As a special class of cathode materials for lithium-sulfur batteries, pyrolyzed polyacrylonitrile/sulfur (pPAN/S) can completely solve the polysulfide dissolution problem and deliver reliable performance. However, the applicable S contents of pPAN/S are usually lower than 50 weight % (wt %), and their capacity utilizations are not sufficient, both of which greatly limit their energy densities for commercial applications. We report a pyrolyzed polyacrylonitrile/selenium disulfide (pPAN/SeS2) composite with dramatically enhanced active material content (63 wt %) and superior performances for both lithium and sodium storage. As a result, pPAN/SeS2 delivers high capacity of >1100 mAh g−1 at 0.2 A g−1 for Li storage with extremely stable cycle life over 2000 cycles at 4.0 A g−1. Moreover, when applied in a room temperature Na-SeS2 battery, pPAN/SeS2 achieves superior capacity of >900 mAh g−1 at 0.1 A g−1 and delivers prolonged cycle life over 400 cycles at 1.0 A g−1.