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Title: Identifying the Structure of the Intermediate, Li 2/3CoPO 4, Formed during Electrochemical Cycling of LiCoPO 4

In situ synchrotron diffraction measurements and subsequent Rietveld refinements are used to show that the high energy density cathode material LiCoPO 4 (space group Pnma) undergoes two distinct two-phase reactions upon charge and discharge, both occurring via an intermediate Li 2/3(Co 2+) 2/3(Co 3+) 1/3PO 4 phase. Two resonances are observed for Li 2/3CoPO 4 with intensity ratios of 2:1 and 1:1 in the 31P and 7Li NMR spectra, respectively. An ordering of Co 2+/Co 3+ oxidation states is proposed within a (a × 3b × c) supercell, and Li +/vacancy ordering is investigated using experimental NMR data in combination with first-principles solid-state DFT calculations. In the lowest energy configuration, both the Co 3+ ions and Li vacancies are found to order along the b-axis. Two other low energy Li +/vacancy ordering schemes are found only 5 meV per formula unit higher in energy. All three configurations lie below the LiCoPO 4–CoPO 4 convex hull and they may be readily interconverted by Li + hops along the b-direction.
 [1] ;  [1] ;  [1] ;  [1] ;  [2] ;  [2] ;  [2] ;  [2] ;  [3]
  1. Univ. of Cambridge (United Kingdom). Dept. of Chemistry
  2. Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
  3. Univ. of Cambridge (United Kingdom). Dept. of Chemistry; State Univ. of New York at Stony Brook (United States). Dept. of Chemistry
Publication Date:
OSTI Identifier:
Grant/Contract Number:
Published Article
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 26; Journal Issue: 21; Journal ID: ISSN 0897-4756
American Chemical Society (ACS)
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