鋰離子電池矽碳複合負極材料製備與分析

Synthesis and Characterization of C-coated Si Composite Anode Materials for Lithium-ion Batteries

嚴佑展(Yu-Chan Yen)

指導教授 ： 吳乃立

國立臺灣大學/工學院/化學工程學研究所/碩士(2006年)

https://doi.org/10.6342/NTU.2006.01331

摘要

本論文之主要目的為開發以矽為主體的鋰離子二次電池負極材料。矽擁有絕佳的比電容量用（~3500 mAh/g），是目前極有可能取代石墨（372 mAh/g）成為新型鋰離子電池的負極材料之一。但由於充放電時伴隨劇烈的體積膨脹與低導電度，使矽在鋰離子電池上的應用受到限制。為了克服前述的問題，我們使用兩種不同的方法合成矽碳複合材料，一是在矽負極材料上批覆碳層，而另一種則是利用噴霧造粒製備多孔性結構的二次粒子。
我們以熱裂解以及流體化床化學氣相沉積法於矽粉體上進行碳的鍍層，發現碳層的覆蓋有很好的均勻性，而且對於電極的循環壽命表現有顯著的提升。經由充放電測試，了解有碳層批覆粉體組裝之電池，於1000mAh/g有80 cycles的循環壽命，大於Si(<10 cycles)，而且減少了在充放電的不可逆(irreversibility)和極化(polarization)現象，對於鋰離子二次電池負極材料之開發，有很好的進展。
本研究也嘗試使用噴霧乾燥法合成具高孔隙度的矽碳複合二次粒子。而所製備的二次粒子，其孔徑大小約為300奈米，孔隙度約50%。然而，此一矽碳負極材料所呈現的電化學表現卻未能達到預期，推測可能是矽加碳的物理混合物並不能忍受矽電極於充放電時所帶來的體積膨脹。

關鍵字

鋰離子電池 ； 負極 ； 矽 ； 矽碳複合材料

並列摘要

The main purpose of this research is to explore new anode materials based on silicon for lithium-ion battery. Silicon possesses a high theoretical capacity (~3500 mAh/g) compared to graphite (372 mAh/g), however, the dramatic volumetric variation during cycling and intrinsic low conductivity, which result in structural instability and poor cyclability, block its commercial application. Si-C composite materials are developed by two different methods to overcome the inherent problems of silicon. One is carbon coating on Si powder, and the other is spray drying method to produce porous-structured Si-C secondary particles.
Carbon-coated Si materials have been synthesized by a fluidized-bed chemical vapor deposition (FBCVD) method or a thermal pyrolysis process. Research reveals that both the FBCVD process and the pyrolysis reaction give the important contribution to the significantly improved morphology stability. As a ductile matrix, the disordered carbon coated from the CVD process could effectively buffer the volume change of Si particles during charge/discharge cycling. On the other hand, the dense-structured carbon coating obtained from the pyrolysis reaction could reduce the volume expansion of Si particles upon cycling.
Porous Si-C particles having a pore size distribution peaks at 300 nm and an intra-particle porosity of nearly 50% have been synthesized by spray drying process. It is expected that the preset intra-particle voids can help accommodate volume expansion arising from alloying of the Si component; nevertheless, the results demonstrate that the porous-structured secondary Si and Si-C particles can not stabilize the electrode architecture during cycling.

並列關鍵字

Lithium-ion batteries ； Anode ； Silicon ； Si-C composite

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