18 research outputs found
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Όλ¬Έ(λ°μ¬) -- μμΈλνκ΅λνμ : 곡과λν μ¬λ£κ³΅νλΆ, 2022. 8. κ°κΈ°μ.μΆ©μ μ λ¦¬ν¬ μ΄μ¨ λ°°ν°λ¦¬λ λμ μλμ§ λ° μ λ ₯ λ°λ, μ°μν μλ μ±λ₯ λ° μμ μ μΈ μ¬μ΄ν΄ νΉμ±μΌλ‘ μΈν΄ μ§λ μμ λ
λμ μλμ§ μ μ₯ μ₯μΉμ νμ€μ΄ λμλ€. ν΄λν μ μκΈ°κΈ°μ μ£Όμ μλμ§μμ΄μλ λ¦¬ν¬ μ΄μ¨μ μ§λ μ¬νμ , νκ²½μ μꡬμ λΆμνμ¬ ν νμ μ°μ
μ μλ‘μ΄ μ§νμμ ν΅μ¬ μλμ§ μ μ₯μ₯μΉλ‘μ νμ°μ μΈ μν μ ν κ²μΌλ‘ κΈ°λλλ€. μΆ©μ κΈ°κΈ°μ ν΄λκ° μ©μ΄νμ§ μμ μΉνκ²½ μ κΈ°μ΄μ‘μ μν λκ·λͺ¨ μλμ§ μ μ₯μ₯μΉλ‘μ κΈκ²©ν μ νμ λμνκΈ° μν΄μλ μ μ§μ μ μ₯ν μ μλ μλμ§ λ°λμ νμ μ μΈ μ¦κ°κ° νμμ μ΄λ€. μ΄μ κ΄λ ¨νμ¬ λ¦¬ν¬μ΄ νλΆν μΈ΅μ μ°νλ¬Ό μκ·Ήμ κΈ°μ‘΄μ ννλλ‘ μ μΈ΅μ λ¦¬ν¬ μ μ΄ κΈμ μ°νλ¬Όμ μλνλ κ³ μ©λμ λνλ΄κΈ° λλ¬Έμ λ체 μ¬λ£λ‘ μ λ§νλ€. κ·Έλ¬λ 리ν¬μ΄ νλΆν μΈ΅μ μ°νλ¬Ό μκ·Ήμ΄ λνλ΄λ κ³ μ©λ νΉμ±μ κ·ΌμμΈ μ°μ μ°ννμ λ°μμ μ¨-μ€νλ₯Ό μ μ΄νλ μμΈμ΄ 무μμΈμ§ μμ§ λͺ
ννμ§ μκΈ° λλ¬Έμ μλ λ©μ»€λμ¦μ μ΄ν΄νλ κ²μ΄ λ§€μ° μ€μνλ€. λν κ³ μ©λ μμμ μ κ·Ήμ μΌλ‘ μ¬μ©νλ©΄ μ¬μ΄ν΄μ ν΅ν΄ μλμ§λ₯Ό μ μ§νλ μ¬λ£μ λ₯λ ₯μ΄ ν¬κ² μ νλλ κ²μΌλ‘ μλ €μ Έ μμΌλ―λ‘ μ κ·Ήμ μ κΈ°ννμ κ°μμ±μ ν보νκΈ° μν μ¬μΈ΅μ μΈ μ΄ν΄λ νμμ μ΄λ€. λ³Έ λ
Όλ¬Έμμλ 리ν¬μ΄ νλΆν μΈ΅μ μ°νλ¬Ό μ κ·Ήμ κ³ μ©λ νΉμ±μ μ°μ μ°ννμ μμ© λ©μ»€λμ¦μ λν μ΄λ‘ μ μ°κ΅¬λ₯Ό μ μνλ©°, ν΄λΉ μ©λμ μ¬μ©ν λ μ κΈ°ννμ κ°μμ±μ μν₯μ λ―ΈμΉλ μμΈμ νμνμ¬ μμ μ μΌλ‘ μλν μ μλ μ¬λ£μ λν μ€κ³ μ λ΅μ μ μνλ €κ³ νλ€.
μ 2μ₯μμλ λ€μν μ μ΄ κΈμ μ°νλ¬Όμ μ μ ꡬ쑰λ₯Ό μ‘°μ¬νμ¬ λ¦¬ν¬μ΄ νλΆν μΈ΅μ μ°νλ¬Όμμ μ°μ μ°ν νμμ κΈ°μμ νꡬνμλ€. μ΄ μ₯μμ λλ κ³ μ©λ νΉμ±μ λ΄λΉνλ μ°μ μ°ν νμ ννμ΄ μ μ΄ κΈμμ μ νμ λ°λΌ λ¬λΌμ§ μ μλ€κ³ μ μνλ€. μ΄μ μ°κ΅¬μμ μ°μ μ°ννμμ μ΄λ°μ 리ν¬μ΄ νλΆν μΈ΅μ μ°νλ¬Ό λ΄μ μ‘΄μ¬νλ λ
νΉν LiβOβLi λΉκ²°ν© μΆμμ λΉλ‘―λλ€λ λ° λμνλ€. κ·Έλ¬λ LiβOβLi μνμ λΉκ²°ν© νΉμ±μλ λΆκ΅¬νκ³ μ°μ μ°ννμ λ°μμ κ°λ₯μ±κ³Ό μ°μ μ°ν λ°μμ μλ μ μμ 리ν¬μ΄ νλΆν μ°νλ¬Όμ ꡬμ±νλ TMμ μ νμ λ°λΌ λ―Έλ¬νκ² λ€λ₯΄λ€. κ³ μ©λμ λ¬μ±νκΈ° μν΄ μ°μ μ°ν νμ λ°μμ μ¬μ© κ°λ₯ν κ²½κ³λ₯Ό λͺ
νν νλ κ²μ μ€νμ μΌλ‘ λ³΄κ³ λ λλΆλΆμ μ°μ μ°ν νμ μ μκ° μ ν΄μ§μ λΆν΄ μ μμ κ±Έμ³ μκΈ° λλ¬Έμ λ§€μ° μ€μνλ€. κ·Έλ¬λ TM κΈμκ³Ό μ°μ μ°ννμ μ μ μ¬μ΄μ λ³Έμ§μ μΈ κ΄κ³λ μμ§ μμ ν μ΄ν΄λμ§ μμλ€. μ΄μ κ΄λ ¨νμ¬ μ§μ νκ²½μ κ³ λ €ν κ΄λ²μν 3μ°¨μ μ μ΄κΈμ νν©λ¬Ό(Li2TMO3)μ μ μ ꡬ쑰μ λν μ λ°ν μ‘°μ¬λ₯Ό ν΅ν΄ 리ν¬μ΄ νλΆν μΈ΅μ μ°νλ¬Όμ μ°μ μ°ν νμ νμ±μ λν ν¬κ΄μ μΈ κ·Έλ¦Όμ μ μνλ€. μ μ΄κΈμκ³Ό μ°μ μ¬μ΄μ Ο-ν μνΈμμ©μ κ΅λΆμ νκ²½μ μ‘°μ μ ν΅ν΄ μ² μ ν μ‘°μ¬λμμΌλ©°, μ΄λ μ°μ μ°ννμ νμ±/μ μμ μλΉν μν₯μ λ―ΈμΉλ κ²μΌλ‘ λ°νμ‘λ€. λμ λͺ¨λΈμ λ€μν μ°μ μ°ν νμ μ μμ λν΄ λ³΄κ³ λ νμνμ μκ΄ κ΄κ³λ₯Ό ν©λ¦¬ννκ³ μ νλ μ κΈ° ννμ μ°½ λ΄μμ μ°μ μ°ν νμ λ°μμ μμ μ μΌλ‘ μ λνκΈ° μν κ³Όνμ κΈ°μ΄λ₯Ό μ 곡ν κ²μΌλ‘ κΈ°λλλ€.
μ 3μ₯μμλ 리ν¬μ΄ νλΆν μΈ΅μ μ°νλ¬Ό μ κ·Ήμ μ μ μ΄ν μμΈμ νμ
νκ³ κ΅¬μ‘°μ κ°μμ±μ ν₯μμν€κΈ° μν μ¬λ£ μ€κ³ μ λ΅μ μ μνλ€. μ μ μ νμ κ°μ μ κΈ°ννμ μ΄νλ μ£Όλ‘ κ΅¬μ‘°μ μ₯μ λ‘ μΈν κ²μΌλ‘ μκ°λμ§λ§ μ΄λ¬ν νμμ΄ μ΄λ»κ² λΉκ°μμ μΈ λ°©ν₯μΌλ‘ μ§ννλμ§μ λν μ΄ν΄λ μμ§ λΆμμ νλ€. μ¬κΈ°μ λλ 리ν¬μ΄ νλΆν μΈ΅μ μ°νλ¬Όμ λΉκ°μμ ꡬ쑰 λ³νκ³Ό μ°ν νμ λΉλμΉμ΄ λμ ꡬ쑰 μ§νμ λν ν¬κ΄μ μΈ μ΄ν΄λ₯Ό ν΅ν΄ ν©λ¦¬μ μΌλ‘ μ€λͺ
λ μ μλ€κ³ μ μνλ€. μ°ννμ κ³Όμ μμ 곡쑴νλ μ¬λλΈ κΈλΌμ΄λ©κ³Ό νλ©΄ μΈ μ μ΄κΈμ λ§μ΄κ·Έλ μ΄μ
μ μ‘°ν©μ λ€μν ꡬ쑰μ μ§ν κ²½λ‘λ₯Ό μμ±νμ¬ ν¨μ¬ λ λμ μμ€μ ꡬ쑰μ 볡μ‘μ±μ μ΄λν μ μλ€. μμ±λ κ²½λ‘ μ€ λ°©μ μ ꡬ쑰μ λ³νμ΄ μΆ©μ μ μμκ³Ό λ€λ₯Έ λΉλμΉ κ²½λ‘λ μλ°μ μΈ κ³Όμ μ΄λ©° κ²°κ΅ λ¬΄μ§μν ꡬ쑰λ₯Ό νμ±νμ¬ μ μ νμ€ν
리μμ€ λ° κ΅¬μ‘°μ λΉκ°μμ±μ μ΄λν μ μλ€. νΉν μ¬λλΈ κΈλΌμ΄λ© λ§€κ° κ³Όμ μ μ μ΄κΈμμ΄ μ§μ μ΄λνμ¬ λ¬΄μ§μν ꡬ쑰λ₯Ό νμ±νλ κ²½λ‘λ³΄λ€ ν¨μ¬ μ¬μ΄ κ²μΌλ‘ λ°νμ Έ μ¬λλΈ κΈλΌμ΄λ©μ μ μ΄κ° ꡬ쑰μ μ΄νλ₯Ό μ΅μ νκ³ μ κΈ°ννμ μ±λ₯μ ν₯μμν€λ ν΅μ¬ μμμμ μμ¬νλ€. λμ μ°κ΅¬ κ²°κ³Όλ 리ν¬μ΄ νλΆν μΈ΅μ μ°νλ¬Όμ λΉκ°μμ ꡬ쑰μ μ§νμ λν ν©λ¦¬μ μΈ μλ리μ€λ₯Ό μ μνκ³ κ°μμ μ°μ μ°ν νμμ μ΅μ ννκΈ° μν μλ‘μ΄ μ μ΄ κ°λ₯ν μμΈμ 곡κ°νλ€.Rechargeable lithium-ion batteries, which have been the main energy source for portable electronic devices, are expected to play an inevitable role as a core energy storage device in a new horizon of the decarbonization industry in response to social and environmental demands. To respond to the rapid transition to large-scale energy storage for eco-friendly electrified transportation where charging devices are not easy to carry, innovatory increase of energy density that can be stored in cells is essential. In this regard, lithium-rich layered oxide cathodes are promising candidate as alternative materials because they exhibit a high-capacity that overwhelms the conventional stoichiometric layered lithium transition metal oxides. However, since it is still unclear what factors control the triggering of oxygen redox reaction, which is the origin of the high-capacity characteristics exhibited by lithium-rich layered oxide cathodes, so it is very important to understand oxygen redox triggering mechanism. In addition, it is known that active use of high-capacity region significantly compromises the material's ability to retain energy through cycles, so an in-depth understanding to secure the electrochemical reversibility of the electrode is also essential. In this thesis, I present a theoretical study on the oxygen redox triggering mechanism which is responsible for the high-capacity characteristics of lithium-rich layered oxide electrodes and propose a design strategy for a material that can be stably maintained high capacity by exploring the factors that affect electrochemical reversibility when using the corresponding capacity.
In chapter 2, I explore the origins of oxygen redox in lithium-rich layered oxides by examining the electronic structures of various transition metal oxide compounds. In this chapter, I propose that the oxygen redox chemistry responsible for the high-capacity properties can depend on the type of transition metal. In previous studies, it was agreed that the triggering of oxygen redox originates from a unique LiβOβLi non-bonding axis present within the lithium-rich layered oxides. However, despite the non-bonding nature of the LiβOβLi state, the availability of oxygen redox reaction and operating voltage of oxygen oxidation reaction subtly differed depending on the different types of TMs constituting the lithium-rich oxides. Clarifying the usable boundaries of oxygen redox reaction to achieve high capacity is very important because the most of oxygen redox potential which are experimentally reported spans the decomposition voltage of the electrolyte. However, their intrinsic relationship between transition metal and oxygen redox potential have not yet been fully understood. In this respect, I present a comprehensive picture of the oxygen redox activity of lithium-rich layered oxides through precise examination of the electronic structures of a wide range of 3d transition metal compounds (Li2TMO3) considering the local environments. The Ο-type interaction between transition metal and oxygen was thoroughly investigated through the control of the local environment, which was found to have a significant effect on the oxygen redox activity/potential. My model rationalizes the reported phenomenological correlations for different oxygen redox potentials and provides a scientific basis for stably inducing oxygen redox reactions within a limited electrochemical window.
In Chapter 3, I identify the factors of irreversible voltage degradation of lithium-rich layered oxide electrodes and propose a material design strategy to improve structural reversibility. Electrochemical degradation, such as voltage depression, is believed to be mainly due to structural disorders, but the understanding of how these phenomena evolve in an irreversible direction is still incomplete. Here, I suggest that the irreversible structural transformation and redox asymmetry of lithium-rich layered oxides can be rationally explained through a comprehensive understanding of dynamic structural evolution. Combination of slab gliding and out-of-plane transition metal migration which are co-existing in the oxygen redox process can generate various structural evolution pathways, leading to even higher levels of structural complexity. Among generated pathways, some asymmetric pathways in which structural transformation upon discharging differ from the reverse order of charging, are spontaneous processes and eventually form disordered structures, resulting in voltage hysteresis and structural irreversibility. Particularly, the slab gliding mediated process was found to be much easier than the pathway in which transition metal migrate directly to form a disordered structure, suggesting that the control of slab gliding is a key factor for suppressing structural degradation and improving electrochemical performance. My findings present a rational scenario for irreversible structural evolution of lithium-rich layered oxides and unveil new controllable factors for optimizing the reversible oxygen redox.Chapter 1. Introduction 1
1.1 Motivation and outline 1
1.2 References 6
Chapter 2. Anionic redox activity regulated by transition metal in lithium-rich layered oxides 9
2.1 Introduction 9
2.2 Computational and experimental details 18
2.2.1 First-principle calculations 18
2.2.2 Material synthesis and electrode preparation 19
2.2.3 Electrochemistry 20
2.3 Result and Discussion 23
2.3.1 Ο-type interaction and change in oxygen energy state 23
2.3.2 Neighboring TM alters LiOLi energy states 30
2.3.3 General indicator of oxygen redox activity in 3d-metal-based Li2TMO3 40
2.4 Concluding remarks 48
2.5 References 50
Chapter 3. Superposition of slab gliding and transition metal migration leads to irreversibility and redox asymmetry in lithium-rich layered oxides 58
3.1 Introduction 58
3.2 Computational and experimental details 64
3.2.1 First-principles calculations 64
3.2.2 Material synthesis and electrode preparation 64
3.2.3 Operando X-ray diffraction 65
3.3 Results and discussion 66
3.3.1 Simultaneous occurrence of slab gliding and TM migration 66
3.3.2 Asymmetric pathways and structural irreversibility resulting from the combination of slab gliding and TM migration 74
3.3.3 Redox asymmetry due to the asymmetric structural transformations 91
3.3.4 Facilitating irreversible deformation pathways by slab gliding 96
3.4 Concluding remarks 104
3.5 References 105
Chapter 4. Summary 111
Abstract in Korean 113λ°
Analyzing the Effect of Changes in the Benchmark Policy Interest Rate Using a Term Structure Model
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Synthesis of Surfactant Free SnS Nanoplates and Morphology Control in an Aqueous Solution
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