Ordered mesoporous carbons obtained by a simple soft template method as sulfur immobilizers for lithium–sulfur cells

Abstract

Carbon materials with ordered mesoporous structures were synthesized using soft template methods and then activated by CO₂ treatment. Sulfur was incorporated in these carbons via a simple chemical deposition method in aqueous solutions and the resulting composites were tested as electrodes in Li–S cells. The electrochemical results showed that well-ordered mesoporous carbons perform better than those with a random mesopore arrangement (wormhole-like mesoporous structure). The mesopore ordering yields a framework of well-connected empty sites that results in an enhancement of both the charge carrier mobility and the reversibility of the electrochemical reaction. Although the activation with CO₂ partially destroys the mesopore arrangement, which adversely affects the electrode performance, it notably increases the surface area and the micropore content which improves the connectivity between the mesopores. The final observation was an irrelevant effect of the activation process at low current densities. However, at higher rates the activated carbon composite delivered higher capacities. The hierarchical pore structure formed by micro- and mesopores should guarantee the required fast mobility of the Li⁺.