Quantenchemische Untersuchungen der Lithiumionendiffusion in Übergangsmetalldichalkogeniden

authored by

Vanessa Werth

supervised by

Paul Heitjans

Abstract

The aim of this thesis is to find an accurate theoretical description of layered transition metal dichalcogenides (MX2), especially TiX2, and investigate their properties regarding the suitability as lithium intercalation material utilized in lithium-ion batteries. The theoretical description of layered MX2 represents a challenge for local density and generalized gradient approximation (GGA) in density functional theory (DFT), since it does not take into account long-range electron correlation effects (London dispersion) which is responsible for the inter-layer interaction. In addition, GGA DFT does not reproduce the electronic and magnetic properties of TiX2, due to the well-known self-interaction error. Using a higher quality hybrid functional is expected to result in a better description but would increase computational costs by one order of magnitude. Keeping the computational costs on the same level as for pure GGA DFT calculations, these challenges are approached in this thesis using a GGA functional developed by Perdew, Burke and Ernzerhof (PBE) together with dispersion and Hubbard correction terms denoted as PBE+U-D3 in the Vienna Ab initio Simulation Package (VASP). With these corrections, the c lattice parameter of TiX2 and LiTiX2 is described within an error of ±3 % while pure PBE leads to an error of up to ±15 %. The description of the TiS2 band structure and vibrational frequency as well as the LiTiS2 quadrupole coupling constant and chemical shift are also improved. PBE+U-D3 calculations of lithiated and delithiated TaX2 and VX2 result in a maximum error of ±3 % for the c lattice parameter. However, applying this method to calculate the voltage vs composition curve for a lithium portion 0 < x <1 result is problematic for tantalum and vanadium dichalcogenides. For LixTiS2 and LixTiSe2 the voltage vs composition curves are in good agreement with the experimental data. The experimentally reported activation barriers for Li1.0TiS2, Li0.7TiS2 and Li0.7TiSe2 are reproduced with the corrected PBE functional. In addition the migration pathways observed for Li1.0TiS2 using various nuclear magnetic resonance techniques are identified. It was also possible to predict concentration-dependent activation barriers in the region of 0 < x < 1 for LixTiX2, which was not yet achieved by other theoretical investigations.

Organisation(s)

Institute of Physical Chemistry and Electrochemistry

Type

Doctoral thesis

No. of pages

127

Publication date

2020

Publication status

Published

Sustainable Development Goals

SDG 7 - Affordable and Clean Energy

Electronic version(s)

https://doi.org/10.15488/10246 (Access: Open)