context: Similarly to TiS2, NbS2 also shows a high electrochemical activity upon Li+ intercalation/deintercalation at potentials between 1.5 and 3.0 V, presenting a specific capacity of about 100 mA h g−1. Xiao et al. systematically investigated the reaction kinetics and electrochemical performance of a ternary hybrid sulfur cathode consisting of sandwich-type NbS2@S enveloped by iodine-doped graphene (IG). As an exhilarating discovery, the active sulfur species can be intercalated in the interlayers of NbS2, which further enhances the intrinsic conductivity and polarity of NbS2. Therefore, the introduction of NbS2 and IG into a Li–S cell cathode shows a synergistic effect for LiPS fixation and utilization. Adsorption experiments indicate that NbS2 and NbS2–IG visibly decolorize the Li2S6 solution, while G and IG only change the solution color from tawny to yellow, suggesting that NbS2 possesses much stronger affinity to LiPSs than G and IG. CV tests using symmetrical cells that are fabricated by sandwiching a Li2S6-containing electrolyte between two identical electrodes reveal that the G and IG electrodes only show a small current density, while the current density in NbS2 is significantly increased, and further improvement is observed in the NbS2–IG electrode. These results suggest that NbS2 is conducive to providing access for electric charge to the NbS2–LiPS interface and synchronously triggers the redox reactions of LiPSs. Consequently, reversible capacities of 195, 107, and 74 mA h g−1 (1.05 mg cm−2) are achieved after 2000 cycles at ultrahigh rates of 20, 30, and 40C, respectively, and a high discharge capacity of 405 mA h g−1 (3.25 mg cm−2) is maintained after 600 cycles at 1C. This work sheds light on the promising application of 2D layered metal sulfides in high-energy, high-power, and long-life Li–S batteries.
answer: sulfur 