Design principles for solid-state lithium superionic conductors

Journal name:
Nature Materials
Volume:
14,
Pages:
1026–1031
Year published:
DOI:
doi:10.1038/nmat4369
Received
Accepted
Published online

Abstract

Lithium solid electrolytes can potentially address two key limitations of the organic electrolytes used in today’s lithium-ion batteries, namely, their flammability and limited electrochemical stability. However, achieving a Li+ conductivity in the solid state comparable to existing liquid electrolytes (>1mScm−1) is particularly challenging. In this work, we reveal a fundamental relationship between anion packing and ionic transport in fast Li-conducting materials and expose the desirable structural attributes of good Li-ion conductors. We find that an underlying body-centred cubic-like anion framework, which allows direct Li hops between adjacent tetrahedral sites, is most desirable for achieving high ionic conductivity, and that indeed this anion arrangement is present in several known fast Li-conducting materials and other fast ion conductors. These findings provide important insight towards the understanding of ionic transport in Li-ion conductors and serve as design principles for future discovery and design of improved electrolytes for Li-ion batteries.

At a glance

Figures

  1. Mapping of the anion sublattice to a bcc/fcc/hcp framework in solid-state Li-ion conductors.
    Figure 1: Mapping of the anion sublattice to a bcc/fcc/hcp framework in solid-state Li-ion conductors.

    ae, Crystal structure of Li-ion conductors Li10GeP2S12 (a), Li7P3S11 (b), Li2S (c), γ-Li3PS4 (d) and Li4GeS4 (e). Li atom, partially occupied Li atom, S atom, PS4 tetrahedra and GeS4 tetrahedra (partially occupied in Li10GeP2S12) are coloured green, green–white, yellow, purple and blue, respectively. In both Li10GeP2S12 and Li7P3S11, the sulphur anion sublattice can be closely mapped to a bcc framework (red circles connected by red lines). In Li2S, the anion sublattice is an exact fcc matrix (yellow–red circles). The anion sublattices in γ-Li3PS4 and Li4GeS4 are closely matched to a hcp framework.

  2. Li-ion migration pathways in bcc/fcc/hcp-type anion lattices.
    Figure 2: Li-ion migration pathways in bcc/fcc/hcp-type anion lattices.

    ac, Li-ion migration path (left panels) and calculated energy path (right panels) in bcc (a), fcc (b) and hcp (c) sulphur lattices. The sulphur anions are coloured yellow, and the Li ions are coloured green, blue and red for different paths. LiS4 tetrahedra and LiS6 octahedra are coloured green and red, respectively.

  3. Activation barrier for Li-ion migration versus lattice volume.
    Figure 3: Activation barrier for Li-ion migration versus lattice volume.

    Activation barrier calculated for the Li-ion migration pathways in the bcc/fcc/hcp S2− lattices at different volumes. Solid and dotted lines are guides to the eye. Experimental activation energies for Li10GeP2S12 (ref. 15), Li10SnP2S12 (refs 17,18), Li10SiP2S12 (ref. 19), Li7P3S11 (ref. 13), Li2S (ref. 42), Li4GeS4 (ref. 26) and γ-Li3PS4 (ref. 26) are marked by a star symbol for comparison. The underestimate of the activation energy for Li2S is due to fact that the experimental value contains contributions from the defect formation energy.

  4. Li-ion probability densities in Li-ion conductors.
    Figure 4: Li-ion probability densities in Li-ion conductors.

    ad, The probability densities of Li ions are obtained from ab initio molecular dynamics simulations at 900K in Li10GeP2S12 (a), Li7P3S11 (b), Li2S (c) and Li4GeS4 (d). Isosurfaces of the ionic probability densities are plotted at increasing isovalues ranging from 2P0 to 32P0, in which P0 is defined as the mean value of the density for each structure. PS4 tetrahedra and GeS4 tetrahedra are coloured purple and blue, respectively. The sulphur atoms are shown as small yellow circles for Li2S.

  5. Similarity of screened ICSD structures containing Li and S to a bcc anion framework using the structural matching algorithm.
    Figure 5: Similarity of screened ICSD structures containing Li and S to a bcc anion framework using the structural matching algorithm.

    Compounds with transition-metal cations are excluded. The lattice length deviation is defined as σl = 1 − min(a, b, c)/max(a, b, c), and the angle deviation is defined as σθ = max(|90° − α|, |90° − β|, |90° − γ|), where a, b, c, α, β and γ are the conventional unit-cell parameters of the transformed lattice (see Methods and Supplementary Fig. 1). For an ideal compound with a perfect bcc anion framework σl = σθ = 0.

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Author information

Affiliations

  1. Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    • Yan Wang,
    • William Davidson Richards,
    • Shyue Ping Ong,
    • Jae Chul Kim,
    • Yifei Mo &
    • Gerbrand Ceder
  2. Department of NanoEngineering, University of California, San Diego, La Jolla, California 92093, USA

    • Shyue Ping Ong
  3. Samsung Advanced Institute of Technology-USA, 1 Cambridge Center, Suite 702, Cambridge, Massachusetts 02142, USA

    • Lincoln J. Miara
  4. Department of Materials Science and Engineering, University of Maryland, College Park Maryland 20742, USA

    • Yifei Mo
  5. Department of Materials Science and Engineering, University of California, Berkeley, California 94720, USA

    • Gerbrand Ceder
  6. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

    • Gerbrand Ceder

Contributions

G.C., W.D.R. and Y.W. proposed the concept. Y.W. carried out the calculations and together with W.D.R. prepared the manuscript initially. W.D.R. conceived and implemented the structural matcher algorithm. All authors contributed to the discussions and revisions of the manuscript.

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The authors declare no competing financial interests.

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