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Sulfur/Nitrogen Doped Carbon Nanotube Binder-Free Electrode for High Performance Li/S Batteries
Due to low cost, environmental friendliness and high theoretical capacity of sulfur, rechargeable Li/S batteries are very promising power sources for various applications. However, the insulating nature of sulfur and solubility of polysulfides as discharge products restrict its practical application [1]. Among the approaches to overcome these problems, carbon nanotubes are widely used to obtain a flexible conductive matrix for S cathode [2]. Nitrogen doping of carbon nanotubes (N-CNTs) significantly improves its electronic conductivity because the nitrogen atoms provide additional free electrons for the conduction band [3].
In this work, we report for the first time on a high performance S/N-CNT cathode for Li/S battery. Exclusion of heat-treatment in the composite preparation avoided the sulfur loss; the composite contained 61 wt% of sulfur. Thanks to the self-weaving behavior of N-CNT, binders and current collectors are rendered unnecessary, thereby simplifying the electrode manufacturing process and increasing the sulfur content in the total electrode weight. The N-CNT core provides a highly conductive and mechanically flexible framework, enhancing the electronic conductivity and consequently the rate capability of the material. This resulting composite cathode sustains 833 mAh g-1 reversible specific discharge capacity after 100 cycles at 0.1 C, and 676 mAh g-1at 1 C with a coulombic efficiensy about 100%.
Experimental
The S/N-CNT composite preparation is schematically shown in Fig. 1. Nitrogen doped carbon nanotubes were dispersed in deionized water by sonication at room temperature. The obtained N-CNT suspension was mixed ultrasonically with the aqueous suspension of nano-sulfur. The resulting system was vacuum-filtered and thoroughly washed with deionized water and ethanol. The binder-free S/N-CNT composite was obtained by further drying in a vacuum oven at 60 °C overnight to remove the solvent.
Acknowledgments
This research was supported by a Research Grant from the Ministry of Education and Science of Kazakhstan and by a Subproject supported under the Technology Commercialization Project by the World Bank and the Government of Kazakhstan.
References
1. X. Ji, K.T. Lee, L.F. Nazar, Nat. Mater., 2009, 8, 500.
2. Y.S. Su, A. Manthiram, Chem. Commun., 2012, 48, 8817.
3. X.G.Sun, X. Wang, R.T. Mayes, S. Dai, ChemSusChem,2012, 5, 2079.