quickly. However, ultracapacitors have fallen short of batteries in one key metric: energy density--high energy density means more energy storage. FastCAP is redesigning the ultracapacitor's internal structure to increase its energy density. Ultracapacitors traditionally use electrodes made of irregularly shaped, porous carbon. FastCAP's ultracapacitors are made of tiny, aligned carbon nanotubes. The nanotubes provide a regular path for ions moving in and out of the ultracapacitor's electrode, increasing the overall efficiency and energy density of the device.

Potential Impact: 

If successful, FastCAP's ultracapacitors would reduce the cost and improve the performance of HEVs and EVs, facilitating their widespread use.


Increased use of HEVs and EVs would decrease U.S. reliance on foreign sources of fossil fuels.


Increased use of HEVs and EVs would decrease harmful greenhouse gas emissions from gasoline-based vehicles.


Making it cheaper and easier to charge HEVs and EVs would save consumers time and money.

Innovation Update: 

(As of August 2016)
FastCap Systems has developed a line of supercapacitors designed to enable the use of safer, lower power batteries while providing the requisite energy and power to drive electric actuators—with the added benefits of extending battery runtime and reducing operating costs. FastCap’s supercaps have been successfully commercialized for down-hole drilling operation in the oil and gas industry. The company has also developed supercaps for space and geothermal applications, the former funded by NASA.

The energy that ultracapacitor devices can store is proportional to the electrode surface area. FastCap designed an electrode comprised of carbon nanotubes, providing considerable surface area, which, in turn, translates to a higher energy density. FastCap’s composite electrode consists of purified amorphous carbon and 5-10% of carbon nanotubes, and a supercap using this carbon nanotube composite electrode shows 3 times the performance relative to one using a bare carbon electrode.

For a detailed assessment of the FastCap team's project and impact, please click here.

ARPA-E Program Director: 
Dr. Timothy Heidel
Project Contact: 
Dr. Riccardo Signorelli
Massachusetts Institute of Technology
Release Date: