검색 상세

Physico-Chemical and Electrochemical Properties of Cathode and Anode Materials for Lithium-ion Batteries

  • Seo, Hyo Ree (서효리, 대학원 화학과 물리화학전공)

초록/요약

Among the key factors of a lithium-ion battery (cathode, anode, electrolyte, separator), electrodes are the most important components which are deeply related with lithium-ion battery capacities. Therefore, a structure of the electrodes have to be stable in reversible lithium reactions, and electrode and/or electrolyte are also stable without any chemical reactions. The development of the electrode materials would be processed based on the understand of the electrochemical behavior and its failure mechanism of the cathode and anode. Therefore, this work focused on investigation and analysis of the structural and electrochemical properties and searches for modification methods for improving lithium-ion battery capacities. First, investigation of electrochemical charge/discharge performance of lithium-rich compound Li2MnO3 having an electrochemically inactive Mn4+ was carried out based on the phase transition phenomenon of the layered-Li2MnO3 confirmed from ex-situ X-ray diffraction data, and synthesis modification was tried to decrease in the structural changes. The Mn4+ in Li2MnO3 is known as electrochemically inactive state due to difficulty to be more oxidation, but it is possible that Li2MnO3 have not only tetravalent Mn but also trivalent Mn as synthesis method and/or surroundings. However, layered-Li2MnO3 accompanies structural changes, so it becomes unstable during charge/discharge cycling. To reduce the structural changes, the modified composite Li2MnO3-MnO(OH) was synthesized, and this showed more improved capacity and cycle life than before modification because of decrease in phase transition. Second, we have studied structural information during electrochemical cycling in full-cell system by neutron diffraction method. Spinel-lithium manganese oxide cathode (Li(Li0.08Al0.08Mn1.84)O3.99 and LiMn2O4) and graphite anode is used for the full-cells, and all the obtained patterns are analyzed by Rietveld refinement and Gaussian peak-fitting method to describe a variation of phase parameter in spinel-LiMn2O4 cathode and phase transition in graphite anode. The structural changes of the components within the fabricated Li-ion batteries (LiMn2O4/graphite full-cells) were determined by measuring in-situ neutron diffraction (ND) patterns at different state of charges (SOCs), and the obtained data were compared with ex-situ powder ND patterns. Phase transitions from graphite to lithiated graphite phases during electrochemical charging processes are clearly shown in the graphite anode. The intercalated Li ions in graphite are not perfectly extracted during delithiaion process in discharging. It is proved by a remained peak of LiC12 phase at SOC 0 %. The contents of LiC12 phase increased as increasing cycle numbers, and the mole fraction of LiC12 and LiC6 phases was changed at SOC 100 %, and the lattice parameters of LiMn2O4 also decreased due to decline of the amounts of Li ions, which can be reversibly intercalated into the structure. Last, in this work for anode, Si-Ti-Ni alloy material(STN) was used to study an alternative anode material instead of graphite with low theoretical capacity. Si-Ti-Ni alloy consists of Si7Ti4Ni4 matrix (inactive phase) and Si nanoparticles (active phase) embedded in the inactive phase. The STN showed improved and stable cycleability because of effective volume control of the inactive phase against the embedded Si nanoparitcles, but steady capacity fading attributed to volume changes of Si nanoparticles limits cycle stability. The volume expansion/contract of the Si nanoparticles during charge/discharge deteriorates contact of the Si nanoparticles. Therefore, in this work, surface coating with PEDOT conductive polymer was tried to improve adhesion between STN particles and between STN particles and a current collector. In addition to the physicochemical and mechanical properties, charge transfer is also improved, and the PEODT-coated STN showed improved cycleabilities at 1 C and rate capabilities at high c-rates (3C and 5 C). In the future, a study of the cell component such as binder and current collector would be carried out with material studies, and through the improvement STN can be a promising candidate material for high capacity lithium-ion batteries.

more

목차

TABLE OF CONTENTS


ABSTRACT…………………………………………………………… i
TABLE OF CONTENTS........................................................ v
LIST OF FIGURES…………………………………………… viii
LIST OF TABLES………………………………………………… xiii


CHAPTER 1. Introduction
1.1. Introduction………………………………………………………… 2


CHAPTER 2. Literature Review
2.1. Secondary batteries……………………………………………… 6
2.2. Lithium-ion secondary batteries……………………………………… 10
2.2.1. Cathode materials……………………………………… 16
2.2.1.1. Layered-structure oxides …………………………………… 20
2.2.1.2. Spinel-structure oxide ……………………………………… 23
2.2.1.3. Olivine-structure oxides …………………………………… 28
2.2.2. Anode materials…………………………………………… 30
2.2.2.1. Graphite anodes …………………………………… 32
2.2.2.2. Alloy anodes ……………………………………… 35
2.2.3. Electrolyte…………………………………………… 38
2.2.4. Separator…………………………………………… 41


CHAPTER 3.
The Synthesis and Electrochemical Properties of Lithium Manganese Oxide (Li2MnO3)

3.1. Introduction………………………………………………………… 44
3.2. Experimental……………………………………………………… 46
3.3. Result and Discussions ……………………………………………… 48
3.4. Conclusions……………………………………………………… 63


CHAPTER 4.
Structural Change and Electrochemical Reaction of Spinel-LiMn2O4 by Neutron Diffraction

4.1. Introduction………………………………………………………… 65
4.2. Experimental……………………………………………………… 68
4.3. Result and Discussions ……………………………………………… 72
4.4. Conclusions……………………………………………………… 103


CHAPTER 5.
Physico-Chemical and Electrochemical Properties of Si-Ti-Ni Alloy Modified with poly(3,4-ethylenedioxythiophene)

5.1. Introduction………………………………………………………… 105
5.2. Experimental……………………………………………………… 108
5.3. Result and Discussions ……………………………………………… 112
5.4. Conclusions……………………………………………………… 134

more
반출 Meta View 목록