The 3R modification of Li_xTiS₂ — insights into local electronic structures from high-temperature in situ NMR spectroscopy

Abstract

Titanium disulphide was one of the very first electrode materials investigated to serve as insertion host in rechargeable, that is secondary lithium-ion batteries. At room temperature the trigonal, layer structured modification exists that can easily accommodate Li ions up to the composition . With increasing temperature, however, the present results give evidence that () transforms into a new crystal structure that is expected to be metastable at room temperature. Here, this high-temperature modification is attributed to the 3R polymorph previously described by Colbow et al. Quite recently, the same phase has been characterized by X-ray diffraction and Rietveld refinement. In the present work, nuclear magnetic resonance (NMR) spectroscopy is used to follow up this transformation in situ; it is able to monitor the associated changes of local electronic structures sensed by the lithium ions. Indeed, via in situ NMR, which has been carried out at temperatures as high as 1023 K, it was possible to directly reveal the evolution of a metastable phase which reversibly forms upon heating the trigonal starting material .

Keywords:

• nuclear magnetic resonance
• layer structured materials
• insertion hosts
• lithium
• electric field gradients
• anode materials
• dichalcogenides

Additional information

Funding

This work was financially supported by the Austrian Federal Ministry of Economy, Family and Youth, and the Austrian National Foundation for Research, Technology and Development. Furthermore, this work was supported by the DFG Research Unit 1277 [grant number WI3600/4-1].