直接成長奈米碳管於導體上做為鋰離子電池陽極的電化學研究

Abstract

在鋰電池的材料研究中所要克服的困難大多是以呈現更高電容量或是更穩定的工作環境兩方面來加以改良，而本實驗室所採用的材料為直接成長奈米碳管於導體上作為鋰電池的陽極。 而在鋰電池操作過程中，電極與電解液中間會形成鈍化層(solid electrolyte interface, 簡稱SEI) ，由於鈍化層是電池中內電阻最主要的來源，故一直是被主要探討的目標，本文將用電化學阻抗頻譜法(Electrochemical Impedance Spectroscopy, 簡稱EIS)來探討碳管成長時候加入氮氣對於鈍化層的影響，而將譜圖以簡單的電阻電容電路圖(equivalent-circuit model, 簡稱ECM)模擬也可由電容(capacitance)值計算出鈍化層的厚度。 從碳管當陽極所組成鋰電池所做的測試中，有加入氮氣成長的碳管的電極在第一次放電過程，電容量高達979.66 mAh/g，而在第二圈可逆電容量可維持原來的54%，其內電阻於充放電20圈後內電阻為50~60歐姆面積單位(Ω× ㎝2) ，相較於未加入氮氣成長的碳管的100~150歐姆面積單位(Ω× ㎝2)內電阻還要低很多，而由簡單的平行電路板公式中也可算出前者的鈍化層厚度將近260nm，後者為450nm，由此可更進一步確定碳管加入氮氣的優點。

In the material research of the lithium battery, the higher capacity and the more stable work environment are important issues. In my laboratory, I grow carbon nanotubes (CNTs) directly on current collector as the anode of the lithium battery. During the charging/discharging process of the lithium battery, the passive film or the solid electrolyte interface (SEI) formed on the electrode surface give a large resistance. In this study, I also use Electrochemical Impedance Spectroscopy (EIS) to know the influence of the CNTs with/without nitrogen. By using equivalent-circuit model, the thickness of SEI can also be calculated from the value of capacitance part. In this results, the 1st discharging capacity of the battery of CNTs with nitrogen is 979.66 mAh/g and during the 2nd cycle, the efficiency is 54%. The resistance is 50~60 ohms×cm2 after charging/discharging 20 cycles and the resistance of the battery of CNTs without nitrogen is 100~150 ohms×cm2. The SEI thickness of the former is 260 nm, and the latter is 450 nm.