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Title: Tracking Sodium-Antimonide Phase Transformations in Sodium-Ion Anodes: Insights from Operando Pair Distribution Function Analysis and Solid-State NMR Spectroscopy

We use operando pair distribution function (PDF) analysis and ex situ 23Na magic-angle spinning solid-state nuclear magnetic resonance (MAS ssNMR) spectroscopy 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 23Na ssNMR in reference to relevant model compounds, identifies two previously uncharacterized intermediate species formed electrochemically; a-Na3–xSb (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-Na1.7Sb, a highly amorphous structure featuring some Sb–Sb bonding. The first sodiation breaks down the crystalline antimony to form first a-Na3–xSb 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-Na1.7Sb, then a-Na3–xSb, whereas lower potentials are required for the sodiation of crystalline antimony, which reacts to form a-Na3–xSb without the formation ofmore » a-Na1.7Sb. a-Na3–xSb is converted to crystalline Na3Sb at the end of the second discharge. In the end, we find no evidence of formation of NaSb. Variable temperature 23Na NMR experiments reveal significant sodium mobility within c-Na3Sb; this is a possible contributing factor to the excellent rate performance of Sb anodes.« less
 [1] ;  [2] ;  [3] ;  [4] ;  [4] ;  [4] ;  [5] ;  [4] ;  [3] ;  [2]
  1. Univ. of Cambridge (United Kingdom). University Chemical Lab.; Gonville and Caius College, Cambridge (United Kingdom)
  2. Univ. of Cambridge (United Kingdom). University Chemical Lab.
  3. Univ. Montpellier, Montpellier (France). Institut Charles Gerhardt Montpellier-UMR; Reseau sur le Stockage Electrochimique de l'Energie (RS2E), Amiens (France)
  4. Argonne National Lab. (ANL), Argonne, IL (United States). X-ray Science Division
  5. Univ. of Cambridge (United Kingdom). Cavendish Lab.
Publication Date:
Grant/Contract Number:
EP/K002252/1; AC02-06CH11357
Published Article
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 138; Journal Issue: 7; Journal ID: ISSN 0002-7863
American Chemical Society (ACS)
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC); European Research Council (ERC)
Country of Publication:
United States
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1261140