矽/碳與一氧化矽/碳複合物於鋰離子電池負極材料之應用

Studies on Si/C and SiO/C Composites as Anode Materials in Lithium Ion Battery

黎根延(Ken-Yen Li)

指導教授 ： 王朝弘

國立中正大學/工學院/化學工程學系/碩士(2015年)

摘要

在3C產品輕薄化之影響下，鋰離子電池在電容量的需求日漸提高。為提升電池電容量，學界與業界發表許多以4A族元素為主的新負極材料。矽可與鋰離子形成鋰矽合金，其可提供之理論電容量高達3579mAh/g，約目前商業化石墨負極之十倍。一氧化矽亦可與鋰離子反應生成Li2O、Li4SiO4及矽，並由矽提供電容量。雖其具高電容量，然而低電導率，及形成合金時之體積膨脹問題仍有待克服。為改善矽及一氧化矽材料導電及膨脹問題，本研究將其與碳材相混合以製備負極材料。碳-12.5wt%矽複合材料之首圈電容量經實驗可達640mAh/g，為石墨之1.7倍之多，且經50圈充放電循環後仍有88%之高存留率。除單純與碳材混合外，本研究另以石油焦與矽混合，並進行熱裂解反應以製備矽碳複合材料。除電化學性能外，另對熱裂解程序中所發生團聚及沉澱現象進行觀察與討論，並探討改變製程順序對最終產物結構、性能之影響。經製程優化後，其首圈庫倫效率可提升至77%以上，經40圈循環後也有90%之高存留率。除純矽之外，以一氧化矽/石墨負極材料進行電化學測試，可發現因不可逆還原反應，其首圈庫倫效率僅55%，不過可逆電容量高達956mAh/g，50圈後亦有92%之高存留率，顯示其優異之電化學性能。為降低一氧化矽電極之不可逆電容量，本研究將一氧化矽不同還原劑混合並進行反應，以嘗試將一氧化矽還原。結果顯示利用還原劑與一氧化矽反應，可將其還原為矽，庫倫效率也因此提升至75%以上。且將惰性物質移除後便可形成矽多孔結構，相較於過去文獻中之繁雜程序，本研究於此提供一相對簡單之製程用以製備多孔矽負極材料。

關鍵字

一氧化矽 ； 熱裂解 ； 鋰離子電池 ； 多孔矽

並列摘要

Lithium ion battery (LIB) is considered the most promising energy storing device in the next decade. Due to the 3C product development in recent years, the demand for more capacity in lithium ion battery is now higher than ever. New materials in 4A group possess higher capacity than graphite. Among them, Si attracts researcher’s attention due to its high gravimetric capacity (3579mAh/g) when forming Li15Si4. On the other hand, SiO can also react with Li+ and form Li2O, Li4SiO4, Si and provide high capacity. However, Si and SiO suffer from low conductivity and severe volume expansion during lithiation, which induce low coulombic efficiency and fast capacity fading during cycling.To improve the electrochemical performance of Si and SiO, this study prepared mechanical milled Si/C and SiO/C composites as anode materials. Our result shows that the 1st cycle reversible capacity of C-12.5wt%Si composite reaches 640mAh/g, which is approximately 170% of graphite anode, 88% capacity retention after 50 cycles is observed. Besides mechanical mixing, pyrolysis method is also performed for the Si/C composite preparation. The coal tar pitch is used here as carbon precursor. In this part, we discuss the performance and physical properties of pyrolysised Si/C composite. After process optimization, the 1st cycle coulombic efficiency reaches 77%, and remains 90% capacity retention at the 40th cycle.SiO/C anode is also studied in this work. Although the irreversible reduction of SiO lowered the 1st cycle coulombic efficiency(55%), the reversible capacity of SiO reached 956mAh/g at the 1st cycle, 92% retention is also observed after 50 cycles, which shows great potential and excellent electrochemical performance of SiO. To reduce the irreversible capacity, this study put an effort on the reduction of SiO. Three substances had been tried as reducing agent. Result shows that SiO can be reduced into Si and inactive material. The coulombic efficiency has therefore risen to over 75%. It is worth mention that porous silicon particle can be attained by removing inactive material. Compare to all relevant studies, we provide one of the most simple way to prepare porous silicon material for LIB anode.

並列關鍵字

Silicon monoxide ； Pyrolysis ； Lithium ion battery ； Porous silicon

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