Conversion reaction mechanisms of multi-anion transition metal compounds as new anodes for Li-ion batteries
- 주제(키워드) Lithium ion battery , Conversion reaction
- 발행기관 고려대학교 대학원
- 지도교수 강윤찬
- 발행년도 2020
- 학위수여년월 2020. 8
- 학위구분 석사
- 학과 대학원 신소재공학과
- 세부전공 신소재공학전공
- 원문페이지 111 p
- UCI I804:11009-000000232069
- DOI 10.23186/korea.000000232069.11009.0001178
- 본문언어 영어
- 제출원본 000046048368
초록/요약
Multi component transition metal compounds (TMCs) containing multiple cations and anions have been applied as energy storage, catalysts, solar cells, and phosphors. Most of all, multi-anion TMCs such as metal hydroxychloride and hydroxysulfide have drawn much attention as new anode materials for Li-ion batteries. Conversion reaction mechanisms of these materials with Li-ions revealed transformation into nanostructured heterointerface with different bandgaps after the first cycle, showing better electrochemical performances. The hetero structures originated from electrochemical reactions boost surface reaction kinetics and expedite charge transport owing to internal electric field at hetero interfaces. This thesis introduces detailed conversion mechanism of mteal hydroxycloride and hydroxysulfide with Li-ions. The inital morphologies and phases were confirmed using various characterization techniques. Furthermore, systematic analyses such as ex-situ X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and in-situ electrochemical impedance spectroscopy (EIS) were conducted to verify newly formed phases. In the first section, nickel hydroxy chloride (Ni(OH)Cl) was prepared by one-pot solvothermal reaction. The flower-like Ni(OH)Cl microspheres are successfully applied to anode materials for Li-ion batteries and exhbit good cycle stability (1236 mA h g-1 for the 150 cycles at current density of 0.2 A g-1) and excellent rate capability (232 mA h g-1 at current density of 30.0 A g-1). The enhanced electrochemical properties result from layered Ni(OH)2/NiCl2 heterointerface after the initial cycle. Additionally, LiOH confirmed as discharge product partially converts into Li2O and LiH, contributing high reversible capacity. In the second section, hollow carbon nanospheres embedded with cobalt hydroxy sulfide (HC-CoOHS) was adopted as a new anode material for Li-ion batteries. It was synthesized by co-precipitation method and room-temperature sulfidation. HC-CoOHS was successfully applied as an efficient anode material for Li-ion batteries, showing stable cycle life (880 mA h g-1 for the 200th cycles) and outstanding rate capability (246 mA h g-1 at current density of 30.0 A g-1). The synergetic effect of the formation of heterostructured Co(OH)2/CoS2 and highly conductive hollow carbon nanospheres were attributed to enhanced electrochemical performances. For the comparison sample, bare cobalt hydroxysulfide(CoOHS) was chosen to analyze conversion mechanism with Li-ions and show effectiveness of hollow carbon nanospehres during electrochemical reactions. In this thesis, rational experiments and multiple analytic tools were utilized, and the conversion mechanisms of metal hydroxychloride and hydroxysulfide were demonstrated as a new concept of anode materials. The hollow carbon nanospheres as well as double-anion transition metal compounds will be used in a wide range of applications including energy storages.
more목차
Chapter 1. Introduction 1
Chapter 2. Theoretical Background 4
2-1. Lithium-ion batteries (LIBs) 4
2-2. Reaction mechanisms of transition metal compounds (TMCs) 8
2-2-1. Intercalation
2-2-2. Alloying
2-2-3. Conversion
2-3. Multicomponent TMCs on LIBs characteristics 16
2-3-1. Multi-cation TMCs 16
2-3-2. Multi-anion TMCs 18
2-4. Carbon composites on TMCs as anode maerials 20
Chapter 3. Experimental 24
3-1. Preparation of nanostructures 24
3-1-1. Preparation of flower-like nickel hydroxychloride (Ni(OH)Cl)
Microspheres. 24
3-1-2. Preparation of hollow carbon nanosphere embedded with
cobalt hydroxysulfide (HC-CoOHS) 26
3-2. Characterization 29
3-3. Electrochemical Characterization 30
3-3-1. Flower-like nickel hydroxychloride (Ni(OH)Cl) for LIBs andoe materials 30
3-3-2. Hollow carbon nanosphere embedded with cobalt hydroxysulfide (HC-CoOHS) for LIBs anode materials 32
Chapter 4. Results & Discussion 33
4-1. Flower-like nickel hydroxychloride (Ni(OH)Cl) for lithium-ion batteries 33
4-1-1. Formation mechanism 33
4-1-2. Phase and morphology analyses 35
4-1-3. Electrochemical properties 43
4-2. Hollow carbon nanospheres embedded with cobalt hydroxysulfide (HC-CoOHS) for lithium-ion batteries 59
4-2-1. Formation mechanism 59
4-2-2. Phase and morphology analyses 61
4-2-3. Electrochemical properties 70
Chapter 5. Conclusions 90
References 92
