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November 17, 2014, Research Highlights

Understanding the Structural and Electronic Evolution of Li2MnO3 During Electron Irradiation Via Electron Microscopy

In-situ electron beam irradiation induces localized pockets of damage (a) and (b) characterized by the Mn atoms migrating to occupy Li sites, as shown in the annular bright field image of (c). This effect is clearly visible in an intensity line profile across material that is either pristine (red) or damaged (blue), wherein the Mn-Mn dumbbells lose intensity because of Mn atom migration into the Li sites in between the dumbbells. Mn atoms are also found to migrate into the Li plane parallel to the Mn dumbbells. Electron energy loss studies indicate that prior to O evolution from the material, the valence of Mn goes beyond 4+, and only after extensive irradiation does the Mn valence decrease to the expected value, near 2+.

Scientific Achievement

  • Electrochemical cycling induces irreversible changes to the oxide structure such as Li/O evolution and crystal rearrangements
  • In-situ electron-beam irradiation provides time- and position-sensitive atomic-resolution tracking ability of these transitions to aid in understanding of electrochemical cycling-induced material failures

Significance and Impact

  • Irradiation induces local pockets of deformation characterized initially by the creation of Li vacancies and the significant motion of Mn into Li sites; Mn valence > 4+
  • Further irradiation leads to structural instability, spinel-like formation, O loss, and a Mn valence near 2+

Research Details

  • Analysis can be extended to compare these irradiation results to electrochemically cycled material
  • Extensions to multivalent intercalation compounds is proposed

Work performed at University of Illinois at Chicago (JCESR partner) and Argonne National Laboratory (JCESR managing partner) by PJ Phillips, H Iddir, DP Abraham and RF Klie, Applied Physics Letters, 2014.

DOI: 10.1063/1.4896264

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