TY - JOUR
T1 - Experimental and Computational Study of the Lithiation of Ba 8 Al y Ge 46- y Based Type i Germanium Clathrates
AU - Dopilka, Andrew
AU - Zhao, Ran
AU - Weller, J. Mark
AU - Bobev, Svilen
AU - Peng, Xihong
AU - Chan, Candace K.
N1 - Publisher Copyright:
© 2018 American Chemical Society.
PY - 2018/11/7
Y1 - 2018/11/7
N2 - In this work, we investigate the electrochemical properties of Ba 8 Al y Ge 46-y (y = 0, 4, 8, 12, 16) clathrates prepared by arc-melting. These materials have cage-like structures with large cavity volumes and can also have vacancies on the Ge framework sites, features which may be used to accommodate Li. Herein, a structural, electrochemical, and theoretical investigation is performed to explore these materials as anodes in Li-ion batteries, including analysis of the effect of the Al content and framework vacancies on the observed electrochemical properties. Single-crystal X-ray diffraction (XRD) studies indicate the presence of vacancies at the 6c site of the clathrate framework as the Al content decreases, and the lithiation potentials and capacities are observed to decrease as the degree of Al substitution increases. From XRD, electrochemical, and transmission electron microscopy analysis, we find that all of the clathrate compositions undergo two-phase reactions to form Li-rich amorphous phases. This is different from the behavior observed in Si clathrate analogues, where there is no amorphous phase transition during electrochemical lithiation nor discernible changes to the lattice constant of the bulk structure. From density functional theory calculations, we find that Li insertion into the three framework vacancies in Ba 8 Ge 43 is energetically favorable, with a calculated lithiation voltage of 0.77 V versus Li/Li + . However, the calculated energy barrier for Li diffusion between vacancies and around Ba guest atoms is at least 1.6 eV, which is too high for significant room-temperature diffusion. These results show that framework vacancies in the Ge clathrate structure are unlikely to significantly contribute to lithiation processes unless the Ba guest atoms are absent, but suggest that guest atom vacancies could open diffusion paths for Li, allowing for empty framework positions to be occupied.
AB - In this work, we investigate the electrochemical properties of Ba 8 Al y Ge 46-y (y = 0, 4, 8, 12, 16) clathrates prepared by arc-melting. These materials have cage-like structures with large cavity volumes and can also have vacancies on the Ge framework sites, features which may be used to accommodate Li. Herein, a structural, electrochemical, and theoretical investigation is performed to explore these materials as anodes in Li-ion batteries, including analysis of the effect of the Al content and framework vacancies on the observed electrochemical properties. Single-crystal X-ray diffraction (XRD) studies indicate the presence of vacancies at the 6c site of the clathrate framework as the Al content decreases, and the lithiation potentials and capacities are observed to decrease as the degree of Al substitution increases. From XRD, electrochemical, and transmission electron microscopy analysis, we find that all of the clathrate compositions undergo two-phase reactions to form Li-rich amorphous phases. This is different from the behavior observed in Si clathrate analogues, where there is no amorphous phase transition during electrochemical lithiation nor discernible changes to the lattice constant of the bulk structure. From density functional theory calculations, we find that Li insertion into the three framework vacancies in Ba 8 Ge 43 is energetically favorable, with a calculated lithiation voltage of 0.77 V versus Li/Li + . However, the calculated energy barrier for Li diffusion between vacancies and around Ba guest atoms is at least 1.6 eV, which is too high for significant room-temperature diffusion. These results show that framework vacancies in the Ge clathrate structure are unlikely to significantly contribute to lithiation processes unless the Ba guest atoms are absent, but suggest that guest atom vacancies could open diffusion paths for Li, allowing for empty framework positions to be occupied.
KW - anode
KW - clathrate
KW - energy storage
KW - germanium
KW - lithium-ion batteries
UR - http://www.scopus.com/inward/record.url?scp=85056091666&partnerID=8YFLogxK
U2 - 10.1021/acsami.8b11509
DO - 10.1021/acsami.8b11509
M3 - Article
C2 - 30360052
AN - SCOPUS:85056091666
SN - 1944-8244
VL - 10
SP - 37981
EP - 37993
JO - ACS Applied Materials and Interfaces
JF - ACS Applied Materials and Interfaces
IS - 44
ER -