Negating interfacial impedance in garnet-based solid-state Li metal batteries

Journal name:
Nature Materials
Volume:
16,
Pages:
572–579
Year published:
DOI:
doi:10.1038/nmat4821
Received
Accepted
Published online

Abstract

Garnet-type solid-state electrolytes have attracted extensive attention due to their high ionic conductivity, approaching 1mScm−1, excellent environmental stability, and wide electrochemical stability window, from lithium metal to ~6V. However, to date, there has been little success in the development of high-performance solid-state batteries using these exceptional materials, the major challenge being the high solid–solid interfacial impedance between the garnet electrolyte and electrode materials. In this work, we effectively address the large interfacial impedance between a lithium metal anode and the garnet electrolyte using ultrathin aluminium oxide (Al2O3) by atomic layer deposition. Li7La2.75Ca0.25Zr1.75Nb0.25O12 (LLCZN) is the garnet composition of choice in this work due to its reduced sintering temperature and increased lithium ion conductivity. A significant decrease of interfacial impedance, from 1,710cm2 to 1cm2, was observed at room temperature, effectively negating the lithium metal/garnet interfacial impedance. Experimental and computational results reveal that the oxide coating enables wetting of metallic lithium in contact with the garnet electrolyte surface and the lithiated-alumina interface allows effective lithium ion transport between the lithium metal anode and garnet electrolyte. We also demonstrate a working cell with a lithium metal anode, garnet electrolyte and a high-voltage cathode by applying the newly developed interface chemistry.

At a glance

Figures

  1. Characterization of as-prepared LLCZN garnet electrolyte.
    Figure 1: Characterization of as-prepared LLCZN garnet electrolyte.

    a, Digital photo of a polished yellowish LLCZN pellet. It is translucent and the underneath letters can be seen. b, XRD pattern comparison of the as-prepared LLCZN and standard Li5La3Nb2O12 with cubic garnet phase. c,d, SEM images for cross-section (c) and top view (d) of the LLCZN pellet. e, EIS of LLCZN pellets at low temperature from 22–50°C. f, Arrhenius plot of the LLCZN ionic conductivity.

  2. Characterizations of garnet solid-state electrolyte/Li metal interface.
    Figure 2: Characterizations of garnet solid-state electrolyte/Li metal interface.

    a, Schematic of the wetting behaviour of garnet surface with molten Li. b, SEM images of the garnet solid-state electrolyte/Li metal interface. Without ALD-Al2O3 coating, garnet has a poor interfacial contact with Li metal even on heating. With the help of ALD-Al2O3 coating on garnet, Li metal can uniformly bond with garnet at the interface on heating. Inset are photos of melted Li metal on top of the garnet surface clearly demonstrating classical wetting behaviour for the ALD-treated garnet surface. c, Comparison of EIS profiles of the symmetric Li non-blocking garnet cells. Inset shows the enlarged impedance curve of the ALD-treated garnet cell. d, Comparison of d.c. cycling for symmetric cells of Li/bare garnet/Li (black curve) and Li/ALD-treated garnet/Li (red curve) at a current density of 0.1mAcm−2. The inset is the magnified curve of the ALD-treated cell. e, Galvanostatic cycling of Li/ALD-treated garnet/Li with a current density of 0.2Acm−2.

  3. Characterization for the interface of ALD-Al2O3-coated garnet solid electrolyte.
    Figure 3: Characterization for the interface of ALD-Al2O3-coated garnet solid electrolyte.

    a, Typical TEM cross-section image at the interface of ALD-Al2O3-coated garnet with Ti protection layer. bg, Typical TEM/HAADF image (b) and corresponding EELS maps (cg, Al, Li, O, overlap of Al and Li, and Ti, respectively) for the interfacial cross-section. h, EELS with energy 250–1,000eV showing peaks of Zr M-edge, O K-edge, and La M4,5-edge. i, EELS with energy 50–120eV showing peaks of Li K-edge and Al L-edge. j, SAED of the interlayer between garnet and ALD-Al2O3.

  4. First-principles calculations of Li metal and garnet interface with and without ALD-Al2O3.
    Figure 4: First-principles calculations of Li metal and garnet interface with and without ALD-Al2O3.

    a,b, The interface model of Li metal on the LiAl5O8  (a) and the Li2CO3 (b) from ab initio molecular dynamics simulations. ce, Li grand potential phase diagrams showing the phase equilibria of a LLZO system at different Li chemical potentials: μLi = 0eV, corresponding to Li metal (c); μLi = −0.06eV (d); and −1.23eV, corresponding to the range of Li chemical potentials in lithiated alumina (e).

  5. High-voltage cell with Li metal anode and LLZCN electrolyte.
    Figure 5: High-voltage cell with Li metal anode and LLZCN electrolyte.

    a, Schematic of the designed full cell using ALD-coated LLCZN, Li metal anode, LFMO/carbon black/PVDF composite cathode. Note a tiny amount of liquid organic electrolyte with a composition of 1M LiPF6 in FEC/FEMC/HFE (20:60:20, by volume) was added to improve the interface between the composite cathode and garnet electrolyte. b, A working cell to light up an LED device. The yellowish pellet in the left photo is the ALD-treated LLCZN solid electrolyte. The LED is connected to the cell with the aid of plastic tweezers. c, The galvanostatic charge and discharge profile of the LFMO/ALD-garnet SSE/Li full cell. d, Cycling performance of the cell.

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Author information

  1. These authors contributed equally to this work.

    • Xiaogang Han,
    • Yunhui Gong &
    • Kun (Kelvin) Fu

Affiliations

  1. University of Maryland Energy Research Center, and Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA

    • Xiaogang Han,
    • Yunhui Gong,
    • Kun (Kelvin) Fu,
    • Xingfeng He,
    • Gregory T. Hitz,
    • Jiaqi Dai,
    • Alex Pearse,
    • Boyang Liu,
    • Howard Wang,
    • Gary Rubloff,
    • Yifei Mo,
    • Eric D. Wachsman &
    • Liangbing Hu
  2. Institute for Systems Research, University of Maryland, College Park, Maryland 20742, USA

    • Alex Pearse &
    • Gary Rubloff
  3. Department of Chemistry, University of Calgary, 2500 University Drive Northwest, Calgary, Alberta T2N 1N4, Canada

    • Venkataraman Thangadurai

Contributions

X.H., Y.G. and K.F. fabricated the samples and carried out the experiments, characterizations, data analysis, and manuscript preparation. X.H. and Y.M. conducted the theoretical analysis. G.T.H. helped prepare samples and analysed the experimental results. J.D. drew the schematics and prepared FIB samples. A.P. and G.R. carried out the XPS and XPS data analysis. B.L. prepared samples and conducted ALD. H.W. carried out NDP and NDP data analysis. V.T. helped review the results, and E.D.W. and L.H. managed the project and reviewed the results, data analysis, and manuscript preparation.

Competing financial interests

The authors declare no competing financial interests.

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