Hydrogen-assisted manganese migration in NaMnO2

ORAL

Abstract

We investigate the structure and energetics of point defects in layered NaMnO2. Our study is aimed at elucidating potential degradation mechanisms when the material is used as a positive electrode in Na-ion rechargeable batteries. Hydrogen has been implicated in this process. Using hybrid density functional theory, we find that hydrogen interstitials and Na vacancies have low formation energies and moderate migration barriers, and the proton/Na+ exchange process can proceed with fast kinetics. Degradation occurs when Mn moves to an antisite position, where it migrates with a low barrier of 0.18 eV. In the absence of hydrogen, formation of MnNa antisites is suppressed due to the high energy of the VMn it leaves behind, and due to the large interlayer-migration barrier for Mn. But when hydrogen is present, VMn is stabilized by forming VMn-3H complexes; in addition, the interlayer-migration barrier for Mn is substantially reduced from 1.48 eV to as low as 0.20 eV in the presence of hydrogen interstitials. Therefore, with the assistance of hydrogen, the formation of MnNa antisites becomes thermodynamically favorable and kinetically allowed, which eventually leads to loss of Mn2+.

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Presenters

  • Zhen Zhu

    Materials Department, University of California - Santa Barbara, Materials, Univ of California - Santa Barbara, University of California, Santa Barbara

Authors

  • Zhen Zhu

    Materials Department, University of California - Santa Barbara, Materials, Univ of California - Santa Barbara, University of California, Santa Barbara

  • Hartwin Peelaers

    Materials Department, University of California, Santa Barbara, University of California, Santa Barbara, Materials, Univ of California - Santa Barbara

  • Chris Van de Walle

    University of California, Santa Barbara, Materials Department, Univ of California - Santa Barbara, Materials Department, University of California, Santa Barbara, Materials, Univ of California - Santa Barbara, Materials Department, University of California - Santa Barbara, Materials Department, University of California