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@PHDTHESIS{Sandt:993520,
author = {Sandt, Roland},
othercontributors = {Spatschek, Robert and Svendsen, Bob},
title = {{M}echanics and microstructure modeling of the solid
electrolyte $\mathrm{{L}i_7{L}a_3{Z}r_2{O}_{12}}$.},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2024-08796},
pages = {1 Online-Ressource : Illustrationen},
year = {2024},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, Rheinisch-Westfälische Technische
Hochschule Aachen, 2024, Kumulative Dissertation},
abstract = {The efficient electrical energy storage is an important
challenge of research, where many crucial topics like the
usage of electrical vehicles are strongly related in the
overall context of the proceeding climate change. Solid
state batteries are suitable candidates for next-generation
battery systems, and especially the solid state electrolyte
$\mathrm{Li_7La_3Zr_2O_{12}}$ (LLZO) influences the ionic
conductivity and the mechanical stability of the whole
battery system. Therefore, a mechanical characterization and
the understanding of microstructure formations of LLZO are
necessary, and are in the scope of the present work. For
that, established and novel developed approaches and scale
bridging descriptions are used in the framework of the
mechanical properties of LLZO.On the electronic scale,
density functional theory (DFT) simulations allow the
precise ab initio calculation of the mechanical properties
of cubic LLZO, which is stabilized via co-substitutions of
aluminium and tantalum. Here, prescreening methods,
exploiting an electronic model, an artificial neural network
and preliminary DFT calculations, determine energetically
suitable substitution positions and therefore increase the
efficiency of the productive computations. The directional
properties of Young's modulus and shear modulus indicate an
anisotropy of LLZO, however, the elastic properties of
isotropic polycrystalline LLZO are not deviating much from
the averaged outcomes. The resulting values of the lattice
constants, elastic moduli and hardness show the influence of
the co-substitutions, but overall the structural and
mechanical properties of cubic LLZO are preserved. Realistic
LLZO is a porous material, whose characteristics cannot be
captured via DFT simulations, therefore a scale bridging
description via a differential effective medium theory
approach is used to investigate the influence of pores on
the mechanical parameters. For a porosity of $10\,\\%$ in
LLZO, a decay of $27\,\\%$ for Young's modulus is expected.
The general agreement between the predicted and experimental
values is good, allowing to use this model for consistency
checks of experimental and theoretical outcomes. Depending
on the doping level, the microstructure consists of a
mixture of a tetragonal and a cubic phase, where the latter
is beneficial due to its higher ionic conductivity. The
formation of an equilibrated microstructure therefore has a
strong influence on the overall electrochemical performance
of this solid electrolyte material. Mechanical mismatches
between the phases are expected to contribute to the spatial
arrangement of the phases, which is difficult to assess with
established modeling approaches. Therefore, a novel quantum
annealing (QA) method for the determination of the
equilibrium microstructure with long-range elastic
interactions between coherent grains was developed.
Comparisons with classical algorithms show that quantum
annealing can accelerate the simulations drastically, even
for huge system sizes with several thousands of grains,
where conventional algorithms exhibit high computational
demand. In order to simulate realistic LLZO microstructures,
Voronoi tesselations are used to generate the grains. The QA
method is demonstrated under consideration of systems with
shear and tetragonal eigenstrains, whose resulting
microstructures are additionally analyzed regarding applied
tensile strains and random grain rotations. For the
application of the developed QA approach to LLZO, the DFT
results are used in order to formulate the eigenstrain. The
resulting microstructures show the interplay between
chemical and elastic contributions, where elastic effects
favor a formation of ion conducting channels in doped
LLZO.In materials science the physical properties at finite
temperatures are of high interest, while so far the
presented DFT and QA simulations of LLZO consider only
ground state energies at $0\,\mathrm{K}$.Thermal expansion
is a crucial issue in solid state batteries, which cannot be
characterised via the presented QA microstructure
equilibrations. Therefore, a QA method for the efficient
sampling of finite temperature properties is developed,
which shows high performance at low temperatures and
operates at low computational demand. The performance of the
approach is demonstrated using benchmarking scenarios of
spin glasses and Ising chains. The QA sampling is very
accurate where conventional approaches fail and therefore
complements classical methods perfectly.},
cin = {525820 / 520000},
ddc = {620},
cid = {$I:(DE-82)525820_20160614$ / $I:(DE-82)520000_20140620$},
pnm = {BMBF 03XP0258C - MEET HiEnD III - Materials and Components
to Meet High Energy Density Batteries (03XP0258C) /
ZeDaBase-Batteriezelldatenbank (KW-BASF-6)},
pid = {G:(BMBF)03XP0258C / G:(HGF)KW-BASF-6},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2024-08796},
url = {https://publications.rwth-aachen.de/record/993520},
}
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