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Implementation and Characterization of Silicon Anode with Metal Alloy Inactive Matrix for Lithium-Ion Secondary Batteries

  • 서순성 (Suh, Soon Sung, 대학원 신소재공학과 신소재공학전공)

초록/요약

Part 1 we fabricated Si-Ti-Ni (STN) alloys by melt spinning method in order to effectively use anode material has a large volume expansion of Si. During Li insertion into the alloy electrodes, Si crystallites (active material) reacted with Li to form LixSi alloys. And STN (inactive material) is the role of the path lithium ion micro-cracks caused by volume expansion. First, using controlling the Si contents ranging from 60 to 68% which is changed into the STN, the electrochemical behavior is investigated to identify that amount of Li-ion affects the STN alloys. Secondly, The STN phase was the inactive matrix. To improve the electrochemical performance (initial efficiency, cycle life, etc.), the structure and composition of the STN anode were optimized. Thirdly, we observed dendrite Si and fine crystalline micro structure during lithiation and delithiation. STN structure can be maintained even after lithiation and delithiation other Si alloys structure. Finally, we founded to the Li- ion diffusion mechanism in the Si alloy anode. First, we examined the XRD peak position and grain size for crystallites with Si contents ranging from 60 to 68 at%. Both 28.5 degree and 47.5 degree peaks are found in all samples, indicating the formation of intermetallics and the successful production of STN alloys. Through the TEM investigations, all the samples are black area and have crystallite Si and a size distribution that ranges from 10 to 50 nm with selected area diffraction (SAD) pattern. Secondly, the optimum ratio of Si content was confirmed by the capacity and initial efficiency in the first cycle. 65STN; for this alloy, the CRR and C/D efficiency are 80% and 99.8%, respectively, after 100 cycles. This indicates that the STN alloy has a buffer effect as an inertial component, which improves the cell performance. Thirdly, STEM was investigated to the micro structure of the STN alloys during lithiation and delithiation. As the charge in the initial cycle Li- ion and Si caused by the stress. And then that made crack in the STN. It is to act as a Li-ion continuous channel as the cycled. Finally, we confirmed to Li-ion diffusion mechanism using STEM, in-situ TEM, EDS, EELS during lithiaion and delithiation. The Si channels are generated in the first charge after charging and discharging is maintained at more strongly. For these reason, as a result STN alloy has a buffer effect as an inertial component, which improves the cell performance. In this paper, an inactive matrix silicon composite anode with long life cycle and high initial efficiency will be present. Part 2 we synthesizing granulated silicon oxide nanoparticles (SiOxNPG) via athermal plasma and water granulation process and determination of the optimum stoichiometry of siliconoxide (SiOx) for achieving high electrochemical performance of an anode based on the developed materialare presented herein. The structure of the SiOxNPGs was confirmed by means of X-ray fluorescence,transmission electron microscopy, and X-ray diffraction. A high initial capacity of ∼1196 mAh/g was achieved using the fabricated SiOx anode with x ∼1.06, giving rise to a Coulombic efficiency of 75% after the first cycle. First, we examined the XRD Identification of fabricated SiOx NPGs to evaluate the effect of the oxygen ratio on the electrochemical behavior of SiOx, SiOxNPGs were prepared and confirm strong Si peaks were observed after granulation indicating a well-crystallized Si phase that shown successful production of SiOx alloys. Secondly, in order to find out the optimum rati x in SiOx XRF spectrometric method was employed for determination of x in SiOx. The oxygen content was calculated by assuming that the SiOxNPGs consisted of Si and O, demonstrating that x ranged from 0.83 to 1.21. Thirdly, measured electrode expansion various x ranged which depend on x and initial capacity that shown oxygen was main factor inside SiOx. Finally combination of SiOx with graphite (3 wt %) for use as an anode gave rise to high capacity (397 mAh/g) and a very high Coulombic efficiency of 99.99% after 200 cycles. The physical properties of the synthesized materials were investigated based on micrometric analysis.

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목차

1. Introduction

2. Literature Review
1) Si alloy anode
1-1) Electrochemical characteristics of Si alloy anode
1-2) Structure of Si alloy anode
2) Reaction mechanism of Si alloy anode

3)Motivation
3. Experimental Procedures (part 1)
1) Preparation of STN anode
2) Electrochemical behavior of STN anode controlling Si atomic ratio
2-1) Charge and discharge condition (half-cell)
2-2) Charge and discharge condition (full-cell)
2-3) XRD analysis
2-4) TEM analysis
2-5) SEM analysis
2-6) STEM and EDS analysis

4. Results and Discussion
1) XRD analysis
2) TEM analysis
3) SEM and EDS analysis
4) Charge and discharge condition (half-cell)
5) Charge and discharge condition (full-cell)
6) Mechanical behavior during charging and discharging in STN
6-1) TEM analysis (initial cycle)
6-2) TEM, EDS analysis (the 1st cycle)
6-3) TEM, EDS analysis (the 2nd cycle)
6-4) TEM, EDS analysis (the 100th cycle)

5. Conclusions

6. Experimental Procedures (part 2)
1) Preparation of SiOx anode
2) Electrochemical behavior of SiOx anode controlling oxygen ratio
2-1) Charge and discharge condition (half-cell)
2-2) Charge and discharge condition (full-cell)
2-3) Electrode expansion tests (half-cell)
2-4) XRD analysis
2-5) TEM analysis
2-6) SEM analysis
2-7) PSA analysis
2-8) XRF analysis
2-9) Electrode expansion analysis

7. Results and discussion
1) The structure of SiOx anode using XRD
2) TEM, SAD anaysis
3) SEM anaysis
4) PSA anaysis
5) XRF anaysis
6) Electrode expansion anaysis
7) Charge and discharge condition (half-cell)
8) Charge and discharge condition (full-cell)

8. Conclusion

9. References

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