고에너지 기계적 밀링 및 탄화공정으로 제조 된 리튬이차전지용 실리콘-실리사이드 복합 음극소재 제조 및 전기화학적 특성평가

다국어 초록 (Multilingual Abstract)

In this study, we report a novel Si-Metal Silicides/Carbon composite anode material for lithium-ion rechargeable batteries. The composite powder comprised of Si, FeSi2 and CrSi2 were synthesized by high-energy mechanical milling and then a primary carbon was formed over the Si-Silicide at 900℃. The prepared composite powder was agglomerated and subsequently a thin carbon layer was coated. The X-ray diffraction results revealed that the Si and Silicide crystal size decrease with respect to milling time. The TEM microstructure revealed homogeneous distribution of nanocomposite powder consists a very fine nanoparticles of the order of ∼50 nm. The prepared Si-Silicide/C composite powders showed a noteworthy cycle life until 70 cycles (994 mAh g−1). with a coulombic efficiency of 99.3%. The composite powders exhibited good capacity retention with an average coulombic efficiency of 99.3 %. Such a high coulombic efficiency and low capacity fading were ascribed to nanosized active Si, dispersed on the carbon supported FeSi2, CrSi2 matrix phase, the stable SEI and electrical conducting pathway provided by thicker carbon phase. The electrode internal microstructure revealed a shell-like carbon-coated Si-Silicide phases, and a complete amorphization of nano-crystalline Si during the initial cycling, while the inactive Silicide phase remains unchanged. Consequently, the size reduction of Si-Silicide and carbon coating over it greatly enhanced the cycling performance of the electrode.

목차 (Table of Contents)

• 1. 서 론 1
• 2. 이론적 배경 3
• 2-1. 리튬이차전지 개요 3
• 2-1-1. 리튬이차전지의 작동원리 3
• 2-1-2. 리튬이차전지의 구성 6
• 2-2. 실리콘계 음극재료 9
• 2-2-1. Nano-size Silicon 10
• 2-2-2. Si-Silicide 13
• 2-2-3. Si-Carbon 15
• 2-3. SEI (Solid Electrolyte Interphase) 16
• 2-4. 고에너지 기계적 밀링 (High energy mechanical milling) 18
• 3. 실험 방법 22
• 3-1. Si-Silicide(Fe,Cr)/C 음극소재 합성 22
• 3-2. 결정구조 및 미세조직 관찰 23
• 3-3. Coin-cell 제작 및 전기화학적 특성평가 25
• 4. 실험 결과 및 고찰 26
• 4-1.Si-Silicide/C의 물성 평가 26
• 4-1-1. Si-Silicide/C의 결정구조 26
• 4-1-2. Si-Silicide/C의 미세조직 29
• 4-1-3. Si-Silicide/C의 입도분포 33
• 4-2. Si-Silicide/C의 기계적 특성 평가 33
• 4-3. Si-Silicide/C의 전기화학적 특성 평가 36
• 4-3-1. 충·방전 메커니즘 및 Rate capability 38
• 4-3-2. 충·방전 시 전극(음극)의 구조변화 43
• 4-3-2-1. 전극(음극)의 미세조직 변화 43
• 4-3-2-2. 전극(음극)의 결정구조 변화46
• 4-4. 전기화학 임피던스 분광법(EIS) 평가 48
• 5. 결론 51
• References 52
• Abstract 56