리튬 이온 전지 양극용 LiCoO₂의 금속산화물 코팅이 전기화학적 특성에 미치는 영향
- 발행기관 고려대학교
- 발행년도 2004
- 학위명 석사
- 학과 및 전공 고려대학교 대학원:재료공학과
- 식별자(기타) DL:000005718352
- 본문언어 한국어
- 서지제어번호 000000870881
초록/요약 도움말
LiCoO₂ has been commercially employed as active material for the cathode of lithium secondary batteries because of its good rate capability and stable capacity. LiCoO₂ has layered-type (rhombohedral) structure with R3m symmetry. The lithium and cobalt ions occupy alternative in octahedral sites between the cubic-close-packed oxygen planes. Hence, lithium ions deintercalate and intercalate during the charge-discharge process. However, its capacity fades rapidly when more Li ions are extracted from the lattice. LiCoO₂ looses their lithium ions and electrons during charge process. During deintercalation of Li ions, Co^(3+) is oxidized to unstable Co^(4+) and being dissolved in the electrolyte. Therefore, increase of Co^(4+) concentration will damage the cathode crystal lattice. The contraction along c axis results mechanical failure in LiCoO₂ particle and rapid capacity fading. In this study, the commercial LiCoO₂ powder with average particle of about 7.7㎛ (Nippon Chemical Industry) was used as raw material and coated with some metal oxide as Al₂O₃, ZrO₂ and TiO₂ by fluidized-bed spray coating method and their coating effects on electrochemical characteristics were investigated. Metal oxide coating on the surface of LiCoO₂ increased surface area and Li-M-Co-O(M=Metal) thin layer was formed near the surface of LiCoO₂ and Atomic absorption spectrophotometer study showed that the dissolved Co contents of metal oxide coated LiCoO₂ were lower than that of bare LiCoO₂. This could be attributed to existence of the thin layer of Li-M-Co-O, which preserves the structure of the LiCoO₂ shell from the electrolyte. Effect of metal oxide coating on discharge capacity was very small at first cycle, while it improved the capacity retention and thermal stability. In our experimental range, the observed optimal coating amount that exhibited the highest capacity retention was 0.2wt.% and ZrO₂ coated LiCoO₂ showed the better electrochemical properties in comparison with the other metal oxide coated LiCoO₂.
more목차 도움말
Abstract = ⅰ
목차 = ⅲ
제1장 서론 = 1
제2장 이론적 배경 = 5
2-1. 양극 활물질 = 9
2-2. 음극 활물질 = 12
2-3. 전해질 = 12
2-4. 분리막 = 13
2-5. 사이클 효율이 줄어드는 이유 = 13
2-6. 유동상 스프레이 코팅 = 14
제3장 실험 방법 = 18
3-1. 유동상 스프레이 코팅에 의한 LiCoO₂ 표면 코팅 및 열처리 = 18
3-2. 표면 개질된 LiCoO₂ 의 특성 분석 = 22
3-2-1. Centrifugal particle size distribution analyzer = 22
3-2-2. AAS(Atomic absorption spectrophotometer) = 22
3-2-3. SEM(Scanning electron microscopy) = 22
3-2-4. BET = 22
3-2-5. AES(Auger electron spectroscopy) = 23
3-3. LiCoO₂ 전극 제조 및 전지 조립 = 23
3-3-1. LiCoO₂ 전극 제조 = 23
3-3-2. 반 전지 조립 = 23
3-4. 전기 화학적 특성 조사 = 27
3-4-1. 충·방전 특성 실험 = 27
3-5. 고온에서 전지의 안정성 조사 = 27
3-5-1. 고온에서 방전 용량 측정 = 27
3-5-2. DSC 분석 = 27
제4장 실험 결과 및 고찰 = 29
4-1. 표면 개질된 LiCoO₂ 의 물성 = 29
4-1-1. LiCoO₂ 입자의 크기 분포 = 29
4-1-2. LiCoO₂ 입자의 표면 형상, 분포 및 표면적의 변화 = 31
4-1-3. LiCoO₂ 입자의 Depth profile 측정 = 35
4-1-4. 전해질에 녹아 들어간 Co 함량 분석 = 37
4-2. 전기 화학적 특성 = 39
4-2-1. 초기 방전 용량 = 39
4-2-2. 충·방전 특성 = 42
4-3. 고온 특성 = 50
4-3-1. 고온에서 방전 용량 측정 = 50
4-3-2. DSC 분석 = 52
제5장 결론 = 54
참고문헌 = 56
