Lithium intercalation behavior in multilayer silicon electrodes

Next generation lithium battery materials will require a fundamental shift from those based on intercalation to elements or compounds that alloy directly with lithium. Intermetallics, for instance, can electrochemically alloy to Li_4.4M (M = Si, Ge, Sn, etc.), providing order-of-magnitude increases in energy density. Unlike the stable crystal structure of intercalation materials, intermetallic-based electrodes undergo dramatic volume changes that rapidly degrade the performance of the battery. Here, the energy density of silicon is combined with the structural reversibility of an intercalation material using a silicon/metal-silicide multilayer. In operando X-ray reflectivity confirms the multilayer's structural reversibility during lithium insertion and extraction, despite an overall 3.3-fold vertical expansion. The multilayer electrodes also show enhanced long-term cyclability and rate capabilities relative to a comparable silicon thin film electrode. This intercalation behavior found by dimensionally constraining silicon's lithiation promises applicability to a wide range of conversion reactions.