Rational Design Of Nanostructured Polymer Electrolytes And Solid Liquid Interphases For Lithium Batteries

This thesis makes significant advances in the design of electrolytes and interfaces in electrochemical cells that utilize reactive metals as anodes. Such cells are of contemporary interest because they offer substantially higher charge storage capacity than state-of-the-art lithium-ion battery technology. Batteries based on metallic anodes are currently considered impractical and unsafe because recharge of the anode causes physical and chemical instabilities that produce dendritic deposition of the metal leading to catastrophic failure via thermal runaway. This thesis utilizes a combination of chemical synthesis, physical & electrochemical analysis, and materials theory to investigate structure, ion transport properties, and electrochemical behaviors of hybrid electrolytes and interfacial phases designed to prevent such instabilities. In particular, it demonstrates that relatively low-modulus electrolytes composed of cross-linked networks of polymer-grafted nanoparticles stabilize electrodeposition of reactive metals by multiple processes, including screening electrode electrolyte interactions at electrochemical interfaces and by regulating ion transport in tortuous nanopores. This discovery is significant because it overturns a longstanding perception in the field of nanoparticle-polymer hybrid electrolytes that only solid electrolytes with mechanical modulus higher than that of the metal electrode are able to stabilize electrodeposition of reactive metals.

This thesis makes significant advances in the design of electrolytes and interfaces in electrochemical cells that utilize reactive metals as anodes. Such cells are of contemporary interest because they offer substantially higher charge storage capacity than state-of-the-art lithium-ion battery technology. Batteries based on metallic anodes are currently considered impractical and unsafe because recharge of the anode causes physical and chemical instabilities that produce dendritic deposition of the metal leading to catastrophic failure via thermal runaway. This thesis utilizes a combination of chemical synthesis, physical & electrochemical analysis, and materials theory to investigate structure, ion transport properties, and electrochemical behaviors of hybrid electrolytes and interfacial phases designed to prevent such instabilities. In particular, it demonstrates that relatively low-modulus electrolytes composed of cross-linked networks of polymer-grafted nanoparticles stabilize electrodeposition of reactive metals by multiple processes, including screening electrode electrolyte interactions at electrochemical interfaces and by regulating ion transport in tortuous nanopores. This discovery is significant because it overturns a longstanding perception in the field of nanoparticle-polymer hybrid electrolytes that only solid electrolytes with mechanical modulus higher than that of the metal electrode are able to stabilize electrodeposition of reactive metals.

This book discusses the roles of nanostructures and nanomaterials in the development of battery materials for state-of-the-art electrochemical energy storage systems, and provides detailed insights into the fundamentals of why batteries need nanostructures and nanomaterials. It explores the advantages offered by nanostructure electrode materials, the challenges of using nanostructured materials in batteries, as well as the rational design of nanostructures and nanomaterials to achieve optimal battery performance. Further, it closely examines the latest advances in the application of nanostructures and nanomaterials for future rechargeable batteries, including high-energy and high-power lithium ion batteries, lithium metal batteries (Li-O2, Li-S, Li-Se, etc.), all-solid-state batteries, and other metal batteries (Na, Mg, Al, etc.). It is a valuable reference resource for readers interested in or involved in research on energy storage, energy materials, electrochemistry and nanotechnology.

In recent years, continuous progress in electronic devices, especially in wearable devices, has attracted surging attention from the consumer market. Therefore, flexible energy storage was developed to fulfill the needs of new flexible devices with ultra-lightweight and small volume. The very recent products and concepts such as touch screens, roll-up displays, wearable sensors, and even implantable medical devices have shown great potential in flexible applications because of their extreme convenience. However, the development of corresponding power sources largely lags behind these emerging technologies of flexible devices. Lithium-ion batteries (LIBs), owing to high energy density and high operating voltage, have been serving as an ideal power source for flexible devices. Nevertheless, direct implementation of commercial LIBs leads to irreversible deformation of structural integrity, short-circuiting or even severe explosion hazard. Such dilemma originates from the poor flexibility of electrode and electrolyte. For electrode side, current electrode sheets used in LIBs are manufactured by holding active material particles and conductive agents by a small weight fraction of polymeric binders. Such fragile electrode structure could easily lose electrical contact under physical deformation, leading to disintegrated electrode sheets, drastic degradations of electrochemical performance, and even safety issue due to internal short-circuiting. For electrolyte side, LIBs employ nonaqueous liquid electrolyte with high ionic conductivity and excellent electrode wettability. However, the drawbacks of such electrolyte system are also evident: poor ion selectivity, flammability, and leakage issue while being deformed render unsuitability of liquid electrolyte for flexible device application. To fabricate flexible LIBs, the current state-of-the-art research employs two design strategies involving electrode structure. One popular strategy is constructing scaffolding structure using carbonaceous materials to function as supportive matrix for active materials. Given carbon nanotubes (CNTs) as an example, the CNTs possess remarkable electrical conductivity and mechanical strength (elastic modulus: 1 TPa, tensile strength: 100 GPa), which contribute to conductive and flexible electrodes as the high-aspect ratio of CNTs can serve as threading materials. Another strategy is rational architecture design of active materials that are conventionally particulate. For example, vanadium pentoxide nanowires can be readily fabricated into free-standing and binder-free electrode membrane. Nevertheless, the most of strategies above still fall short of practicality due to reduced portion of active materials and consequently compromised energy density. In comparison with the mobile liquid electrolyte, the emerging solid-state electrolytes could largely solve circumventing issues of ion selectivity, flammability and leakage. As one prevailing category, solid polymer electrolytes comprising polymers and lithium salts feature decent manufacturing flexibility. Meanwhile, their poor ionic conductivity (10 8 ~ 10 5S cm 1) could be ameliorated by gel polymer electrolytes with organic solvents (plasticizers) and/or inorganic solid fillers (e.g., SiO2). Nevertheless, the non-conductive fillers block ion-transport pathways while allow partial electrical conduction, limiting the interfacial engineering and compatibility with electrodes. In this dissertation, we tackle the aforementioned critical issues of flexible batteries in two aspects. Firstly, we design and synthesize flexible electrode from prospective of material and architecture. A novel cathode constructed by entangling networks of V2O5, CNTs and polytetrafluoroethylene (PTFE) is design and fabricated. Notably, the resulting flexible battery simultaneously achieves excellent mechanical strength (800 MPa young's module), superior cycle durability (86% retention after 1000 times bending) and intriguing capacity (300 mAh g-1 at 0.25C). Furthermore, a Zr-based metal-organic framework (MOF) possessing open-metal sites (OMSs) was used as the microporous filler to facilitate cation (Li+) conduction in GPL. Compared with the state-of-the-art research, our work significantly enhanced tLi+ of GLP from 0.39 up to 0.66 while maintained 1.5 mS cm 1 ionic conductivity. Notably, a reduced thermal activation energy (from 113 to 76 meV) was observed, suggesting diffusion energy barriers was eased by selective promotion of Li+ conduction. To conclude, flexible Li-ion batterie system research is still at early developing stage. Above work provides rational design and improvement of the current FLIBs system in rather facile and cost-effective way. The methodology we proposed are hoped to bring further innovation toward FLIBs field and be extended to numerous applications in the future.

This book provides the first complete and up-to-date summary of the state of the art in HAXPES and motivates readers to harness its powerful capabilities in their own research. The chapters are written by experts. They include historical work, modern instrumentation, theory and applications. This book spans from physics to chemistry and materials science and engineering. In consideration of the rapid development of the technique, several chapters include highlights illustrating future opportunities as well.

Solid-electrolyte interphase (SEI) is a nanoscale composite layer of organic and inorganic lithium (Li) salts formed on the electrode surface by electrolyte decomposition. It is ionically conductive and electrically insulating, thus allowing facile Li-ion transport and preventing further electrolyte decomposition. Owing to these features, SEI stability is crucial to the performance of rechargeable Li batteries. Unfortunately, SEI layer are unstable for most advanced battery materials, including high-capacity anodes materials (e.g., silicon (Si) and Li) in liquid electrolyte and Li anodes in solid electrolytes (e.g., Li10GeP2S12 (LGPS)). An unstable SEI layer may cause poor battery performance including consumption of active materials and electrolyte, capacity fading, resistance increase., etc. The structure and property of SEI have generally eluded rational control since its formation and growth processes involve a series of complex and competitive electrochemical reactions. The main efforts to addressing this issue have been made on the development of new electrolyte systems to form alternative SEI layers and preformed artificial SEI layers on the electrode surface to replace the electrolyte-derived SEI.This dissertation focuses on intrinsically regulating the chemical composition and nanostructure of SEI for advanced battery materials in conventional electrolyte systems, which enables not only optimized chemical and physical properties of SEI but improved battery performance. This is realized by developing chemical and electrochemical reactive materials and allowing them to participate in the SEI formation. These materials can contribute functional components in the SEI layer and therefore alter the structure and property of the SEI deliberately. The design of functional material is based on the requirement of SEI layers for different anodes. In Chapters 2 and 3, I presented approaches to manipulating the formation process, chemical composition, and morphology of SEI for nano-sized and micro-sized Si anodes, respectively. The SEI layers were fabricated through a covalent anchoring of multiple functional components onto the Si surface, followed by electrochemical decomposition of the functional components and conventional electrolyte. We showed that to covalently bond organic oligomeric species at the surface of nano-sized Si anodes can effectively increase its SEI flexibility and realized an intimate contact between SEI and Si surface (Chapter 2). In the case of micro-sized Si anodes, we reported that to covalently bond a functional salt, N-methyl-N-propyl pyrrolidinium bis(fluorosulfonyl)imide (PYR13FSI), at the surface of micro-sized Si anodes can effectively stabilize the interface and SEI (Chapter 3). In Chapters 4 and 5, we designed chemically and electrochemically active organic polymer, namely poly((N-2,2-dimethyl-1,3-dioxolane-4-methyl)-5-norbornene-exo-2,3-dicarboximide), and polymeric composite containing poly(vinylsulfonyl fluoride-ran-2-vinyl-1,3-dioxolane) and graphene oxide (GO) nanosheets to alter SEI formation process and regulate the composition and nanostructure of SEI for Li metal anodes. The reactive organic polymer and polymeric composite can generate stable SEI layers in situ by reacting with Li to occupy surface sites and then electrochemically decomposing to form nanoscale SEI components. The formed SEI layers presented excellent surface passivation, homogeneity, and mechanical strength. Using the polymer, we can implant polymeric ether species in the electrolyte-derived SEI, enabling improved SEI flexibility and homogeneity. In the case of polymeric composite, the SEI is mainly generated by the composite instead of electrolyte. In this way, we realized an intrinsic control of SEI structure and property. The formed SEI presented excellent homogeneity, mechanical strength, ionic conductivity, and surface passivation.In Chapter 6, we reported a novel approach based on the use of a nanocomposite consisting of organic elastomeric salts (LiO-(CH2O)n-Li) and inorganic nanoparticle salts (LiF, -NSO2-Li, Li2O), which serve as an interphase to protect Li10GeP2S12 (LGPS), a highly conductive but reducible SSE. The nanocomposite is formed in situ on Li via the electrochemical decomposition of a liquid electrolyte, therefore possessing excellent chemical and electrochemical stability, affinity for Li and LGPS, and limited interfacial resistance. We concluded this dissertation work in Chapter 7 and briefly discussed the possible future work.

Ceramic and Specialty Electrolytes for Energy Storage Devices, Volume II, investigates recent progress and challenges in a wide range of ceramic solid and quasi-solid electrolytes and specialty electrolytes for energy storage devices. The influence of these electrolyte properties on the performance of different energy storage devices is discussed in detail. Features: • Offers a detailed outlook on the performance requirements and ion transportation mechanism in solid polymer electrolytes • Covers solid-state electrolytes based on oxides (perovskite, anti-perovskite) and sulfide-type ion conductor electrolytes for lithium-ion batteries followed by solid-state electrolytes based on NASICON and garnet-type ionic conductors • Discusses electrolytes employed for high-temperature lithium-ion batteries, low-temperature lithium-ion batteries, and magnesium-ion batteries • Describes sodium-ion batteries, transparent electrolytes for energy storage devices, non-platinum-based cathode electrocatalyst for direct methanol fuel cells, non-platinum-based anode electrocatalyst for direct methanol fuel cells, and ionic liquid-based electrolytes for supercapacitor applications • Suitable for readers with experience in batteries as well as newcomers to the field This book will be invaluable to researchers and engineers working on the development of next-generation energy storage devices, including materials and chemical engineers, as well as those involved in related disciplines.

Volume 3 of a 4-volume series is a concise, authoritative and an eminently readable and enjoyable experience related to lithium ion battery design, characterization and usage for portable and stationary power. Although the major focus is on lithium metal oxides or transition metal oxide as alloys, the discussion of fossil fuels is also presented where appropriate. This monograph is written by recognized experts in the field, and is both timely and appropriate as this decade will see application of lithium as an energy carrier, for example in the transportation sector. This Volume focuses on the fundamentals related to batteries using the latest research in the field of battery physics, chemistry, and electrochemistry. The research summarised in this book by leading experts is laid out in an easy-to-understand format to enable the layperson to grasp the essence of the technology, its pitfalls and current challenges in high-power Lithium battery research. After introductory remarks on policy and battery safety, a series of monographs are offered related to fundamentals of lithium batteries, including, theoretical modeling, simulation and experimental techniques used to characterize electrode materials, both at the material composition, and also at the device level. The different properties specific to each component of the batteries are discussed in order to offer tradeoffs between power and energy density, energy cycling, safety and where appropriate end-of-life disposal. Parameters affecting battery performance and cost, longevity using newer metal oxides, different electrolytes are also reviewed in the context of safety concerns and in relation to the solid-electrolyte interface. Separators, membranes, solid-state electrolytes, and electrolyte additives are also reviewed in light of safety, recycling, and high energy endurance issues. The book is intended for a wide audience, such as scientists who are new to the field, practitioners, as well as students in the STEM and STEP fields, as well as students working on batteries. The sections on safety and policy would be of great interest to engineers and technologists who want to obtain a solid grounding in the fundamentals of battery science arising from the interaction of electrochemistry, solid-state materials science, surfaces, and interfaces.