Lithium Transport in Li_4.4M_0.4M′_0.6S₄ (M = Al³⁺, Ga³⁺, and M′ = Ge⁴⁺, Sn⁴⁺): Combined Crystallographic, Conductivity, Solid State NMR, and Computational Studies

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Leube, Bernhard T, Inglis, Kenneth K, Carrington, Elliot J, Sharp, Paul M, Shin, J Felix, Neale, Alex R ORCID: 0000-0001-7675-5432, Manning, Troy D ORCID: 0000-0002-7624-4306, Pitcher, Michael J, Hardwick, Laurence J ORCID: 0000-0001-8796-685X, Dyer, Matthew S ORCID: 0000-0002-4923-3003 et al (show 3 more authors) , Blanc, Frederic ORCID: 0000-0001-9171-1454, Claridge, John B ORCID: 0000-0003-4849-6714 and Rosseinsky, Matthew J ORCID: 0000-0002-1910-2483 (2018) Lithium Transport in Li_4.4M_0.4M′_0.6S₄ (M = Al³⁺, Ga³⁺, and M′ = Ge⁴⁺, Sn⁴⁺): Combined Crystallographic, Conductivity, Solid State NMR, and Computational Studies CHEMISTRY OF MATERIALS, 30 (20). pp. 7183-7200. ISSN 0897-4756, 1520-5002

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Abstract

To understand the structural and compositional factors controlling lithium transport in sulfides, we explored the Li<inf>5</inf>AlS<inf>4</inf>-Li<inf>4</inf>GeS<inf>4</inf> phase field for new materials. Both parent compounds are defined structurally by a hexagonal close packed sulfide lattice, where distinct arrangements of tetrahedral metal sites give Li<inf>5</inf>AlS<inf>4</inf> a layered structure and Li<inf>4</inf>GeS<inf>4</inf> a three-dimensional structure related to γ-Li<inf>3</inf>PO<inf>4</inf>. The combination of the two distinct structural motifs is expected to lead to new structural chemistry. We identified the new crystalline phase Li<inf>4.4</inf>Al<inf>0.4</inf>Ge<inf>0.6</inf>S<inf>4</inf>, and investigated the structure and Li⁺ ion dynamics of the family of structurally related materials Li<inf>4.4</inf>M<inf>0.4</inf>M′<inf>0.6</inf>S<inf>4</inf> (M = Al³⁺, Ga³⁺ and M′ = Ge⁴⁺, Sn⁴⁺). We used neutron diffraction to solve the full structures of the Al-homologues, which adopt a layered close-packed structure with a new arrangement of tetrahedral (M/M′) sites and a novel combination of ordered and disordered lithium vacancies. AC impedance spectroscopy revealed lithium conductivities in the range of 3(2) × 10^-6 to 4.3(3) × 10^-5 S cm^-1 at room temperature with activation energies between 0.43(1) and 0.38(1) eV. Electrochemical performance was tested in a plating and stripping experiment against Li metal electrodes and showed good stability of the Li<inf>4.4</inf>Al<inf>0.4</inf>Ge<inf>0.6</inf>S<inf>4</inf> phase over 200 h. A combination of variable temperature ⁷Li solid state nuclear magnetic resonance spectroscopy and ab initio molecular dynamics calculations on selected phases showed that two-dimensional diffusion with a low energy barrier of 0.17 eV is responsible for long-range lithium transport, with diffusion pathways mediated by the disordered vacancies while the ordered vacancies do not contribute to the conductivity. This new structural family of sulfide Li⁺ ion conductors offers insight into the role of disordered vacancies on Li⁺ ion conductivity mechanisms in hexagonally close packed sulfides that can inform future materials design.

Item Type:	Article
Uncontrolled Keywords:	3402 Inorganic Chemistry, 3403 Macromolecular and Materials Chemistry, 34 Chemical Sciences, 3406 Physical Chemistry, 40 Engineering, 4016 Materials Engineering
Depositing User:	Symplectic Admin
Date Deposited:	16 Nov 2018 10:58
Last Modified:	16 Jun 2026 06:02
DOI:	10.1021/acs.chemmater.8b03175
Open Access URL:	https://doi.org/10.1021%2Facs.chemmater.8b03175
Related Websites:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3027806
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