有機電極材料之設計、合成與其在鋰離子電池上之應用

Abstract

鋰離子電池 (lithium-ion battery) 因為其高能量密度的特性被廣泛運用在許多電子穿戴裝置甚至電動交通工具上。然而無機電極材料存在生產、製造成本高以及環境危害等問題， 使 近年來許多研究團隊將 研究重點轉移至有機電極材料(organic electrode materials)上。它具有高理論電容量、結構多樣、質量輕且具可撓性 等優點。除此之外，成本低廉以及環境友善更是 能夠 取代傳統無機材料的優勢，因此被視為目前有發展潛力的儲能材料之一。 在本論文中第一部分我們將進行p型反應的吩噁嗪(phenoxazine, PXZ)作為氧化還原活性材料，設計、合成出了六個有機小分子p-PXZTRZ、m-PXZTRZ、p-PXZPy、m-PXZPy、PXZPhC與PXZPhSi運用於鋰離子電池的正極當中。利用改變小分子核心結構與活性位點phenoxazine的數量，討論其中的電化學性質並比較鋰離子電池表現的差異。 第二部分則是以能夠進行電聚合的官能基咔唑(carbazole)與三苯胺(triphenylamine)同時作為聚合位點及氧化還原活性位點設計有機小分子電極材料。期望能在鋰離子電池作用過程中，透過氧化還原反應，使材料在電極表面原位(in-situ)生成聚合物，以達到降低有機小分子溶解度的目的，並進一步提升鋰離子電池的工作效率。其中TPAPNZ分子，作為鋰離子電池中的正極材料，第一圈放電電容量為140.7 mAh/g。經過五次充放電循環後電容 量提升至160.4 mAh/g，與理論值非常接近。在充放電循環壽命表現上，經過300次充放電後電容量保持率為 99%。最後利用質譜鑑定鋰離子電池充放電前後的電極表面材料，證實有寡聚物的生成，能有效抑制有機分子在電解液中的溶解度，達到優異的循環壽命表現。

Lithium-ion batteries (LIBs) have been widely used in various electronic devices and even electric vehicles due to their high energy density. However, inorganic electrode materials suffer from high production costs and environmental hazards. In recent years, many research teams have shifted their focus to organic electrode materials. These materials exhibit high theoretical capacity, diverse structures, lightweight, and flexibility. Moreover, their advantages of low cost and environmental friendliness make them potential alternatives to traditional inorganic materials, thus being considered as one of the promising energy storage materials under development. The first part focuses on utilizing phenoxazine (PXZ) as a p-type redox-active center. A series of six target molecules, namely p-PXZTRZ, m-PXZTRZ, p-PXZPy, m-PXZPy, PXZPhC, and PXZPhSi, were designed and synthesized for application in organic electrode materials. By modifying the core structure of the small molecules and the number of PXZ active sites, we investigate the electrochemical properties and performance differences in lithium-ion batteries. The second part is dedicated to the design of organic small molecule electrode materials utilizing functionalized carbazole and triphenylamine moieties that serve as both polymerization and redox-active sites. The objective of this study is to promote in-situ polymerization on the electrode surface by means of redox reactions during the operation of lithium-ion batteries. This approach aims to reduce the solubility of organic small molecules and subsequently enhance the cycle life of lithium-ion batteries. The TPAPNZ molecule, as a cathode material in lithium-ion batteries, exhibits a first discharge capacity of 140.7 mAh/g. After five charge-discharge cycles, the capacity increases to 160.4 mAh/g, which is very close to the theoretical value. In terms of charge-discharge cycle life, the capacity retention rate remains at 99% after 300 charge-discharge cycles. Finally, the electrode material before and after the charge-discharge cycles of the lithium-ion battery was analyzed using mass spectrometry, confirming the formation of oligomers. This demonstrates that the generation of oligomers effectively inhibits the solubility of organic molecules in the electrolyte, leading to excellent battery performance and cycle life.