In this talk, I will summarize the results from recent structural studies and the electrochemical properties of a series of clathrates with nominal compositions Ba8AlxSi46–x and Ba8AlxGe46–x (x = 0, 4, 8, 12, 16). All samples were prepared by arc-melting and structurally characterized by single-crystal X-ray diffraction (XRD). The structural refinements indicate the presence of vacancies at the Wyckoff 6c site of the clathrate framework as the Al content decreases (Figure). Ball-milling is found to cause significant amorphization, more so in the Ge than in the Si clathrates, suggesting that the Ge framework is less structurally stable. From electrochemical, XRD, and transmission electron microscopy analysis, it can be deduced that all of the Ge-based clathrate compositions undergo two-phase reactions to form Li-rich amorphous phases. In distinct contrast, different behavior observed in the Si-based clathrate analogues, where there is no amorphous phase transition during electrochemical lithiation. A composition dependence on the electrochemical properties is observed in the Ge clathrates, with the capacity and lithiation voltage decreasing as the degree of Al substitution increases. The latter results are suggestive of framework vacancies as potential sites for Li insertion, in addition to the cages within the open-framework-like structures, making these type-I clathrates potentially interesting anodes for lithium-ion batteries.

Experimental study of the lithiation of Si- and Ge-based type-I clathrates

2019 Spring National Meeting

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