Research ArticleAPPLIED SCIENCES AND ENGINEERING

Toward garnet electrolyte–based Li metal batteries: An ultrathin, highly effective, artificial solid-state electrolyte/metallic Li interface

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Science Advances  07 Apr 2017:
Vol. 3, no. 4, e1601659
DOI: 10.1126/sciadv.1601659
  • Fig. 1 Schematic of improved wettability of SSE against Li metal and demonstration of hybrid solid-liquid electrolyte system for Li-ion, Li-S, and Li-O2 batteries.

    (A) Schematic of engineered garnet SSE/Li interface using Li-metal alloy. The pristine garnet SSE has poor contact with Li. Al-coated garnet SSE exhibits good contact with Li due to the Li-Al alloy that forms between the SSE and the Li metal. The garnet SSE surface becomes “lithiophilic,” enabling a low ASR when Li metal is used. (B) Schematic of the hybrid solid-liquid electrolyte system for Li-ion, Li-S, and Li-O2 batteries. Solid-state garnet SSE/Li is on the anode side, and liquid electrolyte is applied to the cathode side.

  • Fig. 2 Characterization of LLCZN SSE.

    (A) Scanning electron microscopy (SEM) image of the surface morphology of the Al-coated LLCZN ceramic surface. The inset is a digital image of an Al-coated LLCZN ceramic disc. The yellow ceramic disc is coated by Al and appears gray in color. (B) XRD pattern of the as-synthesized LLCZN. (C) EIS profiles of the LLCZN at different temperatures. (D) Arrhenius plot of LLCZN conductivity.

  • Fig. 3 Wetting behavior and interfacial morphology characterization of Li | garnet SSE and Li | Al-coated garnet SSE.

    (A) Wetting behavior of molten Li with garnet SSE and Al-coated garnet SSE. The inset is a schematic showing the contact angles of a molten Li droplet wetting the surface of both uncoated and Al-coated garnet SSEs. Improved Li wettability is demonstrated after Al-coating the garnet surface. (B and C) SEM images of Li | garnet SSE, showing the poor Li wettability of uncoated garnet. (D to F) SEM images of Li | Al–garnet SSE–Al exhibiting superior Li wettability with Al-coated garnet. (G) Phase diagram of Li-Al. (H) Elemental mapping of Li | Al–garnet SSE in cross section. The Al signal was detected in bulk Li. (I and J) Elemental mapping of the very top area of Li metal to show the diffusion process of Al.

  • Fig. 4 Electrochemical stability of the Li and garnet interface.

    (A) Schematic of the symmetric cell preparation and a digital image of Li metal melting on a garnet SSE. (B and C) Comparison of Nyquist plots of Li | garnet SSE | Li and Li | Al–garnet SSE–Al | Li in the frequency of 1 MHz to 100 mHz at 20°C. (D) Nyquist plots of Li | Al–garnet SSE–Al | Li symmetric cell at various elevated temperatures. (E) The interfacial resistance of the Li | Al–garnet SSE–Al | Li symmetric cell as a function of temperature during heating. (F) Voltage profile depicting the Li plating/striping behavior for the Li | garnet SSE | Li symmetric cell at a current density of 0.05 mA/cm2. The voltage plateau continued to increase each cycle due to the high polarization at the unfavorable Li/SSE interface. The high voltage range reflects the large interfacial resistance for the pristine garnet with Li metal. (G) Li plating of the symmetric Li | Al-garnet-Al | Li cell at 60°C with a current density of 0.05 mA/cm2 for 24 hours. (H to K) Voltage profiles for the Li | Al–garnet SSE–Al | Li symmetric cell at current densities of 0.1 and 0.2 mA/cm2. The voltage plateau remained flat and stable during cycling, which proves that the Li-Al alloy creates a stable interface between the garnet SSE and the Li metal. The low voltage range illustrates the small interfacial resistance in the cell.

  • Fig. 5 Schematic and first-principles computation of the Li-Al alloy interface between the Li metal and the garnet SSE.

    (A) The reaction between Al and Li promotes enhanced molten Li infusion onto the garnet’s rough surface, whereas the formation of a Li-Al alloy fills the gap between the garnet solid electrolyte and the Li metal to improve interfacial contact and enhance Li+ transport. (B) Calculated mutual reaction energy ΔED,mutual of the garnet and Li-Al alloy interfaces.

  • Fig. 6 Hybrid solid-state battery demonstrations.

    (A) EIS of the hybrid solid-liquid LIBs. LiFePO4 cathode is used with a conventional electrolyte on the cathode side: 1 M LiPF6 in ethylene carbonate (EC)/diethyl carbonate (DEC) [1:1 (v/v)]. (B) Galvanostatic charge/discharge profiles of the hybrid solid-liquid Li-ion cell. (C) Cycling performance of the cell over 100 cycles at different current densities. (D) Electrochemical performance of the hybrid solid-liquid Li-S cell. Elemental sulfur was used as the cathode, and 1 M LiTFSI in dimethoxyethane (DME)/1,3-dioxolane (DOL) [1:1 (v/v)] was used as the electrolyte on the cathode side. (E) Electrochemical performance of the hybrid solid-liquid Li-O2 battery. Highly conductive carbon was used as the cathode, and 1 M LiTFSI in tetraethylene glycol dimethyl ether (TEGDME) was used on the cathode side.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/4/e1601659/DC1

    fig. S1. Cross sectional SEM image of garnet SSE.

    fig. S2. Cross section of Al-coated garnet SSE pellet.

    fig. S3. Magnified SEM image of Al-coated garnet SSE.

    fig. S4. Cross section of garnet-Li metal.

    fig. S5. Cross section of the interface between Li metal and Al-coated garnet SSE.

    fig. S6. Digital image and XRD of the lithiated Al-coated garnet SSE.

    fig. S7. Preparation of Li | Al–garnet SSE–Al | Li.

    fig. S8. Symmetric cell setup for charge and discharge tests.

    fig. S9. Digital image of the symmetric cells assembled into 2032 coin cells.

    fig. S10. Cross-sectional SEM images of the cycled Li | Al-coated garnet SSE interface.

    fig. S11. Electrochemical performance of the hybrid solid-state Li-S battery: Cycling stability of the cell and coulombic efficiency of the cell.

    fig. S12. SEM image of the garnet SSE in cycled Li-S cell.

    fig. S13. XRD profile of the garnet after cycling in Li-S cell.

    table S1. The phase equilibria and decomposition energies of the garnet SSE and Li-Al alloy interfaces.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Cross sectional SEM image of garnet SSE.
    • fig. S2. Cross section of Al-coated garnet SSE pellet.
    • fig. S3. Magnified SEM image of Al-coated garnet SSE.
    • fig. S4. Cross section of garnet-Li metal.
    • fig. S5. Cross section of the interface between Li metal and Al-coated garnet SSE.
    • fig. S6. Digital image and XRD of the lithiated Al-coated garnet SSE.
    • fig. S7. Preparation of Li | Al–garnet SSE–Al | Li.
    • fig. S8. Symmetric cell setup for charge and discharge tests.
    • fig. S9. Digital image of the symmetric cells assembled into 2032 coin cells.
    • fig. S10. Cross-sectional SEM images of the cycled Li | Al-coated garnet SSE interface.
    • fig. S11. Electrochemical performance of the hybrid solid-state Li-S battery: Cycling stability of the cell and coulombic efficiency of the cell.
    • fig. S12. SEM image of the garnet SSE in cycled Li-S cell.
    • fig. S13. XRD profile of the garnet after cycling in Li-S cell.
    • table S1. The phase equilibria and decomposition energies of the garnet SSE and Li-Al alloy interfaces.

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