Fast Lithium Ion Conduction in Lithium Phosphidoaluminates

Tassilo M F Restle; Christian Sedlmeier; Holger Kirchhain; Wilhelm Klein; Gabriele Raudaschl-Sieber; Volker L Deringer; Leo van Wüllen; Hubert A Gasteiger; Thomas F Fässler

doi:10.1002/anie.201914613

Fast Lithium Ion Conduction in Lithium Phosphidoaluminates

Angew Chem Int Ed Engl. 2020 Mar 27;59(14):5665-5674. doi: 10.1002/anie.201914613. Epub 2020 Jan 7.

Authors

Tassilo M F Restle¹, Christian Sedlmeier², Holger Kirchhain³, Wilhelm Klein¹, Gabriele Raudaschl-Sieber⁴, Volker L Deringer^{5

6}, Leo van Wüllen³, Hubert A Gasteiger², Thomas F Fässler¹

Affiliations

¹ Department of Chemistry, Chair for Inorganic Chemistry with Focus on New Materials, Technische Universität München, Lichtenbergstraße 4, 85747, Garching, Germany.
² Department of Chemistry and Catalysis Research Center, Chair of Technical Electrochemistry, Technische Universität München, Lichtenbergstraße 4, 85747, Garching, Germany.
³ Department of Physics, University of Augsburg, Universitätsstraße 1, 86159, Augsburg, Germany.
⁴ Department of Chemistry, Chair of Inorganic and Metal-Organic Chemistry, Technische Universität München, Lichtenbergstraße 4, 85747, Garching, Germany.
⁵ Department of Engineering, University of Cambridge, Cambridge, CB2 1PZ, UK.
⁶ Present address: Department of Chemistry, University of Oxford, Oxford, OX1 3QR, UK.

Abstract

Solid electrolyte materials are crucial for the development of high-energy-density all-solid-state batteries (ASSB) using a nonflammable electrolyte. In order to retain a low lithium-ion transfer resistance, fast lithium ion conducting solid electrolytes are required. We report on the novel superionic conductor Li₉ AlP₄ which is easily synthesised from the elements via ball-milling and subsequent annealing at moderate temperatures and which is characterized by single-crystal and powder X-ray diffraction. This representative of the novel compound class of lithium phosphidoaluminates has, as an undoped material, a remarkable fast ionic conductivity of 3 mS cm^-1 and a low activation energy of 29 kJ mol^-1 as determined by impedance spectroscopy. Temperature-dependent ⁷ Li NMR spectroscopy supports the fast lithium motion. In addition, Li₉ AlP₄ combines a very high lithium content with a very low theoretical density of 1.703 g cm^-3 . The distribution of the Li atoms over the diverse crystallographic positions between the [AlP₄ ]^9- tetrahedra is analyzed by means of DFT calculations.

Keywords: all-solid-state batteries; impedance spectroscopy; lithium; solid electrolytes; solid-state structures.

Abstract

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