Cobalt-embedded carbon nanofiber as electrocatalyst for polysulfide redox reaction in lithium sulfur batteries

Efficient redox conversions between polysulfides and sulfur or lithium sulfide have a significant impact on the electrochemical performance of lithium-sulfur batteries especially with high sulfur loading. Herein, a readily available cobalt-embedded carbon nanofiber (Co-CNF) is designed as the current collector for sulfur cathodes. It is shown that the Co-CNF promotes electron and Li-ion transfer, thus leading to fast redox conversion, which mitigates the dissolution and shuttling of polysulfides. Furthermore, the embedded cobalt metal facilitates the uniform nucleation of lithium sulfide on the surface of the carbon nanofiber, which reduces the polarization and leads to high specific capacity. The Co-CNF with 4.6 mg cm(-2) sulfur loading delivers 970 mA h g(-1) (4.5 mA h cm(-2)) at 0.1 C and 670 mA h g(-1) at 1 C. Even when sulfur loading reaches as high as 9.6 mg cm(-2), the reversible capacity of 730 mA h g(-1) (7 mA h cm(-2)) is obtained. The Co-CNF/Li2S6 cathode shows a degradation rate at 0.06% per cycle over 300 cycles. This work demonstrates the effect of cobalt metal catalysis and a simple but useful sulfur cathode design for high performance Li-S batteries. (C) 2019 Elsevier Ltd. All rights reserved.