Research ArticleELECTROCHEMISTRY

Unraveling the storage mechanism in organic carbonyl electrodes for sodium-ion batteries

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Science Advances  18 Sep 2015:
Vol. 1, no. 8, e1500330
DOI: 10.1126/sciadv.1500330
  • Fig. 1 Resolved crystal structure of Na2C6H2O4.

    (A) XRD pattern and Rietveld refinement of Na2C6H2O4 sample. The black (red) line represents the experimental (calculated) data. The residual discrepancy is shown in yellow. The refinement is preformed in the P–1 space group. Inset shows the molecular structure. (B to D) Schematic illustration of the triclinic Na2C6H2O4 (B) layered structure (green color refers to Na-O octahedron), (C) along the a axis and (D) along the b axis. For clarity, 2,5-DBQ molecules and sodium ions are expressed using tubes and balls in (D).

  • Fig. 2 Sodium storage behavior.

    (A) First and second discharge/charge curves of Na2C6H2O4 electrode at a current rate of C/10 (29 mA g−1) in the voltage range of 1.0 to 2.0 V versus Na+/Na. (B) First and second CV curves of Na2C6H2O4 electrode at a scan rate of 0.03 mV s−1.

  • Fig. 3 Structure evolution during sodiation and desodiation.

    In situ XRD patterns collected during the first and second discharge/charge of the Na/Na2C6H2O4 cell under a current rate of C/20 at the voltage range between 1.0 and 2.0 V. (A and B) Structure evolution in the first cycle. (C and D) Structure evolution processes in the second cycle. a.u., arbitrary units.

  • Fig. 4 Reaction mechanism.

    The different reaction paths in the first two cycles of the Na2C6H2O4 electrode.

  • Fig. 5 Crystal structures of Na3C6H2O4 and Na4C6H2O4.

    (A to F) Schematic illustration of Na3C6H2O4 (A) layered structure (yellow color refers to Na-O square pyramid, and green color refers to Na-O octahedron), (C) along the a axis and (E) along the b axis, and Na4C6H2O4 (B) layered structure (yellow color refers to Na-O square pyramid), (D) along the a axis and (F) along the b axis. For clarity, 2,5-DBQ molecules and sodium ions are expressed using tubes and balls in (E) and (F).

  • Fig. 6 Benzene ring rotation.

    (A to C) Angles between benzene rings and bc plane (blue) in (A) Na2C6H2O4, (B) Na3C6H2O4, and (C) Na4C6H2O4. (D to F) Rotation of benzene rings in (D) Na2C6H2O4, (E) Na3C6H2O4, and (F) Na4C6H2O4.

  • Fig. 7 Charge compensation mechanism.

    (A to C) Change in the electron density near the benzene ring in Fourier map obtained from the Rietveld refinement (A) Na2C6H2O4, (B) Na3C6H2O4, and (C) Na4C6H2O4. (D to F) DOS for (D) Na2C6H2O4, (E) Na3C6H2O4, and (F) Na4C6H2O4. The Fermi level is set to zero.

  • Fig. 8 Na+ ion diffusion mechanism.

    Trajectories (small purple bullets) of Na+ ion in Na2C6H2O4 (A and B) and Na4C6H2O4 (D and E) obtained by the MD simulation at 1200 K for 15 ps. Mean square displacement (MSD) plots of H, C, O, and Na atoms under 1200 K in Na2C6H2O4 (C) and Na4C6H2O4 (F).

  • Table 1 DFT calculation.

    Total energies for Na2C6H2O4, Na3C6H2O4, and Na4C6H2O4 structures and comparison of DFT calculated and experimental reaction voltages.

    StructureNa2C6H2O4Na3C6H2O4Na4C6H2O4Na
    Energy (eV/U)−95.139−97.815−100.056−2.586
    Reaction processNa2→Na4Na4→Na3Na3→Na2
    Calculated voltage (V versus Na+/Na)1.170.951.38
    Experimental voltage (V versus Na+/Na)1.211.311.49
  • Table 2 Bader charge.

    Bader charge change in the three structures.

    StructureNa2C6H2O4Na3C6H2O4Na4C6H2O4
    AtomValue charge (e)Bader charge (e)Bader charge (e)Bader charge (e)
    O167.16587.21987.2390
    O267.16477.19587.2449
    C144.07994.16064.1575
    C243.27583.36973.5519
    C343.25223.31723.4727

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/1/8/e1500330/DC1

    Fig. S1. TG and DSC curves of (A) precursor C6H4O4 and (B) Na2C6H2O4.

    Fig. S2. Microstructure of as-prepared Na2C6H2O4.

    Fig. S3. Different structure evolution processes between the first and the second cycle.

    Structure solution and Rietveld refinement of Na3C6H2O4 and Na4C6H2O4

    Fig. S4. XRD pattern and Rietveld refinement of Na3C6H2O4 structure.

    Fig. S5. XRD pattern and Rietveld refinement of Na4C6H2O4 structure.

    Fig. S6. The positions and coordination environment of sodium atoms in Na2C6H2O4, Na3C6H2O4, and Na4C6H2O4.

    Fig. S7. Change of sodium atom local structure during sodium extraction.

    Fig. S8. The atomic position illustration of C and O atoms.

    Fig. S9. The molecular structure (A) and schematic illustration (B) of the orthorhombic Na2C8H4O4.

    Model construction of DFT calculations

    Fig. S10. Polarization between discharge and charge.

    Fig. S11. UV-vis absorption spectra of Na2C6H2O4.

    Fig. S12. The second discharge/charge curves of Na2C6H2O4 at a current rate of C/10.

    Table S1. The sodium storage properties for different reported negative electrode materials for sodium-ion batteries.

    Table S2. Structural parameters.

    Table S3. Structural parameters.

    Table S4. Structural parameters.

    Table S5. Bond lengths for Na2C6H2O4, Na3C6H2O4, and Na4C6H2O4.

    References (3335)

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. TG and DSC curves of (A) precursor C6H4O4 and (B) Na2C6H2O4.
    • Fig. S2. Microstructure of as-prepared Na2C6H2O4.
    • Fig. S3. Different structure evolution processes between the first and the second cycle.
    • Structure solution and Rietveld refinement of Na3C6H2O4 and Na4C6H2O4
    • Fig. S4. XRD pattern and Rietveld refinement of Na3C6H2O4 structure.
    • Fig. S5. XRD pattern and Rietveld refinement of Na4C6H2O4 structure.
    • Fig. S6. The positions and coordination environment of sodium atoms in Na2C6H2O4, Na3C6H2O4, and Na4C6H2O4.
    • Fig. S7. Change of sodium atom local structure during sodium extraction.
    • Fig. S8. The atomic position illustration of C and O atoms.
    • Fig. S9. The molecular structure (A) and schematic illustration (B) of the orthorhombic Na2C8H4O4.
    • Model construction of DFT calculations
    • Fig. S10. Polarization between discharge and charge.
    • Fig. S11. UV-vis absorption spectra of Na2C6H2O4.
    • Fig. S12. The second discharge/charge curves of Na2C6H2O4 at a current rate of C/10.
    • Table S1. The sodium storage properties for different reported negative electrode materials for sodium-ion batteries.
    • Table S2. Structural parameters.
    • Table S3. Structural parameters.
    • Table S4. Structural parameters.
    • Table S5. Bond lengths for Na2C6H2O4, Na3C6H2O4, and Na4C6H2O4.
    • References (33–35)

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