Research ArticleChemistry

Enabling reversible redox reactions in electrochemical cells using protected LiAl intermetallics as lithium metal anodes

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Science Advances  25 Oct 2019:
Vol. 5, no. 10, eaax5587
DOI: 10.1126/sciadv.aax5587
  • Fig. 1 Physical characterizations of the LiAl anode.

    (A) XRD profile of the LiAl anode composed of 80 wt % Li and 20 wt % Al. The dominant XRD peaks correspond to Li (110) and Li9Al4 (−121) crystal facets. (B) Optical images of 200-μm-thick Li and 200-μm-thick LiAl anodes. SEM micrographs of LiAl taken in (C) SE mode and (D) BSE mode. The dark and bright regions correspond to Li and Li9Al4 domains in the LiAl anode. (E) Corresponding EDX elemental mapping of Al for (C). a.u., arbitrary units.

  • Fig. 2 First-principles calculations for Li binding energies for the LiAl anode.

    (A) Binding energy of Li adatoms on Li (110) and Li9Al4 (−121) surfaces at three stable energy minima of Li9Al4*, Li9Al4**, and Li9Al4***. (B) Activation energy barrier for Li adatom surface diffusion on Li (110) and Li9Al4 (−121) for three minimum energy pathways, pathway I, pathway II, and pathway III, corresponding to the three stable energy minima of Li9Al4*, Li9Al4**, and Li9Al4***. The minimum energy pathway is the lowest energy path, connecting two energy minima on the potential energy surface. Theoretical scans over the whole surface were performed to find the energy minima and to identify the three lowest-energy stable sites for Li9Al4. (C) Diffusion paths for Li on the Li9Al4 (−121) surface at three stable energy minima of Li9Al4*, Li9Al4**, and Li9Al4***. Top view of the atomic arrangement of Li and Al atoms on the Li9Al4 (−121) surface to visualize the Li migration on Li9Al4 (−121) along (D) pathway I, (E) pathway II, and (F) pathway III. The energy values at the bottom of each image are the relative energies calculated with respect to the energy at the initial stable configuration. The initial configuration is the first energy minima from where the Li migration initiates. For the reference, the energy at the first minima is considered as 0 eV. Red and light blue spheres are Li and Al atoms, respectively, and the highlighted yellow sphere is the migrating Li adatom along the minimum energy pathways. (G) The atomic arrangement of Li and Al atoms in the unit cell of Li9Al4.

  • Fig. 3 Electrochemical analysis for the LiAl anode.

    Surface morphologies of the LiAl anode after galvanostatic stripping of Li in LiAl|LiAl symmetric cells at the fixed current density of 1 mA cm−2 and for the different amounts of charge passed: (A) 1 mAh cm−2, (B) 2 mAh cm−2, (C) 3 mAh cm−2, and (D) 4 mAh cm−2. SEM images of Li electrodeposits on LiAl when 1 mAh cm−2 of Li is first stripped followed by 1 mAh cm−2 Li deposition on Li9Al4 taken in (E) SE mode and (F) BSE mode. SEM images of Li electrodeposits on LiAl when 4 mAh cm−2 of Li is first stripped followed by 4 mAh cm−2 Li deposition on Li9Al4 taken in (G) SE mode and (H) BSE mode. (I) Galvanostatic Li migration voltage profiles measured for Li|Li and LiAl|LiAl symmetric cells at a fixed current density of 1 mA cm−2 and a capacity of 1 mAh cm−2. Magnified Li migration voltage profiles in (I), (J) from 0 to 10 hours and (K) from 274 to 284 hours. (L) Cycling profiles based on the discharge capacities (filled symbols) and Coulombic efficiencies (open symbols) for Li|NCM811 and LiAl|NCM811 full cells at C rate charging (CC) and C rate discharging (CD) of 0.5 CC and 1 CD with a voltage window of 2.7–4.3 V. (M) Corresponding voltage profiles for the Li|NCM811 full cell from (L) for the 1st to the 90th cycle. Region i represents the initial voltage profiles during the cell discharge. Region ii represents the initial voltage profiles during the cell charge. Region iii represents the voltage profiles at the constant voltage charging. The current densities for charging and discharging rates are 2.05 mA cm−2|0.5 CC and 4.1 mA cm−2|1 CD, with a cathode areal capacity of 4.1 mAh cm−2. (N) Corresponding voltage profiles of the LiAl|NCM811 full cell from (L) for the 1st to the 90th cycle. Region i represents the initial voltage profiles during the cell discharge. Region ii represents the initial voltage profiles during the cell charge. Region iii represents the voltage profiles at the constant voltage charging. The current densities for charging and discharging rates are 2.05 mA cm−2|0.5 CC and 4.1 mA cm−2|1 CD, with a cathode areal capacity of 4.1 mAh cm−2.

  • Fig. 4 First-principles calculations for MoS2 LBASEI.

    (A) In situ free-energy transition of MoS2 2H to MoS2 T with respect to Li concentrations. The inset images are the atomic models of the unit cells of MoS2 2H and MoS2 T. The vertical dashed line represents the transition state of 2H to T phase of MoS2 at 30% lithiation, which is the critical Li concentration in which the phase transition occurs. (B) Binding energy of Li based on the Li concentrations for MoS2 2H and MoS2 T. (C) Diffusion paths of Li on the surfaces of MoS2 2H and lithiated MoS2 T along the t-h-t pathway, where t is the top site of the Mo atom and h is the hollow site in the hexagonal ring of Mo and S atoms. Top view of the atomic arrangement of Mo and S atoms in the MoS2 surface to visualize Li migration on (D) MoS2 2H and (E) lithiated MoS2 T along the t-h-t pathway. The energy value below each image is the relative energy with respect to the initial configuration for corresponding phases of MoS2. The initial configuration is the first stable site from where Li migration initiates. Plum, light purple, and red spheres are Mo, S, and Li atoms, respectively, and the highlighted yellow sphere is the migrating Li atom along the minimum energy pathway.

  • Fig. 5 Electrochemical performances of the MoS2 LiAl anode.

    (A) Surface morphology of the uncycled MoS2 LBASEI–coated LiAl (MoS2 LiAl) anode. The SEM image exhibits uniform coating of the MoS2 LiAl anode. (B) SEM image of the MoS2 LiAl anode (left) with EDX elemental mappings of Mo (middle) and S (right). (C) Galvanostatic Li migration voltage profiles of LiAl|LiAl and LiAl MoS2|MoS2 LiAl symmetric cells at a fixed current density of 1 mA cm−2 and a capacity of 1 mAh cm−2. Magnified Li migration voltage profiles of (C) from (D) 0 to 10 hours, from (E) 410 to 430 hours, and from (F) 780 to 800 hours. Surface morphologies of (G) 1 mAh cm−2, (H) 2 mAh cm−2, (I) 3 mAh cm−2, and (J) 4 mAh cm−2 Li deposited onto MoS2 LiAl from a LiAl MoS2|MoS2 LiAl symmetric cell at a fixed current density of 1 mA cm−2. (K) Galvanostatic Li deposition voltage profiles of Cu MoS2|MoS2 LiAl asymmetric cells based on MoS2 LBASEI thicknesses measured at the fixed current density of 0.05 mA cm−2. The nucleation overpotentials of MoS2 LBASEI are measured by taking the differences between the tip potential and the mass transfer-controlled potential. The horizontal dashed line represents 0 V where the Li deposition, the overplating of Li on MoS2 LBASEI, starts. (L) The Li nucleation overpotentials based on MoS2 LBASEI thicknesses ranging from 0 to 3.076 μm from Cu MoS2|MoS2 LiAl asymmetric cells.

  • Fig. 6 Investigating full-cell operations with the MoS2 LiAl anode.

    Morphologies of Li electrodeposits for the charged MoS2 LiAl anode from the MoS2 LiAl|NCM811 full cell taken (A) at the edge, (B) between the edge and the center, and (C) at the center of the charged MoS2 LiAl anode. The charging C rate used is 0.5 CC. SEM images of (D) the charged MoS2 LiAl anode and (E) the discharged MoS2 LiAl anode, in which the electrodeposits of Li and the corresponding SEI are shown. (F) Cycling profiles based on the discharge capacities (filled symbols) and Coulombic efficiencies (open symbols) for LiAl|NCM811 and MoS2 LiAl|NCM811 full cells at 0.5 CC and 1 CD with a voltage window of 2.7 to 4.3 V. (G) Cycling profiles based on the discharge capacities (filled symbols) and Coulombic efficiencies (open symbols) for the MoS2 LiAl|NCM811 full cell at 0.3 CC and 1 CD with a voltage window of 2.7 to 4.3 V. (H) Corresponding voltage profiles of the MoS2 LiAl|NCM811 full cell in (G) for the 1st to the 500th cycle. Region i represents the initial voltage profiles during the cell discharge. Region ii represents the initial voltage profiles during the cell charge. Region iii represents the voltage profiles at the constant voltage charging. Cyclic voltammograms of (I) MoS2 LiAl|NCM811 and (J) LiAl|NCM811 full cells at a scan rate of 0.1 mV s−1 with a voltage window of 2.7 to 4.3 V. (K) Cycling profiles based on the areal and gravimetric discharge capacities (filled symbols) and Coulombic efficiencies (open symbols) for the MoS2 LiAl|NCM811 pouch cell at 0.1 CC and 1 CD with a voltage window of 2.7 to 4.3 V. The specifications for the pouch cell are 196 mAh, 294 Wh kg−1, and 513 Wh liter−1, and details are further provided in Materials and Methods. The insets represent the real image of and the stacking configuration used for the pouch cell. (L) Schematic illustration for and comparison of the Li migration process occurring at MoS2 LiAl, LiAl, and Li anodes.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/10/eaax5587/DC1

    Fig. S1. LiAl phase diagram and XRD patterns of the LiAl anode.

    Fig. S2. SEM and FIB analysis of the LiAl anode.

    Fig. S3. Li migration behavior of the Li (110) surface.

    Fig. S4. SEM image of Li electrodeposits on the Li anode.

    Fig. S5. AC impedance measurements for LiAl and Li anodes.

    Fig. S6. SEM images of cycled LiAl and Li anodes from the full cell.

    Fig. S7. Optical images of LiAl and MoS2 LiAl anodes.

    Fig. S8. Atomic structures of MoS2 2H and MoS2 T.

    Fig. S9. SEM images of Li electrodeposits on the MoS2 LiAl anode.

    Fig. S10. AC impedance and practical areal capacity measurements for Li, LiAl, and MoS2 LiAl anodes.

    Fig. S11. SEM images of SEI for Li, LiAl, and MoS2 LiAl anodes.

    Table S1. The binding energies of Li clusters on Li (110) and Li9Al4 (−121) surfaces.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. LiAl phase diagram and XRD patterns of the LiAl anode.
    • Fig. S2. SEM and FIB analysis of the LiAl anode.
    • Fig. S3. Li migration behavior of the Li (110) surface.
    • Fig. S4. SEM image of Li electrodeposits on the Li anode.
    • Fig. S5. AC impedance measurements for LiAl and Li anodes.
    • Fig. S6. SEM images of cycled LiAl and Li anodes from the full cell.
    • Fig. S7. Optical images of LiAl and MoS2 LiAl anodes.
    • Fig. S8. Atomic structures of MoS2 2H and MoS2 T.
    • Fig. S9. SEM images of Li electrodeposits on the MoS2 LiAl anode.
    • Fig. S10. AC impedance and practical areal capacity measurements for Li, LiAl, and MoS2 LiAl anodes.
    • Fig. S11. SEM images of SEI for Li, LiAl, and MoS2 LiAl anodes.
    • Table S1. The binding energies of Li clusters on Li (110) and Li9Al4 (−121) surfaces.

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