Ternary Type I Silicon Clathrates for Lithium-Ion Battery Anodes

Silicon clathrates contain cage-like structures that can encapsulate various guest atoms or molecules. Here we present an electrochemical evaluation of type I silicon clathrates based on Ba₈Al_ySi_46-y as the anode material for lithium-ion batteries. Post-cycling characterization with NMR and XRD show no discernible structural or volume changes even after electrochemical insertion of 44 Li (~1 Li/Si) into the clathrate structure. The observed properties are in stark contrast with lithiation of other silicon anodes, which become amorphous and suffer from large volume changes. The electrochemical reactions are proposed to occur as single phase reactions at approximately 0.2 and 0.4 V vs. Li/Li⁺ during lithiation and delithiation, respectively, distinct from diamond cubic or amorphous silicon anodes. Reversible capacities as high as 499 mAh g^-1 at a 5 mA g^-1 rate were observed for silicon clathrate with composition Ba₈Al_8.54Si_37.46, corresponding to ~1.18 Li/Si. These results show that silicon clathrates could be promising durable anodes for lithium-ion batteries. Changing the composition of the clathrate, namely replacing the Ba guest atom and Al framework substitution with other metals, was found to have a strong effect on the number of Li reversible inserted into the structure. The cycling performance of the clathrate electrodes in different liquid and solid electrolytes will also be presented.

Reference:

Y. Li, R. Raghavan, N.A. Wagner, S.K. Davidowski, L. Baggetto, R. Zhao, Q. Cheng, J.L. Yarger, G.M. Veith, C. Ellis-Terrell, M.A. Miller, K.S. Chan, C.K. Chan, Advanced Science, DOI: 0.1002/advs.201500057, (2015).