Battery life is becoming an increasingly important issue for mobile computing users. With screens getting larger and brighter and laptop CPUs getting more powerful, the strains on batteries have continued to increase, and the technology just isn't keeping pace. Five years ago, my iBook routinely got five hours from a single charge, yet new laptops struggle to achieve the same results. Some alternatives, such as fuel cells, look promising, but size and weight issues continue to limit their potential.
However, help may be at hand. Researchers at the Massachusetts Institute of Technology have been working on (PDF file) an interesting new way of extending battery life. Their technique uses a device called an "ultracapacitor," which, unlike the time-traveling flux capacitor, actually exists as a product:
"A number of electronic devices already use commercial ultracapacitors for specialized functions," said Joel Schindall, a professor in MIT's Department of Electrical Engineering and Computer Science, in Cambridge, Massachusetts.
"For example, a clock radio may use an ultracapacitor as a keep-alive source in case of power failure, and even the old Palm III used an ultracapacitor to retain its memory while the AA batteries were changed."
A capacitor is, at its most basic level, a device for storing electrical charge. Two large, flat, metal plates are positioned a tiny distance apart from each other with a non-conducting material sandwiched in the middle. An electrical charge is applied to each end. The electrons accumulate on one plate, building up a large negative charge, while an equivalent positive charge appears on the other plate. The capacitor can later discharge this energy if needed. The amount of charge that can be stored varies with the surface area of the plates, which is why large capacitors roll up the plates into large tubes to pack more area in a smaller volume. Ultracapacitors are industrial-strength versions of capacitors, but physical constraints on electrode surface area and spacing have limited ultracapacitors to an energy storage capacity around 25 times less than a similarly sized Lithium-Ion battery.
The innovation at MIT is to use nanotechnology to increase the surface area of the plates much further. They attach millions of nanotubes, which are tiny synthesized "straws" comprised of a lattice of carbon atoms, to the capacitor plates. This increases the capacitance by a large amount, which offers huge potential increases in battery life:
"This configuration has the potential to maintain and even improve the high performance characteristics of ultracapacitors while providing energy storage densities comparable to batteries," Schindall said. "Nanotube-enhanced ultracapacitors would combine the long life and high power characteristics of a commercial ultracapacitor with the higher energy storage density normally available only from a chemical battery."
The nano-enhanced ultracapacitors are still three to five years from being ready for release in commercial products. Until these products get closer to release, there is no firm data about what kind of battery life increases can be expected, but Schindall hopes to achieve a power density of up to 100 kW/kg, which is three orders of magnitude greater than conventional Lithium-Ion batteries. The ultracapacitors also aim to achieve an energy density of 60 Wh/kg.