March 23, 2009 It has been a big week for news on advances in energy storage technology. We recently reported on new research that makes a Lithium Ion battery perform more like a supercapacitor, now we can report on research on a supercapacitor that performs more like a battery. Researchers at the University of Maryland and the Korea Advanced Institute of Science and Technology have developed a supercapacitor with 10 billion nanoscale capacitors per square centimeter, giving it 250 times greater surface area than that of a conventional capacitor of comparable size. The Nano Supercapacitor is being developed primarily as part of a hybrid battery-capacitor system for electric cars.
Batteries, particularly lithium-ion, store large amounts of energy but have more difficulty with high power or fast recharge. Capacitors, on the other hand, can be charged or discharged at a very high rate. Existing supercapacitors have an energy densities around 1/10th that of a conventional battery, but their power density is generally ten to one-hundred times as great
The Maryland/KAIST research team’s new devices are electrostatic nanocapacitors which increase the energy storage density of such devices by a factor of 100 over that of commercially available devices without sacrificing the high power they traditionally characteristically offer. Current commercial supercapacitors range from 0.5 to 30 Wh/kg, while the research is in its early stages, if they reach their claim of a 100 increase that will result in 3,000 Wh/kg. For comparison, a conventional lead-acid battery is typically 30 to 40 Wh/kg and modern lithium-ion batteries are about 160 Wh/kg. In automobile applications gasoline contains around 12,000 wh/kg, which operates at 15% tank-to-wheel efficiency giving an effective energy density of 1800 Wh/kg
Using Atomic fabrication techniques the process starts with a sheet of aluminum foil that is anodized to form a regularly spaced array of nanopores across its surface. Each nanopore as small as 50 nanometers in diameter and up to 30 micrometers deep. Next a sandwich of two layers of titanium nitride (TiN) metal separated by an insulation layer are deposited using Atomic layer deposition into the pores topped with another layer of aluminum foil. The two outer foil layers act as the electrical contacts.
The researchers have made a prototype with 125-micrometer-wide arrays, each containing one million nanocapacitors. There are many scale-up issues as they want to make a large area that contains billions of nanocapacitors to store large amounts of energy and they have to make sure that they can effectively connect multiple arrays to one another. The team are still deciding how best to commercialize this. The hybrid battery-capacitor system for electric cars would contain multiple energy storage panels stacked together inside a car battery system. The energy storage panels could also be integrated into solar panels and the flat panel displays seen in most portable devices.
Paul Evans
Via: Maryland Nanocenter.