Crumpled sheets of graphene (one-atom-thick carbon) could one day offer a solution for storing energy in your electric car. A Dayton, Ohio-based company, Nanotek Instruments, has recently revealed their vision about making ultracapacitors, for the moment only used in hybrid buses, suited for electric cars and how to replace the classic batteries.
I don’t think it makes much sense talking about how ultracapacitors are basically better than batteries. Well, they’re cheaper, much lighter, have a charge time in the range of seconds, and a much longer lifetime. Batteries, on the other hand, are expensive, heavy, charge within hours and last for only a few years, at best.
Oh, and ultracapacitors discharge fast, providing huge amounts of energy almost instantly. That’s why they’re used in accelerating buses.
The difference between ultracapacitors and batteries is that the first store their energy in an electrostatic field, and the second use chemical reactions, often toxic to the environment and damaging for the battery itself.
The researchers from Nanotek made graphene electrodes that they mounted inside coin-sized ultracapacitors and that gave them five times the energy density commercial ultracapacitors had so far (5 to 10 watt-hours per kilogram).
The electrodes are made from sheets of carbon crumpled just like sheets of paper. The researchers found a way so the sheets don’t stack up face-to-face to reduce their surface volume, like they do in today’s ultracapacitors.
Nanotek developed their graphene electrodes to store 85.6 watt-hours/kg, but they lose 10 percent of their potential after some 500 charge/discharge cycles. Another company, Graphene Energy, has developed a similar product but with an endurance of some 10,000 cycles – now we’re talking. This is somewhere in the range of lead acid batteries, but still far off lithium ion batteries, with over 120 Wh/kg.
Joe Schindall, an MIT electrical engineering and computer science professor thinks that a battery with 20 percent of the energy density of a lithium ion, but which has a fast charge/discharge time and a way longer lifespan can actually compete with batteries in some cases, given most of the time batteries will be operated at 20 to 50 percent of their total charge capacity.
So batteries might not be the final solution for our cars, after all. Seeing how the ultracapacitor technology evolves, in a few years we’ll have super-fast charging times with dozens of advantages batteries don’t have.
[via technologyreview]
