Influence of the amount of sulfur supported on sustainable ordered mesoporous carbons from tannin for high-performance electrodes in lithium‒sulfur batteries

Abstract

Technological options for batteries are currently in great demand, and among them, lithium-sulfur batteries (Li-S) are promising. The low electrical conductivity of sulfur, the large volume variation, and the formation of soluble lithium polysulfides are the main challenges facing Li-S. This work proposes addressing these challenges by using sustainable ordered mesoporous carbon as a support for the sulfur in the cathode. The study showed how different contents of incorporated sulfur impact the electrochemical properties. Mesoporous carbons were obtained from tannins with a distribution of micro- and mesopores, and after the introduction of sulfur, the micropores were occupied. The sulfur contents in the MCS0.7, MCS1, and MCS2 composites obtained from the TG curves were 29 wt%, 39 wt%, and 61 wt%, respectively. XPS results indicated that the presence of S₈ atoms infiltrated into the mesopores, and in smaller quantities, S_2-4 atoms infiltrated into the interior of the micropores due to spatial constraints. The specific capacity at 0.1C was 1033 mA h g_S⁻¹ for MCS0.7, 830 mA h g_S⁻¹ for MCS1, and 666 mA h g_S⁻¹ for MCS2. The capacity values are greater for composites with lower sulfur contents, which favors charge transfer. This behavior can be explained by considering that a greater fraction of the elemental sulfur is in direct contact with the surface of the carbon matrix in these cases, as observed by the characterization of the materials. Furthermore, the MCSs showed an excellent rate capability due to their mesoporous structure. MCS1 was chosen for the cyclic stability tests, and a coulombic efficiency close to 99 % was observed during the test. The performance of these materials is among the best for Li-S batteries based on biomass-derived carbon. The results highlight the great potential of sustainable mesoporous carbon materials from biomass as efficient and environmentally friendly components for high-performance lithium‒sulfur batteries.