No / Polymer gel electrolytes (PGE) based on polyvinylidene fluoride (PVDF), lithium salts and appropriate solvent systems, developed at Leeds University, have been shown to form tough rigid films with conductivities approaching 10¿2 S cm¿1. A continuous process has now been developed for the construction of rechargeable lithium cells by extruding the PGE as a melt and directly laminating between the anode and cathode electrodes. On cooling, the solid PGE acts as electrolyte and separator and binds the cell laminate together from within requiring no external case. This process has been successfully applied for the fabrication of cells with electrodes developed by SpectraPower Inc. in a commercial process enabling cell laminates with PGE thickness less than 0.1 mm and with energy densities approaching 170 Wh kg¿1. A prototype manufacturing facility has been set up to produce rechargeable cells of high specific capacity and high energy density. Future developments will enable rechargeable lithium ion cells to be produced on a continuous process as flat sheets opening the way for novel battery geometries.

Energy storage systems such as batteries and supercapacitors store electrical energy in the form of chemical energy and release it when required. Among the various electrode materials, manganese oxides (MnOx) are promising electrode materials for these devices. Despite its outstanding theoretical capacitance, Mn-based oxide electrodes have several limitations that impede their electrochemical performance. Understanding how the charges are efficiently stored in the electrodes or across the electrode/electrolyte interface is crucial for developing advanced electrode material in the field of energy storage applications. The goal of my thesis is to develop and apply synchrotron-based scanning transmission X-ray microscopy (STXM) to investigate changes in the oxidation state of Mn and their spatial distributions in MnOx electrodes in the context of energy storage and release. To achieve high- precision qualitative and quantitative STXM identification and mapping of different MnOx species, calibrated and high-quality reference Mn 2p and O 1s NEXAFS (near edge X-ray absorption fine structure) spectra were measured. In collaboration with Wenjuan Yang and her PhD supervisor, Prof. Igor Zhitomirsky, I performed ex-situ STXM studies on Mn3O4-based supercapacitor electrode materials to investigate the influence of different synthesis methods and activation protocols on the charging behavior and capacitance performance. In collaboration with Pablo Ingino and his supervisor, Prof. Martin Obst (Bayreuth University), and my colleague, Dr. Chunyang Zhang, I helped develop a three-electrode, microfluidic-based flow electrochemical device for in-situ STXM. This device was used to electrodeposit MnO2 on the working electrode (WE) and track the oxidation state and morphological changes by STXM while scanning the potential of the cell in different electrolyte pH. The in-situ STXM studies showed a spontaneous reduction of the initially deposited MnO2 resulting from the local pH change at the WE. Additionally, a significant change from a quasi-uniform MnO2 film to a dendritic MnO2 structure was observed at oxidative potential. This dendritic growth resulted from dissolution/redeposition of MnO2 during charging/discharging processes, indicating a partial reversibility of dissoluble Mn species. The ex-situ and in-situ STXM studies I performed provide mechanistic insights that will help further improve Mn oxides-based electrodes and their applications as energy storage devices. / Thesis / Doctor of Philosophy (PhD)

No description available.

The purpose of this research project was to determine the processing conditions necessary for preparing flexible carbon nanofiber electrodes by electrospinning and to explore various applications for those electrodes. It was found that by varying only the relative humidity while electrospinning a poly(acrylonitrile) precursor, fragile or flexible freestanding carbon nanofiber electrodes were prepared. The relative humidity during electrospinning controlled the fiber diameter, the bulk porosity of the material, and flexibility of the final carbon electrode. Higher porosity mats electrospun in a high relative humidity environment prevented fiber sintering, which if not minimized, resulted in non-flexible carbon electrodes. Both flexible and fragile electrodes were freestanding, binderless, and collectorless. Additionally, they required no further processing before use and were 100 wt.% active material. When cycled galvanostatically as a lithium ion battery anode, the flexible electrode exhibited a specific capacity of 379 mAH g-1 at the 100th cycle and capacity retention was 97.4% relative to the fifth cycle. When applied as an active material support electrode for lithium ion battery cathodes, the carbon support was successfully utilized with both micron and nano structured active material and cycled for 100 cycles with limited capacity loss. The same electrodes were also found to be a viable replacement for Pt electrode based actuators/artificial muscles. However, this application requires much further research to understand better the required processing and effects of the physical properties of the electrode on actuator performance. In addition to this, the flexible electrodes have a wide variety of other potential applications including, electrochemical storage and conversion devices, chemical sensing, and filtration. The focus of this work was electrochemical storage and conversion devices in the form of lithium ion battery anodes and cathodes as well as ionic polymer composite actuators. / PHD

Thesis advisor: Udayan Mohanty / Rechargeable batteries, especially lithium ion batteries, have greatly transformed mobile electronic devices nowadays. Due to the ever-depletion of fossil fuel and the need to reduce CO2 emissions, the development of batteries needs to extend the success in small electronic devices to other fields such as electric vehicles and large-scale renewable energy storage. Li-ion batteries, however, even when fully developed, may not meet the requirements for future electric vehicles and grid-scale energy storage due to the inherent limitations related with intercalation chemistry. As such, alternative battery systems should be developed in order to meet these important future applications. This dissertation presents our successes in improving Li-O2 battery performance for electric vehicle application and integrating a redox flow battery into a photoelectrochemical cell for direct solar energy storage application. Li-O2 batteries have attracted much attention in recent years for electric vehicle application since it offers much higher gravimetric energy density than Li-ion ones. However, the development of this technology has been greatly hindered by the poor cycling performance. The key reason is the instability of carbon cathode under operation conditions. Our strategy is to protect the carbon cathode from reactive intermediates by a thin uniform layer grown by atomic layer depostion. The protected electrode significantly minimized parasitic reactions and enhanced cycling performance. Furthermore, the well-defined pore structures in our carbon electrode also enabled the fundamental studies of cathode reactions. Redox flow batteries (RFB), on the other hand, are well-suited for large-scale stationary energy storage in general, and for intermittent, renewable energy storage in particular. The efficient capture, storage and dispatch of renewable solar energy are major challenges to expand solar energy utilization. Solar rechargeable redox flow batteries (SRFBs) offer a highly promising solution by directly converting and storing solar energy in a RFB with the integration of a photoelectrochemical cell. One major challenge in this field is the low cell open-circuit potential, mainly due to the insufficient photovoltages of the photoelectrode systems. By combining two highly efficient photoelectrodes, Ta3N5 and Si (coated with GaN), we show that a high-voltage SRFB could be unassistedly photocharged and discharged with a high solar-to-chemical efficiency. / Thesis (PhD) — Boston College, 2018. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

As an efficient means of energy storage, rechargeable batteries, especially the lithium-ion batteries (LIBs) have been a vital component in solving the upcoming energy crisis and environmental problems. Recently, the development of electric vehicle market puts new requirement on the next generation LIBs, including superior energy density, safety and cycling stability, etc. Compared with experimental investigation, Physics-based models provide a surrogate method to not only tackle the underlying physics of the complex battery system, but also optimize the design of battery systems. In this thesis, I will show how I use the physics-based continuum model and cooperate with some experimental methods to understand the lithium transport phenomena inside the multiscale battery electrode systems, based on which the models are then applied to guide the experimental optimization of battery electrode design and to quantitively understand the degradation of high-performance electrodes. The thesis is divided into three parts. First part (Chapter 2) presents a systematical model selection study on the multiscale LiNi₀.₃₃Mn₀.₃₃Co₀.₃₃O₂ (NMC₁₁₁) electrode. Discharge and voltage relaxation curves, interrogated with theory, are used to distinguish between lithium transport impedance that arise on the scale of the active crystal and on the scale of agglomerates (secondary particles) comprised of nanoscale crystals. Model-selection algorithms are applied to determine that the agglomerate scale transport is dominant in the NMC₁₁₁ electrode studied here. This study not only discovers the dominant length scale for lithium transport, but also provide a validated model (the agglomerate model) for later study. The second part (Chapter 3 & 4) talks about understanding & optimization of ion transport in porous electrodes. In Chapter 3, multi-scale physics-based models for different active material systems, which have been parameterized and validated with discharge experiments, are optimized by varying porosity and mass loading to achieve maximum volumetric energy density. The optimization results show that with a re-scaling of the current rate, the optimal results follow a general design rule that is captured in a convenient correlation. Chapter 4 extends the model to simulate the performance of advanced electrode architectures utilizing aligned channels, by quantifying the impact of aligned channel electrode structures on cell rate capability. Then the optimization algorithm in Chapter 3 is applied to these aligned-channel electrodes. The final part (Chapter 5) shows how I use the physics-based model to quantitatively analyze the battery degradation. The validated model is applied to cycling data to obtain parameter estimates indicative of degradation modes. It’s found that growth rates of interfacial impedance and active material loss are greater at 4.5 V, as might be expected. However, when charged to 4.5V, degradation rates are lower at a cycling C-rate of 1.0 h⁻¹ than at 0.5 h⁻¹. Once performance changes are quantified, we use further simulation to evaluate the contribution of individual degradation modes to fade of cell performance metric such as capacity, power density, and energy density.

No description available.

Three-dimensional macroporous structures (‘opals’ and ‘inverse opals’) can be produced by colloidal crystal templating, one of the most intensively studied areas in materials science today. There are several potential advantages of lithium-ion battery electrodes based on inverse opal structures. High electrode surface, easier electrolyte access to the bulk of electrode and reduced lithium diffusion lengths allow higher discharge rates. Highly open structures provide for better mechanical stability to volume swings during cycling. Silicon is one of the most promising anode materials for lithium-ion batteries. Its theoretical capacity exceeds capacities of all other materials besides metallic lithium. Silicon is abundant, cheap, and its use would allow for incorporation of microbattery production into the semiconductor manufacturing. Performance of silicon is restricted mainly by large volume changes during cycling. The objective of this work was to investigate how the inverse opal structures influence the performance of silicon electrodes. Several types of silicon-based inverse opal films were synthesised, and their electrochemical performance was studied. Amorphous silicon inverse opals were fabricated via chemical vapour deposition and characterised by various techniques. Galvanostatic cycling of these materials confirmed the feasibility of the approach taken, since the electrodes demonstrated high capacities and decent capacity retentions. The rate performance of amorphous silicon inverse opals was unsatisfactory due to low conductivity of silicon. The conductivity of silicon inverse opals was improved by crystallisation. Nanocrystalline silicon inverse opals demonstrated much better rate capabilities, but the capacities faded to zero after several cycles. Silicon-carbon composite inverse opal materials were synthesised by depositing a thin layer of carbon via pyrolysis of a sucrose-based precursor onto the silicon inverse opals in an attempt to further increase conductivity and achieve mechanical stabilisation of the structures. The amount of carbon deposited proved to be insufficient to stabilise the structures, and silicon-carbon composites demonstrated unsatisfactory electrochemical behaviour. Carbon inverse opals were coated with amorphous silicon producing another type of macroporous composites. These electrodes demonstrated significant improvement both in capacity retentions and in rate capabilities. The inner carbon matrix not only increased the material conductivity, but also resulted in lower silicon pulverisation during cycling.

Three-dimensional macroporous structures (‘opals’ and ‘inverse opals’) can be produced by colloidal crystal templating, one of the most intensively studied areas in materials science today. There are several potential advantages of lithium-ion battery electrodes based on inverse opal structures. High electrode surface, easier electrolyte access to the bulk of electrode and reduced lithium diffusion lengths allow higher discharge rates. Highly open structures provide for better mechanical stability to volume swings during cycling. Silicon is one of the most promising anode materials for lithium-ion batteries. Its theoretical capacity exceeds capacities of all other materials besides metallic lithium. Silicon is abundant, cheap, and its use would allow for incorporation of microbattery production into the semiconductor manufacturing. Performance of silicon is restricted mainly by large volume changes during cycling. The objective of this work was to investigate how the inverse opal structures influence the performance of silicon electrodes. Several types of silicon-based inverse opal films were synthesised, and their electrochemical performance was studied. Amorphous silicon inverse opals were fabricated via chemical vapour deposition and characterised by various techniques. Galvanostatic cycling of these materials confirmed the feasibility of the approach taken, since the electrodes demonstrated high capacities and decent capacity retentions. The rate performance of amorphous silicon inverse opals was unsatisfactory due to low conductivity of silicon. The conductivity of silicon inverse opals was improved by crystallisation. Nanocrystalline silicon inverse opals demonstrated much better rate capabilities, but the capacities faded to zero after several cycles. Silicon-carbon composite inverse opal materials were synthesised by depositing a thin layer of carbon via pyrolysis of a sucrose-based precursor onto the silicon inverse opals in an attempt to further increase conductivity and achieve mechanical stabilisation of the structures. The amount of carbon deposited proved to be insufficient to stabilise the structures, and silicon-carbon composites demonstrated unsatisfactory electrochemical behaviour. Carbon inverse opals were coated with amorphous silicon producing another type of macroporous composites. These electrodes demonstrated significant improvement both in capacity retentions and in rate capabilities. The inner carbon matrix not only increased the material conductivity, but also resulted in lower silicon pulverisation during cycling.

ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, Nevada / As technological advances continue to be made in the commercial sectors of portable and wireless communication products, additional advancements in battery technology have also been made. These advancements have allowed for the rapid growth of a large variety of commercially available batteries which have the capability to meet or even exceed the current power and size requirements for numerous ballistic telemetry systems. The replacement of a custom built battery with a COTS battery would provide immediate advantages such as lower cost, shorter lead times and higher availability. The overall objective of this paper is to provide ballistic telemetry systems engineers and designers with multiple low cost, readily available alternatives to traditional custom made power sources.