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標題: | 研究鋰離子電池正極材料鋰鎳鈷錳氧之表面高分子修飾 Characterization of LiNi1/3Co1/3Mn1/3O2 Cathode of Lithium-ion Batteries with Artificial Polymeric Coatings |
作者: | Bing-Yi Shih 施秉逸 |
指導教授: | 吳乃立 |
關鍵字: | 鋰離子電池,正極材料,層狀三元系過渡金屬氧化物,固態電解質介面層,高溫及高截止電壓之電化學表現,高分子表面改質, Li-ion batteries,cathode material,Li mixed transition metal oxides,SEI,electrochemical performance at high temperature and high voltage window,polymeric surface modification, |
出版年 : | 2017 |
學位: | 碩士 |
摘要: | 鋰離子電池正極材料層狀鋰離子三元系過渡金屬氧化物 LiNixCoyMn1-x-yO2 鋰鎳鈷錳氧於現今市場中越趨重要,其市佔率僅低於層狀正極材料 LiCoO2 鋰鈷氧,且需求量年年攀升。正極材料鋰鎳鈷錳氧之特性為高比電容量、高熱穩定性、成本低以及毒性小安全之優點,然而,其面對之問題為由於鋰鎳鈷錳氧與電解液之間的直接接觸,產生電解液之降解反應,導致固態電解液介面層 (Solid electrolyte interfaces) 的形成阻擋鋰離子之嵌入脫出,進而使電池壽命衰退,另外電解液之降解反應也會產生氫氟酸腐蝕正極材料鋰鎳鈷錳氧,導致過度金屬離子溶出而形成相轉變甚至結構崩塌,而這些副反應尤其會在高溫及高操作電壓下更加劇烈。
許多研究學者們提出方法來改善此現象,像是在電解液中加入添加劑、於活物中嵌入其他特性金屬離子、無機化合物之表面修飾以及高分子分表面修飾,然而於此論文中注重於高分子表面修飾之討論,相比於其他改善方法,高分子表面修飾之製程簡單許多且省時,其有利於大規模生產,更加貼近於實際面。 高分子表面修飾製程之用意於形成一層高分子膜在正極材料鋰鎳鈷錳氧表面上,減少電極材料與電解液之間的直接接觸,間接降低於充放電中活物與電解液之間的副反應於第一段所提及,進而改善電池之電化學表現以及延長電池之循環壽命。 在高分子表面修飾之過程中,也遇上了其他問題像是高分子導致離子傳導阻抗的增加、團聚現象等等,因此於本研究當中亦加入了助導劑來改善離子傳導阻抗之問題,分散劑幫助高分子與助導劑均勻分布以及交聯劑使高分子膜更加穩定且不溶於水。 於高分子表面修飾製程過後,即進行電化學測試像是活化,不同電流密度以及循環壽命之測試,在循環壽命測試當中也分成室溫以及高溫環境兩部分,除了高溫測試之外,本論文中亦提及高截止電壓之電化學表現。從結果當中可以得知高分子表面修飾有效提升高溫下循環壽命之穩定性以及高截止電壓下不同電流密度之表現,從阻抗圖中也發現高分子表面修飾有效地降低表面阻抗相比於未經改質之材料。另外,其他儀器對於高分子表面改質之特性以及活物表面機制之原理和分析也將會於本論文中有進一步之探討。 The layered structure LiNixCoyMn1-x-yO2 (NCM) cathode material of Lithium-ion batteries is more and more important which just less than layered structure LiCoO2 cathode material in market share and the demanding is getting higher year by year. The advantages of NCM are high specific capacity, high thermal stability, low cost and safe. However, the problem of NCM is direct contact between NCM and electrolyte which causes electrolyte decomposition leading the formation of solid electrolyte interfaces (SEI) to block the transfer of lithium ions and poor cycle life of the batteries. Moreover, the electrolyte decomposition generates hydrofluoric acid to corrosion NCM surface leading the dissolution of transition metal ions which causes structure defect and phase transformation. All of these side reactions happen especially at high temperature and high operating voltage. Many researchers mentioned many methods to improve this problem, for example, mixing additive in electrolyte, doping of foreign metal ions, surface coating with inorganic compounds and surface coating with polymers. In this thesis is focusing on surface coating with polymers which process is easier and saving time comparing with other methods and benefit for scale-up production. The application of polymeric modification on NCM surface is forming a polymer film as a protective layer to decrease the contact between NCM and electrolyte and suppressing the side reactions as mentioned in first paragraph then improves the electrochemical performance and cycle life stability for batteries. There were some problems like larger charge transfer resistance and aggregation phenomenon during polymer coating process. Therefore, we mixing with conducive agent to improve charge transfer resistance problem, mixing with dispersant to help to disperse conductive carbon and polymer uniformly and mixing with crosslinking agent to stable the polymer film. After polymeric surface modification process, then we started to do electrochemical test such as formation, C-rate and cycle life test. In cycle test, we tested the cells at room temperature and high temperature, on top of that, we did high voltage window test as well. From the electrochemical results, we can obtained that polymer coating effectively improved cycle stability at high temperature and C-rate performance at high voltage window. From Nyquist plots also got much smaller surface resistance comparing with pristine one. Besides, other instrument analysis for characterization of polymeric surface modification and surface mechanisms will be discussed in the thesis as well. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/77759 |
DOI: | 10.6342/NTU201702221 |
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顯示於系所單位: | 化學工程學系 |
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