Book/Dissertation / PhD Thesis

FZJ-2018-03374

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Herstellung und Charakterisierung von Lithiumlanthanzirkonat-Funktionsschichten für Lithium-Festkörperbatterien

Reppert, T. (Corresponding author)FZJ*

2018
Forschungszentrum Jülich GmbH Zentralbibliothek Verlag Jülich
ISBN: 978-3-95806-331-0

Please use a persistent id in citations: http://hdl.handle.net/2128/18923

Abstract: The aim of this work is to produce a lithium ion conducting solid electrolyte as basic material for application in new efficient energy storage such as solid state batteries. If the liquid electrolyte in lithium ion batteries (LIB) is replaced by a self-supported solid electrolyte, safety, durability and energy density can be improved. Tape casting is a suitable method to process aforementioned self-supported solid electrolytes. The focus is on the powder synthesis of lithium lanthanum zirconate (Li$_{7}$La$_{3}$Zr$_{2}$O$_{12}$;LLZO)which can be optimized by substitution with elements like Al, Ta or Y. These substituted LLZO compositions show improved mechanical and (electro-) chemical stability, and have the highest lithium ion conductivity for all oxide electrolytes. Furthermore, a comparison between the synthesis by solid state reaction and by spray pyrolysis is made. In respect of the influence of process parameters, the microstructure, mechanical properties and the ionic conductivity of sintered pellets are examined. Spray pyrolysis has proved to be a scalable method which was used to synthesize Al-LLZO in a purely cubic phase. Moreover, in this work it is shown that Ta-LLZO has the most suitable cross-section profile in matters of sinterbility, the mechanical properties (hardness and elastic modulus) and lithium ion conductivity. Another main focus is the characterization of LLZO’s crystal structure. Several LLZO electrolytes have been sintered in an air or an argon atmosphere and were subsequently examined by complementary characterization methods in the context of a cooperation with the $\textit{Oak Ridge National Laboratory}$ (ORNL). Next to the crystal structure, especially the atomic positions as well as the occupancies of lithium were determined for several LLZO compositions. A water-free synthesis of LLZO powders was proven by inelastic neutron scattering and in addition, a lithium-proton exchange was prevented. Furthermore, neutron backscattering is used to determine LLZO’s self-diffusion constants and related activation energies. Thus, it could be shown that the tetragonal LLZO phase doesn’t contribute significantly to lithium ion’s self-diffusion. Spray pyrolyzed Al-LLZO was used for a tape casting slurry’s development. A defect-free thin electrolyte film was cast and used for sintering experiments. The microstructure of sintered solid state electrolytes still is not sufficient for a self-supported solid electrolyte. Though, a promising candidate for continuing tape casting is tantalum substituted LLZOsynthesized by spray pyrolysis. Its suitable particle size distribution and sinterbility enable the fabrication of self-supported LLZO functional layer for solid state lithium ion batteries.

Note: Universität Bochum, Diss., 2017

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Contributing Institute(s):

1. Werkstoffsynthese und Herstellungsverfahren (IEK-1)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

Appears in the scientific report 2018

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