Microporous activated carbon derived from azulmic acid precursor with high sulfur loading and its application to lithium-sulfur battery cathode

•A carbon matrix confining a large amount of sulfur can be prepared from azulmic acid-derived carbon (AZC)•A mild activator K2CO3 can form porous AZC with a large volume of inner space without collapsing micropores.•The activated AZC can contain 70 wt.% sulfur in its micropores.•The highly sulfur-filled microporous AZC can be repeatedly cycled as a sulfur cathode exhibiting a high coulombic efficiency of almost 100% We have previously reported that an effective activation method for azulmic acid carbon (AZC: AZC is a carbide of azulmic acid, a nitrogen-containing organic material) as a precursor can produce microporous activated carbon. By improving the activation method of AZC, we succeeded in producing an AZC-based activated carbon that can support a larger amount of sulfur than that of previously reported one while keeping its microporous property. We have found that the present AZC activated carbon has a BET specific surface area of 2633 m2 g−1 and a pore volume of 1.286 cc g−1 and can contain up to 70 wt.% sulfur when an optimum alkaline activator and activation temperature are used. The cathode of this activated carbon can be stably charged and discharged in a lithium-sulfur battery with a glyme-based electrolyte. The present highly sulfur-filled microporous AZC is a promising sulfur host material for lithium sulfur batteries.