title: Tracking Sodium-Antimonide Phase Transformations in Sodium-Ion Anodes: Insights from Operando Pair Distribution Function Analysis and Solid-State NMR Spectroscopy.
abstract: Operando pair distribution function (PDF) analysis and ex situ (23)Na magic-angle spinning solid-state nuclear magnetic resonance (MAS ssNMR) spectroscopy are used to gain insight into the alloying mechanism of high-capacity antimony anodes for sodium-ion batteries. Subtraction of the PDF of crystalline NaxSb phases from the total PDF, an approach constrained by chemical phase information gained from (23)Na ssNMR in reference to relevant model compounds, identifies two previously uncharacterized intermediate species formed electrochemically; a-Na(3-x)Sb (x ≈ 0.4-0.5), a structure locally similar to crystalline Na3Sb (c-Na3Sb) but with significant numbers of sodium vacancies and a limited correlation length, and a-Na(1.7)Sb, a highly amorphous structure featuring some Sb-Sb bonding. The first sodiation breaks down the crystalline antimony to form first a-Na(3-x)Sb and, finally, crystalline Na3Sb. Desodiation results in the formation of an electrode formed of a composite of crystalline and amorphous antimony networks. We link the different reactivity of these networks to a series of sequential sodiation reactions manifesting as a cascade of processes observed in the electrochemical profile of subsequent cycles. The amorphous network reacts at higher voltages reforming a-Na(1.7)Sb, then a-Na(3-x)Sb, whereas lower potentials are required for the sodiation of crystalline antimony, which reacts to form a-Na(3-x)Sb without the formation of a-Na(1.7)Sb. a-Na(3-x)Sb is converted to crystalline Na3Sb at the end of the second discharge. We find no evidence of formation of NaSb. Variable temperature (23)Na NMR experiments reveal significant sodium mobility within c-Na3Sb; this is a possible contributing factor to the excellent rate performance of Sb anodes.
authors.affiliation: University of Cambridge , University Chemical Laboratory, Lensfield Road, Cambridge, CB2 1EW, U.K.|Gonville and Caius College , Trinity Street, Cambridge, CB2 1TA, U.K.
authors.forename: Phoebe K
authors.initials: PK
authors.lastname: Allan
authors.affiliation: University of Cambridge , University Chemical Laboratory, Lensfield Road, Cambridge, CB2 1EW, U.K.
authors.forename: John M
authors.initials: JM
authors.lastname: Griffin
authors.affiliation: Institut Charles Gerhardt Montpellier-UMR 5253 CNRS, ALISTORE European Research Institute (3104 CNRS) , Université Montpellier 2, 34095, Montpellier, France.|Réseau sur le Stockage Electrochimique de l'Energie (RS2E) , FR CNRS 3459, 80039 Amiens Cedex, France.
authors.forename: Ali
authors.initials: A
authors.lastname: Darwiche
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory , Lemont, Illinois 60439, United States.
authors.forename: Olaf J
authors.initials: OJ
authors.lastname: Borkiewicz
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory , Lemont, Illinois 60439, United States.
authors.forename: Kamila M
authors.initials: KM
authors.lastname: Wiaderek
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory , Lemont, Illinois 60439, United States.
authors.forename: Karena W
authors.initials: KW
authors.lastname: Chapman
authors.affiliation: Theory of Condensed Matter Group, Cavendish Laboratory, University of Cambridge , J. J. Thomson Avenue, Cambridge CB3 0HE, U.K.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Morris
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory , Lemont, Illinois 60439, United States.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Chupas
authors.affiliation: Institut Charles Gerhardt Montpellier-UMR 5253 CNRS, ALISTORE European Research Institute (3104 CNRS) , Université Montpellier 2, 34095, Montpellier, France.|Réseau sur le Stockage Electrochimique de l'Energie (RS2E) , FR CNRS 3459, 80039 Amiens Cedex, France.
authors.forename: Laure
authors.initials: L
authors.lastname: Monconduit
authors.affiliation: University of Cambridge , University Chemical Laboratory, Lensfield Road, Cambridge, CB2 1EW, U.K.
authors.forename: Clare P
authors.initials: CP
authors.lastname: Grey
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