How well a battery works isn’t just about how much energy it can store. Among other factors, how fast the battery can deliver its stored energy is particularly important for electric cars and other high-power applications. (See the article by Héctor Abruña, Yasuyuki Kiya, and Jay Henderson, Physics Today, December 2008, page 43.) In lithium-ion batteries those measures depend on how many, and how quickly, Li+ ions can be inserted into and extracted from the anodes and cathodes.
A lithium-ion battery’s electrochemically active components are the two electrodes—typically graphite for anodes and a Li metal oxide for cathodes—and the electrolyte layer in between. Standard electrodes consist of densely packed micrometer-sized particles and a labyrinthine network of electrolyte-filled pores.
In a charged battery, Li atoms reside in the spaces between graphite’s hexagonal layers. As the battery pushes electrons through an external circuit to do work, Li+ ions...
