Insight into the loading temperature of sulfur on sulfur/carbon cathode in lithium-sulfur batteries

•A cost-effective chemical activation method to prepare porous carbon nanospheres.•Carbon nanospheres with bimodal microporous structure show high specific area and large micropore volume.•The S/C composite cathodes with in-situformed SC bond exhibit high sulfur activity with a reversible capacity of 1000 mA h g−1.•SC bond enables well confinement on sulfur and polysulfides.

Lithium–sulfur batteries are highly desired because of their characteristics such as high energy density. However, the applications of Li-S batteries are limited because they exist dissolution of polysulfides into electrolytes. This study reports the preparation of sulfur cathodes by using bimodal microporous (0.5 nm and 0.8 nm to 2.0 nm) carbon spheres with high specific area (1992 m2 g−1) and large micropore volume (1.2 g cm−1), as well as the encapsulation of polysulfides via formation of carbon–sulfur bonds in a sealed vacuum glass tube at high temperature. Given that sulfur and polysulfides are well confined by the SC bond, the shuttle effect is effectively suppressed. The prepared S/C cathodes with a sulfur loading of up to 75% demonstrate high sulfur activity with reversible capacity of 1000 mA h g−1 at the current density of 0.1 A g−1 and good cycling stability (667 mA h g−1 after 100 cycles).