以酚醛樹脂被覆於矽/石墨複合物應 用於鋰電池陽極材料之研究

Abstract

本研究的目的主要在探討藉由矽與石墨埋入經由熱裂解所形成之基質中，以形成複合物的方式，來取代使用碳系材料做為鋰電池負極材料。本實驗所採用的材料分別為球形石墨、矽，藉由酚酫樹脂於高溫中裂解成非結晶碳，在石墨表面上形成碳層被覆，穩定石墨的層狀結構，同時對矽之體積改變有緩衝效應，複合物於鋰離子二次電池充放電過程中，不僅具有高電容，當球形石墨酚酫樹脂含量高達45 wt%與矽含量10wt%，第一次充電容量高達794 mA h /g ，增強了鋰離子電池的效能。在添加20wt% TiN於複合物後，其電池更可表現出較高之庫倫效率，降低不可逆電容量，對於維持電容量有所幫助，經過七圈充放電後仍有443mAh/g之可逆電容量。 經過DTA、Raman、SEM與XPS分析，發現球形石墨經過1100°C的高溫熱處理後，由於酚酫樹脂於高溫中發生裂解成碳，於石墨表面形成ㄧ非晶質碳，使得石墨化度降低，而且在顆粒與顆粒之間有凝聚的現象，矽晶粒分別散佈於複合物中，利用XRD來探討複合物充放電後，晶格上之變化，以此瞭解複合物整體之變化。

The purpose of this study focusd on the impact on silicon and graphite embedded in amorphous carbon pyrolyzing from phenolic resin and formed graphite/silicon composites to replace carbonaceous materials as anode for Li-ion battery. The ingredients of composites are graphite, silicon and amorphous carbon caused by heat process. Amorphous carbon pyrolyzed from phenolic resin functions not only surface modification but also an elastic network which prevents active particle-particle interactions and holds silicon steadfastly. The electrochemical characterization of the composites with different amounts of phenolic resin was investigated. The amount of ingredients is the key point in composite and results have been found out that more capacity obtains with 45 wt% phenolic resin contained in composite and amount of silicon cannot be exceeded 10wt%, or the capacity will decay too fast to use commercially. We also added TiN to enhance the conductivity because silicon is one type of semiconductor. 20wt% of TiN additive enhanced the cyclic performance and coulombic efficiency. The capacity retained about 443 mAh/g after 7 cycles. Depending on XRD, Raman, and XPS analysis, more amorphous carbon decreased the graphitization degree and increased amount of rhombohedral structures in graphite which contributed to decreasing irreversible capacity.