Book/Dissertation / PhD Thesis

FZJ-2017-03385

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Quantitative Analyse der Lithiumverteilung in Kathoden und Elektrolyt-Dünnschichten für Festkörperbatterien

Dellen, C. (Corresponding author)FZJ*

2017
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-95806-214-6

Please use a persistent id in citations: http://hdl.handle.net/2128/14347

Abstract: When searching for new powerful energy storage systems for mobile consumer electronics and a sustainable energy supply, the development in the field of lithium ion batteries was highly pushed in last years. As part of this development the so called solid state batteries have recently attracted a lot of attention as a promising energy storage system for future applications. In a solid state battery the combustible liquid electrolyte, which is used in conventional lithium ion batteries, is replaced by a solid state li ion conductor. Hereby the safety and the performance of the battery system can be increased tremendously. Within this work the quantitative analysis of the lithium distribution in cathode and electrolyte thin films for solid state batteries is addressed as one major issue of the current battery research. The lithium distribution can be regarded as a crucial parameter within the processing of battery materials as well as in the operation of the whole battery system. Unfortunately lithium cannot be quantified by the commonly used characterization techniques. Therefore secondary ion mass spectrometry (SIMS) was used in this work to derive depth resolved concentration profiles of lithium containing thin films. As model systems for the quantitative analysis of lithium, thin films of the cathode material LiCoO$_{2}$ and the solid state electrolyte Li$_{6.6}$La$_{3}$Zr$_{1.6}$Ta$_{0.4}$O$_{12}$ were selected. These were prepared by magnetron sputtering and characterized with a variety of analytical techniques. In addition to the SIMS as the primary analytical method, further techniques like nuclear reaction analysis (NRA), Rutherford backscattering (RBS) and glow discharge optical emission spectroscopy (GDOES) were employed. In case of the LiCoO$_{2}$ thin films, the lithium distribution was investigated as a function of the cathode’s state of charge. Therefore the thin films were first cycled in the voltage range from 3.0 V to 4.1 V vs. Li/Li$^{+}$ and afterwards the elemental composition was analyzed. These measurements revealed a stepwise lithium profile in the charged LiCoO$_{2}$ thin films, showing a delithiated area close to the electrolyte facing surface and a fully lithiated area in the proximity of the substrate. In addition, quantitative SIMS concentration profiles were calculated with relative sensitivity factors (RSF), derived from NRA reference measurements. These profiles showed that the surface area of the charged thin film cathodes is delithiated below the reversible limit of Li$_{0.5}$CoO$_{2}$, which is well known for bulk LiCoO$_{2}$ cathodes. The elemental distribution within the Li$_{6.6}$La$_{3}$Zr$_{1.6}$Ta$_{0.4}$O$_{12}$ thin films was analysed as a function of the deposition temperature. The combined SIMS and NRA analysis of thin films deposited in the temperature range between 150 $^{\circ}$C and 800 $^{\circ}$C revealed an increasing lithium concentration with temperature. At elevated temperatures, the formation of an Al$_{2}$O$_{3}$ interlayer on top of the used FeCrAlY substrates was observed as well as the reaction of this interlayer with lithium from the Li$_{6.6}$La$_{3}$Zr$_{1.6}$Ta$_{0.4}$O$_{12}$. The measured elemental distribution was also affected by a surface reaction of the lithium rich Li$_{6.6}$La$_{3}$Zr$_{1.6}$Ta$_{0.4}$O$_{12}$ thin films. In principle, the quantitative SIMS analyses were able to visualize the depth resolved changes in the lithium concentration. But in comparison to the NRA results, the SIMS analyses systematically overestimated the absolute lithium content.

Note: Universität Bochum, Diss., 2016

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Contributing Institute(s):

1. Werkstoffsynthese und Herstellungsverfahren (IEK-1)

Research Program(s):

1. 131 - Electrochemical Storage (POF3-131) (POF3-131)

Appears in the scientific report 2017

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