離子凝膠固態電解質及高分子固態電解質在高效能鋰離子電池及鋰金屬電池之應用

Abstract

隨著能量需求日漸提升，具有高能量密度的鋰離子電池被視為最有發展性的二次電池。在目前的鋰離子電池系統中，有機電解液的使用產生了許多問題，例如:液態電解液的有機性質和易燃性會限制電池的工作電壓且產生漏夜等安全性問題；在充放電的過程中，鋰枝晶的生成會影響電池壽命；電解液在充放電的過程中和陰陽極發生反應後會產生大量的氣體，也會造成安全性問題。為了解決鋰離子電池系統中的問題，許多解決辦法被提出，其中一項就是用固態電解質替代有機電解液。固態電解質可以有效的解決有機電解液造成限制和問題，甚至可以抑制鋰枝晶的生成。然而，固態電解質的低離子導電度和高介面電阻限制了其在電池領域中的發展，所以許多研究團隊都致力於發展具有高離子導電度和低介面電阻的固態電解質材料。為了能夠更深入的了解固態電解質在電池系統中的工作機制，鑑定技術的發展也是不可或缺。但相對於液態電解液電池系統，固態電解質的材料性質使得鑑定技術的建立更加困難。現階段通常以固態電解質在電池中的充放電表現或是材料鑑定作為判定電池材料的依據，但我們仍需要建立強力的臨場鑑定技術來分析固態電池系統的工作機制。本研究工作中，我們建立了臨場X射線技術、線上氣相層析系統和線上電化學質譜系統來鑑定離子凝膠固態電解質及高分子固態電解質在鋰離子電池和鋰金屬電池中的工作機制。在離子凝膠固態電解質系統中我們分別探討兩種離子凝膠固態電解質(hBN/FSI和hBN/TFSI離子凝膠固態電解質)對於鋰金屬和陰極材料的表現機制。透過臨場銳角廣度X光散射技術及臨場X射線穿透式顯微鏡技術，我們發現在鍍鋰的過程中，具有較好鍍剝鋰表現的離子凝膠固態電解質(hBN/FSI離子凝膠固態電解質)會產生具有結晶性的鋰金屬和較均勻的鋰生成；而具有較差表現的離子凝膠固態電解質(hBN/TFS離子凝膠固態電解質)會產生非晶態的鋰金屬和不均勻的鋰生成。在鋰鎳鈷錳氧化物陰極材料和離子凝膠固態電解質的全電池系統中，藉由臨場X射線繞射和臨場X射線吸收光譜，我們可以觀察到陰極材料在充放電過程中的晶格變化和過度金屬的價態變化。在高分子固態電解質系統中，我們探討氧化鉬奈米帶對聚環氧乙烷高分子固態電解質表現的影響。透過臨場銳角廣度X光散射技術及臨場X射線穿透式顯微鏡技術的分析，我們發現在鍍鋰的過程中，不論是否添加氧化鉬奈米帶，都不影響在聚環氧乙烷高分子固態電解質中生成的非晶態鋰金屬及變粗糙的電解質形貌。透過線上氣相層析系統我們測得未加入氧化鉬奈米帶的高分子固態電解質會多產生40%的氫氣，意味著加入氧化鉬奈米帶後會降低高分子固態電解質和鋰金屬陽極的活性反應面積。另外，我們建立一個快速且簡易測量電解質分解的鑑定方式，在高分子固態電解質電池系統運作的過程中，透過線上電化學質譜系統可以快速測量道高分子電解質的碎片產物，進而提供高分子固態電解質被分解的資訊。Solid-state electrolytes can effectively solve the limitations and problems caused by organic liquid-based electrolytes. Nowadays, many researchers are committed to developing new solid-state electrolyte materials that possess higher ionic conductivity and lower interfacial resistance. Characterization techniques are also indispensable for a deeper understanding of the mechanism of solid-state electrolytes in battery systems. However, building the characterization methodology for solid-state electrolytes is challenging. At the current stage, the methodology to characterize solid-state electrolyte materials relies on monitoring their cycling performances or ex-situ techniques, but we still need to develop more robust in-situ characterization methods. In this work, we have developed in situ X-ray techniques, online gas chromatography systems (online GC), and online electrochemical mass spectrometry systems (OEMS) to characterize ionogel electrolytes and polymer electrolytes in Li-ion and Li-metal batteries.In ionogel electrolyte systems, we investigate the behavior of two ionogel electrolytes (hBN/FSI and hBN/TFSI ionogel electrolyte) in the battery systems. By in-situ GIWAXS and in-situ TXM measurements, we found that a crystalline deposited lithium and a more uniform lithium plating occurred in the hBN/FSI ionogel electrolyte in the lithium plating process; while amorphous deposited lithium and an ununiform lithium plating occurred in the hBN/TFSI ionogel electrolyte. In the NCM523││Li full cell, we can observe the lattice and oxidation state changes of transition metal in NCM523 during cycling by in situ XRD and in situ XAS measurements.We investigate the effect of MoO3-x nanobelts (PMNBs-SPE) in PEO-based solid polymer electrolytes (PEO-SPE). By GIWAXS and in-situ TXM measurements, we found that it had similar crystallinity and morphology changes during the lithium plating process with PEO-SPE and PMNBs-SPE. By online GC, we measured that PEO-SPE generates 40% more hydrogen than PMNBs-SPE, which indicates that PMNbs-SPE showed a less active lithium surface area. In addition, we have developed a fast and simple methodology for measuring the electrolyte decomposition of solid polymer electrolyte systems by OEMS system.