Catalytically altering the redox pathway of sulfur in carbonate electrolyte

Lithium-sulfur batteries (LSBs) are a promising high-energy system, potentially offering an energy density 3–5 times higher than that of commercial lithium-ion batteries (LIBs). LSBs typically employ ether electrolytes, as ether solvents are compatible with sulfur cathodes and allow for relatively easy achievement of high capacity in these systems. However, during cycling, polysulfides generated as intermediates from the sulfur cathode can dissolve in ether electrolytes. This dissolution leads to shuttle effects, which result in poor Coulombic efficiency, reduced cyclability, and severe self-discharge.

Due to the widespread use of carbonate electrolytes in commercial LIBs, they are also considered highly attractive for LSBs. Polysulfides have been reported to have low solubility in certain carbonate solvents, which offers the potential to mitigate shuttle effects using carbonate electrolytes. However, sulfur cathodes are typically non-chargeable in carbonate electrolytes due to poor compatibility, primarily caused by side reactions between polysulfides and the electrolytes. As a result, significant efforts have been dedicated to improve the compatibility between carbonate electrolytes and sulfur cathodes. Despite notable progress, various challenges remain. For instance, the sulfur content in sulfur composites is often low, around 40%, and optimized carbonate electrolytes tend to be expensive. Therefore, enhancing the compatibility between carbonate electrolytes and sulfur cathodes remains a significant challenge.

Recently, a research team led by Prof. Zhicuan Xu from Nanyang Technological University, Singapore, and Prof. Linghui Yu from Wuhan Textile University, China, reported a catalytic approach to overcome the compatibility issue. With a porous carbon material containing dual-nitrogen and oxygen functional groups as a host for sulfur, the side reactions between polysulfides and carbonate electrolytes can be significantly reduced. In a regular sulfur electrode, polysulfides generated during discharge typically react with carbonate electrolytes, leading to compatibility issues. However, in the presence of dual-nitrogen/oxygen-containing groups on the host carbon, the polysulfides interact with these functional groups. Such interactions stabilize the polysulfides in the carbonate electrolytes, preventing side reactions between the polysulfides and the electrolytes. These stabilized polysulfides can be reduced to Li₂S upon further discharge and can be reversibly oxidized back to polysulfides during charging. A density functional theory study shows that four specific nitrogen/oxygen functional groups, i.e., graphitic nitrogen + COOH, pyridinic nitrogen + COOH, pyridinic nitrogen + COH, and pyrrolic nitrogen + C=O, exhibit high adsorption energies towards polysulfides. Therefore, these four functional groups are proposed to be favorable for stabilizing polysulfides in carbonate electrolytes. The results were published in the Chinese Journal of Catalysis (https://doi.org/10.1016/S1872-2067(24)60096-3).

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About the Journal

Chinese Journal of Catalysis is co-sponsored by Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Chinese Chemical Society, and it is currently published by Elsevier group. This monthly journal publishes in English timely contributions of original and rigorously reviewed manuscripts covering all areas of catalysis. The journal publishes Reviews, Accounts, Communications, Articles, Highlights, Perspectives, and Viewpoints of highly scientific values that help understanding and defining of new concepts in both fundamental issues and practical applications of catalysis. Chinese Journal of Catalysis ranks among the top one journals in Applied Chemistry with a current SCI impact factor of 15.7. The Editors-in-Chief are Profs. Can Li and Tao Zhang.

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