Research ArticleELECTROCHEMISTRY

Na+/vacancy disordering promises high-rate Na-ion batteries

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Science Advances  09 Mar 2018:
Vol. 4, no. 3, eaar6018
DOI: 10.1126/sciadv.aar6018
  • Fig. 1 Structure of P2-NaNM and P2-NaNMT materials.

    (A and B) XRD and Rietveld plots of (A) P2-NaNM and (B) P2-NaNMT samples. a.u., arbitrary units. (C) P2-type crystal structure viewed along the a axis (left) and c axis (right). (D and E) (D) ABF and (E) HAADF-STEM image of P2-NaNMT at the [010] zone axis. (F and G) (F) ABF and (G) HAADF-STEM image of P2-NaNMT at the [001] zone axis. (H) Transmission electron microscopy (TEM) image and EDS maps of P2-NaNMT samples.

  • Fig. 2 Electrochemical performance of P2-NaNM and P2-NaNMT compounds in Na cells.

    (A and B) Typical charge/discharge profiles of (A) P2-NaNM and (B) P2-NaNMT between 2.5 and 4.15 V at a rate of 0.1 C. (C) Charge/discharge profiles of P2-NaNMT during the 2nd, 5th, 10th, 20th, 50th, and 100th cycles at 0.1 C, demonstrating no obvious decay in the voltage and capacity. (D) Rate performance comparison of P2-NaNM and P2-NaNMT samples at different rates. (E) Capacity retention with Coulombic efficiency of P2-NaNM and P2-NaNMT over 500 cycles cycled at 1 C.

  • Fig. 3 Charge compensation mechanism of P2-Na2/3−xNMT upon Na+ extraction/insertion.

    (A and B) Ex situ XANES spectra at the (A) Ni K-edge and (B) Mn K-edge of Na2/3−xNMT electrodes collected at different charge/discharge states. (C and D) Corresponding ex situ EXAFS spectra at the (C) Ni K-edge and (D) Mn K-edge of Na2/3−xNMT electrodes collected at different charge/discharge states. FT, Fourier transform.

  • Fig. 4 Crystal structural evolution under electrochemical Na+ (de)intercalation.

    (A and B) In situ XRD patterns collected during the first charge/discharge of the (A) Na/Na2/3−xNM and (B) Na/Na2/3−xNMT cells under a current rate of 0.1 C between 2.5 and 4.15 V.

  • Fig. 5 2D Na+/vacancy ordering-disordering transition mechanism.

    (A) Typical charge/discharge profiles of P2-NaNM. The two voltage plateaus indicates the rearrangement of Na+/vacancy ordering. (B) In-plane Na+/vacancy orderings of NaδNi1/3Mn2/3O2 in the triangular lattice at δ = 2/3, δ = 1/2, and δ = 1/3, respectively (empty red circles, Na+ on Nae sites; solid blue circles, Na+ on Naf sites; thick green lines, unit cell). (C) Calculated energy difference between the Nae and Naf site for P2-NaNM (purple background) and P2-NaNMT (blue background).

  • Fig. 6 Na+ kinetics of P2-NaNMT obtained by FPMD simulations.

    (A) Trajectories of Na+ in P2-Na0.57NMT simulated at a temperature of 800 K. The top view of each Na+ layer is given in the right panel. (B) Arrhenius plot of Na+ diffusion coefficients.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/3/eaar6018/DC1

    fig. S1. Powder XRD patterns of as-synthesized P2-NaNM and P2-NaNMT samples.

    fig. S2. In situ XRD patterns of P2-NaNM and P2-NaNMT powders at different temperatures.

    fig. S3. SEM images of P2-NaNM and P2-NaNMT sample.

    fig. S4. TEM and HRTEM images of P2-NaNMT sample.

    fig. S5. Cycling performance comparison of P2-NaNM and P2-NaNMT electrodes at 0.1 C in the voltage range of 2.5 to 4.15 V during 100 cycles.

    fig. S6. SEM images of P2-NaNM and P2-NaNMT electrodes after long cycles.

    fig. S7. Charge/discharge profiles of P2-NaNM and P2-NaNMT electrodes between 2.5 and 4.3 V.

    fig. S8. Cycling performance comparison of P2-NaNM and P2-NaNMT electrodes at 0.1 C in the voltage range of 2.5 to 4.3 V during 100 cycles.

    fig. S9. CVs of P2-NaNM and P2-NaNMT electrodes.

    fig. S10. XPS spectra of P2-NaNM and P2-NaNMT powders.

    fig. S11. Variation of lattice constants and unit cell volume during cycling.

    fig. S12. Schematic illustration for P2-O2 phase transition.

    fig. S13. In situ XRD patterns of P2-NaNM and P2-NaNMT electrodes between 2.5 and 4.3 V.

    fig. S14. GITT curves and the quasi-equilibrium potential as a function of the stoichiometry.

    fig. S15. Calculated Na chemical diffusion coefficients from GITT.

    fig. S16. OCV decay of P2-NaNM and P2-NaNMT electrodes.

    fig. S17. Nyquist plots of EIS and the fit for P2-NaNM and P2-NaNMT electrodes.

    fig. S18. MSD curves for each kind of ions in P2-Na0.58NMT.

    table S1. Crystallographic parameters of P2-NaNM refined by the Rietveld method.

    table S2. Crystallographic parameters of P2-NaNMT refined by the Rietveld method.

    table S3. Atomic distances, slab thickness, and d-spacing of the Na layer and interslab distance for as-prepared materials.

    table S4. Summary of Na+ diffusion coefficients and activation energies in layered oxides.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Powder XRD patterns of as-synthesized P2-NaNM and P2-NaNMT samples.
    • fig. S2. In situ XRD patterns of P2-NaNM and P2-NaNMT powders at different temperatures.
    • fig. S3. SEM images of P2-NaNM and P2-NaNMT sample.
    • fig. S4. TEM and HRTEM images of P2-NaNMT sample.
    • fig. S5. Cycling performance comparison of P2-NaNM and P2-NaNMT
      electrodes at 0.1 C in the voltage range of 2.5 to 4.15 V during 100 cycles.
    • fig. S6. SEM images of P2-NaNM and P2-NaNMT electrodes after long cycles.
    • fig. S7. Charge/discharge profiles of P2-NaNM and P2-NaNMT electrodes between 2.5 and 4.3 V.
    • fig. S8. Cycling performance comparison of P2-NaNM and P2-NaNMT electrodes at 0.1 C in the voltage range of 2.5 to 4.3 V during 100 cycles.
    • fig. S9. CVs of P2-NaNM and P2-NaNMT electrodes.
    • fig. S10. XPS spectra of P2-NaNM and P2-NaNMT powders.
    • fig. S11. Variation of lattice constants and unit cell volume during cycling.
    • fig. S12. Schematic illustration for P2-O2 phase transition.
    • fig. S13. In situ XRD patterns of P2-NaNM and P2-NaNMT electrodes between 2.5 and 4.3 V.
    • fig. S14. GITT curves and the quasi-equilibrium potential as a function of the stoichiometry.
    • fig. S15. Calculated Na chemical diffusion coefficients from GITT.
    • fig. S16. OCV decay of P2-NaNM and P2-NaNMT electrodes.
    • fig. S17. Nyquist plots of EIS and the fit for P2-NaNM and P2-NaNMT electrodes.
    • fig. S18. MSD curves for each kind of ions in P2-Na0.58NMT.
    • table S1. Crystallographic parameters of P2-NaNM refined by the Rietveld method.
    • table S2. Crystallographic parameters of P2-NaNMT refined by the Rietveld method.
    • table S3. Atomic distances, slab thickness, and d-spacing of the Na layer and interslab distance for as-prepared materials.
    • table S4. Summary of Na+ diffusion coefficients and activation energies in layered oxides.

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