Additives used in the cathode of a Lithium-ion (Li-ion) battery to improve electrical conductivity can negatively impact the ionic conductivity and specific capacity. Therefore, recent focus on the design of Li-ion battery is on the additive-free cathodes. This research work aims to provide a simple rule for the design of cathode microstructure using extensive study of the effect of particle size and volume fraction on effective electrical conductivity. Most design methods used to model the effective transport properties of lithium ion battery electrodes utilize the approximations based on Bruggeman’s formula. However, this formula does not consider the microstructure geometry and hence cannot accurately predict the effective transport properties of complicated microstructure like those of Li-ion battery electrodes. In this thesis, based on the principles of mathematical homogenization, an extensive analysis of randomly generated two-phase microstructures idealized for li-ion battery cells is carried out to obtain more accurate estimates of the effective electrical conductivity. To this end, a wide range of values of particle size, volume fraction and conductivity ratios are considered to evaluate the effective conductivity values. From these results, an explicit formulation based on these three parameters to predict the effective conductivity is provided to establish a framework for a simple design rule for additive-free cathode microstructures. Finally, the significance of the microstructural information is highlighted by studying the discharge characteristics of a battery for a theoretical battery model using the Brugemman’s formulation as well as the proposed formulation based on the mathematical homogenization technique. / Thesis / Master of Applied Science (MASc)

The purpose of this investigation was to determine if there was a relationship between the quantity of inhibitor known to diminish the corrosion rate and the potential of a cathodic surface. The potential required to keep a constant current of one milliampere flowing from cathodic corrosion specimens through dilute acid solutions to which one or more known or commercial inhibitors had been added was measured against a saturated calomel reference electrode. Platinum, mild steel, copper, monel, inconel, yellow brass, nickel and tin were used as cathodic specimen electrodes. Platinum was also used as the anode. Four point nine per cent sulfuric acid, five per cent acetic acid and five per cent phosphoric acid were used as electrolytes. / Master of Science

This thesis investigates several approaches to the development of high-performance batteries. A general background to the field and an introduction to the experimental methods used are given in Chapters 1 and 2 respectively. Chapter 3 presents a study of ordered and disordered LiNi₀.₅Mn₁.₅O₄ materials produced using an optimised resorcinol-formaldehyde gel (R-F gel) synthetic technique. Both materials exhibited good electrochemical properties and minimal side reaction with the electrolyte. Structural analyses of the materials in various states of discharge and charge were undertaken, and from these the charge / discharge processes were elucidated. In chapter 4 R-F gel synthesised Li(Ni₁/₃Mn₁/₃Co₁/₃)O₂ is studied and found to exhibit a high degree of structural stability on cycling, as well as excellent capacity, cyclability and rate capability. Photoelectron spectroscopy studies revealed that the R-F gel derived particles have highly stable surfaces. A discussion of the results and their significance, with particular regard to the outstanding electrochemical performance observed, is also presented. Chapter 5 sets out an investigation into the nature of R-F gel synthesised 0.5Li₂MnO₃:0.5LiNi₁/₃Mn₁/₃Co₁/₃O₂. The electrochemical data revealed that, after an initial activation stage, the R-F gel derived material exhibited a high capacity, good cyclability and exceptional rate capability. This chapter also considers some initial structural investigations and the electrochemical processes occurring on charge. In chapter 6 the use of ether-based electrolytes, combined with various cathode materials, in lithium-oxygen batteries is examined. The formation of decomposition products was observed, and a scheme suggesting probable reaction pathways is given. It was noted that significant quantities of the desired discharge product, lithium peroxide, were formed on the 1st cycle discharge, implying some electrolyte / cathode combinations do demonstrate a degree of stability. A summary of the results and a discussion of their significance are also included.

The design of high quality electron generators to meet specific requirements is important in the application of these devices to a variety of materials processing systems (including welding, cutting and additive manufacture), X-ray tubes for medical, scientific and industrial applications, microscopy and lithography. Designs can be analysed by field solvers, and electron trajectories plotted to provide an indication of the beam quality. Incremental improvement of designs has normally been executed by trial and error, and this can be a time consuming activity requiring expert intervention for each iteration of the design process. The unique contribution made to knowledge by this work is the application of optimisation techniques to the design of electron guns to produce beams with the required optical properties. This thesis presents a review of the design of electron guns, including a discussion of thermionic cathode material properties and their suitability for use in electron guns for processing materials, the influence of space-charge on gun design and the derivation of salient beam metrics to characterise the beam. Beam quality metrics have been developed that allow quantification of electron beam characteristics, allowing objectives to be set for the optimisation process. Additionally, a method is presented that enables real world measurements to be directly compared with modelled beams. Various optimisation methods are reviewed. A genetic algorithm was selected, which would use gun modelling and beam characterisation calculations as the objective function, as a suitable method for application to this problem. However, it was recognised that selections for the best evolutionary parameters, the population size, number of parents, the mutation rate and mutation scale, were not readily determined from published work. An investigation is presented where a range of evolutionary parameters was tested for a set of geometrical problems, which had some similarity to electron gun design but could be computed sufficiently quickly to enable an extensive survey, and the most efficient combination of parameters was identified. Detail is given of the customisation of a genetic evolutionary optimisation method for the design of electron guns. Examples are presented of electron gun design optimisation processes to meet specified beam requirements within defined geometric and electrical constraints. The results of this work show that optimum evolutionary parameter settings for the geometric problem vary with the complexity of the problem and trends have been identified. Application of these parameters to an electron gun optimisation has been successful. The derived beam parameter metrics have been applied to electron guns as an objective function. Comparisons of modelled predictions of the beam characteristics with the measured real world values have been shown to be reasonable.

C.S. Hung. / "From a doctoral thesis submitted to the M.I.T. Department of Physics." "July 20, 1949." / Bibliography: p. 16. / Army Signal Corps Contract No. W36-039-sc-32037 Project No. 102B Dept. of the Army Project No. 3-99-10-022

A. Eisenstein. / "August 19, 1948." / Bibliography: p. 30. / Signal Corps contract no. W-36-039-sc-32037 Project No. 102B Dept. of the Army Project No. 3-99-10-022

In this thesis, photocrosslinked ferrocene-based methacrylate polymers for thin-film cathodes in lithium batteries have been synthesized. Patterned thin-film electrodes of the ferrocene-based methacrylate polymers are fabricated by photocrosslinking. The structure and composition of the photocrosslinkable polymers are characterized by infrared spectra, nuclear magnetic resonances, and gel permeation chromatography. The result of quartz crystal microbalance shows that the crosslinked polymers prevent the polymers from dissolving into organic electrolytes. The cyclic voltammogram shows the photocrosslinked ferrocene-based methacrylate polymers have a redox couple. The energy capacity of the polymer for lithium batteries is about 40-50 mAh g-1 at a discharge rate of 10 C. The results show that the photocrosslinked ferrocene-based methacrylate polymers also improve the batteries.

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Thesis (M.Phil.) - University of St Andrews, September 2007.