Synthesis, structure and diffusion pathways of fast lithium-ion conductors in the polymorphs α- and β-Li8SnP4. Issue 27 (5th July 2021)

• Record Type: Journal Article
• Authors: Strangmüller, Stefan; Eickhoff, Henrik; Klein, Wilhelm; Raudaschl-Sieber, Gabriele; Kirchhain, Holger; Kutsch, Tobias; Baran, Volodymyr; Senyshyn, Anatoliy; van Wüllen, Leo; Gasteiger, Hubert A.; Fässler, Thomas F.
• Is Part Of: Journal of materials chemistry. Volume 9:Issue 27(2021)
• Page Start: 15254
• Page End: 15268
• Publication Date: 2021-07-05
• Subjects: Materials -- Research -- Periodicals; Chemistry, Analytic -- Periodicals; Environmental sciences -- Research -- Periodicals; 543.0284
• DOI: 10.1039/d1ta03021c
• Languages: English
• ISSNs: 2050-7488

Abstract

Abstract : The increasing demand for a high-performance battery technology promotes the search for Li + -conducting materials. Abstract : The increasing demand for a high-performance and low-cost battery technology promotes the search for Li + -conducting materials. Recently, phosphidotetrelates and -aluminates were introduced as an innovative class of phosphide-based Li + -conducting materials featuring ionic conductivities of up to 3 mS cm −1 at ambient temperature. In order to get a deeper understanding in structure–property relationship of lithium ion conductors closely related structures that differ in their ionic conductivity are of special interest. Here, we report on the two polymorphs α- and β-Li8 SnP4, which show ionic conductivities of up to 0.7 mS cm −1 and low activation energies E A of about 28 kJ mol −1 (0.29 eV) at 298 K. The structures of the two phases are determined by single crystal X-ray and powder neutron diffraction experiments at different temperatures, and their significantly different ionic conductivities allow for a detailed insight into the structure–property relationship. The investigations are completed by 6 Li, 31 P and 119 Sn solid state magic angle spinning NMR, temperature-dependent 7 Li NMR experiments and electrochemical impedance spectroscopy. Negative nuclear density maps reconstructed from experimental structure factors were analyzed by the maximum entropy method (MEM) and the one-particle-potential (OPP) formalism. Distinct Li + migration pathways including divergent activation barriers have been identified, which allow to interpret the different conductivities of the two modifications. The importance of partially occupied octahedral sites in the β-phase is ascertained to cause considerably lower energy barriers to adjacent tetrahedral voids, which promote the higher conductivity in comparison to the α-phase. The title compounds complete the series of three phosphidotetrelates (α-)Li8 SiP4, α-Li8 GeP4 and β-Li8 GeP4, and allow a detailed investigation of the structure–property relationships for further tailoring of the material properties.