Sulfur with a high specific capacity of 1673 mAh g(-1) is yet to be used as commercial cathode for lithium batteries because of its low utilization rate and poor cycle stability. In this work, a tube-in-tube carbon structure is demonstrated to relieve the critical problems with sulfur cathode: poor electrical conductivity, dissolution of lithium polysulfides, and large volume change during cycling. A number of small carbon nanotubes (∼20 nm in diameter) and a high loading amount of 85.2 wt % sulfur are both filled completely inside a large amorphous carbon nanotube (∼200 nm in diameter). Owing to the presence of these electrically conductive, highly flexible and structurally robust small CNTs and a large CNT overlayer, sulfur material exhibits a high utilization rate and delivers a large discharge capacity of 1633 mAh g(-1) (based on the mass of sulfur) at 0.1 C, approaching its theoretical capacity (1673 mAh g(-1)). The obtained S-CNTs@CNT electrode demonstrates superior high-rate cycling performances. Large discharge capacities of ∼1146, 1121, and 954 mAh g(-1) are observed after 150 cycles at large current rates of 1, 2, and 5 C, respectively.

Iron oxides and iron sulfides have attracted significant research concerns for Lithium-ion batteries (LIBs) due to their larger theoretic capacity than the commercial electrode. However, they both suffer from large volume expansion during cycling and poor electrical conductivity. Iron sulfides have another problem of the dissolution of polysulfides into organic electrolyte. This work reports a sulfur-doped graphene aerogels (GAs) supported FeS 2 @carbon composite with better lithium ion storage properties than its intermediate precursors (GAs supported Fe-Fe 3 O 4 @C and Fe 2 O 3 ). It exhibits large reversible capacities of ~1000 mAh g -1 at 0.1 C during cycling with good rate capabilities. These enhanced electrochemical properties have been mainly attributed to the synergetic effect of GAs support, carbon coating and sulfur doping.

The nanorice–nanosheet core–satellite structure of FeS2 synthesized by heterogeneous sulfuration from a MIL-88-Fe precursor achieves highly reversible larger-than-theoretical Li-storage capacities.