氧化鈷複合石墨烯奈米材料的製備與鋰離子電池負極材料應用

Fabrication of CoO/reduced graphene oxide nanocomposites as anode materials for lithium ion battery

葉名修(Ming-Hsiu Yeh)

指導教授 ： 董瑞安

國立清華大學/原子科學院/生醫工程與環境科學系/碩士(2014年)

https://doi.org/10.6843/NTHU.2014.00427

摘要

在鋰離子電池電極材料的選擇中，由於氧化鈷具有較高的理論電容值(715 mAh/g，高於石墨372 mAh/g)，且因氧化鈷可催化電解質反應提供額外電容值，使氧化鈷成為被廣泛使用的電極材料，但在大顆粒下，氧化鈷在進行電化學反應時鋰離子傳遞不易以及電子難以在氧化鋰的副產物中傳遞，導致在提高掃速時氧化鈷的電容值有衰減現象。透過加入載體複合分散降低氧化鈷顆粒的尺寸有助於改善鋰離子與電子在材料中的傳遞，但加入大量載體後使氧化鈷的含量減少，使總體電容值下降。在這個研究中，發展出一項新的合成出小顆粒氧化鈷且氧化鈷沉積在還原氧化石墨烯的方法以維持氧化鈷的量且同時提高氧化鈷的利用率，我們利用過程方便簡單的水相下合成硼酸鈷並熱解成氧化鈷的方法，因石墨烯表面上的氧官能基與金屬產生的鍵結以及硼元素，導致經過熱處理後具有分隔CoO顆粒的特性，通過最佳化熱處理時間及氧化鈷負載量後，在氮氣環境下熱處理一小時中，CoO複合量在80 wt%時，可以製備出在XRD下晶粒小於10 nm，且TEM下顆粒小於10 nm的氧化鈷顆粒分散在還原氧化石墨烯上，小顆粒的結果使EIS顯示鈍化模阻抗及電荷轉移阻抗僅56.2Ω，材料經過充放電測試後，CoO/rGO在高掃速2400 mA/g下具有電容值接近500 mAh/g，與低掃速150 mA/g相比有維持率接近60%的結果。未來也可透過利用其他金屬的硼酸鹽製備高負載量和小顆粒的零價金屬或金屬氧化物，在其他領域改善鈷和其他零價金屬或金屬氧化物的應用。

關鍵字

鋰離子電池 ； 負極材料 ； 氧化鈷 ； 石墨烯 ； 奈米複合材料

並列摘要

Cobalt oxide is a promosing electrode material for lithium ion battery because of the high theoretical capacity of 715 mAh/g. In addition, cobalt oxide can proceed another electrolyte catalyzation to provide additional capacity. However, the lithium ions and electrons can not be easily moved through the CoO particles and lithium oxide byproducts when the cobalt oxide particle is large, resulting in the decrease in capacity as the current density increases. Addition of dispersing agents and the decrease in particle size of CoO can improve the transportation of lithium ions and electrons. .However, the decrease in total amounts of CoO also decrease the overall capacity of the CoO nanocomposite. In this study, a novel fabrication method has been developed to synthesize ultrafine CoO nanopaticles and then deposited onto the surface of reduced graphene oxide (CoO/rGO) to maintain the CoO amount as well as to increase the electrochemical reaction efficiency simultaneously. We used a simple and facile aqueous system to produce CoO after the heat treatment of Co3(BO3)2. Since the oxy group on the graphene surface can bond to the metal and boron element, resulting in the separation of CoO particle during the heat treatment. After optimizing the heat treatment time 1 hour in N2 gas and cobalt oxide amount 80 wt% in rGO composite, XRD showed the nano grain size lower than 10 nm, and TEM images showed that particle sizes of CoO was lower than 10 nm and can well disperse in the rGO.Because of the small particle size, The EIS showed the SEI impedance and charge transfer resistance are only 56.2 Ω.After the charge/discharge test, CoO/rGO capacity was up to 500 mAh/g when current rate was 2400 mA/g. In addition, a 60% of retention was obtaiend when the current was 150 mA/g. In the future, It can produce high loading amount and small particle of other metal or metal oxide through the metal borate decomposition. It can improve zero valent metal or metal oxide application through this method

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