In order to develop higher energy density lithium batteries, new anode materials must be investigated. A new detailed study of the electrochemical capabilities of silicon clathrates has found that they show minimal structural and volume changes after the insertion of lithium, in contrast to amorphous silicon (a-Si) and diamond cubic silicon (c-Si). This suggests that silicon clathrates may represent a promising option for lithium-ion battery anodes.

Polyhedral wire-frame representation of the type I clathrate framework.

Silicon clathrates represent a new potential anode material due to their high charge storage capacities, which are related to their cage-like structure. a-Si and c-Si are also attractive options for Li-ion batteries, but undergo large volume changes that can limit their applications. Though attempts have been made to solve this problem using nanostructured electrodes, a solution that allows silicon anodes to be used more widely is still being sought. Silicon clathrates exhibit a cage-like framework into which guest atoms can be inserted. Li et al. specifically investigate the electrochemical characteristics of type I clathrates – those based on M_xSi₄₆ where M represents the guest atoms.

The authors use barium guest atoms and doped with aluminium (forming Ba₈Al_ySi_46−y ) to prepare ternary type I silicon clathrates using three different preparation methods. Clathrates prepared using vacuum arc-melting showed the best electrochemical characteristics when compared to those prepared using thermal annealing and Ar arc-melting. Lithium was then electrochemically inserted into the clathrates. The results showed that the lithiation and delithiation processes occur in single phase, solid solution-type reactions, with no discernible associated structural or volume changes.