Building a Better Battery

Controlling the charge-induced morphological changes of electrode materials may provide a route to improved battery performance. Innovations in the battery field are infrequent and hard-won. New electrochemical systems (a new positive or negative electrode, electrolyte, or combination thereof) reach the marketplace only once every few years, and the energy density of lithium-ion batteries as a class has increased on average by only 8 to 9% per year since the early 1990s. Thus, in the burgeoning field of nanoscale electrode materials, skepticism regarding new claims is perhaps not surprising because of the many requirements that any battery electrode must simultaneously meet to be commercialized. One route by which battery performance can be compromised is by mechanical failure due to the large volume changes associated with the charge-discharge cycle. On page 1515 of this issue, Huang et al. (1) report an ingenious in situ transmission electron microscope (TEM) experiment that uses a low–vapor pressure ionic liquid electrolyte to allow imaging of a SnO2 nanowire electrode in an “open” electrochemical cell. They observe a reaction mechanism in the SnO2 nanowires that progresses sequentially along the nanowire from end to end, allowing them to accommodate a ∼250% volume change without fracturing and at practical charging rates. These intriguing results raise the question of whether such one-dimensional phase transformations can be induced in other materials.