Fabrication of high-entropy oxides as Li-on battery anode materials via combustion synthesis
연소 공정을 통한 리튬 이온 배터리 음극재 하이엔트로피 산화물 개발
- 주제(키워드) Lithium ion batteries
- 발행기관 고려대학교 대학원
- 지도교수 최원준
- 발행년도 2023
- 학위수여년월 2023. 8
- 학위구분 석사
- 학과 대학원 기계공학과
- 세부전공 기계공학 전공
- 원문페이지 57 p
- UCI I804:11009-000000277450
- DOI 10.23186/korea.000000277450.11009.0000123
- 본문언어 영어
초록/요약
This thesis discusses the improved performance of Li-ion battery (LIB) anode for electrochemical energy storage system by synthesizing high-entropy oxides (HEOs) using facile combustion synthesis. Recently, transition metal oxides (TMOs) with high theoretical capacity have been studied to replace the traditional graphite of low thoeretical capacity (372 mAh g-1). HEOs, one of the TMOs, are emerging as novel anode materials for their improved stability due to entropy stabilization effect. First, HEOs consisting of five transition metal elements (Mn, Fe, Co, Ni, Cu) were fabricated by one step combustion synthesis controlling the fuel to oxidizer ratio from 0.9 to 1.05 in this paper. Depending on the reductive atmosphere, samples had different physicochemical properties and thereby different electrochemical performance could be shown. To achieve entropy stabilization effect, selective precipitation of metal elements should be successfully prevented. At the same time, low integrity of too porous structure should be prevented to endure the stress during the rapid lithiation process. HEO sample which was fabricated under the optimized condition of combustion synthesis with 0.95 of fuel to oxidizer ratio (φ-0.95) had high crystallinity, homogeneous elemental distribution, porous structure and higher oxidation state of spinel phase. As a result, φ-0.95 presented the highest rate capability and stability in long cycle test. φ-0.95 of homogeneous elemental distribution without selective precipitation enabled entropy stabilization effect and its mechanical integrity of porous structure could endure the inward stress during lithiation process. Next, HEOs with multi-walled carbon nanotube (MWCNT) composite was fabricated by ultrafast combustion synthesis to enhance the electrical conductivity of HEOs to improve electrochemical performance under high current condition. MWCNT has superior electrical conductivity and heat conductivity. Not only it can enhance the heat transfer during combustion synthesis but also provide higher rate capability of anode materials. Five-element transition metal nitrate, glycine with optimized ratio and MWCNT were mixed in DI water. Then combustion synthesis was applied on the hot plate for 10 seconds. Interconnected porous structure of HEOs that MWCNT embedded could be achieved in a very short time. HEOs with MWCNT exhibited higher rate capability and stability in 1000 cycles under 2 C-rate, even higher electrochemical performance than φ-0.95. This ultrafast and facile synthesis can save time and the cost as post-heat treatment for several hours is not necessary. Therefore, this approach can contribute to the development of high-performance nanocomposites for LIB anodes and their nano/micro structures.
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TABLE OF CONTENTS
ABSTRACT i
국문 초록 ii
TABLE OF CONTENTS v
LIST OF FIGURES vi
CHAPTER 1. INTRODUCTION 1
1.1 Motivation and background 1
CHAPTER 2. High entropy oxides for high-performance LIBs anode by optimizing fuel to oxidizer ratio 4
2.1 Introduction 6
2.2 Experimental 7
2.3 Results and discussion 8
2.4 Conclusion 23
CHAPTER 3. High entropy oxides / MWCNT for high-performance LIBs anode 24
3.1 Introduction 24
3.2 Experimental 25
3.3 Results and discussion 27
3.4 Conclusion 36
CHAPTER 4. CONCLUSION 38
References 41
