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차세대 리튬이차전지 양극활물질 A₂MnPO₄F/C (A=Li, Na) 복합체의 전기화학적 특성

Electrochemical Properties of A₂MnPO₄F/C composite(A=Li, Na) as Cathode Materials for Lithiun-ion Batteries

  • 김동진 (대학원 화학과 무기화학전공)

초록/요약

ABSTRACT Electrochemical properties of A2MnPO4F/C composite (A=Li, Na) as cathode materials for lithium-ion batteries Dong-Jin Kim1.2 Advised by Prof. Keon Kim1 and Jun-Ho Song2 1. Department of Chemistry, Korea University 2. Advanced Batteries Research Center, Korea Electronics Technology Institute Fluorophosphates, A2MPO4F (A=Li, Na, M=Fe, Mn) has 2 Li or Na ions in the tunnel sites. Comparing to olivine LiMPO4 (M=Fe, Mn) materials, theoretical capacity of A2MPO4F is double, if all alkali metal ions are inserted / extracted from host structure. However, poor electrochemical activity due to low electrical conductivity limits this material to be used as a cathode material for Li-ion battery. It is expected that nano-sized particle with short diffusion pathway and uniform carbon coating improve the electrical conductivity of material. In this study, Na2MnPO4F/C composite was synthesized by carbothermal reduction method followed by additional carbon coating to improve the electrochemical reactivity of Li+ intercalation on Na2MnPO4F. Prepared Na2MnPO4F showed the particle size under 100 nm without impurity phase. Li+ insertion into Na2MnPO4F was carried out successfully with bothchemical and electrochemical methods, respectively. Noable improvement of Li+ intercalation was achieved on Na2MnPO4F/C composite material. Keywords : Lithium ion battery, Cathode material, Poly anion material, Fluorophosphates, A2MPO4F, Na2MnPO4F, carbon coating

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ABSTRACT ⅰ
LIST OF TABLES ⅵ
LIST OF FIGURES ⅶ

제 1장 서 론 1
1-1. 연구 목적 및 필요성 1

제 2장 이론적 배경 4
2-1. 전지의 역사와 리튬이차전지 4
2-2. 리튬이차전지의 구성요소와 양극 활물질 6
2-2-1. 층상 구조 산화물 11
2-2-2. 스피넬 구조 화합물 14
2-2-3. 올리빈 구조 화합물 16
2-2-4. Poly-anion 계열 화합물 18

제 3장 실험 방법 21
3-1. 합성방법 21
3-1-1. 고상법 (Solid state Reaction) 21
3-1-2. 탄소열환원법 (Carbothermal Reduction) 24
3-1-3. 수열합성법 (Hydrothermal Synthesis) 30
3-2. 분석방법 35
3-2-1. X-ray Diffraction (XRD) Measurements 35
3-2-2. Rietveld Analysis 35
3-2-3. Scanning electron microscope (SEM) Observations 36
3-2-4. Inductively Coupled Plasma - Atomic Emission Spectroscope (ICP-AES) 36
3-2-5. Thermogravimetric Analysis (TGA) 37
3-3. 전기화학적 특성 38
3-3-1. 전극 제조 38
3-3-2. 전지 조립 38
3-3-3. 충 · 방전 실험 39

제 4장 실험 결과 및 고찰 40
4-1. 고상법으로 제조된 Na2MnPO4F의 특성 40
4-1-1. 입자 크기 제어를 통한 효과 40
4-1-2. 카본 코팅을 통한 효과 48
4-2. Carbothermal reduction으로 제조된 Na2MnPO4F의 특성 52
4-2-1. Super-P를 이용한 carbothermal reduction 효과 52
4-2-2. Sucrose를 이용한 carbothermal reduction 효과 59
4-3. 최적의 Carbothermal reduction으로 제조된 Na2MnPO4F의 특성 65
4-3-1. Citric acid를 이용한 carbothermal reduction 효과 65
4-3-2. 추가 Carbon coating을 통한 Na2MnPO4F/C 특성 70
4-3-3. 후열처리로 결정성 회복을 통한 Na2MnPO4F/C 특성 74

제 5장 결 론 79

제 6장 참 고 문 헌 83

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