Tin, silicon, and a few other elements have long been languishing on chemists' list of electrode materials that could, in theory, help lithium-ion batteries hold more energy. A new way of structuring these materials could at last allow them to be used in this way.

Researchers at the Lawrence Berkeley National Laboratory made tin electrodes by using layers of graphene to protect the normally fragile tin. These first tin electrodes are a sign that materials scientists have made a great deal of progress in using nanoscale structures to improve batteries.

Making battery electrodes from tin or silicon can boost the battery's overall energy storage. That's because such materials can take in more lithium during charging and recharging than carbon, which is normally used. But silicon and tin tend to be unstable as electrodes. Tin takes up so much lithium that it expands in volume by a factor of two to three during charging. "This forms cracks, and the tin leaks into the electrolyte and is lost," says Yuegang Zhang, a scientist at Lawrence Berkeley.

Zhang's clever solution is to layer the tin between sheets of graphene, single-atom-thick sheets of carbon mesh. Graphene is highly conductive, and while it's flexible, it's also the strongest material ever tested.