Theoretical and experimental design of electrodes for advanced battery systems

Advanced batteries such as Ni/MH and Li-ion are now widely used as power sources for numerous applications including electronic products and electric vehicles (EVs). Lithium-ion batteries are now the preferred power source for cellular phones, portable computers, and camcorders. They are also candidates for the next generation hybrid and electric vehicles. There has thus been a tremendous research effort in recent years to develop these advanced battery systems.; However, the optimization and development of design criteria of these battery systems is still progressing. One of the key aspects of battery development involves the design of the electrodes, because they are the pivot around which the whole battery system revolves. The electrodes have a direct impact on the performance of the battery system depending upon the two important factors--discharge rate (i.e., how fast one utilizes the battery) and discharge capacity (i.e., amount of total energy in the system). This dissertation addresses some of the underlying issues in the manufacture and design of nickel electrodes (used in Ni/MH and Ni/H{dollar}sb2{dollar} cells) and intercalation electrodes (used in Li-ion cells). It also investigates ways to obtain better performance from these electrodes by accounting for the key issues in chemical engineering, viz., kinetics, thermodynamics, and mass transfer that dictate these systems.; A mathematical model simulating the deposition of nickel hydroxide in porous electrode, the primary commercial process for the preparation of positive electrodes for nickel batteries has been developed. The model predicts the influence of design parameters on the process and the time dependent distributions of porosity, precipitation rate, and Ni(OH){dollar}sb2{dollar} loading across the thickness of the porous electrode for changes in the bulk pH, concentrations, applied current densities, and various plaque parameters. Predictions for both constant current and constant potential operating conditions are presented. For example, it is shown that when the current density is changed from 30 to 40 mA/cm{dollar}sp2,{dollar} the uniformity decreased by 20% for a plaque of the same thickness with a tortuosity of 1.6 at the same loading.; An experimental study is also presented for the characterization of commercially available AA-size Ni/MH batteries to determine the charge and discharge behavior at different rates. Characterization of commercially available cells offers an understanding of the current stage in the development of these batteries and helps distinguish performance differences that might exist between these batteries based on the fundamentals of battery design. The oxygen recombination reaction in sealed Ni/MH cells was characterized. The effects of electrolyte saturation and charge rate, the two most important parameters that influence the recombination kinetics, are studied. A mechanism for the oxygen recombination reaction is proposed based on the observed data.; A mathematical model is presented to study the effect of the particle size distribution (PSD) on the galvanostatic charge and discharge behavior of the lithium/separator/intercalation electrode system. A recently developed packing theory has been incorporated into a first principles model of an intercalation electrode to provide a rational basis for including the effect of PSD on packing density. This study shows that the PSD significantly impacts the discharge capacity of intercalation electrodes. Accounting for PSD is essential when dealing with transient behavior. The model developed here is thus an useful tool for designing superior electrodes.