Li, Z. / Welle, A. / Vincent, S. / Wang, L. / Fuchs, S. / Riedel, S. / Roy, A. / Bosubabu, D. / García-Lastra, J. M. / Fichtner, M. / Zhao-Karger, Z. (2023)

Advanced Energy Materials 2023, 13, 42, 2302905

Abstract

A key challenge for practical magnesium–sulfur (Mg–S) batteries is to overcome the sluggish conversion kinetics of sulfur cathodes, achieving a high energy density and long-lasting battery life. To address this issue, a doping strategy is demonstrated in a model Ketjenblack sulfur (KBS) cathode by introducing selenium with a high electronic conductivity. This leads to a significantly enhanced charge transfer in the resultant KBS1−xSex cathodes, giving rise to a higher S utilization and less polysulfide dissolution. Compared to the bare S cathode, the S-Se composite cathodes exhibit a higher capacity, smaller overpotentials, and improved efficiency, serving as better benchmark compounds for high-performance Mg–S batteries. First principles calculations reveal a charge transport mechanism via electron polaron diffusion in the redox end-products, that enhances the reaction kinetics. By suppressing polysulfide dissolution in the electrolyte, the use of the KBS1−xSex cathodes also enables a more uniform anode reaction, and thereby significantly extends the cyclability of the cells. To improve the performance, further efforts are made by implementing a Mo6S8 modified separator into the cell. With an optimized cathode composition of KBS0.86Se0.14, the cell applying modified separator shows an improvement of capacity retention by >50% after 200 cycles.

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