Investigation of battery materials and sonic enhancements
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] The effect of carbon surface area on capacity is investigated in cathodes for lithium sulfur batteries. Carbon additives help overcome the low electrical conductivity of sulfur. Cathodes were prepared at 30wt% sulfur on different activated carbons having unloaded BET surface areas of 1200 to 3200 m2/g. Sulfur utilization ranged from 33% to 83% of the theoretical capacity (1672 mAh/g) with a strong correlation to the accessible pore volumes having pore widths between 1-5 nm. Additionally, cathodes prepared at 12.5wt%-68wt% on an activated carbon having unloaded BET surface area of 3200 m2/g showed excessive sulfur loading provided little additional capacity. Current battery technology relies on thin materials in order to limit the overpotential losses due to diffusion within the cell, which generally leads to increased cost and lower energy densities. Another study in this thesis analyzes the use of sonication as a means to reduce losses associated with diffusion using Electrochemical Impedance Spectroscopy (EIS) for Zinc-Manganese Oxide (Zn-MnO2) cells. Impedance changes in the Warburg diffusion controlled regions are compared for different membrane materials.
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