Research ArticleELECTROCHEMISTRY

Stabilizing electrochemical interfaces in viscoelastic liquid electrolytes

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Science Advances  23 Mar 2018:
Vol. 4, no. 3, eaao6243
DOI: 10.1126/sciadv.aao6243
  • Fig. 1 Electrochemical characteristics of the viscoelastic electrolytes.

    (A) I-V curves of electrolytes with different polymer concentrations. (B to D) Voltage versus time profiles measured in electrolytes with (B) no PMMA, (C) 2 wt % PMMA, and (D) 8 wt % PMMA at current densities ranging from 0.316 to 2.526 mA/cm2. (E) Average tracer particle velocities measured in an optical lithium||stainless steel cell containing control (no polymer) and viscoelastic liquid electrolytes containing 4 wt % polymer. (F) Average tracer particle velocities measured in control and viscoelastic liquid electrolytes as a function of current density.

  • Fig. 2 Physical characteristics of viscoelastic liquid electrolytes.

    (A) Frequency-dependent dynamic storage G′ (filled symbols) and loss G″ (open symbol) moduli for PMMA–EC/PC (v/v, 1:1)–1 M LiTFSI electrolytes as a function of polymer concentration. (B) Concentration regimes of zero shear viscosity and conductivity at 25°C. (C) Extended stability regime (from Fig. 1A) in viscoelastic electrolytes as a function of electrolyte viscosity. The dashed line through the data shows that the experimental data can be approximated by the scaling relation, ΔV : η1/4. (D) DC ionic conductivity of the viscoelastic liquid electrolytes as a function of temperature. The solid lines are Vogel-Fulcher-Tammann fits for the temperature-dependent ionic conductivity. (E) Nyquist plot obtained from EIS measurements in electrolytes with different polymer concentrations. The solid lines are fitted by an equivalent electrical circuit model shown in the supporting information (fig. S7). (F) Polymer contribution to the ASR of an electrolyte/Li interface as a function of electrolyte viscosity. The dashed line through the data shows that the experimental data obey an approximate scaling relation, Rint3 : η1/4.

  • Fig. 3 Snapshots of interface evolution during electrodeposition in Li||stainless steel and Na||stainless steel optical cells operated above the limiting current.

    (A to D) Electrodeposition of Li in a Newtonian liquid control electrolyte (EC/PC–1 M LiTFSI). (E to H) Li electrodeposition in a viscoelastic liquid electrolyte (4 wt % PMMA in EC/PC–1 M LiTFSI). (I to L) Na deposition in a Newtonian liquid electrolyte [EC/PC–1 M sodium perchlorate (NaClO4)]. (M to P) Na electrodeposition in a viscoelastic electrolyte (4 wt % PMMA in EC/PC–1 M NaClO4). Scale bars, 100 μm. (Q to S) Flow patterns obtained by tracking tracer particle motions at different stages of the lithium electrodeposition in a Newtonian liquid EC/PC–1 M LiTFSI. (T to V) Flow patterns in a viscoelastic liquid electrolyte (4 wt % PMMA in EC/PC–1 M LiTFSI).

  • Fig. 4 Analysis of electrodeposition of different metals in Newtonian and viscoelastic liquid electrolytes.

    (A) Average lithium dendrite tip height as a function of time in the Newtonian control liquid electrolyte (EC/PC–1 M LiTFSI) and viscoelastic liquid electrolyte (4 wt % PMMA in EC/PC–1 M LiTFSI) at current densities below and above the limiting current. (B) Average sodium dendrite tip height as a function of time in the Newtonian control liquid electrolyte (EC/PC–1 M NaClO4) and viscoelastic liquid electrolyte (4 wt % PMMA in EC/PC–1 M NaClO4) at current densities below and above the limiting current. (C) Comparison of average dendrite growth rate for different metals in the Newtonian and viscoelastic liquid electrolytes at a fixed current density of 5 mA/cm2.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/3/eaao6243/DC1

    fig. S1. An illustration showing the lithium symmetric coin cell used for the I-V electrokinetic measurements.

    fig. S2. Electrokinetic characteristics of viscoelastic electrolytes as a function of measurement time.

    fig. S3. Linear sweep voltammetry as a function of PMMA concentration at a scan rate of 1 mV/s.

    fig. S4. Schematic drawing of the experimental setup used to perform the visualization experiment for electrodeposition.

    fig. S5. Tracer particle velocities in the Newtonian liquid electrolyte (EC/PC–1 M LiTFSI) and a representative viscoelastic electrolyte (4 wt % PMMA in EC/PC–1 M LiTFSI) as a function of voltage.

    fig. S6. Complex shear viscosity at 25°C for viscoelastic liquid electrolytes containing varying concentrations of PMMA.

    fig. S7. EIS measurements and analysis for viscoelastic electrolytes with different polymer concentrations.

    fig. S8. Depth-profiling XPS spectra of a lithium metal surface after electrodeposition for 1 hour at a current density of 1 mA/cm2.

    fig. S9. Photographic images showing evolution of various metal electrode/electrolyte interfaces during electrodeposition.

    table S1. Measured Li+ transference numbers and calculated limiting current densities [in the optical cell (J1) and O-ring coin cell (J2)] for electrolytes used in the study.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. An illustration showing the lithium symmetric coin cell used for the I-V electrokinetic measurements.
    • fig. S2. Electrokinetic characteristics of viscoelastic electrolytes as a function of measurement time.
    • fig. S3. Linear sweep voltammetry as a function of PMMA concentration at a scan rate of 1 mV/s.
    • fig. S4. Schematic drawing of the experimental setup used to perform the visualization experiment for electrodeposition.
    • fig. S5. Tracer particle velocities in the Newtonian liquid electrolyte (EC/PC–1 M LiTFSI) and a representative viscoelastic electrolyte (4 wt % PMMA in EC/PC–1 M LiTFSI) as a function of voltage.
    • fig. S6. Complex shear viscosity at 25°C for viscoelastic liquid electrolytes containing varying concentrations of PMMA.
    • fig. S7. EIS measurements and analysis for viscoelastic electrolytes with different polymer concentrations.
    • fig. S8. Depth-profiling XPS spectra of a lithium metal surface after electrodeposition for 1 hour at a current density of 1 mA/cm2.
    • fig. S9. Photographic images showing evolution of various metal electrode/electrolyte interfaces during electrodeposition.
    • table S1. Measured Li+ transference numbers and calculated limiting current densities in the optical cell (J1) and O-ring coin cell (J2) for electrolytes used in the study.

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