A new freestanding Fe3C/carbon nanofiber (CNF) film is developed using a facile one-pot electrospinning method as an interlayer for high performance lithium–sulfur (Li–S) batteries. The interlayer placed between the separator and the sulfur cathode plays many synergistic roles, offering (i) a number of macropores within the nanofiber web to facilitate ion transport and electrolyte penetration, (ii) nitrogen-containing functional groups that entrap soluble polysulfides by strong interatomic attraction, and (iii) much enhanced electron/ion transfer due to the high electrical conductivity of the CNF web. The battery delivers an excellent specific discharge capacity of 893 mA h/g after 100 cycles, maintaining 76% of its initial capacity of 1177 mA h/g. These values are among the highest for those reported recently with similar nanocarbon-based interlayers in terms of rate capability and cyclic stability.