Tailoring fluorophosphate cathode materials for high-performance sodium and lithium ion battery
리튬 및 소듐 이온 배터리용 불화인산염 양극물질 연구

DC Field Value Language
dc.description학위논문 (박사)-- 서울대학교 대학원 : 재료공학부, 2015. 2. 강기석.-
dc.description.abstractLithium-ion battery (LIB), which has been widely used to power portable electronic devices, is on the verge of being applied to new automobile applications. To expand this emerging market, however, an electrode that combines fast charging capability, long-term cycle stability, and high energy density is needed. In Chap. 2, a novel layered lithium vanadium fluorophosphate, Li1.1Na0.4VPO4.8F0.7, is introduced as a promising positive electrode contender. This new material has two-dimensional lithium pathways and is capable of reversibly releasing and reinserting ~1.1 Li+ ions at 4 V (vs. Li+/Li) to give a capacity of ~156 mAh g–1 (energy density of 624 Wh kg–1). Moreover, outstanding capacity retentions of 98% and 96% after 100 cycles were achieved at 60°C and room temperature, respectively. Unexpectedly high rate capability was delivered for both charge and discharge despite the large particle size (a few microns), which promises further enhancement of power density with proper nano-engineering.

Large-scale electric energy storage is a key enabler for the use of renewable energy. Low-cost and highly durable battery chemistry is required in affordable large-scale storage applications. In this respect, the room-temperature Na-ion battery (NIB) has been re-highlighted recently as a low-cost alternative technology to LIB. A cheap and earth-abundant element, Na, will be advantageous if a large amount of material is demanded for renewable energy solutions. However, significant challenges such as energy density and long term stability must be addressed. In Chap. 3, a novel cathode material for Na-ion battery, Na1.5VPO4.8F0.7, is introduced. This new material provides a high energy density of ~600 Wh kg–1, originating from both the multi-electron redox reaction (1.2 e– per formula unit) and high potential (~3.8 V vs. Na+/Na) of the tailored vanadium redox couple (V3.8+/V5+). Furthermore, an outstanding cycle life (~95% capacity retention for 100 cycles) could be achieved, which is attributed to small volume change (2.9%) upon cycling. The open crystal framework with two-dimensional Na diffusion paths leads to low activation barriers for Na diffusion, enabling excellent rate capability.

In Chap. 4, the first successful synthesis of a series of Na3(VO1−xPO4)2F1+2x (0 ≤ x ≤ 1) compounds is introduced, which is a new family of high-performance cathode materials for NIB. The Na3(VO1−xPO4)2F1+2x series can function as high-performance cathodes for NIB with high energy density and good cycle life, although the redox mechanism varies depending on the composition. The combined first-principles calculations and experimental analysis revealed the detailed structural and electrochemical mechanisms of the various compositions in solid solutions of Na3(VOPO4)2F and Na3V2(PO4)2F3. The comparative data for the Nay(VO1−xPO4)2F1+2x electrodes showed a clear relationship among V3+/V4+/V5+ redox reactions, Na+−Na+ interactions, and Na+ intercalation mechanisms in NIB.
dc.description.tableofcontentsTable of Contents

Chapter 1. Introduction

Chapter 2. A High-Energy Cathode for a Na-Ion Battery with High Stability
2.1. Introduction
2.2. Experimental and Computational Details
2.3. Results and Discussion
2.3.1. Material Characterization of Na1.5VPO4.8F0.7
2.3.2. Electrochemical Properties of Na1.5VPO4.8F0.7
2.3.3. Structural Evolution of the NaxVPO4.8F0.7 Electrode upon Cycling
2.3.4. Kinetics of the NaxVPO4.8F0.7 Electrode
2.3.5. Charge/Discharge Mechanism of the NaxVPO4.8F0.7 Electrode
2.4. Summary

Chapter 3. A Family of Cathodes for Na-ion Batteries, Na3(VO1−xPO4)2F1+2x
3.1. Introduction
3.2. Experimental and Computational Details
3.3. Results and Discussion
3.3.1. Characterization of a Family of Na3(VO1−xPO4)2F1+2x Compounds
3.3.2. Electrochemical Mechanisms of Nay(VO1−xPO4)2F1+2x Electrodes
3.3.3. Possibility of Multi-Electron Transfer in Nay(VO1−xPO4)2F1+2x System
3.4. Summary

Chapter 4. Tailoring a Fluorophosphate as a 4 V Cathode for Li-Ion Batteries
4.1. Introduction
4.2. Experimental and Computational Details
4.3. Results and Discussion
4.3.1. Fluorination of the Pristine Na Phase of Na1.5VPO5F0.5
4.3.2. Evidence for Reduced Oxidation State of Vanadium in Na1.5VPO4.8F0.7
4.3.3. Na+/Li+ Ion-Exchange for Lithium Derivative of Na1.5VPO4.8F0.7
4.3.4. Electrochemical Properties of Li1.1Na0.4VPO4.8F0.7
4.3.5. The Origin of the Fast Charging and Discharging
4.4. Summary

Chapter 5. Conclusion


Abstract in Korean

Curriculum Vitae
dc.format.extent10795677 bytes-
dc.publisher서울대학교 대학원-
dc.subjectsodium ion battery-
dc.subjectlithium ion battery-
dc.subjectcathode materials-
dc.subjectmulti-electron redox reaction-
dc.subjection-exchange reaction-
dc.titleTailoring fluorophosphate cathode materials for high-performance sodium and lithium ion battery-
dc.title.alternative리튬 및 소듐 이온 배터리용 불화인산염 양극물질 연구-
dc.contributor.affiliation공과대학 재료공학부-
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College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Material Science and Engineering (재료공학부) Theses (Ph.D. / Sc.D._재료공학부)
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