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Title: | 建構與研究鋰離子電池正極鋰鎳鈷錳氧表面高分子固態-電解液介面層 Construction of Polymeric Artificial Solid-Electrolyte-Interphases on LiNi1/3Co1/3Mn1/3O2 Cathode for Lithium-ion Batteries |
Authors: | Pei-Sian Shao 邵培賢 |
Advisor: | 吳乃立(Nae-Lih Wu) |
Keyword: | 鋰離子電池,層狀三元系過渡金屬氧化物,層狀富鋰氧化物,相轉變,固態電解質介面層,表面改質, Li-ion batteries,Li mixed transition metal oxides,Li-rich layered oxide,phase transformation,SEI,Surface modification, |
Publication Year : | 2016 |
Degree: | 碩士 |
Abstract: | 層狀鋰離子三元系過渡金屬氧化物 LiNixCoyMn1-x-yO2 以及層狀富鋰錳基過渡金屬氧化物材料xLi2MnO3•(1-x)Li(Mn, M)O2 (M= Mn, Ni, Co),此系列之材料具有甚高的比電容量、熱穩定性、低成本與毒性小的優點,使它們成為鋰離子電池中頗具發展性的正極材料。然而,它們的循環壽命穩定性卻會隨著操作溫度的增加而導致嚴重的劣化, 較高的操作溫度會使固態電解液介面層上,電解液與電極材料間的交互作用更激烈,因而導致固態電解液介面層急速的生成於電極表面,除了造成電池內阻抗的增加外也會造成過渡金屬的溶出。
在本研究中,有別於傳統的方式,吾人發展了一套新穎且簡單的製程,藉由高分子人造固態電解液介面層來對正極材料進行表面改質,進而提升鋰離子電池在高溫環境下循環與充放速率的表現。在本實驗中,兩種不同的方式應用在正極材料的表面改質上,且數種高分子與高分子摻合物被選用作為鋰離子正極材料表面改質的原料以達到提升鋰離子電池在高溫下操作的性能 在第一個方法中,聚四氟乙烯亦為熟知的鐵氟龍被選用作為表面改質劑,而此高分子對正極材料的表面改質是應用在富鋰鎳錳氧化物的電極極板,並且藉由電漿輔助化學氣相層析的製程將鐵氟龍鍍於極板上。在本實驗中,經不同層積時間處理的極板會組成鈕扣型半電池進行性能測試。其對電性表現的影響亦會在此研究中討論。 在第二個方法中,正極材料的表面改質會直接在層狀鋰離子三元系過渡金屬氧化物的粉體上進行修飾,並藉由水系的批覆製程,將離子型高分子如聚苯乙烯磺酸基以及聚二烯丙基二甲基氯化銨高分子批覆於粉體表面。此外,為了增加經高分子批覆之金屬氧化物材料的電子導電性,導電性添加劑如Super P以及奈米碳管亦會參與於高分子披覆的製程。在本實驗中,材料在電化學操作前後的表面型態與結構變化都會加以檢視以及進一步的分析與研究來了解高分子披覆的影響。 結果顯示,吾人所建構之人造高分子固態電解液介面層能夠大幅的抑制電極材料與電解液間的劣化反應,進而增進材料的結構穩定性,並在電化學操作過程中,降低電極材料的極化效應。相較於未經改質的材料,改質後的材料在循環壽命以及充放速率的電性表現上都有較佳的結果,並且,因為有效的降低電解液的分解以及提升材料的結構穩定性,改質後的材料,其半電池也能因而保有較低的內部阻抗。 最後在這些提升電池性能表現的後面,其原理以及機制亦會在此研究中進一步的討論。 Layered lithium ternary transition metal oxides, LiNixCoyMn1-x-yO2 (abbreviated as NCM) and the layered lithium-rich manganese-transition metal oxide composites cathode, xLi2MnO3•(1-x)Li(Mn, M)O2 (M= Mn, Ni, Co) (abbreviated as LrMOs), are important cathode materials for lithium ion batteries because of their high specific capacity, thermal stability, lower cost, and less toxicity. However, their cycle life deteriorates rapidly with increasing operating temperature, because of strong interaction at the solid-electrolyte interface causing rapid solid-electrolyte-interphase (SEI) formation and dissolution of the transitional metal ions. In this research, distinct from traditional methods, a novel simple approach is developed using polymeric artificial SEIs (A-SEIs) to modify the surface of cathode materials to enhance the cyclic and rate performance of Li-ion batteries at the elevated temperatures. Two different modification approaches were applied to modify the cathode surfaces and various polymeric blends were employed to promote the cell performance at the elevated temperature. In the first approach, the surface modification was performed on the surface of the electrode using plasma enhanced chemical vapor deposition (PECVD) process. Polytetrafluoroethene known as Teflon was selected for the deposition on electrodes and the lithium-rich Nickel-Manganese Oxide (LrMNO) electrodes were adopted for the modification. PECVD deposition time on electrodes was varied and their impact on the electrochemical performance discussed in detail. In the second approach, the modification was directly conducted onto the NCM particles. Here, the polymeric coating was achieved using water-based coating process with polystyrene sulfonate-based polymers (PSS) and Poly dially dimethyl ammonium chloride (PDDA). Conductive additives such as Super P and carbon nanotube (CNT) were incorporated into the coating procedure for the purpose of improving the conductivity loss due to the polymeric coating on the metal oxide materials. Impact of polymeric coating on materials were examined by investigating structure and morphological changes before and after the electrochemical operations. The result showed that the polymeric artificial SEIs could substantially suppress the side reactions between the electrolyte and electrode, improve the structural stability and decrease the polarization of the material during the electrochemical operations. Compared to the pristine cell, the modified cells showed better performance both in terms of cycle life and rate capability, maintained lower cell impedance due to the reduced electrolyte decomposition and enhanced structure stability. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/78132 |
DOI: | 10.6342/NTU201601970 |
Fulltext Rights: | 有償授權 |
Appears in Collections: | 化學工程學系 |
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