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Thin Films of Lithium Ion Conducting Garnets and Their Properties

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Thin Films of Lithium Ion Conducting Garnets and Their Properties Thin films of lithium ion conducting garnets and their properties dem Fachbereich Biologie und Chemie der Justus-Liebig-Universität Gießen vorgelegte Dissertation zur Erlangung des Grades Doktor der Naturwissenschaften – Dr. rer. nat. – von Jochen Reinacher geboren am 07.09.1984 Gießen 2014 II Dekan / Dean Prof. Dr. Holger Zorn 1. Gutachter / Reviewer Prof. Dr. Jürgen Janek 2. Gutachter / Reviewer Prof. Dr. Bruno K. Meyer Arbeit eingereicht: 10.06.2014 Tag der mündlichen Prüfung: 11.07.2014 III IV Abstract Different lithium ion conducting garnet-type thin films were prepared by pulsed laser deposition. Of these garnet-type thin films Li6BaLa2Ta2O12, cubic Li6.5La3Zr1.5Ta0.5O12 (additionally stabilized by Al2O3) and cubic Li7La3Zr2O12 stabilized by Ga2O3 were investigated in more detail. Conductivity measurements of these thin films performed in lateral geometry showed total conductivities of σ = 1.7∙10–6 S∙cm–1, σ = 2.9∙10–6 S∙cm–1 and σ = 1.2∙10–6 S∙cm–1, respectively. Electrochemical impedance spectroscopy was performed in axial geometry (orthogonal to the substrate), revealing conductivities of –5 –1 σ = 3.3∙10 S∙cm for Li6BaLa2Ta2O12 which is comparable to the bulk conductivity of –5 –1 Li6BaLa2Ta2O12 (σ = 4∙10 S∙cm ). The comparatively low lateral conductivity of the garnet-type material could be increased to a maximum of σ = 2.8∙10–5 S∙cm–1 for multilayer structures of two different alternating garnet-type materials (Li6.5La3Zr1.5Ta0.5O12:Al2O3, Li7La3Zr2O12:Ga2O3). These investigations revealed a strong influence of the thin film microstructure on the total conductivity. Additionally the electronic partial conductivity of Li6BaLa2Ta2O12 as bulk and thin film material was determined. The garnet-type thin films were successfully tested as protective coatings and as ion-selective membranes in “hybrid battery cells” (liquid and solid electrolyte combined in one cell). The ion-selective membranes successfully suppressed the undesired polysulfide shuttle mechanism inside a lithium sulfur battery. Keywords: Lithium solid electrolyte, garnet, separator, solid state battery, hybrid battery, PLD V Zusammenfassung Eine Reihe unterschiedlicher Lithium-ionenleitender Dünnfilme aus Oxiden vom Granat- Typ wurde mittels gepulster Laserdeposition abgeschieden. Hervorzuheben sind die Präparation von Li6BaLa2Ta2O12, kubischem Li6.5La3Zr1.5Ta0.5O12, welches zusätzlich durch Al2O3 stabilisiert wurde, und kubischem Li7La3Zr2O12, stabilisiert durch Ga2O3. Leitfähigkeitsmessungen in lateraler Geometrie ergaben für diese Materialien jeweils Gesamtleitfähigkeiten von σ = 1.7∙10–6 S∙cm–1, σ = 2.9∙10–6 S∙cm–1 und σ = 1.2∙10–6 S∙cm–1. Darüber hinaus wurde die Leitfähigkeit an einem Li6BaLa2Ta2O12-Dünnfilm in axialer Geometrie (senkrecht zum Substrat) mit einem Wert von σ = 3.3∙10–5 S∙cm–1 bestimmt. Dieser Wert ist vergleichbar mit der Leitfähigkeit des Volumenmaterials von –5 –1 Li6BaLa2Ta2O12 (σ = 4∙10 S∙cm ). Die vergleichsweise geringe laterale Leitfähigkeit der Granat-Typ-Dünnfilme konnte auf maximal σ = 2.8∙10–5 S∙cm–1 für Multilagen-Dünnfilme bestehend aus zwei alternierenden Granat-Typ Phasen (Li6.5La3Zr1.5Ta0.5O12:Al2O3, Li7La3Zr2O12:Ga2O3) erhöht werden. Weiterführende Experimente zeigten, dass die Mikrostruktur des Dünnfilms einen starken Einfluss auf die Gesamtleitfähigkeit hat. Zusätzlich wurde die elektronische Teilleitfähigkeit einer Volumenprobe und eines Dünnfilms, bestehend aus Li6BaLa2Ta2O12, bestimmt. Dünnfilme aus Lithium-Granaten wurden erfolgreich als Schutzschicht und als ionenselektive Membran in „Hybrid-Zellen“ (Kombination aus Flüssig- und Festelektrolyt in einer Zelle) getestet. Die ionenselektiven Membranen waren in der Lage, den unerwünschten Polysulfid-Shuttle-Mechanismus innerhalb einer Lithium-Schwefel-Zelle zu unterdrücken. Stichwörter: Lithium-Festelektrolyt, Granat, Separator, Festelektrolytbatterie, Hybrid-Batterie, PLD VI Danksagung An dieser Stelle möchte ich mich ganz herzlich bei all denjenigen bedanken, die mir während meiner Promotion zur Seite standen. Sie alle haben zum Gelingen dieser Arbeit beigetragen. Herr Prof. Dr. Jürgen Janek hat mich in all den Jahren, die ich in seiner Arbeitsgruppe verbracht habe, tatkräftig unterstützt. Sei es durch anregende Diskussionen oder das Vertrauen in mich und meine Arbeit, welches er mir tagtäglich entgegen gebracht hat. Insbesondere dafür möchte ich mich an dieser Stelle bedanken. Herr Prof. Dr. Bruno K. Meyer bin ich für die Übernahme des Korreferats und für die Zusammenarbeit im Bereich der Dünnfilmfestelektrolyte sehr dankbar. Desweiteren gilt mein Dank Herrn Dr. Stefan Berendts und Herrn Dr. Joachim Sann für die wissenschaftliche Unterstützung während meiner Promotion. Bei Sebastian Wenzel, Alexander Braun, Rabea Dippel, Martin Busche, Matthias Geiß, Dr. Bjoern Luerßen und Dr. Hany El Shinawi möchte ich mich für die gute und freundschaftliche Zusammenarbeit bedanken. Einen großen Beitrag zum Gelingen des Projektes haben zudem die Werkstätten (Feinmechanik und Elektronik) geleistet. Ohne Harry Heidt, Gerd Pfeiffer und Harald Weigand hätte es einige Versuchsaufbauten sicherlich nicht gegeben. Herrn Dr. Kiran Chakravadhanula und Herrn Dr. Christian Kübel vom „Institute of Nanotechnology“ (INT) des „Karlsruher Institute of Technology“ (KIT) möchte ich für die Zusammenarbeit im Bereich der TEM-Charakterisierung meinen Dank aussprechen. Herrn Dr. Heino Sommer und Herrn Artur Schneider vom „Battery and Electrochemistry Laboratory“ (BELLA) des KIT möchte ich für die erfolgreiche Kooperation im Bereich der Lithium-Schwefel Zellen danken. Teile dieser Arbeit wurden durch die finanzielle Unterstützung der BASF ermöglicht. Meinen Eltern und meinem Bruder möchte ich meinen Dank ausdrücken für die immerwährende Unterstützung bei und neben der Promotion. Meine Partnerin Gesche Mareike Müntze hat mich stets liebevoll unterstützt und es geschafft, mich auch dann aufzuheitern, wenn es mal nicht so gut lief. Nicht nur dafür sei ihr an dieser Stelle herzlich gedankt. VII VIII Table of Contents Abstract ........................................................................................................... 5 Danksagung ..................................................................................................... 7 1. Introduction ................................................................................................ 1 2. Motivation ................................................................................................... 4 3. Fundamentals .............................................................................................. 6 3.1 Solid lithium ion conductors .................................................................. 6 3.2 Lithium ion conducting thin films ........................................................ 11 3.3 All solid state batteries ......................................................................... 14 3.4 Ion conducting membranes................................................................... 25 4. Experimental ............................................................................................. 30 4.1 Synthesis .............................................................................................. 30 4.1.1 Synthesis of garnet-type bulk materials ..................................... 30 4.1.2 Synthesis of garnet-type thin films ............................................ 32 4.2 Characterization ................................................................................... 41 4.2.1 X-ray diffraction ....................................................................... 41 4.2.2 Conductivity measurements of garnet-type bulk material .......... 41 4.3 Characterization of garnet-type thin films............................................. 44 4.3.1 Scanning electron microscopy .................................................. 44 4.3.2 Transmission electron microscopy ............................................ 45 4.3.3 Conductivity measurements in lateral geometry ........................ 45 4.3.4 Conductivity measurements in axial geometry .......................... 46 4.3.5 Ion-selective membranes .......................................................... 48 5. Results and Discussion .............................................................................. 52 5.1 Characterization of garnet-type bulk material ....................................... 52 5.1.1 X-ray diffraction ....................................................................... 52 5.1.2 Conductivity measurements ...................................................... 55 5.2 Characterization of garnet-type thin films............................................. 62 5.2.1 X-ray diffraction ....................................................................... 62 5.2.2 Scanning electron microscopy .................................................. 65 5.2.3 Transmission electron microscopy ............................................ 69 5.2.4 Conductivity measurements in lateral geometry ........................ 72 5.2.5 Conductivity measurements in axial geometry .......................... 80 5.2.6 Conductivity model .................................................................. 88 5.2.7 Protective coatings .................................................................... 91 5.2.8 Ion-selective membranes .......................................................... 94 IX 6. Summary and Conclusions ........................................................................ 99 7. References ...............................................................................................
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