Research ArticleAPPLIED SCIENCES AND ENGINEERING

Designer interphases for the lithium-oxygen electrochemical cell

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Science Advances  19 Apr 2017:
Vol. 3, no. 4, e1602809
DOI: 10.1126/sciadv.1602809
  • Fig. 1 Artificial SEI concept and experimental verification of its proposed operating mechanism.

    (A) Schematic for the reaction of lithium 2-bromoethanesulfonate with lithium metal forming LiBr and lithium-based organometallic. (B) SEM image of the interfacial layer between an intact electrolyte and a lithium electrode, revealed in a cross section produced by cryo-FIB milling. (C) Lithium 1s peak obtained from XPS of the lithium metal anode of a Li-O2 battery with the electrolyte ionomer [10% (by weight)] in 1 M LiNO3-DMA. (D) Oxygen 1s peak of the lithium anode. (E) Bromine 3d peak of the lithium anode. In (C) to (E), the first row shows the postmortem analysis after discharging until 2 V, the second row shows the result after cycling once with each half-cycle 5 hours long, and the third row shows the result after cycling five times with each half-cycle 1 hour long. (F) Three-dimensional diagram of Nyquist plots obtained by impedance measurements at different intervals of time using symmetric lithium cells, in which -Zim is the imaginary component of the impedance and -Zreal is the real component of the impedance. (G) Comparison of interfacial and bulk impedance values for ionomer-based and control electrolytes as a function of time. In (F) and (G), the red symbols denote results with the control electrolyte (1 M LiNO3-DMA), whereas the black and blue symbols represent batteries with 10 and 5% (by weight) ionomer additive, respectively, with the same electrolyte.

  • Fig. 2 Stabilizing the lithium-electrolyte interface.

    (A) SEM images of stainless steel (SS) electrode after depositing lithium (10 mAh/cm2) in a Li||SS cell with and without the ionomer additive using the same electrolyte of 1 M LiNO3-DMA. (B) Voltage profile of the Li||SS cell plotted over time. In this experiment, Li+ ions were deposited onto the stainless steel side at a current density of 1 mA/cm2 for 10 hours, after which the cell was kept at rest for an additional 10 hours, as shown in the current-versus-time curve. In the voltage-versus-time graph, the red line represents the profile of the control electrolyte (1 M LiNO3-DMA), whereas the black line is for the same electrolyte enriched with 10% (by weight) ionomer additive. The dashed blue line in the current-versus-time graph is the applied current for both cases. (C) Linear scan voltammetry showing current as a function of voltage versus Li/Li+, with Li as both working and reference electrode and SS being the counter electrode. (D) In a Li||SS cell, lithium with 10-mAh/cm2 capacity is deposited onto SS, and the battery was charged and discharged consecutively at various current densities. The cycle number associated with the divergence of voltage is plotted against the respective current densities. (E) Voltage profile for the strip-and-plate experiment under the abovementioned condition using a current density of 0.05 mA/cm2. In all figures, red indicates the control electrolyte (1 M LiNO3-DMA) and black represents the addition of 10% (by weight) ionomer additive, whereas blue denotes 5% (by weight) addition.

  • Fig. 3 Characterization and electrochemical analysis of oxygen cathode.

    (A) Full charge-discharge cycle of a Li||O2 cell using ionomer-enriched 1 M LiNO3-DMA electrolyte operated at a current density of 31.25 μA/cm2. The different points on the voltage profile indicate various stages at which the same-type cells were stopped for ex situ analysis. The images below the voltage profile show the surface of a carbon cathode at the D1, D2, and D3 discharge phases. The size of the Li2O2 is seen to be increasing over the course of discharge. C1 and C2 show the stages of recharge; it is seen in C1 that the cathode is absent of Li2O2 particles. (B) XRD analysis showing various characteristic peaks for a fully discharged and a recharged Li||O2 battery. Here, diamonds denote Li2O2 peak and circles represent carbon. The red lines refer to the control electrolyte (1 M LiNO3-DMA), whereas black lines show the result for the same electrolyte with the ionomer additive. (C) The diameter of Li2O2 particles obtained by fully discharging a Li||O2 cell is plotted as a function of current density. Here, black indicates the electrolyte (1 M LiNO3-DMA) with the ionomer additive, whereas red represents data from Lau and Archer’s paper that used the electrolyte 1 M LiTF in TEGDME. *From Lau and Archer (10).

  • Fig. 4 Galvanostatic cycling performance of lithium-oxygen electrochemical cell.

    (A) Voltage profile for batteries fully discharged and recharged with 1 M LiNO3-DMA + ionomer electrolyte (shown with a solid black line) and a low–donor number electrolyte, 1 M LiTFSI-diglyme (shown with a dashed black line), at a current density of 31.25 μA/cm2. (B) Comparison of cycling voltammetry results for the control electrolyte (1 M LiNO3-DMA; shown with dashed lines) and the same electrolyte with the ionomer additive (shown with solid lines). The inset shows three cycles of cyclic voltammetry for the ionomer case. (C) Voltage profile of the Li||O2 battery with a cutoff capacity of 3000 mAh/g and a current density of 0.04 mA/cm2. The solid lines indicate ionomer-based electrolytes, whereas the control is shown with dashed lines. The inset shows the noisy profile of the fifth cycle with the control electrolyte. (D) Voltage profile with a capacity cutoff of 800 mAh/g and a current density of 0.08 mA/cm2 for a Li||O2 cell using the control electrolyte (1 M LiNO3-DMA). (E) Voltage-versus-capacity curve with the same cutoff of 800 mAh/g using the ionomer additive in the electrolyte. (F) End voltage of charging cycle for the control and the ionomer-added electrolyte is plotted as function of cycle number.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/4/e1602809/DC1

    fig. S1. Two-dimensional EDAX mapping of lithium-deposited stainless steel substrate with 1 M LiNO3-DMA electrolyte and 10% ionomer additive.

    fig. S2. XPS results showing the binding energy of Li and O atoms with the control electrolyte (1 M LiNO3-DMA).

    fig. S3. Nyquist plots of 1 M LiNO3-DMA enriched with 5% (by weight) ionomer additive, showing impedance for different storage times of the battery.

    fig. S4. Equivalent circuit model to fit the Nyquist plot obtained from impedance spectroscopy measurement comprising bulk resistance, interfacial resistance parallel to a constant phase element, and a solid-state diffusion element.

    fig. S5. Nyquist plots showing experimental as well as circuit model–fitted results of impedance measurements with symmetric cells for the control electrolyte and ionomer-added batteries after 48 and 56 hours of storage.

    fig. S6. Stripping and plating of Li versus stainless steel cell after depositing lithium (10 mAh/cm2) onto stainless steel.

    fig. S7. Size analysis of lithium peroxide particles after discharging a Li-O2 cell with 1 M LiNO3-DMA electrolyte and the ionomer additive at different current densities, as indicated in the box.

    table S1. Atomic percentage of detected elements on lithium anodes.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Two-dimensional EDAX mapping of lithium-deposited stainless steel substrate with 1 M LiNO3-DMA electrolyte and 10% ionomer additive.
    • fig. S2. XPS results showing the binding energy of Li and O atoms with the control electrolyte (1 M LiNO3-DMA).
    • fig. S3. Nyquist plots of 1 M LiNO3-DMA enriched with 5% (by weight) ionomer additive, showing impedance for different storage times of the battery.
    • fig. S4. Equivalent circuit model to fit the Nyquist plot obtained from impedance spectroscopy measurement comprising bulk resistance, interfacial resistance parallel to a constant phase element, and a solid-state diffusion element.
    • fig. S5. Nyquist plots showing experimental as well as circuit model–fitted results of impedance measurements with symmetric cells for the control electrolyte and ionomer-added batteries after 48 and 56 hours of storage.
    • fig. S6. Stripping and plating of Li versus stainless steel cell after depositing lithium (10 mAh/cm2) onto stainless steel.
    • fig. S7. Size analysis of lithium peroxide particles after discharging a Li-O2 cell with 1 M LiNO3-DMA electrolyte and the ionomer additive at different current densities, as indicated in the box.
    • table S1. Atomic percentage of detected elements on lithium anodes.

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