질화규소탄화규소 적층복합재료의 역학적 특성에 관한 연구

학위논문(석사)--서울대학교 대학원 :무기재료공학과,1998.Maste

리튬 과잉 복합 양극 소재 상형성 기구 연구

학위논문 (박사)-- 서울대학교 대학원 : 재료공학부, 2017. 2. 김현이.The composite material LixNi0.25Co0.10Mn0.65O(3.4+x)/2 (x=1.6, 1.4, 1.2, 1.0, 0.8) were synthesized and characterized for their structural, morphological, and performance as cathode materials in Li-ion batteries. The Rietveld refinement results indicate the presence of two phases at high lithium levels (x=1.6 and 1.4): Li2MnO3 (C2/m) and LiMO2 (M = Ni, Co, Mn) (R3¯m)the latter contains Ni2+ and Ni3+. At low lithium levels (x=1.2, 1.0, and 0.8) an additional spinel phase LiM2O4 (Fd3¯m) emerges, which is known to affect the electrochemical performance of the oxide. Structural analysis reveals that the spinel phase contains mixed transition metals Ni, Co, and Mn as [Li+,Co2+][Ni2+,Co3+,Mn4+]2O4. A low lithium level is found to induce primary particle growth, as well as Co and Ni segregation within the secondary particles. These results are expected to contribute to material optimization and commercialization of lithium-rich oxide cathodes. The composite material Li2MnO3·Li(Ni,Co,Mn)O2·LiM0.5Mn1.5O4 (M = Mn, Ni, Co) were synthesized and characterized for their structural, morphological, and performance as cathode materials in Li-ion batteries. XRD analysis indicates the presence of Li2MnO2 (C2/m), Li(Ni,Co,Mn)O2 (R3¯m), and spinel phase LiM0.5Mn1.5O4 (M = Mn, Ni, Co) (Fd3¯m). In LiM0.5Mn1.5O4 (M = Mn) (Fd3¯m) composition spinel LiMn2O4 phase is embedded. At 20mol% embedding additionally LiNi0.5Mn1.5O4 phase is also detected. Rocksalt NiO phase is formed in LiM0.5Mn1.5O4 (M = Ni) composition even in oxygen atmosphere. LiM0.5Mn1.5O4 (M = Co) composite composition is homogeneously synthesized even in 20mol% embedding. By embedding LiCo0.5Mn1.5O4 phase the electrochemical performance in 18650 full cell using graphite anode is improved. Spinel embedding in lithium-rich composite oxide can improve the electrochemical performance through structural stability. The phase content, crystal size and lattice parameters were analyzed through the Rietveld refinement in LiM0.5Mn1.5O4 (M = Co) composite composition. Spinel embedding induces primary particle growth during heat-treatment, as well as Co and Ni segregation within the secondary particles. Ab initio calculation shows that spinel embedding in lithium-rich composite oxide can lower the formation energy by stabilizing the structure. The phase evolution process was analyzed during high temperature XRD method.Chapter 1. Introduction (Theoretical Review) 1 1.1 Lithium ion battery 2 1.2 Cathode material for lithium ion battery 2 Chapter 2. Phase evolution of lithium-rich oxide 11 2.1 Introduction 12 2.2 Experimental Procedure 13 2.2.1 Synthesis 13 2.2.2 Instrumental Characterization 14 2.2.3 Computational Methods 15 2.2.4 Electrochemical Measurement 15 2.3 Results and discussion 16 2.3.1 Material Characterization 16 2.3.2 Identification of Composite phases and Their Growth Mechanism 21 2.4 Conclusions 23 Chapter 3. Spinel phase composite of lithium-rich oxide 41 3.1 Introduction 42 3.2 Experimental Procedure 43 3.2.1 Synthesis 43 3.2.2 Characterization and evaluation 43 3.2.3 Computational Methods 44 3.3. Results and Discussion 45 3.3.1 Spinel LiMn2O4 composite 45 3.3.2 Spinel LiNi0.5Mn1.5O4 composite 56 3.3.3 Spinel LiCo0.5Mn1.5O4 composite 65 3.4. Conclusions 83 Chapter 4. Conclusion 91 References 94 초 록 101Docto