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Preparation and Research of Si-based Materials for Lithium Ion Batteries

Author: WangLong
Tutor: ChenMeng
School: Harbin Engineering University
Course: Applied Chemistry
Keywords: lithium ion battery Si/C composites Si/G/PANI composite
CLC: TM912
Type: Master's thesis
Year: 2012
Downloads: 167
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Abstract


As anode materials, much attention is paid to silicon due to its high theory specificcapacity. However, the serious volume change during the lithium insertion/extractionprocess, which leads to the electrode structure to be unstable and the cycling stabilitybecome poor and finally hinder its practical application. This paper reviewed the currentresearch situation of the silicon material. Here we adopted the diazotization method toprepare the Si/C core-shell composites, and the in-situ polymerization method tosynthesize the Si/G/PANI composites, we also investigated their structures,morphologies, compositions and electrochemical performance.The Si/C core-shell composite was made by diazotization reaction, TEM, XRD,FT-IR, XPS, TG and SEM methods were employed to investigate its composition andstructure, then we found that the carbon layer was about10nm thick. Compared to nanosilicon, it showed good electrical conductivity, and there is no serious reunionphenomenon.The charging and discharging test results indicated the initial reversiblecapacity of Si/C nanocomposites was1066mAh·g-1, and the initial coulombicefficiency of77.87%, after30cycles the capacity remained881.7mAh·g-1, thecapacity-keeping rate was as high as82.6%.In conclusion, the Si/C composites showedhigher reversible capacity, higher coulombic efficiency and better good cycle stabilitythan the nano silicon.In the water-ethanol solvent system, we adopted the in-situ polymerization methodto prepare Si/G/PANI composites. The physical characterization results proved the nanosilicon was evenly coated by PANI. the Si/G/PANI composites electrode was heated at220℃, and the electrochemical test results found that the initial reversible capacity was1400mAh·g-1, the initial coulombic efficiency was69.8%, after95cycles the specificcapacity still remained866mAh·g-1, the capacity-keeping rate was63%. And the EIStest results furtherly confirmed the Si/G/PANI composites have good electrochemicalperformance. In the water-ethanol system we prepared the Si/PANI composites, and then thecomposite was heated at950℃to make polyaniline carbonized, finally we obtained thenano silicon-carbon composites. From TEM images we can see that after carbonizationthe composites had uniform coating structure; Nano silicon-carbon composites initialreversible capacity was1214mAh g-1, the initial coulombic efficiency reached up to78.75%, which was much higher than the Si/G/PANI composites,and after45cyclesthe capacity-keeping rate was70%.

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CLC: > Industrial Technology > Electrotechnical > Independent power supply technology (direct power) > Battery
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