Effective Polysulfide Anchoring via Single Atom Catalyst on Porous Carbon Framework for Lithium-sulfur Batteries
Creators: Majid, Mahrima
Publisher: name: University of Alberta Library
Year: 2024

<p>Lithium-sulfur batteries (LSBs) have the potential to replace conventional Lithium-ion batteries (LIBs) due to higher theoretical energy density, lower raw material costs, improved safety, and reduced environmental impact. However, the practical implementation of LSBs faces significant challenges. The major issues include the lack of electronic conductivity of sulfur and its reaction products, inherently slow conversion kinetics and inefficient use of active materials. Volume changes during cycling also damage the sulfur cathode, while the soluble polysulfide (LiPS) dissolution in the electrolyte leads to capacity degradation, low sulfur utilization, and low energy efficiency. The rise in demand for advanced energy storage devices have therefore made it crucial for these issues to be addressed.<br>
Herein, we present a review of some of the recent research advancements for the diverse applications of LSBs which includes practical factors such as temperature resilience, enhanced safety, and flexibility as well as rapid charging, long cycling life, and scalability for widespread commercialisation. The review also outlines the challenges and future perspectives of the development of practical LSBs. The aim of the review is to highlight the versatility that LSBs can bring to the energy transition sector and the recent progresses that can take LSBs closer to their practical implementations. <br>
We have also conducted experimental studies to address the research gap by developing a multifunctional cathode host for LSBs to address issues regarding low active material utilization and fast capacity decay. In the first work, a mesoporous hollow carbon sphere (HMCS) was designed to act as a sulfur reservoir, trap LiPS species, enhance mass and electron transport, and accommodate volume changes. This cathode composite delivered significantly higher specific capacities and better rate performance than a commercially used electrode material. A study was also conducted to determine whether the pore sizes of HMCS affected the electrochemical performance. It was discovered that the initial specific capacities and capacity retention both increased with increase in the pore size. The HMCS with 12nm pore size delivered the best performance (1033.1 mAh g-1 at 0.2 C and capacity retention of 77.0% after 45 cycles) and it was chosen as the carbon framework for cathode host in the following works. To further increase LiPS adsorption and catalyze the conversion reaction, a vanadium single atom catalyst was introduced to HMCS (VHMCS) using spatial confinement and coordination engineering strategies, leading to improved electrochemical performance. As a result, VHMCS was able to deliver high discharge capacities of 1321 and 660.2 mAh g-1 at 0.1 C and 1.0 C rates, respectively. The composite also showed stable cycling performance for 200 cycles at 0.2 C with a capacity retention rate of more than 80%. In our last study, a Molybdenum single atom catalyst was introduced in a Nitrogen-doped HMCS. However, the attempts were unsuccessful possibly due to the incomplete transformation of Mo-precursor to Mo single atom and blockage of HMCS pores. Finally, we conclude this thesis with a summary of the experimental findings discussed in our studies and offer insights into the future directions related to single atom catalysts for cathode hosts for advanced LSBs.</p>