Because this advance, described online this week in Nature Materials, applies so far to negative electrodes, the percentage increase in capacity over today’s batteries will depend on the capacity of the positive electrode as well. (See “Battery Breakthrough” for a description of one possible positive electrode candidate cited by the researchers.) The first applications of the technology will likely be extremely small batteries, Simon says. These could be useful for remote sensors or medical implants. Further applications will require increasing the size of the electrodes that the researchers can make, and also optimizing the active material they use.
The materials used in reported experiments are not energy efficient – about 20-25 percent of the energy used to charge them cannot be recovered while discharging them. This energy loss is not a big problem with cell-phone batteries, says Gerbrand Ceder, materials science and engineering professor at MIT. “Over the lifetime you probably spend a few pennies in charging the cell phone,” he says. But for larger energy applications, such as electric vehicles, this lack of efficiency could be costly, especially with high electricity prices. For this reason, the researchers are incorporating different high-capacity active materials into their nanostructured electrodes that do not have this energy efficiency problem.
In turning to nanotechnology to improve batteries, the French researchers are not unique. At least two companies, A123 Systems, in Watertown, MA, and Altair Nano, in Reno, NV, have made batteries that include electrodes with nanostructured active materials; and numerous research groups around the world are developing such electrodes. Simon describes his group’s process as being simpler and cheaper than many other methods for making nanostructures. It is also versatile, capable of being used with a variety of active materials, he says.
It could also be important for another key trend in battery research: the move away from flat layers of electrode materials to positive and negative electrodes that interpenetrate – a three-dimensional architecture that can improve the mobility of ions and electrodes, thereby increasing battery power. The French group is also now working on a three-dimensional battery, says Simon, that will combine their negative electrodes with a high-performance positive electrode.