Research ArticleELECTROCHEMISTRY

Fluorinated solid electrolyte interphase enables highly reversible solid-state Li metal battery

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Science Advances  21 Dec 2018:
Vol. 4, no. 12, eaau9245
DOI: 10.1126/sciadv.aau9245
  • Fig. 1 Schematic illustration of the pretreated processes for the formation of an LiF-rich SEI layer between the Li metal and the LPS SSEs.
  • Fig. 2 Electrochemical performances of the Li plating/stripping in the Li|LiFSI@LPS|Li cell and the Li|LPS|Li cell.

    Galvanostatic Li plating/stripping profiles in the Li|LPS|Li cell (A) and the Li|LiFSI@LPS|Li cell (B) at step-increased current densities. Galvanostatic cycling of Li plating/stripping profiles in the Li|LPS|Li cell (C) and the Li|LiFSI@LPS|Li cell (D) at a constant current density of 0.3 mA cm−2. All tests were performed at room temperature (25°C).

  • Fig. 3 Electrochemical properties of the Li|LPS|SS cells.

    Li plating/stripping profiles on an SS working electrode using (A) the pristine LPS as the SSE, (B) the Au-coated LPS as the SSE, and (C) the 6 M LiFSI DME pretreated LPS as the SSE. (D) Li plating/stripping CEs in different LPS. The current density is 0.1 mA cm−2.

  • Fig. 4 Surface analyses for the cycled LPS SSE from the Li|LPS|SS cell.

    (A) SEM image of the cycled LPS recovered from the untreated cell. (B) SEM image of cycled LPS recovered from the pretreated cell. (C) High-resolution XPS analysis of P-containing species in the LPS recovered from an untreated SSE cell. a.u., arbitrary units. (D) Ternary phase diagram of Li-P-S. (E and F) High-resolution XPS analysis of P- and F-containing species in the LPS recovered from the pretreated cell. (G) Crater sputtered by a Ga+ ion beam for the pretreated LPS after cycling. (H) ToF-SIMS analysis for the fluorine element in the pretreated LPS after cycling. (I) F and S element distribution in the sputtered LPS SSE as shown in (G).

  • Fig. 5 DFT calculations for the mechanism of the LiF-rich SEI layer on suppression of the Li dendrite in SSEs.

    (A) Schematic illustration of the electrochemical deposition process of the Li metal anode. (B) Energy-based analysis (interfacial energy and strain energy) of Li dendrite formation. (C) Plot of the relationship between the interfacial energy for possible SEI components and the number of Li metal formula units. (D) Calculated interfacial energies γ, bulk modulus E from MP (45), and Li dendrite suppression ability γE for different interface components. DFT-optimized atomic structures of (E) LPS/Li and (F) LiF/Li interfaces and its corresponding DOS (G and H) profiles by atomic layer with Fermi level at 0 eV. The green, purple, yellow, and gray balls in (E) and (F) represent Li, P, S, and F atoms, respectively.

  • Fig. 6 Electrochemical performance of Li|LiFSI@LPS|LCO.

    (A) Charge/discharge curves in different cycles at 0.3 mA cm−2 at room temperature. (B) Cycling performance of the cell at 0.3 mA cm−2 at room temperature. The area loading is 1.0 mAh cm−2.

  • Fig. 7 Interphase types between the Li metal and the SSEs.

    (A) Thermodynamically stable interphase. (B) Reactive but forming an electron insulator SEI layer. (C) Reactive and forming a degradation layer with high electron conductivity. (D) Li potentials between the Li metal and the SSEs in the above three interphase types. The difference between the green dash line (III) and the red dash (III′) is that the red dash line (III′) includes the overpotentials during the Li plating process.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/12/eaau9245/DC1

    Fig. S1. XRD pattern and the electrochemical impedance spectra of the as-synthesized LPS SSE.

    Fig. S2. Impedance plot of the Li|LPS|Li cell before cycling and after cycling.

    Fig. S3. Impedance plot of the pretreated Li|LPS|Li cell before cycling and after cycling.

    Fig. S4. ToF-SIMS analysis of the positive ions for the interface of the LPS.

    Fig. S5. Comparison of the bandgaps for different materials.

    Fig. S6. XPS spectra of cycled LPS recovered from the pretreated SSE cell and untreated cell.

    Fig. S7. SEI components in the LPS recovered from the pretreated cell by XPS.

    Fig. S8. ToF-SIMS analysis of the negative ions for the interface of the cycled LPS SSE.

    Fig. S9. Relationship between the total energy, the interfacial energy, and the strain energy with the dendrite length during the dendrite formation in the SSEs.

    Fig. S10. Charge/discharge curves for the Li|LPS|LCO cell.

    Note S1. Critical Li dendrite length and the Li dendrite suppression ability for the SSEs.

    Note S2. Computational model and method for the interfacial energy.

    References (4648)

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. XRD pattern and the electrochemical impedance spectra of the as-synthesized LPS SSE.
    • Fig. S2. Impedance plot of the Li|LPS|Li cell before cycling and after cycling.
    • Fig. S3. Impedance plot of the pretreated Li|LPS|Li cell before cycling and after cycling.
    • Fig. S4. ToF-SIMS analysis of the positive ions for the interface of the LPS.
    • Fig. S5. Comparison of the bandgaps for different materials.
    • Fig. S6. XPS spectra of cycled LPS recovered from the pretreated SSE cell and untreated cell.
    • Fig. S7. SEI components in the LPS recovered from the pretreated cell by XPS.
    • Fig. S8. ToF-SIMS analysis of the negative ions for the interface of the cycled LPS SSE.
    • Fig. S9. Relationship between the total energy, the interfacial energy, and the strain energy with the dendrite length during the dendrite formation in the SSEs.
    • Fig. S10. Charge/discharge curves for the Li|LPS|LCO cell.
    • Note S1. Critical Li dendrite length and the Li dendrite suppression ability for the SSEs.
    • Note S2. Computational model and method for the interfacial energy.
    • References (4648)

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