In the exciting search for efficient electrode materials for Na-ion batteries, some p-block elements were found to be viable alternatives to hard carbon, showing interesting performance with reversible capacities exceeding 400 mAh/g. Among them, Sb seems to have a specific affinity for Na, showing excellent cycling stability even in the simplest form of bulk Sb powder despite a huge volume expansion during the alloying process. The reason of this affinity has not been totally understood yet: while the electrochemical signature suggests the formation of several possible intermediates, the Na-Sb phase diagram indicates the existence of only one phase between the end member species formed during cycling, Sb and Na3Sb. Moreover, such intermediates are amorphous and thus totally indistinguishable by X-ray diffraction (XRD). Recently, we have studied the mechanism by Pair Distribution Function (PDF) analysis of synchrotron XRD data, and proposed possible short-range structures and compositions for the intermediates formed with pure Sb. In parallel, we have studied the performance and the role of the second metal in the binary antimonides FeSb2 and SnSb. With the goal of better understanding this specific affinity of Na for Sb, we have very recently undertaken a thorough study of the electrochemical reaction of Sb, FeSb2 and SnSb with Na by operando X-ray absorption spectroscopy (XAS). Sb and Sn K-edge XAS data were analysed using adapted chemometric tools (Principal Component Analysis and Multivariate Curve Resolution) in order to extract all information on the mechanisms of three compounds. The results of this analysis show that, while it is possible to gather important information for the reconstruction of the reaction paths, it is intrinsically impossible to prove by XAS the formation of some of the intermediates proposed in the case of Sb.

Reaction mechanism of Sb-based negative electrode materials for Na batteries investigated by operando x-ray absorption spectroscopy: What can we really learn?

253rd National Meeting (2017)

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