Electrochemically-driven solid-state amorphization in lithium-silicon alloys and implications for lithium storage

Lithiated metal alloys such as Li-Si are of great interest as high energy density anodes for future rechargeable battery technology. We show that the mechanism of electrochemical alloying is electrochemically-driven solid-state amorphization, a process closely analogous to the diffusive solid-state amorphization of thin films. X-ray diffraction and HREM experiments reveal that the crystallization of equilibrium intermetallic compounds is circumvented during lithiation at room temperature, and that formation of highly lithiated Li-Si glass instead occurs. This glass is shown to be metastable with respect to the equilibrium crystalline phases. Similar behavior is observed in the diffusive reaction of Li and Si bilayer films, suggesting that lithium-metal alloys in general are likely candidates for solid-state amorphization.