Highly insulating nature of sulfur species and the shuttling effects caused by soluble lithium polysulfides have been blamed for hindering the development of lithium–sulfur (Li–S) batteries. A variety of carbonaceous materials have been investigated to ameliorate these problems by providing a conductive matrix with physical trapping and chemical binding capabilities, but inevitably resulted in typically low sulfur content in the cathode and hence low gross specific energy when considering all the active and inactive masses. A highly conductive and crosslinked matrix with superior trapping and binding capability to sulfur species but a very low mass density is essential. Herein, crosslinked carbon nanofiber aerogel (CNFA) with extremely low density, attained from pyrolysis of bacterial cellulose (BC) aerogel, was studied for sulfur cathodes. With its unique combination of several merits, in particular the capability of strong absorption of catholyte, CNFA based sulfur electrodes exhibit outstanding performance. With 75% sulfur content of the gross cathode mass, cells demonstrated an initial capacity of 1360 mA h g−1 at 0.2 C, and exhibited excellent cycling stability with 76% of the initial capacity retained after 200 cycles.