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Title: Theoretical exploration of various lithium peroxide crystal structures in a Li-air battery

We describe a series of metastable Li2O2 crystal structures involving different orientations and displacements of the O22– peroxy ions based on the known Li2O2 crystal structure. Within the vicinity of the chemical potential ΔG ~ 0.20 eV/Li from the thermodynamic ground state of the Li2O2 crystal structure (i.e., Föppl structure), all of these newly found metastable Li2O2 crystal structures are found to be insulating and high-k materials, and they have a common unique signature of an O22– O-O vibration mode (ω ~ 799–865 cm–1), which is in the range of that commonly observed in Li-air battery experiments, regardless of the random O22– orientations and the symmetry in the crystal lattice. From XRD patterns analysis, the commercially available Li2O2 powder is confirmed to be the thermodynamic ground state Föppl-like structure. However, for Li2O2 compounds that are grown electrochemically under the environment of Li-O2 cells, we found that the XRD patterns alone are not sufficient for structural identification of these metastable Li2O2 crystalline phases due to the poor crystallinity of the sample. In addition, the commonly known Raman signal of O22– vibration mode is also found to be insufficient to validate the possible existence of these newly predicted Li2O2 crystal structures,more » as all of them similarly share the similar O22– vibration mode. Therefore considering that the discharge voltage in most Li-O2 cells are typically several tenths of an eV below the thermodynamic equilibrium for the formation of ground state Föppl structure, the formation of these metastable Li2O2 crystal structures appears to be thermodynamically feasible.« less
Authors:
 [1] ;  [2] ;  [2] ;  [3] ;  [1] ;  [2] ;  [2]
  1. Argonne National Lab. (ANL), Argonne, IL (United States). Materials Science Div.
  2. Argonne National Lab. (ANL), Argonne, IL (United States). Chemical Sciences and Engineering Div.
  3. Purdue Univ., West Lafayette, IN (United States). School of Chemical Engineering.
Publication Date:
OSTI Identifier:
1201754
Grant/Contract Number:
AC02-06CH11357
Type:
Accepted Manuscript
Journal Name:
Energies (Basel)
Additional Journal Information:
Journal Name: Energies (Basel); Journal Volume: 8; Journal Issue: 1; Journal ID: ISSN 1996-1073
Publisher:
MDPI AG
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 25 ENERGY STORAGE; Li-air battery; lithium peroxide; crystal structure; DFT calculation; energy storage (including batteries and capacitors); charge transport; materials and chemistry by design; synthesis (novel materials)