Cellulose as a Precursor of High‐Performance Energy Storage Materials in Li–S Batteries and Supercapacitors

Energy storage materials consisting of sulfur/carbon composites or highly porous carbons are successfully synthesized from cellulose or cellulose acetate, respectively, by chemical activation with sodium thiosulfate. It is a versatile synthesis approach that allows the production of sulfur/carbon composites or porous carbons depending on the washing procedure used after the high‐temperature treatment. By acid washing, sulfur/carbon composites with sulfur contents in the 62–74 wt% range are produced when cellulose is used as precursor. These composites show a good electrochemical performance in Li–S batteries, providing a capacity of 7.4 mAh cm −2 at 0.05 C and 5.5 mAh cm −2 at 0.2 C under high sulfur loading conditions, and still preserving 4.1 mAh cm −2 after more than 100 cycles. Meanwhile, by water washing, highly micro–mesoporous carbons ( S BET  ≥ 2500 m 2  g −1 ) with good electronic conductivity (≈5–6 S cm −1 ) are produced when cellulose acetate is used as precursor. These porous carbons exhibit high capacitance values (170 F g −1 at 0.2 A g −1 ) in an ionic liquid electrolyte, good long‐term stability, and low self‐discharge.