Research ArticleAPPLIED SCIENCES AND ENGINEERING

Minimized lithium trapping by isovalent isomorphism for high initial Coulombic efficiency of silicon anodes

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Science Advances  15 Nov 2019:
Vol. 5, no. 11, eaax0651
DOI: 10.1126/sciadv.aax0651
  • Fig. 1 Density functional theory calculations of energy barriers of Li diffusion in Li-Si-Ge.

    (A) Schematic of Li diffusion and lithiation/delithiation process in a Li-Si anode. (B) Schematic of Li diffusion and lithiation/delithiation process in a Li-Si-Ge anode. (C) Schematic unit cell of Li15Si4 alloy, in which Si and Li atoms are represented by blue and yellow balls, respectively. (D) Two types of Li atoms in Li15Si4 alloy. The Li1 atoms at 12a sites have the same distances from the four nearest Si atoms and are located in the center of tetrahedrons composed of these Si atoms, while three adjacent Li2 atoms at 48e sites constitute an equilateral triangle. (E) Schematics of two sets of pathways for Li migration in Li15Si4. (F) Relationships between energy barriers of Li migration along two pathways versus atomic ratios of Si to Ge in Li-Si-Ge.

  • Fig. 2 Characterizations of the obtained Si-Ge alloy nanoparticles.

    (A) SEM and (B) TEM image of Si15Ge nanoparticles (inset: diffraction pattern). (C) High-resolution TEM of the selected part in (B). (D) STEM and corresponding EDX mapping images of Si and Ge (scale bar, 50 nm). (E) X-ray diffraction and (F) Raman results of various ratios of Si-Ge alloy nanoparticles. a.u., arbitrary units.

  • Fig. 3 Electrochemical performance of Si-Ge anodes with different atomic ratios.

    (A) CV curves of Si-Ge alloy electrodes with various atomic ratios. (B) Corresponding initial voltage profiles at the current density of 0.1 C, respectively. (C) Statistical results of initial charge capacities and CE of Si-Ge electrodes with various atomic ratios from 10 samples at the same rate of 0.1 C. (D) Initial CE values of our work and other strategies reported before.

  • Fig. 4 Characterizations of Si-Ge alloy anodes before/after initial cycle.

    (A) Top view and cross section of Si electrode and (B) Si15Ge electrode before and after initial cycle [scale bars, 10 μm (top view) and 5 μm (cross section)]. (C) TEM of Si and (D) Si15Ge nanoparticle after initial cycle (scale bar, 10 nm). (E) X-ray photoelectron spectroscopy results of Si and Si15Ge electrodes after initial cycle. (F) Electrochemistry impedance spectroscopy (EIS) result of Si and Si15Ge after initial cycle. (G) The statistical results of RSEI and SEI thickness from five different samples. (H) LiSEI and trapped Li from ICP results and η value.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/11/eaax0651/DC1

    Diffusion model in the Li insertion and extraction

    DFT calculations of Si-Ge alloy

    DFT calculations of Si-Sn alloy

    Characterizations of Si-Ge alloy with various atomic ratios

    Characterizations of Si-Sn alloy anodes

    Fig. S1. Schematic of diffusion modeling in lithiation and delithiation processes.

    Fig. S2. Relationship between average scaled bond orders BOavers and the atomic ratio Si to Ge in Li15Si4−xGex.

    Fig. S3. Relationship between average scaled bond orders BOavers versus the atomic ratio of Si to Sn in Li15Si4−xSnx (x = 0, 0.25, 0.5, 1.0, and 4.0) alloys.

    Fig. S4. SEM images of the obtained particles after ball milling.

    Fig. S5. The electrochemical performance of Si-Ge electrodes with various atomic ratios.

    Fig. S6. SEM of top view and cross-sectional view of electrodes based on Si-Ge alloy with various atomic ratios before and after initial cycle.

    Fig. S7. TEM images of the SEI after initial cycle of Si2.6Ge, SiGe2.7, and Ge, respectively.

    Fig. S8. EIS results of Si2.6Ge, SiGe2.7, and Ge electrodes after initial cycle.

    Fig. S9. The voltage profile of various Si-Sn alloy electrodes in the first cycle and statistic CE.

    Table S1. Space group, experimental, and first-principles (GGA) calculated lattice parameters (Å) of Li15Si4−xGex.

    Table S2. The Li migration energy barriers (eV) along two sets of pathways in Li15Si4−xGex.

    Table S3. Space group, experimental, and first-principles (GGA) calculated lattice parameters (Å) of Li15Si4−xSnx (x = 0.25, 0.5, 1.0, and 4.0) alloys and their scaled BOs and number (α and β) of Li-Si and Li-Li covalent bonds on each Li atom.

    Table S4. The Li migration energy barriers (eV) along two sets of pathways in Li15Si4−xSnx.

    Table S5. The LiSEI, trapped Li, and η for the different Si-Sn anodes after initial cycle based on ICP test.

  • Supplementary Materials

    This PDF file includes:

    • Diffusion model in the Li insertion and extraction
    • DFT calculations of Si-Ge alloy
    • DFT calculations of Si-Sn alloy
    • Characterizations of Si-Ge alloy with various atomic ratios
    • Characterizations of Si-Sn alloy anodes
    • Fig. S1. Schematic of diffusion modeling in lithiation and delithiation processes.
    • Fig. S2. Relationship between average scaled bond orders BOavers and the atomic ratio Si to Ge in Li15Si4−xGex.
    • Fig. S3. Relationship between average scaled bond orders BOavers versus the atomic ratio of Si to Sn in Li15Si4−xSnx (x = 0, 0.25, 0.5, 1.0, and 4.0) alloys.
    • Fig. S4. SEM images of the obtained particles after ball milling.
    • Fig. S5. The electrochemical performance of Si-Ge electrodes with various atomic ratios.
    • Fig. S6. SEM of top view and cross-sectional view of electrodes based on Si-Ge alloy with various atomic ratios before and after initial cycle.
    • Fig. S7. TEM images of the SEI after initial cycle of Si2.6Ge, SiGe2.7, and Ge, respectively.
    • Fig. S8. EIS results of Si2.6Ge, SiGe2.7, and Ge electrodes after initial cycle.
    • Fig. S9. The voltage profile of various Si-Sn alloy electrodes in the first cycle and statistic CE.
    • Table S1. Space group, experimental, and first-principles (GGA) calculated lattice parameters (Å) of Li15Si4−xGex.
    • Table S2. The Li migration energy barriers (eV) along two sets of pathways in Li15Si4−xGex.
    • Table S3. Space group, experimental, and first-principles (GGA) calculated lattice parameters (Å) of Li15Si4−xSnx (x = 0.25, 0.5, 1.0, and 4.0) alloys and their scaled BOs and number (α and β) of Li-Si and Li-Li covalent bonds on each Li atom.
    • Table S4. The Li migration energy barriers (eV) along two sets of pathways in Li15Si4−xSnx.
    • Table S5. The LiSEI, trapped Li, and η for the different Si-Sn anodes after initial cycle based on ICP test.

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