Researchers in France have created lithium-ion battery electrodes with several times the energy capacity, by weight and volume, of conventional electrodes. The new electrodes could help shrink the size of cell-phone and laptop batteries, or else increase the length of time a device could run on a charge. What’s more, the nanotech methods used to make these electrodes could provide a simple and inexpensive way to structure new materials for next-generation batteries for plug-in hybrid and all-electric vehicles.
The key advance is the development of an inexpensive and simple way to organize tiny particles into a desired nanostructure, says Patrice Simon, a chemistry professor at the Université Paul Sabatier, who participated in the work along with other researchers at the university and Université Picardie Jules Verne.
In a conventional battery electrode, ions and electrons will move quickly into and out of the active material – allowing fast charging and discharging – only if the material is deposited in a very thin film. Thin films, however, limit the amount of active material that can be incorporated into a battery. For high-capacity batteries, engineers typically increase the thickness of the active material, trading off fast charging and high-power bursts for more energy storage.
This new nanostructure allows for both high power and high storage capacity. Active materials are applied in a very thin film to copper nanorods anchored to sheets of copper foil. This thin film allows for fast movement of ions and electrons – providing the power. At the same time, the high surface area of the forest of nanorods makes it possible to pack much more active material into an electrode than thin films typically allow, thus increasing energy capacity. The rods provide 50 square centimeters of surface area for every square centimeter of electrode.
In addition, the high ion and electron mobility of the thin layer makes it possible to use a new active material and a new chemical reaction for lithium-ion batteries. This new chemistry is attractive because it can accommodate far more lithium ions, and their electron counterparts, than the chemistry used now, thereby potentially storing more energy.
The new electrodes, which would be used as the negative electrodes in lithium-ion batteries, also showed the ability to retain their high capacity after being charged and discharged many times, suggesting that the electrodes may have a long useable lifetime, Simon says, although more extensive tests are needed to confirm this supposition.