Claire Villevieille, head of PSI’s battery materials research group, said that, while most researchers concentrate on the development of new materials, the team took a different approach. “We checked existing components with a view to fully exploiting their potential.” By optimising the graphite anode on a conventional Li-ion battery, researchers boosted battery performance.
“Under laboratory conditions,” she said, “we were able to enhance storage capacity by a factor of up to three. Owing to their complex construction, commercial batteries will not be able to fully replicate these results, but performance will definitely be enhanced – perhaps by as much as 50% – and further experiments should yield more accurate prognoses.”
Changing the way in which anodes work was said to be the key to success. Anodes are made from densely packed graphite flakes. When the battery is in use, lithium ions pass back to the cathode but are forced to take many detours through the densely packed mass and this compromises battery performance, says the team. These detours can be avoided if graphite flakes are arranged vertically and point in the direction of the cathode.
Adapting a method used in the production of synthetic composite materials, this alignment was achieved by an ETH team led by André Studart. The method involves coating the graphite flakes with nanoparticles of iron oxide sensitive to a magnetic field and suspending them in ethanol. The suspended flakes – already magnetised – are subsequently aligned using a magnetic field of 100mT.
If the field remains turned on during the drying process, the platelets keep their new orientation, enabling the lithium ions to flow more readily. Storage capacity is also increased, says the team, by allowing more ions to ‘dock’ during the charging process.
