Oral Defense Examination : Selected Strategies for Addressing the Operational Issues of Rechargeable Lithium-Sulfur Batteries

Speaker Yang Liuqing (Supervisor: Prof Lee Jim Yang)

Host Department of Chemical and Biomolecular Engineering

Date/Time 07 Dec - 07 Dec, 2.00PM

Venue E5-02-32 , Faculty of Engineering, National University of Singapore

Synopsis

The very high theoretical specific capacity in the sulfur (S) to sulfide (S2-) transformation (1672 mAh g-1) suggests that S has the potential to be a high capacity cathode material for the next generation lithium batteries. The insulating property of S; and the propensity of S to form soluble intermediate products (lithium polysulfides, LiPS) during the transformation; are however formidable technical challenges. The challenges, as well as the lure of an energy density substantially higher than what is possible with the advanced lithium-ion batteries, have resulted in a significant amount of work on rechargeable lithium-sulfur (Li-S) batteries for decades. One of the most recent developments is the implementation of the Li-S batteries as redox flow batteries (i.e. the redox flow Li-S batteries, or RFLSBs in short) as an attempt to combine the high energy density of Li-S batteries with the scalability of redox flow batteries. In the RFLSBs, the LiPS dissolution problem is transformed from an issue into an opportunity. While preliminary studies have demonstrated the novel features of the combination, high performance and long cycle life in actual operations are still below expectations.

This thesis is an effort to address the most salient operational issues in rechargeable Li-S batteries in both coil-cell and flow-cell formats, with several selected strategies. Specifically, separator modifications (a controlled coating for collaborative interfacial  effects, enhanced Li+ conduction through the separator), Li anode protection, and the use of redox targeting for charge transfer; are used to increase the capacity and the cycle life of rechargeable Li-S batteries.

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