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NANOSTRUCTURED SULFUR COMPOSITE CATHODES FOR LITHIUM-SULFUR BATTERIES
Title
NANOSTRUCTURED SULFUR COMPOSITE CATHODES FOR LITHIUM-SULFUR BATTERIES
Creator
Dunya, Hamza
Date
2018
Description
Since the high demand for clean and efficient energy is the main motivation in the research of renewable energy, there have been extensive...
Show moreSince the high demand for clean and efficient energy is the main motivation in the research of renewable energy, there have been extensive studies on secondary lithium batteries. As a part of this initiative, lithium-ion batteries (LIBs) were introduced by Sony Corporation in 1991. Currently, LIBs are exclusively used in portable devices, such as laptops and cell phones. In the last decade, LIBs have also been widely used in hybrid electric vehicles (HEVs). However, state of the art has reached its limitation barriers due to high cost and low specific energy density. Lithium-sulfur batteries (LSBs) are considered promising next-generation energy storage systems due to high theoretical specific capacity and specific energy,1675 mAh g-1 and 2500 Wh g-1, respectively. The elemental sulfur as cathode material in LSBs is inexpensive, nontoxic, and abundant on the earth.Although LSBs have many advantages mentioned above, there are many challenges for commercialization of LSBs. The main roadblock is polysulfide shuttle (PSS), which is the migration of discharged lithium polysulfide intermediates from the cathode to the anode, leading to fast capacity fading and low Coulombic efficiency. Other important issues include volume change of sulfur during discharge (~80% expansion) and the insulating nature of sulfur.This dissertation describes two different approaches to achieve a decreased polysulfide shuttle effect for lithium-sulfur batteries; first approach, major focus, is nanostructured dual core-shell sulfur cathode composites and second is to design and synthesize new solvents as the electrolyte additives. For the cathode study, we synthesized two shells in the core-shell design. The inner shell was used as the carbon material (nanospheres and nanorods) to enhance the electrical conductivity of the cathode matrix. The outer shell was polysulfide retention materials (g-C3N4, TiO2, AlF3, and MnO2). g-C3N4, TiO2, and AlF3 coatings were used with hollow carbon nanospheres and MnO2 was coated on the nitrogen-doped hollow carbon nanorods. Significant enhancement in capacity retention was observed for all polysulfide resistant coated materials. g-C3N4-coated composite displayed the highest specific capacity among the materials with hollow nanosphere design. The nitrogen-doped hollow carbon nanorod coated with MnO2 displayed one of the highest initial discharge capacities reported in the literature. For electrolyte study, we designed and synthesized four new fluoroether sulfones as the electrolyte via Michael addition reaction of divinyl sulfone and fluoro alcohols to decrease the dissolution of polysulfides intermediates.
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