Chalcogen-carbon nanocomposite cathodes for rechargeable lithium batteries
Lee, Jung Tae
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Current electrochemical energy storage systems are not sufficient to meet ever-rising energy storage requirements of emerging technologies. Hence, development of alternative electrode materials is inevitable. This thesis aims to establish novel electrode materials demonstrating both high energy and power density with prolonged cycle life derived from fundamental understandings on electrochemical reactions of chalcogens, such as sulfur (S) and selenium (Se). First, the effects of the pore size distribution, pore volume and specific surface area of porous carbons on the temperature-dependent electrochemical performance of S-infiltrated carbon cathodes in electrolytes having different salt concentrations are investigated. Additionally, the carbide derived carbon (CDC) synthesis temperature, electrolyte composition, and electrochemical S utilization have been correlated. The effects of thin Li-ion permeable but polysulfide non-permeable Al2O3 layer coating on the surface of S infiltrated carbon cathode are also examined. Similar with S studies, Se infiltrated ordered meso- and microporous CDC composites are prepared and the correlations between pore structure designing and electrolyte molarity are explored. Finally, this thesis demonstrates a simple process to form a protective solid electrolyte layer on the Se cathode surface in-situ. This technique adopts fluoroethylene carbonate to convert into a layer that remains permeable to Li ions, but prevents transport of polyselenides. As a whole, the correlations of multiple cell parameters, such as the cathode structure, the electrolyte composition, and operating temperature on the performances of lithium-chalcogen batteries are discussed.