Improvement of electrochemical performance of sulfur-based materials for lithium-sulfur batteries

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Improvement of electrochemical performance of sulfur-based materials for lithium-sulfur batteries
Lee, Ju Kyoung
Lee, Kyu Tae
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Graduate school of UNIST
Lithium ion batteries (LIBs) have been considered as one of the most promising energy storage/conversion devices as desirable power sources for portable electronic devices and transportation such as EV and HEV. However conventional cathode materials (i.e., LiCoO2, LiMnO2, and LiFePO4) have clear limitations for commercialization as above mentioned power sources owing to their limitative theoretical capacity under 300mAhg-1. Recently, Sulfur is emerged as an attractive cathode material candidate due to its high capacities of up to 1675mAhg-1. In addition, it is abundant and environmentally friendly material which is one of the important factors for next generation batteries. Nevertheless Li-Sulfur batteries have some problems like polysulfide dissolution and involving insoluble polysulfide such as Li2S2, Li2S which are electronically nonconductive. These problems result in capacity fading during charge-discharge process and loss of active material. Therefore many researchers have been dedicated to tackle these problems by developing various methods for sulfur based composite materials (i.e., sulfur-carbon composite, hybrid sulfur composite and sulfur- polymer composite) and additives in electrolyte (i.e., LiNO3, toluene). However, there still remain a number of challenges to avoid polysulfide dissolution and formation of insoluble polysulfide. In this regard, here we first report the PTCDA organic/Sulfur composite material and demonstrate how we can efficiently reduce polysulfide dissolution and formation of insoluble polysulfide enabling extended cycle life. In addition, the impacts of the electrolyte additives such as a fluoroethylene carbonate (FEC), LiNO3 and polysulfide to the electrochemical performance and SEI layer of Li-Sulfur batteries were investigated. And also to prevent polysulfide dissolution, SEI layer on cathode was formed by forcing decomposition of electrolyte. To confirm the effects of additive, the surface chemistry with several electrolyte additives were investigated using X- ray photoelectron spectroscopy (XPS). It is found that LiNO3 formed stable protective layer which involved LiN3 species component. This layer prevents polysulfide dissolution and a shuttle effect.
Battery Science and Technology
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