About the cover

March 2014 Volume 9 No 3

Silicon anodes have been actively researched for applications in lithium batteries because they have ten times the theoretical capacity of their carbon-based counterpart. Unfortunately nanostructured silicon anodes have challenging drawbacks, such as a large volume change during cycling, side reactions with the electrolyte and low volumetric capacity. Yi Cui and colleagues now show that these problems can be alleviated by using a hierarchically structured silicon anode whose design was inspired by a pomegranate. Silicon nanoparticles are first enclosed within a carbon shell, which allows them to freely expand and contract during cycling. These silicon-containing shells are then grouped together and surrounded by a thicker outer carbon layer that protects them from the electrolyte, yet lithium exchange with the solution phase still occurs. The cover is an artist's impression of these hierarchical structures.

Letter p187