製備碳矽複合材料應用於鋰離子電池負極之研究

Abstract

本論論文主要目的是研究以矽為主體的鋰離離子二次電池負極材料料。由於矽本身 擁有較高的比電容量量(~3500 mAh/g),有相當大的潛力力能夠取代目前常用的石墨 (372 mAh/g)負極材料料。但由於矽在充放電的過程中會伴隨著劇烈烈的體積變化(400 %)與本身的低導電度度,使得其在鋰離離子電池中的應用性受到了了侷限。為了了解決上 述所存在的問題,在本研究中使用了了兩兩種不不同的方法試圖解決其體積變化的問題, 第一種方種是碳披覆在矽表面上,第二種是利利用碳纖維將矽粒粒子完整的包覆。 首先是以空氣氣氛下熱處理理使得矽粒粒子上形成碳的披覆,之後再利利用惰性氣 體在高溫下反應使披覆在矽粒粒子表面上的碳能完全碳化形成良良好的披覆,這對於 電極材料料的循環次數數有明顯的增加。經過充放電測試之後,可發現在高溫下燒結 而得的碳矽複合材料料的電極所製成之電池,於 800 mAh/g 的設定電容量量下有約 70 次的循環壽命,除此之外還降降低了了在充放電過程中所發生的不不可逆(irreversibility) 電容量量及極化(polarization)現象,也因此而提升了了其庫侖效率率率(coulombic efficiency)。 另外,本研究也利利用了了電紡絲方法來來製備具有高比面積的碳矽奈奈米纖維結構 的電極材料料。而所製備出的奈奈米纖維結構直徑約為 200 nm。但此一碳矽奈奈米纖維 結構經由充放電的測試,結果顯示出電化學性能並未能符合預期,原因可能是纖 維間彼此堆疊狀狀況不不加及經煅燒後其活性物質的裸裸露露,使得在充放電過程中矽粒粒 子的體積膨脹及收縮使其無法與外層所包覆的碳有良良好的接觸,造成電容量量的急 劇下降降。

The main purpose of this research is to explore new anode materials based on silicon for lithium-ion battery. Due to the high theoretical capacity of silicon (~3500 mAh/g), it has the potential to replace graphite (372 mAh/g) as anode materials. However, Si has the dramatic volumetric variation (400%) problem during cycling and its low conductivity. This limits the application in commercial. Si/C composite materials are prepared by two different methods to overcome the problems just mentioned. One is carbon coating on Si particle, and the other one is Electrospinning method to produce Si@C nanofiber structure. Carbon-coated Si materials have been prepared by thermal treatment in air atmosphere, and then put the composite to the quartz tube through calcination in inert gas at high temperature to form the homogeneous carbon layer onto the surface of Si particle. Research shows that the calcination process contributes to the significantly proved cycling performance. Si@C nanofiber with high specific surface area and its average diameter after calcination is about 200 nm have been prepared by Electrospinning process. During the cycling tests, it seems the Si@C nanofiber structure electrode is not stable while charging/discharging because of the bad connection of fibers and the severe exposedness of Si particle after calcination.