The High-Temperature Transformation from 1T- to 3R-Li _x TiS₂ (x = 0.7, 0.9) as Observed in situ with Neutron Powder Diffraction

Abstract

Layered titanium disulfide is used as lithium-ion intercalating electrode material in batteries. The room-temperature stable trigonal 1T polymorphs of the intercalates Li x TiS 2 ( ≤ 1) are widely-investigated. However, the rombohedral 3R polymorphs, being stable at higher temperatures for large , are less well known.In this study, we report on the synthesis of phase-pure 1T-Li x TiS 2 ( = 0.7, 0.9) and its transformation to the 3R phase between 673 and 873 K as monitored using high-temperature neutron powder diffractometry. For the 3R polymorph, full Rietveld refinements show lithium ions to be statistically distributed over octahedral voids at the fractional coordinates 0, 0, 1 / 2 , exclusively. The comparison of Madelung energies with results of periodic quantum-chemical calculations reveals that the evolution of lattice parameters and the room-temperature stability of the 1T phase are not governed by electrostatics, but by correlation and polarization. The insights gained do not only elucidate the structure of 3R-Li x TiS 2 , but also help to understand and control polymorphism in layered transition-metal sulfides.

Lithium Diffusion Pathways in 3R-LixTiS2: A Combined Neutron Diffraction and Computational Study

“…Two classes of probable migration pathways have been identified from the scattering-length density distributions (filtered using the maximum-entropy method [MEM]) and the probability density functions (PDFs, modeled from anharmonic Debye−Waller factors): direct diffusion in the (001) plane as the major mechanism and indirect diffusion through adjacent tetrahedral voids as a minor mechanism. Calculated activation barriers agree well with one-particle potentials (OPPs) derived from measurements for Li 0.7 TiS 2 (0.484 [14] and 0.88[4] eV) but deviate for Li 0.9 TiS 2 . The discrepancy at low defect concentration is attributed to the failure of the OPP derivation and the different nature of the methods (space-time averaged vs individual-ion perspective).…”

“…This finding is in accordance with the experimental observations for layered lithium titanium sulfides. 10,14,55 Therefore, we have considered lithium ions solely occupying octahedral sites for all following steps of our study.…”

Dual Cation- and Anion-Based Redox Process in Lithium Titanium Oxysulfide Thin Film Cathodes for All-Solid-State Lithium-Ion Batteries

“…Solid state reaction of a mixture of TiS 2 (Aldrich, 99.9%, 1 μm), Ti powder (Alfa Aesar, 99.9%, 150 mesh), and Li 2 S (Alfa Aesar, 99.9%) with a molar ratio of 3:1:2 was used as an alternative route (referred to as R2) and allowed the preparation of larger batches of LiTiS 2 . 20 Precursors were ground together using a planetary ball-mill and an argon-filled agate jar, prior to being annealed under argon. All material transfers were carried out without any air exposure.…”

Lithium-rich layered titanium sulfides: Cobalt- and Nickel-free high capacity cathode materials for lithium-ion batteries

“…It can be synthesized either by lithium intercalation in TiS 2 (electrochemical or chemical) at room temperature or by solid state reaction at high temperature. Note that a high temperature form, having the same 3R (O3) structure than LiMO 2 layered oxides, is metastable below 500 C [15,16]. Regarding Li 2 TiS 3 , only a limited number of A 2 MS 3 layered compounds are been reported in the literature, and within these known examples, only a few exhibit AM 2 honeycomb type ordering in the [AM 2 ]S 2 slabs: Li 2 SnS 3 [17], Na 2 ZrS 3 [18], Li 2 US 3 and Na 2 US 3 [19].…”