This thesis addresses the introduction of redox mediator into lithium-oxygen batteries to improve their electrochemical performance especially in terms of practical energy density and round-trip efficiency. In chapter 1, basic electrochemistry regarding lithium-oxygen batteries and redox mediators are introduced. In chapter 2 to 4, comprehensive researches including the discovery of a new redox mediator inspired by biological system, the investigation on kinetic property of redox mediator, and the prevention of shuttle phenomenon are introduced, followed by chapter 5 summarizing the contents. This thesis is targeted to students and researchers interested in electrochemistry and energy storage systems.
The importance of energy storage in shifting humanity towards a more sustainable and efficient energy infrastructure is becoming increasingly clear. Electrochemical energy storage systems in particular promise to substantially reduce the financial and environmental cost of electricity -- through a range of grid services such as load shifting and frequency regulation -- and transportation -- by enabling the use of electric vehicles. Of these, lithium ion batteries have received substantial interest due to their low cost, high energy densities, long lifetimes, and ease of integration into existing energy infrastructures. In all of these next-generation applications, however, the performance and cost requirements for lithium ion batteries far exceed what is typical for technologies in which they currently find use, such as portable electronics. Most significantly, the energy density of the positive electrode is a major bottleneck. One of the most promising strategies to increase the positive electrode energy density is by increasing the voltage and useable atomic fraction of lithium in intercalation materials. These materials are designed to undergo reversible delithiation with a concomitant oxidation of the otherwise mostly rigid host lattice and generation of vacancies at the former lithium sites. Oxygen redox, wherein electrons are reversibly removed from lattice oxygen during delithiation, has been recently shown to be able to support deep delithiation from oxide intercalation materials with a high average voltage, making it extremely attractive for developing high energy density electrodes. However, oxygen redox almost invariably results in irreversible voltage fading with cycling, which drains energy density over time, as well as charge-discharge voltage hysteresis, which reduces the round-trip energy storage efficiency. The origin of these unfavourable electrochemical properties has remained mostly a mystery due to the lack of understanding of the nature of the oxidised oxygen species and the materials properties governing their stability and the reversibility of their formation. Consequently, oxygen redox is yet to find commercial application. In this thesis, by revealing the mechanism of oxygen redox, I establish the origin of its associated unfavourable electrochemical properties. I show that when oxygen is oxidised, it experiences a strong driving force to change its local bonding configuration in order to stabilise its higher oxidation state. Bonding changes that can stabilise oxidised oxygen include increasing the bond order with a neighbouring transition metal through a substantial contraction of their existing bond, or forming a new bond with another oxygen to form a short O--O dimer. Crucially, these bonding changes cannot typically be accommodated by minor distortions to the host crystal structure, and so structural defects form within which the desired bonding changes can take place. It is the generation of these structural defects -- most commonly observed as migration of transition metals into vacant lithium sites during delithiation -- that gives rise to the disordering of the host lattice that is at the root of the poor electrochemical properties of oxygen redox. This new understanding reveals a dilemma, in which the structural disordering that results in unfavourable electrochemical properties also allows for the bonding changes necessary to stabilise oxidised oxygen. I propose strategies that resolve this dilemma, which mainly aim at making structural and chemical modifications to the host lattice that promote the stabilising bonding changes while avoiding an overall disordering of the lattice during cycling. This work lays the foundation for the development of practical, high energy density intercalation electrodes employing oxygen redox.
This book presents studies and discussions on anionic redox, which can be used to boost the capacities of cathode electrodes by providing extra electron transfer. This theoretically and practically significant book facilitates the implementation of anionic redox in electrodes for real-world use and accelerates the development of high-energy-density lithium-ion batteries. Lithium-ion batteries, as energy storage systems, are playing a more and more important role in powering modern society. However, their energy density is still limited by the low specific capacity of the cathode electrodes. Based on a profound understanding of band theory, the author has achieved considerable advances in tuning the redox process of lithium-rich electrodes to obtain enhanced electrochemical performance, identifying both the stability mechanism of anionic redox in lithium-rich cathode materials, and its activation mechanism in these electrode systems.
Flow batteries have received attention in large-scale energy storage due to their flexible design, high safety, high energy efficiency, and environmental friendliness. In recent years, they have been rapidly developed and tested in a variety of scales that prove their feasibility and advantages of use. As energy becomes a global focus, it is important to consider flow battery systems. This book offers a detailed introduction to the function of different kinds of redox flow batteries, including vanadium flow batteries, as well as the electrochemical processes for their development, materials and components, applications, and near future prospects. Redox Flow Batteries: Fundamentals and Applications will give readers a full understanding of flow batteries from fundamentals to commercial applications.
Lithium air rechargeable batteries are the best candidate for a power source for electric vehicles, because of their high specific energy density. In this book, the history, scientific background, status and prospects of the lithium air system are introduced by specialists in the field. This book will contain the basics, current statuses, and prospects for new technologies. This book is ideal for those interested in electrochemistry, energy storage, and materials science.
A comprehensive overview of the research developments in the burgeoning field of metal-air batteries An innovation in battery science and technology is necessary to build better power sources for our modern lifestyle needs. One of the main fields being explored for the possible breakthrough is the development of metal-air batteries. Metal-Air Batteries: Fundamentals and Applications offers a systematic summary of the fundamentals of the technology and explores the most recent advances in the applications of metal-air batteries. Comprehensive in scope, the text explains the basics in electrochemical batteries and introduces various species of metal-air batteries. The author-a noted expert in the field-explores the development of metal-air batteries in the order of Li-air battery, sodium-air battery, zinc-air battery and Mg-O2 battery, with the focus on the Li-air battery. The text also addresses topics such as metallic anode, discharge products, parasitic reactions, electrocatalysts, mediator, and X-ray diffraction study in Li-air battery. Metal-Air Batteries provides a summary of future perspectives in the field of the metal-air batteries. This important resource: -Covers various species of metal-air batteries and their components as well as system designation -Contains groundbreaking content that reviews recent advances in the field of metal-air batteries -Focuses on the battery systems which have the greatest potential for renewable energy storage Written for electrochemists, physical chemists, materials scientists, professionals in the electrotechnical industry, engineers in power technology, Metal-Air Batteries offers a review of the fundamentals and the most recent developments in the area of metal-air batteries.
New strategies and materials are needed to increase the energy and power capabilities of lithium storage devices for electric vehicle and grid-scale applications. Systems based on oxygen electrochemistry are promising due to the relatively high potentials (~ 3 V vs. Li) of Li-oxygen redox couples, which can enable high energy to be stored in the absence of heavy and expensive transition metal-based compounds used in conventional Li-ion battery electrodes. This thesis explores two strategies to incorporate Li-oxygen redox electrochemistry into electrodes for high-power or high-energy devices: (1) oxygen functionalization of carbon surfaces for fast surface Li storage, and (2) bulk oxygen reduction and Li storage in Li-air batteries with a theoretical cell-level gravimetric energy up to 4 times higher than Li-ion batteries. First, we study the charge storage mechanisms in oxygen-functionalized multiwalled carbon nanotube (MWNT) positive electrodes for high-power Li batteries. Thin-film (below 3 im) electrodes are used as a platform for probing the kinetics of surface redox reactions between Li+ and oxygen on MWNTs in asymmetric and symmetric cell configurations. We next extend this concept to the development of freestanding electrodes with more practical thicknesses (tens of pm). By varying the MWNT functionalization time, we show that the surface oxygen concentration can be controlled to yield electrodes with tunable energy and power characteristics, with typical gravimetric energies of ~200 Wh/kgelectode at ~10 kW/kgeectrode. The second part of this thesis investigates fundamental and design considerations to enable development of Li-air battery electrodes with high gravimetric energy, improved round-trip efficiency, and increased stability upon cycling. Using aligned carbon nanofiber (CNF) or nanotube (CNT) electrodes synthesized in-house, we report the first observations of Li2O2 particle formation and shape evolution during discharge. Highly porous (> 90% void volume) CNF electrodes achieve one of the highest gravimetric energies (2400 Wh/kgdischarged at 30 W/kgdischarged) to date, demonstrating the role of electrode structure in realizing the theoretical energy advantage of Li-air systems at the laboratory scale. We next use CNT electrodes as a platform for studying chemical and morphological changes occurring in the electrode during cycling, and find that poor cycle life can be attributed to gradual accumulation of parasitic Li2CO3 promoted by reactivity of the carbon substrate. Finally, we study the influence of Li2O2 discharge rate-dependent structure and surface chemistry on the oxidation kinetics to probe the fundamental origins of high overpotentials required on charge. An integrated morphological, chemical, and electrochemical approach highlights new considerations for the design of practical electrodes for increased round-trip efficiency and improved cycle life.
Over the past decade the topic of energy and environment has been ackno- edged among many people as a critical issue to be solved in 21st century since the Kyoto Protocol came into e?ect in 1997. Its political recognition was put forward especially at Heiligendamm in 2007, when the e?ect of carbon dioxide emission and its hazard in global climate were discussed and shared univ- sallyascommonknowledge.Controllingtheglobalwarmingintheeconomical framework of massive development worldwide through this new century is a very challenging problem not only among political, economical, or social c- cles but also among technological or scienti?c communities. As long as the humans depend on the combustion of fossil for energy resources, the waste heat exhaustion and CO emission are inevitable. 2 In order to establish a new era of energy saving and environment benign society, which is supported by technologies and with social consensus, it is important to seek for a framework where new clean energy system is inc- porated as infrastructure for industry and human activities. Such a society strongly needs innovative technologies of least CO emission and e?cient en- 2 ergy conversion and utilization from remaining fossil energies on the Earth. Energy recycling system utilizing natural renewable energies and their c- version to hydrogen may be the most desirable option of future clean energy society. Thus the society should strive to change its energy basis, from foss- consuming energy to clean and recycling energy.
Battery Technologies A state-of-the-art exploration of modern battery technology In Battery Technologies: Materials and Components, distinguished researchers Dr. Jianmin Ma delivers a comprehensive and robust overview of battery technology and new and emerging technologies related to lithium, aluminum, dual-ion, flexible, and biodegradable batteries. The book offers practical information on electrode materials, electrolytes, and the construction of battery systems. It also considers potential approaches to some of the primary challenges facing battery designers and manufacturers today. Battery Technologies: Materials and Components provides readers with: A thorough introduction to the lithium-ion battery, including cathode and anode materials, electrolytes, and binders Comprehensive explorations of lithium-oxygen batteries, including battery systems, catalysts, and anodes Practical discussions of redox flow batteries, aqueous batteries, biodegradable batteries, and flexible batteries In-depth examinations of dual-ion batteries, aluminum ion batteries, and zinc-oxygen batteries Perfect for inorganic chemists, materials scientists, and electrochemists, Battery Technologies: Materials and Components will also earn a place in the libraries of catalytic and polymer chemists seeking a one-stop resource on battery technology.
