Date of Award

Fall 2025

Document Type

Open Access Dissertation

Department

Chemical Engineering

First Advisor

Golareh Jalilvand

Second Advisor

William Mustain

Abstract

Lithium-Sulfur (Li-S) batteries have recently received significant attention as a potential candidate for next-generation energy storage technology. This is due to its high theoretical capacity (1675 mAh/g) which can provide theoretical energy density of 2500 Wh/kg as compared to 400 Wh/kg of the current Lithium-ion batteries. Moreover, the earth-abundant sulfur element as well as its environmental friendliness endows unique advantages on the cost and environmental impact. However, there are several roadblocks that need to be addressed for commercial adoption of Li-S batteries, such as: (i) poor conductivity of sulfur and its discharged product; (ii) solubility of lithium polysulfides and their eventual transport between the electrodes through the electrolyte; and (iii) repetitive phase change during discharge and charge process causing cycling stresses, particle destruction and morphological changes of the electrode. Dissolution and transport of the lithium polysulfides within the electrolyte is considered by researchers to be the most substantial challenge to commercial viability of Li-S battery. In a typical discharge process, long chain polysulfides are formed when lithium-ions react with sulfur. These polysulfides are dissolved in the common ether-based electrolytes and subsequently shuttled between the electrodes during battery operation. As shown in Chapter 1 of this thesis, the transport of the polysulfides has several consequences on the performance of batteries such as depletion of active materials leading to rapid capacity fading; deposition of insulating products on the lithium anode raising battery impedance; and decreasing the coulombic efficiency of the battery. As a result, Li-S batteries have catastrophic cycle performance as they hardly cycle for more than 100 cycles, which is practically insufficient for commercial applications. There is a whole body of literature proposing and designing different cathode structures to address polysulfide shuttling problem by encapsulating sulfur in different carbon structures, some of which are too complicated, not scalable, which jeopardize the energy density of the Li-S battery. One of the primary outcomes of this dissertation project is the development of a cheap and scalable electrode processing method that can significantly mitigate the polysulfide shuttling issue. A novel method involving no complex material or processing technique is introduced which leads to a self-structured binder shell around sulfur particles, and consequently, minimizes the polysulfide movement into the electrolyte. It is demonstrated that the binder dissolution dynamics can significantly affect the formation of the physical barrier shell around the sulfur particles, allowing much improved durability and cyclability from 56% to 90% for 500 cycles in Li-S batteries. With the capacity retention significantly improved, the enhancement of the achieved capacity was the next focus of this work, through understanding the influence of structural and geometric properties of the conductive carbon materials on the sulfur redox reactions. Furthermore, the influence of solvent volume in the electrode slurry on the structure and morphological characteristics of sulfur cathodes are explored and correlated to their electrochemical performance. More importantly, the broad applicability of the proposed method in both organic and aqueous solvent systems are investigated, suggesting that optimization of the binder-solvent molecular interaction is necessary to improved structural necessities for fast and efficient redox reactions. Implementing the learnings of those studies, the capacity retention of Li-S batteries was successfully improved to >91% and the achieved capacity was increased to >900 mAh/g with cycle stability at more than 1000 cycles without using any additional material to artificially enhance the performance while maintaining sulfur composition at 70 wt %. In summary, this dissertation proposes a new understanding of the effect of electrode microstructure on the electrochemical performance of Li-S battery cathodes. Particularly, the untapped potential of electrode engineering on achieving desired electrode microstructure high performance and commercially viable Li-S batteries is highlighted.

Rights

© 2025, Saheed Adewale Lateef

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