High Lithium Content and Site Disorder in the Transition Metal Oxide Argyrodites Li₇TiO₅X (X = Cl^-, Br^-)

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Morscher, Alexandra, Corti, Lucia, Goodwin, Samuel L, Acin-Lalanza, Andres, Wright, Matthew A, Surta, T Wesley, Chen, Ruiyong ORCID: 0000-0002-5340-248X, Dyer, Matthew S ORCID: 0000-0002-4923-3003, Blanc, Frederic ORCID: 0000-0001-9171-1454, Daniels, Luke M ORCID: 0000-0002-7077-6125 et al (show 2 more authors) , Claridge, John B ORCID: 0000-0003-4849-6714 and Rosseinsky, Matthew J ORCID: 0000-0002-1910-2483 (2026) High Lithium Content and Site Disorder in the Transition Metal Oxide Argyrodites Li₇TiO₅X (X = Cl^-, Br^-) CHEMISTRY OF MATERIALS, 38 (13). pp. 6312-6322. ISSN 0897-4756, 1520-5002

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Abstract

Sulfide lithium argyrodites are a key materials family that are studied as solid electrolytes in commercial all-solid-state batteries (ASSBs), while their oxide analogues remain relatively unexplored. This study presents the discovery of Li<inf>7</inf>TiO<inf>5</inf>X (X = Cl^–, Br^–), the first lithium argyrodite materials in which a transition metal is used as the framework-forming cation, expanding the chemical space that is accessible for oxide argyrodites. Incorporation of Ti⁴⁺ enables the lithium content to be maximized to 7 Li⁺ per formula unit. Interestingly, even with the high lithium content, Li<inf>7</inf>TiO<inf>5</inf>Cl retains a Li⁺ site disordered cubic F4̅3m structure at room temperature with Li⁺ occupancy of the T5, T5a, and T3 positions, and exhibits an ionic conductivity of 2.2(2) × 10^–6 S cm^–1 with the lowest reported activation energy (0.36(2) eV) for bulk Li⁺ ion transport in an oxide argyrodite. Conversely, Li<inf>7</inf>TiO<inf>5</inf>Br adopts the same F4̅3m symmetry at room temperature but with an ordered arrangement of Li⁺ positions via full occupancy of the T5a and T3 positions, and thus has an ionic conductivity that is 3 orders of magnitude lower (∼10^–9 S cm^–1) and a much higher activation energy (0.58(2) eV) than Li<inf>7</inf>TiO<inf>5</inf>Cl. Order–disorder behavior is observed below 250 K in Li<inf>7</inf>TiO<inf>5</inf>Cl, where a Li⁺ site ordering pattern is observed that is distinct from Li<inf>7</inf>TiO<inf>5</inf>Br and all sulfide argyrodites, yielding a tetragonal symmetry (I4̅) for only the second time to date in the argyrodite structure type. This unique order–disorder behavior, alongside the ability to incorporate transition metal cations within this material family emphasizes the potential to access much greater structural diversity via the expansive chemical space that is available for exploration in oxide argyrodites.

Item Type:	Article
Uncontrolled Keywords:	40 Engineering, 4016 Materials Engineering, 34 Chemical Sciences, 3406 Physical Chemistry, 7 Affordable and Clean Energy
Divisions:	Faculty of Science & Engineering Faculty of Science & Engineering > School of Physical Sciences Faculty of Science & Engineering > School of Physical Sciences > Chemistry
Depositing User:	Symplectic Admin
Date Deposited:	24 Jun 2026 13:26
Last Modified:	01 Aug 2026 01:32
DOI:	10.1021/acs.chemmater.6c00177
Related Websites:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3199125
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