臺灣博碩士論文加值系統

在1990年代早期，已經提出使用無機離子導體作為固態電解質的鋰離子二次電池。由於固態電池可以改善電池的安全性，所以引起了極大的關注。在幾種無機離子導體中，石榴石結構的Li7La3Zr2O12（LLZO）在用作鋰電池應用的固態電解質時，顯示出足夠的離子傳導性和結構穩定性。此外，鋰金屬具有極高的克電容量，使用鋰金屬作為負極一直是長期的目標，LLZO對金屬鋰具有優異的還原穩定性。然而，Li和LLZO之間的固體-固體接觸導致LLZO和鋰金屬之間的界面極化很大。目前許多團隊已經使用多種不同金屬或氧化物作為LLZO和鋰金屬之間的中介層，透過熔化態之鋰金屬與中介層形成鋰化合金，進而改善鋰於固態電解質上的潤濕效果，結果顯示出低極化的現象並改善了界面行為，但在化學及電化學穩定性上的測試，例如合金含量在充放電過程中的變化等，仍鮮少被探索。濺鍍是用於獲得金屬和氧化物薄膜的優異薄膜沉積技術之一。因此，本研究的主要目的是（i）濺鍍金薄膜作為鋰與無機固態電解質的中介層的可行性，（ii）評估具有和不具中介層的界面極化; （iii）分析鋰插入金屬薄膜層的過程和行為，（v）證明金中介層在鋰對電極電池和全電池測試對界面極化減小方面的有效性。
本研究中，先已固相反應法合成具有較高離子導電率的Ta摻雜的LLZO奈米粉末並將塊材燒結緻密化至95％相對密度以上。使用射頻磁控濺射將金薄膜沉積在LLZO的拋光表面上。其次，加熱鋰金屬至鋰的熔點附近時，將鋰金屬置於Au膜上，將對可能的合金成形加工進行SEM觀察。在恆定電流下進行鋰對電極電池，並監回饋的電壓。透過電化學阻抗譜（EIS）測量界面產生的阻抗約為455Ω，比沒有Au夾層的阻抗低約20倍。最後，將測試Li / Au（中間層）/ LLZO / LCO的電池，並與沒有Au中介層的電池進行比較，以顯示金屬中介層的有效果。

In early 1990s, rechargeable batteries using inorganic ionic conductors as solid electrolytes have been proposed. Because of their improved safety features, solid state batteries have received great attention recently. Among several inorganic ionic conductors, Garnet-structured Li7La3Zr2O12 (LLZO) show adequate ionic conduction and excellent structural stability when used as the solid electrolyte for Li battery applications. Using Li metal as anode has been a long-term target. Moreover, LLZO exhibits superior reduction stability against metallic Li. However, the poor contact between Li and LLZO has caused large interface polarization between LLZO and Li metal. Several metals and oxides have been used as the interlayer between LLZO and Li metal, and shown improved interface behaviour with lower polarization. Through molten Li, metal interlayer is lithiated and form Li alloy to improve the poor wetting behavior. The effect of Li alloy between garnet and Li interface was demonstrated and evaluated by electrochemical impedance spectroscopy (EIS), but the phenomenon between the chemical and electrochemical stability of garnet against alloy compositions is not to be explored. Sputtering has been one of excellent thin-film deposition techniques for obtaining metallic and oxide thin film. Thus, the main objective of this study is to (i) to investigate the feasibility of sputtering metallic thin film as an interlayer for inorganic solid state battery using Li as anode, (ii) to evaluate the interface polarization with and without interlayer; (iii) to analyze and understand the process and behaviour of Li insertion into metal thin film layer, (v) to demonstrate the effectiveness of metallic interlayer on reduction of interface polarization based on Li stripping/plating and full cell tests.
In this study, Ta doped LLZO with higher ionic conductivity will be densified to 〉95% dense using nanosized powder by solid state reaction. Gold thin film will be first deposited on the polished surface of LLZO using rf magnetron sputtering. Secondly, Li metal will be placed on top of Au film under heating near melting point of Li. Li stripping and plating will be conducted under constant current with monitoring of applied voltage. Impedance resulted from interface is around 455Ω which is around twenty times lower than the one without Au interlayer measured by Electrochemical impedance spectroscopy (EIS). SEM observation will be performed for possible alloy forming processing. Finally, a full cell based on Li/Au (interlayer)/LLZO/LCO will be tested and compared with the one without Au interlayer to show the effectiveness of metallic interlayer.

Contents
中文摘要 III
ABSTRACT V
LIST OF FIGURES IX
LIST OF TABLES XI
Chapter 1 Introduction 1
1.1 Preface 1
1.2 Research Motivation 2
1.3 Research Objectives 4
Chapter 2 Theoretical Background 5
2.1 Lithium ion Battery 5
2.2 Types of Electrolyte 8
2.2.1 Organic liquid electrolyte 8
2.2.2 Polymer electrolyte 12
2.2.3 Inorganic solid electrolyte 15
2.3 Basic Characteristics of Crystalline Oxide Solid Electrolyte [38, 39] 21
2.4 Garnet Type Oxide 23
2.5 Challenges and Solutions for SSE 27
2.5.1 Soft interlayer 28
2.5.2 Surface engineering 29
Chapter 3 Experimental Procedure 31
3.1 Material 31
3.2 Sample Preparation 31
3.2.1 Preparation of Li7-xLa3Zr2-xTaxO12 (x=0.5) pellets 31
3.2.2 Preparation of cathode 32
3.3 Battery Assembling 33
3.3.1 Preparation of stripping and plating cell 33
3.3.2 Preparation of LCO/SSE/Au/Li 34
3.4 Characterization and Measurement 35
3.4.1 X-Ray Diffraction (XRD) 35
3.4.2 Inductively coupled plasma mass spectrometer (ICP-MS) 35
3.4.3 Particle size analyzer 35
3.4.4 Scanning electron microscope (SEM) 36
3.4.5 Porosity measurement 36
3.4.6 AC Impedance analysis 36
3.4.7 Battery testing 37
Chapter 4 Result and Discussion 38
4.1 Characterization of Solid State Electrolyte 38
4.1.1 Characterization of calcined powders 38
4.1.2 Characterization of sintered pellets 40
4.2 Li Wetting Behavior of Li-Au / Li6.5La3Zr1.5Ta0.5O12 44
4.3 Electrochemical Test 47
4.3.1 Stability test 47
4.3.2 Electrochemical evaluation of interfacial resistance 49
4.3.2.1 Evaluation from EIS data 49
4.3.2.2 Evaluation from Lithium stripping and plating test 51
4.3.3 Phase transformation of gold 54
4.3.4 Maximum atomic percentage of Lithium in Au interlayer 57
4.4 Performance of solid state battery 61
Chapter 5 Conclusion 65
Reference 67


 
LIST OF FIGURES
Figure 2.1 Schematic illustration of the discharge and charge processes in a rechargeable lithium ion battery. 6
Figure 2.2 Framework of polymer lithium battery 13
Figure 2.3 (a) Schematic cross-section illustrating the layout of a thin-film battery. [26]; (b) Schematic representation of the stacked cells. 19
Figure 2.4 Unit cell of garnet-type structure C3A2D3O12 with space group Ia3-d (No. 230). The crystal structures were drawn with a computer program VICS. [40] 24
Figure 2.5 Loop arrangement of different Li sites: tetrahedral Li1 site (yellow), octahedral Li2 (pink), and Li3 (green) sites: (a) tetragonal LLZO, (b) cubic LLZO. 26
Figure 2.6 Schematic diagram of main restrictions in ASSLBs by using SSEs as electrolyte. Chemical electrochemical compatibility, interfacial stability, small resistance between SSE and electrodes are the most important factors[50] 27
Figure 2.7. (a)Voltage profiles of Li/LiFePO4 cell without interlayer, which results in short-circuit less than 20 hours. (b) Cycling performance was obtained when the cell with CPMEA polymer interlayer 29
Figure 2.8 Schematic diagram of engineered garnet SSE/Li interface by using Li-Al alloy 30
Figure 3.1 Preparation Method of Li6.5La3Zr1.5Ta0.5O12 32
Figure 3.2 Preparation Method of cathode 33
Figure 3.3 Schematic Representation of heating the symmetric cell 34
Figure 3.4 Schematic Representation of solid state assembling 34
Figure 4.1 XRD pattern of Li6.5La3Zr1.5Ta0.5O12 38
Figure 4.2 Particle size analysis of Li6.5La3Zr1.5Ta0.5O12 39
Figure 4.3 Cross section of Li6.5La3Zr1.5Ta0.5O12 pellet sinter at 1250oC with different magnification 42
Figure 4.4 Nyquist plot of the impedance spectrum for Li6.5La3Zr1.5Ta0.5O12 sintered pellet 43
Figure 4.5 Phase diagram of lithium and gold 44
Figure 4.6 Wetting behavior of pure Li6.5La3Zr1.5Ta0.5O12 pellet after heating with Li metal at 180oC 45
Figure 4.7 Wetting behavior of Au sputtered Li6.5La3Zr1.5Ta0.5O12 pellet after heating with Li metal at 180oC 46
Figure 4.8 Open circuit voltage (OCV) change of Li / Li6.5La3Zr1.5Ta0.5O12 / air with time 48
Figure 4.9 Stripping and plating test with the Li/Au/SSE/Au/Li cell at 0.005mA 49
Figure 4.10 Comparison of Nyquist plots of Li / Au / Li6.5La3Zr1.5Ta0.5O12 / Au / Li and Li / Li6.5La3Zr1.5Ta0.5O12 / Li in the frequency of 1MHz to 0.1Hz 50
Figure 4.11 Stripping and plating test with different current (0.005, 0.01, 0.02, 0.05, 0.08, 0.1mA) 52
Figure 4.12 Calculation of interfacial impedance with different current (0.005, 0.01, 0.02, 0.05, 0.08, 0.1mA) 53
Figure 4.13 Discharge pattern of Au//Li cell with 0.005mA 55
Figure 4.14 XRD pattern of gold with substrate before and after discharge until 5mV 56
Figure 4.15 Charge and discharge curve with (a) 2 hours charging, (b) 4 hours charging, and (c) 6 hours charging, and then discharge to 0 V 58
Figure 4.16 Sample of Au / Li6.5La3Zr1.5Ta0.5O12 after charging 6 hours, and then discharge to 0 V 59
Figure 4.17 XRD pattern of Au / Li6.5La3Zr1.5Ta0.5O12 59
Figure 4.18 Thickness of Au layer 60
Figure 4.19 Charge and discharge test of LCO/ Ta-LLZO/Li cell 62
Figure 4.20 Charge and discharge test of LCO/Ta-LLZO/Au/Li cell 62
Figure 4.21 Cycle performance of Li/Au/Ta-LLZO/LCO 64

 
LIST OF TABLES
Table 2-1 Performances, and properties of secondary batteries [19]. 7
Table 2-2 Property of solvent used for liquid electrolyte 9
Table 2-3 Decomposition voltage of liquid electrolytes 10
Table 2-4 Comparison of electrolytes used in lithium ion battery 16
Table 2-5 Common solid-state lithium battery systems 18
Table 2-6 Typical values of electrical conductivity. [38] 21
Table 3-1 Physical Properties of Materials for Li7-xLa3Zr2-xTaxO12 (x=0.5) 31
Table 4-1 Calculation of lattice constant with the dopant of Ta 39
Table 4-2 Calculation of chemical ratio from ICP-MS result after calcination 40
Table 4-3 Calculation of chemical ratio from ICP-MS result after sinter desification 41
Table 4-4 Au-Li Lattice Parameter Data at 25oC 56

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