Strong Lithium Polysulfide Chemisorption on Electroactive Sites of Nitrogen-Doped Carbon Enables High-Performance Lithium-Sulfur Battery Cathodes

Lithium-sulfur (Li-S) batteries have attracted great of interest due to their high theoretical capacity of 1672 mAh/g and low cost.¹ Unlike batteries with intercalation chemistries, Li-S batteries experience dissolution and diffusion of reaction intermediated (lithium polysulfides, Li₂S_x, 2<x≤8) in the electrolyte. This behavior can lead to loss of active material from the cathode and to a polysulfide shuttle phenomenon, resulting in capacity fading and poor coulombic efficiency.^{2, 3}

Here, we report a novel functional carbon composite (carbon-nanotube-interpenetrated mesoporous nitrogen-doped carbon spheres, MNCS/CNT) as a sulfur host which can strongly adsorb lithium polysulfides. The nitrogen functional groups of this composite enable effective trapping of lithium polysulfides on electroactive sites within the cathode, leading to much improved electrochemical performance (1200 mAh/g after 200 cycles). The enhancement in adsorption can be attributed to chemical bonding of lithium ion with nitrogen functional groups in the MNCS/CNT framework. In addition, the micron-sized spherical structure of the material yields a high areal capacity (~6 mAh/cm²) with a high sulfur loading of ~5 mg/cm², ideal for practical applications of Li-S batteries.

Acknowledgements

This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy (DOE) under Contract No. DE-EE0005475.

References

1.         A. Manthiram, Y. Fu, S.-H. Chung, C. Zu and Y.-S. Su, Chem. Rev., 2014.

2.         J. Song, T. Xu, M. L. Gordin, P. Zhu, D. Lv, Y.-B. Jiang, Y. Chen, Y. Duan and D. Wang, Adv. Funct. Mater., 2014, 24, 1243-1250.

3.         J. Song, Z. Yu, T. Xu, S. Chen, H. Sohn, M. Regula and D. Wang, J. Mater. Chem. A, 2014, 2, 8623.