Freestanding Sulfur/3D Carbon Fiber Membrane Cathodes for Advanced Lithium-Sulfur Batteries

A freestanding membrane of a 3D network of carbon fibers coated with nitrogen-doped carbon spheres (NC@FCF) was designed through the carbonization of modified filter paper, on the surface of which polydopamine spheres were deposited. It is found that the NC@FCF membrane is composed of interlaced and circuitous carbon fibers, and the carbon spheres are distributed in the interspaces among carbon fibers. After infiltration with sulfur, the S-NC@FCF membrane was directly used as a cathode for Li-S batteries. The freestanding cathode exhibits an excellent rate capability, large charge-discharge capacity, and outstanding cycle performance, exhibiting an initial discharge capacity of 1143.7mAhg(-1) and maintaining 778.2mAhg(-1) after 200 cycles at 0.5C. The excellent electrochemical performance results from the synergistic effect of the 3D carbon-fiber network, which provides electronic conduction pathways, and the porous structure formed through the accumulation of carbon spheres, which can encapsulate S, absorb polysulfides, and facilitate Li+ transfer.