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Title: Structure-electrochemical evolution of a Mn-rich P2 Na 2/3Fe 0.2Mn 0.8O 2 Na-ion battery cathode

The structural evolution of electrode materials directly influences the performance of sodium-ion batteries. In this work, in situ synchrotron X-ray diffraction is used to investigate the evolution of the crystal structure of a Mn-rich P2-phase Na 2/3Fe 0.2Mn 0.8O 2 cathode. A single-phase reaction takes place for the majority of the discharge–charge cycle at ~C/10, with only a short, subtle hexagonal P2 to hexagonal P2 two-phase region early in the first charge. Thus, a higher fraction of Mn compared to previous studies is demonstrated to stabilize the P2 structure at high and low potentials, with neither “Z”/OP4 phases in the charged state nor significant quantities of the P'2 phase in the discharged state between 1.5 and 4.2 V. Notably, sodium ions inserted during discharge are located on both available crystallographic sites, albeit with a preference for the site sharing edges with the MO 6 octahedral unit. The composition Na ~0.70Fe 0.2Mn 0.8O 2 prompts a reversible single-phase sodium redistribution between the two sites. Sodium ions vacate the site sharing faces (Naf), favoring the site sharing edges (Nae) to give a Nae/Naf site occupation of 4:1 in the discharged state. This site preference could be an intermediate state prior to themore » formation of the P'2 phase. Furthermore, this work shows how the Mn-rich Na 2/3Fe 0.2Mn 0.8O 2 composition and its sodium-ion distribution can minimize phase transitions during battery function, especially in the discharged state.« less
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6]
  1. UNSW Sydney, Sydney, NSW (Australia); Argonne National Lab. (ANL), Argonne, IL (United States)
  2. UNSW Sydney, Sydney, NSW (Australia)
  3. UNSW Sydney, Sydney, NSW (Australia); Australia Nuclear Science and Technology Organisation, Kirrawee, DC NSW (Australia)
  4. Australian Synchrotron, Clayton, VIC (Australia)
  5. Parque Tecnologiva de Alava, Minano (Spain)
  6. Parque Tecnologiva de Alava, Minano (Spain); Univ. del Pais Vasco UPV/EHU, Bilbao (Spain)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 29; Journal Issue: 17; Journal ID: ISSN 0897-4756
American Chemical Society (ACS)
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
Spanish Ministerio de Economia y Competitividad (MINECO); University of New South Wales (UNSW); Australian Nuclear Science and Technology Organisation; Australian Institute of Nuclear Science and Engineering (AINSE); Australian Research Council; USDOE
Country of Publication:
United States
36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; in situ synchrotron X-ray diffraction; positive electrodes; sodium site occupancy evolution; structure-function relationships
OSTI Identifier: