Although lithium–sulfur batteries exhibit a high initial capacity, production costs and lack of cyclability are major limitations. Here we report a liquid-based, low-cost and reliable synthesis method of a lithium–sulfur composite cathode with improved cyclability. An open network of Conductive Carbon Black nanoparticles (Cnet) is infused with a sulfur network (Snet) to form sponge-like networks (Cnet + Snet). Initially, Snet is open to the outside, allowing liquid electrolyte to infiltrate and impart Snet Li⁺ conductivity. During lithiation, Cnet could accommodate the volume expansion of Snet largely without losing electrical contact. During delithiation, the carbon nanoparticles would preferably flocculate on the outer surface due to polysulfide dissolution and depletion of sulfur, to form a passivation layer that still allows Li⁺ exchange, but prevents more polysulfides from escaping, thus slowing the leaching of polysulfides into the bulk electrolyte liquid. The plausibility of a carbonaceous passivation layer was checked using an extra carbon deposition layer to achieve an improved performance of ∼400 mA h g⁻¹ after 250 cycles under a high rate 2.0 C. A 763 mA h g⁻¹ discharge specific capacity of this sulfur nanosponge cathode (abbreviated as “SULFUN”) was obtained after 100 cycles under a rate of 0.2 C. Discharge capacities of 520 mA h g⁻¹ and 290 mA h g⁻¹ were attained after 300 and 500 cycles, respectively, making this cathode material attractive for rechargeable battery applications.