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Microstructural control of new intercalation layered titanoniobates with large and reversible d-spacing for easy Na+ ion uptake

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Science Advances  06 Oct 2017:
Vol. 3, no. 10, e1700509
DOI: 10.1126/sciadv.1700509
  • Fig. 1 Structural and morphological characterization of KTNO.

    (A) Unit cell structures of the representative planes of the layered KTNO with orthorhombic structure (Pnma) projected along the [100], [010], [001], and [101] directions. Potassium ions in the bottom cell were removed to show the channels better. (B) XRD patterns of as-prepared KTNO calcined at different temperatures from 500° to 1100°C. The reference data of KTNO were indexed at the bottom (ICDD card no. 54-1155). a.u., arbitrary units. (C to F) Schematic illustrations of morphologies, TEM images, high-resolution TEM (HRTEM) images, and their corresponding SAED patterns of KTNO calcined at 700°, 900°, and 1100°C.

  • Fig. 2 Characterization of a topotactic reaction of H0.43Ti0.93Nb1.07O5.

    (A) SEM images of KTNO-700 before and after a cation exchange. (B) A TGA curve of as-prepared H0.85−xTi0.97Nb1.07O5 in the temperature range of 25° to 900°C. (C) XRD patterns of as-prepared HTNO dried at 100°C (I) and HTNO calcined at temperatures of 300°C (II), 450°C (III), and 700°C (IV). The reference data of HTNO were indexed at the bottom (ICDD card no. 54-1157). The black arrows show the shift of the original (002) plane of HTNO to higher angles caused by the topotactic reaction. (D to G) Inverse FFT images of each sample (I, II, III, and IV) and their corresponding line profiles across the (Ti/Nb)O6 layers (in a distance of 5 nm).

  • Fig. 3 Rietveld refinement on characterization of lattice parameters.

    Observed, calculated, phase, and difference profiles of (A) HTNO-100, (B) HTNO-300, (C) HTNO-450, and (D) HTNO-700 are plotted in the same 2θ range of 5° to 120°.

  • Fig. 4 Sodium storage properties of H0.43Ti0.93Nb1.07O5 and its derivatives in a voltage window of 0.01 to 3.0 V versus Na+/Na at room temperature (25°C).

    (A) First voltage profiles of H0.85−xTi0.97Nb1.07O5 and its derivatives at a current rate of 0.1 C (36.0 mA g−1 for HTNO-100/300, 36.2 mA g−1 for HTNO-450, and 37.8 mA g−1 for HTNO-700). (B) Cycle performance over 150 cycles at a current rate of 1 C. (C) Rate capability at various current rates of 0.2 to 5 C. (D) Charge curves under a fixed discharge rate of 0.1 C and various charge rates of 0.2 to 20 C. (E) GITT curve at a rate of 0.1 C. (F) Sodium ion diffusion coefficient versus voltage plot calculated from the corresponding GITT curve.

  • Fig. 5 Structure evolution of H0.43Ti0.93Nb1.07O5 upon sodiation/desodiation.

    Ex situ XRD patterns obtained from H0.43Ti0.93Nb1.07O5 electrodes during cycling at different cutoff voltages at a current rate of 0.05 C. Charging cutoff: 1.0/0.8/0.6/0.4/0.2/0.01 V; discharging cutoff: 0.4/1.0/1.2/1.8/2.3/3.0 V.

  • Fig. 6 Characterization of Na+ ion insertion mechanism of H0.43Ti0.93Nb1.07O5.

    (A) TEM image of (Na1.6, H0.43)Ti0.93Nb1.07O5 after full sodiation (discharging) to 0.01 V at a current rate of 0.1 C along the [010] direction. (B) High-resolution STEM image and EELS element map obtained from the yellow box in (A). Blue color represents Na ions that occupy the sites between the (Ti/Nb)O6 layers. (C) Schematic illustration of the unit cell structure of Na1.0Ti0.97Nb1.07O5 projected in the a-c plane. (D) DFT calculation; the energy barrier of Na ions in TiNbO5 specifically through the [010] direction. (E to G) Na K-edge, Ti L3,2-edge, Nb M5,4-edge, and O K-edge EELS spectra after background subtraction before (black lines) and after sodiation (red lines).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/10/e1700509/DC1

    fig. S1. HR-XRD patterns of as-prepared KTNO calcined at 700°C.

    fig. S2. SEM observation of as-prepared KTiNbO5 particles.

    fig. S3. DFT calculation for defect chemistry of HTiNbO5.

    fig. S4. Change in unit cell structures through a and c directions as a fuction of post-annealing temperatures.

    fig. S5. Sodium storage properties.

    fig. S6. Ex situ TEM observation.

    table S1. Rietveld lattice parameters of KTNO calcined at 700°C.

    table S2. Refined unit cell parameters and R values of HTNO and its derivatives.

    table S3. Refined atomic coordinates and site occupancies of HTNO-100.

    table S4. Refined atomic coordinates and site occupancies of HTNO-300.

    table S5. Refined atomic coordinates and site occupancies of HTNO-450.

    table S6. Refined atomic coordinates and site occupancies of HTNO-700.

    table S7. Electrochemical performances of titanium-based oxide materials as negative electrodes for NIBs by virtue of the insertion/deinsertion mechanism.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. HR-XRD patterns of as-prepared KTNO calcined at 700°C.
    • fig. S2. SEM observation of as-prepared KTiNbO5 particles.
    • fig. S3. DFT calculation for defect chemistry of HTiNbO5.
    • fig. S4. Change in unit cell structures through a and c directions as a fuction of post-annealing temperatures.
    • fig. S5. Sodium storage properties.
    • fig. S6. Ex situ TEM observation.
    • table S1. Rietveld lattice parameters of KTNO calcined at 700°C.
    • table S2. Refined unit cell parameters and R values of HTNO and its derivatives.
    • table S3. Refined atomic coordinates and site occupancies of HTNO-100.
    • table S4. Refined atomic coordinates and site occupancies of HTNO-300.
    • table S5. Refined atomic coordinates and site occupancies of HTNO-450.
    • table S6. Refined atomic coordinates and site occupancies of HTNO-700.
    • table S7. Electrochemical performances of titanium-based oxide materials as negative electrodes for NIBs by virtue of the insertion/deinsertion mechanism.

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