Nanostructures improve lithium-ion batteries

Li-ion batteries are currently seen as the best candidates for use in vehicles or for stationary energy storage. But even the most modern battery with a weight of around 100 kilograms would only give an electric car a range of around 100 kilometres, while long charging times and aging features are problematical. We are working on new materials to substantially increase the energy density of such Li-ion batteries,” explains Dr. Sylvio Indris, Young Investigators Group Leader at the Institute of Nanotechnology, Karlsruhe Institute of Technology.

Indris and his team are studying ceramic materials for this, such as oxides and chalcogenides, which they have provided with three-dimensional nanostructures. “We are working with crystallites of 4 to 50 nanometres, but are also studying structures made of hollow spheres of 14 nanometres diameter and 3 nanometres wall thickness,” says Indris. Electrodes made of such structured materials can absorb much more lithium than conventional electrodes made of graphite or cobalt oxides and store much more energy. Charging is also quicker. “To charge and discharge the battery, lithium constantly has to be inserted into or extracted from the electrodes.

These composite materials can be fitted quickly and so accelerate the charging process,” explains Indris. Using methods like X-ray scattering and nuclear spin resonance spectroscopy, the researchers headed by Indris are studying how the structures in the electrodes change and how various materials for electrodes and electrolytes act during battery operation. In so doing, they try out lots of different concepts, ranging from ultra stable solid state batteries made of vapour deposited components through to batteries where the electrodes are printed on paper. “We need batteries for all different kinds of applications and so have to pursue various approaches,” says Indris.